Patent ID: 8007675

Claim:
A method for controlling an etch process that is applied to a crystal material, said method comprising the steps of: providing a crystal that is made of a first material; forming a buried layer at a depth in the first material of the crystal at which it is desired to terminate an etch process, the buried layer made of a second material, wherein said second material is stoichiometrically different than said first material, wherein the buried layer is partially made up of a smaller amount of the first material in proportion to a composition of the second material, and wherein the buried layer does not affect the electrical properties of the first material; applying the etch process to said crystal; monitoring the etch process using a reactant detector and a mass spectrometer, wherein said reactant detector is used to detect a level of at least one particle that is released during the etch process and the mass spectrometer is used to monitor the level of the at least one particle that is released during the etch process; and determining when said etch process reaches said buried layer.