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

Abstract

The processing of N-polar GaN (0001) samples has been studied, motivated by applications in which extensive back side thinning of freestanding GaN (FS-GaN) 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 (ICP) etch processes, employing Cl{sub 2}/Ar or Cl{sub 2}/BCl{sub 3}Ar gas mixtures. Application of a standard etch recipe, optimized for feature etching of Ga-polar GaN (0001) 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-based) 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 andmore » possible factors contributing to residual surface roughness are discussed. This study also included work on chemomechanical polishing (CMP). The optimized CMP process had stock removal rates of {approx}500 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 {approx}2 nm.« less

Authors:
; ; ; ; ; ;  [1];  [2];  [2];  [3]
  1. Institute of Photonics, SUPA, University of Strathclyde, Wolfson Centre, 106 Rottenrow, Glasgow G4 0NW (United Kingdom) and Department of Physics, SUPA, University of Strathclyde, 107 Rottenrow, Glasgow G4 0NG (United Kingdom)
  2. (United Kingdom)
  3. (China)
Publication Date:
OSTI Identifier:
20979383
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Vacuum Science and Technology. A, International Journal Devoted to Vacuum, Surfaces, and Films; Journal Volume: 25; Journal Issue: 2; Other Information: DOI: 10.1116/1.2433987; (c) 2007 American Vacuum Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CHLORINE; EPITAXY; ETCHING; GALLIUM NITRIDES; MECHANICAL POLISHING; MORPHOLOGY; OPTIMIZATION; PLASMA; ROUGHNESS; SCANNING ELECTRON MICROSCOPY; SEMICONDUCTOR MATERIALS; SURFACES

Citation Formats

Rizzi, F., Gu, E., Dawson, M. D., Watson, I. M., Martin, R. W., Kang, X. N., Zhang, G. Y., Institute of Photonics, SUPA, University of Strathclyde, Wolfson Centre, 106 Rottenrow, Glasgow G4 0NW, Department of Physics, SUPA, University of Strathclyde, 107 Rottenrow, Glasgow G4 0NG, and Research Center for Wide-Gap Semiconductors, State Key Laboratory for Mesoscopic Physics, Peking University, Beijing 100871. Thinning of N-face GaN (0001) samples by inductively coupled plasma etching and chemomechanical polishing. United States: N. p., 2007. Web. doi:10.1116/1.2433987.
Rizzi, F., Gu, E., Dawson, M. D., Watson, I. M., Martin, R. W., Kang, X. N., Zhang, G. Y., Institute of Photonics, SUPA, University of Strathclyde, Wolfson Centre, 106 Rottenrow, Glasgow G4 0NW, Department of Physics, SUPA, University of Strathclyde, 107 Rottenrow, Glasgow G4 0NG, & Research Center for Wide-Gap Semiconductors, State Key Laboratory for Mesoscopic Physics, Peking University, Beijing 100871. Thinning of N-face GaN (0001) samples by inductively coupled plasma etching and chemomechanical polishing. United States. doi:10.1116/1.2433987.
Rizzi, F., Gu, E., Dawson, M. D., Watson, I. M., Martin, R. W., Kang, X. N., Zhang, G. Y., Institute of Photonics, SUPA, University of Strathclyde, Wolfson Centre, 106 Rottenrow, Glasgow G4 0NW, Department of Physics, SUPA, University of Strathclyde, 107 Rottenrow, Glasgow G4 0NG, and Research Center for Wide-Gap Semiconductors, State Key Laboratory for Mesoscopic Physics, Peking University, Beijing 100871. Thu . "Thinning of N-face GaN (0001) samples by inductively coupled plasma etching and chemomechanical polishing". United States. doi:10.1116/1.2433987.
@article{osti_20979383,
title = {Thinning of N-face GaN (0001) samples by inductively coupled plasma etching and chemomechanical polishing},
author = {Rizzi, F. and Gu, E. and Dawson, M. D. and Watson, I. M. and Martin, R. W. and Kang, X. N. and Zhang, G. Y. and Institute of Photonics, SUPA, University of Strathclyde, Wolfson Centre, 106 Rottenrow, Glasgow G4 0NW and Department of Physics, SUPA, University of Strathclyde, 107 Rottenrow, Glasgow G4 0NG and Research Center for Wide-Gap Semiconductors, State Key Laboratory for Mesoscopic Physics, Peking University, Beijing 100871},
abstractNote = {The processing of N-polar GaN (0001) samples has been studied, motivated by applications in which extensive back side thinning of freestanding GaN (FS-GaN) 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 (ICP) etch processes, employing Cl{sub 2}/Ar or Cl{sub 2}/BCl{sub 3}Ar gas mixtures. Application of a standard etch recipe, optimized for feature etching of Ga-polar GaN (0001) 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-based) 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 (CMP). The optimized CMP process had stock removal rates of {approx}500 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 {approx}2 nm.},
doi = {10.1116/1.2433987},
journal = {Journal of Vacuum Science and Technology. A, International Journal Devoted to Vacuum, Surfaces, and Films},
number = 2,
volume = 25,
place = {United States},
year = {Thu Mar 15 00:00:00 EDT 2007},
month = {Thu Mar 15 00:00:00 EDT 2007}
}
  • A parametric study of the etch characteristics of GaN, AIN and InN has been earned out with IC1/Ar and IBr/Ar chemistries in an Inductively Coupled Plasma discharge. The etch rates of InN and AIN were relatively independent of plasma composition, while GaN showed increased etch rates with interhalogen concentration. Etch rates for all materials increased with increasing rf chuck power, indicating that higher ion bombardment energies are more efficient in enhancing sputter resorption of etch products. The etch rates increased for source powers up to 500 W and remained relatively thereafter for all materials, while GaN and InN showed maximummore » etch rates with increasing pressure. The etched GaN showed extremely smooth surfaces, which were somewhat better with IBr/Ar than with IC1/Ar. Maximum selectivities of- 14 for InN over GaN and >25 for InN over AIN were obtained with both chemistries.« less
  • This article reports fabrication of n-ZnO photonic crystal/p-GaN light emitting diode (LED) by nanosphere lithography to further booster the light efficiency. In this article, the fabrication of ZnO photonic crystals is carried out by nanosphere lithography using inductively coupled plasma reactive ion etching with CH{sub 4}/H{sub 2}/Ar plasma on the n-ZnO/p-GaN heterojunction LEDs. The CH{sub 4}/H{sub 2}/Ar mixed gas gives high etching rate of n-ZnO film, which yields a better surface morphology and results less plasma-induced damages of the n-ZnO film. Optimal ZnO lattice parameters of 200 nm and air fill factor from 0.35 to 0.65 were obtained from fittingmore » the spectrum of n-ZnO/p-GaN LED using a MATLAB code. In this article, we will show our recent result that a ZnO photonic crystal cylinder has been fabricated using polystyrene nanosphere mask with lattice parameter of 200 nm and radius of hole around 70 nm. Surface morphology of ZnO photonic crystal was examined by scanning electron microscope.« less
  • BC13, with addition of Nz, Ar or Hz, is found to provide smooth anisotropic pattern transfer in GaAs, GaN, GaP, GaSb and AIGriAs under Inductively Coupled Plasma conditions, Maxima in the etch rates for these materials are observed at 33% N2 or 87$'40 Hz (by flow) addition to BC13, whereas Ar addition does not show this behavior. Maximum etch rates are typically much higher for GaAs, Gap, GaSb and AIGaAs (-1,2 @rein) than for GaN (-0.3 ymu'min) due to the higher bond energies of the iatter. The rates decrease at higher pressure, saturate with source power (ion flux) and tendmore » to show maxima with chuck power (ion energy). The etched surfaces remain stoichiometric over abroad range of plasma conditions.« less
  • Inductively coupled plasma (ICP) etch rates for GaN are reported as a function of plasma pressure, plasma chemistry, rf power, and ICP power. Using a Cl{sub 2}/H{sub 2}/Ar plasma chemistry, GaN etch rates as high as 6875 A/min are reported. The GaN surface morphology remains smooth over a wide range of plasma conditions as quantified using atomic force microscopy. Several etch conditions yield highly anisotropic profiles with smooth sidewalls. These results have direct application to the fabrication of group-III nitride etched laser facets. {copyright} {ital 1996 American Institute of Physics.}
  • In this study, the plasma characteristics and GaN etch properties of inductively coupled Cl{sub 2}/Ar plasmas were investigated. It has shown that the results of a study of inductively coupled plasma (ICP) etching of gallium nitride by using Cl{sub 2}/Ar is possible to meet the requirement (anisotropy, high etch rate and high selectivity), simultaneously. We have investigated the etching rate dependency on the percentage of Argon in the gas mixture, the total pressure and DC voltage. We found that using a gas mixture with 20 sccm of Ar, the optimum etch rate of GaN was achieved. The etch rate weremore » found to increase with voltage, attaining a maximum rate 2500 A/min at -557 V. The addition of an inert gas, Ar is found to barely affect the etch rate. Surface morphology of the etched samples was verified by scanning electron microscopy and atomic force microscopy. It was found that the etched surface was anisotropic and the smoothness of the etched surface is comparable to that of polished wafer.« less