Monitoring InP and GaAs etched in Cl2/Ar using optical emission spectroscopy and mass spectrometry

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Abstract
Optical emission spectroscopy (OES) and mass spectrometry (MS) have been used to monitor the etching of InP and GaAs in a Cl2/Ar plasma. The plasma was generated by an electron cyclotron resonance source. Emission from atomic In and Ga has been detected with the strongest signal to background measured at 410.2 nm for In and 417.2 nm for Ga. The optical emission signals have been studied for varying etch conditions to determine their effectiveness for real‐time control applications. It was found that, by increasing the total gas flow rate, the etch rate remained unchanged but the detected etch product signals decreased due to reduced residue in the plasma system. The residence time of the etch products causes the optical emission signals to be dependent upon previous etch conditions. The In and Ga emission signals have been correlated to the etch rate for various etch conditions. A downstream mass spectrometer was able to detect P and As etch products. The strongest signal for InP etching was 101PCl+2 and the strongest signal for GaAs etching was 145AsCl+2. The ability of the mass spectrometer to detect the group V etch products coupled with the ability of OES to detect the group III elements allows for noninvasive study of a variety of III–V material systems. Smooth, vertical etching of InP via holes at 2.7 μm/min for GaInAs/AlInAs‐based power devices has been monitored. Optical emission measurements showed that the surface oxide removal time for the via hole etching can be decreased from 95 s to an immediate removal by increasing the self‐induced dc bias (‖Vdc‖) from 50 to 300 V, in agreement with MS results. End point detection for via hole etching of GaInAs/AlInAs power devices to Ti/Au contacts on InP substrate was studied using 145AsCl+2 and 155TiCl+3 signals. The thickness of Ti removed can be limited to 18 nm. The optical emission from Ga and Al (at 396.1 nm) have been used to monitor etching of GaInAs/AlInAs heterojunction bipolar transistors. Less than 10 nm of the GaInAs base material is removed at the end of the emitter etch.

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