Optics: measuring and testing – By alignment in lateral direction – With registration indicia
Patent
1991-03-13
1992-08-25
Rosenberger, Richard A.
Optics: measuring and testing
By alignment in lateral direction
With registration indicia
G01B 1100, H01L 21027
Patent
active
051413221
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INDUSTRIAL USE
The present invention relates to illumination methods with plural wavelength rays and with wavelength-band rays when a double-focus optical apparatus utilizing chromatic aberration is applied to a position detector such as an X-ray exposure apparatus.
BACKGROUND OF THE ART
In a stepper such as an X-ray exposure apparatus, it is necessary to adjust a mask and a wafer in place with a high accuracy.
In a stepper, a resist film, transparent film and the like are provided on a surface of a wafer. Since these films are not uniformly formed, a reflection intensity of an alignment mark on the wafer varies sinusoidally due to a standing wave effect based on optical interferences and a relative intensity of signal rays to detect the alignment mark varies largely, resulting in that an accuracy of alignment is remarkably reduced.
To eliminate such disadvantages and improve the accuracy of alignment a variety of proposals have been offered. For example, the scientific lecture report of the 48th Meeting of Applied Physics Society (the second separate volume 18a-F-6, P.426, Autumn, 1987) shows that when two wavelength rays or two inclination illuminations are applied in detection an alignment mark on a wafer in a bright visual field, the unsymmetry of a detected pattern with respect to unevenness in resist coating is reduced to improve an accuracy of detecting a mark.
In a stepper manufactured by CENSOR company, two rays of wavelengths of 547 nm (e ray) and 578 nm (d ray) are employed as an alignment ray and when a sufficient signal ray is not obtained by one of the rays, a changeover to the other wavelength ray is made to conduct an alignment operation. According to experiments conducted by CENSOR, a relation between alignment signals by the two wavelength rays and a film thickness is shown in FIG. 15 (The practical hand-book of apparatus for manufacturing semiconductors, Science Forum Co. Ltd, PP. 224 to 225, Dec. 25. 1984).
Furthermore, LFF Process Control Division reports sinusoidal variation in reflection intensity due to interferences caused by each of two rays of wavelengths of 405 nm (h ray) and 436 nm (g ray) and variation in reflection intensity due to interferences caused by plural wavelength rays of g ray+h ray and g ray+h ray+i ray (LEE Corporation Process Control Division (60), Trapelo Road Walhm, Mass. 02154, (617) 890 to 2000).
This gives, as shown in FIG. 16, that with two wavelength rays of g+e an interference intensity of reflected rays is greatly improved at 10,000.+-.200 .ANG..
An example of contemplating improvement in terms of process has been indicated in the scientific lecture report of the 48th Meeting of Applied Physics Society (the second separate volume 18a-F-9, P.427, Autumn, 1987). According to the report, variations in interference intensity and unsymmetry of a mark are reduced by making thickness of a resist film on a wafer uniform to improve an accuracy of alignment.
DISCLOSURE OF THE INVENTION
There are many cases that a transparent thin film such as resist, SiO.sub.2, Si.sub.3 O.sub.4 or the like is formed on a wafer mark. When a single wavelength ray is employed for alignment in an optical aligner, optical stepper, X-ray aligner and the like, a reflection intensity of a wafer mark signal is reduced due to the standing wave effect in these thin film with variation in film thickness on a wafer and a contrast of optical images is reduced. As a result, an accuracy of alignment is greatly reduced ("Precision machinery", Vol. 5 PP.156 to 161, 1985).
In the case that a film formed on a wafer surface is a single layer and two layers, an intensity of rays reflected by a wafer mark is given by the following equation.
A reflectivity of a single layer film: ##EQU1## where r.sub.1.0 represents an amplitude reflectivity of a wafer mark to the first layer film and r.sub.2.1 represents an amplitude reflectivity of the first layer film to the atmosphere.
A reflectivity of a two-layer film:
Let it be that r.sub.3.2 represents an amplitude reflectivity of the second layer
REFERENCES:
patent: 4918301 (1990-04-01), Miyatake
patent: 5026976 (1991-06-01), Miyatake
Rosenberger Richard A.
Sumitomo Heavy Industries Co. Ltd.
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