U.S. patent application number 09/794340 was filed with the patent office on 2001-08-09 for exposure apparatus and device manufacturing method.
Invention is credited to Hasegawa, Noriyasu, Kurosawa, Hiroshi, Ozawa, Kunitaka, Yoshimura, Keiji.
Application Number | 20010012100 09/794340 |
Document ID | / |
Family ID | 26534445 |
Filed Date | 2001-08-09 |
United States Patent
Application |
20010012100 |
Kind Code |
A1 |
Kurosawa, Hiroshi ; et
al. |
August 9, 2001 |
Exposure apparatus and device manufacturing method
Abstract
An exposure apparatus includes a light source for providing
pulse light, a mask scanning machanism for scanning a mask having a
pattern, a wafer scanning mechanism for scanning a wafer onto which
the pattern is to be projected, wherein the mask scanning machanism
and the wafer scanning mechanism serve to scan the mask and the
wafer in a timed relation so that the mask is illuminated while
superposing portions of an illumination region defined by the pulse
light and being narrower than the pattern such that the pattern is
lithographically transferred onto the wafer, and a scan speed
determining system for determining scan speed of the mask and the
wafer, the scan speed being variable on the basis of a tolerance
ratio of exposure non-uniformness.
Inventors: |
Kurosawa, Hiroshi;
(Matsudo-shi, JP) ; Ozawa, Kunitaka;
(Utsunomiya-shi, JP) ; Hasegawa, Noriyasu;
(Utsunomiya-shi, JP) ; Yoshimura, Keiji;
(Utsunomiya-shi, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Family ID: |
26534445 |
Appl. No.: |
09/794340 |
Filed: |
February 28, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09794340 |
Feb 28, 2001 |
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08705089 |
Aug 29, 1996 |
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6204911 |
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Current U.S.
Class: |
355/53 ; 355/67;
355/69; 355/71; 355/77 |
Current CPC
Class: |
G03F 7/70558 20130101;
G03F 7/70358 20130101 |
Class at
Publication: |
355/53 ; 355/69;
355/67; 355/71; 355/77 |
International
Class: |
G03B 027/42 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 30, 1995 |
JP |
245427/1995 |
Aug 22, 1996 |
JP |
239842/1996 |
Claims
What is claimed is:
1. An exposure apparatus, comprising: a light source for providing
pulse light; mask scanning means for scanning a mask having a
pattern; wafer scanning means for scanning a wafer onto which the
pattern is to be projected; wherein said mask scanning means and
said wafer scanning means serve to scan the mask and the wafer in a
timed relation so that the mask is illuminated while superposing
portions of an illumination region defined by the pulse light and
being narrower than the pattern such that the pattern is
lithographically transferred onto the wafer; and scan speed
determining means for determining scan speed of the mask and the
wafer, the scan speed being variable on the basis of a tolerance
ratio of exposure non-uniformness.
2. An apparatus according to claim 1, wherein the scan speed is
larger with a larger tolerance ratio of exposure
non-uniformness.
3. An apparatus according to claim 2, wherein the scan speed is
highest within a range in which the tolerance ratio of exposure
non-uniformness is satisfied.
4. An apparatus according to claim 1, wherein the tolerance ratio
of exposure non-uniformness is determined on the basis of a minimum
linewidth of the pattern.
5. An apparatus according to claim 4, wherein the tolerance ratio
of exposure non-uniformness is larger with a wider minimum
linewidth of the pattern.
6. An exposure apparatus, comprising: a light source for providing
pulse light; mask scanning means for scanning a mask having a
pattern; wafer scanning means for scanning a wafer onto which the
pattern is to be projected; wherein said mask scanning means and
said wafer scanning means serve to scan the mask and the wafer in a
timed relation so that the mask is illuminated while superposing
portions of an illumination region defined by the pulse light and
being narrower than the pattern such that the pattern is
lithographically transferred onto the wafer; and light emission
period determining means for determining the period of emission of
the pulse light, the light emission period being variable on the
basis of a tolerance ratio of exposure non-uniformness.
7. An apparatus according to claim 6, wherein the light emission
period is larger with a larger tolerance ratio of exposure
non-uniformness.
8. An apparatus according to claim 7, wherein the light emission
period is highest within a range in which the tolerance ratio of
exposure non-uniformness is satisfied.
9. An apparatus according to claim 8, wherein the light emission
period is determined on the basis of a scan speed of the mask and
the wafer, and wherein the scan speed is highest as much as
possible.
10. An apparatus according to claim 9, wherein the scan speed is
restricted by an alignment precision of the mask and the wafer.
11. An apparatus according to claim 6, the tolerance ratio of
exposure non-uniformness is determined on the basis of a minimum
linewidth of the pattern.
12. An apparatus according to claim 11, wherein the tolerance ratio
of exposure non-uniformness is larger with a wider minimum
linewidth of the pattern.
13. An exposure apparatus, comprising: a light source for providing
pulse light; mask scanning means for scanning a mask having a
pattern; wafer scanning means for scanning a wafer onto which the
pattern is to be projected; wherein said mask scanning means and
said wafer scanning means serve to scan the mask and the wafer in a
timed relation so that the mask is illuminated while superposing
portions of an illumination region defined by the pulse light and
being narrower than the pattern such that the pattern is
lithographically transferred onto the wafer; illumination range
limiting means for limiting a range of illumination for the mask by
the pulse light, said illumination range limiting means is adapted
to change the range of illumination for the mask; and illumination
range determining means for determining the range of illumination
for the mask, wherein the width of the illumination range with
respect to a scan direction is variable on the basis of a tolerance
ratio of exposure non-uniformness.
14. An apparatus according to claim 13, wherein the width of the
illumination range with respect to the scan direction is narrower
with a larger tolerance ratio of exposure non-uniformness.
15. An apparatus according to claim 13, wherein the tolerance ratio
of exposure non-uniformness is determined on the basis of a minimum
linewidth of the pattern.
16. An apparatus according to claim 15, wherein the tolerance ratio
of exposure non-uniformness is larger with a wider minimum
linewidth of the pattern.
17. An exposure apparatus, comprising: a light source for providing
pulse light; mask scanning means for scanning a mask having a
pattern; wafer scanning means for scanning a wafer onto which the
pattern is to be projected; wherein said mask scanning means and
said wafer scanning means serve to scan the mask and the wafer in a
timed relation so that the mask is illuminated while superposing
portions of an illumination region defined by the pulse light and
being narrower than the pattern such that the pattern is
lithographically transferred onto the wafer; illumination range
limiting means for limiting a range of illumination for the mask by
the pulse light, said illumination range limiting means is adapted
to change the range of illumination for the mask; position changing
means for changing a position of said illumination range limiting
means with respect to a direction of an optical axis; and position
determining means for determining the position of said illumination
range limiting means, the position of said illumination range
limiting means with respect to the optical axis direction being
variable on the basis of a tolerance ratio of exposure
non-uniformness.
18. An apparatus according to claim 17, wherein the position of the
illumination range limiting means with respect to the optical axis
direction has a deviation from a position being optically conjugate
with the mask, the deviation being smaller with a larger tolerance
ratio of exposure non-uniformness.
19. An apparatus according to claim 17, wherein the tolerance ratio
of exposure non-uniformness is determined on the basis of a minimum
linewidth of the pattern.
20. An apparatus according to claim 19, wherein the tolerance ratio
of exposure non-uniformness is larger with a wider minimum
linewidth of the pattern.
21. A device manufacturing method including lithographically
transferring a pattern of a mask onto a wafer, said method
comprising the steps of: providing pulse light; scanning the mask
and the wafer in a timed relation; illuminating the mask while
superposing portions of an illumination region defined by the pulse
light and being narrower than the pattern such that the pattern is
lithographically transferred onto the wafer; and determining scan
speed of the mask and the wafer, the scan speed being variable on
the basis of a tolerance ratio of exposure non-uniformness.
22. A method according to claim 21, wherein the scan speed is
larger with a larger tolerance ratio of exposure
non-uniformness.
23. A method according to claim 22, wherein the scan speed is
highest within a range in which the tolerance ratio of exposure
non-uniformness is satisfied.
24. A method according to claim 21, wherein the tolerance ratio of
exposure non-uniformness is determined on the basis of a minimum
linewidth of the pattern.
25. A method according to claim 22, wherein the tolerance ratio of
exposure non-uniformness is larger with a wider minimum linewidth
of the pattern.
26. A device manufacturing method including lithographically
transferring a pattern of a mask onto a wafer, said method
comprising the steps of: providing pulse light; scanning the mask
and the wafer in a timed relation; illuminating the mask while
superposing portions of an illumination region defined by the pulse
light and being narrower than the pattern such that the pattern is
lithographically transferred onto the wafer; and determining a
period of emission of the pulse light, the light emission period
being variable on the basis of a tolerance ratio of exposure
non-uniformness.
27. A method according to claim 26, wherein the light emission
period is larger with a larger tolerance ratio of exposure
non-uniformness.
28. A method according to claim 27, wherein the light emission
period is highest within a range in which the tolerance ratio of
exposure non-uniformness is satisfied.
29. A method according to claim 28, wherein the light emission
period is determined on the basis of a scan speed of the mask and
the wafer, and wherein the scan speed is highest as much as
possible.
30. A method according to claim 29, wherein the scan speed is
restricted by an alignment precision of the mask and the wafer.
31. A method according to claim 26, wherein the tolerance ratio of
exposure non-uniformness is determined on the basis of a minimum
linewidth of the pattern.
32. A method according to claim 26, wherein the tolerance ratio of
exposure non-uniformness is larger with a wider minimum linewidth
of the pattern.
33. A device manufacturing method including lithographically
transferring a pattern of a mask onto a wafer, said method
comprising the steps of: providing pulse light; scanning the mask
and the wafer in a timed relation; illuminating the mask while
superposing portions of an illumination region defined by the pulse
light and being narrower than the pattern such that the pattern is
lithographically transferred onto the wafer; and determining an
illumination range for illumination of the mask by the pulse light,
wherein the width of the illumination range with respect to a scan
direction is variable on the basis of a tolerance ratio of exposure
non-uniformness.
34. A method according to claim 33, wherein the width of the
illumination range with respect to the scan direction is narrower
with a larger tolerance ratio of exposure non-uniformness.
35. A method according to claim 33, wherein the tolerance ratio of
exposure non-uniformness is determined on the basis of a minimum
linewidth of the pattern.
36. A method according to claim 35, wherein the tolerance ratio of
exposure non-uniformness is larger with a wider minimum linewidth
of the pattern.
37. A device manufacturing method including lithographically
transferring a pattern of a mask onto a wafer, said method
comprising the steps of: providing pulse light; scanning the mask
and the wafer in a timed relation; illuminating the mask while
superposing portions of an illumination region defined by the pulse
light and being narrower than the pattern such that the pattern is
lithographically transferred onto the wafer; determining a position
of illumination range limiting means, for limiting a range of
illumination of the mask by the pulse light, with respect to a
direction of an optical axis, the position of the illumination
range limiting means with respect to the optical axis direction
being variable on the basis of a tolerance ratio of exposure
non-uniformness.
38. A method according to claim 37, wherein the position of the
illumination range limiting means with respect to the optical axis
direction has a deviation from a position being optically conjugate
with the mask, the deviation being smaller with a larger tolerance
ratio of exposure non-uniformness.
39. A method according to claim 37, wherein the tolerance ratio of
exposure non-uniformness is determined on the basis of a minimum
linewidth of the pattern.
40. A method according to claim 39, wherein the tolerance ratio of
exposure non-uniformness is larger with a wider minimum linewidth
of the pattern.
Description
FIELD OF THE INVENTION AND RELATED ART
[0001] This invention relates to an exposure apparatus and, more
particularly, to an exposure apparatus suitably usable in a
lithographic process of device manufacturing processes for a
semiconductor device such as IC or LSI, a liquid crystal device, an
image pickup device such as CCD or a magnetic head, for
example.
[0002] With the need of miniaturization of an IC pattern, strict
precision is required to exposure non-uniformness in a lithographic
process. For a dynamic RAM of 256 MB, as an example, a line width
processing precision of 0.25 micron is required and, in this case,
a tolerable exposure non-uniformness is estimated as about 1%.
[0003] Also, in respect to the wavelength of exposure light, for
enhancement of resolution, those light sources which provide light
of shorter wavelength than i-line of conventional Hg lamps have
been recently used. Excimer lasers are a typical example of them.
However, excimer lasers are interrupted light emission type lasers,
and they produce light of pulses. At an upper limit level, for
light emission spacings of about 2.5 msec., the duration of light
emission is about several tens nsec. Further, there is a problem
that the emitted light intensity of each pulse light disperses
largely to a controlled variable applied externally.
[0004] In a case of scan type exposure apparatus having a light
source of excimer laser, for example, since the number of light
pulses necessary for exposure of one shot is about fifty (50), if
the emitted light intensity varies by one pulse due to dispersion
of the intensity of each pulse, then a quantized error results and,
by plural light pulses, a deterministic error of integrated
exposure amount is produced.
[0005] In an exposure apparatus which uses a light source
comprising a pulse light source such as an excimer laser wherein
the emitted light intensity varies with emissions of light, as
compared with an exposure apparatus having a conventional light
source of Hg lamp, for example, it is not easy to make uniform the
integrated exposure amount upon a substrate to be exposed.
[0006] In scanning exposure apparatuses, the integrated exposure
amount in an arbitrary unit scan exposure region involves a
non-correctable residual error which is provided by an intensity
error of a last pulse light emitted last in the process of scan
exposure. This causes non-uniformness of exposure. If the emitted
light intensity of each pulse is lowered and, on the other hand,
the light emission frequency of the pulse light source is
increased, the error by the last emitted pulse light becomes
relatively small, relative to the integrated exposure amount. Thus,
the exposure non-uniformness may be reduced.
[0007] However, there is an upper limit to the light emission rate
of a pulse light source. Currently, about 400 Hz is the upper
limit. As a result, if the method described above is to be used to
make the integrated exposure amount uniform, the emitted light
intensity of the pulse light source as well as the scan speed have
to be lowered to enlarge the number of average light pulses
received by a unit scan exposure region. This necessarily results
in slower throughput.
[0008] On the other hand, in manufacture of semiconductor device,
exposure processes of a number ten (10) to twenty (20) are
repeatedly executed to one semiconductor substrate (wafer). These
exposure processes have different linewidth precisions and
alignment precisions to patterns to be printed by respective
processes. In consideration of this, a method has been proposed in
which different exposure apparatuses are used for a critical layer
where a high precision is required and for a rough layer where a
precision as high as that for the critical layer is not required.
As for the exposure apparatus for the exposure process of rough
layers, an apparatus which enables a high throughput, though
precision is not required therefor, has been used.
SUMMARY OF THE INVENTION
[0009] It is an object of the present invention to provide an
exposure apparatus which enables optimization of performance such
as throughput or exposure precision, for example, as required to an
exposure apparatus, in accordance with the fineness of a pattern,
this being able to be done by changing a parameter related to scan
exposure on the basis of a tolerance ratio of exposure
non-uniformness.
[0010] In accordance with an aspect of the present invention, there
is provided an exposure apparatus, comprising: a light source for
providing pulse light; mask scanning means for scanning a mask
having a pattern; wafer scanning means for scanning a wafer onto
which the pattern is to be projected; wherein said mask scanning
means and said wafer scanning means serve to scan the mask and the
wafer in a timed relation so that the mask is illuminated while
superposing portions of an illumination region defined by the pulse
light and being narrower than the pattern such that the pattern is
lithographically transferred onto the wafer; and at least one of
(i) scan speed determining means for determining scan speed of the
mask and the wafer, (ii) light emission period determining means
for determining the period of emission of the pulse light, (iii)
illumination range determining means for determining the range of
illumination for the mask, and (iv) position determining means for
determining the position of illumination range limiting means with
respect to a direction of an optical axis, such that a parameter
related to scan exposure such as the scan speed, the light emission
period, the illumination range or the position of the illumination
range limiting means with respect to the optical axis direction,
can be made variable on the basis of a tolerance ratio of exposure
non-uniformness.
[0011] The tolerance ratio of exposure non-uniformness may
preferably be determined on the basis of a minimum linewidth of the
pattern.
[0012] The tolerance ratio of exposure non-uniformness may
preferably be larger with a wider minimum linewidth of the
pattern.
[0013] In an exposure apparatus according to the present invention,
if there is a margin to the tolerance ratio of exposure
non-uniformness, the light emission period of the light source may
be prolonged while maintaining the exposure non-uniformness at
about a tolerable level, by which the lifetime of the light source
can be prolonged.
[0014] With an exposure apparatus according to the present
invention, accurate manufacture of a device such as semiconductor
device, a liquid crystal device, an image pickup device or a
magnetic head, for example, is enabled.
[0015] These and other objects, features and advantages of the
present invention will become more apparent upon a consideration of
the following description of the preferred embodiments of the
present invention taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a schematic and diagrammatic view of an exposure
apparatus according to a first embodiment of the present
invention.
[0017] FIG. 2 is a schematic view of a main portion of a movable
slit 6 as viewed in the direction of an optical axis of an
illumination optical system.
[0018] FIG. 3 is a schematic view for explaining changes in
intensity profile as a width w of an exposure slit 6a is
changed.
[0019] FIG. 4 is a schematic view for explaining changes in width
of a half shadow region as a movable slit 6 moves in the direction
of an optical axis.
[0020] FIG. 5 is a flow chart for explaining operations made in the
first embodiment.
[0021] FIG. 6 is a graph for explaining a model of intensity
profile of exposure light upon a substrate 11.
[0022] FIG. 7 is a graph for explaining estimation of integrated
exposure amount upon a substrate 11 in a case where the substrate
is exposed with exposure light having an intensity profile such as
shown in FIG. 6.
[0023] FIG. 8 is a schematic view for explaining the mechanism of
production of non-uniformness .DELTA.S of integrated exposure
amount.
[0024] FIG. 9 is a schematic view for explaining the principle of
control in a second embodiment of the present invention.
[0025] FIG. 10 is a flow chart for explaining semiconductor device
manufacturing processes.
[0026] FIG. 11 is a flow chart for explaining details of a wafer
process among the processes of FIG. 10.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] FIG. 1 is a schematic view showing the structure of an
exposure apparatus according to a first embodiment of the present
invention. In this embodiment, the invention is applied to an
exposure apparatus for manufacture of devices such as semiconductor
devices (ICs or LSIs), image pickup devices such as CCDs or
magnetic heads, for example. The exposure apparatus is arranged so
that light from a light source is projected to a reticle through an
illumination optical system and a circuit pattern formed on the
reticle is projected and printed by a projection lens, in a reduced
scale, on a substrate which is coated with a photosensitive
material.
[0028] Denoted in the drawing at 1 is a light source which
comprises a pulse laser such as an excimer laser, for example, and
it emits pulse light. Denoted at 2 is a beam shaping optical system
for transforming light from the light source 1 into a desired
shape, the resultant light being projected on a light entrance
surface of an optical integrator 3. The optical integrator 3
comprises a fly's eye lens having a number of small lenses. Plural
secondary light sources are defined in the vicinity of the light
exit surface of the integrator. Denoted at 4 is a condenser lens
which serves to Kohler illuminate a movable slit 6 with light from
the secondary light sources adjacent to the light exit surface of
the optical integrator 3.
[0029] The light illuminating the movable slit 6 then illuminates a
reticle 9 by way of an imaging lens 7 and a mirror 8. The movable
slit 6 is disposed at a position slightly shifted from a position
which is optically conjugate with the reticle 9, and the movable
slit 6 is made movable along a direction of an optical axis. The
shape of an opening of the movable slit 6 is effective to determine
the shape and size of an illumination region on the reticle 9.
Denoted at 18 is a voice coil motor for movement control of the
movable slit 6 in the optical axis direction. Denoted at 12A is an
exposure amount detector (detector A) for detecting the light
quantity of a portion of pulse illumination light, being divided by
a half mirror 5. It applies an output signal to an exposure amount
calculator 102.
[0030] The beam shaping optical system 2, the optical integrator 3,
the condenser lens 4, the movable slit 6, the imaging lens 7 and
the mirror 8 are components of an illumination optical system. The
illumination optical system further includes a light attenuating
means (not shown), such that the light quantity from the light
source 1 can be adjusted at plural stages.
[0031] The reticle 9 has a circuit pattern formed thereon, and it
is held on a reticle stage 13. Denoted at 10 is a projection lens
for projecting the circuit pattern of the reticle 9 upon a
semiconductor substrate 11 in a reduced scale. The semiconductor
substrate 11 is called a wafer, and a resist material
(photosensitive material) is applied to the surface thereof. The
wafer is placed on a wafer stage which is movable
three-dimensionally. Here, the relation between an exposure slit 6a
as defined by the movable slit 6 and an image of the exposure slit
6a as formed on the semiconductor substrate 11, that is, the
magnification, is denoted by .beta..sub.S-W.
[0032] Mounted on the wafer stage 14 is an exposure amount detector
(detector B) 15 by which the exposure amount with exposure light
can be monitored through the projection lens 10.
[0033] Denoted at 101 is a stage drive control system, and it
serves to control the reticle stage 13 and the wafer stage 14 so
that they are moved in opposite directions at speeds of a ratio the
same as the projection magnification of the projection lens 10 (1:4
in this embodiment), exactly at constant speeds. The exposure
amount calculator 102 serves to transform an electric signal, being
photoelectrically converted by the exposure amount detector
(detector A) 12 or exposure amount detector (detector B) 15, into a
logic value, and to apply the result to a main control system 104.
It is to be noted that, since the exposure amount detector
(detector A) 12 can perform the intensity measurement even during
the exposure process, it is used for estimation of integrated value
of exposure light to be projected. The exposure amount detector
(detector B) 15 detects, at an initial stage of the exposure
process, the intensity of light passing the projection lens 10 and
impinging on the substrate 11. Then, the correlation between the
thus detected light intensity and the light intensity as detected
by the exposure amount detector (detector A) 12 is determined. In
actual exposure process, the value as detected by the exposure
amount detector (detector A) 12 is corrected by using the thus
determined correlation, to determine the exposure amount upon the
substrate 11. Thus, the exposure amount detector (detector B) 15
does not perform measurement of exposure light intensity during the
exposure process of the substrate 11.
[0034] Denoted at 103 is a laser control system which produces a
trigger signal 16 and a charging voltage signal 17 in accordance
with a desired exposure amount, and it controls the output energy
and the light emission spacing of the light source 1. When the
laser control system 103 produces the trigger signal 16 or charging
voltage signal 17, an illuminance monitor signal 108 from the
exposure amount calculator 102, a current position signal 107 from
the stage drive control system 101 and hysteresis information from
the main control system 104, for example, are used as
parameters.
[0035] Desired exposure amount and tolerance for exposure
non-uniformness are inputted into the main control system 104, from
an input device 105 which is a man-machine interface or a media
interface. The result obtained through the exposure amount detector
(detector A) 12 or exposure amount detector (detector B) 15, or the
result of estimation of integrated exposure amount are displayed in
a display 106.
[0036] From the data applied by the input device 105, from
parameters peculiar to the exposure apparatus and/or from the data
measured by the measuring means such as the exposure amount
detectors (detectors A and B) 12 and 15, for example, the main
control system 104 calculates a parameter group necessary for
execution of scan exposure and transmits it to the laser control
system 103 or the stage control system 101.
[0037] FIG. 2 is a schematic view of a main portion of the movable
slit 6 as viewed in the direction of the optical axis of the
illumination optical system. Denoted in the drawing at 701 are two
movable aperture blades which can be moved in opposite directions,
along a direction Xs (scan direction), by means of an aperture
driving device 702, and an exposure slit 6a is defined between
these blades. The size of the exposure slit 6a is determined by the
width w between the two movable aperture blades 701 and by the
length h (fixed) in a direction perpendicular to the direction Xs.
When the width w of the exposure slit 6a changes, the intensity
profile upon the substrate 11 of exposure light passing this slit
changes such as shown in FIG. 3.
[0038] FIG. 3 is a schematic view for explaining changes in
intensity profile as the width w of the exposure slit 6a of this
embodiment changes. The drawing illustrates changes in intensity
profile upon the substrate 11 as the width w of the two aperture
blades 701 changes from w1 to w2. The axis of abscissa in the
drawing corresponds to x.sub.w coordinate which is the scan
direction of the substrate 11. The axis of ordinate corresponds to
the intensity of exposure light upon the substrate 11. As the width
w changes from w1 to w2, upon the substrate 11, the distance
between mid points on opposite slant sides (half shadow or penumbra
portions) of a trapezoidal intensity profile changes from
d1=w1.multidot..beta..sub.S-W (profile 1) to
d2=w2.multidot..beta..sub.S-- W (profile 2). Namely, only the
portions corresponding to the top and bottom of the trapezoid
expand or contract, and the inclination of the slant sides (half
shadow portions) does not change. Thus, if the width w is enlarged,
the exposure area by one pulse increases, which is effective to
enlarge the throughput. Since however the length of diagonal of the
range (w.multidot..beta..sub.S-W.times.h.multidot..beta..sub.S-W)
of the image of the exposure slit upon the substrate 11 is unable
to extend beyond the diameter .phi..sub.0 of the effective picture
field of the projection lens 10 upon the substrate 11, there is an
upper limit w.sub.max= d.sub.max/.beta..sub.S-W to the width w of
the exposure slit 6a.
[0039] FIG. 4 is a schematic view for explaining changes in width
of half shadow region in a case where the movable slit of this
embodiment moves in the optical axis direction. The drawing
illustrates a change in intensity profile as the movable slit 6 is
moved by the voice coil motor 18 along the optical axis of the
illumination optical system. When the movable slit 6 moves while
the width w of the exposure slit 6a is held unchanged, the
intensity profile upon the substrate 11 changes from profile 1 to
profile 3 illustrated. In this occasion, the inclination of the
slant sides of the trapezoid changes, and the width r of the half
shadow upon the plane of projection changes from r1 to r2. Thus, if
the width r of the half shadow portion is to be changed, the
movable slit 6 may be moved.
[0040] FIG. 5 is a flow chart of this embodiment. This flow chart
covers the procedure from determination of the slit width w, the
position of the movable slit 6 in the optical axis direction and
the scan speed v of the wafer stage 14 on the basis of given
environment variables, to execution of the scan exposure process.
The following reference characters are used in the flow chart:
[0041] .beta..sub.S-W: magnification of projection of exposure slit
6a onto substrate 11
[0042] w: width of exposure slit 6a (width in scan direction)
[0043] h: length of exposure slit 6a in a direction perpendicular
to scan direction
[0044] d: width of image of exposure slit 6a upon substrate 11, and
d=w.multidot..beta..sub.S-W
[0045] e: length of image of exposure slit 6a upon substrate 11 in
a direction perpendicular to scan direction, and
e=h.multidot..beta..sub.S-- W
[0046] v: scan speed of wafer stage 14
[0047] .delta.: dispersion coefficient of emitted light
intensity
[0048] .delta..sub.m: maximum level of dispersion coefficient of
emitted light intensity
[0049] r: width of half shadow region on substrate 11
[0050] r.sub.c: intensity correction point
[0051] i.sub.c: light intensity at intensity correction point
[0052] i.sub.0: reference emission light intensity of light source
1 upon substrate 11
[0053] N: number of light emissions necessary for achieving target
value of integrated exposure amount
[0054] S: target value of integrated exposure amount
[0055] .DELTA.S: tolerance value for non-uniformness of integrated
exposure amount
[0056] .DELTA.S/S: tolerance ratio for non-uniformness of
integrated exposure amount
[0057] T: light emission period (light emission spacing)
[0058] .phi..sub.0: diameter of effective picture field of
projection lens (on wafer side)
[0059] Now, description will be made with reference to the flow
chart.
[0060] Step 801
[0061] Dispersion rate .delta. of emitted light intensity as the
light source is pulse oscillated is measured. To this end, the
light source 1 is caused to emit light for measurement. Charging
voltage signals of constant level and trigger signals of constant
intervals are applied to the light source 1, and emitted light
intensities are measured through the exposure amount detector
(detector A or B) 12 or 15. As for the dispersion coefficient
.delta., a statistically representative value among thus measured
values, e.g., 2.sigma., is used.
[0062] Step 802
[0063] Integrated exposure amount S and tolerance ratio .DELTA.S/S
of non-uniformness of integrated exposure amount are inputted
through the input device 105. Generally, the tolerance ratio
.DELTA.S/S of non-uniformness of integrated exposure amount should
be smaller with smaller linewidth of a circuit pattern on a reticle
9. Thus, the value .DELTA.S/S is determined while taking into
account the linewidth of a circuit.
[0064] Step 803
[0065] By using these values, the main control system 104
determines the scan speed v of the wafer stage 14, the width w of
the exposure slit 6a, and the position of the movable slit 6. The
manner of determination will be described later. Then, the
throughput is predicted.
[0066] Step 804
[0067] The display 106 displays the thud determined scan speed v,
width w of exposure slit 6a and position of movable slit 6 as well
as calculated throughput. The operator determines whether the
operation should be executed under these conditions or not. If the
conditions being displayed are satisfactory, the procedure goes to
step 806. If any of conditions displayed should be changed, the
procedure goes to step 805.
[0068] Step 805
[0069] Tolerance ratio .DELTA.S/S of non-uniformness of integrated
exposure amount is set again. As regards the throughput, if the
tolerance value .DELTA.S of non-uniformness of integrated exposure
amount is too much regarded, the reference emission light intensity
i.sub.0 of the light source 1 has to be lowered optically by using
a filter or the like to increase the number N of light emissions.
This makes the throughput lower. If therefore a higher throughput
is desired even though a slight exposure non-uniformness has to be
accepted, a larger tolerance ratio .DELTA.S/S of non-uniformness of
integrated exposure amount may be inputted again through the input
device 105.
[0070] Step 806
[0071] The movable slit 6 is set and placed at the calculated
position, and the width of the exposure slit 6a is set at the
calculated value. Namely, the main control system 104 operates to
set the exposure slit 6a at the size as determined, and also to
cause the voice coil motor 18 to move and set the movable slit 6 at
a determined position along the optical axis.
[0072] Step 807
[0073] The scan exposure process starts.
[0074] Of the steps of the flow chart described above, the
procedure at step 803 will be described in more detail. FIG. 6 is a
graph showing a model of intensity profile of exposure light upon
the wafer 11. The axis of abscissa corresponds to the distance
along the scan direction (x.sub.W direction), and the axis of
ordinate corresponds to intensity I of exposure light. The origin
is at an end of the bottom of a regular trapezoid (with slants of
the same length), the end facing the wafer movement direction. The
intensity has a peak value i.sub.0. The configuration depicted by a
broken line in the drawing corresponds to a profile of exposure
light to be provided by a subsequent light emission.
[0075] The left and right half shadow portions at the slant sides
of the regular trapezoid have the same span, and the length is
denoted by r. The distance d in the x.sub.W direction connecting
the mid points of the slant sides of the trapezoid, corresponds to
the width w of the exposure slit 6a, and there is a relation:
d=w.multidot..beta..sub.S-W (1)
[0076] The distance from the origin to the intensity correction
point r.sub.c corresponds to the movement distance of the wafer
through which the wafer 11 moves in a period before subsequent
emission of exposure light, and r.sub.c=vT. It is at the point most
unexposed-region side of the exposure region to be exposed last
during this light emission, of the profile depicted by a solid
line. The intensity of exposure light at this point is denoted by
i.sub.c.
[0077] The intensity correction calculation at each pulse light
emission is set so that at the intensity correction point r.sub.c
the intensity i.sub.c accomplishes a desired target value S to the
integrated exposure amount. The intensity I(x.sub.W) at an
arbitrary coordinate, in this model, can be expressed by the
following equation: 1 I ( x W ) = [ 0 ; x W 0 , x W r + d ( i 0 / r
) x W ; 0 < x W < r i 0 ; r x W d - ( i 0 / r ) { x W - ( d +
r ) } ; d < x W < d + r ] ( 2 )
[0078] FIG. 7 is a schematic view for explaining estimation of
integrated exposure amount of a wafer which is to be exposed by
exposure light having an intensity profile as shown in FIG. 6. The
drawing illustrates a case where, while moving the wafer stage 14
at a constant speed v, the substrate 11 is exposed by pulse light
being emitted at regular emission intervals T.
[0079] The integrated exposure amount at an arbitrary position on
the x.sub.W axis along the substrate scan direction (the x.sub.W
coordinate axis is fixed to the substrate), can be considered as
being the total of the intensities of trapezoids through which a
broken line in the drawing extends. Reference characters H.sub.0,
H.sub.1, H.sub.2, . . . , and H.sub.k denotes the light emission
numbers. Using this drawing, the process of determining the scan
speed v, the width w of the exposure slit 6a, and the position of
the movable slit 6 from a designated tolerance ratio .DELTA.S/S of
non-uniformness of integrated exposure amount, will be
explained.
[0080] The number N of light emissions necessary for achieving a
target value S at an arbitrary exposure position, can be determined
from the reference emission light intensity i.sub.0 of the light
source 1 and the target value S of the integrated exposure amount,
in accordance with the following equation:
N=S/i.sub.0 (3)
[0081] Between the width d of the image of the exposure slit 6a
upon the substrate 11 and the scan speed v, there is a relation
such as follows:
N.multidot.T=d/v (4)
[0082] In this embodiment, when the emission light intensity of a
pulse to be emitted last is so controlled that the integrated
exposure amount at an exposure position reaches a target value S,
the intensity dispersion coefficient .delta..sub.m of the last
emitted pulse produces non-uniformness .DELTA.S of integrated
exposure amount.
[0083] Referring now to FIG. 8, the mechanism of production of
non-uniformness .DELTA.S of integrated exposure amount will be
explained. Upper portion of FIG. 8 illustrates, like FIG. 7, the
intensity of exposure light taken on the axis of abscissa and
x.sub.W coordinate system (substrate scan direction) taken on the
axis of ordinate. It is to be noted that in FIG. 8, for convenience
of illustration, higher the position of the intensity profile is,
the earlier it is produced by light emission. Lower portion of FIG.
8 illustrates integrated exposure amount taken on the axis of
abscissa and x.sub.W coordinate system taken on the axis of
ordinate. Namely, the lower portion of FIG. 8 depicts integrated
exposure amount distribution.
[0084] At a point on the substrate 11 as denoted by x.sub.j+1, when
the exposure slit 6a passes, there is produced non-uniformness
.DELTA.S of integrated exposure amount such as illustrated in FIG.
8, this being attributable to intensity dispersion coefficient
.delta..sub.m of the last emitted light pulse (H.sub.j) at that
point. The non-uniformness .DELTA.S of integrated exposure amount
is produced in proportion to dispersion of intensity i.sub.c at the
intensity correction point x.sub.j+1 for H.sub.j, and it can be
expressed as .DELTA.S=.delta..sub.m.- multidot.i.sub.c. Therefore,
the tolerance ratio .DELTA.S/S of non-uniformness of integrated
exposure amount can be expressed by the following relation:
.DELTA.S/S=(.delta..sub.m.multidot.i.sub.c)/S (5)
[0085] From the inclination of the trapezoidal profile and from the
distance r.sub.c through which the image of the exposure slit 6a
displaces on the substrate 11 per one light emission, the value of
i.sub.c can be expressed as follows:
i.sub.c=(i.sub.O/r).multidot.v.multidot.T (6)
[0086] Also, since the range of irradiation of exposure light
having the profile shown in FIG. 6 should be within the diameter
.phi..sub.0 of the effective picture field of the projection lens
10, the following limiting relation applies to d and r:
.phi..sub.0.sup.2.gtoreq.(d+r).sup.2+e.sup.2 (7)
[0087] where
e=h.multidot..beta..sub.S-W (8)
[0088] In this embodiment, since the whole diameter of the
effective picture field of the projection lens 10 is used, both
sides of equation (7) are equal to each other. Also, h is fixed.
Thus, if
d+r=W.sub.0 (9)
[0089] is set, then, from equation (7), it follows that:
W.sub.0=(.phi..sub.0.sup.2-e.sup.2).sup.1/2 (10)
[0090] Thus, W.sub.0 becomes a constant.
[0091] Synthesizing equations (2)-(10), the relation between the
tolerance ratio .DELTA.S/S of non-uniformness of integrated
exposure amount and the parameters can be expressed as follows:
.DELTA.S/S=[.delta..sub.m.multidot.(v.multidot.T).sup.2]/[(W.sub.0-r).mult-
idot. r] (11)
[0092] In equation (11), .delta..sub.m is a maximum value of
emission intensity dispersion coefficient .delta. as determined by
measurement, and it is a fixed value peculiar to the instrument.
Also, while the light emission spacing T of the light source can be
changed, here it is set at a minimum value for enhancement of
throughput. Thus, once a tolerance ratio .DELTA.S/S of
non-uniformness of integrated exposure amount is designated, the
relation between the wafer scan speed v and the width r of the half
shadow region (i.e., remaining parameters) can be determined. By
using the thus determined r and from equations (1) and (9), the
width w of the exposure slit 6a can be determined in accordance
with the following equation:
w=(W.sub.0-r)/.beta..sub.S-W (12)
[0093] The value of width r of the half shadow region can be
achieved by moving the position of the movable slit 6 (exposure
slit 6a) along the optical axis of the illumination optical
system.
[0094] At step 803, by using equations (11) and (12), one of the
following procedures is performed to determine the scan speed v,
the width w of the exposure slit 6a and the width r of the half
shadow region:
[0095] 1) Holding the width r of the half shadow region at an
arbitrary value, the scan speed v is determined from the width w of
the exposure slit 6a and the inputted tolerance ratio .DELTA.S/S of
non-uniformness of integrated exposure amount; and
[0096] 2) Holding the scan speed v at an arbitrary value, the width
r of the half shadow region is determined from the inputted
tolerance ratio .DELTA.S/S of non-uniformness of integrated
exposure amount and, then, the width w of the exposure slit 6a is
determined.
[0097] This procedure is performed by the main control system 104.
Thus, the main control system 104 serves as a component of scan
speed determining means. Also, the main control system 104 and the
voice coil motor 18 are components of exposure slit determining
means.
[0098] According to the investigation made by the inventors of the
subject application, it has been confirmed that a practical scan
speed of the wafer stage 14 during scan exposure process is about
100 mm/sec. If the scan speed over 100 mm/sec. is achieved, then
synchronous following difference between the reticle stage 13 and
the wafer stage 14 does not satisfy a predetermined alignment
precision of the reticle 9 and the substrate 11. Further, in this
embodiment, since the reticle stage 13 is high-speed scanned at a
ratio four times the speed of the wafer stage 14, there arise
technical problems such as deformation of the reticle during
acceleration and deceleration of the reticle stage 13 and how to
keep attraction of the reticle to the reticle stage, for
example.
[0099] On the other hand, the lifetime of a gas of a KrF excimer
laser used in an exposure apparatus is currently about ten (10) to
fifteen (15) million emissions. If the scan speed can not be
increased for the reason described above, for maintaining
integrated exposure amount per unit area at a target value S there
will be a method in which the reference emission light intensity
i.sub.0 is controlled to a desired value through light attenuating
means such as an ND filter (not shown) accommodated in the beam
shaping optical system 2 or by controlling the charging voltage
signal 17 and a method in which the number of light pulses received
is controlled to a desired number by controlling the light emission
frequency (light emission period T) of the light source. This can
be predicted by the following equation which is derived from
equations (3) and (4), that is:
S=(i.sub.0.multidot.d)/(v.multidot.T) (13)
[0100] Namely, there is an alternative method that, for extending
the lifetime of the light source 1 which comprises an excimer
laser, for example, the light emission period T of the light source
1 may be made larger to thereby reduce the number of light
emissions of the light source 1 necessary for the exposure of one
shot. As a matter of course, when such method is executed, the
tolerance value of non-uniformness of integrated exposure amount in
equation (1) should be satisfied. That is, if the non-uniformness
of integrated exposure amount can be sufficiently kept within the
tolerance .DELTA.S, the exposure apparatus of the present invention
may be so arranged that the magnitude of non-uniformness of
integrated exposure amount is enlarged to a level near the
tolerance .DELTA.S and the light emission frequency of the light
source is lowered to reduce the number of light emissions per one
shot, thereby to prolong the gas lifetime of the light source
1.
[0101] It is seen from equations (11) and (12) that generally the
product of scan speed v and light emission period T can be set
large when the integrated exposure amount tolerance ratio
.DELTA.S/S is large. Thus, it is a possible form that the parameter
setting may be chosen appropriately in accordance with situations,
out of one in which the throughput is particularly regarded, one in
which the lifetime of the light source is particularly regarded,
and one in which both of them are regarded. Particularly, in a case
where there is a limitation to the scan speed v as described
hereinbefore, the light emission period T may preferably be set
largest within a range in which the integrated exposure amount
tolerance ratio .DELTA.S/S is satisfied. If on the other hand the
integrated exposure amount tolerance ratio .DELTA.S/S is small,
parameter setting will be the one in which exposure precision is
particularly regarded, such that the product of scan speed v and
light emission period T is made small or, alternatively, the
product of the width w of the exposure slit 6a and the width r of
the half shadow region is made large.
[0102] In a scan exposure apparatus according to this embodiment of
the present invention, as described hereinbefore, a tolerance ratio
for non-uniformness of integrated exposure amount as required to
exposure shots on a photosensitive substrate is given and, by using
scan speed determining means and/or exposure slit determining
means, the scan speed v of the wafer, the width w of the exposure
slit, the light emission period T of the light source and so on are
determined. The exposure process is performed by using the thus
determined scan exposure parameters. Thus, an exposure process in
which the performance of the light source is effectively used, is
achieved.
[0103] Since in the exposure apparatus of this embodiment the
exposure parameters can be determined while setting a tolerance
value .DELTA.S of non-uniformness of integrated exposure amount in
accordance with the linewidth of a circuit pattern, it is possible
to switch the exposure condition (by choosing one for regarding
exposure precision or one for regarding throughput, for example) in
accordance with the state of layer.
[0104] While in the embodiment described above the tolerance ratio
.DELTA.S/S of non-uniformness of integrated exposure amount,
corresponding to the linewidth of pattern, is designated manually,
the exposure parameter determination may be made automatically by,
for example, recording information on a reticle 9 (using a bar
code, for example) and by reading the recorded information.
[0105] It is a possible alternative (second embodiment) that a
deviation of a preceding emission light intensity I.sub.n from a
designated target value i.sub.0 is added to a subsequent emission
light intensity designation level (charging voltage designation
value), and that the scan speed v and the width r of the half
shadow region are determined from the tolerance ratio .DELTA.S/S of
non-uniformness of integrated exposure amount.
[0106] It is a further alternative (third embodiment) that the
light emission period T of the light source is changed to control
the integrated exposure amount, and the scan speed v and the width
r of the half shadow region are determined from the tolerance ratio
.DELTA.S/S of non-uniformness of integrated exposure amount.
[0107] Now, a second embodiment of the present invention will be
explained. FIG. 9 is a schematic view for explaining concept of
control in the second embodiment. In the drawing, for a second
pulse light emission H.sub.2, for example, if the intensity I.sub.1
of a first pulse light emission H.sub.1 does not reach a desired
emission light intensity i.sub.0, an intensity designation level
E.sub.2 wherein the deviation is added is applied with reference to
the second pulse light emission H.sub.2. Here, the emission light
intensity level E is applied by means of the laser control system
103 in the form of a charge voltage signal 17. Namely, assuming now
that:
[0108] E.sub.n: emission light intensity designation level (charge
voltage designation level) for an n-th pulse light emission
[0109] I.sub.n: peak value of emitted light intensity of n-th
pulse,
[0110] between them there is a relation such as follows:
I.sub.n=A.multidot.E.sub.n.multidot.b.sub.n (14)
[0111] where A is a proportion constant and b.sub.n is dispersion
of emitted light intensity of the n-th pulse light to an emission
light intensity designation level.
[0112] The procedure of adding the deviation (shortage) of the
emitted light intensity I.sub.n measured with reference to the just
preceding pulse emission with respect to the target intensity
i.sub.0, can be expressed by the following equation:
E.sub.n+1=i.sub.0/A+[(i.sub.0-I.sub.n)/A] (15)
[0113] Also, from equation (13) it follows that:
I.sub.n+1=A.multidot.E.sub.n+1+b.sub.n+1 (16)
[0114] Thus the following recurrence formula is obtainable:
I.sub.n+1=i.sub.0+b.sub.n+1+(i.sub.0-I.sub.n) (17)
[0115] If the initial value is I.sub.0=i.sub.0, then a general term
of I.sub.n is given by the following equation: 2 I n = i 0 + k n [
{ ( - 1 ) ** ( n - k ) } b k ] ( 18 )
[0116] The integrated exposure amount up to n-th pulse light
emission can be expressed by the following equation: 3 S ( n v T )
= k = 0 n [ ( I n / i 0 ) I { ( n - k ) v T } ] ( 19 )
[0117] The value 2.sigma. of S(n.multidot.v.multidot.T) detected as
described above is then substituted into .DELTA.S of equation (11),
by which a similar procedure like that of the first embodiment can
be done.
[0118] In determination of scan speed v, light emission period T
and width w of exposure slit 6a, it is not possible to predetect
the value of dispersion b.sub.n of emitted light intensity. In
place thereof, a data group having been produced on the basis of
preceding measurement made under the same condition may be used or,
alternatively, random numbers having similar dispersion may be
used.
[0119] Next, an embodiment of semiconductor device manufacturing
method which uses an exposure apparatus such as shown in FIG. 1,
will be explained.
[0120] FIG. 10 is a flow chart of the sequence of manufacturing a
semiconductor device such as a semiconductor chip (e.g. IC or LSI),
a liquid crystal panel or a CCD, for example. Step 1 is a design
process for designing the circuit of a semiconductor device. Step 2
is a process for manufacturing a mask on the basis of the circuit
pattern design. Step 3 is a process for manufacturing a wafer by
using a material such as silicon.
[0121] Step 4 is a wafer process which is called a pre-process
wherein, by using the so prepared mask and wafer, circuits are
practically formed on the wafer through lithography. Step 5
subsequent to this is an assembling step which is called a
post-process wherein the wafer processed by step 4 is formed into
semiconductor chips. This step includes assembling (dicing and
bonding) and packaging (chip sealing). Step 6 is an inspection step
wherein operability check, durability check and so on of the
semiconductor devices produced by step 5 are carried out. With
these processes, semiconductor devices are finished and they are
shipped (step 7).
[0122] FIG. 11 is a flow chart showing details of the wafer
process. Step 11 is an oxidation process for oxidizing the surface
of a wafer. Step 12 is a CVD process for forming an insulating film
on the wafer surface. Step 13 is an electrode forming process for
forming electrodes on the wafer by vapor deposition. Step 14 is an
ion implanting process for implanting ions to the wafer. Step 15 is
a resist process for applying a resist (photosensitive material) to
the wafer. Step 16 is an exposure process for printing, by
exposure, the circuit pattern of the mask on the wafer through the
exposure apparatus described above. Step 17 is a developing process
for developing the exposed wafer. Step 18 is an etching process for
removing portions other than the developed resist image. Step 19 is
a resist separation process for separating the resist material
remaining on the wafer after being subjected to the etching
process. By repeating these processes, circuit patterns are
superposedly formed on the wafer.
[0123] While the invention has been described with reference to the
structures disclosed herein, it is not confined to the details set
forth and this application is intended to cover such modifications
or changes as may come within the purposes of the improvements or
the scope of the following claims.
* * * * *