Investigating positive DUV resist profile on TiN

It is well known that chemically amplified positive tone DW resists are sensitive to substrate contamination, manifesting themselves as a ''foot'' on TiN substrates. Studies have proposed that there is an interaction between nitrogen used in the formation of the TiN and the chemically amplified resist. This reaction occurs when the acid generated in the resist is neutralized by nitrogen and hence a foot is formed. However, the ''foot'' abnormality of DW resist over TiN substrates has not been fully understood or eliminated. In this paper, we study the performance of 0.25 mm features using Shipley's UVIIHS resist on a TiN/metal layer. When UVIIHS was initially evaluated the primary problem was the presence of a ''foot'' at the bottom of the resist line. Subsequent studies were conducted on the effects of TiN thickness and composition. The results show the TiN thickness has little effect on the ''foot'' while the TiN composition has a profound effect. As the N content in the TiN film increases the size of the foot decreases. The foot decreases significantly when a very low nitrogen concentration is used and eliminated completely when using a barrier layer of 100 Ang Ti. Our results also demonstrate that surface pre-treatment of TiN using oxygen plasma can result in good 0.25 mm resist profiles with no noticeable foot present. The results we obtained indicate that chemical and physical properties of the TiN surface play a critical role in DUV resist performance. Therefore multiple spectroscopies have been employed to characterize TiN films including Rutherford backscattering, X-ray photoelectron, and time of flight secondary ion mass. These analysis provide many insights into the mechanism of the resist ''foot'' phenomenon.