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Claims  |
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We claim:
1. In combination for inscribing a pattern on a photoresist layer on a
substrate,
means for providing a beam of energy having first characteristics,
means for focussing on the photoresist layer the beam of energy having the
first characteristics for reflection of such energy in accordance with the
characteristics of such photoresist layer at the position of focus on the
photoresist layer,
means for producing a scanning of the beam relative to the photoresist
layer in a raster scan represented by progressive lines each extending in
a first direction and displaced from each other in a second direction
co-ordinate with the first direction,
means for providing an indication, in the scanning of the energy beam, of
the scanning of particular positions in progressive lines by the energy
beam,
means for providing markers representing particular positions in the
progressive lines being scanned, and
means for adjusting the rate of scanning of the energy beam in the
progressive lines in accordance with any differences between the scanning
of the particular positions in the progressive lines and the production of
the markers representing the particular positions in the progressive
lines.
2. In a combination as set forth in claim 1,
means for providing a physical movement of the substrate in a second
direction co-cordinate with the first direction, and
means for providing a scanning, concurrently with the physical movement of
the substrate in the second direction of the energy beam through a limited
distance in the first direction less than the complete distance of the
pattern inscribed on the photoresist layer in the first direction.
3. In a combination as set forth in claim 2,
means for concurrently providing a plurality of energy beams displaced from
one another in the second direction, and
means for simultaneously displacing the plurality of energy beams in the
first direction.
4. In a combination as set forth in claim 3,
means responsive to the energy reflected from the photoresist layer for
adjusting the focus of the energy beam on the photoresist layer.
5. In combination for inscribing a pattern on a photoresist layer on a
substrate,
means for providing a first energy beam having first characteristics,
means for focussing the first energy beam on the photoresist layer of the
substrate to obtain an inscribing of the photoresist layer and a
reflection of the beam from the substrate,
means for producing a scanning of the first energy beam relative to the
substrate at a first rate,
means for modulating the intensity of the first energy beam during the
scanning of the first energy beam relative to the substrate at the
particular rate to control the pattern inscribed on the photoresist layer,
means responsive to the energy reflected in the first energy beam from the
photoresist layer for regulating the scanning of the first energy beam at
the first rate,
means for providing a second energy beam co-ordinated in scanning with the
first energy beam and having second characteristics different from the
first characteristics,
means for producing a scanning of the second energy beam at a second rate
different from the first rate, means for focussing the second energy beam
on the photoresist layer of the substrate to obtain a reflection of the
energy in the second energy beam from the photoresist layer on the
substrate in accordance with the pattern inscribed on the substrate, and
means for using the energy reflected in the second energy beam from the
photoresist layer of the substrate at individual positions in the
substrate to enhance the focussing of the first energy beam on the
substrate at such individual positions.
6. The combination as set forth in claim 5 wherein
the scanning means produces a scanning of the energy in the first energy
beam in progressive lines of limited displacement in a first direction and
a displacement of the progressive lines from each other in a second
direction.
7. In combination for inscribing a pattern on a photoresist layer on a
substrate,
means for providing a first energy beam having first characteristics,
means for focussing the first energy beam on the photoresist layer of the
substrate to obtain an inscribing of the photoresist layer and a
reflection of the beam from the substrate,
means for producing a scanning of the first energy beam relative to the
substrate,
means for modulating the intensity of the first energy beam during the
scanning to control the pattern inscribed on the photoresist layer,
means responsive to the energy reflected in the first energy beam from the
photoresist layer for regulating the scanning of the first energy beam,
means for providing a second energy beam co-ordinated in scanning with the
first energy beam and having second characteristics different from the
first characteristics,
means for focussing the second energy beam on the photoresist layer of the
substrate to obtain a reflection of the energy in the second energy beam
from the photoresist layer on the substrate in accordance with the pattern
inscribed on the substrate,
means for using the energy reflected in the second energy beam from the
photoresist layer of the substrate to enhance the focussing of the first
energy beam on the substrate,
the focus-enhancing means including an active mirror,
means for providing an ideal point-spread function of the first beam,
means responsive to the energy reflected in the second energy beam from the
photoresist layer for providing an actual point-spread function of the
energy, and
means responsive to the relative characteristics of the ideal and actual
point-spread functions for adjusting the active mirror to have the actual
point-spread function approach coincidence with the ideal point-spread
function.
8. In a combination as set forth in claim 7,
means for moving the substrate in the first and second co-ordinate
directions concurrently with the scanning of the first energy beam in the
first and second co-ordinate directions.
9. In a combination as set forth in claim 8,
the first energy beam having a first wavelength and the second energy beam
having a second wavelength different from the first wavelength and the
energy constituting light.
10. In combination for inscribing a pattern on a photoresist layer on a
substrate,
means for providing a beam of energy,
means for operating upon the beam of energy to provide a plurality of beams
of energy displaced from each other in a particular direction,
means for directing the beams of energy in the plurality toward the
photoresist layer on the substrate,
means for focussing the beams of energy in the plurality on the photoresist
layer on the substrate,
means for simultaneously obtaining a scan of the beams of energy in the
plurality in the particular direction and in a second direction
co-ordinate with the particular direction to obtain a raster scan of the
beams of energy, and
means for modulating the beams of energy in the plurality during the raster
scan to inscribe the pattern on the photoresist layer on the substrate.
11. In a combination as set forth in claim 10, including,
means for providing a movement of the substrate relative to the beams of
energy in the particular and second directions,
the means for providing the raster scan of the beams of energy in the
plurality relative to the substrate providing movement of the beams of
energy in the particular and second directions.
12. In a combination as set forth in claim 10,
means for providing an indication of a desired positioning of the energy
beams in the plurality at periodic times, and
means responsive to the indications of the desired positioning of the
energy beams in the plurality in the particular direction at the periodic
times and to the actual positioning of the energy beams in the plurality
at such periodic times for simultaneously adjusting the rate at which the
beams in the plurality are scanned by the scanning means in accordance
with any differences between such desired and actual positionings.
13. In a combination as set forth in claim 10,
means for providing a scanning of the photoresist layer on the substrate
with an additional energy beam different from the energy beams in the
plurality to obtain a reflection of the positions in the layer in
accordance with the characteristics of the photoresist layer at such
individual positions, and additional energy beam from the photoresist
layer at the individual positions in the photoresist layer for maintaining
the energy beams in the plurality focussed on the photoresist layer at
such individual positions.
14. In combination for inscribing a pattern on a photoresist layer on a
substrate,
means for providing a beam of energy,
means for operating upon the beam of energy to provide a plurality of beams
of energy displaced from each other in a particular direction,
means for directing the beams of energy in the plurality toward the
photoresist layer on the substrate,
means for focussing the beams of energy in the plurality on the photoresist
layer on the substrate,
means for obtaining a scan of the beams of energy in the plurality in the
particular direction and in a second direction co-ordinate with the
particular direction to obtain a raster scan of the beams of energy,
means for modulating the beams of energy in the plurality during the raster
scan to inscribe the pattern on the photoresist layer on the substrate,
means for providing an indication of a desired positioning of the energy
beams in the plurality at periodic times,
means responsive to the indications of the desired positioning of the
energy beams in the plurality in the particular direction at the periodic
times and to the actual positioning of the energy beams in the plurality
at such periodic times for simultaneously adjusting the rate at which the
beams in the plurality are scanned by the scanning means in accordance
with any difference between such desired and actual positioning,
means for directing to the photoresist layer an additional energy beam
having characteristics different from those in the energy beams in the
plurality to obtain a reflection of the energy in such beam from the
photoresist layer,
means responsive to the energy reflected from the photoresist layer in the
additional beam for detecting such energy, and
means responsive to the energy detected in the second beam for maintaining
the energy beams in the plurality focussed on the photoresist layer.
15. In a combination as set forth in claim 14,
an active mirror adjustable in a plurality of different positions,
the active mirror being adjustable in the different positions in accordance
with the energy detected in the additional beam to maintain the energy
beams in the plurality focussed on the photoresist layer.
16. In combination for inscribing a pattern on a photoresist layer on a
substrate,
means for providing a beam of energy,
means for focussing the beam of energy on the substrate in a spot size
defined by particular external dimensions,
means for providing a movement of the substrate in first and second
co-ordinate directions, and
means for providing a raster scan of the energy beam in the first direction
through limited and progressive positions having dimensions less than the
dimension of the pattern of the photoresist layer in the first direction
and for simultaneously providing a raster scan of the energy beam in a
second direction coordinate with the first direction, and
means for modulating the energy beam, in accordance with the pattern to be
inscribed on the photoresist layer, during the scan of the energy beam in
the first direction through the limited and progressive positions in the
first direction and through the simultaneous and repetitive scans in the
second direction.
17. In a combination as set forth in claim 16,
the energy beam directed to the photoresist layer being reflected from the
photoresist layer,
means responsive to the energy beam reflected from the photoresist layer
for producing first signals having characteristics representative of such
energy beam at the individual positions on the photoresist layer,
means for providing a second energy beam having characteristics different
from the first energy beam,
means for providing a scanning of the second energy beam in the first and
second coordinate directions to obtain a reflection of the second energy
beam from the photoresist layer of the substrate,
means responsive to the reflection of the second energy beam from the
photoresist layer for producing second signals representing such
reflection,
means for providing signals representing a desired focussing of the energy
beam on the photoresist layer, and
means responsive to any differences between the signals representing the
desired focussing of the energy beam and the signals representing the
reflected second energy beam for the individual positions on the
photoresist layer for adjusting the characteristics of the first energy
beam at such indivdual positions to minimize any such differences at such
individual positions.
18. In a combination as set forth in claim 16,
the adjusting means including a plurality of elements each constructed to
provide a focussing action on an individual portion of the energy beam,
and
the adjusting means further including means operative on the different ones
of the elements in the plurality to produce the focussing of the energy
beam on the photoresist layer in accordance with any differences between
representing the desired focussing of the energy beam and the signals
representing the reflected second energy beam.
19. In a combination as set forth in claim 16,
means for providing marker signals representing a particular position in
each limited and progressive line scan of the energy beam in the first
direction, and
means responsive to the marker signals and the signals representing the
scan of the energy beam past the paritcular position in the first
direction for adjusting the rate of the scan to obtain a coincidence
between the occureence of the marker signals and the scanning of the
energy beam past the particular position in each line in the first
direction.
20. In combination for inscribing a pattern on a photoresist layer on a
substrate,
means for providing a first energy beam having first characteristics,
means for operating upon the first energy beam to convert the first energy
beam into a plurality of beams displaced from one another in a first
direction,
means for obtaining a scan of the energy beams in the plurality in the
first direction through successive lines displaced from one another in a
second direction co-ordinate with the first direction,
means for modulating the energy beams in the plurality, during the scanning
of the successive lines, to inscribe the pattern on the photoresist layer,
means for providing a second energy beam having second characteristics,
means for obtaining a scan of the second energy beam asynchronously with
the scan of the first energy beam to obtain a reflection of energy in the
second beam from the photoresist layer in accordance with the pattern
inscribed on the photoresist layer, and
means responsive to the reflected energy in the second beam for adjusting
the focus of the energy beams in the plurality on the photoresist layer.
21. In a combination as set forth in claim 20,
means for regulating the scanning of the energy beams in the plurality to
maintain the scanning of the energy beams in the plurality at a particular
rate.
22. In a combination as set forth in claim 21,
the focussing means for the energy beams in the plurality including an
active mirror having a plurality of elements and further including means
responsive to the energy reflected in the second beam from the photoresist
layer for individually activating the elements in the plurality to provide
for the focussing fo the energy beam in the plurality on the photoresist
layer.
23. In a combination as set forth in claim 20,
means for providing signals indicating the desired timing in the scanning
of the energy beams in the plurality past a particular position in the
first direction,
means for detecting the energy reflected from the photoresist layer in one
of the beams in the plurality.
means responsive to the reflected energy for indicating the actual timing
in the scanning of the energy beam in the plurality past the particular
position in the first direction, and
means responsive to any differences in the timing of the signals
representing the desired and actual timing in the scanning of the energy
beams in the plurality past the particular position in the first direction
for adjusting the rate of scanning of the energy beams in the plurality to
compensate for any such differences in timing.
24. In a combination as set forth in claim 23,
the means converting the first energy beam into the energy beams in the
plurality including a pair of active mirrors each including a plurality of
spherical facets, individual ones of the spherical facets on the first
active mirror being associated with individual ones of the spherical
facets on the second active mirror to provide pairs of associated
spherical facets and to provide a converging of energy from one of the
associated spherical facets in each pair on the other one of the
associated spherical facets in each pair.
25. A method of inscribing a pattern on a photoresist layer on a substrate,
including the steps of:
providing a plurality of energy beams displaced from one another in a first
direction,
simultaneously scanning the energy beams in the plurality in a second
direction coordinate with the first direction through a plurality of lines
displaced from one another in the first direction,
focussing the energy beams in the plurality on the photoresist layer, and
simultaneously modulating the energy beams in the plurality at progressive
instants of time in accordance with the pattern to be inscribed on the
photoresist layer in the second direction.
26. A method as set forth in claim 25, including the step of:
producing the energy beams in the plurality by providing a single beam of
energy and dividing the beam of energy into the energy beams in the
plurality.
27. A method as set forth in claim 25 including the step of:
moving the substrate in the first and second co-ordinate directions, and
simultaneously scanning the energy beams in the plurality in the second
direction through limited and progressive positions defining a distance
less than the distance of the pattern in the second direction while
providing a movement of the substrate in the first direction.
28. A method of inscribing a pattern on a photoresist layer on a substrate,
including the steps of:
providing a first energy beam,
directing the energy beam to the photoresist layer,
scanning the first energy beam in a first direction in lines displaced from
one another in a second direction co-ordinate with the first direction;
modulating the first energy beam, during the scanning of the first energy
beam, in accordance with the pattern to be inscribed on the photoresist
layer,
focussing the first energy beam on the photoresist layer,
providing a second energy beam having characteristics different from those
of the first energy beam,
directing the second energy beam to the photoresist layer for reflection by
the photoresist layer,
scanning the second energy beam asynchronously with the first energy beam,
focussing the second energy beam on the photoresist layer, and
operating upon the energy reflected from the photoresist layer in the
second beam to adjust the focussing of the first energy beam on the
photoresist layer.
29. In a method as set forth in claim 28,
the energy in the first beam constituting light at a first wavelength and
the energy in the second beam constituting light at a second wavelength
different from the first wavelength.
30. A method as set forth in claim 29, including the step of:
synchronizing the scanning of the first beam to obtain the scanning of the
successive lines in the first direction at pre-set time intervals.
31. A method as set forth in claim 30, including the step of:
dividing the first energy beam into a plurality of energy beams,
and providing for the synchronous scanning of the energy beams in the
plurality.
32. In combination for inscribing a pattern on a photoresist layer on a
substrate,
means for providing a first energy beam,
means for directing the first energy beam to the photoresist layer of the
substrate to obtain an inscribing of the photoresist layer and a
reflection of the beam from the photoresist layer,
means for modulating the first energy beam in accordance with the pattern
to be inscribed on the substrate,
means for producing a scanning of the first energy beam on the substrate at
a first rate,
means responsive to the energy reflected from the substrate in the first
energy beam for regulating the scanning of the first energy beam to
maintain the first rate,
means for providing a second energy beam,
means for providing a scanning of the second energy beam at a second rate
different from the first rate,
means for directing the second energy beam to the photoresist layer of the
substrate to obtain a reflection of the second energy beam from the
photoresist layer,
means responsive to the energy reflected from the substrate in the second
energy beam for regulating the scanning of the second energy beam to
maintain the second rate, and
means responsive to the reflection of the second beam from the photoresist
layer at individual positions on the photoresist layer for adjusting the
characteristics of the first energy beam at such individual positions to
maintain the first energy beam focussed on the photoresist layer.
33. In a combination as recited in claim 32,
the scanning means for the first energy beam providing a first marker at
specified positions in the scan,
means for providing a first reference signal at spaced time intervals in
the first scan,
means responsive to the relative times of production of the first marker
and the first reference signal for adjusting the rate of the scan of the
first energy beam to minimize any difference in the time between the
production of the first marker and the production of the first reference
signal,
the scanning means for the second energy beam providing a second marker at
specified positions in the scan,
means for providing a second reference signal at spaced time intervals in
the second scan, and
means responsive to the relative times of production of the second marker
and the second reference signal to minimize any difference in the time
between the production of such second marker and of such second reference
signal.
34. In a combination as recited in claim 32,
the adjusting means including an active mirror having a plurality of
elements individually adjustable to adjust the characteristics of the
first energy beam at such positions.
35. In a combination as set forth in claim 32,
means for dividing the first energy beam into a plurality of energy beams
displaced from one another in a first direction and movable by the
associated scanning means in a second direction coordinate with the first
direction.
36. In combination for inscribing a pattern on a photoresist layer on a
substrate,
means for providing a first energy beam,
means for directing the first energy beam to the photoresist layer of the
substrate to obtain an inscribing of the photoresist layer and a
reflection of the beam from the photoresist layer,
means for modulating the first energy beam in accordance with the pattern
to be inscribed on the substrate,
means for deriving from the reflected beam a point-spread function of the
photoresist layer at individual positions on the layer, and
means for adjusting the characteristics of the beam at the individual
positions on the photoresist layer in accordance with the chracterisitics
of the point-spread function at such individual positions.
37. In a combination as set forth in claim 36,
the adjusting means including an active mirror having a plurality of
elements each adjustable to adjust the characteristics of the energy beam
at an individual position on the photoresist layer.
38. In a combination as set forth in claim 36,
means disposed relative to the photoresist layer for focussing the energy
beam at a particular distance from the photoresist layer,
means for detecting the reflected light, and
means disposed relative to the detecting means for focussing the energy
beam at the particular distance from the detecting means.
39. In combination as set forth in claim 36,
the scanning means providing a scan of the energy beam in a first direction
relative to the photoresist layer, and
means for providing a movement of the substrate in a second direction
coordinate with the first direction.
40. In a combination as set forth in claim 38,
the scanning means providing a scan of the energy beam relative to the
photoresist layer in a first direction through progressive positions
defining a distance significantly less than the distance of the pattern in
the first direction, and
means for providing a movement of the substrate in a second direction
coordinate with the first direction through a distance corresponding to
the distance of the pattern in the second direction and for then moving
the substrate in the first direction through a distance defined by the
progressive positions of the scan in the first direction. |
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Claims |
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Description |
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This invention relates to a system which uses a laser to inscribe a pattern
directly on a substrate. The invention also relates to methods of
inscribing a pattern on a photoresist layer on a substrate. The invention
is intended to be used primarily for the production of large-scale
integrated circuits.
In lithographic systems, a laser beam is used to print a desired
microstructure on a photosensitive resist layer disposed on a substrate.
In such systems, a master beam is split into a multiple number of beams to
reach a high working frequency by opposing an increased number of such
beams on the photoresist layer. Such a laser-beam writer has been
developed and marketed by TRE Semiconductor Equipment Corporation,
California, USA.
One of the disadvantages of the TRE laser-beam writer is that focussing of
all beams is only possible at one single focal plane. Thus, the use of
such writers is, apart from mask production, feasible only if a so-called
two-level resist strategy is applied. In such a strategy, a thick resist
layer compensates for the rough wafer surface. This thick resist layer is
then covered by a relatively thin layer on which the desired pattern is
then written. As will be seen, this system is cumbersome and expensive.
Another disadvantage of such laser-beam lithography is that each of the
light beams in the plurality has to be conducted in optical paths of the
same length to guarantee focussing on one planar surface. This has to
occur because beam control can be obtained only with a single reflector.
The technological effort required to operate a laser-beam writer as
described in the previous paragraphs is considerable. For example,
functional adjustments of the beam writer are difficult and can be
provided only by specialists. Thus the employment of laser-beam
lithography as described above has so far been restricted to laboratory
use only. Furthermore, the writer is limited in its printing speed since
the deflection unit in the writer limits the writing speed to
approximately ten megahertz (10 mhz).
Electron-beam writers used for the production of integrated circuits
provide a working frequency to twenty megahertz (20 mhz). However, such
writers require large-scale vacuum installations and complex control
systems. These are expensive and are susceptible to failure.
A considerable effort has been made to provide a system which employs a
laser to write on a substrate and which overcomes the disadvantages
specified in the previous paragraphs. In spite of such efforts, the laser
writers now in use still have the disadvantages specified above. Thus one
aim of the invention is to provide a pattern generator which uses a laser
and which operates at a high frequency and has a compact and simple
construction and a reliable operation to provide a direct exposure of the
wafer surface.
The pattern generator of this invention provides a writing speed in the
order of forty megahertz (40 mhz) and thus a reduction of the total
exposure period by half in comparison to an electron-beam lithographic
writer and by a quarter in comparison to laser-beam writers offered by
TRE. The laser-beam writer according to this invention requires only a
minimal adjustment and can be easily adjusted when needed. It also
provides an automatic refocussing for laser spot to control the size of
the spot within optimal limits. Accuracy of the patterns to be printed by
exposing photosensitive resists is thus considerably enhanced.
The laser pattern generator of this invention may be provided in the form
of a multi-channel system which provides for an increase in the operating
speed by a factor corresponding to the number of channels provided in the
system. These channels are obtained from a single light beam and are
synchronously scanned.
A pattern is inscribed on a photoresist layer on a substrate by directing
an energy (i.e. laser) beam to the layer. The beam is scanned in a first
direction through lines progressively displaced from one another in a
second coordinate direction. In this way, stripe areas of a wafer are
exposed sequentially in a first direction by the system of this invention.
The thickness of the stripe areas is dependent upon the size of the laser
spot focussed on the beam.
The scanning rate of the beam is adjustable to obtain time coincidence
between the ocurrence of markers in a computer and the scanning of a
particular position in the progressive lines. The beam is modulated during
the scan to inscribe the pattern on the layer. The substrate may also be
moved in the co-ordinate directions to facilitate the scan.
The beam is focussed on, and reflected from, the photoresist layer. The
reflection is used to maintain the focussing of the beam on the layer.
This may be accomplished by providing an active mirror with a plurality of
individual elements and adjusting the individual elements in accordance
with the characteristics of the reflected beam.
The beam may be split into a plurality of beams displaced from one another
in the first direction. This may be accomplished by providing associated
pairs of spherical facets in a lens system and by directing portions of
the beam between the facets in each pair. The beams in the plurality are
synchronously scanned to increase the scanning frequency.
A second beam may be provided with different characteristics than the first
beam. The second beam may be scanned asynchronously with the first beam
such as at a lower speed than the first beam and may be focussed on the
photoresist layer in a manner similar to that described above. Light
reflected in the second beam from the layer is used to verify the pattern
inscribed on the layer by the first beam.
This application corresponds to an application Ser. No. P34 27 611.4 filed
by applicants in the Federal Republic of Germany on July 25, 1984.
Applicants accordingly claim the benefit of the Convention date of July
25, 1984. Furthermore, the apparatus disclosed and claimed in this
application is similar in several respects to apparatus disclosed and
claimed in application Serial No. 706,619 filed by Josef Bille in the U.S.
Patent Office on Feb. 28, 1985, and application Ser. No. 742,531 filed by
Josef Bille and Siegfried Hunklinger in the U.S. Patent Office on June 7,
1985.
Further details and elements of the invention derive from a subsequent
description of several different embodiments which are shown in the
drawings.
In the drawings:
FIG. 1 is a block diagram of a single channel system for inscribing a
pattern on a photoresist layer on a substrate.
FIG. 2 is a diagram schematically illustrating how the photoresist layer is
scanned by the system of FIG. 1 to inscribe the pattern on the layer;
FIG. 3 is a block diagram of an electrical sub-system which may be included
in the system of FIG. 1 to automatically refocus a beam on the photoresist
layer to inscribe the pattern on the layer;
FIG. 4 is a simplified partial display of an active mirror which is
included in the system of FIG. 1 and which can be electrically stimulated
to enhance the focussing of the beam on the photoresist layer; and
FIG. 5 shows apparatus for converting the single channel system of FIG. 1
into a multi-channel system.
In the course of producing large-scale integrated circuits on substrates on
wafers such as a substrate 11, the integrated circuits are illustratively
produced by a variety of single-process steps. In at least some of these
steps, a photoresist covers the microstructured surface of the substrate
11 and is prepared for exposure to sputtering, diffusion, implantation
and/or oxidation processes. Such exposure may be provided by using a
system, generally indicated at 10, to inscribe the surface of the
photoresist layer. After such exposure, either the exposed or the
unexposed portions of the photoresist layer may be removed from the
substrate 11. The resist remaining on the substrate 11 is then used as a
mask during the following process steps.
In one expedient utilization, the photo-resist can also be used as a base
for another layer, e.g. a conducting metal-film. Under such circumstances,
the respective areas of the additional layer and the exposed or unexposed
areas of the resist (according to resist type) may be removed as by
etching. The laser pattern generator 10 of this invention provides an
accurate exposure of the respective resists for the production steps and
provides such exposures faster and more accurately and reliably than that
provided in the prior art.
The system 10 shown in FIG. 1 constitutes a single-channel system, where
only one laser beam 12 is used to expose the photoresist layer. This laser
beam is focussed on the surface of the photoresist layer on the substrate
or wafer 11 by means of a microscope objective 13. The laser beam 12 is
focussed on the wafer as a wafer spot which has a representative diameter
of approximately one quarter of a micrometer (0.25 .mu.m) in accordance
with the half-width value of the Gaussian intensity profile of a laser
beam.
The intensity of the laser beam may be altered in a ratio to 500-1 by means
of an acousto-optical modulator 14. If required, the intensity can be
fine-tuned. The substrate 11 can be moved by a conveyor 16 (only
schematically outlined) to-and-fro along an x-coordinate and a
y-coordinate respectively marked by arrows 17 and 18 to expose the full
surface of the photoresist layer of the substrate 11.
An optical scanner (indicated in broken lines as a block 19) is included to
provide a horizontal sweep of the laser beam in the x-direction. This beam
is focussed by the microscope objective 13 to provide a laser spot 21
(FIG. 2) with a field size in the order of two hundred and fifty
micrometers (250 .mu.m). In the exposing process, the substrate 11 is
moved past the microscope objective 13 by a conveyor 16 on a meander- or
square-wave path illustrated by full and dotted lines in FIG. 2. Typical
feed rates in the y-direction are between one millimeter per second (1
mm/s) and five millimeters per second (5 mm/s). At the same time, the
laser spot moves with a considerably higher rate in the x-direction, i.e.
with a rate of five meters per second (5 m/s). Because of the simultaneous
movement of the substrate 11 and the scanning of the laser beam, the laser
beam covers a band area 24 while the substrate 11 moves along an area 23
of a meander path generally indicated at 22. By providing an appropriate
adjustment of the sweep rate of the laser beam in the x-direction and the
feed rate of the substrate in the y-direction, the band area 24 can be
fully exposed. By exposing successive ones of the band areas 24, the full
area of the photoresist layer on the substrate 11 may be fully exposed.
Line control is achieved, in the system shown in FIG. 1, by a rotatable
motor-driven polygonal mirror 26. As a result, the laser spot 21 moves in
parallel lines 27 (FIG. 2) from one edge to an opposite edge 29 of each
band 24. Because of the special layout of the conveyor for the substrate
11, the feed rate of the substrate 11 in the y-direction can be adjusted
so that the distance in the y-direction of pairs of successive lines is
equal to substantially the radius of the laser spot 21. Thus, the distance
measured between the lines in each successive pair is in the order of one
eighth of a micrometer (0.125 .mu.m) in the example discussed above.
The acousto-optical modulator 14 controls intensity--i.e. brightness--of
the laser-beam 12. The modulator 14 can be stimulated by a forty megahertz
(40 mhz) signal. In other words, the intensity of the laser beam 12 can be
adjusted forty million different times within one second. If, in each line
27, two thousand (2,000) scanning points are to be exposed, their distance
relative to one another in the x-direction is one eighth of a micrometer
(0.125 .mu.m). This means that twenty thousand (20,000) lines 27 can be
exposed point-by-point per second, where the distance between the lines is
also one eighth of a micrometer (0.125 m). Thus, a dot-responsive line
scanning pattern is obtained for exposure where the dots are equidistant
in both the x-direction and the y-direction.
The pattern to be produced by exposure of the photoresist on the substrate
11 may be stored on a disk memory connected to a computer 31. During
exposure of the photoresist, this pattern can be sequentially read from
the computer 31 and then processed by the computer for appropriate control
of the acousto-optical modulator 14. During this process, the movement of
the substrate 11 is synchronized with the signals from the computer 31 by
signals received from the conveyor 16. These signals provide information
to the computer 31 about the position of the substrate 11 at each instant.
This synchronization is provided by the introduction of signals to the
computer 31 through lines 33, 34 and 36. The signals on the line 36
indicate the rate at which the laser beam is being swept in a horizontal
direction. The signals on the lines 33 and 34 indicate the rate at which
output signals are obtained from the surface of the substrate 11 as a
result of the passage of the laser beam to the substrate. The computer 31
then processes these signals and introduces signals to the conveyor 16
through lines 33a and 34a to control the subsequent operation of the
conveyor.
For exposing the photoresist on the substrate 11, an ionized argon-laser 37
may be used to emit an ultra-violet (UV) light band of approximately
.lambda..sub.1 =270 nm. The standard type of photoresists on the substrate
11 are sufficiently sensitive to ultraviolet light at this wavelength. The
laser also emits a light band of approximately .lambda..sub.2 =514 nm.
This light band is used by another laser scanner (generally indicated in
broken lines at 38), also working as a laser scanning microscope, for
covering a so-called point-spread-function, i.e. the spatial distribution
of the intensity of the light reflection in selected spots or areas of the
substrate surface. The scanner 38 is driven asynchronously with respect to
the scanner 19 such as at a considerably reduced scanning frequency than
that of the scanner 19. The light reflected from the surface of the
substrate 11 into the path of the scanner 38 is received in its
two-dimensional-spatial distribution of intensity by photoelectric sensors
39 disposed in two dimensions in a matrix relationship. The sensors may
preferably comprise diodes.
The intensity distribution of the portion of the light beam reflected from
an exposed surface element on the photoresist surface of the substrate 11
is stored for further processing. A comparison can be made between the
stored intensity distribution of the light beam and an ideal point spread
function to obtain precise focussing of the scanning beam, schematically
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