U.S. patent application number 10/394261 was filed with the patent office on 2003-11-20 for pattern writing apparatus and pattern writing method.
This patent application is currently assigned to DAINIPPON SCREEN MFG., CO., LTD.. Invention is credited to Kuwabara, Akira, Shirota, Hiroyuki.
Application Number | 20030214644 10/394261 |
Document ID | / |
Family ID | 29267810 |
Filed Date | 2003-11-20 |
United States Patent
Application |
20030214644 |
Kind Code |
A1 |
Shirota, Hiroyuki ; et
al. |
November 20, 2003 |
Pattern writing apparatus and pattern writing method
Abstract
A pattern writing apparatus for writing a pattern on a
photosensitive material comprises a head provided with a DMD having
a micromirror group which modulates reflected light, a stage
holding a substrate, and mechanisms for moving the head and the
stage relative to each other. Light from the micromirrors of the
DMD are directed to irradiation regions (61) on the substrate,
respectively. The irradiation regions (61) are moved over the
substrate with movement of the substrate relative to the head. The
DMD is provided within the head so that the direction of
arrangement of the irradiation regions (61) is tilted relative to
the main scanning direction, and a center-to-center distance (L1)
along the sub-scanning direction between two adjacent irradiation
regions (61) arranged in the main scanning direction is made equal
to a pitch (P1) of writing cells (620) on the substrate with
respect to the sub-scanning direction. This allows multiple
exposures centered about each of the writing cells (620), thereby
achieving high-speed pattern writing while permitting precise
control of the pattern linewidth.
Inventors: |
Shirota, Hiroyuki; (Kyoto,
JP) ; Kuwabara, Akira; (Kyoto, JP) |
Correspondence
Address: |
McDermott, Will & Emery
600 13th Street, N.W.
Washington
DC
20005-3096
US
|
Assignee: |
DAINIPPON SCREEN MFG., CO.,
LTD.
|
Family ID: |
29267810 |
Appl. No.: |
10/394261 |
Filed: |
March 24, 2003 |
Current U.S.
Class: |
355/67 |
Current CPC
Class: |
G03F 7/70291 20130101;
G03F 7/70558 20130101; G03F 7/70466 20130101; G03F 7/70358
20130101; G03F 7/70283 20130101 |
Class at
Publication: |
355/67 |
International
Class: |
G03B 027/54 |
Foreign Application Data
Date |
Code |
Application Number |
May 16, 2002 |
JP |
P2002-141320 |
Claims
What is claimed is:
1. A pattern writing apparatus for writing a pattern on a
photosensitive material, comprising: a head applying light to an
irradiation region group arrayed in a lattice arrangement; a
scanning mechanism for scanning said irradiation region group over
a photosensitive material in a scanning direction which is tilted
relative to a direction of arrangement of said irradiation region
group, and passing a plurality of irradiation regions over a
plurality of writing regions on said photosensitive material; and a
controller controlling an amount of light applied to each of said
writing regions on said photosensitive material by exercising
individual ON/OFF control of light irradiation of said irradiation
region group in synchronization with scanning of said irradiation
region group.
2. The pattern writing apparatus according to claim 1, wherein said
head comprises: a spatial light modulator having a lattice
arrangement of a light modulating element group which spatially
modulates reflected light; a light source emitting light applied to
said spatial light modulator; and an optical system directing light
from said light modulating element group to said irradiation region
group, respectively.
3. The pattern writing apparatus according to claim 2, wherein each
element of said light modulating element group is a micromirror
that changes its position.
4. The pattern writing apparatus according to claim 1, wherein
irradiation regions in said irradiation region group are arranged
at equal pitches in two directions perpendicular to each other.
5. The pattern writing apparatus according to claim 1, wherein a
center-to-center distance along a direction perpendicular to said
scanning direction between adjacent irradiation regions arranged in
a direction which extends approximately along said scanning
direction out of two directions of arrangement of said irradiation
region group, is equal to a center-to-center distance between
adjacent writing regions arranged in said direction perpendicular
to said scanning direction.
6. The pattern writing apparatus according to claim 1, wherein said
controller performs ON/OFF control of said light irradiation once
while said irradiation region group is scanned by a distance that
is twice a center-to-center distance between two adjacent writing
regions arranged in said scanning direction.
7. The pattern writing apparatus according to claim 1, wherein a
pattern is written on a photoresist film on a substrate for a
printed circuit board.
8. The pattern writing apparatus according to claim 1, wherein said
scanning mechanism continuously moves said irradiation region
group.
9. A pattern writing method for writing a pattern on a
photosensitive material, comprising the steps of: applying light to
an irradiation region group arrayed in a lattice arrangement and,
by scanning said irradiation region group over a photosensitive
material in a scanning direction which is tilted relative to a
direction of arrangement of said irradiation region group, passing
a plurality of irradiation regions over a plurality of writing
regions on said photosensitive material; and controlling an amount
of light applied to each of said writing regions on said
photosensitive material by exercising individual ON/OFF control of
light irradiation of said irradiation region group in
synchronization with scanning of said irradiation region group.
10. The pattern writing method according to claim 9, wherein light
is applied to said irradiation region group through a spatial light
modulator having a lattice arrangement of a light modulating
element group which spacially modulates reflected light.
11. The pattern writing method according to claim 10, wherein each
element of said light modulating element group is a micromirror
that changes its position.
12. The pattern writing method according to claim 9, wherein
irradiation regions in said irradiation region group are arranged
at equal pitches in two directions perpendicular to each other.
13. The pattern writing method according to claim 9, wherein a
center-to-center distance along a direction perpendicular to said
scanning direction between adjacent irradiation regions arranged in
a direction which extends approximately along said scanning
direction out of two directions of arrangement of said irradiation
region group, is equal to a center-to-center distance between
adjacent writing regions arranged in said direction perpendicular
to said scanning direction.
14. The pattern writing method according to claim 9, wherein in
said step of controlling an amount of light, ON/OFF control of said
light irradiation is performed once while said irradiation region
group is scanned by a distance that is twice a center-to-center
distance between two adjacent writing regions arranged in said
scanning direction.
15. The pattern writing method according to claim 9, wherein a
pattern is written on a photoresist film on a substrate for a
printed circuit board.
16. The pattern writing method according to claim 9, wherein said
irradiation region group moves continuously.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an apparatus and method of
writing a pattern by light irradiation to a photosensitive
material.
[0003] 2. Description of the Background Art
[0004] Conventionally well known are techniques for applying a
light beam modulated by a spatial light modulator such as a digital
micromirror device (DMD) onto a photoresist film formed on a
substrate such as a semiconductor substrate or a printed circuit
board.
[0005] Japanese Patent Application Laid-open No. 62-21220 discloses
a technique for writing a fine pattern by applying a light beam
which is spatially modulated by a micromirror group of a DMD onto a
photosensitive material and by moving the photosensitive material
and controlling a signal given to the DMD every time the
photosensitive material passes a predetermined distance.
[0006] Also, Japanese Patent Application Laid-open No. 2001-133893
suggests a technique for writing a finer pattern by tilting an
image formed by a DMD on a photosensitive material at 45 degrees
relative to a main scanning direction. FIG. 1 is a diagram for
explaining the pattern writing suggested in Japanese Patent
Application Laid-open No. 2001-133893. In an image 90 formed by a
DMD on a photosensitive material in FIG. 1, an irradiation region
group 91 arranged in a row in a direction perpendicular to the main
scanning direction corresponds to a set of main scan mirrors of the
DMD, and another irradiation region group 92 which is arranged in
the direction perpendicular to the main scanning direction and each
of whose regions is located between adjacent regions of the
irradiation region group 91, corresponds to a set of interpolation
main scan mirrors of the DMD. The image 90 is scanned on the
photosensitive material in a direction indicated by arrow 94, i.e.,
the main scanning direction, and at some point in time, a space
between adjacent regions on the photosensitive material which are
exposed by the respective main scan mirrors is exposed by each of
the interpolation main scan mirrors. This achieves fine pattern
writing.
[0007] When changing an image (i.e., a pattern indicating spatial
modulation of a light beam) formed on a photosensitive material,
the spatial light modulator such as a DMD requires, for example,
time to write data into memory cells each corresponding to one
light modulating element and time between receiving a reset pulse
and holding each light modulating element in position (i.e., fixing
the position (orientation) of each micromirror of the DMD).
However, there are technical limitations to what we can do to
shorten such times. Thus, it is not easy to drive the spatial light
modulator at higher speed and thereby to speed up pattern writing
by exposure.
[0008] For example, in a DMD where 16 blocks of micromirrors, each
block containing 48 rows and 1024 columns of micromirrors, are
arranged in a column direction to form a matrix of 768 rows and
1024 columns, control is exercised block by block. However,
addressing and writing data into the blocks is generally performed
on line by line; therefore, when this DMD is employed in the
technique shown in FIG. 1, data must be written into every block
containing part of the main scan mirrors and the interpolation main
scan mirrors, which makes it difficult to achieve high speed
pattern writing.
SUMMARY OF THE INVENTION
[0009] An object of the present invention is to write a fine
pattern at high speed.
[0010] The present invention is directed to a pattern writing
apparatus for writing a pattern on a photosensitive material.
[0011] According to a preferred embodiment of the present
invention, the pattern writing apparatus comprises a head applying
light to an irradiation region group arrayed in a lattice
arrangement, a scanning mechanism for scanning the irradiation
region group over a photosensitive material in a scanning direction
which is tilted relative to a direction of arrangement of the
irradiation region group and passing a plurality of irradiation
regions over a plurality of writing regions on the photosensitive
material, and a controller controlling the amount of light applied
to each of the writing regions on the photosensitive material by
exercising individual ON/OFF control of light irradiation of the
irradiation region group in synchronization with scanning of the
irradiation region group.
[0012] The present invention allows multiple light irradiation on
the photosensitive material with efficiency, thereby achieving
high-speed pattern writing.
[0013] According to a further preferred embodiment of the present
invention, each element of a light modulating element group is a
micromirror that changes its position, and the irradiation regions
are arranged at equal pitches in two directions perpendicular to
each other.
[0014] In one aspect of the present invention, a center-to-center
distance along a direction perpendicular to the scanning direction
between adjacent irradiation regions arranged in a direction which
extends approximately along the scanning direction out of the two
directions of arrangement of the irradiation region group, is equal
to a center-to-center distance between adjacent writing regions
arranged in the direction perpendicular to the scanning
direction.
[0015] More preferably, the controller performs ON/OFF control of
the light irradiation once while the irradiation region group is
scanned by a distance that is twice the center-to-center distance
between two adjacent writing regions arranged in the scanning
direction.
[0016] This increases the speed of pattern writing.
[0017] The scanning mechanism accelerates high-speed pattern
writing by continuously moving the irradiation region group.
[0018] More specifically, the pattern writing apparatus writes a
pattern on a photoresist film on a substrate for a printed circuit
board.
[0019] The present invention is also directed to a pattern writing
method for writing a pattern on a photosensitive material.
[0020] These and other objects, features, aspects and advantages of
the present invention will become more apparent from the following
detailed description of the present invention when taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a diagram for explaining an exposure operation by
a conventional pattern writing apparatus;
[0022] FIG. 2 is a diagram illustrating a general structure of a
pattern writing apparatus according to the present invention;
[0023] FIG. 3 is a diagram illustrating a DMD;
[0024] FIGS. 4, 6 and 7 are diagrams for explaining an exposure
operation by the pattern writing apparatus;
[0025] FIG. 5 is a flowchart showing the flow of the exposure
operation;
[0026] FIGS. 8A, 8B and 8C are diagrams for explaining light
irradiation of writing cells with respect to a main scanning
direction;
[0027] FIGS. 9A, 9B and 9C are diagrams for explaining light
irradiation of writing cells with respect to a sub-scanning
direction;
[0028] FIG. 10 is a diagram for explaining another example of the
exposure operation by the pattern writing apparatus;
[0029] FIGS. 11A, 11B, 11C and 11D are diagrams for explaining
light irradiation of writing cells with respect to the main
scanning direction in double-speed mode operation;
[0030] FIGS. 12A and 12B are diagrams for comparison between a
comparative example and the pattern writing apparatus according to
the present invention; and
[0031] FIG. 13 is a diagram illustrating an image formed by the DMD
on a substrate.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] FIG. 2 is a diagram illustrating the structure of a pattern
writing apparatus 1 according to one preferred embodiment of the
present invention. In FIG. 2, part of the apparatus is shown by
dashed lines for illustration of the internal structure of the
apparatus. The pattern writing apparatus 1 comprises a stage 2
holding a substrate 9 on which a resist film is formed, a stage
moving mechanism 31 for moving the stage 2 in the Y direction in
FIG. 2, a head 4 emitting a light beam toward the substrate 9, a
head moving mechanism 32 for moving the head 4 in the X direction
in FIG. 2, and a controller 5 connected to the stage moving
mechanism 31, the head 4 and the head moving mechanism 32.
[0033] The head 4 includes a light source 41 which is a lamp for
emitting light and a DMD 42 having a micromirror group arrayed in a
lattice arrangement, wherein the micromirror group reflects a light
beam from the light source 41 to provide a spatially modulated
light beam.
[0034] More specifically, the light emitted from the light source
41 is directed through a mirror 431 and a lens 432 to a light
control filter 44 in which the light beam is controlled to a
desired amount of light. The light beam transmitted through the
light control filter 44 is directed through a rod integrator 433, a
lens 434 and a mirror 435 to a mirror 436 which then focuses and
directs the light beam onto the DMD 42. The light beam incident on
the DMD 42 is uniformly applied to the micromirror group of the DMD
42 at a predetermined angle of incidence (e.g., 24 degrees). Thus,
the mirror 431, the lens 432, the rod integrator 433, the lens 434,
the mirror 435 and the mirror 436 constitute an illumination
optical system 43a for directing light from the light source 41 to
the DMD 42.
[0035] A light beam (i.e., a spatially modulated light beam)
generated from only reflected light from part of micromirrors of
the DMD 42 which are set in a predetermined position (a position
(or orientation) corresponding to an ON state later to be described
in description of light irradiation by the DMD 42) enters a zoom
lens 437 in which the light beam is controlled in magnification and
directed through a mirror 438 to a projector lens 439. The light
beam from the projector lens 439 is then applied to a region on the
substrate 9 which is optically conjugate to the micromirror group.
In the pattern writing apparatus 1, therefore, the zoom lens 437,
the mirror 438 and the projector lens 439 constitute a projection
optical system 43b for directing light from each of the
micromirrors to a corresponding irradiation region on the substrate
9.
[0036] The stage 2 is fixed on a movable side of the stage moving
mechanism 31 which is a linear motor, and the controller 5 controls
the stage moving mechanism 31 so that the irradiation region group
irradiated with light from the micromirror group (herein, one
micromirror corresponds to one irradiation region) relatively moves
in the Y direction in FIG. 2 over the photoresist film. That is,
the irradiation region group is fixed relative to the head 4 and
moves over the substrate 9 with movement of the substrate 9.
[0037] The head 4 is fixed on a movable side of the head moving
mechanism 32 and intermittently moves in a sub-scanning direction
(X direction) perpendicular to the main scanning direction (the Y
direction in FIG. 2) of the irradiation region group. That is,
every time a main scan is completed, the head moving mechanism 32
moves the head 4 in the X direction to a start position for the
next main scan.
[0038] FIG. 3 is a diagram illustrating the DMD 42. The DMD 42 is a
spatial light modulator having a micromirror group 422 in which a
number of micromirrors are arrayed at equal pitches in a lattice
arrangement on a silicon substrate 421 (hereinafter, they are
described as an array of M rows and N columns in two directions
perpendicular to each other). Each of the micromirrors is tilted at
a predetermined angle by the action of the static electric field,
according to data written into its corresponding memory cell.
[0039] When a reset pulse is applied from the controller 5 shown in
FIG. 2 to the DMD 42, each of the micromirrors is tilted in unison
in a predetermined position about a diagonal line of its reflecting
surface according to data written in its corresponding memory cell.
Thereby, the light beam applied to the DMD 42 is reflected in
directions of the tilting of the respective micromirrors and light
irradiation of the irradiation regions is ON/OFF controlled. That
is, when micromirrors whose memory cells are written with data
indicating the ON state receive a reset pulse, light incident on
those micromirrors is reflected onto the zoom lens 437 and applied
to corresponding irradiation regions. On the other hand,
micromirrors in the OFF reflect incident light to a predetermined
position other than that of the zoom lens 437; thus, no light is
directed to their corresponding irradiation regions.
[0040] FIG. 4 is a diagram illustrating irradiation regions 61 and
writing cells 620 on the substrate 9 in the pattern writing
apparatus 1. The irradiation regions 61 are regions fixed relative
to the head 4, and the writing cells 620 are regions fixed on the
substrate 9 and corresponding to the smallest unit of writing. With
movement of the head 4 relative to the substrate 9, the irradiation
regions 61 move over the writing cells 620. The writing cells 620
are exposure regions obtained by dividing the region on the
substrate 9 with reference to central positions of the irradiation
regions 61 (more precisely, central positions of the continuously
moving irradiation regions 61) during one cycle of exposure control
by the DMD 42. In FIG. 4, the lattice irradiation region group
irradiated with light from the respective micromirrors of the DMD
42 is indicated by dash-double-dot lines and the writing cell group
on the substrate 9 is indicated by solid lines. It is noted that
only parts of the writing cells 620 and the irradiation regions 61
are shown in FIG. 4.
[0041] The writing cells 620 are rectangular exposure regions
arranged at pitches P1 in the X direction (sub-scanning direction)
and at pitches P2 in the Y direction (main scanning direction) in
FIG. 4, and light irradiation centered about the writing cells 620
is performed according to corresponding writing cell data (data
written in the DMD 42). The irradiation regions 61 irradiated with
reflected light from the respective micromirrors of the DMD 42 are
approximately square regions which correspond in shape to the
micromirrors. The irradiation regions 61 are arranged at equal
pitches in two directions perpendicular to each other, and the DMD
42 is provided in a tilted (or inclined) position within the head 4
so that the directions of arrangement of the irradiation regions 61
are tilted (or inclined) relative to the main scanning
direction.
[0042] The tilt angle of the irradiation region group relative to
the main scanning direction is determined so that a
center-to-center distance L1 along the sub-scanning direction (X
direction) between two adjacent irradiation regions 61 arranged in
a direction which extends approximately along the main scanning
direction (i.e., in a direction which forms a smaller angle with
the main scanning direction) out of the two directions of
arrangement of the irradiation region group, is equal to the pitch
P1 of the writing cells 620 in the X direction (a center-to-center
distance between adjacent writing cells 620 in the sub-scanning
direction). In the following description, a direction approximately
along the Y direction is referred to as a "column direction" of the
DMD 42 and another direction approximately along the X direction is
referred to as a "row direction".
[0043] Next, the operation of the pattern writing apparatus 1 for
writing a pattern on a photoresist film on the substrate 9 is
described with reference to FIG. 5. In the following description of
the operation of the pattern writing apparatus 1, the irradiation
region group moves relative to the writing cell group in both the
main scanning direction and the sub-scanning direction (step
S1).
[0044] At the start of exposure, writing cell data to be written
into writing cells 621 which correspond to first locations of the
irradiation regions 61, out of the writing cells 620 in FIG. 4,
(i.e., the writing cells 621 located at the centers of the
respective irradiation regions 61) is transmitted from the
controller 5 to corresponding memory cells of the respective
micromirrors of the DMD 42 (step S2). The controller 5 then
transmits a reset pulse to the DMD 42, whereby each of the
micromirrors is tilted in a position (orientation) responsive to
the memory cell data and a first exposure (i.e., ON/OFF control of
light irradiation) of the writing cells 621 is performed (step
S3).
[0045] After the transmission of the reset pulse, writing cell data
corresponding to the next writing cells 622 (i.e., the writing
cells 622 located adjacent to the writing cells 621 on the (-Y)
side) is transmitted and written into memory cells of the
respective micromirrors. The transmission of a reset pulse to the
DMD 42 is performed in synchronization with the operation of the
stage moving mechanism 31 for continuously moving the stage 2 in
the main scanning direction. More specifically, when the
irradiation regions 61 move the pitch P2 in the main scanning
direction (the (-Y) direction in FIG. 4) after the application of
the first reset pulse, the next reset pulse is transmitted to the
DMD 42 and each of the micromirrors is tilted in a position
responsive to the writing cell data. Thereby, as shown in FIG. 6,
the exposure of the writing cells 622 is performed with the second
reset pulse.
[0046] When the controller 5 repeats the above exposure operation
in synchronization with control of the stage moving mechanism 31
and the DMD 42, a second exposure centered about the writing cells
621 which were exposed by the first exposure is performed with the
eighteenth reset pulse. FIG. 7 is a diagram illustrating the
exposure with the eighteenth reset pulse. In FIG. 7, writing cells
623 exposed only once and writing cells 624 exposed twice are
distinguished by the direction of cross-hatching.
[0047] Looking at, for example, a writing cell 621a corresponding
to an irradiation region 61a at the first reset pulse shown in FIG.
4. As illustrated in FIG. 7, the irradiation region 61b (located on
the (+Y) side of the irradiation region 61a) performs an exposure
centered about the writing cell 621a with the eighteenth reset
pulse. That is, the irradiation region 61b which is spaced four
irradiation regions in the column (+Y) direction of the DMD 42 and
one irradiation region in the row (-X) direction from the
irradiation region 61a, passes over and exposes again the writing
cell 621a which was irradiated with light by the irradiation region
61a.
[0048] By repeating the above operation, the pattern writing
apparatus 1, when employing the DMD 42 comprised of M rows of
micromirrors, repeats exposures on the substrate 9 (M/4) times,
thereby permitting exposures centered about each of the writing
cells 620 with a (M/4)-step gradation.
[0049] Next, the relationship between ON/OFF control of light
irradiation of the irradiation regions 61 and photosensitivity of
the writing cells 620 is described. Since exposure of a single
writing cell 620 actually causes light irradiation of approximately
the whole area of a single irradiation region 61, light is applied
also to writing cells 620 located around a writing cell 620
concerned (see FIGS. 4, 6 and 7).
[0050] FIG. 8A is a diagram illustrating a pattern written on the
writing cells 620 arranged in the main scanning direction, when
ON/OFF control of light irradiation of a single irradiation region
61 is carried out for every five writing cells 620. FIG. 8B
illustrates the path of movement of a single irradiation region 61
relative to the writing cells 620 in a direction indicated by arrow
71 (main scanning direction). FIG. 8C is a chart indicating the
variation of the amount of light applied from the irradiation
region 61 in FIG. 8B with respect to the Y direction (main scanning
direction). FIG. 8C is drawn on the presumption that exposure
control of the irradiation regions 61 passing over positions
displaced in the sub-scanning direction is also done in the same
way.
[0051] Since the irradiation region 61 in either the ON state
(indicated by solid lines) or in the OFF state (indicated by dashed
lines) moves continuously relative to the writing cells 620 as
illustrated in FIG. 8B, the cumulative amount of light applied to
the writing cells 620 has an angular distribution as indicated by
line 72 in FIG. 8C. Thus, the pattern writing as illustrated in
FIG. 8A can be achieved by, for example, controlling the angular
shaped cumulative amount of light indicated by the line 72 such
that a distance in the main scanning direction that the irradiation
region 61 remains in the ON state (a distance five times the pitch
P2 of the writing cells 620 in FIG. 8A) is equal to a length L2
that the photoresist film is exposed with an amount of light Q1
(per unit area) in FIG. 8C. (More precisely, the cumulative amount
of light is controlled by controlling the intensity of a light beam
applied from the light control filter 44 shown in FIG. 2 to the DMD
42.)
[0052] FIGS. 9A, 9B and 9C are diagrams for explaining the
cumulative amount of light with respect to the sub-scanning
direction when the ON/OFF control of the irradiation regions 61 is
carried out for every five writing cells 620. FIG. 9A illustrates a
pattern written on the writing cells 620 with respect to the
sub-scanning direction, and FIG. 9B illustrates that a plurality of
irradiation regions 61 move in the direction indicated by arrow 71
(main scanning direction) relative to the writing cells 620 and
pass over a predetermined position in the main scanning direction.
FIG. 9C is a chart indicating the variation of the cumulative
amount of light applied from the plurality of irradiation regions
61 in FIG. 9B with respect to the X direction (sub-scanning
direction). FIG. 9C is drawn on the presumption that the ON/OFF
control of light irradiation of the irradiation regions 61 is not
carried out during one main scan.
[0053] In FIG. 9B, five irradiation regions 61 in their ON states
(indicated by solid lines) are arranged with the center-to-center
distances L1 (i.e., at pitches P1) and next to those regions, five
irradiation regions 61 in their OFF states (indicated by dashed
lines) are arranged similarly with the center-to-center distances
L1. Since each of the irradiation regions 61, as a general rule,
moves only in the main scanning direction during the exposure
operation, the cumulative amount of light with respect to the
sub-scanning direction essentially varies discontinuously. However,
because each of the irradiation regions 61 continuously moves in
the main scanning direction in a tilted position, in practice the
cumulative amount of light with respect to the X direction
continuously varies in an angular shape as indicated by line 74 in
FIG. 9C. Thus, as is the case of FIG. 8C, the pattern writing as
illustrated in FIG. 9A can be achieved by controlling the intensity
of light applied to the DMD 42 such that a distance five times the
pitch P1 is equal to a length L3 that the photoresist film is
exposed with an amount of light Q2 as indicated by the line 74.
[0054] As above described, when looked at with respect to only the
main scanning direction or the sub-scanning direction, the amount
of light applied onto the substrate 9 can be varied in an angular
shape with respect to those directions. Further in the pattern
writing apparatus 1, as previously described, the controller 5
performs individual ON/OFF control of light irradiation of the
irradiation region group in synchronization with the scanning of
the irradiation region group; therefore, when the DMD 42 comprised
of M rows of micromirrors is employed, the amount of light
irradiation centered about each of the writing cells 620 can be
controlled with a (M/4)-step gradation. The pattern writing
apparatus 1 can, therefore, achieve pattern writing while
permitting highly precise control of the pattern linewidths with
respect to both the main scanning direction and the sub-scanning
direction. Furthermore, multiple exposures result in a reduction in
the influence of variations in the intensity of reflected light
from the DMD 42.
[0055] In general, the pitches P1 and P2 are made equal and the
irradiation regions 61 are square in shape; thus, the smallest
controllable units of linewidths in the main scanning direction and
in the sub-scanning direction can be made equal.
[0056] Next, another example of the operation of the pattern
writing apparatus 1 for writing a pattern onto a photoresist film
on the substrate 9 by exposure is described with reference to FIG.
10. In FIG. 10, the irradiation regions 61 and the writing cells
620 are arranged in the same form as shown in FIGS. 4, 6 and 7, and
ON/OFF control of the irradiation regions 61 is performed once
while the irradiation regions 61 move through a distance that is
twice the pitch P2 in the (-Y) direction relative to the writing
cells 620 (hereinafter, this operation is referred to as a
"double-speed mode operation").
[0057] More specifically, looking at a column of writing cells 620
on the (-X) side. With a first reset pulse, exposures centered
about a writing cell 621c on the (+Y) side, about a writing cell
621d spaced a distance that is 17 times the pitch P2 from the
writing cell 621c in the (-Y) direction, and about a writing cell
621e spaced a distance that is 34 times the pitch P2 from the
writing cell 621c in the (-Y) direction are performed respectively
by the irradiation regions 61c, 61d and 61e.
[0058] Subsequently, when the irradiation region group moves a
distance that is twice the pitch P2 relative to the writing cell
group in the (-Y) direction, a second reset pulse is applied to the
DMD 42 and exposures of a writing cell 621f spaced a distance that
is 2 times the pitch P2 from the writing cell 621c in the (-Y)
direction, of a writing cell 621g spaced a distance that is 19
times the pitch P2 from the writing cell 621c in the (-Y)
direction, and of a writing cell 621h spaced a distance that is 36
times the pitch P2 from the writing cell 621c in the (-Y) direction
are performed respectively by the irradiation regions 61c, 61d and
61e.
[0059] From the above operation, it is seen that, for example when
the writing cell 621e is exposed by the irradiation region 61e in a
first half of the duration between the first and second reset
pulses, a multiple exposure of the writing cell 621e is performed
by the irradiation region 61d in a second half of the duration
between the ninth and tenth reset pulses. Further, in a first half
of the duration between the eighteenth and nineteenth reset pulses,
another multiple exposure of the writing cell 621e is performed by
the irradiation region 61c. Thus, in the double-speed mode
operation, multiple exposures of each of the writing cells 620 are
performed at the same time as exposures of its adjacent writing
cells 620 arranged in the main scanning direction.
[0060] Next, we describe the relationship between light irradiation
of the irradiation regions 61 and the amount of light applied to
the writing cells 620 in the double-speed mode operation. FIG. 11A
illustrates a pattern written on the writing cells 620 with respect
to the main scanning direction in the double-speed mode operation,
and FIG. 11B illustrates the path of movement of an antecedent
irradiation region 61e relative to the writing cells 620 in the
direction indicated by arrow 71 (main scanning direction). FIG. 11C
illustrates the path of movement of a subsequent irradiation region
61d relative to the writing cells 620 in the direction indicated by
arrow 71, and FIG. 11D is a chart illustrating the variation of the
cumulative amount of light applied from the irradiation regions 61e
and 61d in FIGS. 11B and 11C with respect to the Y direction (main
scanning direction).
[0061] In FIG. 11B, ON/OFF control is performed every time the
irradiation region 61e moves through a distance that is twice the
pitch P2, wherein the irradiation region 61e remains in the ON
state during three cycles of the ON/OFF control and then remains in
the OFF state during two cycles of the ON/OFF control. In FIG. 11C,
ON/OFF control is performed also every time the irradiation region
61d moves through a distance that is twice the pitch P2, wherein
the irradiation region 61d remains in the ON state during two
cycles of the ON/OFF control and then remains in the OFF state
during three cycles of the ON/OFF control. In this exposure
operation, the cumulative amount of light applied onto the writing
cells 620 arranged in the Y direction has an angular distribution
with respect to the Y direction as indicated by line 76 in FIG. 11D
(more precisely, multiple exposures are performed also by other
irradiation regions 61 arranged in the main scanning direction).
Further, when the photoresist film is exposed with an the amount of
light Q3 shown in FIG. 11D, the pattern writing as illustrated in
FIG. 11A can be achieved.
[0062] Since, as previously described, multiple exposures allow the
amount of light irradiation to be controlled with a multiple-step
gradation, the angular distribution of the light amount illustrated
in FIG. 11D can be varied in shape, and even in the double-speed
mode operation, the width of a pattern written on the photoresist
film in the main scanning direction (the pattern linewidth in the
sub-scanning direction) can be controlled with high precision. It
is noted that the pattern width in the sub-scanning direction can
also be controlled with high precision because the cumulative
amount of light applied from a plurality of irradiation regions 61
arranged in the sub-scanning direction can also has an angular
distribution as described with reference to FIG. 9.
[0063] As above described, in the double-speed mode operation of
the pattern writing apparatus 1, the controller 5 performs ON/OFF
control of light irradiation of the irradiation regions 61 by
transmitting a reset pulse once while the irradiation regions 61
are scanned by a distance that is twice the pitch P2. The pattern
writing apparatus 1 can thus achieve high-speed exposures while
permitting control of the pattern linewidth.
[0064] In the double-speed mode operation, light amount control of
each of the writing cells 620 is not so flexible as in the
operation illustrated in FIGS. 4, 6 and 7 in which light amount
control with a (M/4)-step gradation is achieved. However, since the
minimum pattern linewidth to be written (i.e., pattern resolution)
is usually set to be about several times greater than the smallest
controllable unit of linewidth (i.e., linewidth accuracy), there is
no problem in practice in the double-speed mode operation. For
example, in the pattern writing apparatus 1, the linewidth or the
width of a space between adjacent lines is 15 .mu.m and the
smallest controllable unit of the linewidth or the width of the
space is 2 .mu.m.
[0065] In the example of the operation shown in FIG. 10, multiple
exposures can also reduce the influence of variations in the amount
of light applied from each of the irradiation regions 61.
[0066] FIGS. 12A and 12B are diagrams for comparison between
pattern writing by the pattern writing apparatus 1 and pattern
writing when the direction of arrangement of the irradiation
regions is not tilted relative to the main scanning direction
(hereinafter, the latter is referred to as a "comparative
example"). FIG. 12A illustrates the pattern writing in the
comparative example, and FIG. 12B illustrates the pattern writing
in the double-speed mode operation of the pattern writing apparatus
1. In the comparative example, each of the irradiation regions
needs to be set equal in size to the writing cells and thus, an
image 42a formed by the DMD 42 in FIG. 12A is smaller than an image
42b in FIG. 12B.
[0067] The DMD employed herein has 16 blocks, each block containing
14-.mu.m-square micromirrors arranged in 48 rows and 1024 columns
at equal pitches in two directions perpendicular to each other (row
and column directions), and those 16 blocks are arranged in a
column direction to form a matrix of 768 rows and 1024 columns of
micromirrors. A group of micromirrors in one block are tilted in
unison at either (+12) degrees or at (-12) degrees relative to a
base plane about diagonal lines of their reflecting surfaces.
[0068] The pitches P1 and P2 of the writing cells in the
sub-scanning direction and in the main scanning direction are set
to 2 .mu.m. In the pattern writing apparatus 1, the zoom lens 437
and the projector lens 439 make reducing projection so that
bidirectional pitches between irradiation regions 61 (pitches with
respect to the row and column directions of the DMD 42) are about
8.25 .mu.m.
[0069] In the comparison of FIGS. 12A and 12B, only one block of
micromirrors, out of 768 rows and 1024 columns of micromirrors, is
used in order to speed up the DMD (i.e., to speed up data writing
or to simplify the operation). FIG. 13 is a diagram schematically
illustrating the image 42b formed by the DMD 42 on the substrate 9,
in which an irradiation region group 423 corresponding to one block
to be used is cross-hatched (in practice, there exist 16 blocks,
each block containing a number of micromirrors.)
[0070] Under the above condition, since the data transfer rate is
7.6 Gigabits per second, the shortest possible time to write data
into memory cells is about 6.5 micro seconds. However, in
consideration of time to hold the micromirrors after reset (i.e.,
time required to fix the positions of the micromirrors; about 15
micro seconds), the shortest exposure time of a single writing cell
620 (i.e., the shortest time until the next reset pulse is applied)
is set to 24 micro seconds. It is noted here that the writing cells
on the substrate 9 are all arranged within a 100-mm-square
area.
[0071] In the comparative example shown in FIG. 12A, since in the
image 42a formed by the DMD on the substrate 9, the two directions
of arrangement of the irradiation regions corresponding to the
micromirrors coincide with the main scanning direction and the
sub-scanning direction, the time required for the image 42a of the
DMD to move a distance of 2 .mu.m which is the pitch of the writing
cells in the main scanning direction is 24 micro seconds, i.e., the
shortest time between reset pulses and thus, the travel speed of
the substrate 9 is 83.3 mm per second. Accordingly, it takes about
1.2 seconds to expose an area having a length of 100 mm in the main
scanning direction. Further, since the length of the image 42a of
the DMD in the X direction is about 2 mm, approximately 50 main
scans are necessary to expose the whole substrate 9 and it takes
about 60 seconds.
[0072] In the pattern writing apparatus 1 shown in FIG. 12B, on the
other hand, since the image 42b formed by the DMD 42 moves a
distance of 4 .mu.m which is twice the pitch P2 of the writing
cells 620 in the main scanning direction during the shortest
exposure time of 24 micro seconds and thus, the travel speed of the
substrate 9 is 166.7 mm per second. From this, the time required to
expose an area with a scanning distance of 100 mm is about 0.6
second. Also, since the pitch between the irradiation regions 61 in
the X direction is 8 .mu.m, the X direction width of an area that
can be exposed by one scan is about 8 mm and thus, 13 main scans
are necessary to expose the whole substrate 9. Accordingly, the
time required for the pattern writing apparatus 1 to write a
pattern on the whole substrate 9 is 7.8 seconds.
[0073] As above described, by tilting a two-dimensional array of
irradiation regions relative to the main scanning direction, the
pattern writing apparatus 1 can achieve high-precision pattern
writing by exposure at extremely high speed.
[0074] The present invention has been described with reference to
the preferred embodiments thereof, but it should be understood that
the present invention is not limited to the aforementioned
preferred embodiments and various modifications are possible.
[0075] The spatial light modulator employed in the pattern writing
apparatus 1 is not limited to the DMD 42 employed in the
aforementioned preferred embodiments; in fact, it may be a liquid
crystal shutter, for example. Also, pattern writing may be achieved
by arranging, for example, a plurality of light emitting diodes in
two dimensions as a light source, tilting the direction of
arrangement of an irradiation region group corresponding to the
light emitting diode group relative to the main scanning direction,
and exercising ON/OFF control of each of the light emitting diodes
in synchronization with relative movement of the irradiation
regions.
[0076] The relative movement of the stage 2 and the head 4 in the
main scanning direction and in the sub-scanning direction (i.e.,
relative movement of the writing cell group and the irradiation
region group on the substrate 9) may be substituted by movement of
only either one of the stage 2 and head 4.
[0077] The pitches of the irradiation regions and the writing cells
are not limited to those described in the aforementioned preferred
embodiments, and they may be changed as appropriate according to
specifications. That is, the tilt angle of the irradiation region
group relative to the main scanning direction can be changed as
appropriate according to the sizes of the irradiation regions 61
and the writing cells 620 and according to the number of multiple
exposures.
[0078] Although the above preferred embodiments do not refer to
control of light irradiation of the irradiation regions 61 located
at the ends of the sub-scanning direction in the irradiation region
group (e.g., part of the irradiation regions 61 on the (-X) and
(-Y) portion in FIG. 4), light irradiation of those irradiation
regions 61 is not performed in terms of simplicity of control.
[0079] While the invention has been shown and described in detail,
the foregoing description is in all aspects illustrative and not
restrictive. It is therefore understood that numerous modifications
and variations can be devised without departing from the scope of
the invention.
* * * * *