日本大学生産工学部　生産工学部研究報告A51-2

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─ 3 ─time scale of practical computation16, 17).3　CN layer formation and etching3.1Etching properties for N, N2, and NH3 injections at 25 eVFig.2: Horizontal views of substrate surface after 73.4 × 1015cm−2 injection dose of (a) N, (b) N2, and (c) NH3 injections. Thick solid line indicates the uppermost position of the initial substrate surface. The green, white, and purple spheres represent hydrogen, carbon, and nitorogen atoms, respectively.(a)(b)(c)Resulting surfaces after (a) N, (b) N2, and (c) NH3 injec-tions at 25 eV are shown in Fig.2, where horizontal solid line indicates the top of the initial substrate surface (Fig. 1). These gures show the horizontal views of substrate surfaces after the injection dose of 73.4 × 1015cm−2. It seems that degree of etching is largest for N atom injections among these three cas-es, which can also be roughly conrmed from the net erosion yields.In the following, the origin of the height for the substrate will be placed at the top of the ordered PPP in Fig. 2.Figure 3 shows the net erosion yields15) YC, YH, and YN as functions of injection dose in the case of (a) N atom, (b) N2 molecule, and (c) NH3 molecule injections. The net erosion yield Yα of species α is determind by Yα≡Ysα −Iα. Here, Ysα is the number of reected or desorbed α atoms, i. e., the sputter-ing yield of α atom, and Iα is the number of α atoms that reach the surface as the incomming particles per injection. For ex-ample, in the case of NH3 injections IN = 1 and IH = 3. Obvi-ously, Yα > 0 (Yα < 0) means net removal of α species from (accumulation of α species in) the substrate.The net erosion yield plotted at a specic dose (i. e., instan-taneous net erosion yield) in Fig.3 is the number of removed species per injection averaged over 200 injections (i. e., 4.8 × 1015cm−2 of injection dose) around the specied dose value. Each simulation was performed up to 73.4 × 1015cm−2 (i. e., 3000 injections) and therefore the instantaneous yields are plotted in the range from 2.4 × 1015cm−2 to 71.0 × 1015cm−2 (i. e., from the 100th to 2900th injection). For N and N2 injec-tions cases, incident N atoms accumulate on the surface at early stage, and after that, the number of N atoms in the sub-strate seems to roughly get close to constant (i. e., YN ~ 0 on average) over ~ 30.0 × 1015cm−2 injection dose (Figs.3(a) and (b)). In Fig.3(c), YN shows wild uctuation due to a number of injected H atoms. It is also indicated that C atoms included in the substrate have been sputtered more eciently for N atom injections than the other two cases (for viewability, see Fig.5). Moreover, making a rough estimation of behavior of YN and YC in Fig.3, at this stage, it is seemed that YC starts to increase when YN approaches zero for all three cases. This in-Fig.3: The net erosin yields Yα (α =C, H, or N atoms) vs. injection dose in the case of (a) N, (b) N2, and (c) NH3 injections. The injectin energy is 25 eV and its direction is normal to the surface.(a)09.619.228.838.44857.667.2−101dose[1015 / cm2]sdleiynoisoretenN injections (25eV)YHYCYN(b)09.619.228.838.44857.667.2−101dose[1015 / cm2]sdleiynoisoretenN2 injections (25eV)YHYCYN(c)9.619.228.838.44857.667.2−101dose[1015 / cm2]sdleiynoisoretenNH3 injections (25eV)YHYCYNYH