GaN etch rate and surface roughness evolution in Cl2/Ar based inductively coupled plasma etching

• Published in: Thin solid films Vol. 520; no. 24; pp. 7212 - 7218
• Main Authors: Rawal, D.S., Arora, Henika, Agarwal, V.R., Vinayak, Seema, Kapoor, Ashok, Sehgal, B.K., Muralidharan, R., Saha, Dipankar, Malik, H.K.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.10.2012; Elsevier
• Subjects: Anisotropy; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Discharges for spectral sources (including inductively coupled plasmas); Electric discharges; Etch rate; Etching; Etching and cleaning; Exact sciences and technology; Gallium; Gallium nitride; Gallium nitrides; High electron mobility transistors; Inductively coupled plasma; Inductively coupled plasma etching; Materials science; Mesa; Mesas; Other semiconductors; Physics; Physics of gases, plasmas and electric discharges; Physics of plasmas and electric discharges; Plasma applications; Radio frequencies; Specific materials; Structure and morphology; thickness; Surface roughness; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thin film structure and morphology; Mesa; Surface roughness; High electron mobility transistors; Inductively coupled plasma etching; Gallium nitride; Etch rate; Gallium; Surface morphology; Roughness; Etching rate; III-V compound; Surface states; Inductively coupled plasma; Anisotropy; Plasma etching; Selective etching; Photoresists; III-V semiconductors
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2012.07.117

Cl2/Ar based inductively coupled plasma (ICP) etching of GaN is investigated using photoresist mask in a consequential restricted domain of pressure<1.2Pa and radio frequency (RF) sample power<100W, for selective mesa etching. The etch characteristics and root-mean-square (rms) surface roughness are studied as a function of process parameters viz. process pressure, Cl2 percentage in total flow rate ratio, and RF sample power at a constant ICP power, to achieve moderate GaN etch rate with anisotropic profiles and smooth surface morphology. The etch rate and resultant surface roughness of etched surface increased with pressure mainly due to dominant reactant limited etch regime. The etch rate and surface roughness show strong dependence on RF sample power with the former increasing and the later decreasing with the applied RF sample power up to 80W. The process etch yield variation with applied RF sample power is also reported. The studied etch parameters result in highly anisotropic mesa structures with Ga rich etched surface. ► n-GaN etch characteristics and surface roughness are investigated in Cl2/Ar plasma. ► Etching optimised with photoresist mask in restricted regime of low power/pressure. ► Mesas of etch depth ~300nm and desired profile obtained with low roughness ~7.8nm. ► A decreasing trend of surface roughness is reported for <100W applied sample power.