Multilayer resist processes

CMP comes next. Its goal is to planarize and pattern the oxide [14]. The CMP step is discussed in more detail in the following two chapters. It should be mentioned here that CMP is not the only option for planarization. More cost-effective solutions have been studied and used, such as multilayer resist processes and spin-on glass in combination with RIE (Fig. 12.4). However, the obtained global planarity for such non-CMP processes is inferior to CMP planarity. They are therefore more suitable for ILD planarization than for STI... 

Figure 3.45. Schematic representations of multilayer resist processes. Reproduced from reference 83. Copyright...

Films of 7 3 mixtures of 1-naphthyl acrylate and ethoxylated bisphenol-A dimethacrylate had better planarizing properties than any of the resins that were examined and may be useful as layers for etchback processing. For use as bottom layers in multilayer-resist structures it will be necessary to bake the films after uv hardening to increase the Tg, and if the exposure wavelength is above 300 nm, an appropriate dye must be added to eliminate substrate reflections that degrade resolution. 

X-ray lithography also takes advantage of the increased resist sensitivity due to the thinner imaging films of multilayer systems. Thinner imaging films further improve X-ray resolution by minimizing the penumbra effect, a problem associated with an uncollimated X-ray beam. Consequently, the oblique exposure of features near pattern edges are minimized by multilevel resist processes, thereby restoring the desired profile. 

Multilayer resist technology offers a number of advantages in the generation of relief images but carries the burden of process complexity. We wish to report a novel process that greatly simplifies the optical MLR sequence. This concept is based on selective surface modification of the resist with a reactive dye which masks selected areas toward later flood exposure and solvent development. 

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 three main approaches to multilayer resist imaging systems (see Chapter 16 for details) include (i) hard mask (HM) processes, (ii) top surface imaging (TSI) processes requiring latent image formation only near the surface of the resist, thus circumventing any transparency requirements, and (iii) bilayer resist (BLR)... 

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 ... 

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