U.S. patent application number 14/194549 was filed with the patent office on 2016-12-29 for capped ald films for doping fin-shaped channel regions of 3-d ic transistors.
The applicant listed for this patent is LAM RESEARCH CORPORATION. Invention is credited to Reza Arghavani, Ananda Banerji, Adrien LaVoie, Jun Qian, Shankar Swaminathan, Samantha Tan, Bhadri N. Varadarajan.
Application Number | 20160379826 14/194549 |
Document ID | / |
Family ID | 53949826 |
Filed Date | 2016-12-29 |
View All Diagrams
United States Patent
Application |
20160379826 |
Kind Code |
A9 |
Arghavani; Reza ; et
al. |
December 29, 2016 |
CAPPED ALD FILMS FOR DOPING FIN-SHAPED CHANNEL REGIONS OF 3-D IC
TRANSISTORS
Abstract
Disclosed herein are methods of doping a fin-shaped channel
region of a partially fabricated 3-D transistor on a semiconductor
substrate. The methods may include forming a multi-layer
dopant-containing film on the substrate, forming a capping film
comprising a silicon carbide material, a silicon nitride material,
a silicon carbonitride material, or a combination thereof, the
capping film located such that the multi-layer dopant-containing
film is located in between the substrate and the capping film, and
driving dopant from the dopant-containing film into the fin-shaped
channel region. Multiple dopant-containing layers of the film may
be formed by an atomic layer deposition process which includes
adsorbing a dopant-containing film precursor such that it forms an
adsorption-limited layer on the substrate and reacting adsorbed
dopant-containing film precursor. Also disclosed herein are
multi-station substrate processing apparatuses for doping the
fin-shaped channel regions of partially fabricated 3-D
transistors.
Inventors: |
Arghavani; Reza; (Scotts
Valley, CA) ; Tan; Samantha; (Fremont, CA) ;
Varadarajan; Bhadri N.; (Beaverton, OR) ; LaVoie;
Adrien; (Newberg, OR) ; Banerji; Ananda; (West
Linn, OR) ; Qian; Jun; (Tualatin, OR) ;
Swaminathan; Shankar; (Beaverton, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LAM RESEARCH CORPORATION |
Fremont |
CA |
US |
|
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20150249013 A1 |
September 3, 2015 |
|
|
Family ID: |
53949826 |
Appl. No.: |
14/194549 |
Filed: |
February 28, 2014 |
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Application
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Patent Number |
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13607386 |
Sep 7, 2012 |
8956983 |
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14194549 |
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13242084 |
Sep 23, 2011 |
8637411 |
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13607386 |
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13084399 |
Apr 11, 2011 |
8728956 |
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13242084 |
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13084305 |
Apr 11, 2011 |
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13242084 |
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61324710 |
Apr 15, 2010 |
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61372367 |
Aug 10, 2010 |
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61379081 |
Sep 1, 2010 |
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61417807 |
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61649114 |
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Current U.S.
Class: |
438/548 ;
118/697; 428/428 |
Current CPC
Class: |
H01L 21/2225 20130101;
C23C 16/045 20130101; H01L 21/223 20130101; H01L 21/2252 20130101;
H01L 21/67155 20130101; C23C 16/45529 20130101; C23C 16/52
20130101; H01L 21/67207 20130101; C23C 16/45544 20130101; C23C
16/50 20130101; H01L 29/66803 20130101 |
International
Class: |
H01L 21/223 20060101
H01L021/223; C23C 16/455 20060101 C23C016/455; C23C 16/52 20060101
C23C016/52; C23C 16/50 20060101 C23C016/50; H01L 21/22 20060101
H01L021/22; H01L 21/67 20060101 H01L021/67 |
Claims
1. A method of doping a fin-shaped channel region of a partially
fabricated 3-D transistor on a semiconductor substrate, the method
comprising: (a) forming a dopant-containing film on the substrate,
wherein multiple dopant-containing layers of the film are formed by
an atomic layer deposition process comprising: (i) adsorbing a
dopant-containing film precursor onto the substrate such that the
precursor forms an adsorption-limited layer on the substrate; (ii)
removing at least some unadsorbed dopant-containing film precursor
from the volume surrounding the adsorbed precursor; (iii) reacting
adsorbed dopant-containing film precursor, after removing
unadsorbed precursor in (ii), to form a dopant-containing layer on
the substrate; (iv) removing desorbed dopant-containing film
precursor and/or reaction by-product from the volume surrounding
the dopant-containing layer when present after reacting the
adsorbed precursor; and (v) repeating (i) through (iv) to form
multiple dopant-containing layers of the dopant-containing film;
(b) forming a capping film comprising a silicon carbide material, a
silicon nitride material, a silicon carbonitride material, or a
combination thereof, the capping film located such that the
dopant-containing film formed in (a) is located in between the
substrate and the capping film; and (c) driving dopant from the
dopant-containing film into the fin-shaped channel region.
2. The method of claim 1, further comprising: (d) after (c),
removing at least a portion of the dopant containing film and/or at
least a portion of the capping film from the substrate.
3. The method of claim 1, wherein the dopant-containing film
substantially conforms to the shape of the fin-shaped channel
region.
4. The method of claim 1, wherein the driving in (c) comprises a
thermal anneal which enhances diffusion of dopant from the
dopant-containing film to the fin-shaped channel region.
5. The method of claim 1, wherein the dopant is boron.
6. The method of claim 5, wherein at least some of the
dopant-containing layers comprise a borosilicate glass.
7. The method of claim 6, wherein the dopant-containing film
precursor is an alkyl borate.
8. The method of claim 7, wherein the alkyl borate is trimethyl
borate.
9. The method of claim 1, wherein the dopant is phosphorous.
10. The method of claim 1, wherein the dopant is arsenic.
11. The method of claim 1, wherein the reacting in (a)(iii)
comprises contacting the adsorbed film precursor with a plasma.
12. The method of claim 1, wherein the reacting in (a)(iii)
comprises reacting the adsorbed film precursor with another
reactive chemical species which may or may not be first adsorbed
onto the substrate.
13. The method of claim 1, wherein forming the capping film
comprises a chemical vapor deposition process.
14. The method of claim 13, wherein the chemical vapor deposition
process is plasma enhanced.
15. The method of claim 1, wherein forming the capping film
comprises an atomic layer deposition process.
16. The method of claim 1, wherein the fin-shaped channel region
has a width of less than about 12 nanometers.
17. The method of claim 1, wherein the average thickness of the
capping layer is between about 10 and 100 Angstroms.
18. The method of claim 1, wherein the relative standard deviation
in the thickness of the capping layer is less than about 10%.
19. The method of claim 1, wherein the average combined
concentration of silicon carbide, silicon nitride and silicon
carbonitride in the capping film is between about 2 and 3
g/cm.sup.3.
20. The method of claim 1, wherein (a) further comprises forming
multiple layers of material substantially free of the dopant, at
least some of the layers formed by an atomic layer deposition
process comprising: (vi) adsorbing a dopant-free film precursor
onto the substrate such that the precursor forms an
adsorption-limited layer on the substrate; (vii) removing
unadsorbed dopant-free film precursor from the volume surrounding
the adsorbed precursor; (viii) reacting the adsorbed dopant-free
film precursor, after removing unadsorbed precursor in (vii), to
form a substantially dopant-free layer on the substrate; (ix)
removing desorbed dopant-free film precursor and/or reaction
by-product from the volume surrounding the substantially
dopant-free layer when present after reacting the adsorbed
precursor; and (x) repeating (vi) through (ix) to form multiple
substantially dopant-free layers of the dopant-containing film.
21. The method of claim 20, wherein at least some of the
substantially dopant-free layers comprise a dielectric
material.
22. The method of claim 21, wherein the dielectric material is
silicon dioxide.
23. The method of claim 20, wherein in (a): a first dopant-rich
portion of the film is formed by depositing multiple
dopant-containing layers in (i) through (v) sequentially, without
intervening deposition of a substantially dopant-free layer; and a
first substantially dopant-free portion of the film is formed by
depositing multiple substantially dopant-free layers in (vi)
through (x) sequentially, without intervening deposition of a
dopant-containing layer.
24. The method of claim 23, wherein in (a): a second dopant-rich
portion of the film is formed by depositing multiple
dopant-containing layers in (i) through (v) sequentially, without
intervening deposition of a substantially dopant-free layer; and a
second substantially dopant-free portion of the film is formed by
depositing multiple substantially dopant-free layers in (vi)
through (x) sequentially, without intervening deposition of a
dopant-containing layer; and wherein the first and second
dopant-rich and substantially dopant-free portions of the film are
deposited in the following sequence: first dopant-rich portion,
then first substantially dopant-free portion, then second
dopant-rich portion, then second substantially dopant-free
portion.
25. A dopant-containing film for doping the fin-shaped channel
region of a partially fabricated 3-D transistor on a semiconductor
substrate, the film comprising: a first dopant-rich portion of the
film formed by conformally depositing multiple dopant-containing
layers sequentially, without intervening deposition of a
substantially dopant-free layer; a first substantially dopant-free
portion of the film formed by conformally depositing multiple
substantially dopant-free layers sequentially, without intervening
deposition of a dopant-containing layer; a second dopant-rich
portion of the film formed by conformally depositing multiple
dopant-containing layers sequentially, without intervening
deposition of a substantially dopant-free layer; a second
substantially dopant-free portion of the film formed by conformally
depositing multiple substantially dopant-free layers sequentially,
without intervening deposition of a dopant-containing layer; and a
capping film comprising a silicon carbide material, a silicon
nitride material, a silicon carbonitride material, or a combination
thereof; wherein: the first substantially dopant-free portion is
located between the first and second dopant-rich portions; the
second dopant-rich portion is located between the first and second
substantially dopant-free portions; and the layer of capping film
is located such that the first and second dopant-rich portions and
the first and second substantially dopant-free portions are in
between the substrate and the capping film.
26. The dopant-containing film of claim 25, wherein the dopant is
boron.
27. The dopant-containing film of claim 26, wherein at least some
of the dopant-containing layers comprise a borosilicate glass.
28. The dopant-containing film of claim 27, wherein the
dopant-containing film precursor is an alkyl borate.
29. The dopant-containing film of claim 25, wherein at least some
of the substantially dopant-free layers comprise a dielectric
material.
30. The dopant-containing film of claim 29, wherein the dielectric
material is silicon dioxide.
31. A multi-station substrate processing apparatus for doping the
fin-shaped channel regions of partially fabricated 3-D transistors
on the surfaces of multiple semiconductor substrates at multiple
process stations, the apparatus comprising: a plurality of process
stations contained in one or more processing chambers, each process
station having a substrate holder; one or more valves for
controlling flow of dopant-containing film precursor to the process
stations; one or more valve-operated vacuum sources for removing
dopant-containing film precursor from the volumes surrounding the
process stations contained in the one or more processing chambers;
and one or more controllers comprising machine-readable
instructions for operating the one or more valves and one or more
vacuum sources to dope the fin-shaped channel regions on the
surfaces of the substrates, including instructions for: (a) forming
a dopant-containing film on a substrate at a process station
contained in a processing chamber, wherein multiple
dopant-containing layers of the film are formed by an atomic layer
deposition process comprising: (i) introducing a dopant-containing
film precursor into the processing chamber containing the process
station having the substrate holder holding the substrate, and
allowing the precursor to adsorb onto the surface of the substrate
such that the precursor forms an adsorption-limited layer on the
substrate; (ii) removing unadsorbed dopant-containing film
precursor from the volume surrounding the adsorbed precursor; (iii)
reacting adsorbed dopant-containing film precursor, after removing
unadsorbed precursor in (ii), to form a dopant-containing layer on
the substrate; (iv) removing desorbed dopant-containing film
precursor and/or reaction by-product from the volume surrounding
the dopant-containing layer when present after reacting the
adsorbed precursor; and (v) repeating (i) through (iv) to form
multiple dopant-containing layers of the dopant-containing film;
(b) forming a capping film comprising a silicon carbide material, a
silicon nitride material, a silicon carbonitride material, or a
combination thereof, the capping film located such that the
dopant-containing film formed in (a) is in between the substrate
and the capping film; and (c) driving dopant from the
dopant-containing film into a fin-shaped channel region.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0001] FIG. 1A displays a side view schematic of a traditional
planar IC transistor.
[0002] FIG. 1B displays a cross-sectional view schematic of a
traditional planar IC transistor.
[0003] FIG. 1C displays a perspective view schematic of a modern
tri-gate IC transistor employing a fin-shaped channel region.
[0004] FIG. 1D displays another perspective view schematic of a
modern tri-gate IC transistor employing a fin-shaped channel
region.
[0005] FIG. 2A schematically illustrates the shadowing effect which
may occur when attempting to dope the channel region of high aspect
ratio fin-shaped structures via conventional ion-implantation
techniques. This figure illustrates the scenario where the
shadowing effect of an adjacent fin structure is increased due to
the presence of deposited gate electrode material.
[0006] FIG. 2B also schematically illustrates the shadowing effect
which may occur when attempting to dope the channel region of high
aspect ratio fin-shaped structures via conventional
ion-implantation techniques. This figure illustrates the scenario
where the shadowing effect of an adjacent fin structure is
increased due to the presence of a pattern mask layer.
[0007] FIG. 2C again schematically illustrates the shadowing effect
which may occur when attempting to dope the channel region of high
aspect ratio fin-shaped structures via conventional
ion-implantation techniques. This figure illustrates the scenario
where the shadowing effect of an adjacent fin structure is
increased due to the presence of deposited gate electrode material
and also by the presence of a pattern mask layer.
[0008] FIG. 3A schematically illustrates a dopant-containing film
having a capping film.
[0009] FIG. 3B schematically illustrates the dopant-containing film
of FIG. 3A disposed on a fin-shaped channel region for doping the
channel region.
[0010] FIGS. 4A and 4B display schematics of a dopant-containing
borosilicate glass (BSG) films sandwiched between silicon dioxide
(SiO.sub.2) layers which are used to demonstrate boron dopant
diffusion through SiO.sub.2 layers via the SIMS experiments shown
in FIG. 4C.
[0011] FIG. 4C displays the results of secondary ion mass
spectroscopy (SIMS) experiments which demonstrate diffusion of
boron dopant through the SiO.sub.2 of the films schematically
illustrated in FIGS. 4A and 4B.
[0012] FIG. 5 displays the results of SIMS experiments
demonstrating reduced diffusion of boron dopant through silicon
carbide (SiC) layers sandwiching a BSG film relative to the dopant
diffusion exhibited through SiO.sub.2 exhibited in FIG. 4C.
[0013] FIG. 6A presents a flowchart schematically illustrating a
method of doping a fin-shaped channel region of a partially
fabricated 3-D transistor on a semiconductor substrate using a
dopant-containing film and a capping film having a silicon carbide
material, a silicon nitride material, a silicon carbonitride
material, or a combination thereof.
[0014] FIG. 6B present a flowchart of an atomic layer deposition
(ALD) process sequence for depositing a dopant-containing film.
[0015] FIG. 7 schematically illustrates a dopant-containing film
similar to that illustrated in FIG. 3A but in FIG. 7 exhibiting a
film structure wherein dopant-rich portions are interspersed with
substantially dopant-free portions.
[0016] FIG. 8 schematically illustrates a substrate processing
station suitable for performing film-forming ALD operations such as
those employed in the methods disclosed herein.
[0017] FIG. 9 schematically illustrates a multi-station substrate
processing tool suitable for performing film-forming ALD operations
such as those employed in the methods disclosed herein.
BACKGROUND
[0018] Traditionally, integrated circuit (IC) transistors have
employed a planar design wherein components of the
transistor--source, drain, and channel--are formed in the surface
of the semiconductor substrate, and the gate component is formed as
a flat structure atop the channel region of the substrate's
surface. More recently, however, the desire for smaller and smaller
device sizes has motivated the development of so-called 3-D
transistors wherein source, drain, and channel are formed in
fin-shaped structures which extend vertically from the substrate
surface, generally with a high aspect ratio. With the channel
formed in these vertical fin structures, the gate component of a
3-D transistor can be made to wrap around the channel region,
substantially increasing the surface area of the channel region
relative to its volume exposed directly to the gate voltage.
[0019] The structural differences between planar and 3-D
transistors is schematically illustrated in FIGS. 1A and 1B. FIG.
1A schematically illustrates a traditional planar IC transistor
100. On the left in the figure is a side view showing source 120,
channel 130, and drain 140 formed in a silicon substrate 110, with
gate 150 sitting atop channel 130 separated by gate dielectric 149.
To the right in the figure is a cross-sectional view of the same
transistor 100 taken from the point-of-view of the vertical dotted
line (as indicated by the horizontal arrow). From both views, it is
seen that gate 150 is only located adjacent to one side of channel
130 (separated by gate dielectric 149). FIG. 1B provides a
simplified illustration of a modern 3-D transistor design 101 with
side view (left) and cross-sectional view (right) similar to that
shown in FIG. 1A for the planar transistor 100. It is seen from the
side view that source 121, channel 131, and drain 141 extend
vertically from the plane of the silicon substrate 110 (unlike
planar transistor 100). However, the cross-sectional view in FIG.
1B (right) shows that gate 151 of 3-D transistor 101 is able to
wrap around the channel region 131 from three sides (in contrast to
the arrangement of the gate 150 in planar transistor 100). This
wrapping of the gate around the vertical fin structure is further
illustrated in FIG. 1C (again showing 3-D transistor 101 with
source 121, drain 141, and gate 151, although channel 131 is
obscured by the gate); and FIG. 1D illustrates how multiple 3-D
transistors 101 formed from parallel vertical fin structures may be
wrapped by a 3-D gate component 151. This fundamental shift in
transistor architecture from planar to 3-D designs has created
challenges for IC fabrication, and to optimally address these
challenges new fabrication techniques must be developed.
SUMMARY
[0020] Disclosed herein are methods of doping a fin-shaped channel
region of a partially fabricated 3-D transistor on a semiconductor
substrate. In some embodiments, the methods include forming a
dopant-containing film on the substrate, forming a capping film
located such that the dopant-containing film is located in between
the substrate and the capping film, and driving dopant from the
dopant-containing film into the fin-shaped channel region. In
certain such embodiments, the capping film includes a silicon
carbide material, a silicon nitride material, a silicon
carbonitride material, or a combination thereof. In certain such
embodiments, multiple dopant-containing layers of the
dopant-containing film are formed by an atomic layer deposition
process which includes adsorbing a dopant-containing film precursor
onto the substrate such that the precursor forms an
adsorption-limited layer, removing at least some unadsorbed
dopant-containing film precursor from the volume surrounding the
adsorbed precursor, reacting adsorbed dopant-containing film
precursor to form a dopant-containing layer on the substrate,
removing desorbed dopant-containing film precursor and/or reaction
by-product from the volume surrounding the dopant-containing layer
when present after reacting the adsorbed precursor, and repeating
this process sequence to form multiple dopant-containing layers of
the dopant-containing film.
[0021] Also disclosed herein are dopant-containing films for doping
the fin-shaped channel region of a partially fabricated 3-D
transistor on a semiconductor substrate. In some embodiments, the
films may include first and second dopant-rich portions, first and
second substantially dopant-free portions, and a capping film
including a silicon carbide material, a silicon nitride material, a
silicon carbonitride material, or a combination thereof. In certain
such embodiments, the first dopant-rich portion of the film may be
formed by conformally depositing multiple dopant-containing layers
sequentially, without intervening deposition of a substantially
dopant-free layer, and the second dopant rich portion may also be
formed by conformally depositing multiple dopant-containing layers
sequentially, without intervening deposition of a substantially
dopant-free layer. Likewise, in certain such embodiments, the first
substantially dopant-free portion of the film may be formed by
conformally depositing multiple substantially dopant-free layers
sequentially, without intervening deposition of a dopant-containing
layer, and the second substantially dopant-free portion of the film
may also be formed by conformally depositing multiple substantially
dopant-free layers sequentially, without intervening deposition of
a dopant-containing layer. In certain such embodiments, the
portions of the films may be located such that the first
substantially dopant-free portion is located between the first and
second dopant-rich portions, the second dopant-rich portion is
located between the first and second substantially dopant-free
portions, and the layer of capping film is located such that the
first and second dopant-rich portions and the first and second
substantially dopant-free portions are in between the substrate and
the capping film.
[0022] Also disclosed herein are multi-station substrate processing
apparatuses for doping the fin-shaped channel regions of partially
fabricated 3-D transistors on the surfaces of multiple
semiconductor substrates. In some embodiments, the apparatuses
include a plurality of process stations having a substrate holder
contained in one or more processing chambers, one or more valves
for controlling flow of dopant-containing film precursor to the
process stations, one or more valve-operated vacuum sources for
removing dopant-containing film precursor from the volumes
surrounding the process stations contained in the one or more
processing chambers, and one or more controllers having, and/or
having access to, machine-readable instructions for operating the
one or more valves and one or more vacuum sources to dope the
fin-shaped channel regions on the surfaces of the substrates. In
some embodiments, included are instructions for forming a
dopant-containing film on a substrate at a process station
contained in a processing chamber, instructions for forming a
capping film located such that the dopant-containing film is in
between the substrate and the capping film, and instructions for
driving dopant from the dopant-containing film into a fin-shaped
channel region. In certain such embodiments, the capping film
includes a silicon carbide material, a silicon nitride material, a
silicon carbonitride material, or a combination thereof. In some
embodiments, the multiple dopant-containing layers of the film are
formed according to the instructions by an atomic layer deposition
process including introducing a dopant-containing film precursor
into the processing chamber containing the process station having
the substrate holder holding the substrate, and allowing the
precursor to adsorb onto the surface of the substrate such that the
precursor forms an adsorption-limited layer on the substrate,
removing unadsorbed dopant-containing film precursor from the
volume surrounding the adsorbed precursor, reacting adsorbed
dopant-containing film precursor to form a dopant-containing layer
on the substrate, removing desorbed dopant-containing film
precursor and/or reaction by-product from the volume surrounding
the dopant-containing layer when present after reacting the
adsorbed precursor, and repeating this process sequence to form
multiple dopant-containing layers of the dopant-containing
film.
DETAILED DESCRIPTION
[0023] In the following description, numerous specific details are
set forth in order to provide a thorough understanding of the
present invention. However, the present invention may be practiced
without some or all of these specific details. In other instances,
well known process operations have not been described in detail so
as to not unnecessarily obscure the present invention. While the
invention will be described in conjunction with specific detailed
embodiments, it is to be understood that these specific detailed
embodiments are not intended to limit the scope of the inventive
concepts disclosed herein.
[0024] The semi-conductive region between source and drain in an IC
transistor is referred to as the channel or the transistor's
channel region. Electrical potential applied by the gate to the
channel region affects its polarization and conductivity,
effectively switching the transistor from `on` to `off` states and
vice versa. Accordingly, channel conductivity and the ability to
consistently adjust it via the gate are key aspects of IC
transistor design and fabrication. In the fabrication of
traditional planar IC transistors, ion implantation techniques are
generally employed to dope the channel region and adjust its
conductivity to a desired level. However, with the move to 3-D
transistors having a channel region formed in a high-aspect ratio
fin-shaped structure (in some cases, having a width of less than
about 32 nanometers, or less than about 22 nanometers, or less than
about 12 nanometers), ion implantation techniques have proven
ineffective for providing uniform and controlled doping.
[0025] The difficulty with ion-implantation techniques is
schematically illustrated in FIGS. 2A and 2B. FIG. 2A provides a
cross-sectional view (analogous to that shown in FIG. 1B) of four
fin-shaped channel regions 231, 232, 233, 234 of four 3-D
transistors arranged in parallel (similar to that shown in FIG.
1D). Two of the channels 233, 234 have had gate material 251
applied to them. Schematically indicated in the figure are the
possible incident angles of ion-flux which will reach the base of
channels 231 and 232--clearing the adjacent vertical structure--and
thus may be used to uniformly dope the side of each channel. `Angle
1` in the figure shows that only a small range of incident angles
will reach the base of channel 231 due to the shadowing effect of
adjacent channel 232. Doping the sides of the channels obviously
requires that the ion-flux have some horizontal component (so as to
not just bombard the top), but the figure illustrates that if the
horizontal component is too great the side of the channel will be
differentially bombarded--with more ions reaching the upper
portions than the lower portions. Thus, for channel 231, uniform
bombardment requires that incident ion-flux angles be restricted to
a range between zero and Angle 1. In practice, however, because the
fin-shaped channels have a high aspect ratio and are closely
spaced, Angle 1 represents a relatively narrow range of ion fluxes
difficult to achieve consistently due to, for example,
electromagnetic field fluctuations in the plasma generating the
ions, intra-ion collisions in the collimated ion flux, etc. Angle
2, also indicated in FIG. 2A, shows that the problem is amplified
for channel 232 due to the presence of gate material 251 atop
adjacent channel 233. FIG. 2B illustrates that the problem is
similarly amplified for channel 232 if the adjacent channel 233 is
masked with a layer of resist material 255. Moreover, FIG. 2C
illustrates that the problem is greatly exacerbated if adjacent
channel 233 is masked with a layer of resist material 255 atop an
already present layer of gate material 251--compare Angle 3 in FIG.
2C with Angle 2 in FIGS. 2A and 2B.
[0026] Accordingly, techniques other than ion-implantation are
sought to achieving consistent, uniform, and cost-effective doping
of fin-shaped channel regions in 3-D transistors. An approach
disclosed herein is to dope high aspect-ratio vertical fin-shaped
channel structures using a dopant-containing film after conformally
depositing it on the vertical structure. The basic idea is
illustrated in FIGS. 3A and 3B. FIG. 3A illustrates the basic
structure of a dopant-containing film 310 combined with a capping
film 320. FIG. 3B illustrates this film conformally deposited on a
vertical fin-shaped channel structure 131. Because the film
substantially conforms to the shape of the target structure,
diffusive transfer of dopant from the film to the target structure,
e.g. with a thermal anneal, will result in uniform doping of the
target structure. Details of such conformal films including
composition, techniques for depositing them, the transferring of
dopant from the film to the channel structure, as well as
associated apparatuses for accomplishing these operations are
described in detail herein. It is also noted, more generally, that
doping via conformally deposited films may also be useful for
doping other types of high aspect ratio devices structures, and may
be appropriately used in many scenarios where conventional ion
implantation or directional doping methods are inadequate. For
instance, in addition to conventional silicon-based
microelectronics, other applications of conformal doping may
include microelectronics and optoelectronics based on III-V
semiconductors such as GaAs, and II-VI semiconductors such as
HgCdTe, as well as photovoltaics, flat panel displays, and
electrochromic technology.
[0027] However, although conformal doping may offer distinct
advantages in terms of the potential for uniform vertical doping of
the target structure (e.g., versus ion implantation techniques), in
practice uniform doping, for example with boron or phosphorous, at
concentrations relevant to IC transistor fabrication have proven
difficult to achieve. The root of this problem has been
investigated and, without being limited to a particular theory, it
is thought that it stems from rapid back-diffusion of dopant out of
the films before sufficient dopant can be driven into the target
channel region. In other words, lack of dopant uniformity and/or
sufficient concentration in the deposited conformal film due to
back-diffusion appears to result in a lack of sufficient uniformity
and/or concentration of dopant in the channel region.
[0028] The problem is demonstrated by the experiments illustrated
in FIGS. 4A, 4B, and 4C. The experiments involve conformal
deposition of boron-containing films--in particular, borosilicate
glass (BSG) films--on the front and back sides of a silicon wafer.
The front-side and back-side boron-containing films are illustrated
in FIGS. 4A and 4B, respectively, and as shown in the figures, each
includes a dopant-containing borosilicate glass film sandwiched
between two silicon dioxide (SiO.sub.2) layers. The SiO.sub.2 film
formed on the side of the BSG film opposite the silicon wafer may
be referred to as a "capping layer" or "capping film," though it
should be understood that these terms do not necessarily imply that
the referred to film/layer is the uppermost film/layer relative to
the wafer. Instead, these terms as used herein simply imply that
some dopant-containing film is located between the "capping"
film/layer and the substrate. FIGS. 4A and 4B indicate that the
dopant-containing films were formed via an ALD (atomic layer
deposition) process and that the BSG film was deposited to a
thickness about double that of the sandwiching SiO.sub.2 films (100
versus 50 Angstroms, respectively). After deposition, the films
were annealed to accelerate the rate of diffusion of boron dopant
out of the BSG film and into the adjacent films and wafer
substrate.
[0029] Concentrations of boron dopant and other chemical species
(silicon, oxygen) were then measured by secondary ion mass
spectroscopy (SIMS) using a 500 keV beam of oxygen ions (O.sup.+)
and the results are shown in FIG. 4C. As indicated in FIG. 4C, the
SIMS experiments reveal a peak in boron concentration at the edge
of the top SiO.sub.2 film adjacent to the BSG film as well as a
corresponding dip in boron concentration at the adjacent edge of
the BSG film, the presence of both effects resulting from
back-diffusion of boron atoms out of the edge of the BSG film. FIG.
4C also shows the presence of some boron in the bottom SiO.sub.2
layer, as well as boron and oxygen deep into the underlying silicon
substrate. However, it is thought that the presence of these
species in these regions is due to the so-called "knock-on effect"
of the 500 keV O.sup.+ ion beam--essentially, that the high kinetic
energy of ions in the beam has "knocked" these atoms deeper into
the film and substrate--and hence these measurements are not
indicate of the film and substrate compositions prior to the
experiment. In any event, the boron peak in the top SiO.sub.2 film
and corresponding adjacent boron dip in the BSG film--which cannot
be a result of "knock-on effect"--demonstrate the occurrence of
dopant back-diffusion, and also the fact that an SiO.sub.2 capping
film does a poor job of preventing it.
[0030] As stated above, back-diffusion of dopant out of a deposited
film adversely affects dopant concentration in the film and thus
the film's utility as a tool for doping an underlying material in a
uniform manner. However, it has been discovered that while a
capping film of SiO.sub.2 does a poor job of preventing boron-back
diffusion out of a conformal dopant-containing film, capping films
formed from a silicon carbide material, a silicon nitride material,
a silicon carbonitride material, or a combination thereof, are
substantially more effective. For example, the effects of using a
silicon carbide (SiC) capping film are demonstrated by the
experimental results shown in FIG. 5. FIG. 5 presents SIMS results
for a boron dopant-containing film having a SiC capping film which
are analogous to the SIMS results presented in FIG. 4 for a
SiO.sub.2 capping film. The structure of the SiC-capped films are
the same as the films schematically illustrated in FIGS. 4A and 4B
but with the substitution of SiC for SiO.sub.2. FIG. 5 shows that
the boron peak appearing in the top SiC film adjacent to the BSG
film is substantially reduced relative to the boron peak at the
same location in the SiO.sub.2 film of FIG. 4, thereby confirming
that a SiC capping film does a substantially better job of
preventing boron back-diffusion than an equivalent capping film
formed from SiO.sub.2 material.
[0031] Accordingly, due to the advantages associated with reducing
or preventing dopant back-diffusion, disclosed herein are methods
of doping the channel regions of partially fabricated 3-D
transistors on semiconductor substrates which include forming a
capping film comprising a silicon carbide (SiC) material, a silicon
nitride material (SiN), a silicon carbonitride (SiCN) material, or
a combination thereof. So as to reduce or prevent dopant diffusion,
the SiC/SiN/SiCN capping film is located such that at least a
portion of the dopant-containing film is located in between the
substrate and the capping film. In this manner, during a thermal
anneal, for example, to transfer dopant to the target region of the
substrate, the capping film may block diffusion of dopant out of
the dopant-containing film and away from the fin-shaped channel
region by 20% or more, or 30% or more, or 40% or more, or 50% or
more, or 60% or more, or 70% or more, or 80% or more, or 90% or
more relative to the rate of diffusion during the same thermal
anneal conditions in the absence of the capping film.
[0032] Certain such methods are schematically illustrated by the
flow diagram of FIG. 6A. As indicated in the figure, the methods
begin with an operation 610 of forming a dopant-containing film on
a substrate having multiple dopant-containing layers formed by an
ALD process. The methods then proceed with an operation 620 of
forming a capping film containing a silicon carbide material, a
silicon nitride material, a silicon carbonitride material, or a
combination thereof, wherein (as indicated above) the capping film
is located such that the dopant-containing film is located in
between the substrate and the capping film. Finally, the transfer
of dopant to the fin-shaped channel region of the 3-D transistor
occurs in an operation 630 involving driving dopant from the
dopant-containing film into the channel region. A thermal anneal
may be used for this purpose, for example. In some embodiments, a
laser anneal, spike anneal, laser spike anneal, rapid thermal
processing (RTP), rapid thermal anneal (RTA), or millisecond
anneal, may be used. In many of these instances, the driving of
dopant into the channel region is achieved within a "low thermal
budget" by generating a high temperature, but for just a short
time. In some embodiments, the dopant may be boron. In other
embodiments, the dopant may be phosphorous or arsenic. Other dopant
species may also be advantageously transferred to a target
structure/region on a semiconductor substrate utilizing these
techniques. In some sequences of IC fabrication operations, at
least a portion of the dopant containing film and/or capping film
may be removed after dopant is driven into the target
structure/region.
[0033] As discussed above, in order to achieve a uniform dopant
concentration in the target structure, it is important that the
deposited dopant-containing film substantially conform to the shape
of the target structure. While, in principle, any workable method
of depositing a conformal dopant-containing film may potentially be
used in conjunction with the foregoing channel region doping
approach, the technique often referred to in the art as atomic
layer deposition (ALD) has been found an effective choice.
[0034] In contrast with chemical vapor deposition (CVD) process,
where activated gas phase reactions are used to deposit films, ALD
processes use surface-mediated deposition reactions to deposit
films on a layer-by-layer basis. For instance, in one class of ALD
processes, a first film precursor (P1) is introduced in a
processing chamber in the gas phase, is exposed to a substrate, and
is allowed to adsorb onto the surface of the substrate (typically
at a population of surface active sites). Some molecules of P1 may
form a condensed phase atop the substrate surface, including
chemisorbed species and physisorbed molecules of P1. The volume
surrounding the substrate surface is then evacuated to remove gas
phase and physisorbed P1 so that only chemisorbed species remain. A
second film precursor (P2) may then be introduced into the
processing chamber so that some molecules of P2 adsorb to the
substrate surface. The volume surrounding the substrate within the
processing chamber may again be evacuated, this time to remove
unbound P2. Subsequently, energy provided to the substrate (e.g.,
thermal or plasma energy) activates surface reactions between the
adsorbed molecules of P1 and P2, forming a film layer. Finally, the
volume surrounding the substrate is again evacuated to remove
unreacted P1 and/or P2 and/or reaction by-product, if present,
ending a single cycle of ALD.
[0035] ALD techniques for depositing conformal films having a
variety of chemistries--and also many variations on the basic ALD
process sequence--are described in detail in U.S. patent
application Ser. No. 13/084,399, filed Apr. 11, 2011, titled
"PLASMA ACTIVATED CONFORMAL FILM DEPOSITION" (Attorney Docket No.
NOVLP405), U.S. patent application Ser. No. 13/242,084, filed Sep.
23, 2011, titled "PLASMA ACTIVATED CONFORMAL DIELECTRIC FILM
DEPOSITION," now U.S. Pat. No. 8,637,411 (Attorney Docket No.
NOVLP427), U.S. patent application Ser. No. 13/224,240, filed Sep.
1, 2011, titled "PLASMA ACTIVATED CONFORMAL DIELECTRIC FILM
DEPOSITION" (Attorney Docket No. NOVLP428), and U.S. patent
application Ser. No. 13/607,386, filed Sep. 7, 2012, titled
"CONFORMAL DOPING VIA PLASMA ACTIVATED ATOMIC LAYER DEPOSITION AND
CONFORMAL FILM DEPOSITION" (Attorney Docket No. NOVLP488), each of
which is incorporated by reference herein in its entirety for all
purposes. As described in these prior applications, a basic ALD
cycle for depositing a single layer of material on a substrate may
include: (i) adsorbing a film precursor onto a substrate such that
it forms an adsorption-limited layer, (ii) removing unadsorbed
precursor from the volume surrounding the adsorbed precursor, (iii)
reacting the adsorbed-precursor to form a layer of film on the
substrate, and (iv) removing desorbed film precursor and/or
reaction by-product from the volume surrounding the layer of film
formed on the substrate. The removing in operations (ii) and (iv)
may be done via purging, evacuating, pumping down to a base
pressure ("pump-to-base"), etc. the volume surrounding the
substrate. It is noted that this basic ALD sequence of operations
(i) through (iv) doesn't necessary involve two chemiadsorbed
reactive species P1 and P2 as in the example described above, nor
does it even necessarily involve a second reactive species,
although these possibilities/options may be employed, depending on
the desired deposition chemistries involved.
[0036] Due to the adsorption-limited nature of ALD, however, a
single cycle of ALD only deposits a thin film of material, and
oftentimes only a single monolayer of material. For example,
depending on the exposure time of the film precursor dosing
operations and the sticking coefficients of the film precursors (to
the substrate surface), each ALD cycle may deposit a film layer
only about 0.5 to 3 Angstroms thick. Thus, the sequence of
operations in a typical ALD cycle--operations (i) through (iv) just
described--are generally repeated multiple times in order to form a
conformal film of the desired thickness. Thus, in some embodiments,
operations (i) through (iv) are repeated consecutively at least 1
time, or at least 2 times, or at least 3 times, or at least 5
times, or at least 7 times, or at least 10 times in a row. Dopant
ALD film may be deposited at a rate of about or between 0.1 .ANG.
and 2.5 .ANG. per ALD cycle, or about or between 0.2 .ANG. and 2.0
.ANG. per ALD cycle, or about or between 0.3 .ANG. and 1.8 .ANG.
per ALD cycle, or about or between 0.5 .ANG. and 1.5 .ANG. per ALD
cycle, or about or between 0.1 .ANG. and 1.5 .ANG. per ALD cycle,
or about or between 0.2 .ANG. and 1.0 .ANG. per ALD cycle, or about
or between 0.3 .ANG. and 1.0 .ANG. per ALD cycle, or about or
between 0.5 .ANG. and 1.0 .ANG. per ALD cycle.
[0037] In some film forming chemistries, an auxiliary reactant or
co-reactant--in addition to what is referred to as the "film
precursor"--may also be employed. In certain such embodiments, the
auxiliary reactant or co-reactant may be flowed continuously during
a subset of steps (i) through (iv) or throughout each of steps (i)
through (iv) as they are repeated. In some embodiments, this other
reactive chemical species (auxiliary reactant, co-reactant, etc.)
may be adsorbed onto the substrate surface with the film precursor
prior to its reaction with the film precursor (as in the example
involving precursors P1 and P2 described above), however, in other
embodiments, it may react with the adsorbed film precursor as it
contacts it without prior adsorption onto the surface of the
substrate, per se. Also, in some embodiments, operation (iii) of
reacting the adsorbed film precursor may involve contacting the
adsorbed film precursor with a plasma. The plasma may provide
energy to drive the film-forming reaction on the substrate surface.
In certain such embodiments, the plasma may be an oxidative plasma
generated in the reaction chamber with application of suitable RF
power (although in some embodiments, it may be generated remotely).
In other embodiments, instead of an oxidative plasma, an inert
plasma may be used. The oxidizing plasma may be formed from one or
more oxidants such as O.sub.2, N.sub.2O, or CO.sub.2, and may
optionally include one or more diluents such as Ar, N.sub.2, or He.
In one embodiment, the oxidizing plasma is formed from O.sub.2 and
Ar. A suitable inert plasma may be formed from one or more inert
gases such as He or Ar. Further variations on ALD processes are
described in detail in the prior patent applications just cited
(and which are incorporated by reference).
[0038] Accordingly, a basic sequence of operations for forming a
dopant-containing film via an ALD process is schematically
illustrated by the flowchart in FIG. 6B. A shown in the figure, an
ALD process for forming multiple dopant-containing layers of film
on a substrate may begin with an operation 611 of adsorbing a
dopant-containing film precursor onto the substrate such that the
precursor forms an adsorption-limited layer on the substrate,
followed by an operation 612 of removing at least some unadsorbed
dopant-containing film precursor from the volume surrounding the
adsorbed precursor. Thereafter, in an operation 613, the adsorbed
dopant-containing film precursor is reacted to form a
dopant-containing layer on the substrate, and following that, in
operation 614, desorbed dopant-containing film precursor and/or
reaction by-product is removed from the volume surrounding the
dopant-containing layer when present after reacting the adsorbed
precursor in operation 613.
[0039] The foregoing sequence of operations 611 through 614
represents once ALD cycle. However, since a single ALD cycle
typically only deposits a thin layer of film, multiple ALD cycles
may be repeated in sequence to form multiple layers of
dopant-containing film (or, equivalently, a multi-layer dopant
containing film of the desired thickness). Thus, referring again to
FIG. 6B, after an ALD cycle concludes with operation 614, in
operation 615, it is determined whether a sufficient number of
layers of dopant-containing film have been formed (or whether a
film of a sufficient thickness has been deposited), and if so, the
film-forming operations conclude, whereas if not, the process
sequence returns to operation 611 to begin another cycle of ALD. It
is noted that FIGS. 6A and 6B may be viewed in combination as a
method of doping a channel region of a 3-D transistor with
operation 610 (FIG. 6A) of forming a dopant-containing film
including the ALD process sequence of operations 611 through 615
(FIG. 6B).
[0040] In some embodiments, a dopant-containing film for doping the
fin-shaped channel region of a partially fabricated 3-D transistor
may include dopant-rich portions as well as substantially
dopant-free portions (in addition to the capping film which may be
dopant-free). Thus, for example, in some embodiments, a
dopant-containing film may include a first dopant-rich portion
formed by conformally depositing multiple dopant-containing layers
sequentially, without intervening deposition of a substantially
dopant-free layer, and a first substantially dopant-free portion
formed by conformally depositing multiple substantially dopant-free
layers sequentially, without intervening deposition of a
dopant-containing layer.
[0041] Moreover, in certain such embodiments, there may be multiple
dopant-rich portions and multiple substantially dopant-free
portions which form a structure of alternating composition in the
deposited film. One reason for doing this arises from the fact
that, in some cases, it has been found that depositing
dopant-containing film layers sequentially, using sequential ALD
cycles, may be self-inhibiting (at least to a certain extent in
some embodiments), and the growth rate may continue to drop after
more and more dopant-rich layers have been deposited. For example,
in one experiment, the total thickness of a B.sub.2O.sub.3 film
deposited using sequential ALD cycles was found to not
significantly change between the 50th ALD cycle and the 100th ALD
cycle. As a result, in some embodiments, for some dopants, and for
some dopant-containing film precursors, the quantity of dopant in
an ALD-formed conformal film may not be effectively increased by
sequentially depositing additional dopant-rich layers. These
aspects are described in detail in U.S. patent application Ser. No.
13/607,386, filed Sep. 7, 2012, and titled "CONFORMAL DOPING VIA
PLASMA ACTIVATED ATOMIC LAYER DEPOSITION AND CONFORMAL FILM
DEPOSITION" (Attorney Docket No. NOVLP488), which is incorporated
by reference herein in its entirety for all purposes.
[0042] Thus, it may be desirable to form dopant-containing films of
alternating composition--alternating between dopant-rich and
substantially dopant-free portions. Therefore, in these sorts of
embodiments, a dopant-containing film may additionally include a
second dopant-rich portion (also formed by conformally depositing
multiple dopant-containing layers sequentially, without intervening
deposition of a substantially dopant-free layer), and also a second
substantially dopant-free portion of the film (again, formed by
conformally depositing multiple substantially dopant-free layers
sequentially, without intervening deposition of a dopant-containing
layer); and these first and second, dopant-rich and substantially
dopant-free portions may be arranged such that they alternate with
one another by composition--e.g., the first substantially
dopant-free portion is located between the first and second
dopant-rich portions, the second dopant-rich portion is located
between the first and second substantially dopant-free portions. In
such an arrangement, the capping film may be located such that the
first and second dopant-rich portions and the first and second
substantially dopant-free portions are in between it and the
substrate. FIG. 7 provides a schematic of one such example film 700
having dopant-rich portions 710 alternating with substantially
dopant-free portions 720, and also having a SiC/SiN/SiCN capping
film 730.
[0043] The dopant-rich portions of such films may be formed in
multiple layers by multiple ALD cycles as described above, e.g.,
with respect to FIG. 6B. However, multiple ALD cycles may also be
used to form multiple layers of the substantially dopant-free
portions of such films, albeit using a dopant-free (instead of a
dopant-containing) film precursor. Thus, for instance, in some
embodiments, forming each of the first and second substantially
dopant-free portions just described (e.g., see FIG. 7) may include
(i) adsorbing a dopant-free film precursor onto the substrate such
that the precursor forms an adsorption-limited layer, thereafter
(ii) removing unadsorbed dopant-free film precursor from the volume
surrounding the adsorbed precursor, then (iii) reacting the
adsorbed dopant-free film precursor after removing unadsorbed
precursor to form a substantially dopant-free layer on the
substrate, and finally (iv) removing desorbed dopant-free film
precursor and/or reaction by-product from the volume surrounding
the substantially dopant-free layer when present after reacting the
adsorbed precursor. As stated, multiple ALD cycles may be used to
form multiple layers, and so the foregoing sequence of operations
(i) through (iv) may be repeated multiple times to form multiple
substantially dopant-free layers of the dopant-containing film. It
is noted that, in some embodiments, these substantially dopant-free
layers may include a dielectric material, and that, in certain such
embodiments, the dielectric material may be SiO.sub.2.
[0044] Further examples of conformal films having portions of
alternating composition--including films used for doping an
underlying target IC structure or substrate region--as well as
methods of forming these films, are described in detail in: U.S.
patent application Ser. No. 13/084,399, filed Apr. 11, 2011, and
titled "PLASMA ACTIVATED CONFORMAL FILM DEPOSITION" (Attorney
Docket No. NOVLP405); U.S. patent application Ser. No. 13/242,084,
filed Sep. 23, 2011, and titled "PLASMA ACTIVATED CONFORMAL
DIELECTRIC FILM DEPOSITION," now U.S. Pat. No. 8,637,411 (Attorney
Docket No. NOVLP427); U.S. patent application Ser. No. 13/224,240,
filed Sep. 1, 2011, and titled "PLASMA ACTIVATED CONFORMAL
DIELECTRIC FILM DEPOSITION" (Attorney Docket No. NOVLP428); and
U.S. patent application Ser. No. 13/607,386, filed Sep. 7, 2012,
and titled "CONFORMAL DOPING VIA PLASMA ACTIVATED ATOMIC LAYER
DEPOSITION AND CONFORMAL FILM DEPOSITION" (Attorney Docket No.
NOVLP488); each of which is incorporated by reference herein in its
entirety for all purposes.
[0045] Details Regarding the Capping Film
[0046] In some embodiments, the capping film may also be formed via
an ALD process. For example, in some embodiments, multiple layers
of the capping film may be deposited via the sequence of operations
(i) through (iv) (just described) repeated multiple times to form
multiple layers of the capping film. However, while substantially
dopant-free layers of SiO.sub.2 may be interspersed with the
dopant-rich portions of the film, for the reasons described above
with respect to FIGS. 4 and 5, the capping film would typically be
composed of a material suitable for blocking dopant back-diffusion
such as SiC, SiN, SiCN, or a combination thereof. In other
embodiments, a chemical vapor deposition (CVD) process may be used
to form the capping film, and in certain such embodiments, a
plasma-enhanced chemical vapor deposition (PECVD) process. However,
since CVD/PECVD processes proceed via gas phase reactions rather
than through the formation of an adsorption-limited layer of
reactants, they produce less conformal films than ALD techniques,
and therefore ALD processes are generally preferred for forming the
capping films described herein.
[0047] The capping film will generally have a sufficient
concentration of SiC, SiN, SiCN, or combination thereof, and be
formed of sufficient thickness to block back-diffusion of dopant to
the desired extent feasible based on the chemistries and rates of
diffusion involved. For instance, in some embodiments, the average
concentration of SiC in the capping film may be between about 1 and
4 g/cm.sup.3, or between about 2 and 3 g/cm.sup.3, or between about
2.2 and 2.8 g/cm.sup.3. Likewise, in some embodiments, the average
concentration of SiCN in the capping film may be between about 1
and 4 g/cm.sup.3, or between about 2 and 3 g/cm.sup.3, or between
about 2.2 and 2.8 g/cm.sup.3, and, in some embodiments, the average
concentration of SiN in the capping film may be between about 1 and
4 g/cm.sup.3, or between about 2 and 3 g/cm.sup.3, or between about
2.2 and 2.8 g/cm.sup.3. Finally, in some embodiments, the average
combined concentration of SiC, SiN, and SiCN in the capping film
may be between about 1 and 4 g/cm.sup.3, or between about 2 and 3
g/cm.sup.3, or between about 2.2 and 2.8 g/cm.sup.3.
[0048] Likewise, depending on the embodiment, a capping film may be
formed having an average thicknesses of about 1, 2, 3, 5, 10, 20,
30, 40, 50, 100, 150, 200, 300, or 500 Angstroms, or the capping
film corresponding to a given embodiment may have an average
thickness within a range defined on the low end and high end by any
pair of the aforementioned thicknesses such as, for example, a
capping film may have an average thickness between about 1 and 500
Angstroms, or between about 5 and 200 Angstroms, or between about
10 and 100 Angstroms. In some embodiments, the capping film may be
a substantially conformal film--such as, for example, if it is
formed via an ALD process--and thus it may be of relatively
consistent thickness, quantifiable, for example, by the relative
standard deviation in the film's thickness. Thus, in embodiments
where the capping film is substantially conformal, the relative
standard deviation in its thickness may be less than about 20%, or
less than about 15%, or less than about 10%, or less than about 5%,
or less than about 4%, or less than about 3%, or less than about
2%, or less than about 1%, or even less than about 0.1%.
[0049] ALD Process Conditions
[0050] ALD processes for forming the dopant-containing films and/or
capping films may be performed at various temperatures. In some
embodiments, suitable temperatures within an ALD reaction chamber
may range from between about 25.degree. C. and 450.degree. C., or
between about 50.degree. C. and 300.degree. C., or between about
20.degree. C. and 400.degree. C., or between about 200.degree. C.
and 400.degree. C., or between about 100.degree. C. and 350.degree.
C.
[0051] Likewise, ALD processes for forming the dopant-containing
films and/or capping films may be performed at various ALD reaction
chamber pressures. In some embodiments, suitable pressures within
the reaction chamber may range from between about 10 mTorr and 10
Torr, or between about 20 mTorr and 8 Torr, or between about 50
mTorr and 5 Torr, or between about 100 mTorr and 2 Torr.
[0052] Various RF power levels may be employed to generate a plasma
if used in operation (iii). In some embodiments, suitable RF power
may range from between about 100 W and 10 kW, or between about 200
W and 6 kW, or between about 500 W, and 3 kW, or between about 1 kW
and 2 kW.
[0053] Various dopant-containing film precursor flow rates may be
employed in operation (i). In some embodiments, suitable flow rates
may range from about or between 0.1 mL/min to 10 mL/min, or about
or between 0.5 mL/min and 5 mL/min, or about or between 1 mL/min
and 3 mL/min.
[0054] Various gas flow rates may be used in the various
operations. In some embodiments, general gas flow rates may range
from about or between 1 L/min and 20 L/min, or about or between 2
L/min and 10 L/min. For the optional inert purge steps in
operations (ii) and (iv), an employed burst flow rate may range
from about or between 20 L/min and 100 L/min, or about or between
40 L/min and 60 L/min.
[0055] Once again, in some embodiments, a pump-to-base step refers
to pumping the reaction chamber to a base pressure by directly
exposing it to one or more vacuum pumps. In some embodiments, the
base pressure may typically be only a few milliTorr (e.g., between
about 1 and 20 mTorr). Furthermore, as indicated above, a
pump-to-base step may or may not be accompanied by an inert purge,
and thus carrier gases may or may not be flowing when one or more
valves open up the conductance path to the vacuum pump.
[0056] Chemistries for Formation of Capping Films
[0057] Various film-forming chemistries may be used for forming the
capping film. Capping films may preferably contain a silicon
carbide (SiC) material, a silicon nitride (SiN) material, a silicon
carbonitride (SiCN) material, or a combination thereof. Methods,
techniques, and operations for depositing these types of films are
described in detail in U.S. patent application Ser. No. 13/494,836,
filed Jun. 12, 2012, titled "REMOTE PLASMA BASED DEPOSITION OF SiOC
CLASS OF FILMS," Attorney Docket No. NOVLP466/NVLS003722; U.S.
patent application Ser. No. 13/907,699, filed May 31, 2013, titled
"METHOD TO OBTAIN SiC CLASS OF FILMS OF DESIRED COMPOSITION AND
FILM PROPERTIES," Attorney Docket No. LAMRP046/3149; and U.S.
patent application Ser. No. 14/062,648, titled "GROUND STATE
HYDROGEN RADICAL SOURCES FOR CHEMICAL VAPOR DEPOSITION OF
SILICON-CARBON-CONTAINING FILMS"; each of which is hereby
incorporated by reference in its entirety and for all purposes.
[0058] Deposition of such films may utilize one or more
silicon-containing film precursors which may be selected from a
variety of compounds. Silicon-carbon-containing films (e.g.,
silicon carbides, silicon-carbon-oxides, silicon carbonitrides, and
silicon-carbon-oxynitrides), for instance, may be formed using
silicon-containing film precursors such as organosilicon reactants
selected and supplied to provide desired composition properties,
and in some cases, physical or electronic properties. Examples of
suitable organo-silicon reactants/film-precursors may include
silanes, alkyl silanes, siloxanes, alkoxy silanes, and amino
silanes, among others.
[0059] Regarding the silanes, non-limiting examples include silane,
disilane, trisilane, and higher silanes.
[0060] Regarding the alkyl silanes, these compounds include a
central silicon atom with one or more alkyl groups bonded to it as
well as one or more hydrogen atoms bonded to it. In certain
embodiments, any one or more of the alkyl groups contain 1-5 carbon
atoms. The alkyl groups may be saturated or unsaturated. In some
embodiments, these alkyl groups may be used to SiC films.
Non-limiting examples of alkyl silanes include dimethylsilane
(2MS), trimethylsilane (3MS), tetramethylsilane (4MS),
triethylsilane (TES), and pentamethyldisilamethane.
[0061] Other types of alkyl silanes can include alkylcarbosilanes,
alkylaminosilanes, and alkyldisilazanes. Alkylcarbosilanes can have
a branched polymeric structure with a carbon bonded to a silicon
atom as well as alkyl groups bonded to a silicon atom. Examples
include dimethyl trimethylsilyl methane (DTMSM) and
bis-dimethylsilyl ethane (BDMSE). Alkylaminosilanes include amines
with alkyl groups and bonded to a silicon atom. Examples include
dimethylamino dimethylsilane (DMADMS), bis-dimethylamino
methylsilane (BDMAMS), and tris-dimethylamino silane (TDMAS). In
some embodiments, these alkyl silanes can form SiCN films.
Alkyldisilazanes include silizanes and alkyl groups bonded to two
silicon atoms. An example includes 1,1,3,3-tetramethyldisilazane
(TMDSN). In some embodiments, TMDSN can form SiCN films.
[0062] Additionally, higher-order silanes may be used in place of
monosilanes. An example of one such disilane from the alkyl silane
class is hexamethyldisilane (HMDS). Another example of a disilane
from the alkyl silane class can include pentamethyldisilane (PMDS),
which can be used to form SiC films. In some embodiments, one of
the silicon atoms can have a carbon-containing or alkoxy-containing
group exclusively attached to it, and one of the silicon atoms can
have a hydrogen atom exclusively attached to it.
[0063] Regarding the siloxanes, also possible class of
organo-silicon film-precursors, in some embodiments, the siloxane
may be cyclic. Cyclic siloxanes may include cyclotetrasiloxanes,
such as 2,4,6,8-tetramethylcyclotetrasiloxane (TMCTS),
octamethylcyclotetrasiloxane (OMCTS), and
heptamethylcyclotetrasiloxane (HMCTS). Other cyclic siloxanes may
include, but are not limited to, cyclotrisiloxanes and
cyclopentasiloxanes. Cyclic siloxanes are ring structures that may
introduce porosity into a SiC film, with the size of the pores
corresponding to the radius of the ring. For example, a
cyclotetrasiloxane ring can have a radius of about 6.7 Angstroms.
In some embodiments, the siloxane may have a three-dimensional or
caged structure. Caged siloxanes have silicon atoms bridged to one
another via oxygen atoms to form a polyhedron or any 3-D structure.
An example of a caged siloxane precursor molecule is
silsesquioxane. Caged siloxane structures are described in further
detail in commonly owned U.S. Pat. No. 6,576,345 to Cleemput et
al., which is incorporated by reference herein in its entirety for
all purposes. Like the cyclic siloxanes, the caged siloxane can
introduce porosity into a SiC film. In some embodiments, the
porosity scale is mesoporous. In some embodiments, the siloxane may
be linear. Linear siloxanes may include, but are not limited to,
disiloxanes, such as pentamethyldisiloxane (PMDSO),
tetramethyldisiloxane (TMDSO), and hexamethyl trisiloxane. PMDSO
and TMDSO may be used to form SiOC films. The structural
configuration (that is, linear, cyclic, or caged) of the siloxane
may affect film porosity properties. For example, cyclic siloxanes
may form microporous films having pores sized according to the
cyclic ring size, and caged siloxanes may form mesoporous
films.
[0064] Silicon-carbon-containing films may also include oxygen
atoms (e.g., silicon-carbon-oxides and silicon-carbon-oxynitrides)
and these may also be formed using siloxanes (e.g., those listed
above), as well as other organosilicon reactants that include
oxygen, such as the alkoxy silanes. The alkoxy silanes include a
central silicon atom with one or more alkoxy groups bonded to it
and one or more hydrogen atoms bonded to it. Examples include but
are not limited to trimethoxysilane (TMOS), dimethoxysilane (DMOS),
methoxysilane (MOS), methyldimethoxysilane (MDMOS),
diethoxymethylsilane (DEMS), dimethylethoxysilane (DMES),
dimethylaminomethoxysilane (DMAMES), and dimethylmethoxysilane
(DMMOS). Many of these precursors may be used to form SiOC
films.
[0065] Silicon-carbon-containing films may also include nitrogen
atoms (e.g., silicon-carbon-nitrides and
silicon-carbon-oxynitrides) and may be formed using an
organosilicon reactant that includes nitrogen, such as amino
silanes and silazanes. Non-limiting examples of amino silanes
include 2,2-bis(dimethylamino)-4,4-dimethyl-2,4-disilapentane,
2,2,4-trimethyl-4-dimethylamino-3,4-disilapentane,
dimethylaminodimethylsilane, bis(dimethylamino)methylsilane, and
tris(dimethylamino)silane. 1,1,3,3-tetramethyldisilazane is a
non-limiting example of a silazane. Further examples of
aminosilanes are mono-, di-, tri- and tetra-aminosilane
(H.sub.3Si(NH.sub.2).sub.4, H.sub.2Si(NH.sub.2).sub.2,
HSi(NH.sub.2).sub.3 and Si(NH.sub.2).sub.4, respectively), as well
as substituted mono-, di-, tri- and tetra-aminosilanes, for
example, t-butylaminosilane, methylaminosilane,
tert-butylsilanamine, bis(tertiarybutylamino)silane
(SiH.sub.2(NHC(CH.sub.3).sub.3).sub.2 (BTBAS), tert-butyl
silylcarbamate, SiH(CH.sub.3)--(N(CH.sub.3).sub.2).sub.2,
SiHCl--(N(CH.sub.3).sub.2).sub.2, (Si(CH.sub.3).sub.2NH).sub.3 and
the like. A further example of an aminosilane is trisilylamine
(N(SiH.sub.3).sub.3).
[0066] Furthermore, in some embodiments, a film-precursor may
include multiple chemical groups combined into a single precursor.
For example, a single precursor can include alkoxy, amino, and
alkyl groups, such as DMADMS.
[0067] In depositing the SiC-containing film, multiple
organo-silicon film precursors may be present in the process gas.
For example, a siloxane and an alkyl silane may be used together,
or a siloxane and an alkoxy silane may be used together. The
relative proportions of the individual precursors can be chosen
based on the chemical structures of precursors chosen and the
application of the resulting SiC film. For example, the amount of
siloxane can be greater than the amount of silane in molar
percentages to produce a porous film.
[0068] For the deposition of silicon nitrides (SiN) and silicon
carbonitrides (SiCN), an appropriate silicon-containing
reactant/film-precursor, such as those described above, may be used
in conjunction with a nitrogen-containing co-reactant. Non-limiting
examples of nitrogen-containing co-reactants which may be used
include ammonia, hydrazine, amines such as methylamine,
dimethylamine, ethylamine, isopropylamine, t-butylamine,
di-t-butylamine, cyclopropylamine, sec-butylamine, cyclobutylamine,
isoamylamine, 2-methylbutan-2-amine, trimethylamine,
diisopropylamine, diethylisopropylamine, di-t-butylhydrazine, as
well as aromatic containing amines such as anilines, pyridines, and
benzylamines. Amines may be primary, secondary, tertiary or
quaternary (for example, tetraalkylammonium compounds). A
nitrogen-containing co-reactant contains at least one nitrogen, but
may also contain heteroatoms other than nitrogen. Thus, for
example, hydroxylamine, t-butyloxycarbonyl amine, and N-t-butyl
hydroxylamine are considered nitrogen-containing reactants.
[0069] Finally, for the deposition of silicon oxides
(SiO.sub.x)--though not preferred by themselves for forming the
capping film, in some embodiments, they are preferred for
interspersing with dopant-rich portions of a dopant-containing
film--an appropriate silicon-containing reactant/film-precursor as
described above may be used in conjunction with an appropriate
oxidizing reactant. Examples of oxidizing reactants include oxygen,
ozone, hydrogen, nitrous oxide, carbon monoxide, mixtures thereof,
etc. In one particular example, an oxide film may be deposited by
an ALD process using bis(tert-butylamino)silane (BTBAS) as a
silicon-containing film precursor in conjunction with oxygen or
nitrous oxide serving as an oxidant, e.g. in ALD operation (iii),
which may or may not, depending on the embodiment, flow
continuously during delivery of the BTBAS (in ALD operation
(i)).
[0070] Chemistries for Formation of Dopant-Containing Films
[0071] As described in the patent applications listed and
incorporated by reference above (US patent application Ser. Nos.
13/084,399, 13/242,084, and 13/224,240), various dopant-containing
film precursors may be used for forming the dopant-containing
films, such as films of boron-doped silicate glass (BSG) (used as
the dopant-containing film in the examples of FIGS. 4 and 5 above),
phosphorous-doped silicate glass (PSG), boron phosphorus doped
silicate glass (BPSG), arsenic (As) doped silicate glass (ASG), and
the like. The dopant-containing films may include B.sub.2O.sub.3,
B.sub.2O, P.sub.2O.sub.5, P.sub.2O.sub.3, As.sub.2O.sub.3,
As.sub.2O.sub.5, and the like.
[0072] One preferred dopant-containing film precursor where the
dopant is boron is trimethyl borate (TMB). Other suitable
boron-containing film precursors may include: other alkyl borates
such as triethyl borate, triisopropyl borate, and tri-n-butyl
borate, as well as trimethylboron, triethylboron, triphenylboron,
tri-i-propyl borate, tri-n-amyl borate, B-tribromoborazine,
tris(pentafluorophenyl)borane, and other similar boron containing
compounds.
[0073] As indicated above, dopant-containing films having dopants
other than boron are also feasible. Examples include gallium,
phosphorous, or arsenic dopants, or other elements appropriate for
doping a semiconductor substrate, such as other valence III and V
elements.
[0074] Particular dopant-containing films having arsenic as the
dopant may include, but are not limited to, arseno-silicate or
arsenic-doped silicate glass (ASG), arsenic oxides (e.g.,
As.sub.2O.sub.3, As.sub.2O.sub.5), and arsenic oxyhydrides.
Dopant-containing film precursors having arsenic as the dopant may
include, but are not limited to, the alkylarsine, alkoxyarsine, and
aminoarsine chemical families, and include, but are not limited to,
the following specific compounds: arsine, triethylaresenate,
trimethylarsine, triethylarsine, triphenylarsine, triphenylarsine
oxide, ethylenebis(diphenylarsine), tris(dimethylamino)arsine, and
As(OR).sub.3 where R is --CH.sub.3 or --C.sub.2H.sub.5 or other
alkyl groups (including saturated and unsaturated alkyl groups),
and other similar arsenic containing compounds.
[0075] Particular dopant-containing films having phosphorous as the
dopant may include, but are not limited to, phosphorus-doped
silicate glass (PSG), and phosphorous oxides (e.g., P.sub.2O.sub.5,
P.sub.2O.sub.3). Dopant-containing film precursors having
phosphorous as the dopant may include, but are not limited to,
triethoxyphosphine oxide, alkyl phosphates such as
trimethylphosphate, trimethylphosphite, and other similar
phosphorous containing compounds. Choice of dopant precursor is
typically dictated by ease of integration into existing delivery
systems, purity requirements, and overall cost.
[0076] In some embodiments, the dopant-containing film precursor
may be used in combination with a silicon-containing film precursor
or other co-reactant. Silicon-containing film precursors that may
be used for this purpose include, but are not limited to, silane
(SiH.sub.4), disilane (Si.sub.2H.sub.6), and organo silanes such as
methylsilane, ethylsilane, isopropylsilane, t-butylsilane,
dimethylsilane, diethylsilane, di-t-butylsilane, allylsilane,
sec-butylsilane, thexylsilane, isoamylsilane, t-butyldisilane,
di-t-butyldisilane, and the like. Other silicon-containing film
precursors listed above as applicable to capping-layer formation
may also be used for dopant-containing film formation, depending on
the embodiment.
[0077] Again, multiple ALD cycles may be repeated to build up
stacks of conformal layers. In some embodiments, each layer may
have substantially the same composition whereas in other
embodiments, sequentially ALD deposited layers may have differing
compositions, or in certain such embodiments, the composition may
alternate from layer to layer or there may be a repeating sequence
of layers having different compositions, as described above. Thus,
depending on the embodiment, certain stack engineering concepts,
such as those disclosed in the patent applications listed and
incorporated by reference above (U.S. patent application Ser. Nos.
13/084,399, 13/242,084, and 13/224,240) may be used to modulate
boron, phosphorus, or arsenic concentration in these films.
[0078] Apparatuses
[0079] The methods described herein may be performed with any
suitable semiconductor substrate processing apparatus. A suitable
apparatus includes hardware for accomplishing the process
operations and a system controller having instructions for
controlling process operations in accordance with the various
channel doping methodologies disclosed herein. In some embodiments,
the hardware may include one or more process stations included in a
multi-station substrate processing tool, and a controller having
(or having access to) machine-readable instructions for controlling
process operations in accordance with the processing techniques
disclosed herein.
[0080] Thus, in some embodiments, an apparatus suitable for doping
the fin-shaped channel regions of partially fabricated 3-D
transistors on the surfaces of semiconductor substrates may include
a plurality of process stations each having a substrate holder
contained in one or more processing chambers, one or more valves
for controlling flow of dopant-containing film precursor to the
process stations, and one or more valve-operated vacuum sources for
removing dopant-containing film precursor from the volumes
surrounding the process stations contained in the one or more
processing chambers. And, such an apparatus may also include a
controller having (or having access to) machine-readable
instructions for operating the one or more valves and one or more
vacuum sources to dope the fin-shaped channel regions on the
surfaces of the substrates. Thus, in some embodiments, said
instructions executed by the controller may include instructions
for forming a dopant-containing film on a substrate at a process
station contained in a processing chamber, wherein multiple
dopant-containing layers of the film are formed by an ALD process.
Thus, in certain such embodiments, said instructions executed by
the controller may include instructions for performing ALD
operations (i) though (iv) as described above, and instructions for
repeating ALD operations (i) through (iv) multiple times to form
multiple layers of dopant-containing film on the multiple
substrates at the multiple process stations of the substrate
processing apparatus. And, in some embodiments, instructions
executed by the controller may further include instructions for
forming a capping film comprising a silicon carbide material, a
silicon nitride material, a silicon carbonitride material, or a
combination thereof, and instructions for driving dopant from the
dopant-containing film into the fin-shaped channel regions of
partially-manufactured 3-D transistors on multiple substrates.
[0081] Accordingly, FIG. 8 schematically shows an embodiment of a
reaction chamber process station 800. For simplicity, process
station 800 is depicted as a standalone process station having a
process chamber body 802 for maintaining a low-pressure
environment. However, it will be appreciated that a plurality of
process stations 800 may be included in a common process tool
environment--e.g., within a common reaction chamber. For example,
FIG. 9 depicts an embodiment of a multi-station processing tool.
Further, it will be appreciated that, in some embodiments, one or
more hardware parameters of process station 800, including those
discussed in detail above, may be adjusted programmatically by one
or more system controllers.
[0082] Process station 800 fluidly communicates with reactant
delivery system 801 for delivering process gases to a distribution
showerhead 806. Reactant delivery system 801 includes a mixing
vessel 804 for blending and/or conditioning process gases for
delivery to showerhead 806. One or more mixing vessel inlet valves
820 may control introduction of process gases to mixing vessel
804.
[0083] Some reactants may be stored in liquid form prior to
vaporization and subsequent delivery to the process chamber 802.
The embodiment of FIG. 8 includes a vaporization point 803 for
vaporizing liquid reactant to be supplied to mixing vessel 804. In
some embodiments, vaporization point 803 may be a heated liquid
injection module. In some embodiments, vaporization point 803 may
be a heated vaporizer. The saturated reactant vapor produced from
such modules/vaporizers may condense in downstream delivery piping
when adequate controls are not in place (e.g., when no helium is
used in vaporizing/atomizing the liquid reactant). Exposure of
incompatible gases to the condensed reactant may create small
particles. These small particles may clog piping, impede valve
operation, contaminate substrates, etc. Some approaches to
addressing these issues involve sweeping and/or evacuating the
delivery piping to remove residual reactant. However, sweeping the
delivery piping may increase process station cycle time, degrading
process station throughput. Thus, in some embodiments, delivery
piping downstream of vaporization point 803 may be heat treated. In
some examples, mixing vessel 804 may also be heat treated. In one
non-limiting example, piping downstream of vaporization point 803
has an increasing temperature profile extending from approximately
100.degree. C. to approximately 150.degree. C. at mixing vessel
804.
[0084] As mentioned, in some embodiments the vaporization point 803
may be a heated liquid injection module ("liquid injector" for
short). Such a liquid injector may inject pulses of a liquid
reactant into a carrier gas stream upstream of the mixing vessel.
In one scenario, a liquid injector may vaporize reactant by
flashing the liquid from a higher pressure to a lower pressure. In
another scenario, a liquid injector may atomize the liquid into
dispersed microdroplets that are subsequently vaporized in a heated
delivery pipe. It will be appreciated that smaller droplets may
vaporize faster than larger droplets, reducing a delay between
liquid injection and complete vaporization. Faster vaporization may
reduce a length of piping downstream from vaporization point 803.
In one scenario, a liquid injector may be mounted directly to
mixing vessel 804. In another scenario, a liquid injector may be
mounted directly to showerhead 806.
[0085] In some embodiments, a liquid flow controller (LFC) upstream
of vaporization point 803 may be provided for controlling a mass
flow of liquid for vaporization and delivery to process station
800. For example, the LFC may include a thermal mass flow meter
(MFM) located downstream of the LFC. A plunger valve of the LFC may
then be adjusted responsive to feedback control signals provided by
a proportional-integral-derivative (PID) controller in electrical
communication with the MFM. However, it may take one second or more
to stabilize liquid flow using feedback control. This may extend a
time for dosing a liquid reactant. Thus, in some embodiments, the
LFC may be dynamically switched between a feedback control mode and
a direct control mode. In some embodiments, the LFC may be
dynamically switched from a feedback control mode to a direct
control mode by disabling a sense tube of the LFC and the PID
controller.
[0086] Showerhead 806 distributes process gases and/or reactants
(e.g., dopant-containing film precursor) toward substrate 812 at
the process station, the flow of which is controlled by one or more
valves upstream from the showerhead (e.g., valves 820, 820A, 805).
In the embodiment shown in FIG. 8, substrate 812 is located beneath
showerhead 806, and is shown resting on a pedestal 808. It will be
appreciated that showerhead 806 may have any suitable shape, and
may have any suitable number and arrangement of ports for
distributing processes gases to substrate 812.
[0087] In some embodiments, a microvolume 807 is located beneath
showerhead 806. Performing an ALD process in a microvolume in the
process station near the substrate rather than in the entire volume
of a processing chamber may reduce reactant exposure and sweep
times, may reduce times for altering process conditions (e.g.,
pressure, temperature, etc.), may limit an exposure of process
station robotics to process gases, etc. Example microvolume sizes
include, but are not limited to, volumes between 0.1 liter and 2
liters.
[0088] In some embodiments, pedestal 808 may be raised or lowered
to expose substrate 812 to microvolume 807 and/or to vary a volume
of microvolume 807. For example, in a substrate transfer phase,
pedestal 808 may be lowered to allow substrate 812 to be loaded
onto pedestal 808. During a deposition on substrate process phase,
pedestal 808 may be raised to position substrate 812 within
microvolume 807. In some embodiments, microvolume 807 may
completely enclose substrate 812 as well as a portion of pedestal
808 to create a region of high flow impedance during a deposition
process.
[0089] Optionally, pedestal 808 may be lowered and/or raised during
portions the deposition process to modulate process pressure,
reactant concentration, etc. within microvolume 807. In one
scenario where process chamber body 802 remains at a base pressure
during the process, lowering pedestal 808 may allow microvolume 807
to be evacuated. Example ratios of microvolume to process chamber
volume include, but are not limited to, volume ratios between 1:500
and 1:10. It will be appreciated that, in some embodiments,
pedestal height may be adjusted programmatically by a suitable
system controller.
[0090] In another scenario, adjusting a height of pedestal 808 may
allow a plasma density to be varied during plasma activation and/or
treatment cycles included, for example, in an ALD or CVD process.
At the conclusion of a deposition process phase, pedestal 808 may
be lowered during another substrate transfer phase to allow removal
of substrate 812 from pedestal 808.
[0091] While the example microvolume variations described herein
refer to a height-adjustable pedestal, it will be appreciated that,
in some embodiments, a position of showerhead 806 may be adjusted
relative to pedestal 808 to vary a volume of microvolume 807.
Further, it will be appreciated that a vertical position of
pedestal 808 and/or showerhead 806 may be varied by any suitable
mechanism within the scope of the present disclosure. In some
embodiments, pedestal 808 may include a rotational axis for
rotating an orientation of substrate 812. It will be appreciated
that, in some embodiments, one or more of these example adjustments
may be performed programmatically by one or more suitable system
controllers having machine-readable instructions for performing all
or a subset of the foregoing operations.
[0092] Returning to the embodiment shown in FIG. 8, showerhead 806
and pedestal 808 electrically communicate with RF power supply 814
and matching network 816 for powering a plasma. In some
embodiments, the plasma energy may be controlled (e.g., via a
system controller having appropriate machine-readable instructions)
by controlling one or more of a process station pressure, a gas
concentration, an RF source power, an RF source frequency, and a
plasma power pulse timing. For example, RF power supply 814 and
matching network 816 may be operated at any suitable power to form
a plasma having a desired composition of radical species. Examples
of suitable powers are included above. Likewise, RF power supply
814 may provide RF power of any suitable frequency. In some
embodiments, RF power supply 814 may be configured to control high-
and low-frequency RF power sources independently of one another.
Example low-frequency RF frequencies may include, but are not
limited to, frequencies between 50 kHz and 500 kHz. Example
high-frequency RF frequencies may include, but are not limited to,
frequencies between 1.8 MHz and 2.45 GHz. It will be appreciated
that any suitable parameters may be modulated discretely or
continuously to provide plasma energy for the surface reactions. In
one non-limiting example, the plasma power may be intermittently
pulsed to reduce ion bombardment with the substrate surface
relative to continuously powered plasmas.
[0093] In some embodiments, the plasma may be monitored in-situ by
one or more plasma monitors. In one scenario, plasma power may be
monitored by one or more voltage, current sensors (e.g., VI
probes). In another scenario, plasma density and/or process gas
concentration may be measured by one or more optical emission
spectroscopy (OES) sensors. In some embodiments, one or more plasma
parameters may be programmatically adjusted based on measurements
from such in-situ plasma monitors. For example, an OES sensor may
be used in a feedback loop for providing programmatic control of
plasma power. It will be appreciated that, in some embodiments,
other monitors may be used to monitor the plasma and other process
characteristics. Such monitors may include, but are not limited to,
infrared (IR) monitors, acoustic monitors, and pressure
transducers.
[0094] In some embodiments, the plasma may be controlled via
input/output control (IOC) sequencing instructions. In one example,
the instructions for setting plasma conditions for a plasma
activation phase may be included in a corresponding plasma
activation recipe phase of a process recipe. In some cases, process
recipe phases may be sequentially arranged, so that all
instructions for a process phase are executed concurrently with
that process phase. In some embodiments, instructions for setting
one or more plasma parameters may be included in a recipe phase
preceding a plasma process phase. For example, a first recipe phase
may include instructions for setting a flow rate of an inert (e.g.,
helium) and/or a reactant gas, instructions for setting a plasma
generator to a power set point, and time delay instructions for the
first recipe phase. A second, subsequent recipe phase may include
instructions for enabling the plasma generator and time delay
instructions for the second recipe phase. A third recipe phase may
include instructions for disabling the plasma generator and time
delay instructions for the third recipe phase. It will be
appreciated that these recipe phases may be further subdivided
and/or iterated in any suitable way within the scope of the present
disclosure.
[0095] In some deposition processes, plasma strikes last on the
order of a few seconds or more in duration. In certain
implementations described herein, much shorter plasma strikes may
be applied during a processing cycle. These may be on the order of
50 milliseconds to 1 second, with 0.25 seconds being a specific
example. Such short RF plasma strikes require quick stabilization
of the plasma. To accomplish this, the plasma generator may be
configured such that the impedance match is preset to a particular
voltage, while the frequency is allowed to float. Conventionally,
high-frequency plasmas are generated at an RF frequency at about
13.56 MHz. In various embodiments disclosed herein, the frequency
is allowed to float to a value that is different from this standard
value. By permitting the frequency to float while fixing the
impedance match to a predetermined voltage, the plasma can
stabilize much more quickly, a result which may be important when
using the very short plasma strikes associated with ALD cycles.
[0096] In some embodiments, pedestal 808 may be temperature
controlled via heater 810. Further, in some embodiments, pressure
control for process station 800 may be provided by one or more
valve-operated vacuum sources such as butterfly valve 818. As shown
in the embodiment of FIG. 8, butterfly valve 818 throttles a vacuum
provided by a downstream vacuum pump (not shown). However, in some
embodiments, pressure control of process station 800 may also be
adjusted by varying a flow rate of one or more gases introduced to
process station 800. In some embodiments, the one or more
valve-operated vacuum sources--such as butterfly valve 818--may be
used for removing dopant-containing film precursor from the volumes
surrounding the process stations during the appropriate ALD
operational phases.
[0097] As described above, one or more process stations may be
included in a multi-station substrate processing tool. FIG. 9
schematically illustrates an example of a multi-station processing
tool 900 which includes a plurality of process stations 901, 902,
903, 904 in a common low-pressure processing chamber 914. By
maintaining each station in a low-pressure environment, defects
caused by vacuum breaks between film deposition processes may be
avoided.
[0098] As shown in FIG. 9, the multi-station processing tool 900
has an inbound load lock 922 and an outbound load lock 924, either
or both of which may comprise a remote plasma source. A robot 926,
at atmospheric pressure, is configured to move wafers from a
cassette loaded through a pod 928 into inbound load lock 922 via an
atmospheric port 920. A wafer is placed by the robot 926 on a
pedestal 912 in the inbound load lock 922, the atmospheric port 920
is closed, and the load lock is pumped down. Where the inbound load
lock 922 comprises a remote plasma source, the wafer may be exposed
to a remote plasma treatment in the load lock prior to being
introduced into a processing chamber 914. Further, the wafer also
may be heated in the inbound load lock 922, for example, to remove
moisture and adsorbed gases. Next, a chamber transport port 916 to
processing chamber 914 is opened, and another robot (not shown)
places the wafer into the processing chamber on a pedestal 918 at
process station 901. While the embodiment depicted in FIG. 9
includes load locks, it will be appreciated that, in some
embodiments, direct entry of a wafer substrate into a processing
chamber may be provided.
[0099] The depicted processing chamber 914 shown in FIG. 9 provides
four process stations, 901, 902, 903, and 904. Each station has a
heated pedestal (shown at 918 for process station 901) and gas line
inlets. It will be appreciated that in some embodiments, each
process station may have different or multiple purposes. For
example, in some embodiments, a process station may be switchable
between an ALD process mode and a CVD process mode. Additionally or
alternatively, in some embodiments, processing chamber 914 may
include one or more matched pairs of ALD/CVD process stations.
While the depicted processing chamber 914 comprises 4 process
stations, it will be understood that a processing chamber according
to the present disclosure may have any suitable number of stations.
For example, in some embodiments, a processing chamber may have 1,
or 2, or 3, or 4, or 5, or 6, or 7, or 8, or 9, or 10, or 11, or
12, or 13, or 14, or 15, or 16, or more process stations (or a set
of embodiments may be described as having a number of process
stations per reaction chamber within a range defined by any pair of
the foregoing values, such as having 2 to 6 process stations per
reaction chamber, or 4 to 8 process stations per reaction chamber,
or 8 to 16 process stations per reaction chamber, etc.).
[0100] FIG. 9 also depicts an embodiment of a wafer handling system
990 for transferring wafers within processing chamber 914. In some
embodiments, wafer handling system 990 may transfer wafers between
various process stations and/or between a process station and a
load lock. It will be appreciated that any suitable wafer handling
system may be employed. Non-limiting examples include wafer
carousels and wafer handling robots.
[0101] FIG. 9 also depicts an embodiment of a system controller 950
employed to control process conditions and hardware states of
process tool 900 and its process stations. System controller 950
may include one or more memory devices 956, one or more mass
storage devices 954, and one or more processors 952. Processor 952
may include one or more CPUs, ASICs, general-purpose computer(s)
and/or specific purpose computer(s), one or more analog and/or
digital input/output connection(s), one or more stepper motor
controller board(s), etc.
[0102] In some embodiments, system controller 950 controls some or
all of the operations of process tool 900 including the operations
of its individual process stations. System controller 950 may
execute machine-readable system control instructions 958 on
processor 952--the system control instructions 958, in some
embodiments, loaded into memory device 956 from mass storage device
954. System control instructions 958 may include instructions for
controlling the timing, mixture of gaseous and liquid reactants,
chamber and/or station pressure, chamber and/or station
temperature, wafer temperature, target power levels, RF power
levels, RF exposure time, substrate pedestal, chuck, and/or
susceptor position, and other parameters of a particular process
performed by process tool 900. These processes may include various
types of processes including, but not limited to, processes related
to deposition of film on substrates. System control instructions
958 may be configured in any suitable way. For example, various
process tool component subroutines or control objects may be
written to control operation of the process tool components
necessary to carry out various process tool processes. System
control instructions 958 may be coded in any suitable computer
readable programming language. In some embodiments, system control
instructions 958 are implemented in software, in other embodiments,
the instructions may be implemented in hardware--for example,
hard-coded as logic in an ASIC (application specific integrated
circuit), or, in other embodiments, implemented as a combination of
software and hardware.
[0103] In some embodiments, system control software 958 may include
input/output control (IOC) sequencing instructions for controlling
the various parameters described above. For example, each phase of
a deposition process or processes may include one or more
instructions for execution by system controller 950. The
instructions for setting process conditions for a dopant-containing
film deposition process phase, for example, may be included in a
corresponding deposition recipe phase, and likewise for a capping
film deposition phase. In some embodiments, the recipe phases may
be sequentially arranged, so that all instructions for a process
phase are executed concurrently with that process phase.
[0104] Other computer-readable instructions and/or programs stored
on mass storage device 954 and/or memory device 956 associated with
system controller 950 may be employed in some embodiments. Examples
of programs or sections of programs include a substrate positioning
program, a process gas control program, a pressure control program,
a heater control program, and a plasma control program.
[0105] A substrate positioning program may include instructions for
process tool components that are used to load the substrate onto
pedestal 918 and to control the spacing between the substrate and
other parts of process tool 900. The positioning program may
include instructions for appropriately moving substrates in and out
of the reaction chamber as necessary to deposit dopant-containing
and capping films on the substrates.
[0106] A process gas control program may include instructions for
controlling gas composition and flow rates and optionally for
flowing gas into the volumes surrounding one or more process
stations prior to deposition in order to stabilize the pressure in
these volumes. In some embodiments, the process gas control program
may include instructions for introducing certain gases into the
volume(s) surrounding the one or more process stations within a
processing chamber during deposition of a dopant-containing film on
a substrates, and for introducing different gases during deposition
of a capping film on the substrates. The process gas control
program may also include instructions to deliver these gases at the
same rates, for the same durations, or at different rates and/or
for different durations depending on the composition of the film
being deposited. The process gas control program may also include
instructions for atomizing/vaporizing a liquid reactant in the
presence of helium or some other carrier gas in a heated injection
module.
[0107] A pressure control program may include instructions for
controlling the pressure in the process station by regulating, for
example, a throttle valve in the exhaust system of the process
station, a gas flow into the process station, etc. The pressure
control program may include instructions for maintaining the same
or different pressures during deposition of the various film types
on the substrates.
[0108] A heater control program may include instructions for
controlling the current to a heating unit that is used to heat the
substrates. Alternatively or in addition, the heater control
program may control delivery of a heat transfer gas (such as
helium) to the substrate. The heater control program may include
instructions for maintaining the same or different temperatures in
the reaction chamber and/or volumes surrounding the process
stations during deposition of the various film types on the
substrates.
[0109] A plasma control program may include instructions for
setting RF power levels, frequencies, and exposure times in one or
more process stations in accordance with the embodiments herein. In
some embodiments, the plasma control program may include
instructions for using the same or different RF power levels and/or
frequencies and/or exposure times during deposition of the
dopant-containing film and capping film types on the
substrates.
[0110] In some embodiments, there may be a user interface
associated with system controller 950. The user interface may
include a display screen, graphical software displays of the
apparatus and/or process conditions, and user input devices such as
pointing devices, keyboards, touch screens, microphones, etc.
[0111] In some embodiments, parameters adjusted by system
controller 950 may relate to process conditions. Non-limiting
examples include process gas compositions and flow rates,
temperatures, pressures, plasma conditions (such as RF bias power
levels and exposure times), etc. These parameters may be provided
to the user in the form of a recipe, which may be entered utilizing
the user interface.
[0112] Signals for monitoring the processes may be provided by
analog and/or digital input connections of system controller 950
from various process tool sensors. The signals for controlling the
processes may be output on the analog and/or digital output
connections of process tool 900. Non-limiting examples of process
tool sensors that may be monitored include mass flow controllers
(MFCs), pressure sensors (such as manometers), thermocouples, etc.
Appropriately programmed feedback and control algorithms may be
used with data from these sensors to maintain process
conditions.
[0113] System controller 950 may provide machine-readable
instructions for implementing the above-described deposition
processes. The instructions may control a variety of process
parameters, such as DC power level, RF bias power level, pressure,
temperature, etc. The instructions may control the parameters to
operate in-situ deposition of film stacks according to various
embodiments described herein.
[0114] The system controller will typically include one or more
memory devices and one or more processors configured to execute
machine-readable instructions so that the apparatus will perform
operations in accordance with the processes disclosed herein.
Machine-readable, non-transitory media containing instructions for
controlling operations in accordance with the substrate doping
processes disclosed herein may be coupled to the system
controller.
[0115] The various apparatuses and methods described above may be
used in conjunction with lithographic patterning tools and/or
processes, for example, for the fabrication or manufacture of
semiconductor devices, displays, LEDs, photovoltaic panels and the
like. Typically, though not necessarily, such tools will be used or
processes conducted together and/or contemporaneously in a common
fabrication facility.
[0116] Lithographic patterning of a film typically includes some or
all of the following operations, each operation enabled with a
number of possible tools: (1) application of photoresist on a
substrate, e.g., a substrate having a silicon nitride film formed
thereon, using a spin-on or spray-on tool; (2) curing of
photoresist using a hot plate or furnace or other suitable curing
tool; (3) exposing the photoresist to visible or UV or x-ray light
with a tool such as a wafer stepper; (4) developing the resist so
as to selectively remove resist and thereby pattern it using a tool
such as a wet bench or a spray developer; (5) transferring the
resist pattern into an underlying film or substrate by using a dry
or plasma-assisted etching tool; and (6) removing the resist using
a tool such as an RF or microwave plasma resist stripper. In some
embodiments, an ashable hard mask layer (such as an amorphous
carbon layer) and another suitable hard mask (such as an
antireflective layer) may be deposited prior to applying the
photoresist.
Other Embodiments
[0117] Although the foregoing disclosed processes, methods,
systems, apparatuses, and compositions have been described in
detail within the context of specific embodiments for the purpose
of promoting clarity and understanding, it will be apparent to one
of ordinary skill in the art that there are many alternative ways
of implementing these processes, methods, systems, apparatuses, and
compositions which are within the spirit of this disclosure.
Accordingly, the embodiments described herein are to be viewed as
illustrative of the disclosed inventive concepts rather than
restrictively, and are not to be used as an impermissible basis for
unduly limiting the scope of any claims eventually directed to the
subject matter of this disclosure.
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