Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
2000-08-28
2001-06-26
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C355S035000, C355S067000, C355S053000, C250S492200, C399S032000, C399S051000, C372S038060
Reexamination Certificate
active
06252650
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure apparatus, an output control method for an energy source and a laser device used in a field of production of semiconductor devices, liquid crystal display devices, etc.
2. Description of the Related Art
When producing semiconductor elements, liquid crystal display elements, image pickup elements (such as a CCD), thin film magnetic heads, etc. by using photo-lithography techniques, a projection exposure apparatus for exposing a wafer by projecting an image via a projection optical system of a pattern formed on a reticle as a mask on to a wafer (or a glass plate, etc.) coated with a photo resist, etc. has been used. As one basic function of the exposure apparatus, there is an exposure dose control function for controlling an integrated exposure amount (integrated exposure energy) so that it is within an appropriate range for respective points in each shot region of the wafer.
Recently, there have been demands for increased resolution of the pattern to be projected on the wafer. To increase the resolution, a method of shortening the wavelength of the exposure light has been used. As a light source for exposure light, pulse emission type laser light sources (pulse light sources), for example, excimer laser light sources such as KrF excimer lasers and ArF excimer lasers, metal vapor laser light sources, and YAG laser light sources, are currently known to emit light of short wavelength.
However, being different from continuously luminescent light sources, such as mercury lamps, there is a characteristic that the exposure energy of an emitted pulse becomes uneven between pulses in a pulse light source. Therefore, the unevenness of the pulse energy in exposure dose control must be considered when using the pulse light source. Generally, when using the pulse light source as a light source for exposure, a minimum pulse number, or so-called minimum exposure pulse number, to be irradiated on respective points on the wafer is regulated by considering the unevenness of the pulse energy in order to control the integrated exposure amount so that it is within a predetermined permissible range.
For exposure dose control in the case of applying the pulse light source to a projection exposure apparatus which is a collective exposure type, such as a stepper, so-called cutoff control using an integrator sensor for monitoring the pulse energy of exposure light for each pulse is commonly used. In the cutoff control, an integrated exposure amount supplied to a wafer is monitored during exposure based on information from the integrator sensor, and emission of the pulse from the pulse light source is stopped at the point where the integrated exposure amount supplied to the wafer exceeds a target integrated exposure amount. There is also a so-called every-pulse control by which the pulse energy is adjusted for every pulse emission in accordance with the information from the integrator sensor.
In the every-pulse control, the above minimum exposure pulse number can be reduced comparing with that in the cutoff control.
Controlling the energy of a pulse to be emitted next from the laser light source is important in order to improve control accuracy of the integrated exposure amount supplied to the wafer. Accordingly, measurement of the energy of every pulse by the integrator sensor provided inside the exposure apparatus and control of the energy of the next pulse based on measured energy information of at least one pulse previously emitted are performed.
In recent years, since the repeated emission frequency (repeated emission cycle) of laser light sources has become higher, as explained above, controlling the energy of the next pulse based on the measured energy information of the latest pulse previously emitted is difficult because sufficient time cannot be secured until an emission of the next pulse so the controlling accuracy of the energy of the next pulse declines in some cases.
For example, when outputting an exposure beam from a laser light source at a predetermined cycle, if detected energy information of a pulse output immediately before is used, calculation of the target energy of the pulse to be output next cannot be completed in time in some cases. Alternately, power charging of the laser light source for emitting the next pulse is not completed in time in some cases if the detected energy information of a pulse output immediately before is used. Furthermore, if the detected energy information of a pulse is output immediately before, an emission of the next pulse from the laser light source will be delayed in some cases. This is caused by an actual emission delay from the laser light source after sending an emission trigger from the exposure apparatus.
SUMMARY OF THE INVENTION
An object of the present invention is to enable light exposure control at high accuracy in an exposure apparatus having an energy source for outputting pulses of an exposure beam.
Also, another object of the present invention is to provide an output control method for an energy source capable of outputting pulses having desired energy.
Still another object of the present invention is to provide a laser device capable of outputting pulses having desired energy.
Other objects of the present invention will become clear from the explanation below.
An exposure apparatus of the present invention comprises an energy source for outputting pulses of an exposure beam, a detector for detecting energy of the exposure beam output from said energy source for every pulse, and a controller for controlling energy of a pulse to be output next without using energy information of a latest output pulse and based on energy information of at least one pulse output prior to the latest output pulse detected by said detector at the time of successively outputting pulses from said energy source.
According to the above configuration, since the controller can control the energy of a pulse to be output next based on the energy information of pulses output prior to the latest output pulse, sufficient time can be used for controlling the energy of the pulse to be output next, thus, control accuracy of an integrated exposure amount supplied to a substrate is improved.
Preferably, said controller controls the energy of a pulse to be output next based on energy information detected by said detector of at least one pulse including a pulse output immediately before the latest output pulse.
According to the present invention, there is provided an exposure apparatus comprising an energy source for outputting pulses of an exposure beam, an illumination system for introducing the exposure beam from said energy source to a mask on which a pattern is formed, a projection system for projecting an image of the pattern from said mask on to a substrate.
The exposure apparatus comprises a detector for detecting energy of the exposure beam output from said energy source for every pulse in said illumination system, an exposure controller for controlling integrated exposure amount to said substrate, and an energy source controller connected to said exposure controller via a communication interface for controlling said energy source in accordance with target energy determined based on energy information detected by said detector of at least one pulse output prior to the latest output pulse during exposure of said substrate.
An output control method for an energy source of the present invention comprises a step of detecting energy of a beam output from an energy source for every pulse, and a step of controlling energy of a pulse to be output next without using detected energy information of a latest output pulse and based on detected energy information of a pulse output prior to that when pulses are successively output from said energy source.
A laser device of the present invention comprises an energy source for outputting pulses of laser light, and an energy source controller for determining target energy of a pulse to be output next based on detected energy information of a
Adams Russell
Brown Khaled
Nikon Corporation
Oliff & Berridg,e PLC
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