Advanced dry etching for oxide deep-trench

This paper is focused on the development of silicon dioxide dry etching for Microsystems application. New requirements for oxide etching have been identified; keys issues are the higher oxide thickness (several microns) and the different design rules (large open areas, isolated patterns). To achieve these requirements, advanced oxide etching processes have been developed in conventional reactor using either photoresist or hard mask. The effects of several process parameters on etch rate, selectivity, oxide pattern profile have,been investigated. When using a photoresist mask, the major process limitation is caused by the oxide to photoresist selectivity. Straight profiles may only be obtained if the polymerisation on the side-walls is well-controlled. So, a compromise has to be made between etch rate, oxide to mask selectivity and pattern profiles. The use of hard mask leads to achieve excellent profile control with very high aspect ratio. But, gas chemistry and process parameters such as pressure, total gas flow and chemistry have to be precisely adjusted in order to avoid the aspect ratio dependant etching in narrow patterns. Vertical profiles in high aspect ratio features can be achieved but lateral oxide erosion have to be drastically controlled.