Method and apparatus for evaluating the thickness of thin films.

摘要

The apparatus includes a laser (20) for generating a linearly polarized probe beam (22). The probe beam (22) is tightly focused (26) on the surface of a sample (12,14) to create a spread of angles of incidence. The reflected probe beam is passed through a quarter-wave plate (42) and linear polarizer (44) before impinging on a quad cell photodetector (40). The output signals from the photodetector (40) represent an integration of the intensity of individual rays having various angles of incidence. By taking the difference between the sums of the output signals of diametrically opposed quadrants, a processor (40) can obtain a value which varies linearly with film thickness for very thin films. The apparatus can be used in conjunction with other prior devices to enhance sensitivity for measurement of thicker films. Compensating measurements for assymetry in the beam (22) can be made by varying the orientation of the linear polarizer (44) and measuring the full beam intensity with another quad cell detector (30) before reflection of the beam (22). <IMAGE>