The Influence of HBr Discharge Ambience on Poly-Si/SiO 2 Etching Selectivity
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THE INFLUENCE OF HBr DISCHARGE AMBIENCE ON Poly-Si/SiO2 ETCHING SELECTIVITY. E.Ikawa, K.Tokashiki, T.Kikkawa, Y.Teraoka" and I.Nishiyama" Microelectronics Research Labs., NEC Corp. 1120, Shimokuzawa, Sagamihara, Kanagawa 229 Japan "Opto-electronics Research Labs., NEC Corp. 34, Miyukigaoka, Tsukuba, Ibaragi, 305, Japan ABSTRACT The influence of HBr discharge ambience on Si0 2 etching is investigated. A batch type parallel-plate reactive ion etching (RIE) dry etcher was used. The discharge ambience was changed by changing the numbers of poly-Si and Si0 2 wafers in the same chamber. It is found that as the number of poly-Si wafers increased, the poly-Si etch rate slightly decreased due to a loading effect and SiO 2 etching rate drastically increased. The selectivity of poly-Si / Si0 2 decreased with increasing the ratio of the loaded poly-Si number in the same chamber. When A120 3 wafers instead of poly-Si wafers were loaded with SiO2 substrates, SiO2 etching rate enhancement did not occur. Therefore, increase of SiO 2 etch rate could not be explained using a loading effect. From the results of mass analysis during etching in Si contained HBr plasma, etching products SiBr, (x=1,2,3) peaks were observed. Namely, when the Si etching products were supplied to Si0 2 surface, SiO 2 etch rate increased. In order to suppress the enhancement of Si0 2 etch rate, the etch temperature must be reduced.
INTRODUCTION Since high device packing density in ultra large scale integrated circuit (ULSI) is achieved by micro-fabrication techniques, a dry etching process is a key technology. It is necessary to establish a poly-Si gate electrode etching technique with high etching rate selectivity on a thin gate oxide film. In order to obtain high etching selectivity, reaction between Si0 2 and halogen plasma should be suppressed. Therefore, conventional carbon contained halogen gas should not be employed. Since Si0 2 etching reaction is enhanced by a carbon contained plasma, conventional halogen gas, such as CF, and CCl,, should not be employed.[l] Recently, HBr gas has been widely used for poly-Si etching, because high etching selectivity against Si0 2 was obtained. However, authors found that a high etching selectivity between poly-Si and Si0 2 drastically diminished, after a lot of poly-Si substrates were etched repeatedly in the same chamber using HBr gas. In this study, the influence of HBr discharge ambience on Si0 2 etching selectivity was investigated. Especially, the existence of Si atoms in HBr plasma caused Si0 2 etching rate enhancement. Mass analysis was carried out during etching in the HBr plasma.
EXPERIMENTAL CONDITIONS A cathode coupled reactive sputter etcher was used in this study. Plasma was exited by 13.56 MHz RF generator in parallel plate reactor. Ten pieces of substrates could be treated in a batch. Therefore, the amounts of Si atoms in HBr plasma was varied by changing the number of loaded Si and SiO 2 substrates in the same chamber. HBr gas was introduced into a treatment chamber with a flow rate of 30 sccm. The
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