Invited Paper PS+TF-WeA1
High Quality Film and Interface Formation using Appropriate Reaction Species

Wednesday, November 9, 2016, 2:20 pm, Room 104B

The strong reactive species are required for the high quality film deposition by CVD or ALD. For oxides or nitrides formation, oxygen radicals or nitrogen radicals generated by the microwave exited plasma are very effective(1-3) because of high density and low plasma damages. The integrity of SiO₂ film formed by the microwave exited PECVD is the same as that formed by the thermal oxidation on Si(100) surface, and is superior than that formed by the thermal oxidation on any other surface of Si(100)(1, 2). The SiO₂ deposition rate of the microwave PECVD is sufficiently large for the practical use. For the SiNx film formation, the microwave PECVD is also effective. The quality of SiNx film formed by the PECVD at 400 °C is the same as that formed by thermal CVD(4, 5). However, the relatively long deposition time is required for high quality film deposition, and relatively low pressure is also required, as a result, the gap fill characteristics is weaker than the thermal CVD. The high quality SiNx film deposition at low temperature and relatively high pressure are required. The nitrogen radical generated by the atmospheric pressure discharge is attractive for these applications(6, 7).

We have to choose the reactive species more carefully when the depositing material is different from the substrate, such as Al₂O₃ on Si or GaN, SiO₂ on GaN. If the reactive species is excessively active, the species react not only the precursor but also the substrate, and the materials of the substrate and the film are mixed at the film/substrate interface, as a result, those mixed materials make defects and interface traps. Al₂O₃ can works as the gate insulator for the GaN-based MOSFET(8, 9) because of the large band gap and the high resistivity to Ga diffusion. The H₂O which has relatively lower oxidation ability than oxygen radical was used as the oxidant at the initial stage of Al₂O₃ ALD for suppressing the oxidation of GaN surface. Following radical oxygen treatment by microwave exited plasma is very effective for improving the film quality of Al₂O₃(9). It is noticed that the oxidation of GaN at the Al₂O₃/GaN interface must not occur during the oxygen treatment.

References

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9. H. Kambayashi, et al., Jpn. J. Appl. Phys., 52, 04CF09 (2013).