U.S. patent application number 10/225590 was filed with the patent office on 2004-02-26 for optical path improvement, focus length change compensation, and stray light reduction for temperature measurement system of rtp tool.
Invention is credited to Brown, Douglas, Koch, Mathias, Meadows, Robert David, Tao, David.
Application Number | 20040037347 10/225590 |
Document ID | / |
Family ID | 31495311 |
Filed Date | 2004-02-26 |
United States Patent
Application |
20040037347 |
Kind Code |
A1 |
Brown, Douglas ; et
al. |
February 26, 2004 |
OPTICAL PATH IMPROVEMENT, FOCUS LENGTH CHANGE COMPENSATION, AND
STRAY LIGHT REDUCTION FOR TEMPERATURE MEASUREMENT SYSTEM OF RTP
TOOL
Abstract
The present invention is directed to a pyrometer system and
comprises an elevator tube. The elevator tube comprises an inner
tube and an outer tube surrounding the inner tube in telescoping
arrangement and extending from a top to a bottom thereof, the
arrangement defining a fluid passageway therebetween. The elevator
tube further comprises a port associated with the outer tube that
is operable to transmit a cooling gas therethrough into the fluid
passageway. A pyrometer head is coupled to the bottom of the inner
tube and is operable to transmit and receive radiation through the
inner tube. The system further comprises a spider collar coupled to
at least one of a top of the inner tube or outer tube, and is
operable to support a work piece for thermal measurement
thereof.
Inventors: |
Brown, Douglas; (South
Hamilton, MA) ; Meadows, Robert David; (Portland,
OR) ; Tao, David; (Saugus, MA) ; Koch,
Mathias; (Andover, MA) |
Correspondence
Address: |
ESCHWEILER & ASSOCIATES, LLC
NATIONAL CITY BANK BUILDING
629 EUCLID AVE., SUITE 1210
CLEVELAND
OH
44114
US
|
Family ID: |
31495311 |
Appl. No.: |
10/225590 |
Filed: |
August 22, 2002 |
Current U.S.
Class: |
374/130 |
Current CPC
Class: |
G01J 5/02 20130101; G01J
5/061 20130101; G01J 5/0255 20130101; G01J 5/046 20130101; G01J
5/0875 20130101; G01J 5/04 20130101; G01J 5/0806 20130101; G01J
5/0893 20130101; H01L 21/67248 20130101; G01J 5/0003 20130101; G01J
5/08 20130101; G01J 5/0846 20130101; G01J 5/084 20130101; G01J
5/0007 20130101; G01J 5/045 20130101 |
Class at
Publication: |
374/130 |
International
Class: |
G01J 005/00 |
Claims
What is claimed is:
1. A pyrometer system, comprising: an elevator tube, comprising: an
inner tube extending from a top to a bottom thereof; and an outer
tube surrounding the inner tube in telescoping arrangement and
extending from a top to a bottom thereof, and defining a fluid
passageway between the inner and outer tubes; a port associated
with the outer tube, and operable to transmit a cooling gas
therethrough into the fluid passageway; a pyrometer head coupled to
the bottom of the inner tube, and operable to transmit and receive
radiation through the inner tube; and a spider collar coupled to at
least one of a top of the inner tube or outer tube, and operable to
support a work piece.
2. The pyrometer system of claim 1, wherein the bottom of the inner
tube and the outer tube are fluidly sealed local to the pyrometer
head to fluidly isolate an interior of the inner tube from the
fluid passageway.
3. The pyrometer system of claim 1, further comprising a lens
positioned at the top of the inner tube and substantially fluidly
isolating an interior of the inner tube at the top thereof.
4. The pyrometer system of claim 1, further comprising a fluid
direction device associated with the top of at least one of the
inner tube and the outer tube, wherein the fluid direction device
is operable to direct the cooling gas from the fluid passageway to
a predetermined area of the work piece.
5. The pyrometer system of claim 4, wherein the fluid direction
device comprises a substantially radiation transparent frustum
shaped cone having a first area at a base portion and a second area
at an end portion, and wherein the base portion is coupled to the
spider collar, the first area is larger than the second area, and
the first area is sufficiently large to direct the cooling gas from
the fluid passageway to a wafer area associated with the second
area of the end portion of the cone.
6. The pyrometer system of claim 1, wherein the inner tube is
fluidly isolated from the fluid passageway.
7. The pyrometer system of claim 6, further comprising: a port
associated with the inner tube; and a vacuum pump operable to
connect to the port associated with the inner tube, and generate a
vacuum within the inner tube.
8. The pyrometer system of claim 1, wherein the spider collar is
coupled to the top of the outer tube, further comprising: a sleeve
having a bottom portion coupled to the top of the inner tube and
extending therefrom to a top portion thereof; and a lens coupled to
the top portion of the sleeve and positioned a predetermined
distance from the work piece when supported by the spider collar,
wherein the sleeve has a coefficient of thermal expansion that
causes the sleeve to thermally expand with an increase in
temperature and thereby alter the predetermined distance between
the lens and the work piece, and wherein the lens has a focal
length that decreases with an increase in temperature, and wherein
the sleeve provides compensation in the predetermined distance for
changes in the focal length of the lens due to variations in
temperature.
9. The pyrometer system of claim 8, wherein the top portion of the
sleeve substantially covers a side portion of the lens, and wherein
the sleeve is substantially opaque to radiation, thereby reducing
an amount of stray light from reflecting off the lens and into the
elevator tube.
10. The pyrometer system of claim 8, further comprising a ring seal
coupled between the top of the inner tube and the bottom portion of
the sleeve in an inner concentric portion, and coupled between a
lower portion and an upper portion of the outer tube in an outer
concentric portion, and having an annular hole in a center portion
corresponding to the fluid passageway for permitting the cooling
gas to pass therethrough.
11. The pyrometer system of claim 1, further comprising a processor
coupled to the pyrometer head, wherein the processor is operable to
receive radiation intensity data and reflectivity data associated
with a radiometry channel and a reflectometry channel,
respectively, and calculate a wafer temperature in accordance
therewith.
12. The pyrometer system of claim 11, wherein the processor is
further operable to extract a wafer emissivity from the
reflectivity data and calculate the wafer temperature using the
radiation intensity data and the wafer emissivity.
13. A pyrometer system, comprising: a tube having a top portion and
a bottom portion associated therewith; a pyrometer head associated
with the bottom portion of the elevator tube, and operable to
transmit and receive radiation through the tube; a sleeve
associated with the top portion of the elevator tube; and a lens
coupled to the sleeve, the lens having a focal length associated
therewith which is related to a distance of a work piece positioned
therefrom, wherein the focal length is a function of temperature,
and wherein the sleeve has a coefficient of thermal expansion, and
wherein the sleeve alters the distance between the lens and the
work piece due to the coefficient of thermal expansion as a
function of temperature to compensate for changes in the focal
length of the lens due to variations in temperature.
14. The pyrometer of claim 13, wherein the tube comprises an
elevator tube.
15. The pyrometer of claim 14, further comprising a spider collar
coupled to the top portion of the elevator tube, the spider collar
comprising a plurality of pins operable to support the work piece
thereon, and operable to secure the lens in a position which is a
predetermined distance from the work piece at a predetermined
temperature.
16. The pyrometer of claim 15, wherein the spider collar comprises
a material having a coefficient of thermal expansion that is
substantially less than that of the sleeve.
17. The pyrometer system of claim 16, wherein the spider collar
comprises quartz and the sleeve comprises Al.sub.2O.sub.3, and
wherein the coefficient of thermal expansion of the sleeve is about
ten times greater than that of the spider collar.
18. The pyrometer system of claim 17, wherein the Al.sub.2O.sub.3
sleeve comprises one of crystalline Al.sub.2O.sub.3 and amorphous
Al.sub.2O.sub.3.
19. The pyrometer system of claim 13, wherein the sleeve is
substantially opaque to radiation, thereby reducing an amount of
stray light from reflecting off the lens and into the elevator
tube.
20. The pyrometer system of claim 14, wherein the elevator tube
further comprises: an inner tube extending from a top to a bottom
thereof, and engaging the sleeve at the top thereof; and an outer
tube surrounding the inner tube and the sleeve in telescoping
arrangement and extending from a top to a bottom thereof, and
defining a fluid passageway therebetween; and a port associated
with the outer tube, and operable to transmit a cooling gas
therethrough into the fluid passageway, wherein the pyrometer head
is coupled to the bottom of the inner tube, and is operable to
transmit and receive radiation through the inner tube.
21. The pyrometer system of claim 20, further comprising a spider
collar coupled to at least one of a top of the inner tube or outer
tube, and operable to support a work piece at a predetermined
distance from the lens.
22. The pyrometer system of claim 20, wherein the bottom of the
inner tube and the outer tube are fluidly sealed local to the
pyrometer head to fluidly isolate an interior of the inner tube
from the fluid passageway.
23. The pyrometer system of claim 20, wherein the lens is
positioned within the sleeve and substantially fluidly isolates an
interior of the inner tube.
24. The pyrometer system of claim 23, further comprising: a port
associated with the inner tube; and a vacuum pump operable to
connect to the port associated with the inner tube, and generate a
vacuum within the inner tube.
25. The pyrometer system of claim 20, further comprising a fluid
direction device associated with the top of at least one of the
inner tube and the outer tube, wherein the fluid direction device
is operable to direct the cooling gas from the fluid passageway to
a predetermined area of the work piece.
26. The pyrometer system of claim 25, wherein the fluid direction
device comprises a substantially radiation transparent frustum
shaped cone having a first area at a base portion and a second area
at an end portion, and wherein the base portion is coupled to the
spider collar, the first area is larger than the second area, and
the first area is sufficiently large to direct the cooling gas from
the fluid passageway to a wafer area associated with the second
area of the end portion of the cone.
27. The pyrometer system of claim 20, further comprising a ring
seal coupled between the top of the inner tube and the bottom
portion of the sleeve in an inner concentric portion, and coupled
between a lower portion and an upper portion of the outer tube in
an outer concentric portion, and having an annular hole in a center
portion corresponding to the fluid passageway for permitting the
cooling gas to pass therethrough.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to semiconductor
processing systems, and more particularly to a pyrometer system for
measuring a wafer temperature employed in a rapid thermal
processing (RTP) tool.
BACKGROUND OF THE INVENTION
[0002] Thermal processing furnaces have been widely known and used
for many years to perform a variety of semiconductor fabrication
processes, including annealing, diffusion, oxidation, and chemical
vapor deposition. As a result, these processes are well understood,
especially with regard to the impact of process variables on the
quality and uniformity of resulting products. Thermal processing
furnaces typically employ either a horizontal-type furnace or a
vertical-type furnace.
[0003] Both conventional types of furnaces are designed to heat
semiconductor wafers to desired temperatures to promote either
diffusion of implanted dopants to a desired depth while maintaining
substantially small line widths (e.g., smaller than 1 micron), or
to perform other conventional processing techniques, such as the
application of an oxide layer to the wafer or deposition of a
chemical vapor layer to the wafer. The heating requirements of the
wafer during processing are known and well understood, and
therefore are closely monitored.
[0004] Conventional vertical-type thermal processing furnaces, such
as tube furnaces, are designed to support the processing tube
within the furnace in the vertical position. The thermal furnace
also typically employs a wafer boat assembly that is mounted to
appropriate translation mechanisms for moving the wafer boat into
and out of the processing tube. A wafer-handling assembly is
deployed adjacent and parallel to the wafer-boat assembly to
transfer the semiconductor wafers from wafer cassettes to the
wafer-boat assembly. The wafers are then raised into a quartz or
silicon heating tube. The tube is then slowly raised to the desired
temperature and maintained at that temperature for some
pre-determined period of time. Afterwards, the tube is then slowly
cooled, and the wafers are removed from the tube to complete the
processing. A drawback of this processing technique is that it
places constraints on the time-at-temperature to which a wafer can
be subjected.
[0005] As the critical dimensions for silicon integrated circuits
are continuously scaled downward into the sub-micron regime,
requirements for within wafer temperature uniformity and
wafer-to-wafer temperature repeatability become more stringent. For
example, in 0.18 micron technology, the required wafer-to-wafer
temperature repeatability is in the order of about +/-3.degree.
C.
[0006] Pyrometry has been one method of choice for non-contact
temperature measurements of a silicon wafer during processing in a
thermal processing furnace. Pyrometry is based on the principle
that all objects at temperatures above absolute zero emit
electromagnetic radiation as a function of temperature in
accordance with Planck's equation. Based upon that relationship,
the temperature of an object may be determined from a distance by
measuring its emitted radiation. However, the spectral emissivity
value of the surface being measured must be known to calculate the
actual temperature. Typically, silicon wafers have backside layers
that can drastically alter the spectral emissivity of the wafer
through interference effects, which can lead to temperature
measurement errors during processing. Furthermore, the emissivity
of the wafer is also dependent on the backside surface roughness
and wafer temperature. All of these drawbacks make the
determination or prediction of wafer emissivity a difficult
task.
[0007] One technique employed to accurately measure the wafer
temperature using pyrometry comprises modified single-color
pyrometry with wafer emissivity compensation. An exemplary prior
art pyrometry system using such compensation is illustrated in
prior art FIG. 1, and designated at reference numeral 10. The
single-color pyrometer 10 includes an elevator tube 12 (not shown
to scale) having a spider collar 14 coupled to a top portion 16
thereof. The spider collar 14 has several legs 18 (e.g., three (3))
and holds a wafer 20 at a predetermined distance from the tube 12.
The spider collar 14 may further hold an edge ring (not shown) that
may be employed for wafer edge temperature uniformity control.
[0008] A pyrometer head 22 is coupled to a bottom portion 24 of the
elevator tube 12. The pyrometer head 22 contains an optical system
(e.g., a number of lenses and apertures) that facilitates a flash
emission to the wafer 20 and receipt of emitted and reflected light
along or parallel to an optical axis 26. The head 22 operates in
conjunction with a radiometry channel 28 and a reflectometry
channel 30 which communicate signals 32 to a processor 34 for
determination of the wafer temperature.
[0009] In addition, the pyrometry system includes a port 36 coupled
to the elevator tube 12 for the introduction of cooling gas 38,
such as nitrogen, thereto through, for example, a supply line 40.
Because a bell jar (not shown) is typically used to heat the wafer
20, non-uniform heating of the wafer can occur, causing a center
portion thereof to become hotter than peripheral areas. The
elevator tube 12 delivers the cooling gas 38 to a center portion of
the wafer 20 via the port 36 to assist in temperature uniformity
thereat.
[0010] In operation, the pyrometry system 10 employs the radiometry
channel 28 and the reflectometry channel 30 to determine the wafer
temperature in the following exemplary manner. The radiometry
channel 28 records the intensity of radiation emitted from the
wafer 20 as well as radiation originating from stray light from the
bell jar (not shown) and reflected from the wafer. The
reflectometry channel 30 records the reflection intensity
associated with a flash generated by the pyrometer head 22. The
channels 28, 30 deliver the emission data and reflectivity data to
the processor 34 that subtracts the stray light from the radiometry
signal to obtain the black body intensity of the wafer. The
processor 34 further calculates the wafer emissivity by assuming
the emissivity is the complement of the wafer reflectivity, and
thus extracts the wafer emissivity from the reflectometry signal.
The wafer temperature is then calculated or otherwise determined by
the processor 34 by dividing the black body intensity by the wafer
emissivity.
[0011] As seen in prior art FIG. 1, the central optical element of
the pyrometer system 10 is the pyrometer head 22. Since the head 22
is mounted at the bottom of the elevator tube 12 to thermally
isolate the components therein from the work piece that is at an
elevated temperature, the optical path between the wafer 20 and the
head 22 is relatively long, for example, about 1 meter. The
relatively long separation between the wafer 20 and the head 22
requires that the wafer be extremely carefully aligned such that
the wafer normal and the head 22 are aligned with the optical axis
26. Even a small angle or offset of the wafer normal with respect
to the axis 26 causes a loss in reflected and emitted signal
intensity, thereby adversely impacting temperature calculation
accuracy.
[0012] For example, as illustrated in prior art FIGS. 2A and 2B, if
the wafer 20 is not warped or offset (FIG. 2A) the radiation 40 is
fully collected at the bottom 24 of the tube 12 by the head 22,
while wafer warpage or offset (FIG. 2B) may cause reflected light
41 that results in signal loss. In order to correct the above
problem, a lens 42 is inserted at the top portion 16 of the
elevator tube 12 and is held in place via, for example, the spider
collar 14 (not shown) at distance from the wafer that ideally is
the lens focal length (e.g., about 50 mm), as illustrated in prior
art FIG. 2C. The lens 42 re-collects 44 any reflected light 41 that
would otherwise not return to the pyrometer head 22. The lens 42
thus allows or corrects for reflections due to warpage or offset,
thus facilitating use of the pyrometer with both polished or
roughed backside wafers.
[0013] Although the pyrometer system 10 having the lens 42 provides
relatively good results, there is a continuing need in the art for
further refinements and improvements in pyrometry in order to
provide high temperature determination accuracy for rapid thermal
process control.
SUMMARY OF THE INVENTION
[0014] The following presents a simplified summary in order to
provide a basic understanding of one or more aspects of the
invention. This summary is not an extensive overview of the
invention, and is neither intended to identify key or critical
elements of the invention, nor to delineate the scope thereof.
Rather, the primary purpose of the summary is to present some
concepts of the invention in a simplified form as a prelude to the
more detailed description that is presented later.
[0015] In accordance with one aspect of the present invention a
pyrometer system and temperature sensing method is disclosed that
overcomes several disadvantages associated with the prior art. In
particular, a pyrometer having an elevator tube comprising two
tubes in a generally telescopic arrangement is disclosed. A cooling
gas is introduced in a fluid passageway between the tubes to
provide directed cooling to a portion of the wafer or work piece
being sensed. The radiation to and from the wafer during analysis
occurs within the inner tube and is substantially isolated from the
cooling gas, and thus any stratification of gas within the inner
tube is independent of changes in the cooling gas flow rate.
Further, the inner tube may be evacuated to substantially prevent
stratification therein and thereby further improve the optical path
of the pyrometer.
[0016] In accordance with another aspect of the present invention,
a pyrometer system is disclosed comprising an elevator tube having
a pyrometer head associated with a bottom portion and a sleeve
associated with a top portion thereof. A lens is coupled to the
sleeve and is operable to focus radiation/light from a work piece
to the pyrometer head. The lens has a focal length that is related
to the distance of the work piece therefrom, and the focal length
is a function of temperature. The sleeve that is coupled to the
lens has a coefficient of thermal expansion that varies the
distance between the lens and the work piece as temperature varies
in order to compensate for changes in the focal length due to
temperature variations. Accordingly, the lens in conjunction with
the sleeve is operable to transmit light from the work piece to the
pyrometer head without substantial signal loss, thereby improving
pyrometer system accuracy.
[0017] To the accomplishment of the foregoing and related ends, the
following description and annexed drawings set forth in detail
certain illustrative aspects and implementations of the invention.
These are indicative of but a few of the various ways in which the
principles of the invention may be employed. Other aspects,
advantages and novel features of the invention will become apparent
from the following detailed description of the invention when
considered in conjunction with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a combined perspective view and block diagram of a
prior art pyrometer system;
[0019] FIG. 2A is a simplified cross section of a portion of the
prior art pyrometer system of FIG. 1, wherein light from a work
piece enters the elevator tube in a relatively aligned fashion;
[0020] FIG. 2B is a simplified cross section of a portion of the
prior art pyrometer system of FIG. 1, wherein light from a work
piece enters the elevator tube in a relatively non-aligned
fashion;
[0021] FIG. 2C is a simplified cross section of a portion of the
prior art pyrometer system of FIG. 1, wherein light from a work
piece approaches the elevator tube in a relatively non-aligned
fashion and is subsequently aligned using a lens;
[0022] FIG. 3 is a combined perspective view and block diagram of a
pyrometer system in accordance with one aspect of the present
invention;
[0023] FIG. 4 is a perspective view of a fluid direction device
associated with a pyrometer system in accordance with another
aspect of the present invention;
[0024] FIG. 5 is a cross section diagram illustrating an elevator
tube structure for a pyrometer system in accordance with yet
another aspect of the present invention; and
[0025] FIG. 6 is a cross section diagram illustrating an elevator
tube structure and spider collar for supporting a work piece in
accordance with still another aspect of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0026] The present invention will now be described with reference
to the drawings wherein like reference numerals are used to refer
to like elements throughout. The present invention is directed to a
pyrometer system and associated method that provides improvements
over the prior art.
[0027] In one aspect of the invention, the conventional elevator
tube is replaced with two concentrically arranged tubes having a
fluid passageway therebetween. Cooling gas is provided in the fluid
passageway between the tubes, but not in the inner tube, thereby
preventing a stratification of gas within the inner tube to vary
substantially with respect to changes in the cooling gas flow rate.
Further, the inner tube may be fluidly sealed and evacuated in
order to substantially prevent stratification therein to improve
the optical path. In another aspect of the invention, a top portion
of the elevator tube comprises a sleeve that is coupled to a lens.
The sleeve has a coefficient of thermal expansion that operates to
compensate for changes in the focal length of the lens over
temperature, thereby improving the accuracy of the pyrometer
temperature measurement.
[0028] Turning now to the figures, FIG. 3 is a combined perspective
view and block diagram illustrating a pyrometer system 50 in
accordance with one aspect of the present invention. In some
respects, the pyrometer system 50 is similar to the system 10 of
prior art FIG. 1; however, the conventional elevator tube 12 is
replaced with a new type of tube structure 52. The elevator tube 52
of the present invention comprises an inner tube 54 that extends
from a top 56 to a bottom 58 thereof. In one example, the inner
tube 54 extends an entire length of the tube 52 (e.g., about 1 m).
The elevator tube 52 further comprises an outer tube 60 that in one
example surrounds the inner tube 54 concentrically in a telescoping
type arrangement, as illustrated. The outer tube 60 also extends
from a top 62 to a bottom 64 and may be co-extensive with the inner
tube 54 as shown.
[0029] The concentric nature of the inner and outer tubes 54, 60
define a fluid passageway 65 therebetween. A cooling gas port 66
couples to or is otherwise associated with the outer tube 60 in
order for a cooling gas 68 to be delivered into the passageway 65
via a gas line 70. The cooling gas 68 generally flows through the
passageway 65 toward the top 56, 62 of the inner and outer tubes
54, 60 in order to provide cooling to one or more selected portions
of a work piece such as the semiconductor wafer 20. Note that in
FIG. 3, the cooling gas 68 exits the tube 52 in a concentric
manner, however, fluid direction devices (as will be discussed in
greater detail infra) may be employed to direct the cooling gas to
one or more portions of the work piece 20 in a controlled
fashion.
[0030] The pyrometer system 50 further comprises a spider collar 74
which is coupled to or otherwise associated with a top portion of
the elevator tube 52. For example, in FIG. 3, the spider collar 74
is coupled to the top 62 of the outer tube 60; however, it may be
coupled to the inner tube 54 and such alternatives are contemplated
as falling within the scope of the present invention. The spider
collar 74 has a plurality of arms 76 having vertically extending
pins 78 associated therewith, wherein a length 80 of the pins 78
defines a distance 82 (e.g., about 50 mm) between the work piece 20
and the elevator tube 52.
[0031] In accordance with another aspect of the present invention,
the pyrometer system 50 of FIG. 3 further comprises a vacuum pump
90 which is coupled to or otherwise associated with the inner tube
54 via an access portion 92. By fluidly sealing the inner tube 54
at the top 56 and bottom 58 thereof, the vacuum pump 90 may be
employed to evacuate the inner tube 54 which contains the optical
axis 93 for the pyrometer head 22 located at the tube bottom. The
pyrometer head 22 in turn is operably coupled to a control system
96 that includes the radiometry channel 28, reflectometry channel
30 and processor 34 as discrete or integrated components.
[0032] In order to appreciate the advantageous features of the
present invention, a brief discussion will be provided regarding a
shortcoming of the prior art that was appreciated by the inventors
of the present invention. In the prior art elevator tube 12, the
cooling gas therein produces a gas column having a radial and axial
temperature gradient, wherein the gradient is not static, but
rather is a function of the gas volume flow rate. The temperature
gradient in turn causes a dynamic gas density gradient within the
tube 12 which causes a dynamic index of refraction gradient for
light traveling within the tube between the work piece 20 and the
pyrometer head 22. This "gradient index lens" in the tube results
in distortions of the radiometry signal and the reflectometry
signal, respectively.
[0033] In some instances, compensation can be provided to
compensate for the gradient in the tube; however, when the gas flow
rate is not constant (e.g., the gas flow rate may frequently change
to accommodate varying process conditions), the gas density
gradient in the tube 12 varies, thus causing the index of
refraction gradient in the tube to also vary undesirably, thus
making compensation for signal distortions extremely difficult or
impossible.
[0034] In appreciation of the above problem, the inventors of the
present invention provide the pyrometer system 50 having the
concentric multi-tube elevator tube 52 having the fluid passageway
therebetween. The cooling gas 68 is provided into the fluid
passageway 65 while the inside of the inner tube 54 is fluidly
isolated therefrom. Therefore in the system 50 of the present
invention, a stratification of the ambient environment within the
inner tube 54 may still occur, but such stratification will not be
a function of changes in the cooling gas volume flow rate.
Therefore compensation may be provided due to such stratification
since the distortion caused by the stratification will remain
substantially constant.
[0035] In accordance with another aspect of the present invention,
the vacuum pump 90 is coupled to or otherwise associated with the
inner tube 54 that is fluidly sealed at the top 56 and bottom 58
thereof via the port 92. The vacuum pump 90 is operable to evacuate
the inner tube 54, thereby generating a vacuum therein. With a
vacuum within the inner tube 54, no stratification exists therein,
thereby establishing a substantially high quality optical path 94
therethrough. With no stratification associated with the optical
path the light signals for the radiometry channel 28 and the
reflectometry channel 30 have substantially no distortion, thereby
making such measurements substantially more precise without the
need for compensation.
[0036] Turning now to FIG. 4, a fluid direction device 100 is
illustrated in accordance with another aspect of the present
invention. The fluid direction device 100 is associated with the
top of the elevator tube 52, for example, coupled to one or more of
the inner or outer tubes 54 and 60 and/or the spider collar 74. In
the example of FIG. 4, the fluid direction device 100 comprises a
frustum shaped device and is coupled to the spider collar 74, and
is operable to direct cooling gas 68 flowing between the inner and
outer tubes 54 and 60 to a predetermined portion 102 of the wafer
20 to provide localized cooling thereat. Although the fluid
direction device 100 in the present example is illustrated as a
truncated, inverted cone, it should be understood that other shapes
and structures may be employed and that any such structure operable
to direct cooling gas to one or more predetermined portions of the
wafer 20 are contemplated as falling within the scope of the
present invention.
[0037] In addition, in FIG. 4 a lens 104 (e.g., made of quartz or
sapphire) is situated at the top portion 56 of the inner tube 54.
The lens 104 preferably fluidly isolates the interior of the inner
tube 54 from the cooling gas 68, thereby preventing any
stratification of gas within the inner tube from being a function
of changes in the cooling gas flow rate. Further, by sealing the
inner tube 54, one may evacuate the inner tube 54 to substantially
prevent any stratification therein. The lens 104, in addition to
sealing the inner tube 54, also serves to focus light/radiation
from the wafer 20 to the pyrometer head 22 in an effective manner
as discussed previously. A distance 106 between the wafer 20 and
the lens 104 preferably is equal to the focal length of the lens
and is, in the present example, dictated by the spider arms 76, 78
associated with the spider collar 74.
[0038] In accordance with another aspect of the present invention,
the elevator tube comprises a sleeve associated with a top portion
thereof. As will be discussed below in greater detail, the sleeve
supports the lens, and has a coefficient of thermal expansion that
alters the distance between the lens and the wafer or work piece as
a function of temperature. As will be further appreciated, such
changes in the distance act to compensate for changes in the focal
length of the lens that also varies with respect to temperature. In
the above manner, the sleeve in conjunction with the lens serve to
image radiation from the wafer down to the pyrometer head in a
substantially consistent manner despite variations in
temperature.
[0039] FIG. 5 is a cross sectional view of an elevator tube 152 in
accordance with still another aspect of the present invention. The
elevator tube 152 may be employed, for example, in the pyrometer
system 50 of FIG. 3 or in other type systems, as may be desired.
The elevator tube 152 is similar in some ways to the tube 52 of
FIG. 3, but differs in several respects. The elevator tube 152 of
FIG. 5 comprises an inner tube 154 that extends from an
intermediate portion 155 of the tube to a bottom 158 thereof. In
one example, the inner tube 154 extends a substantial length of the
entire tube 152, but may vary as desired.
[0040] The elevator tube 152 further comprises an outer tube 160
that surrounds the inner tube 154 concentrically in a telescoping
type arrangement, as illustrated. The outer tube 160 extends from a
top 162 to a bottom 164 as shown. The concentric nature of the
inner and outer tubes 154, 160 define a fluid passageway 165
therebetween. A cooling gas port (not shown) couples to or is
otherwise associated with the outer tube 160 for delivery of a
cooling gas 168 into the passageway 165 via, for example, a gas
line (not shown).
[0041] The elevator tube 152 further comprises a sleeve 170
associated with the intermediate portion 155 of the inner tube 154.
The sleeve 170 has a bottom portion that engages a ring seal 174
that separates the outer tube 160 into a top portion 160a and a
bottom portion 160b, respectively. The sleeve 170 further includes
a top portion 176 that supports or is otherwise associated with the
lens 104.
[0042] In one exemplary aspect of the present invention, the sleeve
170 comprises a material such as sapphire (Al.sub.2O.sub.3) or
alumina (amorphous Al.sub.2O.sub.3) that exhibits a coefficient of
thermal expansion that causes the distance 106 (see, e.g., FIG. 4)
between the lens 104 and the wafer 20 to change with respect to
changes in temperature. More preferably, an amount of change in the
distance 106 due to a change in temperature generally corresponds
to a change in the focal length of the lens 170 due to the same
temperature change.
[0043] Therefore if a change in temperature (.DELTA.T) causes a
change in the focal length (.DELTA.f) of the lens 104, the sleeve
170 exhibits a coefficient of thermal expansion that alters the
distance 106 (.DELTA.D), wherein .DELTA.f.apprxeq..DELTA.D. In the
above manner, the imaging of radiation from the wafer 20 by the
lens 104 to the pyrometer head 22 is substantially the same over a
large temperature range, thereby improving the accuracy of the
pyrometer system. Although sapphire and alumina are presented as
exemplary materials for the sleeve 170, any material that provides
such a coefficient of thermal expansion may be employed and such
materials are contemplated as falling within the scope of the
present invention.
[0044] In the present example, the spider collar (not shown) which
supports the wafer 20 at the predetermined distance 106 from the
lens 104 is made of quartz which has a substantially smaller
coefficient of thermal expansion than that of the sleeve 170 (e.g.,
1:10) such that variations in distance due to temperature may be
considered negligible. Alternatively, although the present example
illustrates a sleeve 170 that exhibits the substantial coefficient
of thermal expansion while the wafer 20 is held relatively still
with respect to the elevator tube 152, the present invention also
contemplates holding the lens 104 in a relatively fixed position
while using a spider collar support structure that exhibits a
substantial coefficient of thermal expansion to compensate for the
change in lens focal length. This alternative solution, however,
may not be as desirable since any substantial movement of the
support structure may result in a variation in the desired heating
of the work piece located thereon.
[0045] Referring still to FIG. 5, the ring seal 174 may comprise an
annular seal that couples together the various portions 154, 160a,
160b and 170 of the elevator tube 152. More particularly, in the
present example the ring seal 174 comprises an inner concentric
portion 176 that couples together the inner tube 154 and the sleeve
170, and an outer concentric portion 178 that couples together the
top and bottom portions of the outer tube 160a and 160b,
respectively. The ring seal 174 further comprises an annular hole
180 through which the cooling gas 168 passes to provide localized
cooling to the wafer (not shown), as described supra.
Alternatively, the ring seal hole 180 may comprise one or more
apertures of various shapes and/or sizes about the annular seal, as
may be desired.
[0046] In accordance with yet another aspect of the present
invention, the sleeve 170 is substantially opaque with respect to
radiation, or at least is diffuse with respect thereto. By making
the sleeve substantially opaque or diffuse, stray light such as
light reflected from the bell jar (not shown) that would otherwise
be imaged undesirably by the lens 104 is substantially reduced or
altogether eliminated. For example, if the sleeve 170 is composed
of sapphire, the sapphire sleeve may be "frosted" by dipping the
sleeve into an HF or equivalent solution. Alternatively, the outer
surface or "OD" of the sleeve 170 may be ground to a predetermined
finish. Any suitable sleeve material may be employed, and any
suitable frosting process may be utilized to achieve the above
structure and such alternatives are contemplated as falling within
the scope of the present invention.
[0047] FIG. 6 is another cross section illustrating additional
exemplary details relating to the elevator tube 152 of FIG. 5 into
a portion of a pyrometer system such as the system 50 of FIG. 3,
having the sleeve 170 and the spider collar 74 as described
previously. In addition, although not shown in FIG. 6, the fluid
direction structure 100 or similar structure may be employed in
conjunction with the tube 152 for localized cooling or one or more
portions of the work piece 20, as may be desired.
[0048] Although the invention has been illustrated and described
above with respect to a certain aspects and implementations, it
will be appreciated that equivalent alterations and modifications
will occur to others skilled in the art upon the reading and
understanding of this specification and the annexed drawings. In
particular regard to the various functions performed by the above
described components (assemblies, devices, circuits, systems,
etc.), the terms (including a reference to a "means") used to
describe such components are intended to correspond, unless
otherwise indicated, to any component which performs the specified
function of the described component (i.e., that is functionally
equivalent), even though not structurally equivalent to the
disclosed structure, which performs the function in the herein
illustrated exemplary implementations of the invention. In this
regard, it will also be recognized that the invention includes a
computer-readable medium having computer-executable instructions
for performing the steps of the various methods of the invention.
In addition, while a particular feature of the invention may have
been disclosed with respect to only one of several implementations,
such feature may be combined with one or more other features of the
other implementations as may be desired and advantageous for any
given or particular application. Furthermore, to the extent that
the terms "includes", "including", "has", "having", "with" and
variants thereof are used in either the detailed description or the
claims, these terms are intended to be inclusive in a manner
similar to the term "comprising".
* * * * *