Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
2001-03-30
2004-04-06
Mathews, Alan (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C355S053000, C355S067000, C355S069000, C250S205000
Reexamination Certificate
active
06717652
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure apparatus and an exposure method employed for pattern exposure on a resist film, and more specifically, it relates to an exposure apparatus and an exposure method capable of correctly managing a light exposure.
2. Description of the Prior Art
A photolithographic process consists of an application step, an exposure step and a development step for a resist film. Among these steps, the exposure step is carried out for transferring a pattern image formed on a reticle to a resist film provided on a wafer. In general, a reduced projection exposure system is employed in the exposure step.
The structure of an exposure apparatus employing the reduced projection exposure system is schematically illustrated with reference to FIG.
8
. This exposure apparatus comprises a light source
102
emitting an exposure beam
100
A, a reflecting mirror
104
reflecting the exposure beam
100
A emitted from the light source
102
, a beam shaping optical system
106
converting the exposure beam
100
A to an exposure beam of a prescribed component, fly-eye lenses
108
and
112
for uniformly illuminating an exposure range, a condenser lens
118
illuminating the overall areas of the reflecting mirror
106
, another reflecting mirror
116
and a reticle
120
, a reduced projection lens
122
for reducing the pattern of the exposure beam passing through the reticle
120
and projecting the exposure beam to a wafer
124
placed on a stage
126
and a control unit
200
for controlling the light exposure time etc. of the light source
102
, the position of the stage
126
, information obtained from an illuminance meter
130
A described later and other elements of the exposure apparatus.
In the exposure step of forming a pattern on a resist film, the light exposure is generally corrected by providing the illuminance meter
130
A on the stage
126
located on the emission side of the reduced projection lens
122
for previously measuring illuminance with the illuminance meter
130
A before the exposure step and controlling the light exposure time so that an integrated light exposure (product of the illuminance and the exposure time) in the exposure step is regularly constant on the basis of the obtained illuminance, as shown in FIG.
10
. In a step-and-repeat batch exposure method, for example, the exposure time is decided on the basis of the obtained illuminance for controlling the integrated light exposure. In a scan exposure system, the moving speed of the stage
126
is calculated on the basis of the obtained illuminance for controlling the integrated light exposure.
In the aforementioned method of correcting the light exposure, however, the illuminance meter
130
A provided on the emission side of the reduced projection lens
122
of the exposure apparatus must be periodically calibrated with another illuminance meter having normal sensitivity, in order to confirm deterioration of sensitivity of or abnormality of the illuminance meter
130
A provided on the exposure apparatus.
As the wavelength of the exposure beam employed for the exposure step is reduced, further, illuminance on the emission side of the reduced projection lens
122
is remarkably reduced due to a blur of the reduced projection lens
122
(reduction of transmittance of the reduced projection lens
122
resulting from solarization) along with progress of the number of applied pulses (exposure time) with the reduced projection lens
122
, as shown in FIG.
10
.
When the exposure apparatus carries out no exposure step for a prescribed time, the surface of the reduced projection lens
122
is so contaminated by organic matter and inorganic matter that the illuminance is disadvantageously reduced on the emission side of the reduced projection lens
122
.
SUMMARY OF THE INVENTION
A first object of the present invention is to provide an exposure apparatus capable of reducing the number of times of calibration of an illuminance meter provided on the emission side of a reduced projection lens of the exposure apparatus, an exposure method and a semiconductor device fabricated with the exposure method.
A second object of the present invention is to provide an exposure apparatus capable of properly setting a light exposure in consideration of a blur of a reduced projection lens, an exposure method and a semiconductor device fabricated with the exposure method.
A third object of the present invention is to provide an exposure apparatus capable of preventing reduction of illuminance resulting from contamination of the surface of a reduced projection lens by organic matter and inorganic matter.
According to an aspect of the present invention, an exposure apparatus setting a prescribed light exposure in exposure for forming a resist pattern with an optical system comprises at least two illuminance meters provided on the emission side of the aforementioned optical system, an average illuminance operation unit operating average illuminance on the basis of measured illuminance values obtained from the aforementioned illuminance meters, and a light exposure control unit controlling the light exposure on the basis of information obtained from the aforementioned average illuminance operation unit.
According to another aspect of the present invention, an exposure method setting a prescribed light exposure in exposure for forming a resist pattern with an optical system comprises an average illuminance operating step of operating average illuminance on the basis of measured illuminance values obtained from at least two illuminance meters provided on the emission side of the aforementioned optical system and a light exposure control step of controlling the light exposure on the basis of information obtained from the aforementioned average illuminance operating step.
According to the aforementioned exposure apparatus and the aforementioned exposure method, the illuminance meters are so provided in plural that dispersion of measured values or the like is averaged and measurement accuracy for the illuminance can be improved.
In the aforementioned exposure apparatus, the aforementioned average illuminance operation unit preferably includes a unit obtaining the average illuminance with remaining measured illuminance values except those of measured illuminance values exceeding a prescribed threshold in illuminance measurement.
In the aforementioned exposure method, the aforementioned average illuminance operating step preferably includes a step of obtaining the average illuminance with remaining measured illuminance values except those of measured illuminance values exceeding a prescribed threshold in illuminance measurement.
When the prescribed threshold is provided for the measured values for obtaining the average illuminance except the measured values exceeding the threshold, deterioration or abnormal values of the illuminance meters can be omitted so that the number of times of calibration of the illuminance meters provided on the emission side of the reduced projection lens of the exposure apparatus can be reduced as compared with the conventional exposure apparatus.
According to still another aspect of the present invention, an exposure apparatus setting a prescribed light exposure in exposure for forming a resist pattern comprises an illuminance measuring unit performing illuminance measurement before exposing an (N−1)th (N: integer) wafer, illuminance measurement after exposing the (N−1)th wafer and illuminance measurement during at least single exposure of the (N−1)th wafer and a light exposure decision unit deciding illuminance for an N-th wafer from measurement results obtained from the aforementioned illuminance measuring unit for deciding the light exposure for exposing the N-th wafer.
According to a further aspect of the present invention, an exposure method setting a prescribed light exposure in exposure for forming a resist pattern comprises an illuminance measuring step of performing illuminance measurement before exposing an (N&mi
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