Ikuo Matsukura

Development of polymer membranes for 157-nm lithography

Fluoropolymers were/are successfully used for pellicle manufacturing in 248 and 193 nm lithography. However, all known fluoropolymers rapidly degrade when exposed to high-energy 157 nm irradiation. Lack of suitable polymer “soft” pellicle has become one of the major obstacles for implementing 157 nm lithography. The goal of this research was to investigate the photodegradation mechanisms in fluoropolymers under 157 nm irradiation using various analytical techniques, and establish correlation between polymer structure and transparency/durability. Various polymer platforms, developed by Asahi Glass Corporation, as well as model polymer based on industrially available materials, have been employed in this study. Polymer structures have been analyzed using solution NMR, FTIR, Raman spectroscopy, TOF-SIMS, nanoindentation, outgassing, contact angle, ellipsometry, refractometry, n and k measurements. Transparency and durability of polymer membranes under 157 nm irradiation were established using an F2 157 nm laser as a source of irradiation, and an environmentally controlled chamber. As the result of this study, photodegradation mechanism for some of the tested polymers was tentatively suggested as cleavage of carbonyl, CO, and/or CFO bonds. Additionally, the following general conclusions have been made: environmental moisture, gas environment, and polymer/adhesive solvents affect structure and durability of the exposed polymers; “skin” surface layer can be formed on the surface of the irradiated polymer; polymer membranes are thinning under 157 nm irradiation; polar groups are formed on the irradiated surface. Effects of gas environment, exposure conditions, technology of the sample preparation on the photodegradation mechanism and kinetics were studied. Possible photodegradation pathways have been derived and assessed. Dependence of polymer durability and transparency on such structural features as number of carbon atoms within the ring, oxygen content, type and number of substituents in the Oxygen containing perfluorinated rings, number and location of carbon-oxygen bonds, structure symmetry, relative ratio of cyclic and linear chains, content and type of the hydrogen bonds, were analyzed. Semi-empirical rules to optimize transparency, durability, and mechanical properties of polymer membranes for 157nm exposure, will be discussed.

Development of fluoropolymers for pellicle in 157nm lithography

Fluoropolymers have been successfully utilized for pellicle manufacturing in 248 and 193nm lithography. Moreover, the pellicle using such fluoropolymers will make a large contribution to the development of 193nm immersion technology that is now expected as NGL for 65nm and 45nm node. On the other hand, 157nm lithography is also considered to be a desirable solution as a future manufacturing technique. However, no fluoropolymers show good laser durability to 157nm irradiation. This is one of major obstacles for implementing 157nm lithography. It follows that the purpose of this research is to find out a polymer that has outstanding durability, and would therefore promote wider use of the 157nm technology. Through this research, we had synthesized some kinds of fluoropolymer platform and investigated their durability. From the investigation, we have found several criteria to control their photo-induced degradation. Based upon these criteria, we have synthesized several new fluoropolymers and investigated their durability. As the result of these evaluations, these polymers showed good initial transmission as expected. Moreover, some polymers showed good mechanical durability when exposed to over 100J/cm2 irradiation. In addition, some new copolymers between monomer containing tert-hydrogen and perfluorinated monomer showed poor mechanical durability, however the polymers showed higher transparency during irradiation. To investigate these phenomena, we have analyzed these polymers using FT-IR and XPS. From these analyses, we estimate and propose possible degradation mechanism of these polymers.