Optimization of KOH Etching for Single Crystal SiC by Dry Air

Abstract

Abstract: KOH etching is a convenient method with high efficiency for characterizing dislocations in SiC. However, the etching process is often affected due to the hydrolysis of KOH. To ensure stability and reproducibility of the etching process, frequent replacement of KOH is necessary, which leads to a large consumption of the etching materials. In this study, an improved method for KOH etching technique was proposed by directly injecting dry air into the molten KOH through a bubbler, in order to quickly remove moisture from the molten KOH and enhance dissolved oxygen. The effectiveness of the method is verified by etching lightly doped n-type epitaxial wafers and heavily doped n-type substrates. The experimental results show that introducing dry air into the molten KOH during the constant temperature stage before etching the SiC epitaxial wafer accelerate the evaporation of moisture in partially deliquescent KOH and achieve a faster etching rate of dislocations than fresh KOH. In the substrate etching experiment, an increase in the concentration of dissolved oxygen in the etchant is obtained by introducing dry air into the molten KOH, which promotes the etching effect through promoting the chemical reaction on SiC surface. As a result, an etching rate of dislocations similar to that of the mixed etchant of Na₂O₂ and KOH is achieved. This research provides a helpful method to improve the etching effect of SiC dislocations, which would have practical value in SiC production.

Key words: SiC, etching, dislocation, defect characterization, bubbler, etching rate

CLC Number:

TM23

SUN Shuai, SONG Huaping, YANG Junwei, WANG Wenjun, QU Hongxia, JIAN Jikang. Optimization of KOH Etching for Single Crystal SiC by Dry Air[J]. Journal of Synthetic Crystals, 2023, 52(5): 753-758.

References

[1] CASADY J B, JOHNSON R W. Status of silicon carbide (SiC) as a wide-bandgap semiconductor for high-temperature applications: a review[J]. Solid-State Electronics, 1996, 39(10): 1409-1422.
[2] WEITZEL C E, PALMOUR J W, CARTER C H, et al. Silicon carbide high-power devices[J]. IEEE Transactions on Electron Devices, 1996, 43(10): 1732-1741.
[3] KIMOTO T. Material science and device physics in SiC technology for high-voltage power devices[J]. Japanese Journal of Applied Physics, 2015, 54(4): 40103.1.
[4] TSUNENOBU K, HEIJI W. Defect engineering in SiC technology for high-voltage power devices[J]. Applied Physics Express, 2020, 13(12): 120101-.
[5] SKOWRONSKI M, HA S. Degradation of hexagonal silicon-carbide-based bipolar devices[J]. Journal of Applied Physics, 2006, 99(1): 011101.
[6] SICHE D, KLIMM D, HÖLZEL T, et al. Reproducible defect etching of SiC single crystals[J]. Journal of Crystal Growth, 2004, 270(1/2): 1-6.
[7] KALLINGER B, POLSTER S, BERWIAN P, et al. Threading dislocations in n- and p-type 4H-SiC material analyzed by etching and synchrotron X-ray topography[J]. Journal of Crystal Growth, 2011, 314(1): 21-29.
[8] HASSAN J, HENRY A, MCNALLY P J, et al. Characterization of the carrot defect in 4H-SiC epitaxial layers[J]. Journal of Crystal Growth, 2010, 312(11): 1828-1837.
[9] GAO Y, ZHANG Z H, BONDOKOV R, et al. The effect of doping concentration and conductivity type on preferential etching of 4H-SiC by molten KOH[C]//Proceedings of the Symposium on Silicon Carbide-Materials, Processing and Devices held at the 2004 MRS Spring Meeting, San Francisco, CA, F Apr 14-15, 2004.
[10] YAKIMOVA R, HYLÉN A L, TUOMINEN M, et al. Preferential etching of SiC crystals[J]. Diamond and Related Materials, 1997, 6(10): 1456-1458.
[11] SAKWE S A, MÜLLER R, WELLMANN P J. Optimization of KOH etching parameters for quantitative defect recognition in n- and p-type doped SiC[J]. Journal of Crystal Growth, 2006, 289(2): 520-526.
[12] SYVÄJÄRVI M, YAKIMOVA R, HYLÉN A L, et al. Anisotropy of dissolution and defect revealing on SiC surfaces[J]. Journal of Physics: Condensed Matter, 1999, 11(49): 10041-10046.
[13] ISHIKAWA Y, SUGAWARA Y, SAITOH H, et al. Characterization of surface defects of highly N-doped 4H-SiC substrates that produce dislocations in the epitaxial layer[J]. Materials Science Forum, 2010, 907(645/646/647/648): 351-354.
[14] YAO Y Z, ISHIKAWA Y, SUGAWARA Y, et al. Molten KOH etching with Na₂O₂ additive for dislocation revelation in 4H-SiC epilayers and substrates[J]. Japanese Journal of Applied Physics, 2011, 50(7): 1-7.
[15] YAO Y Z, ISHIKAWA Y, SUGAWARA Y, et al. Correlation between etch pits formed by molten KOH+Na₂O₂ etching and dislocation types in heavily doped n⁺-4H-SiC studied by X-ray topography[J]. Journal of Crystal Growth, 2013, 364: 7-10.
[16] WEYHER J L, LAZAR S, BORYSIUK J, et al. Defect-selective etching of SiC[J]. Phys Status Solidi A-Appl Mat, 2005, 202(4): 578-583.
[17] NA M, KANG I H, MOON J H, et al. Role of the oxidizing agent in the etching of 4H-SiC substrates with molten KOH[J]. Journal of the Korean Physical Society, 2016, 69(11): 1677-1682.
[18] HA S, MIESZKOWSKI P, SKOWRONSKI M, et al. Dislocation conversion in 4H silicon carbide epitaxy[J]. Journal of Crystal Growth, 2002, 244(3/4): 257-266.
[19] WU P, XU X, ZWIEBACK I, et al. Study of etching processes for SiC defect analysis[C]//2016 European Conference on Silicon Carbide & Related Materials (ECSCRM). September 25-29, 2016, Halkidiki, Greece. IEEE, 2017: 1.
[20] CUI Y X, HU X B, XIE X J, et al. Threading dislocation classification for 4H-SiC substrates using the KOH etching method[J]. CrystEngComm, 2018, 20(7): 978-982.