U.S. patent number RE36,050 [Application Number 08/722,360] was granted by the patent office on 1999-01-19 for method for repeatable temperature measurement using surface reflectivity.
This patent grant is currently assigned to Micron Technology, Inc.. Invention is credited to Annette L. Martin, Gurtej S. Sandhu, Randhir P. S. Thakur.
United States Patent |
RE36,050 |
Thakur , et al. |
January 19, 1999 |
Method for repeatable temperature measurement using surface
reflectivity
Abstract
A method is disclosed for continuously measuring the temperature
of a semiconductor substrate in a chamber is disclosed. The first
step of the method involves providing a substantially clean
semiconductor substrate having a layer a reflective surface thereon
into a chamber. A film is formed superjacent the surface by
introducing a gas comprising at least one of N.sub.2, NH.sub.3,
O.sub.2, N.sub.2 O, Ar, Ar--H.sub.2, H.sub.2, GeH.sub.4, or any
fluorine based gas and photon energy in situ. The photon energy,
having a wavelength substantially in the absorption band of
silicon, generates a temperature substantially within the range of
500.degree. C. to 1250.degree. C. Subsequently, the reflectivity of
the surface is measured prior to introducing the gas, and
continuously, while forming the film until the film is
substantially formed. The substrate is exposed to photon energy
having a power level responsive to the measured reflectivities of
the film.
Inventors: |
Thakur; Randhir P. S. (Boise,
ID), Sandhu; Gurtej S. (Boise, ID), Martin; Annette
L. (Boise, ID) |
Assignee: |
Micron Technology, Inc. (Boise,
ID)
|
Family
ID: |
21841294 |
Appl.
No.: |
08/722,360 |
Filed: |
September 27, 1996 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
028051 |
Mar 8, 1993 |
05350236 |
Sep 27, 1994 |
|
|
Current U.S.
Class: |
374/161; 374/129;
356/43 |
Current CPC
Class: |
G01J
5/0003 (20130101); G01J 5/0007 (20130101); G01J
5/041 (20130101); G01K 11/14 (20130101); G01J
2005/0059 (20130101) |
Current International
Class: |
G01K
11/14 (20060101); G01J 5/00 (20060101); G01K
11/00 (20060101); G01J 5/04 (20060101); G01J
005/54 () |
Field of
Search: |
;374/120,121,123,128,129,161 ;356/43,445,448 ;250/341 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
FY. Sorrell et al. Applied RTP Optical Modeling: An Argument for
Open Loop Control, SRC Contract 91-MP-132 SRC PUB C92470, Aug.
1992, pp. 1-8. .
Tsutomu Sato, Spectral Emissivity of Silicon, Japanese Journal of
Applied Physics vol. 6, No. 3, Mar. 1967 pp. 339-347. .
JM Dihac et al. . . . In Situ Wafer Emmissivity Measurement in a
Rapid Thermal Processor, Mat Res. Soc Symp, Proc vol. 224 Materials
Research Society, 1991 pp. 3-8. .
W. A. Barron, The Principals of Infrared Thermometry, Sensors Dec.
1992, pp. 10-19. .
F. Yates Sorrell et al. . . . Temperature Uniformity in RTP
Furnaces, IEEE Transactions on Electron Devices vol. 39 No. 1, Jan.
1992, pp. 75-79..
|
Primary Examiner: Bennett; G. Bradley
Attorney, Agent or Firm: Trask, Britt & Rossa
Claims
What is claimed is:
1. A method for measuring the temperature of a substrate comprising
the steps of:
providing a su in a chamber, said substrate, having a reflective
surface;
exposing said substrate to a gas and radiant energy to form a film
superjacent said substrate, said energy having a power level;
comparing the reflectivity of said surface prior to said exposing
and while said film is being formed, said power level responsive to
differences in said compared reflectivity.
2. A method for measuring the temperature of a substrate according
to claim 1, wherein said method is performed in situ under
substantially high vacuum.
3. A method for measuring the temperature of a substrate, according
to claim 1, wherein said surface comprises a layer formed
superjacent said substrate.
4. A method for measuring the temperature of a substrate, according
to claim 3, wherein said layer comprises a masking pattern.
5. A method for measuring the temperature of a substrate, according
to claim 3, wherein said layer is formed by at least one of
Chemical Vapor Deposition ("CVD"), Rapid Thermal Processing
Chemical Vapor Deposition ("RTPCVD"), Low Pressure Chemical Vapor
Deposition ("LPCVD"), Molecular Beam Epitaxy ("MBE"), Reactive Ion
Sputtering ("RIS"), Physical Vapor Deposition ("PVD") and Plasma
Processing.
6. A method for measuring the temperature of a substrate, according
to claim 5, wherein said layer functions as a barrier layer, said
layer comprising at least one of TiN and TaN.
7. A method for measuring the temperature of a substrate, according
to claim 1, wherein the reflectivity of said surface prior to said
exposing is continuously compared with the reflectivity of said
surface during said exposing until said film is substantially
formed.
8. A method for measuring the temperature of a substrate, according
to claim 1, wherein said substrate comprises at least one of single
crystal silicon, polycrystalline silicon, and amorphous
silicon.
9. A method for measuring the temperature of a substrate, according
to claim 8, wherein said energy compresses photon energy
substantially in the absorption band of said substrate.
10. A method for measuring the temperature of a substrate,
according to claim 9, wherein said photon energy comprises a
wavelength range substantially between substantially low
ultraviolet to substantially high infrared.
11. A method for measuring the temperature of a substrate,
according to claim 10, wherein said range is substantially between
0.2 .mu.m and 2.2 .mu.m.
12. A method for continuously measuring the temperature of a
semiconductor substrate, comprising the steps of:
providing a substrate in a chamber, said substrate comprising a
layer, said layer having a reflective surface;
forming a film superjacent said surface;
comparing the reflectivity of said surface prior to forming said
film and while said film is forming; and
exposing said surface to radiant energy, said energy having a power
level, said power level responsive to said compared
reflectivities.
13. A method for continuously measuring the temperature of a
semiconductor substrate, according to claim 12, wherein said
forming a film comprises the step of:
exposing said substrate to a first gas and said radiant energy in
situ.
14. A method for continuously measuring the temperature of a
semiconductor substrate according to claim 13, wherein said first
gas comprises at least one of N.sub.2, NH.sub.3, O.sub.2, N.sub.2
O, Ar, Ar--H.sub.2, H.sub.2, GeH.sub.4, and a Fluorine based
gas.
15. A method for continuously measuring the temperature of a
semiconductor substrate, according to claim 14, wherein said
radiant energy generates heat substantially within the range of
500.degree. C. to 1250.degree. C.
16. A method for continuously measuring the temperature of a
semiconductor substrate, according to claim 15, wherein said
substrate is exposed to said first gas for approximately 5 seconds
to 60 seconds at a flow rate substantially in the range of 50 sccm
to 20,000 sccm.
17. A method for continuously measuring the temperature of a
semiconductor substrate, according to claim 12, wherein the
reflectivity of said surface prior to said forming is continuously
compared with the reflectivity of said surface during said forming
until said film is substantially formed.
18. A method for continuously measuring the temperature of a
substrate, according to claim 16, further comprising the step
of:
substantially cleaning said substrate prior to said forming.
19. A method for continuously measuring the temperature of a
semiconductor substrate, according to claim 18, wherein said
cleaning comprises introducing a second gas at a temperature
substantially within the range of 500.degree. C. to 1250.degree. C.
for approximately 10 to 60 seconds, said second gas comprising at
least one of: CF.sub.4 ; C.sub.2 F.sub.2 ; C.sub.2 F.sub.6 ;
C.sub.4 F.sub.8 ; CHF.sub.3 ; HF; NF.sub.3 ; NF.sub.3 diluted with
ar--H.sub.2 ; and GeH.sub.4, HF, and H.sub.2 diluted with
Ar--H.sub.2.
20. A method for externally measuring the continuous temperature of
a semiconductor substrate in chamber, comprising the steps of:
providing a substantially clean semiconductor substrate in said
chamber, said substrate having a layer superjacent said substrate,
said layer having a reflective surface;
forming a film superjacent said surface by introducing a gas and
photon energy in situ, said gas comprising at least one of N.sub.2,
NH.sub.3, O.sub.2 and N.sub.2 O, said energy generating a
temperature substantially within the range of 500.degree. C. to
1250.degree. C., said energy substantially in the absorption band
of silicon;
measuring the reflectivity of said surface prior to said forming
and continuously during said forming until said film is
substantially formed; and
exposing said substrate to said photon energy, said energy having a
power level, said power level responsive to the measured
reflectivities of said film. .Iadd.
21. A method for measuring the temperature of a substrate,
comprising:
providing a substrate in a chamber, said substrate having a
reflective surface;
exposing said substrate to a gas and radiant energy to form a film
over said substrate, said energy having a power level;
controlling said power level responsive to comparing the
reflectivity of said surface prior to said exposing to the
reflectivity of said surface while said film is being formed.
.Iaddend..Iadd.22. A method for measuring the temperature of a
substrate according to claim 21, wherein said method is performed
under substantially high vacuum. .Iaddend..Iadd.23. A method for
measuring the temperature of a substrate, according to claim 21,
wherein said surface comprises a layer formed over said substrate.
.Iaddend..Iadd.24. A method for measuring the temperature of a
substrate, according to claim 23, wherein said layer comprises a
masking pattern. .Iaddend..Iadd.25. A method for measuring the
temperature of a substrate, according to claim 23, wherein said
layer is formed by at least one of Chemical Vapor Deposition
("CVD"), Rapid Thermal Processing Chemical Vapor Deposition
("RTPCVD"), Low Pressure Chemical Vapor Deposition ("LPCVD"),
Molecular Beam Epitaxy ("MBE"), Reactive Ion Sputtering ("RIS"),
Physical Vapor Deposition ("PVC") and Plasma Processing.
.Iaddend..Iadd.26. A method for measuring the temperature of a
substrate, according to claim 23, wherein said layer functions as a
barrier layer, said layer comprising
at least one of TiN and TaN. .Iaddend..Iadd.27. A method for
measuring the temperature of a substrate, according to claim 21,
wherein the reflectivity of said surface prior to said exposing is
substantially continuously compared with the reflectivity of said
surface during said exposing until said film is substantially
formed. .Iaddend..Iadd.28. A method for measuring the temperature
of a substrate, according to claim 21, wherein said substrate
comprising at least one of single crystal silicon, polycrystalline
silicon and amorphous silicon. .Iaddend..Iadd.29. A method for
measuring the temperature of a substrate, according to claim 21,
wherein said energy comprises photon energy substantially in the
absorption band of said substrate. .Iaddend..Iadd.30. A method for
measuring the temperature of a substrate, according to claim 29,
wherein said photon energy comprises a wavelength range
substantially between substantially low ultraviolet to
substantially high infrared. .Iaddend..Iadd.31. A method for
measuring the temperature of a substrate, according to claim 30,
wherein said range is substantially between 0.2 .mu.m and 2.2
.mu.m. .Iaddend..Iadd.32. A method for measuring the temperature of
a semiconductor substrate, comprising:
providing a substrate in a chamber, said substrate comprising a
layer, said layer having a reflective surface;
exposing said reflective surface to radiant energy, said energy
having a power level;
forming a film over said reflective surface; and
controlling said power level responsive to comparing the
reflectivity of said reflective surface prior to forming said film
and while said film is
forming. .Iaddend..Iadd.33. A method for measuring the temperature
of a semiconductor substrate, according to claim 32, wherein said
forming a film further comprises exposing said substrate to a first
gas and said radiant energy. .Iaddend..Iadd.34. A method for
measuring the temperature of a semiconductor substrate, according
to claim 33, wherein said first gas comprises at least one of
N.sub.2, NH.sub.3, O.sub.2, N.sub.2 O, Ar, Ar--H.sub.2, H.sub.2,
GeH.sub.4, and a Fluorine based gas. .Iaddend..Iadd.35. A method
for measuring the temperature of a semiconductor substrate,
according to claim 32, wherein said radiant energy generates heat
substantially within the range of 500.degree. C. to 1250.degree. C.
.Iaddend..Iadd.36. A method for measuring the temperature of a
semiconductor substrate, according to claim 35, wherein said
substrate is exposed to said first gas for approximately 5 seconds
to 60 seconds at a flow rate substantially in the range of 50 sccm
to 20,000 sccm. .Iaddend..Iadd.37. A method for measuring the
temperature of a semiconductor substrate, according to claim 32,
wherein the reflectivity of said surface prior to said forming is
continuously compared with the reflectivity of said surface during
said forming until said film is substantially formed.
.Iaddend..Iadd.38. A method for measuring the temperature of a
substrate, according to claim 32, further comprising substantially
cleaning said substrate prior to said forming.
.Iaddend..Iadd.39. A method for continuously measuring the
temperature of a semiconductor substrate, according to claim 38,
wherein said cleaning comprises introducing a second gas at a
temperature substantially within the range of 500.degree. C. to
1250.degree. C. for approximately 10 to 60 seconds, said second gas
comprising at least one of: CF.sub.4 ; C.sub.2 F.sub.2 ; C.sub.2
F.sub.6 ; C.sub.2 F.sub.8 ; CHF.sub.3 ; HF; NF.sub.3 ; NF.sub.3
diluted with Ar--H.sub.2 ; and GeH.sub.4, HF, and H.sub.2 diluted
with Ar--H.sub.2. .Iaddend..Iadd.40. A method for externally
measuring the continuous temperature of a semiconductor substrate
in a chamber, comprising:
providing a substantially clean semiconductor substrate having a
layer over said substrate, said layer having a reflective
surface;
forming a film over said layer by exposing said layer to a gas and
photon energy, said gas comprising at least one of N.sub.2,
NH.sub.3, O.sub.2 and N.sub.2 O, said energy generating a
temperature substantially within the range of 500.degree. C. to
1250.degree. C., said energy substantially in the absorption band
of silicon;
measuring the reflectivity of said surface prior to said forming
and continuously during said forming until said film is
substantially formed; and
controlling a power level of said photon energy responsive to said
measured reflectivities. .Iaddend..Iadd.41. A method for
controlling the temperature of a semiconductor substrate having a
reflective surface comprising:
exposing the reflective surface to radiant energy, said energy
having a power level;
sensing changes in reflectivity of the reflective surface while a
layer is formed on the reflective surface; and
controlling said power level in response to said sensed changes in
reflectivity. .Iaddend..Iadd.42. The method of claim 41, wherein
said
method is performed under substantially high vacuum.
.Iaddend..Iadd.43. The method of claim 41, wherein the reflectivity
of said surface prior to said exposing is substantially
continuously compared with the reflectivity of said surface during
said exposing until said layer is substantially formed.
.Iaddend..Iadd.44. The method of claim 41, wherein said substrate
comprises at least one of single crystal silicon, polycrystalline
silicon, and amorphous silicon. .Iaddend..Iadd.45. The method of
claim 41, wherein said energy comprises photon energy substantially
in the absorption band of said substrate. .Iaddend..Iadd.46. The
method of claim 45, wherein said photon energy comprises a
wavelength range substantially between substantially low
ultraviolet to substantially high infrared. .Iaddend..Iadd.47. The
method of claim 30, wherein said range is substantially between 0.2
.mu.m and 2.2 .mu.m. .Iaddend..Iadd.48. A method for controlling
the temperature of a semiconductor substrate, comprising:
providing a semiconductor substrate having a reflective
surface;
forming a film on said reflective surface by introducing a first
gas and photon energy;
measuring the reflectivity of said reflective surface prior to said
forming and during said forming until said film is substantially
formed; and
controlling a power level of said photon energy in response to said
measured reflectivity. .Iaddend..Iadd.49. The method of claim 48,
wherein said first gas comprises at least one of N.sub.2, NH.sub.3,
O.sub.2, N.sub.2 O, Ar, Ar--H.sub.2, H.sub.2, GeH.sub.4, and a
Fluorine based gas.
.Iaddend..Iadd.50. The method of claim 48, wherein said radiant
energy generates heat substantially within the range of 500.degree.
C. to 1250.degree. C. .Iaddend..Iadd.51. The method of claim 48,
wherein said substrate is exposed to said first as for
approximately 5 seconds to 60 seconds at a flow rate substantially
in the range of 50 sccm to 20,000 sccm. .Iaddend..Iadd.52. The
method of claim 48, wherein the reflectivity of said surface prior
to said forming is continuously compared with the reflectivity of
said surface during said forming until said film is substantially
formed. .Iaddend..Iadd.53. The method of claim 48, further
including substantially cleaning said substrate prior to said
forming. .Iaddend..Iadd.54. The method of claim 49, wherein said
cleaning comprises introducing a second gas at a temperature
substantially within the range of 500.degree. C. to 1250.degree. C.
for approximately 10 to 60 seconds, said second gas comprising at
least one of: CF.sub.4 ; C.sub.2 F.sub.2 ; C.sub.2 F.sub.6 ;
C.sub.4 F.sub.8 ; CHF.sub.3 ; HF; NF.sub.3 ; NH.sub.3 diluted with
Ar--H2; and GeH.sub.4, HF, and H.sub.2 diluted with Ar--H.sub.2.
.Iaddend..Iadd.55. A method for controlling the temperature of a
semiconductor substrate having a reflective surface,
comprising:
forming a film over said surface;
exposing said reflective surface to radiant energy, said energy
having a power level;
measuring the reflectivity of said reflective surface prior to
forming said film and while said film is forming; and
controlling said power level in response to said measured
reflectivities. .Iaddend..Iadd.56. The method of claim 55, wherein
said forming a film further comprises exposing said substrate to a
first gas and said radiant
energy. .Iaddend..Iadd.57. The method of claim 56 wherein said
first gas comprises at least one of N.sub.2, NH.sub.3, O.sub.2,
N.sub.2 O, Ar, Ar--H.sub.2 ; H.sub.2 ; GeH.sub.4, and a Fluorine
based gas. .Iaddend..Iadd.58. The method of claim 55, wherein said
radiant energy generates heat substantially within the range of
500.degree. C. to 1250.degree. C. .Iaddend..Iadd.59. The method of
claim 56, wherein said substrate is exposed to said first gas for
approximately 5 seconds to 60 seconds at a flow rate substantially
in the range of 50 sccm to 20,000 sccm. .Iaddend..Iadd.60. The
method of claim 55, wherein the reflectivity of said surface prior
to said forming is continuously compared with the reflectivity of
said surface during said forming until said film is substantially
formed. .Iaddend..Iadd.61. The method of claim 55, further
comprising substantially cleaning said substrate prior to said
forming. .Iaddend..Iadd.62. The method of claim 61, wherein said
cleaning comprises introducing a second gas at a temperature
substantially within the range of 500.degree. C. to 1250.degree. C.
for approximately 10 to 60 seconds said second gas comprising at
least one of: CF.sub.4 ; C.sub.2 F.sub.2 ; C.sub.2 F.sub.6 ;
C.sub.4 F.sub.8 ; CHF.sub.3 ; HF; NF.sub.3 ; NF.sub.3 diluted with
Ar--H2; and GeH.sub.4, HF, and H.sub.2 diluted with Ar--H.sub.2.
.Iaddend.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
This application is related copending application of Ser. No.
08/028040, filed on Mar. 5, 1993.
FIELD OF THE INVENTION
This invention relates to a method for measuring the temperature of
a semiconductor wafer.
BACKGROUND OF THE INVENTION
In the fabrication of semiconductor wafers one recurring problem
has been temperature measurement and control. When processing a
semiconductor substrate, the temperature of the to side of the
substrate being processed is of critical importance. Overheating
can cause dopants to permeate subjacent layers, and under-heating
can produces layers which are unreliable and subject to lower
tolerances. In this light, several solutions have been put forth to
gauge the substrate's temperature to avoid overheating and
underheating, and thus provide a uniform ramp up, steady state
and/or ramp down cycle.
Referring to FIG. 1, a pyrometric system for measuring the
temperature of a semiconductor substrate in a chamber known in the
art is illustrated In this system, a lamp 100 is employed to heat
substrate 110. Substrate 110 is situated within chamber 120, and
the substrate's top side 115 is positioned in association with lamp
100 accordingly. To maintain the stability of substrate 100, a
series of supports, 130 and 130', emanate from the bottom of
chamber 120. A sensor (not shown) is positioned between supports
130 and 130' and in association with the underside 116 to sense the
temperature of the underside 116 of substrate 110.
The pyrometric system depicted in FIG. 1 is inadequate for precise
temperature measurements. By measuring the underside of the
substrate, this approach yields only an approximate measurement of
the top side at best. Moreover, the underside is not traditionally
processed, and as such, measurements with regards to that portion
of the wafer are superfluous.
Referring to FIG. 2, a system configuration for measuring the
temperature of a semiconductor substrate in a chamber known in the
art is illustrated. In this system, a substrate 210, positioned
within a chamber 220, is positioned in association with lamp 200
for heating purposes. Instead of the approach of FIG. 1, here a
sensor 230, positioned on the side of substrate 210, is employed to
detect the thermal expansion of substrate 210, which is directly
translatable to the substrate's temperature
However, the system depicted in FIG. 2 also has several
shortcomings. Firstly, though a relationship exists between thermal
expansion and temperature, an accurate temperature measurement is
formidable to obtain because of the difficulties in fabricating
sufficiently sensitive sensors to detect expansion. Second, several
layers are formed superjacent the substrate, with each layer having
a different thermal coefficient As such, most measurements of the
thermal expansion of the substrate are inaccurate. Third, in actual
semiconductor manufacturing, substrate's are exposed to several
thermal steps. Thus, actual measurements of expansion are
transitory.
SUMMARY OF THE INVENTION
In light of the limitations of the known approaches to measuring
the temperature of the side of a substrate to be processed, several
alternatives have been examined. One such alternative explores
optical pyrometry as means for accurately measuring the temperature
of a substrate. The basis for this approach is the relationship
between the surface reflectivity, surface emissivity, and surface
temperature. Fundamentally, the relationship between emissivity and
a substrate optical properties can be expressed, in light of
Kirchoff's law, by the following:
where
.epsilon.=spectral emissivity
R=reflectivity,
.tau.=transmissivity,
.lambda.=wavelength, and
T=temperature
As such, the emissivity of a plane parallel specimen for normal
incidence has been expressed by the following mathematical
formula:
where R, the true reflectivity, is given by the following
equation:
while .tau., the true transmissivity, is given by the following
formula:
where
n=refractive index,
k=extinction coefficient,
K=absorption coefficient,
.lambda.=wavelength, and
t=thickness of the specimen
Given these mathematical expressions, under quasi-steady state
conditions the heat, generated from a lamp, and absorbed by the
substrate is equal to the emission from the wafer, an additional
formula can be derived representing the relationship between
temperature and emissivity:
where
Q=heat flux from the lamp presumably constant over the
substrate
.epsilon..sub.A =absorptivity of the substrate
.epsilon..sub.E =emissivity of the substrate
.sigma.=Stephan-Boltzman constant, and
T=temperature of the wafer.
In light of the above, the primary object of the present invention
is to eliminate the aforementioned drawbacks of the prior art.
It is a further object of the present invention to provide a system
and method for accurately measuring the temperature surface of the
top side of a substrate being processed.
Another object of the present invention is to provide a system and
method for effectively controlling the temperature surface of a
substrate being processed.
Still another object of the present invention is to provide a
system and method for accurately measuring the temperature of a
substrate regardless of the number of layers formed superjacent the
substrate.
Yet another object of the present invention is to provide a system
and method for accurately measuring the temperature of a substrate
independent of the number of thermal steps applied to the
substrate.
A further object of the present invention is to provide a system
and method for accurately measuring the temperature of a substrate
which is particularly useful in where the substrate's surface
characteristics are constantly changing.
In order to achieve the hereinabove objects, as well as others
which will become apparent hereafter, a method for externally
measuring the continuous temperature of a semiconductor substrate
in chamber is disclosed. The fist step of the method involves
providing a substantially clean semiconductor substrate having a
layer a reflective surface superjacent into a chamber. Once
provided, a film is formed superjacent the surface by introducing a
gas comprising at least one of N.sub.2, NH.sub.3, O.sub.2, N.sub.2
O, Ar, Ar--H.sub.2, H.sub.2, GeH.sub.4, or any Fluorine based gas,
and photon energy in situ. The photon energy, having a wavelength
substantially in the absorption band of silicon, generates a
temperature substantially within the range of 500.degree. C. to
1250.degree. C. Subsequently, the reflectivity of the surface is
measured prior to introducing the gas and continuously while
forming the film until the film is substantially formed. The
substrate is exposed to the photon energy, the energy having a
power level responsive to the measured reflectivities of the
film.
Moreover, in order to achieve additional objects, a system for
externally measuring the temperature of a substrate having a
reflective surface within a chamber is disclosed. The system
comprises a first light source having sufficient intensity for
bombarding the reflective surface with photons, thereby heating the
surface. The first light source has an output level and a
wavelength substantially in the absorption band of silicon. The
wavelength ranges from substantially low ultraviolet to
substantially high infrared, or 0.2 .mu.m to 2.2 .mu.m. The system
also comprises means for exposing the substrate to a gas in order
to form a layer superjacent the reflective surface. Moreover, a
sensor, preferably a photo detector, for sensing changes in the
reflectivity of the surface caused by the first light source and
the exposing means are included. In one embodiment of the present
invention, the sensor comprises a second light source, having an
initial transmissivity and a wavelength range substantially spaced
from the first light source, for reflecting photons off the surface
and a sensor, preferably a photo detector, for sensing the
reflectivity of the surface caused by the reflecting photons. The
sensor can also comprise a spectrophotometer or light sensor.
Furthermore, the system comprises control circuitry for controlling
the first light source in response to the sensor; the control
circuitry being coupled to the sensor by a feedback loop. The
feedback loop comprises a differentiating amplifier for
differentiating between the initial transmissivity and the changes
in the reflectivity, thereby generating a signal. In response to
the signal, the control system controls the first light source's
output level.
Other objects and advantages will become apparent to those skilled
in the art from the following detailed description read in
conjunction with the appended claims and the drawings attached
hereto.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be better understood from reading the
following description of non-limiting embodiments, with reference
to the attached drawings, wherein below:
FIG. 1 is a system for measuring the temperature of a semiconductor
substrate in a chamber known in the art;
FIG. 2 is a system for measuring the temperature of a semiconductor
substrate in a chamber known in the art;
FIG. 3 is a cross-sectional view of a semiconductor substrate prior
to undergoing the steps of the present invention;
FIG. 4 is a cross-sectional view of undergoing the first step of
the present inventive method;
FIG. 5 is a cross-sectional view of undergoing the second step of
the present inventive method;
FIG. 6 is the preferred embodiment of present inventive system
configuration;
FIG. 7 is a first alternate embodiment of present inventive system
configuration;
FIG. 8 is a second alternate embodiment of present inventive system
configuration;
FIG. 9 is a third alternate embodiment of present inventive system
configuration; and
FIG. 10 is a fourth alternate embodiment of present inventive
system configuration.
It should be emphasized that the drawings of the instant
application are not to scale but are merely schematic
representations and are not intended to portray the specific
parameters or the structural details of the invention, which can be
determined by one of skill in the art by examination of the
information herein.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 3, a semiconductor substrate 10 is illustrated
prior to undergoing the present inventive method. Semiconductor
substrate 10, comprising single-crystal silicon, polycrystalline
silicon, amorphous silicon, or any other semiconductive, conductive
or insulative substrate--such as Indium Phosphide or Gallium
Arsenide for example--is first provided into a chamber, such as a
Rapid Thermal Processing ("RTP") chamber or a Chemical Vapor
Deposition ("CVD") chamber. Further, substrate 10 can be rugged
and/or smooth.
In the preferred embodiment, substrate 10 has been atomically
cleaned prior to undergoing the present inventive method. A native
silicon dioxide layer (not shown) can easily form superjacent
substrate 10 by simple exposure to the atmosphere. Unfortunately,
native silicon dioxide has inferior electrical and structural
characteristics when compared with other dielectric type materials,
such as grown silicon dioxide. As such, the overall electrical and
structural characteristics of the completed wafer having native
silicon dioxide are substantially impacted. Thus, in order to
maintain the wafer's integrity, any native silicon dioxide formed
should be removed by atomically cleaning substrate 10.
There are a variety of techniques for removing native oxide. Those
known to one of ordinary skill in the art are not described. In the
preferred embodiment of the present inventive method, native
silicon dioxide is removed by introducing a relative gas as
CF.sub.4, C.sub.2 F.sub.2, C.sub.2 F.sub.6, C.sub.4 F.sub.8,
CHF.sub.3, HF, NF.sub.3, NF.sub.3 dilute with Ar--H.sub.2,
GeHF.sub.4, or H.sub.2 diluted with Ar--H.sub.2, at a temperature
substantially within the range of 500.degree. C. to 1250.degree. C.
for appropriatly 10 to 60 seconds. Relying on this approach, any
native silicon dioxide formation between 10.ANG. and 20.ANG. can be
easily removed.
Referring to FIG. 4, a first embodiment of the present inventive
method is depicted, illustrating a layer 20 positioned superjacent
clean substrate 10. Layer 20 comprises a reflective surface 25.
Surface 25 is preferably uniformly reflective. Alternately, in a
second embodiment, substrate 10 itself comprises a, preferably
uniformly, reflective surface (not shown). In a further embodiment
of the present inventive method, layer 20 comprises a mask pattern
formed as a result of masking step or steps of layer 20 after layer
20 is positioned superjacent substrate 10.
Layer 20 can be formed superjacent substrate 10, preferably in situ
under substantially high vacuum, through a variety of approaches
known in the art, including Chemical Vapor Deposition ("CVD"),
Rapid Thermal Processing Chemical Vapor Deposition ("RTPCVD"), Low
Pressure Chemical Vapor Deposition ("LPCVD"), Molecular Beam
Epitaxy ("MBE"), Reactive Ion Sputtering ("RIS"), Physical Vapor
Deposition ("PVD") and Plasma Processing. It should be obvious to
one of ordinary skill in the art that other methods can also be
employed in the herein inventive method for forming layer 20
superjacent substrate 10.
Layer 20 can comprise a variety of characteristics in addition to
its reflectivity. For example layer 20 can comprise conductive,
semiconductive, or insulative properties. In that light, in the
event that layer 20 functions as a barrier type layer, TiN or TaN
are preferable compounds. Nonetheless, one of ordinary skill in the
art can select another compound having similar qualities for
functioning as a barrier layer.
Referring to FIG. 5, a film 30 is shown superjacent surface 25.
Subsequent to forming layer 20 having reflective layer 25
superjacent substrate 20 in the first embodiment, or solely
providing a substrate having a reflective sure in the second
embodiment (not shown) film 30 is formed by exposing substrate 20
to a reactive gas and radiant energy, preferably in situ under
substantially high vacuum. Film 30 can comprise conductive,
semiconductive, or insulative properties. The gas can be selected
from a diverse number of reactive compounds, such as N.sub.2,
NH.sub.3, O.sub.2, N.sub.2, Ar, Ar--H.sub.2, H.sub.2, GeHF.sub.4,
or any Fluorine based gas. Substrate 10 is exposed to the gas for
approximately 5 seconds to 60 seconds at a flow rate substantially
in the range of 50 sccm to 20,000 sccm. Further, radiant energy is
introduced into the chamber in order to generate heat substantially
within the range of 500.degree. C. to 1250.degree. C.
It is important to note first, that the introduction of radiant
energy can begin at any time prior to the formation of film 30.
Nevertheless, the energy must be present during the formation of
film 30. Secondly, the flow rate, temperature, and length of
exposure are variables dependent on each other. As such, it should
be obvious to one of ordinary skill in the art that an exact flow
rate is dependent on the length of exposure, the temperature,
etc.
The radiant energy employed in the present invention consists of
photon energy having a wavelength substantially in the absorption
band of the substrate. Further, the energy comprises a wavelength
range from substantially low ultraviolet to substantially high
infrared, or 0.2 .mu.m to 2.2 .mu.m. Moreover, a light source, such
as a Halogen, Ultra Violet, Infrared lamp, or discharge lamp is
preferably used to generate the radiant energy.
To achieve a more uniform film by more uniformly heating the
substrate, unlike the known art, the reflectivity of surface 25 is
measured while the gas and radiant energy are being introduced. As
reflectivity is directly proportional to intensity and temperature,
the temperature of the substrate 10 can be easily obtained, once a
system capable of employing the herein inventive method is properly
calibrated. Thus, by comparing the reflectivity of the surface
prior to exposing it to gas and radiant energy and during the step
of forming the film 30, changes in the surface 25 temperature can
be calculated. Having this formation the intensity or power
associated with the radiant energy can be properly compensated, in
light of the changing surface characteristics, in order to maintain
steady heating. As such, during the step of introducing the gas and
radiant energy, the surface reflectivity is monitored. This step in
comparing the reflectivities is preferably continuous until film 30
is substantially formed to allow for uniform heating in its
formation.
In order to achieve the benefits of the hereinabove inventive
method, an inventive system can be configured for repeatably
measuring the temperature of a substrate based on the surface
reflectivity of the substrate. Referring to FIG. 6, the preferred
embodiment of such a system is illustrated. Provided with a chamber
60, is a substrate 50 having a top reflective surface 55. To enable
photon energy to pass through chamber 60 and onto surface 55,
chamber 60 comprises a transparent window 62. Window 62 can
comprise any transparent material with minimum absorption of
incident photons, such as quartz, enabling energy in substantially
low ultraviolet to substantially high infrared range to pass
through. Window 62 should also preferably promote minimum transfer
of photon energy by use of appropriate materials, such as calcium
fluoride for example.
In cooperation with surface 55 and window 62 is a light source 65.
Light source 65 is employed for the purpose of bombarding
reflective surface 55 with photon energy to thereby heat surface
55. As such, source 65 requires a wavelength substantially in the
option band of silicon. The wavelength of light source 65 has a
range substantially between substantially low ultraviolet to
substantially high infrared, or 0.2 .mu.m to 2.2 .mu.m. To maximize
the output of light source 65, a reflector 67 is positioned in
association with light source 65. Reflector 67 comprises a highly
reflective material coating, such as gold film.
In the preferred embodiment of the present inventive system, light
source 65 comprises a lamp array. In such a scheme, a Halogen Ultra
Violet, or Infrared filament lamp is preferable. In an alternate
embodiment, however, light source 65 comprises a single lamp, such
as either an arc discharge lamp or Xe discharge lamp.
Moreover, chamber 60 comprises means for exposing (not shown)
substrate 50 to a reactive gas within the chamber. This means
includes all the necessary equipment known by one of ordinary skill
in the art to introduce a gas into a chamber, such as a gas reserve
tank and means for controlling the flow rate of the gas for
example. By introducing substrate 50 to a reactive gas and radiant
energy, a layer (not shown) can be formed superjacent substrate 50.
The reactive gas can be selected from a diverse number of reactive
compounds, such as N.sub.2, NH.sub.3, O.sub.2, N.sub.2 O, Ar,
Ar--H.sub.2, H.sub.2, GeH.sub.4, or any Fluorine based gas.
Substrate 50 is exposed to the gas for approximately 5 seconds to
60 seconds at a flow rate substantially in the range of 50 sccm to
20,000 sccm, and the heat required to be generated the radiant
energy is substantially within the range of 500.degree. C. to
1250.degree. C.
In the preferred embodiment of the present inventive system, a pair
of light sensory 70 and 72, are employed for sensing the
temperature of the top reflective surface 55. Light sensors 70 and
72 comprise at last one of a spectrophotometer and photo detector.
As light source 65 bombards substrate 50 with energy, some photons
are reflected off surface 55. In light of the relationship between
the reflectivity/emissivity of a surface and its temperature,
changes in the temperature of top reflective surface 55 caused by
exposing substrate 50 to the reactive gas and photon energy are
detectable by light sensors 70 and 72. Light sensor 70 initially
measures the reflectivity of surface 55 at the onset of the
introduction of photon energy yet prior to exposure to reactive
gas. The output of sensor 70 is a reference signal 71. In contrast,
light sensor 72 continuously senses the reflectivity of surface 55
while substrate 50 is exposed to both photon energy and reactive
gas until the layer is substantially formed superjacent substrate
50. The output of sensor 72 results in a sensing signal 73.
As a result of securing reference signal 71 and sensing signal 73,
changes in the reflectivity of surface 55, and thus, changes in the
temperature of surface 55 can be calculated. By doing so, the
temperature of substrate and surface 55 can be controlled to
provide uniform ramp up, steady state or ramp down cycle. To
achieve this control feature, both reference signal 71 and sensing
signal 73 are first fed to a differential amplifier 75.
Differential amplifier 75 differentiates between both signals,
providing an output differential signal comprising information
relating to changes in reflectivity of surface 55. Differential
signal is then fed into an amplifier stage 77, which amplifies the
differential signal. This amplified differential signal is then fed
to a lamp control system 79. Lamp control system 79, having the
amplified differential signal as an input systematically controls
of the output level of light source 65. This can be accomplished in
a variety of ways known to one of ordinary skill in the art, such
as a microcomputer for example. By employing this feedback control
scheme, such as Proportional Integral Derivative ("PID") for
example, the output level of light source 65 can be calibrated so
as to provide a more uniform ramp up, steady state or ramp down
cycle.
Referring to FIG. 7, a first alternate embodiment of the present
inventive system is provided. As before, substrate 50, with its
reflective surface 55, is positioned within chamber 60, in
association with transparent window 62. Nevertheless, in this
embodiment, in place of measuring the initial reflectivity of
surface, a light sensor 80 is employed to sense the initial
transmissivity of light source 65. Given the direct relationship
between transmissivity, reflectivity and temperature, light sensor
80 generates a reference signal 81. Likewise, light sensor 82
continuously senses the reflectivity of surface 55 while substrate
50 is exposed to both photon energy and reactive gas until the
layer is substantially formed superjacent substrate 50. Light
sensors 80 and 82 comprise at least one of a spectrophotometer and
photo detector. The output of sensor 82 results in a sensing signal
83.
As a result of securing reference signal 81 and sensing signal 83,
changes in the reflectivity of surface 55, and thus, changes in the
temperature of surface 55 can be calculated. By doing so, the
temperature of substrate 50 and surface 55 can be controlled to
provide uniform ramp up, steady state or ramp down cycle. To
achieve this control feature, both reference signal 81 and sensing
signal 83 are first fed to a differential amplifier 75.
Differential amplifier 75 differentiates between both signals,
providing an output differential signal comprising information
relating to changes in reflectivity of surface 55. Differential
signal is then fed into an amplifier stage 77, which amplifies the
differential signal. This amplified differential signal is then fed
to a lamp control system 79. Lamp control system 79, having the
amplified differential signal as an input, systematically controls
the output level of light source 65. This can be accomplished a
variety of ways known to one of ordinary skill in the art, such as
a microcomputer for example. By employing this feedback control
scheme, such as PID for example, the output level of light source
65 can be calibrated so as to provide a more uniform ramp up,
steady state or ramp down cycle.
Referring to FIG. 8, a second alternate embodiment of the present
inventive system is provided. As before, substrate 50, with its
reflective surface 55, is positioned within chamber 60, in
association with transparent window 62. Nonetheless, in this
embodiment, the changing reflectivity of chamber 60 and its
interior is accounted in the control of light source 65. As the
reflectivity of the interior of chamber 60 directly effects the
temperature of substrate 50, a light sensor 90 is positioned in
association with window 62. As such, sensor 90 senses the initial
reflectivity of the interior of chamber 60, generating a reference
signal 91. Likewise, light sensor 92 continuously senses the
reflectivity of surface 55 while substrate 50 is exposed to both
photon energy and reactive gas until the layer is substantially
formed superjacent substrate 50. Light sensors 90 and 92 comprise
at least one of a spectrophotometer and photo detector. The output
of sensor 92 results is a sensing signal 93.
As a result of securing reference signal 91 and sensing signal 93,
changes in the reflectivity of surface 55, and thus, changes in the
temperature of surface 55 can be calculated. By doing so, the
temperature of substrate 50 and surface 55 can be controlled to
provide uniform ramp up, steady state or ramp down cycle. To
achieve this control feature, both reference signal 91 and sensing
signal 93 are first fed to a differential amplifier 75.
Differential amplifier 75 differentiates between both signals
providing an output differential signal comprising information
relating to changes in reflectivity of surface 55. Differential
signal is then fed into an amplifier stage 77, which amplifies the
differential signal. This amplified differential signal is then fed
to a lamp control system 79. Lamp control system 79, having the
amplified differential signal as an input, systematically controls
the output level of light source 65. This can be accomplished by a
variety of ways known to one of to ordinary skill in the art, such
as a microcomputer for example. By employing this feedback control
scheme, such as PID for example, the output level of light source
65 can be calibrated so as to provide a more uniform ramp up,
steady state or ramp down cycle.
Referring to FIG. 9, a third alternate embodiment of the present
inventive system is provided. As before, substrate 50, with its
reflective surface 55, is positioned within chamber 60, in
association with transparent window 62. However, in this
embodiment, a second light source 100, preferably a laser, such as
a CO.sub.2 laser, He--Ne laser, or semiconductor diode, is employed
in association with transparent window 62 for ascertaining the
reflectivity of surface 55. Second light source 100 comprises an
initial transmissivity. Given the direct relationship between
transmissivity, reflectivity and temperature second light source
100 generates a reference signal 101 from its level transmissivity.
In cooperation with second light source 100, a light sensor 102 is
employed in association with transparent window 62 for continuously
sensing the reflectivity of surface 55 while substrate 50 is
exposed to both photon energy and reactive gas until the layer is
substantially formed superjacent substrate 50. Sensor 102 senses
the reflection of those photons emanating from second light some
102 through window 62. Sensor 102 comprises at last one of a
spectrophotometer and photo detector. To avoid potential for
interference caused by first light source 65 in sensing second
light source 100, first light source 65 has a wavelength source
100. Further, sensor 102 can be tuned, accordingly, to sense photon
energy within a certain wavelength range. The output of sensor 102
results in a sensing signal 103.
As a result of securing reference signal 101 and sensing signal
103, changes in the reflectivity of surface 55, and thus, changes
in the temperature of surface 55 can be calculated. By doing so,
the temperature of substrate 50 and surface 55 can be controlled to
provide uniform ramp up, steady state or ramp down cycle. To
achieve this control feature, both reference signal 101 and sensing
signal 103 are first fed to a differential amplifier 75.
Differential amplifier 75 differentiates between both signals,
providing an output differential signal comprising information
relating to changes in reflectivity of surface 55. Differential
signal is then fed into an amplifier stage 77, which amplifies the
differential signal. This amplified differential signal is then fed
to a lamp control system 79. Lamp control system 79, having the
amplified differential signal as an input, systematically controls
of the output level of light source 65. This can be accomplished a
variety of ways known to one of ordinary skill in the art, such as
a microcomputer for example. By employing this feeds control
scheme, such as PID for example, the output level of light source
65 can be calibrated so as to provide a more uniform ramp up,
steady state or ramp down cycle
Referring to FIG. 10, a fourth alternate embodiment of the present
inventive system is provided. As before, substrate 50, with its
reflective surface 55, is positioned within chamber 60, in
association with transparent window 62. However, in this
embodiment, first light source 65 comprises two lamp arrays 64 and
66. Each lamp array comprises a series of individual
lamps--64(a)-64(e) and 66(a)-66(e)--preferably comprised of a
Halogen, Ultra Violet, or Infrared filament. Functionally, lamp
array 64 bombards top reflective surface 55 with photon energy,
while, in contrast, lamp array 66 bombards the bottom surface 56 of
substrate 50. Though the layer forms superjacent surface 55, the
heat generated by bombarding the bottom surface 56 of substrate 50
through lamp array 66 expedites the overall time in processing
substrate 50.
Furthermore, like the previous embodiment second light source 100,
preferably a laser, such as a CO.sub.2 laser, He--Ne laser, or
semiconductor diode, is employed for ascertaining the reflectivity
of surface 55. Second light source 100 comprises an initial
transmissivity. Given the direct relationship between
transmissivity, reflectivity and temperature, second light source
100 generates reference signal 101 from its level transmissivity.
In cooperation with second light source 100, light sensor 102 is
employed for continuously sensing the reflectivity of surface 55
while substrate 50 is exposed to both photon energy and reactive
gas until the layer is substantially formed superjacent substrate
50. Sensor 102 senses the reflection of those photons emanating
from second light source 102. Sensor 102 comprises at least one of
a spectrophotometer and photo detector. To avoid potential for
interference caused by first light source 65 in sensing second
light source 100, first light source 65 has a wavelength
substantially spaced from the wavelength of second light source
100. The intensity of second light source 100 is moreover
substantially low such that the neither surface 55 nor the layer
being formed will be caused react. Further, sensor 102 can also be
tuned, accordingly, to sense photon energy within a certain
wavelength range. The output of sensor 102 results in sensing
signal 103.
As a result of securing reference signal 101 and sensing signal
103, changes in the reflectivity of surface 55, and thus, changes
in the temperature of surface 55 can be calculated. By doing so,
the temperature of substrate 50 and surface 55 can be controlled to
provide uniform ramp up, steady state or ramp down cycle. To
achieve this control feature, both reference signal 101 and sensing
signal 103 are first fed to a differential amplifier 75.
Differential amplifier 75 differentiates between both signals,
providing an output differential signal comprising information
relating to changes in reflectivity of surface 55. Differential
signal is then fed into an amplifier stage 77, which amplifies the
differential signal 75. This amplified differential signal is then
fed to a lamp control system 79. Lamp control system 79, having the
amplified differential signal as an input, systematically controls
of the output level of lamp arrays 64 and 66. This can be
accomplished a variety of ways known to one of ordinary skill in
the art, such as a microcomputer for example. By employing this
feedback control scheme, such as PID for example, the output level
of lamp arrays 64 and 66 can be calibrated so as to provide a more
uniform ramp up, steady state or ramp down cycle.
It should be obvious to one of ordinary skill in the art that the
lamp array (64 and 66) configuration of FIG. 10 is applicable to
the system configurations of FIGS. 6 through 9. In that same light,
the singular lamp array configuration can also be employed in any
of the hereinabove embodiments.
While the particular invention has been described with reference to
illustrative embodiments, this description is not meant to be
construed in a limiting sense. It is understood that although the
present invention has been described in a preferred embodiment,
various modifications of the illustrative embodiments, as well as
additional embodiments of the invention, will be apparent to
persons skilled in the art upon reference to this description
without departing from the spirit of the invention, as recited in
the claims appended hereto. For example, while in several
embodiments of the present invention, a pair of light sensors have
been employed to sense changes in a surface's reflectivity.
However, it should be obvious to one of ordinary skill in the art
that one light sensor can sense the initial reflectivity as well as
the reflectivity continuously during the process of forming a
layer. It is therefore contemplated that the appended claims will
cover any such modifications or embodiments as fall within the true
scope of the invention.
* * * * *