Mask making

Another class of "chain scission" positive resists is the poly(olefin sulfones). These polymers are alternating copolymers of an olefin and sulfur dioxide. The relatively weak C-S bond is readily cleaved upon irradiation and several sensitive resists have been developed based on this chemistry (49,50). One of these materials, poly(butene-l sulfone) (PBS) has been made commercially available for mask making. PBS exhibits an e-beam sensitivity of 1.6 pC cm-2 at 20 kV and 0.25 pm resolution. 

However, the pinhole density in the imaging layer has to be reduced. This can be done by searching among all the commercial novolak - based resists for an acceptable candidate or by setting an MLR specification for resist vendors improve their quality control. Because thin resists have been used for mask making with an acceptable defect level, no fundamental pinhole problem is anticipated. 

EBES-like systems are used extensively for mask making. They can make masks with dimensions as small as 0.5 jxm, and 3a overlay accuracy approaching 0.1 jam. They generally use a small round beam, although shaped beam versions have also been described (40). 

In spite of the large amount of work over the past ten years, the ideal resist is yet to be developed. Most materials are deficient in one or more requirements so that resists have tended to be designed for specific applications such as mask making and usually for a specific set of exposure conditions dictated by machine design. For example, the electron beam mask maker EBES, designed at Bell Laboratories, requires resists with sensitivity better than 10-6 C/cm2 at 10 kV for maximum machine throughput. 

Bi>m materials and proeatse mnm materials and processes Mask making resists... 

Charged beam materials ana processes Nanxiw Mask making resists and processes Options... 

EUV materials ar d processes (UTR) Charged beam materials and processes Innovative beam materials and processes Mask making resists and processes... 

Economical mask-making using desk-top publishing is described at http //fas.sfu.ca/-ensc/research/groups/micromachining/file2.html by M. Parameswaran... 

The 1X, fully reflecting systems demand 1X masks. Hence, even if the NA of such systems can be increased sufiiciently to provide submicrometer printing capability in the DUV, the fabrication of full-field 1X masks with accurate, defect-free submicrometer dimensions would require enormous improvements over the state of the mask-making art. Therefore, a reduction lens system of some sort will likely become the dominant approach. 

It should be recognized now that the mask making, the selection of the polarity, and the relation of the photoresist are intimately related. 

Because of the above limitations of PBS and SNS resist systems, poly(chloro-acrylate-co-a-methylstyrene) (XXVIII) resist was developed at Nippon Zeon in the 1990s. Based on chain scission events, the resist has found wide acceptance in mask-making applications, particularly for device design rule <180 nm at doses of 8 p.C/cm on 10 kV electron-beam exposure tools. It is marketed under the brand name ZEP. In spite of the widespread acceptance... 

Microlithography mask making, VLSI Research Inc. Report (1992). 

While the original pattern-generation tools of the early 1970s were optical systems, in 1974, AT T BeU Laboratories introduced an electron-beam direct exposure mask-making system called MEBES," which was subsequently licensed to ETEC for commercialization. By 1980, electron-beam mask writers became... 

The mask-making process consists of generating the pattern of the circuit on a chrome-covered quartz plate coated with a resist film. There are four types of equipment used in writing mask optical pattern generators, electron-beam writers, focused-ion-beam writers, and laser writers. Lithographic exposure of the resist-coated, chrome-covered quartz plate involves the repeated exposure of the circuit pattern with a stepper or a scanner. In earlier times, lithographic... 

Typical optical and laser writer mask-making resists include 895i from ARCH (formerly OCG and now Fuji Films) and iP3500 from TOK for 364-nm exposure systems. Typical resists for electron-beam writers include poly(butene-l-sulfone) (PBS) developed at Bell Laboratories, EBR-900 Ml (novolac-based resist) from Toray Industries, ZEP 7000 from Nippon Zeon, and KRS-XE from IBM. ... 

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