Oxidation and Removal of Thin Organic Films From A Wafer Surface: Fundamentals of Ozonated Water Application and Water Recycle.

Abstract

A comprehensive Ultrapure Water (UPW) simulator program has been developed to model each unit process in UPW systems, including the entire dynamic system in real time. The program estimates the removal efficiencies for contaminants generated in semiconductor processes and in municipal water supplies. Calculations are performed using flow balance and concentration profile determinations at each unit process throughout the system. Simulator validation occurred using existing industrial facilities. Spent rinsewater (SRW) recycling in semiconductor facilities has been shown to provide significant UPW quality improvements. Contrary to many perceptions, this recycling is not a compromise to the quality, but an improvement. Benefits to the cost, reliability, and environmental improvements have also been identified. Processing risks have also been identified as the use of UPW with even minute quantities of contaminants, in particular the organic contaminants, could cause process problems. The simulator has been shown to be quite capable of predicting the impact on UPW quality due to excursions in SRW quality from semiconductor processes. Photolithography is a primary semiconductor process where organic photoresist is removed from wafers with corrosive chemistries. SRW is contaminated with both organic residues and corrosive chemicals. Ozonated UPW has recently become an alternative chemical for photoresist removal. A single-wafer tool was fabricated out of quartz designed for various processes. With direct observation of the wafer possible. Ultraviolet light experiments were also performed, directing light through the quartz, process solution, and onto the wafer. Experimental procedures were developed to study the effects of turbulence, wafer pretreatment, in-situ process treatments, and vibration on the kinetics and mechanism of photoresist removal by ozonated UPW. Data was obtained to determine which oxidation pathway was dominant; direct ozone, or indirect oxidation through radical formation. Intermediate products were determined using Fourier Transform Infrared Spectroscopy. Two distinct mechanisms were observed: film dissolution via a uniform sheeting method, and a non-uniform vapor-phase bubble mechanism where film dissolution occurred underneath the bubble. Models were developed that describe the film removal under both mechanisms. The uniform sheeting model describes typical process conditions in current tools. This model was validated and found in good agreement with experimental data.