U.S. patent application number 10/966125 was filed with the patent office on 2005-05-12 for molecular airborne contaminants (macs) film removal and wafer surface sustaining system and method.
This patent application is currently assigned to Rudolph Technologies, Inc.. Invention is credited to Darwin, Michael, Wolf, Robert Gregory.
Application Number | 20050098264 10/966125 |
Document ID | / |
Family ID | 34465197 |
Filed Date | 2005-05-12 |
United States Patent
Application |
20050098264 |
Kind Code |
A1 |
Wolf, Robert Gregory ; et
al. |
May 12, 2005 |
Molecular airborne contaminants (MACs) film removal and wafer
surface sustaining system and method
Abstract
A MACs mitigation system includes a MACs film removal sub-system
(14) and a wafer surface sustaining sub-system (16) for sustaining
or maintaining the cleaned surface (18A) of a wafer (18) in a
substantially MACs-free condition for some predetermined period of
time, such as the typical amount of time required after MACs film
removal to perform a desired measurement on the wafer using a
metrology tool (12). The MACs film removal sub-system can comprise
a source (14A) of microwave energy that beneficially both heats and
dissociates the chemical constituents of the MACs film. The wafer
surface sustaining sub-system can be co-located with a measurement
stage portion of the metrology tool, and preferably includes an
atmosphere provided by a source (20) of clean gas.
Inventors: |
Wolf, Robert Gregory;
(Hackettstown, NJ) ; Darwin, Michael; (Long
Valley, NJ) |
Correspondence
Address: |
HARRINGTON & SMITH, LLP
4 RESEARCH DRIVE
SHELTON
CT
06484-6212
US
|
Assignee: |
Rudolph Technologies, Inc.
|
Family ID: |
34465197 |
Appl. No.: |
10/966125 |
Filed: |
October 14, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60511209 |
Oct 14, 2003 |
|
|
|
Current U.S.
Class: |
156/345.32 ;
134/1.1; 134/2 |
Current CPC
Class: |
H01L 21/0206 20130101;
H01L 21/67028 20130101 |
Class at
Publication: |
156/345.32 ;
134/001.1; 134/002 |
International
Class: |
C23F 001/00; C25F
001/00 |
Claims
What is claimed is:
1. A molecular airborne contaminates (MACs) mitigation system
comprising: a first system for removing a MACs film from a surface
of a wafer by directing energy towards the surface; and a second
system for sustaining the surface of the wafer in a substantially
MACs-free condition for some predetermined period of time.
2. A MACs mitigation system as in claim 1, where the predetermined
period of time is at least equal to the time required after MACs
film removal to perform a desired measurement sequence or a series
of measurements on the wafer using a metrology tool.
3. A MACs mitigation system as in claim 1, where said first system
comprises a source of microwave energy that is directed towards the
MACs film.
4. A MACs mitigation system as in claim 3, where the source of
microwave energy both heats and dissociates chemical constituents
of the MACs film.
5. A MACs mitigation system as in claim 1, where said first system
further comprises a source of heated or clean, dry gas that is
directed towards the MACs film.
6. A MACs mitigation system as in claim 1, where said first system
comprises a source of ultraviolet radiation that is directed
towards the MACs film.
7. A MACs mitigation system as in claim 1, where said first system
comprises a source of microwave energy that is directed towards the
MACs film, and a source of heated or dry, clean gas that is
directed towards the MACs film.
8. A MACs mitigation system as in claim 1, where said first system
comprises a source of microwave energy that is directed towards the
MACs film, and a source of ultraviolet radiation that is directed
towards the MACs film.
9. A MACs mitigation system as in claim 1, where said first system
comprises a source of microwave energy that is directed towards the
MACs film, a source of heated or clean, dry gas that is directed
towards the MACs film; and a source of ultraviolet radiation that
is directed towards the MACs film.
10. A MACs mitigation system as in claim 1, where said second
system is co-located with a measurement stage portion of the
metrology tool, and comprises an atmosphere provided by a source of
clean gas characterized by a complete or partial absence of at
least one of hydrocarbons, water and any other substance capable of
promoting the growth of a MACs film on the surface of the
substrate.
11. A MACs mitigation system as in claim 1, where said first system
and said second system are subject to the same environment.
12. A metrology system, comprising: a metrology tool; and a
molecular airborne contaminates (MACs) mitigation system comprising
a first system for removing a MACs film from a surface of a wafer
by directing energy towards the surface and a second system for
sustaining the surface of the wafer in a substantially MACs-free
condition for some predetermined period of time.
13. A metrology system as in claim 12, where said second system is
co-located with a measurement stage portion of said metrology tool
and comprises an atmosphere provided by a source of clean gas
characterized by a complete or at least partial absence of at least
one of hydrocarbons, water and any other substance that is capable
of promoting the growth of a MACs film on the surface of the
substrate.
14. A metrology system as in claim 12, where said metrology tool
comprises an ellipsometer.
15. A metrology system as in claim 12, where said metrology tool
comprises a reflectometer.
16. A molecular airborne contaminates (MACs) mitigation system
comprising: a first system for removing a MACs film from a surface
of a wafer comprising MACs removal means comprised of directed
energy means; and a second system for sustaining the surface of the
wafer in a substantially MACs-free condition for some predetermined
period of time at least equal to the time required after MACs film
removal to perform a desired measurement on the wafer using a
metrology tool.
17. A MACs mitigation system as in claim 16, where said directed
energy means comprises a source of RF energy.
18. A MACs mitigation system as in claim 16, where said directed
energy means comprises a source of ultraviolet optical energy.
19. A MACs mitigation system as in claim 16, where said directed
energy means comprises a jet of heated gas.
20. A MACs mitigation system as in claim 16, where said directed
energy means comprises a curtain of heated gas.
21. A MACs mitigation system as in claim 16, further comprising
means for cooling said wafer at least during operation of said
first system.
22. A MACs mitigation system as in claim 16, where at least one of
an entrance to or an exit from said first system comprises a
curtain of gas.
23. A MACs mitigation system as in claim 16, further comprising a
hot plate that heats the MACs film by conduction via the wafer.
24. A molecular airborne contaminates (MACs) removal system,
comprising a source providing a stream of gas that is directed
towards a surface of a wafer for removing a MACs film from the
surface.
25. A MACs removal system as in claim 24, where said source
provides chemically clean gas.
26. A MACs removal system as in claim 24, where said source
provides ozone-enriched gas.
27. A MACs removal system as in claim 24, where said source
provides chemically clean gas that is also provided to a MACs film
formation inhibiting system.
28. A MACs removal system as in claim 24, where said source
provides chemically clean gas and comprises a catalytic converter
to remove at least hydrocarbons.
29. A MACs removal system as in claim 28, where heat generated from
a catalytic reaction is used to warm the gas.
30. A MACs removal system as in claim 24, where said source
comprises a heat exchanger.
31. A MACs removal system as in claim 24, further comprising a
heater thermally coupled to a gas flow path for producing a heated
gas flow at least for combusting impurities in the gas flow.
32. A MACs removal system as in claim 3 1, further comprising a
chiller for reducing the temperature of the heated gas flow for at
least one of cooling the wafer and maintaining the wafer at a
temperature that is suitable for operation of a metrology tool.
33. A MACs removal system as in claim 24, further comprising an
ozone generator for generating an ozone-enriched stream of gas.
34. A MACs removal system as in claim 24, further comprising a MACs
film formation inhibiting system for sustaining the surface of the
wafer in a substantially MACs-free condition for some predetermined
period of time at least equal to the time required after MACs film
removal to perform a desired measurement on the wafer using a
metrology tool.
35. A method to inhibit formation of a molecular airborne
contaminates (MACs) film on a surface, comprising: removing a MACs
film from the surface by directing energy towards the surface; and
maintaining the surface in a substantially MACs-free condition for
some predetermined period of time during which a procedure is
performed on or through the surface.
36. A method as in claim 3 5, where the predetermined period of
time is at least equal to the time required after MACs film removal
to perform at least one measurement on a wafer using a metrology
tool.
37. A method as in claim 35, where removing includes directing
microwave energy towards the MACs film.
38. A method as in claim 37, where the microwave energy is selected
to both heat the MACs film and dissociate at least one chemical
constituent of the MACs film.
39. A method as in claim 35, where removing includes directing at
least one of heated gas towards the MACs film, and dry, clean gas
towards the MACs film.
40. A method as in claim 35, where removing includes directing
ultraviolet radiation towards the MACs film.
41. A method as in claim 35, where removing includes directing
microwave energy towards the MACs film, and directing at least one
of heated gas, and dry, clean gas towards the MACs film.
42. A method as in claim 35, where removing includes directing
microwave energy towards the MACs film, and directing ultraviolet
radiation towards the MACs film.
43. A method as in claim 35, where removing includes directing
microwave energy towards the MACs film, directing at least one of
heated gas, and dry, clean gas towards the MACs film, and directing
ultraviolet radiation towards the MACs film.
44. A method as in claim 35, where maintaining occurs at a location
associated with a measurement stage portion of a metrology tool,
and comprises providing an atmosphere from a source of gas having a
complete or at least partial absence of at least one of
hydrocarbons, water and any other substance that is capable of
promoting the growth of a MACs film on the surface.
45. A method as in claim 35, where removing and maintaining are
carried out within the same environment.
46. A method as in claim 35, where said procedure comprises a
measurement procedure that is performed on a surface associated
with a semiconductor wafer.
47. A method as in claim 35, where said procedure comprises an
ellipsometry-based metrology procedure that is performed on or
through a surface associated with a semiconductor wafer.
48. A method as in claim 35, where said procedure comprises a
reflectometry-based metrology procedure that is performed on or
through a surface associated with a semiconductor wafer.
Description
CLAIM OF PRIORITY FROM COPENDING PROVISIONAL PATENT APPLICATION
[0001] This patent application claims priority under 35 U.S.C.
.sctn.119(e) from Provisional Patent Application No. 60/511,209,
filed Oct. 14, 2003, the disclosure of which is incorporated by
reference herein in its entirety.
TECHNICAL FIELD
[0002] This invention relates generally to semiconductor wafer
metrology systems and methods and, more specifically, relates to
methods and apparatus for removing a MACs layer or film from a
surface of a wafer prior to a metrology operation, and for
inhibiting the formation of another MACs film subsequent to the
removal of the MACs film and the start of the metrology
operation.
BACKGROUND
[0003] The measurement of thin transparent layers for semiconductor
applications is an important part of the fabrication process for
advanced transistors. As the geometry and layer thicknesses of
modem transistor devices decrease, the process control requirements
become more stringent. For example, modem transistors require a
gate oxide (e.g., SiO.sub.2) layer thickness in the sub-30 Angstrom
regime.
[0004] It is known that when a gate oxide layer is exposed to the
atmosphere both water and hydrocarbons adhere to the surface of the
layer, causing an immediate growth of a contaminant film at the
rate of a few tenths of an Angstrom per hour (see FIG. 1). These
surface contaminates are also known as molecular airborne
contaminants (MACs), and the resulting contamination film as a MACs
film. Since at present the refractive index of the contamination is
not known, the MACs film thickness is measured as if the film had
the refractive index of the underlying oxide layer. Several
techniques for removing MACs are known in the art, including
thermal, photo-thermal, and other techniques. For example, U.S.
Pat. No. 6,624,393 B2, "Method and Apparatus for Preparing
Semiconductor Wafers for Measurement", Howell et al., discloses a
wafer-cleaning module for removing contaminants from a
semiconductor wafer prior to measurement in a metrology tool. The
cleaning module includes a heating chamber that includes a heater
plate for heating the wafer by conduction. A separate cooling
chamber is provided to cool the wafer. The system is controlled so
that the heating cycle, cooling cycle and the time periods between
these cycles and the measurement cycle are uniform for all
wafers.
[0005] Also by example, U.S. Pat. No. 6,325,078 B2, "Apparatus and
Method for Rapid Photo-Thermal Surface Treatment", Kamieniecki,
discloses a system for surface treating a semiconductor wafer that
includes a surface treatment chamber and a source of radiation. The
semiconductor wafer is disposed inside the chamber and is
illuminated with radiation sufficient to create or generate a
plurality of electron-hole pairs near the surface of the wafer.
This technique is said to desorb ions and molecules adsorbed on the
surface of the wafer.
[0006] Once the MACs film is removed, however, the re-growth of the
MACs film on the wafer surface begins anew. Further, and referring
again to FIG. 1, it can be seen that during the initial stage of
MACs film growth the growth rate is the most rapid.
[0007] The gate oxide layer measurement problems that arise due to
the presence of the MACs film have to do with the relative apparent
thickness of the MACs film as a fraction of the total (desired)
layer thickness. As the desired layer(s) become thinner (e.g., when
a gate oxide layer is required to have a thickness of less than 30
Angstroms), the percent of the total layer thickness due to the
presence of the MACs film becomes substantial. These effects cause
the most difficulty for metrology tool calibration and matching,
but also complicate and detrimentally affect tool acceptance
qualification, tool monitoring and overall process control. As but
one example, if a metrology tool is expected to exhibit some
stringent degree of repeatability of layer thickness measurements
(e.g., less than one tenth Angstrom) over a period of, for example
several days, and if a MACs film is continually increasing in
thickness on a test wafer over the same period of time (e.g.,
starting at an initial rate of a few tenths of an Angstrom per
hour), then the required degree of layer thickness measurement
repeatability will be impossible to meet. Furthermore, it becomes
very difficult to ascertain whether the metrology tool is operating
within its required parameters, or whether there may actually be a
tool-related repeatability problem.
[0008] Thus, given that the repeatability of an advanced metrology
system, such as an ellipsometry-based metrology tool system, may be
0.04 Angstroms for a period of five days, it can be appreciated
that it is most desirable to remove the MACs film, and to also
sustain the underlying wafer surface in a MACs-free condition, to a
degree that is better than the repeatability level of the metrology
tool. The effectiveness of the MACs film removal system should thus
be substantially better than the repeatability of the metrology
tool, and the wafer surface sustaining system should have the
ability to maintain the surface state to be essentially MACs-free
for at least the duration of the longest typical tool measurement.
Since the longest measurement may last up to 10 minutes or more, a
system is needed that will maintain the clean surface of the wafer
for at least that duration of time. Without the surface sustaining
system, the MACs film removal system alone will operate so as to
de-stabilize the wafer surface, resulting in the MACs film being in
its most rapid state of re-growth (see FIG. 1 once again) as soon
as the MACs film is removed.
[0009] Proposed solutions to this problem to date include
aggressive methods to drive off the MACs film by baking the wafer.
However, the amount of heating required may cause problems for
process wafers since the temperatures required are in excess of 100
degrees C. What is needed is a process compatible method that will
quickly remove the MACs from a wafer surface, and then sustain the
surface in a MACs free state for the duration of the longest
typical measurement run.
[0010] Additionally, in order to be compatible with current
metrology, the process compatible MACs film removal method should
not impede the throughput of the system. For example, the
conduction-based heater plate approach may require some number of
minutes to heat the wafer surface sufficiently to drive off a MACs
film. Further, in order to achieve process compatibility, the
method should also have a low thermal and UV exposure level.
Furthermore, the MACs film removal process should not generate
undesirable environmental effects, such as excessive amounts of
ozone that can be generated by UV radiation-based MACs film removal
techniques.
[0011] The use of microwave plasmas and microwave energy for the
general pre-heating, as well as cleaning, of semiconductor wafers
is known. Reference can be made, as examples, to U.S. Pat. No.
5,449,411, "Microwave Plasma Processing Apparatus", Fukuda et al.,
and to U.S. Patent No.: 5,261,965, "Semiconductor Wafer Cleaning
Using Condensed-Phase Processing", Moslehi. This latter U.S. Patent
describes a method and system for semiconductor wafer cleaning
within a condensed-phase processing environment that is based on
first cooling the semiconductor wafer to a predetermined
temperature (e.g., -100 degrees Celsius to -150 degrees Celsius) in
order to condense a liquid film on the surface of the semiconductor
wafer from a condensable process gas or gas mixture (e.g., water,
alcohol, HCl, HF and Cl). Thermally activated surface reactions are
then promoted in order to rapidly evaporate the liquid film from
the semiconductor wafer surface using a high peak power, short
pulse duration energy source, such as a pulsed microwave source.
This process is said to both dissolve surface contaminants and
produce drag forces sufficiently large to remove particulates and
other surface contaminants from the surface of the semiconductor
wafer. The method and system are said to be capable of removing
various organic, metallic, native oxide, and particulate
contaminants from the surface of the wafer. The method and system
can be used for both pre-process and post-process wafer
cleaning.
[0012] At least one disadvantage of the Moslehi technique is the
requirement to cool the wafer in the presence of the condensable
process gas or gas mixture in order to form the liquid film layer
of the wafer surface.
[0013] What is thus needed is a method to remove the MACs-based
contamination layer from the surface of a wafer, and to also then
sustain the wafer surface in a substantially MACs-free state to
prevent or inhibit the formation of another MACs film prior to
making a desired metrology measurement or measurements.
[0014] Based on the foregoing discussion, it should be apparent
that there are a number of problems with the existing conduction
heating, optical energy and microwave energy wafer cleaning
systems, as well as with maintaining a cleaned wafer in a condition
that inhibits the rapid re-growth of another MACs film. Prior to
this invention these problems were not adequately addressed.
SUMMARY OF THE PREFERRED EMBODIMENTS
[0015] The foregoing and other problems are overcome, and other
advantages are realized, in accordance with the presently preferred
embodiments of these teachings. Disclosed in accordance with
embodiments of this invention is a MACs mitigation system that
comprises a first system for removing a MACs film from a surface of
a wafer by directing energy towards the surface, and a second
system for sustaining the surface of the wafer in a substantially
MACs-free condition for some predetermined period of time.
[0016] Also disclosed in accordance with embodiments of this
invention is a metrology system that includes a metrology tool and
a MACs mitigation system that comprises a first system for removing
a MACs film from a surface of a wafer by directing energy towards
the surface and a second system for sustaining the surface of the
wafer in a substantially MACs-free condition for some predetermined
period of time.
[0017] Also disclosed in accordance with embodiments of this
invention is a MACs mitigation system that comprises a first system
for removing a MACs film from a surface of a wafer, where the first
system comprises a MACs removal means having directed energy means;
and a second system for sustaining the surface of the wafer in a
substantially MACs-free condition for some predetermined period of
time at least equal to the time required after MACs film removal to
perform a desired measurement on the wafer using a metrology
tool.
[0018] Also disclosed in accordance with embodiments of this
invention is a MACs removal system that comprises a source that
provides a stream of gas that is directed towards a surface of a
wafer for removing a MACs film from the surface.
[0019] Also disclosed in accordance with embodiments of this
invention is a method to inhibit formation of a MACs film on a
surface, comprising removing a MACs film from the surface by
directing energy towards the surface; and maintaining the surface
in a substantially MACs-free condition for some predetermined
period of time during which a procedure is performed on or through
the surface.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The foregoing and other aspects of these teachings are made
more evident in the following Detailed Description of the Preferred
Embodiments, when read in conjunction with the attached Drawing
Figures, wherein:
[0021] FIG. 1 is graph showing the increase in thickness of a MACs
film as a function of time;
[0022] FIG. 2 is an overall metrology system block diagram, where
the metrology system includes a MACs film removal station or
sub-system, and a wafer surface sustaining station or sub-system;
and
[0023] FIG. 3 is a block diagram of a system for providing clean
gas to the wafer surface sustaining station, and possibly also to
the MACs film removal station.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] Reference may be had to commonly assigned U.S. Pat. Nos.
6,519,045; 6,621,582; 6,504,618, 6,256,097; and 5,166,752,
incorporated by reference herein in their entireties, for
describing various aspects of metrology systems and methods for
performing at least reflectometry-based and ellisometry-based
measurements. Interferometry-based measurements are also within the
scope of these teachings.
[0025] For example, commonly-assigned U.S. Pat. No. 6,519,045
describes in part a thickness metrology apparatus and method for
accurately determining the actual thickness of thin dielectric film
on a semiconductor wafer. As described in the commonly-assigned
U.S. Patent the wafer is subjected to a heat treatment, such as
baking at a heating station of the apparatus, to cause desorption
of organic compounds from the film. The treated wafer is
transferred to a measurement stage where the thickness of the film
is measured by an ellipsometer, for example. The actual thickness
of the film is determined from the measured thickness and a change
in the measured film thickness as a function of time for the film
due to absorption of organic compounds onto the film following
desorption of organic compounds therefrom. U.S. Pat. No. 6,519,045
also describes the use of an optional inert atmosphere system,
whether in the form of purging the wafer with inert gas or in the
form of a vacuum chamber, that serves to extend the period of time
during which the actual thickness of the thin film oxide on the
wafer can be measured without the accumulation of organic compounds
on the surface of the wafer causing an increase in the measured
thickness of the oxide layer. The duration of this extended period
of time is said to range up to tens of minutes. In the absence of
the inert atmosphere system, there is a stable thickness time of
approximately three minutes.
[0026] Referring now to FIG. 2, there is shown a metrology system
10 in accordance with embodiments of this invention that has a
metrology tool or instrument 12, such as an ellipsometer tool, and
a MACs film removal system 14 and a wafer surface sustaining system
16. As used herein the wafer surface sustaining system 16 is
considered to be some means that is suitable for inhibiting the
regrowth of a MACs film on a surface 18A of a wafer 18 from which a
MACs film was removed by the MACs film removal system 14, or by
some other technique, such as by processing the wafer 18 in such a
manner as to drive off a pre-existing MACs film. The wafer surface
sustaining system 16 is preferably co-located with the tool 12
measurement stage for maintaining the surface 18A of wafer 18
substantially free of MACs layer re-growth, after the MACs layer is
removed by the MACs film removal system 14, both prior to and
during the operation of the metrology tool 12. The MACs film
removal system is also preferably located within the region of the
surface sustaining environment such that there are no contaminants
available to re-contaminate the surface of the wafer 18.
[0027] In FIG. 2 the MACs film removal system 14 can comprise hot
clean gas comprised of air, or N.sub.2, or some other suitable gas
or mixture of gases, including one containing ozone, where "clean"
refers to a complete or at least partial absence of hydrocarbons
and/or water and/or any other substance that is capable of
promoting the growth of a MACs film on the surface 18A of the
substrate 18. The hot clean gas can be applied as one or more jets,
or by an air knife, and can be used to remove or aid in the removal
of the MACs film.
[0028] The MACs film removal system 14 can also include a source
14A of microwave energy, such as a magnetron or a klystron having
an operating frequency in a range of about 1 GHz to about 10 GHz,
and an output power in a range of about 10.sup.2-10.sup.5 Watts.
One suitable embodiment uses a magnetron operating at a frequency
of about 2.4 GHz and an output power of about 1 KW. Under these
conditions a 20 second exposure of the wafer 18 to the microwave
energy has been found to be sufficient to remove substantially all
of the MACs film from the surface 18A of the wafer 18. This
contrasts very favorably with the several minutes required to bake
off the MACs film using the conduction-based hot plate approach.
The use of microwave energy is not believed to generate or create
any electron-hole pairs in the semiconductor material of the wafer
18. The wafer 18 appears to the microwave energy at the frequencies
of interest as a resistive element, and any already available free
electrons in the semiconductor wafer 18 are caused to move within
the wafer crystalline lattice by the oscillating electrical field
of the microwave energy, thereby generating heat in the wafer 18
(e.g., it has been found that the surface 18A of the wafer 18 is
raised to about 250 degrees Celsius after 20 seconds of microwave
energy exposure at 2.4 GHz and an output power of about 1 KW). The
heating effect is, however, also felt directly by the overlying
gate oxide layer and by the MACs film disposed atop the gate oxide
layer. Thus, the use of the microwave source 14A can more rapidly
drive off the MACs by both heating the wafer 18 and the
contaminating molecules themselves. The use of the microwave energy
is also believed to directly heat and/or dissociate at least some
of the organic molecules found in the MACs film, or heat to such an
extent that an oxygen takes place on at least some of the organic
molecules found in the MACs film, thereby even more effectively
removing the MACs film from the surface 18A of the wafer 18. If
desired, the wafer 18 can be maintained on a cool surface, such as
on a thermoelectric (TE). cooler 14B, during the RF excitation. In
this case it is clearly just the MACs film, and possibly also the
underlying gate oxide layer, that are raised significantly in
temperature by the RF microwave energy.
[0029] The MACs film removal system 14 can also comprise ozone
enriched water, a hot-plate, and/or a UV light source 14C.
[0030] The wafer surface sustaining system 16 can have an
atmosphere comprised of a chemically clean gas or gas mixture, such
as N.sub.2, or air, or an ozone-enriched air or nitrogen atmosphere
at ambient or elevated temperatures. A source 20 of chemically
clean gas can be shared between the removal system 14 and the
sustaining system 16, such that each is subject to the same
environment, and can comprise a chemical filter and/or a system
that "burns" or converts, via a catalytic converter (e.g., one
based on platinum or palladium metal), any remaining hydrocarbons
and other contaminates to gases. In this regard it is noted that
most if not all organic materials of interest to this invention
burn at or below about 300 degrees Celsius, and that the hot gas
can be cooled by expansion and a heat exchanger 32 (see FIG. 3,
discussed below). In this embodiment any residual heat from the
catalytic reaction may be used to warm the gas for the removal
system 14 and/or the sustaining system 16. The residual heat from
the catalytic system may be removed via the heat exchanger 32, such
as one located between the gas input and output so as to both
pre-heat the input gas and cool the output gas.
[0031] Reference in this regard can be made to FIG. 3, which shows
that the source 20 of chemically clean gas may comprise a gas
source 30 (e.g., a cylinder of purified clean air or nitrogen), the
heat exchanger 32, a catalytic converter 34, a heater 36 (e.g., a
gas torch or an electrical heating element) thermally coupled to a
gas flow line 38 for combusting any remaining impurities in the gas
flow, and a chiller 40 (such as a water bath or some other heat
removal means) for reducing the temperature of the clean gas flow
to a desired temperature for at least one of cooling the wafer 18,
after the MACs film removal operation, and maintaining the wafer 18
at a temperature that is suitable for operation of the metrology
tool 12 (e.g., less than about 30 degrees Celsius). In accordance
with an aspect of this invention the gas at the output 42 of the
gas delivery system shown in FIG. 3 is ultra-clean, and is used to
form the atmosphere in the wafer surface sustaining system 16 for
inhibiting the re-growth of a MACs film prior to the operation of
the metrology tool 12, and possibly also in the MACs film removal
system 14, as was noted above. Another output 44 can be taken
before the heat exchanger 32 and chiller 40 to provide a source of
hot clean gas for the air knife and or hot air curtain 22B, if
used.
[0032] The source 20 of chemically clean gas can also comprise an
ozone assisted chemical reaction, and a method of producing the
clean gas can be a part of a method for producing ozone for use in
the ozone-enriched air or other gas.
[0033] A wafer removal system 22 of the metrology system 10,
between the MACs film removal system 14 and the surface sustaining
system 16, can include a clean air or gas curtain 22A. This can be
placed at an entrance to the environment of the sustaining system
16 (e.g., at the entrance to the measurement stage area of the
metrology tool 12). In this case the wafer measurement environment
that forms a part of the metrology tool 12 can thus be treated to
remove contaminants. For example, the clean gas delivery tubing can
be treated to remove contaminants, such as by using a chemical
filter, or a thermal process to burn off contaminates, and/or a
catalytic converter to trap and remove contaminates, as was
described above with respect to FIG. 3.
[0034] In one presently preferred embodiment the MACs film removal
system 14 includes a radio frequency (RF) device, such as a
microwave source, that simultaneously heats the surface adsorbed
contaminants (the MACs film) and the wafer 18. The RF heating
device can be designed as a wafer pass-through system, and it may
include a second integral clean air curtain 22B that isolates the
atmosphere of the removal system 14 from the ambient atmosphere by
excluding external air, as well as possibly facilitating the
removal of the MACs film (such as with the heated air knife) as the
wafer 18 is placed within the removal system 14. The first air
curtain 22A can also be used to facilitate the cooling of the wafer
18 prior to the start of a metrology operation, so that the wafer
temperature is within a range of acceptable temperatures for
operation of the metrology tool. The use of the air curtain or air
stream 22A to cool the wafer 18 prior to the measurement can be
used to beneficially eliminate a separate cooling stage at the
output of the MACs film removal system 14.
[0035] While it is known in the prior art to employ a stream of air
for preventing the entry of ambient air into a chamber, the use of
an air curtain or stream or knife for MACs film removal, and for
the other related purposes described herein, has not, to the
knowledge of the inventors, been previously proposed or used.
Reference with regard to one prior art technique can be made to
U.S. Pat. No. 6,056,544, "Apparatus for Baking Resists on
Semiconductor Wafers", Cho. This U.S. Patent describes an apparatus
for baking resists on semiconductor wafers that is capable of
preventing cold air from entering the interior of the baking
chamber during a baking process. This is accomplished by
controlling the temperature of ambient air surrounding the baking
chamber to equal the internal temperature of the baking chamber.
The control is achieved by providing a hot air supply unit and
nozzles. The hot air supply unit generates hot air heated to a
desired temperature and supplies the generated hot air to the
nozzles that are arranged near the baking chamber. The nozzles
inject the hot air onto the outer surface of the baking chamber.
The nozzles may be arranged around the entrance ofthe baking
chamber where a wafer to be baked is loaded. In this case, the
nozzles are said to inject heated air onto opposite surfaces of a
wafer being loaded or unloaded. The baking apparatus may have a
configuration including a cooling chamber, a feeding chamber and a
baking chamber. In this case, the baking apparatus carries out a
baking process in a sealed condition.
[0036] Based on the foregoing description, it can be appreciated
that in one aspect thereof this invention provides a MACs
mitigation system that includes a MACs film removal sub-system and
a wafer surface sustaining sub-system (i.e., a sub-system for
sustaining or maintaining the cleaned surface of the wafer in a
substantially MACs-free condition for some predetermined period of
time, such as the typical amount of time required after MACs film
removal to perform a desired measurement on the wafer using a
metrology tool).
[0037] In another aspect thereof this invention provides a MACs
removal system where a MACs film is removed by a hot air knife that
flows a dry, clean gas. If desired, a rinse with de-ionized (DI)
water may precede the use of the hot air knife.
[0038] In another aspect thereofthis invention provides a MACs
removal system where a MACs film is removed by radio frequency
energy, either alone or in combination with a clean gas.
[0039] In another aspect thereof this invention there is provided a
MACs removal system where a MACs film is removed by a combination
of a hot, clean gas and optical excitation, preferably ultraviolet
(UV) light excitation, such as Vacuum UV (VUV).
[0040] In a further aspect thereof this invention provides a system
where a wafer surface sustaining environment involves chemically
filtered gas that is integrated into a metrology tool.
[0041] In a still further aspect thereof this invention provides a
MACs removal and a wafer surface sustaining system where the
sustaining and removal systems are linked such that the hot gas
knife acts also as an air curtain for excluding MACs-contaminated
gasses out of the sustaining environment.
[0042] In another aspect thereof this invention provides a MACs
film removal system where thermal energy is applied to the wafer
surface via an air knife, and where the thermal insult to the wafer
is reduced. Since the MACs effectively boil off, most of the energy
applied goes into the desorption until the MACs film is completely
removed. The air knife also serves as a barrier to contaminated air
that would otherwise enter the measurement environment.
[0043] In accordance with embodiments of this invention there is
provided a MACs mitigation system that includes a first system for
removing a MACs film from a surface of a wafer and a second system
for sustaining the surface of the wafer in a substantially
MACs-free condition for some predetermined period of time. The
predetermined period of time is at least equal to the time required
after MACs film removal to perform a desired measurement on the
wafer using a metrology tool. The first system may comprise a
source of microwave energy that is directed towards the MACs film.
Preferably the source of microwave energy both heats and
dissociates chemical constituents of the MACs film. The first
system can also comprise a source of heated gas that is directed
towards the MACs film (e.g., as in an air knife embodiment), and/or
it can comprise a source of ultraviolet radiation that is directed
towards the MACs film. In a presently preferred embodiment the
second system is co-located with a measurement stage portion of the
metrology tool, and comprises an atmosphere provided by a source of
clean gas, where "clean" refers to a complete or at least partial
absence of hydrocarbons and/or water and/or any other substance
that is capable of promoting the growth of a MACs film on the
surface of the substrate.
[0044] Also disclosed herein in accordance with further embodiments
of this invention is a metrology system that includes a metrology
tool, such as an ellipsometer or a reflectometer, and a MACs
mitigation system. The MACs mitigation system includes a first
system for removing a MACs film from a surface of a wafer and a
second system for sustaining the surface of the wafer in a
substantially MACs-free condition for some predetermined period of
time.
[0045] Also disclosed herein in accordance with further embodiments
of this invention is a MACs mitigation system that includes a first
system for removing a MACs film from a surface of a wafer using any
suitable means, including one or more of thermal, optical, and
chemical means, and a second system for sustaining the surface of
the wafer in a substantially MACs-free condition for some
predetermined period of time at least equal to the time required
after MACs film removal to perform a desired measurement on the
wafer using a metrology tool.
[0046] As non-limiting examples, the thermal means can comprise one
or more of RF energy, a hot plate that heats the MACs film by
conduction via the wafer, and a source of heated gas that is
directed towards the MACs film. The optical means may comprise a
source of ultraviolet optical energy, such as a lamp or a
laser.
[0047] The foregoing description has provided by way of exemplary
and non-limiting examples a full and informative description of the
best method and apparatus presently contemplated by the inventors
for carrying out the invention. However, various modifications and
adaptations may become apparent to those skilled in the relevant
arts in view of the foregoing description, when read in conjunction
with the accompanying drawings and the appended claims. As but some
examples, the use of other similar or equivalent temperatures,
wafers, layer thicknesses and the like may be attempted by those
skilled in the art. However, all such and similar modifications of
the teachings of this invention will still fall within the scope of
this invention.
[0048] Further, while this invention has been described in the
context of an ellipsometer metrology tool, the teachings herein
apply as well to reflectometry-based metrology tools.
[0049] Further still, some of the features of the present invention
could be used to advantage without the corresponding use of other
features. For example, the MACs film removal system 14 could be
used without the wafer surface sustaining system 16, if the start
of the wafer measurement can be assured to occur within some short
period of time, and if a received wafer is guaranteed to be free of
a MACs film (e.g., a wafer that has just undergone high temperature
processing), then the wafer surface sustaining system 16 could be
used without the MACs film removal system 14. As such, the
foregoing description should be considered as merely illustrative
of the principles of the present invention, and not in limitation
thereof.
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