Model resist development process

For many catalytic processes involving hydrocarbons the major deactivation pathway comes from the formation and deposition of carbonaceous species. Often referred to as coke, on many catalytic materials its deposition leads to transport resistances for reactants and products and blocks access to active sites. U nderstanding its rate of formation and impact on catalyst deactivation is of great importance in developing and modeling new catalytic processes. Developing a fundamental understanding of coke deposition enables the proper selection of catalytic materials and process conditions to minimize the impact of deactivation on a process. 

The origin of this phenomenon can he traced to the drying step of the liquid development process. During the development step, after the resist-patterned wafer has been contacted with the developer solution for a given length of time and subsequently rinsed with deionized water, the level of the rinse liquid at some point attains a condition similar to that shown in Fig. 11.45, where the space between adjacent resist lines is partially filled with fluid. The fluid meniscus exhibits a curvamre due to the differences in pressure across the fluid interface that result from surface tension in the confined space between the resist lines. Tanaka et al. developed a cantilever beam mechanical model for describing pattern collapse. The Laplace equation relates the pressure differential across the meniscus... 

In the frequency response method, first applied to the study of zeolitic diffusion by Yasuda [29] and further developed by Rees and coworkers [2,30-33], the volume of a system containing a widely dispersed sample of adsorbent, under a known pressure of sorbate, is subjected to a periodic (usually sinusoidal) perturbation. If there is no mass transfer or if mass transfer is infinitely rapid so that gas-solid mass-transfer equilibrium is always maintained, the pressure in the system should follow the volume perturbation with no phase difference. The effect of a finite resistance to mass transfer is to cause a phase shift so that the pressure response lags behind the volume perturbation. Measuring the in-phase and out-of-phase responses over a range of frequencies yields the characteristic frequency response spectrum, which may be matched to the spectrum derived from the theoretical model in order to determine the time constant of the mass-transfer process. As with other methods the response may be influenced by heat-transfer resistance, so to obtain reliable results, it is essential to carry out sufficient experimental checks to eliminate such effects or to allow for them in the theoretical model. The form of the frequency response spectrum depends on the nature of the dominant mass-transfer resistance and can therefore be helpful in distinguishing between diffusion-controlled and surface-resistance-controlled processes. 

The deprotection kinetics of alicyclic polymer resist systems designed for 193 nm lithography was examined using JR and fluorescence spectroscopic techniques. A kinetic model was developed that simulates the deprotection of the resists fairly well. A new, simple, and reliable method for monitoring photoinduced acid generation in polymer films and in solutions of the kind used in 193 nm and deep-UV lithography was developed. This technique could find application in the study of diffusional processes in thin polymer films. 

Reiser expanded the diffusion model for dissolution of novolac 13-24) using percolation theory (25, 2d) as a theoretical framework. Percolation theory describes the macroscopic event, the dissolution of resist into the developer, without necessarily understanding the microscopic interactions that dictate the resist behavior. Reiser views the resist as an amphiphilic material a hydrophobic solid in which is embedded a finite number of hydrophilic active sites (the phenolic hydrogens). When applied to a thin film of resist, developer diffuses into the film by moving from active site to active site. When the hydroxide ion approaches an active site, it deprotonates the phenol generating an ionic form of the polymer. In Reiser s model, the rate of dissolution of the resin. .. is predicated on the deprotonation process [and] is controlled by the diffusion of developer into the polymer matrix (27). 

A model was developed to analyze the conductivity of materials filled with conductive particles. This model was compared with experimental data for four commercial adhesives containing silver flakes. It was discovered that the resistivity is higher in the planar direction (thin films) than in three-dimensional space. Figure 15.5 shows the effect of carbon fibers obtained firom different processes on the elec-... 

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