Near UV lithography

PHOST is the resin for deep UV lithography as much as novolac resins are for near UV lithography. All the advanced 248 nm chemical amplification resists, both positive and negative, are built on this structure at least in part. PHOST provides aqueous base developability, which is mandatory in today s semiconductor manufacturing, dry etch resistance, and high deep UV transmission. Because of its very important and unique role in chemical amplification resists and also in order to facilitate better understanding of the subsequent sections, this phenolic polymer is separately described. 

The concept was first demonstrated using poly(methylvinylsiloxane) as the top resist Meanwhile, many specially designed Si-containing resists have been demonstrated for application in the bilayer system but only a few of them are suited for near UV lithography. These resists will be discussed in some more detail in Sect. 8.3.2. 

Deep-W Lithography. The important issues for deep-UV lithography (200-250 nm) are aligner optics and resist materials. Problems in aligner optics stem from the decreased transparency of standard lens materials in this frequency range, which necessitates the use of more-expensive construction materials such as quartz. Typical near-UV positive resists are not useful for deep-UV lithography because of unacceptable absorption at... 

The conventional bilayer resist systems in which the top imaging layer (typically organosilicon polymer) also serves as an etch mask was first proposed by Hatzakis et al. in 1981, ostensibly for electron-beam lithography. Since then, a number of organosilicon resists for bilayer resist systems have been reported for use in near-UV, DUV, mid-UV, electron-beam, and x-ray applications, a good review of which has been provided by Ohnishi et al. In recent times, negative-tone resist systems and processes based on silicon-backbone polymers such as polysilanes,polysilynes, and plasma-deposited polymers have been developed for 193-nm lithography. 

Lithographic methods (near-UV photolithography or electron beam lithography) can also yield topologies at this size scale. The latter technique does not need a mask and can produce array features of 30-40 nm in dimension (Norman and Desai 2006). 

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