Vaporization and deposition apparatus

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, titanium oxide (BST) film, on a silicon wafer to make integrated circuit capacitors useful in high capacity dynamic memory modules.

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 Invention
 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.sub.2 --Si.sub.3 N.sub.4 --SiO.sub.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. The goal has
 not been satisfactorily achieved because the precursors are finicky and
 the deposition equipment requires a complex design.
 For example, one difficulty encountered is that the delivery of liquid
 precursors has typically required positive displacement pumps. Pumps can
 become clogged and require replacement if the precursors deposit on the
 surfaces of the pumping system. In addition, use of positive displacement
 pumps becomes problematic when the delivery lines or the vaporizer become
 clogged with deposits because the pump can rupture the pressure seals or
 continue to operate until the pressure relief valves on the pump are
 tripped. Either result may require maintenance and repair and over time
 repair and replacement of pumps becomes very expensive and increases the
 cost of ownership of the equipment.
 Another difficulty encountered is that BST precursors have a narrow range
 of vaporization between decomposition at higher temperatures and
 condensation at lower temperatures thereby requiring temperature
 controlled flow paths from the vaporizer into the chamber and through the
 exhaust system. In addition, the liquid precursors tend to form deposits
 in the delivery lines and valves disposed throughout the system.
 Another difficulty encountered is the difficulty or 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. This too results in a reduction in vaporization efficiency of
 the liquid precursors and negatively affects process repeatability and
 deposition rate. Still further, 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 in the vaporizer and
 premature condensation or unwanted decomposition of the precursors.
 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.degree. C. and the annealing
 process is performed at substrate temperatures in the range of about
 550.degree.-850.degree. C. These high temperature requirements impose
 demands on the chambers 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.degree. C. for many fabrication cycles. Seal failure
 may result in loss of proper chamber 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 system components 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 deposition apparatus and method which can
 deliver liquid precursors to a vaporizer, efficiently vaporize the
 precursors, deliver the vaporized precursors to the surface of a substrate
 and exhaust the system while maintaining elevated temperatures in the
 chamber, preventing unwanted condensation or decomposition of precursors
 along the pathway and avoiding temperature gradients in the system. 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 invention, a deposition chamber is provided for
 depositing BST and other materials which require vaporization, especially
 low volatility precursors which are transported as a liquid to a vaporizer
 to be converted to vapor phase and which must be transported at elevated
 temperatures to prevent unwanted condensation on chamber components.
 Preferably, the internal surfaces of the chamber are maintainable at a
 suitable temperature above ambient, e.g., 200-300.degree. C., to prevent
 decomposition and/or condensation of vaporized material on the chamber and
 related gas flow surfaces. The chamber comprises a series of heated
 temperature controlled internal liners which are configured for rapid
 removal, cleaning and/or replacement and preferably are made of a material
 having a thermal coefficient of expansion close to that of the deposition
 material. The chamber also preferably includes features that protect
 chamber 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. This concept is generally referred to
 as a "hot reactor" within a "cool reactor".
 The invention also provides a vaporizing apparatus having large vapor
 passageways for high conductance to prevent clogging for consistently
 mixing and efficiently vaporizing liquid precursor components, and
 delivering the vaporized material to the 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 increased surface area and a tortuous pathway with
 wide passages to reduce the likelihood of fouling or clogging typically
 associated with existing vaporizers.
 The invention also provides a system for delivering liquid source
 components to the vaporizer without requiring high pressure pumps and
 which provides gravity assisted feed and cleaning of the lines.
 Pressurized ampoules deliver the liquid precursors into the vaporizer. The
 ampules are preferably chargeable up to about 500 psi using an inert gas
 such as argon. The use of pressurized ampoules eliminates the need for
 high pressure pumps to deliver the liquid precursors into the vaporizer.
 The invention also provides a liquid and gas plumbing system which allows
 access into the chamber without requiring that any hard plumbing lines be
 disrupted. Preferably, vaporized materials are delivered from the
 vaporizer through the chamber body and into a gas distribution assembly in
 the lid which includes a mixing gas manifold and a gas distribution plate.
 The chamber body and the mixing gas manifold of the lid sealably connect
 gas passages disposed therein on engagement.
 Still further, the invention provides a flushable system which can operate
 in a continuous flow mode or a discontinuous mode where it is turned off
 during the transfer of substrates into or out of the chamber. One or more
 zero dead volume valves and a gravity feed system enable the system to
 cycle between a deposition mode where the liquid precursors are vaporized
 and delivered to the chamber and a substrate transfer mode where solvent
 is delivered to the lines and valves to flush the system to prevent
 build-up of material in the liquid/vapor delivery lines. The solvent be
 can routed through the liquid delivery lines, the vaporizer and through a
 bypass line and into a disposal system. In addition, the system may
 continually vaporize precursors but deliver the vaporized material to the
 exhaust system through a bypass line. This enables stabilization of the
 process over a number of substrates through optimization and maintenance
 of the vaporization process.
 Still further, the invention provides a pumping system for the chamber
 which can maintain chamber pressures at a high vacuum state and which has
 a plumbing system configured to protect the pumps from deposition of
 deposits therein. In one aspect of the invention, cold traps are disposed
 upstream from an exhaust pump to remove vaporized gas from the system. In
 another aspect of the invention, a high vacuum pump is selectively
 isolated from the exhaust passage by a suitable valve such as a gate valve
 to enable selective communication with the high vacuum pump in the absence
 of process gases.
 The chemical vapor deposition system of the present invention is
 characterized by its use in the manufacture of capacitor films of
 consistently high quality, with significantly reduced maintenance times
 and easier 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.

DETAILED DESCRIPTION OF THE INVENTION
 The present invention is directed to a liquid delivery chemical vapor
 deposition (CVD) system useful in depositing thin metal-oxide films as
 well as other films requiring vaporization of precursor liquids. The
 system 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 electrode material deposited on a
 substrate.
 FIG. 1 is a perspective view of a CVD system 10 of 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.
 Not shown in this figure, but a feature of the invention, is a liquid
 delivery system for supplying the liquid precursors to the vaporizer
 module. The size and dimensions of the system are dictated by the size and
 shape of the workpiece on which processes of the present invention are
 performed. A preferred embodiment of the invention will be described
 herein with reference to a chamber adapted to process a circular
 substrate, such as a 200 mm silicon wafer.
 The inventors have recognized that deposition layer uniformity can be
 enhanced, and system maintenance can be reduced, if substantially all of
 the system components (other than the substrate and substrate heater)
 which "see" the process chemistry are substantially maintained at an ideal
 isothermal system temperature (e.g., 250.degree. C. .+-.5.degree. for
 BST). The deposition chamber incorporates several active and passive
 thermal control systems, including features for minimizing temperature
 gradients that can be created as a result of the relatively high
 temperature of the substrate and the substrate support member. The
 deposition chamber also includes thermal control features which serve to
 protect a main chamber seal by cooling it below the ideal isothermal
 system temperature. Other similar thermal control features maintain a
 cover enclosing the chamber lid at a relatively safe temperature to
 prevent burn injuries. Cooling is achieved without inducing significant
 temperature fluctuations and gradients in the system components exposed to
 the system chemistry, and without excessive cooling and heating power
 losses.
 The Deposition Chamber
 FIG. 2 is a cross sectional view of one embodiment of a deposition chamber
 showing the chamber body 12 supporting a heated lid assembly 14. The
 chamber body 12 defines an inner annular processing region 20 defined on
 the perimeter by an inner wall 22. A substrate support member 24 extends
 through the bottom of the chamber and defines the lower end of the
 processing region 20. A gas distribution plate 26 mounted on the lid forms
 the upper limit of the processing region 20. The chamber body 12 and the
 lid assembly 14 are preferably made of a rigid material such as aluminum,
 stainless steel or combinations thereof. The chamber body 12 also defines
 a pumping port for purging the remains of the deposition vapor once it has
 been delivered over the substrate. A generally U-shaped passage
 surrounding the gas distribution assembly forms a pumping channel through
 which gases are drawn into the exhaust system.
 The substrate support member 24 may comprise a metal, e.g., aluminum, with
 a resistive heating element attached thereto or embedded therein.
 Alternatively, the support member may comprise a ceramic block and
 embedded ground plate which generates heat when subjected to RF energy
 emitted by an adjacent electrode. A suitable substrate support member and
 related lift assembly is shown and described in co-pending U.S. patent
 application Ser. No. 08/892,612 entitled Improved "Self Aligning Lift
 Mechanism," filed on Jul. 14, 1997, and is incorporated herein by
 reference. This substrate support member is available from Applied
 Materials, Inc. of Santa Clara, Calif. under the model name CxZ Heater.
 The substrate support member generally is movable up and down on a central
 elevator shaft 30 to move a substrate between a deposition position
 adjacent the gas distribution plate 26 and a substrate insertion/removal
 position below a slit valve formed through the chamber body. The entry
 point of the shaft into the chamber is sealed with a collapsible bellows
 (not shown). The substrate is lifted from or placed on a robot blade by a
 set of lifting pins 32 slidably retained in a set of four passageways 34
 extending through the substrate support member 24. Directly below each of
 the pins is a lifting plate 36 which moves the pins vertically within the
 chamber to allow a substrate to be lifted off or placed on a robot blade
 which is moved into the chamber through the slit valve opening (not
 shown).
 The chamber body 12 defines one or more passages 38 for receiving a heated
 gas delivery feedthrough 40 having an inlet 42 and an outlet 44 to deliver
 one or more precursor gases into the gas distribution plate 26 mounted on
 the lid assembly 14. The passage 38 defines an upper and a lower end of
 differing diameters to form a shoulder 58 where the upper and lower ends
 meet. The gas outlet 44 is fluidically connected to a mixing gas manifold
 46 which includes at least a first gas passage 48 to deliver a gas(es)
 into the gas distribution plate 26. An O-ring seal 50, preferably made of
 TEFLON.RTM. with a stainless steel c-spring, is located around the outlet
 44 on the upper chamber wall to provide a sealing connection between the
 gas delivery feedthrough 40 and the gas manifold 46.
 One or more oxidizer gas passages 52, similar to passage 38, are also
 formed in the chamber body 12 adjacent the passage 38 for receiving an
 oxidizer gas delivery feedthrough which can be heated if desired to
 deliver one or more oxidizer gases through the chamber wall to the mixing
 gas manifold 46. A gas passage 54 is formed in the mixing gas manifold 46
 to deliver the oxidizer gas to a gas outlet 56, which provides a mixing
 point, located in the gas manifold adjacent the entry port into the gas
 distribution plate 26. A restrictive gas passage 37 connects the end of
 the oxidizer gas passage 54 to the end of the vaporized gas passage 48 to
 provide high velocity delivery as well as mixing of the gas mixture
 upstream from the gas distribution plate 26.
 FIG. 3a is a cross sectional view showing a heated gas delivery feedthrough
 40 disposed in the annular passage 38 formed through the chamber wall. The
 passage includes a shoulder 58 disposed on the upper end of the passage
 and includes an O-ring seal 50. The feedthrough preferably includes an
 outer shell 41 and an inner conduit 45 disposed within the outer shell.
 The outer shell includes a mounting shoulder 43 which is mounted on
 shoulder 58 of the passage. The outer shell also includes a lower end
 having threads thereon for receiving a lock nut 51 or other fastener to
 secure the feedthrough in a sealing position within the passage 38 against
 the shoulder 58 and O-ring seal 50. The gas feedthrough 40 includes a
 connector 57 disposed on the lower end of the feedthrough for connection
 to a gas source. The inner conduit and outer shell can be welded together,
 such as near the upper surface of the outer shell. The inner conduit 45
 defines an upper mounting surface 49 for forming a seal with the lid
 assembly at O-ring seal 50 and also includes a flange 62 on its lower end
 for mating with the bottom of the chamber body. A cable type heater 64, or
 other suitable heater, is disposed in intimate contact with the inner
 conduit of the feedthrough to heat the feedthrough to a desired
 temperature. A radiation shield 65 is disposed over the heater to prevent
 thermal radiation from heating the outer shell 41. A gap 53 can be formed
 between the heater 64 and the radiation shield 65. A power lead 67 extends
 from the lower end of the feedthrough and is connected to a suitable power
 source to heat the feedthrough. A thermocouple 66 is inserted or otherwise
 disposed in the heated gas delivery feedthrough 40 to monitor the
 temperature thereof. The feedthrough is mounted in the passage and secured
 therein using a screw type connector or other suitable connector.
 The upper wall 47 of the outer shell 41 is thinned and sized to define a
 gap 55 between its outer surface and the inner wall of the chamber body to
 provide a heat choke adjacent the O-ring seal 50. O-ring seal 50 is
 preferably a hot O-ring which can withstand temperatures of about
 250.degree. C. The thin wall minimizes heat conduction down to the
 shoulder 58 to protect O-ring seal 50. By minimizing heat conduction, less
 power is required to heat the feedthrough. Additionally, less thermal mass
 provides better thermal control and faster response for the feedback
 control. Still further, the heat choke on the outer shell prevents heat
 loss from the mixing gas manifold 46 which is directly connected to the
 insert and which is heated by the lid body. This avoids generation of cold
 spots along the path of the vaporized gas.
 FIG. 3b illustrates an embodiment of a gas feedthrough which is not heated.
 The oxidizer gas(es) are flown through this non-heated feedthrough.
 However, in applications where a heated oxidizer gas feedthrough is
 required, one similar to that shown in FIG. 3a can be used. The
 feedthrough of FIG. 3b resembles that of FIG. 3a except that the cable
 heater and thermocouple are removed. In addition, the sizes of the
 feedthrough may vary depending on the requirements of the process. In one
 embodiment, the non-heated oxidizer gas feedthrough has a smaller gas
 passage and the overall dimensions are therefor somewhat smaller.
 FIG. 4 is a cross sectional view of an alternative embodiment of the
 present system. A deposition vapor inlet passageway 68 which communicates
 directly with a vaporizer outlet port may extend axially through the lid
 body assembly 14. An annular recess surrounding the inlet passageway is
 formed on a top side of the main lid body.
 Referring again to FIG. 2, removable deposition chamber liners (which can
 be used at a number of different locations) facilitate periodic cleaning
 of the deposition chamber. A liner in accordance with a preferred
 embodiment of the invention includes an integral or functionally integral
 (i.e., assembled from one or more components as attached or overlapping
 units) generally chamber liner 28 that covers upper chamber surfaces
 adjacent the substrate support member 24 and a bottom liner 21 covers the
 lower chamber wall surfaces below substrate support member. The liner
 material may be made of a metal, e.g., stainless steel or aluminum, a
 ceramic material (e.g., Al.sub.2 O.sub.3) or quartz, and can be equipped
 with an active PID controlled heating element which maintains the liner
 walls substantially at the optimum isothermal system temperature to
 inhibit both condensation and decomposition of gas vapor on the chamber
 surfaces. The material from which the liner is made preferably
 demonstrates chemical resistance to halogens and halogenated in situ
 cleaning compounds, and is preferably not adversely affected by, nor
 adversely affects, the process chemistry.
 Referring again to FIG. 2, a chamber liner 28 is preferably disposed
 adjacent the inner wall 22 of the chamber to provide a removable surface
 within the chamber which can be easily cleaned and/or replaced. The liner
 28 is supported in the chamber on supports 23, preferably three, which are
 equally spaced around the lower surface of the liner. The supports 23 are
 sized to minimize the contact area between the chamber liner 28 and the
 chamber body and thereby minimize heat conduction between the liner and
 the chamber body. In one embodiment, the liner is heated by radiation from
 the heated lid and the heated substrate support member. This embodiment is
 referred to as a passive floating liner. Alternatively, the liner may also
 include a resistive heater 25 (shown in FIG. 5), or other suitable heater,
 disposed therein so that it can be actively heated and maintained at an
 ideal isothermal temperature. This actively heated embodiment is referred
 to as an active floating liner. FIG. 5 is a substantially bottom
 perspective view of a heated liner 28 having a resistive heater 25
 disposed therein and an electrical connector 27 mounted on the lower
 surface of the liner which houses the electrical connections to the coil.
 FIG. 6 is a cross sectional view through the active floating liner 28
 showing an external housing mounted on the bottom of the chamber through
 which the electrical connector 27 is disposed. Due to thermal expansion of
 the liner, accommodation of the expansion is preferably provided or
 resisted by the external housing mounted on the chamber. The external
 housing includes a first conduit 29 having a flange 31, 33 disposed on
 each end thereof for mounting to the bottom of the chamber and for
 mounting a bellows 35, respectively. The bellows is mounted on one end to
 the lower end of flange 33 and at the other end to a second conduit 137 at
 a flange 39 provided therefor. The bellows is sized and adapted to flex to
 accommodate any thermal expansion in the electrical connector 27 or the
 liner 28. The electrical connections to the coil extend through the end of
 the second conduit 137 for easy connection to a power source.
 Since the portions of the liner below the substrate support member are
 typically isolated from the vapor flow, temperature control of these parts
 is less critical. However, the portion of the liner below the substrate
 support member may also be actively heated using a resistive type heating
 element, or other suitable heating member. Preferably, the temperature of
 the liner both above and below the substrate support member should be
 maintainable within the optimum isothermal system temperature range, e.g.,
 between about 200.degree. C. and 750.degree. C., or other temperature
 range suitable for the desired deposition material.
 A sealing edge ring 160 (shown in FIG. 2) is disposed in the chamber and
 supported on the substrate support member 24 to contact and overlap a
 circumferential edge of the substrate support member 24. A circumferential
 rib can be provided on the underside of the ring in order to maintain the
 ring in an aligned position. The edge ring serves to close-off the annular
 space 162 between the liner 28 and the substrate support member 24, and
 thereby substantially reduce the amount of deposition vapor which flows
 into the lower part of the deposition chamber. In addition, the edge ring
 acts as a radiation shield. The outer circumferential portion of the gas
 distribution plate 26 typically extends beyond the diameter of the
 substrate. The edge ring 160 protects this part of the gas distribution
 plate 26 from heat directly radiated by the substrate support member. The
 edge ring 160 is preferably made of a material having a thermal
 coefficient of expansion similar to that of the deposition material to
 reduce the possibility of particle generation due to flaking during
 thermal cycling. In the case of BST, one such edge ring material is
 titanium.
 The lid assembly 14 preferably comprises a main body 70 machined or
 otherwise formed of a metal having a high thermal conductivity, e.g.,
 aluminum. The main lid body defines an annular channel 74 formed around
 its perimeter to define a thin outer wall 76. A support ring 78,
 preferably made of stainless steel or other thermal insulator, is disposed
 in the channel to provide structural support for the lid and to prevent
 thermal conduction to the outer wall 76. The thin outer wall of the body
 member provides a thermal choke for the base 71 of the lid which is sealed
 to the chamber body during processing at the O-ring seal 72. The O-ring
 seal 72 is positioned at a circumferential interface of the chamber body
 12 and the lid assembly to maintain a hermetic and vacuum tight seal of
 the chamber. In order to actively cool the O-ring seal, one or more
 cooling channels 73 are preferably disposed in the lower lip of the outer
 wall 76. A heat exchange fluid (e.g., water, ethylene glycol, silicone
 oil, etc.) circulates through the channel to remove heat at the O-ring
 seal.
 The thermal choke provided by the thin outer wall 76 isolates the O-ring
 seal 72 between chamber lid assembly 14 and the chamber body 12 from the
 heat generated by heating elements 80 disposed in the lid. The heat choke
 provides thermal protection of the O-ring seal 72 by allowing localized
 active cooling within the channel on top of the O-ring 72, without
 inducing significant detrimental cooling effects on the other system
 components. The thin wall 76 presents an effective thermal barrier between
 the heating elements and the O-ring due to its small cross-sectional area
 (A) and long length (1).
 The upper surface of the main lid body 70 defines a plurality of annular
 recesses 79, such as spiral grooves, for receipt of a heating element 80
 therein. In a preferred embodiment, a heater with a power output of about
 6200 W is used. However, the amount of power will vary depending on the
 lid design and geometry, including material composition of the lid, and
 the process temperature. Power is delivered to the heating elements
 through a feedthrough 85 disposed in the lid. The heater is preferably
 controlled with conventional PID feedback control, based on signals
 received from a thermocouple 82 positioned or otherwise disposed in the
 lid. An annular plate 84 serving as a heat shield is mounted on the top of
 the heating elements. Preferably, the plate 84 is brazed to the lid body
 to form an integral part of the lid body. A water cooled cover plate 86 is
 disposed on or over the plate 84 to provide a controlled mechanism for
 pulling heat out of the lid for active feedback temperature control.
 A cooling channel 100 is preferably formed in top cover plate 86 of the lid
 assembly 14. Cooling channel 100 removes heat from the lid. In addition, a
 thermal choke gap, preferably about 25 mils, is used to control the amount
 of heat removed from the lid during cooling. During deposition of a
 material such as BST, the substrate will be heated by the substrate
 support member to a temperature of over 500.degree. C. Heat from the
 substrate and the substrate support member will radiate onto the gas
 distribution plate 26 thereby tending to increase its temperature above
 the optimum isothermal system temperature. By increasing the thermal
 conduction or transfer between the lid and the gas distribution plate 26,
 the substrate and substrate support member induced temperature gradients
 and fluctuations can be reduced. In order to improve heat conductivity
 between the lid and the gas distribution plate 26, an inert gas (e.g.,
 helium, hydrogen, etc.) is circulated about the annular interface of these
 elements. The inert gas is introduced into channel 102, which may be
 circular, spiral or other shape, disposed in the lid. The channel can be
 formed in the mating annular surface(s) of the gas distribution plate 26
 and the main lid body 70 and/or in the cover plate 86. The inert gas can
 be introduced from the top through the cooling plate or through the bottom
 of the chamber via a feedthrough connected to the gas manifold. Gas
 pressure in the channels can be maintained within the range from about
 1-100 Torr, preferably within the range of about 1-20 Torr. Due to its
 high thermal conductivity, the circulating inert gas can improve heat
 transfer between the lid assembly 14 and the gas distribution plate 26.
 The lid assembly, including the heating element, is configured to maintain
 the vapor inlet passageway and gas distribution plate at an ideal
 isothermal system temperature, e.g., 250.degree. C..+-.5.degree.. Passive
 and active cooling elements are used to maintain the top cover of the lid,
 and the O-ring seal 72 positioned between the chamber body and the lid
 assembly, at a substantially lower temperature, e.g., 100.degree. C. or
 lower.
 Referring again to FIG. 2, the mixing gas manifold 46 includes a central
 opening 88 which delivers the gases to a blocker plate 90 to initially
 disperse or distribute the gas(es) over a large area above a face plate
 92. Each of the blocker plate and the face plate have a plurality of holes
 formed therethrough which evenly disperse the gas over the area of the
 plates 90, 92 and together form the gas distribution plate 26. The face
 plate 92 delivers the gas uniformly over the area of a substrate
 positioned on the substrate support member 24. The gas distribution plate
 26 and the mixing gas manifold 46 are preferably made of aluminum and are
 sufficiently thick to allow heat transfer from the gas distribution plate
 to the temperature controlled lid assembly 14.
 With respect to the gas distribution plate assembly, the use of a
 conventional thin blocker plate 90 with a relatively thicker face plate 92
 also serves as a thermal control system. The mixing gas manifold 46 serves
 as a heated mass whose heat capacity and high thermal conductivity act as
 a source of thermal inertia resisting temperature variations from the
 center of gas distribution plate to its periphery. The gas mixing manifold
 46 also avoids the effects of gas "channeling" through the material of the
 plate for providing a more even distribution of gas volume across the
 substrate surface. While the gas distribution plate is preferably made of
 aluminum, another thermally conductive material may also be used.
 FIG. 7 is a top view of a chamber lid showing the heating element 80 and
 the mixing gas manifold 46. The lower surface of the lid body defines one
 or more channels 104 for mounting a gas manifold 46. FIG. 8 is a partial
 cross sectional view of a gas manifold 46. The gas manifold 46 includes a
 gas delivery block 61 which defines one or more gas passages 48, 54
 therein having one or more gas inlets 38, 52 on one end and a gas outlet
 56 on the other end. The gas outlet 56 serves as a gas inlet of the gas
 distribution plate 26. An annular conductance restrictor plate 63 is
 mounted on the lower surface of the gas delivery block to mount the gas
 distribution plate and prevent gas leakage at the interface between the
 gas manifold and the gas distribution plate. The conductance restrictor
 plate 63 is sized and adapted to define an annular mounting recess 65 to
 which the gas distribution plate is secured.
 A vaporized first gas passage 48 and an oxidizer gas passage 54 extend at
 least partially along the length of the gas manifold from the gas inlets
 to the gas outlet. The restricting gas passage 37 is disposed between the
 vapor gas passage and the oxidizer gas passage to optimally mix and
 deliver the oxidizer gas into the gas outlet and then to the blocker plate
 and face plate. The restrictive gas passage 37 delivers the oxidizer gas
 into the vaporized gas passage at a relatively high velocity to assist in
 mixing of the gases. Alternatively or additionally, a second set of a
 vaporized gas passage and an oxidizer gas passage, a carrier gas passage
 or a cleaning gas passage (to deliver a cleaning gas species from a remote
 plasma source) may also be provided through the chamber wall to deliver
 these gases to a second gas manifold.
 FIG. 4 shows a partial cross sectional view of a pumping system 18 of the
 present invention. The pumping system 18 includes a pumping nose 106
 mounted on the chamber which connects an exhaust passage and related pumps
 to the chamber. The pumping nose 106 includes a housing 108 which defines
 a gas passage 110 along its length. The housing supports a removable
 heated liner 112. Both the housing and the liner define a pair of ports
 114, 116, one port 114 connected to a cold trap and exhaust pump and the
 other port 116 connected to a turbopump 118, or other high vacuum pump,
 with a gate valve 120 disposed therebetween.
 The removable heated liner 112 is shaped and sized to slidably mount within
 the nose housing 108 and includes a mounting flange 122 on one end to
 mount to the end of the housing. A second mounting plate 123 is mounted on
 the first and sealed thereto using an O-ring seal 125. The removable
 heated liner includes a body 124 which defines a central gas passage 110
 opening into the removable heated manifold in the chamber and the two exit
 ports, preferably connecting a high vacuum pump and an exhaust pump and
 related cold traps. Six mounting blocks 126, 128, 130 (three of which are
 shown) extend at least partially along the length of the central passage
 to mount four cartridge heaters 132 and two thermocouples 134. The
 multiple thermocouples provide a back up as well as enable checking
 temperature uniformity. In one embodiment, the thermocouples extend along
 the bottom of the liner while the heaters are disposed along the top and
 in the central portion of the liner. However, other configurations such as
 heaters on the top and bottom and thermocouples in the middle or heaters
 on the bottom and middle and thermocouples on the top are contemplated by
 the present invention. The heaters are preferably connected in parallel
 and two connections are provided on the mounting flange of the liner for
 easy connection to a power source. A cap may be mounted over the mounting
 plates when removed from the system so that the removable heated liner can
 be easily cleaned without the risk of jeopardizing the electrical
 connections to the heaters. The cap can be sealed to the second mounting
 plate 123 using an O-ring seal or other suitable seal. Also, a handle is
 preferably mounted on the second mounting plate to facilitate easy removal
 of the liner from the nose and submersion in a cleaning bath. Preferably,
 the second mounting plate 123 includes quick connects for the heaters and
 the thermocouple cables. FIG. 12 is a front view of the second mounting
 flange 122 showing the heater and thermocouple connections and positions.
 FIG. 11 is a cross sectional view of an removable heated liner 112. The end
 of the liner adjacent mounting flange 122 includes a thin walled portion
 136 around its circumference which acts as a thermal choke. The thermal
 choke ensures that an O-ring disposed between the mounting flange 122 and
 the exhaust housing is not subjected to elevated temperatures.
 Additionally, the thermal choke regulates the amount of heat transferred
 to the housing thereby minimizing (i.e., optimizing) the amount of power
 required to heat the liner. The end proximate the chamber is curved to
 match the curvilinear contour of the inner wall of the exhaust manifold.
 TEFLON.RTM. screws 138 are inserted at the chamber of the liner on at
 least the bottom and/or the sidewalls of the liner, preferably both, to
 provide a smooth surface on which the liner can slide on insertion into or
 removal from the housing to prevent scratching of the nose liner and/or
 housing. TEFLON.RTM. is preferred because it can withstand 250.degree. C.
 temperatures, it does not outgas unwanted contaminants and is compatible
 with various aggressive cleaning solutions. However, screws or plugs
 formed of other materials possessing these characteristics can be used
 effectively.
 Referring to FIG. 4, a turbopump 118, or other high vacuum pump, is mounted
 to an outlet port 116 of the pumping nose. A gate valve 120 is disposed
 between the turbopump and the nose to enable selective communication of
 the turbopump with the chamber. The turbopump enables the vacuum chamber
 to be evacuated down to a very low pressure to be compatible with
 processing platforms such as an Endura.RTM. platform available from
 Applied Materials, Inc. of Santa Clara, Calif. An exhaust pump such as a
 roughing pump, dry pump or other pump used in the industry is connected to
 the chamber at the exhaust port 114 in the nose to pump the chamber during
 processing. A cold trap 140 is disposed in the conduit connecting the
 exhaust pump to filter out the deposition material which may be
 detrimental to the pump. Additionally, a second cold trap 142 is disposed
 below the first cold trap and is connected to a bypass line from the
 vaporizer. The bypass line and related cold trap allow the system to
 operate in a continuous flow made by allowing delivery of vaporized
 material thereto during wafer transfer.
 FIG. 13 is a perspective view of a cold trap filter of the present
 invention. The cold trap is housed in a tubular housing 144 (shown in FIG.
 1) and includes a filtering member 146 which includes a plurality of
 cooled passages 148 for condensation of material thereon. The filtering
 member includes a base portion 147 and a filtering portion 149. The
 filtering portion 149 includes the plurality of cooled passages 148 formed
 therein. A water inlet 151 and water outlet 153 are disposed in conduits
 155, 157. The gases pass through the filtering member and continue through
 an exhaust passage deposed in communication with a central portion 150 of
 the filtering member. This structure enables gases to pass through the
 filtering portion 149 and on through the exhaust system. The housing 144
 mounts a conduit connected to the exhaust pump having an inlet fluidically
 connected to the central chamber portion 150 so that the gases pass
 through the cold trap and continue on through the conduit to a disposal
 system.
 A purge gas arrangement provides a purge gas in the lower part of the
 chamber resulting in a gas shield with upwardly directed flow of gas
 emanating from the bottom of the chamber. The gas shield strength is
 adjustable with a mass flow controller. Suitable purge gases include
 helium, argon and nitrogen, which can be introduced through a purge line
 and a circular manifold for distributing the gas evenly about the
 substrate support member and the elevator shaft, within the sealing
 bellows. The gas flow rate must be set relatively low, e.g., 50 sccm, in
 order to avoid interference with the deposition process. Additionally, the
 purge gas is directed into the exhaust plenum adjacent the liner and away
 from the edge of the wafer.
 The Vaporizer
 FIG. 14 is a perspective view showing the vaporizing module 16 mounted
 adjacent to the chamber 12. A vaporizer 154 is mounted in a vaporizer
 cabinet 155 and includes an outlet line 156 connected to the inlet into
 the chamber. Disposed along the outlet line 124 is a first valve 157 which
 is connected in turn to a bypass line (not shown) extending out through
 the back of the cabinet 155 and is connected to the exhaust system by a
 conduit in which the cold trap 142 is disposed (see FIG. 1). The bypass
 line is adapted to deliver both vaporized gas as well as liquid solvent
 into a cold trap disposed downstream from the valve in preparation of
 delivering vaporized gas to the chamber or during cleaning of the system.
 This valve controls delivery of the vaporized material to the chamber or
 through the cold trap in the exhaust system. A second valve 158 is
 disposed downstream from the first valve to selectively deliver the
 vaporized gas into the chamber. The second valve is mounted to the lower
 portion of the chamber via a rod and washer assembly 159. This assembly
 enables adjustment of the delivery line as well as the valve in relation
 to the chamber. The mount generally includes first and second rings 160,
 161, respectively, one disposed in the other, to allow rotatable
 adjustment of an second valve 158 and the delivery line. The second valve
 158 is mounted to the second ring 161 via a plurality of rods 162 (four
 shown here) which are mounted from the ring and include a spring 163
 disposed above the upper portion of the rod and the second ring 161. The
 two rings 160, 161 enable rotation of the assembly while the spring and
 rod arrangement allow vertical adjustment of the assembly to ensure proper
 alignment of the gas feed line 156 into the chamber through the
 feedthrough 40, shown in FIG. 2. In general, the suspension apparatus
 provides automatic compensation for thermal expansion/contraction to
 maintain vacuum seals without the mechanical and thermal stress.
 FIG. 15 is a cross sectional view of one embodiment of a vaporizer 154 of
 the present invention. The vaporizer generally includes an injection
 nozzle 170 disposed through an inlet port 172 of the vaporizer. A
 concentric passage 174 is disposed about the outer perimeter of the gas
 injection nozzle 170 to deliver one or more carrier gases to the tip of
 the nozzle. Preferably, the concentric gas passage is made of PTFE for low
 friction coefficient and prevention of clogging. The carrier gases are
 flown concentrically about the nozzle to prevent liquid droplets from
 forming on the tip of the nozzle and moving up the outer cylinder of the
 nozzle. The liquid delivered to the nozzle 170 is carried in a carrier
 gas, such as argon, and delivered to a central cup-shaped portion 176 of
 the vaporizer. The cup-shaped portion of the vaporizer forms the central
 receptacle for the liquid injection stream where vaporization commences. A
 plurality of fins 178 are disposed around the central cup-shaped portion
 176 to define a tortuous path or labyrinth along which vaporization
 occurs. The fins 178 are spaced from one another in rings which are offset
 to form the path along which the gas vapor diffuses and are spaced a
 sufficient distance to reduce the likelihood of clogging. One or more
 notches 180 are formed in the upper portion of the fins to define a gas
 flow passage which allows gas flow but which enables the fins to trap any
 liquid which is not vaporized. This prevents liquids from passing through
 the vaporizer and into the chamber, as well as enabling a solvent to be
 delivered into the vaporizer for cleaning without the risk of having the
 solvent enter the chamber.
 Connected with the circular path defined between the outermost circle of
 fins and internal cylindrical wall surrounding the vaporizer section are a
 plurality of ports 182 (e.g., six) and associated gas delivery passages
 converging to a main outlet 184. The arrangement of angled ports 182
 provide a large conductance for shorter resonance time in the vaporizer
 and also facilitate inspection and cleaning of the vapor flow paths. All
 of the passages are surrounded by a large solid mass of a lower block 186
 and an upper block 188 which are assembled together to form the vaporizer
 and include a metal-to-metal seal 187. The upper and lower blocks define
 grooves 190 to mount heating elements. This arrangement helps to ensure
 that the vaporizing surfaces as well as the vapor are maintained at the
 optimum isothermal temperature downstream of (as well as in) the main
 vaporizing section.
 The fins 178 of the vaporizing section are preferably formed as integral
 parts of the upper and lower block, and not as separate attached parts.
 Thus, in contrast to previous designs, the heating surfaces do not
 constitute thermally "floating pieces," i.e., pieces whose temperature
 "floats" or varies (less controllably) in relation to the temperature of
 one or more separate thermal masses to which the pieces are attached. In a
 preferred embodiment, respective sets of fins are machined directly into
 the mating surfaces of the upper and lower blocks in complimentary
 configurations which interleaf or interdigitate with each other to form
 the multi-path, maze-like structure shown in FIG. 16. In addition to their
 vaporizing function, the twists and turns of the pathways of the main
 vaporizing section also serve to vigorously mix the precursor components
 and carrier gases and to filter out entrained droplets by impaction as the
 carrier gas changes direction in the labyrinth.
 The radial spacing between the concentrically arranged fins is preferably
 about 0.5 mm (0.020"), in order to minimize the effects of any deposits
 which might form. A preferred radial spacing is within the range of about
 1-3 mm (0.039-0.118"), and most preferably about 2 mm. In a preferred
 embodiment, the circular fins have a height of about 2-8 mm and a density
 of 2-6 fins per inch (measured in the radial direction). The overall inner
 diameter of the preferred main vaporizer section is 75 mm, and 6
 concentric circles are provided with a radial spacing of about 2 mm. Each
 of the circles has four fins; the size and circumferential (end-to-end)
 spacings of the fins varies directly with the diameters of the circles.
 Maximum and minimum end-to-end spacings of the fins are 30 mm and 2 mm,
 respectively, depending on carrier gas flow, the vaporization behavior of
 the precursors and thermal stability of the precursors. The spacing
 between the fins is important to prevent clogging of the vaporizer and to
 provide maximum surface area on which vaporization can occur. The
 precursors with low volatility require relatively high conductance and
 fewer fins. Precursors with low thermal stability require relatively short
 resonance time and therefore high carrier gas flow, a short flow path and
 fewer fins. Precursors with violent or droplet generating boiling
 phenomenon require relatively higher numbers of fins to enhance impaction
 filtering of the droplets.
 An important feature of the vaporizer assembly is the arrangement provided
 for delivery of the liquid precursor mixture to the main vaporizing
 section, and for mixing the precursor liquid with the carrier gas. The
 mixture of liquid precursor components is delivered through the nozzle 170
 or capillary tube (e.g., 2-20 mil inner diameter) to a point just above
 the center of the main vaporizing section. 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 capillary tube and enter the main
 vaporizing section as a jet of liquid and gas with a high nozzle velocity.
 Importantly, all but a final short segment of the path of the liquid
 mixture is kept relatively cool by a thermal choke structure 195 to reduce
 thermal decomposition of the liquid precursor components prior to
 vaporization. In particular, the capillary tube extends within a
 relatively thin tube or neck 192 attached to or forming an integral part
 of the upper block as shown in FIG. 15. Thermal insulation of the
 capillary tube along this stretch is provided by the relatively thin wall
 of the neck, e.g., 10-100 mil thickness, as well as by the space between
 the capillary tube and surrounding internal surface of the neck and by the
 thermal insulating value of the material. The neck is preferably made of
 PTFE, stainless steel or other material having a relatively low thermal
 conductivity. A cooling block 197 and cooling channel 199 enable
 temperature control of the nozzle 170.
 The liquid precursor components are mixed with a concentrically delivered
 carrier gas as the former is jetted-out of the capillary tube just above
 the main vaporizing section. The concentrically delivered carrier gas is
 delivered to this point by a supply line 193 or tube fluidly connected,
 e.g., with a standard VCR fitting, with an upper part of the internal bore
 of the neck. The gas flows downwardly within the passage 174 defined
 between the injection nozzle 170 and the internal neck surface. At the
 level of the nozzle outlet, the carrier gas picks-up the liquid precursor
 mixture jetting-out of the capillary tube and carries the mixture down
 into the main vaporizing section 176 where the liquid precursor is
 vaporized. To allow for optimization of this initial "flash" vaporization,
 the spacing between the injection nozzle 170 and the main vaporization
 section 176 is preferably adjustable. For example, the capillary tube can
 be made axially movable within a thermal choke structure 195 mounted
 within the central neck bore. 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. Any
 liquid droplets remaining after the initial "flash" vaporization are
 vaporized as the mixture advances through the tortuous paths of the main
 vaporizer section, in contact with the heated fins. The resultant
 deposition gas then passes through the ports and angled ports 182 to the
 central main outlet 184, and through the vaporizer outlet port for direct
 delivery to the deposition chamber. The mixture is substantially
 maintained at the predetermined optimum isothermal system temperature
 (e.g., 250.degree. C..+-.5.degree.). The exit ports are designed for large
 conductance so that precursor vapors are readily carried from the
 vaporizer into the chamber.
 The vaporizer operates to vaporize a mixture of precursor components, such
 as BST, and a carrier gas by providing a main vaporizer section with
 increased surface area provided along a tortuous pathway which expose the
 mixture to a large area of evenly heated surfaces and filter out liquid
 droplets entrained in the flow by droplet impaction during changes in gas
 flow direction in the tortuous path. The flow velocity, and therefore
 impaction filtering efficiency, is independently controlled by the flow of
 an auxiliary argon or other carrier gas input to he vaporizer injection
 plumbing. 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. 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/min 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. As will be understood, a metering valve can be used to
 control the amount of gas flow in direct relation to the flow rate of the
 liquid precursor component mixture.
 In accordance with the invention, the thermal power transferred to the
 vaporizer 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., 200-300 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.degree.
 C..+-.5.degree.) 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.degree. C.
 Also, the vaporizer body is configured to help ensure the maintenance of an
 isothermal temperature of the main vaporizing section. Specifically, the
 heating surfaces are preferably integrally formed in adjoining surfaces of
 upper and lower blocks of metal, e.g., aluminum or stainless steel. The
 blocks provide a relatively large thermal mass for retention and
 transmission of thermal energy generated by one or a pair of heating
 elements surrounding the blocks. In a preferred embodiment, the upper and
 lower blocks are provided as segments of a cylindrical rod and one or a
 pair of heating elements, such as a cable heater, are wrapped helically
 about the circumference, and along the lengths, of the rod segments.
 As one specific example, the top and bottom cylindrical blocks may each
 have an outer diameter of 3.5". The top segment may have a length of 1",
 and the bottom segment a length of 2". The segments may be bolted together
 by a plurality of bolts, e.g., eight, extending in an axial direction and
 equally spaced around the perimeter of the blocks. Preferably, the
 segments are sealed to each other with a known type of high temperature
 metal-to-metal seal situated in a circular groove provided in one or both
 of the blocks and surrounding the main vaporizer section. One example of a
 metal-to-metal seal is the aluminum Delta seal from Helicoflex.
 The heating elements preferably deliver a total heating power of between
 about 1000 W and 3000 W to the blocks. If separate heaters are used to
 heat the top and bottom segments, a 1500 W bottom heater and a 675 W top
 heater may be used to provide a total heating power of 2175 W. Helical
 grooves (not shown) are preferably formed on the outer surface of the
 blocks and the heating elements are secured in the grooves, e.g., by
 welding. The heater is controlled to maintain the main vaporizing section
 at the optimum isothermal temperature by a conventional PID controller.
 The controller is connected with a thermocouple positioned within one, and
 preferably both, of the upper and lower segments directly adjacent the
 heated vaporizing surfaces.
 In an alternative embodiment shown in FIG. 17, the upper and lower block do
 not provide interdigitating fins, but rather provide a fin structure 178
 is disposed only on the lower block. The upper block defines an upper roof
 179 of the vaporizing chamber. The fins 178 are spaced from one another
 and include passages therethrough to enable flow of vaporized gas through
 the fin structure and out through the outlets. It is believed that this
 arrangement enables greater conductance of vaporized gas and to reduce
 resonance time in the vaporizer.
 Applications of the System
 Exemplary metal-oxide layers which can be deposited using the present
 system may include tantalum pentoxide (Ta.sub.2 O.sub.5), a zirconate
 titanate (ZrxTiy Oz), strontium titanate (SrTiO.sub.3), barium strontium
 titanate (BST), lead zirconate titanate (PZT), lanthanum-doped PZT,
 bismuth titanate (Bi.sub.4 Ti.sub.3 O.sub.12), barium titanate
 (BaTiO.sub.3), BST, PZT, lanthanum-doped PZT, or the like. Other materials
 which can be deposited include those materials having a narrow range
 between vaporization and decomposition.
 Substrates used in the present invention include primarily P-type and
 N-type silicon. Depending on the particular process chemistry and desired
 end product, other substrate materials may be usable, including other
 semiconductors, e.g., germanium, diamond, compound semiconductors, e.g.,
 GaAs, InP, Si/Ge, SiC, and ceramics.
 The selection of materials for the layers above the circuit element in an
 integrated circuit device depends on the device that is formed and other
 layers that a particular layer currently or subsequently contacts. For
 example, a DRAM requires a high,permittivity capacitor, but the
 metal-oxide dielectric layer does not need to have ferroelectric
 properties.
 Devices that can be made with the present system include, but are not
 limited to, 64 Mbit, 256 Mbit, 1 Gbit and 4 Gbit DRAMs.
 The system also has particular application with other liquid precursors
 which are volatile as well as materials such as copper.
 Liquid Delivery System
 FIG. 18 is a perspective view showing a liquid delivery system 200 of the
 present invention. The liquid delivery system generally includes a liquid
 precursor module 202, a solvent module 204 and a vaporizer module 206. In
 one embodiment, the liquid precursor module 202 includes two pressurized
 ampoules 208, 210 and a liquid delivery line 212 connected to each
 ampoule. Valves are disposed along the length of the liquid delivery lines
 to control flow of liquid from the ampoules to a mixing port and then into
 the vaporizer. Preferably, zero dead volume valves, which are described
 below, are used to prevent collection of precursor therein which can
 compromise the valves as well as negatively affect process stabilization
 and/or repeatability. The zero dead volume valves enable rapid flushing of
 precursor from the lines using solvent. Solvent is plumbed to the liquid
 delivery line 212 by line 214 to flush the system during maintenance.
 Additionally, a purge gas line is plumbed to the liquid delivery line to
 rapidly purge solvent from the line so that the system, including the
 ampoules, valves and/or LFCs, can be prepared for maintenance in ten (10)
 to thirty (30) minutes. The valving is designed so that when necessary,
 solvent can be introduced into the liquid delivery line upstream form the
 mixing port to flush the line through a bypass line 218 and out through a
 recovery system which includes a cold trap and exhaust manifold.
 The ampoules are designed to deliver the liquid precursors at high
 pressure, e.g., up to 500 psi, without having to rely on high pressure
 pumps, i.e., no high cycle mechanical pump with rubbing parts exposed to
 precursors. To provide the pressure, an inert gas such as argon is charged
 into the ampoules at a pressure of about 90 psi through line 220. A liquid
 outlet line 222 is disposed in the ampoule so that as the inert gas, e.g.,
 argon, is delivered to the ampoule and the appropriate valves are opened,
 the liquid is forced out through the outlet through a suitable valve and
 into the liquid delivery line.
 The liquid delivery line 212 is connected from each ampoule to the
 vaporizer. A first zero dead volume valve is disposed on the outlet of the
 ampoule to control delivery of the liquid to the delivery line 212. The
 valve is preferably a three-way valve connecting the bypass line 218 and
 the liquid delivery line 212. The bypass line 218 in turn is connected to
 a cold trap and an exhaust manifold (not shown). A high pressure gauge 224
 and a LFC 226 are disposed downstream from a valve 228 introducing the
 solvent and the purge gas. The LFC controls delivery of the liquid to the
 mixing port 230 connected between the liquid precursor delivery lines. A
 low pressure gauge 232 is disposed on the bypass line 218 to monitor
 pressure in the line so that completion of the maintenance routine can be
 determined.
 The liquid precursor delivery lines 212 deliver liquid precursors into the
 mixing port 230 upstream from the vaporizer 154. A solvent delivery line
 234 also delivers a solvent into the liquid delivery line downstream from
 the mixing port where the liquid precursors and the solvent are mixed and
 delivered into the vaporizer. At the vaporizer, a carrier gas line 236
 delivers a carrier gas into the delivery line to carry the liquid
 precursors and the solvent into the vaporizer through the capillary tube
 or nozzle. In addition, a concentric carrier gas line 238 delivers a
 carrier gas around the nozzle or injection tip to ensure that even a small
 amount of liquid is delivered to the vaporizing surfaces. The delivery
 line from the mixing port and into the vaporizer is preferably made of a
 material having a low coefficient of friction, such as TEFLON.RTM. PTFE,
 and does not hang up in the line. This feature assists in the delivery of
 small volumes of liquid precursor.
 The solvent module 204 includes one or more chargeable ampoules similar to
 the liquid precursor ampoules. Preferably, there are two solvent ampoules
 240, 242 and two liquid precursor ampoules 208, 210. The liquid precursor
 ampoules can deliver two separate precursors which can be mixed at the
 mixing port or can deliver the same precursor together or alternatively.
 The liquid precursor ampoules are designed with a slotted/sculptured bottom
 to draw the liquid downwardly in the ampule so that the liquid may (1) be
 detected at very low levels and (2) be drawn out of the ampule even at low
 levels. This is particularly important in dealing with expensive liquids
 which are preferably not wasted. In addition, the ampoules include an
 ultrasonic detector for discerning the volume of liquid in the ampoule
 even at low levels so that continuous processing may be achieved.
 FIG. 19 is a perspective view of a zero dead volume valve. The valve
 includes a liquid precursor inlet 252 and a solvent inlet 254 and a single
 outlet 256. The solvent is routed through the solvent inlet through a
 solvent control actuator 258 and into the liquid precursor control
 actuator 260. A plunger 262 controls entry of the solvent into and
 consequently out of the solvent control actuator as shown in FIG. 20. The
 liquid precursor is routed through the precursor inlet 252 and into
 precursor control actuator 260 when the plunger 264 in the actuator is in
 the open position. When the plunger is in the closed position, the
 precursor is prevented from entering the actuator and is flushed out of
 the valve by the plunger and by flow of solvent through the valve. The
 solvent is able to enter the precursor control actuator 260 whether the
 plunger is in the open or closed position to enable solvent purge of the
 valve as shown in FIG. 20. The plunger is contoured to seal the liquid
 precursor inlet while enabling solvent flow into the actuator. Continuous
 solvent flow allows the system to be continuously purged with solvent when
 the liquid precursors are shut off.
 Additionally, a single actuator valve is disposed on the outlets of the
 ampules to control delivery of liquid precursor and to prevent clogging in
 the actuator. Also, the two way valves are preferably disposed on the
 downstream side of the liquid flow controllers in the vaporizer panel.
 The delivery tubes are preferably made of a material such as TEFLON.RTM. to
 promote frictionless fluid flow therein to prevent clogging and deposition
 along the path of the tubes. It has been learned that TEFLON.RTM. provides
 a better conduit for materials such as the barium, strontium and titanium
 precursor liquids used in the deposition of BST.
 The plumbing system is designed to enable rapid flushing of the lines and
 valves during routine maintenance. Additionally, the system is adapted to
 enable sequential shutdown of each of the valves as well as to deliver an
 automatic flush of a controlled amount of solvent through the vaporizer
 and the delivery lines in case of a power outage. This safety feature
 ensures that during uncontrolled power outages, the system will not be
 subject to clogging.
 The delivery system may also comprise a bubbler system where a carrier gas
 such as argon can be bubbled through a solvent to suppress premature
 solvent evaporation from the precursor, thereby ensuring the precursor
 liquid will not be dried out en route to the vaporizer.
 In situ liquid flow controllers and pisoelectric control valves are also
 used to maintain heightened control over the system. The high pressure
 gauges present on precursor and solvent lines as well as vacuum gauges on
 the vacuum manifolds are used to measure whether chemicals remain in the
 lines. These gauges are also used for on board leak integrity
 measurements.
 A preferred embodiment of the present invention includes a liquid CVD
 component delivery system having two pressurized ampoules of liquid CVD
 component and a related LFC, such as a needle valve, which operates
 without sliding seals and can be used at pressures of less than 250 psi.
 Two solvent ampoules deliver solvent into the liquid delivery lines for
 cleaning and maintenance as well as into the mixing port during
 processing.
 BST Process
 The vapor desired for use in the deposition process is shown as a mix of
 first and second vaporized liquid precursors combined in predetermined
 mass or molar proportions. For use in deposition of BST, the first liquid
 precursor is preferably one of a mixture of Ba and Sr polyamine compounds
 in a suitable solvent such as butyl acetate. The preferred mixtures
 combine bis(tetra methyl heptandionate) barium penta methyl diethylene
 triamine, commonly known as Ba PMDET (tmhd).sub.2, and bis(tetra methyl
 heptandionate) strontium penta methyl diethylene triamine, commonly known
 as Sr PMDET (tmhd).sub.2, or, in the alternative, bis(tetra methyl
 heptandionate) barium tetraglyme, commonly known as Ba (tmhd).sub.2
 tetraglyme, and bis(tetra methyl heptandionate) strontium tetraglyme,
 commonly known as Sr (tmhd).sub.2 tetraglyme. The second liquid precursor
 is preferably bis(tetra methyl heptandionate) bis isopropanide titanium,
 commonly known as Ti (I-pr-o)(tmhd).sub.2, or other titanium metal organic
 sources, such as Ti(tBuO).sub.2 (tmhd).sub.2. The molar ratio between the
 combined metals in the first liquid precursor and the second liquid
 precursor is preferably about 2:1:4 Ba:Sr:Ti. The molar ratio can vary
 from about 2:1:2 to about 2:1:8.
 The BST process mixes the vaporized first and second liquid precursors with
 an oxidizing gas such as oxygen, N.sub.2 O, O.sub.3 or combinations
 thereof, at a temperature above the vaporization temperature of the
 precursors and below a temperature which degrades the components. The
 process is very sensitive to changes in temperature of the substrate,
 solvent content of the liquid precursors, and concentration of the
 oxidizer in the combined gases. Increasing the wafer temperature increases
 the deposition rate, reducing the solvent content of the liquid precursors
 reduces the haze of the films, and controlling the oxidizer flow rate
 controls the roughness of the film and crystalline phase.
 FIG. 21 is a graph of the deposition rate versus heater temperature in a
 CVD BST 200 mm substrate process of a preferred embodiment of the present
 invention. A heater temperature of 600.degree. C. provides a high
 deposition rate without substantial degradation of the precursors. The
 heater temperature can vary from about 300.degree. C. to about 800.degree.
 C. For the examples shown in FIG. 21, the first precursor was a mixture of
 Ba PMDET (tmhd).sub.2 and Sr PMDET (tmhd).sub.2 in butyl acetate having a
 molar ratio of Ba:Sr of 2:1. The second precursor was Ti (I-pr-o)
 (tmhd).sub.2 in butyl acetate which provides a molar ratio of Ba:Sr:Ti of
 2:1:4. The substrate was a Pt/SiO.sub.2 /Si substrate. A deposition rate
 of 220 .ANG./minute was achieved at a heater temperature of 600.degree. C.
 using a total liquid flow rate of the precursors at 200 mg/m and a process
 gas flow rate of 1500 sccm (that is, a combination of oxygen, nitrogen and
 argon, each at a flow rate of 500 sccm). A vaporizer according to the
 present invention was also used, wherein the vaporizer lines for the
 precursors were maintained at 240.degree. C.
 As shown by FIG. 21, the deposition rate increases an average of 1.3
 .ANG./min for each 1.degree. C. increase in the heater temperature,
 showing that there is a strong sensitivity to temperature. A deposition
 rate of over 200 .ANG./minute indicates high vaporizer efficiency.
 A high deposition rate of 150 .ANG./minute process can provide a high
 quality film having good uniformity within the wafer and from wafer to
 wafer. A heater temperature of 550.degree. C. provided a wafer temperature
 of 470.degree. C. and a deposition rate of 160 .ANG./minute. Satisfactory
 electrical properties have been obtained with a deposition rate as high as
 169 .ANG./minute.
 FIG. 22 is a graph of the log of the deposition rate shown in FIG. 21
 versus 1 divided by the temperature of the wafer heater in 1000.degree. K.
 As shown in FIG. 22, there are two distinct regimes with respect to the
 deposition rate. Mass transport of the precursors limits the deposition
 process were the log of the deposition rate is around 5 or greater. The
 deposition process is surface reaction limited where the log of the
 deposition rate is about 4 or smaller. The transition between these two
 regimes takes place at about 550.degree. C., or about a 470.degree. C.
 wafer temperature. A 500-550.degree. C. regime provides good uniformity
 for step coverage optimization. Results were obtained by simply varying
 the temperature and observing the deposition rate. The significance is
 that the PMDETA precursors are permitting high decomposition rates and a
 well behaved reaction mechanism with a simple single transition in rate
 controlling reaction at a 470.degree. C. wafer temperature.
 FIG. 23 demonstrates the high quality films produced by this invention
 using the process conditions described for FIG. 21. Three deposition runs
 were made over a two day period to deposit films having thicknesses of
 1150 .ANG., 550 .ANG., and 550 .ANG.. The uniformity of the wafers is
 shown by a graph of measured titanium concentration (mole %) versus wafer
 number as well as measured deposition rate (.ANG./min) versus wafer
 number. This graph shows that wafer-to-wafer deposition rates are uniform
 and meet the desired target rate. This graph also illustrates a rapid
 change in Ti concentration for the first several wafers in each run which
 presents an opportunity for improvement of the process. This graph further
 shows that the composition is not very sensitive to deposition time as had
 been expected. FIG. 23 shows reasonably tight process control which can be
 further improved through the use of 3-part barium, strontium and titanium
 mixtures and by running the vaporizer in continuous flow mode.
 FIG. 24 is a table of a Ti sensitivity test with a wafer heater temperature
 of plus or minus 0.5.degree. C. during deposition. This figure shows the
 mole % for Ti, Ba, and Sr for two separate wafers. Si Prime means
 non-previously used silicon. Si Recl means reclaimed silicon from other
 processes. Pt/ox 1 is an oxidized silicon substrate with platinum
 sputtered thereon using physical vapor deposition techniques. Pt/ox 2 is
 an oxidized platinum substrate further characterized as electron beam
 platinum. The matrix results show that plus or minus 0.5.degree. C. during
 deposition yields the best repeatability in 5 out of six cases. In
 addition, the matrix results show that the substrate is coated with about
 8-10 mole % more Ti on Pt versus Si, and about 2 mole % Ti for 20%
 Ti(I-pr-O) demonstrating substrate sensitivity.
 FIG. 25 is a graph of the composition sensitivity of Ti, Ba and Sr to
 temperature in the CVD BST process described for FIG. 21, where
 concentration (mole %) of Ti, Ba and Sr are each plotted versus wafer
 heater temperature. At about 600.degree. C., the Ti concentration of the
 deposited film increases 1 mole % for each increase in heater temperature
 of 2.degree. C. At about 600.degree. C., the Ba concentration of the
 deposited film decreases 1 mole % for each increase in heater temperature
 of 2.5.degree. C. At about 600.degree. C., the Sr concentration of the
 deposited film decreases 1 mole % for each increase in heater temperature
 of 10.degree. C. demonstrating strong temperature dependence. This
 temperature dependence is substantially reduced at a 680.degree. C. heater
 temperature.
 In the preferred embodiment of the present invention, it is critical to
 maintain the heater in the 600-750.degree. C. range to optimize electrical
 properties and for optimal step coverage. It has been found that certain
 chemicals used in a certain temperature range produce good results.
 Specifically, polyamine based Ba and Sr precursors and Ti (I-pr-o) are the
 precursors that are believed to work the best in the present invention. A
 wafer control of plus or minus 0.50.degree. C. is preferred for the
 above-mentioned precursors.
 EXAMPLE 1
 A preferred process according to the present invention deposits a BST film
 on a 200 mm wafer mounted on a heated substrate holder spaced 550 mils
 from a gas distribution showerhead or face plate. The deposition occurs at
 1.7 Torr with a wafer temperature of 600.degree. C. and the following flow
 rates. The first precursor was 33 mg/min to 200 mg/min of a mixture of Ba
 PMDET (tmhd).sub.2 and Sr PMDET (tmhd).sub.2 in butyl acetate having a
 molar ratio of Ba: Sr of 2:1. The second precursor was 17 mg/min to 77
 mg/min of Ti (I-pr-o) (tmhd).sub.2 in butyl acetate which provides a molar
 ratio of Ba:Sr:Ti of 2:1:4. The substrate was a Pt/SiO.sub.2 /Si. A
 deposition rate of 40 to 160 .ANG./minute is achieved using process gas
 flow rate of 2900 sccm (that is, a combination of O.sub.2 at 500 sccm,
 N.sub.2 O at 500 sccm, Ar.sub.A at 1500 sccm, and Ar.sub.B at
 approximately 900 sccm). A vaporizer according to the present invention
 was also used, wherein the vaporizer lines for the precursors were
 maintained at 240.degree. C.
 EXAMPLE 2
 In another example, a process according to the present invention deposits a
 BST film on a 200 mm wafer mounted on a heated substrate holder spaced 550
 mils from a gas distribution showerhead. The deposition occurs at 7 Torr
 with a heater temperature of about 680.degree. C. and the following flow
 rates. The first precursor was 33 mg/min to 200 mg/min of a mixture of Ba
 PMDET (tmhd).sub.2 and Sr PMDET (tmhd).sub.2 in butyl acetate having a
 molar ratio of Ba:Sr of 2:1. The second precursor was 17 mg/min to 77
 mg/min of Ti (I-pr-o) (tmhd).sub.2 in butyl acetate which provides a molar
 ratio of Ba:Sr:Ti of 2:1:4. The substrate was a Pt/SiO.sub.2 /Si. A
 deposition rate of 151 .ANG./minute was achieved using process gas flow
 rate of 1300 sccm (that is, a combination of O.sub.2 at 250 sccm, N.sub.2
 O at 500 sccm, Ar.sub.A at 1500 sccm, and Ar.sub.B at approximately 300
 sccm). A vaporizer according to the present invention was also used,
 wherein the vaporizer lines for the precursors were maintained at
 240.degree. C. As shown in FIGS. 26 and 27, a two mixture process showed
 repeatable results over a twenty five wafer run.
 EXAMPLE 3
 In another example, the system was cleaned using acetone as a solvent. The
 acetone used was not dried. A deposition process according to that
 described in Example 1 was then performed. A 2.times. increase in the
 deposition rate was observed indicating that residual acetone solvent
 stabilized the precursors on delivery to the substrate and consequently
 resulted in the higher deposition rate. It is believed that the acetone
 stabilizes the precursors through hydrogen bonding so that more precursor
 is delivered to the substrate surface for reaction.
 EXAMPLE 4
 It is believed that use of a solvent such as acetone during the deposition
 process will stabilize the precursors and result in a higher deposition
 rate.
 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 thereof, and the scope thereof is
 determined by the claims which follow.