Laser stress measurement apparatus and method

Details Laser stress measurement apparatus and method Laser stress measurement apparatus and method

1988-08-26

1991-02-12

Willis, Davis L.

Optics: measuring and testing

By polarized light examination

With light attenuation

356 32, G01B 1130

Patent

active

049919644

ABSTRACT:
In semiconductor processing, it is desirable to protectively cover the wafer (40) prior to sawing the wafer (40) into individual chips. The compressive nitride protective cover tends to bow the normally flat surface of the wafer (40). If the compressive stress is too great, the wafer (40) and the circuits thereon may be damaged. The laser stress measurement apparatus (10) provides a method for checking the wafer (40) for excess stress without destroying the wafer (40). A light source (12) emits a beam of light onto a reflector (22) which reflects the light onto wafer (40). The light is deflected by wafer (40) back to the reflector (22) and thence to a light detector (52). The light detector (52) is positioned to receive the light in an exact center such that subsequent readings may be taken to determine a change in deflection. The change in deflection is then used in a formula to determine the compressive stress on wafer (40).

REFERENCES:
patent: 4332477 (1982-06-01), Sato
Chetverikov et al., "Measurement of Internal Stresses in Films", Translated from Zavodskaya Laboratoriya, vol. 46, No. 1 pp. 76-77, Jan., 1980 copy in class 356, subclass 32.

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