Photo-Chemical Pattern Etching of Silicon-Carbide by Using Excimer Laser and Hydrogen Peroxide Solution
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PHOTO-CHEMICAL PATTERN ETCHING OF SILICON-CARBIDE BY USING EXCIMER LASER AND HYDROGEN PEROXIDE SOLUTION D. Sasaki and M. Murahara Department of Electrical Engineering, Tokai University 1117 Kitakaname, Hiratsuka, Kanagawa 259-1292, Japan ABSTRACT A circuit pattern etching of a Silicon-carbide (SiC) surface was conducted with KrF excimer laser irradiation in the presence of HF and H2 O2 mixed solutions. SiC have excellent properties of a high hardness, high melting point, wide band gap, high resistance to radiation and chemical stability. This material has come to attract attention as an integrated circuit material for high resistance to environment. However, the material is very difficult in minute processing by the photo-lithography because of its chemical stability. Thus, we developed the new etching method in which a SiC surface was photo-oxidized with H2 O or H2 O2 by using excimer laser irradiation and was etched by HF water solution. In this experiment, the mixed solution was poured into the thin gap between an Al2 O3 glass and the SiC surface with capillary phenomenon. A patterned excimer laser light was, then, irradiated on the SiC surface. The H2 O or H2 O2 in the reaction solution was photo-dissociated, and the photo-dissociated active oxygen reacted with the SiC. CO2 and SiO 2 were formed only on the part exposed by the pattered light forcibly, and an oxidized layer was formed. In this chemical reaction, the CO2 evaporated, and the SiO 2 remained on the sample surface. The SiO 2 layer was then dissolved by the HF water solution. Thus, etching was conducted by the repetition of the forced oxidization of the SiC and the dissolving of the oxidized layer. In this experiment, the most effective conditions were 20% of H2 O2 water solution, 15% HF water solution and 256mJ/cm2 of KrF excimer laser. The etching depth was 80 Å at the laser shot number of 10000. It significantly improved compared with that of using an ArF excimer laser (256mJ/cm2 , 193nm), 50 Å. INTRODUCTION Silicon-Carbide (SiC) has excellent properties such as a high melting point (2830degrees Celsius), a high hardness, a wide band gap (3C-SiC; 2.2eV), high resistance to X-ray radiation and chemical stability. This material has come to attract attention as a semiconductor material for high resistance to environment owing to its properties. However, it is difficult to etch
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patterns on SiC because of the chemical stability. Presently, most of 3C-SiC and 6H-SiC etching have been done using reactive ion etching (RIE) or electron cyclotron resonance (ECR) method with the combination of oxygen and halide-containing gases such as CHF 3 , CF4 , NF3 or SF6 [1,2]. However, the RIE and ECR methods require a more chemically stable resist than SiC for pattern etching. On the other hand, the photo-electro chemical (PEC) method requires no resist. In the previous studies on PEC, it was reported that β-SiC was etched by Ar+ laser (257nm) in focused to a 2-3µm spot [3]. This direct drawing method is, however, very difficult for pattern etching.
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