PURPOSE: To find damage to a sample while an etching process is carried out, by using an apparatus comprising an ion beam etching system, a Raman microscopic spectrophotometry system for detecting the spectrum of Raman scattered light, and a control system for changing the setting of conditions on the basis of the Raman spectrum obtained.

CONSTITUTION: An etching sample 8 is a GaAs substrate, on which a focused ion beam 7 is repeatedly scanned in X and Y directions through a bias voltage at a bias electrode 4. An etching gas of Cl2 is introduced on the sample 8 and is supplied to all over the scanning area. As a liquid metallic ion source 1, Ga is employed, and a pattern is formed through local reactive etching, which is carried out in an area irradiated with the ion beam. The Raman spectrum is measured in the Raman microscopic spectrophotometry. Raman scattered light, Rayleigh scattered light, and reflected light of an exciting laser beam, which have been generated, are dispersed by a spectroscope 46 so as to provide a spectrum. The setting for etching conditions can be changed with the use of a microcomputer 44 on the basis of the Raman spectrum obtained.