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Response Time For Optical Emission And Mass Spectrometric Signals During Etching Of Heterostructures
Published online by Cambridge University Press: 15 February 2011
Abstract
Plasma etching of III-V heterostructures has been monitored using optical emission spectroscopy and mass spectrometry. For the Ga optical emission signal at 417.2 nm, a response time as fast as 0.2 s has been measured. The response time of the mass spectrometer is limited by the transit time of etch products from the wafer surface to the ionizer. A minimum response time of 0.9 s was measured by reducing the signal integration time of the mass spectrometer. Saturation of the optical emission signal has been shown to be related to the residence time of etch gases by varying the flow rate or pressure. Decreasing residence time by reducing the pressure from 6 to 2 mTorr and maintaining a constant flow rate caused the Ga emission signal saturation time to decrease from 7 to 3 min. The 145ASC12+ signal saturated before the Ga emission signal at 417.2 nm. Endpoint detection for etching an AlInAs emitter and stopping on a GaInAs base was studied. By monitoring the changes in the Ga emission intensity, only 2 nm of the GaInAs base layer had been removed when the emitter etch was stopped.
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- Copyright © Materials Research Society 1996