Low-pressure UV ozone and $UV/NF_3-H_2$ cleaning of the silicon surface coated with a commercial photoresist, AZ1512

Abstract

Due to its scale, thin film has quite different physical properties from the bulk material, depending on the surface condition of underlying substrate as well as deposition procedure. It has been known that single crystalline silicon can grow only on smooth and clean surface free of carbon, oxygen and metal contamination at high temperature. Thus this study focused on the surface phenomena and mechanism during low-pressure UVOC and $UV/NF_3$ treatments as surface preparation processes. Silicon substrate coated with a commercial photoresist, AZ1512, as carbon contamination source, was subjected to UVOC and $UV/NF_3$ process, and examined using various surface and bulk analysis methods. From the result of Fourier Transform Infrared Spectroscopic analysis and organic elemental analysis, AZ1512 is thought to consist of Novolak resin and diazonaphthoquinone carboxylic acid ester derivatives as structural material and photosensitizer. Calorimetric analysis showed thermal decomposition starts near 150℃. Both Norrish type photochemical reaction and photo-oxidation decompose AZ1512 during UVOC. There appeared the slow-down of removal in 10 min, which is explained as depletion of ketone structure. A model for UVOC decomposition of AZ1512 is proposed. In $UV/NF_3-H_2$ experiment, the interaction between surface and HF molecules produced in gas phase reaction is found to be responsible for the smoothing of surface. A model of $UV/NF_3-H_2$ oxide cleaning mechanism based on the observations in Atomic Force Microscopy and reflectance spectra is suggested.