Method of producing two-dimensional phase type optical element

Details Method of producing two-dimensional phase type optical element Method of producing two-dimensional phase type optical element

2000-02-15

2003-12-16

Angebranndt, Martin (Department: 1756)

Radiation imagery chemistry: process, composition, or product th

Plural exposure steps

C430S321000, C216S012000, C216S051000, C216S024000

Reexamination Certificate

active

06664032

ABSTRACT:

FIELD OF THE INVENTION AND RELATED ART
This invention relates to a method of producing a two-dimensional phase type optical element such as a phase type CGH, a two-dimensional binary structure or a phase modulation plate, for example, which can be used in an optical interconnection or a reduction projection exposure apparatus for manufacture of semiconductor devices, for example.
A method of producing an element having plural phase levels, called “multiple-level phase type optical element”, is discussed in “O Plus E”, No. 11, pp95, 100(1996), for example. The manufacture of this type of element involves repetition of sequential procedures including a step for processing a substrate by photolithography, a step for applying a resist, for example, to the substrate, a step for positioning the substrate with respect to a pattern of a reticle, a step for exposing the resist with the pattern of the reticle, a step for developing the resist to produce a mask on the basis of the resist (image), and a step for etching the substrate by using the mask, for example. Here, if the number of masks to be formed on a substrate by use of a resist is L, phase levels of a number 2
L
can be defined on the substrate.
For example, in production of a two-dimensional phase type optical element, as shown in
FIG. 152A
, first, a resist is applied to the whole surface of a substrate
1
a.
Then, an exposure process and a development process are performed to the resist, on the basis of a reticle of an exposure apparatus, whereby a resist pattern
2
a
is produced. Subsequently, while using the resist pattern
2
a
as a mask, an etching process is performed, by which, as shown in
FIG. 153A
, a substrate
1
b
having a surface level
3
a
and a level
3
b
with a depth 61 nm, is produced.
Subsequently, similar operations are repeated to form a resist pattern
2
b
on the substrate
1
b
, as shown in
FIG. 152B
, and then, by etching the substrate
1
b
, a substrate
1
c
(
FIG. 153B
) having additional levels
3
c
and
3
c
with depths 122 nm and 183 nm is produced. Finally, as shown in
FIG. 152C
, a resist pattern
2
c
is produced on the substrate
1
c
and, by etching the substrate
1
c,
a substrate
1
d
(
FIG. 153C
) having further levels
3
e
-
3
h
with depths 244 nm, 305 nm, 366 nm and 427 nm, is produced.
In this producing method, however, the resist patterns
2
a
,
2
b
and
2
c
are formed through lithographic processes, sequentially upon the substrates
1
a
,
1
b
and
1
c
. As a result, there is a large possibility of alignment error between the substrate
1
a
,
1
b
or
1
c
and the resist pattern
2
a
,
2
b
or
2
c
. If it occurs, an idealistic substrate
1
d
(
FIG. 154A
) having levels
3
a
,
3
d
,
3
e
and
3
h
is not obtained, but rather a substrate
1
e
(
FIG. 154B
) having deformed portions such as at
3
i
and
3
k
is produced. Thus, levels with accurate shapes are not obtainable.
Further, in this producing method, the segment of a reticle in the exposure apparatus has a rectangular shape. However, a resist pattern
2
a
to be produced with right-angle segment corners (
FIG. 153A
) may not be produced but, rather, a resist pattern
2
d
(
FIG. 155
) with rounded segment corners may be produced. Also in this respect, levels with accurate shapes are not obtainable.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide a method of producing a two-dimensional phase type optical element by which levels can be formed very accurately.
In accordance with an aspect of the present invention, there is provided a method of producing a two-dimensional phase type optical element, characterized in that a first mask and a second mask made of different materials and both having a stripe-like shape are superposedly formed on a substrate, along different directions, respectively, and that positions of all levels to be defined are determined on the basis of at least one of the first and second masks.
In accordance with another aspect of the present invention, there is provided a method of producing a two-dimensional phase type optical element, characterized in that a first mask and a second mask made of different materials and both having a stripe-like shape are superposedly formed on a substrate, along different directions, respectively, and that the substrate is etched by use of at least one of the first and second masks.
In accordance with a further aspect of the present invention, there is provided a method of producing a two-dimensional phase type optical element, characterized in that a first mask and a second mask made of different materials and both having a stripe-like shape are superposedly formed on a substrate, along different directions, respectively, and that positions of all levels to be defined are determined on the basis of (i) at least one of the first and second masks and (ii) a third mask having been formed by transferring one of the first and second masks.
In accordance with a yet further aspect of the present invention, there is provided a method of producing a two-dimensional phase type optical element, characterized in that a first mask and a second mask made of different materials and both having a stripe-like shape are superposedly formed on a substrate, along different directions, respectively, and that the substrate is etched by use of (i) at least one of the first and second masks and (ii) a third mask having been formed by transferring one of the first and second masks.
In these aspects of the present invention, the substrate and the masks are made of different materials.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.


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O Plus E, No. 204, pp. 95-100 (Nov. 1996).

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