Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
1999-07-20
2001-06-26
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
Reexamination Certificate
active
06251545
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to semiconductor fabrication, and more particularly to lithography in semiconductor fabrication.
BACKGROUND OF THE INVENTION
Lithography is conventionally used in the fabrication of semiconductor devices. In optical lithography, a photosensitive film, a photoresist, is patterned by a photomask. The photomask has areas composed of chrome, or some other opaque or partially transmitting material, in a pattern which corresponds to the desired circuitry for the device. The photomasked photoresist is exposed to light from a light source. After exposure, the photomask is removed, leaving a photoresist with the desired pattern. An etch or implantation of the device's substrate may be performed based upon the photoresist pattern.
FIG. 1
illustrates a conventional photomask
110
and photoresist
130
as used in lithography. The photomask
1
10
may comprise fused silica. On the bottom side of the photomask
110
are areas
120
. The photomask
110
and photoresist
130
are treated with light from a light source (not shown). The light shines through the photomask
110
where there are no areas
120
. The light is reflected or absorbed where there are areas
120
. Some of the light that passes through the photomask
110
continues through a lens
140
, which projects an image of the mask pattern onto the photoresist
130
, which undergoes a chemical reaction when exposed to light. Portions of the photoresist
150
are exposed to the light while portions of the photoresist
160
are ideally not exposed to the light.
However, approximately 4-5% of the light is lost through reflections off each of the two surfaces of the photomask, as illustrated by arrows
170
in FIG.
1
. When a large number of devices are fabricated on a substrate, this amount of loss is costly for the manufacturer. In addition, light reflected from the substrate can be transmitted back through the lens and back to the photomask
110
. A portion of this light is then reflected by the photomask
110
back to the photoresist
160
on the wafer. Such reflected light is not part of the intended image of the photomask
110
, and it can degrade the quality of the light pattern in the photoresist
160
.
Accordingly, what is needed is a system and method for improving the transmission of light through photomasks. The method and system should decrease the loss of light due to reflections and decrease undesired exposure of portions of the photoresist. The present invention addresses such a need.
SUMMARY OF THE INVENTION
The present invention provides a method and system for improving the transmission of light through a photomask. The method includes providing a photomask substrate, and applying at least one anti-reflection coating to at least one side of the photomask substrate. The anti-reflection coating reduces the loss of light during lithography due to reflections. This increases the efficiency of the lithography. The method and system has the added advantage of reducing the amount of undesired exposure of a photoresist.
REFERENCES:
patent: 5279911 (1994-01-01), Kamon et al.
patent: 5422206 (1995-06-01), Kamon
patent: 5780161 (1998-07-01), Hsu
patent: 5879866 (1999-03-01), Starikov et al.
“Characteristics of Deep UV Optics at 193nm & 157 nm,” Glen P. Callahan and Bruce K. Flint 1998.
Advanced Micro Devices , Inc.
Rosasco S.
Sawyer Law Group LLP
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