Sensitivities photo-resist material

The latest addition to this list of dry developing resist materials is a contribution from IBM s San Jose Research Laboratory (66-67) that evolved from efforts to design positive-tone resist materials that incorporate chemical amplification. These efforts were stimulated by the fact that the quantum yield of typical diazoquinones of the sort used in the formulation of positive photoresists is 0.2 to 0.3 thus, three or four photons are required to transform a single molecule of sensitizer. This places a fundamental limit on the photo-sensitivity of such systems. 

In order to circumvent this sensitivity limitation, the San Jose researchers sought to design resist materials that incorporate chemical amplification of the sort that characterizes the silver halide photographic emulsion system. In these systems a single photo event initiates a cascade of subsequent chemical reactions that ultimately result in the intended function. 

Wilkins and coworkers have redesigned both the sensitizer and the matrix resin (78-79). They have tested a variety of o-nitrobenzyl esters of cholic acid as sensitizers. These substances, like the diazoquinones, are insoluble in aqueous base but undergo a photo-reaction that yields base soluble products. The matrix resin chosen for the new sensitizer materials is a copolymer of methyl methacrylate and methacrylic acid that is far more transparent than novolac resins in the DUV. The new resist materials are reported to have useful sensitivity (ca. 00mJ/cm ) and extremely high contrast. The resist formulation is essentially aliphatic in nature and would be expected to be less stable to dry etching environments than the aromatic-based novolac resin materials (24). 

It is known that the diazo sensitizer is temperature sensitive and decomposes almost completely on heating above 110°c. for 30 min. The decomposition products in the presence of moisture (in the atmosphere) are nitrogen (N ) and indene acid, a base developer soluble material. On extended heating at higher temperature there is a marked decrease in the dissolution rate of both P(MMA)(see figure 1) and the photo resist (figure 2). 

In the case of a photoresist, the ultimate definable feature size together with the ability of the material to withstand either chemical etchants or plasma environments determines the domain of utility. The feature size is in turn determined by the wavelength required for exposure, the sensitivity and contrast of the resist, and the dimensional stability of the material during exposure, development, and subsequent processing. Adhesion of the resist to the substrate is critical both for patterning and use, and adhesion can be affected by surface preparations, and by residual stresses developed during deposition and cure. While photo-imagable polyimides have been introduced, their principal intended application is as a component of the finished part, either as passivant or interlevel dielectric (see below). 

Calix[4]resorcinare (1) and calix[4]resorcinarene dendrimer (2) were prepared as new photoresist materials. These compounds acted as excellent photoresist matrix with the photo acid generator, DIAS, and the cross-linker, MBP or BMHP. Both resists showed the high sensitivity and contrast such as 2.2 mJ-cm"2 and 3.1 for 1, and 2.3 mJ-cm and 17 for 2. 

The sensing element of an ER probe may be a wire, tube, or cylinder made of the test material. The principle of ER corrosion monitoring is based on measurement of electrical resistance of the sensing element. This is a function of its thickness, which dep>ends on how much corrosion it has experienced. The higher the sensitivity of the probe, the shorter its life. A cylindrical element probe with 25 mils life will take 20 h to detect a corrosion rate of 100 mpy. A tube element probe with 2 mils life will detect a corrosion rate of 100 mpy in 2 h. Thus, the thicker the probe element the less the sensitivity, but the longer the life, and vice versa. However, thicker element probes, such as cylindrical element, are less firagUe than thinner element probes, such as wire element. The maximum life of standard ER probes is 25 mils. See Fig. 6 for photo of an ER probe. 

Several combinations of chemical deposition process of the conductor materials and photo-sensitive resists have been tried. Unfortunately, there is no good combination that satisfies the needs for both high-resolutions and physical performances. Further improvement is required to have practical high density flexible circuits. 

Chemical additives are usually used for light-stabilization of plastic materials, while UV resistant coatings (e.g. clear polyurethane coatings) are applied for wood products protection, since photo-degradation processes cause increased water sensitivity and further their biodegradation under outdoor exposure conditions [32]. In most cases, it is preferable to use materials with greater resistance to UV radiation in order to prevent the increased damage of these materials under outdoor exposure to solar radiation. 

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