Lithographic performance

The third approach employs modifications of the polymer s physical properties and/or resist processing to minimize contaminant absorption, and is described in the section, "Polymer Properties and Lithographic Performance". 

Polymer Properties and Lithographic Performance in Chemically Amplified Resins. 

The polymer TBSS is known to undergo radiation induced chain scission and provides an improvement in the sensitivity compared to resists formulated with polymers which do not undergo chain scission. The lithographic performance of a resist formulated from this polymer and 2,6-dinitrobenzyl tosylate acid generator is reported. 

Much less work has been focused on the effect of polymer structure on the resist performance in these systems. This paper will describe and evaluate the chemistry and resist performance of several systems based on three matrix polymers poly(4-t-butoxycarbonyloxy-a-methylstyrene) (TBMS) (12), poly(4-t-butoxycarbonyloxystyrene-sulfone) (TBSS) (13) and TBS (14) when used in conjunction with the dinitrobenzyl tosylate (Ts), triphenylsulfonium hexafluoroarsenate (As) and triphenylsulfonium triflate (Tf) acid generators. Gas chromatography coupled with mass spectroscopy (GC/MS) has been used to study the detailed chemical reactions of these systems in both solution and the solid-state. These results are used to understand the lithographic performance of several systems. 

The PEB temperature and temperature uniformity must be tightly controlled for the same reasons discussed above. It has been found that it is feasible to drive the deprotection reaction in t-butoxycarbonyl protected systems to completion, providing the side reactions are minimized or controlled. This is a necessary requirement for satisfactory lithographic performance. 

The lithographic performance, as measured by sensitivity and contrast for the TBS, TBMS and TBSS polymers containing two onium salt AG systems and the tosylate AG is given in Table V. The absorbance of these films at 248nm was -0.3 im-1 in each case. 

TABLE V Lithographic Performance of Resist Systems Formulated with TBS, TBSS and TBMS Matrix Polymers and 5 wt% Tf, Ar and TS Acid Generators... 

TABLE VI Lithographic Performance of a 2 1 TBSS and TBMS Polymer with the Ts Acid Generator... 

Ultrathin LB PMMA and novolac/diazoquinone films have been demonstrated to act as high resolution electron beam and optical resists, respectively. Structural rearrangements in the LB PMMA films have been observed by using fluorescence spectroscopy. However, this rearrangement did not appear to influence the lithographic performance when seven or more layers of LB PMMA films were used as the resist. A more comprehensive study of the relationship between lithographic performance and LB film structure is currently underway. 

In addition, there are four other resist-related criteria, viz., adhesion, shelf life, supply and quality assurance that must be taken into account. Lithographic performance with respect to these parameters is dictated and/or limited by the hardware, materials, and processing used to generate the requisite pattern as summarized in Table I. 

TABLE V. Chemical and Physical Processing Variables that Affect Lithographic Performance. 

C The Improvement Era. The improvement era started in 1980 following major discoveries between 1978 and 1979. The siloxane system of Hat-zakis (7), though reported in 1981, is a unique and promising system. Therefore it was included in the renaissance era. The MLR systems have evolved into either RIE PCM or deep-UV PCM by this time and many of the researchers in this period have been more concerned with applying the MLR principle to improve lithographic performance. A list of the MLR systems reported in this period is shown in Table VIII. Because of the increased volume of publication in this period, the list is meant to be representative rather than exhaustive. 

We have seen that two important lithographic parameters of a resist are sensitivity and contrast. This leads to a consideration of the design features that must be incorporated into the resist in order to optimize these parameters and, in turn, requires a fundamental understanding of the interaction of radiation with matter and how the polymer molecular parameters affect lithographic response. These aspects have been extensively covered in the literature, (5,6) and only the conclusions relating to lithographic performance will be summarized. 

These different synthetic approaches result in structurally different materials and it is important to quantify these effects in terms of lithographic performance so that an optimum synthetic procedure might be identified. In particular, it is important to quantify lithographic performance as a function of the position of chlorine substitution on the polymer molecule. 

Chlorination. Chlorination conditions were varied to give a series of polymers with a range of chlorination for each base polymer. The degree of chlorination varied between 0.5 (15% w/w Cl) and 2.5 (44% w/w Cl) per monomer unit. Samples with approximately one chlorine per repeat unit (23.3% w/w Cl) were prepared in order to compare their lithographic performance with that of polychloromethylstyrene and chloromethylated polystyrene. 

In this paper we examine the effect of molecular weight on the lithographic performance of SNR with the objective of developing materials suitable for practical E-beam lithography and nanometer E-beam lithography using 2-level processing techniques. 

Three mixtures of CO-PNNA were blended together for analysis of lithographic performance. Compositions of 20, 33, and 50% CO by weight were blended by dissolution in THF to form a 13% (total solids) solution. Cyclohexanone was added to the blend to form a 7% solution to impart proper viscosity and volatility.for casting films. In the case of PNNA with N - 950 x 10, CO was dissolved in hot chlorobenzene and tnen mixed with PNNA (also in chlorobenzene). Solvent choice was a matter of convenience. 

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