Sensitivity lithographic

It can be seen in Table 1 that the lithographic sensitivity of the copolymers blended with 10% sulfonium salt increases as the percentage of latent electrophile (vinylbenzyl acetate) units is increased,. For a 50/50 copolymer the lithographic sensitivity is approximately 0.5 mJ/cm2 with a very high contrast of over 4. It should be noted however that aqueous development is no longer possible for the 50/50 copolymer for which some isopropanol must be added to the aqueous base developer. 

Table 1 Lithographic sensitivity and contrast data for various copolymers...

Table VI. Lithographic Sensitivity as a Function of the Amount and Position of Chlorine in Poly(styrene) Polymers...

There are two aspects of resist sensitometry 1) the measuiement of resist response to radiation which involves measurements designed to determine the intrinsic radiation sensitivity of the materials from which the resist is constituted and 2) lithographic sensitivity which is a measure of the efficiency with which these radiochemical conversions can be expressed in relief image formation. 

The measurement of intrinsic radiation sensitivity of various materials (defined by 0, Gis) or G(x)), in one laboratory correlates well with meas-urenients made in other laboratories. Measurement of lithographic sensitivity, on the other hand, is not nearly as precise. The literature is pervaded by papers describing resist sensitivity simply in terms of dose per unit area without the relevant experimental details. Interpretation of such results and their utility in comparing one resist with another demands extreme caution. 

Figure 29. The 15 kV e-beam sensitivity and the y-ray G(s) of a variety of PMMA analogs. Note that increasing G (s) is inversely related to the lithographic sensitivity.

The UV-insensitive Novolak resins are expected to be inert upon exposure. Despite this expectation, the selection of proper Novolak resins is very important for such overall resist performance as lithographic sensitivity, resolution, thermal image stability, adhesion, and so on. The reasons why Novolak resins are so important as resist materials and why specific kinds of Novolak resins are being investigated are the main subject of this paper. 

A lithographic sensitivity curve for PVTMSK is shown in Figure 6. The sensitivities for both deep-UV and mid-UV exposures were similar, although the deep-UV source emitted only —5% of its radiation at 365 nm. The range marked by an arrow denotes the radiation dose for which the partially developed film had a very rough texture. 

Figure 6. Lithographic sensitivity curve for PVTMSK exposed to deep-UV radiation. The pattern was spray developed for 10 s with 2-propanol at...

Table 7.4 Lithographic sensitivity of PMMA and derivatives. (Adapted with permission from Ref. 170. 1989 John Wiley Sons.)...

Models for Dissolution Rate. Unlike the senativiiy of typical negative resists, lithographic sensitivity for a positive resist depends on relative dissolution rates of exposed and unexpos areas. A numbin of studies have been reported on tiie effect of molecular weight, M, on rate of dissolution, R. 

Low Dielectric Constant Lithographic Sensitivity High Mechanicals... 

In simple terms the lithographic sensitivity of a resist is a measure of the exposure required to delineate the resist pattern. In practical terms, however, the actual exposure required depends on a wide number of factors so that figures quoted for the sensitivity of the same resist tend to differ between users, not least because they are defined in different ways. Naturally the sensitivity is primarily determined by the concentration and efficiency of the radiation-sensitive groups in the resist film be they sensitive to photons, electrons or otherwise and the nature of these groups will be described later for each lithographic system. In addition, however, the required exposure dose is affected by polymer parameters such as molecular weight, process details and the development process in particular. 

Also, it will be shown that the absorbance and lithographic sensitivity engendered in a typical t-BOC based resist by 1 and that of a model compound without the DISCA feature, 4-(methotycarbonyI)-2,6-dinitrobentyl totylate 2, are comparable to that found when using 2,6-dinitrobenzyl tosylate 3. 

Compound 3 and 2,6-dinitrobenzyl 4-nitrobenzenesulfonate 5 are two examples of PAG s which have been successfully used in chemicalty amplified r-BOC based resist systems (2). Table 1 shows a comparison of the absorbance at 248 nm of a 6 mole% solutions of these materials and 1 and 2 in acetonitrile. As can be seen the absorbance in solution of compounds 1 and 2 are somewhat lower than that of 3 and considerably lower than that of 2,6-dinitroben 4-nitroben-zenesulfonate 5. Table 1 also shows the absorbance per fim (ABS//u,m) of 1, 2 and 3 in a PTBSS polymer matrix. Since the ABS//tm of 1 and 2 are similar to 3 and the same acid is liberated in all three PAG s, it was eiq>ected (based upon our previously established relationship between the lithographic sensitivity and the product of the ABS/ju,m, , and catalytic chain length) (9) that the sensitivities of 1 and 2 should depend primarity on the relative values of the quantum yields. 

The matrix polymer chosen for the lithographic experiments was PTBSS. Compound 2 being incapable of undergoing acidolysis, but having the same o-nitrobentyl chromophore as 1, was used to determine whether lithographic sensitivity was affected by the presence of a t-butyl ester in a PTBSS matrix. Table 1 summarizes the results of lithographic sensitivity and contrast for 1, 2 and 3. 

The lithographic sensitivities of 1,2, and 3 are similar. This indicates that no significant competition occurs between the addolytic deprotection of 1 and PTBSS, and that the quantum yield for photogeneration of add in 1 and 2 are only slightly lower than 3 (0.16) (8), namely 0.11. 

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