The advanced mask CD MTT control using dry etch process for sub 65 nm tech - art. no. 673008

As the design rule of the semiconductor circuit shrinks, the specification for photomask becomes tighter. So, more precise control of CD MTT (Critical Dimension Mean to Target) is required. We investigated the CD MTT control of the attenuated PSM (Phase Shift Mask) by additional Cr dry etch. In conventional process, it is difficult to control CD MTT precisely because about 5 factors - Blank Mask, E-beam writing, Resist develop, Cr dry etch, MoSiN dry etch - affect CD MTT error. We designed the new process to control CD MTT precisely. The basic concept of the new process is to reduce the number of factors which affect the CD MTT error. To correct CD MTT error in the new process, we measured CD before MoSiN dry etch, and then additional corrective Cr dry etch and MoSiN dry etch was performed. So, the factors affecting CD MTT error are reduced to 2 steps, which is additional corrective Cr dry etch and MoSiN dry etch. The reliability of CD measurement before MoSiN dry etch was evaluated. The generable side-effect of the additional corrective Cr dry etch was analyzed. The relationship between 'CD shift' and 'additional corrective Cr dry etch time' was found for various patterns. As a result, accurate CD MTT control and significant decrease of CD MTT error for attenuated PSM is achieved.