Resist materials resolution

The pursuit of further miniaturization of electronic circuits has made submicrometer resolution Hthography a cmcial element in future computer engineering. LB films have long been considered potential candidates for resist appHcations, because conventional spin-coated photoresist materials have large pinhole densities and variations of thickness. In contrast, LB films are two-dimensional, layered, crystalline soHds that provide high control of film thickness and are impermeable to plasma down to a thickness of 40 nm (46). The electron beam polymerization of CO-tricosenoic acid monolayers has been mentioned. Another monomeric amphiphile used in an attempt to develop electron-beam-resist materials is a-octadecylacryUc acid (8). 

The structures of the dimethylsiloxane block copolymers and respective parent homopolymers prepared for use as positive, bilevel resist materials are shown in Figure 1. Most copolymers were synthesized with >10 wt % silicon. The selection of PDMSX block length and novolac chemical composition proved to be the two most critical variables in achieving adequate resolution. 

The incorporation of PDMSX into conventional novolac resins has produced potential bilevel resist materials. Adequate silicon contents necessary for O2 RIE resistance can be achieved without sacrificing aqueous TMAH solubility. Positive resist formulations using an o-cresol novolac-PDMSX (510 g/mole) copolymer with a diazonaphthoquinone dissolution inhibitor have demonstrated a resolution of coded 0.5 pm L/S patterns at a dose of 156 mJ/cm2 upon deep-UV irradiation. A 1 18 O2 etching selectivity versus hard-baked photoresist allows dry pattern transfer into the bilevel structure. 

The resist materials that were developed for the printing industry are also useful for the manufacture of semi-conductor devices. In retrospect, this is fortuitous since the demands of the two technologies are quite different. Consider, for example, the resolution required to print a newspaper where the goal is to generate legible print. Here the resolution need only be a fraction of a millimeter, whereas typical semi-conductor devices that are in production today have minimum features of two or three microns. These features are smaller than a typical bacterium and are comparable in size to the organelles of cells. 

The measured G(x) value of representative epoxy polymers is approximately 10, but this value depends strongly on the structure of the polymer, its glass transition temperature and other characteristics. Since the crosslinking reaction that characterizes the COP resist functionality is a chain reaction, in theory, a single, electron-initiated event could result in the insolublization of an entire film of the resist material. Fortunately, because of the existence of chain terminating reactions, this does not occur and high resolution imaging of the resist material can be accomplished. 

Attempts to improve the DUV sensitivity of PMMA have spawned a variety of new DUV resist materials. Notable among these are copolymers of methyl methacrylate and indenone (80) which are reported to provide positive-tone resist function at 20 to 60 mJicnP in the DUV and copolymers of methyl methacrylate and 3-oximino-2-butanone (81). The latter materials provide a substantial increase in sensitivity over PMMA and are capable of 1 micron resolution. 

Mass production poses strict requirements on resist materials, most important of which are sensitivity, spatial resolution, contrast, and etch resistance. The sensitivity of the next-generation resists is required to be less than 10 pC/cm (EB), 100 mJ/cm (x-ray), and 25 mJ/cm (EUV) [89]. It should be noted that the resist sensitivity is traditionally expressed not by absorbed dose but exposure charge or energy per unit area. As for the spatial resolution, 45 nm is needed for the production of dynamic random access memory (DRAM) in 2010 [89]. Although resist patterns below 10 nm are presently fabricated by some kinds of resists, they do not have enough sensitivity required for the mass production [90,91]. 

In the course of our research on organic metals, we discovered that certain of these materials can function as electron-beam resists for high resolution lithography with a combination of unique features that have no parallel among conventional resist materials. ... 

A major consequence of these considerations is that new exposure sources and/or very sensitive resist materials must be developed in order to realize the resolution enhancement offered by deep-UV lithography without the penalty of extremely long exposure times. Considerable advances have been made on both fronts. 

The UV-insensitive Novolak resins are expected to be inert upon exposure. Despite this expectation, the selection of proper Novolak resins is very important for such overall resist performance as lithographic sensitivity, resolution, thermal image stability, adhesion, and so on. The reasons why Novolak resins are so important as resist materials and why specific kinds of Novolak resins are being investigated are the main subject of this paper. 

The LDPE production with tubular reactors (see Section 5.1) requires some sophisticated control valves [45]. The let-down valve (Fig. 4.2-6 B) controls the polymerization reaction via the pressure and temperature by a high-speed hydraulic actuator (9) together with an electronic hydraulic transducer. The position of the valve relative to the stem is determined by a high-resolution electronic positioner (7). The cone-shaped end of the valve stem (2), as well as the shrunk valve seat (3) are made from wear-resistant materials (e.g., sintered tungsten carbide) in order to tolerate the high differential pressure of around 3000 bar during the expansion of the polymer at that location. 

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