Photo-Chemical Etching on Silicon-Carbide by Using Krf Excimer Laser and Xe 2 * Excimer Lamp
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INTRODUCTION Silicon-carbide (SIC) has very unique properties such as a high melting point of 2830 0C, a wide band gap (2.2eV for /P-SIC) and a high resistance to vacuum ultra violet (VUV) or X-ray radiation. By etching into a circuit pattern, it potentially will be an excellent electric device. In addition, SiC has a high refractivity in the range of soft X-ray. With a grating pattern etched, it will diffract SR light. It is,however, extremely difficult to etch on SiC as it is very hard and inert. Today, diamnond etching and thermal etching by ablation are effective and popular, but cause many problems with manufacturing. Most of the etching of 3C-SiC or 6H-SiC has been done using reactive ion etching (RIE) method with a combination of oxygen and halide-containing gases such as CHF3, CBrF3, CF4,
SF 6, or NF3/O 2 -13
However, the RIE method requires a more chernically stable
resist than SiC. On the contrary, the photo-electro chemical (PEC) methods by Ar' laser at 257nm (second harmonics) require no resists. In the previous studies on PEC, it was reported that [3-SiC was placed in HF solution of 2.5% with an electric current of 4-10 pi A/cm2, was etched by Are laser infocused to a 2-3 p m spot.14' 5 However, this direct drawing method accordingly, isvery difficult inetch patterns. We, therefore, have studied resistless pattern etching in which the SiC surface is selectively irradiated by excimer laser light so as to chemically react. 1-19 The resistless pattern etching reported inthis paper requires two light sources. The first is employed to photodecompose an etchant gas, NFý, the second, to excite the surface for photochermically pattern etching. Having utilized an ArF excimer laser beam of 193nm to decompose NF 3 before, we here employed the Xe2* excimer lamp light of 172 nrm, which has an emission spectrum inthe strong absorption band ofNF3 . This lamp is begun to utilized for photochemical light source. (201 As a result, the etching efficiency improved about seven times over the ArF excimer laser irradiation. To excite the SiC surface for etching, the 193 nm ArF or 248 nm KrF exicimer laser beam was used for the following two reasons: the first reason was for the surface reaction to take place with a high photon energy and the second, to form even finer patterns. This photo-chemical etching was performed by the simultaneous reactions of NF3 decomposition and SiC surface excitation, using two beam lights with different wavelengths. The substrate surface was measured by the X-ray photoelectron spectoroscopy (XPS), and the etchant gas was observed before and after its reaction by the Fourier-transformation infrared (FTIR) spectromater and Quadrapole mass spectoroscopy (QMS) inorder to study the mechanism and determine the optimum conditions for etching effectivelly. The etching of the SiC surface was evaluated by the interference roughness meter (ZYGO), and the results were reported later. 549 Mat. Res. Soc. Symp. Proc. Vol. 397 * 1996 Materials Research Society
ETCHING MECHANISM OF PHOTO-CHEMICAL REACTIONS
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