| AVS 60th International Symposium and Exhibition | |
| Plasma Science and Technology | Thursday Sessions |
| Session PS-ThA |
| Session: | Low Damage Processing |
| Presenter: | M. Sekine, Nagoya University, Japan |
| Authors: | R. Kometani, Nagoya University, Japan K. Ishikawa, Nagoya University, Japan K. Takeda, Nagoya University, Japan H. Kondo, Nagoya University, Japan M. Sekine, Nagoya University, Japan M. Hori, Nagoya University, Japan |
| Correspondent: | Click to Email |
Plasma etching of GaN is necessary for fabricating high performance GaN devices, however plasma exposure generates defects and produces residues, which results in degradation. It is strongly required that the damage induced by plasma etching should be reduced. Post annealing can recover damages, however, preferentially N lost causes Ga-rich surface. The stoichiometric surface was reported to be deteriorated under annealing of 200 to 1000°C after N2+ sputtering at room temperature.1 We have revisited the surface reactions at high temperature (HT).
We constructed a high-temperature plasma reactor,2 where a CCP was generated by 13.56-MHz rf power to the substrate electrode. Ion bias energy was determined about 250 eV. SiC sample stage can be rapidly heated up to 800°C by an IR lamp as fast as 100°C/s.
As the GaN was exposed to Ar plasma at 600°C, a rough surface appeared with a root-mean-squared (RMS) value of 9.88 nm in AFM image. By XPS analysis of the shoulder peak at 18.9 eV in the Ga 3d region, it revealed Ga metallic state or Ga cluster formation. In contrast, no significant increase of roughness (1.46 nm) was observed after N2 plasma exposure even at 600 °C.
On the other hand, for Cl2 plasma, the etch rate increased at HT, from 293 to 534 nm/min for 300 to 600°C, and hexagonal pits were formed for 600°C etching. These mean that the heating would prompt the chemical reaction. The optical properties were investigated for YL (deep level defects such as N vacancy), BE (GaN band gap emission), and their ratio indicates crystal quality. Ar plasma exposure increased the YL/BE. It means crystal quality deterioration and deep level defects generation. The shallow level defects were also increased and not only YL but also lower energy side of BE increased. However, the crystal quality after Cl2 plasma etching was much better than that of Ar plasma.
In Cl2 plasma, no metallic gallium at any temperature, etch rate increasing and smooth surface was retained at HT except the hexagonal pits formation at 600°C. Consequently, HT etching is effective to enhance the surface chemical reaction and reducing plasma damages.
This work was supported by the Knowledge Cluster Initiative (Second Stage), MEXT, Japan.
1 Y. H. Lai et al., J. Phys. Chem. B 105, 10029 (2001).
2 R. Kometani et al., Appl. Phys. Express 6 (2013) 056201.