Influence of resist process on proximity bias

Abstract

When linewidths in optical lithography are reduced, proximity bias, defined here as isolated to dense linewidth offsets, can consume large parts of the CD budget. This paper describes the resist thickness influence on proximity bias. If reflective substrates are used, proximity bias shows a cyclic behaviour. This can be seen as secondary swing caused by the spatial location of the remnant standing wave which results in photo active compound (PAC) concentration differences near the surface after diffusion. PAC acts as a dissolution barrier and influences the CD, resulting in different proximity biases for different resist thicknesses. When low-reflective substrates are used, as is the case with bottom anti-reflective coatings (BARCs), standing waves are less pronounced. On BARC substrates, a constant proximity bias was found, both in i-line and deep UV.