Comparison of plasma chemistries for inductively coupled plasma etching of InGaAlP alloys

Two plasma chemistries, i.e., ${\mathrm{CH}}_{\mathrm{4}}{\mathrm{/H}}_{\mathrm{2}}\mathrm{/Ar}$ and ${\mathrm{Cl}}_{\mathrm{2}}\mathrm{/Ar},$ were compared for the etching of InGaP, AlInP, and AlGaP under inductively coupled plasma (ICP) conditions. While the etching with ${\mathrm{CH}}_{\mathrm{4}}{\mathrm{/H}}_{\mathrm{2}}\mathrm{/Ar}$ discharges appears to be ion driven, ${\mathrm{Cl}}_{\mathrm{2}}\mathrm{/Ar}$ discharges showed an additional strong chemical enhancement. The highest etch rate (∼1 μm/min) for InGaP was achieved at high ICP source power (⩾750 W) with the ${\mathrm{Cl}}_{\mathrm{2}}\mathrm{/Ar}$ chemistry. ${\mathrm{Cl}}_{\mathrm{2}}\mathrm{/Ar}$ discharges provided very smooth surfaces in all three materials with root-mean-square roughness measured by atomic force microscopy around 2 nm. This result may be due to the efficient ion-assisted product desorption in this chemistry. The etched near-surface region of InGaP (∼100 Å) with ${\mathrm{Cl}}_{\mathrm{2}}\mathrm{/Ar}$ maintained almost the same stoichiometry as that of the unetched control. By contrast, the ${\mathrm{CH}}_{\mathrm{4}}{\mathrm{/H}}_{\mathrm{2}}\mathrm{/Ar}$ plasma chemistry produced somewhat rougher surfaces and depletion of phosphorous (P) from the surface of InGaP.