Contrast enhancement lithography

Contrast enhancement lithography is a clever procedure which uses a bleachable contrast enhancing layer to restore the distorted aerial image of the mask which has been blurred by diffraction effects into a sharp image at the underlying photoresist surface. The process is too complicated to explain in detail here and the interested reader is referred to the cited literature (60,61). Suffice it to say that the large extinction coefficients of most polysilane derivatives coupled with their ready bleachability make them ideally suited for such purposes and we have demonstrated this application at 313 nm (16,18). 

In recent years, demands on microlithographic techniques have become much more severe along with the reduced sizes of semiconductor devices. Various techniques to enhance the performance of microlithographic resist systems have been developed. Contrast enhanced lithography (CEL) is one... 

Water soluble aromatic diazoniim salts have been evaluated as photobleachable dyes for contrast enhancement lithography using a g-line stepper. The diazoniun salts used in this experiment are zinc chloride salts of 4-diazo-2-ethoxy- N,N-dimethylaniline... 

Contrast-Enhanced Lithography. Contrast-enhanced lithography is a clever technique that uses a thin layer of a bleachable contrast-enhancing layer coated over a conventional photoresist to sharpen the mask image. 

Figure 2.6. SEM images of 0.8-p.m lines and spaces printed with (right) and without (left) contrast-enhancement lithography. (Courtesy of Cliff Takemoto of National Semiconductor.)...

Diazo compounds are the photosensitive components for the contrast enhanced lithography (CEL) materials and the photoadd generator(PAG) for PS printing plates based on thermal crosslinking. 

Bendig, 1. Mitzner, R. Daehne, L. Lan,A. Pfeiffer,M. Rosenfeld,A. Wemcke,W.Contrast-enhancing photoresist for laser lithography containing reversible optical switching material. Ger. (East) DD 271969,1989 Chem. Abstr. 1990,112, 207961. 

The principle of contrast enhancement by photobleachable layers has been known in photography for quite a long time. New formulations were developed for application in lithography and used for the production of cathode ray tubes More recently, a family of arylnitrones have been investigated and described as effective contrast-enhancing materials (CEM) for use in IC-lithography The photochemical reaction which occurs is a cyclization reaction ... 

Normal CA resists shown in Chapter 2 are available for immersion lithography. However, significant improvements to immersion lithography are also expected when the refractive index (RI) of the resist is increased beyond the current average value of 1.65. Specifically, theoretical calculations have shown that an increase in the RI of the polymeric resist, to a value around 1.9-2.0, will result in an increase in the exposure latitude, contrast, and mask error enhancement factor (MEET), R(ACD f /ACD, ., i,). A. Whittaker et ai 10,11 have reported that the design and S3mthesis of novel polymers with increased RI achieved 193 resist formulations. An essential part of the discovery process is the use of quantitative structure-property relationship (QSPR) models to predict the RI of small molecules and polymers. ... 

In the last decade, several techniques have been developed in order to improve the resolution that can be obtained with optical lithography. This review describes a number of these techniques. Some techniques make use of a photosensitive layer on top of the photoresist, which results in enhancement of the contrast of the aerial image (Sects. 3.1.1 and 3.1.2). Other techniques use the possibility of slope control during development (Sects. 3.1.3 and 3.1.4). Also discussed are some techniques involving anisotropic plasma etching. 

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