| AVS 62nd International Symposium & Exhibition | |
| Plasma Science and Technology | Tuesday Sessions |
| Session PS1-TuA |
| Session: | Novel Materials and Etch Chemistry |
| Presenter: | Makoto Sekine, Nagoya University, Japan |
| Authors: | M. Sekine, Nagoya University, Japan Z. Liu, Nagoya University, Japan J. Pan, Nagoya University, Japan K. Ishikawa, Nagoya University, Japan K. Takeda, Nagoya University, Japan H. Kondo, Nagoya University, Japan M. Hori, Nagoya University, Japan |
| Correspondent: | Click to Email |
Plasma etching of GaN is necessary for fabricating high performance Nitride semiconductor devices. However plasma exposure causes defects and residues, which could reduce the performances. It is required that the plasma induced damages (PID) should be removed especially in the power electronics device fabrication. Post annealing could recover PID, but preferential N loss causes Ga-rich surface. The stoichiometric surface was reported to be deteriorated with annealing up to 1000°C after N2+ sputtering at room temperature (RT)1, We have revisited the surface reactions at high temperature (HT). We made a HT etcher. A VHF-ICP was generated and 13.56-MHz rf power was applied to the substrate. Sample stage can be heated up to 800°C by an IR lamp as fast as 100°C/s.
GaN surface was roughened with 9.88 nm RMS as exposed to Ar plasma at 600°C. XPS showed Ga metallic state or Ga cluster with the shoulder peak at 18.9 eV in Ga 3d. In contrast, no significant roughness increase (1.46 nm) was observed after N2 plasma at 600°C. Nevertheless, the HT N2 plasma failed to provide a preferable PL property2.
For Cl2 plasma, PL spectra of GaN etched at HT showed no obvious variation of yellow luminescence at 2.2-2.3 eV, suggested no Ga vacancies were formed. We focused on the near band edge emission (NBE) at 3.4 eV. The PID in bulk GaN behave as nonradiative centers of deep level states, which trap and recombine carriers. The NBE intensities for all GaN films etched at HT were degraded and as a consequence, the etching process at 400°C was optimum, because of its preferable stoichiometry, PL and smooth surface.
By covering the sample surface with a transparent window with or without the gap, we separated the effects of ion, photon and radical exposures. It was found the ion-induced damages dominated at 300°C, then decreased at 400°C, and removed at 500°C. Furthermore, photon-induced damages were not observed up to 400°C. Above 500°C, PL properties were degraded by photon. Since photons could not mainly induce damages at RT4, the synergy with thermal annealing enhanced the PL deterioration.
Therefore, by the results of depressed ion-induced damages and undeveloped photon-induced damages with a smooth surface at 400°C, the Cl2 plasma etching at 400°C is most appropriate to the low-damage process for GaN-based devices.
This work was supported by the Knowledge Cluster Initiative (Second Stage), MEXT, Japan.
1. Z.-Q. Fang, et al., Appl. Phys. Lett. 82, 1562 (2003).
2. R. Kometani, et al., Appl. Phys. Express 6, 056201 (2013).
3. Z. Liu, et al., To be published in Jpn. J. Appl. Phys. 54, (2014).
4. M. Minami, et al., Jpn. J. Appl. Phys. 50, 08JE03 (2011).