Processing Latitude

In other work, the impact of thermal processing on linewidth variation was examined and interpreted in terms of how the resist s varying viscoelastic properties influence acid diffusion (105). The authors observed two distinct behaviors, above and below the resist film s glass transition. For example, a plot of the rate of deprotection as a function of post-exposure processing temperature show a change in slope very close to the T of the resist. Process latitude was improved and linewidth variation was naininiized when the temperature of post-exposure processing was below the film s T. 

As indicated above, one of the main attributes of acrylic PSAs is their broad formulation and processing latitude. While this is an important benefit to the end user, it also poses a significant challenge to the adhesive developer not only to understand what each component can do for the performance of the adhesive, but also on how to combine these components to get the best balance of properties. To help understand acrylic PSA formulation, one needs to know the major components and their impact on the PSA properties. 

To meet the products functional needs the wall thickness of the part can be varied. However, to obtain optimum processing cycles and reduce the chance of sink- and flow-mark formation, wall thickness should be kept as uniform as possible. Where variation in wall thickness is unavoidable, gradual transitions in the wall thickness should be provided to ease the polymer melt flow transitions. Part design, mold design, and gate location should work together to allow the material from heavier section into thinner walls for best appearance and process latitude. 

It is predicted that CEM techniques will extend resolution to feature sizes as small as 0.4X/NA, or -0.6 (tm for currently available exposure tools operating at 405 and 436 nm (91). The currently available materials afford improved resolution and yield, and increased process latitude (92). Further developments to achieve practical, water soluble systems plus a better match with the absorption characteristics of the resist would be desirable. 

Lithographic Characteristics. Based on the potential of crosslinker 3 to show high sensitivity and contrast and wide process latitude, it was of interest to evaluate its lithographic capability, using crosslinker 1 as the standard for comparison. Crosslinkers 1 and 3 (equal weight) were each incorporated into otherwise identical experimental AHR resist formulations. E-beam exposures were performed so that differences in DUV absorbance characteristics of the crosslinkers could be ignored. The e-beam sensitivities of the resists containing crosslinkers 1 and 3 were 6.2 and 4.2 (lC/cm2,... 

S. Pennington, S. Luce, Improved Process Latitude with Chemical-Mechanical Polishing, Proceedings of the VMIC Conference, pp. 168-172 Santa Clara, CA, June 9-10, 1992. 

Although DNQ-novolac systems were first used more that 40 years ago in the printing-plate industry, they continue to be the focus of significant interest. For example, several recent studies have addressed the optimization of novolac properties through manipulation of molecular weight, isomeric structure of the phenolic starting materials, and methylene bond position (26-28). These changes are reported to influence resist sensitivity, contrast, and process latitude. 

Postdevelopment Treatment. Descum. A photoresist plasma descum step is typically but not always used after development. This step removes unwanted resist residues that were not cleared out during development and, in effect, increases the process latitude of the occasionally troublesome exposure-development sequence. Likewise, the descum step can smooth out minor irregularities of the resist side wall. This mild plasma treatment is done with 02 or 02-CF4 gases with low power and pressure settings, short process times, or both. The same plasma under more-vigorous conditions may be used later to strip the resist at the end of the masking operation. 

Process latitude and substrate sensitivity Catalytic chain length for acidolysis, acid strength, protective group chemistry... 

There is relatively poor control over process variables with narrow process latitude New types of defects from CMP can affect die yield. These defects become more critical for sub-0.25 pm feature sizes... 

All future alternatives will require new resists and processes, and for the first time, manufacturing lines will be using at least two different resists. These new materials must have satisfactory sensitivity, resolution, and process latitude. In addition, the deep-UV tools will have limited depth of focus (1-2 (xm) and will be useful only with relatively planar surfaces. Multilayer-resist schemes have been proposed to overcome these limitations, and the simplest is the bilevel scheme that requires a resist that can be converted, after development, to a mask resistant to O2 reactive ion etching (RIE). Resistance to O2 RIE can be achieved by incorporating an element into the resist structure that easily forms a refractory oxide. Silicon performs this function very well and is relatively easy to include in a wide variety of polymer structures. 

PMMA offers several advantages as a resist. These include extremely high resolution, ease of handling, excellent film-forming characteristics, wide processing latitude, and ready availability. Unfortunately, PMMA is a rel-... 

Etch uniformity This has been highlighted under section 2.3.4. It is clear that for maximal process latitude the etch rate non-uniformity but also the tungsten thickness uniformity should be minimal. 

In this work, a quantitative evaluation method has been developed to measure photoresist sensitivity or speed (2,3) and process latitude (2,4) in order to compare positive photoresist performance under equivalent conditions. Performance data using this method will be reported and compared for an extensive group of first and second generation commercial photoresists. 

Cobilt Evaluations. The photoresist sensitivity, relative process latitude (RPL) and development information data is located in Tables I and II. The observed sensitivities atA= 0 range from... 

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