Multilayer resist processing scheme

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. 

Multilayer resist systems can improve the performance of optical, electron beam. X-ray, and ion beam lithography (83,86). Whereas these schemes increase processing complexity, they appear to be gaining popularity and are currently used in several manufacturing areas. Both DUV blanket-ex-posure-PCM and DUV imaging and RIE-PCM schemes are strong candidates for submicrometer lithography. 

The other change in resist processing involves the use of multilayer schemes in place of a simple photoresist coating. Microimaging using multilayer materials and technology has revolutionized the electronics industry. Many silicon chips used in calculators and computers are produced in some variation of the following sequence of operations ... 

The first decision in choosing a synthetic method for a PPV material is the way in which the material will be processed (Scheme 7.8). The precursor routes will enable the preparation of solvent-resistant and more durable thin films of PPV. This is particularly desirable if a multilayer device structure is required for the application. When choosing different precursor methods, it is important to assess the criteria of the application. Most precursor methods involve a thermal elimination step to convert the precursor polymer to the PPV material. Sul-fonium precursors require higher-temperature elimination compared to sulfinyl precursors. This makes the sulfinyl route compatible with deposition on plastic substrates. Another factor to consider in precursor methods is the nature of the elimination byproducts. Sulfonium precursors convert to PPV with elimination of acids, such as HCl or HBr, which has been shown to be detrimental to device performance. Xanthate and dithiocarbamate routes involve the elimination of amine and CO2 and CS2, respectively. 

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