Radiation sensitization

The detector setup consists of four 256 x 256 pixel amorphous silicon technology sensor flat panels with 0.75 x 0.75 mm pixel size, having an active area of 192 x 192 mm [5j. These sensors are radiation sensitive up to 25 MeV and therefor well suited for detecting the LINAC radiation. The four devices are mounted onto a steel Irame each having the distance of one active area size from the other. With two vertical and two horizontal movements of the frame it is possible to scan a total area of about 0.8 x 0.8 m with 1024 x 1024 pixel during four independent measurements. 

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. 

Radiation sensitive cast polymers from DADC are also used in resists for microelectronic circuitry. Relief images result from differential rates of solution in alkali induced by exposure to high energy radiations. 

The anodized surface is often subjected to additional treatment before the radiation-sensitive coating is appHed. The use of aqueous sodium siUcate is well known and is claimed to improve the adhesion of diazo-based compositions ia particular (62), to reduce aluminum metal-catalyzed degradation of the coating, and to assist ia release after exposure and on development. Poly(viQyl phosphonic acid) (63) and copolymers (64) are also used. SiUcate is normally employed for negative-workiag coatings but rarely for positive ones. The latter are reported (65) to benefit from the use of potassium flu o r o zirc onate. 

Resists used to define circuit patterns are radiation-sensitive and may be either positive- or negative-working. As a result of the fine lines, there has been movement away from optical Hthography and iato the mid- or deep-uv regioas. Developmeatal work has also beea focused oa electroa beam, x-ray, and ion-beam exposure devices and resists (9,10). 

Not usually, sometimes from available core levels No, some beam damage to radiation-sensitive material... 

In general the nitroso rubbers also suffer from a poor resistanee to ionising radiation, sensitivity to degradation by organie bases, highly toxic degradation products and an exceptionally high cost. The advent of the rubbers based on perfluorofmethyl vinyl ether) considered above and of the phosphonitrilic elastomers considered below would appear to put the commercial future of these materials in extreme doubt. 

The radiation sensitivity of a substrate is measured in terms of its GR value or free radical yield, which is the number of free radicals formed per 100 eV energy absorbed per gram. The highest grafting yields will occur for polymer monomer combinations in which the free radical yield of the polymer is much greater than for the monomer. It also follows that the grafting yield will increase at a lower monomer concentration. 

There are a number of important factors that must be considered before applying gamma radiation-induced grafting. These factors include the radiation sensitivity of the polymer/monomer system, radiation dose and dose rate, type and concentration of inhibitor, type of solvent or diluent, and monomer concentration. The effect of such parameters on the grafting efficiency during mutual grafting is given below. 

During mutual graft copolymerization, homopolymerization always occurs. This is one of the most important problems associated with this technique. When this technique is applied to radiation-sensitive monomers such as acrylic acid, methacrylic acid, polyfunctional acrylates, and their esters, homopolymer is formed more rapidly than the graft. With the low-molecular weight acrylate esters, particularly ethyl acrylate, the homopolymer problem is evidenced not so much by high yields as by erratic and irreproducible grafting. 

The radiation sensitivity of polymers and monomers is characterized by a G value the number of radicals formed per 100 e.v. (16 aJ) absorbed. Radiation sensitive groups include -COOH, C-halogen, -S02-, -NH2 and -C=C, Radiation resistant groups are aromatic rings. It appears that the presence of aromatic moieties also offers some degree of radiation protection to the polymer chain as a whole. 

The most radiation-stable poly(olefin sulfone) is polyethylene sulfone) and the most radiation-sensitive is poly(cyclohexene sulfone). In the case of poly(3-methyl-l-butene sulfone) there is very much isomerization of the olefin formed by radiolysis and only 58.5% of the olefin formed is 3-methyl-l-butene. The main isomerization product is 2-methyl-2-butene (37.3% of the olefin). Similar isomerization, though to a smaller extent, occurs in poly(l-butene sulfone) where about 10% of 2-butene is formed. The formation of the olefin isomer may occur partly by radiation-induced isomerization of the initial olefin, but studies with added scavengers73 do not support this as the major source of the isomers. The presence of a cation scavenger, triethylamine, eliminates the formation of the isomer of the parent olefin in both cases of poly(l-butene sulfone) and poly(3-methyl-1-butene sulfone)73 indicating that the isomerization of the olefin occurred mainly by a cationic mechanism, as suggested previously72. 

Koch CJ, Biaglow JE (1978) Toxicity, radiation sensitivity modification, and metabolic effects of dehydroascorbate and ascorbate in mammalian cells. J Cell Physiol 94 299-306... 

These values may reflect either a radiation sensitivity or the presence of varying amounts of HMn(CO)j. 

We shall concern ourselves here with the use of an X-ray probe as a surface analysis technique in X-ray photoelectron spectroscopy (XPS) also known as Electron Spectroscopy for Chemical Analysis (ESCA). High energy photons constitute the XPS probe, which are less damaging than an electron probe, therefore XPS is the favoured technique for the analysis of the surface chemistry of radiation sensitive materials. The X-ray probe has the disadvantage that, unlike an electron beam, it cannot be focussed to permit high spatial resolution imaging of the surface. 

X-ray photoelectron spectroscopy is frequently applied in the fields of catalysis and polymer technology. It has poor spatial resolution, and is generally limited to homogenous samples. Radiation sensitive materials are more appropriate for XPS analysis, as the X-ray beam is less damaging to the specimen surface than the electron beam used in AES, partly due to the lower flux densities that are used. 

Poly silanes represent an interesting class of radiation sensitive polymers for which new applications have been discovered. 

Certain applications which are dependent on this radiation sensitivity are described. 

To date, we have exercised these materials in basically three types of multilayer lithographic applications (1) as short wavelength contrast enhancing layers, (2) as imagable 02-RIE resistant materials in bilayer processes and (3) as radiation sensitive materials for multilayer, e-beam processes. 

In summary, the polysilanes comprise a new class of scientifically interesting, radiation sensitive materials for which many applications have become recently apparent. There is every reason to believe that future investigations will continue to be scientifically rewarding and result in new applications. 

The high radiation sensitivity of substituted silane polymers is an interesting phenomenon upon which a number of current applications are based. Detailed... 

We acknowledge with gratitude the financial support of the Office of Naval Research for the radiation sensitive polymer research and the University of Massachusetts Institute for Interface Science and IBM for the surface active polymer research. 

Haley, N. F. Corbiere, S. L. Radiation-Sensitive Composition Containing a Resole Resin and a Novolac Resin and Use Thereof in Lithographic Printing Plates. U.S. Patent 5,372,907, December 13, 1994. 

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