Photosensitization photoresists

Dichromated Resists. The first compositions widely used as photoresists combine a photosensitive dichromate salt (usually ammonium dichromate) with a water-soluble polymer of biologic origin such as gelatin, egg albumin (proteins), or gum arabic (a starch). Later, synthetic polymers such as poly(vinyl alcohol) also were used (11,12). Irradiation with uv light (X in the range of 360—380 nm using, for example, a carbon arc lamp) leads to photoinitiated oxidation of the polymer and reduction of dichromate to Ct(III). The photoinduced chemistry renders exposed areas insoluble in aqueous developing solutions. The photochemical mechanism of dichromate sensitization of PVA (summarized in Fig. 3) has been studied in detail (13). 

Positive-Tone Photoresists based on Dissolution Inhibition by Diazonaphthoquinones. The intrinsic limitations of bis-azide—cycHzed mbber resist systems led the semiconductor industry to shift to a class of imaging materials based on diazonaphthoquinone (DNQ) photosensitizers. Both the chemistry and the imaging mechanism of these resists (Fig. 10) differ in fundamental ways from those described thus far (23). The DNQ acts as a dissolution inhibitor for the matrix resin, a low molecular weight condensation product of formaldehyde and cresol isomers known as novolac (24). The phenoHc stmcture renders the novolac polymer weakly acidic, and readily soluble in aqueous alkaline solutions. In admixture with an appropriate DNQ the polymer s dissolution rate is sharply decreased. Photolysis causes the DNQ to undergo a multistep reaction sequence, ultimately forming a base-soluble carboxyHc acid which does not inhibit film dissolution. Immersion of a pattemwise-exposed film of the resist in an aqueous solution of hydroxide ion leads to rapid dissolution of the exposed areas and only very slow dissolution of unexposed regions. In contrast with crosslinking resists, the film solubiHty is controUed by chemical and polarity differences rather than molecular size. 

Similar types of cross-linking reactions are observed for polymers to which photosensitive molecules ate chemically attached to the backbone of the polymer stmcture (Fig. 7). Radiation curing of polymers using uv and visible light energies is used widely in photoimaging and photoresist technology (Table 8) (58,59). 

Photopolymerizable coatings relief-image-forming systems, 6,125 Photoreactivity environmental effects, 1, 394 Photoredox properties bipyridyl metal complexes, 2, 90 Photoresist systems, 6,125 Photosensitive materials, 6, 113 Photosynthesis anoxygenic, 6, 589 magnesium and manganese, 6, 588 water decomposition models, 6, 498... 

These polymers need to be made photosensitive for use as photoresists and this is achieved by the incorporation of bisazide sensitisers. On exposure to light the photochemical reaction induced by the bisazide results in rapid crosslinking of the polymer rendering it insoluble in the developing solvent. 

Metal and polysilicon films are formed by a chemical-vapor deposition process using organometallic gases that react at the surface of the IC structure. Various metal silicide films may also be deposited in this manner by reaction with the surface of the silicon wafer to form metal silicides. Glass and pol3uner films are deposited or spin cast or both, as are photoresist films (those of a photosensitive material). This process is accomplished by applying a liquid polymer onto a rapidly rotating wafer. The exact method used varies from manufacturer to manufacturer and usually remains proprietary. 

Positive imaging techniques, 19 201 Positive ion spectroscopy, 24 107 Positive photochromism, 6 588 Positive photoresists, 20 280-281 Positive photosensitive polyimides,... 

The development of new classes of cationic photoinitiators has played a critical role in the production of highly sensitive, acid-catalyzed deep-uv photoresists. Sulfonium salts have been widely used in this respect (4). These materials are relatively easy to prepare and structural modifications can be used to produce desired wavelength sensitivity. Triphenylsulfonium salts are particularly well suited for deep-uv application and in addition can be photosensitized for longer wavelength. These salts are quite stable thermally and certain ones such as the hexafluoroantimonate salt are soluble in casting solvents and thus easily incorporated within resist materials. 

Polymethacrylates containing 6-cyanouracil or 5-bromouracil units in the side chain of the polymer displayed the highest photosensitivity. Copolymers of butadiene with the methacrylate monomer with pendant 6-cyanouracil are capable of resolving 1 o features and behaved as negative photoresists. 

Even if a same azide is used as the sensitizer, such properties of the photoresist as photosensitivity, photocurability and adhesion to base surfaces differ depending on the property of the base polymer. That is, degree of cyclization, content of the unsaturated groups and molecular weight of the polymer affect the photoresist properties mentioned above. H.L.Hunter et al. have discussed the dependence of the sensitivity of polybutadiene photoresist on the polymer structure, and have concluded that a higher sensitivity was obtained when 1,2- and 3, -isomers were used( 7.) ... 

The first modern day negative photoresists were developed by the Eastman Kodak Company which utilized cyclized rubbers and cinnamic acid derivatives as photosensitive crosslinking agents (42). The first commercially important photoresist based on this chemistry was known as KPR, which was of a cinnamate ester of polyvinyl alcohol. It was introduced by Kodak in 1954. 

The principles of photolithography are as follows Onto the surface of a semiconductor is spread a thin film of a photosensitive composition that consists of several chemicals. This composition is called photoresist and it is characterized by the effect that it changes its solubility upon irradiation. Thus, when the thin film is irradiated through a mask, the structure of this mask is projected onto the film which changes its solubility at the exposed segments. If the photoresist con-... 

Nonhnear absorption is the key mechanism responsible for 3D structuring of materials, including photoresists and photosensitive resins. Optical nonhn-earities take place when intensity of the irradiating electrical approaches that of molecular couphng, which occurs at the levels of approximately 10 ° V/m or 100 GW/cm. Detailed description of optical properties of polymers can be foimd in the literature [8]. Among the optical nonhnearities, multipho-... 

Title Adamantane Derivative, Process for Producing the Same, and Photosensitive Material for Photoresist... 

Research Focus Preparation of photosensitive adamantane resins for use in photoresists. Originality This is the first example of using dimethyl sulfoxide to prepare 3-... 

The basic steps of the lithographic process are shown schematically in Figure 1. The example shown corresponds to photolithography in which the photosensitive resist or photoresist is applied as a thin film to the substrate (Si02 on Si) and subsequently exposed in an image-wise fashion through a mask. The mask contains clear and opaque features that define the circuit pattern. The areas in the photoresist that are exposed to light are made either... 

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