Resists films

Fig. 1. The hthographic process. A substrate is coated with a photosensitive polymer film called a resist. A mask with transparent and opaque areas directs radiation to preselected regions of the resist film. Depending on resist characteristics, exposed or unexposed portions of the film are removed using a developer solvent. The resulting pattern is then transferred to the substrate surface and the resist is stripped.

The resist must have suitable radiation sensitivity. Today s exposure tools are so costiy that tool throughput is a key measure of performance. The overall time to expose a resist film is the sum of the times to load and position the substrate in the exposure tool, to align the substrate and the mask, to irradiate the film, and to unload the complete part. In the optimum case the resist exhibits sufficient radiation sensitivity so that the fraction of the overall cycle apportioned to irradiate the film does not limit the number of substrates exposed in a given period of time. 

Fig. 12. Photo-induced chemistry of a 4-sulfonyl DNQ. The intermediate species reacts with adventitious water in the resist film to produce a sulfonic acid...

A second approach modifies the CA resist chemistry. Eor example, researchers have introduced basic additives into the resist formulation to minimize the impact of surface contamination of the resist film (82,83). A resist that already contains added base (and consequendy requites a larger imaging dose) should be less affected by the absorption of small amounts of basic contaminants. Systems of this type have been claimed to have improved resolution as well. The rationalization here is that the acid that diffuses into the unexposed regions of the resist film is neutralized and does not contribute to image degradation (84,85). 

In other work, the impact of thermal processing on linewidth variation was examined and interpreted in terms of how the resist s varying viscoelastic properties influence acid diffusion (105). The authors observed two distinct behaviors, above and below the resist film s glass transition. For example, a plot of the rate of deprotection as a function of post-exposure processing temperature show a change in slope very close to the T of the resist. Process latitude was improved and linewidth variation was naininiized when the temperature of post-exposure processing was below the film s T. 

Natural Gums. These were used in early styling products, formerly called wave sets. Natural gums generally make hazy solutions and the dried film tends to flake. For these reasons they are rarely used. Some of these gums, eg, tragacanth and alginates, can create humidity-resistant films and have limited use for specific product concepts. 

Fuhy aromatic, thermally (up to 250°C) and hydrolyticahy resistant films of PODs have been reali2ed from polyhydra2ides (56). Films of these polymers are useful as seawater desalination membranes. 

Vinyl fluoride (fluoroethene), is manufactured from the cataly2ed addition of hydrogen fluoride to acetylene. It is used to prepare poly(vinyl fluoride) which has found use in highly weather-resistant films (Tedlar film, Du Pont). Poly(vinyhdene fluoride) also is used in weather-resistant coatings (see Eluorine compounds, organic). The monomer can be prepared from acetylene, hydrogen fluoride, and chlorine but other nonacetylenic routes are available. 

Polymers are only marginally important in main memories of semiconductor technology, except for polymeric resist films used for chip production. For optical mass memories, however, they are important or even indispensable, being used as substrate material (in WORM, EOD) or for both substrate material and the memory layer (in CD-ROM). Peripheral uses of polymers in the manufacturing process of optical storage media are, eg, as binder for dye-in-polymer layers or as surfacing layers, protective overcoatings, uv-resist films, photopolymerization lacquers for repHcation, etc. 

Alkan olamines ate used in urethane coatings for glass shatter proofing (68) and have been utilized as amides, salts, or free amines in providing antifrosting, antifogging, and dirt-resistant films on glass and plastics (69—72). 

Clear, water-soluble, oU-and grease-resistant films of moderate strength can be cast from hydroxyethylceUulose solutions. Elexible, nontacky, heat-sealable packaging films and sheets can be produced from hydroxypropylceUulose by conventional extmsion techniques. Both gums can be used in the formulation of coatings, and both can be used to form edible films and coatings. 

Cellulose esters of unsaturated acids, such as the acetate methacrylate, acetate maleate (34), and propionate crotonate (35), have been prepared. They are made by treating the hydrolyzed acetate or propionate with the corresponding acyl chloride in a pyridine solvent. Cellulose esters of unsaturated acids are cross-linkable by heat or uv light solvent-resistant films and coatings can be prepared from such esters. 

The chemical name for such materials is poly(bisbenzimid-azobenzophenan-throlines) but they are better known as BBB materials. Such polymers have a Tg in excess of 450°C and show only a low weight loss after aging in air for several hundred hours at 370°C. Measurements using thermal gravimetric analysis indicate a good stability to over 600°C. The main interest in these materials is in the field of heat-resistant films and fibres. 

The outstanding resistance to corrosion exhibited by the high-silicon alloys is believed to be due to the development of a corrosion-resistant film containing a large proportion of silica. The full protective value of the film does not develop for most applications until at least 14-25% silicon is present in the alloy (Fig. 3.61). Increase in the content of silicon above 14-5% does not have a dramatic effect upon the corrosion resistance of the alloy (Fig. 3.61), although the further increase in film density is of service if the casting is to be exposed to solutions containing halide ions, especially hydrochloric acid. 

The hardness of the film is markedly affected by the conditions of anodising. By means of special methods involving dilute electrolytes at low temperatures and relatively high voltages , with or without superimposed alternating current, it is possible to produce compact abrasion-resistant films with thicknesses of 50-75/im and hardnesses of 200-500 VPN, for special applications. 

Polybenzaylene benzimidazoles (pyrrones) Polybenzoxazoles Thermally stable to 600°C (1112°F) insoluble in common solvents good mechanical properties. Stable in air to 500°C (932°F) insoluble in common solvents except sulfuric acid nonflammable chemical resistant film. 

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