tailieunhanh - Smart Material Systems and MEMS - Vijay K. Varadan Part 12

Tham khảo tài liệu 'smart material systems and mems - vijay k. varadan part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Fabrication Examples of Smart Microsystems 331 SiO2 p-type silicon substrate SiO2 p-Si 1 Grow field oxide 2 Open S D diffusion windows mask 1 SiO2 SiO2 1 ww ww 1 p-Si p-Si 3 Phosphorus predeposition 4 Phosphorus drive-in 5 Open gate windows mask 2 Gate oxide 6 Grow thin gate oxide Source Gate Drain 8 Deposite and pattern metal A1 mask 4 7 Open contact windows mask 3 9 Deposite and pattern SU-8 mask 5 10 Deposite and pattern A1 for sensing pad mask 6 Source Drain i SiO2 Jk- p-Si 11 Glue PVDF onto the chip Figure Process flow for a PVDF-based MEMS hydrophone. turned out to be difficult to make the connection between the second metal layer with the first one through the via holes. Two means were used in the following steps to solve this problem. First during the second metal-deposition step the sample was rotated around the top of the evaporator by using a rotatable sample holder. Therefore the sidewalls of the via holes could be covered with metal. Secondly in the following lithography step a thick positive photoresist AZ 4620 supplied by AZ Electronic Materials was used to provide good step coverage over the already patterned features. In order to protect the metal deposited on the sidewalls of the via holes the resist was dispersed on the surface at a low spin speed. However since this photoresist is much more viscous than the commonly used Shipley 1800 series photoresist it is difficult to obtain a uniform layer of AZ 4620 at a low spin speed. After experimentation it was found that a well-coated surface could be obtained by dispersing the photoresist at a spin speed of 2000 rpm. The processing of AZ 4620 is very similar to that for normal positive photoresists except that it requires longer times for soft bake and development. For a layer 332 Smart Material Systems and MEMS Figure Cross-section of the hydrophone with passivation. spin-coated at 2000 rpm with a thickness of 10 mm both the soft bake and development times are about 3 min. The developer for