Improvement of the quality of polished SiC wafers using chemical oxidation and heat treatment

Halina Sakowska 1Krystyna Mazur 1Dominika N. Teklińska 1,2Maciej Gała 1

1. Institute of Electronic Materials Technology (ITME), Wólczyńska 133, Warszawa 01-919, Poland
2. Warsaw University of Technology, Faculty of Materials Science and Engineering, Woloska 141, Warsaw 02-507, Poland

Abstract

Silicon carbide (SiC) is categorized as hard-to-process material. Usually, standard wafers manufacturing like chemical-mechanical polishing (CMP) with SiO2 or diamond abrasive is used [1]. Such processing does not guarantee perfect surface which is expected to grown epitaxial films on them or to use it as a substrate. Because of physical hardness and chemical inertness is difficult to obtain atomic level surface flatness without subsurface damage [2, 3].

The efforts of finding extra process which could be applied after standard polishing of SiC wafers are demonstrated.

Two methods of improvement of the quality of the polished surface have been presented:

1. chemical oxidation using Fenton process,

2. thermal annealing with assorted conditions.

According to Fenton reaction, (OH) radicals which is are an oxidizing agent, are generated during the decomposition of a hydrogen peroxide (H2O2) solution in the presence of ion Fe2+ as a catalyst.

Fe2+ + H2O2 → Fe3+ + OH + OH-

 In the second step, SiC surface is oxidizing as follows:

 SiC  + 4OH  +  O2  =  SiO2  + 2H2O  +  CO2

Thin film of SiO2 is dissolved in HF solution or removed by polishing. As a result, the quality of the surface roughness parameters was improved (Ra ≈ 0.39 nm).

The thermal annealing in vacuum, T = 900 ºC caused very smooth surface with Ra ≤0.10 nm and significantly reduced subsurface damaged layers [4].

            To check the effectiveness of this improvement, two silicon carbide wafers were prepared as substrates for new grown process of SiC crystals: one of them following standard technique and another one using chemical oxidation. The surface smoothness before and after processing was measured using atomic force microscope (AFM) and optical microscope.

To compare crystallographic quality of new SiC crystals the X-ray methods were used.

Acknowledgements: This work was supported by the SICMAT Project co-financed by the European Regional Development Fund under the Operational Programme Innovative Economy (Contract No. UDA-POIG.01.03.01-14-155/09).

 

References:

[1] H. Aida, T. Doi, H. Takeda, H. Kakatura, S.-W. Kim, K. Koyama, T. Yamazaki,
M. Uneda, Current Applied Physics 12 (2012) S41-S46.

[2] A. N. Hattori, T. Okamoto, S. Sadakuni, J. Murata, K. Arima, Y. Sano, K. Hattori,
H. Daimon, K. Endo, K. Yamauchi, Surface Science 605 (2011) 597-605.

[3] L. Zhou, V. Audurier, P. Piruoz, J.A. Powell, Journal of Electrochemical Society 144 (6) (1997) L 161-163.

[4] C. Richtarch: Method of preparing a surface of a semiconductor wafer to make it epiready, United States Patent: US 7,060, 620, B2, 2006.

 

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Presentation: Poster at 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17, Topical Session 9, by Halina Sakowska
See On-line Journal of 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17

Submitted: 2013-05-23 14:59
Revised:   2013-05-23 15:11