Minimized response time of optical emission and mass spectrometric signals for optimized endpoint detection

The response times of optical emission spectroscopy (OES) and mass spectrometry (MS) have been measured for plasma etching of III–V heterostructures. For the Ga optical emission signal at 417.2 nm, a response time as fast as 0.2 s was obtained. The minimum response time of the 145AsCl+2 partial pressure, measured by MS, was found to be 0.9 s. The saturation times of the optical emission signal and the partial pressure signal have been shown to be related to the residence time of etch gases by varying the total gas flow rate and the chamber pressure. Decreasing residence time by reducing the pressure from 6 to 2 mTorr and maintaining a constant flow rate caused the saturation time of the Ga emission signal at 417.2 nm to decrease from 7 to 3 min. The 145AsCl+2 partial pressure signal saturated before the Ga emission signal. Endpoint detection for etching an AlInAs emitter and stopping on a GaInAs base of a heterojunction bipolar transistor was studied. Algorithms which monitor the change in Ga emission int...