29 June 1998 Resist deposition without spinning by using novel inkjet technology and direct lithography for MEMS
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Abstract
This article presents a technique for resist deposition using a novel fluid ejection method. An ejector has been developed to deposit photoresist on silicon wafers without spinning. Drop-on-demand coating of the wafer reduces waste and the cost of coating wafers. The novel piezoelectric fluid ejector is based on a variation of the design of a flextensional transducer that excites axisymmetric resonant modes in a clamped circular membrane. The ejector is made by bonding a thin piezoelectric ring to a thin, fully supported, circular membrane. The ejector design is optimized for maximum flexure at the lowest order resonant frequency using finite element modeling. The resist is placed behind one face of the membrane which has a small orifice (50 - 150 micrometers diameter) in its center. By applying an ac signal across the piezoelectric element, continuous or drop-on-demand ejection of the resist is achieved. Shipley 1400-21, 1400-27, 1805, and 1813 resists were used to coat sample 3' wafers. Later, these wafers were exposed and developed. The deposited resist films was 3.5 micrometers thick and had a surface roughness of about 0.2 micrometers . The ultimate goal is to deposit resist films with a thickness of the order of 0.5 micrometers , and a surface roughness of the order of 30 Ao. Such goals can be attained by using micromachined multiple ejectors presently under development, or with better control over the deposition environment. In the micromachined configuration, thousands of ejectors will be made into a silicon die and thus allow for full coating of a wafer in a few seconds. Coating in a clean environment will allow the lithography of circuits for microelectronic applications.
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Gokhan Percin, Gokhan Percin, Tom Hyongsok Soh, Tom Hyongsok Soh, Butrus T. Khuri-Yakub, Butrus T. Khuri-Yakub, } "Resist deposition without spinning by using novel inkjet technology and direct lithography for MEMS", Proc. SPIE 3333, Advances in Resist Technology and Processing XV, (29 June 1998); doi: 10.1117/12.312434; https://doi.org/10.1117/12.312434
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