Mask-making resists

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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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... 

The chemistry of negative tone and positive tone mask making resists is covered in Chapters 6 and 7, respectively. 

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. 

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. 

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... 

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... 

Practical Applications of X-Ray and EB Resists Today, EB lithography is applied industrially as the primary tool of choice for fabricating masks for other lithographies, and occasionally it is also used for the production of special microdevices. Commercially available resists that can be used for mask making are listed in Table 5.12. 

Kohlmann, K., Reimer, K., Dammel, R., Hessemer, W, Lingnau, J., Scheunemann, U., and Theis, J. (1989) E-beam application of highly sensitive positive and negative-tone resists for X-ray mask making. Proc. SPIE, 1089, 303. 

Masked exposure of a coating containing a polymeric binder, a polymerizable monomer and a photoactivated initiator can be used to make resist images. The coating can be prepared by solution evaporation or by lamination of a premanufactured film to a substrate. In the exposed areas the photolyzed initiator yields reactive species that initiate the polymerization of the monomer to form an interpenetrating network of the binder and the new polymer. The monomers that are used are... 

PMMA has been the most studied of the e-beam positive resist polymers. Images approaching 200 A have been resolved in PMMA. In addition, PMMA has excellent coating and development properties for resist applications. However, the low sensitivity of PMMA (8 x 10 Ccm at 20 keV) and the poor resistance to fluorine plasmas have minimized its use in practical applications other than mask making. 

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