Characterisation and comparison of water and alcohol as catalysts in vapour phase HF etching of silicon oxide films

The comparison of etch rates and selectivities for thin films of silicon dioxide and silicon nitride with respect to water and alcohol based (ethanol in this case) catalysts in a vapour phase HF etching process is discussed. Observation of etch rates for both PECVD Oxide and Nitride films are used to describe the behaviour of silicon dioxide etching. These behaviour characteristics can also be used to develop selectivity behaviours between the two films based on each of the catalysts. A number of factors are considered in the vapour phase etching process: the total gas flow for the etching process, process temperature and the etching pressure. The paper discusses the differences between both water and ethanol as process catalysts for the improvement of silicon dioxide etching selectivity with respect to silicon nitride. Results show that using water as a catalyst, a selectivity of up to 40:1 can be achieved while with a direct comparison of the same etch process with ethanol, the highest achievable selectivity is 15:1. On the other hand, with comparable etch rates to that of the water catalyst process, the highest selectivity achieved was 10:1.