X-ray or gamma ray systems or devices – Specific application – Lithography
Patent
1987-11-19
1990-01-02
Howell, Janice A.
X-ray or gamma ray systems or devices
Specific application
Lithography
378 34, G03F 100, G03F 720
Patent
active
048918300
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a reflective mask element which will be suitably applied to submicron-level lithography by X-ray projection and a system for image formation with use of the same.
BACKGROUND ART
Conventionally, in the process of manufacture of LSI, optical lithography technology has normally been applied for reproduction of a pattern drawn on a mask. But the optical lithography technology is known to reach its patterning limit up to 0.5 .mu.m and besides, because of effect of Fresnel diffraction and shortness of focal distance, formation of a more compact pattern with less than 1 .mu.m requires introduction of a multi-layer resist and CEL process. On account of such, the process involved becomes complicated and results in a low product yield, which leads to an assessment that such a method will come to end in the near future. Probable replacing new methods are thought to be the direct drawing with electron beam and X-ray lithography. Wherein, the direct drawing with electron beam is defective in throughput, accuracy of stage connection and inevitable introduction of multi-layer resist to attain a height aspect ratio. In contrast, the X-ray lithography is based on image copy or transfer, for which it is advantageous to mass reproduction and it is also based on use of a ray having several angstroms to several tens of angstroms in wavelength, for which the effect of undesirable diffraction may be disregarded in substance and resolution thereby is expected to reach up to 0.1 .mu.m.
The X-ray lithography includes, simply classed, two methods. One is a method that is presently prevailed, proxim method which comprises X-ray exposure in a proximate distance of about 10 .mu.m between a mask and a wafer to transfer a pattern on the mask. Another one is X-ray projection and exposure method which transmits a pattern shadow to a wafer with aid of an X-ray imaging device.
DISCLOSURE OF THE INVENTION
This invention is firstly concerned with a mask element which is applied in the latter of the X-ray projection and exposure method. But the inventive mask element is different, as will be described in detail below, from conventional masks of transmission type. Avoidance of that type comes from, briefly noted, that X-ray used normally in the X-ray lithography has several angstroms to several tens of angstroms in wavelength or soft X-ray and impediment involved therein is that, because an X-ray of such wave range is easy to be absorbed by general materials, a mask substrate for such an X-ray should be an extremely thin membrane having several .mu.m in thickness made of X-ray transmissive material, for instance, BN (boron nitride) and thereon conventionally a resist film is formed with a X-ray absorbent material, for instance, Au. On such account, conventional transmissive masks are physically brittle or fragile, which brings a number of problems; difficulty in handling, easy deformation due to handling or heat, complicated in manufacture and resultantly such brings a proximity apparatus to be so expensive and difficult to operate.
This invention intends to offer a mask element which comprises an X-ray absorbent patterned mask film coated on an X-ray reflective substrate capable of focussing the reflected X-ray toward image formation, and this also intends to offer a system for reproducing a pattern image onto a target plate, including said mask plate, an X-ray source and an image formation device and thereby this intends to solve the problems attendant with the art based on conventional transmission type masks.
The patterned mask element comprising X-ray reflective substrate in the present invention is summarized in that a substrate is a plate which was cut out or worked out of a crystalline substance having its original lattice surfaces for X-ray diffraction curved or arched outwardly to effect converging function to a reflecting X-ray, wherein such a crystalline body is worked out by regulating an angle assumed between curvature of lattice plates and a newly cut-out substrate face so as to mai
REFERENCES:
patent: 3772522 (1973-11-01), Hammond et al.
patent: 4192994 (1980-03-01), Kastner
patent: 4231657 (1980-04-01), Takasu et al.
patent: 4411013 (1983-10-01), Takasu et al.
Matsumura et al., "Demagnified Projection Printing by a New X-ray Lithographic Technique Using no Thin Film Masks", applied Physics Letters, pp. 3-5, Jul. 1, 1984.
IBM Technical Disclosure Bulletin, vol. 16, No. 9, Feb., 1974, Feder et al., "Ultrafine Line Projection System", pp. 3121-3122.
Howell Janice A.
Hynds Joseph A.
Shimadzu Corporation
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