Patent Publication Number: US-6663716-B2

Title: Film processing system

Description:
RELATED APPLICATION 
     This is a continuation-in-part application of U.S. Ser. No. 09/060,007 filed on Apr. 14, 1998, the entire contents of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Chemical vapor deposition (CVD) is a process of forming a film on a substrate, typically, by generating vapors from liquid or solid precursors and delivering those vapors to the surface of a heated substrate where the vapors react to form a film. Systems for chemical vapor deposition are employed in applications such as semiconductor fabrication, where CVD is employed to form thin films of semiconductors, dielectrics and metal layers. Three types of systems commonly used for performing CVD include bubbler-based systems, liquid-mass-flow-control systems, and direct-liquid-injection systems. 
     Bubbler-based systems, or “bubblers,” essentially bubble a stream of gas through a heated volume of liquid precursor. As the stream of gas passes through the liquid precursor, vapors from the liquid precursor are absorbed into the gas stream. This mixture of gases is delivered to a process chamber, where the gases react upon a surface of a heated substrate. Bubblers typically heat the volume of liquid precursor at a constant temperature. Over time, the constant heat often causes the precursor to decompose rendering it useless for CVD. In an effort to minimize decomposition, the bubbler is typically maintained at a temperature lower than that at which the vapor pressure of the liquid precursor is optimal. 
     Liquid mass flow control systems attempt to deliver the precursor in its liquid phase to a vaporizer typically positioned near the substrate. The precursor is vaporized and is then typically entrained in a carrier gas which delivers it to the heated substrate. A liquid mass flow controller, which is a thermal mass flow controller adapted to control liquids, is used to measure and control the rate of flow of liquid precursor to the vaporizer. 
     Liquid mass flow controllers present a number of drawbacks. First, liquid mass flow controllers are extremely sensitive to particles and dissolved gases in the liquid precursor. Second, liquid mass flow controllers are also sensitive to variations in the temperature of the liquid precursor. Third, liquid mass flow controllers typically use a gas to assist in the vaporization of the liquid precursor, thereby increasing the probability of generating solid particles and aerosols and ensuring a high gas load in the process system. Fourth, most liquid mass flow controllers cannot operate at temperatures above 40° C., a temperature below which some precursor liquids, such as tantalum pentaethoxide (TAETO), have high viscosity. Due to its sensitivities, the liquid flow controller is accurate and repeatable to about 1% of full-scale liquid flow. Further, when a liquid mass flow controller wetted with TAETO or one of a number of other precursors is exposed to air, the precursor will generally react to produce a solid which may destroy the liquid flow controller. 
     Liquid pump-based systems pump the liquid precursor to the point of vaporization, typically at a position near the heated substrate. Liquid pump-based systems are generally one of two main types. One type uses a liquid flow meter in line with a high-pressure liquid pump. The other type uses a high-precision, high-pressure metering pump. Both of these systems are extremely sensitive to particles in the liquid. The liquid-flow-meter based system is also sensitive to gas dissolved in the liquid. Both are extremely complex to implement, and neither can tolerate high temperatures (maximum 50° C.). The system with the metering pump has difficulty vaporizing high viscosity liquids. Finally, both are generally difficult to implement in a manufacturing environment due to their extreme complexity and large size. 
     Existing CVD equipment design is generally optimized for high process pressures. The use of high process pressures is most likely due to the fact that, until recently, CVD precursors were either generally relatively high-vapor-pressure materials at room temperature or were, in fact, pressurized gases. Examples include tetraethyloxy silicate (TEOS), TiCl 4 , Silane, and tungsten hexafluoride, etc. These materials were chosen because they had high vapor pressures and could therefore be easily delivered. The process pressure was generally well within the stable vapor pressure range of each of these materials. 
     DISCLOSURE OF THE INVENTION 
     The present invention relates to systems and methods for chemical vapor deposition for the fabrication of materials and structures for a variety of applications. The system is well suited for use in the fabrication of devices for the semiconductor industry, but can also be used in other applications involving thin film deposition and processing. 
     In addition to the fabrication of dielectric layers, metalization layers, and epitaxially grown semiconductor films including silicon, germanium, II-VI and III-V materials, the system can be used for precision manufacture of optical thin films such as anti-reflective coatings or stacked dielectric structures including optical filters, diamond thin films or composite structures for multichip modules or optoelectronic devices. 
     In contrast to thin films of traditional CVD materials, future thin films require new materials that have low vapor pressures and that are often near their decomposition temperature when heated to achieve an appropriate vapor pressure. Some of the precursors having both intrinsically low vapor pressure and low thermal decomposition temperature are considered the best choices for deposition of films of tantalum oxide, tantalum nitride, titanium nitride, copper, and aluminum. 
     An apparatus of this invention includes a vaporizer within a vaporization chamber and a dispenser positioned for dispensing a precursor to the vaporizer. A delivery conduit joins the vaporization chamber with a process chamber, where a chemical vapor is deposited on a substrate. A flow meter is positioned to measure vapor flow through the delivery conduit, and a flow controller is positioned to control vapor flow through the delivery conduit. Both the flow meter and flow controller are communicatively coupled with a processor programmed to control the flow controller to govern vapor flow through the delivery conduit in response to the measured vapor flow. 
     In a preferred embodiment, the flow meter includes a tube with a pair of open ends, which acts as a laminar flow element. The flow meter further includes a pair of capacitance manometers aligned with the open ends of the tube to measure the pressure drop across the laminar flow element. In a further preferred embodiment, the flow controller is a proportional control valve in communication with the flow meter. 
     A still further preferred embodiment of the apparatus includes a reservoir for supplying precursor to the dispenser. The dispenser is controlled by the processor and the vaporizer which receives precursor from the dispenser includes a heated surface for vaporizing the precursor. Preferably, a pressure sensor communicatively coupled with the processor is positioned in the vaporization chamber. Accordingly, the processor can, in some embodiments, control the rate at which vapor is generated by the vaporizer, by, for example, controlling the rate at which the dispenser dispenses precursor from the reservoir to the vaporizer. 
     In another embodiment of the apparatus, an outlet of the delivery conduit is positioned in the process chamber, and a showerhead divides the process chamber into an upstream section and a downstream section, wherein the outlet is in the upstream section and a substrate chuck is in the downstream section. An upstream pressure sensor is positioned to measure vapor pressure in the upstream section, and a downstream pressure sensor is positioned to measure vapor pressure in the downstream section. Both the upstream and downstream pressure sensors are communicatively coupled with a processor. In a further preferred embodiment, the showerhead is “active,” enabling control over the vapor flow rate through the showerhead. 
     Other features found in preferred embodiments of the apparatus include a heater in thermal contact with the delivery conduit, a DC or AC source connected to the substrate chuck, and an elevator for raising and lowering the substrate chuck. Another embodiment of this invention is a cluster tool for semiconductor processing including a CVD apparatus, described above, connected to a central wafer handler. 
     In a method of this invention, a precursor is vaporized in a vaporization chamber, gas flow between the vaporization chamber and a process chamber is measured, and the rate of gas flow between the vaporization chamber is controlled in response to the measured gas flow. In another embodiment of a method of this invention, the vapor pressure of a precursor is measured, and the rate at which the precursor is vaporized is controlled in response to the measured vapor pressure, preferably by controlling the rate at which precursor is dispensed from a reservoir onto a vaporizer. Preferably, deposition occurs via a surface-driven reaction. Nevertheless, embodiments of the invention also cover methods where deposition occurs via non-surface driven reactions. 
     The systems and methods of this invention provide numerous benefits. First, they allow the precursor to be delivered to the substrate in a much purer and higher-pressure or high-flux form than is achievable with the use of systems that use a carrier gas. As a result, the likelihood of gas-phase reactions and consequent formation of particles can be greatly reduced. Because of the higher concentration, which leads to a higher deposition rate, this invention does not necessitate the introduction of plasma into the process chamber. Consequently, the apparatus is simplified, and plasma-induced polymerization of precursor is reduced or eliminated. Second, control over the concentration of precursor delivered to the process chamber is enhanced, thereby improving control over film thickness and uniformity. Third, the direct delivery of vapor flow into the process chamber at low temperature and low pressure and without a carrier gas increases the efficiency of use of costly precursors in many applications by a factor of up to 10 or more over standard systems utilizing a carrier gas, which infer precursor vapor flow rates either from a theoretical pickup rate, which is carrier-gas and temperature dependent, or from a thermal mass-flow controller or liquid delivery system. Likewise, emissions of unreacted process gases from the process chamber can be maintained at very low levels because the absence of a carrier gas and generally lower flow rates and better residence times leads to a higher utilization efficiency of the precursor. Fourth, decomposition of the precursor is limited due to its short contact time with the heated vaporizer. While small amounts of precursor are delivered to the vaporizer, as needed, the useful life of the bulk of the precursor is preserved by maintaining it at a lower temperature in the reservoir. Fifth, the highly conformal nature of deposits that can be formed by methods of this invention are useful in forming integrated circuits with line-widths of 0.25 microns (250 nm) or less. 
     Other advantages of this invention include the low sensitivity of the system to impurities such as dissolved gases and particles in the precursor, the relative ease of alternating between multiple precursors in a single system as a result of the ability to coordinate the use of each with a common precursor delivery system, the ease of accessing and maintaining all subsystems, the low power requirements of the system, the use of only low voltages in the operating elements of the system and the small overall size of the system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects, features and advantages of the invention will be apparent from the following, more particular description of preferred embodiments of the invention, as illustrated in the accompanying figures. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
     FIGS. 1A and 1B provide a schematic illustration of an apparatus of this invention. 
     FIGS. 1C and 1D provide a schematic illustration of another embodiment of an apparatus of this invention. 
     FIG. 2 a  is a cross-sectional illustration of a vaporization subsystem of this invention. 
     FIG. 2 b  is a cross-sectional illustration of another embodiment of a vaporization subsystem of this invention. 
     FIG. 2 c  is a schematic illustration of a control system of this invention. 
     FIG. 3 a  is an illustration of a gas-flow-control subsystem of this invention. 
     FIG. 3 b  is an illustration of another embodiment of a gas-flow-control subsystem of this invention. 
     FIG. 4 a  is a view, partially in cross section, of a process subsystem of this invention. 
     FIG. 4 b  is a cross-sectional view of another embodiment of a process subsystem of this invention, with the substrate chuck in a retracted position. 
     FIG. 4 c  is a cross-sectional view of the embodiment of FIG. 4 b , with the substrate chuck raised to a processing position. 
     FIG. 4 d  is another cross-sectional view of the embodiment of FIG. 4 b , with the substrate chuck in a fully-extended position. 
     FIG. 5 a  is an illustration of a shower head of this invention. 
     FIG. 5 b  is a top view of a replaceable showerhead mounted within a ring. 
     FIG. 5 c  is a cross-sectional side view of the showerhead and ring illustrated in FIG. 5 b . 
     FIG. 5 d  is an illustration of a typical deposited layer formed in a cavity via PVD processes. 
     FIG. 5 e  is an illustration of a typical deposited layer formed in a cavity via conventional CVD processes. 
     FIG. 5 f  is an illustration of a deposited layer that can be formed with the apparatus and method of this invention. 
     FIGS. 6 a ,  6   b  and  6   c  are perspective views of one embodiment of the CVD apparatus of this invention. 
     FIG. 7 illustrates the control architecture of a CVD apparatus according to one embodiment of the invention. 
     FIG. 8 illustrates the main process control routine according to one embodiment of the invention. 
     FIGS. 9 a  and  9   b  illustrate the operation of the vaporizer sub-process according to one embodiment of this invention. 
     FIG. 10 illustrates the processing performed by the vapor phase flow control sub-process according to one embodiment of this invention. 
     FIG. 11 illustrates a process chamber pressure control sub-process according to this invention. 
     FIGS. 12 a  through  12   d  illustrates the operation of inserting a wafer into the process chamber of one embodiment of this invention. 
     FIG. 13 illustrates the cleanup sub-process according to one embodiment of this invention. 
     FIG. 14 illustrates an example portion of a schematic showing the closed loops present in a CVD apparatus according to one embodiment of the invention. 
     FIG. 15 is an illustration of a cluster tool embodiment of this invention. 
     FIG. 16 illustrates multiple cluster tools configured to be controlled by a single factory automation controller according to this invention. 
     FIG. 17 illustrates multiple cluster tools, each controlled by separate cluster tool controllers which are in turn controlled by a factory automation controller according to this invention. 
     FIG. 18 illustrates an example of the processing steps performed by a cluster tool controller according to one embodiment of this invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The features and other details of the method of the invention will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. Numbers that appear in more than one figure represent the same item. It will be understood that the particular embodiments of the invention are shown by way of illustration and not as limitations of the invention. The principle features of this invention can be employed in various embodiments without departing from the scope of the invention. 
     As illustrated in FIGS. 1A and 1B, a preferred embodiment of a CVD apparatus  10  of this invention includes four integrated subsystems, including a vaporization subsystem  12 , a gas-flow-control subsystem  14 , a process subsystem  16 , and an exhaust subsystem  18 . A distributed processing system, described below, provides integrated control and management of each of these subsystems. The distributed processing system and each of the subsystems  12 ,  14 ,  16  and  18  are all within a single free-standing CVD module  10  (illustrated in FIGS. 6 a-c ). The dimensions of the CVD module generally will not exceed a 1 m by 2 m footprint and preferably are no greater than about 1.2 m in length by about 0.6 m in width by about 1.8 m in height to achieve conformity with existing standards for integration with a wafer handler such that the free-standing CVD module can fit within the typically allotted footprint in a larger cluster tool configuration. In a further preferred embodiment, the CVD module fits within a standard footprint, as established by MESC, the standard design architecture adopted by Semiconductor Equipment and Materials International (SEMI), a trade organization of semiconductor industry suppliers, for connection to a wafer handler or transport module. 
     Each of boxes  103 ,  105 ,  107 ,  109 ,  111 ,  113 ,  115 ,  117  and  119  represents a separate control zone. Each of the control zones is independently heated with a separate cartridge heater  121 . Further, the temperature in each control zone and at other heated elements of the apparatus is monitored by a resistance temperature detector or resistance thermometry detector (RTD)  131 , of which one embodiment is a platinum resistance thermometer. The RTD is preferably encapsulated by a silicon nitride coating because of the heat conduction and low thermal mass of the silicon nitride. Alternatively, thermocouples or other temperature sensing devices can he used in place of the RTD&#39;s. 
     The vaporization subsystem  12 , illustrated in FIG. 2 a , is designed to generate a controlled supply of precursor vapor for deposition. The precursor, initially in liquid or solid form, is stored in a reservoir  20  fabricated from Inconel® or Inconel® alloys, such as Incoloy® 850 (available from Inco Alloys International, Inc., Huntington, W. Va.). Alternatively, the reservoir  20  is formed of  316 L stainless steel. A funnel  22  is provided at the base of the reservoir  20 , with a dispenser in the form of a dispensing valve  24  at the focal point of the funnel  22  for dispensing precursor from the reservoir  20 . Where a liquid precursor is used, the dispensing valve  24  is an axial displacement pulse valve. Where a solid precursor is used, the dispensing valve  24  is a rotary valve. The reservoir  20  is thermally insulated from the vaporization chamber  26 , discussed below, and is maintained at a temperature below that at which the precursor will be subjected to significant decomposition. Optionally, multiple reservoirs  20  are provided, each filled with a different precursor and each feeding into the vaporization chamber  26 . As each precursor is needed, the appropriate reservoir  20  can be utilized. Alternatively, multiple reservoirs  20  each feed into their own vaporization chamber. 
     A system for governing the supply of various precursors to a cluster tool  120  having one or more vaporization chambers  26  is illustrated in FIG. 2 c . A cluster tool controller  802  is controlled by a programmable host computer or data processor  804  to regulate the delivery of precursors  806 ,  808 ,  810  for the deposition of titanium nitride, copper, and aluminum, respectively, for example. The cluster tool controller  802  is further programmed by the host computer  804  to regulate a pair of modules for annealing/diffusion  812 ,  814  and a separate module for pre-heating and pre-cleaning  816 . Communication between each of these modules  806 ,  808 ,  810 ,  812 ,  814  and  816  and the cluster tool controller  802  is facilitated by a bus architecture that can include, for example, a ProfiBus data bus  818  in combination with an EtherNet/Epics data bus  820 . Connected to the EtherNet/Epics data bus  820  is the cluster tool  120 , allowing the cluster tool controller  802  to likewise govern operation of the cluster tool  120  to which the precursors from modules  806 ,  808 ,  810  are delivered. The system further includes a console for monitoring operation of the system  822  and a console for system maintenance  824 . Both consoles  822  and  824  are connected to the cluster tool controller  802 . 
     In operation, the cluster tool controller  802 , as controlled by the host computer  804 , can, in relatively rapid sequence, select various precursors from module  808 ,  810  and  812  for delivery to one or more vaporization chambers  26  (FIG. 2 a ). This capability allows for a sequencing of starting materials in a single system, thereby allowing for a rapid sequence of depositions of different layers on a substrate in process modules of the cluster tool  120 . Additional details regarding the various components of FIG. 2 c , alternative embodiments thereof, and methods of using the same are described in greater detail below. 
     A vaporizer  28  that has ever-increasing surface area at distances away from the dispensing valve  24  is used to vaporize the precursor. The vaporizer  28  functions as a falling film molecular still, in which a liquid precursor generates a wavefront flowing down the surface of the vaporizer  28 . The temperature of the vaporizer  28  is set to vaporize the precursor over the course of its travel across the vaporizer  28  surface. Contaminants with higher vaporizing temperatures will generally flow down the surface of the vaporizer  28  and fall off without vaporizing. 
     Preferably, the vaporizer  28  is in the form of an inverted cone and is positioned to receive precursor flowing from the dispensing valve  24 . The vaporizer  28  is made from a thermally-conductive material coated or plated, as required, for the best chemical compatability with the precursor. In a preferred embodiment, the vaporizer  28  includes an electroless-nickel-plated OFHC substrate coated with a sulphamate nickel overplate, which in turn is optionally coated with rhodium overplating for very high corrosion resistance and inertness. The vaporizer  28  illustrated in FIGS. 1A and 1B is designed for vaporizing a liquid precursor. Alternatively, a multi-stepped-shape cone is used for solid precursors, wherein ridges are provided on the cone to collect the solid as it is delivered from the reservoir  20 . One suitable embodiment of the vaporizer  28  includes a cone with a height of 4.20 inches and a base diameter of 3.70 inches. The vaporizer  28  and the reservoir  20  are removable so that they can be cleaned and replaced during scheduled maintenance. When in use, the vaporizer  28  is heated to a temperature sufficient to vaporize the precursor without causing it to suffer thermal decomposition. 
     The vaporizer  28  includes a plurality of bores  29 . Heaters, e.g., Watt-Flex® cartridge heaters  90  (available from Dalton Electric Heating Co., Inc., Ipswich, Mass.) are inserted into four of these bores  29 . In one example, the heaters are 3.0 inches in length and 0.25 inches in diameter. The heaters supply 50 watts at 24-25 VAC, and can be heated above 1000° C. Typically, though, the heaters are operated in the vicinity of 200° C. A platinum resistance thermometer is inserted into a central bore  31 . 
     The vaporizer  28  is not intended to be used as a “flash vaporizer.” Rather, it is intended that the precursor will spread across the vaporizer  28  surface, from which vapors will evolve. The vaporizer  28  offers the advantage of not being sensitive to small particles suspended in standard grades of liquid CVD precursor used in the semiconductor industry. In this embodiment, suspended particulates are left behind on the vaporizer  28 . 
     A vaporization chamber  26  surrounds the vaporizer  28  and is made of OFHC copper plated with electroless nickel and sulfamate nickel and also rhodium if highly reactive or unstable precursors are used. The vaporization chamber  26  includes a principal cylinder  30  and a vapor outlet  32 . The vaporization chamber  26  essentially serves as an expansion volume and reservoir for gases produced by the vaporizer  28 . 
     A pressure sensor  34  is preferably positioned in the vapor outlet  32  for measuring the vapor pressure in the vaporization chamber  26 . Alternatively, the pressure sensor  34  can be positioned in the principal cylinder  30 . The pressure sensor  34  is heated to about the same temperature as the vaporizer  28  during operation to prevent condensation of the vaporized precursor. The pressure sensor  34  is coupled in a processor-driven control loop with the dispenser  24  to achieve a fairly constant pressure in the vaporization chamber  26 . As pressure drops in the vaporization chamber  26 , the dispenser  24  is signaled to dispense more precursor. Accordingly, the pressure sensor  34  and dispenser  24  work in concert to maintain the pressure in the vaporization chamber in a range between the pressure in the process chamber  70 , discussed below, and the standard vapor pressure of the precursor at the temperature of the vaporizer. In this system, the response time for reestablishing the desired vapor pressure is typically about 10 seconds. Preferably, the pressure sensor  34  is a capacitance manometer with a 1000 torr full-scale range, or other, similar direct-measuring gauge. 
     FIG. 2 b  illustrates an alternative embodiment of the vaporization subsystem in which the base  21  of the neck  23  includes a groove, where the base is hollowed out to prevent thermal degradation of the precursor as it flows down rod  33  on the way to the vaporization chamber  26 . Heat from the vaporizer  28  travels through the walls of the vaporization chamber  26  and into the neck  23 . By hollowing out the neck  23 , the inner wall  25  is spatially removed from the flow of precursor down the rod  33 . The hollowed out section extends approximately midway up the neck  21 . It ends at angled surface  27 , above which the inner diameter of the neck is constricted. Vapor flowing up into the hollowed out section is prone to condense on angled surface  27 , which directs condensed vapors back toward rod  33 . 
     The vapor pressure throughout the system is maintained at relatively low levels. One reason why the system can be operated at low pressure levels is the close physical proximity of all of the subsystems. Accordingly, the vapors need travel only very short distances from vaporization to deposition. Because the vapor pressure and the velocity of the gas are low, the transport of particles throughout the system is significantly reduced in comparison to higher pressure systems, such as those which use a carrier gas. 
     The gas-flow-control subsystem  14  is illustrated in FIG. 3 a . All items in the gas-flow-control subsystem  14  are enclosed in a heated conductive sheath, preferably of aluminum, which heats the items to approximately the same temperature as the vaporizer  28 . The conductive sheath has a 3-inch by 3-inch square cross-section with a bore of just over 1-inch diameter in the center to accommodate the delivery conduit  40 . Further, the conductive sheath includes casts of pressures sensors  48 ,  50  and other instruments, allowing the conductive sheath to conform to the exterior shape of the gas-flow subsystem. The conductive sheath includes bores into which heaters, e.g., Watt-Flex cartridge heaters and temperature sensors, are inserted. A delivery conduit  40  joins the vaporization chamber  26  and the process chamber  70 . Preferably neither the length of the delivery conduit  40  nor the distance between the vaporization chamber  26  and the process chamber  70  exceeds 25 cm. A series of valves controls the flow of vapor between chambers  26 ,  70 . An isolation valve  42  seals the vaporization chamber  26  from the delivery conduit  40 . In one embodiment the isolation valve  42  is an HPS Lopro® valve modified to operate at high temperatures. In elements, such as the isolation valve  42 , which must withstand high temperatures, all elastomer seals are a special high temperature material, such as DuPont Kalrez® 8101, Sahara® or Dry. A proportional control valve  44  (for example, those made by MKS Instruments, Andover, Mass.) designed to withstand high temperatures, provide high conductance and provide chemical compatibility with wet precursors is illustrated in FIG. 2 a . Alternatively, a plurality of valves  44 ′ connected in parallel, as illustrated in FIG. 1A, can be used in place of a single proportional control valve  44 . The proportional control valve  44  is positioned downstream from the isolation valve  42  and is upstream from a flow meter  46  consisting of a pair of pressure sensors  48 ,  50  and a laminar-flow element  54 . In the illustrated embodiment, the laminar-flow element is an open-ended tube  54  inserted through an orifice in an otherwise solid block  56  blocking flow through the delivery conduit  40 . In one embodiment, the tube  54  has a length of 8.0 inches, an outer diameter of 0.375 inches, and an inner diameter of 0.280 inches. The tube  54  is oriented concentrically with and within the delivery conduit  40 . In one embodiment of the method of this invention, the pressure drop across the tube  54 , as vapor flows through the delivery conduit  40 , is on the order of 0.1 torr. 
     The delivery conduit  40  has an internal diameter (I.D.) that is larger than that of pipes conventionally used for vapor precursor delivery in existing CVD systems. Preferably the internal diameter of delivery conduit  40  is between 12 and 40 mm. More preferably, the internal diameter is about 25 mm. The use of such a wider-I.D. conduit for vapor transport between the vaporization chamber  26  and the process chamber  70  (see FIGS. 4 a-d ) permits higher conductance for the vapor flow therein and, consequently, allows for adequate vapor flow at lower pressures. The vaporized precursor is delivered to the process chamber  70  through conduit  40  at no more than 50% dilution. In preferred embodiments, the vaporized precursor is delivered to the process chamber in a substantially undiluted state (i.e., less than 10% dilution). In further preferred embodiments, the vaporized precursor is delivered in an intrinsically pure form. Additional conduits  141  can also be provided to deliver vaporized precursors from other vaporizers to the process chamber  70 . 
     Each of a pair of pressure sensors  48 ,  50 , preferably capacitance manometers, is respectively aligned with an open end  57 / 59  of the tube  54 . Accordingly, the difference in pressure measurements from the two pressure sensors  48 ,  50  will reflect the pressure drop across the tube  54 , thereby allowing the rate of gas flow through the tube  54  to be calculated. A capacitance manometer is an electronic gauge providing a direct measurement of pressure in the delivery conduit  40 . Where capacitance manometers are used, each manometer preferably has the same full-scale range, typically 10 torr. Suitable capacitance manometers include a specially-constructed Baratron® 121-based absolute pressure transducer (available by special order from MKS Instruments) and the model  622  Barocel® bakeable vacuum/pressure transducer (available from Edwards High Vacuum International, Wilmington, Mass.). The Baratron transducer is specially built and calibrated to operate at 200° C., in comparison to a standard Baratron® transducer, which is typically limited to 150° C. 
     The transducers are modified to remove all unnecessary mass and to promote uniform temperature distribution across the transducer. Accordingly, as a first step, the cover or shell of the transducer is removed. To do so, the cables attached to the Baratron® transducer are removed, the shell of the transducer is removed and discarded, and the cables are shortened and reattached. The housing support ring is also removed and discarded. Further, the port of the transducer is removed. Its length is machine cut, and it is then reattached. The electronics of the transducer are then re-calibrated to match the changed capacitance of the modified transducer. While the Barocel® transducer is available, off the shelf, for use at 200° C., as with the Baratron® transducer, the case of the Barocel transducer is removed, and its cables are removed and replaced. 
     In an alternative embodiment, illustrated in FIG. 3 b , the solid block  56  surrounding the laminar flow element  54  extends further toward the ends of the laminar flow element  54 . By lengthening the block  56 , the volume of open volume surrounding the laminar flow element  54  is reduced. This open volume is generally considered to be “dead space.” Reduction of this dead space is thought to provide a more direct and efficient flow path through the delivery conduit  40 . In a further preferred embodiment, all or nearly all dead space is removed as the block  56  and the laminar flow element  54  essentially form a single tubular component such that vapor flowing through the conduit  40  will hit a wall at the capacitance manometer  48  and be directed through a bore, which acts as the laminar flow element  54 , within that wall. 
     Also shown in FIG. 3 b  is a heated aluminum sheath  55 , which is in thermal contact with the delivery conduit  40  and other components of the precursor delivery system. 
     The proportional control valve  44  is coupled with the flow meter  46  in a processor-driven control loop to regulate the flow of vapor through the delivery conduit  40 . Accordingly, the flow meter  46  provides feedback regarding the pressure differential in the delivery conduit  40 , and this feedback is used to direct the proportional control valve  44  to increase or decrease flow, which in turn, will respectively increase or decrease the pressure differential in the delivery conduit  40 , as measured by the flow meter  46 . This responsive regulation of the proportional control valve  44  is continued until the pressure differential, as measured by the flow meter  46 , matches that which is needed to supply the precursor at the desired rate for reaction in the process chamber  70 . 
     Alternatively, a single differential pressure transducer capacitance manometer, which measures a pressure drop across the laminar flow element, can be used along with a single absolute pressure transducer in place of the pair of capacitance manometers. Other alternative means for inducing a predictable pressure drop include a choked flow element or a molecular flow element in place of the laminar flow element. 
     The gas-flow-control subsystem  14  further includes a second isolation valve  58 , e.g., an HPS Lopro® valve modified for high temperatures, positioned downstream from the flow meter  46 . 
     In parallel with the vaporization and gas-flow-control subsystems  12 ,  14 , a process gas subsystem  150  supplies additional reactant, purge and other process gases to the process chamber  70 . The illustrated subsystem  150  includes sources of argon  152 , helium  154 , and nitrous oxide (N 2 O)  156 . Gas flow from each of these sources is regulated by a plurality of valves  162 / 164 / 169  and  161 / 163 / 168  with a mass flow controller  165 / 166 / 167 . 
     Nitrous oxide from source  156  flows through valve  157  into process chamber  70  through exit port  143  for reaction with the vaporized precursor delivered through delivery conduit  40 . After deposition is performed, argon from source  152  flows through valve  157  into process chamber  70  to purge the chamber  70 . By opening valve  160  in conjunction with at least one of valves  155 ,  158  or  159 , particular subsystems or segments of CVD apparatus  10  can be independently isolated and evacuated or backfilled. Additional reactant sources and plasma can be linked in parallel with the nitrous oxide for delivery to the process chamber  70 . 
     Helium from source  154  is delivered through valve  157  into process chamber  70 , where it is channeled through a conduit for release between a substrate chuck  74  and a substrate  88  upon which vapors are deposited to improve the transfer of heat between the substrate chuck  74  and the substrate  88 . 
     The process subsystem  16  is designed to perform the actual deposition of reacted precursor vapor onto a substrate. The process subsystem  16 , illustrated in FIG. 4 a , includes a process chamber  70 , a showerhead  72  and a substrate chuck  74 . 
     The process chamber  70  typically is formed of electroless-nickel- and sulphamate-nickel-plated 6061 aluminum and is operated between 50° C. and 300° C. The process chamber  70  includes an access port  123 , which can be joined to a wafer handler or cluster tool for transporting wafers into and out of the process chamber  70 . A gate valve  125  is mounted to the access port  123  for controlling access there through. The process chamber  70  further includes an inlet port  76  in an upstream section  78  of the chamber  70  and an exhaust port  80  in a downstream section  82  of the chamber  70  through which vapor flow is managed. An outlet of the delivery conduit  40  projects into the chamber  70  through the inlet port  76 , while the exhaust port  80  is connected to the exhaust subsystem  18 . A pressure sensor  51  (e.g., a capacitance manometer) is positioned to measure the vapor pressure in the upstream section  78 . At least one other pressure sensor  53  (e.g., a capacitance manometer) is positioned to measure the vapor pressure in the downstream section  82 . 
     A showerhead  72  segregates the process chamber  70  into upstream and downstream sections  78 ,  82 . In one embodiment, the showerhead  72  comprises electroless-nickel- and sulphamate-nickel-plated 6061 aluminum and is in the form of a flat, circular plate with passages  84  for gas flow. The showerhead  72  is either passive, as illustrated in FIG. 4 a , or active. An “active” showerhead is a showerhead which undergoes a change to alter the rate at which gas flows through it. In a preferred embodiment, the active showerhead includes an array of phase-change eutectic milliscale valves in place of the small holes  84  illustrated in FIG. 5 a . These valves, which are available from TiNi Alloy Company (San Leandro, Calif.), are made of a thermal-phase-change material comprising a micromachined titanium and nickel alloy. The valves, which, in one embodiment, are about 0.1 inch in diameter, can be formed in situ on the showerhead plate en masse. The valves open when current is applied. The valves react in milliseconds, so they can be used in real time. They can also be used to effect dynamic patterns of valve actuation, e.g., sweeping action, pulsing, spots, etc. 
     In an alternative embodiment, the showerhead  72  is a smaller plate with a diameter approximating that of the wafer  88 . This embodiment is shown from a top view in FIG. 5 b  and, in cross-section, from a side view in FIG. 5 c . As shown, the showerhead  72  is replaceably fitted into a larger ring  73  and is no larger than a confined process volume, described below. Accordingly, various showerheads may be exchanged in the larger ring for use with different sized wafers and with different process conditions. The use of smaller showerheads reduces cost, provides greater flexibility in processing, and concentrates the flow of process gases exclusively into the volume immediately above the substrate  88 . 
     A substrate chuck  74 , positioned in the downstream section  82 , comprises electroless-nickel-plated OFHC copper, with an electroplated sulphamate nickel overplate, and, optionally, an overcoat of a flame-sprayed aluminum oxide or other, similar insulating ceramic. The substrate chuck  74  is designed to hold a substrate  88  upon which the precursor is to be reacted. The substrate chuck  74  includes a plurality of bores  75  radiating outward and into the substrate chuck  74 . A platinum resistance thermometer is inserted through one of the bores  75  to measure the temperature of the substrate chuck  74  The substrate chuck  74  is heated by Watt-Flex® cartridge heaters (available from Dalton Electric Heating Co., Inc., Ipswich, Mass.) inserted into the remaining bores  75 . In this embodiment, the heaters are 3.0 inches in length and 0.25 inches in diameter. The heaters supply 50 watts at 24-25 VAC, and can be heated above 1000° C. The heaters, however, are typically operated at a maximum of 650° C., and, more commonly, around 300-500° C. These temperatures are considerably lower than the temperatures to which a wafer is typically heated in conventional thermal CVD processes, i.e., 800-1300° C. The reason why, in the system of this invention, the substrate can be operated at lower temperatures is that the vaporized precursor is provided at higher concentrations at the wafer due to the absence of a carrier gas, the shorter delivery paths, and the higher conductance of the conduits. 
     As an alternative or supplement to the above-described heating means, the substrate can be heated by a laser, an ion beam, an electron beam and/or photon-assisted energy sources. In any case, the substrate is heated to a temperature higher than the temperature of the walls of the process chamber. 
     In one embodiment, a DC or AC bias is supplied to the substrate chuck  74  by a voltage source  79 . The elevator shaft can also be biased in order to provide electrical bias across the substrate. The electromagnetic field generated by the bias can influence the crystalline structure of the thin film as it grows on the substrate. It has been shown that an otherwise uniform film (with a lattice orientation of &lt;100&gt; for example) can be induced to grow in a different crystalline structure (&lt;111&gt; for example). In some cases, a film is induced to grow in a gradient from one structure (e.g., &lt;100&gt;) to another (e.g., &lt;111&gt;) by applying either a DC or AC bias to the substrate  88  relative to the rest of the chamber. To achieve this bias, a ceramic ring is used to electrically isolate the substrate chuck  74  from the process chamber  70  and other components within the process chamber  70 , which are held at ground. Alternatively, and more commonly, the lower portion of the process chamber  18  coated with aluminum oxide of sufficient thickness to isolate the chuck and bellows from the chamber. 
     A substrate  88 , e.g., a silicon semiconductor wafer, is mounted on the substrate chuck  74  and is subject to the generated DC or AC bias. A mask (or clamp)  94  extends down from the showerhead  72  and forms a ring which masks the outer 0.5 to 3.5 mm or more but more typically 1.5 to 2.0 mm from the edge of the substrate  88 . The mask  94  also shrouds the edge of the substrate  88  and prevents CVD from occurring on the edge or underside of the substrate  88 . The mask  94  is formed of a material having very low thermal conductivity to minimize heat loss to any area, other than the substrate, that is exposed to unreacted process gas. Preferably, the mask is formed of either Incoloy® 850, Elgiloy® (available from Elgiloy Ltd. Partnership, Elgin, Ill.) or molybdenum and, optionally, includes a coating of either aluminum oxide (Al 2 O 3 ), silicon dioxide (SiO 2 ) or other, similar dielectric material. Alternatively, the mask  94  is formed of ceramic. 
     When the substrate chuck  74  is lowered, the mask  94  is suspended above the substrate  88 . 
     A flow shield  77  extends down from the showerhead  72  and forms a ring within which the substrate  88  is positioned. The flow shield  77  channels the flow of reactant gases through the showerhead  72  and across the exposed face of the substrate  88 . 
     The substrate chuck  74  is raised and lowered by an elevator  96 , upon which the substrate chuck  74  is mounted. The elevator  96  is electrically isolated. The elevator  96  is powered by a stepping motor  97 , with the power being transmitted by a drive shaft  99 . The position of the elevator  96  is continuously adjustable over a range from fully retracted to fully extended, providing a working stroke of about 70 mm. The changing position of the substrate chuck  74  is measured by a linear voltage differential transformer  101 , which can measure the height of the elevator with sub-micron precision. By raising and lowering the substrate chuck  74 , the flow character of vapor reactants above the substrate  88  can be altered. Accordingly, the substrate chuck  74 , when raised and lowered by the elevator  96 , can be used as a throttle valve controlling the flow rate through the showerhead  72 . The vertical position of the chuck  74  can also be changed to modify the microstructure and properties of the deposited film. 
     Further, the showerhead  72 , the mask  94 , the replaceable gettering ring  89 , the flow shield  77  and the substrate  88  are positioned to cooperatively define a confined process volume to which the vapor precursor and, if required, reactant gas are delivered and in which deposition will occur. The diameter of this volume (i.e., as defined by the mask  94 ) is preferably no more than about 120% the diameter of the substrate. The height (or depth) of the volume is a function of the position of the elevator, which governs the height of the substrate  88 . This volume, where processing occurs, is much smaller than that of conventional CVD reactors and, consequently, improves the efficiency of deposition on the substrate. 
     In the method of this invention, deposition occurs when process gases contact the heated substrate  88  and react to form a solid thereon. Deposition at the surface of the substrate can be rate-limited either by the rate of precursor transport or by the rate of reaction at the surface. In a typical CVD and plasma-enhanced, plasma-assisted or plasma-promoted vapor deposition (PECVD, PACVD, PPCVD) process, the limiting factor is the rate of precursor transport. Consequently, the rate of surface reaction will be sub-optimal and the vaporized or dissociated precursor will tend to react and deposit in a line-of-sight manner on the first hot surface that it contacts. Moreover, the use of a plasma, causes vapor-phase reactions which also mitigate against conformal coverage on the surface. As a consequence, and as shown in FIG. 5 e , the deposited layer  192  formed at the mouth of an etched cavity  194  in a substrate will grow much more quickly than will a layer  192  forming on more remote areas of the cavity  194 . 
     For further comparison, FIG. 5 d  illustrates a typical deposited layer  192  formed via physical vapor deposition (PVD). The deposited structure  192  has a similar pinched-off shape with very little deposit forming at the deeper regions of the cavity  194 . This imbalance results from the directional, line-of-sight deposition that is characteristic of PVD. 
     In contrast, however, FIG. 5 f  illustrates the approximate structure of a conformal deposit  192  that can be formed in accordance with the equipment described herein and in accordance with the method of this invention. In this embodiment, the pinching effect at the mouth of the cavity  194  is noticeably diminished because the deposition process is limited by the reaction kinetics at the surface rather than by the rate of precursor transport, with the resulting tendency for deposition to occur simultaneously and uniformly on all exposed surfaces of the substrate. 
     A plurality of pins (preferably, at least three) engage the substrate chuck  74  through bores within the substrate chuck  74 . The pins are cylindrical with rounded ends. One such pin  74   a  is illustrated in FIG. 4 a . In this embodiment, the pins are mounted to the base of the downstream section  82  of the process chamber  70 . On the other hand, when the elevator  96  is lowered, the substrate chuck  74  slides down the pins toward the base of the downstream section  82 . When the substrate chuck  74  is fully retracted, the pins extend through the top surface of the substrate chuck  74  to lift the substrate  88  off the chuck  74 . After it is lifted off the chuck  74 , the substrate  88  can then be removed from the process chamber  70  by a robot arm. A similar process, illustrated in FIGS. 12 a-d , is performed to place the wafer on the substrate. 
     In an alternative embodiment, illustrated in FIG. 4 b , each self-aligned pin  74   a  is attached to the substrate chuck  74  by bellows  81 . The bellows  81  provides a spring-like support because the free height of the bellows  81  is greater than the depth of the cavity in which it is mounted. When the chuck  74  is fully retracted, as shown in FIG. 4 b , the pin  74   a  is forced through the chuck  74 , lifting the substrate  88  off the surface of the chuck  74 . When the elevator  96  is used to raise the chuck  74  toward the showerhead  72 , the pin  74   a  drops back down to a position where it remains held in place by the bellows  81  within the chuck  74  below its top surface. 
     FIG. 4 b  also illustrates a replaceable gettering ring  89  to mask the side of the chuck  74  from deposition. The side of the chuck  74 , which is heated throughout, typically is subject to an accumulation of deposits from unreacted precursors which do not react on the substrate  88 . After deposits build on the replaceable gettering ring  89 , the ring  89  can be simply replaced without any damage to the chuck  74  and without requiring that the chuck  74  be replaced. Accordingly, use of the replaceable gettering ring  89  can greatly extend the useful life of the chuck  74 . 
     The replaceable gettering ring  89  also serves as a support for the substrate  88  when the pins  74   a  are retracted. Accordingly the substrate  88  is not in physical contact with the substrate chuck  74 . Rather, a gap of about 0.015 inches (0.38 mm) exists between the substrate  88  and the chuck  74 . As noted, this gap is filled with helium gas which transfers heat between the chuck  74  and the substrate  88 . The mask  94  seals the gap at the edge of the substrate  88 , thereby containing the helium gas. The pressure of the helium gas between the substrate  88  and the chuck  74  is controlled, and the flow of helium is also monitored and/or controlled. 
     FIG. 4 c  illustrates the apparatus of FIG. 4 b  with the chuck in position for wafer processing. FIG. 4 d  also shows this same apparatus, this time with the shaft of the elevator fully extended. In this position, the chuck  74  is lifted out of the processing chamber  70 , providing access to the chuck for service/maintenance. 
     Optionally, a sensor  87 , e.g., an optical thickness sensor including a grazing incidence laser, is provided in the process chamber  70  for measuring the thickness or chemistry of the deposited film or the ambient conditions in the process chamber  70 . 
     The final subsystem, i.e., the exhaust subsystem  18 , is designed, in part, to maintain a pressure differential across the showerhead  72 . The exhaust subsystem  18  includes an exhaust conduit  110  connected to the downstream section  82  of the process chamber  70 , a trap vessel  85 , and a vacuum pump  112  (IQDP  80 , available from Edwards High Vacuum International, Wilmington, Mass., or equivalent) connected to the exhaust conduit  110  opposite the process chamber  70  to thereby pump vapors from the process chamber  70 , through the exhaust conduit  110 . Alternatively, more than one vacuum pump  112  can be used. A throttle valve  83  is positioned in the exhaust conduit  110  to regulate the amount of vapor pumped from the process chamber  70  and, accordingly, to maintain a desired vapor pressure in the process chamber  70 . In this embodiment, the trap vessel  85  is situated between the vacuum pump  112  and the throttle valve  83 . The purpose of the trap vessel  85  is to trap a majority of the unreacted precursor vapor before it reaches the vacuum pump(s)  112 . The trap vessel  85  includes surfaces that cause the precursor to react or be otherwise retained thereupon due to chemical or thermal decomposition or an entrainment process. 
     In an alternative, preferred embodiment, illustrated in FIGS. 1C-D, a scrubber  85 ′ is used in place of the trap  85 . The scrubber  85 ′ actively removes harmful contaminants from the gas stream before exiting the process subsystem thereby providing a cleaner effluent leaving the system. A small, dry, low-power, dynamic, variable-speed pump  95  is also provided within the process subsystem cabinet  16 . A preferred embodiment of pump  95  is manufactured by Pfeiffer Vacuum (Nashua, N.H., USA), which pumps at rates up to 50 m 3 /hr. The pump  95  is integrated with the control system, through a ProfiBus data bus, such that the pumping speed of the pump  95  is controlled to govern the rate at which vapor is drawn through the system via a closed loop processing system. By so controlling the pumping speed, the throttle valve  83  upstream from the pump  95  can be omitted. 
     Each of the subsystems  12 ,  14 ,  15 ,  18 ,  150  are enclosed in sealed vessels to contain leaks of any hazardous gases from the system. The vaporization and gas-flow-control subsystems  12  and  14  are both contained in a first sealed vessel  180 . An exhaust line  182  is connected to the first sealed vessel  180  for the controlled release and removal of gases escaping from the system. A second sealed vessel  184 , which likewise includes an exhaust line  186 , encloses the process gas subsystem  150 . 
     A CVD module  10  incorporating the various subsystems described herein is illustrated from three different perspectives in FIGS. 6 a-c . FIG. 6 a  illustrates a rear view (from the vantage point of a connected wafer handler) of the CVD module  10 . FIG. 6 b  illustrates a side view of that same CVD module. Finally, FIG. 6 c  illustrates a front view of the CVD module  10 . Components that are all included within the module include a process module controller  205 , a vaporization subsystem  12 , a power input module  142 , a gas-flow-control subsystem  14 , a process subsystem  16 , an elevator  96 , a scrubber  85 ′, and a gate valve  125 . 
     FIG. 7 illustrates a general control architecture diagram  200  for control of a single CVD apparatus  10  and its associated subsystems. Control of a CVD apparatus  10  is facilitated through a process module controller  205  operating under software control in a distributed manner to independently control temperature control modules  210 , pressure control modules  215 , flow control modules  220 , and elevator control modules  225 . While the preferred embodiment is illustrated as a distributed system, the overall chemical vapor deposition concepts and techniques presented within this invention do not have to be implemented in a distributed fashion. Rather, they may be performed in a linear manner with a single main controller executing all processing steps itself, while still overcoming many of the problems of the prior art system. However, the distributed nature of the preferred embodiment provides significant advantages over a linear system operation, as will be explained. 
     Modules  210  through  225  are representative of the main processing tasks of the CVD apparatus  10 , and there may be other control modules not shown which may be used for other specific tasks noted throughout this specification. Each of the previously described subsystems, including the vaporization subsystem  12 , gas-flow-control subsystem  14 , process subsystem  16 , and exhaust subsystem  18  can include certain components that are operated by the modules  210 ,  215 ,  220  and/or  225  of the overall control architecture shown in FIG.  7 . 
     For example, in FIGS. 2 a  and  2   b , the vaporizer subsystem  12  involves, among other tasks, controlling the temperature of reservoir  20 , controlling the position of, and therefore the amount of precursor flow from dispensing valve  24 , controlling the temperature of the vaporizer  28 , and monitoring the pressures within the vaporization chamber  26 . Each of these tasks is generally coordinated via software operating within process module controller  205  and is physically carried out by one or more of modules  210  through  225 . 
     Through the distributed nature of the various system components, the process module controller  205  can manage wafer processing for an individual CVD apparatus  10 , which requires multiple simultaneous events. If wafer processing for a single CVD apparatus  10  is not too complex, it may be the case that an alternative embodiment of the invention may use a single process module controller to monitor and control more than one CVD apparatus. That is, two physical CVD systems  10  could be controlled by a single process module controller  205 , without overloading the processing capacity of the process module controller  205 . The preferred embodiment however uses a separate process module controller  205  per CVD apparatus  10 . By using distributed processing, certain steps in the overall wafer processing procedure can be performed in parallel with each other which results in more efficient wafer yields and allows real time management of vapor deposition. 
     Actual process control is accomplished by providing separate control modules  210  through  225  for each of the individual operational components (i.e., valves, temperature monitoring and heating devices, motors, etc.) in each of the subsystems. The modules can be programmed to do specific tasks related to a specific portion of that subsystem&#39;s functionality. When given a task, each control module reports back to the process module controller  205  when the task is complete, its status, and/or if the task fails to complete. 
     For example, all of the temperature control processing may be done in a distributed fashion, such that the high level process module controller  205  can merely instruct one or more specific temperature control modules  210  to set and maintain specific temperatures. The process module controller  205  can then move on to the next main task in the overall wafer processing routine. Achieving and maintaining the set point temperature(s) can then be carried out by the independent temperature control module  210  in a closed loop manner. 
     An example of a control module is the Intelligent Module No. S7-353 or the S7-355, both manufactured by Siemens Corporation. Such modules may be used for intensive closed-loop type control tasks, while an Intelligent Module No. S7-331, also manufactured by Siemens Corporation, may be used for precision signal conditioning type tasks, such as voltage measurements from capacitance manometers resulting in adjustments in flow control. 
     These particular control modules used in the preferred embodiment, as well as most other electrical components in the system, operate at low voltage (i.e., 24 Volts AC or DC) in order to prevent injury in the event of a short circuit, and also to prevent interference with vapor deposition. Low voltage operation also allows the system of the invention to operate with 120 Volt or 240 Volt power supplies, or with other international power systems of differing voltages. 
     Accordingly, all aspects of control, beginning with the vaporization subsystem  12  and ending with the process subsystem  16 , are handled by modules which may be independently activated, and which can then handle the given task on their own. 
     There are, however, instances where modules can provide information or communications directly to other modules to establish adaptive relationships in order to maintain certain process settings. In such instances, these modules can adapt their task without the need for further instructions or tasks from the process module controller  205 . That is, two or more modules may establish a relationship such as a master/slave or client/server type relationship, and can adjust themselves accordingly to either back off from a task, or move ahead faster with a task, depending upon the feedback of other inter-related modules involved in adaptative relationships. 
     For example, a pressure control module  215  may be used to monitor pressure sensor  34 , which detects the pressure output from the vaporization chamber  26 . The pressure control module  215  can provide direct feedback to a separate flow control module  220  which operates isolation valve  42 . If the process module controller  205  initially instructs isolation valve  42 , through flow control module  220 , to maintain a certain flow of vapor gas, the flow control module  220  can obtain pressure data from the pressure control module  215  that controls pressure sensor  34 . This data may be used to determine if there is enough pressure in the delivery conduit to deliver the requested flow. If the pressure is too low or too high, pressure control module  215  may, depending upon the implementation, signal to the process module controller  205  that the task cannot be completed due to lack of pressure, or may, via an established adaptive relationship, signal in real time directly to a vaporization chamber pressure control module in order to increase or decrease vaporization chamber pressure. 
     In other words, while the overall processing of chemical vapor deposition is controlled in the CVD apparatus by the process module controller  205  with a master control routine, certain control module loops may incorporate data from other modules to adapt or detect changes in other system components, without the need for communication with process module controller  205 . Most frequently, this is done where the output of one module directly affects the performance or operation of another module. 
     Communication between the modules  210  through  225  and the process module controller  205  may be accomplished in a number of ways. Direct Memory Access (DMA) can be used to directly read and write data to commonly accessible memory locations within a shared memory  230 , as shown in FIG. 7. A data bus (not shown in FIG.  8 ), such as, for example, a ProfiBus data bus, which typically operates at 12 Megahertz and uses DB-9 connectors to interface to modules, can interconnect modules  210  through  225  with each other and the process module controller  205 , to allow data communications and sharing of information. It is to be understood that common networking and data communications processes and principles are contemplated herein as being applicable to communications between devices, modules and components in this invention. 
     It is also contemplated in this invention that faults in modules and componentry may occur and therefore, the invention can use redundant or fault tolerant modules, components and processors and can provide swappable dedicated processors for each module  210  through  225  and the process module controller  205 . By providing swappable componentry, parts may be replaced without shutting down the entire system. This is beneficial, for example, when an expensive precursor has been preheated and will be damaged if returned to a lower temperature. If a fault occurs, for example, in an elevator control module  215 , this module may be replaced or deactivated by another redundant module which may take over for the lost functionality of the failed module. The swapping or redundant failover may be performed without having to stop the wafer deposition process, which saves wafers and reduces precursor waste and reduces system down-time. 
     FIG. 8 illustrates a flow chart of the main processing tasks performed by the process module controller  205  from FIG.  7 . The steps  300  through  305  are, in a preferred embodiment, implemented in software or firmware and are performed when the CVD apparatus  10  is activated to process wafers. In the preferred embodiment being described, the main process control steps  300  through  305  are wafer-centric in nature. That is, these steps focus mainly upon wafer handling and execution of a process recipe which performs the CVD operation on a particular wafer. Generally, the master routine sets tasks to be performed, sets variables for those tasks and system operation, and instructs the dedicated modules to perform the tasks. In parallel with this main process routine, as will be explained, are a set of other concurrently executing routines which perform other tasks. The sub-processes are necessary for the success of the major process sequence (i.e., steps  300  through  305 ) of FIG. 8 to complete. The sub-processes, shown in FIGS. 9 a ,  9   b ,  10  and  11 , are, respectively, the vaporizer sub-process, the vapor phase flow controller sub-process, and the process chamber pressure control sub-process. Other sub-process may exist as well, such as, for example a cleanup process, a housekeeping process, a safety interlock process, and other which are explained herein. 
     In step  300  of the main process control subroutine of FIG. 8, the CVD apparatus  10  is pre-prepared to accept a wafer. This step includes, for example, the process of pre-heating the pre-cursor in reservoir  20  to the desired temperature and loading a process recipe for the wafer process to be performed by the CVD apparatus  10 . Parameters for the process recipe are loaded into memory  230  from an external source, such as, for example, a cluster tool controller (to be explained). The recipe parameters control the various settings such as temperature, pressure, and which vapors and gases are to be processed with the wafer  88 . 
     In a preferred embodiment, there may be as many as ten or more steps that constitute the recipe for wafer processing. Each step allows a user who is processing a wafer to select parameters, such as, for example, the “step number”, “step duration” (in seconds), “target process pressure” (in millitorr), “precursor flow rate” (milli-sccm), “reactant flow rate” (milli-sccm) and “wafer temperature” (degrees C). These parameters make up the recipe for a wafer and govern the general temperature, flow, pressure and operation of the CVD apparatus  10 . For example, the last parameter, “wafer temperature”, is a function of the substrate chuck temperature, since, as will be explained, the wafer is in contact with the substrate chuck for much of the time during processing. Hence, the wafer temperature is a parameter that typically does not change too much from one wafer to another, and may be provided merely for reference for the process recipe. 
     Step  301  prepares to accept a wafer and signals to an external wafer provider mechanism (e.g., central wafer handler robot arm  134 —to be explained in detail later) that the CVD apparatus  10  is ready to accept a wafer. Step  302  then coordinates the movement of the wafer into the process chamber  70  and placement of the wafer on the substrate chuck  74 . 
     FIGS. 12 a  through  12   d  pictorially illustrate the process of coordinating the movement of the wafer (step  302 ) into the process chamber  70 . Each of these figures includes top and side perspective views of the process chamber  70  area and robot arm  134 . In FIG. 12 a , substrate chuck  74  includes pins  74   a-c , upon which the substrate or wafer  88  is loaded prior to the CVD operation. Before entering the process chamber  70 , the wafer  88  rests upon an end effector of robot arm  134  outside of the process chamber  70 . As shown in FIG. 12 b , as the robot arm extends and enters into the process chamber  70 , the wafer  88 , carried on the end of the robot arm  134 , passes over substrate chuck  74  and substrate chuck pins  74   a-c  and passes under showerhead  72 , which is not in use during the process of accepting a wafer. FIG. 12 c  illustrates the wafer  88  fully inserted into process chamber  70 , prior to the retraction of the robot arm  134 . The wafer  88  rests on pins  74   a-c , after the robot arm  134  lowers slightly and retracts, as shown in FIG. 12 d.    
     Returning to the main processing routine shown in FIG. 8, step  303  then runs the current process recipe that has been programmed into the CVD apparatus  10 . The recipe (i.e. the parameters) may be changed between wafers, but once the recipe has been started in step  303 , the pre-loaded parameters used for processing do not change for the current wafer  88 . As will be explained in FIGS. 9 a ,  9   b ,  10  and  11 , running the recipe in step  303  includes aspects of temperature control (step  303   a ), pressure control (step  303   b ) and flow control (step  303   c ). The sub-processes in FIGS. 9 a ,  9   b ,  10  and  11  provide details as to the operation of these aspects of the invention. 
     In one embodiment of the invention, a recipe loaded into process module controller  205  governs the various processing steps of the wafer according to, for example, the “step duration” parameter. That is, this embodiment can be governed by timers set by parameters that determine, for instance, how long a particular vapor is deposited onto a wafer. 
     In another embodiment, the sensor sub-system  19  (FIG. 1B) can be used to calculate, measure, or determine the deposition activity on the wafer itself. This information can be used to determine when the next step in the recipe is performed. For example, if a step in the recipe calls for depositing 100 angstroms of copper using a copper vapor onto a wafer, the sensor sub-system, by monitoring the deposition activity, can indicate when this has been completed. As such, the steps in the recipe in this embodiment are not driven so much by timers, as by when processing steps are actually physically completed. 
     The sensor modules  227 , illustrated in the control architecture in FIG. 7 are used to control and provide feedback to process module controller  205  from wafer subsystem  19  as illustrated in FIGS. 1A and 1B. Wafer sensing equipment  87  in wafer subsystem  19 , for example, may comprise a laser measurement system that can measure the thickness of any layer of material being deposited onto the wafer  88  during a CVD operation. This layer thickness information may be monitored by sensor modules  227 , and when the task of detecting 100 angstroms of copper, for example, is complete, the sensor modules  227  can indicate to the process module controller  205  that the task has been completed. Other wafer sensing equipment that may be used to sense CVD progress may include reflectivity sensors that detect the reflectiveness of the wafer surface. As more material is deposited onto a wafer, the surface may become more or less reflective thus indicating deposition progress. Another sensing device may be an x-ray diffraction system used to measure composition of the wafer surface, thus indicating deposition progress. Those skilled in the art will now readily understand that other common real-time measurement and sensing hardware may used within sensor sub-system  19  to detect and indicate recipe step completion, depending upon the task. 
     After the recipe is complete, the wafer  88  has been processed by the vapor and gases in the process chamber  70 . Step  304  in FIG. 8 then removes the wafer, which is generally the reverse process of that illustrated in FIGS. 12 a  through  12   d . The robot arm  134  returns and picks up the wafer  88  off of the substrate chuck pins  74   a-c , and carries the wafer  88  out of the process chamber  70 . Step  305  then performs cleanup of the CVD apparatus  10 , which will also be described in more detail later. 
     FIG. 10 illustrates the steps of the vaporizer sub-process that is continually performed during the main control processing steps that execute as explained with respect to FIG.  8 . The vaporizer sub-process steps  330  through  334  generally control the vaporization of the precursor in reservoir  20  and the maintenance of pressure at the inlet port  76  to the process chamber  70 . The vaporizer sub-process is also responsible for the cleanup of the vaporizer  28  between processing wafers during standby modes. 
     The vaporizer sub-process shown in FIG. 9 a  is driven primarily by the “vaporizer temperature” parameter that gets loaded during the programming of the recipe into memory  230 . This variable drives the temperature setting for all of the other temperature controlled surfaces except the wafer chuck  74  (set by a “wafer chuck temperature” setting) and the funnel temperature (set by a “funnel temperature” setting). The vaporizer pressure largely relies on the pressure control modules  215  which operate and monitor the capacitance manometers  34 ,  48 ,  50 ,  51  and  53  located throughout the system, as previously described. 
     In step  330 , the pressure at pressure sensor  34  must be greater than the pressure at pressure sensor  48 . In step  331 , the pressure at pressure sensor  48  must be greater than the pressure at pressure sensor  50 . In step  332 , the pressure at pressure sensor  50  must be greater than the pressure at pressure sensor  51 . And finally, in step  333 , the pressure measured at pressure sensor  51  must, in this embodiment, be approximately 1.5 times (or more) greater than the pressure measured at pressure sensor  53 . If any of these steps  330  through  333  fail, feedback is provided back to the vaporizer subsystem  12  by step  334 , at which point the appropriate modules in various subsystems are adjusted so as to maintain the optimum pressure at the wafer, as measured by the difference in pressure between pressure sensors  51  and  53 . 
     The recipe parameter “process pressure” is referred to as the “target pressure” since this is the pressure to be maintained by the system at the wafer  88 , and is attained in cooperation between the vaporizer sub-process (FIG.  10 ), the vapor phase flow controller sub-process (FIG. 10) and the process chamber pressure control sub-process (FIG.  11 ). 
     Hence, as explained above, during wafer processing, the reservoir  20  deposits small amounts of precursor onto vaporizer  28  which is heated. Each small amount of precursor, which typically flows slowly down the vaporizer  28  inverted cone structure, forms a thin film and resides on the cone for a period of time during vaporizing. As this vaporization occurs, an upward ramp in pressure is measured by capacitance manometer  34 . The upper limit of the vapor pressure that is measured by pressure sensor  34  is a function of the temperature of the vaporizer  28  (and the rest of the system) as well as the material used as the precursor. Thus, too high of a temperature may cause the premature chemical decomposition of the precursor prior to its exposure to the wafer  88 , and too low of a temperature may result in a low vapor pressure, low flow rate, and low process pressure which results in a low chemical vapor deposition rate. 
     The vaporizer sub-processes in FIGS. 9 a  and  9   b  may be in either a processing state or a standby state. The processing state is used, as explained above with respect to FIG. 9 a , after a wafer has been accepted. The standby state governs a cleanup process and is shown in FIG. 9 b  and will be described in conjunction with FIGS. 1A through 1D. 
     During cleanup of the vaporizer sub-process, in step  340 , no precursor is introduced into the vaporization chamber  26 . In step  341 , isolation valve  42  isolates the entire vaporization subsystem  12  from the other subsystems. Step  342  then fully opens valve  160 . Next, in step  343 , Argon gas provided from valves  161  and  162  and mass flow controller  165  is introduced into the vaporization chamber  26  until a pressure of approximately 50 torr is measured at pressure sensor  34 . Then, step  343  evacuates the pressure in vaporization chamber  26 , by opening valve  170  and closing valves  161  and  162 , and operating exhaust subsystem  118  to suck out the argon gas. Step  344  then detects a vacuum pressure. Step  345  then repeats steps  343  and  344  N times, where N may be one, two or more times, for example. This N repeat count may be varied, depending upon the properties of substances used. Step  346  then evacuates the vaporization chamber  26  and step  347  maintains the entire volume of vaporization chamber  26  in a vacuum until the vaporization sub-process is instructed to go active to begin processing wafers. 
     The second sub-process is the vapor phase flow controller sub-process and is illustrated by the processing steps in FIG.  11 . During wafer processing, this sub-process ensures that the gas-flow-control subsystem maintains a steady flow of vapor to the process chamber  70 , in concert with the variations in pressure that occur at various critical points in the system as explained above during wafer processing. The main objective of this sub-process is to maintain the target mass flow and total aggregated mass flow of vapor to the wafer  88 . Unlike traditional mass flow controllers, where pressures are typically 20 psig or more at inlets to the wafer and that flow into a vacuum at or below the wafer, the present invention uses this sub-process to control the flow of vapor in upstream section  78 , where the pressure is only one to five torr, and where the “process pressure” is targeted at approximately 800 to 1000 millitorr. 
     To accomplish this, this sub-process uses the proportional control valve(s)  44  ( 441  in FIG. 1A,  44  in FIG. 1C) to maintain the appropriate flow and target pressure drop as measured from pressure sensor  34  to pressure sensor  48 . Step  360  in FIG. 10 monitors this pressure difference. Step  361  then determines if adaptive flow control is operational. If so, step  362  is executed which calculates the desired flow (“Q”) of the vapor being applied to the wafer and adjusts, in step  363 , the process time system variable to compensate for any variations from the target pressure experienced during the normal set process time. That is, step  363  lengthens or shortens the check time between determining system pressures, so that the pressure will have the correct time to build based upon the precursor material being used for vapor flow. 
     In step  361 , if adaptive flow control is not being used, step  364  determines if the pressure across the proportional control valve(s)  44  ( 441  in FIG. 1A,  44  in FIG. 1C) is insufficient to attain the targeted flow rate, and if so, step  365  detects this and signals to the other two sub-processes to attain the desired flow rate by varying appropriate settings. 
     The vapor phase flow controller sub-process in FIG. 10 is also responsible for controlling modules that set the flow rate of oxidizing reactants via step  366 . That is, nitrous oxide, for example, from valves  168  and  169  may be provided as a reactant gas along with the precursor vapor, into the process chamber during flow control of the vapor from the vaporization chamber  26 . Step  366  determines the flow rate of any reactant gas by a “reactant flow rate” parameter provided in the recipe. Typically, the reactant flow rate is expressed as a ratio to the flow rate of the vapor from the vaporization chamber  26 . 
     For example, a target pressure that might be typically set is 1.5 to 2.0:1. Since the flow rate of vapor can vary somewhat (as explained above), the flow rate of the reactant from one or more of the mass flow controllers  165 ,  166  or  167  must also vary in concert with the flow rate of the precursor vapor. Note that in the embodiments shown in the figures, the system is well damped such that variations are on the order of plus or minus 10 percent of the target pressure or flow rate, and are dependent upon variations in the lots of precursor used as received from different suppliers, for example. That is, oscillatory swings may not be noticed within one batch of precursor, but subtle shifts may be observed based upon chemical lots. The sub-process in FIG. 10 helps eliminate these shifts. 
     The vapor phase flow control sub-process, if in a standby state, as shown in standalone step  367 , independently checks any output offsets that might have occurred between pressure sensor  48  and pressure sensor  50 , and can use this calculated offset to adjust the pressure sensors apparent output accordingly during subsequent calculations while in active mode. Step  367  can also cross-check pressure measurements of sensors  48  and  50  in standby mode against pressure sensors  34 ,  51  and  53 . 
     FIG. 11 illustrates the third sub-process, referred to as the process chamber pressure control sub-process, which is associated with maintaining the pressure at the wafer  88 . In step  380 , the pressure is measured at capacitance manometer  53 , which is the pressure in the process chamber  70  below the showerhead  72  at the wafer. Step  381  then directs throttle valve  58  to increase or decrease the pressure as measured in step  380 , to maintain the pressure as defined by the parameter “process pressure”. 
     FIG. 13 illustrates the processing steps performed in a cleanup sub-process that runs continuously and which is transparent to the other sub-processes in the system. Upon startup of the CVD apparatus, without a signal of an approaching wafer, the cleanup sub-process is the default process. The cleanup sub-process, in step  390  enables a mechanical circuit breaker to isolate the electrical system components in the event of a power surge. Step  391  maintains all heat zones at the system set points. The parameter “vaporizer temperature” is used as the temperature set point for all heated zones except the reservoir  20  and funnel  22  temperatures, and wafer chuck  74  temperatures. This step can also detect heating wire breaks or shorts. Step  392  ensures that adequate vacuum is present for the process module by testing the vacuum pump control. Step  393  monitors the state of the door and housing covers surrounding the CVD apparatus  10 . Steps  394  and  395  monitor system power and pressures, and looks for excursions outside of the normal operating state. Step  396  tracks gauge status and can detect gauge problems and can cross calibrate gauges in the system. Step  397  sets up and calibrates the mass flow controllers  165 ,  166  and  167 . Step  398  cross calibrates the pressure sensors in the system, and step  399  initializes the system parameters to a default state. 
     FIG. 14 illustrates a schematic architecture of a CVD apparatus of this invention, with each of the previously described sub-processes  600  through  604  of FIGS. 8 through 13 illustrated as a closed loop. Process module controller  205  interfaces with the other hardware components of the system via data bus  605 , which carries serial analog and digital commands to the components. Each of the control modules  210  through  227  interfaces to the data bus  605 , to communicate with process module controller  205 , and in certain instances where adaptive relationship exists, with each other. The process module controller  205  is also connected to a Profibus data bus  607  via which provides deterministic communication with any of a cluster tool controller, a transport module controller, or another process module controller. At higher levels of communication, not shown in FIG. 14, communication is generally via Ethernet, which is non-deterministic. 
     In the vaporizer loop  600 , a pressure control module  215  monitors pressure from capacitance manometers  34 ,  48 ,  50 ,  51 , and  53 , according to the processing explained above, and can provide data to temperature control module  210  which controls vaporizer heating element  29 , in order to provide proper vapor for the system to operate. To interface  606  between pressure control module  215  and temperature control module  210  is an example of a closed loop adaptative relationship, since the temperature is controlled based upon feedback from the pressure control module  215 . 
     In flow control loop  601 , which is responsible for maintaining the proper flow of vapor in the system, pressure control module  215  monitors pressure from each of pressure sensors  34 ,  48  and  50 , in order to provide feedback data to flow control module  220 , which operates proportional relief valve  44 , as well as valves  161  through  164 ,  168 ,  169  and  170 , in order to provide vapor and reactant gases at a proper flow rate. 
     Process chamber pressure control loop  602  uses pressure control module  215  to detect pressure at pressure sensors  51  and  53  within the process chamber  70 . This pressure information is used in an adaptative relationship between the pressure sensors and the throttle valve  83 , operated by the flow control module  220 . This closed loop  602  ensures that the pressure in the process chamber is correct during wafer processing by using the throttle relief valve  83  to maintain a continuous flow. 
     Elevator control loop  603  illustrates the adaptative relationship between the elevator  96 , which is operated by elevator control module  225 , and the sensor control module  227  which uses sensor equipment  87  to detect how much material has been deposited on a wafer. In this closed loop, which is used when the recipe calls for sensor control, the elevator  96  may be lowered when the sensor equipment  83  detects enough material is present on the wafer. Thus, direct communications is provided between the elevator control module  225  and the sensor control module  227 . 
     The elevator control loop  603  is also related to the sensor loop  604 , in that when sensor equipment  96  detects enough deposition material on a wafer, sensor control module  227  notifies flow control module  220  to activate throttle valve  83  in order to turn on the exhaust pump to full power. This empties the process chamber  70  of any leftover vapor so as to immediately stop the deposition process. Sensor loop  604  is thus another example of an adaptive loop, but acts more like a one way trigger since the sensor equipment  96  causes the throttle valve  83  to open when deposition is complete. 
     In each of the aforementioned loops  600  through  604 , the process control module  205  can merely provide the appropriate tasks to each of the control modules  210  through  227 . The control modules will execute the given task on their own. By allowing adaptive relationships as explained above, closed loops are formed for the basic underlying sub-processes required for the CVD apparatus to operate efficiently. The process module controller  205  monitors the progress of each closed loop via status data that is provided from each control module. Thus, the process module controller  205  is fully aware of how a specific CVD process is progressing while the process is taking place. In this manner, the process module controller  205  can report to a higher level process, such as the main process taking place within a cluster tool controller  207 . 
     The “processing hierarchy” formed by the lower closed loops and control modules, the intermediate process module controller routine executing on the process module controller  205 , and the master cluster tool controller routine executing on the cluster tool controller  120  allows modifications to processing code at one level to have little or no adverse impact on the programs or processes used for other aspects of the CVD process. Moreover, any modifications made to one aspect of the CVD processing, for example, in the flow control loop, which may happen to impact the processing of other loops, will be properly accounted for due to the adaptive relationships and feedback of information between control modules. This hierarchy also allows easy code maintenance and a structured environment where features may be added to one area of CVD processing without having to re-tool or re-code other areas. 
     In one embodiment, the CVD apparatus  10  is used to deposit a number of leading edge films on a single wafer. This embodiment is designed to operate at low pressure (0.001 to 10.0 torr) and is aimed at the deposition of films with geometries of 0.25 microns or less. The same embodiment, with changes only in temperature and flow control components, will be used in a number of different processes to limit costs and maintenance requirements. 
     Films that can be deposited by this system include, but are not limited to, the following: aluminum from dimethyl aluminum hydroxide (DMAH), copper from one of the Cu I (hfac)(tmvs, tevs, teovs) precursors, tantalum nitride from a solid precursor such as TaBr 4 , titanium nitride from a liquid precursor such as tetrakisdiethylamido titanium (TDEAT), tetrakisdimethylamido titanium (TDMAT) or TiBr 4 , low-k dielectric films from hexasilsesquioxane (HSQ) or a fluorinated tetraethylorthosilicate (TEOS), and tantalum oxide from tantalum pentaethoxide (TAETO) and either ozone or N 2 O. 
     As an example of a process performed in accordance with this invention, a tantalum oxide film is deposited on a wafer using liquid TAETO as a precursor and gaseous N 2 O as an oxidant. The reservoir  20  is filled with TAETO either with the reservoir  20  in place in the system or with the reservoir  20  temporarily removed for filling. While in the reservoir  20 , the TAETO is stored at a temperature above its melting point but below that at which it decomposes. In this embodiment, the TAETO is stored at near room temperature. From the reservoir  20 , the TAETO is delivered to the vaporizer  28  through the axial displacement pulse valve in an amount that is just sufficient to generate a workable vapor pressure to deliver to the process chamber  70 . The temperature of the vaporizer  28  is tightly controlled, in one embodiment, at 180° C., to vaporize the TAETO as it flows across the surface of the vaporizer  28  without causing the TAETO to thermally decompose. 
     The vapor pressure of TAETO that is generated in the vaporization chamber  26  is a function of the temperature of the vaporizer  28 . Specifically for TAETO, the log of vapor pressure can be calculated with the following formula: 
     
       
         Log  P= 11.693−(4987.12/ T ),  
       
     
     where P is pressure, 11.693 is the estimated coefficient of vaporization, and T is temperature in Kelvin. The vapor pressure of TAETO (measured in torr) is provided in Table 1, below, over a range of temperatures from 100° C. to 220° C. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Log P 
                 T in K 
                 T in C 
                 Coefficient 
                 P in torr 
               
               
                   
               
             
            
               
                 −1.71324  
                 372 
                 100 
                 11.693 
                 0.0194 
               
               
                 −1.67729  
                 373 
                 101 
                 11.693 
                 0.0210 
               
               
                 −1.64155  
                 374 
                 102 
                 11.693 
                 0.0228 
               
               
                 −1.60599  
                 375 
                 103 
                 11.693 
                 0.0248 
               
               
                 −1.57062  
                 376 
                 104 
                 11.693 
                 0.0288 
               
               
                 −1.53644  
                 377 
                 105 
                 11.693 
                 0.0291 
               
               
                 −1.50044  
                 378 
                 106 
                 11.693 
                 0.0316 
               
               
                 −1.48583  
                 379 
                 107 
                 11.693 
                 0.0342 
               
               
                 −1.43100  
                 380 
                 108 
                 11.693 
                 0.0371 
               
               
                 −1.39666  
                 381 
                 109 
                 11.693 
                 0.0401 
               
               
                 −1.36229  
                 382 
                 110 
                 11.693 
                 0.0434 
               
               
                 −1.32822  
                 383 
                 111 
                 11.693 
                 0.0470 
               
               
                 −1.29429  
                 384 
                 112 
                 11.693 
                 0.0508 
               
               
                 −1.26056  
                 385 
                 113 
                 11.593 
                 0.0542 
               
               
                 −1.22700  
                 386 
                 114 
                 11.693 
                 0.0593 
               
               
                 −1.19361  
                 387 
                 115 
                 11.693 
                 0.0640 
               
               
                 −1.16040  
                 388 
                 116 
                 11.693 
                 0.0891 
               
               
                 −1.12736  
                 389 
                 117 
                 11.693 
                 0.0746 
               
               
                 −1.09449  
                 390 
                 118 
                 11.893 
                 0.0804 
               
               
                 −1.06178  
                 391 
                 119 
                 11.693 
                 0.0867 
               
               
                 −1.02924  
                 392 
                 120 
                 11.693 
                 0.0935 
               
               
                 −0.99687  
                 393 
                 121 
                 11.693 
                 0.1007 
               
               
                 −0.98466  
                 394 
                 122 
                 11.693 
                 0.1085 
               
               
                 −0.93262  
                 395 
                 123 
                 11.693 
                 0.1168 
               
               
                 −0.90074  
                 396 
                 124 
                 11.693 
                 0.1257 
               
               
                 −0.86902  
                 397 
                 125 
                 11.693 
                 0.1352 
               
               
                 −0.83745  
                 398 
                 126 
                 11.693 
                 0.1454 
               
               
                 −0.80605  
                 399 
                 127 
                 11.693 
                 0.1563 
               
               
                 −0.77450  
                 400 
                 128 
                 11.693 
                 0.1880 
               
               
                 −0.74371  
                 401 
                 129 
                 11.693 
                 0.1804 
               
               
                 −0.71277  
                 402 
                 130 
                 11.693 
                 0.1937 
               
               
                 −0.66199  
                 403 
                 131 
                 11.893 
                 0.2080 
               
               
                 −0.65136  
                 404 
                 132 
                 11.693 
                 0.2252 
               
               
                 −0.62088  
                 405 
                 133 
                 11.693 
                 0.2394 
               
               
                 −0.59055  
                 406 
                 134 
                 11.693 
                 0.2667 
               
               
                 −0.56037  
                 407 
                 135 
                 11.693 
                 0.2752 
               
               
                 −0.53033  
                 408 
                 136 
                 11.693 
                 0.2949 
               
               
                 −0.50045  
                 409 
                 137 
                 11.693 
                 0.3159 
               
               
                 −0.47071  
                 410 
                 138 
                 11.693 
                 0.3383 
               
               
                 −0.44111  
                 411 
                 139 
                 11.693 
                 0.3621 
               
               
                 −0.41168  
                 412 
                 140 
                 11.693 
                 0.3876 
               
               
                 −0.38235  
                 413 
                 141 
                 11.693 
                 0.4148 
               
               
                 −0.35318  
                 414 
                 142 
                 11.693 
                 0.4434 
               
               
                 −0.32416  
                 415 
                 143 
                 11.693 
                 0.4741 
               
               
                 −0.29527  
                 416 
                 144 
                 11.693 
                 0.6067 
               
               
                 −0.26652  
                 417 
                 145 
                 11.693 
                 0.5414 
               
               
                 −0.23791  
                 418 
                 146 
                 11.693 
                 0.5782 
               
               
                 −0.20943  
                 419 
                 147 
                 11.693 
                 0.6174 
               
               
                 −0.18110  
                 420 
                 148 
                 11.693 
                 0.5590 
               
               
                 −0.15289  
                 421 
                 149 
                 11.693 
                 0.7032 
               
               
                 −0.12482  
                 422 
                 150 
                 11.693 
                 0.7502 
               
               
                 −0.0988  
                 423 
                 151 
                 11.693 
                 0.8001 
               
               
                 −0.06908  
                 424 
                 152 
                 11.693 
                 0.8530 
               
               
                 −0.04140  
                 425 
                 153 
                 11.693 
                 0.9091 
               
               
                 −0.01385  
                 426 
                 154 
                 11.693 
                 0.9888 
               
               
                 0.01366 
                 427 
                 155 
                 11.693 
                 1.0317 
               
               
                 0.04085 
                 428 
                 156 
                 11.693 
                 1.0988 
               
               
                 0.06601 
                 429 
                 157 
                 11.693 
                 1.1885 
               
               
                 0.09505 
                 430 
                 158 
                 11.693 
                 1.2446 
               
               
                 0.12186 
                 431 
                 159 
                 11.693 
                 1.3242 
               
               
                 0.14874 
                 432 
                 160 
                 11.693 
                 1.4084 
               
               
                 0.17540 
                 433 
                 161 
                 11.693 
                 1.4976 
               
               
                 0.20194 
                 434 
                 162 
                 11.693 
                 1.5620 
               
               
                 0.22836 
                 435 
                 163 
                 11.693 
                 1.6918 
               
               
                 0.25466 
                 436 
                 164 
                 11.693 
                 1.7974 
               
               
                 0.28083 
                 437 
                 165 
                 11.693 
                 1.9091 
               
               
                 0.30688 
                 438 
                 166 
                 11.693 
                 2.0271 
               
               
                 0.33282 
                 439 
                 167 
                 11.693 
                 2.1619 
               
               
                 0.35864 
                 440 
                 168 
                 11.693 
                 2.2837 
               
               
                 0.35434 
                 441 
                 169 
                 11.693 
                 2.4229 
               
               
                 0.40992 
                 442 
                 170 
                 11.693 
                 2.5699 
               
               
                 0.43539 
                 443 
                 171 
                 11.693 
                 2.7252 
               
               
                 0.46075 
                 444 
                 172 
                 11.693 
                 2.8880 
               
               
                 0.48599 
                 445 
                 173 
                 11.693 
                 3.0619 
               
               
                 0.51112 
                 446 
                 174 
                 11.693 
                 3.2443 
               
               
                 0.53613 
                 447 
                 175 
                 11.693 
                 3.4386 
               
               
                 0.56104 
                 448 
                 176 
                 11.693 
                 3.6394 
               
               
                 0.58583 
                 449 
                 177 
                 11.693 
                 3.8533 
               
               
                 0.61051 
                 450 
                 178 
                 11.693 
                 4.0786 
               
               
                 0.53508 
                 451 
                 179 
                 11.693 
                 4.3160 
               
               
                 0.65955 
                 452 
                 180 
                 11.693 
                 4.5661 
               
               
                 0.68591 
                 453 
                 181 
                 11.693 
                 4.8295 
               
               
                 0.70815 
                 454 
                 182 
                 11.693 
                 5.1069 
               
               
                 0.73230 
                 455 
                 183 
                 11.693 
                 5.3888 
               
               
                 0.75633 
                 456 
                 184 
                 11.593 
                 5.7060 
               
               
                 0.78026 
                 457 
                 185 
                 11.693 
                 6.0293 
               
               
                 0.80409 
                 458 
                 186 
                 11.693 
                 5.3583 
               
               
                 0.92781 
                 459 
                 187 
                 11.693 
                 6.7269 
               
               
                 0.35143 
                 460 
                 188 
                 11.693 
                 7.1029 
               
               
                 0.87495 
                 461 
                 189 
                 11.693 
                 7.4981 
               
               
                 0.89837 
                 462 
                 190 
                 11.693 
                 7.9135 
               
               
                 0.92168 
                 463 
                 191 
                 11.693 
                 8.3499 
               
               
                 0.94490 
                 464 
                 192 
                 11.693 
                 8.8084 
               
               
                 0.96801 
                 465 
                 193 
                 11.693 
                 9.2899 
               
               
                 0.99103 
                 466 
                 194 
                 11.693 
                 8.7955 
               
               
                 1.01384 
                 467 
                 195 
                 11.693 
                 10.3262  
               
               
                 1.03676 
                 468 
                 196 
                 11.693 
                 10.8833  
               
               
                 1.05948 
                 469 
                 197 
                 11.693 
                 11.4678  
               
               
                 1.08211 
                 470 
                 198 
                 11.693 
                 12.0811  
               
               
                 1.10463 
                 471 
                 199 
                 11.693 
                 12.7243  
               
               
                 1.12707 
                 472 
                 200 
                 11.693 
                 13.3989  
               
               
                 1.14841 
                 473 
                 201 
                 11.693 
                 14.1061  
               
               
                 1.17165 
                 474 
                 202 
                 11.693 
                 14.8474  
               
               
                 1.19380 
                 475 
                 203 
                 11.693 
                 15.5243  
               
               
                 1.21688 
                 476 
                 204 
                 11.693 
                 18.4383  
               
               
                 1.23782 
                 477 
                 205 
                 11.693 
                 17.2911  
               
               
                 1.25888 
                 478 
                 206 
                 11.693 
                 18.1842  
               
               
                 1.28148 
                 479 
                 207 
                 11.693 
                 19.1185  
               
               
                 1.30317 
                 480 
                 208 
                 11.693 
                 20.0986  
               
               
                 1.32477 
                 481 
                 209 
                 11.693 
                 21.1236  
               
               
                 1.34528 
                 482 
                 210 
                 11.693 
                 22.1882  
               
               
                 1.36770 
                 483 
                 211 
                 11.693 
                 23.3185  
               
               
                 1.38903 
                 484 
                 212 
                 11.693 
                 24.4825  
               
               
                 1.41028 
                 485 
                 213 
                 11.693 
                 28.7204  
               
               
                 1.43144 
                 486 
                 214 
                 11.693 
                 27.0045  
               
               
                 1.45251 
                 487 
                 215 
                 11.693 
                 28.3470  
               
               
                 1.47349 
                 488 
                 216 
                 11.693 
                 29.7503  
               
               
                 1.49439 
                 489 
                 217 
                 11.693 
                 31.2170  
               
               
                 1.57820 
                 490 
                 218 
                 11.693 
                 32.7495  
               
               
                 1.53593 
                 491 
                 219 
                 11.693 
                 34.3605  
               
               
                 1.55688 
                 492 
                 220 
                 11.693 
                 36.0228  
               
               
                   
               
            
           
         
       
     
     With the vaporizer  28  at a temperature of 180° C., a pressure of 4.57 torr is generated in the vaporization chamber  26  without significant decomposition of the TAETO. With this pressure at the inlet to the delivery conduit  40 , the process chamber  70  is held at 800 to 900 millitorr. With this pressure differential, about 1.0 sccm of TAETO vapor along with 1.5 sccm N 2 O are delivered to a wafer heated to about 385° C. Under these conditions, a tantalum oxide film will grow at a rate of approximately 75 to 80 angstroms per minute. The wafer is pre-heated to about the deposition temperature or higher either in a preheat module or, less desirably, in the process chamber  70 . Direct thermal coupling between the wafer and the substrate chuck  74  is nominal. Heat is transferred between the wafer and the substrate chuck  74  primarily by way of helium gas flowing between the substrate chuck  74  and the underside of the wafer. 
     In one embodiment, a target film thickness of 100 angstroms is achieved by running the process for 10 seconds at a reduced flow of reactants to seed the wafer with tantalum oxide. The process is then run for 75 seconds at full flow to build the desired film thickness. 
     The deposition rate can be either reduced or slightly increased. An increase in the deposition rate may require an increase in the temperature of the vaporizer  28 . The temperature of the vaporizer  28 , however, should generally be limited to 190° C. for TAETO because there is a risk that the quality of the deposited film will suffer as a result of TAETO degradation. 
     If the temperature of the vaporizer  28  is reduced to 170° C., the net effect will be a reduction in the rate of TAETO deposition. The maximum pressure available at the inlet to the gas-flow-control subsystem  14  would be reduced to about 2.57 torr. This reduction will nearly halve the possible flow rate and will result in a process pressure of about 450 millitorr. The reduced process pressure will yield a deposition rate of about 22-25 angstrom per minute. 
     As the TAETO vaporizes, it expands within the principal cylinder  30  and vapor outlet  32  of the vaporization chamber  26 . All components, including valves and pressure sensors, within the vaporization chamber  26  and delivery conduit  40  are maintained at the temperature of the vaporizer  28  to prevent the TAETO from condensing. As the pressure in the vaporization chamber  26  is depleted by the flow of vapor through the delivery conduit  40  and into the process chamber  70 , the pressure in the vaporization chamber  26  is reestablished by dispensing more TAETO from the reservoir  20  onto the heated vaporizer  28 . While the vaporization subsystem  12  can operate continuously to maintain a pressurized supply of TAETO in the vaporization chamber  26 , it will preferably maintain a low vapor pressure within the chamber  26  until a demand is signaled by the processor. When no demand is signaled, the vaporization chamber  26  will be purged of TAETO and evacuated. 
     This cyclic process is established to accommodate the thermal sensitivity of the precursor (in this case, TAETO). The precursor, if held at an elevated temperature for any length of time, will decompose before delivery into the process chamber  70 . 
     Further, with careful selection of precursors, the apparatus and method of this invention allow the sequential deposition of different but complementary materials in the same chamber without moving the wafer. As a result, multiple deposition steps can be performed without wafer movement and the accompanying cycles of pump down, purge, vent up to atmospheric pressure, and wafer heat up. 
     Complementary processes thus far identified include the following: titanium nitride (TiN) from TiBr 4  or TDEAT and ammonia, followed by aluminum from DMAH; tantalum nitride (TaN) from TaBr 4  and ammonia, followed by copper from Cu I (hfac) (tmvs); and titanium nitride (TiN) from TiBr 4  or TDEAT, and ammonia, followed by aluminum from DMAH, followed by 0.5 atomic percent copper from Cu I (hfac) (tmvs). 
     The CVD apparatus  10  is also suitable for depositing barium titanate, barium strontium titanate, strontium bismuth tantalate, and other similar depositions. 
     The apparatus and method of this invention, and many of the processes, described above, are particularly relevant to semiconductor processing procedures. More particularly, the apparatus and method of this invention are well suited to the deposition of advanced dielectrics and interconnect metals on a wafer. 
     A cluster tool  120  for semiconductor processing is illustrated in FIG.  15 . The illustrated cluster tool  120  includes a number of process modules assembled around a transport module  122  and interfaced with a central control system. Alternatively, the cluster tool  120  can have an inline, rather than radial geometry of process modules in relation to the transport module  122 . One or more of these process modules include a CVD apparatus  10  of this invention. In addition to the CVD apparatus  10  of this invention, the cluster tool  120  includes an entrance load lock  126 , an exit load lock  128 , a preheat module  130 , a cool module  132 , and a transport module  122 . In the illustrated embodiment, three CVD apparatus  10 , which can operate in parallel to enhance throughput, are provided. Alternatively, a variety of other process modules can be provided, e.g., a CVD apparatus  10  in combination with an etch module. These modules can be operated sequentially in series, or in parallel. The cluster tool  120  is designed in accordance with MESC, the standard design architecture adopted by the Semiconductor Equipment and Materials International (SEMI), a trade organization of semiconductor industry suppliers. Accordingly, a variety of other standardized components, such as process modules for different deposition and etch processes, can be readily integrated into the cluster tool  120 , as desired. 
     Each process module in a cluster tool  120  is generally designed to process a single wafer at a time. Typical production requirements are for the tool  120  to process 60 wafers per hour. This rate is achieved by implementing different process steps in separate process modules clustered around the transport module  122 . The tool  120 , illustrated in FIG. 15, is designed for a 300 mm tantalum oxide process system, which uses an eight-sided transport module  122  typically connected to three tantalum oxide CVD apparatus  10 . Optionally, the tool might also accommodate a rapid thermal anneal (RTA) module. In an alternative embodiment, a plurality of cluster tools  120  are interfaced together so that a wafer can be sequentially passed between tools  120  for a series of processing stages without ever removing the wafer from the vacuum established within the cluster tools  120 . 
     The operation of a cluster tool  120  commences with wafers being loaded into an input cassette  136  in an entrance load lock  126 . A robot arm  134  (available from Brooks Automation) in the transport module  122  removes one wafer at a time from the input cassette  136  and moves each wafer to an alignment station  138 . At the alignment station  138 , a standard notch in each wafer is precisely aligned before further processing, eliminating wafer orientation effects within a process module and aiding in process uniformity. Once aligned, the robot arm  134  moves the wafer to a preheat module  130  where the wafer remains for approximately 30 seconds while being heated to 300-500° C. When a CVD apparatus  10  becomes available, the wafer is moved to the process chamber of that CVD apparatus  10  for tantalum oxide deposition. Deposition occurs over a period of approximately 120 seconds. After deposition, the wafer is moved to the cool module  132 , where the wafer resides for 30 seconds and is cooled enough to place it in the output cassette  140  in the exit load lock  128 . 
     The process time for tantalum oxide deposition on a wafer is on the order of 120 seconds for a 0.01-micron-thick film on a preheated wafer. Wafer movement from the input cassette  136 , to the alignment station  138 , to a CVD apparatus  10  and back to an output cassette  140  will consume approximately another ten seconds. The cluster tool  120 , with three tantalum oxide CVD apparatus  10 , would have a throughput of one wafer every 45 seconds, excluding ramp-up and ramp-down. The tool  120  in this configuration can process up to 75 wafers per hour. 
     In this context, the deposition process is used to form integrated circuits on the wafer. An integrated circuit is simply a large number of transistors, resistors, and capacitors connected together by metal lines. A general goal is to miniaturize the components to the greatest extent possible. 
     FIG. 16 illustrates a configuration of the invention in which multiple cluster tools  120   a  and  120   b  are arranged to process wafer in conjunction with each other. Wafer handoff mechanism  701  can pass wafers from transport module  122   a  in cluster tool controller  120   a  to an entire second cluster tool controller  120   b . Wafer handoff mechanism  701  may be, for example, a conveyor-belt apparatus which transports the wafers  88  from the robot arm  134   a  to the second robot arm  134   b  of transport module  122   b . Alternatively, the wafer handoff mechanism  701  can be accomplished by physically passing individual wafers  88  from robot arm  134   a  to robot arm  134   b.    
     The CVD apparatus  10   a-c  in FIG. 16 may be used for a certain processing of the wafers, and when complete, the wafers can be transported, through wafer handoff mechanism  701 , to the second configuration of CVD apparatus  10   d-f  and secondary transport module  122   b  for a second type of processing. During the entire processing of wafers by the configuration in FIG. 16, the wafers may be maintained under a vacuum and may be maintained at a relatively constant temperature. Since the cluster tools  120   a  and  120   b  are an entirely closed system, wafers experience reduced exposure to contamination and outside atmosphere while being processed. 
     The large scale wafer processing illustrated in FIG. 16 is referred to herein as a factory automation wafer processing system. According to one aspect of factory automation processing in this invention, the entire set of CVD apparatus  10   a-f , transport modules  122   a  and  122   b , and cluster tools  120   a  and  120   b  may all be controlled by a single factory automation controller  702  which handles all scheduling of wafer processing from beginning to end. Factory automation controller  702  contains a master central processing unit that governs the operation of each cluster tool  120   a  and  120   b . Data bus  703  interconnects each CVD apparatus  10   a-f  with factory automation controller  702 . 
     FIG. 17 illustrates an alternative configuration for a factory automated CVD processing system. In FIG. 17, the individual components (i.e., CVD apparatus  10 , preheat modules  130 , cooling modules  132 , transport modules  122 ) of each cluster tool  120   a  and  120   b  are controlled by separate cluster tool controllers  705   a  and  705   b . Factory automation controller  702  controls each cluster tool controller  705   a  and  705   b , and can control wafer handoff mechanism  701 . 
     In yet another alternative embodiment, one of the cluster tool controllers, for example,  120   a , can control the wafer handoff mechanism  701  and can signal to the other cluster tool  120   b  that it has completed its wafer processing and that wafer are on route via wafer handoff mechanism  701  and should be accepted by robot arm  134   b.    
     Each of these arrangements are shown by way of example only, and the invention is not limited to only two cluster tools in the factory automation configurations shown in FIG. 16 and 17. Rather, there may be many cluster tools arranged in any number of ways, each having a cluster tool controller which is controlled by one or more master factory automation controllers. By distributing processing as shown in these examples, real-time wafer processing can be accomplished from beginning to end in a more efficient, clean, and timely manner. 
     FIG. 18 illustrates an example of the typical steps involved in controlling a single cluster tool  120   a  via cluster tool controller  705   a , as illustrated in FIG.  17 . In step  710 , robotic arm  134   a  accepts a wafer from the input cassette  136   a , which is attached to the entrance load lock  126   a . The robotic arm  134 , in step  711 , then aligns the wafer on the armature itself. 
     Wafer alignment on the robotic arm  134  is performed at the alignment station  138 , where a notch in the side of the wafer is mechanically aligned with a reference indicator. 
     Once the wafer is correctly oriented, in step  712 , which is an optional step, the wafer may be pre-heated in pre-heat module  130 . Heating the wafer brings the wafer up to a temperature at or near the operating or substrate chuck temperature of the first CVD apparatus  10  that will accept the wafer. Next, the robotic arm  134 , in step  713 , places the wafer into one of the CVD apparatus  10   a-c  of the current cluster tool controller  120   a  for CVD processing in step  714 , as explained above. While three CVD apparatus  9   a  through  10   c  are illustrated in FIG. 16, the invention is not limited to three, and there may be one, two, three or many more such system all accessible by a single robotic arm  134 . After the wafer has completed CVD processing in step  714  in CVD apparatus  9   a , in step  715 , the robotic arm extracts the wafer. Next, the wafer either moves to the next CVD apparatus (i.e., back to step  713 ), or finishes processing (step  716 ) by being cooled in cool module  132  and exiting the cluster tool  12   a  via output cassette  140 , or the wafer is passed to another cluster tool  120   b  via wafer handoff mechanism  701  (step  717 ). Generally, wafer processing repeats until the correct sequence of heating, CVD processing and cooling has been performed, as dictated by the wafer processing program executing in cluster tool controller  705   a  controlling the operation of cluster tool  120   a.    
     New generations of semiconductor processing attempt to build this structure using the latest technologies and equipment to create the smallest possible features. Accordingly, it is intended that the transistors, wires, capacitors, and resistors occupy as little space on the wafer surface, as possible, providing more devices per wafer while limiting costs. As the size of features decreases, new materials are often needed to maintain the proper conductivity of the finer wires and the capacitance values of the smaller-area capacitors. 
     The apparatus of this invention are specifically intended for the deposition of thin films of metals, dielectric layers used as liners for these metals, low-k interlayer dielectric layers, and capacitor dielectrics (denoted as high-k) required for 0.25 micron or smaller linewidth processes. The processes can be used to form integrated circuits with clock speeds of 400 MHZ or faster and 256 Mbit or more DRAM. 
     Semiconductor deposition processes that can be performed with a cluster tool  120  incorporating a CVD apparatus  10  of this invention include the deposition of high-k capacitor dielectrics such as tantalum oxide; the deposition of liner layers that serve as barriers and adhesions promoters, like titanium nitride, a liner used for aluminum, and tantalum nitride, a copper liner; and the deposition of copper metal for interconnects. 
     Further, the methods and apparatus of this invention are suitable for the deposition of stacked gate dielectrics, which include successively deposited layers of extremely thin films (on the order of 15 angstroms for each film) of two different dielectrics to minimize gate capacitance. Stacked dielectric gates may generally be used in devices with geometries of less than 0.15 microns and in devices with geometries of up to 0.25 microns where an increase in speed beyond 400 MHZ is needed. 
     Further still, the methods and apparatus of this invention offer advantages in the processing of stacked dielectrics, where sequential deposition of two different dielectrics is generally required. The design of a precursor delivery system, in accordance with this invention, allows deposition of both materials in the same process chamber. As a result, the wafer will not be exposed to random oxidation, which would destroy the gate. Further, because the wafer need not be moved, the system is expected to have an intrinsically higher throughput than existing systems. 
     Other materials that can be suitably deposited on semiconductor wafers with an apparatus and method of this invention include aluminum, aluminum/copper (an alloy with reduced liner requirements), barium titanate (a potential high-k dielectric film), and barium strontium titanate (another high-k dielectric film). 
     Other suitable applications for the CVD apparatus and methods of this invention include processing of flat panel displays and coated drill bits. Further still, the apparatus and methods of this invention can be used to deposit optical dielectric coatings, anti-reflection coatings, and coatings to reduce friction and wear. 
     While this invention has been particularly shown and described with references to preferred embodiments thereof, those skilled in the art will understand that various changes in form and details may be made therein without departing from the scope of the invention as defined by the appended claims.