U.S. patent application number 11/031400 was filed with the patent office on 2006-07-13 for integrated metrology chamber for transparent substrates.
Invention is credited to Scott Anderson, Corey Collard, Richard Lewington, Khiem Nguyen.
Application Number | 20060154388 11/031400 |
Document ID | / |
Family ID | 36098810 |
Filed Date | 2006-07-13 |
United States Patent
Application |
20060154388 |
Kind Code |
A1 |
Lewington; Richard ; et
al. |
July 13, 2006 |
Integrated metrology chamber for transparent substrates
Abstract
The embodiments of the invention relate to a method and
apparatus for measuring the etch depth between etching for an
alternate phase shift photomask in a semiconductor photomask
processing system. The apparatus for measuring the etch depth of a
substrate in an etch processing system comprises a measurement cell
coupled to a mainframe of the etch processing system, and an etch
depth measurement tool coupled to the bottom of the measurement
cell, wherein an opening at the bottom of the measurement cell
allows light beams to pass between the etch depth measurement tool
and the substrate. The embodiments of the invention also relate to
the method of preparing an alternate phase shift mask by partially
etching the quartz substrate to an initial etch depth, followed by
measuring the etch depth with an integrated measurement tool. The
substrate is then etched and measured repeatedly until the targeted
etch depth has been reached.
Inventors: |
Lewington; Richard;
(Hayward, CA) ; Collard; Corey; (San Jose, CA)
; Anderson; Scott; (Livermore, CA) ; Nguyen;
Khiem; (San Jose, CA) |
Correspondence
Address: |
PATTERSON & SHERIDAN, LLP
3040 POST OAK BOULEVARD, SUITE 1500
HOUSTON
TX
77056
US
|
Family ID: |
36098810 |
Appl. No.: |
11/031400 |
Filed: |
January 8, 2005 |
Current U.S.
Class: |
438/17 ;
204/192.33; 216/12; 257/E21.252; 430/5 |
Current CPC
Class: |
H01L 21/67742 20130101;
H01L 21/31116 20130101; G03F 1/30 20130101 |
Class at
Publication: |
438/017 ;
204/192.33 |
International
Class: |
H01L 21/66 20060101
H01L021/66; C23C 14/00 20060101 C23C014/00 |
Claims
1. An apparatus for measuring the etch depth of a substrate in an
etch processing system, comprising: a measurement cell coupled to a
mainframe of the etch processing system; and an etch depth
measurement tool coupled to the bottom of the measurement cell,
wherein an opening at the bottom of the measurement cell allows
light beams to pass between the etch depth measurement tool and the
substrate.
2. The apparatus of claim 1, further comprising: a substrate
transfer robot placed in the mainframe to transfer the substrate to
the measurement cell, wherein the substrate transfer robot having a
robot blade to hold a substrate and the robot blade having an
opening to allow light beam to be shined on the substrate
backside.
3. The apparatus of claim 1, wherein the opening at the bottom of
the measurement cell is circular.
4. The apparatus of claim 2, wherein the opening of the robot blade
is a square.
5. The apparatus of claim 2, wherein the robot blade comprises a
calibration pad used to calibrate the etch depth measurement
tool.
6. The apparatus of claim 2, wherein the robot blade has roll and
tilt function to position the surface of the substrate to be
perpendicular to the light beam emitted from the etch depth
measurement tool.
7. The apparatus of claim 1, wherein the measurement cell can be
under vacuum.
8. The apparatus of claim 2, wherein the depth measurement tool is
configured to test a substrate having an optically transparent
layer.
9. An apparatus for measuring the etch depth of a substrate in an
etch processing system, comprising: a measurement cell coupled to a
mainframe of the etch processing system; an etch depth measurement
tool coupled to the bottom of the measurement cell, wherein an
opening at the bottom of the measurement cell allows light beams to
pass between the etch depth measurement tool and the substrate; and
a substrate transfer robot placed in the mainframe to transfer
substrate to the measurement cell, wherein the substrate transfer
robot having a robot blade to hold a substrate and the robot blade
having an opening to allow light beam to be shined on the substrate
backside.
10. The apparatus of claim 9, wherein the opening at the bottom of
the measurement cell is circular.
11. The apparatus of claim 9, wherein the opening of the robot
blade is a square.
12. The apparatus of claim 9, wherein the robot blade comprises a
calibration pad used to calibrate the etch depth measurement
tool.
13. The apparatus of claim 12, wherein the calibration pad
comprises a bare silicon.
14. The apparatus of claim 9, wherein the robot blade has roll and
tilt function to position the surface of the substrate to be
perpendicular to the light beam emitted from the etch depth
measurement tool.
15. The apparatus of claim 9, wherein the measurement cell can be
under vacuum.
16. The apparatus of claim 9, wherein the depth measurement tool is
configured to test a substrate having an optically transparent
layer.
17. A method of preparing an alternate phase shift mask,
comprising: a) placing a substrate in an etch processing chamber,
wherein the substrate is made of an optically transparent material
and has a first patterned opaque layer and a second patterned
photoresist layer on the optically transparent material; b) etching
the quartz to a first etch depth; c) transferring the substrate to
a measurement cell coupled to a substrate transfer chamber; d)
measuring the etch depth from the substrate backside by a etch
depth measurement tool coupled to the bottom of the measurement
cell to determine the etch time of next etch; e) placing the
substrate back to the etch processing chamber; f) etching for the
etch time determined by the etch depth measurement; g) transferring
the substrate to the measurement cell; h) measuring the etch depth
from the substrate backside by a etch depth measurement tool
coupled to the bottom of the measurement cell to determine the etch
time of next etch; and i) repeating "e" to "h" until a targeted
etch depth has been reached.
18. The method of claim 17, wherein the etch depth measurement is
performed by collecting reflected light beams from the backside of
the substrate.
19. An apparatus for measuring the etch depth of a substrate in an
etch processing system, comprising: a measurement cell coupled to a
mainframe of the etch processing system; an etch depth measurement
tool coupled to the bottom of the measurement cell, wherein an
opening at the bottom of the measurement cell that allows light
beams to pass between the etch depth measurement tool and the
substrate; a CD measurement tool coupled to the top of the
measurement cell, wherein an opening at the top of the measurement
cell allows light beams to pass between the CD measurement tool and
the substrate; and a substrate transfer robot placed in the
mainframe to transfer the substrate to the measurement cell,
wherein the substrate transfer robot having a robot blade to hold
the substrate and the robot blade having an opening to allow light
beam to be shined on the substrate.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to the fabrication of
photomasks useful in the manufacture of integrated circuits.
[0003] 2. Background of the Related Art
[0004] Photolithography techniques use light patterns and
photoresist materials deposited on a substrate surface to develop
precise patterns on the substrate surface prior to the etching
process. In conventional photolithographic processes, a photoresist
is applied on the layer to be etched, and the features to be etched
in the layer, such as contacts, vias, or interconnects, are defined
by exposing the photoresist to a pattern of light through a
photolithographic photomask which corresponds to the desired
configuration of features. A light source emitting ultraviolet (UV)
light, for example, may be used to expose the photoresist to alter
the composition of the photoresist. Generally, the exposed
photoresist material is removed by a chemical process to expose the
underlying substrate material. The exposed underlying substrate
material is then etched to form the features in the substrate
surface while the retained photoresist material remains as a
protective coating for the unexposed underlying substrate material.
Since photomasks are used repeatedly to create device patterns,
quality control of photomask manufacturing is very important.
[0005] Photolithographic photomasks, or reticles, include binary
(or conventional) photomasks and phase shift masks (PSM), which
could be used in sub 0.13 .mu.m technology. Binary (or
conventional) masks typically include a substrate made of an
optically transparent silicon based material, such as quartz (i.e.,
silicon dioxide, SiO.sub.2), having an opaque light-shielding layer
of metal, such as chromium, on the surface of the substrate. Phase
shift masks improve the resolution of the aerial image by phase
shifting. The principle of phase shift mask is described in P.
230-234 of Plummer, Deal and Griffin, "Silicon VLSI Technology
Fundamentals, Practice and Modeling", 2000 by Prentice Hall, Inc.
Phase shift masks could be either attenuated phase shift or
alternate phase shift mask. An attenuated phase shift mask
typically includes a substrate made of an optically transparent
silicon based material, such as quartz, having a translucent layer
of material, such as molybdenum silicide (MoSi) or molybdenum
silicon oxynitride (MoSiON), on top. When the photolithographic
light, e.g. at 248 nm wavelength, shines through the patterned mask
surface covered by the translucent layer, the transmission (e.g. 6%
at 248 nm wavelength) and the thickness of the translucent layer
create a phase shift, e.g., 180.degree., compared to the
photolithographic light that shines through the patterned mask
surface not covered by the translucent layer. An alternate phase
shift mask typically includes a substrate made of an optically
transparent silicon based material, such as quartz, which is etched
to a certain depth to create a phase shift with the un-etched
transparent substrate when the photolithographic light shines
through the patterned mask. It also has a chrome layer with the
same pattern as the quartz. There is another type of phase shift
mask, the Chromeless Phase Lithography (CPL) Mask, which has the
chrome layer removed.
[0006] Photomasks allow light to pass therethrough in a precise
pattern onto the substrate surface. The metal layer on the
photomask substrate is patterned to correspond to the features to
be transferred to the substrate. The patterns on the photomask
could be 1.times., 2.times. or 4.times. the size of patterns that
will be patterned on the wafer substrate. Typically, a
photolithographic stepper reduces the image of the photomask by
4.times. and prints the pattern on the photoresist covering the
wafer surface. Conventional photomasks are fabricated by first
depositing one to two thin layers of metal, which could either be
opaque or translucent depending on the types of masks being formed,
on a substrate comprising an optically transparent silicon based
material, such as quartz, and depositing a photoresist layer on
substrate. The photomask is then patterned using conventional laser
or electron beam patterning equipment to define the critical
dimensions in the photoresist. The top metal layer, typically
opaque, is then etched to remove the metal material not protected
by the patterned photoresist, thereby exposing the underlying
silicon based material. For a binary mask, the photomask is formed
after the metal etching step. While for attenuate and alternate
phase shift masks, additional photoresist patterning and etching of
transparent substrate or translucent metal layer are needed to form
the photomask.
[0007] Since photomasks are used repeatedly to create device
patterns, the accuracy and tight distribution of the critical
dimensions, and the phase shift angle and its uniformity across the
substrate are key requirements for binary and phase shift
photomasks. For alternate phase shift mask, the phase angle is
affected by the depth of the transparent material, such as quartz.
Since precise control of the phase shift is very important, the
etching of the transparent material, such as quartz, is often
accomplished after multiple etching processes and multiple etch
depth measurements to ensure phase shift of the mask is within
control limit. If the etch depth measurement is performed in a
system not integrated with the etching system, process cycle time
could be very long and the approach could increase the total defect
counts.
[0008] Therefore, there remains a need in the art for an integrated
metrology tool to measure etch depth (or phase shift angle) of
photomask in a semiconductor photomask processing system.
SUMMARY OF THE INVENTION
[0009] The embodiments of the invention relates to a method and
apparatus for measuring the etch depth between etching for an
alternate phase shift photomask in a semiconductor photomask
processing system. In one embodiment, an apparatus for measuring
the etch depth of a substrate in an etch processing system
comprises a measurement cell coupled to a mainframe of the etch
processing system, and an etch depth measurement tool coupled to
the bottom of the measurement cell, wherein an opening at the
bottom of the measurement cell allows light beams to pass between
the etch depth measurement tool and the substrate.
[0010] In another embodiment, an apparatus for measuring the etch
depth of a substrate in an etch processing system comprises a
measurement cell coupled to a mainframe of the etch processing
system, an etch depth measurement tool coupled to the bottom of the
measurement cell, wherein an opening at the bottom of the
measurement cell allows light beams to pass between the etch depth
measurement tool and the substrate, and a substrate transfer robot
placed in the mainframe to transfer substrate to the measurement
cell, wherein the substrate transfer robot having a robot blade to
hold a substrate and the robot blade having an opening to allow
light beam to be shined on the substrate backside.
[0011] In another embodiment, a method of preparing an alternate
phase shift mask comprises a) placing a substrate in an etch
processing chamber, wherein the substrate is made of an optically
transparent material and has a first patterned opaque layer and a
second patterned photoresist layer on the optically transparent
material, b) etching the quartz to a first etch depth, c)
transferring the substrate to a measurement cell coupled to a
substrate transfer chamber, d) measuring the etch depth from the
substrate backside by a etch depth measurement tool coupled to the
bottom of the measurement cell to determine the etch time of next
etch, e) placing the substrate back to the etch processing chamber,
f) etching for the etch time determined by the etch depth
measurement, g) transferring the substrate to the measurement cell,
h) measuring the etch depth from the substrate backside by a etch
depth measurement tool coupled to the bottom of the measurement
cell to determine the etch time of next etch, and i) repeating "e"
to "h" until a targeted etch depth has been reached.
[0012] In another embodiment, an apparatus for measuring the etch
depth of a substrate in an etch processing system comprises a
measurement cell coupled to a mainframe of the etch processing
system, n etch depth measurement tool coupled to the bottom of the
measurement cell, wherein an opening at the bottom of the
measurement cell that allows light beams to pass between the etch
depth measurement tool and the substrate, a CD measurement tool
coupled to the top of the measurement cell, wherein an opening at
the top of the measurement cell allows light beams to pass between
the CD measurement tool and the substrate, and a substrate transfer
robot placed in the mainframe to transfer the substrate to the
measurement cell, wherein the substrate transfer robot having a
robot blade to hold the substrate and the robot blade having an
opening to allow light beam to be shined on the substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] So that the manner in which the above recited aspects of the
invention are attained and can be understood in detail, a more
particular description of the invention, briefly summarized above,
may be had by reference to the embodiments thereof which are
illustrated in the appended drawings.
[0014] It is to be noted, however, that the appended drawings
illustrate only typical embodiments of this invention and are
therefore not to be considered limiting of its scope, for the
invention may admit to other equally effective embodiments.
[0015] FIGS. 1A-1F are cross-sectional views showing an etching
sequence for processing an alternate phase shift photomask.
[0016] FIG. 2 is a block diagram of key components of an integrated
etch system.
[0017] FIG. 3 is a diagram of one embodiment of an integrated etch
system.
[0018] FIG. 4 is a schematic diagram showing a substrate, a
measurement tool, and the impeding and reflected light beams
between the substrate and the measurement tool.
[0019] FIG. 5A shows a schematic drawing of the end of the robot
arm with a robot blade.
[0020] FIG. 5B shows a schematic drawing of a measurement cell and
an etch depth metrology tool.
[0021] FIG. 5C shows a schematic drawing of a measurement cell with
an etch depth measurement tool and a CD measurement tool.
DETAILED DESCRIPTION
[0022] For convenience, the present invention is described herein
primarily with reference to the etching of alternate phase shift
masks. The concept of the invention can be used for etching other
types of photomasks.
[0023] FIGS. 1A-1F illustrate an exemplary process flow of creating
an alternate phase shift mask. A substrate 100 is introduced into a
processing chamber. The substrate 100 (or reticle) comprises a base
material of an optically transparent material 110, for example,
optical quality quartz, calcium fluoride, alumina, sapphire, or
combinations thereof, typically made of optical quality quartz
material. An opaque (or light-shielding) metal layer 120, such as
chromium, is deposited on the optically transparent material 110 as
shown in FIG. 1A. The light-shielding metal layer, such as chromium
layer, may be deposited by conventional methods known in the art,
such as by physical vapor deposition (PVD) or chemical vapor
deposition (CVD) techniques. The light-shielding (or opaque) metal
layer 120 is typically deposited to a thickness between about 50
and about 150 nanometers (nm) thick, however, the depth of the
layer may change based upon the requirements of the manufacturer
and the composition of the materials of the substrate or metal
layer.
[0024] Referring to FIG. 1B, the substrate 100 is then transferred
to another processing chamber where a layer of resist material 130,
such as "RISTON" resist, manufactured by Du Pont de Nemours
Chemical Company, is deposited upon the opaque metal layer 120 to a
thickness between about 200 and 600 nm thick. The resist material
130 is then pattern etched using conventional laser or electron
beam patterning equipment to form a first opening 125 which is used
to define the dimensions of the second opening 135 to be formed in
the opaque metal layer 120.
[0025] The substrate 100 is then transferred to an etch system,
such as the Tetra II.TM. photomask etch chamber in the Tetra II.TM.
photomask etch system described in FIG. 3 (described below),
manufactured by Applied Materials, Inc., of Santa Clara, Calif.
Aspects of the invention will be described below in reference to an
inductively coupled plasma etch chamber that includes the Tetra
II.TM. photomask etch chamber. However, other process chambers may
be used to perform the processes of the invention, including, for
example, capacitively coupled parallel plate chambers and
magnetically enhanced ion etch chambers as well as inductively
coupled plasma etch chambers of different designs.
[0026] The light-shielding metal layer 120 is etched using metal
etching techniques known in the art or by new metal etching
techniques that may be developed to form the second opening 135
which expose the underlying transparent material 110 as shown in
FIG. 1C.
[0027] Referring to FIGS. 1A-1C, after etching of the
light-shielding metal layer 120 is completed, the substrate 100 is
transferred to a processing chamber, where the remaining resist
material 130 is usually removed from the substrate 100. The resist
removal could be accomplished by an oxygen plasma process, or other
resist removal technique known in the art.
[0028] Referring to FIGS. 1D-1F, the substrate 100 may be further
processed by etching the transparent material 110. In etching the
transparent material 110, the resist material 130 is removed and a
second photoresist 140 is applied and patterned to expose the
underlying transparent material 110 within the second opening 135.
The resist material is deposited to a depth between about 200 nm
and 600 nm thick, but may be of any thickness and may also be of
the same thickness as the depth of the features to be etched in the
transparent material 110 to form the photomask. The photoresist 140
is then etched to form a third opening 145 in the resist layer 140
and the metal layer 120. The patterned substrate 100 is then
transferred to an etch chamber, such as the Tetra II.TM. photomask
etch system described in FIG. 3 (described below), for plasma
etching the transparent material 310.
[0029] Since the etch depth 175 in the transparent material 110
determines the phase shift angle, the precise control of the etch
depth 175 is very critical. For example, In order to achieve a
phase shift angle of 180.degree. for alternate phase shift mask for
KrF excimer laser lithography, the quartz etch depth is about 2400
.ANG.. To avoid over-etch, the initial etching only etches
partially, such as 50%-75%, of the targeted etch depth. The etch
depth 175 (or phase shift angle) of the etched substrate 100 is
measured at an integrated metrology tool. The substrate 100
subsequently undergoes additional etch and etch depth measurement
until the targeted etch depth 175 is reached. Performing etch depth
measurement in an integrated metrology tool has the advantage of
avoiding the need of transferring the substrate to an area not
under the same vacuum environment. Transferring substrates to an
area not under the same vacuum environment repeatedly is time
consuming, due to breaking vacuum, and could result in particle
generation, which is very undesirable for photomask making.
[0030] After the targeted etch depth 175 is reached, the second
resist material 140 is then removed to form a patterned substrate
surface 155. An alternate phase shift mask with a patterned
substrate surface 165 is formed after the metal layer 120 is
removed. Occasionally, dry etching in an etch chamber only etches
to reach a percentage of the final etch depth and the final step is
a wet etch step, since wet etch could reduce the surface roughness
and could reduce the micro-trenching on the photomask
substrate.
[0031] Alternate phase shift photomask etching processes for
light-shielding layers such as chromium, and optically transparent
materials, such as quartz, include dry etching processes. Plasmas
of etching gases, such as chlorine-containing gases (e.g. Cl.sub.2)
or fluorine-containing gases (e.g. SF.sub.6 or CF.sub.4), oxidizing
gases, such as oxygen, and inert gases, such as helium, could be
used to etch the metal layers formed on the substrate or the
substrate itself. Details of etching chemistries that are used to
etch light-shielding layer for this application have been disclosed
in commonly assigned U.S. patent application Ser. No. 10/418,795,
titled "Process For Etching Photomasks", and filed on Apr. 18, 2003
and U.S. patent application Ser. No. 10/235,223, titled "Methods
And Apparatus For Etching Metal Layers on Substrates", and filed on
Sep. 4, 2002. Etching of the silicon based material of the
substrate is described in commonly assigned U.S. Pat. No.
6,534,417, titled "Method and Apparatus For Etching Photomasks",
issued Mar. 18, 2003 and U.S. Pat. No. 6,391,790, also titled
"Method and Apparatus For Etching Photomasks", issued May 21, 2002.
The disclosures of all of these applications are incorporated
herein by reference to the extent not inconsistent with aspects of
the invention.
[0032] Etch depth metrology techniques as employed by the present
invention are advanced process control (APC) enablers. It detects
the reflection of a substrate over a broad wavelength range. The
detected wavelength spectra are fitted to a theoretical model to
enable the characterization of the film. The metrology can be used
to measure transparency, etch depth, film thickness and phase shift
angle at multiple locations on the substrate. An example of the
etch depth (or phase shift angle) measuring tool is the n&k
Analyzer 1512RT available from n&k Technology, Inc. of Santa
Clara, Calif.
[0033] An exemplary embodiment of the present invention is
implemented using a etch depth measuring tool in a processing
system 200, as shown in FIG. 2, comprising a measuring tool 210,
e.g., a etch depth (or phase shift angle) measurement tool.
Processing system 200 further comprises a processor 220, which
performs the analysis disclosed herein electronically, and a
monitor 230 for displaying results of the analyses of processor
220. Processor 220 can be in communication with a memory device
240, such as a semiconductor memory, and a computer
software-implemented database system 250 known as a "manufacturing
execution system" (MES) conventionally used for storage of process
information. Processor 220 can also be in communication with the
measuring tool 210, and etcher 270.
[0034] An example of an etch system that is integrated with an
ex-situ metrology tool with the capability of measuring etch depth
(or phase shift angle) is shown in FIG. 3. The system, Tetra
II.TM., comprises a chamber or "mainframe" 301, such as the
Centura.TM. processing system available from Applied Materials,
Inc. of Santa Clara, Calif., for mounting a plurality of processing
chambers, e.g., Tetra II.TM. photomask reactors (or chambers) 302,
and one or more transfer chambers 303, also called "load locks". In
one embodiment of the present invention, three etch reactors 302
and one metrology tool 306 are mounted to the mainframe 301. The
metrology tool 306 can be placed under the same vacuum as the
mainframe 301, since there is an opening (not shown) between the
mainframe 301 and the metrology tool 306 to make them in fluid
communication. In one exemplary embodiment, three etchers 302 are
used for etching. A robot 304 is provided within the mainframe 301
for transferring wafers between the processing reactors 302, the
transfer chambers 303, and an integrated metrology tool 306. The
integrated metrology tool 306 can measure the etch depth (or phase
shift angle). The transfer chambers 303 are connected to a factory
interface 305, also known as a "mini environment", which maintains
a controlled environment. In one embodiment of the invention, the
metrology (or measurement) tool 306, mounted to the mainframe 301,
has high-speed data collection and analysis capabilities. Cassette
holders 308 are connected to the other end of the factory interface
305. A robot 307 is placed inside 305 to transfer substrate between
cassette holders (308), and "load locks" (303).
[0035] The etch depth measurement tool 306 is mounted to the
mainframe 301 to allow the etched substrate from the etch chamber
302 to be measured and be sent back to etch chamber 302 to be
etched again. The etch and measurement process sequence could
repeat several times until the targeted etch depth (or phase shift
angle) is reached. Due to the nature of repeated etch and
measurement to target etch depth of transparent material 110, it's
desirable to have the etch depth measurement tool (or phase shift
angle measurement tool) mounted to the mainframe 301. Both
mainframe 301 and the metrology tool 306 are under integrated
vacuum environment and can avoid the need of transferring the
substrate to an area not under vacuum, which could be time
consuming due to additional substrate transport and breaking the
vacuum. Repeated transferring substrate between processing areas
that are under vacuum and not under vacuum is not only time
consuming, but also particle generating.
[0036] In another embodiment of the invention, the metrology tool
306 is placed at the location of one of the transfer chambers 303.
Placing the metrology tool 306 at the location of one of the
transfer chambers 303 also has the advantage of avoiding the need
of transferring the substrate to an area not under vacuum.
[0037] Since the substrate is transparent, the phase shift angle
(or etch depth) can be measured by analyzing reflected light from
the backside of the substrate, which does not require the removal
the opaque film 320 and the photoresist film 340. Conventional
phase shift angle measurement is performed from the substrate front
side and requires the removal of the opaque film 320 and the
photoresist film 340 prior to phase shift angle measurement. The
additional processing steps of removing films can cause particles
or other processing defects, which are highly undesirable for
photomask preparation. Besides, if the phase shift angle (or etch
depth) is found to have not reached the target, the opaque film 320
and photoresist film 340 would need to be re-deposited and
re-patterned again to allow further etching of the transparent
material 310, which could worsen the particles and other processing
defects problems.
[0038] FIG. 4 shows a schematic drawing of an etch depth
measurement tool (or phase shift angle measurement tool) 460,
placed below the backside of a substrate 400. The substrate 400 has
an etch depth 450 and also has an opaque film 410 and a photoresist
film 420 on the front side. On the back side of the substrate 400,
there are incident light beams 430, 430 and 432, and reflected
light beams 430', 431' and 432'. The light source of incident light
beams could be from the measurement tool 460. The light source is
preferably a broadband light source. Part of incident light beam
430, reflected light beam 430', is reflected from the interface
between the substrate 400 and the environment 470. Reflected light
beam 431' is reflected from the interface between the substrate
etch interface 451 with the environment 470. Reflected light beam
432' is reflected from the interface between the opaque layer 410
and the substrate 400. The etch depth measurement tool collects
reflected light beams over a range of substrate backside surface.
By calculating the phase shift between the light beams such as 431'
and 432', the etch depth 450 and the phase shift of the transparent
substrate can be determined without removing the films on the front
side, such as opaque film 410 and photoresist film 420, of the
substrate 400.
[0039] In one embodiment of the invention a robot arm 500, which is
part of robot 304 of the mainframe 301 of FIG. 3, is designed to
include a substrate holder 501. The substrate holder 501 has an
opening that allows the incident light beams and reflected light
beams on the substrate backside to pass through, as shown in FIG.
5A. FIG. 5A shows a schematic drawing of the end of the robot arm
500 that contains a robot blade 510, which has a substrate holder
501. The substrate holder 501 has an aperture 502 that is
proportional to the size of the substrate. In one embodiment, the
aperture 502 is about 4 inches by 4 inches for a 6 inches by 6
inches substrate. The size of the aperture 502 is smaller than the
size of the substrate to allow the edge of the substrate to be
supported by the substrate holder. In one embodiment, the thickness
of the robot blade 510 is about inch (1.02 cm). The size of the
aperture 502 should be as large as possible to allow measurement
data to be collected across large area on the substrate.
[0040] FIG. 5B shows the substrate 520 is placed inside the
metrology tool 306 of FIG. 3. The metrology tool 306 comprises a
measurement cell 550 and an etch depth measurement tool 460. The
substrate is moved by the robot arm 500 to be over the measurement
point. Underneath the measurement point 560 is a etch depth
measurement tool 460. The etch depth measurement tool 460 comprises
a broadband light source (not shown), which emits light to the
backside of the substrate 520. The robot blade 510 is attached to
the robot arm 500 and it has roll and tilt function to allow the
surface of substrate 520 to be perpendicular to the measurement
light beam emitted from the measurement tool 460. The etch depth
measurement tool 460 collects the reflected light from the
substrate backside. The data generated from the reflected light are
analyzed to calculate the etch depth by the measurement tool 460.
In one embodiment of the invention, there is a calibration pad 580,
which contains an etch depth measurement calibration device, such
as a piece of bare silicon, on the robot blade 510. In one
embodiment, the size of the calibration pad is about 1/2 inch (1.27
cm) in diameter. Periodically, the calibration pad 580 can be moved
to be above the measurement point 560 to calibrate the measurement
tool 460. A native oxide layer is typically present on the bare
silicon surface. The presence of the native oxide layer is
important for calibration of some measurement tools. In one
embodiment, the measurement point 560 is a circular opening with a
diameter, such as about 1 inch (2.54 cm).
[0041] The advantage of backside etch depth measurement is that the
measurement does not require the removal of the front side films.
Therefore the substrate can be partially etched first, then be
measured to target the next etch amount. The substrate can then be
re-etched and re-measured multiple times with out the need of
moving the substrate to another system to perform photoresist layer
stripping. For alternate phase shift mask making, the precise
control of the phase shift angle (or etch depth) is very critical.
Since the substrate is transparent and the phase shift angle can be
measured from the backside, the processing time can be greatly
reduced, since the fine tuning of the substrate etch does not
require removal of the substrate from the etching module.
[0042] In addition to the mounted etch depth measurement tool 460
on the bottom of the measurement cell 306, in one embodiment of the
invention, a CD measurement tool 590 is mounted on top of the
measurement cell 306 to collect critical dimension (CD) measurement
data through an opening 595 (as shown in FIG. 5C). The collected CD
measurement data can be fed forward and backward to the etcher to
adjust the substrate etch recipe. Since CD measurement has more
stringent measurement location requirement than etch depth
measurement, the robot arm 500, which is part of robot 304 in the
mainframe 301, might not have sufficient precision control as
required. The CD measurement tool 590 could include a moving device
(not shown), to allow a measuring device (not shown) in the CD
measurement tool to be moved over to a particular measurement
location above the substrate 520. The movement of the moving device
is controlled by a controller to control its precise movement. FIG.
5C shows a schematic drawing of metrology cell 306 with a top CD
measurement tool 590 and a bottom etch depth measurement tool
460.
[0043] The CD measurement tool 590 can employ OCD (optical critical
dimension) metrology techniques. OCD metrology techniques are
advanced process control (APC) enablers. For example, normal
incidence spectroscopic OCD metrology systems provide detailed line
profiles not possible with in-line non-destructive SEMs. For
photomasks, the OCD metrology can operate under reflective mode
(utilizing reflected light) or transmission mode (utilizing
transmitted light). The compact size and speed of OCD technology
enables the measurement system of the present invention to be fully
integrated into a process tool, such as Applied Materials' Tetra
II.TM. or DPS.RTM. II etch system. When combined with APC software,
this provides a complete, feed-forward solution for wafer-to-wafer
closed loop control. An example of the optical CD measuring tool is
the Nano OCD 9000 available from Nanometrics of Milpitas, Calif.,
or an optical imager as disclosed in U.S. Pat. No. 5,963,329. The
optical CD measuring tool can utilize scatterometry, reflectometry
or transmission ellipsometry techniques.
[0044] While the foregoing is directed to the preferred aspects of
the invention, other and further aspects of the invention may be
devised without departing from the basic scope thereof, and the
scope thereof is determined by the claims that follow.
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