Title: Exposure method and apparatus, and device manufacturing method
Abstract: A scanning exposure apparatus is provided that is capable of increasing the overlay accuracy. Every time a reticle is exchanged, a direction overlay correction table is updated. A control device for the exposure apparatus corrects the target positions (target locus) of a wafer stage on the basis of the direction overlay correction table.
Patent Number: 6,870,599 Issued on 03/22/2005 to Kurosawa
| Inventors:
|
Kurosawa; Hiroshi (Chiba, JP)
|
| Assignee:
|
Canon Kabushiki Kaisha (Tokyo, JP)
|
| Appl. No.:
|
050581 |
| Filed:
|
January 18, 2002 |
Foreign Application Priority Data
| Jan 29, 2001[JP] | 2001-020683 |
| Current U.S. Class: |
355/53; 355/52; 356/399 |
| Intern'l Class: |
G03B 027//42; G03B 027//68; G01B 011//00 |
| Field of Search: |
355/52,53,55
356/399,400,401
430/5
|
References Cited [Referenced By]
U.S. Patent Documents
| 5182615 | Jan., 1993 | Kurosawa et al. | 356/400.
|
| 5898477 | Apr., 1999 | Yoshimura et al. | 355/53.
|
| 5914773 | Jun., 1999 | Kurosawa et al. | 355/53.
|
| 6128067 | Oct., 2000 | Hashimoto | 355/52.
|
| 6204911 | Mar., 2001 | Kurosawa et al. | 355/53.
|
| 6228561 | May., 2001 | Hasebe et al. | 430/311.
|
| 6262792 | Jul., 2001 | Higashiki | 355/52.
|
| 6268903 | Jul., 2001 | Chiba et al. | 355/53.
|
| 6304316 | Oct., 2001 | Jain et al. | 355/53.
|
| 6549271 | Apr., 2003 | Yasuda et al. | 355/55.
|
Primary Examiner: Mathews; Alan
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper & Scinto
Claims
What is claimed is:
1. An exposure method of transferring a master pattern onto a substrate
while moving a controlled element concerning exposure operation,
comprising:
transferring the master pattern onto the substrate while moving the
controlled element in accordance with a target locus generated in
correspondence with a shape characteristic of the mask pattern and a shape
characteristic of a pattern already formed on the substrate.
2. A device manufacturing method comprising:
the first coating step of coating a substrate with a first resist;
the first exposure step of transferring a first master pattern onto the
substrate coated with the first resist;
the first developing step of developing the substrate bearing the first
master pattern;
the second coating step of coating the developed substrate with a second
resist;
the second exposure step of transferring a second master pattern onto the
substrate coated with the second resist; and
the second developing step of developing the substrate bearing the second
master pattern,
wherein the second exposure step includes
the correction step of correcting a target locus of a controlled element
concerning exposure operation on the basis of correction information
corresponding to a shape characteristic of the second master pattern
and/or a shape characteristic of a pattern formed on the substrate after
the first developing step, and
the transfer step of transferring the second master pattern onto the
substrate while moving the controlled element toward the corrected target
locus.
3. The method according to claim 2, wherein different types of exposure
apparatuses are used in the first and second exposure steps.
4. An exposure method of transferring a pattern onto a substrate while
moving an element concerning the transfer, said method comprising a step
of:
transferring a second pattern onto the substrate, onto which a first
pattern has been transferred, while moving the element based on
information prepared with respect to each position of the element for
correcting an overlay error between the first and second patterns.
5. A method according to claim 4, wherein the information is prepared with
respect to at least one of a group of a shape characteristic of the first
pattern already transferred onto the substrate, a shape characteristic of
the second pattern, a characteristic of an exposure apparatus used for the
transfer, a direction in which the element is to be moved, and a speed at
which the element is to be moved.
6. A method according to claim 5, further comprising a step of synthesizing
first and second information, the first and second information being
prepared as information with respect to each of two of a shape
characteristic of the first pattern already transferred onto the
substrate, a shape characteristic of the second pattern, and a
characteristic of an exposure apparatus used for the transfer, wherein in
said transferring step the element is moved based on information obtained
in said synthesizing step.
7. A method according to claim 5, wherein the shape characteristic of the
second pattern is obtained based on a master to be used of the transfer.
8. A method according to claim 4, further comprising a step of providing a
user interface for setting the information.
9. A method according to claim 4, wherein the element includes at least one
of the substrate, a master having a second pattern and an element of an
optical system.
10. An exposure apparatus for transferring a pattern onto a substrate while
moving an element concerning the transfer, said apparatus comprising:
a moving unit which moves the element; and
a control unit which controls said moving unit so as to move the element
based on information prepared with respect to each position of the element
for correcting an overlay error between first and second patterns during
transferring the second pattern onto the substrate onto which the first
pattern has been transferred.
11. An apparatus according to claim 10, wherein the information is prepared
with respect to at least one of a group of a shape characteristic of the
first pattern already transferred onto the substrate, a shape
characteristic of the second pattern, a characteristic of said exposure
apparatus used for the transfer, a direction in which the element is to be
moved, and a speed at which the element is to be moved.
12. An apparatus according to claim 10, further comprising a synthesizing
unit which synthesizes first and second information, the first and second
information being prepared as the information with respect to each of the
two of a shape characteristic of the first pattern already transferred
onto the substrate, a shape characteristic of the second pattern, and a
characteristic of an exposure apparatus used for the transfer, wherein
said control unit controls said moving unit so as to move the element
based on information obtained by said synthesizing unit.
13. An apparatus according to claim 11, wherein the shape characteristic of
the second pattern is loaded based on a master designated in a job file.
14. An apparatus according to claim 10, further comprising a system which
provides a user interface for setting the information.
15. An apparatus according to claim 10, wherein the element includes at
least one of the substrate, a master having the second pattern and an
element of an optical system.
16. A device manufacturing method comprising a step of transferring a
second pattern onto a substrate, onto which a first pattern has been
transferred, using a second exposure apparatus defined in claim 10.
17. A method according to claim 16, wherein the first pattern has been
transferred using a first exposure apparatus different from the second
exposure apparatus.
18. An exposure method of scan-exposing a surface of a substrate placed on
a substrate stage to a pattern of an original placed on an original stage
through a projection optical system, said method comprising steps of:
setting a target locus, of the substrate stage, corresponding to the
original;
preparing a correction table for correcting a shape error of a pattern of
the original formed on the substrate; and
correcting the target locus of the substrate stage based on the correction
table.
19. An exposure method of scan-exposing a surface of a substrate placed on
a substrate stage to a pattern of an original placed on an original stage
through a projection optical system, said method comprising:
setting a target locus, of the original stage, corresponding to the
original;
preparing a correction table for correcting a shape error of a pattern of
the original formed on the substrate; and
correcting the target locus of the original stage based on the correction
table.
Description
FIELD OF THE INVENTION
The present invention relates to an exposure method and apparatus and a
device manufacturing method and, more particularly, to an exposure method
and apparatus for transferring a master pattern onto a substrate while
moving a controlled element concerning exposure operation on the basis of
a target locus, and a device manufacturing method.
BACKGROUND OF THE INVENTION
There is a scanning exposure apparatus for projecting part of a master
pattern onto a substrate via a projection optical system, and scanning the
master and substrate perpendicularly to the optical axis of the projection
optical system, thereby transferring the master pattern to the substrate.
This scanning exposure apparatus adopts a method of correcting target
positions for all the axes of a substrate stage for holding a substrate or
those of a master stage for holding a master in accordance with a
polynomial whose variable is the position, along the scan axis, of the
substrate or master stage in a coordinate system defined using the center
of an exposure shot on the substrate or the center of the master pattern
as an origin.
With micropatterning of semiconductor integrated circuits, an insufficient
overlay (alignment) accuracy within a shot is becoming typical when
different types of exposure apparatuses are used in mix-and-match. That
is, only the function of faithfully transferring a master pattern onto a
substrate is not satisfactory. Demands are arising for deforming a master
pattern in accordance with the distortion within a shot on a layer already
formed on a substrate and transferring the master pattern onto the
substrate.
In recent years, a pellicle is generally attached to a master in order to
prevent a projected image from being deteriorated by contamination of a
master. However, adding a pellicle to a master mechanically distorts the
master, which distorts the master pattern. An overlay error by the
distortion of a master pattern is also increasing to a non-negligible
degree.
However, the conventional method cannot cope with changes in combinations
of exposure apparatuses or the distortion of a master pattern because the
target position of the master or substrate stage is corrected in
accordance with a fixed polynomial. The conventional method, therefore,
suffers from a low overlay accuracy.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above
situation, and has as its object to increase the overlay accuracy.
According to the first aspect of the present invention, there is provided
an exposure method of transferring a master pattern onto a substrate while
moving a controlled element concerning exposure operation on the basis of
a target locus, comprising the correction step of correcting the target
locus on the basis of correction information prepared in correspondence
with the master, and the transfer step of transferring the master pattern
onto the substrate while moving the controlled element toward the
corrected target locus.
The correction information includes, e.g., information corresponding to a
shape characteristic (e.g., distortion) of the master pattern and/or
information corresponding to a shape characteristic (e.g., distortion) of
a pattern already formed on the substrate.
The controlled element includes, e.g., a stage which moves while holding
the substrate or the master in an exposure operation, and in the transfer
step, the master pattern is transferred onto the substrate by a scanning
exposure method while the stage is moved.
The correction information preferably includes information corresponding to
a moving direction of the stage and/or information corresponding to a
moving speed of the stage.
The correction information is given as, e.g., a set of discrete correction
values.
In the correction step, the target locus is corrected on the basis of,
e.g., pairs of pieces of correction information. More specifically, the
correction step includes, e.g., the steps of synthesizing pairs of pieces
of correction information to generate a pair of pieces of correction
information, and correcting the target locus on the basis of the
synthesized correction information.
According to the second aspect of the present invention, there is provided
an exposure method of transferring a master pattern onto a substrate while
moving a controlled element concerning exposure operation, comprising
transferring the master pattern onto the substrate while moving the
controlled element in accordance with a target locus generated in
correspondence with a shape characteristic of the master pattern.
According to the third aspect of the present invention, there is provided
an exposure method of transferring a master pattern onto a substrate while
moving a controlled element concerning exposure operation, comprising
transferring the master pattern onto the substrate while moving the
controlled element in accordance with a target locus generated in
correspondence with a shape characteristic of a pattern already formed on
the substrate.
According to the fourth aspect of the present invention, there is provided
an exposure method of transferring a master pattern onto a substrate while
moving a controlled element concerning exposure operation, comprising
transferring the master pattern onto the substrate while moving the
controlled element in accordance with a target locus generated in
correspondence with a shape characteristic of the mask pattern and a shape
characteristic of a pattern already formed on the substrate.
According to the fifth aspect of the present invention, there is provided
an exposure apparatus for transferring a master pattern onto a substrate
while moving a controlled element concerning exposure operation on the
basis of a target locus, comprising a correction unit for correcting the
target locus on the basis of correction information prepared in
correspondence with the master, and a transfer unit for transferring the
master pattern onto the substrate while moving the controlled element
toward the target locus corrected by the correction unit.
According to the sixth aspect of the present invention, there is provided a
device manufacturing method comprising the coating step of coating a
substrate with a resist, the exposure step of transferring a master
pattern onto the substrate coated with the resist by the above exposure
method, and the developing step of developing the substrate bearing the
pattern.
According to the sixth aspect of the present invention, there is provided a
device manufacturing method comprising the first coating step of coating a
substrate with a first resist, the first exposure step of transferring a
first master pattern onto the substrate coated with the first resist, the
first developing step of developing the substrate bearing the first master
pattern, the second coating step of coating the developed substrate with a
second resist, the second exposure step of transferring a second master
pattern onto the substrate coated with the second resist, and the second
developing step of developing the substrate bearing the second master
pattern. The second exposure step includes the correction step of
correcting a target locus of a controlled element concerning exposure
operation on the basis of correction information corresponding to a shape
characteristic of the second master pattern and/or a shape characteristic
of a pattern formed on the substrate after the first developing step, and
the transfer step of transferring the second master pattern onto the
substrate while moving the controlled element toward the corrected target
locus.
The device manufacturing method according to the sixth aspect of the
present invention is preferable when different types of exposure
apparatuses are used in the first and second exposure steps.
Other features and advantages of the present invention will be apparent
from the following description taken in conjunction with the accompanying
drawings, in which like reference characters designate the same or similar
parts throughout the figures thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part
of the specification, illustrate embodiments of the invention and,
together with the description, serve to explain the principles of the
invention.
FIG. 1 is a sectional view showing the schematic structure of a scanning
exposure apparatus according to a preferred embodiment of the present
invention;
FIG. 2 is a view showing the central locus of an exposure slit when viewed
from above a wafer (locus a is obtained when the target value of a wafer
stage is corrected in a direction perpendicular to the scan direction by
using an overlay error correction table in the preferred embodiment of the
present invention, and a locus b is obtained when the target value of the
wafer stage is not corrected);
FIG. 3 is a block diagram showing a control unit for controlling the wafer
stage shown in FIG. 1;
FIG. 4 is a block diagram showing an example of signal processing in a
correction processing unit shown in FIG. 3;
FIG. 5 is a block diagram showing a detailed arrangement of an overlay
correction unit and a subtractor in FIG. 3;
FIG. 6 is a view showing an example of a direction overlay correction
table;
FIG. 7 is a graph showing two correction functions for the X-axis that are
attained by linearly interpolating the forward and reverse overlay
correction tables of the direction overlay correction table 503 shown in
FIG. 6;
FIG. 8 is a view showing an example of a user interface for setting the
direction overlay correction table;
FIG. 9 is a graph showing an example of the distribution shapes of
correction amounts in the first and second direction overlay correction
tables and their synthesized direction overlay correction table in FIG.
10;
FIG. 10 is a block diagram for explaining a method of synthesizing two
direction overlay correction tables as an example of a method of
synthesizing a plurality of direction overlay correction tables;
FIG. 11 is a flow chart showing a job processing sequence in the exposure
apparatus according to the preferred embodiment of the present invention;
FIG. 12 is a flow chart showing manufacturing flow for a microdevice (e.g.,
a semiconductor chip such as an IC or LSI, a liquid crystal panel, a CCD,
a thin-film magnetic head, a micromachine, or the like); and
FIG. 13 is a flow chart showing the detailed flow of the wafer process
shown in FIG. 12.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the present invention will be described below with
reference to the accompanying drawings.
FIG. 1 is a sectional view showing the schematic structure of a scanning
exposure apparatus according to a preferred embodiment of the present
invention. Exposure light emitted by a light source unit such as an
excimer laser reaches a slit 4 via a first condenser lens group 2. The
slit 4 narrows down the exposure light to a slit-like beam with a width of
about 7 mm in the Z direction. Further, the slit 4 adjusts the illuminance
integrated in the Z direction to be uniform over a predetermined range in
the X-axis direction. A masking blade 1 moves following the end of the
pattern drawing field angle of a reticle (master) 6 in exposure by
scanning a reticle stage (master stage) 5 and a wafer stage (substrate
stage) 16. The masking blade 1 prevents exposure light from entering the
light-transmitting portion of the reticle 6 and reaching a wafer 21 while
the reticle stage 5 decelerates after the end of pattern transfer onto the
reticle 6. The exposure light having passed through the masking blade 1
irradiates the reticle 6 on the reticle stage 5 via a second condenser
lens group 3. The exposure light having passed through the pattern of the
reticle 6 forms the imaging plane of the pattern near the surface of the
wafer (substrate) 21 via a projection lens 11. The projection lens 11
incorporates an NA stop 12 which can change the illumination mode in
exposure.
One-dimensionally movable TTL scopes 8 measure the X-, Y- and Z-axis
positions of an alignment mark formed on a reference mark 19 on the
reticle 6, wafer 21, or wafer stage 16 on the basis of the absolute
position references of the TTL scopes 8. Relay lenses 7 are used to adjust
the focuses of the TTL scopes 8. The focus of an object to be detected
(position in the Z-axis direction) can be measured by referring to the
positions of the relay lenses 7 while the alignment mark is in the best
in-focus state. In FIG. 1, two TTL scopes 8 are arranged in the Y
direction for illustrative convenience. In practice, another TTL scope is
arranged in the X direction. This arrangement enables measuring tilts in
.omega.x and .omega.y directions between the reticle alignment mark and
the wafer 21 or reference mark 19. The TTL scopes 8 shown in FIG. 1 can be
driven toward the center of a field angle (Y-axis direction).
The reticle stage 5 is controlled in the X, Y, and .theta. directions by
using three reticle laser interferometers 10. Only one reticle laser
interferometer 10 is shown in FIG. 1, but two reticle laser
interferometers 10 along the Y-axis and one reticle laser interferometer
10 along the X-axis are arranged in practice. The reticle stage 5 is
movable in the X, Y, and .theta. directions along guides on the lens
barrel surface plate 13. As for the Y-axis, the reticle stage 5 can move
over a long stroke in order to execute scanning exposure while moving in
synchronism with the wafer stage 16. As for the X- and .theta.-axes, the
reticle stage 5 can move only within a small range because it suffices to
eliminate an error upon chucking the reticle 6 by the reticle stage 5. In
this exposure apparatus, a reaction force upon driving the reticle stage 5
escapes to a reaction force absorption device (not shown) rigidly
connected to a base plate 18. A lens barrel surface plate 13 does not
shake in reaction to driving. The reticle stage 5 supports a reference
plate 9 on which a mark observable by the TTL scope 8 is drawn.
A focus detector 14 measures the positions of the wafer 21 or reference
mark 19 on the wafer stage 16 in the Z, .omega.x, and .omega.y directions
at a high speed without the mediacy of the projection lens 11 regardless
of the presence/absence of the mark. The focus detector 14 is used to
detect the focus in exposure during sync scan of the reticle stage 5 and
wafer stage 16. To ensure long-term stability of the measurement
precision, the focus detector 14 performs self-calibration by comparing
the result of measuring the reference mark 19 on the wafer stage 16 by the
TTL scope 8 with the result of measuring the reference mark 19 by the
focus detector 14.
An off-axis scope 20 has a single-lens focus measurement function and an
alignment error measurement function in the X and Y directions. In
aligning a wafer in a general mass production job, the off-axis scope 20
executes global tilt measurement and global alignment measurement. The
global tilt correction amount and global alignment correction amount are
reflected at once when the wafer stage 16 is so stepped as to position the
exposure area of a wafer below the projection lens 11.
The lens barrel surface plate 13 is a base for attaching the high-precision
measurement device of the exposure apparatus. The lens barrel surface
plate 13 is positioned while slightly floating from the base plate 18
directly placed on the floor. The above-described focus detector 14 and
TTL scope 8 are attached to the lens barrel surface plate 13, so that the
measurement values of these measurement devices are the results of
measuring relative distances from the lens barrel surface plate 13. A
surface plate interferometer 15 measures the relative positional
relationship between the lens barrel surface plate 13 and a stage surface
plate 17. In this embodiment, control (to be described with reference to
FIG. 6) is executed such that the sum of a measurement result by the
surface plate interferometer 15 and a measurement result by a triaxial Z
sensor (not shown) mounted on the wafer stage 16 coincides with a target
value designated by a host sequence. Thus, the wafer 21 on the wafer stage
16 is maintained with respect to the lens barrel surface plate 13 so as to
coincide with the target value designated by the host sequence. Three
wafer stage interferometers 22 are arranged, similar to the
interferometers for the reticle stage 5, and used to control the wafer
stage 16 in the X, Y, and .theta. directions.
Similar to the lens barrel surface plate 13, the stage surface plate 17 is
positioned while slightly floating from the base plate 18. The stage
surface plate 17 has a function of removing vibrations transmitted from
the floor to the wafer stage 16 via the base plate 18, and a function of
reducing a reaction force upon driving the wafer stage 16 and transmitting
the force to the base plate 18. The wafer stage 16 is mounted on the stage
surface plate 17 while floating by a small distance.
FIG. 2 is a view showing the central locus of an exposure slit (slit-like
exposure light projected via the projection lens 11) when viewed from
above the wafer 21. In FIG. 2, a locus a is obtained when the target value
of the wafer stage 16 is corrected in a direction perpendicular to the
scan direction by using an overlay error correction table (overlay
correction table) in the preferred embodiment of the present invention. A
locus b is obtained when the target value of the wafer stage 16 is not
corrected. Outer shot shapes 201a and 201b of the exposure slit are along
the loci a and b, respectively. The overlay error correction table
provides information for correcting the loci a and b.
FIG. 3 is a block diagram showing a control unit for controlling the wafer
stage 16 shown in FIG. 1. Outputs from Z sensors mounted on the wafer
stage interferometer 22, surface plate interferometer 15, and wafer stage
16 are input to a sensor signal input unit 301. These signals are
transferred to a correction processing unit 302 (to be described in detail
with reference to FIG. 4) where they receive correction processing such as
Abbe correction and orthogonality correction. The corrected signals are
output as data representing the current positions of respective axes from
the correction processing unit 302.
A profiler 307 smoothes stepwise changes in target value designated by the
host sequence so as not to apply acceleration more than a default value to
the wafer stage 16. An overlay correction unit 308 determines the
coordinates of the center of the exposure slit using the center of the
current exposure shot as an origin on the basis of the sequential target
positions (target locus) of the wafer stage 16 that are provided by the
profiler 307. Further, the overlay correction unit 308 determines a
correction amount by referring to a direction overlay correction table in
a memory 309 on the basis of the determined coordinates and the scan
direction, and outputs the correction amount to a subtractor 303. The
subtractor 303 compares the sum (i.e., corrected target position) of a
target position provided by the profiler 307 and the correction amount
provided by the overlay correction unit 308 with an output (i.e., current
position of the wafer stage) from the correction processing unit 302 to
calculate the deviation of the current position along each axis from the
corrected target position, and sends the deviation to a servo compensator
304.
The servo compensator 304 has a compensator (e.g., a PID controller or
notch filter) which considers the mechanical characteristics of the wafer
stage 16. An output from the servo compensator 304 is distributed by a
thrust distributor 305 as a manipulated variable for a plurality of
actuators of the wafer stage 16. The manipulated variable is output to
these actuators via a drive output unit 306.
FIG. 4 is a block diagram showing an example of signal processing in the
correction processing unit 302 shown in FIG. 3. FIG. 4 shows the flow of
reading, by a data processing system, outputs (measurement values) from
the Z sensors mounted on the wafer stage interferometer 22, surface plate
interferometer 15, and wafer stage 16, as described with reference to FIG.
1, and converting these outputs into the current position in the
mode-separated abstract coordinate system. Reference numerals 401 to 403
denote measurement values for the respective axes of the wafer stage
interferometer 22; 404 to 406, measurement values by the Z sensor of the
wafer stage 16; and 407 to 409, measurement values by the surface plate
interferometer 15. A laser beam used by each interferometer varies in
wavelength under the influence of the atmospheric pressure, temperature,
and humidity, so the measurement value of the interferometer must undergo
environmental correction (410a and 410b). As an example of the
environmental correction method, the measurement value is multiplied by a
variable magnification with respect to the reference length by using a
wavelength tracker.
Reference numeral 411 denotes mirror surface reformation processing. An
interferometer mirror along a long-stroke driving axis such as the X- and
Y-axes of the wafer stage 16 is difficult to process into an ideal
curvature of 0. Thus, the mirror curvature is corrected by software by a
correction value obtained by measuring the mirror flatness (mirror surface
reformation). The .theta.-axis value of the wafer stage 16 is attained by
calculating the difference between the measurement value (401) of an X1
interferometer (not shown) and the measurement value (402) of an X2
interferometer (not shown) (413), and dividing (415) the difference by the
span (Lq) between the X1 and X2 interferometers. The value attained by
this processing is subjected to magnification correction (416a).
The measurement values 404 to 406 of the Z sensor of the wafer stage 16 and
the measurement values 407 to 409 of the surface plate interferometer 15
are subjected to coordinate transformation (412a and 412b), added to each
other (414a to 414c), and subjected to magnification correction (416b).
The sums of the measurement values of the Z sensor of the wafer stage 16
and the measurement values of the surface plate interferometer 15
represent distances between the lens barrel surface plate 13 and the wafer
chuck on the wafer stage 16.
The measurement values (X", Y", .theta.", Z", .omega.x", and .omega.y")
obtained by these processes undergo inter-axial interference correction
(417). Inter-axial interference correction (417) includes Abbe correction
of correcting a measurement value error caused by a shift of measurement
light of the laser interferometer from a design position on the mirror and
a shift of the irradiation angle of measurement light of the laser
interferometer from a design angle, and guide flatness correction of
correcting the distortion of the guide flatness from the X-Y plane of the
wafer stage 16.
FIG. 5 is a block diagram showing a detailed arrangement of the overlay
correction unit 308 and subtractor 303 in FIG. 3. A table selector 501
reads a direction overlay correction table 503 (to be described with
reference to FIG. 6), and determines an overlay correction table
(forward/reverse table) to be used in accordance with a scan direction
(forward/reverse) 506 of the wafer stage 16. An interpolation processing
unit 502 linearly interpolates the overlay correction table selected by
the table selector 501, and calculates a correction amount in accordance
with a current position 504 of the wafer stage 16 and a central shot
position 507 obtained by the host sequence. The subtractor 303 adds the
result to a profile 508 serving as sequential target positions (target
locus) provided by the profiler 307, and subtracts the current position
504 of the wafer stage 16 provided by the correction processing unit 302
from the sum, obtaining a deviation output 505. In this example, the
sequential target positions (target locus) provided by the profiler 307
are corrected based on the overlay correction table in parallel to
exposure operation. This correction may be executed before exposure
operation. In this case, corrected target positions (target locus) are
saved, and the wafer stage 16 is driven in accordance with the target
positions (target locus) in exposure operation.
FIG. 6 shows an example of the direction overlay correction table 503. The
direction overlay correction table 503 is provided by, e.g., the user via
a terminal (not shown). The origin and data interval of the overlay
correction table are preferably variables in order to give flexibility to
a measurement reticle for creating a direction overlay correction table.
The direction overlay correction table includes two overlay correction
tables for "forward" and "reverse" scan directions of the wafer stage 16
in scanning exposure.
The present inventors have made extensive studies to find out that the
difference in controlled variables due to the difference in scan direction
(so-called scan direction difference) occurs by several nm when processing
shifts to exposure with a small relative sync error between the wafer
stage 16 and the reticle stage 5, or when the lens barrel surface plate 13
deforms owing to load variations at the position of the reticle stage 5.
The overlay accuracy can be increased by reducing the influence of the
scan direction difference as a shift generated when forward scanning
exposure and reverse scanning exposure are done at the same target value
of the shot center, or by positively correcting the shot shape and central
shot position in order to establish mix-and-match for a wafer exposed by
another type of scanning exposure apparatus which suffers from various
shot distortions in accordance with the scan position. The direction
overlay correction table may be set in accordance with a reticle used, or
may be selected from direction overlay correction tables registered for
respective reticles in accordance with a reticle used. If the scan
direction difference or shot distortion tends to change depending on the
scan speed, the direction overlay correction table may be set in
accordance with the scan speed, or a direction overlay correction table
corresponding to the scan speed may be selected from direction overlay
correction tables registered for respective scan speeds.
FIG. 7 shows two correction functions for the X-axis that are attained by
linearly interpolating the forward and reverse overlay correction tables
of the direction overlay correction table 503 shown in FIG. 6. The
interval between data of the overlay correction table is interpolated by a
linear function. Correction values at the two ends of a section where the
overlay correction table is defined are set to the same values as
correction values at the two ends of the overlay correction table for each
adjacent section. This can prevent abrupt changes in target value when the
wafer stage 16 comes to the end of the section where the overlay
correction table is defined. The correction function is defined for six
axes (X, Y, .theta., Z, .omega.x, and .omega.y) in each of the two,
forward and reverse scan directions.
The overlay correction table is interpolated as follows. Letting (Xtgt,
Ytgt) be the target value of the central point of the scanning exposure
shot, and (xc, yc) be the current coordinate values of the wafer stage 16,
a scanning exposure position (yk) in the current shot is given by
yk=-(yc-Ytgt) (1)
Letting Df(k) be data of the forward overlay correction table in the
direction overlay correction table 503, Dr(k) be data of the reverse
overlay correction table, Org be the origin of the overlay correction
table, 1 be the data interval, F(k) be the linear interpolation function
between Df(k-1) and Df(k), and G(k) be the linear interpolation function
between Dr(k-1) and Dr(k), correction functions in functional sections
partitioned by respective data are given by
Functional Section Function Functional Equation
yk .ltoreq. Org F(b) Df(0) (2)
Org .ltoreq. yk .ltoreq. Org + 1 F(1) Df(0) + (Df(1) -
Df(0)) (yk - Org)/1
Org + 1 .ltoreq. yk .ltoreq. Org + 21 F(2) Df(1) + (Df(2) -
Df(1)) (yk - Org - 1)/1
. . .
. . .
. . .
Org + (n - 1)1 .ltoreq. yk .ltoreq. F(n) Df(n - 1) + (Df(n) -
Org + n1 Df(n - 1)) (yk -
Org - nl)/1
Org + zl .ltoreq. yk F(E) Df(z)
(data of the overlay correction table is up to z) where n is given by
n=(int)((yk-Org)/l)+1 (3)
Reverse correction functions can be obtained based on an equation in which
F(n) and Df(n) in equation (2) are respectively replaced by G(n) and
Dr(n).
An interpolation method other than the above interpolation method is
preferably one using a function of second or higher order or a spline
function. If a discrete value is mixed in the overlay correction table and
directly used, the wafer stage 16 does not follow the target value, and
the sync error between the reticle stage 5 and the wafer stage 16
increases. To prevent this, data which form an overlay correction table
may be approximated into a simple shape such as a quadratic function by
using the least square method or the like.
Also, when a function which connects correction values formed based on the
overlay correction table has a complicated shape with many sharp
inflections, the wafer stage 16 does not follow the target value,
increasing the sync error. To prevent this, the shift amount at each point
is approximated by a low-order polynomial, and the coefficient value of
the approximate expression is held for each reticle, instead of holding
the shift amount at each point for each reticle in the above-mentioned
table form.
FIG. 8 is a view showing an example of a user interface for setting the
direction overlay correction table. This user interface is provided by
software installed in a terminal connected to the exposure apparatus. To
define one direction overlay correction table, the user interface allows
setting the origin of table data common to respective control axes, the
data interval, and the maximum number of data. In the example shown in
FIG. 8, twenty data (data 0 to data 19) can be set per axis at a maximum.
The data interval and the number of data are typically defined to cover
the exposure shot range or the range including the pre-scan region in
addition to the exposure shot region. Entry of data exceeding the maximum
number of data is ignored. In one direction overlay correction table, data
entries for six axes are preferably prepared for each of the two scan
directions.
The direction overlay correction table is used (1) to ensure the absolute
shape and layout reproducibility of the shot in the exposure apparatus
(i.e., to correct an alignment error caused by the machine), (2) to
correct a mask deformation or manufacturing error (this appears as a shape
characteristic such as the distortion of a pattern formed on the mask)
(i.e., to correct an alignment error caused by the mask), and (3) to
positively distort a pattern to be transferred or change the central
position in accordance with the shape characteristic such as the
distortion of a pattern formed on a wafer to be exposed (i.e., to correct
an alignment error caused by the process).
The machine-caused alignment error may be caused by the distortion of the
reticle due to a processing accuracy of a reticle-chucking portion of the
reticle stage. The machine-caused alignment error may also occur when the
positional relationship between the reticle and the mirror of the reticle
stage and the positional relationship between the wafer and the mirror of
the wafer stage change with a large time constant. Of machine-caused
alignment errors, the reproducibility error is measured in assembling and
adjusting the exposure apparatus. A direction overlay correction table for
correcting this error is created on the basis of the measurement result
and saved in a memory medium such as the hard disk of the exposure
apparatus. In exposure, the target locus of the wafer stage 16 is
corrected based on the direction overlay correction table. As for a
machine-caused alignment error generated after assembly/adjustment, for
example, a pattern is formed on a wafer by using a measurement reticle
(exposure, developing, etching, and the like), and a direction overlay
correction table for correcting this error is created on the basis of the
result. The target locus of the wafer stage 16 is corrected based on the
direction overlay correction table, thereby correcting the error.
The mask-caused alignment error may occur when the reticle deforms owing to
that stress of a pellicle attached to the reticle, which acts on the
reticle. As for the mask-caused alignment error, for example, a pattern is
formed on a wafer by using the reticle, and a direction overlay correction
table for correcting the error is created on the basis of the result
(shape characteristic such as the distortion of the formed pattern). The
target locus of the wafer stage 16 is corrected based on the direction
overlay correction table, thereby correcting the error.
The process-caused alignment error may occur when an underlayer is exposed
by using an exposure apparatus having a machine-caused alignment error or
a deformed reticle. As for the process-caused alignment error, a direction
overlay correction table for correcting the error is created on the basis
of the shape characteristic such as the distortion of a pattern formed by
an exposure apparatus for forming an underlayer. The target locus of the
wafer stage 16 is corrected based on the direction overlay correction
table, thereby correcting the error.
To correct all the machine-, mask-, and process-caused alignment errors, a
direction overlay correction table for correcting the machine-caused
alignment error, that for correcting the mask-caused alignment error, and
that for correcting the process-caused alignment error are effectively
synthesized into a new direction overlay correction table.
FIG. 10 is a block diagram for explaining a method of synthesizing two
direction overlay correction tables as an example of the method of
synthesizing a plurality of direction overlay correction tables. A first
direction overlay correction table 1002 input from a user interface 1001
as shown in FIG. 8 is used to correct a process-caused error. A second
direction overlay correction table 1004 is used to correct a
machine-caused error. The second direction overlay correction table 1004
is measured in factory adjustment, saved in a hard disk 1003 of a
pre-processing unit 1006 in the exposure apparatus shown in FIG. 1, and
read out in operating the exposure apparatus. The first and second
direction overlay correction tables are synthesized (e.g., added) by a
table synthesis logic 1005. The synthesized direction overlay correction
table is provided to the overlay correction unit 308.
In the above example, error factors are classified into machine and process
factors, but may be classified finely or in accordance with another
classification method. In this case, direction overlay correction tables
are created for respective factors and synthesized.
FIG. 9 is a graph showing an example of the distribution shapes of
correction amounts in the first and second direction overlay correction
tables and their synthesized direction overlay correction table in FIG.
10. The second direction overlay correction table set in factory
adjustment and the first direction overlay correction table set by the
user must assume different table origins and intervals because the pattern
used to measure a distortion within an exposure shot depends on the
reticle. That is, data of the two tables cannot always be simply added.
When the two tables have different origins and intervals, the origin and
interval of a synthesized direction overlay correction table are
determined. Then, the first and second direction overlay correction tables
are interpolated to generate data corresponding to the determined origin
and interval. The generated data are synthesized to create a synthesized
direction overlay correction table. In general, the second direction
overlay correction table for correcting a machine-caused error is rarely
changed after measurement is performed only once and the absolute layout
precision of the scanning exposure shot is adjusted to fall within the
allowable value. The first direction overlay correction table for
correcting a process-caused error is set based on the measurement result
every time the user process changes (including change of the reticle).
FIG. 11 is a flow chart showing a job processing sequence in the exposure
apparatus according to the preferred embodiment of the present invention.
If the job starts, a control device for controlling the exposure apparatus
reads out a job file which defines the shot layout, shot size, and
exposure amount of a wafer, the reticle index, and the like from a data
storage in the exposure apparatus or a file server on a network into the
memory of the control device in step S1101. Steps S1102 and S1105, steps
S1103 and S1106, and step S1104 are parallel-executed.
In step S1102, the control device loads a reticle parameter file
corresponding to a reticle designated in the job file. This reticle
parameter file describes parameters depending on the reticle, e.g.,
reticle alignment mark information and the exposure light transmittance of
the reticle. The reticle parameter file preferably includes the
above-described direction overlay correction table. By giving the reticle
parameter file the direction overlay correction table, the target
positions (target locus) of the wafer stage 16 can be corrected in
scanning exposure for each reticle. Also, when the direction overlay
correction table is loaded as another file in accordance with the reticle
designated in the job file, the target positions (target locus) of the
wafer stage can be corrected in scanning exposure for each reticle.
In step S1105, the loaded direction overlay correction table is transferred
to the memory 309 in the control unit shown in FIG. 3.
In step S1103, the reticle used in the previous job is exchanged for
another one designated in the job file under the control of the control
device. In step S1106, the exchanged reticle is aligned under the control
of the control device, thereby accurately specifying a position where the
pattern of the reticle is to be drawn. If necessary, the exposure light
transmittance is also measured.
In step S1104, a wafer is loaded under the control of the control device in
parallel with loading of the reticle parameter file and exchange of the
reticle.
After steps S1104, S1105, and S1106 end, wafer alignment measurement
processing is executed under the control of the control device in step
S1107. In step S1108, the target positions (target locus) of the wafer
stage 16 are corrected by the overlay correction unit 308 on the basis of
the direction overlay correction table under the control of the control
device. Exposure processing is performed while the wafer stage 16 is
driven in accordance with the corrected target positions (target locus).
In step S1109, the control device checks whether exposure processing ends
for all the wafers designated as the job. If NO in step S1109, the control
device loads the next wafer in step S1110 and repeats the sequence from
step S1107. If YES in step S1109, the job ends.
In the above embodiment, the target positions (target locus) of the wafer
stage 16 are corrected in accordance with the reticle. In addition to or
instead of this, the target positions (target locus) of the reticle stage
5 may be corrected in accordance with the reticle.
In addition to or instead of this, another controlled element, e.g., the
target value or target locus (e.g., projection magnification) of an
optical system such as a projection lens may be corrected in accordance
with the reticle.
An embodiment of a device production method using an exposure apparatus
represented by the scanning exposure apparatus described in the above
embodiment will be explained.
FIG. 12 is a flow chart showing a manufacturing flow for a microdevice
(e.g., a semiconductor chip such as an IC or LSI, a liquid crystal panel,
a CCD, a thin-film magnetic head, a micromachine, or the like). In step 1
(circuit design), a semiconductor device circuit is designed.
In step 2 (reticle formation), a reticle is formed on the basis of the
designed circuit pattern. In step 101, information for creating a
direction overlay correction table is acquired by setting the formed
reticle in the exposure apparatus, actually executing exposure processing,
and evaluating the exposure result, by evaluating a shape characteristic
such as the deformation of the formed reticle or the manufacturing error,
or by another appropriate method. It is also effective to acquire
information for creating another direction overlay correction table by
evaluating a shape characteristic such as the deformation of a pattern on
a wafer to be exposed to the reticle pattern in order to perform
mix-and-match. In step 102, a direction overlay correction table for the
reticle is set by using, e.g., the user interface shown in FIG. 8 on the
basis of the information acquired in step 101.
In step 3 (wafer formation), a wafer is formed by using a material such as
silicon. In step 4 (wafer process), called a pre-process, an actual
circuit is formed on the wafer by lithography including the step of
setting the reticle in the exposure apparatus and transferring the reticle
pattern onto the wafer while correcting the target value of a controlled
element such as the stage in accordance with the reticle. Step 5
(assembly), called a post-process, is the step of forming a semiconductor
chip by using the wafer formed in step 4, and includes an assembly process
(dicing and bonding), and a packaging process (chip encapsulation). In
step 6 (inspection), inspections such as the operation confirmation test
and durability test of the semiconductor device manufactured in step 5 are
conducted. After these steps, the semiconductor device is completed and
shipped (step 7).
FIG. 13 shows the detailed flow of the wafer process shown in FIG. 12. In
step 11 (oxidation), the wafer surface is oxidized. In step 12 (CVD), an
insulating film is formed on the wafer surface. In step 13 (electrode
formation), an electrode is formed on the wafer by vapor deposition. In
step 14 (ion implantation), ions are implanted in the wafer. In step 15
(resist processing), a photosensitive agent is applied to the wafer. In
step 16 (exposure), the circuit pattern is transferred to the wafer by the
exposure apparatus while the target value of the controlled element such
as the stage is corrected in accordance with the reticle. In step 17
(developing), the wafer bearing the pattern is developed. In step 18
(etching), the resist is etched except for the developed resist image. In
step 19 (resist removal), an unnecessary resist after etching is removed.
These steps are repeated to form multiple circuit patterns on the wafer.
The exposure step (step 16) executed a plurality of number of times in
order to form multiple circuit patterns can use different types of
exposure apparatuses (mix-and-match). At this time, the target position of
the controlled element such as the stage can be so corrected as not to
generate any overlay error by the difference in type.
The manufacturing method according to the embodiment can manufacture a
highly integrated semiconductor device at low cost, which is difficult to
manufacture by a conventional method.
The present invention can increase the overlay accuracy.
As many apparently widely different embodiments of the present invention
can be made/without departing from the spirit and scope thereof, it is to
be understood that the invention is not limited to the specific
embodiments thereof except as defined in the claims.
*
