Photolithography, improvements

Before photolithography, a photoresist film is usually spin-coated on glass. To improve the adhesion of photoresist on glass, it is first spin-coated with a film of hexamethyldisiazane. On the other hand, to coat photoresist on glass plates with holes, the glass should be dip-coated [103-105]. 

The plastic film with interconnection layers, denoted (2) in Fig. 16.1, can be made by a process similar to that used to manufacture flexible circuit boards. First, plastic films coated with copper foil are processed by a numerically controlled (NC) drilling machine to make via holes. Plating is then used to make interconnections between top and bottom sides though via holes. Finally, the copper layers are patterned by conventional photolithography and etching. Gold plating is occasionally employed to improve electronic interconnections. 

The influence of interface area on Voc is utilized in high efficiency crystalline silicon solar cells with the so-called point contact concept to increase the open circuit voltage by suppressing area related recombination [149], Recently, the point contact concept has been applied also in pc-Si H solar cells using photolithography or self-organized zinc oxide etch masks [150], However, so far Voc improvement could not be demonstrated. For more details of preparation and application of ZnO etch masks the reader is referred to the original work [118]. 

Perfluoroacetal or perfluoroketal polymethacrylates containing norbornene substituents and having improved transparency were prepared and were suitable for use in photolithography with far-ultraviolet light at a wavelength of 180 nm or shorter. These materials are particularly useful in the formation of a fine resist patterns. 

A norbornene terpolymer containing a lactone or sulton substituent has been prepared that is effective in photoresist compositions in the 193 and 157 nm ranges in photolithography. An improvement in etch resistance was also observed. 

Design and fabrication of the objects The design and fabrication of the individual objects are two important and closely related problems in this area. Useful techniques for fabrication include the combination of photolithography and electrodeposition of metals (this technique was employed to make the objects in Figure 15B), the use of a mold (this technique was employed to make the objects in Figure 15C), soft lithography, synthesis of colloids, and reactive ion etching. Improved techniques will be needed in the future to make complex objects on a nanometer and micron scale. 

Three kinds of water soluble diazoniun salts were evaluated as photobleachable dyes for the enhancement of contrast in photolithography. CEL layers formed from these deazoniim salts and polyvinyl pyrrolidone have good optical characteristics and they can improve the ability of the conventional photoresist. 

In current semiconductor fabrication, photolithography with 193 nm UV irradiation is able to pattern features that are 37 nm wide. However, the rapid miniaturization of ICs demands improvements in photolithography in order to sharpen the line resolution at size regimes far below 37 nm (Figure4.30). Although immersion lithography has been suggested as a candidate for sub-50-nm line resolution, there... 

Forty years ago, someone interested in owning a computer would have paid approximately 150,000 for 16 megabytes of random-access memory that would have occupied a volume the size of a small desk. Today, someone can buy eight times as much computer memory for 20 and fit the chips into their shirt pocket. The difference between then and now is due to improvements in photolithography, the process by wdiich integrated-circuit chips are made. 

The need for an ever-increasing resolution in photolithography has resulted in an ongoing improvement of laser systems which have replaced UV lamp systems for high-resolution applications. The decrease of the irradiation... 

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