Comparison of dry and wet etch processes for patterning SiO2/TiO2 distributed Bragg reflectors for vertical-cavity surface-emitting lasers

A dry etch process for patterning SiO2/TiO2 distributed Bragg reflectors (DBRs) for vertical-cavity surface-emitting lasers was demonstrated. The etching was conducted using an inductively coupled plasma (ICP) system. Both SF6/Ar and Cl-2/Ar based etching chemistries were investigated. Very slow etch rates were obtained for TiO2 when using a Cl-2/Ar chemistry due to the low volatility of the etch products, TiClx. Using an SF6/Ar based chemistry, similar etch rates for TiO2 and SiO2 were obtained, which is desired for etching through the alternating SiO2 and TiO2 layers of the DBR. An average etch rate of 1200 Angstrom /min was achieved at ICP and radio frequency (rf) powers of 500 and 250W, respectively. Wet chemical etch processing was also explored using a buffered oxide etchant (BOE) and diluted HF. Etch rates of similar to 2050 Angstrom /min and similar to2.7 mum/min were obtained for BOE and HF:H2O (1:3), respectively. However, a significant etch-undercut of the DBR structure and delamination at the SiO2/TiO2 interfaces, due to internal stress created between these layers, were observed when these wet etchants were used. (C) 2001 The Electrochemical Society. All rights reserved.