U.S. patent application number 11/422212 was filed with the patent office on 2006-10-12 for use of enhanced turbomolecular pump for gapfill deposition using high flows of low-mass fluent gas.
This patent application is currently assigned to Applied Materials, Inc.. Invention is credited to Steven H. Kim, Muhammad M. Rasheed.
Application Number | 20060225648 11/422212 |
Document ID | / |
Family ID | 37081942 |
Filed Date | 2006-10-12 |
United States Patent
Application |
20060225648 |
Kind Code |
A1 |
Rasheed; Muhammad M. ; et
al. |
October 12, 2006 |
USE OF ENHANCED TURBOMOLECULAR PUMP FOR GAPFILL DEPOSITION USING
HIGH FLOWS OF LOW-MASS FLUENT GAS
Abstract
High flows of low-mass fluent gases are used in an HDP-CVD
process for gapfill deposition of a silicon oxide film. An enhanced
turbomolecular pump that provides a large compression ratio for
such low-mass fluent gases permits pressures to be maintained at
relatively low levels in a substrate processing chamber, thereby
improving the gapfill characteristics.
Inventors: |
Rasheed; Muhammad M.;
(Fremont, CA) ; Kim; Steven H.; (Union City,
CA) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW LLP / AMAT
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
Applied Materials, Inc.
Santa Clara
CA
|
Family ID: |
37081942 |
Appl. No.: |
11/422212 |
Filed: |
June 5, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10884628 |
Jul 1, 2004 |
|
|
|
11422212 |
Jun 5, 2006 |
|
|
|
Current U.S.
Class: |
118/692 ;
257/E21.279 |
Current CPC
Class: |
H01L 21/31612 20130101;
H01L 21/02164 20130101; C23C 16/045 20130101; H01L 21/02274
20130101; C23C 16/4412 20130101 |
Class at
Publication: |
118/692 |
International
Class: |
B05C 11/00 20060101
B05C011/00 |
Claims
1. A substrate processing system comprising: a housing defining a
substrate processing chamber; a substrate holder configured to hold
a substrate within the substrate processing chamber during
substrate processing; a gas-delivery system configured to introduce
gases into the substrate processing chamber; a high-density plasma
generating system operatively coupled to the substrate processing
chamber to generate a plasma having at least 10.sup.11
ions/cm.sup.3 from gases in the substrate processing chamber; and a
pressure-control system for maintaining a selected pressure within
the substrate processing chamber, the pressure-control system
including a pump in fluid communication with an outlet of the
substrate processing chamber and providing a compression ratio
greater than 10.sup.5 for a gas of molecules having an average
molecular mass less than 10 atomic mass units.
2. The substrate processing system recited in claim 1 wherein the
pump is a turbomolecular pump.
3. The substrate processing system recited in claim 1 wherein the
pump provides a compression ratio for H.sub.2 between 10.sup.5 and
10.sup.6.
4. The substrate processing system recited in claim 1 wherein the
pump provides a compression ratio for He between 10.sup.6 and
10.sup.7.
5. The substrate processing system recited in claim 1 wherein the
pump provides a pumping speed that exceeds 2800 L/s for the gas of
molecules having an average molecular mass less than 10 atomic mass
units.
6. The substrate processing system recited in claim 5 wherein the
pumping speed is between 2800 and 3500 L/s for a gas selected from
the group consisting of H.sub.2 and He.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of U.S. patent application
Ser. No. 10/884,628, entitled "USE OF ENHANCED TURBOMOLECULAR PUMP
FOR GAPFILL DEPOSITION USING HIGH FLOWS OF LOW-MASS FLUENT GAS,"
filed Jul. 1, 2004 by Muhammad M. Rasheed, the entire disclosure of
which is incorporated herein by reference for all purposes.
BACKGROUND OF THE INVENTION
[0002] One of the primary steps in the fabrication of modern
semiconductor devices is the formation of a film, such as a silicon
oxide film, on a semiconductor substrate. Silicon oxide is widely
used as an insulating layer in the manufacture of semiconductor
devices. As is well known, a silicon oxide film can be deposited by
a thermal chemical-vapor deposition ("CVD") process or by a
plasma-enhanced chemical-vapor deposition ("PECVD") process. In a
conventional thermal CVD process, reactive gases are supplied to a
surface of the substrate, where heat-induced chemical reactions
take place to produce a desired film. In a conventional
plasma-deposition process, a controlled plasma is formed to
decompose and/or energize reactive species to produce the desired
film.
[0003] Semiconductor device geometries have decreased significantly
in size since such devices were first introduced several decades
ago, and continue to be reduced in size. This continuing reduction
in the scale of device geometry has resulted in a dramatic increase
in the density of circuit elements and interconnections formed in
integrated circuits fabricated on a semiconductor substrate. One
persistent challenge faced by semiconductor manufacturers in the
design and fabrication of such densely packed integrated circuits
is the desire to prevent spurious interactions between circuit
elements, a goal that has required ongoing innovation as geometry
scales continue to decrease.
[0004] Unwanted interactions are typically prevented by providing
spaces between adjacent elements that are filled with an
electrically insulative material to isolate the elements both
physically and electrically. Such spaces are sometimes referred to
herein as "gaps" or "trenches," and the processes for filling such
spaces are commonly referred to in the art as "gapfill" processes.
The ability of a given process to produce a film that completely
fills such gaps is thus often referred to as the "gapfill ability"
of the process, with the film described as a "gapfill layer" or
"gapfill film." As circuit densities increase with smaller feature
sizes, the widths of these gaps decrease, resulting in an increase
in their aspect ratio, which is defined by the ratio of the gap's
height to its depth. High-aspect-ratio gaps are difficult to fill
completely using conventional CVD techniques, which tend to have
relatively poor gapfill abilities. One family of electrically
insulating films that is commonly used to fill gaps in intermetal
dielectric ("IMD") applications, premetal dielectric ("PMD")
applications, and shallow-trench-isolation ("STI") applications,
among others, is silicon oxide (sometimes also referred to as
"silica glass" or "silicate glass").
[0005] Some integrated circuit manufacturers have turned to the use
of high-density plasma CVD ("HDP-CVD") systems in depositing
silicon oxide gapfill layers. Such systems form a plasma that has a
density greater than about 10.sup.11 ions/cm.sup.3, which is about
two orders of magnitude greater than the plasma density provided by
a standard capacitively coupled plasma CVD system. Examples of
HDP-CVD systems include inductively coupled plasma ("ICP") systems
and electron-cyclotron-resonance ("ECR") systems, among others. One
factor that allows films deposited by HDP-CVD techniques to have
improved gapfill characteristics is the occurrence of sputtering
simultaneous with deposition of material. Sputtering is a
mechanical process by which material is ejected by impact, and is
promoted by the high ionic density of the plasma in HDP-CVD
processes. The sputtering component of HDP deposition thus slows
deposition on certain features, such as the corners of raised
surfaces, thereby contributing to the increased gapfill
ability.
[0006] A variety of known techniques have often used to promote the
sputtering effect, and have proved successful for gaps with
relatively modest aspect ratios and widths. For example, one
technique to promote sputtering is to introduce argon or a similar
heavy inert gas to further promote the sputtering effect. Another
technique is to create an electric field that biases the plasma
towards the substrate, such as by using an electrode within a
substrate support pedestal to generate the electric field. It was
thus initially thought that the simultaneous deposition and
sputtering characteristics of an HDP-CVD process could be used to
fill the gaps that were created in almost any application.
Semiconductor manufacturers discovered, however, that there is a
practical limit to the aspect ratio of gaps that HDP-CVD films are
able to fill. For example, one HDP-CVD process commonly used to
deposit a silicon oxide gapfill film forms a plasma from a process
gas that includes silane SiH.sub.4, molecular oxygen O.sub.2, and
argon Ar. It has been reported that when such a process is used to
fill certain narrow-width, high-aspect-ratio gaps, the sputtering
caused by the argon in the process gas may hamper gapfill efforts.
Specifically, it has been reported that material sputtered by argon
in the process redeposits on the upper portions of the sidewalls of
the gaps being filled at a rate faster than at the lower portions.
This, in turn, may result in the formation of a void in the gap if
the upper areas of regrowth join before the gap is completely
filled.
BRIEF SUMMARY OF THE INVENTION
[0007] Embodiments of the invention make use high flows of low-mass
fluent gases in an HDP-CVD process for gapfill deposition of a
silicon oxide film. An enhanced turbomolecular pump that provides a
large compression ratio for such low-mass fluent gases permits
pressures to be maintained at relatively low levels in a substrate
processing chamber, thereby improving the gapfill
characteristics.
[0008] Thus, in one set of embodiments, a method is provided for
depositing a silicon oxide film over a substrate disposed in a
substrate processing chamber. The substrate has a trench formed
between adjacent raised surfaces. A process gas that comprises a
silicon source, an oxygen source, and a fluent gas is flowed into
the substrate processing chamber. The fluent gas has an average
molecular mass less than 10 atomic mass units and is flowed into
the substrate processing chamber with a flow rate that exceeds 400
sccm. A plasma having an ion density of at least 10.sup.11
ions/cm.sup.3 is formed from the process gas to deposit the silicon
oxide film over the substrate and within the trench. The process
gas is pumped from the substrate processing chamber with a pump hat
provides a compression ratio for the fluent gas that exceeds
10.sup.5.
[0009] In some such embodiments, the fluent gas comprises H.sub.2,
in which case the pump may provide a compression ratio for H.sub.2
between 10.sup.5 and 10.sup.6 in some instances. In other
embodiments, the fluent gas comprises He, in which case the pump
may provide a compression ratio for He between 10.sup.6 and
10.sup.7 in some instances. In still other embodiments, the fluent
gas comprises a plurality of molecules having different chemical
structures, at least some of the molecules being selected from the
group consisting of H.sub.2 and He. In different embodiments, the
flow rate for the fluent gas may also exceed 800 sccm or may exceed
1200 sccm. The silicon source may comprise SiH.sub.4 and/or the
oxygen source may comprise O.sub.2. In addition, in some instances,
the process gas may further comprise a dopant source to dope the
silicon oxide film.
[0010] In another set of embodiments, a method is also provided for
depositing a silicon oxide film over a substrate disposed in a
substrate processing chamber. The substrate has a trench formed
between adjacent raised surfaces. A process gas that comprises a
silicon source, an oxygen source, and a fluent gas is flowed into
the substrate processing chamber. The fluent gas has an average
molecular mass less than 10 atomic mass units and is flowed into
the substrate processing chamber with a flow rate that exceeds 400
sccm. A plasma having an ion density of at least 10.sup.11
ions/cm.sup.3 is formed from the process gas to deposit the silicon
oxide film over the substrate and within the trench. A chamber
pressure is maintained within the substrate processing chamber less
than 15 mtorr. In certain specific embodiments, different fluent
gases may be used with different flow rates, and certain specific
silicon and oxygen sources may be used, as described above. In some
embodiments, the chamber pressure may be maintained less than 10
mtorr or less than 5 mtorr.
[0011] Methods of the invention may be implemented using a
substrate processing system that comprises a housing defining a
substrate processing chamber. A substrate holder is configured to
hold a substrate within the substrate processing chamber during
substrate processing. A gas-delivery system is configured to
introduce gases into the substrate processing chamber. A
high-density plasma generating system is operatively coupled to the
substrate processing chamber to generate a plasma having at least
10.sup.11 ions/cm.sup.3 from gases in the substrate processing
chamber. A pressure-control system maintains a selected pressure
within the substrate processing chamber. The pressure-control
system includes a pump in fluid communication with on outlet of the
substrate processing chamber and provides a compression ratio
greater than 10.sup.5 for a gas of molecules having an average
molecular mass less than 10 atomic mass units.
[0012] The pump may be a turbomolecular pump. In a specific
embodiment, the pump provides a compression ratio for H.sub.2
between 10.sup.5 and 10.sup.6. In another specific embodiment, the
pump provides a compression ratio for He between 10.sup.6 and
10.sup.7. The pump may also provide certain pumping speeds for the
gas of molecules having an average molecular mass less than 10
atomic mass units. For instance, in one embodiment, that pumping
speed exceeds 2800 L/s. In another embodiment the pumping speed is
between 2800 and 3500 L/s for a gas selected from the group
consisting of H.sub.2 and He.
[0013] Embodiments of the invention also provide a method for
upgrading a semiconductor processing facility to accommodate a
high-density-plasma deposition process that uses a flow of a gas
having an average molecular mass less than 10 amu at a rate that
exceeds 400 sccm. The semiconductor processing facility includes a
high-density-plasma substrate processing system that has a
substrate processing chamber in fluid communication with a
turbomolecular pump, a rough pump, and a foreline. The
turbomolecular pump controls a pressure inside the substrate
processing chamber. The rough pump provides a pressure intermediate
between a desired operational pressure and atmospheric pressure.
The foreline provides fluid communication between the
turbomolecular pump and the rough pump. A pressure inside the
substrate processing chamber during the high-density-plasma
deposition process is determined. The foreline is reconfigured to
reduce a pressure at an outlet of the turbomolecular pump to the
foreline. The pressure inside the substrate processing chamber
during the high-density-plasma process is consequently reduced.
[0014] The foreline may be reconfigured by increasing a diameter of
at least a portion of the foreline, by reducing a number of bends
comprised by the foreline, and the like. In one embodiment, the
method further comprises upgrading a flow capacity of the rough
pump.
[0015] A further understanding of the nature and advantages of the
present invention may be realized by reference to the remaining
portions of the specification and the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIGS. 1A-1C are simplified cross-sectional views of a
silicon oxide film at different stages of deposition within a
narrow-width, high-aspect-ratio gap according to a prior-art
silicon oxide deposition process;
[0017] FIG. 2 is a flow diagram illustrating an embodiment for
depositing a gapfill layer with a high flow of a low-mass fluent
gas;
[0018] FIG. 3 is a simplified cross-sectional view of a trench in a
shallow-trench isolation structure, which embodiments of the
invention may be used to fill;
[0019] FIG. 4 is a simplified cross-sectional view of a partially
completed integrated circuit having trenches to be filled with a
dielectric material in both a densely packed area and an open
area;
[0020] FIG. 5 is a graph illustrating the effect of chamber
pressure on relative ion density in HDP-CVD processes;
[0021] FIG. 6A is a simplified cross-sectional view of an exemplary
substrate processing system according to an embodiment of the
invention;
[0022] FIG. 6B is a simplified cross-sectional view of a gas ring
that may be used in conjunction with the exemplary CVD processing
chamber of FIG. 7A;
[0023] FIG. 6C is a perspective view of the substrate processing
system of FIG. 6A, illustrating the integration of a
small-molecule-enhanced turbo pump;
[0024] FIG. 7 is a schematic illustration of a structure that may
be used for a small-molecule-enhanced turbo pump in embodiments of
the invention;
[0025] FIG. 8 is a graph illustrating the effect on chamber
pressure of flow rates for different fluent gases with a prior-art
configuration for a turbo molecular pump;
[0026] FIGS. 9A and 9B are graphs showing a comparison of chamber
pressure versus flow rate for small-molecule-enhanced and prior-art
turbo pumps;
[0027] FIG. 10 is an illustration of a foreline layout for an
exemplary semiconductor-processing facility;
[0028] FIG. 11 is a graph illustrating the effect of the outlet
pressure of a foreline in a semiconductor processing facility on
the chamber pressure of a substrate processing chamber; and
[0029] FIG. 12 is a graph illustrating the effect of a change in
foreline diameter on chamber pressure.
DETAILED DESCRIPTION OF THE INVENTION
[0030] Embodiments of the invention are directed to methods and
systems that permit improved gapfill characteristics during the
deposition of silica glass films. The effect of redeposition on
gapfill that is addressed by embodiments of the invention is
illustrated with FIGS. 1A-1C, which are simplified cross-sectional
views of a silicon oxide film at different stages of deposition.
The sequence of these drawings demonstrates how the gapfill limits
of conventional HDP-CVD processing may be reached for certain
small-width gaps having relatively large aspect ratios. For
purposes of illustration, the gapfill problem illustrated in this
sequence of drawings has been exaggerated.
[0031] FIG. 1A shows the initial stages of film deposition over a
substrate having a gap 110 defined by two adjacent features 112 and
114 formed over the substrate. The conventional HDP-CVD silicon
oxide deposition process results in direct silicon oxide deposition
on the horizontal surface 116 at the bottom of the gap 110, and on
horizontal surfaces 118 above the features 112 and 114. The process
also results in indirect deposition, referred to herein as
"redeposition," of silicon oxide material on the sidewalls 120 as a
result of recombination of material sputtered from the silicon
oxide film as it grows. In certain small-width high-aspect-ratio
applications, the continued growth of the silicon oxide film
results in formations 122 on the upper section of the sidewall 120.
These formations grow towards each other at a rate of growth
exceeding the rate at which the film grows laterally on lower
portions 124 of the sidewalls, as illustrating for an intermediate
time in FIG. 1B. The final result of this process is shown in FIG.
1C, in which a void has been formed within the deposited material
because the formations 122 have grown together.
[0032] It has recently been discovered that the gapfill capability
for aggressive gaps may be improved through the use of relatively
high flows of fluent gases that have a low average molecular mass.
Such a technique may be used in the fabrication of a variety of
integrated circuits, particularly in the fabrication of integrated
circuits having minimum features sizes of 90 nm or less, and may be
used with minimum feature sizes as small as 65 nm, 45 nm, or 30 nm.
References herein to a "molecular mass" are intended to include the
atomic mass of single-atom molecules, such as may exist for inert
elements like helium, etc. A "low" average molecular mass
corresponds in some embodiments to an average molecular mass less
than about 10 atomic mass units ("amu"), and in some instances may
be as low as about 4 amu or about 2 amu. A "high" flow rate
corresponds to a flow rate that exceeds 400 sccm, and which may in
some embodiments be 800 sccm or more, be 1200 sccm or more, or even
as high as about 2500 sccm or more in certain specific
applications.
[0033] The technique is outlined generally with the flow diagram of
FIG. 2, which illustrates deposition of an undoped silica glass
("USG"), and FIG. 3, which is a simplified cross-sectional view of
a substrate having a trench etched therein as part of an STI
structure. It should be understood that in other embodiments, the
techniques of the invention may be applied to IMD and PMD
applications, among others. As indicated at block 204, the
technique begins by loading a substrate into a substrate processing
chamber. The substrate has one or more gaps formed between adjacent
raised features, such as trench 304 shown in FIG. 3. The raised
features may be, for example, dielectric hardmasks, adjacent metal
lines, transistor gates, or other features. In the specific example
of FIG. 3, the raised features represent areas of a silicon
substrate 320 between trenches etched in the substrate 320. The STI
structure shown in FIG. 3 also includes silicon nitride portions
316 formed above the raised features and a silicon oxide interface
or pad oxide 308 formed between the silicon nitride portions 316
and the silicon substrate 320. Also shown in FIG. 3 is an oxide or
nitride liner layer 312, such as an in situ steam generation
("ISSG") oxide or other thermal oxide layer, or an LPCVD or PECVD
silicon nitride layer. In some applications, the trench 304 has an
aspect ratio of between 4:1 and 6:1, and the formation of a highly
conformal film such as oxide or nitride layer 312 may increase the
aspect ratio even further.
[0034] Once the substrate is properly positioned, a high-density
plasma is formed at block 208 of FIG. 2 from a process gas to
provide simultaneous deposition and sputtering components, with
which the silicon oxide is deposited as a gapfill layer. The
process gas includes a fluent gas having a low average molecular
mass provided at a high flow rate. The low average molecular mass
may be provided with a flow of a single low-mass molecule, such as
with a flow of H.sub.2 or He, or may be provided in some
embodiments with a mixture of gases in relative proportions that
ensure the average molecular mass of the mixture is low. Examples
of suitable mixtures include H.sub.2/He mixtures, as well as
H.sub.2/Ar and He/Ar (or H.sub.2/Ne and He/Ne) mixtures in cases
where the Ar (or Ne) flow is substantially less than the H.sub.2 or
He flow, and may include mixtures of more than two gases as in
cases where a H.sub.2/He/Ar or H.sub.2/He/Ne flow is used. Mixtures
may be provided with separate flows of the individual gases or may
be provided by premixing the gases before flowing the fluent gas to
the process chamber. Inclusion of small amounts of relatively heavy
gases in the fluent, even while maintaining the average molecular
mass low, may improve deposition uniformity and may permit a
significant cost saving because of the relatively high cost of
H.sub.2 and He sources compared with sources of other inert gases.
These benefits may be realized even when the flow of H.sub.2 or He
is significantly greater than the flow of a heavier gas such as
Ar.
[0035] The process gas also includes a silicon source, such as
monosilane SiH.sub.4 and an oxygen source such as molecular oxygen
O.sub.2. Dopants may be added to the film by including a precursor
gas with the desired dopant, such as by including a flow of
SiF.sub.4 to fluorinate the film, including a flow of PH.sub.3 to
phosphorate the film, including a flow of B.sub.2H.sub.6 to
boronate the film, including a flow of N.sub.2 to nitrogenate the
film, and the like. Even when such dopants are included in the
deposited film, it is still considered herein to be a "silicon
oxide film." After deposition of the gapfill layer is complete, the
substrate is transferred out of the deposition chamber at block 212
in preparation for subsequent processing.
[0036] The specific gapfill characteristics for production of a
given integrated circuit may differ. For example, FIG. 4 provides
an illustration of an integrated circuit 400 that has areas 404 of
densely packed active devices where transistors are formed, and
areas 408 where the active devices are relatively isolated. These
isolated areas 408 are sometimes referred to in the art as "open
areas," and may have devices that are separated by distances more
than an order of magnitude or more than the spacing between devices
in the densely packed active are 404. Sidewall deposition has been
found to occur at a significantly higher rate on gaps formed in the
densely packed portion of the integrated circuit 400 than on gaps
formed in the open areas 408. The use of a high flow of a low-mass
fluent gas is thus especially suitable for deposition in densely
packed areas.
[0037] A number of specific parameters using such techniques have
been described in copending, commonly assigned U.S. patent
application Ser. No. 09/854,406, entitled "HYDROGEN ASSISTED
UNDOPED SILICON OXIDE DEPOSITION PROCESS FOR HDP-CVD," filed May
11, 2001 and U.S. patent application Ser. No. 10/350,445 entitled
"HYDROGEN ASSISTED HDP-CVD DEPOSITION PROCESS FOR AGGRESSIVE
GAP-FILL TECHNOLOGY," filed Jan. 23, 2003 by Bikram Kapoor et al.,
the entire disclosures of both of which are incorporated herein by
reference for all purposes. A relatively high flow rate of a
low-mass fluent gas acts to reduce redeposition on the sidewalls,
thereby enabling narrow-width, high-aspect-ratio gaps to be filled
in more of a bottom-up manner. As is known to those of skill in the
art, some HDP gapfill applications operate the chamber with a
throttle valve that controls flow to an exhaust foreline in a fully
open position. When the system is used with the throttle valve in a
fully open position, the pressure within a given chamber is
controlled by the pumping capacity of a vacuum pump(s) and the rate
at which gases are introduced into the chamber. It has generally
been desirable during HDP-CVD processes for chamber pressure levels
to be maintained at a low level because dissociated species of the
process gas then have a longer mean free path and reduced angular
distribution, thus enabling them to reach and take place in
chemical reactions at the bottom of trenches. This has thus tended
to improve the bottom-up gapfill characteristics of gapfill
processes.
[0038] In experiments using a high flow of low-mass fluent gases,
it was found that deposition was improved despite an increase in
the chamber pressure above what is normally considered desirable.
For example, in some experiments using high flows of H.sub.2, the
chamber pressure would approach 50 mtorr even with the throttle
valve fully open. The inventors hypothesized that still better
deposition might be achieved if the pressure within the process
chamber could be reduced while still providing a high flow rate of
a low-mass gas. When the pressure of the chamber is relatively
high, the flow of gases within the chamber is dominated by the flow
profile generated by the gas input sources; conversely, when the
pressure is lower, the flow profile is more diffusive, allowing
application of bias and such factors to improve the control over
where the ions react to form the silicon oxide layer. Another
reason contributing to this expectation is illustrated with the
graph in FIG. 5, which shows the results of measurements of
relative levels of ionic and neutral species in a plasma as a
function of chamber pressure. In particular, the ordinate plots the
normalized density of ionic species to neutral species in the
plasma, with the different symbols corresponding to a different
number of process parameters. The legend identifies the flow rates
of gases provided to a chamber in sccm, as well as rf power levels
applied to the top and sides of the chamber, with an indication of
whether measurements were taken near the edge or near the center of
a process wafer. For example, the notation "O2 102/He 100, 4.8/3.5
kW (edge") indicates a process with an O.sub.2 flow of 102 sccm, a
He flow of 100 sccm, a top rf power of 4.8 kW, a side rf power of
3.5 kW, for measurements taken near the wafer edge.
[0039] The results of FIG. 5 show consistently that the ratio of
ionic to neutral species in the plasma deceases exponentially with
chamber pressure. This ratio is, however, relevant for bottom-up
gapfill because it is the ionic species that react more readily in
the formation of the silicon oxide film as it is deposited. The
ions in the plasma thus contribute, in a relative sense, more to
bottom-up deposition within the gap than they do to growth of the
film above the raised features adjacent to the gap. The effect of
the exponential decrease is very marked in FIG. 5 and demonstrates
that a very significant improvement in the density of ionic species
to neutral species is achieved when the chamber pressure is less
than about 10 mtorr.
[0040] The inventors were thus prompted to consider how the chamber
pressure could be reduced despite the very high flow rates of the
low-mass fluent gas. Attempts to vary the configuration of existing
HDP deposition systems had proved incapable of reducing the
pressure, including attempts to vary the opening level of the
throttle valve, to vary the operating power, to vary the flow
rates, and the like, consistent with constraints dictated by
process characteristics. The inventors eventually hypothesized that
perhaps the performance characteristics of the vacuum pump varied
depending on the mass of individual molecules or ions, so that
less-massive molecules were being pumped out of the processing
chamber less efficiently than more-massive molecules. Accordingly,
the inventors requested the special manufacture of pumps having
specified performance characteristics specifically for low-mass
molecules, which they substituted for pumps in existing HDP
deposition systems. It was not immediately apparent when requesting
the modified performance characteristics what effect they would
have on the overall deposition because the efficiency of exhausting
the higher-mass silane and oxygen species from the chamber could
also be affected. The effect of including pumps having the
specified performance characteristics was, however, discovered to
successfully lower the chamber pressure and to further enhance the
gapfill characteristics of the process.
[0041] One example of an HDP substrate processing system with which
such a modified pump may be used is the ULTIMA.TM. system,
manufactured by APPLIED MATERIALS, INC., of Santa Clara, Calif.,
and described in commonly assigned U.S. Pat. No. 6,170,428, filed
Jul. 15, 1996, entitled "Symmetric Tunable Inductively-Coupled
HDP-CVD Reactor," having Fred C. Redeker, Farhad Moghadam, Hirogi
Hanawa, Tetsuya Ishikawa, Dan Maydan, Shijian Li, Brian Lue, Robert
Steger, Yaxin Wang, Manus Wong and Ashok Sinha listed as
co-inventors, the entire disclosure of which is incorporated herein
by reference. A specific description of a modified HDP substrate
processing system provided in accordance with an embodiment of the
invention is described below. FIGS. 6A-6C provide a general
overview of the system, with certain aspects of the
small-molecule-enhanced turbomolecular pump integrated to the
system described in connection with FIGS. 7-9. FIG. 6A
schematically illustrates the structure of such an HDP-CVD system
610, which includes a chamber 613, a vacuum system 670, a source
plasma system 680A, a bias plasma system 680B, a gas delivery
system 633, and a remote plasma cleaning system 650.
[0042] The upper portion of chamber 613 includes a dome 614, which
is made of a ceramic dielectric material, such as aluminum oxide or
aluminum nitride. Dome 614 defines an upper boundary of a plasma
processing region 616. Plasma processing region 616 is bounded on
the bottom by the upper surface of a substrate 617 and a substrate
support member 618.
[0043] A heater plate 623 and a cold plate 624 surmount, and are
thermally coupled to, dome 614. Heater plate 623 and cold plate 624
allow control of the dome temperature to within about
.+-.10.degree. C. over a range of about 100.degree. C. to
200.degree. C. This allows optimizing the dome temperature for the
various processes. For example, it may be desirable to maintain the
dome at a higher temperature for cleaning or etching processes than
for deposition processes. Accurate control of the dome temperature
also reduces the flake or particle counts in the chamber and
improves adhesion between the deposited layer and the
substrate.
[0044] The lower portion of chamber 613 includes a body member 622,
which joins the chamber to the vacuum system. A base portion 621 of
substrate support member 618 is mounted on, and forms a continuous
inner surface with, body member 622. Substrates are transferred
into and out of chamber 613 by a robot blade (not shown) through an
insertion/removal opening (not shown) in the side of chamber 613.
Lift pins (not shown) are raised and then lowered under the control
of a motor (also not shown) to move the substrate from the robot
blade at an upper loading position 657 to a lower processing
position 656 in which the substrate is placed on a substrate
receiving portion 619 of substrate support member 618. Substrate
receiving portion 619 includes an electrostatic chuck 620 that
secures the substrate to substrate support member 618 during
substrate processing. In a preferred embodiment, substrate support
member 618 is made from an aluminum oxide or aluminum ceramic
material.
[0045] Vacuum system 670 includes throttle body 625, which houses
twin-blade throttle valve 626 and is attached to gate valve 627 and
small-molecule-enhanced turbomolecular pump 628. As described in
detail below, the turbomolecular pump 628 has the modified
performance characteristics making it suitable for efficient
exhaustion of low-mass molecular species. It should be noted that
throttle body 625 offers minimum obstruction to gas flow, and
allows symmetric pumping. Gate valve 627 can isolate pump 628 from
throttle body 625, and can also control chamber pressure by
restricting the exhaust flow capacity when throttle valve 626 is
fully open. The arrangement of the throttle valve, gate valve, and
small-molecule-enhanced turbomolecular pump allow accurate and
stable control of chamber pressures from between about 2 millitorr
to about 2 torr.
[0046] The source plasma system 680A includes a top coil 629 and
side coil 630, mounted on dome 614. A symmetrical ground shield
(not shown) reduces electrical coupling between the coils. Top coil
629 is powered by top source RF (SRF) generator 631A, whereas side
coil 630 is powered by side SRF generator 631B, allowing
independent power levels and frequencies of operation for each
coil. This dual coil system allows control of the radial ion
density in chamber 613, thereby improving plasma uniformity. Side
coil 630 and top coil 629 are typically inductively driven, which
does not require a complimentary electrode. In a specific
embodiment, the top source RF generator 631A provides up to 2,500
watts of RF power at nominally 2 MHz and the side source RF
generator 631B provides up to 5,000 watts of RF power at nominally
2 MHz. The operating frequencies of the top and side RF generators
may be offset from the nominal operating frequency (e.g. to 1.7-1.9
MHz and 1.9-2.1 MHz, respectively) to improve plasma-generation
efficiency.
[0047] A bias plasma system 680B includes a bias RF ("BRF")
generator 631C and a bias matching network 632C. The bias plasma
system 680B capacitively couples substrate portion 617 to body
member 622, which act as complimentary electrodes. The bias plasma
system 680B serves to enhance the transport of plasma species
(e.g., ions) created by the source plasma system 680A to the
surface of the substrate. In a specific embodiment, bias RF
generator provides up to 5,000 watts of RF power at 13.56 MHz.
[0048] RF generators 631A and 631B include digitally controlled
synthesizers and operate over a frequency range between about 1.8
to about 2.1 MHz. Each generator includes an RF control circuit
(not shown) that measures reflected power from the chamber and coil
back to the generator and adjusts the frequency of operation to
obtain the lowest reflected power, as understood by a person of
ordinary skill in the art. RF generators are typically designed to
operate into a load with a characteristic impedance of 50 ohms. RF
power may be reflected from loads that have a different
characteristic impedance than the generator. This can reduce power
transferred to the load. Additionally, power reflected from the
load back to the generator may overload and damage the generator.
Because the impedance of a plasma may range from less than 5 ohms
to over 900 ohms, depending on the plasma ion density, among other
factors, and because reflected power may be a function of
frequency, adjusting the generator frequency according to the
reflected power increases the power transferred from the RF
generator to the plasma and protects the generator. Another way to
reduce reflected power and improve efficiency is with a matching
network.
[0049] Matching networks 632A and 632B match the output impedance
of generators 631A and 631B with their respective coils 629 and
630. The RF control circuit may tune both matching networks by
changing the value of capacitors within the matching networks to
match the generator to the load as the load changes. The RF control
circuit may tune a matching network when the power reflected from
the load back to the generator exceeds a certain limit. One way to
provide a constant match, and effectively disable the RF control
circuit from tuning the matching network, is to set the reflected
power limit above any expected value of reflected power. This may
help stabilize a plasma under some conditions by holding the
matching network constant at its most recent condition.
[0050] Other measures may also help stabilize a plasma. For
example, the RF control circuit can be used to determine the power
delivered to the load (plasma) and may increase or decrease the
generator output power to keep the delivered power substantially
constant during deposition of a layer.
[0051] A gas delivery system 633 provides gases from several
sources, 634A-634E chamber for processing the substrate via gas
delivery lines 638 (only some of which are shown). As would be
understood by a person of skill in the art, the actual sources used
for sources 634A-634E and the actual connection of delivery lines
638 to chamber 613 varies depending on the deposition and cleaning
processes executed within chamber 613. Gases are introduced into
chamber 613 through a gas ring 637 and/or a top nozzle 645. FIG. 6B
is a simplified, partial cross-sectional view of chamber 613
showing additional details of gas ring 637.
[0052] In one embodiment, first and second gas sources, 634A and
634B, and first and second gas flow controllers, 635A' and 635B',
provide gas to ring plenum 636 in gas ring 637 via gas delivery
lines 638 (only some of which are shown). Gas ring 637 has a
plurality of source gas nozzles 639 (only one of which is shown for
purposes of illustration) that provide a uniform flow of gas over
the substrate. Nozzle length and nozzle angle may be changed to
allow tailoring of the uniformity profile and gas utilization
efficiency for a particular process within an individual chamber.
In a preferred embodiment, gas ring 637 has 12 source gas nozzles
made from an aluminum oxide ceramic.
[0053] Gas ring 637 also has a plurality of oxidizer gas nozzles
640 (only one of which is shown), which in a preferred embodiment
are co-planar with and shorter than source gas nozzles 639, and in
one embodiment receive gas from body plenum 641. In some
embodiments it is desirable not to mix source gases and oxidizer
gases before injecting the gases into chamber 613. In other
embodiments, oxidizer gas and source gas may be mixed prior to
injecting the gases into chamber 613 by providing apertures (not
shown) between body plenum 641 and gas ring plenum 636. In one
embodiment, third, fourth, and fifth gas sources, 634C, 634D, and
634D', and third and fourth gas flow controllers, 635C and 635D',
provide gas to body plenum via gas delivery lines 638. Additional
valves, such as 643B (other valves not shown), may shut off gas
from the flow controllers to the chamber. In implementing certain
embodiments of the invention, source 634A comprises a silane
SiH.sub.4 source, source 634B comprises a molecular oxygen O.sub.2
source, source 634C comprises a silane SiH.sub.4 source, source
634D comprises a helium He source, and source 634D' comprises a
molecular hydrogen H.sub.2 source.
[0054] In embodiments where flammable, toxic, or corrosive gases
are used, it may be desirable to eliminate gas remaining in the gas
delivery lines after a deposition. This may be accomplished using a
3-way valve, such as valve 643B, to isolate chamber 613 from
delivery line 638A and to vent delivery line 638A to vacuum
foreline 644, for example. As shown in FIG. 6A, other similar
valves, such as 643A and 643C, may be incorporated on other gas
delivery lines. Such three-way valves may be placed as close to
chamber 613 as practical, to minimize the volume of the unvented
gas delivery line (between the three-way valve and the chamber).
Additionally, two-way (on-off) valves (not shown) may be placed
between a mass flow controller ("MFC") and the chamber or between a
gas source and an MFC.
[0055] Referring again to FIG. 6A, chamber 613 also has top nozzle
645 and top vent 646. Top nozzle 645 and top vent 646 allow
independent control of top and side flows of the gases, which
improves film uniformity and allows fine adjustment of the film's
deposition and doping parameters. Top vent 646 is an annular
opening around top nozzle 645. In one embodiment, first gas source
634A supplies source gas nozzles 639 and top nozzle 645. Source
nozzle MFC 635A' controls the amount of gas delivered to source gas
nozzles 639 and top nozzle MFC 635A controls the amount of gas
delivered to top gas nozzle 645. Similarly, two MFCs 635B and 635B'
may be used to control the flow of oxygen to both top vent 646 and
oxidizer gas nozzles 640 from a single source of oxygen, such as
source 634B. The gases supplied to top nozzle 645 and top vent 646
may be kept separate prior to flowing the gases into chamber 613,
or the gases may be mixed in top plenum 648 before they flow into
chamber 613. Separate sources of the same gas may be used to supply
various portions of the chamber.
[0056] A remote microwave-generated plasma cleaning system 650 is
provided to periodically clean deposition residues from chamber
components. The cleaning system includes a remote microwave
generator 651 that creates a plasma from a cleaning gas source 634E
(e.g., molecular fluorine, nitrogen trifluoride, other
fluorocarbons or equivalents) in reactor cavity 653. The reactive
species resulting from this plasma are conveyed to chamber 613
through cleaning gas feed port 654 via applicator tube 655. The
materials used to contain the cleaning plasma (e.g., cavity 653 and
applicator tube 655) must be resistant to attack by the plasma. The
distance between reactor cavity 653 and feed port 654 should be
kept as short as practical, since the concentration of desirable
plasma species may decline with distance from reactor cavity 653.
Generating the cleaning plasma in a remote cavity allows the use of
an efficient microwave generator and does not subject chamber
components to the temperature, radiation, or bombardment of the
glow discharge that may be present in a plasma formed in situ.
Consequently, relatively sensitive components, such as
electrostatic chuck 620, do not need to be covered with a dummy
wafer or otherwise protected, as may be required with an in situ
plasma cleaning process.
[0057] A perspective view of the substrate processing chamber 610
with the integrated small-molecule-enhanced turbomolecular pump 628
is shown in FIG. 6C. Input flows to the turbomolecular pump are
controlled by gate valve 627 and output flows are provided to
exhaust 690, which may be connected with a foreline system as
described further below.
[0058] A structure for the small-molecule-enhanced turbomolecular
pump 628 is illustrated for an embodiment with FIG. 7. This drawing
provides a schematic view of how gas incoming to the pump along
flows 732 is mechanically driven to exhaust 690, with a
corresponding increase in pressure from P.sub.in at the inlet to
P.sub.out at the outlet. A typical inlet pressure P.sub.in
corresponds to the chamber pressure and may less than about 10
mtorr, although in some embodiments may be as low as 5 mtorr or as
low as 2 mtorr. The outlet pressure P.sub.out is generally
intermediate between the inlet pressure P.sub.in and atmospheric
pressure P.sub.out at and may be about 150 mtorr. The performance
of the turbomolecular pump 628 for specific species may be
characterized by the relative partial pressures for those species
in terms of a "compression ratio," defined as P.sub.out/P.sub.in.
The turbomolecular pump 628 has a frame 716 that includes a flange
704 for connection with the gate valve 627. A plurality of stator
blades 708 extend radially inwards from the frame and are fixed in
position relative to the frame. An interior rotor 720 includes a
plurality of rotor blades 712 that extend radially outwards from
the rotor such that the rotor blades 712 are interleaved with the
fixed stator blades 708. Each combination of a stator and rotor
blade is sometimes referred to herein as a "turbine stage" of the
pump. The turbomolecular pump 628 is typically cooled with a water
cooling system and includes electrical connections to provide power
for rotating the rotor 720.
[0059] Gas that is introduced into the turbomolecular pump along
flows 732 is forced downwards mechanically as the rotor 720
rotates. The atoms, molecules, and ions that may be comprised by
the gas are successively forced into successive stages through the
mechanical interaction of the rotating rotor blades 712 and fixed
stator blades 708, thereby also successively increasing the
pressure of the gas. One or more drag stages 724 may also be
included to further compress the gas mechanically before it is
exhausted through exhaust 690 along flow 734.
[0060] There are a number of factors that may affect the
compression efficiency of the turbomolecular pump 628 for different
molecule sizes, including such factors as the overlap between the
stator and rotor blades, the shape of the stator and rotor blades,
the relative angles of inclination of the stator and rotor blades,
the separation between the stator and rotor blades, the rotational
speed of the rotor, the number of turbine stages, the number of
drag stages, the inlet flange size, the exhaust size, and the like.
Essentially, a variation in any of such factors may affect the
statistical chance of a given molecule being trapped within a
successive one of the turbine stages and thereby forced downwards.
Generally, an increase in the number of turbine stages is more
effective at compressing lighter molecules. In some embodiments,
for example, between 20 and 25 turbine stages has been found
effective at compressing hydrogen molecules, with one embodiment
using 23 turbine stages. Also, the rotor and stator blades may
approximately be characterized by a width b that accounts for
shaping factors; a decrease in the ratio of the distance between
blades S to the width b generally results in improved
small-molecule compression, with S/b being equal to about 1.05 in
one embodiment. In one embodiment, the turbomolecular pump 628 has
a single drag stage.
[0061] The compression efficiency for the smallest molecule present
in the process gas is not the only factor that dictates the desired
pump characteristics. For example, it is still necessary to pump
other molecules at reasonable efficiencies consistent with the flow
rates of the gases that provide those other molecules. Thus, in
some embodiments it may be appropriate to sacrifice
hydrogen-pumping efficiency in favor of improved large-molecule
pumping efficiency, particularly if dopants may be provided through
flows of heavy dopant molecules. The inventors have found the
following pump characteristics suitable for processes that deposit
gapfill silicon oxide with a silane SiH.sub.4 flow of 15-100 sccm,
an oxygen O.sub.2 flow of 25-500 sccm, and an H.sub.2 flow of
500-2500 sccm: TABLE-US-00001 TABLE I Turbomolecular Pump
Performance Characteristics Range Value Flange Size (inches) 200-mm
wafer 8-12 10 300-mm wafer 12-16 14 Pumping Speed (L/s) H.sub.2
2800-3500 3150 He 2800-3500 3150 N 3000-3600 3200 Compression Ratio
H.sub.2 (1-10) .times. 10.sup.5 2 .times. 10.sup.5 He (1-10)
.times. 10.sup.6 2 .times. 10.sup.6 N (5-20) .times. 10.sup.8 1
.times. 10.sup.9 Rated Speed (rpm) 200-mm wafer 2400-3000 2700
300-mm wafer 2000-2600 2400
In this table, the values set forth for N are used for convenience
to illustrate pumping rates and compression ratios suitable for
heavier species in the plasma. With these pump performance
characteristics for the exemplary process described above, the
chamber pressure may be maintained at less than 10 mtorr for both
200-mm-wafer and 300-mm-wafer processes. This may be contrasted
with pressures that exceed 25 mtorr using the same process in a
system that uses a conventional turbomolecular pump.
[0062] A comparison of the effects of using a turbomolecular pump
having these performance characteristics is illustrated with
graphical results in FIGS. 8-9B. FIG. 8 provides a plot of chamber
pressure as a function of fluent flow for H.sub.2, He, and Ar using
a prior-art turbomolecular pump. It is evident that the effect of
flow rate on pressure is greater for smaller molecules, and
especially for H.sub.2 since there is even a dramatic increase in
pressure when H.sub.2 is used even in regions up to about 500 sccm
where the difference in pressures when using He versus Ar is still
modest. Thus, while a reduction in pressure is desirable for
processes that use high flow rates of He, the benefit of being able
to reduce the pressure with the enhanced turbomolecular pump is
especially acute for processes that use high flow rates of
H.sub.2.
[0063] FIGS. 9A and 9B compare the pressures provided as a function
of flow rate between systems that use the prior-art and enhanced
turbomolecular pumps for H.sub.2 and He respectively. The effect of
using the enhanced turbomolecular pump is seen particularly in the
results for H.sub.2, in which the pressure may be reduced by more
than a factor of four at flow rates above 500 sccm. The effect is
also significant for He flows when the flow rates are large,
producing approximately a factor-of-two reduction in chamber
pressure when the flow rate is about 1200 sccm. Thus, the use of a
small-molecule-enhanced turbomolecular pump as described herein
enables gapfill deposition using high flows of fluent gases at
chamber pressures that are below 15 mtorr, below 10 mtorr, or below
5 mtorr in different embodiments.
[0064] Another factor that the inventors have identified as
enabling a reduction in chamber pressure for such high-flow
processes is the layout of the foreline. Generally, the exhaust 690
of the turbomolecular pump 628 is connected with a rough pump that
further compresses the exhausted gas to atmospheric pressure so
that scrubbing processes may be used on any output toxic gases. It
will be understood in the art that a "rough pump" is a pump used to
bring pressure in a system to a pressure intermediate between a
desired operational pressure and atmospheric pressure. The
connection between the turbomolecular pump 628 and the rough pump
is made by the foreline, which may be routed according to physical
layouts of a facility that holds the substrate processing chamber.
One such facility may, in some instances, have multiple forelines
connecting different substrate processing systems with a single
rough pump. The inventors have recognized that because the foreline
provides part of a fluid communication between the rough pump and
the substrate processing chamber, certain specific characteristics
of the foreline may affect the pressure. Accordingly, modifications
in the foreline may be used in embodiments of the invention to
achieve even further reductions in chamber pressure.
[0065] Merely for purposes of illustration, FIG. 10 shows an
example of a foreline 1004 that connects the exhaust 690 of a
turbomolecular pump 628 to an inlet 1024 of a rough pump 1016. The
foreline 1004 may comprise a plurality of sections, such as
sections 1008, 1012, and 1020 that have different tubing sizes. For
example, the initial and final sections 1008 and 1020 in the
example may have tubing sizes of about 2 inches, while the
intermediate section has a tubing size of about 4 inches. An
increase in the tubing size of all or a portion of the foreline
1004 may thus result in a decrease in chamber pressure. For
example, in one instance, a decrease in chamber pressure may be
achieved by replacing the 2-inch section 1020 of tubing with 4-inch
tubing. In another instance, both the 2-inch sections 1008 and 1020
of tubing may be replaced with 4-inch tubing, and the intermediate
4-inch tubing section 1012 replaced with 6-inch tubing. By making
such modifications, the outlet pressure P.sub.out of the
turbomolecular pump may be reduced, thereby providing a reduction
in the inlet pressure P.sub.in that corresponds to the chamber
pressure.
[0066] The level of improvement that may be achieved with such
replacements is illustrated for several examples in FIG. 11, which
provides a set of curves relating the outlet pressure P.sub.out of
the small-molecule-enhanced turbomolecular pump to the inlet
pressure P.sub.in for a number of different fluent flows, namely
1000 sccm H.sub.2 (top curve), 500 sccm H.sub.2 (second curve), 900
sccm H.sub.2+125 sccm Ar (third curve), and 750 sccm H.sub.2+125
sccm Ar (bottom curve). In all instances, it is apparent that
achieving a reduction in outlet pressure by reconfiguring the
foreline 1004 may provide a further reduction in chamber pressure.
While dependent on which curve is relevant and on what the flow
rate is, the inventors have found that a reduction in outlet
pressure of about 50 mtorr achieved by reconfiguring the foreline
may generally translate into about a 2-mtorr reduction in chamber
pressure.
[0067] This effect is illustrated more directly with FIG. 12, which
provides results of experiments in which the two-inch foreline
connected with a substrate processing system was substituted with a
four-inch foreline. The resulting chamber pressure is plotted for
different flow rates of H.sub.2 for both the two-inch and four-inch
configurations, with the top curve corresponding to the two-inch
configuration and the bottom curve corresponding to the four-inch
configuration. It is apparent from these results that the increase
in tubing size provides a further reduction in chamber pressure.
This reduction may be provided with both a prior-art turbomolecular
pump or with the small-molecule enhanced turbomolecular pump.
[0068] In addition to the absolute size of the tubing that connects
the turbomolecular pump 628 with the rough pump 1016, the inventors
have found that the exhaust pressure may also be affected by the
number of bends in the tubing. For example, FIG. 10 shows a
foreline layout 1004 in which the first section 1008 has three 900
bends, the second section 1012 has two 90.degree. bends, and the
third section has two 90.degree. bends. If the facility that houses
the substrate processing system may accommodate a foreline layout
that reduces the number of bends, the chamber pressure may be
reduced further.
[0069] The following table sets forth an example of a foreline
specification that may be provided to customers to ensure that the
exhaust pressure of the turbomolecular pump is maintained within a
range consistent with the desired chamber pressure. The
specification is provided for stainless steel tubing with a rough
pump that has a pumping speed of about 500 m.sup.3/h at 50 Hz, and
is suitable for an H.sub.2 fluent gas used in gapfill deposition on
a 200-mm wafer. Depending on the size of the tubing, as identified
in Column A, a maximum allowable tubing length is set forth in
Column C. For each 90.degree. bend in the tubing layout, the number
in Column B should be subtracted from the standard allowable length
set forth in Column C. TABLE-US-00002 TABLE 2 Foreline
Specification for 200-mm H.sub.2 Gapfill Process Column B Column C
Column A Equivalent Length Maximum Allowable Tubing Diameter for
each 90.degree. Bend Tubing Length 2'' (5.1 cm) 2.5' (76.2 cm)
20.0' (6.1 m) 3'' (7.6 cm) 3.0' (91.4 cm) 40.0' (12.2 m) 4'' (10.1
cm) 3.5' (106.7 cm) 60.0' (18.3 m) 5'' (12.7 cm) 4.0' (121.9 cm)
60.0' (18.3 m) 6'' (15.2 cm) 4.5' (137.2 cm) 60.0' (18.3 m)
[0070] Still a further way in which the foreline arrangement may be
modified to reduce the outlet pressure of the turbomolecular pump
is to increase the pumping speed of the rough pump, such as by
replacing the rough pump with another pump having a higher rated
speed. A typical pump used in HDP-processing systems has a pumping
speed of about 500 m.sup.3/h, but in certain embodiments that use
high flows of small molecules, a rough having a pumping speed of at
least 1000 m.sup.3/h or of at least 1500 m.sup.3/h may be used to
achieve reduced chamber pressure.
[0071] Those of ordinary skill in the art will realize that
processing parameters can vary for different processing chambers
and different processing conditions, and that different precursors
can be used without departing from the spirit of the invention.
Other variations will also be apparent to persons of skill in the
art. These equivalents and alternatives are intended to be included
within the scope of the present invention. Therefore, the scope of
this invention should not be limited to the embodiments described,
but should instead be defined by the following claims.
* * * * *