Semiconductor lithography

The beginning of semiconductor lithography dates to 1957, when Andruss, using etch-resistant photoresist, successfully transferred patterns of a device into a 

Computing in a parallel universe, Am. Scientist, pp. 476 480 (Nov. Dec. 2007). Levinson, Private Communication (2007). 

Following exposure, the exposed resist film may be baked again, causing the catalytic photoacid generated from the photoactive compound contained in 

Whitesides and J.C. Love, The art of building small, Set. Am. Reports V7 ), 13 21 (2007) W.M. Moreau, Semiconductor Lithography Principles, Practices, and Materials, Plenum, New York (1988) L.F. Thompson, C.G. Willson, and M.J. Bowden, Introduction to Microlithography, 2nd ed., American Chemical Society, Washington, DC (1993). 

Resists function by radiation-induced alteration of the solubility of the materials. There are two basic classes of resist materials, namely, negative and positive resists (see Fig. 4.5). Negative resists become less soluble on exposure to radiation i.e., the unexposed areas can be selectively removed by treatment with an appropriate developer solvent. Positive resists selectively undergo an increase in solubility on exposure, enabling the exposed regions to be selectively removed in the developer. Both types of resists are formulated from polymers designed to have physical and chemical properties consistent with semiconductor 

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Moreau, W.M., Semiconductor Lithography, Principles, Practices, and Materials. Plenum, New York, 1988, pp. 1-79. 

Moreau, W. M. Semiconductor Lithography Plenum New York, 1988 pp. 68-73 and references cited therein. 

The photoresponsive properties of molecular glasses also have been applied in the design of resists for semiconductor lithography. In a resist, irradiation changes the solubility of the materials, making it more or less soluble (positive or negative resist, respectively). The search for new resist materials follows the development of lithographic techniques toward deep-UV and electron beam... 

W. Moreau, Semiconductor Lithography, Plenum Press, New York, 1988. 

Moreau WM (1988) Semiconductor lithography principles and materials, Plenum, New York... 

All books, reviews, and entries on CPs describe the potential applications. Chandrasekhar and others ° have reviewed in comprehensive fashion the applications of CPs, including batteries sensors electro-optic and optical devices microwave- and conductivity-based technologies electrochromic devices electrochemomechanical and chemomechanical devices corrosion protection semiconductor, lithography, and electrically related applications— photovoltaics, heterojunction, and photoelectrochemical cells capacitors electrolytic and electroless metal plating CP-based molecular electronic devices catalysis and delivery of drugs and chemicals membranes and LEDs. 

As stated above, this book attempts to systematically reappraise the main developments in chemistry and optics that have ultimately led to lithography as practiced today, especially in semiconductor lithography—the most advanced form of lithography. The task is no doubt an onerous one, but one that must be done in order to unearth the hidden connections between the various streams of thoughts that materialized as lithography and subsequently as semiconductor lithography. 

Figure 4.6 Evolution of semiconductor lithography. (Courtesy of R. Dammel.)...

It must he mentioned that SC CO2 has been touted as the solvent of choice for potentially replacing a few, if not all, wet processes in the semiconductor lithography clean room of the future because of a number of inherent advantageous attributes. It is nonhazardous and inexpensive. It has high diffusivity (very comparable to that of a gas), which may aid in rapid effective dissolution. It has no surface tension since its liquid and vapor state are not simultaneously present, which may thus aid in mitigating pattern collapse issues of high aspect ratio features. Its solution properties can be tuned with minor adjustments of temperature and pressure. 

In their search for higher-resolution resists and potential replacements for KTFR, lithographers tested many photosensitive coatings, one of which was the positive-tone printing plate material from the Kalle Company of Wiesbaden, invented by Oskar Siiss, and based on the DNQ-novolac resist system described above. This material turned out to be the first DNQ-novolac resist used in semiconductor lithography. 

This is the second chemical amplification resist invented for use in semiconductor lithography. Invented by Willson, Frechet, and Ito, the resist on exposure spontaneously and uncontrollably depol ymerizes in an exothermic reaction that is sufficiently energetic to evaporate the monomer. These inventors were unaware of a 3M Corporation patent on a similar concept, G.H. Smith and J.A. Bonham, Photosolubilizable compositions and elements, U.S. Patent No. 3779,778 (1973). 

The object of semiconductor lithography is to transfer patterns of ICs drawn on the mask or reticle to the semiconductor wafer substrate. The transfer is carried out by projecting the image of the reticle with the aid of appropriate optical elements of an exposure tool onto a radiation-sensitive resist material coated on the semiconductor wafer, typically made of silicon, and stepping the imaging field across the entire wafer to complete a layer. The shape of the IC pattern transferred to the wafer substrate is dependent entirely on the wafer layer being patterned. Examples of patterns include gates, isolation trenches, contacts, metal interconnects, and vias to interconnect metal layers. An advanced CMOS (complementary... 

W.A. Moreau, Semiconductor Lithography Principles, Practices and Materials, pp. 289 291, 651 665, Plenum Press, New York (1988). 

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