Photocopying – Projection printing and copying cameras – With temperature or foreign particle control
Reexamination Certificate
1997-11-10
2001-04-24
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
With temperature or foreign particle control
C355S067000
Reexamination Certificate
active
06222609
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an optical aligner and, more particularly, to an optical aligner free from reaction product tarnishing photo-mask and a method for transferring a pattern image through the photo-mask.
DESCRIPTION OF THE RELATED ART
A typical example of the reduction projection aligner is disclosed in Japanese Patent Publication of Unexamined Application No. 62-86724. An air evacuating system is incorporated in the prior art reduction projection aligner for reducing undesirable particles in the wafer chamber.
FIG. 1
illustrates the prior art reduction projection aligner. The reduction projection aligner comprises a light source
1
, a vessel
2
defining a vacuum chamber
2
a
, a vacuum pump
3
connected to the vacuum chamber
2
a
, a movable wafer stage
4
provided outside of the vessel
2
and exposure windows
5
a
/
5
b
formed in the vessel
2
on the optical path from the light source
1
to the movable wafer stage
4
. A semiconductor wafer
6
is placed on the movable wafer stage
4
, and the movable wafer stage
4
two-dimensionally moves the semiconductor wafer
6
. The light source
1
is implemented by an ultra high-pressure mercury lamp, and radiates ultra-violet light through the exposure window
5
a
. The vacuum pump
3
evacuates the air from the vacuum chamber
2
a.
The prior art reduction projection aligner further comprises a movable reticle stage
7
installed in the vacuum chamber
2
a
, a reticle loader
8
provided under the exposure window
5
a
, a reduction projection lens unit
10
provided between the movable reticle stage
7
and the exposure window
5
b
and an inspection unit
11
also provided in the vacuum chamber
2
a
. The reticle loader
8
picks up a reticle
9
at a loading port (not shown), and moves it onto the movable reticle stage
7
. A pattern to be transferred is formed in the reticle
9
. The ultra-violet light passes the exposure window
5
a
, the reticle
9
, the reduction projection lens unit
10
and the exposure window
5
b
, and transfers the pattern image onto the semiconductor wafer
6
, and the reduction projection lens unit
10
demagnifies the pattern image. The inspection unit
11
checks the reticle
9
to see whether or not the reticle is contaminated with dust particles.
The pattern is repeatedly transferred from the reticle
9
from the semiconductor wafer
6
as follows. First, an operator supplies the reticle
9
to the loading port, and the inspection unit
11
checks the reticle
9
to see whether or not the reticle,
9
is contaminated with dust particles. If the dust particles are not found, the reticle loader
8
transfers the reticle
9
onto the movable reticle stage
7
. The vacuum pump
3
evacuates the air from the vacuum chamber
2
a
together with dust particles. For this reason, the reticle
9
is hardly contaminated in the vacuum chamber
2
a
. The movable wafer stage
4
moves the semiconductor wafer
6
in such a manner as to align a small area on the semiconductor wafer with the optical path
12
of the ultra violet light.
The light source
1
radiates the ultra-violet light toward the exposure window
5
a
. The ultra-violet light passes the exposure window
5
a
and the reticle
9
, and carries the pattern image. The image-carrying ultra-violet light passes through the reduction projection lens unit
10
, and the pattern image is reduced by the reduction projection lens unit
10
. The image-carrying ultra-violet light falls onto the small area, and forms a latent image therein. The movable wafer stage
4
aligns another small area with the optical path, and the optical image transfer is repeated. In this way, the pattern is optically transferred from the reticle to the semiconductor wafer, and the inspection unit
11
and the vacuum pump
3
prevent the semiconductor wafer
6
from undesirable defects due to the dust particles.
A known modification of the prior art reduction projection aligner has the reticle and the movable wafer stage installed in the vertical direction, and a pattern image is transferred from the vertical reticle to a semiconductor wafer vertically supported by the movable wafer stage. In this instance, the possibility of the dust contamination is further decreased. However, the prior art reduction projection aligner encounters a problem in that the exposure windows
5
a
/
5
b
are tarnished. The tarnished exposure windows
5
a
/
5
b
deteriorate the uniformity of the ultra-violet light, and decrease the throughput.
SUMMARY OF THE INVENTION
It is therefore an important object of the present invention to provide an aligner, which maintains the uniformity of light radiated through exposure windows.
The present inventor analyzed the contaminant on the exposure windows, and found that the contaminant was reaction product unintentionally produced from gaseous component of the air in the presence of short-wavelength light components contained in the ultra-violet light. The reaction product tarnished the exposure windows. The ultra high-pressure mercury lamp contained the short-wavelength light. The present inventor changed the light source from the ultra high-pressure mercury lamp to another kind of lamp. However, the reaction product was produced from the certain gaseous component in so far as the exposure light contained the certain short-wavelength light components, and the reaction product tarnished the exposure windows. The present inventor concluded that the undesirable short-wavelength light components had to be eliminated from the light before the reaction. Alternatively, when the optical path from the light source to the photo-mask was in vacuum, the reaction product was not produced without the filtering.
To accomplish the object, the present invention proposes to cause light to pass an optical filter before radiating into the air or accommodate the light path from a light source to a photo-mask in vacuum.
In accordance with one aspect of the present invention, there is provided an optical aligner for transferring a pattern image to a photo-sensitive layer, comprising: an illumination system including a light source producing light containing a light component available for a pattern transfer and another light component promoting reaction of a gaseous component; a photo-mask having a pattern to be transferred, and illuminated with the light; an projection optical system provided between the photo-mask and the photo-sensitive layer for forming a latent image in the photo-sensitive layer; an air-tight vessel accommodating at least a part of the illumination system containing the light source; an optical filter for eliminating the another light component from the light before the light is radiated from the air tight vessel toward the photo-mask; and an evacuating system for creating vacuum in the air-tight vessel.
In accordance with another aspect of the present invention, there is provided an optical aligner for transferring a pattern image to a photo-sensitive layer, comprising: an illumination system including a light source producing light containing a light component available for a pattern transfer and another light component promoting reaction of a gaseous component; a photo-mask having a pattern to be transferred, and illuminated with the light; an projection optical system provided between the photo-mask and the photo-sensitive layer for forming a latent image in the photo-sensitive layer; an air-tight vessel accommodating at least the light source and the photo-mask; and an evacuating system for creating vacuum in the air-tight vessel.
In accordance with yet another aspect of the present invention, there is provided a method for transferring a pattern image from a photo-mask to a photo-sensitive layer, comprising the steps of: a) providing the photo-mask in an optical path from a light source to the photo-sensitive layer; b) evacuating the air from a vacuum chamber accommodating the light source; and c) radiating light from the light source through an optical filter provided on a boundary between the vacuum chamber and the photo-mas
Adams Russell
NEC Corporation
Nguyen Hung Henry
Sughrue Mion Zinn Macpeak & Seas, PLLC
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