Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2001-04-17
2003-09-30
Young, Christopher G. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
Reexamination Certificate
active
06627357
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a reticle or photomask used in photolithography, and more particularly to a reticle which is capable of forming a rectangular mask pattern with high accuracy.
2. Description of the Related Art
As a semiconductor device has been required to have a higher integration and a smaller size, a pattern to be formed on semiconductor device is also required to be reduced in a size.
In a method of fabricating a semiconductor device, photolithography steps are generally carried out. In order to increase a throughput and enable a semiconductor device to have an increased capacity, a unit for exposing a pattern to a light is required to expose a pattern to a light in a wide area at a time.
As a result, a minification ratio in the unit is reduced down to 4 from 5. In addition, a pattern is formed in a smaller size than before. Accordingly, it is necessary to reduce a size of a mask pattern formed on a reticle, resulting in an increase in difficulty in fabrication of a reticle.
There is an increased need for a highly accurate reticle. In particular, edges of a pattern or corners of a minute pattern in a reticle are likely to be rounded. Rounded edges or corners of a pattern would deteriorate an accuracy at which a pattern is formed on a semiconductor device, and further deteriorate a fabrication yield of a semiconductor device.
Specifically, since a pattern is formed on a reticle by etching a light-impermeable film formed on a transparent substrate by photolithography, it would be quite difficult to form a desired pattern with high accuracy, as a size of a pattern is reduced. In particular, sharpness in edges and/or corners is likely to be degraded due to diffraction and/or interference when a pattern is exposed to a light, resulting in that edges and/or corners of a pattern are rounded.
As a solution to such a problem, Japanese Unexamined Patent Publication No. 6-118624 has suggested a method of exposing a pattern to a light. In the suggested method, there are used a first reticle including a pattern extending in an X-axis direction, and a second reticle including a pattern extending in a Y-axis direction. A pattern is exposed twice to a light through the use of the first and second reticles. As a result, a pattern with high accuracy can be formed at an area having been exposed twice to a light.
However, the suggested method is accompanied with problems that a step of exposing a pattern to a light has to be carried out twice, and that it is necessary to make registration between the first and second reticles in the two steps of exposing a pattern to a light. If the registration is not made properly, it would be impossible to have a desired pattern with high accuracy.
Japanese Unexamined Patent Publication No. 60-7431 has suggested a reticle including a transparent plate, a first thin film pattern composed of opaque material and formed partially on a surface of the transparent plate, a transparent spacer formed on the surface of the transparent plate such that the spacer covers at least a part of the first thin film pattern therewith, and a second thin film pattern composed of opaque material and formed partially on the spacer.
Japanese Unexamined Patent Publication No. 62-45026 has suggested a method of fabricating a semiconductor integrated circuit, including the steps of exposing a resist to a light through a first mask having a pattern extending in a first direction, and exposing the resist to a light through a second make having a pattern extending in a second direction perpendicular to the first direction.
Japanese Patent Publication No. 4-56477 has suggested a method of fabricating a Josephson junction device including a lower electrode, an insulating film formed on the lower electrode and formed with a hole, a barrier layer formed above the lower electrode, and an upper electrode formed above the insulating film and the barrier layer. The method includes the steps of forming a first insulating film on the lower electrode through a first line resist pattern, removing the first line resist pattern to form a first hole in the form of a line, forming a second insulating film through a second line resist pattern intersecting with the first hole, and removing the second line resist pattern to thereby form a hole for making Josephson junction.
Japanese Unexamined Patent Publication No. 7-106764 has suggested a ceramic multi-layered circuit board including a plurality of first line patterns each comprised of broken lines with a space therebetween and extending in a X-axis direction, and a plurality of second line patterns each comprised of broken lines with a space and extending in a Y-axis direction. The first and second line patterns are arranged on a ceramic insulating layer in matrix such that the space defines a cross-point. The first and second line patterns sandwiching the cross-point therebetween are electrically connected to each other through a first hole formed through the ceramic insulating layer at the cross-point. The first hole does not reach a bottom surface of the ceramic insulating layer. The above-mentioned first and second line patterns are electrically connected to first and second patterns formed on a surface of a lower ceramic insulating layer, through a via-hole formed throughout the ceramic insulating layer at the cross-point.
The problem that a rectangular pattern cannot be formed with high accuracy remains unsolved even in the above-mentioned Publications.
SUMMARY OF THE INVENTION
In view of the above-mentioned problems, it is an object of the present invention to provide a reticle which can expose a rectangular pattern to a light with high accuracy without increasing complexity in a step of exposing a pattern to a light.
There is provided a reticle including (a) a first substrate including a first light-permeable substrate, and a first pattern formed on the first light-permeable substrate and having a first light transmittance, and (b) a second substrate including a second light-permeable substrate, and a second pattern formed on the second light-permeable substrate and having a second light transmittance, the first and second substrates being coupled to each other such that the first and second patterns face each other, a part of the first and second patterns at which the first and second patterns overlap each other, defining a light-impermeable pattern.
It is preferable that the first and second patterns are composed of the same material.
For instance, the light-impermeable pattern may be a rectangular pattern.
It is preferable that the first and second light transmittances are equal to or smaller than 0.7.
It is preferable that the reticle further includes a light-permeable adhesive layer to be sandwiched between the first and second substrates for coupling the first and second substrates together, in which case, the light-permeable adhesive layer is formed preferably in an area at which the first and second patterns do not overlap each other.
There is further provided a reticle including (a) a first substrate including a first light-permeable substrate formed at a surface thereof with first recesses in a pattern, and a first pattern formed in the first recesses and having a first light transmittance, and (b) a second substrate including a second light-permeable substrate formed at a surface thereof with second recesses in a pattern, and a second pattern formed in the second recesses and having a second light transmittance, the first and second substrates being coupled to each other such that the first and second patterns face each other, a part of the first and second patterns at which the first and second patterns overlap each other, defining a light-impermeable pattern.
There is still further provided a reticle including (a) a first substrate including a first light-permeable substrate, and a first pattern formed on the first light-permeable substrate and having a first light transmittance, and (b) a second substrate including a second light-permeable substrate formed at a surface
Katten Muchin Zavis & Rosenman
NEC Electronics Corporation
Young Christopher G.
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