Diazonaphthoquinone Based Resists Pdf Download !!HOT!!
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The majority of photoresists and many e-beam resists are developed with aqueous-alkaline developers which either contain metal ions or are metal ion-free (MIF). Metal ions interfere with many semiconductor processes; they modify the properties if e.g. a subsequent plasma etching step after development is intended. Metal ions (mainly sodium or potassium) are incorporated into the semiconductor material and change the microelectronic properties. For this reason, preferably MIF developers based on TMAH (tetramethylammonium hydroxide) are used. These developers are fast and aggressive, which is generally beneficial for the efficiency of the process. If however a higher contrast and/or resolution is aimed at or if very thick resist films are developed, developers containing sodium hydroxide, potassium hydroxide, phosphates or borates are often favoured.
Broadband UV wavelengths are applied for the exposure of many different resists, most commonly positive resists based on naphthoquinonediazides or novolaks. But also some other resists (positive, negative, image reversal, chemically amplified or not chemically amplified) for special applications are exposed to broadband UV. Broadband UV lithography is thus the imaging technology with the greatest variety of applicable resist and processes. The highest resolution achieved with this lithography process is currently in a range of 0.25 µm.
The first electron beam devices were produced at the end of the 1970s. The first resists consisted of poly(methyl methacrylate) (PMMA) and are still widely used today because PMMA resists are extremely reliable, versatile, and easy to handle. The principle of action is based on the cleavage of the molecular chain. Generally used PMMAs have a molar mass between 50,000 g/mol (50 k) and 950,000 g/mol (950 k). If the long-chain molecules are irradiated with electrons, the main chain is cleaved in many places. The resulting fragments of < 5,000 g/mol are readily soluble in special solvent developers, while the unexposed high molecular weight polymers remain insoluble. With PMMA resists, resolutions down to 5 nm can be achieved. If a PMMA copolymer with methacrylic acid is used, the sensitivity can be increased by a factor of 3. Due to its aliphatic structure, PMMA is however relatively susceptible to plasma etching processes. For this reason, positive e-beam resists like ZEP 520 and CSAR 62 are better suited for such applications. Both are copolymers of chloroacrylates (to increase the sensitivity) and styrenes (to improve the plasma etching stability). With CSAR 62, a resolution of 8 nm with a layer thickness of 180 nm could be demonstrated [64]. As already mentioned in section 5.1.2, chemically amplified positive resists are also used for e-beam lithography (FEP 171). The chemical structure and mode of action are similar to the resists described here.
Novolak-based positive photoresists take a special position; they are primarily used as positive e-beam resist for mask production. Particularly interesting is the chemical reaction (see section 5.2.2).
Both SU-8 and Atlas 46 can be used as electron beam resists with high sensitivity, but in both cases, layers are difficult to remove after exposure. The electron beam resist HSQ based on hydrogen silsesquioxane polymers creates negative structures that are known for their high resolutions (2.5 nm) and high etch stability. The low sensitivity and process instability are however disadvantageous. Now a more sensitive and more process-stable alternative is available, Medusa 82. Due to its similar (but modified) chemical structure, the sensitivity could be increased by a factor of 20 while the high resolution is maintained.
One solution is to vapour-coat the resist with a 10 nm-thin gold layer deriving the charges. After extensive vapour deposition, the gold must however be removed before development. A more elegant solution is to apply a conductive organic layer by spin coating. Currently, two conductive resists are commercially available for this purpose: Espacer, (Showa Denko) and Electra 92 (Allresist). Both resists are water-based and can thus be spun onto the electron beam resist without dissolution. After irradiation, they are simply removed with water. Electra 92 is characterized by a particular long-term stability. Another application is the replacement of metal vapour deposition in scanning electron microscope (SEM) images. Also in this case the organic layers discharge the electrical charges and high-contrast images are generated. Since these conductive layers can be removed with water, the substrates can be used further. 2b1af7f3a8