Thin film dissolution behavior

Thin film dissolution behavior has been the subject of stuity for many applications. In the case of positive photoresists, a number of techniques have been used to characterize the kinetics of dissolution (1-12). The earliest such e q>eriments were performed by exposing the resist to a solvent for a fixed time and then measuring the thidmess of the remaining film (2). From repeated measurements of this type, a bulk development rate could be determined. 

A metal is passive if, on increasing its potential to more positive values, the rate of dissolution decreases, exhibiting low rates at high potentials (also known as thin film passivity). The anodic Evans diagram for this type of behavior is shown in Fig. 2. 

Thin films deposited by various techniques usually have preferential orientations, which have a significant influence on the electrochemical behavior of the material. For example, electrodeposited copper films on silicon wafers may have most crystal grains orientated in such a way that their (111) planes are parallel to the surface. Cu(lll) planes have a higher dissolution rate than Cu(lOO) planes in the active potential region of an electrochemical process. 

The theoretical equations for scissioning and crosslinking can be used to correlate the results of lithographic behavior of thin films on irradiation. The same deviations can be expected that are found wheat the equations are used for bulk samples exposed to gamma radiation. Positive resists of the type considered here depend on a change in dissolution rate, R, with polymer molecular weight, M. The form of the relationship between R and M is still a matter of some controversy. 

An alternative approach depicted in Figure 21.1.17 involves a sequential method where synthesized particles are coated with polymeric thin films by simultaneous nucleation of polymeric material out of a supercritical fluid, encapsulating the particles fluidized in the supercritical fluid, followed by further polymerization and binding of the encapsulating material on the particle surface. The method involves a recirculatory system that includes dissolution of the polymer in the supercritical solvent and coating the particles through a temperature swing operation in the fluidized bed that contains the particles. The particulate material coated with the tailor polymeric material possesses unique timed-re-lease characteristics, improved stability, and often-enhanced behavior. 

The dissolution behavior of P(la-aft-S02) was studied on QCM in a 0.21 N TMAH solution using thin films cast from ethyl lactate and baked at 130 °C for 60 sec. Figure 4 presents the dissolution kinetics curve of the polysulfone film. The 450-nm-thick film dissolved away in 0.15 sec, with an extremely fast dissolution rate of 30,000 A/sec, which was nicely observed by our QCM setup. The dissolution rate of poly(4-hydroxystyrene) (PHOST) in the same 0.21 N developer is in the range of 3000-200 A/sec depending on its molecular weight (27). Thus, the fiuoroalcohol polymer dissolves at least one order of magnitudes faster than PHOST, which was unexpected considering the similar pKa values of the fiuoroalcohol and phenol. In... 

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). 

Liu CP, Hsieh HJ, Li C, Chang KY, Yang CC. Dissolution of Cu nanoparticles and antibacterial behaviors of TaN-nanocomposite thin films. Thin Solid Films 2009 517 4956-60. 

Manjkow, J., Papanu, J. S., Soong, D. S., Hess, D. W., et al. (1987). An in situ study of dissolution and swelling behavior of poly(methyl methacrylate) thin-films in solvent/nonsolvent binary-mixtures. Journal of Applied Physics, 62(2), 682-688. 

In contrast to PPSu which is a new polyester, PCL is well-known and extensively studied polymer. It is also biocompatible and has found many applications in pharmaceutical technology and medicine. Thus, it was also an interesting idea to explore miscibility and biodegradation behavior of blends made of these two very important polyesters. PCL/PPSu blends with concentrations 90/10, 80/20, 70/30 and 60/40 w/w were prepared by solutioncasting [47]. Proper amounts of both polymers were dissolved in chloroform as common solvent, at room temperature. Sonication was applied in order to achieve complete dissolution and fine mixing of the components. The blends in the form of thin films (200-250 pm) were set up after solvent evaporation at room temperature, under a gentle air stream. They were characterized by DSC, WAXD, HNMR, SEM, and Tensile testing. Finally, their enzymatic hydrolysis was studied. The PCL/PPSu blend system however proved to be only partially... 

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