U.S. patent application number 09/850454 was filed with the patent office on 2002-06-20 for film processing system.
This patent application is currently assigned to CVD Systems, Inc.. Invention is credited to Loan, James F., Salerno, Jack P..
Application Number | 20020076492 09/850454 |
Document ID | / |
Family ID | 26739454 |
Filed Date | 2002-06-20 |
United States Patent
Application |
20020076492 |
Kind Code |
A1 |
Loan, James F. ; et
al. |
June 20, 2002 |
Film processing system
Abstract
An apparatus for chemical vapor deposition includes a dispenser
for dispensing a precursor to a vaporizer positioned within a
vaporization chamber. A delivery conduit joins the vaporization
with a process chamber. A flow meter is positioned within the
delivery conduit for measuring the flow of precursor through the
delivery conduit. A flow controller is likewise positioned within
the delivery conduit for controlling the flow of precursor in
response to the measured flow rate.
Inventors: |
Loan, James F.; (Mansfield,
MA) ; Salerno, Jack P.; (Waban, MA) |
Correspondence
Address: |
Thomas O. Hoover, Esq.
Bowditch & Dewey, LLP
161 Worcester Road
Framingham
MA
01701-9320
US
|
Assignee: |
CVD Systems, Inc.
North Billerica
MA
|
Family ID: |
26739454 |
Appl. No.: |
09/850454 |
Filed: |
May 7, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09850454 |
May 7, 2001 |
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09421823 |
Oct 20, 1999 |
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09421823 |
Oct 20, 1999 |
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09291871 |
Apr 14, 1999 |
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09291871 |
Apr 14, 1999 |
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09060007 |
Apr 14, 1998 |
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Current U.S.
Class: |
427/255.28 |
Current CPC
Class: |
F16K 31/1262 20130101;
C23C 16/455 20130101; F16K 31/1221 20130101; C23C 16/52 20130101;
C23C 16/45561 20130101; C23C 16/4404 20130101; C23C 16/54 20130101;
C23C 16/4585 20130101; C23C 16/4485 20130101; C23C 16/44 20130101;
C23C 16/4402 20130101; F16K 51/02 20130101 |
Class at
Publication: |
427/255.28 |
International
Class: |
C23C 016/00 |
Claims
What is claimed is:
1. A method for forming stacked gate dielectrics comprising
depositing silica by reacting TEOS with N.sub.2O at temperatures
less than 600.degree. C.
2. A method for performing multiple depositions on a wafer,
comprising the steps of: vaporizing a first precursor in a
vaporization chamber; delivering the first vaporized precursor to a
process chamber; depositing the first vaporized precursor on a
substrate in the process chamber; then vaporizing a second
precursor; delivering the second vaporized precursor to the process
chamber; and depositing the second vaporized precursor on the
substrate in the process chamber.
3. The method of claim 2 wherein the second precursor is vaporized
in a second vaporization chamber.
4. The method of claim 3 wherein the first precursor and the second
precursor are vaporized by delivering the first precursor and the
second precursor to respective vaporizers in each vaporization
chamber.
5. The method of claim 2 wherein each precursor is delivered onto a
heated, sloped vaporizer surface across which the precursor
spreads, the precursor vaporizing as it spreads.
6. The method of claim 2 wherein the substrate remains stationary
throughout the method.
7. The method of claim 2 wherein the first precursor is a copper
source and the second precursor is an aluminum source.
8. The method of claim 2 wherein the first precursor is a silicon
source and the second precursor is a tantalum source.
Description
RELATED APPLICATIONS
[0001] This application is a divisional application of U.S.
application Ser. No. 09/421,823, filed Oct. 20, 1999 which is a
continuation-in-part application of U.S. application Ser. No.
09/291,871, filed Apr. 14, 1999, which is a continuation-in-part
application of U.S. application Ser. No. 09/060,007 filed on Apr.
14, 1998, the entire contents of both applications are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] Chemical vapor deposition (CVD) is a process of forming a
film on a substrate, typically, by generating vapors from liquid or
solid precursors and delivering those vapors to the surface of a
heated substrate where the vapors react to form a film. Systems for
chemical vapor deposition are employed in applications such as
semiconductor fabrication, where CVD is employed to form thin films
of semiconductors, dielectrics and metal layers. Three types of
vapor delivery systems commonly used for performing CVD include
bubbler-based systems, liquid-mass-flow-control systems, and
direct-liquid-injection systems.
[0003] Bubbler-based systems, or "bubblers," essentially bubble a
stream of gas through a heated volume of liquid precursor. As the
stream of gas passes through the liquid precursor, vapors from the
liquid precursor are absorbed into the gas stream. This mixture of
gases is delivered to a process chamber, where the precursor vapor
reacts upon a surface of a heated substrate. Bubblers typically
heat the volume of liquid precursor at a constant temperature. Over
time, the constant heat often causes the precursor to decompose
rendering it useless for CVD. In an effort to minimize
decomposition, the bubbler is typically maintained at a temperature
lower than that at which the vapor pressure of the liquid precursor
is optimal.
[0004] Liquid mass flow control systems attempt to deliver the
precursor in its liquid phase to a vaporizer typically positioned
near the substrate. The precursor is vaporized and is then
typically entrained in a carrier gas which delivers it to the
heated substrate. A liquid mass flow controller, which is a thermal
mass flow controller adapted to control liquids, is used to measure
and control the rate of flow of liquid precursor to the
vaporizer.
[0005] Liquid mass flow controllers present a number of drawbacks.
First, liquid mass flow controllers are extremely sensitive to
particles and dissolved gases in the liquid precursor. Second,
liquid mass flow controllers are also sensitive to variations in
the temperature of the liquid precursor. Third, liquid mass flow
controllers typically use a gas to assist in the vaporization of
the liquid precursor, thereby increasing the probability of
generating solid particles and aerosols and ensuring a high gas
load in the process system. Fourth, most liquid mass flow
controllers cannot operate at temperatures above 40.degree. C., a
temperature below which some precursor liquids, such as tantalum
pentaethoxide (TAETO), have high viscosity. Due to its
sensitivities, the liquid flow controller is accurate and
repeatable to about 1% of full-scale liquid flow. Further, when a
liquid mass flow controller wetted with TAETO or one of a number of
other precursors is exposed to air, the precursor will generally
react to produce a solid which may destroy the liquid flow
controller.
[0006] Liquid pump-based systems pump the liquid precursor to the
point of vaporization, typically at a position near the heated
substrate. Liquid pump-based systems are generally one of two main
types. One type uses a liquid flow meter in line with a
high-pressure liquid pump. The other type uses a high-precision,
high-pressure metering pump. Both of these systems are extremely
sensitive to particles in the liquid. The liquid-flow-meter based
system is also sensitive to gas dissolved in the liquid. Both are
extremely complex to implement, and neither can tolerate high
temperatures (maximum 50.degree. C.). The system with the metering
pump has difficulty vaporizing high viscosity liquids. Finally,
both are generally difficult to implement in a manufacturing
environment due to their extreme complexity and large size.
[0007] Existing CVD equipment design is generally optimized for
high process pressures. The use of high process pressures is most
likely due to the fact that, until recently, CVD precursors were
either generally relatively high-vapor-pressure materials at room
temperature or were, in fact, pressurized gases. Examples include
tetraethylorthosilicate (TEOS), TiCl.sub.4, Silane, and tungsten
hexafluoride, etc. These materials were chosen because they had
high vapor pressures and could therefore be easily delivered. The
process pressure was generally well within the stable vapor
pressure range of each of these materials.
DISCLOSURE OF THE INVENTION
[0008] The present invention relates to systems and methods for
chemical vapor deposition for the fabrication of materials and
structures for a variety of applications. The system is well suited
for use in the fabrication of devices for the semiconductor
industry, but can also be used in other applications involving thin
film deposition and processing.
[0009] In addition to the fabrication of dielectric layers,
metalization layers, and epitaxially grown semiconductor films
including silicon, germanium, II-VI and III-V materials, the system
can be used for precision manufacture of optical thin films such as
anti-reflective coatings or stacked dielectric structures including
optical filters, diamond thin films or composite structures for
multichip modules or optoelectronic devices.
[0010] In contrast to thin films of traditional CVD materials,
future thin films require new source materials that have low vapor
pressures and that are often near their decomposition temperature
when heated to achieve an appropriate vapor pressure. Some of the
precursors having both intrinsically low vapor pressure and low
thermal decomposition temperature are considered the best choices
for deposition of films of tantalum oxide, tantalum nitride,
titanium nitride, copper, and aluminum.
[0011] An apparatus of this invention includes a vaporizer within a
vaporization chamber and a dispenser positioned for dispensing a
precursor to the vaporizer. A delivery conduit joins the
vaporization chamber with a process chamber, where a chemical vapor
is deposited on a substrate. A flow meter is positioned to measure
vapor flow through the delivery conduit, and a flow controller is
positioned to control vapor flow through the delivery conduit. Both
the flow meter and flow controller are communicatively coupled with
a processor programmed to control the flow controller to govern
vapor flow through the delivery conduit in response to the measured
vapor flow.
[0012] In a preferred embodiment, the flow meter includes a tube
with a pair of open ends, which acts as a laminar flow element. The
flow meter further includes a pair of capacitance manometers
aligned with the open ends of the tube to measure the pressure drop
across the laminar flow element. In a further preferred embodiment,
the flow controller is a proportional control valve in
communication with the flow meter.
[0013] A still further preferred embodiment of the apparatus
includes a reservoir for supplying precursor to the dispenser. The
dispenser is controlled by the processor and the vaporizer which
receives precursor from the dispenser includes a heated surface for
vaporizing the precursor. Preferably, a pressure sensor
communicatively coupled with the processor is positioned in the
vaporization chamber. Accordingly, the processor can, in some
embodiments, control the rate at which vapor is generated by the
vaporizer, by, for example, controlling the rate at which the
dispenser dispenses precursor from the reservoir to the
vaporizer.
[0014] In another embodiment of the apparatus, an outlet of the
delivery conduit is positioned in the process chamber, and a
showerhead divides the process chamber into an upstream section and
a downstream section, wherein the outlet is in the upstream section
and a substrate chuck is in the downstream section. An upstream
pressure sensor is positioned to measure vapor pressure in the
upstream section, and a downstream pressure sensor is positioned to
measure vapor pressure in the downstream section. Both the upstream
and downstream pressure sensors are communicatively coupled with a
processor. In a further preferred embodiment, the showerhead is
"active," enabling control over the vapor flow rate through the
showerhead.
[0015] Other features found in preferred embodiments of the
apparatus include a heater in thermal contact with the delivery
conduit, a DC or AC source connected to the substrate chuck, and an
elevator for raising and lowering the substrate chuck. Another
embodiment of this invention is a cluster tool for semiconductor
processing including a CVD apparatus, described above, connected to
a central wafer handler.
[0016] In a method of this invention, a precursor is vaporized in a
vaporization chamber, vapor flow between the vaporization chamber
and a process chamber is measured, and the rate of vapor flow
between the vaporization chamber is controlled in response to the
measured vapor flow. In another embodiment of a method of this
invention, the vapor pressure of a precursor is measured, and the
rate at which the precursor is vaporized is controlled in response
to the measured vapor pressure, preferably by controlling the rate
at which precursor is dispensed from a reservoir onto a vaporizer.
Preferably, deposition occurs via a surface-driven reaction.
Nevertheless, embodiments of the invention also cover methods where
deposition occurs via non-surface driven reactions.
[0017] The invention also includes the vaporization subsystem,
alone (i.e., without the vapor-flow-control subsystem or process
subsystem). The vaporizer has a sloped surface, preferably in the
approximate shape of a dome or cone. More specifically, the
vaporizer can be in the form of a stepped cone. The invention also
includes embodiments where a plurality of vaporizers are coupled to
a process chamber. Each vaporizer can be coupled to a respective
vapor-flow-control subsystem. This embodiment enables multiple
depositions to be performed using different precursors in a single
process chamber. Specific precursors that are preferred for use
with this invention include copper sources, tantalum sources,
titanium sources and silicon sources. Another method achievable
with the apparatus of this invention is the deposition of silica by
reacting TEOS and N.sub.2O at temperatures less than 600.degree.
C.
[0018] Another aspect of the invention includes a unitary metal
block with a through-bore through which the vaporized precursor
flows from the vaporization chamber to the process chamber.
Preferably, the block includes a laminar flow element mounted in
the through-bore and a plurality of bores through which pressure
sensors, a proportional control valve and heaters are mounted. An
advantage of the use of a unitary metal block as a component of the
vapor-flow-control subsystem is the high level of temperature
uniformity that it provides.
[0019] The systems and methods of this invention provide numerous
benefits. First, they allow the precursor to be delivered to the
substrate in a much purer and higher-concentration or high-flux
form than is achievable with the use of systems that use a carrier
gas. As a result, the likelihood of gas-phase reactions and
consequent formation of particles can be greatly reduced. Because
of the higher concentration, which leads to a higher deposition
rate, this invention does not necessitate the introduction of
plasma into the process chamber. Consequently, the apparatus is
simplified, and plasma-induced polymerization of precursor is
reduced or eliminated. Second, control over the concentration of
precursor delivered to the process chamber is enhanced, thereby
improving control over film thickness and uniformity. Third, the
direct delivery of vapor flow into the process chamber at low
temperature and low pressure and without a carrier gas increases
the efficiency of use of costly precursors in many applications by
a factor of up to 10 or more over standard systems utilizing a
carrier gas, which infer precursor vapor flow rates either from a
theoretical pickup rate, which is carrier-gas and temperature
dependent, or from a thermal mass-flow controller or liquid
delivery system. Likewise, emissions of unreacted process gases
from the process chamber can be maintained at very low levels
because the absence of a carrier gas and generally lower flow rates
and better residence times leads to a higher utilization efficiency
of the precursor. Fourth, decomposition of the precursor is limited
due to its short contact time with the heated vaporizer. While
small amounts of precursor are delivered to the vaporizer, as
needed, the useful life of the bulk of the precursor is preserved
by maintaining it at a lower temperature in the reservoir. Fifth,
the highly conformal nature of deposits that can be formed by
methods of this invention are useful in forming integrated circuits
with line-widths of 0.25 microns (250 nm) or less.
[0020] Other advantages of this invention include the low
sensitivity of the system to impurities such as dissolved gases and
particles in the precursor, the relative ease of alternating
between multiple precursors in a single system as a result of the
ability to coordinate the use of each with a precursor delivery
system, the ease of accessing and maintaining all subsystems, the
low power requirements of the system, the use of only low voltages
in the operating elements of the system and the small overall size
of the system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The foregoing and other objects, features and advantages of
the invention will be apparent from the following, more particular
description of preferred embodiments of the invention, as
illustrated in the accompanying figures. The drawings are not
necessarily to scale, emphasis instead being placed upon
illustrating the principles of the invention.
[0022] FIGS. 1A and 1B provide a schematic illustration of an
apparatus of this invention.
[0023] FIGS. 1C and 1D provide a schematic illustration of another
embodiment of an apparatus of this invention.
[0024] FIG. 2a is a cross-sectional illustration of a vaporization
subsystem of this invention.
[0025] FIG. 2b is a cross-sectional illustration of another
embodiment of a vaporization subsystem of this invention.
[0026] FIG. 2c is a schematic illustration of a control system of
this invention.
[0027] FIG. 2d is an illustration, partially schematic, of an
apparatus of this invention, including a plurality of vaporization
subsystems coupled to a single process chamber.
[0028] FIG. 2e is an illustration of a stepped vaporizer of this
invention.
[0029] FIG. 3a is an illustration of a vapor-flow-control subsystem
of this invention.
[0030] FIG. 3b is an illustration of another embodiment of a
vapor-flow-control subsystem of this invention.
[0031] FIG. 3c is a side view of a plurality of vapor-flow-control
subsystems of the apparatus shown in FIG. 2d.
[0032] FIG. 3d is a chart of a representative vapor pressure in a
vaporizer of this invention versus time.
[0033] FIG. 3e is a chart of a representative vapor pressure
exiting a vapor-flow-control subsystem of this invention.
[0034] FIG. 4a is a view, partially in cross section, of a process
subsystem of this invention.
[0035] FIG. 4b is a cross-sectional view of another embodiment of a
process subsystem of this invention, with the substrate chuck in a
retracted position.
[0036] FIG. 4c is a cross-sectional view of the embodiment of FIG.
4b , with the substrate chuck raised to a processing position.
[0037] FIG. 4d is another cross-sectional view of the embodiment of
FIG. 4b , with the substrate chuck in a fully-extended
position.
[0038] FIG. 5a is an illustration of a shower head of this
invention.
[0039] FIG. 5b is a top view of a replaceable showerhead mounted
within a ring.
[0040] FIG. 5c is a cross-sectional side view of the showerhead and
ring illustrated in FIG. 5b.
[0041] FIG. 5d is an illustration of a typical deposited layer
formed in a cavity via PVD processes.
[0042] FIG. 5e is an illustration of a typical deposited layer
formed in a cavity via conventional CVD processes.
[0043] FIG. 5f is an illustration of a deposited layer that can be
formed with the apparatus and method of this invention.
[0044] FIG. 5g is a graph of pressure differential across a chuck
versus the position of the chuck in a process chamber of this
invention.
[0045] FIGS. 6a , 6b and 6c are perspective views of one embodiment
of the CVD apparatus of this invention.
[0046] FIG. 7 illustrates the control architecture of a CVD
apparatus according to one embodiment of the invention.
[0047] FIG. 8 illustrates the main process control routine
according to one embodiment of the invention.
[0048] FIGS. 9a and 9b illustrate the operation of the vaporizer
sub-process according to one embodiment of this invention.
[0049] FIG. 10 illustrates the processing performed by the vapor
phase flow control sub-process according to one embodiment of this
invention.
[0050] FIG. 11 illustrates a process chamber pressure control
sub-process according to this invention.
[0051] FIGS. 12a through 12d illustrates the operation of inserting
a wafer into the process chamber of one embodiment of this
invention.
[0052] FIG. 13 illustrates the cleanup sub-process according to one
embodiment of this invention.
[0053] FIG. 14 illustrates an example portion of a schematic
showing the closed loops present in a CVD apparatus according to
one embodiment of the invention.
[0054] FIG. 15 is an illustration of a cluster tool embodiment of
this invention.
[0055] FIG. 16 illustrates multiple cluster tools configured to be
controlled by a single factory automation controller according to
this invention.
[0056] FIG. 17 illustrates multiple cluster tools, each controlled
by separate cluster tool controllers which are in turn controlled
by a factory automation controller according to this invention.
[0057] FIG. 18 illustrates an example of the processing steps
performed by a cluster tool controller according to one embodiment
of this invention.
[0058] FIG. 19 is a graph of CVD source vapor pressure curves for
various sources versus temperature.
[0059] FIG. 20 is a graph showing the refractive index of a silica
layer at various positions across the surface of a wafer formed by
methods of this invention.
[0060] FIG. 21 is a graph showing the thickness of a silica layer
at various positions across the surface of a wafer formed by
methods of this invention.
[0061] FIG. 22 is a schematic illustration of a cluster tool for
gate oxide deposition.
[0062] FIG. 23 is a schematic illustration of a cluster tool for
depositing aluminum and copper metallization films.
[0063] FIG. 24 is a graph of vapor pressure versus source
temperature for several copper sources.
[0064] FIG. 25 is a chart illustrating a relative cost comparison
of copper sources.
[0065] FIG. 26 is a cross-sectional illustration of a device for
microelectronics applications.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0066] The features and other details of the method of the
invention will now be more particularly described with reference to
the accompanying drawings and pointed out in the claims. Numbers
that appear in more than one figure represent the same item. It
will be understood that the particular embodiments of the invention
are shown by way of illustration and not as limitations of the
invention. The principle features of this invention can be employed
in various embodiments without departing from the scope of the
invention.
[0067] As illustrated in FIGS. 1A and 1B, a preferred embodiment of
a CVD apparatus 10 of this invention includes four integrated
subsystems, including a vaporization subsystem 12, a
vapor-flow-control subsystem 14, a process subsystem 16, and an
exhaust subsystem 18. A distributed processing system, described
below, provides integrated control and management of each of these
subsystems. The distributed processing system and each of the
subsystems 12, 14, 16 and 18 are all within a single free-standing
CVD module 10 (illustrated in FIGS. 6a-c). The dimensions of the
CVD module generally will not exceed a 1 m by 2 m footprint and
preferably are no greater than about 1.2 m in length by about 0.6 m
in width by about 1.8 m in height to achieve conformity with
existing standards for integration with a wafer handler such that
the free-standing CVD module can fit within the typically allotted
footprint in a larger cluster tool configuration. In a further
preferred embodiment, the CVD module fits within a standard
footprint, as established by MESC, the standard design architecture
adopted by Semiconductor Equipment and Materials International
(SEMI), a trade organization of semiconductor industry suppliers,
for connection to a wafer handler or transport module.
[0068] Each of boxes 103, 105, 107, 109, 111, 113, 115, 117 and 119
represents a separate control zone. Each of the control zones is
independently heated with a separate cartridge heater 121. Further,
the temperature in each control zone and at other heated elements
of the apparatus is monitored by a resistance temperature detector
or resistance thermometry detector (RTD) 131, of which one
embodiment is a platinum resistance thermometer. The RTD is
preferably encapsulated by a silicon nitride coating because of the
heat conduction and low thermal mass of the silicon nitride.
Alternatively, thermocouples or other temperature sensing devices
can be used in place of the RTD's.
[0069] The vaporization subsystem 12, illustrated in FIG. 2a, is
designed to generate a controlled supply of precursor vapor for
deposition. The precursor, initially in liquid or solid form, is
stored in a reservoir 20 fabricated from Inconel.RTM. or
Inconel.RTM. alloys, such as Incoloy.RTM. 850 (available from Inco
Alloys International, Inc., Huntington, W. Va.). Alternatively, the
reservoir 20 is formed of 316L stainless steel. A funnel 22 is
provided at the base of the reservoir 20, with a dispenser in the
form of a dispensing valve 24 at the focal point of the funnel 22
for dispensing precursor from the reservoir 20. Where a liquid
precursor is used, the dispensing valve 24 is an axial displacement
pulse valve. Where a solid precursor is used, the dispensing valve
24 is a rotary valve. The reservoir 20 is thermally insulated from
the vaporization chamber 26, discussed below, and is maintained at
a temperature below that at which the precursor will be subjected
to significant decomposition. Optionally, multiple reservoirs 20
are provided, each filled with a different precursor and each
feeding into the vaporization chamber 26. As each precursor is
needed, the appropriate reservoir 20 can be utilized.
Alternatively, multiple reservoirs 20 each feed into their own
vaporization chamber.
[0070] A system for governing the supply of various precursors to a
cluster tool 120 having one or more vaporization chambers 26 is
illustrated in FIG. 2c. A cluster tool controller 802 is controlled
by a programmable host computer or data processor 804, which sends
high-level commands to a process module to govern the deposition
process, including regulation of the delivery of precursors 806,
808, 810 for the deposition of titanium nitride, copper, and
aluminum, respectively, for example. The cluster tool controller
802 is further programmed by the host computer 804 to regulate a
pair of modules for annealing/diffusion 812, 814 and a separate
module for pre-heating and pre-cleaning 816. Communication between
each of these modules 806, 808, 810, 812, 814 and 816 and the
cluster tool controller 802 is facilitated by a bus architecture
that can include, for example, a ProfiBus data bus 818 in
combination with an EtherNet/Epics data bus 820. Connected to the
EtherNet/Epics data bus 820 is the cluster tool 120, allowing the
cluster tool controller 802 to likewise govern operation of the
cluster tool 120 to which the precursors from modules 806, 808, 810
are delivered. The system further includes a console for monitoring
operation of the system 822 and a console for system maintenance
824. Both consoles 822 and 824 are connected to the cluster tool
controller 802.
[0071] In operation, the cluster tool controller 802, as controlled
by the host computer 804, can, in relatively rapid sequence, select
various precursors from module 808, 810 and 812 for delivery to one
or more vaporization chambers 26 (FIG. 2a). This capability allows
for a sequencing of starting materials in a single system, thereby
allowing for a rapid sequence of depositions of different layers on
a substrate in process modules of the cluster tool 120. Additional
details regarding the various components of FIG. 2c, alternative
embodiments thereof, and methods of using the same are described in
greater detail below.
[0072] A vaporizer 28 that has ever-increasing surface area at
distances away from the dispensing valve 24 (e.g., the vaporizer
having the approximate form of a cone or a dome) is used to
vaporize the precursor. The vaporizer 28 functions as a falling
film molecular still, in which a liquid precursor generates a
wavefront flowing down the surface of the vaporizer 28. The
temperature of the vaporizer 28 is set to vaporize the precursor
over the course of its travel across the vaporizer 28 surface.
Contaminants with higher vaporizing temperatures will generally
flow down the surface of the vaporizer 28 and fall off without
vaporizing.
[0073] Preferably, the vaporizer 28 is in the form of an inverted
cone and is positioned to receive precursor flowing from the
dispensing valve 24. The vaporizer 28 is made from a
thermally-conductive material coated or plated, as required, for
the best chemical compatability with the precursor. In a preferred
embodiment, the vaporizer 28 includes an electroless-nickel-plated
OFHC substrate coated with a sulphamate nickel overplate, which in
turn is optionally coated with rhodium overplating for very high
corrosion resistance and inertness. The vaporizer 28 illustrated in
FIGS. 1A and 1B is designed for vaporizing a liquid precursor.
Alternatively, a multi-stepped-shape cone, illustrated in FIG. 2e,
is used for solid precursors, wherein ridges are provided on the
cone to collect the solid as it is delivered from the reservoir 20.
In the embodiment of the stepped cone illustrated in FIG. 2e, the
width of each step 171 is 0.050 inch, and the distance from the
apex 173 to the first step 171' is 0.75 inch.
[0074] One suitable embodiment of the vaporizer 28 illustrated in
FIGS. 2a and 2b includes a cone with a height of 4.20 inches and a
base diameter of 3.70 inches. The vaporizer 28 and the reservoir 20
are removable so that they can be cleaned and replaced during
scheduled maintenance. When in use, the vaporizer 28 is heated to a
temperature sufficient to vaporize the precursor without causing it
to suffer thermal decomposition.
[0075] The vaporizer 28 includes a plurality of bores 29. Heaters,
e.g., Watt-Flex.RTM. cartridge heaters 90 (available from Dalton
Electric Heating Co., Inc., Ipswich, Mass.) are inserted into four
of these bores 29. In one example, the heaters are 3.0 inches in
length and 0.25 inches in diameter. The heaters supply 50 watts at
24-25 VAC, and can be heated above 1000.degree. C. Typically,
though, the heaters are operated in the vicinity of 200.degree. C.
Depending on the precursor, though, the vaporizer can be operated
at least up to 250-300.degree. C. A platinum resistance thermometer
is inserted into a central bore 31.
[0076] The vaporizer 28 is not intended to be used as a "flash
vaporizer." Rather, it is intended that the precursor will spread
across the vaporizer 28 surface, from which vapors will evolve. The
vaporizer 28 offers the advantage of not being sensitive to small
particles suspended in standard grades of liquid CVD precursor used
in the semiconductor industry. In this embodiment, suspended
particulates are left behind on the vaporizer 28.
[0077] A vaporization chamber 26 surrounds the vaporizer 28 and is
made of OFHC copper plated with electroless nickel and sulfamate
nickel and also rhodium if highly reactive or unstable precursors
are used. The vaporization chamber 26 includes a principal cylinder
30 and a vapor outlet 32. The vaporization chamber 26 essentially
serves as an expansion volume and reservoir for vapors produced by
the vaporizer 28.
[0078] A pressure sensor 34 is preferably positioned in the vapor
outlet 32 for measuring the vapor pressure in the vaporization
chamber 26. Alternatively, the pressure sensor 34 can be positioned
in the principal cylinder 30. The pressure sensor 34 is heated to
about the same temperature as the vaporizer 28 during operation to
prevent condensation of the vaporized precursor. The pressure
sensor 34 is coupled in a processor-driven control loop with the
dispenser 24 to achieve a fairly constant pressure in the
vaporization chamber 26. Because vapor flow in this system is
driven by pressure differentials, the pressure in the vaporization
chamber 26 is maintained above that in the process chamber 70. As
pressure drops in the vaporization chamber 26, the dispenser 24 is
signaled to dispense more precursor. Accordingly, the pressure
sensor 34 and dispenser 24 work in concert to maintain the pressure
in the vaporization chamber in a range between the pressure in the
process chamber 70, discussed below, and the standard vapor
pressure of the precursor at the temperature of the vaporizer. In
this system, the response time for reestablishing the desired vapor
pressure is typically about 10 seconds. Preferably, the pressure
sensor 34 is a capacitance manometer with a 1000 torr fill-scale
range, or other, similar direct-measuring gauge.
[0079] FIG. 2b illustrates an alternative embodiment of the
vaporization subsystem in which the base 21 of the neck 23 includes
a groove, where the base is hollowed out to prevent thermal
degradation of the precursor as it flows down rod 33 on the way to
the vaporization chamber 26. Heat from the vaporizer 28 travels
through the walls of the vaporization chamber 26 and into the neck
23. By hollowing out the neck 23, the inner wall 25 is spatially
removed from the flow of precursor down the rod 33. The hollowed
out section extends approximately midway up the neck 21. It ends at
angled surface 27, above which the inner diameter of the neck is
constricted. Vapor flowing up into the hollowed out section is
prone to condense on angled surface 27, which directs condensed
vapors back toward rod 33.
[0080] The vapor pressure throughout the system is maintained at
relatively low levels. One reason why the system can be operated at
low pressure levels is the close physical proximity of all of the
subsystems. Accordingly, the vapors need travel only very short
distances from vaporization to deposition. Because the vapor
pressure and the velocity of the vapor are low, the transport of
particles throughout the system is significantly reduced in
comparison to higher pressure systems, such as those which use a
carrier gas.
[0081] Alternatively, a plurality of vaporization subsystems
similar to that illustrated in FIGS. 2a or 2b can be coupled to a
single process chamber 70 through respective vapor-flow-control
subsystems, as shown in FIG. 2d. The apparatus of FIG. 2d includes
three vaporization subsystems 12, 12', 12", three
vapor-flow-control subsystems 14, 14', 14" and a process chamber
70. Each of the components are covered with a layer of thermal
insulation 199 to allow each element to operate thermally
independent of one another. As an alternative to the embodiment
illustrated in FIG. 2d, each of the vaporization subsystems 12,
12', 12" can feed to a single vapor-flow-control subsystem for
delivery to the process chamber 70. In one embodiment, the lines
175 leaving each vapor-control-subsystem 14, 14', 14" are merged to
form a single input into the process chamber 70. In an alternative
embodiment, one or more lines 175' can form completely separate
inputs to the process chamber; such an embodiment is advantageous
where the lines 175 are heated to different temperatures to prevent
condensation therein or where vapors in the different lines 175 can
react with one another.
[0082] In this apparatus, each vaporizer is aligned with a
dispenser filled with a different precursor. The benefit of
employing a plurality of vaporization chambers 12, 12', 12" is that
each can be used to generate a distinct vapor that can be deposited
in sequence on the substrate. Accordingly, multiple layers of
differing compositions can be deposited on the substrate without
ever moving the substrate from its position in the process
subsystem 16. For example, one embodiment of an apparatus used for
forming stacked gate dielectrics has one vaporization subsystem 12
with a reservoir 20 filled with TEOS for forming a silica deposit,
a second vaporization subsystem 12' having a reservoir 20' filled
with TAETO for forming a tantalum oxide deposit, and a third
vaporization subsystem 12" having a reservoir 20" filled with
TiBr.sub.4 or TDEAT for forming titanium nitride.
[0083] In this example, the process commences with the generation
of TEOS vapor in the first vaporization subsystem 12. The TEOS
vapor is reacted with N.sub.2O to form a low-k dielectric film
(SiO.sub.2) on a heated semiconductor wafer. Background discussion
of deposition of silicon dioxide from TEOS/N.sub.2O mixtures is
provided in D. Davazoglou, "Thermodynamic Study, Composition, and
Microstructure of Low-Pressure Chemical Vapor Deposited Silicon
Dioxide Films Grown from TEOS/N.sub.2O Mixtures," 145 J.
Electrochem. Soc. 1310 (April 1998), which is incorporated herein
by reference in its entirety.
[0084] After a sufficient thickness of the low-k dielectric film is
deposited, the TEOS dispenser shuts off and vaporization commences
in the second vaporization chamber 12', where TAETO vapor is
generated and delivered to the process chamber 70, where the TAETO
vapor is reacted with N.sub.2O to form a high-k dielectric film,
tantalum oxide (Ta.sub.2O.sub.5), on the first (SiO.sub.2)
dielectric film. Finally, TiBr.sub.4 or TDEAT vapor is generated in
the third vaporization chamber 12" and reacted with ammonia
(NH.sub.3) to form a very thin titanium nitride (TiN) deposit,
which serves as a capping material for the tantalum oxide layer.
The wafer can then be removed from the chamber. In alternative
methods, the step of depositing TiN can be performed in a separate
process chamber.
[0085] Performing such a process in a single chamber is possible
because the entire apparatus is designed to operate without a need
for using plasma or other energy source to facilitate deposition.
When plasma, for example, is used to enhance deposition, films tend
to be deposited on the walls of the chamber, thereby leading to
cross-contamination if alternating sources were delivered to the
same chamber. In contrast, the surfaces of the chamber remains
clean with the methods of this invention.
[0086] The bodies of the vapor-flow-control subsystems 14, 14', 14"
illustrated in FIG. 2d are formed of an aluminum block 197 with a
flow path bored out of the interior. Bores in the aluminum block
197 are also formed for accommodating heaters and components that
are exposed to the flow paths, such as pressure sensors 34, 48, 50
and valves 42, 44, 159, 58, with fittings machined into the
aluminum block 197 for mounting each of the components. As in
previously-described embodiments, a laminar flow element is mounted
between the pressure sensors in the through-bore through which the
vaporized precursor flows. By forming the structure from a single,
unitary block of material, temperature uniformity throughout the
vapor-flow-control subsystem is promoted. Alternatively, the
aluminum block 197 can be formed of stainless steel or other
material that does not react with the precursor vapor.
[0087] Another embodiment of a vapor-flow-control subsystem 14 is
illustrated in FIG. 3a . All items in the vapor-flow-control
subsystem 14 are enclosed in a heated conductive sheath, preferably
of aluminum, which heats the items to approximately the same
temperature as the vaporizer 28. The conductive sheath has a 3-inch
by 3-inch square cross-section with a bore of just over 1-inch
diameter in the center to accommodate the delivery conduit 40.
Further, the conductive sheath includes casts of pressures sensor
48, 50 and other instruments, allowing the conductive sheath to
conform to the exterior shape of the vapor-flow subsystem. The
conductive sheath includes bores into which heaters, e.g.,
Watt-Flex.RTM. cartridge heaters and temperature sensors, are
inserted. A delivery conduit 40 joins the vaporization chamber 26
and the process chamber 70. Preferably neither the length of the
delivery conduit 40 nor the distance between the vaporization
chamber 26 and the process chamber 70 exceeds 25 cm. A series of
valves controls the flow of vapor between chambers 26, 70. An
isolation valve 42 seals the vaporization chamber 26 from the
delivery conduit 40. In one embodiment the isolation valve 42 is an
HPS Lopro.RTM. valve modified to operate at high temperatures. In
elements, such as the isolation valve 42, which must withstand high
temperatures, all elastomer seals are a special high temperature
material, such as CHEMRAZ E38 seals (or other CHEMRAZ seals,
depending on the application intended) from Greene, Tweed & Co.
(Kulpsville, Pa., U.S.A.). DuPont KALREZ 8101, SAHARA or DRY seals
may also be used but have been observed to offer poorer thermal
stability relative to the CHEMRAZ seals. These o-ring seals
preferably have dimensions meeting the standards established by the
International Organization for Standardization (ISO 2861/1). A
proportional control valve 44 (for example, those made by MKS
Instruments, Andover, Ma.) designed to withstand high temperatures,
provide high conductance and provide chemical compatibility with
wet precursors is illustrated in FIG. 2a. Alternatively, a
plurality of valves 44' connected in parallel, as illustrated in
FIG. 1A, can be used in place of a single proportional control
valve 44. The proportional control valve 44 is positioned
downstream from the isolation valve 42 and is upstream from a flow
meter 46 consisting of a pair of pressure sensors 48, 50 and a
laminar-flow element 54. In the illustrated embodiment, the
laminar-flow element is an open-ended tube 54 inserted through an
orifice in an otherwise solid block 56 blocking flow through the
delivery conduit 40. In one embodiment, the tube 54 has a length of
8.0 inches, an outer diameter of 0.375 inches, and an inner
diameter of 0.280 inches. The tube 54 is oriented concentrically
with and within the delivery conduit 40. In one embodiment of the
method of this invention, the pressure drop across the tube 54, as
vapor flows through the delivery conduit 40, is on the order of 0.1
torr.
[0088] The delivery conduit 40 has an internal diameter (I.D.) that
is larger than that of pipes conventionally used for vapor
precursor delivery in existing CVD systems. Preferably the internal
diameter of delivery conduit 40 is between 12 and 40 mm. More
preferably, the internal diameter is about 25 mm. The use of such a
wider-I.D. conduit for vapor transport between the vaporization
chamber 26 and the process chamber 70 (see FIGS. 4a-d) permits
higher conductance for the vapor flow therein and, consequently,
allows for adequate vapor flow at lower pressures. The vaporized
precursor is delivered to the process chamber 70 through conduit 40
at no more than 50% dilution. In preferred embodiments, the
vaporized precursor is delivered to the process chamber in a
substantially undiluted state (i.e., less than 10% dilution). In
further preferred embodiments, the vaporized precursor is delivered
in an intrinsically pure form. Additional conduits 141 can also be
provided to deliver vaporized precursors from other vaporizers to
the process chamber 70.
[0089] Each of a pair of pressure sensors 48, 50, preferably
capacitance manometers, is respectively aligned with an open end
57/59 of the tube 54. Accordingly, the difference in pressure
measurements from the two pressure sensors 48, 50 will reflect the
pressure drop across the tube 54, thereby allowing the rate of
vapor flow through the tube 54 to be calculated. A capacitance
manometer is an electronic gauge providing a direct measurement of
pressure in the delivery conduit 40. Where capacitance manometers
are used, each manometer preferably has the same full-scale range,
typically 10 torr. Suitable capacitance manometers include a
specially-constructed Baratron.RTM. 121-based absolute pressure
transducer (available by special order from MKS Instruments) and
the model 622 Barocel.RTM. bakeable vacuum/pressure transducer
(available from Edwards High Vacuum International, Wilmington,
Ma.). The Baratron.RTM. transducer is specially built and
calibrated to operate at 200.degree. C., in comparison to a
standard Baratron.RTM. transducer, which is typically limited to
150.degree. C.
[0090] The transducers are modified to remove all unnecessary mass
and to promote uniform temperature distribution across the
transducer. Accordingly, as a first step, the cover or shell of the
transducer is removed. To do so, the cables attached to the
Baratron.RTM. transducer are removed, the shell of the transducer
is removed and discarded, and the cables are shortened and
reattached. The housing support ring is also removed and discarded.
Further, the port of the transducer is removed. Its length is
machine cut, and it is then reattached. The electronics of the
transducer are then re-calibrated to match the changed capacitance
of the modified transducer. While the Barocel.RTM. transducer is
available, off the shelf, for use at 200.degree. C., as with the
Baratron.RTM. transducer, the case of the Barocel.RTM. transducer
is removed, and its cables are removed and replaced.
[0091] In an alternative embodiment, illustrated in FIG. 3b , the
solid block 56 surrounding the laminar flow element 54 extends
further toward the ends of the laminar flow element 54. By
lengthening the block 56, the volume of open volume surrounding the
laminar flow element 54 is reduced. This open volume is generally
considered to be "dead space." Reduction of this dead space is
thought to provide a more direct and efficient flow path through
the delivery conduit 40. In a further preferred embodiment, all or
nearly all dead space is removed as the block 56 and the laminar
flow element 54 essentially form a single tubular component such
that vapor flowing through the conduit 40 will hit a wall at the
capacitance manometer 48 and be directed through a bore, which acts
as the laminar flow element 54, within that wall.
[0092] Also shown in FIG. 3b is a heated aluminum sheath 55, which
is in thermal contact with the delivery conduit 40 and other
components of the precursor delivery system.
[0093] The proportional control valve 44 is coupled with the flow
meter 46 in a processor-driven control loop to regulate the flow of
vapor through the delivery conduit 40. Accordingly, the flow meter
46 provides feedback regarding the pressure differential in the
delivery conduit 40, and this feedback is used to direct the
proportional control valve 44 to increase or decrease flow, which
in turn, will respectively increase or decrease the pressure
differential in the delivery conduit 40, as measured by the flow
meter 46. This responsive regulation of the proportional control
valve 44 is continued until the pressure differential, as measured
by the flow meter 46, matches that which is needed to supply the
precursor at the desired rate for reaction in the process chamber
70.
[0094] Alternatively, a single differential pressure transducer
capacitance manometer, which measures a pressure drop across the
laminar flow element, can be used along with a single absolute
pressure transducer in place of the pair of capacitance manometers.
Other alternative means for inducing a predictable pressure drop
include a choked flow element or a molecular flow element in place
of the laminar flow element.
[0095] The vapor-flow-control subsystem 14 further includes a
second isolation valve 58, e.g., an HPS Lopro.RTM. valve modified
for high temperatures, positioned downstream from the flow meter
46. Charts showing representative vapor pressure over time at the
inlet of the vapor-flow-control subsystem 14 of this invention is
provided in FIG. 3d, while representative source flow at the outlet
of the vapor-flow-control subsystem 14 is provided in FIG. 3e.
[0096] In parallel with the vaporization and vapor-flow-control
subsystems 12, 14, a process gas subsystem 150 supplies additional
reactant, purge and other process gases to the process chamber 70.
The illustrated subsystem 150 includes sources of argon 152, helium
154, and nitrous oxide (N.sub.2O) 156. Gas flow from each of these
sources is regulated by a plurality of valves 162/164/169 and
161/163/168 with a mass flow controller 165/166/167.
[0097] In specific processes, nitrous oxide from source 156 flows
through valve 157 into process chamber 70 through exit port 143 for
reaction with the vaporized precursor delivered through delivery
conduit 40. Other gas sources or reactants may be used for
deposition of other specific materials. After deposition is
performed, argon from source 152 flows through valve 157 into
process chamber 70 to purge the chamber 70. By opening valve 160 in
conjunction with at least one of valves 155, 158 or 159, particular
subsystems or segments of CVD apparatus 10 can be independently
isolated and evacuated or backfilled. Additional reactant sources,
including plasma-ionized gas can be linked into the process gas
subsystem in parallel and with or without the nitrous oxide for
delivery to the process chamber 70.
[0098] Helium from source 154 is delivered through valve 157 into
process chamber 70, where it is channeled through a conduit for
release between a substrate chuck 74 and a substrate 88 upon which
vapors are deposited to improve the transfer of heat between the
substrate chuck 74 and the substrate 88.
[0099] The process subsystem 16 is designed to perform the actual
deposition of reacted precursor vapor onto a substrate. The process
subsystem 16, illustrated in FIG. 4a , includes a process chamber
70, a showerhead 72 and a substrate chuck 74.
[0100] The process chamber 70 typically is formed of
electroless-nickel- and sulphamate-nickel-plated 6061 aluminum and
is operated between 50.degree. C. and 300.degree. C. The process
chamber 70 includes an access port 123, which can be joined to a
wafer handler or cluster tool for transporting wafers into and out
of the process chamber 70. A gate valve 125 is mounted to the
access port 123 for controlling access there through. The process
chamber 70 further includes an inlet port 76 in an upstream section
78 of the chamber 70 and an exhaust port 80 in a downstream section
82 of the chamber 70 through which vapor flow is managed. An outlet
of the delivery conduit 40 projects into the chamber 70 through the
inlet port 76, while the exhaust port 80 is connected to the
exhaust subsystem 18. A pressure sensor 51 (e.g., a capacitance
manometer) is positioned to measure the vapor pressure in the
upstream section 78. At least one other pressure sensor 53 (e.g., a
capacitance manometer) is positioned to measure the vapor pressure
in the downstream section 82.
[0101] A showerhead 72 segregates the process chamber 70 into
upstream and downstream sections 78, 82. In one embodiment, the
showerhead 72 comprises electroless-nickel- and
sulphamate-nickel-plated 6061 aluminum and is in the form of a
flat, circular plate with passages 84 for gas flow. The showerhead
72 is either passive, as illustrated in FIG. 4a , or active. An
"active" showerhead is a showerhead which undergoes a change to
alter the rate at which vapors flow through it. In a preferred
embodiment, the active showerhead includes an array of phase-change
eutectic milliscale valves in place of the small holes 84
illustrated in FIG. 5a . These valves, which are available from
TiNi Alloy Company (San Leandro, Calif.), are made of a
thermal-phase-change material comprising a micromachined titanium
and nickel alloy. The valves, which, in one embodiment, are about
0.1 inch in diameter, can be formed in situ on the showerhead plate
en masse. The valves open when current is applied. The valves react
in milliseconds, so they can be used in real time. They can also be
used to effect dynamic patterns of valve actuation, e.g., sweeping
action, pulsing, spots, etc.
[0102] In an alternative embodiment, the showerhead 72 is a smaller
plate with a diameter approximating that of the wafer 88. This
embodiment is shown from a top view in FIG. 5b and, in
cross-section, from a side view in FIG. 5c . As shown, the
showerhead 72 is replaceably fitted into a larger ring 73 and is no
larger than a confined process volume, described below.
Accordingly, various showerheads may be exchanged in the larger
ring for use with different sized wafers and with different process
conditions. The use of smaller showerheads reduces cost, provides
greater flexibility in processing, and concentrates the flow of
process gases exclusively into the volume immediately above the
substrate 88.
[0103] A substrate chuck 74, positioned in the downstream section
82, comprises electroless-nickel-plated OFHC copper, with an
electroplated sulphamate nickel overplate, and, optionally, an
overcoat of a flame-sprayed aluminum oxide or other, similar
insulating ceramic. The substrate chuck 74 is secured with
Hastalloy screws and lock washers and is designed to hold a
substrate 88 upon which the precursor is to be reacted. The
substrate chuck 74 includes a plurality of bores 75 radiating
outward and into the substrate chuck 74. A platinum resistance
thermometer or thermocouple is inserted through one of the bores 75
to measure the temperature of the substrate chuck 74 The substrate
chuck 74 is heated by Watt-Flex.RTM. cartridge heaters (available
from Dalton Electric Heating Co., Inc., Ipswich, Ma.) inserted into
the remaining bores 75. In this embodiment, the heaters are 2 to 3
inches in length and 0.25 to 0.5 inches in diameter. The heaters
supply 225 watts at 208 VAC, and can be heated above 1000.degree.
C. Comparable wattage heaters at 24-25 VAC can alternatively be
used. The heaters, however, are typically operated at a maximum of
650.degree. C., and, more commonly, around 300-500.degree. C. These
temperatures are considerably lower than the temperatures to which
a wafer is typically heated in conventional thermal CVD processes,
i.e., 800-1300.degree. C. The reason why, in the system of this
invention, the substrate can be operated at lower temperatures is
that the vaporized precursor is provided at higher concentrations
at the wafer due to the absence of a carrier gas, the shorter
delivery paths, and the higher conductance of the conduits.
[0104] As an alternative or supplement to the above-described
heating means, the substrate can be heated by a laser, an ion beam,
an electron beam and/or photon-assisted energy sources. In any
case, the substrate is heated to a temperature higher than the
temperature of the walls of the process chamber.
[0105] In one embodiment, a DC or AC bias is supplied to the
substrate chuck 74 by a voltage source 79. The elevator shaft can
also be biased in order to provide electrical bias across the
substrate. The electromagnetic field generated by the bias can
influence the crystalline structure of the thin film as it grows on
the substrate. It has been shown that an otherwise uniform film
(with a lattice orientation of <100> for example) can be
induced to grow in a different crystalline structure (<111>
for example). In some cases, a film is induced to grow in a
gradient from one structure (e.g., <100>) to another (e.g.,
<111>) by applying either a DC or AC bias to the substrate 88
relative to the rest of the chamber. To achieve this bias, a
ceramic ring is used to electrically isolate the substrate chuck 74
from the process chamber 70 and other components within the process
chamber 70, which are held at ground. Alternatively, and more
commonly, the lower portion of the process chamber 18 coated with
aluminum oxide of sufficient thickness to isolate the chuck and
bellows from the chamber.
[0106] A substrate 88, e.g., a silicon semiconductor wafer, is
mounted on the substrate chuck 74 and is subject to the generated
DC or AC bias. A mask (or clamp) 94 extends down from the
showerhead 72 and forms a ring which masks the outer 0.5 to 3.5 mm
or more but more typically 1.5 to 2.0 mm from the edge of the
substrate 88. The mask 94 also shrouds the edge of the substrate 88
and prevents CVD from occurring on the edge or underside of the
substrate 88. The mask 94 is formed of a material having very low
thermal conductivity to minimize heat loss to any area, other than
the substrate, that is exposed to unreacted process gas.
Preferably, the mask is formed of either Incoloy.RTM. 850,
Elgiloy.RTM. (available from Elgiloy Ltd. Partnership, Elgin, Ill.)
or molybdenum and, optionally, includes a coating of either
aluminum oxide (Al.sub.2O.sub.3), silicon dioxide (SiO.sub.2) or
other, similar dielectric material. Alternatively, the mask 94 is
formed of ceramic. When the substrate chuck 74 is lowered, the mask
94 is suspended above the substrate 88.
[0107] A flow shield 77 extends down from the showerhead 72 and
forms a ring within which the substrate 88 is positioned. The flow
shield 77 channels the flow of reactant gases through the
showerhead 72 and across the exposed face of the substrate 88.
[0108] The substrate chuck 74 is raised and lowered by an elevator
96, upon which the substrate chuck 74 is mounted. The elevator 96
is electrically isolated. The elevator 96 is powered by a stepping
motor 97, with the power being transmitted by a drive shaft 99. The
position of the elevator 96 is continuously adjustable over a range
from fully retracted to fully extended, providing a working stroke
of about 70 mm. The changing position of the substrate chuck 74 is
measured by a linear voltage differential transformer 101, which
can measure the height of the elevator with sub-micron precision.
By raising and lowering the substrate chuck 74, the flow character
of vapor reactants above the substrate 88 can be altered.
Accordingly, the substrate chuck 74, when raised and lowered by the
elevator 96, can be used as a throttle valve controlling the flow
rate through the showerhead 72. The vertical position of the chuck
74 can also be changed to modify the microstructure and properties
of the deposited film. The differential in pressures measured by
sensors 51 and 53 is charted in FIG. 5g, wherein chuck position is
measured in mils and pressure differential across the chuck is
measured in torr. This pressure differential can be used to control
or monitor the process.
[0109] Further, the showerhead 72, the mask 94, the replaceable
gettering ring 89, the flow shield 77 and the substrate 88 are
positioned to cooperatively define a confined process volume to
which the vapor precursor and, if required, reactant gas are
delivered and in which deposition will occur. The diameter of this
volume (i.e., as defined by the mask 94) is preferably no more than
about 120% the diameter of the substrate. The height (or depth) of
the volume is a function of the position of the elevator, which
governs the height of the substrate 88. This volume, where
processing occurs, is much smaller than that of conventional CVD
reactors and, consequently, improves the efficiency of deposition
on the substrate.
[0110] In the method of this invention, deposition occurs when
process gases contact the heated substrate 88 and react to form a
solid thereon. Deposition at the surface of the substrate can be
rate-limited either by the rate of precursor transport or by the
rate of reaction at the surface. In a typical CVD and
plasma-enhanced, plasma-assisted or plasma-promoted vapor
deposition (PECVD, PACVD, PPCVD) process, the limiting factor is
the rate of precursor transport. Consequently, the rate of surface
reaction will be sub-optimal and the vaporized or dissociated
precursor will tend to react and deposit in a line-of-sight manner
on the first hot surface that it contacts. Moreover, the use of a
plasma, causes vapor-phase reactions which also mitigate against
conformal coverage on the surface. As a consequence, and as shown
in FIG. 5e , the deposited layer 192 formed at the mouth of an
etched cavity 194 in a substrate will grow much more quickly than
will a layer 192 forming on more remote areas of the cavity
194.
[0111] For further comparison, FIG. 5d illustrates a typical
deposited layer 192 formed via physical vapor deposition (PVD). The
deposited structure 192 has a similar pinched-off shape with very
little deposit forming at the deeper regions of the cavity 194.
This imbalance results from the directional, line-of-sight
deposition that is characteristic of PVD.
[0112] In contrast, however, FIG. 5f illustrates the approximate
structure of a conformal deposit 192 that can be formed in
accordance with the equipment described herein and in accordance
with the method of this invention. In this embodiment, the pinching
effect at the mouth of the cavity 194 is noticeably diminished
because the deposition process is limited by the reaction kinetics
at the surface rather than by the rate of precursor transport, with
the resulting tendency for deposition to occur simultaneously and
uniformly on all exposed surfaces of the substrate.
[0113] A plurality of pins (preferably, at least three) engage the
substrate chuck 74 through bores within the substrate chuck 74. The
pins are cylindrical with rounded ends. One such pin 74a is
illustrated in FIG. 4a . In this embodiment, the pins are mounted
to the base of the downstream section 82 of the process chamber 70.
On the other hand, when the elevator 96 is lowered, the substrate
chuck 74 slides down the pins toward the base of the downstream
section 82. When the substrate chuck 74 is fully retracted, the
pins extend through the top surface of the substrate chuck 74 to
lift the substrate 88 off the chuck 74. After it is lifted off the
chuck 74, the substrate 88 can then be removed from the process
chamber 70 by a robot arm. A similar process, illustrated in FIGS.
12a-d, is performed to place the wafer on the substrate.
[0114] In an alternative embodiment, illustrated in FIG. 4b , each
self-aligned pin 74a is attached to the substrate chuck 74 by
bellows 81. The bellows 81 provides a spring-like support because
the free height of the bellows 81 is greater than the depth of the
cavity in which it is mounted. When the chuck 74 is fully
retracted, as shown in FIG. 4b, the pin 74a is forced through the
chuck 74, lifting the substrate 88 off the surface of the chuck 74.
When the elevator 96 is used to raise the chuck 74 toward the
showerhead 72, the pin 74a drops back down to a position where it
remains held in place by the bellows 81 within the chuck 74 below
its top surface.
[0115] FIG. 4b also illustrates a replaceable gettering ring 89 to
mask the side of the chuck 74 from deposition. The side of the
chuck 74, which is heated throughout, typically is subject to an
accumulation of deposits from unreacted precursors which do not
react on the substrate 88. After deposits build on the replaceable
gettering ring 89, the ring 89 can be simply replaced without any
damage to the chuck 74 and without requiring that the chuck 74 be
replaced. Accordingly, use of the replaceable gettering ring 89 can
greatly extend the useful life of the chuck 74.
[0116] The replaceable gettering ring 89 also serves as a support
for the substrate 88 when the pins 74a are retracted. Accordingly
the substrate 88 is not in physical contact with the substrate
chuck 74. Rather, a gap of about 0.015 inches (0.38 mm) exists
between the substrate 88 and the chuck 74. As noted, this gap is
filled with helium gas which transfers heat between the chuck 74
and the substrate 88. The mask 94 seals the gap at the edge of the
substrate 88, thereby containing the helium gas. The pressure of
the helium gas between the substrate 88 and the chuck 74 is
controlled, and the flow of helium is also monitored and/or
controlled.
[0117] FIG. 4c illustrates the apparatus of FIG. 4b with the chuck
in position for wafer processing. FIG. 4d also shows this same
apparatus, this time with the shaft of the elevator fully extended.
In this position, the chuck 74 is lifted out of the processing
chamber 70, providing access to the chuck for
service/maintenance.
[0118] Optionally, a sensor 87, e.g., an optical thickness sensor
including a grazing incidence laser, is provided in the process
chamber 70 for measuring the thickness or chemistry of the
deposited film or the ambient conditions in the process chamber
70.
[0119] The final subsystem, i.e., the exhaust subsystem 18, is
designed, in part, to maintain a pressure differential across the
showerhead 72. The exhaust subsystem 18 includes an exhaust conduit
110 connected to the downstream section 82 of the process chamber
70, a trap vessel 85, and a vacuum pump 112 (such as the IQDP 80,
available from Edwards High Vacuum International, Wilmington,
Mass., USA, or equivalent) connected to the exhaust conduit 110
opposite the process chamber 70 to thereby pump vapors from the
process chamber 70, through the exhaust conduit 110. Alternatively,
more than one vacuum pump 112 can be used. A throttle valve 83 is
positioned in the exhaust conduit 110 to regulate the amount of
vapor pumped from the process chamber 70 and, accordingly, to
maintain a desired vapor pressure in the process chamber 70. In
this embodiment, the trap vessel 85 is situated between the vacuum
pump 112 and the throttle valve 83. The purpose of the trap vessel
85 is to trap a majority of the unreacted precursor vapor before it
reaches the vacuum pump(s) 112. The trap vessel 85 includes
surfaces that cause the precursor to react or be otherwise retained
thereupon due to chemical or thermal decomposition or an
entrainment process.
[0120] In an alternative, preferred embodiment, illustrated in
FIGS. 1C-D, a scrubber 85' is used in place of the trap 85. The
scrubber 85' actively removes harmful contaminants from the gas
stream before exiting the process subsystem thereby providing a
cleaner effluent leaving the system. A small, dry, low-power,
dynamic, variable-speed pump 95 is also provided within the process
subsystem cabinet 16. A preferred embodiment of pump 95 is
manufactured by Pfeiffer Vacuum (Nashua, N.H., USA), which pumps at
rates up to 50 m.sup.3/hr. The pump 95 is integrated with the
control system, through a ProfiBus data bus, such that the pumping
speed of the pump 95 is controlled to govern the rate at which
vapor is drawn through the system via a closed loop processing
system. By so controlling the pumping speed, the throttle valve 83
upstream from the pump 95 can be omitted.
[0121] Each of the subsystems 12, 14, 15, 18, 150 are enclosed in
sealed vessels to contain leaks of any hazardous gases from the
system. The vaporization and vapor-flow-control subsystems 12 and
14 are both contained in a first sealed vessel 180. An exhaust line
182 is connected to the first sealed vessel 180 for the controlled
release and removal of gases escaping from the system. A second
sealed vessel 184, which likewise includes an exhaust line 186,
encloses the process gas subsystem 150.
[0122] A CVD module 10 incorporating the various subsystems
described herein is illustrated from three different perspectives
in FIGS. 6a-c. FIG. 6a illustrates a rear view (from the vantage
point of a connected wafer handler) of the CVD module 10. FIG. 6b
illustrates a side view of that same CVD module. Finally, FIG. 6c
illustrates a front view of the CVD module 10. Components that are
all included within the module include a process module controller
205, a vaporization subsystem 12, a power input module 142, a
vapor-flow-control subsystem 14, a process subsystem 16, an
elevator 96, a scrubber 85', and a gate valve 125.
[0123] FIG. 7 illustrates a general control architecture diagram
200 for control of a single CVD apparatus 10 and its associated
subsystems. Control of a CVD apparatus 10 is facilitated through a
process module controller 205 operating under software control in a
distributed manner to independently control temperature control
modules 210, pressure control modules 215, flow control modules
220, and elevator control modules 225. While the preferred
embodiment is illustrated as a distributed system, the overall
chemical vapor deposition concepts and techniques presented within
this invention do not have to be implemented in a distributed
fashion. Rather, they may be performed in a linear manner with a
single main controller executing all processing steps itself, while
still overcoming many of the problems of the prior art system.
However, the distributed nature of the preferred embodiment
provides significant advantages over a linear system operation, as
will be explained.
[0124] Software control of process operations can be achieved using
a Siemens programmable logic controller (PLC) running software
conforming with the following ISO-standard: DIN EN 6.1131-3. This
software can be integrated with software from Wonderware Corp.
(Irvine, Calif., USA) to create an interactive graphical user
interface to the process control.
[0125] Modules 210 through 225 are representative of the main
processing tasks of the CVD apparatus 10, and there may be other
control modules not shown which may be used for other specific
tasks noted throughout this specification. Each of the previously
described subsystems, including the vaporization subsystem 12,
vapor-flow-control subsystem 14, process subsystem 16, and exhaust
subsystem 18 can include certain components that are operated by
the modules 210, 215, 220 and/or 225 of the overall control
architecture shown in FIG. 7.
[0126] For example, in FIGS. 2a and 2b, the vaporizer subsystem 12
involves, among other tasks, controlling the temperature of
reservoir 20, controlling the position of, and therefore the amount
of precursor flow from dispensing valve 24, controlling the
temperature of the vaporizer 28, and monitoring the pressures
within the vaporization chamber 26. Each of these tasks is
generally coordinated via software operating within process module
controller 205 and is physically carried out by one or more of
modules 210 through 225.
[0127] Through the distributed nature of the various system
components, the process module controller 205 can manage wafer
processing for an individual CVD apparatus 10, which requires
multiple simultaneous events. If wafer processing for a single CVD
apparatus 10 is not too complex, it may be the case that an
alternative embodiment of the invention may use a single process
module controller to monitor and control more than one CVD
apparatus. That is, two physical CVD systems 10 could be controlled
by a single process module controller 205, without overloading the
processing capacity of the process module controller 205. The
preferred embodiment however uses a separate process module
controller 205 per CVD apparatus 10. By using distributed
processing, certain steps in the overall wafer processing procedure
can be performed in parallel with each other which results in more
efficient wafer yields and allows real time management of vapor
deposition.
[0128] Actual process control is accomplished by providing separate
control modules 210 through 225 for each of the individual
operational components (i.e., valves, temperature monitoring and
heating devices, motors, etc.) in each of the subsystems. The
modules can be programmed to do specific tasks related to a
specific portion of that subsystem's functionality. When given a
task, each control module reports back to the process module
controller 205 when the task is complete, its status, and/or if the
task fails to complete.
[0129] For example, all of the temperature control processing may
be done in a distributed fashion, such that the high level process
module controller 205 can merely instruct one or more specific
temperature control modules 210 to set and maintain specific
temperatures. The process module controller 205 can then move on to
the next main task in the overall wafer processing routine.
Achieving and maintaining the set point temperature(s) can then be
carried out by the independent temperature control module 210 in a
closed loop manner.
[0130] An example of a control module is the Intelligent Module No.
S7-353 or the S7-355, both manufactured by Siemens Corporation.
Such modules may be used for intensive closed-loop type control
tasks, while an Intelligent Module No. S7-331 , also manufactured
by Siemens Corporation, may be used for precision signal
conditioning type tasks, such as voltage measurements from
capacitance manometers resulting in adjustments in flow
control.
[0131] These particular control modules used in the preferred
embodiment, as well as most other electrical components in the
system, operate at low voltage (i.e., 24 Volts AC or DC) in order
to prevent injury in the event of a short circuit, and also to
prevent interference with vapor deposition. Low voltage operation
also allows the system of the invention to operate with 120 Volt or
240 Volt power supplies, or with other international power systems
of differing voltages.
[0132] Accordingly, all aspects of control, beginning with the
vaporization subsystem 12 and ending with the process subsystem 16,
are handled by modules which may be independently activated, and
which can then handle the given task on their own.
[0133] There are, however, instances where modules can provide
information or communications directly to other modules to
establish adaptive relationships in order to maintain certain
process settings. In such instances, these modules can adapt their
task without the need for further instructions or tasks from the
process module controller 205. That is, two or more modules may
establish a relationship such as a master/slave or client/server
type relationship, and can adjust themselves accordingly to either
back off from a task, or move ahead faster with a task, depending
upon the feedback of other inter-related modules involved in
adaptative relationships.
[0134] For example, a pressure control module 215 may be used to
monitor pressure sensor 34, which detects the pressure output from
the vaporization chamber 26. The pressure control module 215 can
provide direct feedback to a separate flow control module 220 which
operates isolation valve 42. If the process module controller 205
initially instructs isolation valve 42, through flow control module
220, to maintain a certain flow of vapor or gas, the flow control
module 220 can obtain pressure data from the pressure control
module 215 that controls pressure sensor 34. This data may be used
to determine if there is enough pressure in the delivery conduit to
deliver the requested flow. If the pressure is too low or too high,
pressure control module 215 may, depending upon the implementation,
signal to the process module controller 205 that the task cannot be
completed due to lack of pressure, or may, via an established
adaptive relationship, signal in real time directly to a
vaporization chamber pressure control module in order to increase
or decrease vaporization chamber pressure.
[0135] In other words, while the overall processing of chemical
vapor deposition is controlled in the CVD apparatus by the process
module controller 205 with a master control routine, certain
control module loops may incorporate data from other modules to
adapt or detect changes in other system components, without the
need for communication with process module controller 205. Most
frequently, this is done where the output of one module directly
affects the performance or operation of another module.
[0136] Communication between the modules 210 through 225 and the
process module controller 205 may be accomplished in a number of
ways. Direct Memory Access (DMA) can be used to directly read and
write data to commonly accessible memory locations within a shared
memory 230, as shown in FIG. 7. A data bus (not shown in FIG. 8),
such as, for example, a ProfiBus data bus, which typically operates
at 12 Megahertz and uses DB-9 connectors to interface to modules,
can interconnect modules 210 through 225 with each other and the
process module controller 205, to allow data communications and
sharing of information. It is to be understood that common
networking and data communications processes and principles are
contemplated herein as being applicable to communications between
devices, modules and components in this invention.
[0137] It is also contemplated in this invention that faults in
modules and componentry may occur and therefore, the invention can
use redundant or fault tolerant modules, components and processors
and can provide swappable dedicated processors for each module 210
through 225 and the process module controller 205. By providing
swappable componentry, parts may be replaced without shutting down
the entire system. This is beneficial, for example, when an
expensive precursor has been preheated and will be damaged if
returned to a lower temperature. If a fault occurs, for example, in
an elevator control module 215, this module may be replaced or
deactivated by another redundant module which may take over for the
lost functionality of the failed module. The swapping or redundant
failover may be performed without having to stop the wafer
deposition process, which saves wafers and reduces precursor waste
and reduces system down-time.
[0138] FIG. 8 illustrates a flow chart of the main processing tasks
performed by the process module controller 205 from FIG. 7. The
steps 300 through 305 are, in a preferred embodiment, implemented
in software or firmware and are performed when the CVD apparatus 10
is activated to process wafers. In the preferred embodiment being
described, the main process control steps 300 through 305 are
wafer-centric in nature. That is, these steps focus mainly upon
wafer handling and execution of a process recipe which performs the
CVD operation on a particular wafer. Generally, the master routine
sets tasks to be performed, sets variables for those tasks and
system operation, and instructs the dedicated modules to perform
the tasks. In parallel with this main process routine, as will be
explained, are a set of other concurrently executing routines which
perform other tasks. The sub-processes are necessary for the
success of the major process sequence (i.e., steps 300 through 305)
of FIG. 8 to complete. The sub-processes, shown in FIGS. 9a, 9b, 10
and 11, are, respectively, the vaporizer sub-process, the vapor
phase flow controller sub-process, and the process chamber pressure
control sub-process. Other sub-process may exist as well, such as,
for example a cleanup process, a housekeeping process, a safety
interlock process, and other which are explained herein.
[0139] In step 300 of the main process control subroutine of FIG.
8, the CVD apparatus 10 is pre-prepared to accept a wafer. This
step includes, for example, the process of pre-heating the
pre-cursor in reservoir 20 to the desired temperature and loading a
process recipe for the wafer process to be performed by the CVD
apparatus 10. Parameters for the process recipe are loaded into
memory 230 from an external source, such as, for example, a cluster
tool controller (discussed, below). The recipe parameters control
the various settings such as temperature, pressure, and which
vapors and gases are to be processed with the wafer 88.
[0140] In a preferred embodiment, there may be as many as ten or
more steps that constitute the recipe for wafer processing. Each
step allows a user who is processing a wafer to select parameters,
such as, for example, the "step number", "step duration" (in
seconds), "target process pressure" (in millitorr), "precursor flow
rate" (milli-sccm), "reactant flow rate" (milli-sccm) and "wafer
temperature" (degrees C). These parameters make up the recipe for a
wafer and govern the general temperature, flow, pressure and
operation of the CVD apparatus 10. For example, the last parameter,
"wafer temperature", is a function of the substrate chuck
temperature, since, as will be explained, the wafer is in contact
with the substrate chuck for much of the time during processing.
Hence, the wafer temperature is a parameter that typically does not
change too much from one wafer to another, and may be provided
merely for reference for the process recipe.
[0141] Step 301 prepares to accept a wafer and signals to an
external wafer provider mechanism (e.g., central wafer handler
robot arm 134, discussed, below) that the CVD apparatus 10 is ready
to accept a wafer. Step 302 then coordinates the movement of the
wafer into the process chamber 70 and placement of the wafer on the
substrate chuck 74.
[0142] FIGS. 12a through 12d pictorially illustrate the process of
coordinating the movement of the wafer (step 302) into the process
chamber 70. Each of these figures includes top and side perspective
views of the process chamber 70 area and robot arm 134. In FIG.
12a, substrate chuck 74 includes pins 74a-c, upon which the
substrate or wafer 88 is loaded prior to the CVD operation. Before
entering the process chamber 70, the wafer 88 rests upon an end
effector of robot arm 134 outside of the process chamber 70. As
shown in FIG. 12b, as the robot arm extends and enters into the
process chamber 70, the wafer 88, carried on the end of the robot
arm 134, passes over substrate chuck 74 and substrate chuck pins
74a-c and passes under showerhead 72, which is not in use during
the process of accepting a wafer. FIG. 12c illustrates the wafer 88
fully inserted into process chamber 70, prior to the retraction of
the robot arm 134. The wafer 88 rests on pins 74a-c, after the
robot arm 134 lowers slightly and retracts, as shown in FIG.
12d.
[0143] Returning to the main processing routine shown in FIG. 8,
step 303 then runs the current process recipe that has been
programmed into the CVD apparatus 10. The recipe (i.e. the
parameters) may be changed between wafers, but once the recipe has
been started in step 303, the pre-loaded parameters used for
processing do not change for the current wafer 88. As will be
explained in FIGS. 9a, 9b, 10 and 11, running the recipe in step
303 includes aspects of temperature control (step 303a), pressure
control (step 303b) and flow control (step 303c). The sub-processes
in FIGS. 9a, 9b, 10 and 11 provide details as to the operation of
these aspects of the invention.
[0144] In one embodiment of the invention, a recipe loaded into
process module controller 205 governs the various processing steps
of the wafer according to, for example, the "step duration"
parameter. That is, this embodiment can be governed by timers set
by parameters that determine, for instance, how long a particular
vapor is deposited onto a wafer.
[0145] In another embodiment, the sensor sub-system 19 (FIG. 1B)
can be used to calculate, measure, or determine the deposition
activity on the wafer itself. This information can be used to
determine when the next step in the recipe is performed. For
example, if a step in the recipe calls for depositing 100 angstroms
of copper using a copper vapor onto a wafer, the sensor sub-system,
by monitoring the deposition activity, can indicate when this has
been completed. As such, the steps in the recipe in this embodiment
are not driven so much by timers, as by when processing steps are
actually physically completed.
[0146] The sensor modules 227, illustrated in the control
architecture in FIG. 7 are used to control and provide feedback to
process module controller 205 from wafer subsystem 19 as
illustrated in FIGS. 1A and 1B. Wafer sensing equipment 87 in wafer
subsystem 19, for example, may comprise a laser measurement system
that can measure the thickness of any layer of material being
deposited onto the wafer 88 during a CVD operation. This layer
thickness information may be monitored by sensor modules 227, and
when the task of detecting 100 angstroms of copper, for example, is
complete, the sensor modules 227 can indicate to the process module
controller 205 that the task has been completed. Other wafer
sensing equipment that may be used to sense CVD progress may
include reflectivity sensors that detect the reflectiveness of the
wafer surface. As more material is deposited onto a wafer, the
surface may become more or less reflective thus indicating
deposition progress. Another sensing device may be an x-ray
diffraction system used to measure composition of the wafer
surface, thus indicating deposition progress. Those skilled in the
art will now readily understand that other common real-time
measurement and sensing hardware may used within sensor sub-system
19 to detect and indicate recipe step completion, depending upon
the task.
[0147] After the recipe is complete, the wafer 88 has been
processed by the vapor and gases in the process chamber 70. Step
304 in FIG. 8 then removes the wafer, which is generally the
reverse process of that illustrated in FIGS. 12a through 12d. The
robot arm 134 returns and picks up the wafer 88 off of the
substrate chuck pins 74a-c, and carries the wafer 88 out of the
process chamber 70. Step 305 then performs cleanup of the CVD
apparatus 10, which will also be described in more detail
later.
[0148] FIG. 10 illustrates the steps of the vaporizer sub-process
that is continually performed during the main control processing
steps that execute as explained with respect to FIG. 8. The
vaporizer sub-process steps 330 through 334 generally control the
vaporization of the precursor in reservoir 20 and the maintenance
of pressure at the inlet port 76 to the process chamber 70. The
vaporizer sub-process is also responsible for the cleanup of the
vaporizer 28 between processing wafers during standby modes.
[0149] The vaporizer sub-process shown in FIG. 9a is driven
primarily by the "vaporizer temperature" parameter that gets loaded
during the programming of the recipe into memory 230. This variable
drives the temperature setting for all of the other temperature
controlled surfaces except the wafer chuck 74 (set by a "wafer
chuck temperature" setting) and the funnel temperature (set by a
"funnel temperature" setting). The vaporizer pressure largely
relies on the pressure control modules 215 which operate and
monitor the capacitance manometers 34, 48, 50, 51 and 53 located
throughout the system, as previously described.
[0150] In step 330, the pressure at pressure sensor 34 must be
greater than the pressure at pressure sensor 48. In step 331, the
pressure at pressure sensor 48 must be greater than the pressure at
pressure sensor 50. In step 332, the pressure at pressure sensor 50
must be greater than the pressure at pressure sensor 51. And
finally, in step 333, the pressure measured at pressure sensor 51
must, in this embodiment, be approximately 1.5 times (or more)
greater than the pressure measured at pressure sensor 53. If any of
these steps 330 through 333 fail, feedback is provided back to the
vaporizer subsystem 12 by step 334, at which point the appropriate
modules in various subsystems are adjusted so as to maintain the
optimum pressure at the wafer, as measured by the difference in
pressure between pressure sensors 51 and 53.
[0151] The recipe parameter "process pressure" is referred to as
the "target pressure" since this is the pressure to be maintained
by the system at the wafer 88, and is attained in cooperation
between the vaporizer sub-process (FIG. 10), the vapor phase flow
controller sub-process (FIG. 10) and the process chamber pressure
control sub-process (FIG. 11).
[0152] Hence, as explained above, during wafer processing, the
reservoir 20 deposits small amounts of precursor onto vaporizer 28
which is heated. Each small amount of precursor, which typically
flows slowly down the vaporizer 28 inverted cone structure, forms a
thin film and resides on the cone for a period of time during
vaporizing. As this vaporization occurs, an upward ramp in pressure
is measured by capacitance manometer 34. The upper limit of the
vapor pressure that is measured by pressure sensor 34 is a function
of the temperature of the vaporizer 28 (and the rest of the system)
as well as the material used as the precursor. Thus, too high of a
temperature may cause the premature chemical decomposition of the
precursor prior to its exposure to the wafer 88, and too low of a
temperature may result in a low vapor pressure, low flow rate, and
low process pressure which results in a low chemical vapor
deposition rate.
[0153] The vaporizer sub-processes in FIGS. 9a and 9b may be in
either a processing state or a standby state. The processing state
is used, as explained above with respect to FIG. 9a, after a wafer
has been accepted. The standby state governs a cleanup process and
is shown in FIG. 9b and will be described in conjunction with FIG.
1A through 1D.
[0154] During cleanup of the vaporizer sub-process, in step 340, no
precursor is introduced into the vaporization chamber 26. In step
341, isolation valve 42 isolates the entire vaporization subsystem
12 from the other subsystems. Step 342 then fully opens valve 160.
Next, in step 343, Argon gas provided from valves 161 and 162 and
mass flow controller 165 is introduced into the vaporization
chamber 26 until a pressure of approximately 50 torr is measured at
pressure sensor 34. Then, step 343 evacuates the pressure in
vaporization chamber 26, by opening valve 170 and closing valves
161 and 162, and operating exhaust subsystem 118 to suck out the
argon gas. Step 344 then detects a vacuum pressure. Step 345 then
repeats steps 343 and 344 N times, where N may be one, two or more
times, for example. This N repeat count may be varied, depending
upon the properties of substances used. Step 346 then evacuates the
vaporization chamber 26 and step 347 maintains the entire volume of
vaporization chamber 26 in a vacuum until the vaporization
sub-process is instructed to go active to begin processing
wafers.
[0155] The second sub-process is the vapor phase flow controller
sub-process and is illustrated by the processing steps in FIG. 11.
During wafer processing, this sub-process ensures that the
vapor-flow-control subsystem maintains a steady flow of vapor to
the process chamber 70, in concert with the variations in pressure
that occur at various critical points in the system as explained
above during wafer processing. The main objective of this
sub-process is to maintain the target mass flow and total
aggregated mass flow of vapor to the wafer 88. Unlike traditional
mass flow controllers, where pressures are typically 20 psig or
more at inlets to the wafer and that flow into a vacuum at or below
the wafer, the present invention uses this sub-process to control
the flow of vapor in upstream section 78, where the pressure is
only one to five torr, and where the "process pressure" is targeted
at approximately 800 to 1000 millitorr.
[0156] To accomplish this, this sub-process uses the proportional
control valve(s) 44 (44' in FIG. 1A, 44 in FIG. 1C) to maintain the
appropriate flow and target pressure drop as measured from pressure
sensor 34 to pressure sensor 48. Step 360 in FIG. 10 monitors this
pressure difference. Step 361 then determines if adaptive flow
control is operational. If so, step 362 is executed which
calculates the desired flow ("Q") of the vapor being applied to the
wafer and adjusts, in step 363, the process time system variable to
compensate for any variations from the target pressure experienced
during the normal set process time. That is, step 363 lengthens or
shortens the check time between determining system pressures, so
that the pressure will have the correct time to build based upon
the precursor material being used for vapor flow.
[0157] In step 361, if adaptive flow control is not being used,
step 364 determines if the pressure across the proportional control
valve(s) 44 (44' in FIG. 1A, 44 in FIG. 1C) is insufficient to
attain the targeted flow rate, and if so, step 365 detects this and
signals to the other two sub-processes to attain the desired flow
rate by varying appropriate settings.
[0158] The vapor phase flow controller sub-process in FIG. 10 is
also responsible for controlling modules that set the flow rate of
oxidizing reactants via step 366. That is, nitrous oxide, for
example, from valves 168 and 169 may be provided as a reactant gas
along with the precursor vapor, into the process chamber during
flow control of the vapor from the vaporization chamber 26. Step
366 determines the flow rate of any reactant gas by a "reactant
flow rate" parameter provided in the recipe. Typically, the
reactant flow rate is expressed as a ratio to the flow rate of the
vapor from the vaporization chamber 26.
[0159] For example, a target pressure that might be typically set
is 1.5 to 2.0:1. Since the flow rate of vapor can vary somewhat (as
explained above), the flow rate of the reactant from one or more of
the mass flow controllers 165, 166 or 167 must also vary in concert
with the flow rate of the precursor vapor. Note that in the
embodiments shown in the figures, the system is well damped such
that variations are on the order of plus or minus 10 percent of the
target pressure or flow rate, and are dependent upon variations in
the lots of precursor used as received from different suppliers,
for example. That is, oscillatory swings may not be noticed within
one batch of precursor, but subtle shifts may be observed based
upon chemical lots. The sub-process in FIG. 10 helps eliminate
these shifts.
[0160] The vapor phase flow control sub-process, if in a standby
state, as shown in standalone step 367, independently checks any
output offsets that might have occurred between pressure sensor 48
and pressure sensor 50, and can use this calculated offset to
adjust the pressure sensors apparent output accordingly during
subsequent calculations while in active mode. Step 367 can also
cross-check pressure measurements of sensors 48 and 50 in standby
mode against pressure sensors 34, 51 and 53.
[0161] FIG. 11 illustrates the third sub-process, referred to as
the process chamber pressure control sub-process, which is
associated with maintaining the pressure at the wafer 88. In step
380, the pressure is measured at capacitance manometer 53, which is
the pressure in the process chamber 70 below the showerhead 72 at
the wafer. Step 381 then directs throttle valve 58 to increase or
decrease the pressure as measured in step 380, to maintain the
pressure as defined by the parameter "process pressure".
[0162] FIG. 13 illustrates the processing steps performed in a
cleanup sub-process that runs continuously and which is transparent
to the other sub-processes in the system. Upon startup of the CVD
apparatus, without a signal of an approaching wafer, the cleanup
sub-process is the default process. The cleanup sub-process, in
step 390 enables a mechanical circuit breaker to isolate the
electrical system components in the event of a power surge. Step
391 maintains all heat zones at the system set points. The
parameter "vaporizer temperature" is used as the temperature set
point for all heated zones except the reservoir 20 and funnel 22
temperatures, and wafer chuck 74 temperatures. This step can also
detect heating wire breaks or shorts. Step 392 ensures that
adequate vacuum is present for the process module by testing the
vacuum pump control. Step 393 monitors the state of the door and
housing covers surrounding the CVD apparatus 10. Steps 394 and 395
monitor system power and pressures, and looks for excursions
outside of the normal operating state. Step 396 tracks gauge status
and can detect gauge problems and can cross calibrate gauges in the
system. Step 397 sets up and calibrates the mass flow controllers
165, 166 and 167. Step 398 cross calibrates the pressure sensors in
the system, and step 399 initializes the system parameters to a
default state.
[0163] FIG. 14 illustrates a schematic architecture of a CVD
apparatus of this invention, with each of the previously described
sub-processes 600 through 604 of FIGS. 8 through 13 illustrated as
a closed loop. Process module controller 205 interfaces with the
other hardware components of the system via data bus 605, which
carries serial analog and digital commands to the components. Each
of the control modules 210 through 227 interfaces to the data bus
605, to communicate with process module controller 205, and in
certain instances where adaptive relationship exists, with each
other. The process module controller 205 is also connected to a
Profibus data bus 607 via which provides deterministic
communication with any of a cluster tool controller, a transport
module controller, or another process module controller. At higher
levels of communication, not shown in FIG. 14, communication is
generally via Ethernet, which is non-deterministic.
[0164] In the vaporizer loop 600, a pressure control module 215
monitors pressure from capacitance manometers 34, 48, 50, 51, and
53, according to the processing explained above, and can provide
data to temperature control module 210 which controls vaporizer
heating element 29, in order to provide proper vapor for the system
to operate. To interface 606 between pressure control module 215
and temperature control module 210 is an example of a closed loop
adaptative relationship, since the temperature is controlled based
upon feedback from the pressure control module 215.
[0165] In flow control loop 601, which is responsible for
maintaining the proper flow of vapor in the system, pressure
control module 215 monitors pressure from each of pressure sensors
34, 48 and 50, in order to provide feedback data to flow control
module 220, which operates proportional relief valve 44, as well as
valves 161 through 164, 168, 169 and 170, in order to provide vapor
and reactant gases at a proper flow rate.
[0166] Process chamber pressure control loop 602 uses pressure
control module 215 to detect pressure at pressure sensors 51 and 53
within the process chamber 70. This pressure information is used in
an adaptative relationship between the pressure sensors and the
throttle valve 83, operated by the flow control module 220. This
closed loop 602 ensures that the pressure in the process chamber is
correct during wafer processing by using the throttle relief valve
83 to maintain a continuous flow.
[0167] Elevator control loop 603 illustrates the adaptative
relationship between the elevator 96, which is operated by elevator
control module 225, and the sensor control module 227 which uses
sensor equipment 87 to detect how much material has been deposited
on a wafer. In this closed loop, which is used when the recipe
calls for sensor control, the elevator 96 may be lowered when the
sensor equipment 83 detects enough material is present on the
wafer. Thus, direct communications is provided between the elevator
control module 225 and the sensor control module 227.
[0168] The elevator control loop 603 is also related to the sensor
loop 604, in that when sensor equipment 96 detects enough
deposition material on a wafer, sensor control module 227 notifies
flow control module 220 to activate throttle valve 83 in order to
turn on the exhaust pump to full power. This empties the process
chamber 70 of any leftover vapor so as to immediately stop the
deposition process. Sensor loop 604 is thus another example of an
adaptive loop, but acts more like a one way trigger since the
sensor equipment 96 causes the throttle valve 83 to open when
deposition is complete.
[0169] In each of the aforementioned loops 600 through 604, the
process control module 205 can merely provide the appropriate tasks
to each of the control modules 210 through 227. The control modules
will execute the given task on their own. By allowing adaptive
relationships as explained above, closed loops are formed for the
basic underlying sub-processes required for the CVD apparatus to
operate efficiently. The process module controller 205 monitors the
progress of each closed loop via status data that is provided from
each control module. Thus, the process module controller 205 is
fully aware of how a specific CVD process is progressing while the
process is taking place. In this manner, the process module
controller 205 can report to a higher level process, such as the
main process taking place within a cluster tool controller 207.
[0170] The "processing hierarchy" formed by the lower closed loops
and control modules, the intermediate process module controller
routine executing on the process module controller 205, and the
master cluster tool controller routine executing on the cluster
tool controller 120 allows modifications to processing code at one
level to have little or no adverse impact on the programs or
processes used for other aspects of the CVD process. Moreover, any
modifications made to one aspect of the CVD processing, for
example, in the flow control loop, which may happen to impact the
processing of other loops, will be properly accounted for due to
the adaptive relationships and feedback of information between
control modules. This hierarchy also allows easy code maintenance
and a structured environment where features may be added to one
area of CVD processing without having to re-tool or re-code other
areas.
[0171] In one embodiment, the CVD apparatus 10 is used to deposit a
number of films on a single wafer. This embodiment is designed to
operate at low pressure (0.001 to 10.0 torr) and is aimed at the
deposition of films with geometries of 0.25 microns or less. The
same embodiment, with changes only in temperature and flow control
components, can be used in a number of different processes to limit
costs and maintenance requirements.
[0172] Films that can be deposited by this system include, but are
not limited to, the following: aluminum from dimethyl aluminum
hydride (DMAH), copper from one of the Cu.sub.I(hfac)(tmvs, tevs,
teovs) precursors, tantalum nitride from a solid precursor such as
TaBr.sub.4, titanium nitride from a liquid precursor such as
tetrakisdiethylamido titanium (TDEAT), tetrakisdimethylamido
titanium (TDMAT), TiBr.sub.4, or TiI.sub.4, low-k dielectric films
from hexasilsesquioxane (HSQ) or a fluorinated
tetraethylorthosilicate (TEOS), and tantalum oxide from tantalum
pentaethoxide (TAETO) and either ozone or N.sub.2O. Other films
that can be deposited in accordance with the methods and apparatus
of this invention include phosphorous-doped silica from
triethylphosphate (TEPO), boron-doped silica from triethylborate
(TEB), and tantalum oxide from tantalum tetraethoxide
dimethylaminoethoxide (TAT-DMAE). FIG. 19 is a graph showing CVD
source vapor pressure curves, expressed in termns of temperature
(.degree. C.) along the abscissa and pressure (torr) on a
logarithmic scale along the ordinate.
[0173] Illustrated curves include functions representing the vapor
pressure of TEPO 401, TEOS 402, TEB 403, TAETO 404, TAT-DMAE 405,
CuTMVS 406 and TDEAT 407. The shaded region 410 represents a
demonstrated operating range between 1 and 10 torr for this
process. This indicates the ability of the system to deposit a
variety of materials over a temperature range between 20.degree. C.
and 200.degree. C in this pressure range. This pressure range is
not limiting, however, as one can work outside of it, as well. The
vapor pressure curve (in torr) for TEB has been expressed as
follows:
Log P=8.4156-2167/T.sub.K.
[0174] The vapor pressure curve (in torr) for TEPO has been
expressed as follows:
Log P=8.1516-2547.5/T.sub.K.
[0175] The vapor pressure curve (in torr) for TAT-DMAE has been
expressed as follows:
Log P=-3.66 (10.sup.3/T.sub.K)+9.33.
[0176] The vapor pressure curve (in torr) for TEOS has been
expressed as follows:
Log P=8.3905-2415.7/T.sub.K.
[0177] Finally, the vapor pressure curve (in torr) for titanium
nitride has been expressed as follows:
Log P=-3.18 (10.sup.3/T.sub.K)+7.79.
[0178] Using nitrous oxide as a reactant, thermal deposition via
reaction with TEOS can occur at temperatures in the vicinity of
475.degree. C., which is significantly cooler than the typical
range of 600.degree. C. to 750.degree. C. (or higher) for other
methods, which typically use oxygen or ozone as opposed to nitrous
oxide as a reactant. The molar ratio of N.sub.2O:TEOS is greater
than 4:1; preferably, between 5:1 and 10:1; and more preferably
about 8:1. FIGS. 20 and 21 illustrate the refractive index and
thickness, respectively measured at multiple points on an
eight-inch wafer that was subjected to deposition of silica using
an 8:1 ratio of N.sub.2O and TEOS in accordance with this
invention. As is evident from FIGS. 20 and 21, the thickness of the
coating is highly uniform across the surface of the wafer, and the
refractive index is near that of thermal oxide. The properties of
films deposited with the methods and apparatus of this invention
are sufficient for applications such as gate dielectric deposition.
Typicallly, silica layers deposited by conventional methods have a
refractive index below 1.44. However, as shown in FIG. 20, silica
layers deposited by methods of this invention can have a refractive
index above 1.44; and in preferred embodiments, the refractive
index is between about 1.45 and about 1.46.
[0179] As an example of a process performed in accordance with this
invention, a tantalum oxide film is deposited on a wafer using
liquid TAETO as a precursor and gaseous N.sub.2O as an oxidant. The
reservoir 20 is filled with TAETO either with the reservoir 20 in
place in the system or with the reservoir 20 temporarily removed
for filling. While in the reservoir 20, the TAETO is stored at a
temperature above its melting point but below that at which it
decomposes. In this embodiment, the TAETO is stored at or near room
temperature. From the reservoir 20, the TAETO is delivered to the
vaporizer 28 through the axial displacement pulse valve in an
amount that is just sufficient to generate a workable vapor
pressure to deliver to the process chamber 70. The temperature of
the vaporizer 28 is tightly controlled, in one embodiment, at
180.degree. C., to vaporize the TAETO as it flows across the
surface of the vaporizer 28 without causing the TAETO to thermally
decompose.
[0180] The vapor pressure of TAETO that is generated in the
vaporization chamber 26 is a function of the temperature of the
vaporizer 28. Specifically for TAETO, the log of vapor pressure can
be calculated with the following formula:
Log P=-4.15(10.sup.3/T.sub.K)+9.60,
[0181] The vapor pressure of TAETO and several other sources
(measured in torr) is provided in Table 1, below, over a range of
temperatures from 20.degree. C. to 200.degree. C.
1 TABLE 1 Silicon Oxides Tantalum Oxide Copper Ti Nitride Degrees
C. TEOS TEPO TEB TAETO TAT-DMAE Cu TMVS TDEAT 20 1.42634 0.292384
8.910782 2.8227E-05 0.00071008 0.059138 0.000887 22 1.621831
0.334796 10.0792 3.5196E-05 0.00086263 0.070819 0.00105 24 1.840931
0.382561 11.38194 4.3756E-05 0.00104521 0.084601 0.001241 26
2.086094 0.436589 12.8322 5.4239E-05 0.00126318 0.100826 0.001463
28 2.359987 0.497247 14.44423 6.7043E-05 0.00152278 0.119882
0.001721 30 2.665499 0.56536 16.23341 8.2638E-05 0.00183122
0.142216 0.00202 32 3.005765 0.641724 18.21633 0.00010158
0.00219681 0.168332 0.002366 34 3.38417 0.727202 20.41082
0.00012453 0.00262914 0.198808 0.002766 36 3.804376 0.822735
22.83606 0.00015227 0.00313927 0.234297 0.003226 38 4.27033
0.929342 25.51263 0.0001857 0.00373984 0.275539 0.003756 40
4.786289 1.048132 28.46262 5.0002259 0.00444535 0.32337 0.004365 42
5.35683 1.180302 31.70966 0.00027411 0.00527239 0.378735 0.005063
44 5.986876 1.327152 35.27905 0.00033181 0.00623986 0.442695
0.005861 46 6.681712 1.490081 39.19781 0.0004007 0.00736929
0.516447 0.006772 48 7.447002 1.670602 43.4948 0.00048275
0.00868514 0.60133 0.007811 50 8.288317 1.870345 48.20076
0.00058060 0.01021516 0.698848 0.008994 52 9.213651 2.091064
53.34844 0.0006959 0.01199077 0.810682 0.010337 54 10.22844
2.334645 58.97271 0.00083272 0.01404748 0.938705 0.011862 56
11.3406 2.603114 65.1106 0.00099428 0.01642535 1.085015 0.013588 58
12.55803 2.898642 71.80144 0.00118466 0.01916951 1.251936 0.01554
60 13.88914 3.223559 79.08693 0.00140849 0.02233068 1.442059
0.017744 62 15.34289 3.580357 87.0113 0.00167118 0.02596582
1.658254 0.020228 64 16.9288 3.971698 95.62132 0.00197885
0.03013876 1.903705 0.023026 66 18.657 4.40043 104.9665 0.00233849
0.03492093 2.181935 0.026168 68 20.53822 4.869588 115.0991
0.0027581 0.04039211 2.496832 0.029695 70 22.58382 5.382408
126.0745 0.00324674 0.04664131 2.852692 0.033648 72 24.80587
5.942338 137.9507 0.00381474 0.05376768 3.254243 0.038073 74
27.21711 6.553044 150.7893 0.0044738 0.06188147 3.706692 0.043018
75 29.83104 7.218422 164.6549 0.00523715 0.07110513 4.215756
0.048538 78 32.66188 7.94261 179.6154 0.00611977 0.08157446
4.787713 0.05469 80 35.72466 8.729997 196.7424 0.00713853
0.09343985 5.429442 0.061539 82 39.03525 9.585236 213.1111
0.00831246 0.1088676 6.148473 0.069154 84 42.61032 10.51325
231.8001 0.00966297 0.12204139 6.953039 0.07761 86 46.46747
11.51926 251.8923 0.01121407 0.13916381 7.85213 0.086988 88
50.62518 12.60877 273.4743 0.01299273 0.15845801 8.855551 0.097376
90 55.10289 13.7876 296.6367 0.01502912 0.18016849 9.973985
0.108869 92 59.92101 15.0619 321.4747 0.01735699 0.20456799
11.21905 0.12157 94 66.10096 16.43814 343.0974 0.02001401
0.23194948 12.60339 0.13559 96 70.66521 17.92315 376.5787
0.02304219 0.26263841 14.14071 0.151048 98 76.6373 19.52411
407.0568 0.02648683 0.29698993 15.84589 0.168073 100 83.04189
21.24858 439.6349 0.03040437 0.33539237 17.73503 0.186802 102
89.90476 23.10452 474.4309 0.03484814 0.37826988 19.82559 0.207386
104 97.25291 25.10027 511.5676 0.03988367 0.42608517 22.13642
0.229982 106 105.1145 27.2446 551.173 0.04558191 0.47934249
24.68786 0.254762 108 113.519 29.5467 593.3803 0.05202133 0.5385907
27.5019 0.28191 110 122.4971 32.01621 638.3279 0.05928865
0.60442664 30.6022 0.311621 112 132.0809 34.66322 686.16 0.06747953
0.67749857 34.01426 0.344105 114 142.3037 37.4983 737.0261
0.07669943 0.75850993 37.7655 0.379586 116 153.2004 40.5325
791.0814 0.08706443 0.8482232 41.8854 0.418304 118 164.8071
43.77739 848.4872 0.09870215 0.94746405 46.4056 0.460514 120
177.1615 47.24503 909.4106 0.11175278 1.05712567 51.36005 0.606488
122 190.3028 50.94804 974.0247 0.1263701 1.17817339 56.78515
0.556515 124 204.2716 54.89955 1042.509 0.14272263 1.31164942
62.71985 0.610904 126 219.1103 59.11329 1115.049 0.16099483
1.45867799 69.20584 0.669982 128 234.8627 63.60355 1191.838
0.1813584 1.62047064 76.2877 0.734098 130 251.5742 68.38522
1273.073 0.20412368 1.7983318 84.01303 0.80362 132 269.2921
73.47379 1358.96 0.22944104 1.99366466 92.43263 0.878942 134
288.0653 78.88538 1449.712 0.25760255 2.20797727 101.6007 0.960477
136 307.9443 84.63675 1545.548 0.28889355 2.44288902 111.5749
1.048667 138 328.9815 90.74531 1646.594 0.32362446 2.70013731
122.4168 1.143977 140 351.2313 97.22913 1753.383 0.36213262
2.98158457 134.1917 1.246899 142 374.7495 104.107 1865.856
0.40478433 3.28922564 146.9691 1.357953 144 399.5941 111.3985
1984.361 0.45197688 3.62519537 160.8229 1.477689 146 425.8251
119.1236 2109.153 0.50414083 3.99177661 175.8315 1.606687 148
453.5041 127.3034 2240.495 0.56174232 4.39140857 192.0779 1.745559
150 482.6949 135.9595 2378.658 0.62528561 4.82669541 209.6503
1.894949 152 513.4633 145.1144 2523.92 0.69531563 5.3004153
228.6419 2.055536 154 545.8771 154.7913 2676.567 0.77242081
5.81552975 249.1517 2.228034 156 580.0063 165.0142 2836.893
0.85723599 6.37519336 271.284 2.413196 158 615.9227 175.8079
3005.202 0.95044545 5.98276392 295.1493 2.611811 160 653.7005
187.1982 3181.803 1.05278619 7.64181289 320.8642 2.82471 162
693.4161 199.2114 3367.014 1.1650513 8.35613626 348.5519 3.052765
164 735.1478 211.875 3561.163 1.28809355 9.12976584 378.3422
3.296889 166 778.9765 225.2172 3764.585 1.42282911 9.96698085
410.3721 3.558042 168 824.985 239.2671 3977.623 1.57024154
10.8723201 444.7858 3.837229 170 873.2587 254.0547 4200.631
1.73138585 11.8505943 481.7353 4.135503 172 923.885 269.611
4433.968 1.90739286 12.9068992 521.3804 4.453966 174 976.9538
285.9678 4678.004 2.09947371 14.0466286 563.8893 4.793772 176
1032.557 303.158 4933.118 2.30892459 15.2754884 609.4385 5.156127
178 1090.79 321.2152 5199.698 2.53713169 16.5995105 658.2137
5.542291 180 1151.75 340.1743 5478.138 2.78557635 18.0250676
710.4098 6.953581 182 1215.535 360.0709 5768.843 3.0558405
19.5588884 756.2311 3.391372 184 1282.248 380.9419 6072.229
3.34961223 21.2080727 825.892 6.857099 186 1351.994 402.8248
6388.718 3.66869166 22.9801076 889.6171 7.352256 188 1424.878
425.7586 6718.741 4.01499711 24.882884 957.8419 7.878405 190
1501.011 449.7829 7062.741 4.39057141 26.9247135 1030.213 8.437171
192 1580.504 474.9388 7421.167 4.79758851 29.1143452 1107.587
9.030245 194 1663.473 501.2679 7794.479 5.23836044 31.4609845
1190.035 9.65939 196 1750.033 528.8135 8183.147 5.71534437
33.9743104 1277.837 10.32644 198 1840.306 557.8195 8587.647
5.23115014 35.6644946 1371.29 11.0333 200 1934.412 587.7311
9008.469 6.78854788 39.5422211 1470.699 11.78194
[0182] Vapor pressure data for additional sources is as follows:
for Cu(hfac).sub.2, P=1 torr at 50.degree. C. and P=10 torr at
96.degree. C.; for Cu(acac).sub.2, P=0.01 torr at 100.degree. C.
and P=1 torr at 164.degree. C.; for Cu(tfa).sub.2, P=0.4 torr at
110.degree. C. and P=1 torr at 140.degree. C.; for Cu(fod).sub.2,
P=0.1 torr at 100.degree. C.
[0183] With the vaporizer 28 at a temperature of 180.degree. C., a
pressure of 2.8 torr is generated in the vaporization chamber 26
without significant decomposition of the TAETO. With this pressure
at the inlet to the delivery conduit 40, the process chamber 70 is
held at 800 to 900 millitorr. With this pressure differential,
about 1.0 sccm of TAETO vapor along with 1.5 sccm N.sub.2O are
delivered to a wafer heated to about 385.degree. C. Under these
conditions, a tantalum oxide film will grow at a rate of
approximately 75 to 80 angstroms per minute. The wafer is
pre-heated to about the deposition temperature or higher either in
a preheat module or, less desirably, in the process chamber 70.
Direct thermal coupling between the wafer and the substrate chuck
74 is nominal. Heat is transferred between the wafer and the
substrate chuck 74 primarily by way of helium gas flowing between
the substrate chuck 74 and the underside of the wafer.
[0184] In one embodiment, a target film thickness of 100 angstroms
is achieved by running the process for 10 seconds at a reduced flow
of reactants to seed the wafer with tantalum oxide. The process is
then run for 75 seconds at full flow to build the desired film
thickness.
[0185] The deposition rate can be either reduced or slightly
increased. An increase in the deposition rate may require an
increase in the temperature of the vaporizer 28. The temperature of
the vaporizer 28, however, should generally be limited to
190.degree. C. for TAETO because there is a risk that the quality
of the deposited film will suffer as a result of TAETO
degradation.
[0186] If the temperature of the vaporizer 28 is reduced to
170.degree. C., the net effect will be a reduction in the rate of
TAETO deposition. The maximum pressure available at the inlet to
the vapor-flow-control subsystem 14 would be reduced to about 1.73
torr. This reduction will nearly halve the possible flow rate and
will result in a process pressure of about 450 millitorr. The
reduced process pressure will yield a deposition rate of about
22-25 angstrom per minute.
[0187] As the TAETO vaporizes, it expands within the principal
cylinder 30 and vapor outlet 32 of the vaporization chamber 26. All
components, including valves and pressure sensors, within the
vaporization chamber 26 and delivery conduit 40 are maintained at
the temperature of the vaporizer 28 to prevent the TAETO from
condensing. As the pressure in the vaporization chamber 26 is
depleted by the flow of vapor through the delivery conduit 40 and
into the process chamber 70, the pressure in the vaporization
chamber 26 is reestablished by dispensing more TAETO from the
reservoir 20 onto the heated vaporizer 28. While the vaporization
subsystem 12 can operate continuously to maintain a pressurized
supply of TAETO in the vaporization chamber 26, it will preferably
maintain a low vapor pressure within the chamber 26 until a demand
is signaled by the processor. When no demand is signaled, the
vaporization chamber 26 will be purged of TAETO and evacuated.
[0188] This cyclic process is established to accommodate the
thermal sensitivity of the precursor (in this case, TAETO). The
precursor, if held at an elevated temperature for any length of
time, will decompose before delivery into the process chamber
70.
[0189] Further, with careful selection of precursors, the apparatus
and method of this invention allow the sequential deposition of
different but complementary materials in the same chamber without
moving the wafer. As a result, multiple deposition steps can be
performed without wafer movement and the accompanying cycles of
pump down, purge, vent up to atmospheric pressure, and wafer heat
up.
[0190] Complementary processes thus far identified include the
following: titanium nitride (TiN) from TiBr.sub.4 or TDEAT and
ammonia, followed by aluminum from DMAH; tantalum nitride (TaN)
from TaBr.sub.4 and ammonia, followed by copper from
Cu.sub.I(hfac)(tmvs); and titanium nitride (TiN) from TiBr.sub.4 or
TDEAT, and ammonia, followed by aluminum from DMAH, followed by 0.5
atomic percent copper from Cu.sub.I(hfac)(tmvs).
[0191] The CVD apparatus 10 is also suitable for depositing barium
titanate, barium strontium titanate, strontium bismuth tantalate,
and other similar depositions.
[0192] The apparatus and method of this invention, and many of the
processes, described above, are particularly relevant to
semiconductor processing procedures. More particularly, the
apparatus and method of this invention are well suited to the
deposition of advanced dielectrics and interconnect metals on a
wafer.
[0193] A cluster tool 120 for semiconductor processing is
illustrated in FIG. 15. The illustrated cluster tool 120 includes a
number of process modules assembled around a transport module 122
and interfaced with a central control system. Alternatively, the
cluster tool 120 can have an inline, rather than radial geometry of
process modules in relation to the transport module 122. One or
more of these process modules include a CVD apparatus 10 of this
invention. In addition to the CVD apparatus 10 of this invention,
the cluster tool 120 includes an entrance load lock 126, an exit
load lock 128, a preheat module 130, a cool module 132, and a
transport module 122. In the illustrated embodiment, three CVD
apparatus 10, which can operate in parallel to enhance throughput,
are provided. These modules can be operated sequentially in series,
or in parallel. The cluster tool 120 is designed in accordance with
MESC, the standard design architecture adopted by the Semiconductor
Equipment and Materials International (SEMI), a trade organization
of semiconductor industry suppliers. Accordingly, a variety of
other standardized components, such as process modules for
different deposition and etch processes, can be readily integrated
into the cluster tool 120, as desired.
[0194] Each process module in a cluster tool 120 is generally
designed to process a single wafer at a time. Typical production
requirements are for the tool 120 to process 60 wafers per hour.
This rate is achieved by implementing different process steps in
separate process modules clustered around the transport module 122.
The tool 120, illustrated in FIG. 15, is designed for a 300 mm
tantalum oxide process system, which uses an eight-sided transport
module 122 typically connected to three tantalum oxide CVD
apparatus 10. Optionally, the tool might also accommodate a rapid
thermal anneal (RTA) module. In an alternative embodiment, a
plurality of cluster tools 120 are interfaced together so that a
wafer can be sequentially passed between tools 120 for a series of
processing stages without ever removing the wafer from the vacuum
established within the cluster tools 120.
[0195] The operation of a cluster tool 120 commences with wafers
being loaded into an input cassette 136 in an entrance load lock
126. A robot arm 134 (available from Brooks Automation) in the
transport module 122 removes one wafer at a time from the input
cassette 136 and moves each wafer to an alignment station 138. At
the alignment station 138, a standard notch in each wafer is
precisely aligned before further processing, eliminating wafer
orientation effects within a process module and aiding in process
uniformity. Once aligned, the robot arm 134 moves the wafer to a
preheat module 130 where the wafer remains for approximately 30
seconds while being heated to 300-500.degree. C. When a CVD
apparatus 10 becomes available, the wafer is moved to the process
chamber of that CVD apparatus 10 for tantalum oxide deposition.
Deposition occurs over a period of approximately 120 seconds. After
deposition, the wafer is moved to the cool module 132, where the
wafer resides for 30 seconds and is cooled enough to place it in
the output cassette 140 in the exit load lock 128.
[0196] The process time for tantalum oxide deposition on a wafer is
on the order of 120 seconds for a 0.01-micron-thick film on a
preheated wafer. Wafer movement from the input cassette 136, to the
alignment station 138, to a CVD apparatus 10 and back to an output
cassette 140 will consume approximately another ten seconds. The
cluster tool 120, with three tantalum oxide CVD apparatus 10, would
have a throughput of one wafer every 45 seconds, excluding ramp-up
and ramp-down. The tool 120 in this configuration can process up to
75 wafers per hour.
[0197] In this context, the deposition process is used to form
integrated circuits on the wafer. An integrated circuit is simply a
large number of transistors, resistors, and capacitors connected
together by metal lines. A general goal is to miniaturize the
components to the greatest extent possible.
[0198] FIG. 16 illustrates a configuration of the invention in
which multiple cluster tools 120a and 120b are arranged to process
wafer in conjunction with each other. Wafer handoff mechanism 701
can pass wafers from transport module 122a in cluster tool
controller 120a to an entire second cluster tool controller 120b.
Wafer handoff mechanism 701 may be, for example, a conveyor-belt
apparatus which transports the wafers 88 from the robot arm 134a to
the second robot arm 134b of transport module 122b. Alternatively,
the wafer handoff mechanism 701 can be accomplished by physically
passing individual wafers 88 from robot arm 134a to robot arm
134b.
[0199] The CVD apparatus 10a-c in FIG. 16 may be used for a certain
processing of the wafers, and when complete, the wafers can be
transported, through wafer handoff mechanism 701, to the second
configuration of CVD apparatus 10d-f and secondary transport module
122b for a second type of processing. During the entire processing
of wafers by the configuration in FIG. 16, the wafers may be
maintained under a vacuum and may be maintained at a relatively
constant temperature. Since the cluster tools 120a and 120b are an
entirely closed system, wafers experience reduced exposure to
contamination and outside atmosphere while being processed.
[0200] The large scale wafer processing illustrated in FIG. 16 is
referred to herein as a factory automation wafer processing system.
According to one aspect of factory automation processing in this
invention, the entire set of CVD apparatus 10a-f, transport modules
122a and 122b, and cluster tools 120a and 120b may all be
controlled by a single factory automation controller 702 which
handles all scheduling of wafer processing from beginning to end.
Factory automation controller 702 contains a master central
processing unit that governs the operation of each cluster tool
120a and 120b. Data bus 703 interconnects each CVD apparatus 10a-f
with factory automation controller 702.
[0201] FIG. 17 illustrates an alternative configuration for a
factory automated CVD processing system. In FIG. 17, the individual
components (i.e., CVD apparatus 10, preheat modules 130, cooling
modules 132, transport modules 122) of each cluster tool 120a and
120b are controlled by separate cluster tool controllers 705a and
705b. Factory automation controller 702 controls each cluster tool
controller 705a and 705b, and can control wafer handoff mechanism
701.
[0202] In yet another alternative embodiment, one of the cluster
tool controllers, for example, 120a, can control the wafer handoff
mechanism 701 and can signal to the other cluster tool 120b that it
has completed its wafer processing and that wafer are on route via
wafer handoff mechanism 701 and should be accepted by robot arm
134b.
[0203] Each of these arrangements are shown by way of example only,
and the invention is not limited to only two cluster tools in the
factory automation configurations shown in FIG. 16 and 17. Rather,
there may be many cluster tools arranged in any number of ways,
each having a cluster tool controller which is controlled by one or
more master factory automation controllers. By distributing
processing as shown in these examples, real-time wafer processing
can be accomplished from beginning to end in a more efficient,
clean, and timely manner.
[0204] FIG. 18 illustrates an example of the typical steps involved
in controlling a single cluster tool 120a via cluster tool
controller 705a, as illustrated in FIG. 17. In step 710, robotic
arm 134a accepts a wafer from the input cassette 136a, which is
attached to the entrance load lock 126a. The robotic arm 134, in
step 711, then aligns the wafer on the armature itself.
[0205] Wafer alignment on the robotic arm 134 is performed at the
alignment station 138, where a notch in the side of the wafer is
mechanically aligned with a reference indicator.
[0206] Once the wafer is correctly oriented, in step 712, which is
an optional step, the wafer may be pre-heated in pre-heat module
130. Heating the wafer brings the wafer up to a temperature at or
near the operating or substrate chuck temperature of the first CVD
apparatus 10 that will accept the wafer. Next, the robotic arm 134,
in step 713, places the wafer into one of the CVD apparatus 10a-c
of the current cluster tool controller 120a for CVD processing in
step 714, as explained above. While three CVD apparatus 9a through
10c are illustrated in FIG. 16, the invention is not limited to
three, and there may be one, two, three or many more such system
all accessible by a single robotic arm 134. After the wafer has
completed CVD processing in step 714 in CVD apparatus 9a, in step
715, the robotic arm extracts the wafer. Next, the wafer either
moves to the next CVD apparatus (i.e., back to step 713), or
finishes processing (step 716) by being cooled in cool module 132
and exiting the cluster tool 12a via output cassette 140, or the
wafer is passed to another cluster tool 120b via wafer handoff
mechanism 701 (step 717). Generally, wafer processing repeats until
the correct sequence of heating, CVD processing and cooling has
been performed, as dictated by the wafer processing program
executing in cluster tool controller 705a controlling the operation
of cluster tool 120a.
[0207] The fabrication of electronic devices using methods of
semiconductor processing are attempting to build these structures
with the smallest possible features. Accordingly, it is desirable
that the transistors, interconnects, capacitors, and resistors, for
example, occupy as little space on the wafer surface as possible,
providing more devices per wafer and reducing costs. As the size of
features decreases, new materials are often needed to maintain the
proper conductivity of the finer lines and the properties of both
active and passive components.
[0208] The apparatus of this invention is specifically intended for
the deposition of thin films of metals, dielectric layers used as
insulators for these metals, low-k interlayer dielectric layers,
capacitor dielectrics (denoted as high-k), and transistor gate
dielectrics required for 0.25 micron or smaller linewidth
processes. The processes can be used to form integrated circuits
with clock speeds of 400 MHZ or faster and 256 Mbit or more DRAM,
for example.
[0209] Semiconductor deposition processes that can be performed
with a cluster tool 120 incorporating a CVD apparatus 10 of this
invention include the deposition of high-k capacitor dielectrics
such as tantalum oxide; the deposition of layers that serve as
barriers and adhesions promoters, like titanium nitride, a liner
used for aluminum, and tantalum nitride, a copper liner; and the
deposition of copper metal for interconnects.
[0210] Further, the methods and apparatus of this invention are
particularly suitable for the deposition of stacked gate
dielectrics. This procedure can involve successive deposition of
layers of thin films (on the order of 15 angstroms for each film)
including two or more different dielectrics to minimize gate
capacitance. Stacked dielectric gates can be used in devices with
geometries of less than 0.15 microns and in devices with geometries
of up to 0.25 microns, where an increase in speed beyond 400 MHZ is
needed, for example. Stacked gate dielectrics can be formed of
silica along with either silicon nitride or tantalum oxide. Other
dielectric materials can also be used, provided that they achieve a
desired dielectric transistor gate.
[0211] An illustration of a device (specifically, an NMOS
transistor) formed by methods of this invention is provided in FIG.
26. The device includes a silicon substrate 1052; a source 1054
formed by ion implantation or diffusion; a drain 1056 formed by ion
implantation or diffusion; a pair of channel stops 1056 also formed
by ion implantation; a gate dielectric 1058 (which can comprise,
e.g., silica) deposited in accordance with methods of this
invention; a gate metallization film 1060, which can be formed of
polysilicon or formed of copper or aluminum deposited in accordance
with methods of this invention; an insulator dielectric 1062
(typically, silica) formed by thermal oxidation; an insulator
dielectric 1064 (typically silica) deposited in accordance with
methods of this invention; and a metallization film 1066
(comprising, e.g., copper, aluminum, or copper/aluminum) deposited
in accordance with methods of this invention.
[0212] Further still, the methods and apparatus of this invention
offer advantages in the processing of stacked dielectrics, where
sequential deposition of two different dielectrics is generally
required. The design of a precursor delivery system, in accordance
with this invention, allows deposition of both materials in the
same process chamber. As a result, the wafer will not be exposed to
random oxidation during transport between chambers, which can
destroy the gate. Further, because the wafer need not be moved, the
system is expected to have an intrinsically higher throughput than
existing systems. Background discussion directed to the synthesis
of stacked gate dielectrics is provided in P. K. Roy, et al.,
"Stacked High-.di-elect cons. Gate Dielectric for Gigascale
Integration of Metal-Oxide-Semiconductor Technologies," 72 Applied
Physics Letters 2835 (Jun. 1, 1998), which is incorporated herein
by reference in its entirety.
[0213] Other materials that can be suitably deposited on
semiconductor wafers with an apparatus and method of this invention
include aluminum, aluminum/copper (an alloy with reduced liner
requirements), barium titanate (a potential high-k dielectric
film), and barium strontium titanate (another high-k dielectric
film).
[0214] An integrated gate oxide cluster tool 920 designed
specifically for semiconductor gate dielectric deposition is
illustrated in FIG. 22. The tool 920 includes an etch module 951.
The etch module 951, like the other modules, operates at low power.
The etch module 951 is used for preheating and soft etching to
provide a surface that is free or nearly-free of atomic residue.
The tool also includes a pair of process modules 910d for silica
deposition, a pair of process modules 910e for tantalum oxide
deposition and a single process module 910f for titanium nitride
deposition.
[0215] Processing within the tool 920 of FIG. 22 proceeds as
follows. A gate to the entrance load lock 926 is lifted and the
wafer handler robot arm 934 mounted in a transport module 922
retrieves a silicon wafer from the stack of wafers in the entrance
load lock 926. The wafer handler robot arm 934 first delivers the
wafer to the etch module 951. After the wafer is preheated and soft
etched in the etch module 951, the robot arm 934 retrieves the
wafer and advances it to one of the silica deposit modules 910d,
where vaporized TEOS is reacted with N.sub.2O to form a silica
deposit on the wafer. After deposition in the silica deposit module
910d is completed, the robot arm 934 retrieves the wafer and
advances it to a tantalum oxide deposit module 910e, where N.sub.2O
is reacted with vaporized TAT-DMAE or with vaporized TAETO to form
a tantalum oxide layer on the silica layer. Next, the robot arm 934
retrieves the wafer and advances it to the titanium nitride deposit
module 910f where TiBr.sub.4 or TDEAT and ammonia are reacted to
form a thin TiN.sub.x capping material on top of the tantalum oxide
layer. Finally, the robot arm 934 again retrieves the wafer and
advances it to the exit load lock 928 for later removal from the
tool 920.
[0216] An integrated aluminum/copper tool 1020 for depositing
aluminum and copper metallization films is illustrated in FIG. 23.
The tool 1020 includes a titanium nitride deposit module 1010g, a
copper deposit module 1010h, two aluminum deposit modules 1010i, as
well as transport module 1022, entrance and exit load locks 1026
and 1028, a preheat/etch module 1051, and a wafer handler robot arm
1034. The tool 1020 is used to deposit a titanium nitride
liner/barrier layer on a silicon wafer followed by successive
depositions of copper and aluminum.
[0217] Copper thin films are emerging as important metallization
films for integrated circuits, and the level of importance
increases as integrated circuit manufacturers introduce products
with copper metallization. Further, more are likely to follow this
lead as linewidths shrink from 0.25 to 0.18 to 0.15 to 0.12 to 0.1
microns. The "transition" technology for significant implementation
of copper metallization is likely to be at 0.13 micron design
rules.
[0218] Integrated circuit linewidths shrink at approximately a
factor of 0.7 per generation. This allows for an approximate
doubling of the density of circuit elements (transistors) with each
generation. This needs to occur at a rate of one every 12 to 18
months to keep the semiconductor industry moving along the
generally accepted Moore's Law curve of doubling performance and
halving cost every one to two years. As circuit size shrinks, the
need to carry electrical signals remains relatively constant, but
as the linewidths shrink, metallization conductivity decreases
because the cross-sectional area of the metal lines decreases. This
requires some combination of thicker metal or more metallization
lines/levels to be implemented on the circuit. An alternative is to
use a higher conductivity metal. Currently, Al is the
industry-standard metallization material. Alternative materials and
their comparison resistivities are:
2 Resistivity (micro- Material ohm-cm) Comments Aluminum (Al) 2.8
Standard industry practice Copper (Cu) 1.7 Implemented Silver (Ag)
1.6 Corrosion risks Gold (Au) 2.4 Contamination risks
[0219] Copper offers significant improvement in resistivity and is
being implemented with what is known as damascene processing due to
the impracticality of dry-etching Cu. Copper is an undesirable
contaminant to silicon integrated circuits, but less so than gold.
To prevent contamination, Cu metallization films are isolated from
the silicon using appropriate line/barrier layers such as
TiN.sub.x, TaN.sub.x or WN.sub.x. Additionally, it is typically
required that the copper be deposited in a fashion that will fill
high aspect ratio features during integrated circuit fabrication.
The liner/barrier layers must also coat these high aspect ratio
features prior to the copper deposition.
[0220] A complete copper deposition process currently consists of
three sequential discrete steps. First, a liner/barrier layer (not
copper) is deposited. Second, a thin copper layer, called the
"seed" layer is deposited on the liner/barrier layer. Third, a
thicker copper layer, called the "fill" layer is deposited.
[0221] The liner/barrier layer deposition is typically done by
physical vapor deposition (PVD, sputtering) but can also be done by
CVD. This layer may typically be 10 to 100 nm thick. The seed layer
is also typically done by PVD but can also be done by CVD and also
is typically between 10 and 100 nm thick.
[0222] The advantage of depositing these layers by CVD is better
conformability for the coverage of high aspect ratio features
relative to PVD. However, CVD is typically more costly than PVD due
partially to equipment complexity and throughput, but mostly due to
the cost of starting source materials. A copper metal "target" is
used as the Cu source in PVD. The most widely accepted source
material for Cu deposition by CVD is Schumacher CupraSelect.TM.
copper source, which is Cu(hfac)(TMVS), or
C.sub.10H.sub.13CuF.sub.6O.sub.2Si, in which a Cu atom is attached
to a molecule of hexaflouroacetylacetonate (hfac, or
CF.sub.3COCHCOCF.sub.3) and to a molecule of trimethylvinylsilane
(TMVS, or C.sub.5H.sub.12Si). This material is unstable and
difficult to work with and is relatively expensive at a cost of up
to approximately $20 per gram. The fill layer, typically 100 to 300
nm thick, is currently typically deposited by an electroplating
process, although CVD and PVD are alternatives. The PVD process is
not a practical alternative, however, due to the need to
conformally fill high aspect ratio features, as the PVD process is
inherently directional. Electroplating offers conformal deposition,
but is done using a wet process which is against industry trends.
Consequently, CVD is a preferred process due to conformality,
similarity with other industry processes, and comparability with
the seed layer deposition process.
[0223] The methods and apparatus of this invention, particularly
with respect to use of the unique precursor delivery system,
provide a preferred method and means for depositing copper seed and
fill layers, as well as liner/barrier layers.
[0224] The methods and apparatus of this invention are unique in
that they allow stable ambient storage of the copper source
chemical (referred to as the precursor) while small amounts of the
pure precursor are introduced to the vaporizer unit. This
represents a unique approach to source vaporization for several
reasons. First, the source precursor is stored at an ambient
temperature at which it is stable so that the source is not subject
to premature decomposition. Second, only small amounts of the
source are introduced for vaporization and only on demand to
generate a sufficient source pressure to execute the transport of
sufficient precursor material, via the vapor-flow-control
subsystem, to produce the required film deposition. Third, the
vaporization of a small quantity of precursor allows the vaporizer
to function without risk of "clogging" due to the formation of a
"skin" of non-volatile vaporization by-products of a precursor
charge. This is a common experience with vaporization methods that
place a "large" quantity (or charge) of precursor in a vaporizer.
This is particularly true when using precursor sources in solid
form, as is likely to be a preferred method for copper CVD.
Generally, in the case of a liquid source, non-volatile materials
can dissipate in the liquid or be displaced, allowing an
appropriate exit path for the generated vapor. However,
non-volatile residues that form on the surface of a solid source
are not readily displaced and interfere with the free path of
vapor. This results in a "clogging" effect (or "poisoning" of the
vaporizer). Methods of this invention avoid this problem by
introducing small amounts of precursor on-demand via a process
control loop, whereby liquid precursors wick along a smooth conical
surface in order to enable vaporization and solid precursors are
dissipated along a stepped conical surface and vaporized. Residual
material left on the stepped conical surface is covered by newly
added material as introduced on-demand by the process control loop.
This is a method of a non-clogging (non-poisoning) precursor
vaporizer.
[0225] In the deposition of copper films in accordance with this
invention, a precursor, such as CuTMVS (CupraSelect.TM.),
Cu(hfac).sub.2, Cu(tfa).sub.2, or Cu(fod).sub.2, will be vaporized
and delivered to the deposition chamber in a controlled fashion
through the vapor-flow-control subsystem. The vapor-flow-control
subsystem, the deposition chamber walls, and other fixtures and/or
plumbing are maintained at or above the same temperature as the
vaporizer to insure that there is no condensation of the generated
precursor vapors in the system prior to the vapors impinging on the
heated substrate (e.g., a silicon wafer) onto which the copper film
is to be deposited. The advantage of the specified precursor
chemicals (and other potential copper source precursor chemicals)
relative to CupraSelect.TM. is that they are inherently more
stable. CupraSelect.TM. is an unstable material that will
degrade/decompose at ambient room temperature and above. All these
materials are intended to be deposited at a substrate (silicon
wafer) temperature of generally between 150.degree. C. and
300.degree. C., although the range can extend beyond these
temperatures depending on the specific precursor.
[0226] It is expected that the copper deposition with the specified
precursors will be thermally induced and will proceed without a
need for other reactants. However, the process may be enhanced by
the introduction of hydrogen gas (H.sub.2) remotely-ionized
hydrogen, or water vapor. Means are provided in the apparatus of
this invention for introducing such reactants (or process-assisting
agents) through a separate gaseous source line.
[0227] The use of pure precursor vapor, due to the inherent
avoidance of a carrier gas in methods of this invention and the
intended omission of a reactant gas, will result in a higher
deposition efficiency than that of other copper CVD processes that
require such gases (and, hence, greatly dilute the precursor flow).
This will result in improved utilization (efficiency) of the
precursor chemical. The table, below, shows a cost comparison for
the deposition of Copper films using known source pricing from
commercial vendors. A 10% efficiency is assumed to be
representative of the methods of this invention while a 3%
efficiency is assumed to be representative of other CVD processes
that utilize a carrier gas (or other effective dilutant) in the CVD
process. The relative cost comparison for the precursor source is
provided in the accompanying chart.
3 acac hfac tfa CupraSelect Source Copper "A" Copper "B" Copper "C"
.TM. Molecular 261.76 477.64 369.7 370.83 weight Cumoleoweight
63.54 63.54 63.54 63.54 Wt % Cu 24.27% 13.30% 17.19% 17.13% Source
$/g $0.19 $1.10 $1.92 $2.75 Cu $/g $0.79 $8.27 $11.17 $16.05
equivalent Relative source 1 10.45415 14.12362 20.290981 cost Grams
0.01 0.01 0.01 0.01 Cu/100 nm dep Cu cost per dep $0.01 $0.08 $0.11
$0.16 Cost at 10% $0.08 $0.83 $1.12 $1.60 efficiency Cost at 3%
$0.26 $2.76 $3.72 $5.35 efficiency
[0228] The cost ratio for this invention, calculated in terms of
the cost of Cu(acac) versus the cost of CuTMVS CVD is 67.6366. A
relative cost comparison for the different copper sources is
illustrated in FIG. 25.
[0229] In the deposition of copper utilizing the methods of this
invention, it is anticipated that the deposition will be carried
out at a process pressure of between 0.01 and 100 torr, with a
nominal process pressure of approximately 1 torr. The vaporizer
pressure will be set at slightly above the deposition process
pressure. The substrate (silicon wafer) will be heated via the
heated wafer chuck (or support). The wafer chuck will be moved to
its selected position for deposition and the precursor will be
introduced in a controlled fashion through the vapor-flow-control
subsystem. The precursor flow will be terminated after a specific
period of time or some other condition, and the wafer chuck lowered
to the wafer transport position.
[0230] Likely vaporizer set points for specific copper sources are
set by targeting the 1 to 10 torr precursor vapor pressure range,
though other vapor pressure ranges may be equally effective.
Representative vaporizer operating temperature set points for
generating a range of vapor pressures are provided in FIG. 24,
which indicates published vapor pressure data for several selected
copper precursors. Based on this data, a vaporizer can be operated
at 60.degree. C. to 70.degree. C. for CupraSelect.TM. (represented
by the curve in FIG. 24 and limited in the upper range by the
inherent thermal instability of this material), 50.degree. to
100.degree. C. for Cu(hfac).sub.2 (represented by diamonds),
140.degree. to 200.degree. C. for Cu(tfa).sub.2 (represented by
triangles), and 160.degree. to 200.degree. C. for Cu(acac).sub.2
(represented by the square). More specifically, the vapor pressure
curve for CupraSelect.TM. can be expressed as follows:
Log P.sub.torr=-3.39 (10.sup.3/T.sub.K)+10.33.
[0231] The CVD apparatus and methods of this invention can also be
used to deposit organic materials such as photoresist or organic
light emitting diode (LED) materials. Further, organometallic
arsenic and/or phosphorous sources can be deposited via the
apparatus and methods of this invention. Further still trimethyl
indium (TMI) or other materials for compound semiconductor
epitaxial crystal growth can be delivered with this invention.
[0232] Other suitable applications for the CVD apparatus and
methods of this invention include processing of flat panel displays
and coated drill bits. Further still, the apparatus and methods of
this invention can be used to deposit optical dielectric coatings,
anti-reflection coatings, and coatings to reduce friction and
wear.
[0233] While this invention has been particularly shown and
described with references to preferred embodiments thereof, those
skilled in the art will understand that various changes in form and
details may be made therein without departing from the scope of the
invention as defined by the appended claims.
* * * * *