U.S. patent application number 09/365102 was filed with the patent office on 2001-12-20 for counter-rotating anamorphic prism assembly with variable spacing.
Invention is credited to BOLT, BRYAN C..
Application Number | 20010053033 09/365102 |
Document ID | / |
Family ID | 23437481 |
Filed Date | 2001-12-20 |
United States Patent
Application |
20010053033 |
Kind Code |
A1 |
BOLT, BRYAN C. |
December 20, 2001 |
COUNTER-ROTATING ANAMORPHIC PRISM ASSEMBLY WITH VARIABLE
SPACING
Abstract
A counter-rotating anamorphic prism pair assembly with variable
spacing allows the simultaneous adjustment of a prism pair using an
adjustment member to circularize in cross section a range of
elliptical laser beam cross sections. A first prism rotates and
translates towards or away from an incident laser beam while a
second prism simultaneously rotates towards or away from the laser
beam in a fixed counter-rotating relationship with the first prism.
The degree of rotation and translation is determined by a
mechanical linkage connecting the two prisms.
Inventors: |
BOLT, BRYAN C.; (BEAVERTON,
OR) |
Correspondence
Address: |
PATENT COUNSEL
LEGAL AFFAIRS DEPT.
APPLIED MATERIALS, INC
BOX 450A
SANTA CLARA
CA
95052
US
|
Family ID: |
23437481 |
Appl. No.: |
09/365102 |
Filed: |
July 30, 1999 |
Current U.S.
Class: |
359/831 |
Current CPC
Class: |
G02B 26/0883 20130101;
G02B 27/09 20130101; G02B 27/0972 20130101; G02B 27/0911
20130101 |
Class at
Publication: |
359/831 |
International
Class: |
G02B 005/04 |
Claims
What is claimed is:
1. An optical apparatus, comprising: a base; a slide mounted on
said base; a first prism mount attached to said base; a second
prism mount attached to said slide; a first prism attached to said
first prism mount; a second prism attached to said second prism
mount; and a slide adjustment member coupled to said slide to
adjustably move said slide relative to said base and adjust said
first prism and said second prism, whereby faces of said first
prism and said second prism move in a fixed counter-rotating
relationship.
2. The apparatus of claim 1, wherein said slide adjustment member
moves said slide parallel to an axis of a laser beam directed onto
said first prism and said first prism rotates and translates
towards or away from said axis of said laser beam in a fixed
relationship to said second prism.
3. The apparatus of claim 2, wherein said slide adjustment member
moves said slide parallel to said axis of said laser beam and said
second prism rotates towards or away from said axis of said input
laser beam in a fixed relationship to said first prism.
4. The apparatus of claim 1, further comprising an adjustment
member attached to said base and coupled to said first prism
mount.
5. The apparatus of claim 4, wherein said angular adjustment member
adjusts an angle of said first prism mount relative to said
base.
6. The apparatus of claim 1, wherein said first prism mount has a
first end and a second end, wherein: said first end is attached by
a first pivot to said base; and said second end is attached by a
second pivot to said slide.
7. The apparatus of claim 1, wherein said second prism mount
comprises a first end and a second end, wherein: said first end is
attached by a first pivot to said slide; and said second end is
attached by a second pivot to said base.
8. The apparatus of claim 6, wherein a face of said first prism is
substantially coplanar with said first pivot.
9. The apparatus of claim 7, wherein a face of said second prism is
substantially coplanar with said second pivot.
10. The apparatus of claim 6, wherein a change in rotational angle
of a first entrant face of said first prism,
.DELTA..theta..sub.first prism, is obtained with a translational
distance, d, in which said slide is displaced, and with a length
from said first pivot to said second pivot, L.sub.1, by the
following: .DELTA..theta..sub.first prism=tan.sup.-1(d/L.sub.1)
.
11. The apparatus of claim 7, whereby a change in rotational angle
of a second entrant face of said second prism,
.DELTA..theta..sub.second prism, is obtained with translational
distance, d, in which said slide is displaced, and with a length
from said first pivot to said second pivot, L.sub.2, by the
following: .DELTA..theta..sub.first prism=tan.sup.-1(d/L.sub.1)
.
12. An optical apparatus, comprising: a base; a slide mounted
movably on said base; a first prism mount rotatably attached to
said base at a first end and rotatably attached to said slide at a
second end; a second prism mount rotatably attached to said slide
at a first end and rotatably attached to said base at a second end;
a first prism attached to said first prism mount at said first end
such that a face of said first prism is substantially coplanar with
a first proximal pivot; a second prism attached to said second
prism mount at said second end such that a face of said second
prism is substantially coplanar with a second proximal pivot; a
slide adjustment member coupled to said base which adjustably moves
said slide relative to said base wherein said slide moves parallel
to an axis of a laser beam incident on said first prism and said
first prism rotates and translates simultaneously in a fixed
relationship to said second prism and said second prism rotates in
a fixed relationship simultaneously with said first prism; and an
angular adjustment member attached to said base and to said first
prism mount wherein said member adjusts a location of said first
end of said first prism mount.
13. A method of adjusting a prism pair, comprising: directing a
laser beam into a first prism; rotating and translating said first
prism towards or away from an axis of said laser beam; and rotating
a second prism towards or away from said axis of said laser beam in
a fixed counter-rotating relationship.
Description
BACKGROUND
[0001] 1. Field of the Invention
[0002] This invention relates to optics, and more particularly to
conversion of a laser beam with an elliptical cross section to a
beam with a circular cross section.
[0003] 2. Description of Related Art
[0004] Elliptically shaped (in cross section) light beams output
from a laser can be converted into a more desirable circular beam
by using a pair of prisms. The output beam from a laser is often in
the cross-sectional shape of an ellipse; however, the elliptical
shape does not lend itself to optimal performance of associated
systems, thereby giving rise to various techniques for converting
the elliptical beam into a circular one. Such beam conversion is
useful, e.g., in laser beam scanning lithography where a group of
parallel laser beams are modulated and scanned over a
photosensitive medium to form an image on the medium. Applications
are, for instance, in the semiconductor industry for lithography
for integrated circuits.
[0005] These methods of converting such beam cross sections usually
involve transmitting a laser beam through a pair of prisms and then
rotating and translating the prisms in relation to each other until
the desired cross section was achieved. An incident laser beam is
applied to the prism pair, and then an iterative process begins of
manipulating the prisms relative to each other. This not only
increases post adjustment alignment time for downstream optics, but
this also increases the complexity of downstream assemblies due to
significant angular and transverse displacement of the output beam
relative to the input beam. Therefore, there is a need to be able
to quickly adjust an anamorphic prism pair to change the
ellipticity of an input laser beam while minimizing angular and
transverse beam displacements resulting from the adjustments.
SUMMARY
[0006] In accordance with the invention, the above problem is
overcome by linking an anamorphic pair of prisms, where a first
prism simultaneously rotates counter to a second prism, by
mechanical linkages. An anamorphic assembly is an optical system
providing two different magnifications along two perpendicular axes
such as the present assembly where prisms convert an elliptically
cross sectioned laser beam into a circularly shaped cross sectioned
beam. The prisms are linked such that the first prism translates
and rotates simultaneously towards or away from the axis of an
input laser beam. Meanwhile, the second prism rotates towards or
away from the axis of the input laser beam in a counter-rotating
relationship with the first prism. These movements are effected by
a single slide adjustment member which translates a slide upon
which both prisms are attached.
[0007] A first prism mount, upon which the first prism is attached,
has a distal end which is attached to the base and a proximal end
which is attached to the slide. A second prism mount, upon which
the second prism is attached, also has a distal end and a proximal
end; however, this distal end is attached to the slide and the
proximal end is attached to the base. This arrangement allows the
simultaneous adjustment of both prisms using a single slide
adjustment member while maintaining the circularity of an output
beam cross section over a range of elliptical input beam cross
sections. This arrangement also allows for minimizing the angular
and transverse displacement of the output beam relative to the
input beam.
[0008] Furthermore, there is an associated method of simultaneously
adjusting a prism pair where a laser beam is input into the entrant
face of the first prism, then the slide adjustment member is
adjusted. This adjusting rotates and translates the first prism
towards or away from the laser beam and rotates the second prism
simultaneously towards or away from the laser beam in a fixed
counter-rotating manner.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 shows a view of the present counter-rotating
anamorphic prism assembly.
[0010] FIG. 2 shows a view of the FIG. 1 counter-rotating
anamorphic prism assembly in the negative extreme position.
[0011] FIG. 3 shows a view of the counter-rotating anamorphic prism
assembly of FIG. 1 in the positive extreme position.
[0012] FIG. 4 shows a view of the angular adjustment member and the
first distal pivot of FIG. 1.
[0013] FIG. 5 shows a view of the anamorphic prism assembly, the
transverse displacement of the laser beam, the angles of rotation
of the prisms, and the angles of incidence and refraction of the
laser beam through the assembly of FIG. 1.
[0014] FIG. 6 shows a view of a prism and the incident area.
[0015] Use of the same reference symbols in different figures
indicates similar or identical items.
DETAILED DESCRIPTION
[0016] FIG. 1 illustrates an optical apparatus in accordance with
this invention. The adjustable prism apparatus 2 has a base 4 which
allows removal of an associated cover (not shown) and also allows
easy access to the internal assembly contained within and which
will be discussed in detail below. On base 4 is mounted a slide 6
which moves translationally over a specified range. Prism apparatus
2 further includes a first prism mount 8 and a second prism mount
10 mounted to base 4 and slide 6.
[0017] Slide 6 translates on base 4 by slide adjustment member 16,
which is, e.g., an adjustment screw anchored to base 4 in this
embodiment. Slide adjustment member 16 has a ball end facing
towards slide 6 and can be translated towards or away from slide 6
by rotating it about its own axis. Slide 6 is maintained in contact
with slide adjustment member 16 at contact point 50 by a small
spring force (e.g., 4 lb. force, nominal) acting on slide 6 (the
spring is not shown); slide 6 is not rigidly fastened to slide
adjustment member 16 thus allowing the rotation of member 16 about
its axis.
[0018] First prism mount 8 has two pivots located respectively at
both its ends. First distal pivot 30 is located at the top of first
prism mount 8, called first distal end 26, and first proximal pivot
32 is located at the lower end of first prism mount 8, called first
proximal end 28. Furthermore, first distal pivot 30 is in contact
with angular adjustment member 18, which is described in further
detail below for FIG. 4. The first distal and proximal pivots 30,
32 are collinearly aligned in first prism mount 8, but this does
not preclude noncollinear arrangements in other embodiments. First
distal pivot 30 is secured onto base 4 near angular adjustment
member 18, located at the top of base 4, and first proximal pivot
32 is secured onto slide 6. Also, first distal pivot 30 is held
within a slotted channel in first prism mount 8 (slot is not shown)
to allow the translation of slide 6. Second prism mount 10 also has
two pivots located at both ends. Second distal pivot 38 is located
near the top of prism mount 10 in second distal end 34 and second
proximal pivot 40 is located near the bottom of prism mount 10 in
second proximal end 36. Second distal and proximal pivots 38, 40
are also aligned collinearly, but again this does not preclude a
noncollinear arrangement in other embodiments. In an opposite
arrangement from first prism mount 8, second distal pivot 38 is
secured onto slide 6 and second proximal pivot 40 is secured onto
base 4. Second distal pivot 38 is also held within a slotted
channel on second prism mount 10 (slot is not shown) to allow the
translation of slide 6. All four pivots 30, 32, 38, 40 are fastened
to either base 4 or slide 6 with, e.g., dowels (not shown) which
allows the rotation of the prism mounts 8, 10 about their
respective pivots. First distal pivot 30 is further attached to
angular adjustment member 18 which is used to correct output laser
beam 24 for manufacturing error in apparatus 2 or in input laser
beam 20 angular errors. Operation of angular adjustment member 18
is described in greater detail below.
[0019] First prism 12 is mounted onto first prism mount 8 at first
proximal end 28 with an adhesive in such a way that a first entrant
face 42 of first prism 12 is substantially coplanar with first
proximal pivot 32. Second prism 14 is also mounted onto second
proximal end 36 in such a way that a second entrant face 46 is
substantially coplanar with second proximal pivot 40. It is not
necessary that first and second entrant faces 42, 46, respectively,
and first and second proximal pivots 32, 40, respectively, are
exactly coplanar. Both entrant faces 42, 46 and both proximal
pivots 32, 40 may be non-coplanar but substantially close. Both
prisms 12, 14 are of fused silica having an index of refraction of
n=1.504 in one particular embodiment.
[0020] FIG. 2 shows the translation towards the negative extreme
position of slide 6 through a distance, d, relative to base 4. As
the input laser beam 20 (from a conventional laser source) is
illuminated through first entrant face 42, slide adjustment member
16 is rotated about its axis to translate slide 6 parallel and
towards input laser beam 20. This causes first prism mount 8 to
rotate about first distal pivot 30 as first proximal end 28 rotates
towards input laser beam 20. Simultaneously, second distal pivot 38
is linearly translated through distance, d, towards input laser
beam 20. This in turn causes second prism mount 10 to rotate about
second proximal pivot 40. The simultaneous rotations of first and
second prism mounts 8, 10 result in the rotation and translation of
first prism 12 and the rotation of second prism 14 in a
counter-rotating manner.
[0021] Additionally, because first prism 12 and second 14 are
mounted such that input laser beam 20 is incident upon entrant
faces 42, 46 and perpendicularly to the axis of first and second
proximal pivots 32, 40, respectively, a sweep of beams may also be
applied in another embodiment. Such a sweep of beams is preferably
illuminated upon first entrant face 42 such that the beams are
coplanar with each other and this plane is parallel with the axis
of first and second proximal pivots 32, 40, respectively. The true
circularity of the resulting output laser beam 24 can be monitored
with a change coupled device (CCD) camera (camera not shown) or any
commercially available beam monitoring device. Such a camera can be
utilized with a beam splitter and placed downstream of prism
apparatus 2. In another embodiment, another type of conventional
camera, utilized with a beam splitter, may be placed either
upstream or downstream of prism apparatus 2, but it is preferable
to locate a camera downstream to monitor the circularity of the
cross section of output laser beam 24.
[0022] FIG. 3 shows the translation towards the extreme positive
position of slide 6 through a distance, d, relative to base 4.
Again, as input laser beam 20 is illuminated through first entrant
face 42, slide adjustment member 16 is rotated about its axis to
translate slide 6 parallel and away from input laser beam 20. This
causes first prism mount 8 to rotate about first distal pivot 30 as
first proximal end 28 rotates away from input laser beam 20.
Simultaneously, second distal pivot 38 is linearly translated
through distance, d, away from input laser beam 20. Again, this
causes second prism mount 10 to rotate about second proximal pivot
40 and the simultaneous rotations of first and second prism mounts
8, 10 further results in the rotation and translation of first
prism 12 and the rotation of second prism 14 in a counter-rotating
manner opposite from the direction as shown in FIG. 2.
[0023] FIG. 4 shows angular adjustment member 18 of FIG. 1 which is
used to correct output laser beam 24 angle errors. Angular
adjustment member 18 is shown as an adjustment screw which is
screwed into base 4 in this embodiment. After slide 6 and prisms
12, 14 have been adjusted to circularize the cross-sectional area
of input laser beam 20 (as discussed above for FIGS. 2 and 3), the
axis of output laser beam 24 might deviate from the axis of input
laser beam 20 due either to manufacturing errors in the mechanical
linkages and prisms 12, 14 or in input laser beam 20 angular
errors. Therefore, in order to keep the axis of output laser beam
24 substantially parallel with the axis of input laser beam 20,
correction of output laser beam 24 angle is effected by rotating
angular adjustment member 18 about its own axis. This rotation
translates first distal pivot 30 in a parallel direction either
towards or away from input laser beam 20 and this translation
adjusts the angle of incidence for input laser beam 20 with first
prism 12 to effect a beam correction.
[0024] FIG. 5 shows geometrically the relationship between first
prism 12 and second prism 14. The input laser beam 20 enters first
entrant face 42 at angle A1, which is the angle of incidence of
input laser beam 20 at first entrant face 42. As input laser beam
20 passes through first prism 12, it defines angle B1, which is the
angle of refraction of input laser beam 20 at first entrant face
42. Input laser beam 20 again refracts as it passes first
refractant face 44 defining angle A2, which is the angle of
incidence of input laser beam 20 at first refractant face 44, and
angle B2, which is the angle of refraction of input laser beam 20
at first refractant face 44. Input laser beam 20 is designated
intermediate refracted laser beam 22 as it passes from first prism
12 to second prism 14. This intermediate refracted beam 22 then
enters second prism 14 defining angle A3, which is the angle of
incidence of intermediate refracted laser beam 22 at second entrant
face 46, and angle B3, which is the angle of refraction of
intermediate refracted laser beam 22 at second entrant face 46. The
angles of first prism 12 and second prism 14 are discussed in
greater detail below. Finally, as intermediate beam 22 passes
second refractant face 48, it defines angle A4, which is the angle
of incidence of intermediate refracted laser beam 22 at second
refractant face 48, and angle B4, which is the angle of refraction
of intermediate refracted laser beam 22 at second refractant face
48. The initial input laser beam 20 enters first prism 12 and
finally emerges from second prism 14 as output laser beam 24. The
linear distance between where input laser beam 20 enters first
entrant face 42 and where output laser beam 24 exits second
refractant face 48 is the transverse displacement, t. Transverse
displacement, t, is ideally held constant over the range of motion
by prism apparatus 2. Furthermore, the angular difference between
input laser beam 20 and output laser beam 24 is preferably
minimized by prism apparatus 2 in maintaining an angular error of
approximately 7.5 arc-min at the negative extreme in FIG. 2 and an
angular error of approximately 6.0 arc-min at the positive extreme
in FIG. 3.
[0025] FIG. 6 shows the dimensions of first and second prisms 12,
14, respectively. Both prisms 12, 14, are defined by a prism height
PH and a prism width PW which are preferably equal in one
embodiment. Prisms 12, 14 are further defined by a prism length PL
and an apex angle .alpha.. Furthermore, the preferable area upon
which input laser beam 20 is incident upon first and second prism
12, 14, is bordered by outside frame OF. The prism material for
this embodiment is fused silica. However, this does not preclude
the use of other materials suitable for the use of prisms. The
aforementioned dimensions for one embodiment are shown in the
following table.
1 Dimension Value .alpha. (degrees) 15.37.degree. PH 25.40 mm PW
25.40 mm PL 12.23 mm OF 3.00 mm
[0026] The wavelength of input laser beam 20, which is to be
circularized, is 257.25 nm in one particular embodiment. Because
prism apparatus 2 circularizes elliptical laser beams with a
variable transverse and lateral radius, apparatus 2 operates over a
range of laser beam cross sections. Apparatus 2 is such that first
and second prism mounts 8, 10, respectively, are in a nominal
position when the transverse radius of the input laser beam 20
measures 0.435 mm and the lateral radius measures 0.223 mm. Slide
adjustment member 16 may then be adjusted to translate slide 6 to
the negative extreme position shown in FIG. 2 to accommodate a
laser beam with a minimum transverse radius of 0.348 mm and to the
positive extreme position shown in FIG. 3 to accommodate a maximum
transverse radius of 0.522 mm, where both beams have a lateral
radius of 0.223 mm. These varying transverse radii may be
summarized by a scale factor in relation to the nominal radius of
0.435 mm, as shown in the following table. (These dimensions, of
course, are only illustrative of one embodiment.)
2 Transverse Radius Lateral Radius Scale Slide (mm) (mm) Factor
Position 0.348 0.223 0.8 Negative extreme 0.435 0.223 1.0 Nominal
0.522 0.223 1.2 Positive extreme
[0027] The absolute value of change in rotation of PI, which is the
angle between first entrant face 42 and a plane perpendicular to an
axis of input laser beam 20, is related to the absolute value of
translational distance, d, which slide 6 travels by the
following:
.DELTA..theta..sub.first prism=tan.sup.-1(d/L.sub.1)
[0028] where L.sub.1 is the length from first distal pivot 30 to
first proximal pivot 32. Likewise P2, which is the angle between
second entrant face 46 and the plane perpendicular to an axis of
input laser beam 20, is also related to the absolute value of
translational distance, d, by the following:
.DELTA..theta..sub.second prism=tan.sup.-1(d/L.sub.2)
[0029] where L.sub.2 is the length from second distal pivot 38 to
second proximal pivot 40. A third value, L.sub.3, is the distance
from first proximal pivot 32 to second proximal pivot 40. All three
values, L.sub.1, L.sub.2, and L.sub.3, are chosen to minimize the
angular displacement and changes in transverse displacement, t, of
output laser beam 24 over the above range of scale factors. The
changes in rotation PI, P2 of first and second prisms 12, 14,
respectively, are such that the changes occur in a counter-rotating
manner as discussed above.
[0030] The relationship between the laser beam radii (scale
factor), the transverse displacement, t, between input laser beam
20 and output laser beam 24, first prism 12 and second prism 14
orientation, and the angles of incidence and refraction from first
prism 12 and second prism 14 (in degrees) is summarized in the
following table.
3 Value by Scale Factor Dimension 0.8 1 1.2 t (mm) 0.2520619
0.2666618 0.2789777 P1 22.800 28.600 31.700 P2 33.491 41.700 46.098
A1 22.800 28.600 31.700 A2 30.304 33.933 35.824 A3 22.307 28.594
31.513 A4 29.991 33.929 35.711 B1 14.934 18.563 20.454 B2 49.354
57.076 61.655 B3 14.621 18.559 20.341 B4 48.733 57.067 61.366
[0031] Although the invention has been described with reference to
particular embodiments, the description is only an example of the
invention's application and should not be taken as a limitation. In
particular, even though much of the preceding discussion is of a
prism material of fused silica and a particular laser beam
wavelength of 257.25 nm, alternative embodiments of this invention
include various other prism materials and laser beam wavelengths.
Various other adaptations and combinations of features of the
embodiments disclosed are within the scope of the invention as
defined by the following claims.
* * * * *