Automation methodology of local defocus monitoring on fixed chips in semiconductor fabrication

Local defocus, which is continuously induced in the photolithography process during the semiconductor manufacturing process, is mainly caused by the backside defect of the wafer. The backside surface defect of the wafer may be generated by various sources. This is caused by contamination and friction of the part facing the backside of the wafer in the equipment, pressure due to the chucking voltage, and height difference between the three lift pins that move the wafer up and down. Since defocus eventually deteriorates the yield and quality of the product, previous studies have focused on establishing the cause and improvement mechanism of its occurrence. This view is effective in finding and solving the cause of the problem, but there is clearly a limit to detecting defects early. This study presents a methodology for early detection of local defocus that occurs chronically in fixed chips. As a result, by automating local defocus detection, monitoring time is dramatically reduced, and the yield drop rate due to defective equipment can be accurately predicted in the fabrication. In addition, the methodology we developed is expected to be widely used as a yield prediction index that can quantitatively calculate the defect improvement effect.