Micro/Nano-Patterned Structures From Photocurable Polysilazanes

As the basic blocks in micro-electromechanical systems(MEMS), integrated circuit(IC) and lab on a chip(LOC) fields, micro/nano- patterned structures play a key role in the modern industry society. Towards the application in silicon patterning, microfluidics devices, imprinting lithography etc., this dissertation fabricated micro/nano- structures with good properties from as-synthesized photocurable polysilazane precursors by novel rapid routes using optics lithography techniques and hydrolysis treatment.Two photocurable polysilazanes-based resins were obtaind by adding methacrylated units onto the polyvinylsilazane and perhydropolysilazane, whose products were donated MPVSZ and MPHPS respectively. Therein, MPHPS was firstly synthesized and characterized by FT-IR, 1H-NMR, 13C-NMR methods.Based on MPVSZ, a novel etch mask with high selectivity for silicon was fabricated in one step photolithography and hydrolytic conversion route. Photocurable MPVSZ mixture liquid containing photo-initiator Irgacure 369 and thermal-initiator Luperox 231 could be spin-coated to smooth films with the thickness up to ~ 6μm. MPVSZ mixture with 50 wt% concentration was spin-coated upon a 6 inches silicon wafer, followed by pre-baking, UV-exposure, developing, post-baking steps, then, the photolithographic MPVSZ microstructures with various shape(dot, square, line, etc.) were obtained, with the smallest feature size of 1μm. A hydrolysis treatment by exposing the MPVSZ microstructures in a 80°C ammonia ambience was taken here to acquire the silicate ceramic microstructures with a denser physical structure. Its hydrolytic conversion mechanism was investigated by FT-IR, XPS methods. SF6/Cl2/Ar mixture gas as the dry plasma etching etchant was used to investigate both of the cured and hydrolyzed MPVSZ patterns as the etch mask. The MPVSZ-derived silicate structure showed a better etching resistance than the microstructues before hydrolysis, its etching selectivity over silicon was achieved 8-16, and attained the highest at SF6/Cl2/Ar = 10/0/10. Besides, sub-100 nm nanostructures were fabricated by nano-imprinting lithography. MPVSZ patterning could be combined well with the conventional MEMS lithography technique, at the same time, the complex multi-steps patterning those conventional etch masks with high selectivities was avoided, thus it largely decreased the fabricating cost for the silicon patterning.Besides, based on MPVSZ, a novel technique to fabricate a rigid and chemically resistant micromixer system was developed. MPVSZ photocurable mixture liquid with a concentration of 75 wt% was injected into a MPTMS surface-treated glass mold and followed by a static liquid photolithography(SLP) step, which resulted in a cured MPVSZ open microchip with a built-in protrudent staggered herringbone mixer(P-SHM) structure. Its photo-polymerization mechanism was discussed. The cured-MPVSZ chip was converted to silicate ceramic chip by hydrolyzing in the vaporized ammonia ambiance at 80°C, and binded with the matched PHPS coated PDMSO micro-channel. Then another hydrolysis treatment at room temperature was taken to convert the PHPS coating to silica, resulting in a rigid and chemically resistant P-SHM microfluidics system being obtained. Two fluids were injected into this system, and realized mixing in 2.3 cm which was much shorter than the blank micro-channel at the same dimension of 101.6 cm. The MPVSZ-derived silicate based microfluidics chip owned good mechanical properties but lower fabricating cost compared to the chips from the conventional rigid materials, moreover, due to its good chemically resistance it could be as an effective complementarity of the widely used PDMSO chip, all these advantages make this it valuable in LOC field.Based on the firstly synthesized MPHPS, a new route to fabricate transparent and rigid micro/nano- structures towards using as the imprint mold was developed. Photocurable MPVSZ mixture liquid mixed with Irgacure 500 as photo-initiator was UV-imprinted to microstructure by using an as-prepared hard-PDMSO mold. The sub-100 nm cured-MPVSZ nanostructure was fabricated by using an as-prepared FP mold, with the feature size of 70 nm and 90 nm. By exposing the cured MPHPS in basic ambience for 10 h at room temperature, the chemical component was converted from SiN0.33O0.40C0.57 to SiO1.5, and the chemical structure was converted from polymer phase to Si-O inorganic phase. The obtained hydrolyzed micro/nano- structures was transparent, with an increased hardness of 4.5 GPa and an increased elastic elastic modulus of 115.1 GPa, which could meet with the requirement of the hard imprint mold used in both lab and industry, moreover, its fabrication cost was much lower than those conventional rigid materials mold made by MEMS routes.Based on the above researches on MPVSZ microstructures and their derived silicate microstructures, this paper made a further investigation on their modified microstructures using carbon nanotubes (CNT). A vertical CVD reactor was firstly designed to fabricate CNT in large scale. The as-prepared CNT with good quality was well dispersed in the photocurable MPVSZ mixture liquid through a designed chemical modification. CNT/MPVSZ solution with series CNT content of 0.1wt%, 0.3wt%, 0.5wt% was fabricated and spin-coated to be smooth film on a 6 inch silicon wafer. After going pre-baking, I-line photolithography, developing steps, MPVSZ microstructures modified by CNT were obtained. The CNT/MPVSZ microstructures were converted to CNT/silicate composite ceramic microstructures by a further hydrolysis treatment. It was concluded that the additive CNT strengthened both of the silicate ceramic matrix and MPVSZ polymer matrix, and the mechanical properties were increased by the increase of the CNT content.