Abstract:
The invention relates to an apparatus and process for the vaporization of liquid precursors and deposition of a film on a suitable substrate. Particularly contemplated is an apparatus and process for the vaporization of a metal-oxide film, such as a barium, strontium, titanium oxide (BST) film, for deposition on a silicon wafer to make integrated circuit capacitors useful in high capacity dynamic memory modules. The vaporizer comprises thermally controlled components which are adapted for easy assembly and disassembly. A main vaporizing section provides a large heated surface for flash vaporization. A high conductance blocker is disposed at a lower end of the vaporizer to provide an extended vaporization surface. Optionally, a filter may be employed to capture unvaporized precursor droplets.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application Ser. No. 60/093,563, entitled “Chemical Vapor Deposition Vaporizer,” filed on Jul. 21, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an apparatus and process for the vaporization of liquid precursors and deposition of a film on a suitable substrate. Particularly contemplated is an apparatus and process for the deposition of a metal-oxide film, such as a barium strontium titanate (BST) film, on a silicon wafer to make integrated circuit capacitors useful in high capacity dynamic memory modules. 
     2. Background of the Related Art 
     The increasing density of integrated circuits (ICs) is driving the need for materials with high dielectric constants to be used in electrical devices such as capacitors for forming 256 Mbit and 1 Gbit DRAMs. Capacitors containing high-dielectric-constant materials, such as organometallic compounds, usually have much larger capacitance densities than standard SiO 2 —Si 3 N 4 —SiO 2  stack capacitors making them the materials of choice in IC fabrication. 
     One organometallic compound of increasing interest as a material for use in ultra large scale integrated (ULSI) DRAMs is BST due to its high capacitance. Deposition techniques used in the past to deposit BST include RF magnetron sputtering, laser ablation, sol-gel processing, and chemical vapor deposition (CVD) of metal organic materials. 
     A liquid source BST CVD process entails atomizing a compound, vaporizing the atomized compound, depositing the vaporized compound on a heated substrate and annealing the deposited film. This process requires control over the liquid precursors and gases from introduction from an ampoule into a liquid delivery system through vaporization and ultimately to the surface of the substrate where it is deposited. The goal is to achieve a repeatable process which deposits a film of uniform thickness under the effects of a controlled temperature and pressure environment. This goal has not been satisfactorily achieved because the precursors are finicky and the deposition equipment requires a complex design. 
     For example, a series of problems result from the use of vaporizers. One difficulty is the lack of efficiency in vaporizing the liquid precursors. Typically, only a portion of the liquid precursors are vaporized due to low conductance in the vaporizer, thereby inhibiting deposition rates and resulting in processes which are not consistently repeatable. In addition, known vaporizers used in CVD processes incorporate narrow passages which eventually become clogged during use and are not adapted for continuous flow processes which can be stabilized. For example, U.S. Pat. No. 5,204,314 entitled, “Method for Delivering an Involatile Reagent in Vapor Form to a CVD Reactor, discloses a flash vaporizer using a matrix structure. The matrix structure generally comprises a heated screen mesh having restricted openings. After extended usage the matrix structure accumulates build up leading to a reduction in vaporization efficiency of the liquid precursors and negative effects on process repeatability and deposition rate. 
     Another difficulty is that BST liquid precursors have a narrow range of vaporization between decomposition at higher temperatures and condensation at lower temperatures. Known vaporizers lack temperature controlled surfaces and the ability to maintain liquid precursors at a low temperature prior to injection into the vaporizer. This results in deposition of material in the injection lines and in the vaporizer and premature condensation or unwanted decomposition of the precursors. The deposits adversely affect not only the vaporizer but also upstream components such as positive displacement pumps because the pump can rupture its pressure seals or continue to operate until the pressure relief valves on the pump are tripped. Damage to system components, of course, requires maintenance and repair and over time becomes very expensive and increases the cost of ownership of the equipment. Additionally, the deposits formed in the vaporizer may be carried downstream to corrupt other components and ultimately even be delivered to the substrate surface thereby compromising its quality. Thus, temperature controlled flow paths through the vaporizer are needed. 
     Still another difficulty encountered in the deposition of BST is that the deposition process is performed at elevated substrate temperatures, preferably in the range of about 400-750° C. and the annealing process is performed at substrate temperatures in the range of about 550°-850° C. These high temperature requirements impose demands on the chambers and its other components used in the deposition process. For example, elastomeric O-rings are typically used to seal the deposition chamber and are not generally made of materials that will resist temperatures in excess of about 100° C. for many fabrication cycles. Seal failure may result in loss of pressure as well as contamination of the process chemistry and the system components, thereby resulting in defective film formation on the wafer. In addition, it is necessary to prevent temperature fluctuations of vaporizer surfaces which result from thermal conduction. Loss of heat due to thermal conduction causes temperature gradients across the surface of the substrate resulting in decreased uniformity in film thickness and also increases the power demands required of the system to maintain the high temperature environment in the chamber. 
     There is a need, therefor, for a high conductance vaporization apparatus which can efficiently vaporize the precursors, deliver the vaporized precursors to downstream system components while maintaining elevated temperatures, preventing unwanted condensation or decomposition of precursors along the pathway and avoiding temperature gradients. It would be preferable if the system were adapted for rapid cleaning and continuous flow operation. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention, a vaporizer is provided for vaporizing BST and other materials which require vaporization, especially low volatility precursors which are transported as a liquid to the vaporizer to be converted to vapor phase and which must be transported at elevated temperatures to prevent unwanted condensation on gas flow surfaces. The vaporizer comprises a series of heated temperature controlled components which are configured for rapid removal, cleaning and/or replacement. The vaporizer also preferably includes features that protect seals (e.g., elastomeric O-rings) from the deleterious effects of high temperatures generated during fabrication of electrical devices, such as capacitors useful for ULSI DRAMs. 
     The invention also provides a vaporizing apparatus having large smooth vapor passageways for high conductance to prevent clogging for consistently mixing and efficiently vaporizing liquid precursor components, and delivering the vaporized material to a deposition chamber with negligible decomposition and condensation of the gas in the vaporizer and gas delivery lines. Preferably, the apparatus increases vaporizing efficiency by providing temperature controlled increased surface area to reduce the likelihood of fouling or clogging typically associated with existing vaporizers. 
     The present invention is characterized by its use in the manufacture of capacitor films of consistently high quality, with significantly reduced and simplified maintenance, and capability for depositing CVD films at high rates with less particle generation. The net result is a fabrication process with enhanced efficiency and economy. 
     In another aspect of the present invention, a main body having a main vaporizing section is equipped with detachable heating elements. A blocker is disposed below the main vaporizing section. High conductance channels formed in the blocker act as an extended vaporizing surface. In a first embodiment, the channels are in parallel relation and lead to an outlet coupled to a downstream gas line. In a second embodiment, the blocker comprises a gas compactor at least partially disposed within the main vaporizing section. The gas compactor has upper and lower ports in communication with an inlet and a outlet, respectively. A gas channel is defined between the gas compactor and the main vaporizing section to provide fluid communication between the inlet and outlet via the ports. Optionally, a filter may be disposed at a lower end of the vaporizer. 
     In still another embodiment of the present invention, a vaporizer comprises separable components selectively coupled. In a first embodiment the vaporizer components are coupled by clamps while in another embodiment the components are coupled by VCR® fittings. In each embodiment the components are easily disassembled for inspection and cleaning. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. 
     It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
     FIG. 1 is a perspective view of a chamber system of the present invention; 
     FIG. 2 is a perspective view of a chamber and vaporizer module; 
     FIG. 3 is a simplified schematic representation of a liquid and gas delivery system; 
     FIG. 4 is a partial schematic cross sectional view of a vaporizer of the present invention; 
     FIG. 5 is partial schematic cross sectional view of an alternative embodiment of the vaporizer. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is directed to a vaporizer for use in a chemical vapor deposition (CVD) system. While the subsequent description makes references to BST deposition it is understood that the invention may be used in any processing system requiring the advantages of superior serviceability, uniform film deposition, and enhanced efficiency resulting from temperature controlled surfaces. The vaporizer has particular application for the fabrication of metal-oxide dielectrics useful in making capacitors used in ULSI DRAMs as well as a number of other electrical devices. In general, devices that can be made with the present system are those characterized by having one or more layers of insulating, dielectric, or conducting material deposited on a substrate. 
     FIGS. 1 and 2 are perspective views of a CVD system  10  incorporating the present invention. The system  10  generally includes a chamber body  12 , a heated lid assembly  14 , an integrated vaporizer module  16  and an exhaust/pumping system  18  comprising a gate valve  20 , a turbo pump  22 , and a first cold trap  24 . The vaporizing module  16  is shown mounted adjacent to the chamber body  12  in a vaporizer cabinet  26  which includes an outlet line  28  connected to the inlet into the chamber body  12  at one end and a vaporizer  100  at another end. Disposed along the outlet line  28  is a first valve  30  which is connected in turn to a bypass line  32  extending out through the back of the cabinet  26  and is connected to the exhaust/pumping system  18  by a conduit in which a second cold trap  34 , located downstream from the valve  30 , is disposed. The bypass line  32  is adapted to deliver both vaporized gas as well as liquid solvent into the cold trap  34  in preparation of delivering vaporized gas to the chamber body  12  during processing or during cleaning of the system  10 . The first valve  30  controls delivery of the vaporized material to the chamber  12  through the cold trap  34 . A second valve  36 , such as an isovalve is disposed downstream from the first valve  30  to selectively deliver the vaporized gas into the chamber body  12 . The second valve  36  is mounted to the lower portion of the chamber  12  via a rod and washer assembly  38 . This assembly  38  enables adjustment of the delivery line as well as the valve  36  in relation to the chamber  12 . The mount generally includes first and second rings  40 ,  42 , respectively, one disposed in the other, to allow rotatable adjustment of an isovalve  36  and the outlet line  28 . The second valve  36  is mounted to the second ring  42  via a plurality of rods  44  (four shown here) which are mounted from the ring  42  and include a spring  46  disposed above the upper portion of the rod and the ring  42 . The two rings  40 ,  42  enable rotation of the assembly  38  while the spring and rod arrangement allow vertical adjustment of the assembly  38  to ensure proper alignment of the gas feed line  30  into the chamber  12 . In general, the suspension assembly  38  provides automatic compensation for thermal expansion/contraction to maintain vacuum seals without the mechanical and thermal stress. The size and dimensions of the system  10  are dictated by the size and shape of the workpiece on which processes of the present invention are performed. 
     FIG. 3 shows a simplified liquid and gas delivery system  50  for supplying the liquid precursors and carrier gases to the vaporizer  100 . A first gas container  52  and second gas container  54  are connected to the vaporizer  100  to provide carrier gases. The function of these gases is described in detail below. A liquid ampoule  56  is shown connected to the vaporizer  100  to provide liquid precursors. So that the flow rates of the gases and liquids may be monitored and controlled, flow meters  58  are disposed in the liquid and gas delivery lines. The gas delivery lines are preferably made of a material having a low coefficient of friction, such as PTFE, to allow for high flow velocities. Other devices which are commonly known and used in the industry but not shown in FIG. 3 include bubblers, degassers, shut-off valves, etc. 
     The inventors have recognized that deposition layer uniformity can be enhanced, and maintenance can be reduced, if the vaporizer is substantially maintained at an ideal isothermal system temperature (e.g. 250° C.±5° for BST). The vaporizer  100  incorporates several active and passive thermal control systems including thermal control features which serve to protect a main seal by cooling it below the ideal isothermal system temperature. Cooling is achieved without inducing significant temperature fluctuations and gradients in the vaporizer components exposed to the system chemistry, and without excessive cooling and heating power losses. 
     FIG. 4 is a cross sectional view of one embodiment of the vaporizer  100  of the present invention. The vaporizer  100  generally includes an input manifold  102 , a cooling head  104 , and a main body  106  comprising a top block  108  and a bottom block  110 . The input manifold  102  is coupled at the upper end of the vaporizer  100  and provides an inlet  112  wherein an injection member  114 , such as a capillary tube, is coaxially disposed. The injection member  114  is connected to the liquid precursor ampoule  56  (shown in FIG. 3) and the first gas container  52  (also shown in FIG.  3 ). 
     The cooling head  104  and the top block  108  are joined at abutting flanges  120  and  122  formed on the head  104  and top block  108 , respectively. Similarly, the top block  108  and the bottom block  110  are joined at flanges  124  and  126  defined on the top block  108  and bottom block  110 , respectively. The flanges  120 ,  122 ,  124 , and  126  are adapted to receive clamps  128 , such as KF clamps, to hold the various vaporizer components together during operation. O-ring seals  130  and  132  disposed in flanges  120  and  124 , respectively, provide hermetic seals at the interfaces of the blocks  108 ,  110  and cooling head  104 . O-rings  130 ,  132  may be any of many high temperature metal-to-metal seals such as the aluminum Delta seal from Helicoflex, for example. 
     One or more cooling channels  134  are preferably disposed in the head  104  in order to actively cool the O-ring seal  130  and the incoming liquid precursors. A heat exchange fluid (e.g., water, ethylene glycol, silicone oil, etc.) circulates through the channel  134  to remove heat at the O-ring seal  130 . Optionally, another cooling channel (not shown) may be disposed in the main body  106  adjacent the O-ring seal  132 . To maximize thermal conductivity the cooling head is preferably made of aluminum or some other thermal conductor. Although not shown in FIG. 4, a thermocouple may be disposed in a slot  222  to monitor the operating temperature at an upper end of the vaporizer  100 . A dispersion/carrier, gas conduit  135  is formed in the cooling head  104  and leads to a recess  137  formed in an upper portion of the top block  108 . An injection line (not shown) connects the second gas container  54  (shown in FIG. 3) to the dispersion/carrier gas conduit  135  to provide a dispersion/carrier gas thereto. The cooling head  104  provides a centrally formed inlet bore  136  wherein the injection member  114  is disposed and secured by a threaded sleeve  138 . The injection member  114  is concentrically received by a gas passageway  140  extending longitudinally through a neck  142  of the top block  108  and terminating near a lower end of the neck  142 . The concentric gas passageway  140 , disposed about the outer perimeter of the injection member  114 , may be of any geometric shape and is adapted to deliver one or more dispersion gases to a tip, or nozzle  144 , of the injection member  114 . Preferably, the concentric gas passageway  140  and the injection member  114  are made of PTFE for low friction coefficient and prevention of clogging. 
     The concentric gas passageway  140  leads to a main vaporizing section  146  which is shown as a frustoconical surface having a diametrically narrower upper end and a diametrically enlarged lower end. The main vaporizing section  146  provides a large, preferably smooth, heated surface area onto which a fluid may be deposited. A blocker  148  aligned with the lower end of the main vaporizing section  146  provides an extended vaporizing surface. The blocker  148  is preferably made of aluminum, or some other thermal conductor, and comprises a plurality of high conductance channels  150 . A commercially available filter  152  such as the one available from PALL is disposed below the blocker  148  and above a high conductance outlet  153 . The filter  152  is seated on an annular shoulder  154  of the bottom block  110  and is secured from above by the top block  108  thereby allowing for ease of periodic replacement by unclamping the two blocks  108 ,  110 . The filter  152  can be any number of commercially available filters such as the one available from PALL. This arrangement provides a large conductance for shorter resonance time in the vaporizer  100  and also facilitates inspection and cleaning of the vapor flow paths. 
     The blocks  108  and  110 , preferably made of stainless steel, provide a relatively large thermal mass for retention and transmission of thermal energy generated by one or more heating elements  156  (shown here as cartridges) surrounding the blocks  108  and  110  thereby ensuring an optimal isothermal temperature on the vaporization surfaces, as well as downstream. The heaters  156  are slidably received in receptacles  158  and may be selectively removed for maintenance and servicing. The heating elements  156  preferably deliver a total heating power of between about 1000 W and 3000 W to the blocks  108 ,  110  and are controlled to maintain the main body  106  at the optimum isothermal temperature by a conventional PID controller (not shown). The controller is connected to a thermocouple (also not shown) positioned within at least one, and preferably both, of the blocks  108 ,  110  proximate to the heated vaporizing surfaces. 
     All the vaporizer components are uniquely designed to facilitate disassembly, maintenance, and replacement. Each component comprises an independent unit which may be individually serviced or replaced. As shown in FIG. 4, the vaporizer  100  of the first embodiment consists of six primary components, i.e., the input manifold  102 , the cooling head  104 , the top block  108 , the bottom block  110 , the heating elements  156 , the filter  152 , and the blocker  148 . As described above, the top block  108  and cooling head  104  are selectively coupled with a KF clamp. The top block  108  is similarly coupled to the bottom block  110 . Thus, the filer  152 , which must be periodically exchanged, and the blocker  148 , which may require periodic cleaning, may be removed by uncoupling the top block  108  from the bottom block  110 . While the blocks  108 ,  110  are shown coupled by KF clamps, other coupling assemblies, such as VCR® fittings may be used to advantage. 
     In operation, the liquid precursor is initially combined with a carrier gas, such as argon, upstream from the vaporizer  100 . The mixture of liquid precursor components and the carrier gas is then delivered through the injection member  114  (preferably 2-20 mils inner diameter) to a point just above the main vaporizing section  146 . The liquid and gas are supplied at a relatively high flow rate, e.g. 10 ml/min. liquid and 100-2000 sccm gas, which causes the liquid to exit the nozzle  144  and enter the main vaporizing section  146  as a jet of liquid and gas with a high nozzle velocity. 
     The flow meter  58  (shown in FIG. 3) can be used to control the amount of gas flowed in direct relation to the flow rate of the liquid precursor component mixture. The flow rate of the liquid is typically controlled by a flow controller such as the flow meter shown in FIG.  3 . As will be understood by a person skilled in the art, the flow velocity of the liquid precursors may be independently controlled by the flow of the carrier gas input to the vaporizer  100 . 
     One or more dispersion/carrier gases, such as argon, are delivered through the dispersion/carrier gas conduit  135  and flowed concentrically about the injection member  114  to prevent liquid droplets from forming on the nozzle  144  and moving up the outer cylinder of the injection member  114 . At the level of the nozzle  144 , the dispersion/carrier gas picks up the liquid precursor mixture jetting out of the injection member  114  and carries the mixture down into the main vaporizing section  146  where the liquid precursor is vaporized. To allow for optimization of this initial “flash” vaporization, the spacing between the injection member nozzle  144  and the main vaporization section  146  is preferably adjustable. Adjustment of the flash vaporization to avoid a liquid droplet “dance on the frying pan” effect is obtained by adjusting the flow rate of the gas and liquid precursor mixture. The vaporized precursors are then channeled through the plurality of high conductance channels  150  formed in the blocker  148 . The blocker  148  acts as a second stage vaporizer while simultaneously collecting unvaporized liquid and directing them into the filter  152 . The filter  152  enables the entrapment of any liquid which is not vaporized. This prevents liquids from passing through the vaporizer  100  and into the chamber  12  (shown in FIGS. 1,  2 , and  3 ). The resultant deposition gas then passes through the vaporizer outlet  153  for delivery to the deposition chamber  12 . The wide-mouthed outlet  153  is designed for large conductance so that precursor vapors are readily carried from the vaporizer  100  into the chamber  12 . 
     All but a final short segment of the path of the liquid mixture is kept relatively cool (0-80° C. for BST) by a thermal choke structure comprising the cooling channel  134  and physical separation of the main body  106  from the other upstream vaporizer components by the neck. The thermal choke isolates the upper portion of the vaporizer  100  from the heat generated by heating elements  156  and prevents heat loss and generation of cold spots without inducing significant detrimental cooling effects on the other system components. In particular, the design allows the main body  106  to be maintained at an optimal isothermal temperature (e.g., 250° C.±5° for BST). 
     FIG. 5 is a cross sectional view of a second embodiment of the vaporizer  100  of the present invention. The vaporizer  100  generally includes the components of the first embodiment, i.e., an input manifold  102 , a cooling head  104 , and a main body  106 . However, the second embodiment comprises some design modifications which are discussed below. 
     FIG. 5 shows the dispersion/carrier gas conduit  202  formed in the main body  106 . The conduit  202  extends from below the main body  106  along a perimeter portion thereof and then terminates in a passageway at the latter portion of the injection nozzle  144 . An injection line  204  connected to the conduit  202  by quick disconnect fittings  206  delivers a dispersion/carrier gas to the conduit  202  from the second gas container  54  (shown in FIG.  3 ). The injection member  114  terminates at the entrance to a main vaporizing section  146  housing a blocker, or gas compactor  208 . The gas compactor  208  is a substantially elongated cylinder having an inlet  210  at an upper end and outlet  212  at a lower end. The inlet  210  receives the nozzle  144  and comprises a plurality of exhaust ports  214  formed in the inlet wall. Similarly, the outlet  212  has a plurality of intake ports  216 . The outer diameter of the gas compactor  208  is slightly less (a few millimeters) than the diameter of the main vaporizing section  146  so that a fluid channel  218  is formed leading from the exhaust ports  214  to the intake ports  216  providing communication therebetween. 
     The main body  106 , preferably made of a monolithic piece of stainless steel, provides a relatively large thermal mass for retention and transmission of thermal energy generated by a heating jacket  220  and has a high specific heat capacity thereby ensuring an optimal isothermal temperature on the vaporization surfaces, as well as downstream. The heating jacket  220  is in the form of a C-clamp having its ends secured by a screw (shown in FIG. 3) such that it is supported on the exterior of the main body  106  and allows for easy removal of the heating jacket  220 . The heating jacket  220  may be electrically heated (e.g., resistive heaters) or fluidly heated and preferably delivers a total heating power of between about 1000 W and 3000 W to the main body  106  for typical sizes and flow rates of these applications. Cartridges such as those used in FIG. 4 may also be used. The heating jacket  220  is controlled to maintain the main vaporizing section  146  at the optimum isothermal temperature by a conventional PID controller (not shown). Although not shown in FIG. 5, the vaporizer  100  of the second embodiment may also comprise a thermocouple, preferably located in the main body  106  proximate the injection member  114 , to monitor the temperature during operation. An additional thermocouple (also not shown) may be received by the slot  222  located partially in the input and partially in the cooling head  104 . 
     A thermal radiation shield  224  is shown circumferentially disposed about the midsection of the vaporizer  100 . Preferably, at least the main body  106  is enclosed within the shield  224 . Most preferably, the cooling head  104  is also enclosed. Preferably, the shield  224  does not directly contact the main body so that an air pocket is formed around the main body  106 . The shield  224  is preferably a metal having a high thermal insulating capacity such as stainless steel. A metal membrane  226 , also preferably comprised of a thermal insulator such as stainless steel, is horizontally interposed between the head  104  and the main body  106  to act as a thermal choke. 
     As shown in FIG. 5, the vaporizer  100  of the second embodiment consists of six primary components, i.e., the input manifold  102 , the cooling head  104 , the main body  106 , the heating jacket  220 , the gas compactor  208 , and the shield  224 . To allow for ease of connecting/disconnecting to one another, the components are equipped with VCR® fittings. However, other coupling devices may be used, such as the KF clamps used in the first embodiment for example. 
     The operation of the vaporizer  100  of the second embodiment is substantially the same as that of the first embodiment described above with a few exceptions. In the second embodiment the dispersion/carrier gas conduit  202  is shown disposed in the main body  106  at least partially adjacent the heating jacket  220 . This allows the dispersion/carrier gas to be heated before its injection into the passageway. Additionally, the injection member  114  is shown in FIG. 5 extending below the neck  142  and terminating at the end of passageway  140  above the gas compactor inlet  210 . This allows the liquid precursors to reach an elevated temperature due to the heat generated by the heating jacket  220  and transmitted by the main body  106 . The precursors are then delivered into the inlet  210  where they are channeled through and around the gas compactor  208  as indicated by the arrows. The vaporized gas then exits the vaporizer  100  through the outlet  212  and is delivered to the deposition chamber  12  downstream. 
     While the number of intake ports  216  (three shown) is preferably less than the exhaust ports  214  (five shown) the total effective cross sectional area of the ports  214 ,  216  is substantially equal such that the volume flow rate (sccm) is substantially equal. Thus, by the equation of continuity A 1 v 1 =A 2 v 2 , wherein A 1  the total cross sectional area of the exhaust ports  214 , v 1  is the velocity of the fluid through the exhaust ports  214 , A 2  is the total cross sectional area of the intake ports  216 , and v 2  is the velocity of the fluid through the intake ports  216 . Bernoulli&#39;s equation may then be solved for the pressure at each end of the gas compactor  208 . The desired pressure is achieved by manipulating the orientation of the vaporizer  100  (to compensate for the effects of gravity), changing the length of the gas compactor  208 , and altering relative size difference between the cross sectional areas of the ports  214 ,  216 . The precise dimensions will also depend on the type of fluid used and the surface friction provided by the main vaporizing section  146  and the gas compactor  208 . A slight pressure differential which biases the fluid downstream is most preferable. 
     As with the first embodiment all but a final short segment of the path of the liquid mixture is kept relatively cool, e.g., 0°-80° C. for BST, by a thermal choke structure comprising the cooling channel  134  and physical separation of the main body  106  from the other upstream vaporizer components. The second embodiment also employs the metal membrane  226  to reduce thermal decomposition of the liquid precursor components prior to vaporization by further inhibiting thermal conduction. Additional thermal insulation of the injection member  114  is provided by the relatively thin wall of the neck  142 , e.g., a few millimeters and by the thermal insulating value of the material. The neck  142 , which forms an integral part of the main body  106 , is preferably made of stainless steel, PTFE, or other material having a relatively low thermal conductivity. 
     While certain design features are shown only with respect to the second embodiment, such as the shield  224 , the heated dispersion/carrier gas conduit  202 , and the heating jacket  220 , these features may also be employed by the vaporizer  100  of the first embodiment. Similarly, the features of the first embodiment, such as the heating cartridges  156 , may also be used to advantage in the second embodiment. Further, adjusts to elements such as the injection member  114  in either embodiment may be made without deviating from the scope of the present invention. 
     The vaporizer  100  of each embodiment operates to vaporize a mixture of precursor components, such as BST, and a carrier gas by providing a main vaporizer section  146  with increased surface area which exposes the mixture to a large area of evenly heated surfaces. The various components of the vaporizer  100 , such as the main vaporizing section  146 , the blocker  148  of the first embodiment, and the gas compactor  208  of the second embodiment each act to vigorously mix and vaporize the precursor components, carrier gases, and dispersion gases. This arrangement provides a large conductance for shorter resonance time in the vaporizer  100 . The maximized surface area serves to vaporize more efficiently as well as prevent clogging. 
     The amount of power required for complete vaporization is a function of the chemistry of the precursor components and carrier gas, and the flow rate of the mixture. As one example, with a BST flow rate of 0.10 ml/mn and a carrier gas, e.g., Ar, flow rate of 200-300 sccm, the amount of power necessary to heat and completely vaporize the flow is approximately 10 W. In contrast to conventional arrangements, the amount of heating (e.g., vaporizing) power supplied to the mixture is set substantially higher than the level of power actually required to achieve complete vaporization. In accordance with the invention, the thermal power transferred to the vaporizer  100  is set to be one to two orders of magnitude higher than the 10 W required for complete vaporization of the mixture, i.e., between about 100 W and 1000 W, and preferably 20-30 times higher, i.e., between 200-300 W and 2000 W-3000 W. In this manner, the heating power absorbed by the flowing mixture is a small fraction of the heating power which is available. Therefore, the power absorbed by the gas vapor presents an insignificant perturbation in relation to the available heating power, making it possible to substantially maintain an ideal isothermal temperature (e.g., 250° C.±5° for BST) of the heating surfaces. In general, depending on the precursor component mixture which is used, the ideal isothermal system temperature will be in the range of about 200-300° C. 
     APPLICATIONS OF THE SYSTEM 
     Example 1 
     Exemplary metal-oxide layers which can be deposited using the present system may include tantalum pentoxide (Ta 2 O 5 ), a zirconate titanate (ZrxTiyOz), strontium titanate (SrTiO 3 ), barium strontium titanate (BST), lead zirconate titanate (PZT), lanthanum-doped PZT, bismuth titanate (Bi 4 Ti 3 O 12 ), barium titanate (BaTiO 3 ), or the like. Other materials which can be deposited include those materials having a narrow range of vaporization between condensation and decomposition. 
     Example 2 
     While the present invention is described primarily with reference to metal oxide layers such as BST, other processes requiring the advantages of isothermal vaporization over a large conductance path may also be carried out. For example, one area of particular interest in the semiconductor industry is copper deposition. 
     A Cu layer may be deposited using by any known CVD Cu process or precursor gas, including copper +2 (hfac) 2  and Cu +2 (fod) 2  (fod being an abbreviation for heptafluoro dimethyl octanediene), but a preferred process uses the volatile liquid complex copper +1 hfac,TMVS (hfac being an abbreviation for the hexafluoro acetylacetonate anion and TMVS being an abbreviation for trimethylvinylsilane) with argon as the carrier gas. One such mixture (i.e., copper +2 (hfac) 2 ) is Cupra Select™ a registered trademark of Schumacher, Inc. Because this complex is a liquid under ambient conditions (i.e., &gt;60° C.), it can be utilized in standard CVD precursor delivery systems currently used in semiconductor fabrication. TMVS and hfac are additives used to enhance adhesion, nucleation, and stability. Specifically, TMVS is a thermal stabilizer which prevents a reaction until a desired temperature is reached while hfac is a deposition controlling compound. Both TMVS and copper +2 (hfac) 2  are volatile byproducts of the deposition reaction that are exhausted from the chamber. The deposition reaction is believed to proceed according to the following mechanism, in which (s) denotes interaction with a surface and (g) denotes the gas phase: 
     
       
         2Cu +1 hfac,TMVS(g)→2Cu +1 hfac,TMVS(s)  step (1) 
       
     
     
       
         2Cu +1 hfac,TMVS(s)→2Cu +1 hfac(s)+2TMVS(g)  step (2) 
       
     
     
       
         2Cu +1 hfac(s)→Cu(s)+Cu +2 (hfac) 2 (g)  step (3) 
       
     
     In step 1, the complex is adsorbed from the gas phase onto a metallic surface. In step 2, the coordinated olefin (TMVS in this specific case) dissociates from the complex as a free gas leaving behind Cu +1 hfac as an unstable compound. In step 3, the Cu +1 hfac disproportionates to yield copper metal and volatile Cu +2 (hfac) 2 . The disproportionation at CVD temperatures appears to be most strongly catalyzed by metallic or electrically conducting surfaces. In an alternative reaction, the organometallic copper complex can be reduced by hydrogen to yield metallic copper. 
     The volatile liquid complex, Cu +1 hfac,TMVS, can be used to deposit Cu through either a thermal or plasma based process, with the thermal based process being most preferred. The substrate temperature for a plasma enhanced process is preferably between about 100 and about 400° C., while that for a thermal process is between about 50 and about 300° C., and most preferably about 170° C. The vaporizer temperature for copper deposition is preferably between 50 and 85° C. and most preferably 65° C. 
     While the foregoing is directed to a preferred embodiment of the invention, other and further embodiments of the invention may be devised without departing from the basic scope of thereof, and the scope thereof is determined by the claims which follow.