William K. Bell

Molecular structure effects on dry etching behavior of Si-containing resists in oxygen plasma

The authors have studied the influence of Si–O bonding in the polymer structure of Si-containing resists on O2 plasma etch behavior. Three polymers were synthesized with the same Si wt % (12.1%) and varying number of Si–O bonds (0, 1, or 2). The etch resistance during the plasma process was measured by monitoring the film thickness removed using real-time in situ ellipsometry. After plasma exposure, surface chemical changes and roughness were characterized by x-ray photoelectron spectroscopy and atomic force microscopy, respectively. For O2 plasma exposure without substrate bias, all polymers showed the formation of a ∼1 nm SiO2 layer at the surface that acted as a barrier to further oxygen etching. Adding Si–O bonds to the polymer structure at constant wt % Si greatly reduced the etch rate and Si loss during oxygen plasma etching relative to the case of no such bonds. Polymers with one Si–O bond in the polymer structure showed identical etch behavior to polymers with the same wt % Si and two Si–O bonds. ...

Planarizing material for reverse-tone step and flash imprint lithography

Reverse-tone Step and Flash Imprint Lithography (S-FIL/R) requires materials that can be spin coated onto patterned substrates with significant topography and that are highly-planarizing. Ideally, these planarizing materials must contain silicon for etch selectivity, be UV or thermally curable, have low viscosity, and low volatility. One such novel material in particular, a branched and functionalized siloxane (Si-12), is able to adequately satisfy the above requirements. This paper describes a study of the properties of epoxy functionalized Si-12 (epoxy-Si-12) as a planarizing layer. An efficient synthetic route to epoxy-Si-12 was successfully developed, which is suitable and scalable for an industrial process. Epoxy-Si-12 has a high silicon content (30.0 %), low viscosity (29 cP @ 25 °C), and low vapor pressure (0.65 Torr @ 25 °C). A planarizing study was carried out using epoxy-Si-12 on trench patterned test substrates. The material showed excellent planarizing properties and met the calculated critical degree of planarization (critical DOP), which is a requirement for a successful etch process. An S-FIL/R process using epoxy-Si-12 was demonstrated using, an ImprioR 100 (Molecular Imprints Inc., USA) imprint tool. The results indicate that epoxy-Si-12 works very well as a planarizing layer for S-FIL/R.

Synthesis and Characterization of a Two Stage, Nonlinear Photobase Generator.

Amine photobase generators (PBGs) are uncommon yet useful compounds. Rarer still are examples of PBGs that are active at visible wavelengths. We report the synthesis and characterization of new photolabile amine protecting groups that are active under visible light. The new chromophore, benzothiophene imino-phenylacetonitrile (BTIPA), was synthesized in four steps without use of chromatography and found to release any one of several amines upon exposure to 405 nm light. The chromophore was also demonstrated to be useful as a Merrifield synthesis protecting group. Experimental evidence suggests a sequential, two stage photolysis mechanism which leads to a nonlinear response to dose.

Reactive fluorinated surfactant for step and flash imprint lithography

Abstract. One of the major concerns with nanoimprint lithography is defectivity. One source of process-specific defects is associated with template separation failure. The addition of fluorinated surfactants to the imprint resist is an effective way to improve separation and template lifetime. This study focuses on the development of new reactive fluorinated additives, which function as surfactants and also have the ability to chemically modify the template surface during the imprint process and thereby sustain a low surface energy release layer on the template. Material screening indicated that the silazane functional group is well suited for this role. The new reactive surfactant, di-(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl)silazane (F-silazane) was synthesized and tested for this purpose. The material has sufficient reactivity to functionalize the template surface and acceptable stability (and thus shelf-life) in the imprint formulation. Addition of F-silazane to a standard imprint resist formulation significantly improved template release performance and allowed for significantly longer continuous imprinting than the control formulation. A multiple-imprint study using an Imprio® 100 tool confirmed the effectiveness of this new additive.

High aspect ratio patterning of photosensitive polyimide with low thermal expansion coefficient and low dielectric constant

Abstract. A photosensitive polyimide system based on amine catalyzed imidization of a precursor poly(amic ester) is described. The material is based on the meta ethyl ester of pyromellitic dianhydride and 2,2’ bis(trifluoromethyl)benzidine. It acts as a negative tone resist when formulated with a photobase generator. The material exhibits a dielectric constant of 3.0 in the gigahertz range, a coefficient of thermal expansion of 6±2  ppm/K, and can be patterned to aspect ratios of >2 when formulated with a highly quantum efficient cinnamide type photobase generator.

Directly patternable dielectric based on fluorinated polyimide

A photosensitive polyimide system based on amine catalyzed imidization of a precursor poly(amic ester) is described. The material is based on the meta ethyl ester of pyromellitic dianhydride and 2,2’ bis(trifluoromethyl)benzidine and acts as a negative tone resist when formulated with a photobase generator. The material exhibits a dielectric constant of 3.0 in the GHz range, a coefficient of thermal expansion of 6±2 ppm/K, and can be patterned to aspect ratios of greater than 2 when formulated with a high efficiency cinnamide type photobase generator.