U.S. patent application number 10/238141 was filed with the patent office on 2003-01-23 for system and method for selectively increasing surface temperature of an object.
This patent application is currently assigned to Micron Technology, Inc.. Invention is credited to Powell, Don Carl.
Application Number | 20030017721 10/238141 |
Document ID | / |
Family ID | 22488962 |
Filed Date | 2003-01-23 |
United States Patent
Application |
20030017721 |
Kind Code |
A1 |
Powell, Don Carl |
January 23, 2003 |
System and method for selectively increasing surface temperature of
an object
Abstract
A system and method for selectively increasing the thermal
effect of a radiant energy source to the surface of an object
relative to the substrate is described in the context of rapid
thermal processing of semiconductor wafers, and apparatus produced
therefrom. A radiation-absorptive atmosphere is introduced between
the radiant energy source and the object to increase conductive
heat transfer to the surface of the object and reduce the available
radiant heat transfer to the substrate, thereby increasing the
thermal effect to the surface relative to the substrate.
Inventors: |
Powell, Don Carl; (Boise,
ID) |
Correspondence
Address: |
SCHWEGMAN, LUNDBERG, WOESSNER & KLUTH, P.A.
P.O. BOX 2938
MINNEAPOLIS
MN
55402
US
|
Assignee: |
Micron Technology, Inc.
|
Family ID: |
22488962 |
Appl. No.: |
10/238141 |
Filed: |
September 10, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10238141 |
Sep 10, 2002 |
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09139934 |
Aug 26, 1998 |
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6451714 |
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Current U.S.
Class: |
438/795 ;
257/E21.324; 438/799 |
Current CPC
Class: |
H01L 21/67115 20130101;
H01L 21/324 20130101 |
Class at
Publication: |
438/795 ;
438/799 |
International
Class: |
H01L 021/26; H01L
021/324; H01L 021/477 |
Claims
What is claimed is:
1. A method of heating an object, comprising: emitting radiation of
at least one wavelength capable of heating the object thus
producing at least one wavelength of emitted radiation; absorbing
radiation of the at least one wavelength of emitted radiation in a
radiation-absorptive atmosphere; and transferring heat to the
object through a combination of radiant heat transfer from the at
least one wavelength of emitted radiation and conductive heat
transfer from the radiation-absorptive atmosphere.
2. The method of claim 1 wherein absorbing radiation occurs in a
radiation-absorptive atmosphere comprising at least one
radiation-absorptive gas.
3. The method of claim 1 wherein absorbing radiation occurs in a
radiation-absorptive atmosphere comprising at least one
radiation-absorptive gas and at least one transparent gas.
4. The method of claim 1 wherein absorbing radiation occurs in a
radiation-absorptive atmosphere comprising at least one
radiation-absorptive gas, further wherein the at least one
radiation-absorptive gas is a gas selected from the group
consisting of H.sub.2O, CO.sub.2, NH.sub.3 and N.sub.2O.
5. The method of claim 1 wherein absorbing radiation occurs in a
radiation-absorptive atmosphere comprising at least one
radiation-absorptive gas and at least one transparent gas, further
wherein the at least one radiation-absorptive gas is a gas selected
from the group consisting of H.sub.2O, CO.sub.2, NH.sub.3 and
N.sub.2O, still further wherein the at least one transparent gas is
a gas selected from the group consisting of Ar and N.sub.2.
6. The method of claim 1 wherein absorbing radiation occurs in a
radiation-absorptive atmosphere comprising: substantially 10-80 mol
% Ar; substantially 10-40 mol % H.sub.2; and substantially 10-50
mol % H.sub.2O.
7. The method of claim 1 wherein emitting radiation of at least one
relevant wavelength capable of heating the object further comprises
emitting at least one wavelength in the range of 0.5 to 3.0
.mu.m.
8. The method of claim 1 further comprising maintaining the
pressure of the radiation-absorptive atmosphere below
atmospheric.
9. The method of claim 1 further comprising maintaining the
pressure of the radiation-absorptive atmosphere at or above
atmospheric.
10. A radiant heating system for heating an object, comprising: a
radiation source for directing radiation toward the object; and a
radiation-absorptive atmosphere positioned between the radiation
source and the object.
11. The radiant heating system of claim 10 wherein the
radiation-absorptive atmosphere comprises at least one
radiation-absorptive gas.
12. The radiant heating system of claim 10 wherein the
radiation-absorptive atmosphere comprises at least one
radiation-absorptive gas and at least one transparent gas.
13. The radiant heating system of claim 10 wherein the
radiation-absorptive atmosphere comprises at least one
radiation-absorptive gas, further wherein the at least one
radiation-absorptive gas is a gas selected from the group
consisting of H.sub.2O, CO.sub.2, NH.sub.3 and N.sub.2O.
14. The radiant heating system of claim 10 wherein the
radiation-absorptive atmosphere comprises at least one
radiation-absorptive gas and at least one transparent gas, further
wherein the at least one radiation-absorptive gas is a gas selected
from the group consisting of H.sub.2O, CO.sub.2, NH.sub.3 and
N.sub.2O, still further wherein the at least one transparent gas is
a gas selected from the group consisting of Ar and N.sub.2.
15. The radiant heating system of claim 10 wherein the
radiation-absorptive atmosphere comprises: substantially 10-80 mol
% Ar; substantially 10-40 mol % H.sub.2; and substantially 10-50
mol % H.sub.2O.
16. The radiant heating system of claim 10 wherein the radiation
source emits radiation comprising at least one wavelength in the
range of 0.5 to 3.0 .mu.m.
17. A method of processing a semiconductor wafer, comprising:
emitting radiation of at least one wavelength capable of heating
the semiconductor wafer thus producing at least one wavelength of
emitted radiation; absorbing radiation of the at least one
wavelength of emitted radiation in a radiation-absorptive
atmosphere; and transferring heat to the semiconductor wafer
through a combination of radiant heat transfer from the at least
one wavelength of emitted radiation and conductive heat transfer
from the radiation-absorptive atmosphere.
18. The method of claim 17 wherein absorbing radiation occurs in a
radiation-absorptive atmosphere comprising at least one
radiation-absorptive gas.
19. The method of claim 17 wherein absorbing radiation occurs in a
radiation-absorptive atmosphere comprising at least one
radiation-absorptive gas and at least one transparent gas.
20. The method of claim 17 wherein absorbing radiation occurs in a
radiation-absorptive atmosphere comprising at least one
radiation-absorptive gas, further wherein the at least one
radiation-absorptive gas is a gas selected from the group
consisting of H.sub.2O, CO.sub.2, NH.sub.3 and N.sub.2O.
21. The method of claim 17 wherein absorbing radiation occurs in a
radiation-absorptive atmosphere comprising at least one
radiation-absorptive gas and at least one transparent gas, further
wherein the at least one radiation-absorptive gas is a gas selected
from the group consisting of H.sub.2O, CO.sub.2, NH.sub.3 and
N.sub.2O, still further wherein the at least one transparent gas is
a gas selected from the group consisting of Ar and N.sub.2.
22. The method of claim 17 wherein absorbing radiation occurs in a
radiation-absorptive atmosphere comprising: substantially 10-80 mol
% Ar; substantially 10-40 mol % H.sub.2; and substantially 10-50
mol % H.sub.2O.
23. The method of claim 17 wherein emitting radiation of at least
one relevant wavelength capable of heating the semiconductor wafer
further comprises emitting at least one wavelength in the range of
0.5 to 3.0 .mu.m.
24. The method of claim 17 further comprising maintaining the
pressure of the radiation-absorptive atmosphere below
atmospheric.
25. The method of claim 17 further comprising maintaining the
pressure of the radiation-absorptive atmosphere at or above
atmospheric.
26. An apparatus, comprising: a semiconductor die having a reduced
thermal budget, wherein the semiconductor die is exposed to emitted
radiation of at least one wavelength capable of heating the
semiconductor die and a radiation-absorptive atmosphere capable of
absorbing radiation of the at least one wavelength of emitted
radiation, further wherein the semiconductor die absorbed heat
through a combination of radiant heat transfer from the at least
one wavelength of emitted radiation and conductive heat transfer
from the radiation-absorptive atmosphere.
27. The apparatus of claim 26, wherein the at least one wavelength
of emitted radiation comprises at least one wavelength in the range
of 0.5 to 3.0 .mu.m.
28. The apparatus of claim 26, wherein the radiation-absorptive
atmosphere comprises at least one radiation-absorptive gas and at
least one transparent gas, further wherein the at least one
radiation-absorptive gas is a gas selected from the group
consisting of H.sub.2O, CO.sub.2, NH.sub.3 and N.sub.2O, still
further wherein the at least one transparent gas is a gas selected
from the group consisting of Ar and N.sub.2.
29. An apparatus, comprising: a semiconductor die having a reduced
thermal budget, wherein the semiconductor die is exposed to emitted
radiation of at least one wavelength capable of heating the
semiconductor die and a radiation-absorptive atmosphere capable of
absorbing radiation of the at least one wavelength of emitted
radiation, further wherein the radiation-absorptive atmosphere
comprises at least one radiation-absorptive gas selected from the
group consisting of H.sub.2O, CO.sub.2, NH.sub.3 and N.sub.2O,
still further wherein the semiconductor die absorbed heat through a
combination of radiant heat transfer from the at least one
wavelength of emitted radiation and conductive heat transfer from
the radiation-absorptive atmosphere.
30. An apparatus, comprising: a semiconductor die having a reduced
thermal budget, wherein the semiconductor die is exposed to emitted
radiation of at least one wavelength capable of heating the
semiconductor die and a radiation-absorptive atmosphere capable of
absorbing radiation of the at least one wavelength of emitted
radiation, further wherein the radiation-absorptive atmosphere
comprises substantially 10-80 mol % Ar, substantially 10-40 mol %
H.sub.2, and substantially 10-50 mol % H.sub.2O, still further
wherein the semiconductor die absorbed heat through a combination
of radiant heat transfer from the at least one wavelength of
emitted radiation and conductive heat transfer from the
radiation-absorptive atmosphere.
31. A radiant heating system for heating an object, comprising: a
radiant heating means for emitting radiation of at least one
relevant wavelength capable of heating the object; and a
radiation-absorbing means for absorbing at least one relevant
wavelength from the radiant heating means and conducting absorbed
energy to the object.
32. A method of processing a semiconductor wafer having a surface
and a substrate, comprising: surrounding the semiconductor wafer
surface with a radiation-absorptive atmosphere; emitting radiation
capable of heating the semiconductor wafer and the
radiation-absorptive atmosphere thus producing emitted radiation;
absorbing at least some of the emitted radiation in the
radiation-absorptive atmosphere; absorbing at least some of the
emitted radiation in the semiconductor wafer; and conducting heat
to the semiconductor wafer from the absorbed energy in the
radiation-absorptive atmosphere such that the combined energy
transfer to the surface of the semiconductor wafer exceeds the
energy transfer to the substrate.
33. A method of processing a semiconductor wafer having a surface
and a substrate, comprising: emitting radiation of at least one
wavelength capable of heating the semiconductor wafer thus
producing at least one wavelength of emitted radiation; absorbing
radiation of the at least one wavelength of emitted radiation in a
radiation-absorptive atmosphere, wherein the radiation-absorptive
atmosphere comprises at least one gas selected from the group
consisting of H.sub.2O, Ar, H.sub.2, CO.sub.2, NH.sub.3, N.sub.2,
NO.sub.2, N.sub.2O.sub.3, N.sub.2O.sub.4, N.sub.2O.sub.5, NO,
N.sub.2O, He, O.sub.3, Kr, Ne, Xe, Rn and Cl.sub.2; and
transferring heat to the semiconductor wafer through a combination
of radiant heat transfer from the at least one wavelength of
emitted radiation and conductive heat transfer from the
radiation-absorptive atmosphere.
34. A circuit module, comprising: at least two semiconductor dies
with at least one semiconductor die having a reduced thermal
budget, wherein the at least one semiconductor die having a reduced
thermal budget is exposed to emitted radiation of at least one
wavelength capable of heating the at least one semiconductor die
having a reduced thermal budget and a radiation-absorptive
atmosphere capable of absorbing radiation of the at least one
wavelength of emitted radiation, further wherein the at least one
semiconductor die having a reduced thermal budget absorbed heat
through a combination of radiant heat transfer from the at least
one wavelength of emitted radiation and conductive heat transfer
from the radiation-absorptive atmosphere.
35. The circuit module of claim 34, wherein the at least two
semiconductor dies comprise at least two semiconductor dies having
differing functionality.
36. The circuit module of claim 34, wherein the at least two
semiconductor dies comprise a semiconductor die in a protective
casing.
37. The circuit module of claim 34, wherein the at least one
wavelength of emitted radiation comprises at least one wavelength
in the range of 0.5 to 3.0 .mu.m.
38. The circuit module of claim 34, wherein the
radiation-absorptive atmosphere comprises at least one
radiation-absorptive gas and at least one transparent gas, further
wherein the at least one radiation-absorptive gas is a gas selected
from the group consisting of H.sub.2O, CO.sub.2, NH.sub.3 and
N.sub.2O, still further wherein the at least one transparent gas is
a gas selected from the group consisting of Ar and N.sub.2.
39. A circuit module, comprising: at least two semiconductor dies
with at least one semiconductor die having a reduced thermal
budget, wherein the at least one semiconductor die having a reduced
thermal budget is exposed to emitted radiation of at least one
wavelength capable of heating the at least one semiconductor die
having a reduced thermal budget and a radiation-absorptive
atmosphere capable of absorbing radiation of the at least one
wavelength of emitted radiation, further wherein the
radiation-absorptive atmosphere comprises at least one
radiation-absorptive gas selected from, the group consisting of
H.sub.2O, CO.sub.2, NH.sub.3 and N.sub.2O, still further wherein
the at least one semiconductor die having a reduced thermal budget
absorbed heat through a combination of radiant heat transfer from
the at least one wavelength of emitted radiation and conductive
heat transfer from the radiation-absorptive atmosphere.
40. A circuit module, comprising: at least two semiconductor dies
with at least one semiconductor die having a reduced thermal
budget, wherein the at least one semiconductor die having a reduced
thermal budget is exposed to emitted radiation of at least one
wavelength capable of heating the at least one semiconductor die
having a reduced thermal budget and a radiation-absorptive
atmosphere capable of absorbing radiation of the at least one
wavelength of emitted radiation, further wherein the
radiation-absorptive atmosphere comprises substantially 10-80 mol %
Ar, substantially 10-40 mol % H.sub.2, and substantially 10-50 mol
% H.sub.2O, still further wherein the at least one semiconductor
die having a reduced thermal budget absorbed heat through a
combination of radiant heat transfer from the at least one
wavelength of emitted radiation and conductive heat transfer from
the radiation-absorptive atmosphere.
41. An electronic system, comprising: at least one circuit module,
wherein the at least one circuit module comprises at least two
semiconductor dies with at least one semiconductor die having a
reduced thermal budget, wherein the at least one semiconductor die
having a reduced thermal budget is exposed to emitted radiation of
at least one wavelength capable of heating the at least one
semiconductor die having a reduced thermal budget and a
radiation-absorptive atmosphere capable of absorbing radiation of
the at least one wavelength of emitted radiation, further wherein
the at least one semiconductor die having a reduced thermal budget
absorbed heat through a combination of radiant heat transfer from
the at least one wavelength of emitted radiation and conductive
heat transfer from the radiation-absorptive atmosphere.
42. The electronic system of claim 41, further comprising a user
interface.
43. The electronic system of claim 41, further comprising
mechanical components.
44. An electronic system, comprising: at least one circuit module,
wherein the at least one circuit module comprises at least two
semiconductor dies with at least one semiconductor die having a
reduced thermal budget, wherein the at least one semiconductor die
having a reduced thermal budget is exposed to emitted radiation of
at least one wavelength capable of heating the at least one
semiconductor die having a reduced thermal budget and a
radiation-absorptive atmosphere capable of absorbing radiation of
the at least one wavelength of emitted radiation, further wherein
the radiation-absorptive atmosphere comprises at least one
radiation-absorptive gas selected from the group consisting of
H.sub.2O, CO.sub.2, NH.sub.3 and N.sub.2O, still further wherein
the at least one semiconductor die having a reduced thermal budget
absorbed heat through a combination of radiant heat transfer from
the at least one wavelength of emitted radiation and conductive
heat transfer from the radiation-absorptive atmosphere.
45. A circuit module, comprising: at least two semiconductor dies
with at least one semiconductor die having a reduced thermal
budget, wherein the at least one semiconductor die having a reduced
thermal budget is exposed to emitted radiation of at least one
wavelength capable of heating the at least one semiconductor die
having a reduced thermal budget and a radiation-absorptive
atmosphere capable of absorbing radiation of the at least one
wavelength of emitted radiation, further wherein the
radiation-absorptive atmosphere comprises substantially 10-80 mol %
Ar, substantially 10-40 mol % H.sub.2, and substantially 10-50 mol
% H.sub.2O, still further wherein the at least one semiconductor
die having a reduced thermal budget absorbed heat through a
combination of radiant heat transfer from the at least one
wavelength of emitted radiation and conductive heat transfer from
the radiation-absorptive atmosphere.
46. A method of processing a semiconductor wafer having a surface
and a substrate, comprising: emitting radiation of at least one
wavelength in the range of 0.5 to 3.0 .mu.m; absorbing radiation of
the at least one wavelength in the range of 0.5 to 3.0 .mu.m in a
radiation-absorptive atmosphere, wherein the radiation-absorptive
atmosphere comprises substantially 10-80 mol % Ar, substantially
10-40 mol % H.sub.2, and substantially 10-50 mol % H.sub.2O;
transferring heat to the semiconductor wafer through radiant heat
transfer from the at least one wavelength in the range of 0.5 to
3.0 .mu.m; and transferring heat to the surface of the
semiconductor wafer through conductive heat transfer from the
radiation-absorptive atmosphere.
47. A method of annealing glass on a surface of a semiconductor
wafer having a substrate, comprising: emitting radiation of at
least one wavelength capable of heating the semiconductor wafer
thus producing at least one wavelength of emitted radiation;
absorbing radiation of the at least one wavelength of emitted
radiation in a radiation-absorptive atmosphere, wherein the
radiation-absorptive atmosphere comprises at least one gas selected
from the group consisting of H.sub.2O, Ar, H.sub.2, CO.sub.2,
NH.sub.3, N.sub.2, NO.sub.2, N.sub.2O.sub.3, N.sub.2O.sub.4,
N.sub.2O.sub.5, NO, N.sub.2O, He, O.sub.3, Kr, Ne, Xe, Rn and
Cl.sub.2; transferring heat to the semiconductor wafer through
radiant heat transfer from the at least one wavelength of emitted
radiation; and transferring heat to the surface of the
semiconductor wafer through conductive heat transfer from the
radiation-absorptive atmosphere.
48. A method of annealing glass on a surface of a semiconductor
wafer having a substrate, comprising: emitting radiation of at
least one wavelength in the range of 0.5 to 3.0 .mu.m; absorbing
radiation of the at least one wavelength in the range of 0.5 to 3.0
.mu.m in a radiation-absorptive atmosphere, wherein the
radiation-absorptive atmosphere comprises substantially 10-80 mol %
Ar, substantially 10-40 mol % H.sub.2, and substantially 10-50 mol
% H.sub.2O; transferring heat to the semiconductor wafer through
radiant heat transfer from the at least one wavelength in the range
of 0.5 to 3.0 .mu.m; and transferring heat to the glass through
conductive heat transfer from the radiation-absorptive atmosphere.
Description
[0001] This application is a Divisional of U.S. application Ser.
No. 09/139,934, filed Aug. 26, 1998, which is incorporated herein
by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to selectively increasing
surface layer temperature during radiant heating, and more
specifically to the use of thermal radiation-absorptive gasses to
selectively increase the surface temperature of a semiconductor
wafer in relation to the substrate during Rapid Thermal
Processing.
BACKGROUND OF THE INVENTION
[0003] Integrated circuits are often fabricated with one or more
devices, which may include diodes, capacitors, and different
varieties of transistors. These devices often have microscopic
features that can only be manufactured with critical processing
steps that require careful alignment of equipment used to build the
devices. These microscopic features contain critical dimensions
that will often define the performance of the device and its
surrounding circuitry.
[0004] Additionally, the functionality of these devices is defined
by creating precisely controlled regions of dopants within the
various layers of a semiconductor wafer. These dopants, however,
are susceptible to diffusion at elevated temperatures.
[0005] Semiconductor fabrication continues to advance, requiring
finer dimensional tolerances and control. Modem integrated circuit
design has advanced to the point where line width may be 0.25
microns or less, with junction depths on the order of 1500-2000
Angstroms. Thus, thermal effect to a semiconductor wafer must be
reduced to limit the lateral diffusion of the dopants, and the
associated broadening of line dimension. Thermal effect to a
semiconductor wafer must also be limited to reduce forward
diffusion of the dopants so junction depth does not shift.
[0006] An additional potential adverse effect of thermal treatment
is chemical change of the materials utilized in the fabrication of
a semiconductor wafer. As an example, refractory metal-silicide
films may be formed during the fabrication of very large scale
integration (VLSI) circuits as a gate or interconnect film. These
refractory metal-silicides can be reduced to their elemental
constituents under elevated thermal conditions, thus destroying the
functionality of the device.
[0007] In an effort to reduce the magnitude of thermal
requirements, and thus lessen the likelihood of adverse effects,
differing processes have been developed. One such process is Rapid
Thermal Processing (RTP). RTP is a short-duration,
high-temperature, radiant-heating process. RTP may be found in a
multitude of semiconductor fabrication processes in a variety of
forms, including rapid thermal annealing (RTA), rapid thermal
cleaning (RTC), rapid thermal chemical vapor deposition (RTCVD),
rapid thermal oxidation (RTO), and rapid thermal nitridation
(RTN).
[0008] RTP seeks to minimize the negative effects of necessary
thermal treatments, and thus reduce the thermal budget of a
semiconductor wafer, by subjecting the semiconductor wafer to high
temperatures (typically 420-1150.degree. C.) only long enough to
achieve the desired process effect. Systems are commercially
available to perform RTP and generally utilize large-area
incoherent energy sources such as radiant heat lamps operating in
the wavelengths of 0.5 to 3 .mu.m. RTP systems typically thermally
isolate the semiconductor wafer being processed such that radiant
heating is the dominant mode of transfer, seeking to minimize heat
transfer by conduction at the wafer surface or convection around
the wafer surface.
[0009] RTP was started as a research technique some 25 years ago
using pulsed laser beams. As the semiconductor industry continues
its trend into submicron devices, RTP is becoming a core technology
step in the development and mass production of ultra-large system
integration (ULSI) devices. Since their introduction more than a
decade ago, RTP processors employing incoherent lamps are now the
mainstay.
[0010] Despite these prior improvements to thermal processing,
difficulties still exist. To achieve desired semiconductor device
characteristics, temperatures and dopant implant depths must be
adjusted within small process windows to achieve the desired
process effect while compensating for the inevitable diffusion. As
device sizes are reduced, control of implant diffusion becomes more
critical. Reducing thermal effect to the semiconductor substrate
relaxes and widens the available process window for control of
implant diffusion.
[0011] Furthermore, in many semiconductor fabrication steps
requiring heat input, the desired process effect relates only to
the surface of the semiconductor wafer. In these cases, there is no
need or desire to provide heat input to the substrate. It should be
noted that all references to the substrate within this disclosure
shall include all layers underlying the surface.
[0012] One such use of RTP is for a process known as contact reflow
following anisotropic etching. Etching in semiconductor fabrication
involves the removal of material from the wafer surface.
Anisotropic etching is typically used to describe etching occurring
only in the direction perpendicular to the wafer surface. This
vertical etching results in sharp edges on contact holes, making
them difficult to fill. Where flowable glass, such as
borophosphosilicate glass (BPSG), is used for isolation,
passivation or surface planarization, these sharp edges may be
rounded through the process of contact reflow.
[0013] Contact reflow involves the heating or annealing of the
glass to cause reflow and, therefore, rounding of surface features.
With rounded surface features, coverage of contact holes by
subsequent metal film layers is improved. Because the process seeks
only to round the surface features of the glass surface layer, heat
input to the underlying layers is neither required nor desired.
[0014] In light of the foregoing, it may be desirable to
selectively increase the processing temperature of the surface
layer of a semiconductor wafer while reducing the thermal effects
to the substrate that would normally occur in pre-existing rapid
thermal processing.
SUMMARY OF THE INVENTION
[0015] The invention allows the user to increase the thermal effect
delivered to the surface layer of a semiconductor wafer in relation
to the thermal effect delivered to the substrate. The desired
effect is produced by introducing radiation-absorptive gas into the
heating chamber of a radiant heating system. Thermal energy
absorbed by the radiation-absorptive gas in contact with the
semiconductor wafer increases heat transfer to the wafer surface
through conduction while reducing radiant heat transfer available
to the substrate. Radiation-absorptive gas may be combined with a
gas that absorbs only minimal or negligible radiant energy to thus
modify or regulate the level of absorptivity of the atmosphere
within the heating chamber.
[0016] By increasing conductive heat transfer to the surface while
reducing radiant heat transfer to the substrate, the surface will
receive more heat input relative to the substrate. The result is
that the surface temperature can be selectively increased in
relation to the substrate, and the thermal budget of the wafer is
reduced. Consequently, semiconductor devices produced according to
the invention will have reduced thermal budgets.
[0017] Using the system and technique of the invention,
semiconductor fabrication steps may be accomplished with reduced
thermal effects to the semiconductor wafer substrate. At a minimum,
a system suitable to practice the invention need only a radiant
energy source, or radiation source, and an atmosphere that absorbs
some radiant energy given off by the radiation source. The
atmosphere must occupy the path of radiation which is emitted from
the radiation source and directed to the surface of the object
being heated.
[0018] In one embodiment of the invention, the atmosphere contains
a single radiation-absorptive gas.
[0019] In another embodiment of the invention, the atmosphere
contains a mixture of radiation-absorptive gases.
[0020] In a further embodiment of the invention, the atmosphere
contains a mixture of a radiation-absorptive gas and a transparent
gas.
[0021] In a still further embodiment of the invention, the
atmosphere contains a mixture of a radiation-absorptive gas and two
or more transparent gases.
[0022] In yet another embodiment of the invention, the atmosphere
contains a mixture of two or more radiation-absorptive gases and a
transparent gas.
[0023] In a further embodiment of the invention, the atmosphere
contains a mixture of two or more radiation-absorptive gases and
two or more transparent gases.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] In the drawings, where like numerals refer to like
components throughout the several views:
[0025] FIG. 1A is a cross-section view of one type of a
pre-existing rapid thermal processing (RTP) system.
[0026] FIG. 1B is a plan view of the RTP system taken through line
1B-1B of FIG. 1A.
[0027] FIG. 2 is a pictorial representation of the relative
radiation loss through a transparent atmosphere.
[0028] FIG. 3 is a graphical representation of the relative
radiation loss through a transparent atmosphere.
[0029] FIG. 4 is a pictorial representation of the relative
radiation loss through a radiation-absorptive atmosphere.
[0030] FIG. 5 is a graphical representation of the relative
radiation loss through a radiation-absorptive atmosphere.
[0031] FIG. 6 is an elevation view of a semiconductor wafer
containing semiconductor dies according to one embodiment of the
invention.
[0032] FIG. 7 is a block diagram of a circuit module incorporating
semiconductor dies according to one embodiment of the
invention.
[0033] FIG. 8 is a block diagram of an electronic system
incorporating circuit modules according to one embodiment of the
invention.
DESCRIPTION OF THE EMBODIMENTS
[0034] In the following detailed description, reference is made to
the accompanying drawings which form a part hereof, and in which is
shown by way of illustration specific embodiments in which the
invention may be practiced. These embodiments are described in
sufficient detail to enable those skilled in the art to practice
the invention, and it is to be understood that other embodiments
may be utilized and that structural, logical and compositional
changes may be made without departing from the spirit and scope of
the invention. The following detailed description is, therefore,
not to be taken in a limiting sense, and the scope of the invention
is defined by the appended claims.
[0035] In general, a typical RTP system contains three major parts
(see FIG. 1A): (a) a high-power lamp system or radiation source 22
heating the wafer 10; (b) a chamber 18 in which the wafer 10 and an
atmosphere (not depicted) are contained; and (c) a pyrometer 20 to
measure the wafer temperature. The lamp system can be either a set
of tungsten-halogen lamps or a high-power arc lamp with a
reflector. The wafer 10 has a backside 14 and a surface 15. The
chamber 18 is generally a quartz chamber. In all cases, the lamps
are separated from the wafer with a quartz window 24.
[0036] The pyrometer 20 measures the radiation that is emitted from
the backside 14 of the wafer and converts this into substrate, or
wafer, temperature. Other non-invasive temperature measurement
techniques based on thermal expansion of the wafer, laser
interferometry, and acoustic interference are being developed to
accurately measure the temperature. The temperature measurement
technique chosen, or whether temperature is measured at all, in no
way limits the invention. As an alternative to or in addition to
pyrometer 20, other sensors may be implemented to measure
temperature, reflectance, or other mechanical properties such as
stress elasticity.
[0037] Other features of this typical RTP system include the quartz
wafer holder 26, the process gas conduits 28, and the reflector 30.
The wafer 10 is placed or positioned on wafer holder 26 such that
radiation from the radiation source 22 is directed at and impinges
on the surface 15 of wafer 10. Process gas conduits 28 act as an
inlet for gas flow in the chamber 18. Depending on the gas flow
rate through process gas conduits 28, it is possible to have both
free and forced convection within the RTP atmosphere. Reflector 30
assists directing radiation from radiation source 22 to the surface
15 of wafer 10. A complete RTP system would contain additional
components, such as robotic handling elements and staging
elevators, but these are not of concern to the invention disclosed
and claimed.
[0038] In typical RTP processing, the wafer 10 would absorb
radiation primarily through surface 15 in chamber 18 from radiation
source 22. While radiation from radiation source 22 is not limited
to a direction perpendicular to the surface 15 of wafer 10, such
direction is a reasonable approximation of the transfer of radiant
energy to wafer 10. Time and temperature within chamber 18 would be
directed by the desired process effect.
[0039] The heating lamp system comes in four basic geometries: the
line source, the square source, the hexagonal source, and the ring
source. FIG. 1B is an example of the ring source lamp system, where
the lamp bank consists of an outer ring, middle ring, and an inner
lamp or ring of lamps.
[0040] RTP is generally carried out with chamber 18 containing an
inert atmosphere of Ar, N.sub.2 or a vacuum. Oxygen and NH.sub.3,
however, have previously been introduced into the processing
chamber of an RTP system when the desired process effect is to
induce the growth of SiO.sub.2 and Si.sub.3N.sub.4, respectively.
The RTP atmospheres are generally transparent to the radiation
source, thus allowing the radiant energy to transfer to the wafer
10 with only negligible absorption by the atmosphere surrounding
the wafer 10.
[0041] The system and process of the invention work equally well at
any pressure, from pressures above atmospheric to those below
atmospheric. In fact, increases or reductions in pressure can be
used to selectively raise or lower desired absorptivity of the
radiation-absorptive atmosphere. An increase in pressure will
increase the molecular density of the gaseous atmosphere, thus
allowing more absorptive gas per unit volume and increasing the
absorptivity. Likewise, a reduction in pressure will decrease the
molecular density of the gaseous atmosphere, thus reducing the
absorptive gas per unit volume and decreasing the absorptivity.
[0042] As stated previously, the gas or atmosphere within chamber
18 of pre-existing RTP systems is generally inert and transparent
to the radiant energy of radiation source 22. In other words, the
intensity of the radiant energy leaving radiation source 22 is
virtually identical to the intensity of the radiant energy arriving
at the surface 15 of wafer 10. FIGS. 2 and 3 are a pictorial and
graphical representation of the change in intensity of the radiant
energy emitted by radiation source 22 as it travels from radiation
source 22, point I, to surface 15, point I', in chamber 18 of
pre-existing RTP systems. FIGS. 2 and 3 are intended to show that
there is negligible reduction in intensity of radiant energy
through the transparent atmosphere. There is no scale as these
figures are offered for conceptual representation only.
[0043] In one embodiment of the invention, a radiation-absorptive
gas replaces the transparent atmosphere in chamber 18. The
radiation-absorptive gas is chosen such that it has an increased
index of absorption, in the wavelength(s) of the radiant energy
from radiation source 22, over the transparent atmosphere generally
utilized in an RTP system.
[0044] The radiation-absorptive gas must absorb radiation in at
least one of the wavelengths of the radiation source, and all
references to radiation-absorptive gases will presume that they
absorb radiation in one or more of the relevant wavelengths emitted
by the provided radiation source. The relevant wavelengths of a
radiation source are the dominant wavelengths providing for heat
transfer to the process object. Conversely, a gas is transparent if
it does not absorb radiant energy of the relevant wavelengths of
the radiation source. Note that due to the wide range of
wavelengths that may be given off by a radiation source due to
factors such as type, degradation or contamination, and that are
not a prominent source of heat transfer to the object, a
transparent gas may absorb wavelengths that are not relevant
wavelengths.
[0045] The result of surrounding surface 15 with a
radiation-absorptive atmosphere is that the intensity of the
radiant energy emitted by radiation source 22 is more significantly
reduced as it travels from radiation source 22 to surface 15. FIGS.
4 and 5 are a pictorial and graphical representation of the change
in intensity of the radiant energy emitted by radiation source 22
as it travels from radiation source 22, point I, to surface 15,
point I', utilizing a radiation-absorptive gas in the atmosphere of
chamber 18. By utilizing the invention, there is now a
non-negligible reduction in intensity of the radiant energy as it
travels through the absorptive atmosphere. There is no scale as
these figures are offered for conceptual representation only.
[0046] By providing an atmosphere with a higher propensity to
absorb radiation in one or more wavelengths of the spectrum
radiated by radiation source 22, two phenomena occur: 1)
temperature increases within chamber 18; and 2) radiant energy
impinging on surface 15 is reduced.
[0047] The temperature within chamber 18 increases as energy is
absorbed by the absorptive atmosphere. The absorbed energy raises
the internal energy of the absorptive atmosphere, thus increasing
its temperature. There will be some increase in convective heat
transfer within the atmosphere of chamber 18 as the temperature
change induces convection. More importantly, however, with the
temperature surrounding surface 15 increased, heat transfer by
conduction of the absorbed energy from the atmosphere within
chamber 18 to surface 15 is increased. It is recognized that heat
transfer by conduction from surface 15 to the substrate of wafer 10
would also increase to some degree.
[0048] The energy absorbed by the absorptive atmosphere within
chamber 18 also results in decreased levels of radiation available
to impinge on surface 15. This results in a decreased level of
radiant heat transfer to surface 15 and wafer 10. It is believed
that the decreased level of heat transfer by radiation to wafer 10
will generally exceed the increased level of conductive heat
transfer to the substrate of wafer 10. Combined, the energy
transfer to surface 15 exceeds the energy transfer to the substrate
of wafer 10, thus supporting the observed phenomena that equivalent
process effects can be achieved at reduced substrate
temperatures.
[0049] In an alternative embodiment of the invention, the
atmosphere of chamber 18 contains a mixture of more than one
absorptive gas. Choosing absorptive gases that absorb radiation of
different wavelengths can increase the total energy absorbed over
that of each individual gas. In addition, mixtures of gases can
interact through bonding or reaction to generate additional
absorption wavelengths. Furthermore, some individual gases will
have strong absorptivity while others will be weak absorbers.
Accordingly, the concentration of individual gases is guided by the
desired level of absorption of one or more wavelengths of radiant
energy and is, therefore, without practical limit. Simply put, the
user is free to choose any number or combination of absorptive
gases. The user can vary the individual concentrations, guided by
the physical characteristics of the individual gases, to achieve
the desired level of absorption and, therefore, the desired process
effect.
[0050] In a further embodiment of the invention, one or more
absorptive gases may be combined with one or more transparent
gases. As with all other embodiments, concentration of any
individual gas is not limited. Two phenomena may occur through the
addition of transparent gases. Transparent gas may act to reduce
the overall level of absorbed radiation by displacing absorptive
gases. Additionally, transparent gas may aid removal of absorbed
energy from an absorptive gas, thereby increasing the overall level
of absorbed radiation by increasing the number of unexcited
absorptive molecules. Regardless of whether one or both phenomena
occur, the user is provided with an additional tool to achieve the
desired level of absorption and, therefore, the desired process
effect.
[0051] For radiation sources operating in the wavelengths of 0.5 to
3 .mu.m, the following gases have been identified for semiconductor
processing incorporating the invention: H.sub.2O, Ar, H.sub.2,
CO.sub.2, NH.sub.3, N.sub.2, NO.sub.2, N.sub.2O.sub.3,
N.sub.2O.sub.4, N.sub.2O.sub.5, NO, N.sub.2O, He, O.sub.3, Kr, Ne,
Xe, Rn and Cl.sub.2. Of these gases, H.sub.2O, CO.sub.2, NH.sub.3
and N.sub.2O are of particular interest due to their absorptive
properties in the relevant wavelengths. Furthermore, N.sub.2 and Ar
are of particular interest due to their transparency in the
relevant wavelengths.
[0052] Although NH.sub.3 has previously been used as a reactant
species, the invention utilizes NH.sub.3 for purposes other than
where nitridation is the desired process effect. An example would
be glass reflow applications where nitridation inhibits glass
reflow. Accordingly, use of NH.sub.3 as an absorptive gas should
occur at process conditions which do not promote nitridation. It is
believed that nitridation will not occur at temperatures below
about 700.degree. C.
[0053] Determination of whether a gas is absorptive or transparent
at a specific wavelength does not require undue experimentation.
Individual gases or mixtures of gas may be subjected to the science
of spectroscopy to determine the absorption of light at various
wavelengths. Spectrophotometers are commercially available to
measure transmission or absorption of wavelengths from the infrared
(IR) and near infrared (NIR) spectra through the ultraviolet (UV)
spectrum.
[0054] In an exemplary embodiment of the invention, the atmosphere
of an RTP system contains an absorptive mixture of Ar, H.sub.2 and
H.sub.2O at approximate molar concentrations of 10-80%, 10-40% and
10-50%, respectively. The RTP system utilizes a radiation source
operating in the relevant wavelengths of 0.5 to 3 .mu.m. A
semiconductor wafer of embedded DRAMs (Dynamic Random Access
Memory) is introduced into the absorptive atmosphere under the
heating element to affect reflow of BPSG on the wafer surface
without adversely affecting implant diffusion or the integrity of
Ti-salicide, a self-aligned silicide. To achieve equivalent process
results of a pre-existing RTP system operating at 800.degree. C.,
the system of the exemplary embodiment may operate at the reduced
temperature of 750.degree. C.
[0055] With reference to FIG. 6, in one embodiment, a die 60 is
produced from the wafer 10 processed according to the invention. A
die is an individual rectangular pattern on a semiconductor wafer
that contains circuitry to perform a specific function. A
semiconductor wafer will typically contain a repeated pattern of
such dies containing the same functionality. Die 60 may contain
circuitry for a simple DRAM, as discussed above, or it may extend
to such complex circuitry as a monolithic processor with multiple
functionality. Die 60 is typically packaged in a protective casing
(not shown) with leads extending therefrom (not shown) providing
access to the circuitry of the die for unilateral or bilateral
communication and control.
[0056] As shown in FIG. 7, two or more dies 60 may be combined,
with or without protective casing, into a circuit module 70 to
enhance or extend the functionality of an individual die 60.
Circuit module 70 may be a combination of dies 60 representing a
variety of functions, or a combination of dies 60 containing the
same functionality. Some examples of a circuit module include
memory modules, power modules, communication modules, processor
modules and application-specific modules and may include
multilayer, multichip modules. Circuit module 70 may be a
subcomponent of a variety of electronic systems, such as a clock, a
radio, a dishwasher, a television, a cell phone, a personal
computer, an automobile, an automated teller machine, an industrial
control system, an aircraft and others. Circuit module 70 will have
a variety of leads extending therefrom (not shown) providing
unilateral or bilateral communication and control.
[0057] FIG. 8 shows one such electronic system 80 containing one or
more circuit modules 70. Electronic system 80 generally contains a
user interface 85. User interface 85 provides a user of the
electronic system 80 with some form of control or observation of
the results of the electronic system 80. Some examples of user
interface 85 include the keyboard, pointing device, CRT and printer
of a personal computer; the tuning dial, display and speakers of a
radio; the ignition switch and gas pedal of an automobile; and the
card reader, keypad, display and currency dispenser of an automated
teller machine. As will be apparent from the lists of examples
previously given, electronic system 80 will often contain certain
mechanical components (not shown) in addition to circuit modules 70
and user interface 85.
[0058] To reiterate, an absorptive gas mixture may contain any
combination of one or more absorptive gases. The absorptive gas
mixture may be void of transparent gases or it may contain one or
more transparent gases. Individual gases may exist in the
absorptive gas mixture at any concentration. Concentration and
choice of gases is guided by the desired process effect or level of
absorption, and the relevant wavelengths of the radiation source.
Of course, the summation of all individual concentrations must
equal 100%.
[0059] Furthermore, in all embodiments of the invention, the
realities of industrial processing must be recognized. Where a
reference is made to purity of the gaseous atmosphere, the reader
must remember that there will always be some incident
contamination, either at the percentage, ppm, ppb or atomic level.
This contamination will come from multiple sources, such as that
inherently found in the gases from their source or re-use, or in
their preparation; that coming from outgassing or evaporation of
the object being processed or the environment of the processing
chamber; and that introduced through leaks or other openings in the
processing chamber. Acceptable levels of contamination will be
dependent on the nature and needs of the process, the processing
equipment and environment utilized, and the source and nature of
the materials used. Thus, composition of the gaseous atmosphere
describes the relevant composition and disregards incident
contamination.
[0060] Use of the invention provides semiconductor wafer and device
fabrication at reduced thermal budgets. Such semiconductor devices
having reduced thermal budgets will have improved performance
characteristics due to reduced dopant diffusion
[0061] Although specific embodiments have been illustrated and
described herein, it will be appreciated by those of ordinary skill
in the art that any arrangement which is calculated to achieve the
same purpose may be substituted for the specific embodiments shown.
For example, the present invention is not so limited to the
exemplary embodiment. Furthermore, more than one object may be
processed simultaneously without departing from the scope herein.
Additionally, those skilled in the art will recognize that
processing may occur batchwise or in a continuous process.
Therefore, this application is intended to cover any adaptations or
variations of the present invention and it is manifestly intended
that this invention be limited only by the claims and the
equivalents thereof.
* * * * *