Resist outgassing in electron projection lithography

The Electron Projection Lithography (EPL) has already presented high resolution capabilities and been developed as one of the candidates of post optical lithography. However, much discussion has not been made for resist chemistry, especially on outgassing during exposure, regardless of utilizing high acceleration voltage and applying vacuum system. Moreover, two types of resist system, positive and negative tones, are required for a complete device manufacturing due to its stencil mask structure. Both resist tones with chemically amplified system were experimentally formulated to examine the partial and total pressure changes after exposure. The mass number of outgassing species was also measured in vacuum. The positive tone resist sample indicated many peaks at high mass numbers, in contrary to that negative tone resist sample showed strong peaks at low mass numbers. In addition, it was found that there was a clear trend between the total exposure doses and the total pressure changes in a certain positive-tone resist formulation. The fact may suggest the necessity of high sensitivity resists for EPL from the different standpoint of high throughput in mass production. The dependency of resist base polymer backbone was also examined under an accelerated exposure condition. The resist comprising of methacrylate base polymer indicated high amount of outgassing than that of poly(hydroxystyrene) (PHS) base polymer, with the same resist formulation. The polymer decomposition other than deprotection was considered since the exposure energy in EPL was much greater than that of optical lithography. We developed a new resist adopting the low outgassing concepts such as high sensitivity, non-methacrylate part, and low protecting ratio. The resist presented 56nm 1:2 contact resolution with resist sensitivity of 5.7 muC/cm(2).