Poly resists, exposure

Poly(vinyl cinnamate) Resists. Dichromated resists exhibit numerous shortcomings which include lot-to-lot variabiUty of the components, aging of the formulated resists in solution and in coated form, poor process stabiUty (due to a sensitivity to variations in temperature and humidity), and intrinsically low photosensitivity requiring long exposure times for adequate insolubilization. 

The most chemical-resistant plastic commercially available today is tetrafluoroethylene or TFE (Teflon). This thermoplastic is practically unaffected by all alkahes and acids except fluorine and chlorine gas at elevated temperatures and molten metals. It retains its properties up to 260°C (500°F). Chlorotrifluoroethylene or CTFE (Kel-F, Plaskon) also possesses excellent corrosion resistance to almost all acids and alkalies up to 180°C (350°F). A Teflon derivative has been developed from the copolymerization of tetrafluoroethylene and hexafluoropropylene. This resin, FEP, has similar properties to TFE except that it is not recommended for continuous exposures at temperatures above 200°C (400°F). Also, FEP can be extruded on conventional extrusion equipment, while TFE parts must be made by comphcated powder-metallurgy techniques. Another version is poly-vinylidene fluoride, or PVF2 (Kynar), which has excellent resistance to alkahes and acids to 150°C (300°F). It can be extruded. A more recent development is a copolymer of CTFE and ethylene (Halar). This material has excellent resistance to strong inorganic acids, bases, and salts up to 150°C. It also can be extruded. 

Many engineering thermoplastics (e.g., polysulfone, polycarbonate, etc.) have limited utility in applications that require exposure to chemical environments. Environmental stress cracking [13] occurs when a stressed polymer is exposed to solvents. Poly(aryl ether phenylquin-oxalines) [27] and poly(aryl ether benzoxazoles) [60] show poor resistance to environmental stress cracking in the presence of acetone, chloroform, etc. This is expected because these structures are amorphous, and there is no crystallinity or liquid crystalline type structure to give solvent resistance. Thus, these materials may have limited utility in processes or applications that require multiple solvent coatings or exposures, whereas acetylene terminated polyaryl ethers [13] exhibit excellent processability, high adhesive properties, and good resistance to hydraulic fluid. 

Resistance to acid erosion depends on brand and varies from 0 04 to 0-54% per hour (Setchell, Teo Kuhn, 1985 Wilson et al, 1986a Walls, McCabe Murray, 1988). It would appear that cements based on copolymers of acrylic and maleic acids are less durable than those based on poly(acrylic acid). The extent of erosion varies inversely with the time allowed for the cement to cure prior to exposure (Walls, McCabe Murray, 1988). 

Table IV compares the X-ray exposure characteristics (at 8.3 X, Al Kai,2 emission line) of the halogenated resists and of PMMA Elvacite 20U1. It can be seen that poly(2-ehloroethyl methacrylates) and poly(2-bromoethyl methacrylates) exhibit a low sensitivity unlike poly(2-fluoroethyl methacrylates) and poly(2-, 2-,2-trifluoroethyl methacrylates) which are more sensitive than PMMA as shown in Figures 2a, 2b, 2c, 2d where the dose-thickness curves of these resists are plotted. The low sensitivity of the PC1EMA and PBrEMA samples may be explained by some competing crosslinking reactions which could occur during exposure as a result of C-Cl and C-Br homolytic bond scissions as noted by Tada...

Poly(butyl methacrylate) (PBMA) began to be used as a picture varnish in the early 1930s. It encountered a considerable success because of its resistance to yellowing, adequate flexibility, no dirt pick-up and good solubility in nonpolar hydrocarbon solvents. Products based on PBMA, such as Elvacite 2044 and Elvacite 2045 by Du Pont, were abandoned when it was discovered that under light exposure they cross-link to an unexpected extent becoming insoluble [64]. From this point of view acrylic copolymers based on methyl and ethyl acrylates/methacrylates show a much better long-term stability. 

Neanthes arenaceodentata is the most sensitive marine organism yet tested. In worms exposed to sublethal concentrations of CC6, feeding was disrupted after 14 days at 79 pg/L (USEPA 1980), reproduction ceased after 440 days (three generations) at 100 pg/L (Oshida et al. 1981), brood size was reduced after 309 to 440 days at 12.5 to 16.0 pg/L (Oshida et al. 1981 Oshida and Word 1982), and abnormalities in larval development increased after 5 months at 25 pg/L (Reish 1977). On the other hand, exposure for 293 days (two generations) in 50,400 pg Cr+3/L caused no adverse effects on survival, maturation time required for spawning, or brood size (Oshida et al. 1981). The poly-chaete Capitella capitata was more resistant than Neanthes, a decrease in brood size was noted only after exposure for 5 months to 50 and 100 pg Cr+6/L (USEPA 1980). 

A photooxidative scheme has been developed to pattern sub half-micron images in single layer resist schemes by photochemical generation of hydrophilic sites in hydrophobic polymers such as poly(styrene) and chlorinated poly(styrene) and by selective functionalization of these hydrophilic sites with TiCU followed by O2 RIE development. Sub half-micron features were resolved in 1-2 pm thick chlorinated poly(styrene) films with exposures at 248 nm on a KrF excimer laser stepper. The polymers are much more sensitive to 193 nm (sensitivity 3-32 mJ/cm2) than to 248 nm radiation (sensitivity -200 mJ/cm2) because of then-intense absorption at 193 nm. 

A photosensitive composition, consisting of an aromatic azide compound (4,4 -diazidodi-phenyl methane) and a resin matrix (poly (styrene-co-maleic acid half ester)), has been developed and evaluated as a negative deep UV resist for high resolution KrF excimer laser lithography. Solubility of this resist in aqueous alkaline developer decreases upon exposure to KrF excimer laser irradiation. The alkaline developer removes the unexposed areas of this resist. 

CEL dye. A CEL solution was obtained by dissolving poly(N-vinylpyrrolidone) (PVP) (7 g) and Dl (5.8 g) in 50 wt% aqueous acetic acid. (87.2 g). The CEL layer was spin-coated onto a photoresist, RI-7000P (Hitachi Chemical Co.), and baked at 80T for 20 minutes. Exposure was performed with an in-house i-line reduction projection aligner. The resist was developed in a 2. 38 wt% tetramethylammonium hydroxide aqueous solution. The film thickness was measured with an Alpha-step 200 (Tencor)... 

Photoacid generator. D1 (4 wt%) was mixed with poly(glycidyl methacrylate) (PGMA) (20 wt%) in ethyl cellosolve acetate. The mixture was spin-coated on a silicon wafer and baked at 80V for 1 minute. Exposure was performed with a 600-W Xe-Hg lamp in conjunction with a UVD2 filter. The resist was developed in a mixture of methyl ethyl ketone to ethanol (7/1 w/w). 

In another application, the diazonium salt (D1 or D2) (2.5 wt%) was dissolved in a mixture of cyclohexanone and acetic acid containing 12.5 wt% poly(4-hydroxystyrene) and 2. 5 wt% Methylone resin (GE 75108). The resist was exposed with a 600-W Xe-Hg lamp through a 313-nm interference filter. After exposure the resist was baked at 80V for 3 minutes and developed in a 1 wt% tetramethylammonium hydroxide aqueous solution. 

Figure 11. Exposure curve of the acid-catalyzed resist system consisting of poly(4-hydroxystyrene), D2, and...

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