U.S. patent application number 11/327118 was filed with the patent office on 2006-06-08 for microfeature workpiece processing apparatus and methods for controlling deposition of materials on microfeature workpieces.
Invention is credited to Cem Basceri, Kevin L. Beaman, Lyle D. Breiner, Trung T. Doan, David J. Kubista, Er-Xuan Ping, Demetrius Sarigiannis, Ronald A. Weimer, Lingyi A. Zheng.
Application Number | 20060121689 11/327118 |
Document ID | / |
Family ID | 34274664 |
Filed Date | 2006-06-08 |
United States Patent
Application |
20060121689 |
Kind Code |
A1 |
Basceri; Cem ; et
al. |
June 8, 2006 |
Microfeature workpiece processing apparatus and methods for
controlling deposition of materials on microfeature workpieces
Abstract
The present disclosure provides methods and apparatus useful in
depositing materials on batches of microfeature workpieces. One
implementation provides a method in which a quantity of a first
precursor gas is introduced to an enclosure at a first enclosure
pressure. The pressure within the enclosure is reduced toga second
enclosure pressure while introducing a purge gas at a first flow
rate. The second enclosure pressure may approach or be equal to a
steady-state base pressure of the processing system at the first
flow rate. After reducing the pressure, the purge gas flow may be
increased to a second flow rate and the enclosure pressure may be
increased to a third enclosure pressure. Thereafter, a flow of a
second precursor gas may be introduced with a pressure within the
enclosure at a fourth enclosure pressure; the third enclosure
pressure is desirably within about 10 percent of the fourth
enclosure pressure.
Inventors: |
Basceri; Cem; (Boise,
ID) ; Doan; Trung T.; (Pflugerville, TX) ;
Weimer; Ronald A.; (Boise, ID) ; Beaman; Kevin
L.; (Boise, ID) ; Breiner; Lyle D.; (Meridian,
ID) ; Zheng; Lingyi A.; (Boise, ID) ; Ping;
Er-Xuan; (Meridian, ID) ; Sarigiannis; Demetrius;
(Boise, ID) ; Kubista; David J.; (Nampa,
ID) |
Correspondence
Address: |
PERKINS COIE LLP;PATENT-SEA
PO BOX 1247
SEATTLE
WA
98111-1247
US
|
Family ID: |
34274664 |
Appl. No.: |
11/327118 |
Filed: |
January 6, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10665099 |
Sep 17, 2003 |
|
|
|
11327118 |
Jan 6, 2006 |
|
|
|
Current U.S.
Class: |
438/448 ;
438/485; 438/487; 438/689; 438/778; 438/788; 438/789 |
Current CPC
Class: |
C23C 16/45546 20130101;
C23C 16/34 20130101; C23C 16/45527 20130101 |
Class at
Publication: |
438/448 ;
438/485; 438/487; 438/689; 438/778; 438/788; 438/789 |
International
Class: |
H01L 21/76 20060101
H01L021/76; H01L 21/20 20060101 H01L021/20; H01L 21/302 20060101
H01L021/302; H01L 21/31 20060101 H01L021/31 |
Claims
1-32. (canceled)
33. A microfeature workpiece processing system comprising: an
enclosure adapted to receive a plurality of microfeature workpieces
for simultaneous treatment; a gas supply adapted to selectively
deliver a first gaseous precursor, a second gaseous precursor, and
a purge gas to the enclosure; a vacuum; and a programmable
controller operatively coupled to the gas supply and the vacuum,
the controller being programmed to: introduce a flow of the first
precursor gas to the enclosure with a pressure within the enclosure
at a first enclosure pressure; terminate the flow of the first
precursor; reduce pressure within the enclosure to a second, lower
enclosure pressure in a pump-down process, the pump-down process
comprising operating the vacuum source to withdraw gas from the
enclosure while introducing the purge gas from the gas supply to
the enclosure at a first flow rate of no greater than about 250
sccm for a first period of time; and after the pump-down process,
purge the enclosure in a purge process, the purge process
comprising introducing the purge gas from the gas supply to the
enclosure at a second flow rate of at least about 1000 sccm for a
second period of time and allowing the enclosure pressure to
increase to a third enclosure pressure that is greater than the
second enclosure pressure.
34. The microfeature workpiece processing system of claim 33
wherein the first flow rate is at least about 50 sccm.
35. The microfeature workpiece processing system of claim 33
wherein the second flow rate is at least about 2000 sccm.
36. The microfeature workpiece processing system of claim 33
wherein the third enclosure pressure is at least about nine times
the second enclosure pressure.
37. The microfeature workpiece processing system of claim 33
wherein the flow rate of the purge gas is increased to the second
flow rate promptly upon reaching the second enclosure pressure.
38. The microfeature workpiece processing system of claim 33
wherein the controller is further programmed to, after the purge
process, introduce a flow of the second precursor gas from the gas
supply to the enclosure with the pressure within the enclosure at a
fourth enclosure pressure, a difference between the third enclosure
pressure and the fourth enclosure pressure being about 0-10% of the
fourth enclosure pressure.
39. The microfeature workpiece processing system of claim 38
wherein the fourth enclosure pressure is approximately equal to the
first enclosure pressure.
40. The microfeature workpiece processing system of claim 38
wherein the third enclosure pressure is approximately equal to the
fourth enclosure pressure.
41. The microfeature workpiece processing system of claim 38
wherein the controller is further programmed to, after introducing
the flow of the second precursor gas: terminate the flow of the
second precursor gas; repeating the pump-down process; then
repeating the purge process.
42. The microfeature workpiece processing system of claim 38
wherein the controller is further programmed to, after introducing
the flow of the second precursor gas: terminate the flow of the
second precursor gas; reduce pressure within the enclosure to a
fifth enclosure pressure while introducing a flow of the purge gas
into the enclosure from the gas supply at a third flow rate,
wherein the fifth enclosure pressure differs from the second
enclosure pressure or the third flow rate differs from the first
flow rate; and increase flow of the purge gas to a fourth flow rate
and increasing the pressure within the enclosure to a sixth
enclosure pressure, a difference between the sixth enclosure
pressure and the fourth enclosure pressure being about 0-10% of the
fourth enclosure pressure.
Description
TECHNICAL FIELD
[0001] The present invention is related to equipment and methods
for processing microfeature workpieces, e.g., semiconductor wafers.
Aspects of the invention have particular utility in connection with
batch deposition of materials on microfeature workpieces by atomic
layer deposition.
BACKGROUND
[0002] Thin film deposition techniques are widely used in the
manufacturing of microfeatures to form a coating on a workpiece
that closely conforms to the surface topography. In the context of
microelectronic components, for example, the size of the individual
components in the devices on a wafer is constantly decreasing, and
the number of layers in the devices is increasing. As a result, the
density of components and the aspect ratios of depressions (e.g.,
the ratio of the depth to the size of the opening) are increasing.
The size of such wafers is also increasing to provide more real
estate for forming more dies (i.e., chips) on a single wafer. Many
fabricators are currently transitioning from 200 mm to 300 mm
workpieces, and even larger workpieces will likely be used in the
future. Thin film deposition techniques accordingly strive to
produce highly uniform conformal layers that cover the sidewalls,
bottoms, and corners in deep depressions that have very small
openings.
[0003] One widely used thin film deposition technique is chemical
vapor deposition (CVD). In a CVD system, one or more precursors
that are capable of reacting to form a solid thin film are mixed in
a gas or vapor state, and then the precursor mixture is presented
to the surface of the workpiece. The surface of the workpiece
catalyzes the reaction between the precursors to form a solid thin
film at the workpiece surface. A common way to catalyze the
reaction at the surface of the workpiece is to heat the workpiece
to a temperature that causes the reaction.
[0004] Although CVD techniques are useful in many applications,
they also have several drawbacks. For example, if the precursors
are not highly reactive, then a high workpiece temperature is
needed to achieve a reasonable deposition rate. Such high
temperatures are not typically desirable because heating the
workpiece can be detrimental to the structures and other materials
already formed on the workpiece. Implanted or doped materials, for
example, can migrate within silicon workpieces at higher
temperatures. On the other hand, if more reactive precursors are
used so that the workpiece temperature can be lower, then reactions
may occur prematurely in the gas phase before reaching the intended
surface of the workpiece. This is undesirable because the film
quality and uniformity may suffer, and also because it limits the
types of precursors that can be used.
[0005] Atomic layer deposition (ALD) is another thin film
deposition technique. FIGS. 1A and 1B schematically illustrate the
basic operation of ALD processes. Referring to FIG. 1A, a layer of
gas molecules A coats the surface of a workpiece W. The layer of A
molecules is formed by exposing the workpiece W to a precursor gas
containing A molecules, and then purging the chamber with a purge
gas to remove excess A molecules. This process can form a monolayer
of A molecules on the surface of the workpiece W because the A
molecules at the surface are held in place during the purge cycle
by physical adsorption forces at moderate temperatures or
chemisorption forces at higher temperatures. The layer of A
molecules is then exposed to another precursor gas containing B
molecules. The A molecules react with the B molecules to form an
extremely thin layer of solid material C on the workpiece W. The
chamber is then purged again with a purge gas to remove excess B
molecules.
[0006] FIG. 2 illustrates the stages of one cycle for forming a
thin solid layer using ALD techniques. A typical cycle includes (a)
exposing the workpiece to the first precursor A, (b) purging excess
A molecules, (c) exposing the workpiece to the second precursor B,
and then (d) purging excess B molecules. The purge process
typically comprises introducing a purge gas, which is substantially
non-reactive with either precursor, and exhausting the purge gas
and excess precursor from the reaction chamber in a pumping step.
In actual processing, several cycles are repeated to build a thin
film on a workpiece having the desired thickness. For example, each
cycle may form a layer having a thickness of approximately 0.5-10
.ANG., and thus it takes approximately 60-120 cycles to form a
solid layer having a thickness of approximately 60 .ANG..
[0007] One drawback of ALD processing is that it has a relatively
low throughput compared to CVD techniques. For example, ALD
processing typically takes several seconds to perform each
A-purge-B-purge cycle. This results in a total process time of
several minutes to form a single thin layer of only 60 .ANG.. In
contrast to ALD processing, CVD techniques only require about one
minute to form a 60 .ANG. thick layer. In single-wafer processing
chambers, ALD processes can be 500%-2000% longer than corresponding
single-wafer CVD processes. The low throughput of existing
single-wafer ALD techniques limits the utility of the technology in
its current state because ALD may be a bottleneck in the overall
manufacturing process.
[0008] One promising solution to increase the throughput of ALD
processing is processing a plurality of wafers (e.g., 20-250)
simultaneously in a batch process. As suggested in International
Publication No. WO 02/095807, the entirety of which is incorporated
herein by reference, such batch processes typically stack the
plurality of wafers in a wafer holder that is positioned in an
enclosure of a processing system. To increase the number of wafers
that can be treated at one time and concomitantly increase the
throughput of the system, the wafers are typically held in a
relatively close spaced-apart relationship. Unfortunately, this
close spacing between adjacent wafers hinders the flow of gas
adjacent the surface of the wafer, particularly adjacent the center
of each wafer.
[0009] In conventional single-wafer ALD systems, a gas "showerhead"
will be spaced in relatively close, parallel proximity with
substantially the entirety of the wafer surface. This facilitates
thorough, effective purging of the excess precursors A and B. In a
batch ALD system, however, gas is typically introduced to flow
longitudinally alongside the wafer holder. As a consequence, gas
exchange between the wafers takes place, in large part, by gas
diffusion rather than a significant flow rate of gas across the
wafer surface. To enhance the removal of excess precursor between
the wafers, conventional batch ALD processing typically involves
introducing a significant quantity of a purge gas to dilute the
remaining precursor, then drawing a vacuum on the enclosure to
remove the diluted gas. Unfortunately, this addition of excess
purge gas and subsequent pump-down can take a relatively long
period of time, further reducing the throughput of the batch ALD
processing system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIGS. 1A and 1B are schematic cross-sectional views of
stages in ALD processing in accordance with the prior art.
[0011] FIG. 2 is a graph illustrating a cycle for forming a layer
using ALD techniques in accordance with the prior art.
[0012] FIG. 3 is a schematic cross-sectional view of a microfeature
workpiece processing system in accordance with an embodiment of the
invention.
[0013] FIG. 4 is a schematic flow diagram illustrating aspects of a
method in accordance with one embodiment of the invention.
[0014] FIG. 5 is a flow diagram schematically illustrating aspects
of one embodiment of the pump/purge steps in FIG. 4.
[0015] FIG. 6 is a graph schematically illustrating gas pressures
and flow rates in accordance with one particular embodiment of the
invention.
[0016] FIG. 7 is a graph schematically illustrating partial
pressure of a precursor gas during various pump and/or purge
processes.
DETAILED DESCRIPTION
A. Overview
[0017] Various embodiments of the present invention provide
microfeature workpiece holders, systems including processing
chambers, and methods for depositing materials onto microfeature
workpieces. Many specific details of the invention are described
below with reference to reactors for depositing materials onto
microfeature workpieces. The term "microfeature workpiece" is used
throughout to include substrates upon which and/or in which
microelectronic devices, micromechanical devices, data storage
elements, read/write components, and other devices are fabricated.
For example, microfeature workpieces can be semiconductor wafers
such as silicon or gallium arsenide wafers, glass substrates,
insulative substrates, and many other types of materials. The
microfeature workpieces typically have submicron features with
dimensions of 0.05 microns or greater. Furthermore, the term "gas"
is used throughout to include any form of matter that has no fixed
shape and will conform in volume to the space available, which
specifically includes vapors (i.e., a gas having a temperature less
than the critical temperature so that it may be liquefied or
solidified by compression at a constant temperature). Several
embodiments in accordance with the invention are set forth in FIGS.
3-6 and the following text to provide a thorough understanding of
particular embodiments of the invention. A person skilled in the
art will understand, however, that the invention may have
additional embodiments, or that the invention may be practiced
without several of the details of the embodiments shown in FIGS.
3-6.
[0018] One embodiment of the invention provides a method of
depositing a material on a microfeature workpiece. In accordance
with this method, a plurality of microfeature workpieces are
positioned in a spaced relationship within an enclosure. A flow of
a first precursor gas is introduced to the enclosure at a first
enclosure pressure. The flow of the first precursor is terminated
and pressure within the enclosure is reduced to a second enclosure
pressure while introducing a flow of a purge gas at a first flow
rate. The processing system has a base pressure at the first flow
rate. A difference between the second enclosure pressure and the
first enclosure pressure is at least 90 percent of the difference
between the base pressure and the first enclosure pressure. After
reducing the pressure within the enclosure to the second enclosure
pressure, the flow rate of the purge gas is increased to a second
flow rate and the pressure within the enclosure is increased to a
third enclosure pressure. After increasing the pressure within the
enclosure to the third enclosure pressure, a flow of a second
precursor gas is introduced to the enclosure at a fourth enclosure
pressure. The third and fourth enclosure pressures may be
substantially the same, with any difference between the third and
fourth enclosure pressures being about 0-10 percent of the fourth
enclosure pressure.
[0019] A method in accordance with another embodiment of the
invention may also be used to deposit a material on a microfeature
workpiece. In this method, a plurality of microfeature workpieces,
each of which has a surface, is positioned within an enclosure. The
surfaces of the microfeature workpieces are exposed to a first
precursor gas at a first enclosure pressure to allow at least a
monolayer of the first precursor gas to be adsorbed on the surfaces
of the microfeature workpieces. Pressure within the enclosure is
reduced to a second, lower enclosure pressure via a pump-down
process. The pump-down process comprises withdrawing gas from the
enclosure, e.g., with a vacuum, while introducing a purge gas at a
first flow rate of no greater than about 250 sccm for a first
period of time. This pump-down process reduces the partial pressure
of the first precursor gas within the enclosure. After the
pump-down process, the enclosure is purged in a purge process that
includes introducing the purge gas at a second flow rate of at
least about 1000 sccm for a second period of time and allowing the
enclosure pressure to increase to a third enclosure pressure that
is greater than the second enclosure pressure. After the purge
process, the surfaces of the microfeature workpieces may be exposed
to a second precursor gas at a fourth enclosure pressure. The third
and fourth enclosure pressures may be substantially the same, with
any difference between the third and fourth enclosure pressures
desirably being about 0-10 percent of the fourth enclosure
pressure.
[0020] Another embodiment of the invention provides a microfeature
workpiece processing system that includes an enclosure, a gas
supply, a vacuum, and a programmable controller. The enclosure is
adapted to receive a plurality of microfeature workpieces for
simultaneous treatment. The gas supply is adapted to selectively
deliver a first gaseous precursor, a second gaseous precursor, and
a purge gas to the enclosure. The programmable controller is
operatively coupled to the gas supply and the vacuum, and the
controller may be programmed to carry out one of the aforementioned
methods or methods in accordance with other aspects of the
invention.
[0021] For ease of understanding, the following discussion is
subdivided into two areas of emphasis. The first section discusses
microfeature workpiece processing systems in accordance with
selected embodiments of the invention. The second section outlines
methods in accordance with other aspects of the invention.
B. Microfeature Workpiece Processing Systems
[0022] FIG. 3 schematically illustrates a reactor 10 in accordance
with one embodiment of the invention. This reactor 10 includes a
processing enclosure 20 coupled to a gas supply 30 and a vacuum 40.
The processing enclosure 20 generally includes an outer wall 22 and
an annular liner 24. A platform 60 seals against the outer wall or
some other part of the processing enclosure 20 to define a
deposition chamber 25. The liner 24 functionally divides the
deposition chamber 25 into a main chamber 28 and an annular exhaust
26.
[0023] One or more microfeature workpieces W, e.g., semiconductor
wafers, may be positioned in the deposition chamber 25 for
processing. In the illustrated embodiment, a plurality of
microfeature workpieces W are held in the processing enclosure 20
in a workpiece holder 70. It should be understood that FIG. 3 is
merely schematic in nature and any number (e.g., 20-250) of
workpieces. W may be held in the workpiece holder 70 for
simultaneous batch processing.
[0024] The reactor 10 also includes at least one heat source to
heat the workpieces W and maintain them at the desired temperature.
The heat source in FIG. 3 is typified as a radiant heater 50
comprising a series of radiant heat panels 50a and 50b arranged
about a circumference of the enclosure 20 to evenly heat the
workpieces W. In one embodiment, these heat panels 50a-b comprise
quartz-halogen lamps or other types of radiative heat sources. In
other embodiments, other types of heat sources may be employed. The
heater 50 may also include a power supply 52 that is coupled to the
first heat panel 50a by a first power line 54a and to the second
heat panel 50b by a second power line 54b.
[0025] Gas is introduced from the gas supply 30 to the deposition
chamber 25 by a gas line 32 and an inlet 36. The inlet 36 directs a
flow of gas into the main chamber 28 of the deposition chamber 25.
Under influence of the vacuum 40, gas introduced via the gas inlet
36 will flow through the main chamber 28, outwardly into the
annular exhaust 26, and out of the deposition chamber 25. A valve
assembly 34 in the gas line 32 may be operated by a controller 90
to selectively deliver gases to the deposition chamber 25 during
the deposition phase. In one embodiment, the controller 90
comprises a computer having a programmable processor programmed to
control operation of the reactor 10 to deposit material on the
workpieces W in accordance with one or more of the methods outlined
below. The controller 90 may be coupled to the vacuum 40 to control
its operation. The controller 90 may also be operatively connected
to the heater 50, e.g., via the power supply 52, to control the
temperature of the workpieces W.
[0026] Some aspects of the gas supply 30 will depend on the nature
of the deposition process to be carried out in the reactor 10. In
one embodiment, the reactor 10 is adapted to carry out an ALD
process employing multiple precursors. The gas supply 30 in such
embodiments can include a plurality of separate gas sources 31a-c,
and the valve assembly 34 may have a plurality of valves. For
example, the gas supply 30 may include one or more gaseous
precursors capable of reacting to deposit titanium nitride. In one
such implementation, the first gas source 31a is adapted to deliver
TiCl.sub.4, the second gas source 31b is adapted to deliver
NH.sub.3, and the third gas source 31c is adapted to deliver a flow
of a purge gas, e.g., nitrogen.
C. Methods of Depositing Materials on Microfeature Workpieces
[0027] As noted above, other embodiments of the invention provide
methods of processing microfeature workpieces. In the following
discussion, reference is made to the particular microfeature
workpiece processing system 10 shown in FIG. 3. It should be
understood, though, that reference to this particular processing
system is solely for purposes of illustration and that the methods
outlined below are not limited to any particular processing system
shown in the drawings or discussed in detail above.
[0028] FIGS. 4 and 5 schematically illustrate aspects of a method
of depositing a material on surfaces of a batch of microfeature
workpieces in accordance with one embodiment of the invention; FIG.
4 provides an overview, whereas FIG. 5 provides details of certain
aspects of FIG. 4. Turning first to FIG. 4, the workpiece
manufacturing process 100 may be initiated by positioning the
workpieces W in the enclosure 20 of an ALD reactor 10 or other
processing system (process 105). In process 110, the ambient
atmosphere that entered the main chamber 25 of the enclosure 20 may
be withdrawn, e.g., by means of the vacuum 40 and a flow of an
inert purge gas (e.g., nitrogen from the third gas source 31c of
the gas supply 30). If necessary, the workpieces W may also be
heated to the desired process temperature by the heaters 50.
[0029] With the majority of any deleterious gases removed from the
deposition chamber 25, a flow of the first precursor gas may be
initiated in process 115 and terminated in process 120. This will
deliver a pulse of the first precursor gas into the deposition
chamber 25, exposing a surface of each of the workpieces W in the
deposition chamber 25 to the first precursor. The first precursor
may be at least chemisorbed on the workpiece W. Theoretically, such
chemisorption will form a monolayer that is uniformly one molecule
thick on the entire surface of the workpiece W. Such a monolayer
may be referred to as a saturated monolayer. As a practical matter,
in some circumstances some minor portions of the workpiece surface
may not chemisorb a molecule of the precursor. Nevertheless, such
imperfect monolayers are still referred to herein as monolayers. In
many applications, a substantially saturated monolayer may be
suitable. A substantially saturated monolayer is a monolayer that
will yield a deposited layer exhibiting the requisite quality
and/or performance parameters.
[0030] As is known in the art, an excess of the first precursor gas
is typically delivered to the processing enclosure 20. This excess
first precursor gas is desirably removed from the vicinity of the
workpiece surface prior to introduction of the second precursor
gas. Inadequate removal of the first precursor gas prior to
introduction of the second precursor gas may result in a gaseous
phase reaction between the precursors that yields a material that
is less conformal to the topography of the workpiece surface or
otherwise adversely affects the quality of the deposited material.
Consequently, in the manufacturing process 100 of FIG. 4, a
pump/purge process 200 (detailed below) is carried out before
introducing the second precursor gas to the enclosure 20. After the
pump/purge process 200, a flow of the second precursor gas may be
initiated in process 130 to deliver a pulse of the second precursor
gas to the enclosure 20. This second precursor may chemisorb on the
first monolayer of the first precursor and/or react with the
monolayer to form a reaction product. This reaction product is
typically one or no more than a few molecules thick, yielding a
very thin, highly conformal nanolayer reaction product. After a
suitable exposure to the second gaseous precursor, the flow of the
second precursor gas may be terminated in process 135 and a
pump/purge process 200 may again be performed.
[0031] This series of first precursor-pump/purge-second
precursor-pump/purge processes may be considered one ALD cycle
adapted to deposit a single nanolayer of material. As noted above,
the ALD process may need to be repeated a number of times to
deposit a layer of material having an appropriate thickness. The
manufacturing process 100 of FIG. 4 may thus include a decision
process 140 that decides whether the layer deposited on the
microfeature workpieces W is thick enough. In many circumstances,
this decision will comprise determining whether a fixed number of
deposition cycles, which has been empirically determined to deposit
an adequate thickness, has been performed. If a sufficient
thickness has not been deposited, the manufacturing process 100 may
return to process 115 to deposit another thickness of the reaction
product. If the thickness is determined in process 140 to be
sufficient, though, the workpieces W may be removed from the
enclosure 20 in process 145.
[0032] FIG. 5 schematically illustrates the pump/purge process 200
of FIG. 4 in greater detail. This pump/purge process 200 generally
includes a pump process 210 and a purge process 220. The pump
process 210 may include introducing a flow of purge gas at a first
flow rate (process 212) and withdrawing gas from the enclosure 20
until a target pressure is reached (process 214). If the vacuum
system 40 of the reactor 10 is sufficiently robust, it may be
possible to omit the flow of purge gas in process 212 and instead
merely withdraw gas from the enclosure 20 with the vacuum 40 in
process 214. This will reduce the pressure within the enclosure 20
more rapidly, reducing the time necessary for the pump process 210.
For many commercial reactors 10, however, it may be advantageous to
continue a flow of purge gas at a relatively low flow rate to
reduce the chances of any backflow from or cross-contamination in
the vacuum 40.
[0033] The first flow rate suitable in process 212 will depend in
part on the design of the reactor 10, including its size and
geometry, and the precursor being removed. In many commercial
applications, though, a first flow rate of no greater than about
250 standard cubic centimeters per minute (sccm) will suffice. A
flow rate of 0-250 sccm will be appropriate for most applications,
but a flow rate of 50-250 sccm, e.g., 50-100 sccm, is preferred for
select embodiments. The particular embodiment illustrated in FIG. 5
shows the introduction of the purge gas in process 212 before
withdrawing gas from the enclosure in process 214. In other
embodiments, the order of processes 212 and 214 may be reversed or
processes 212 and 214 may start and end simultaneously.
[0034] After the pump process 210, the pump/purge process 200 of
FIG. 5 continues with the purge process 220. This purge process 220
includes increasing the flow of purge gas to a second flow rate in
process 222 and increasing pressure in the enclosure 20 to a
process pressure 224 that is higher than the target pressure in
process 214. In one embodiment, the second flow rate in process 222
is at least about four times the first flow rate (process 212),
though this multiple may be significantly higher. It is anticipated
that a second flow rate of at least 1000 sccm will be best in most
circumstances. In embodiments employing commercial-scale batch ALD
reactors 10, a second flow rate of no less than 2000 sccm may be
advantageous.
[0035] FIGS. 4 and 5 provide an overview of the manufacturing
process 100. FIG. 6 provides a schematic illustration of one
particular implementation of the manufacturing process 100 that
highlights some of the aspects and advantages of select embodiments
of the invention. The upper graph of FIG. 6 illustrates the
pressure in the processing enclosure 20 over the course of part of
the manufacturing process 100. The bottom graph of FIG. 6 is a
schematic plot of the flow rate of a purge gas, a first precursor
gas, and a second precursor gas as a function of time. The time
scale in both graphs of FIG. 6 is the same.
[0036] The timeline of FIG. 6 starts with the initiation of the
flow of the first precursor gas in process 115 of FIG. 4. (Like
reference numbers are used in FIGS. 4-6 to indicate like
processes.) The flow of the first precursor gas will continue until
it is terminated in process 120, whereupon the pump/purge process
200 may begin. As shown in the top graph of FIG. 6, the pressure in
the main chamber 28 of the enclosure 20 may remain substantially
constant at a selected process pressure P during the first
precursor gas pulse. The process pressure P will vary depending on
the nature of the deposition process being carried out, e.g., the
nature of the first and second precursor gases, the temperature of
the workpieces W, the volume and dimensions of the enclosure 20,
and other operating parameters.
[0037] As noted above, the pump/purge process 200 includes a
pump-down process 210 and a purge process 220. In the pump-down
process 210, the flow of purge gas may be relatively low, e.g.,
50-100 sccm. With the vacuum 40 activated, the pressure in the main
chamber 28 of the enclosure will drop fairly rapidly, as suggested
by curve X in the upper graph of FIG. 6. For any particular reactor
10 design and first flow rate during the pump-down process 210, the
main chamber 28 of the enclosure 20 will have a substantially
steady-state lower pressure identified in FIG. 6 as base pressure
B.
[0038] In the purge process 220, the flow rate of the purge gas is
increased and the pressure within the main chamber 28 of the
enclosure 20 is allowed to increase (curve Y). In one particular
embodiment, the enclosure pressure at the end of the purge process
220 is similar to the process pressure P at which the workpieces W
will be exposed to the second precursor gas. In one particular
embodiment, a difference between the enclosure pressure at the end
of the purge process 220 and the desired process pressure P at
which the workpieces W will be exposed to the second precursor gas
is about 0-10% of the process pressure P. In the particular
scenario illustrated in the top graph of FIG. 6, the pressure in
the enclosure may slightly exceed the process pressure P, but be
brought back down to the process pressure P by the end of the
pump/purge process 200. If the flow of the second precursor gas
were initiated in process 130 when the enclosure pressure is at or
close to the base pressure B, the controller 90 is likely to
overshoot the desired process pressure P before stabilizing the
enclosure pressure. Overshooting the process pressure P with the
flow of the second precursor can introduce undesirable variations
in the exposure of the workpieces W to the second precursor gas
from one cycle to the next. By increasing the enclosure pressure
during the purge process 220, the likelihood of overshooting the
process pressure P with the second precursor gas can be materially
reduced. In the particular scenario illustrated in FIG. 6, the
enclosure pressure may overshoot the process pressure P during the
purge process 220, but the enclosure pressure may be substantially
stabilized at the process pressure P before the flow of the second
precursor gas is initiated in process 130. This can enhance
uniformity of the process from one cycle to the next.
[0039] One objective of the pump/purge process 200 is to reduce the
concentration of any excess, nonadsorbed precursor gas in at least
the main chamber 28 of the enclosure 20 to an acceptable level. The
first precursor-pump/purge-second precursor-pump/purge cycle
typically must be repeated numerous times to deposit a suitable
thickness of material on the surfaces of the workpieces W. Reducing
the time of the pump/purge process 200, therefore, can materially
decrease the time needed to reach the suitable material
thickness.
[0040] FIG. 7 is a schematic graph comparing the expected
concentration of a precursor, expressed as a partial pressure of
the precursor in the enclosure, during a purge process 220 only,
during a pump-down process 210 only, and during a pump/purge
process 200 in accordance with embodiments of the invention. In
this graph, the process pressure P at which the pump/purge process
200 is initiated is arbitrarily set at 1 (i.e., 0 on the log scale
of FIG. 7).
[0041] If the pump-down process 210 were omitted and the purge
process 220 alone were relied on to reduce concentration of the
precursor, one would expect to see the log of the partial pressure
of the precursor decrease at a fairly constant rate over time. This
is represented in FIG. 7 by dashed curve 320a, which is generally
linear and has a relatively constant first slope S.sub.1. The slope
S.sub.1 will vary with a number of factors, including the geometry
of the enclosure 20, the relative spacing of the workpieces W, and
the rate at which the vacuum withdraws gas from the enclosure. All
other factors being equal, though, the slope S.sub.1 generally will
increase (i.e., the partial pressure will drop more quickly) with
increasing flow rates of purge gas into the enclosure. It should be
recognized that curve 320a is stylized and the partial pressure of
the precursor may deviate noticeably from this relatively straight
line, particularly at higher purge gas flow rates or higher vacuum
extraction rates.
[0042] If the purge process 220 were omitted and the pump-down
process alone were employed, one would expect to see a marked
drop-off in the partial pressure of the precursor in a first phase
310, as illustrated in the solid curve of FIG. 7. Once the base
pressure B (FIG. 6) is reached, though, further extraction of
precursor from the main chamber 28 of the enclosure 20 is limited
largely by the rate at which the precursor diffuses out of the
spaces between adjacent workpieces W. Hence, one would expect to
see the log of the partial pressure of the precursor decrease at a
fairly constant terminal rate during a second phase 312, yielding a
generally linear curve having a second slope S.sub.2. This second
slope S.sub.2 is expected to be less than the first slope S.sub.1
of curve 320a. One advantage of the pump-down process 210 is that
the partial pressure of the precursor drops off rapidly in the
first phase 310 to quickly reduce the partial pressure below a
level that promotes further adsorption. This facilitates more
precise control over the time the workpieces W are exposed to
material concentrations of the precursor.
[0043] The pump/purge process 200 illustrated in FIGS. 4-6 is
expected to achieve benefits of both the pump-down process 210 and
the purge process 220, yet reduce the total time needed to reduce
the concentration of precursor in the enclosure to an acceptable
level before introducing the next precursor. In the particular
example shown in FIG. 7, the pump-down process 210 continues until
the enclosure pressure reaches the base pressure B, taking
advantage of the rapid decrease in partial pressure of the
precursor in the first phase 310 of the pump-down. Rather than
continuing the second phase 312 of the pump-down process 210,
though, the purge process 220 is initiated promptly after reaching
the base pressure B. Curve 320b, which illustrates the partial
pressure of precursor during this purge process 220, may be a
relatively straight line having a slope S.sub.3 that is greater
than the slope S.sub.2 of the partial pressure curve in the second
phase 312 of the pump-down process 210. It is anticipated that the
slopes S.sub.1 and S.sub.3 of curves 320a and 320b, respectively,
will be similar and may be substantially the same. As illustrated
in FIG. 7, the increased slope S.sub.3 of curve 320b compared to
slope S.sub.2 during the second pump-down phase 312 will result in
a time savings .DELTA.t in achieving the same partial pressure of
the precursor. As a consequence, the pump/purge process 200 will
allow the concentration of precursor in the main chamber 28 of the
enclosure 20 to be reduced to the same level in a shorter period of
time than either the pump-down process 210 alone (the solid curve
in FIG. 7) or the purge process 220 alone (curve 320a), increasing
throughput of the reactor 10.
[0044] In the particular embodiment shown in FIG. 7, the purge
process 220 is initiated promptly upon reaching the base pressure
B. In other embodiments, the pump-down process 210 is allowed to
continue for a limited time (e.g., 3 seconds or less) thereafter.
Because the slope S.sub.2 of the partial pressure curve in the
second phase 312 of the pump-down 210 is less than the slope
S.sub.3 of curve 320b, though, delaying initiation of the purge
process 220 will reduce the time savings .DELTA.t. In other
embodiments, the time purge process 220 is initiated before the
base pressure B is reached. In the particular embodiment
illustrated in FIG. 6, for example, the purge process 220 starts
while the enclosure pressure is slightly higher than the base
pressure B achievable in a steady state second phase 312 of the
pump-down process 210. In some embodiments of the invention, the
purge process 220 is initiated when the difference between the
enclosure pressure and the process pressure P is at least 90% of
the difference between the base pressure B and the process pressure
P. In one particular embodiment, the purge process 220 is initiated
when the difference between the enclosure pressure and the process
pressure P is at least 90% of the difference between the base
pressure B and the process pressure P, but no later than reaching
the base pressure. This will achieve the rapid initial drop-off in
partial pressure of the precursor, but initiate the purge process
220 before the less productive second phase 312 of the pump-down
process 210.
[0045] The diffusion rate of any given gas will vary with pressure,
with the diffusion rate increasing as pressure is reduced.
Different gases diffuse at different rates, though. For example,
the diffusion rate D for TiCl.sub.4 in nitrogen is expected to be
on the order of 0.032 m.sup.2/s at an enclosure pressure of about 1
torr, but this diffusion rate will increase to about 0.80 m.sup.2/s
at about 0.04 torr. In contrast, NH.sub.3, which may be used as a
second precursor with TiCl.sub.4 to deposit TiN, has a diffusion
rate D in nitrogen of about 0.088 m.sup.2/s at about 1 torr, which
climbs to about 2.2 m.sup.2/s at about 0.04 torr. NH.sub.3,
therefore, should diffuse out of the spaces between the workpieces
W more readily than TiCl.sub.4.
[0046] The curves 310, 312, 320a, and 320b in FIG. 7 are expected
to follow the same general relationship for most precursor gases,
but the precise shapes of the curves (e.g., the slopes S.sub.1-3)
will vary from one gas to another. If the pump-down process 210
continues for a fixed time in all pump/purge processes 200 in the
manufacturing process 100 of FIG. 4, this time may be selected so
the enclosure pressure is reduced by at least 90% of the difference
between the base pressure B and the process pressure P for both
precursor gases. This may dictate that the enclosure pressure at
the end of the pump-down process 210 will vary from one pump/purge
process 200 to the next. In another embodiment, the parameters of
the pump/purge process 200 may be varied depending on the diffusion
characteristics of the precursor gas being purged: This will allow
each pump/purge process 200 to be optimized, further enhancing
throughput of the reactor 10 without compromising product
quality.
[0047] The above-detailed embodiments of the invention are not
intended to be exhaustive or to limit the invention to the precise
form disclosed above. Specific embodiments of, and examples for,
the invention are described above for illustrative purposes, but
those skilled in the relevant art will recognize that various
equivalent modifications are possible within the scope of the
invention. For example, whereas steps are presented in a given
order, alternative embodiments may perform steps in a different
order. The various embodiments described herein can be combined to
provide further embodiments.
[0048] Unless the context clearly requires otherwise, throughout
the description and the claims, the words "comprise," "comprising,"
and the like are to be construed in an inclusive sense as opposed
to an exclusive or exhaustive sense, i.e., in a sense of
"including, but not limited to." Use of the word "or" in the claims
in reference to a list of items is intended to cover a) any of the
items in the list, b) all of the items in the list, and c) any
combination of the items in the list.
[0049] In general, the terms used in the following claims should
not be construed to limit the invention to the specific embodiments
disclosed in the specification unless the above-detailed
description explicitly defines such terms. While certain aspects of
the invention are presented below in certain claim forms, the
inventors contemplate various aspects of the invention in any
number of claim forms. Accordingly, the inventors reserve the right
to add additional claims after filing the application to pursue
such additional claim forms for other aspects of the invention.
* * * * *