Patent ID: 7381978

Claim:
Apparatus for monitoring an etch process, the apparatus comprising: a particle beam source, adapted to direct a beam of charged particles to irradiate test openings within a test pattern created in a sample, said sample having a first layer that is at least partially conductive and a second layer formed over the first layer, said second layer having the test pattern and at least one contact opening created by an etch process, and wherein at least two test openings have different, respective transverse dimensions; and a current measuring device, coupled to measure, in response to the beam, at least one of a specimen current flowing through the first layer and a total yield of electrons emitted from a surface of the sample, thus producing an etch indicator signal; and a controller, configured to monitor the etch indicator signal and, responsive to said etch indicator signal, assess a characteristic of the etch process by analyzing the etch indicator signal as a function of the transverse dimensions of the test openings, wherein a first test opening has a first transverse dimension and a second test opening has a second transverse dimension that is less than said first transverse dimension; assess a residual thickness of a dielectric layer at a bottom of the test openings as a function of the transverse dimensions, and control the etch process so that the first test opening is sufficiently deep to reach the first layer, while at least the second test opening is not sufficiently deep to reach the first layer.