Thinning of N-face GaN (000-1) samples by inductively coupled plasma etching and chemomechanical polishing

F. Rizzi, E. Gu, M.D. Dawson, I.M. Watson, R.W. Martin, X.N. Kang, G.Y. Zhang

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6 Citations (Scopus)

Abstract

The processing of N-polar GaN (000 (1) over bar) 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-2/Ar or Cl-2/BCl3Ar 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 similar to 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 similar to 2 nm.
LanguageEnglish
Pages252-260
Number of pages8
JournalJournal of Vacuum Science and Technology A
Volume25
Issue number2
DOIs
Publication statusPublished - 2007

Fingerprint

Plasma etching
Inductively coupled plasma
plasma etching
Polishing
polishing
Surface roughness
surface roughness
Etching
etching
Processing
Gas mixtures
Surface morphology
gas mixtures
Scanning electron microscopy
Lasers
Substrates
scanning electron microscopy
optimization
Experiments
lasers

Keywords

  • semiconductors
  • fabrication
  • etching
  • plasmas
  • photonics
  • optics

Cite this

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title = "Thinning of N-face GaN (000-1) samples by inductively coupled plasma etching and chemomechanical polishing",
abstract = "The processing of N-polar GaN (000 (1) over bar) 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-2/Ar or Cl-2/BCl3Ar 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 similar to 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 similar to 2 nm.",
keywords = "semiconductors, fabrication, etching, plasmas, photonics, optics",
author = "F. Rizzi and E. Gu and M.D. Dawson and I.M. Watson and R.W. Martin and X.N. Kang and G.Y. Zhang",
year = "2007",
doi = "10.1116/1.2433987",
language = "English",
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pages = "252--260",
journal = "Journal of Vacuum Science and Technology A",
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TY - JOUR

T1 - Thinning of N-face GaN (000-1) samples by inductively coupled plasma etching and chemomechanical polishing

AU - Rizzi, F.

AU - Gu, E.

AU - Dawson, M.D.

AU - Watson, I.M.

AU - Martin, R.W.

AU - Kang, X.N.

AU - Zhang, G.Y.

PY - 2007

Y1 - 2007

N2 - The processing of N-polar GaN (000 (1) over bar) 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-2/Ar or Cl-2/BCl3Ar 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 similar to 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 similar to 2 nm.

AB - The processing of N-polar GaN (000 (1) over bar) 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-2/Ar or Cl-2/BCl3Ar 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 similar to 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 similar to 2 nm.

KW - semiconductors

KW - fabrication

KW - etching

KW - plasmas

KW - photonics

KW - optics

UR - http://dx.doi.org/10.1116/1.2433987

U2 - 10.1116/1.2433987

DO - 10.1116/1.2433987

M3 - Article

VL - 25

SP - 252

EP - 260

JO - Journal of Vacuum Science and Technology A

T2 - Journal of Vacuum Science and Technology A

JF - Journal of Vacuum Science and Technology A

SN - 0734-2101

IS - 2

ER -