Highly Sensitive Positive Electron Beam Resists by Adding Quaternary Ammonium Salts

Abstract

Polymethyl methacrylate (PMMA) has been widely used as a positive resist in electron beam lithography. The main feature of PMMA is its high resolution, but the sensitivity is not high enough for practical use. Highly sensitive resists are required in low‐energy electron beam exposure systems such as the EBES type. The sensitivity of PMMA could be increased from 24 to 0.8 μC/cm2 (accelerating voltage 20 kV) by adding 15 w/o tetra‐n‐butyl ammonium perchlorate (TnBAP) to PMMA. Using this resist, 0.75 μm patterns were obtained. TnBAP does not affect the breaking of PMMA molecules by electron beam exposure, but TnBAP makes the PMMA film more soluble in a developer. It is considered that the orientation of the PMMA molecules in the film is disrupted by adding TnBAP, and the PMMA film with TnBAP is easily dissolved in the developer due to an increase of the noncrystalline parts.