LOW-TEMPERATURE PLASMA-ETCHING OF GAAS, ALGAAS, AND ALAS

Dry etching of compound semiconductors is becoming increasingly important as design rules shrink for electronic devices. For photonic device applications, dry or plasma etching is used for device isolation, fine-line pattern transfer, and fabrication of optical quality interfaces. As has been well established for Si and W, plasma etching at reduced temperatures can provide superior critical dimension control and obviate the need for operating at high bias voltages that produce excessively energetic ion bombardment. In this work, we explore low-temperature (-60-degrees-C to +60-degrees-C) etching of the compound semiconductors GaAs, AlGaAs, and AlAs. In addition to improving etch anisotropy, which provides critical dimension control, we find that processing at lower temperatures improves microuniformity and reduces loading effects. At high temperatures, where larger samples are observed to etch more slowly than smaller pieces (loading effect), etching rates appear limited by reactant transport to the wafer. In this regime, both microuniformity and macrouniformity are poor. As the temperature is reduced, the etching rate becomes limited by surface processes as a residue containing the semiconductor elements, etchant gases, and residual background gases forms on the surface. In this regime, the etch rate becomes independent of surface area and uniformity is improved