Resist developing conditions

A further development is the use of a combined chromium-nickel-chromium or nickel-chromium-nickel-chromium deposit on steel- or zinc-base alloy articlesAn advantage of this system is that the first chromium layer need not be plated within the bright range of the chromium bath, so that plating can be carried out under conditions giving deposits of maximum corrosion resistance such conditions do not coincide with those under which fully bright chromium plate is obtained. 

In order to determine the appropriate development conditions, we examined dissolution characteristics for resist films in the aqueous alkaline developers by measuring film thickness as a function of development time. In Figure 7, dissolution characteristics for the new resist before and after exposure to KrF excimer laser are compared with those for the styrene resin matrix. 

Electron Beam Lithography. LB PMMA films with thicknesses of 6.3 nm (7 layers) are sufficient for patterning a Cr film suitable for photomask fabrication. For ultrathin PMMA films the resolution (see Fig. 1) is limited by the smallest spot diameter available on MEBES I (1/8 pm). However, it is not possible to obtain this resolution if a thicker resist (>100 nm) is used under the same exposure and development conditions, which demonstrates that ultrathin resists are able to minimize the proximity effect. Also, since the radius of gyration of 188,100 Mw PMMA is about 10 nm in the bulk, and the thickness of the 7 layer film (6.3 nm) is less than 10 nm, it is reasonable to assume there must be an alteration of chain configuration in the ultrathin films. This will be particularly true when the post-deposition baking temperature of the multilayer films is less than the glass transition temperature (115°C), as is the case for the present experiments. In such a case, interdiffusion of PMMA chains between the deposited layers may not result in chain configurations characteristic of the bulk. 

Alternating copolymers of N-allyl maleimide with a substituted styrene are promising negative working x-rav resists. These materials have sensitivities of 10-50 mJ/cm, providing a contrast of 1.5 or better, and appear capable of at least 0.5 m resolution. Further improvements in resist performance should be possible by optimization of polymer Mw and development conditions. 

Empirically it is known that effective drug concentrations are needed for at least 3 parasite-life cycles (=6 days) to obtain cure without recrudescence. By combining a drug with a fast action but short half life such as artemether and an agent with a slow action and long half life the treatment course can be short (2-3 days) which will benetit compliance, the patients condition will improve fast and resistance-development might be delayed. 

Variation of Cross-linked Methacrylate Resist Properties with Developing Conditions... 

IQiowledge of parameters such as reactivity ratios, is necessary for synthesis of polymer based resists, and an accurate method of analysis should be useful in various areas associated with resist development such as quality control. Raman spectroscopy provides a convenient, absolute, nondestructive method for compositional analysis of polymer systems which, if an internal standard is present, does not require standards of known composition or ancillary calibration curves. The accuracy, with appropriate selection of experimental conditions such as slit width and integration time, is limited only by the instrumentation. 

A variety of techniques have been used in the present work to establish the relative sensitivity of positive electron-beam resists made from copolymers of maleic anhydride (Table I). The term sensitivity is used rather loosely at times. In the most practical sense, sensitivity is a comparative measure of the speed with which an exposure can be made. Thus, the exposure conditions, film thickness, developing solvent and temperature may be involved. Most often, the contrast curve is invoked as a more-or-less objective measure of sensitivity. The dose needed to allow removal of exposed film without removing more than about 70% of the unexposed film can be a measure of sensitivity. The initial film thickness and the developing conditions still must be specified so that this measure is not, strictly speaking, an intrinsic property of the polymeric material. 

Many papers have been published on positive electron-beam resists. These resists are mostly polymers which are degraded upon electron-beam irradiation. The resulting lower molecular weight polymer in the exposed area can be selectively removed by a solvent under certain developing conditions. The development is accomplished by the difference in the rate of dissolution between the exposed and unexposed areas, which is a function of the molecular weight of the polymer. Recently, Willson and his co-workers reported the new type of positive resist, poly(phthalaldehyde), the exposure of which in the presence of certain cationic photoinitiators resulted in the spontaneous formation of a relief image without any development step (/). 

The human immunodeficiency virus (HIV) is one of only a few retroviruses known to infect humans. It is estimated that approximately twenty-two million people are now infected worldwide [1]. With only a tiny number of exceptions, infection ultimately leads to the development of the lethal condition of acquired immunodeficiency syndrome, or AIDS. To date, only a handful of drugs have been shown to have any effect on the course of the disease. These are, in general, relatively ineffective at significantly prolonging life, and drug resistance develops rapidly. Equally discouraging, vaccines have not yet been developed to prevent infection. 

Figure 3. Response curves for positive and negatives resists. Marked on the curves are incipient and completion doses, which indicate the onset and com-pletion of observable events. The variables monitored are film attrition for positive resists and film remaining for negative resists. These traces can be affected by a number of process parameters, particularly development conditions.

The ultimate test of usefulness is, of course, the lithographic performance of a resist. The often-quoted sensitivity of PMMA of 50 pC/cm2 assumes conventional developing conditions and is measured by competitive dissolution rates of exposed and unexposed films. A secondary measure of sensitivity for positive-working resists is the G(s) value, the yield of chain scissions per 100 e.v. of absorbed energy. In this case, mea-... 

Figure 2. Dependence of reduced resist film thickness after development on the radiation do e for PFCPM-3. Development conditions (up to 3 x 10 C/cm ) l min, fixture 1,4-dioxane/ 807. vol. heptane and (from 5 x 10 C/cm ) 2 min, 1,4-dioxane.

---