Reactive ion etching of aluminum using SiCl4

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Abstract
Reactive ion etching of aluminum using SiCl4 is described and compared with that using CCl4. In SiCl4 plasmas, a high aluminum etch rate is maintained which is slightly dependent on gas pressure in the range of 2 to 15 Pa. However, the etch rates of other materials, such as SiO2, Si3N4, polycrystalline silicon, and photoresist decrease with an increase of pressure. This results in high aluminum etching selectivity to other materials at a relatively high gas pressure. On the other hand, when using CCl4 for the etching gas, aluminum etching is abruptly suppressed at gas pressures higher than 5 Pa because of carbonic film deposition on the surface, which limits the etching selectivity. Auger electron spectra indicate that the surface after etching in SiCl4 plasma is almost free from any residual contamination. At a relatively high gas pressure, greater than 3 Pa, the etched figure becomes somewhat isotropic when plasma CVD Si3N4 films are used for etching masks. However, using organic resist masks, lateral etching under the mask is significantly suppressed. As a result, no side etching profile is achieved at a higher gas pressure such as 8 Pa, where high selectivity can be obtained. These characteristics of reactive ion etching using SiCl4 lead to a highly directional and selective aluminum etching method which is free from residual contamination.

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