Resist resolution limit issues

Advanced Resist Processing and Resist Resolution Limit Issues... 

How the balance between the above-named requirements are struck in each of the major advanced resist-processing schemes in use today is discussed below, along with the advantages and drawbacks of each technique. In particular, we discuss the material basis of the resolution limit issues of resists, especially as they concern those based on chemical amplification systems, since these constitute the majority of resists in use in advanced lithographic processing today. 

The DQN resist system is able to resolve images much smaller than 0.5 Jim. Thus, the resists available today are not the limiting factor in defining device dimensions. In feet, the resolution limit that can be reached in a manufacturing environment is limited not by the intrinsic properties of the resist materials available but by the physical limitations of the exposure equipment and by practical issues that include contamination control, level-to-level alignment capability, etc. Consequently, resist materials research has been, and will continue to be, focused on devising material approaches to extending the resolution limits imposed by the physics of the available exposure equipment. 

ED paints may be thermally or photochemically cured for improved performance. None the less, it was some time before serious attempts were made to use ED photocurable films as resists for metal patterning. It had been foreseen that dry-film photoresists, which have been the mainstay of the printed circuit board inner-layer fabrication process for the last two decades, would soon reach their resolution limit and that a process that coated much thinner layers of resist would take over. ED resists that were capable of coating layers up to five times thinner than dry film seemed the natural successors. In 1986 the Rohm and Haas Co. [2] issued a patent describing a photoresist composition for cataphoretic deposition onto copper during the process of forming a printed circuit board. Many other patents in this field, describing both cataphoretic and anaphoretic deposition of a wide variety of resins, have been issued since then. 

Each approach has its characteristic advantages and disadvantages due to the underlying technology and the materials issues involved (see the remainder of this section). In contrast, SLR schemes are relatively simple processes, can have moderate levels of resolution and etch resistance, and good hnearity, but they suffer from reflective swing problems and small depths of focus, and are limited to low aspect ratios. Irrespective of the resist process approach chosen, chemical amplification continues to be the dominant exposure mechanism of the imaging layer. 

Finally, there has been some evidence that the coefficient for shear elasticity may be a function of the surface extension, increasing with increasing deformation. This was first proposed by Fischer in an effort to resolve discrepancies between theoretical predictions and observed behavior of red cells undergoing dynamic deformations in fluid shear [Fischer et al., 1981 ]. Increasing elastic resistance with extension has also been proposed as an explanation for discrepancies between theoretical predictions based on a constant modulus and measurements of the length of a cell projection into a micropipette [Waugh and Marchesi, 1990]. However, due to the approximate nature of the mechanical analysis of cell deformation in shear flow, and the limits of optical resolution in micropipette experiments, the evidence for a dependence of the modulus on extension is not clear-cut, and this issue remains unresolved. 

Until recently, temperature measurements in microfluidic systems were limited to measures of bulk fluid temperature at the inlet and outlet of microfluidic sections or simply measurement of the substrate temperature. With regard to local temperature measurements, thermocouple probes provide highly accurate measures of fluid and/or substrate temperature with excellent temporal response. However, thermocouples can often be physically intrusive and generally suffer from poor spatial resolution since most probes have a characteristic size of several micrOTs or more. Alternatively, microfluidic devices can be fabricated with integrated microscale resistance temperature detectors (RTDs s) embedded in the substrate with spatial extents on the order of a few microns [13]. Micro-RTDs overcome the intrusiveness issues of thermocouples however, their fabrication can be quite complex and RTDs still suffer from poor spatial resolution which limits their ability to resolve local thermal... 

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