(A) study on UV enhanced gas phase cleaning of silicon wafer

Abstract

In this work, removal of organic contaminants and native/chemical oxide was studied to understand UV enhanced reactive gas phase cleaning at low pressure. Silicon epi-layer on cleaned surface was grown to confirm effectiveness of cleaning process and to evaluate the effect of surface roughness on epi-growth. First, wet-cleaning process has been analyzed to compare with dry-cleaning process. Good hydrogen termination and removal of native oxide is possible with lower HF concentration and shorter rinse time in ultra-pure de-ionized water if dipping time is sufficient. But, thorough removal of native oxide and perfect hydrogen termination is very difficult, and native oxide regrowth and carbon contamination is easily recurred. Second, removal of organic contaminants by UV enhanced gas-phase cleaning was studied using PEG and PMMA as contaminants. Removal rate of PEG substantially increased with higher temperature than the glass transition temperature by enhancing the mass transfer rate and the surface desorption, suppressing the self-recombination. Optimal flow rate and pressure condition can be understood by considering the proportion of UV energy between gas phase and organic film on substrate. The role of UV light on PEG removal is to accelerate the dissociation rate by forming end-aldehyde at above the glass transition temperature. $O_2$ with UV exposure can effectively react with radicals generated by UV irradiation to form per oxide radicals and/or terminate the propagation reaction forming peroxide. Rate of decomposition of PEG by UV/$O_2$ is very fast, and the composition of remained residual film was mainly composed of C-O and C=O. From the experimental results, it is speculated that removal of PMMA was mainly proceeded with photo-dissociation by the absorption of the wavelength with 184.9nm. New gas shower-head was designed to enhance photo- chemical reaction between PMMA and reaction gas with minimal loss of photon energy. The new gas shower-head sh...