Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
1999-11-10
2001-06-26
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C355S053000, C355S067000
Reexamination Certificate
active
06252651
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a lithography technique for manufacturing a semiconductor and, more particularly, to an exposure method using a phase-shifting mask (PSM) and an exposure apparatus using the exposure method.
In a pattern formation method of transferring a pattern drawn on a mask to a wafer by using lithography, the pattern to be transferred must be fine and sharp. As one technique for meeting this demand, various phase-shifting masks are proposed. As a typical one, a alternating phase-shifting mask formed by setting on phase difference of 180° between two adjacent transparent portions is well known.
When, however, a mask (bright field mask) having a transparent peripheral portion in a main pattern is used as an alternating phase-shifting mask, if exposure light is irradiated on this mask, a dark portion is formed at the shifter edge of the pattern end portion. As a result, part of a resist corresponding to the shifter edge is undesirably left without being exposed. Therefore, when a fine pattern or the like is to be formed using an alternating phase-shifting mask, the mask must be elaborated to prevent generation of any unwanted residual resist.
BRIEF SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide an exposure method and apparatus in which generation of residual resist by formation of a dark portion at a shifter edge can be suppressed without complicating the mask structure or requiring any multiple exposure process or the like, and the exposure margin such as the exposure energy tolerance and the focal depth can be increased.
To solve the above problems, according to the first aspect of the present invention, there is provided an exposure method comprising
the phase-shifting mask supply step, the phase-shifting mask being prepared by selectively forming a light-shielding portion and a phase shifter on a substrate, and
the resist exposure step of performing both exposure of a resist by dark field illumination light and exposure of the resist by bright field illumination light by using the phase-shifting mask, thereby removing residual resist generated by influence of an edge of the phase shifter.
The resist exposure step preferably comprises controlling an exposure energy ratio of exposure by dark field illumination to exposure by bright field illumination to be substantially 3 to 5. It is important to control the exposure ratio so as to obtain sharp contrast between an image at a portion corresponding to the light-shielding portion and an image at a portion corresponding to the edge of the phase shifter.
The resist exposure step comprises the step of splitting illumination light emitted by an illumination light source into bright and dark field illumination light components by using a beam-splitting mechanism. With this step, exposure by bright field illumination and exposure by dark field illumination can be performed with a single illumination light source.
The beam-splitting mechanism is preferably a grating, and 0th-order and 1st-order diffracted light components obtained by the grating can be respectively used as the bright and dark field illumination light components to realize dark field illumination and bright field illumination with a single light source.
The beam-splitting mechanism may split the illumination light emitted by the illumination light source into the bright and dark field illumination light components by using an optical element having a first optical portion for directing incident illumination light to a direction to serve as dark field illumination, and a second optical portion for directing the incident illumination light to a direction to serve as bright field illumination. In this case, an intensity ratio of the dark field illumination light component to the bright field illumination light component can be controlled by controlling a ratio of a projection area of an incident surface of the first optical portion of the beam-splitting mechanism in an incident direction to a projection area of an incident surface of the second optical portion in the incident direction.
According to the second aspect of the present invention, there is provided an exposure apparatus comprising
a phase-shifting mask prepared by selectively forming a light-shielding portion and a phase shifter portion on a substrate,
a phase-shifting mask holding mechanism,
an exposure optical system for performing both exposure of a resist by dark field illumination light and exposure of the resist by bright field illumination light by using the phase-shifting mask, and
exposure control means for controlling exposure energy by the dark field illumination light and exposure energy by the bright field illumination light to remove residual resist generated by influence of an edge of the phase shifter.
By applying the method of the first aspect to this apparatus, residual resist generated by the influence of the edge of the phase shifter can be removed, and satisfactory exposure can be performed.
According to the third aspect of the present invention, there is provided a phase-shifting mask capable of removing residual resist generated by the influence of the edge of the phase shifter. The phase-shifting mask is prepared by integrally arranging the beam-splitting mechanism on the illumination light source side of the substrate on which the light-shielding portion and the phase shifter are selectively formed.
With this arrangement, exposure by dark field illumination and bright field illumination can be realized by a single light source without using a special exposure apparatus, thereby removing any unwanted residual resist.
Additional object and advantages of the invention will be set forth in the description that follows, and in part will be obvious from the description, or may be learned by practice of the invention. The object and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
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Fujisawa Tadahito
Inoue Soichi
Mimotogi Akiko
Mimotogi Shoji
Tanaka Satoshi
Adams Russell
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Nguyen Hung Henry
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