Optical exposer

Details Optical exposer Optical exposer

1985-08-05

1987-09-01

Haroian, Harry N.

Optics: image projectors

Miscellaneous

33613, 353101, 355 43, G03B 2752

Patent

active

046905294

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to an optical exposer, and is particularly concerned with an optical exposer wherein a predetermined pattern is projected onto a work piece such as semiconductor wafer or the like through a projector lens, and an alignment mark put on the work piece is detected through the projector lens.


BACKGROUND ART

In an optical exposer for projecting and transferring a predetermined pattern onto a work piece through a projector lens, there prevails a superposed exposure whereby a plurality of predetermined patterns are projected successively and so transferred onto the work piece. However, such superposed exposure calls for strict precision hence, a correcting or realignment must be carried out.
For this positional correction, a common method employed is a technique wherein an alignment mark is formed on the work piece, and the alignment mark is detected through a projector lens. With this technique, the alignment mark is detected as an electrical signal waveform, therefore a position of the alignment mark is determined by the electrical signal waveform.
However, according to the inventor's experimental research, the electrical signal waveform detected is not actually a true electrical signal waveform representation of the alignment mark; consequently, it has been found that an accurate positioning of the alignment mark cannot be decided easily. As a result of the inventor having further studied the cause, it has been found that a projector lens is normally designed so as to use a monochromatic light only for enhancing the resolving power of the exposure; consequently, said monochromatic light must be used also as the light for detecting the alignment mark; therefore, there is distortion of the light due to the non-uniform thickness of a resist film formed on the surface of the work piece, the thickness of which is roughly the same as the wavelength of the monochromatic light; thus, the electrical signal waveform of the alignment is distorted to a considerable degree.


DISCLOSURE OF INVENTION

An object of this invention is to provide an optical exposer suitable for solving the problem of placing the alignment mark correctly in position due to the light distortion.
According to this invention, there is provided an optical exposer comprising a means for generating a light, a means for orienting the light toward a predetermined pattern, a projector lens for producing an image of the predetermined pattern on a work piece provided with an alignment mark, and a means for detecting the focused image of the alignment mark in first and second light wavelengths through the projector lens.


BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of an optical exposer given in one embodiment of this invention;
FIG. 2 is a drawing showing an electrical signal waveform of an alignment mark through a ray g;
FIG. 3 is a drawing showing an electrical signal waveform of the alignment mark through a ray e;
FIG. 4 is an explanatory drawing of the light distortion effect;
FIG. 5 is a drawing showing the relation of relative reflected light intensity to the thickness of photoresist due to distortion of the ray g;
FIG. 6 is a drawing showing the relation of a relative reflected light intensity to the thickness of the photoresist due to a distortion of the ray e;
FIG. 7 is a drawing showing a relation of a mean relative reflected light intensity to the thickness of photoresist due to the rays g and e;
FIG. 8 is a drawing showing a motion flow of the embodiment of FIG. 1;
FIG. 9 is a perspective view of an optical exposer given in another embodiment of this invention;
FIG. 10 is a perspective view of an optical exposer given in a further embodiment of the invention.


BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 represents one embodiment of this invention. Referring to the drawing, a shutter 1 opens during exposure and closes during alignment. Such operation of the shutter 1 is controlled by giving a command to a driving device 4 from a computer 3 through a terminal 301.
While the shutter

REFERENCES:
patent: 3844655 (1974-10-01), Johannsmeier
patent: 4367046 (1983-01-01), Lacombat
patent: 4414749 (1983-11-01), Johannsmeier

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