Processing steps, resist

The blanket deposition is then sputter etched through a resist to pattern the metallisation. Selective deposition of W, under development, would deposit metal only in desired areas, and would reduce process steps and costs. 

In the processing of petroleum the first step is the removal of salt water. The presence of salt water in any processing steps would mean that expensive corrosion-resistant materials are required for those steps. This would greatly increase the price of the equipment (see Chapter 9). After removing the salt water, the next major separation is the crude still where the feed is split into six or more large-volume streams to reduce the size of future processing equipment. 

The chemically amplified resists reported here for deep-UV applications require a post-exposure thermal treatment process step to effect the deprotection reaction. This step has proven to be critical, and in order to understand the processing considerations it is instructive to discuss, qualitatively, the various primary and secondary reactions that occur with these systems during both exposure and PEB, ie ... 

Figure 1. The processing steps for a bilayer resist using 02-RIE.

Figure 1. Flow chart for a typical resist process. Steps in broken lines are not used for all materials.

Device defects stem from hardware, processes, and materials. Hardware-related defects include mask defects and contamination in the exposure environment. Those cauused by processing are determined by the cleanliness of the process and the number of processing steps. Material-related defects are caused by particulate matter in the resist or to the formation of unwanted insoluble particulate matter after the resist is coated and patterned. In summary, defects are generally caused by dirt and/or polymer particles, and great care must be exercised in eliminating unwanted contamination at every step in the lithographic process. 

Once a satisfactory film has been obtained, the coated substrate should be transferred to a suitable storage container and moved directly to the subsequent processing step, viz., prebaking. It is important that unbaked, freshly spun films not be stored for periods of time in excess of a few hours at this stage, since many resists are particularly vulnerable to particulate contamination. Once particles contact a resist surface prior to prebaking, they are almost impossible to remove and will cause opaque spots or pinholes after exposure and development. 

As in all processing steps, cleanliness of the exposure hardware is of paramount importance. Any particle that lands on the resist prior to exposure, will shield the film underneath the particle from the exposing radiation and give rise to opaque spots in the case of positive resist, or pinholes in the case of negative resists. Particulate contamination is especially troublesome with electron beam and ion beam systems where the probability of a particle landing on a substrate is increased relative to other techniques because of the much longer exposure times involved. 

Figure 13. Schematic of plasma-developed resist film composed of polymer host (P) and volatile monomer (m). Processing steps are (a) exposure which locks monomer in place, (b) fixing which removes unlocked monomer, (c) plasma development. (Reproduced with permission from...

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