Inductively Coupled Plasma Etching of III-V Nitrides

Acknowledgement ....................................................................... 659 R eferences....................................................................................... 659 Plasma etching of the III-V nitrides has played a prominent role in the fabrication of blue, green, and ultraviolet (UV) light-emitting diodes (LEDs) and laser diodes [1]. The majority of plasma etch development for such devices has been directed toward mesa structures where high etch rates, anisotropic profiles, smooth sidewalls, and equi-rate etching of dissimilar layers is required. For example, reactive ion etch (RIE) has been used to expose the «-layer of the heterostructure for commercially available LEDs [2-4] as well as to form laser facets for GaN-based laser diodes [5]. However, as interest in high power, high temperature electronic devices [6-10] increases many of the etch requirements change due to shallower etch depths and smaller critical dimensions than those required for photonic devices. The etch requirements often include smooth surface morphology and low plasma-induced damage for post-etch ohmic and Schottky metal contacts and selective etching of one material over another to control threshold voltage uniformity or to accurately stop on specific layers for metal contacts or epitaxial regrowth. The etch process is further complicated by the fact that the III-V nitrides etch at much slower rates than conventional III-V compound semiconductors. For example, GaN etches at much slower rates than GaAs in chlorine-based plasmas despite similar volatilities of the etch products. The low boiling points of the Ga-and the nitrogen-based etch products shown in Table 1 implies that GaN etch rates are not limited by desorption of the etch products. However, due to the strong bond energies of the III-V nitrides, the rate limiting step may be the initial breaking of the group-IH-N bond, which must precede the etch product formation [1]. For example, GaN has a bond energy of 8. 92 eV/atom, InN 7. 72 eV/atom, and AIN 11. 52 eV/atom as compared to GaAs which has a bond energy of 6. 52 eV/atom [11]. Thus, more versatile, well-controlled etch techniques and processes are required to fill the demands for both photonic and electronic devices.