Bulk etching of III-V materials in liquid phase solutions is typically accomplished using an oxidizer such as H2O2 and an acid such as HCl. Both the oxidation step and the etching step are self-limiting. The etching rate in this chemistry follows a so-called volcano dependence as a function of a reactant concentration. For example, GaAs and InAs etch at about the same rate in 0.01 M HCl mixed with H2O2 over the range 0.01 to 1 M. A maximum etching rate of about 1 nm/s was measured at 0.1 M H2O2. Similar behavior was observed for GaSb and InSb. These materials etched at about the same rate over the range of H2O2 concentrations from 0.0001 to 0.01 M. Yet the maximum rate occurred at 0.001 M H2O2, which is a much lower concentration than where the maximum was measured for the arsenides. Bulk etching of III-V materials in aqueous oxidizing-acid chemistries is dominated by removal of the group V atom, which is the rate limiting step. In device fabrication, we would like to avoid processes that depend on the sacrificial growth of oxides from the group III and V atoms. If not removed completely, these oxides contain defects and create energy states in the band gap of the semiconductor that degrade electrical performance. Gas phase plasma chemistries based on oxidizers that do not contain oxygen are used to etch III-V materials. Although very low etching rates have been achieved, these processes are not truly self-limiting. A kind of self-limiting behavior has been achieved by resorting to timed etches. Atomic layer deposition (ALD) deposits conformal films on high aspect ratio structures because each half reaction is self-limiting. Increasing the temperature can cause another reaction to dominate and etch the surface instead of depositing a film. One example is the etching of GaAs oxides by TiCl4. TiO2 deposits below about 150°C. Above this temperature oxides are removed without depositing Ti leaving adsorbed Cl on the As-rich surface. The As-Cl termination blocks subsequent ALD of TiCl4 and water vapor up to 50 cycles. If the As-Cl is desorbed by heating, TiO2 deposits. Although oxide removal is very different from bulk etching of III-V semiconductors, common ALD precursors combined with an understanding of liquid phase etching reactions could identify candidate self-limited etching reactions for III-V materials.

Selectivity in liquid phase etching of III-V materials on the path to developing a gas phase self-limited etching method

253rd National Meeting (2017)

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