Bilevel process

Bilevel Processes. A bilevel system consists of a thick resist at the base and a thin imaging resist on top. Many variations have now been reported. Conventional image transfer into the bottom layer is accomplished... 

Figure 13 Schematic representation of the bilevel resist process employing an oxygen reactive ion etching pattern transfer technique.

On a larger scale, Tsiakis, Shah and Pantelides (2001) developed a supply chain design for multiple markets and plants of steady-state continuous processes. Similarly, Ryu, Dua and Pistikopoulos (2004) presented a bilevel framework for planning... 

Iyer, R.R. and Grossmann, I.E. (1998) A bilevel decomposition algorithm for long-range planning of process networks. Industrial el Engineering Chemistry Research, 37, 474. 

Ryu, J., Dua, V., and Pistikopoulos, E.N. (2004) A bilevel programming framework for enterprise-wide process networks under uncertainty. Computers ei Chemical Engineering, 28, 1121. 

Figure 8. Schematic of a bilevel-resist process using a silicon-containing top layer. Pattern transfer to the bottom planarizing layer is achieved by oxygen...

All future alternatives will require new resists and processes, and for the first time, manufacturing lines will be using at least two different resists. These new materials must have satisfactory sensitivity, resolution, and process latitude. In addition, the deep-UV tools will have limited depth of focus (1-2 (xm) and will be useful only with relatively planar surfaces. Multilayer-resist schemes have been proposed to overcome these limitations, and the simplest is the bilevel scheme that requires a resist that can be converted, after development, to a mask resistant to O2 reactive ion etching (RIE). Resistance to O2 RIE can be achieved by incorporating an element into the resist structure that easily forms a refractory oxide. Silicon performs this function very well and is relatively easy to include in a wide variety of polymer structures. 

Brominated poly(l-trimethylsilylpropyne) is an example of a substituted polyacetylene that is suitable for bilevel-resist processes (34). Requiring both exposure and postexposure bake (PEB) steps, samples of the polypropyne having a mole fraction of bromine from 0.1 to 0.2 per monomer unit exhibit sensitivities in the order of 25 mj/cm. Submicrometer resolution has been demonstrated, and etching-rate ratios relative to hard-baked photoresist planarizing layers are —1 25. 

Kim, K Lee, K.S., and Lee, J.H. (2010a) Bilevel optimizing control structure for a simulated moving bed process based on a reduced-order model using the cubic spline collocation method. Ind. Eng. Chem. Res., 49, 3689-3699. 

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