Low damage and low surface roughness GaInP etching in Cl-2/Ar electron cyclotron resonance process

Electron cyclotron resonance Cl-2/Ar plasma etching characterization was pe rformed to obtain low damage and low surface roughness conditions for GaInP lattice matched to GaAs. Micro-Raman spectroscopy, atomic force microscopy (AFM) and surface profiling were used to characterize the near-surface qua lity and etch rate of GaInP. The results show that near-surface damage incr eases with do self-bias voltage in both Ar and Cl-2/Ar plasmas. Etching in pure Ax plasma results in significant increase in the transverse-optic (TO) intensity at high do self-bias voltage of 50 and 70 V, with the longitudin al-optic (LO) peaks downshifted in frequency. A normalized LO/TO intensity was quantified in this study to represent the combined effect of increase i n TO intensity and slight decrease in LO intensity. In the case of Cl2/Ar p lasma, substantial shifting of the GaP-like LO peak position to lower frequ ency was observed at do self-bias voltage of 70 V at 120 degreesC with incr ease in the TO peak intensity. In addition, the decreasing trend of the nor malized LO/TO intensity of GaP-like LO and InP-like LO peak was observed fo r samples etched under do self-bias voltages of 40-70 V Both observations f rom Cl-2/Ar plasma etching indicate the alteration of the GaInP near-surfac e region by etch induced damage within the de self-bias voltage range of 40 to 70 V. AFM studies showed surface damage consistent with the change in R aman spectrum. The damaged layer was caused by enhanced physical etching, w hich may result in InClx formation and therefore etch rate fluctuation at 7 0 V. The Raman spectrum of the sample etched at 30 V do self-bias voltage w as similar to that of the reference spectrum with normalized LO/TO intensit y values comparable to that of the reference values, indicating a low damag e process with root-mean-square (rms) surface roughness of 5.5 nm. Substrat e temperature dependence of the surface roughness was studied at 20 V do se lf-bias voltage. At 110 degreesC and 20 V do self-bias voltage, desorption of volatile products results in low rms surface roughness of 1.28 run and s low etch rate of 0.4 nm/s. The 20 V dry etch process was compared favorably to a HCl-based wet etch process. The low damage, low surface roughness and low etch rate process has excellent potential in compound semiconductor de vice processing, such as for GaInP emitter layer etching in heterojunction bipolar transistors fabrication. (C) 2001 American Vacuum Society.