Sensitivity thinning curves

Another useful contrast values are related to the resist chemistry in the film, which will subsequently affect the lithographic contrast. Sensitivity (contrast) curves similar to Fig. 3 can be generated by following the degree of reaction (deprotection, for example) with IR or by measuring thinning (in deprotection, for example) as the function of exposure dose. Comparison of a chemical contrast curve with a development contrast curve provides useful information on resist behavior, such as a degree of deprotection at E0. 

The first application of a quartz crystal for use as a nonisothermal thermobalance was reported by Henderson ei al. (66). This was accomplished through the use of a minicomputer to characterize the temperature-frequency relationship for the crystal and to correct numerically the frequency-temperature-mass relationship to obtain the TG curve of the sample. One advantage of such a system is that very fast heating rates may be employed due to small sample size (t-40 jug typical) and high sensitivity. Thin films of sample exhibit rapid gas diffusion and thus permit thermal equilibrium to be maintained at heating rates of l00°C/min or greater. Applications of this thermobalance include the evaluation of thin films and coatings as well as various polymer studies of pyrolysis, flammability, and so on. 

The surface forces apparatus (SEA) can measure the interaction forces between two surfaces through a liquid [10,11]. The SEA consists of two curved, molecularly smooth mica surfaces made from sheets with a thickness of a few micrometers. These sheets are glued to quartz cylindrical lenses ( 10-mm radius of curvature) and mounted with then-axes perpendicular to each other. The distance is measured by a Fabry-Perot optical technique using multiple beam interference fringes. The distance resolution is 1-2 A and the force sensitivity is about 10 nN. With the SEA many fundamental interactions between surfaces in aqueous solutions and nonaqueous liquids have been identified and quantified. These include the van der Waals and electrostatic double-layer forces, oscillatory forces, repulsive hydration forces, attractive hydrophobic forces, steric interactions involving polymeric systems, and capillary and adhesion forces. Although cleaved mica is the most commonly used substrate material in the SEA, it can also be coated with thin films of materials with different chemical and physical properties [12]. 

To add insult to injury, a new calibration curve will perhaps need to be constructed after each time the cell is dismantled if the internal geometry of the cell is particularly sensitive (cf. the in situ EPR cells (discussed in the next chapter) can be very thin). 

Measurements of the common physical constants such as boiling point or refractive index are not sufficiently sensitive to determine the trace amounts of impurities in question. Besides the common spectroscopic methods, techniques like gas chromatography (GC), high-pressure liquid chromatography (HPLC), or thin-layer chromatography (TLC) are useful. The surest criterion for the absence of interfering foreign compounds lies in the polymerization itself the purification is repeated until test polymerizations on the course of the reaction under standard conditions are reproducible (conversion-time curve, viscosity number of the polymers). 

In recent years, flyer plate shock sensitivity tests have begun to be used extensively. Basically these tests consist of propelling a thin plate against the expl sample. The variables in this test are plate velocity, plate material and plate thickness. The shock phenomena involved in the flyer plate expts are sketched in Fig 1. The plate velocity at impact is Ufs, the so-called free surface velocity. The intersection of the reflected characteristics of the shock Hugoniot of the plate material (drawn upwards from Ufs) with the P—u curve of the expl then gives the shock state in the expl at the impacted expl surface (P2, u2 in the example)... 

Films of PMMA with 20 to 30% poly(epi-chlorohydrin) require only 1/2 to 1/4 the exposure to produce patterns compared to PNNA alone. Thinning-exposure curves also suggest a sensitivity increase of 3 or 4 times. Contrast suffers somewhat, but patterns are producible when a nitride-supported gold mask is used. 

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