Arrangement for the interferometric testing of the flatness of technical surfaces

摘要

The invention can be applied to the automatic interferometric testing of the flatness of reflective technical surfaces, for example semiconductor wafers. The object is to develop a test interferometer, which can be connected to a computer, in such a manner that a pure double-beam interferogram containing the information concerning the surface of the test piece is prepared for evaluation. In the beam path of a laser (L) there are disposed a lambda /2 plate (PL) and a broadening system (A). Behind the broadening system (A) there is a deflecting mirror (S1), downstream of which a Fizeau interferometer comprising a 90 DEG prism (P) and a test piece (PR) is provided. In the beam path emerging from the Fizeau interferometer stands a further deflecting mirror (S2), downstream of which a Moiré interferometer is provided. This Moiré interferometer comprises a first and a second objective (O3, O4) with an interposed spatial frequency filter (F1), an adjoining diffractive element (BE), which is displaceable by means of an actuating motor (M) in its element plane, and a third and fourth objective (O5, O6) with an interposed spatial frequency filter (F2). Downstream of the Moiré interferometer there is provided a surface detector (FE), to which an analog/digital converter (A/D) is connected, the output of which converter is connected to a computer (R). IMAGE