U.S. patent application number 10/717881 was filed with the patent office on 2005-05-19 for gas distribution showerhead featuring exhaust apertures.
This patent application is currently assigned to APPLIED MATERIALS, INC., A Delaware corporation. Invention is credited to Gianoulakis, Steven, Janakiraman, Karthik.
Application Number | 20050103265 10/717881 |
Document ID | / |
Family ID | 34574628 |
Filed Date | 2005-05-19 |
United States Patent
Application |
20050103265 |
Kind Code |
A1 |
Gianoulakis, Steven ; et
al. |
May 19, 2005 |
Gas distribution showerhead featuring exhaust apertures
Abstract
Embodiments in accordance with the present invention relate to
systems and methods for distributing process gases over the surface
of a workpiece. In accordance with one embodiment of the present
invention, process gases are flowed from a source to a workpiece
surface through a gas distribution showerhead defining a plurality
of orifices. The gas distribution showerhead also features a
plurality of exhaust orifices for removing material above the wafer
surface. The supplemental exhaust afforded by the showerhead
exhaust orifices serves to reduce variations in gas velocity
attributable to radial flow across the wafer surface, thereby
enhancing the uniformity between resulting processing at the wafer
edge and center. The ratio of the distribution and exhaust aperture
areas may vary or remain constant across the faceplate.
Additionally, the size and number of distribution and exhaust
apertures may be selected to optimize gas distribution across the
semiconductor wafer surface.
Inventors: |
Gianoulakis, Steven;
(Pleasanton, CA) ; Janakiraman, Karthik; (San
Jose, CA) |
Correspondence
Address: |
Patent Counsel
Applied Materials, Inc.
Legal Affairs Department
P.O. Box 450A, M/S 2061
Santa Clara
CA
95052
US
|
Assignee: |
APPLIED MATERIALS, INC., A Delaware
corporation
Santa Clara
CA
|
Family ID: |
34574628 |
Appl. No.: |
10/717881 |
Filed: |
November 19, 2003 |
Current U.S.
Class: |
118/715 |
Current CPC
Class: |
C23C 16/4412 20130101;
C23C 16/45565 20130101; C23C 16/455 20130101 |
Class at
Publication: |
118/715 |
International
Class: |
C23C 016/00 |
Claims
What is claimed is:
1. An apparatus comprising: walls enclosing a process chamber; a
wafer susceptor positioned within the chamber; a first exhaust
conduit in fluid communication with the chamber; and a processing
gas source in fluid communication with the chamber through a gas
distribution showerhead, the gas distribution showerhead
comprising; a first channel in fluid communication with the
processing gas source and with apertures distributed over a lower
surface of the showerhead; and a second channel separate from the
first channel and in fluid communication with a second exhaust
conduit and with exhaust apertures distributed over the lower
surface of the showerhead.
2. The apparatus of claim 1 wherein the apertures define a first
area and the exhaust apertures define a second area.
3. The apparatus of claim 2 wherein a ratio of the first area to
the second area is substantially constant as a function of radial
distance from the center of the gas distribution showerhead.
4. The apparatus of claim 2 wherein a ratio of the first area to
the second area varies as a function of radial distance from the
center of the gas distribution showerhead.
5. The apparatus of claim 4 wherein the ratio of the first area to
the second area varies linearly as a function of radial distance
from the center of the gas distribution showerhead.
6. The apparatus of claim 4 wherein the ratio of the first area to
the second area varies nonlinearly as a function of radial distance
from the center of the gas distribution showerhead.
7. The apparatus of claim 4 wherein the ratio of the first area to
the second area increases as a function of radial distance from the
center of the gas distribution showerhead.
8. The apparatus of claim 4 wherein the ratio of the first area to
the second area decreases as a function of radial distance from the
center of the gas distribution showerhead.
9. The apparatus of claim 1 wherein the first exhaust conduit and
the second exhaust conduit are in fluid communication with a common
foreline.
10. The apparatus of claim 9 wherein the plurality of second
channels are in fluid communication with the foreline through a
first valve and the second exhaust conduit is in fluid
communication with the foreline through a second valve.
11. The apparatus of claim 1 wherein the first exhaust conduit and
the second exhaust conduit are in communication with a common
vacuum pump.
12. The apparatus of claim 1 wherein the first exhaust conduit and
the second exhaust conduit are in communication with separate
vacuum pumps.
13. A method of processing a semiconductor workpiece, the method
comprising: flowing a process gas to a semiconductor workpiece
through a first plurality of orifices positioned in a gas
distribution faceplate; and removing gas from over the
semiconductor workpiece through a chamber exhaust port and a second
plurality of orifices positioned in the gas distribution
faceplate.
14. The method of claim 13 further comprising removing the gas
through only the chamber exhaust port prior to flowing the process
gas.
15. The method of claim 13 further comprising removing the gas
through the chamber exhaust port and the second plurality of
orifices prior to flowing the process gas.
16. The method of claim 13 further comprising initially removing
gas through only the chamber exhaust port.
17. The method of claim 13 further comprising initially removing
gas through only the second plurality of orifices.
18. The method of claim 13 wherein the processing chamber is
evacuated to a pressure below 20 Torr.
19. The method of claim 18 further comprising generating a plasma
in the processing chamber prior to flowing the process gas.
20. The method of claim 13 further comprising adjusting a rate of
removal of gas through the chamber exhaust port during
processing.
21. The method of claim 13 further comprising adjusting a rate of
removal of gas through the second plurality of orifices is adjusted
during processing.
22. A method of processing a semiconductor wafer in a chamber
comprising: inserting a semiconductor wafer into the chamber;
evacuating the chamber through a first exhaust port; introducing at
least one process gas through a first set of orifices located on a
surface of a showerhead; removing gas through the first exhaust
port; and removing gas through a plurality of orifices positioned
on the surface of the showerhead.
23. The method of claim 22 wherein a larger volume of gas is
removed through the first exhaust port than is removed through the
plurality of orifices.
24. The method of claim 22 wherein the chamber is evacuated to a
pressure below 20 Torr.
25. The method of claim 24 wherein a plasma is generated in the
chamber prior to the step of introducing the at least one process
gas.
26. The method of claim 22 wherein removal of the gas through the
first exhaust port and through the plurality of orifices occurs
substantially simultaneously.
27. A method of controlling uniformity of a property of a film
deposited on a semiconductor wafer, the method comprising:
positioning a wafer in a processing chamber; introducing gases to
the wafer through a first plurality of orifices positioned on a
faceplate; removing the gases through a second plurality of
orifices positioned on the faceplate; and simultaneously removing
the gases across a radial exhaust path.
28. The method of claim 27 further comprising evacuating the
chamber across the radial exhaust path only, prior to flowing the
gases.
29. The method of claim 27 further comprising evacuating the
chamber across the radial exhaust path and the second plurality of
orifices prior to flowing the gases.
30. The method of claim 27 further comprising initially removing
the gases through only the radial exhaust path.
31. The method of claim 27 further comprising initially removing
the gases through only the second plurality of orifices.
32. The method of claim 27 wherein the chamber is evacuated to a
pressure below about 20 Torr.
33. The method of claim 32 further comprising generating a plasma
in the chamber.
34. The method of claim 27 wherein a rate of removing gas across
the radial exhaust path is adjusted during processing.
35. The method of claim 27 wherein a rate of removing gas through
the second plurality of orifices is adjusted during processing.
Description
BACKGROUND OF THE INVENTION
[0001] Semiconductor wafer processing systems generally contain a
process chamber having a pedestal or susceptor for supporting a
semiconductor wafer within the chamber proximate a processing
region. The chamber forms a vacuum enclosure defining, in part, the
process region. A gas distribution assembly or showerhead provides
one or more process gases to the process region. The gases may then
be heated and/or supplied with energy to form a plasma which
performs certain processes upon the wafer. These processes may
include chemical vapor deposition (CVD) to deposit a film upon the
wafer, or an etch reaction to remove material from the wafer.
[0002] As the size and complexity of semiconductor devices has
increased, wafer real estate has become more valuable.
Consequently, it is desirable to locate devices not only near the
center of the wafer, but as close to the outer edge of the wafer as
possible. Location of devices near the wafer periphery has
increased the demands on the radial uniformity of wafer processing
steps. As a result, it is desirable if semiconductor fabrication
processes achieve uniformity across nearly the entire wafer
surface.
[0003] FIG. 2 shows a prior art deposition chamber 210 with a prior
art showerhead 220. The prior art showerhead 220 features a
plurality of equally spaced holes 222 in the lower surface 225 of
the showerhead. Process gases flow into the showerhead 220 through
the inlet pipe 214 along the direction marked 215. The holes 222
serve to distribute the process gases along directions 218 inside
the showerhead. The process gases exit the showerhead through holes
222 and interact with the surface of the semiconductor wafer 230.
The spatial distribution of the gases inside the showerhead
determines the uniformity of gas distributed across the surface of
the semiconductor wafer.
[0004] During a deposition process, the process gases flow over the
top surface 235 of the semiconductor wafer 230 and react with the
surface 235 or with other gaseous species to form the desired film
236 on the wafer surface 235. The gases flow in directions 238 over
the edge of the wafer and are exhausted through the annular exhaust
port 250.
[0005] In the prior art deposition chamber illustrated in FIG. 2,
to reach the exhaust port 250, process gases introduced by the
showerhead over the center of the wafer generally flow in a radial
direction along the wafer surface and over the edges of the wafer
along directions 238. Therefore, the velocity of gaseous species
may increase as the gases flow in a radial direction toward the
edge of the wafer.
[0006] In a deposition process, the rate of deposition typically
depends on the flow of reactive species to the semiconductor wafer
surface. If the velocity of reactive species increases in the
radial direction, the deposition rate may be greater near the wafer
periphery than near the wafer center, resulting in non-uniform film
thickness.
[0007] Therefore, there is a need in the art for an apparatus
exhibiting improved uniformity of films deposited on semiconductor
wafers.
SUMMARY OF THE INVENTION
[0008] Embodiments in accordance with the present invention relate
to systems and methods for distributing process gases over the
surface of a workpiece. In accordance with one embodiment of the
present invention, process gases are flowed from a source to a
workpiece surface through a gas distribution showerhead defining a
plurality of orifices. The gas distribution showerhead also
features a plurality of exhaust orifices for removing material from
above the wafer surface. The supplemental exhaust afforded by the
showerhead exhaust orifices serves to reduce variations in gas
velocity attributable to radial flow across the wafer surface,
thereby enhancing the uniformity of processing at the edge of the
wafer versus the center of the wafer.
[0009] An embodiment of an apparatus in accordance with the present
invention comprises walls enclosing a process chamber, and a wafer
susceptor positioned within the chamber. A first exhaust conduit is
in fluid communication with the chamber, and a processing gas
source is in fluid communication with the chamber through a gas
distribution showerhead. The gas distribution showerhead comprises
a first channel in fluid communication with the processing gas
source and with apertures distributed over a lower surface of the
showerhead, and a second channel separate from the first channel
and in fluid communication with a second exhaust conduit and with
exhaust apertures distributed over the lower surface of the
showerhead.
[0010] An embodiment of a method in accordance with the present
invention for processing a semiconductor workpiece, comprises,
flowing a process gas to a semiconductor workpiece through a first
plurality of orifices positioned in a gas distribution faceplate.
Gas is removed from over the semiconductor workpiece through a
chamber exhaust port and a second plurality of orifices positioned
in the gas distribution faceplate.
[0011] An embodiment of a method in accordance with the present
invention for processing a semiconductor wafer in a chamber,
comprises, inserting a semiconductor wafer into the chamber, and
evacuating the chamber through a first exhaust port. At least one
process gas is introduced through a first set of orifices located
on a surface of a showerhead. Gas is removed through the first
exhaust port, and gas is removed through a plurality of orifices
positioned on the surface of the showerhead.
[0012] An embodiment of a method in accordance with the present
invention of controlling uniformity of a property of a film
deposited on a semiconductor wafer, comprises, positioning a wafer
in a processing chamber, and introducing gases to the wafer through
a first plurality of orifices positioned on a faceplate. The gases
are removed through a second plurality of orifices positioned on
the faceplate, and the gases are simultaneously removed across a
radial exhaust path.
[0013] These and other embodiments of the present invention, as
well as its features and some potential advantages are described in
more detail in conjunction with the text below and attached
figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1A is a simplified schematic diagram of a CVD
system.
[0015] FIG. 1B is a simplified schematic illustration of an
exploded, perspective view of the chamber wall portion of a CVD
system.
[0016] FIG. 1C is a simplified schematic illustration of an
exploded, perspective view of the chamber lid assembly of a CVD
system.
[0017] FIG. 2 is a simplified schematic diagram of a prior art
deposition chamber and showerhead.
[0018] FIG. 3A is a simplified schematic diagram of a deposition
chamber according to an embodiment of the present invention.
[0019] FIG. 3B is a simplified schematic diagram of a deposition
chamber according to an alternative embodiment of the present
invention.
[0020] FIG. 3C is a simplified schematic diagram of a deposition
chamber according to an additional embodiment of the present
invention.
[0021] FIG. 4A is a simplified side, cross sectional view of a
showerhead according to an embodiment of the present invention.
[0022] FIG. 4B is a simplified bottom view of a showerhead
according to an embodiment of the present invention.
[0023] FIG. 4C is a simplified bottom view of a showerhead
illustrating the relationship between the bottom view figures.
[0024] FIG. 4CA is an enlarged view of a portion of the underside
of the showerhead shown in FIG. 4C.
[0025] FIG. 5 is a simplified bottom view of a showerhead according
to another embodiment of the present invention.
[0026] FIG. 6 is a simplified bottom view of a radial section of a
showerhead according to an embodiment of the present invention.
[0027] FIG. 7 is a simplified bottom view of a radial section of a
showerhead according to another embodiment of the present
invention.
[0028] FIG. 8 is a simplified bottom view of a radial section of a
showerhead according to another embodiment of the present
invention.
[0029] FIG. 9A is a flowchart illustrating an embodiment of a
method of operating a deposition chamber in accordance with the
present invention.
[0030] FIG. 9B is a flowchart illustrating an alternative
embodiment of a method of operating a deposition chamber in
accordance with the present invention.
[0031] FIG. 9C is a flowchart illustrating another alternative
embodiment of a method of operating a deposition chamber in
accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0032] Embodiments in accordance with the present invention relate
to systems and methods for distributing process gases over the
surface of a workpiece. In accordance with one embodiment of the
present invention, process gases are flowed from a source to a
workpiece surface through a gas distribution showerhead defining a
plurality of orifices. The gas distribution showerhead also
features a plurality of exhaust orifices for removing material from
above the wafer surface. The supplemental exhaust afforded by the
showerhead exhaust orifices serves to reduce variations in gas
velocity attributable to radial flow across the wafer surface,
thereby enhancing the uniformity of processing at the edge of the
wafer versus the center of the wafer.
[0033] FIG. 3A illustrates a deposition chamber 300 according to an
embodiment of the present invention. Process gases enter the
chamber through the showerhead 310 with dual channel faceplate 311
and flow into a cylindrical volume 305 located above the surface of
the semiconductor wafer 320. The flow of process gases into the
chamber is illustrated by arrows 312 extending through the
faceplate on the lower surface of the showerhead. The cylindrical
volume 305 defined by the area of the wafer and the distance
between the wafer and the faceplate is sometimes referred to as the
reaction region. Reaction of the deposition gases with each other
and the semiconductor wafer result in deposition of film 321 on the
upper surface of the semiconductor wafer 320.
[0034] After passing over the edge of the susceptor, gases are
exhausted through the primary or main annular exhaust port 340,
which in certain embodiments may be separated from the process
chamber by a ceramic ring 341 containing holes 349. Exhaust gases
passing from the region near the wafer surface through this exhaust
path are labeled with arrows 322 located on the peripheral edges of
the susceptor 330. This main exhaust port has sufficient capacity
to maintain a desired process pressure by controlling the quantity
of exhaust gas flowing through the exhaust port 340.
[0035] In an embodiment in accordance with the present invention,
the quantity of exhaust gases is identified by a specific recipe.
In some embodiments, this main exhaust port has sufficient capacity
to ensure maintenance within the processing chamber of sufficiently
low pressures to sustain a plasma therein. The exhaust of gases
through port 340 also minimizes re-deposition, which may occur if
unreacted gases are not exhausted from the chamber and pass back
over the surface of the wafer.
[0036] The operator may wish to control the distance between the
semiconductor wafer 320 and faceplate 310 to compensate for the
impact of various process parameters dependent upon the wafer to
faceplate distance. Such process parameters include but are not
limited to, the concentration of reactive species, the residence
times of reactive species, and the temperature.
[0037] In addition to the primary exhaust path 325 provided around
the edge of the susceptor, embodiments in accordance with the
present invention also provide additional supplemental exhaust
paths through the dual channel showerhead. Specifically, arrows 314
and 316 of FIG. 3A illustrate the supplemental exhaust path that
passes through the lower surface of faceplate 311 and out the side
of the showerhead. As illustrated in FIG. 3A, exhaust lines 318
connected to the showerhead are routed outside the main chamber
300, separating the supplemental showerhead exhaust gases flowing
along paths 314 and 316 from the primary radial exhaust gases
flowing along paths 322. Valves 346 are installed in exhaust lines
318 to provide control over the supplemental exhaust gas flow rate
and pressure. In the particular embodiment illustrated in FIG. 3A,
the exhaust line 342 connected to the main exhaust port 340 and the
exhaust lines 318 connected to the supplemental exhaust paths in
the showerhead are rejoined outside the chamber 300 and are
connected to the same foreline pump 344. Valve 348 is installed in
exhaust line 342 to provide control over the primary exhaust gas
flow rate and pressure.
[0038] FIG. 3B illustrates an alternative embodiment in accordance
with the present invention in which exhaust lines 367 connected to
showerhead 360 remain inside the chamber 350. Process gases enter
the chamber through the showerhead 360 with dual channel faceplate
361. The flow of process gases into the chamber is illustrated by
arrows 362 extending through the faceplate on the lower surface of
the showerhead. Reaction of the deposition gases with each other
and with the semiconductor wafer result in film deposition 371 on
the upper surface of the semiconductor wafer 370. The gap proximate
to the outer edge of the susceptor 355 defines a primary exhaust
path. Exhaust gases passing from the region near the wafer surface
through this exhaust path are labeled with arrows 372 located on
the peripheral edges of the susceptor 355.
[0039] The exhaust gases from the showerhead 366 and the radial
exhaust gases 372 are combined in region 368 and are removed
through main exhaust port 373 by means of vacuum pump 374. A single
foreline pump is connected to exhaust port 373 to exhaust the
chamber 350.
[0040] An additional embodiment in accordance with the present
invention is illustrated in FIG. 3C. In the processing chamber
architecture shown in FIG. 3C, both primary pump 390 and secondary
pump 391 exhaust gases from the chamber.
[0041] Process gases enter the chamber 376 through the showerhead
377 with dual channel faceplate 378. The flow of process gases into
the chamber is illustrated by arrows 385 extending through the
faceplate on the lower surface of the showerhead. Reaction of the
deposition gases with each other and with the semiconductor wafer
result in the deposition of film 382 on the upper surface of the
semiconductor wafer 381.
[0042] Primary pump 390 exhausts gases along radial exhaust path
386 and secondary pump 391 exhausts gases along supplemental
exhaust path 387 and 388.
[0043] The annular exhaust port proximate to the outer edge of the
susceptor 380 defines an exhaust path for deposition gases. Exhaust
gases passing from the region near the wafer surface through this
exhaust path are labeled with arrows 386, located on the peripheral
edges of the susceptor 380. The exhaust lines 395 connected to the
showerhead 377 are routed outside the main chamber 376, separating
the showerhead exhaust gases 387 and 388 from the radial exhaust
gases 386.
[0044] In the embodiment illustrated in FIG. 3C, the exhaust line
396 connected to the main exhaust port 394 is connected the a
primary foreline pump 390. A separate foreline pump 391 is
connected to the exhaust line 393, which is connected to the
supplemental exhaust lines 395 in communication with the
showerhead. Consequently, in the embodiment illustrated in FIG. 3C,
separate pumps exhaust the gases from the separate radial and
supplementary exhaust paths.
[0045] Furthermore, in the embodiment illustrated in FIG. 3C, valve
397 is located in exhaust line 396 and valve 392 is located in
exhaust line 393. In some embodiments of the present invention, the
valves 392 and 392 may be used to create differential pumping
pressure between the primary and supplemental exhaust paths.
[0046] In some embodiments, the area of the faceplate dedicated to
exhaust paths is a function of radial distance from the center of
the faceplate. The additional exhaust paths provided by the dual
channel faceplate enable one skilled in the art to optimize the
deposition process by exercising precise control over the process
parameters as a function of radial distance from the center of the
wafer. These parameters may include but are not limited to, for
example, the concentration of reactive species, the residence time
of the reactive species, the concentration of carrier gases, the
velocity of gas flow, and the gas pressure in the reaction
region.
[0047] The optimization of the deposition process utilizing the
dual channel faceplate architecture in accordance with an
embodiment of the present invention may increase uniformity of film
thickness across the wafer surface. Optimization of the process may
also result in preferential variation in film thickness, density,
index of refraction, dielectric constant, or other film properties
as a function of radial distance from the center of the wafer.
[0048] FIG. 4A is an enlarged cross section view showing details of
a distribution/exhaust showerhead according to an embodiment of the
present invention. The showerhead 400 is a component of a larger
chamber 440. This embodiment of the distribution/exhaust showerhead
400 includes gas distribution apertures 410 located at various
locations on the bottom surface of the faceplate 405. Process gases
are injected through distribution channels 410 and distribution
apertures 411, flow along lines 412 and contact the top surface of
semiconductor wafer 430. Exhaust gases flow along lines 418 and
through exhaust path 419 as they are exhausted over the edge of the
semiconductor wafer 430 in a radial direction. In certain
embodiments of the present invention, the exhaust path 419 may be
referred to as the primary exhaust path.
[0049] The distribution/exhaust showerhead 400 also includes gas
exhaust apertures 415 located at various locations on the bottom
surface of the faceplate 405. Additional exhaust gases flow from a
region near the top surface of the semiconductor wafer 430 and
through the gas exhaust apertures 415 and gas exhaust channels 416.
These exhaust gases flow along lines 417 and are exhausted from the
reaction chamber. In some embodiments of the present invention, the
exhaust path through channel 416 is referred to as the
supplementary exhaust path. The percentage of gases exhausted
through exhaust channel 419 and through exhaust channel 416 will
depend on the gas pressure along the surface of the wafer and in
the primary and supplementary exhaust channels, among other
factors.
[0050] FIG. 4B shows a partial bottom view of an embodiment of the
faceplate according to the present invention. In this embodiment,
gas distribution apertures include injection holes 450 located at
various locations across the bottom of the faceplate. Gas exhaust
apertures include exhaust holes 455 located at various other
locations across the bottom of the faceplate.
[0051] In the simplified partial bottom view illustrations
presented herein (FIG. 4B-FIG. 8), cylindrically symmetric features
have been omitted for ease of description and illustration. FIGS.
4C-4CA illustrates how the simplified partial bottom view
illustrations presented in FIG. 4B-FIG. 8 relate to the larger
faceplate design. These partial bottom view illustrations represent
a magnified view 480 in FIG. 4CA, of a portion 485 of the faceplate
475 shown in FIG. 4C. Consequently, details related to the circular
nature of the faceplate, which are obvious to one of skill in the
art, are omitted from these bottom view illustrations.
[0052] If a deposition process requires that reactant gases are not
commingled prior to reaching the surface of the semiconductor
wafer, the gas distribution channels and the corresponding
apertures can be subdivided to prevent the gases from mixing prior
to reaching the surface. U.S. Pat. No. 6,086,677, assigned to the
assignee of the present invention and incorporated herein by
reference, describes a faceplate and gas distribution manifold
assembly in which process gases may be delivered to the process
region through a common faceplate without commingling.
[0053] In the embodiment illustrated in FIG. 4B, the area of the
faceplate comprising gas distribution apertures can be summed to
determine a combined (or total faceplate) distribution area.
Likewise, the area of the faceplate comprising exhaust apertures
can be summed to determine a combined (or total faceplate) exhaust
area. In the embodiment illustrated in FIG. 4B, the ratio of the
combined distribution area to the combined exhaust area is
approximately 4:1. Furthermore, this ratio of the combined
distribution/exhaust area is constant across the surface of the
faceplate.
[0054] In accordance with embodiments of the present invention, the
number of both the gas distribution apertures and the gas exhaust
apertures can be selected to optimize the ratios and flow rates of
the various process gases. For example, in accordance with one
embodiment, the number of exhaust apertures, and thus the exhaust
aperture area, may be varied as a function of faceplate position to
control the localized flow of gaseous species in accordance with
process requirements.
[0055] Alternatively, in addition to varying the number of gas
distribution and exhaust apertures, the size of both the gas
distribution and exhaust apertures can be varied in accordance with
process requirements. In an embodiment in which small aperture size
is desirable, a larger number of small apertures can be located on
the faceplate to attain the same aperture area as that attained
with a smaller number of large apertures. Conversely, where a
particular application dictates that a smaller number of large
apertures are desirable, embodiments in accordance with the present
invention provide the required flexibility to attain this goal.
[0056] While the embodiment shown in FIG. 4B features a
distribution/exhaust area ratio that is constant as a function of
radial distance, this is not required by the present invention. In
accordance with alternative embodiments, the ratio of the
distribution aperture area to the exhaust aperture area may be
varied across the faceplate to promote either process uniformity or
variation, as desired.
[0057] FIG. 5 accordingly illustrates another embodiment of the
present invention in which the number of exhaust apertures 520 is
increased relative to that illustrated in FIG. 4B, resulting in an
increase in the combined exhaust area. In this embodiment, the
number of distribution apertures 510 have remained unchanged.
Similar effects could be achieved by increasing the size of the gas
exhaust apertures shown in FIG. 4B, thereby decreasing the ratio of
combined distribution area to combined exhaust area while
maintaining the same number of distribution and exhaust
apertures.
[0058] In some deposition applications, the semiconductor wafer may
be spun in a horizontal plane during the deposition process. The
spinning of the wafer may result in increased flow of gases along
the wafer surface due to centripetal forces. Accordingly, FIG. 6
illustrates another embodiment of the present invention that may be
utilized to further ensure radial uniformity of the deposited
films. In this partial bottom view, the number of exhaust apertures
520 increases as the radial distance 630 from the center of the
wafer increases. Therefore, the embodiment of FIG. 6 provides
additional exhaust aperture area as the radial distance from the
wafer center increases. The embodiment of FIG. 6 increases the
localized ratio of gas distribution area to gas exhaust area as a
function of radial distance from the center of the wafer. By
contrast, FIG. 7 illustrates an alternative functional
relationship, in which the exhaust aperture area decreases with
radial distance 630.
[0059] In certain embodiments in accordance with the present
invention, the increase in exhaust area can be linear with respect
to the radial distance as shown in Eqn. 1. FIG. 6 illustrates a
step-wise linear relationship, as the exhaust area increases by an
additional exhaust aperture 520 per unit area with each group of
two distribution blocks.
Area.sub.exhaust=K.smallcircle.dist.sub.radial (Eqn. 1)
[0060] However, with alternative embodiments, the increase in
exhaust aperture area on the showerhead can be non-linear with
respect to the radius. Such a non-linear relationship could take
the form of a function that monotonically increases or decreases
with distance, for example increasing the exhaust area with the
square of the radial distance.
[0061] FIG. 8 illustrates an alternative functional relationship,
in which, starting at the center of the wafer, the exhaust aperture
area increases with radial distance, reaches a maximum, then
decreases as the radial distance increases to the radius of the
faceplate. Various other non-linear functional relationships will
be apparent to those skilled in the art. Decreases in aperture size
and increased aperture density can serve to "smooth out" the
step-wise variations illustrated in FIGS. 6, 7, and 8.
[0062] The embodiments discussed above increase or decrease the
localized exhaust area to produce variation in the localized ratio
of gas distribution area to gas exhaust area as a function of
radial distance. Alternatively, the local gas distribution area as
a function of radial distance from the center of the wafer could be
varied to achieve the desired results. As discussed with respect to
variation of the exhaust area, the size and number of gas
distribution apertures can be varied to achieve the desired
distribution of reactive species.
[0063] As mentioned previously, the susceptor is controllably
translatable in the vertical direction. The vertical motion of the
susceptor is often used in wafer loading and unloading operations,
as well as to vary the distance from the wafer to the faceplate
during deposition.
[0064] Variation of the distance from the wafer to the faceplate
during deposition can have several impacts on the deposition
process. Typically, deposition processes have used a wide spacing
(.gtoreq.150 mils) between the wafer and the faceplate. At a
spacing of 150 mils or less, the gas pressure in the reaction
region may be non-uniform across the wafer surface, with the
pressure at the wafer edge typically less than the pressure at the
wafer center. This decreased pressure at the wafer periphery lowers
the concentration of reactive species and reduces deposition at the
wafer edge.
[0065] However, using a faceplate according to an embodiment of the
present invention, it is possible to counteract this edge thinning
by increasing the exhaust area corresponding to the edge of the
wafer, thereby increasing the flow of reactive species to the wafer
edge. The particular embodiment illustrated in FIG. 6 would be
useful in such an application, as the exhaust area increases with
the radial distance. Alternative embodiments exhibiting a
non-linear increase in exhaust area with radial distance could also
be useful.
[0066] Other applications may call for a decrease in the spacing
between the wafer and the faceplate to less than 150 mils in order
to enhance processing speed and throughput. As the showerhead
approaches the wafer and the reaction region decreases in volume,
reactive species distributed near the center of the wafer
experience longer residence times, resulting in a greater thickness
of the deposited film near the wafer center.
[0067] Accordingly, in certain embodiments of the present
invention, additional exhaust area may be provided on the
showerhead to increase flow of exhaust gases near the wafer center,
reducing on a local scale the concentration of reactive species and
the resulting deposition rate. FIG. 7 illustrates such an
embodiment, in which the number of exhaust apertures and
consequently, the exhaust area, is greater in the center of the
faceplate than near the edges. Alternatively, or in conjunction
with changing the number of exhaust apertures, the size of the
individual exhaust apertures could be increased to achieve the same
increase in exhaust area.
[0068] In still other processing systems, the susceptor or other
support structure may be characterized by a non-uniform temperature
distribution. For example, the temperature at the center of
susceptor may be maintained at a higher temperature than the
susceptor periphery to enable rapid cooling of the susceptor
without introduction of tensile stress and possible fracture of the
susceptor assembly. As deposition rate is partly a function of
temperature, an increased temperature at the susceptor center may
decrease the local deposition rate with respect to the susceptor
edge. Embodiments of the present invention can counteract such
non-uniform deposition by increasing the exhaust flow near the
center of the wafer, thereby increasing the concentration of
reactive species and hence the reaction rate.
[0069] The desire to impose different processing regimes at various
regions of a substrate may also arise due to the dictates of other
processing steps. For example, chemical mechanical polishing (CMP)
techniques are widely used to planarize layers of material that
have been deposited by CVD. However, rather than producing a
completely planarized wafer surface, the CMP process itself can
introduce radial variations in surface planarity and film
thickness. Therefore, in some processes utilizing CMP techniques,
the deposition of films with specifically tailored non-uniform
thickness profiles can be desirable.
[0070] Accordingly, an embodiment in accordance with the present
invention may be used to deposit films having non-uniform thickness
as a function of radial distance from the center of the wafer,
thereby counteracting non-uniform effects of the CMP process. The
end result of such a two-step deposition/polishing process will
produce a film exhibiting desired thickness uniformity.
[0071] Embodiments in accordance with the present invention provide
the system operator with several methods of processing a
semiconductor wafer. For example, FIG. 9A is a flowchart
illustrating a method 900 in which a deposition system may be
operated in accordance with the present invention. First, in step
910 a wafer is inserted into the deposition chamber by means known
to those skilled in the art. In step 912 the chamber is sealed and
evacuated to a reduced pressure. In the embodiment illustrated in
FIG. 9A, the chamber may be evacuated by opening the valve in the
foreline connected to the primary pump. In alternative embodiments,
the chamber may be evacuated by opening the valve in the foreline
connected to the secondary exhaust pump or both the primary and
secondary pumps in combination. In some embodiments in accordance
with the present invention, the pressure may be lowered to a level
sufficient to support the generation of a plasma in the chamber.
For example, the pressure may be lowered to a pressure between 5
and 20 torr.
[0072] Once the chamber reaches the desired pressure, in step 912
process gases are introduced into the chamber through a plurality
of orifices located on the faceplate of the showerhead. The number,
size, and distribution of these gas distribution apertures has been
described extensively above. The process gases flow over the top
surface of the semiconductor wafer and react with the surface or
with other gaseous species to form the desired film on the wafer
surface.
[0073] Process gases and reaction byproducts are simultaneously
exhausted from the chamber through the primary radial exhaust path
in step 916 and the secondary exhaust path comprising exhaust
channels in the showerhead in step 918. The ratio of gas volume
passing through these alternate exhaust paths may be controlled by
the relative positions of the valves installed in the exhaust lines
of the respective paths.
[0074] Upon the completion of the deposition process, in step 920
the delivery of process gases is discontinued. In steps 922 and
924, respectively, the chamber is returned to atmospheric pressure,
and the wafer is removed.
[0075] FIG. 9B is a flowchart illustrating an alternative
embodiment of a method of operating the deposition system in
accordance with the present invention. In step 930 of method 901, a
wafer is inserted into the deposition chamber. The chamber is
sealed and evacuated to a reduced pressure using the primary
exhaust path in step 932. In the alternative embodiment of the
method illustrated in FIG. 9B, the chamber is evacuated by opening
of a valve located in the foreline connected to the primary exhaust
pump. Once the chamber reaches the desired pressure, process gases
are introduced through a plurality of orifices located on the
faceplate of the showerhead in step 934. In step 936 initial
exhaust of the process gases and reaction byproducts is
accomplished through the use of the primary exhaust channel.
Subsequently, the process gases and reaction byproducts are
simultaneously exhausted from the chamber through the first radial
exhaust path in step 938 and the second exhaust path comprising
exhaust channels in the showerhead in step 940. In the alternative
embodiment of the method 901 shown in FIG. 9B, the majority of the
exhaust gases pass through the primary exhaust channel, lines, and
pump. The secondary exhaust path is used to remove gases from the
chamber in smaller amounts than the primary exhaust path, thereby
providing the operator with a "fine-tuning" control over the
process parameters. The ratio of gas volume passing through the
secondary and primary exhaust paths may be varied between a value
close to zero and 1.
[0076] Upon the completion of the deposition process, in step 942
the delivery of process gases is discontinued. In steps 944 and
946, respectively, the chamber is returned to atmospheric pressure,
and the wafer is removed.
[0077] FIG. 9C is a flowchart of yet another alternative embodiment
of a method of operating the chamber in accordance with the present
invention. In step 950 of method 902, the wafer is inserted into
the chamber. The chamber is evacuated in step 952 and a plasma is
struck in the chamber in step 954. The chamber may be evacuated by
the exhaust of gases through either the primary or secondary
exhausts, or a combination of the two. After the plasma has
stabilized, in step 956 process gases are introduced into the
chamber through a plurality of orifices located on a surface of the
faceplate.
[0078] Process gases and reaction byproducts are removed from the
chamber through both the primary and secondary exhaust paths in
steps 958 and 960, respectively. In the embodiment of the method
902 illustrated in FIG. 9C, the exhaust rates of the primary and
secondary exhaust paths are adjusted during the deposition process
in steps 962 and 964. In some embodiments, the exhaust rates may be
varied during the deposition process to modulate the properties of
the deposited film. These properties may include, but are not
limited to film thickness, density, index of refraction, or
dielectric constant.
[0079] Upon the completion of the deposition process, in step 966
the flow of process gases is discontinued. In steps 968 and 970,
respectively, the chamber is vented to atmospheric pressure, and
the wafer is removed.
[0080] The supplemental exhaust path provided through the
showerhead of embodiments in accordance with the present invention
offer certain advantages over the prior art. In addition to the
traditional exhaust paths offered at the susceptor edge (see flow
lines 322 in FIG. 3A), the exhaust apertures present in the
showerhead offer a supplemental exhaust path useful in optimizing
the flow of reactive species near the wafer surface. Additionally,
the variability in the ratio of the distribution to exhaust area as
a function of radial distance provides spatial control over both
the distribution and exhaust of process gases and reaction
byproducts.
[0081] In accordance with one embodiment of the present invention,
the volume of gases flowing in the radial direction across the
wafer surface and out through the radial exhaust path may be
modified by design of the faceplate. In such an embodiment, the
volume and concentration of reactive gas species flowing laterally
across the wafer surface may be controlled by the selective exhaust
of process gases and reaction byproducts through the supplementary
showerhead exhaust paths. In a specific embodiment, the volume and
concentration of reactive gas species flowing across the wafer may
be maintained at a constant value as a function of radial distance,
by increasing the exhaust aperture area in regions of increased
lateral flow volume. Such improved process control may result in
greater film uniformity.
[0082] In other embodiments of the present invention, the residence
time of reactive species at the wafer surface may be controlled by
the spatial distribution of exhaust aperture area of the
showerhead. For example, FIG. 8 shown an embodiment in accordance
with the present invention wherein the exhaust aperture area
provided by the showerhead near the wafer center 835 and edge 840
is less than the exhaust aperture area at a distance equal to 1/2
the faceplate radius. The region at a distance equal to 1/2 the
faceplate radius may be referred to as the mid-radius region 830.
Consequently, process gases introduced at the wafer center 835
travel a larger distance across the wafer surface before exiting
the reaction region through the faceplate in the mid-radius region
830 than process gases introduced closer to the mid-radius region
830. In alternative embodiments, the flow of process gases across
the wafer surface near the mid-radius region is enhanced by
selective placement of gas distribution and exhaust apertures.
[0083] One suitable CVD apparatus in which the method of the
present invention can be carried out is shown in FIG. 1A, which is
a vertical, cross-sectional view of a CVD system 10, having a
vacuum or processing chamber 15 that includes a chamber wall 15a
and chamber lid assembly 15b. Chamber wall 15a and chamber lid
assembly 15b are shown in exploded, perspective views in FIGS. 1B
and 1C.
[0084] CVD system 10 contains a gas distribution manifold 11 for
dispersing process gases to a substrate (not shown) that rests on a
heated pedestal 12 centered within the process chamber. During
processing, the substrate, for example, a semiconductor wafer, is
positioned on a flat (or slightly convex) surface 12a (FIG. 1B) of
pedestal 12. The pedestal can be moved controllably between a lower
loading/off-loading position (not shown) and an upper processing
position (shown in FIG. 1A), which is closely adjacent to manifold
11. A centerboard (not shown) includes sensors for providing
information on the position of the wafers.
[0085] Deposition and carrier gases are introduced into chamber 15
through perforated holes 13b (FIG. 1C) of a flat, circular gas
distribution faceplate 13a, as has been described extensively
above. More specifically, deposition process gases flow into the
chamber through the inlet manifold 11 (indicated by arrow 40 in
FIG. 1A), through a conventional perforated blocker plate 42 and
then through holes 13b in gas distribution faceplate 13a.
[0086] Before reaching the manifold, deposition and carrier gases
are input from gas sources 7a through gas supply lines 8 of gas
delivery system 7 (FIG. 1A) into a mixing system 9 where they are
combined and then sent to manifold 11. Generally, the supply line
for each process gas includes (i) several safety shut-off valves
(not shown) that can be used to automatically or manually shut-off
the flow of process gas into the chamber, and (ii) mass flow
controllers (also not shown) that measure the flow of gas through
the supply line. When toxic gases (for example, ozone or
halogenated gas) are used in the process, the several safety
shut-off valves are positioned on each gas supply line in
conventional configurations.
[0087] The deposition process performed in CVD system 10 can be
either a thermal process or a plasma-enhanced process. In a
plasma-enhanced process, an RF power supply 44 applies electrical
power between the gas distribution faceplate 13a and the pedestal
so as to excite the process gas mixture to form a plasma within the
cylindrical region between the faceplate 13a and the pedestal,
referred to as the "reaction region." Constituents of the plasma
react to deposit a desired film on the surface of the semiconductor
wafer supported on pedestal 12. RF power supply 44 is a mixed
frequency RF power supply that typically supplies power at a high
RF frequency (RF.sub.1) of 13.56 MHz and at a low RF frequency
(RF.sub.2) of 360 KHz to enhance the decomposition of reactive
species introduced into the vacuum chamber 15. In a thermal
process, RF power supply 44 would not be utilized, and the process
gas mixture thermally reacts to deposit the desired films on the
surface of the semiconductor wafer supported on pedestal 12, which
is resistively heated to provide thermal energy for the
reaction.
[0088] During a plasma-enhanced deposition process, the plasma
heats the entire process chamber 10, including the walls of the
chamber body 15a surrounding the exhaust passageway 23 and the
shut-off valve 24. When the plasma is not turned on or during a
thermal deposition process, a hot liquid is circulated through the
walls 15a of the process chamber to maintain the chamber at an
elevated temperature. Fluids used to heat the chamber walls 15a
include the typical fluid types, i.e., water-based ethylene glycol
or oil-based thermal transfer fluids. This heating beneficially
reduces or eliminates condensation of undesirable reactant products
and improves the elimination of volatile products of the process
gases and other contaminants that might contaminate the process if
they were to condense on the walls of cool vacuum passages and
migrate back into the processing chamber during periods of no gas
flow.
[0089] The remainder of the gas mixture that is not deposited in a
layer, including reaction products, is evacuated from the chamber
by a vacuum pump 50 connected to the exhaust passageway 23 by
foreline 55. Specifically, the gases are exhausted through an
annular, slot-shaped orifice 16 surrounding the reaction region and
into an annular exhaust plenum 17. The annular slot 16 and the
plenum 17 are defined by the gap between the top of the chamber's
cylindrical side wall 15a (including the upper dielectric lining 19
on the wall) and the bottom of the circular chamber lid 20. The
360.degree. circular symmetry and uniformity of the slot orifice 16
and the plenum 17 are typically important to achieving a uniform
flow of process gases over the wafer so as to deposit a uniform
film on the wafer.
[0090] From the exhaust plenum 17, the gases flow underneath a
lateral extension portion 21 of the exhaust plenum 17, past a
viewing port (not shown), through a downward-extending gas passage
23, past a vacuum shut-off valve 24 (whose body is integrated with
the lower chamber wall 15a), and into the exhaust outlet 25 that
connects to the external vacuum pump 50 through foreline 55.
[0091] The wafer support platter of the pedestal 12 (preferably
aluminum, ceramic, or a combination thereof) is resistively-heated
using an embedded single-loop embedded heater element configured to
make two full turns in the form of parallel concentric circles. An
outer portion of the heater element runs adjacent to a perimeter of
the support platter, while an inner portion runs on the path of a
concentric circle having a smaller radius. The wiring to the heater
element passes through the stem of the pedestal 12.
[0092] Typically, any or all of the chamber lining, gas inlet
manifold faceplate, and various other reactor hardware are made out
of material such as aluminum, anodized aluminum, or a ceramic. An
example of such a CVD apparatus is described in U.S. Pat. No.
5,558,717 entitled "CVD Processing Chamber". The U.S. Pat. No.
5,558,717 is assigned to Applied Materials, Inc., the assignee of
the present invention, and is incorporated by reference for all
purposes.
[0093] A lift mechanism and motor (not shown) raises and lowers the
heated pedestal assembly 12 and its wafer lift pins 12b as wafers
are transferred into and out of the body of the chamber by a robot
blade (not shown) through an insertion/removal opening 26 in the
side of the chamber 10. The motor raises and lowers pedestal 12
between a processing position 14 and a lower, wafer-loading
position. The motor, valves or flow controllers connected to the
supply lines 8, gas delivery system, throttle valve, RF power
supply 44, and chamber and substrate heating systems are all
controlled by a system controller 34 (FIG. 1A) over control lines
36, of which only some are shown. Controller 34 relies on feedback
from optical sensors to determine the position of movable
mechanical assemblies such as the throttle valve and susceptor
which are moved by appropriate motors under the control of
controller 34.
[0094] In one embodiment, the system controller includes a hard
disk drive (memory 38), a floppy disk drive and a processor 37. The
processor contains a single-board computer (SBC), analog and
digital input/output boards, interface boards and stepper motor
controller boards. Various parts of CVD system 10 conform to the
Versa Modular European (VME) standard which defines board, card
cage, and connector dimensions and types. The VME standard also
defines the bus structure as having a 16-bit data bus and a 24-bit
address bus.
[0095] System controller 34 controls all of the activities of the
CVD machine. The system controller executes system control
software, which is a computer program stored in a computer-readable
medium such as a memory 38. Preferably, memory 38 is a hard disk
drive, but memory 38 may also be other kinds of memory. The
computer program includes sets of instructions that dictate the
timing of introduction and evacuation of gases, the mixture of
gases, chamber pressure, chamber temperature, RF power levels,
susceptor position, and other parameters of a particular process.
Other computer programs stored on other memory devices including,
for example, a floppy disk or other another appropriate drive, may
also be used to operate controller 34.
[0096] The above reactor description is mainly for illustrative
purposes, and other plasma CVD equipment such as electron cyclotron
resonance (ECR) plasma CVD devices, induction coupled RF high
density plasma CVD devices, or the like may be employed.
Additionally, variations of the above-described system, such as
variations in pedestal design, heater design, RF power frequencies,
location of RF power connections and others are possible. For
example, the wafer could be supported by a susceptor and heated by
quartz lamps. The layer and method for forming such a layer of the
present invention is not limited to any specific apparatus or to
any specific plasma excitation method.
[0097] It should be understood that the inventions described herein
can be employed in any substrate processing system which uses a
showerhead to distribute process gas to the substrate. This
includes CVD, nitridation, oxidation, etch and cleaning systems, to
name just a few examples. Although various embodiments which
incorporate teachings of the present invention have been shown and
described in detail herein, those skilled in the art can readily
devise many other varied embodiments that still incorporate these
teachings.
[0098] Other embodiments are within the following claims.
* * * * *