Line-edge roughness characterized by polymer aggregates in photoresists

We investigate the origin of the line-edge roughness (LER) of line patterns of chemically amplified photo resists for the purpose of reducing size fluctuations of patterns in present and future deep-UV lithography. An atomic force microscope analysis of the pattern sidewall reveals that there are two kinds of roughness in the LER: short-range roughness with an average period of about 50 nm and long-range roughness with an average period of about 500 nm. The short-range roughness can be identified as polymer aggregates, which are essentially formed by the base polymer in the resist Nm. This is because the average period of the surface roughness due to polymer aggregates observed in the base polymer films is about the same as that of the short-range roughness. In addition, it is confirmed that aggregate extraction development occurs in the photoresist. On the other hand, the long-range roughness is generated not by the base polymer only but also by the exposure process because its average period increases with the exposure dose. The origin of the long-range roughness is also discussed.