Behavior and control of resist dissolution in the development process

Abstract

As the emphasis on critical dimension (CD) control in sub-micron lithography becomes more important, the mechanism of the development process and the different contributing factors will need to be further explored by equipment manufacturers. It was observed that the use of reticles with smaller exposed area ratio (EAR) have different affects on CD uniformity. To gain better control of CDs, we examined several of the contributing factors in the development process. Some significant factors are the affects of EAR and the affects of the rapid concentration changes of tetrametylammonium hydroxide (TMAH) surrounding the resist patterns that appears to slow the reaction rates of the developer. Using several chemically amplified resists (positive) and reticles with varying EAR, we determined that there are two phases (First Term & Second Term) of the development process. Within each term, there are significantly important processes taking place in and around the resist patterns. In the First Term, the importance is on proper amount of equally distributed developer on the wafer surrounding the resist patterns. In the Second Term, there is a rapid change to CD's meaning a greater possibility of control. Once determining the two terms of the development process, different concentrations of TMAH were experimented with to examine the mechanism of the resist dissolution movement. After observing the movement on the surface of the wafer, we believe that the resist dissolution moves within the puddle of the developer impeding the reaction rate for proper CD formation. By controlling the impeding affects of the dissolved resist in the Second Term, we believe that CD uniformity can be greatly improved.