Effect of modulation condition on oxide layer thickness of a S

Figure 4.16 shows the lateral distribution of the oxide layer thickness on the sur- faces of the Si substrate for surface oxidation. The thickness of the oxide layers irra- diated by the non-modulated and modulated ICTP were compared to study its effect on the uniformity of the oxidation processing. It is significantly evident that the oxide layer with non-modulation is thinner and its uniformity is lower. The uniformity of the oxide layer thickness can be improved by adopting the coil current modulation. Among the modulation conditions, the oxide layer is moderately more uniform along the substrate with a higher thickness around x= 0 mm under a modulation condition with 40 Hz and 51%. Decreasing the modulation frequency to 20 Hz at the same duty factor of 51% causes the higher thickness layer around the edges of the substrate and the lower thickness around the center compared to 40 Hz modulation. This means decreasing modulation frequency makes the uniformity of oxide layer thickness lower.

4.5 Conclusions 121

On the other hand, increasing duty factor to 60% at the same modulation frequency of 40 Hz lessens the uniformity of the oxide layer thickness compared to 51% duty factor. This means increasing the duty factor with same frequency elevates the thickness of oxide layer around the edges and lower the thickness layer around the center. There- fore, we confirmed that the higher modulation frequency with a lower duty factor could improve the uniformity of oxide layer thickness.

4.5

Conclusions

In summary, a planar type of Ar induction thermal plasma system with O2 gas

with the coil current modulation was adopted for the rapid large-area surface oxida- tion processing. The required amounts of Ar and O2 was studied for stable operation

of a modulated planar ICTP were investigated. Electrical properties, such as time variations in active output power and effective electrical impedance change, were cal- culated to check the change in thermal plasma impedance. In addition, spectroscopic observations were carried out to investigate the controllability of the atomic O density distribution in thermal plasmas during the on-time and off-time of the modulation. This planar Ar–O2 ICTP was used to irradiate to Si substrates for a period of one

minute to study adaptability of planar ICTP for large-area rapid oxidation processing with the modulation and non-modulation. Results indicate that a planar Ar–O2 ICTP

can be adopted for the rapid large-area oxidation of Si substrates and coil current modulation could improve the uniformity in thickness of the oxide layer fabricated.

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