U.S. patent application number 10/701191 was filed with the patent office on 2005-05-05 for method for forming an electronic device.
This patent application is currently assigned to International Business Machines Corporation. Invention is credited to Balasubramanyam, Karanam, Biesemans, Serge, Park, Byeongju.
Application Number | 20050095831 10/701191 |
Document ID | / |
Family ID | 34435530 |
Filed Date | 2005-05-05 |
United States Patent
Application |
20050095831 |
Kind Code |
A1 |
Balasubramanyam, Karanam ;
et al. |
May 5, 2005 |
METHOD FOR FORMING AN ELECTRONIC DEVICE
Abstract
Under the present invention, a layer of amorphous silicon is
formed over a layer of gate dielectric. Over the layer of amorphous
silicon, a gate cap dielectric is formed. The layer of amorphous
silicon is then confined by at least one spacer, which is deposited
under a low temperature process. Once the at least one spacer is in
place, the amorphous silicon is exposed to a temperature
sufficiently high to convert the amorphous silicon to polysilicon.
By waiting until the amorphous silicon is confined within the at
least one spacer before converting it to polysilicon, the variation
in gate length is reduced
Inventors: |
Balasubramanyam, Karanam;
(Hopewell Junction, NY) ; Biesemans, Serge;
(Leuven, BE) ; Park, Byeongju; (Wappingers Falls,
NY) |
Correspondence
Address: |
HOFFMAN WARNICK & D'ALESSANDRO, LLC
3 E-COMM SQUARE
ALBANY
NY
12207
|
Assignee: |
International Business Machines
Corporation
Armonk
NY
|
Family ID: |
34435530 |
Appl. No.: |
10/701191 |
Filed: |
November 4, 2003 |
Current U.S.
Class: |
438/585 ;
257/E21.197; 257/E29.155 |
Current CPC
Class: |
H01L 21/28035 20130101;
H01L 29/6656 20130101; H01L 29/4925 20130101 |
Class at
Publication: |
438/585 |
International
Class: |
H01L 021/8238 |
Claims
We claim:
1. A method for forming an electronic device, comprising: providing
a layer of gate dielectric; forming a layer of amorphous silicon on
the layer of gate dielectric; forming a gate cap dielectric on the
layer of amorphous silicon; providing at least one spacer adjacent
the layer of amorphous silicon; and exposing the amorphous silicon
to a temperature sufficiently high to convert the amorphous silicon
to polysilicon after the at least one spacer has been provided.
2. The method of claim 1, wherein the exposing step comprises
exposing the amorphous silicon to a temperature of at least
approximately 750.degree. C. to convert the amorphous silicon to
polysilicon after the at least one spacer has been provided.
3. The method of claim 1, wherein the exposing step comprises
exposing the amorphous silicon to a temperature of at least
approximately 800.degree. C. to convert the amorphous silicon to
polysilicon after the at least one spacer has been provided.
4. The method of claim 1, wherein the exposing step comprises
performing a rapid thermal anneal at a temperature sufficiently
high to convert the amorphous silicon to polysilicon after the at
least one spacer has been provided.
5. The method of claim 1, further comprising performing a gate
sidewall oxidation at a temperature sufficiently low to avoid
transformation of the amorphous silicon to polysilicon before
providing the at least one spacer.
6. The method of claim 1, wherein the at least one spacer is
provided at a temperature of less than approximately 750.degree.
C.
7. The method of claim 1, further comprising: performing
lithography and etching after the gate cap dielectric has been
formed; and implanting a source and a drain into the electronic
device after the at least one spacer has been provided.
8. The method of claim 1, wherein the gate cap dielectric is
selected from the group consisting of silicon nitride and silicon
dioxide.
9. The method of claim 1, wherein the electronic device is a
field-effect transistor (FET) device.
10. A method for forming an electronic device, comprising:
providing a layer of gate dielectric; forming a layer of amorphous
silicon on the layer of gate dielectric; forming a gate cap
dielectric on the layer of amorphous silicon; providing at least
one spacer adjacent the layer of amorphous silicon; and performing
a rapid thermal anneal at a temperature of at least approximately
750.degree. C. after the at least one spacer has been provided to
convert the amorphous silicon to polysilicon.
11. The method of claim 10, wherein the exposing step comprises
performing a rapid thermal anneal at a temperature of at least
approximately 750.degree. C. to convert the amorphous silicon to
polysilicon after the at least one spacer has been provided.
12. The method of claim 10, further comprising performing a gate
sidewall oxidation at a temperature below approximately 750.degree.
C. to avoid transformation of the amorphous silicon to polysilicon
before providing the at least one spacer.
13. The method of claim 10, further comprising: performing
lithography and etching after the gate cap dielectric has been
formed and implanting a source and a drain into the electronic
device after the at least one spacer has been provided.
14. The method of claim 10, wherein the gate cap dielectric is
selected from the group consisting of silicon nitride and silicon
dioxide.
15. The method of claim 10, wherein the electronic device is a
field-effect transistor (FET) device.
16. A method for forming a field-effect transistor (FET) device,
comprising: providing a layer of gate dielectric; forming a layer
of amorphous silicon on the layer of gate dielectric; forming a
gate cap dielectric on the layer of amorphous silicon; providing a
first spacer adjacent the layer of amorphous silicon; providing a
second spacer adjacent the layer of amorphous silicon; and exposing
the amorphous silicon to a temperature of at least approximately
750.degree. C. after the second spacer has been provided to convert
the amorphous silicon to polysilicon.
17. The method of claim 16, wherein the exposing step comprises
performing a rapid thermal anneal at a temperature of at least
approximately 750.degree. C. to convert the amorphous silicon to
polysilicon after the at least one spacer has been provided.
18. The method of claim 16, further comprising performing a gate
sidewall oxidation at a temperature below approximately 750.degree.
C. to avoid transformation of the amorphous silicon to polysilicon
before providing the at least one spacer.
19. The method of claim 16, further comprising: performing
lithography and etching after the gate cap dielectric has been
formed; implanting an extension into the FET device after the first
spacer has been provided; and implanting a source and a drain into
the FET device after the second spacer has been provided.
20. The method of claim 16, wherein the gate cap dielectric is
selected from the group consisting of silicon nitride and silicon
dioxide.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention generally relates to a method for
forming an electronic device such as a field-effect transistor
(FET) device. Specifically, the present invention relates to a
method for forming an electronic device in which gate length
variation is reduced.
[0003] 2. Related Art
[0004] In the process of manufacturing electronic devices such as
FET devices, several factors can lead to gate length variation. One
such factor is the incapability of the lithographic tools to
produce straight edge gate lines. Another factor is the etching
process whereby uneven gate lines are produced. However, a
prevailing cause of gate length variation is the grain structure of
polycrystalline silicon. Specifically, in the manufacture of many
electronic devices such as FET devices, the gate polysilicon is
deposited as polycrystalline silicon. The grain-like structure of
the polysilicon typically causes gate line roughness during
polysilicon etching. In addition, during high temperature
processing of the device such as during rapid thermal anneal (RTA)
gate sidewall oxidation, the gate polysilicon line roughness is
increased as the polysilicon material undergoes further changes in
crystal structure in an unconfined environment.
[0005] This gate line problem is partly alleviated through the use
of amorphous silicon for the gate silicon. Specifically, through
the use of amorphous silicon, the increase in the roughness of the
gate line is minimized during the gate silicon etch. However, in
the conventional use of the amorphous silicon, high temperature
processing such as the RTA gate sidewall oxidation and/or high
temperature low pressure (LP) chemical vapor deposition (LPCVD) of
nitride immediately follows. Exposure of the amorphous silicon to
high temperatures causes structural transformation, which when
occurring in an unconfined environment, cause movement of the
silicon material during the polysilicon grain growth. Thus, the
roughness of the gate silicon line is increased, which leads to
variation in the gate length. Referring to FIG. 1, a scanning
electron micrograph (SEM) image 10 of a polysilicon gate line 12 as
produced under the prior art is depicted. As shown, the surface of
the polysilicon gate line 12 is rough, which causes variation in
the gate length 14. For example, at point 16 gate length 14 is
approximately 115 nm. Conversely, at point 18, gate length 14 is
approximately 128 nm. Such a variation in gate length 14 can raise
significant performance issues in the device.
[0006] In view of the foregoing, there exists a need for a method
for manufacturing an electronic device. Specifically, a need exists
for a method of manufacturing an electronic device in which gate
length variation is reduced. A further need exists for a method of
manufacturing an electronic device in which amorphous silicon is
used as the gate silicon. However, another need exists for the
amorphous silicon to be exposed to high temperatures for
transformation to polysilicon only in a confined environment.
SUMMARY OF THE INVENTION
[0007] In general, the present invention provides a method for
forming an electronic device such as a FET device. Specifically,
under the present invention, a layer of amorphous silicon is formed
over a layer of gate dielectric. After the layer of amorphous
silicon is formed, a gate cap dielectric is deposited. Implantation
of dopants is then performed as needed. Thereafter, gate lines are
patterned lithographically and the gate cap dielectric, amorphous
silicon, and gate dielectric are etched to form the gate lines. It
should be noted that the state of silicon is amorphous at the time
of etching to minimize the line edge roughness. The absence of
grain boundaries, which would be present in polysilicon, reduces
the line edge roughness at the time of etching. Further, the
amorphous silicon is confined on the top by gate cap dielectric and
on the bottom by gate dielectric. The sides of amorphous silicon
are then confined by at least one spacer, which is deposited under
a low temperature process. Low temperature processing in this
manner preserves the chrystallographical state of the amorphous
silicon material throughout the spacer deposition(s). Once the at
least one spacer is in place, the amorphous silicon is exposed to a
temperature sufficiently high to convert the amorphous silicon to
polysilicon. By waiting until the amorphous silicon is confined
within the at least one spacer before converting it to polysilicon,
the movement of the silicon atoms within the silicon material is
confined within the at least one spacer laterally and the variation
in gate length is reduced.
[0008] A first aspect of the present invention provides a method
for forming an electronic device, comprising: providing a layer of
gate dielectric; forming a layer of amorphous silicon on the layer
of gate dielectric; forming a gate cap dielectric on the layer of
amorphous silicon; providing at least one spacer adjacent the layer
of amorphous silicon; and exposing the amorphous silicon to a
temperature sufficiently high to convert the amorphous silicon to
polysilicon after the at least one spacer has been provided.
[0009] A second aspect of the present invention provides a method
for forming an electronic device, comprising: providing a layer of
gate dielectric; forming a layer of amorphous silicon on the layer
of gate dielectric; forming a gate cap dielectric on the layer of
amorphous silicon; providing at least one spacer adjacent the layer
of amorphous silicon; and performing a rapid thermal anneal at a
temperature of at least approximately 750.degree. C. after the at
least one spacer has been provided to convert the amorphous silicon
to polysilicon.
[0010] A third aspect of the present invention provides a method
for forming a field-effect transistor (FET) device, comprising:
providing a layer of gate dielectric; forming a layer of amorphous
silicon on the layer of gate dielectric; forming a gate cap
dielectric on the layer of amorphous silicon; providing a first
spacer adjacent the layer of amorphous silicon; providing a second
spacer adjacent the layer of amorphous silicon; and exposing the
amorphous silicon to a temperature of at least approximately
750.degree. C. after the second spacer has been provided to convert
the amorphous silicon to polysilicon.
[0011] Therefore, the present invention provides a method for
forming an electronic device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] These and other features of this invention will be more
readily understood from the following detailed description of the
various aspects of the invention taken in conjunction with the
accompanying drawings in which:
[0013] FIG. 1 depicts an illustration of an SEM image of a
polysilicon gate line as produced according to the prior art.
[0014] FIG. 2 depicts a FET device as produced according to the
present invention.
[0015] FIG. 3 depicts an illustration of an SEM image of a
polysilicon gate line as produced according to the present
invention.
[0016] FIG. 4 depicts a method flow diagram according to the
present invention.
[0017] The drawings are merely schematic representations, not
intended to portray specific parameters of the invention. The
drawings are intended to depict only typical embodiments of the
invention, and therefore should not be considered as limiting the
scope of the invention. In the drawings, like numbering represents
like elements.
DETAILED DESCRIPTION OF THE INVENTION
[0018] As indicated above, the present invention provides a method
for forming an electronic device such as a FET device.
Specifically, under the present invention, a layer of amorphous
silicon is formed over a layer of gate dielectric. After the layer
of amorphous silicon is formed, a gate cap dielectric is deposited.
Implantation of dopants is then performed as needed. Thereafter,
gate lines are patterned lithographically and the gate cap
dielectric, amorphous silicon, and gate dielectric are etched to
form the gate lines. It should be noted that the state of silicon
is amorphous at the time of etching to minimize the line edge
roughness. The absence of grain boundaries, which would be present
in polysilicon, reduces the line edge roughness at the time of
etching. Further, the amorphous silicon is confined on the top by
gate cap dielectric and on the bottom by gate dielectric. The sides
of amorphous silicon are then confined by at least one spacer,
which is deposited under a low temperature process. Low temperature
processing in this manner preserves the chrystallographical state
of the amorphous silicon material throughout the spacer
deposition(s). Once the at least one spacer is in place, the
amorphous silicon is exposed to a temperature sufficiently high to
convert the amorphous silicon to polysilicon. By waiting until the
amorphous silicon is confined within the at least one spacer before
converting it to polysilicon, the movement of the silicon atoms
within the silicon material is confined within the at least one
spacer laterally and the variation in gate length is reduced.
[0019] Prior to the present invention, the amorphous silicon was
subjected to high temperatures in an unconfined environment, with
the result being that shown and described above in conjunction with
FIG. 1. Specifically, under previous methods, the device was
subjected to high temperature gate sidewall oxidation at a
temperature of approximately 1000.degree. C. when the amorphous
silicon was in an unconfined environment (e.g., prior to
implantation of any spacers). This high temperature process
transformed the amorphous silicon to polysilicon. However, because
it was performed in an unconfined environment, the aforementioned
increased surface roughness and gate line variation were
exhibited.
[0020] Referring now to FIG. 2, an electronic device 20 produced
according to the present invention is shown. It should be
understood in advance that although FIG. 2 depicts a typical FET
device produced according to the present invention, many
alternatives are possible. Specifically, the teachings described
herein could be used to produce any type of electronic device
(e.g., MOSFET, CMOS, etc.) in which a polysilicon gate material is
traditionally used. In any event, under the present invention,
layer of gate dielectric 22 (e.g., a thermal oxide) is formed. On
top of layer of gate dielectric 22, layer of amorphous silicon 24
is formed (e.g., deposited at 500.degree. C. or 550.degree. C.).
Once layer of amorphous silicon 24 is in place, gate cap dielectric
26 is formed. In a typical embodiment, gate cap dielectric 26 is
silicon nitride, silicon oxide or the like and can be deposited on
layer of amorphous silicon 24. In any event, once gate cap
dielectric 24 is in place, the device 20 is subjected to
lithography and gate stack etch.
[0021] After the etching process, device 20 is subjected to a gate
sidewall oxidation process at a temperature sufficiently low (e.g.,
at 600.degree. C. for high pressure oxidation such as at 10 ATM) so
that the amorphous silicon 24 does not transform to polysilicon. In
general, the gate sidewall oxidation process is carried out at a
temperature lower than approximately 700.degree. C. (e.g.,
675.degree. C.). However, in another embodiment, the gate sidewall
oxidation process is carried out at a temperature lower than
approximately 750.degree. C.
[0022] In any event, after the low temperature gate sidewall
oxidation process, at least one spacer 28A and 28B is deposited
(e.g., via BTBAS LPCVD) adjacent the layer of amorphous silicon 24
at low temperatures (e.g., less than approximately 750.degree. C.
or 700.degree. C. such as 675.degree. C. or 600.degree. C.). In a
typical embodiment, a first spacer 28A is deposited at low
temperature, followed by implantation of an extension 30.
Subsequent to extension 30 implantation, second spacer 28B is
deposited at the low temperature. Once all desired spacers 28A-B
are in place, source 32 and drain 34 can be implanted. Thereafter,
layer of amorphous silicon 24 is exposed to a temperature
sufficiently high and for a duration of time sufficient to
transform the amorphous silicon to polysilicon.
[0023] Under the present invention, layer of amorphous silicon 24
is subject to RTA at a temperature of at least approximately
750.degree. C. to achieve the transformation. However, in other
embodiments, layer of amorphous silicon 24 can be exposed to a
temperature of at least approximately 800.degree. C. after spacers
28A-B are in place to achieve the transformation. Still yet, in the
illustrative examples set forth below, layer of amorphous silicon
24 was exposed to temperatures of 1000.degree. C. for 90 seconds or
1100.degree. C. for 60 seconds. In any event, layer of amorphous
silicon 24 is not exposed to the high temperatures until spacers
28A-B are in place. This causes the transformation to occur in an
enclosed or confined environment, which reduces silicon movements,
surface roughness and gate length variation.
[0024] It should be understood that under the present invention,
any quantity of spacers could be provided. For example, although
FIG. 2 shows two spacers 28A-B, the present invention could be
carried out with more or fewer spacers. It should also be
understood that the description of device 20 of FIG. 2 is not
intended to be an all inclusive description. Those of ordinary
skill in the art will recognize that other layers/components not
described and/or shown are part of device 20.
ILLUSTRATIVE EXAMPLE
[0025] Under experiment, twenty FET wafers were prepared under
different conditions. Some of the wafers were prepared under the
previous conventional techniques, while other were prepared
according to the present invention. The table below shows the
manner in which the twenty wafers were prepared. It should be
understood in advance that wafers 2 and 14 represent wafers
produced according to the present invention, while wafer 19
represents a wafer produced according to the previous conventional
technique described above.
1 Gate Sidewall Silicon Oxidation Gate Spacer 1 Spacer 2 Final RTA
Wafer No. Temp. Process Implant Dep. Dep. Temp. 1 525.degree. C.
HIPOX P type BTBAS BTBAS 1000.degree. C. 175 900 2 525.degree. C.
HIPOX P type BTBAS BTBAS 1000.degree. C. 175 900 3 525.degree. C.
HIPOX P type BTBAS BTBAS 1000.degree. C. 175 900 4 525.degree. C.
HIPOX P type RTCVD RTCVD 1000.degree. C. 175 900 5 525.degree. C.
HIPOX P type BTBAS BTBAS 700.degree. C. 175 900 6 525.degree. C.
HIPOX P type BTBAS BTBAS 1100.degree. C. 175 900 7 525.degree. C.
RTA P type BTBAS BTBAS 700.degree. C. 175 900 8 525.degree. C. SVG
700.degree. C. P type BTBAS BTBAS 1000.degree. C. 175 900 9
525.degree. C. HIPOX N type BTBAS BTBAS 1000.degree. C. 175 900 10
525.degree. C. HIPOX N type BTBAS BTBAS 1000.degree. C. 175 900 11
525.degree. C. HIPOX N type BTBAS BTBAS 1000.degree. C. 175 900 12
525.degree. C. HIPOX N type RTCVD RTCVD 1000.degree. C. 175 900 13
525.degree. C. HIPOX N type BTBAS BTBAS 700.degree. C. 175 900 14
525.degree. C. HIPOX N type BTBAS BTBAS 1100.degree. C. 175 900 15
525.degree. C. RTA N type BTBAS BTBAS 700.degree. C. 175 900 16
525.degree. C. SVG 700.degree. C. N type BTBAS BTBAS 1000.degree.
C. 175 900 17 550.degree. C. HIPOX P type BTBAS BTBAS 1000.degree.
C. 175 900 18 550.degree. C. HIPOX N type BTBAS BTBAS 1000.degree.
C. 175 900 19 620.degree. C. RTA P type RTCVD RTCVD 700.degree. C.
175 900 20 620.degree. C. RTA N type RTCVD RTCVD 700.degree. C. 177
900
[0026] Under the table above, the amorphous silicon deposition
temperature was either 525.degree. C. or 550.degree. C., whereas
the polysilicon deposition temperature was 620.degree. C. The
sidewall oxidation temperature was 600.degree. C. for the high
pressure oxidation (e.g., 10 ATM) process (HIPOX), and 700.degree.
C. for the SVG 700.degree. C. process. The RTA sidewall oxidation
temperature was 1000.degree. C. for 90 seconds. Further spacer 1
was 17.5 nm thick and was deposited at a temperature of 575.degree.
C. for the BTBAS 175 process and 720.degree. C. for the RTCVD 175
process. Spacer 2 was 90 nm thick and was deposited at a
temperature of 600.degree. C. for the BTAS 900 process and
720.degree. C. for the RTCVD 900 process.
[0027] With the new scheme, the reduction in line roughness was
readily apparent. The total range of the gate length decreased from
17 nm for the conventional polysilicon gate process, to 8 nm for
the amorphous silicon gate with 1000.degree. C. RTA for 90 seconds,
to 5 nm for the amorphous silicon gate with 1100.degree. C. RTA for
60 seconds. FIG. 3 depicts a SEM image 40 of a polysilicon gate
line 42 formed subsequent to RTA of the layer of amorphous silicon
at a temperature of 1000.degree. C. for 90 seconds. As shown, the
surface of polysilicon gate line 42 of the polysilicon is
significantly less rough than surface of polysilicon gate line 12
shown in FIG. 1. To this extent, gate length 44 variation is also
reduced. For example, at point 46 gate length 44 is approximately
78 nm. Conversely, at point 48, gate length 44 is approximately 76
nm.
[0028] Referring not to FIG. 4, a method flow diagram 100 according
to the present invention is shown. As depicted, first step S1 of
method 100 is to providing a layer of gate dielectric. Second step
S2 is to forming a layer of amorphous silicon on the layer of gate
dielectric. Third step S3 is to forming a gate cap dielectric on
the layer of amorphous silicon. Fourth step S4 is to provide at
least one spacer adjacent the layer of amorphous silicon. As
indicated above, all processing of the device before the deposition
of the spacers is complete is done at a temperature sufficiently
low so as to not result in transformation of the amorphous silicon
to polysilicon. Once the at least one spacer is provided, the
amorphous silicon is exposed to a temperature sufficiently high to
convert the amorphous silicon to polysilicon in step S5. As
indicated above, this temperature is at least approximately
750.degree. C. or 800.degree. C. In the illustrative examples shown
above, the temperatures used to transform the amorphous silicon to
polysilicon were 1000.degree. C. and 1100.degree. C.
[0029] The foregoing description of the preferred embodiments of
this invention has been presented for purposes of illustration and
description. It is not intended to be exhaustive or to limit the
invention to the precise form disclosed, and obviously, many
modifications and variations are possible. Such modifications and
variations that may be apparent to a person skilled in the art are
intended to be included within the scope of this invention as
defined by the accompanying claims.
* * * * *