Thinning of N-face GaN (0001 ¯) samples by inductively coupled plasma etching and chemomechanical polishing

Abstract

Fabrication of ZnO photonic crystals by nanosphere lithography using inductively coupled-plasma reactive ion etching with CH 4 / H 2 / Ar plasma on the ZnO/GaN heterojunction light emitting diodes J. Vac. Sci. Technol. A 28, 745 (2010); 10.1116/1.3357282 Removal of chemical-mechanical polishing-induced damage layer in single crystal La 3 Ga 5 Si O 14 by inductively coupled plasma etching Evolution of surface roughness of AlN and GaN induced by inductively coupled Cl 2 / Ar plasma etching J. Appl. Phys. 95, 4635 (2004); 10.1063/1.1688993 Nonselective and smooth etching of GaN/AlGaN heterostructures by Cl 2 / Ar / BCl 3 inductively coupled plasmas J.The processing of N-polar GaN ͑0001͒ samples has been studied, motivated by applications in which extensive back side thinning of freestanding GaN ͑FS-GaN͒ substrates is required. Experiments were conducted on FS-GaN from two commercial sources, in addition to epitaxial GaN with the N-face exposed by a laser lift-off process. The different types of samples produced equivalent results. Surface morphologies were examined over relatively large areas, using scanning electron microscopy and stylus profiling. The main focus of this study was on inductively coupled plasma ͑ICP͒ etch processes, employing Cl 2 /Ar or Cl 2 /BCl 3 Ar gas mixtures. Application of a standard etch recipe, optimized for feature etching of Ga-polar GaN ͑0001͒ surfaces, caused severe roughening of N-polar samples and confirmed the necessity for specific optimization of etch conditions for N-face material. A series of recipes with a reduced physical ͑sputter-based͒ contribution to etching allowed average surface roughness values to be consistently reduced to below 3 nm. Maximum N-face etch rates of 370-390 nm/ min have been obtained in recipes examined to date. These are typically faster than etch rates obtained on Ga-face samples under the same conditions and adequate for the process flows of interest. Mechanistic aspects of the ICP etch process and possible factors contributing to residual surface roughness are discussed. This study also included work on chemomechanical polishing ͑CMP͒. The optimized CMP process had stock removal rates of ϳ500 nm/ h on the GaN N face. This was much slower than the ICP etching but showed the important capability of recovering smooth surfaces on samples roughened in previous processing. In one example, a surface roughened by nonoptimized ICP etching was smoothed to give an average surface roughness of ϳ2 nm.

Double-dielectric-mirror InGaN/GaN microcavities formed using selective removal of an AlInN layer

“…Post-growth processing followed a multistep route, fuller details of which are presented in Ref. [8]. This paper contains a diagrammatic process flow showing the processing sequence employed here for MCs grown on FS-GaN, plus a variant involving laser lift-off.…”

“…FS-GaN substrates are next thinned to ∼40 µm using mechanical grinding, and a smooth surface is recovered by chemomechanical polishing. Structures are then thinned further using inductively coupled plasma etching, which can remove material at a rate of ∼380 nm/min, using recipes developed to minimize roughening during processing on the N-polar (0001) crystal face [8]. A reactive ion etching (RIE) process, employing a tool equipped for endpoint detection using laser reflectometry, was then used for the final stages of GaN removal.…”

Study of dry etched N-polar (Al)GaN surfaces obtained by inductively coupled plasma etching

“…Wet etching in hot alkaline solutions such as potassium hydroxide [19] and dry etching in inductively coupled plasma (ICP) system by chlorine-based gases [20][21][22] are the two main processes used for N-polar materials removal. N-polar surfaces after wet-etching are usually of poor morphology with a high density of pyramidal hillocks [19,23], whereas dry-etching can lead to much smoother surface morphologies [24]. In previous studies, it has been reported that for both Ga-polar and N-polar films, their surface roughness are sensitive to the etching rate [15].…”

Nanofabrication of gallium nitride photonic crystal light-emitting diodes

“…In this situation, the GaN is etched on the gallium-polar (0 0 0 1) crystal plane of the wurtzite-phase material. Processing of flip-chip and vertical-current LEDs mentioned in the introduction involves dry-etching of GaN on the nitrogen-polar ð0 0 0 1Þ crystal plane, which may show dissimilar behaviour with respect to both etch rate and roughening [35,36]. The need for separate optimisation of such processes has not been widely recognised in the literature.…”