To make photomasks with high overlay accuracy, “Charge Dissipation Layer (CDL)” materials have been developed. Commercialized CDL materials can reduce electro-static charging on the surface of resist during electron beam exposure. However, some side effects are introduced to the mask-making process. The resolution performance of chemically amplified resist (CAR) is degraded owing to acid diffusion from the CDL components to the resist surface. A newly developed CDL solved this problem by controlling the acid diffusion. A positive-tone CAR with the CDL showed no resolution degradation, and performance was maintained for over 30 days after coating CDL and resist. Furthermore, the CDL has been evaluated on a negative-tone CAR which is more sensitive to CDL.
A novel adhesion promoting material has been developed to prevent very small resist patterns from collapse. One target for the development of the material is to make an advanced negative-tone mask with 40 nm sub-resolution assist features (SRAF). The SRAF on photomasks has become shorter and shorter as well as narrowing. The 2-dimensional resist patterns easily collapse during the resist developing process. Resist under-coating material controlled the surface condition on a chrome absorber film, and it improved the resolution of the SRAF. As a result, SRAFs of 46nm width and 200nm length were achieved using the material. A negative-tone resist on the under-coating layer demonstrated 35 nm isolated line patterns on a mask without pattern collapse.