Environmentally Friendly Polysilane Photoresists

Abstract

HAY I fi 1325Several novel polysilanes synthesized by the free-radical hydrosilation of oligomeric polyphenylsilane or poly@-tert-butylphenylsilane) were examined for lithographic behavior. This recently developed route into substituted polysilanes has allowed for the rational design of a variety of polysilanes with atypical chemical properties such as alcohol and aqueous base solubility. Many of the polysilane resists made could be developed in aqueous sodium carbonate and sodium bicarbonate solutions. These materials represent environmentally friendly polysilane resists in both their synthesis and processing, '@ s 1J-For over a decade, polysilanes have received a great deal of attention as unusual materials with many potential applications. Polysilanes owe much of their unusual properties to the delocalization of the Si-Si sigma bonds along the polymer backbone (I). This delocalization allows the silicon catenates to absorb strongly in the W region. Polysilanes have potential applications as photoconductors (2,3,4), semiconductors (3, nonlinear optical materials (a, LEDs (7) and photoresists (8).Polysilanes can perform as positive photoresists because exposure to UV light can lead to depolymerization via homolytic cleavage of the Si-Si bond (9). With some polysilanes, depolymerization leads cleanly to volatile products. Miller and coworkers (10,11) and Zeigler (12) demonstrated early on that some polysilanes behave as self-developing resists (a resist that does not require solvents to remove the exposed areas). Resists that self-develop would have a large competitive advantage over traditional resists because they require less processing to create an image. More importantly, dry developing does not generate the large volumes of hazardous waste associated with wet developing (increasingly restrictive EPA regulations on waste treatment have recently put a large financial burden on the electronics industry). Polysilanes also show submicron resolution and excellent oxy gen-etch resistance in bilayer microlithography (10-13).Despite their potential, polysilanes have yet to see industrial implementation in the United States (polysilanes are produced on an industrial scale in Japan as precursors to silicon carbide). A major factor hindering the use of polysilanes in industry is the method of their synthesis. Currently, the best synthesis of high molecular weight polysilanes is the Wurtz coupling of dichlorosilanes (Equation 1). This reaction has several drawbacks. The Wurtz couple gives low yields (5-60%) and variable molecular weights. As large quantities of molten sodium metal are used, the reaction is inherently dangerous even on a small scale. The harsh conditions exclude the incorporation of polar side groups on the monomer so only a limited number of monomers can be used. Consequently, most polysilanes synthesized by this method are soluble only in non-polar solvents. The reaction also generates large volumes of metal and solvent waste. T-.

Synthesis, Properties, and Derivatization of Poly(dihydrogermane): A Germanium-Based Polyethylene Analogue

“…Polymers with backbones made up of catenated silicon (i.e., polysilanes) and germanium (i.e., polygermanes) atoms are far less prevalent. Correspondingly, their uses are not as far reaching; polysilanes are primarily employed as lithography resists [2][3][4] and polygermanes largely remaining as research curiosities. [5][6][7] The limited scope of impact of these materials arises in part because of complications related to preparation and reactivity.…”

“…Polymers with backbones made up of catenated silicon (i.e., polysilanes) and germanium (i.e., polygermanes) atoms are far less prevalent. Correspondingly, their uses are not as far reaching; polysilanes are primarily employed as lithography resists, − and polygermanes largely remaining as research curiosities. − The limited scope of impact of these materials arises in part because of complications related to their preparation and reactivity. Still, they remain subjects of considerable interest because, unlike PE, their structures afford electrical conductivity that arises from σ-delocalization of electrons. − Furthermore, these electronic properties (in particular band gaps) can be tailored by defining molecular weight, side-group substitution, and/or introducing tensile strain. − As such, polysilanes and germanes exhibit tunable optical and electrical properties, such as nonlinear optical response and photoinduced electron transfer .…”