Multilayer resists

Passivation layers, multilayer resist stacks, diffusion barriers, interlevel dielectrics, side-wall spacers, trench masks, oxidation masks, etc., in semiconductor devices. 

Films of the NA-EBDMA mixture absorbed light strongly only at wavelengths below about 300 nm and appropriate dyes would have to be added if films of these materials were used as bottom layers in multilayer-resist structures to be patterned at 366 or 436 nm. 

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. 

Electron beam resists to be used in direct wafer writing for submicron devices need significant improvement in sensitivity, resolution and dry etching durability. Multilayer resist (MLR) systems are now regarded as the most important technology to perform practical submicron lithography for VLSI fabrication (1-3). Many advantages in MLR compared with one layer resists (1LR) are listed here ... 

Photoresist compositions have been prepared that consist of silsesquioxanes containing sulfonamide substituents. These materials are useful in multilayer resist systems that provide contrast upon exposure to photogenerated acid. 

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. 

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... 

There have also been investigations of using multilayer resist/spin-on material techniques for planarization with a combination of RIE and CMP... 

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. 

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

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. 

---