The feasibility of the additional process for improving pattern collapse in develop process

As EUV(Extreme Ultraviolet) Lithography has been delayed because of technical difficulties, ArF-immersion technology is continued to be utilized in the several future years. To progress constantly chip's minimization and pattern shrink with ArF wavelength, the adoption of aggressive SRAF(Sub Resolution Assist Feature) is inevitable. This trend is giving the big challenge in Photomask industry such as pattern collapse, pattern wiggling and bending. Generally, the reduction of the resist thickness is being tried to solve these problems. But this approach has the limitation, because of depending on the margin of etch process. Additionally, finding appropriate resist must be evaluated by a variety of experiments for verifying the stability of the process. According to several papers, the main reason of pattern collapse is the unbalanced capillary force at drying step in develop process. The capillary stresses (sigma) experienced by the resist can be described as shown in equation (1.1) and Figure 1[1] sigma = 6 gamma cos theta[H/W](2)[1/S-1] (1.1) Here gamma is surface tension, theta is contact angle of the rinse liquid on the photoresist, H/W is aspect ratio (height to width), S-1 is space between resist patterns. As it can be seen in equation (1.1), the smaller feature size is, the higher the capillary stresses forced on resist patterns is. And the capillary stress (sigma) is proportional to surface tension. In this paper, we studied the way to decrease surface tension by using the surfactant at drying step in develop process and verified the effect of this process on preventing pattern collapse.