Surface modification and etch product detection during reactive ion etching in InP in CH4-H-2 plasma

A detailed plasma-surface interaction study has been conducted using mass spectrometry and optical emission spectroscopy for the plasma characterization, and quasi in situ XPS analyses to central the surface chemistry modifications. The experimental results clearly evidence the different etching behaviour of In and P in the CH4-H-2 plasma environment. A signature of the In and P etching mechanisms is available from the diagnostic of the plasma phase through the detection of phosphine as the major etching product of P and of excited In atoms related to the In etching reaction. The observation of the In emission line at 451.1 nm indicates a probable decomposition in the discharge of the organoindium compound which is regarded as the etch product of the group III element. XPS reveals the presence of P-H, C-In, In-In-C and In-In-P as surface species, and allows us to quantify precisely the P surface depletion. A time dependent etching mechanism is shown, first suggested by the etched thickness measurements and further confirmed by both etch product signal intensity and surface stoichiometry evolution with the plasma exposure time. Mass spectrometric PH3+ signal and In* emission line intensities monitored as a function of time indicate that the in etching mechanism is responsible for this situation, It is concluded that the reactive ion etching of InP is under the control of the removal mechanism of In. The combination of surface analysis and plasma diagnostics is shown to be capable of providing an understanding of the plasma-surface interaction.