Imaging Resist processing

After image transfer, the patterned resist must be readily and completely removable without substrate damage. The pattern often can be stripped from the substrate with a mild organic solvent. Proprietary stripper formulations or plasma oxidation treatments are utilized when the imaging chemistry or image transfer process has iasolubilized the pattern. 

Organosilicon polymers are especially important as imaging layers in bilayer resist processes(1). A wide range of organosilicon resist materials, in which the organosilicon compound has been incorporated either into the polymer main chain or into pendant groups, has appeared in the literature(2-8). However, almost all polymers have been... 

Depth of field depends on substrate reflectivity, the degree of partial coherence and the minimum feature size (5). In practice, however, the classical depth of field for the incoherent case (X-f2(N.A.)2) gives a reasonable approximation. Two layer resist processes in which the image is formed in a thin, flat, resist layer on top of a much thicker planarizing layer, alleviate the need for a large depth of field and make it easier to form high resolution, high aspect ratio, resist patterns (6,7). Satisfactory results can be obtained at contrast levels as low as 40%. 

Vital disadvantages in three layer resist (3LR) as MLR systems are a substantial increase in process steps and the need for the evaporation equipment that is used for forming the middle isolation layer. 3LR system consisting of a thin topmost imaging layer, a middle isolation layer and planarizing layer needs more than 11 steps to form a resist pattern (/). To minimize the processing steps, several materials for two layer resist (2LR) system have been proposed (4-8). A 2LR system can eliminate the middle isolation layer. It takes only 6 steps to accomplish the resist process and it is just a 2 step increase compared with 1LR system. 

X-ray lithography also takes advantage of the increased resist sensitivity due to the thinner imaging films of multilayer systems. Thinner imaging films further improve X-ray resolution by minimizing the penumbra effect, a problem associated with an uncollimated X-ray beam. Consequently, the oblique exposure of features near pattern edges are minimized by multilevel resist processes, thereby restoring the desired profile. 

Figure 6. Schematic of a trilevel-resist process, (a) The top imaging layer is separated from the bottom planarizing layer by a transfer (or isolation) layer, (b) The pattern of the top image is transferred into the isolation layer. (c) The top layer is removed, and the pattern is transferred from the isolation layer to the substrate through the planarizing layer, (d) The remaining planarizing layer is stripped to complete the process.

Bilevel Processes. A bilevel system consists of a thick resist at the base and a thin imaging resist on top. Many variations have now been reported. Conventional image transfer into the bottom layer is accomplished... 

In this review, tomography systems of capacitance (ECT), resistance (ERT), and positron emission (PET) are presented. Their applications in imaging industrial processes highlight the importance and advantages of each technique. However, the common favored advantage among the three techniques is their ability to provide non-invasive measurements of various processes. 

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