Microlithography development

Microlithography, Xerography. Because of their photosensitivity, polysilanes are under intense investigation for use as positive photoresist materials (94) (see Lithographic resists). They are particularly attractive because both wet and dry development techniques can be used for imaging (131,132). The use of polysilanes for xeroprinting has been reported (133). Thermal and optical sensors based on the photodegradation of polysilanes have been developed (134). 

The development and implementation of new resists for microlithography require considerable engineering development, and chemical engineering is central to that development. Many polymer systems have lithographic properties that appear to be useful for each of the lithographic options [12],... 

This historical development of the radiation technology of polymers is reviewed in this outline. The important applications of this technology are divided into two classes - large scale processes such as cross-linking of rubbers and plastics and specialized sophisticated processes such as microlithography. The initial fundamental studies that led to these applications are outlined and the slow process of commercialization is emphasized in this review. 

NTEGRATED CIRCUIT (IC) TECHNOLOGY has moved Steadily toward increasing circuit density and improved performance during its brief history. These improvements have been achieved through the development of the microlithography process, which now permits production of devices with feature sizes of 1 fim. Submicrometer devices are actively being developed, and production is expected later in this decade. 

Cole et al. (2001) reviewed physical models for most stages of the microlithography process. For the curing stage, they state that there has been no recent development of cure models since the work of Dill (1975). Dill (1975) presented models that incorporate both light absorption and photopolymer cure kinetics modelling, as shown by the following equations ... 

Resolution has become a crucial requirement for microlithography. It depends not only on material itself, but also on lithographic apparatus limitations, development processes and so many other complex factors. In designing a high resolution resist, therefore, starting material, or basic structure has to be chosen by an evidence of resolution capability. Low molecular weight (Mw = 3 x 10 0 poly(2-vinylnaphthalene) showed high resolution less than 0.1 p. m line on Si substrate by ordinary procedure. 

An alternative approach to the complicated photoresist systems could be the application of APD (ablative photodecomposition), where a strong absorbance at the irradiation wavelength is one of the conditions for successful ablation. A logical approach to the use of APD as a dry etching technique in microlithography is the development of polymers designed for APD. This is especially true for photolithographic applications that do not require a submicron resolution, such as thin film transistor (TFT) fabrication for liquid crystal displays (LCD) which require a resolution around 1 pm. 

This special volume Polymers and Light deals with very recent developments of photon interactions with polymers, in areas outside the scope of the familiar photoresist technique and optical lithography. Recent developments in microlithography still apply the same processing steps (irradiation of the photoresist through a mask followed by a subsequent wet chemical development step), but with new photoresist materials, and new irradiation sources, i.e. excimer lasers that emit in the UV, e.g. at 157, 193, and 248 nm. Excimer lasers are now the main photon sources for microlithography in many research laboratories and in industry. 

Miniaturization and mass production of biosensors could increase their availability and decrease their unit cost. Technologies such as microlithography, ultrathin membranes, and molecular self-assembly have the potential to facilitate the development and diversification a wide variety of biosensors. Miniature biosensors could be incorporated into food packages to monitor temperature stress, microbial contamination, or remaining shelf life, and to provide a visual indicator to consumers of product state at the time of purchase (3,51,52). 

FIGURE 15. Bilayer polysilane photoresist after exposure, development and oxygen plasma etching. Conversion of the polysilane surface to Si02 is evident. By courtesy of IBM Almaden Research Laboratories. Reprinted with permission from Materials for Microlithography, Am. Chem. Soc., Symposium Series. Copyright (1984) American Chemical Society... 

---