Limitations pattern transfer processes

In the design of an industrial scale reactor for a new process, or an old one that employs a new catalyst, it is common practice to carry out both bench and pilot plant studies before finalizing the design of the commercial scale reactor. The bench scale studies yield the best information about the intrinsic chemical kinetics and the associated rate expression. However, when taken alone, they force the chemical engineer to rely on standard empirical correlations and prediction methods in order to determine the possible influence of heat and mass transfer processes on the rates that will be observed in industrial scale equipment. The pilot scale studies can provide a test of the applicability of the correlations and an indication of potential limitations that physical processes may place on conversion rates. These pilot plant studies can provide extremely useful information on the temperature distribution in the reactor and on contacting patterns when... 

Two general types of multilayer process may be distinguished, depending on whether they use oxygen reactive ion etching (RIE) (4) or optical exposure (5-11) to transfer the pattern into the resist. Optical pattern transfer may suffer from some limitation due to substrate reflections, but has an advantage in the simplicity of the equipment compared to RIE. 

While modeling approaches are inherently more desirable, empirical methods are presently the only approaches used. As indicated above, simulation of the atmospheric boundary layer is quite complex, requires substantial amounts of computing, and cannot currently predict with requisite accuracy. Our knowledge of turbulent diffusion, of the effects of terrain on ffow patterns, and of energy transfer processes is insufficient now to permit accurate predictions. Investigators have adopted the more reliable, but more limited, methods of interpolation and map construction to specify wind fields. Here, we discuss both approaches— numerical... 

In addition, aspect ratio considerations, dependent on mechanical stability and pattern collapse propensity of resist lines, limit the thickness of resists designed for these technology nodes to ultrathin resist thickness regimes ( 100 nm and lower). However, the aspect ratio considerations must be balanced against the etch stability requirements that ensure successful pattern transfer to underlying substrates in a device. Both the aspect ratio and etch stability requirements must be balanced against the intrinsic resolution, particularly pitch resolution, of the resist in question. Hence, there is a trade-off between aspect ratio requirements and etch stability requirements on the one hand, and pitch resolution on the other. Therein lies the motivation for these advanced resist-processing schemes. 

The most common method of pattern transfer to the substrate is by wet chemical etching. However, all semiconductor wet etching processes exhibit the same basic limitation. This limitation is due to the isotropy of the process, which makes linewidth control difficult for features less than 2 pm when thick substrate layers are used. The need to transfer fine features in thick substrates has led to the development of anisotropic etching techniques such as plasma etching, reactive ion etching (RIE) and sputter etching. 

In the case of HRP, kn/kp data for compound I formation are consistent with a partially rate limiting proton transfer. Hydrocyanic acid does not fit the pattern of the other ligands and its behavior may be rationalized as follows. The H2O2 molecule is bent which could facilitate a concerted process involving proton transfer and binding of the 00H residue. 

For a specific circuit design, there is often a question of the appropriate process sequence. Although the capabilities of imaging and the pattern transfer step dictate the overall limitations, the decision depends on the unique capabilities of the manufacturing line to be used. Some general considerations can clarify the true issues for most production situations. 

It is common for product designs to have a fixed pitch, whether it refers to the I/Os for direct chip or packaging attachment or to the spacing between PTHs. This space is often divided equally between conductors and spacing. For etching or pattern-plating processes, avoiding their respective resolution limitations can increase the pattern transfer yield. 

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