|
Production yield of LSI devices mostly depends on the defect level of photomasks. A larger die size, higher packing density, and finer pattern size require photomasks, to have a lower defect density and a smaller defect size. Therefore, cleaning of masks to remove contamination and foreign particles from its surface has become more and more important to keep production yield of LSI in high level. Many cleaning methods have been proposed over the years and every mask manufacturer and wafer fabrication department has their own cleaning systems designed by themselves. However, new cleaning processes are still being developed due to the demand for higher levels of cleanliness every year and every month. Methods to remove contamination and foreign particles from a Cr mask are principally classified into two categories: a chemical way and a mechanical way. In the chemical way, acid solutions, oxidized solutions, alkaline solutions and organic solvents are used, depending on the nature and sort of contamination. In the mechanical way, there are several methods, such as scrubbing with a nylon brush, scanning a mask surface by pulsed high-pressure distilled water, organic solvents or chemical solutions, and so on. .Most of the current cleaning systems consist of both the chemical and mechanical methods. Today I would like to talk about damages or deterioration of Cr masks induced by the chemical and mechanical cleanings. First I will discuss the damage of Cr patterns due to rubbing after chemical cleaning treatment. We studied the dependence of the strength of the patterns upon the glass substrates and the chemicals which were used in the cleaning. The Cr films were coated by a sputtering method on five glass substrates, namely Q18, LE30, SL, SLW, and 7059. After making a Cr pattern on these substrates by a usual lithographic method, the plates were dipped in a chemical solution, and then subjected to a scrubbing test with a glass fiber bundle.
|
