CMP of GaN using sulfate radicals generated by metal catalyst

Abstract

A method for preparing atomically smooth gallium nitride (GaN) surface with high material removal rate that involves chemical mechanical polishing with sulfate radical (SO 4•-) oxidizer and Fe 2+ activator in slurry is presented. The results indicate that complexing agent with Fe 2+ activator is the key point to obtain atomically smooth GaN surface and higher removal rate of GaN. Atomic force microscope (AFM) shows that the average surface roughness (Ra) is 0.0601nm.

Influence of Polishing Parameters on Abrasive Free Chemical Mechanical Planarization (AFCMP) of Non-Polar (11-20) and Semi-Polar (11-22) GaN Surfaces

“…[3][4] To avoid this problem, GaN based devices grown along non-polar and semi-polar directions are getting increasing attention of the scientific community. [5][6][7] Non-polar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) and semi polar GaN (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) faces { (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) and (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) represents the miller indexes (hkil) of the crystal planes for hexagonal GaN crystal structure in four coordinate axis scheme} are generally grown hetero-epitaxially on miscut r-plane and mplane s...…”

“…9 CMP using different slurry chemistries and abrasive particles has been proven successful for preparing smooth GaN surfaces. [10][11][12][13][14] CMP of Ga polar (0001), N polar (000-1), and non-polar planes such as, a-plane (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) and m-plane (1-100) GaN surfaces was reported by Hanser et al 15 For the non-polar (a-plane) surfaces, a RMS roughness of about <0.2 nm was achieved on a scan area of 5 μm z E-mail: ddse@uohyd.ernet.in × 5 μm. In another work by the same research group, CMP of two non-polar planes such as, (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) and GaN surfaces was reported and the RMS roughness was found to be ∼ 0.43 nm on a scan area of 1 μm × 1 μm.…”

“…[10][11][12][13][14] CMP of Ga polar (0001), N polar (000-1), and non-polar planes such as, a-plane (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) and m-plane (1-100) GaN surfaces was reported by Hanser et al 15 For the non-polar (a-plane) surfaces, a RMS roughness of about <0.2 nm was achieved on a scan area of 5 μm z E-mail: ddse@uohyd.ernet.in × 5 μm. In another work by the same research group, CMP of two non-polar planes such as, (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) and GaN surfaces was reported and the RMS roughness was found to be ∼ 0.43 nm on a scan area of 1 μm × 1 μm. 16 Further, an average roughness of 0.5-0.1 nm was achieved by Kucharski et al using a combination of mechanical polishing and CMP for non polar GaN surface in the spatial range of 2.2 mm × 1.6 mm.…”

“…Therefore, use of nanoparticle abrasive containing slurries in CMP process is not economic. 19 The purpose of this study is to investigate the effect of abrasive free CMP on the MRR and surface quality of semi-polar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) and non-polar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) GaN surfaces.…”

“…In this work a novel single step, abrasive-free CMP (AFCMP) process, using proprietary slurry chemistry and processing parameters, has been investigated to polish non-polar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) and semipolar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) GaN epilayers grown on 2 inch sapphire wafers. This AFCMP process is an efficient, relatively low damage causing and cost effective surface planarization method for non-polar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) and semi-polar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) GaN surfaces. Also, the post-CMP cleaning becomes relatively easier since the polishing slurry does not contain any abrasive particles that may remain on the surface after polishing.…”