Resist positive e-beam

Dry-etch selectlvlties for several negative e-beam resists are also listed in Table V. They are more resistant than the positive e-beam resists of the Table except PMCN and the positive photoresists, AZ2400 and PC 129. The positive-behaving vinyl polymer resists tested are generally less resistant than the negative-behaving systems. This generality, however, does not hold for the photoresists tested, as the data of Table VII verifies. 

We have also demonstrated other lithographic uses for polysilanes as nonimageable O2-RIE barrier layers (9), as short wavelength contrast enhancing materials (26) and more recently as sensitive, positive e-beam resists (36). 

Poly(methyl methacrylate) (PMMA) is the standard positive e-beam resist, usually purchased in two high molecular weight forms (495 or 950 kg moP ) in a casting solvent such as chlorobenzene or anisole. For example 950 kg mol PMMA, 4 % in anisole is a commonly used solution. Electron beam exposure breaks the polymer into fragments (as shown in Scheme 13.7) that can be dissolved in a 1 1 MIBK IPA developer (where MIBK is methyl isobutyl ketone and IPA is isopropyl alcohol). 

Fig. 36. Representative bilayer resist systems. Both CA and non-CA approaches are illustrated (116—119). (a) Cross-linking E-beam resist, 193-nm thin-film imaging resist (b) acid-cataly2ed negative-tone cross-linking system (c) positive-tone CA resist designed for 193-nm appHcations and (d) positive-tone...

Figure 11. A sensitivity plot for a positive-tone experimental e-beam resist. The data is from Figure 8.

Another interesting positive-tone polyacrylate DUV resist has been reported by Ohno and coworkers (82). This material is a copolymer of methyl methacrylate and glycidyl methacrylate. Such materials are negative e-beam resists, yet in the DUV they function as positive resists. Thermal crosslinking of the images after development provides relief structures with exceptional thermal stability. The reported sensitivity of these copolymers is surprising, since there are no obvious scission mechanisms available to the system other than those operative in PMMA homopolymer, and the glylcidy side-chain does not increase the optical density of the system. 

The etch rate measurements for positive and negative-behaving e-beam resists are found in Table V. It is apparent that the etch resistance is lower the more sensitive the positive resist. The exception would be PMCN, which exhibits better dry-etch resistance than that which would be predicted based on e-beam sensitivity alone. Where e-beam sensitivity and etch resistance are needed, copolymerization becomes very important. This has been demonstrated for the MCN/MMA and MCA/MCN model copolymer systems in references 9 and 10, respectively. 

As was mentioned previously, resists based on the acid-catalyzed deblocking of poly(f-BOC-styrene) have been used also as e-beam resists (68). In fact, these materials are capable of <40-nm resolution in both the positive and negative modes. The sensitivity of these resists is six times that of PMMA. 

Both negative and positive acting, oxygen RIE resistnt e-beam resist systems have been prepared through the incorporation of the trimethylsilylmethyl functionality into standard resist chemistry. Resins containing >10 wt% silicon display an RIE resistance more than 10 times greater than conventional photoresists and allow submicron pattern transfer with minimum linewidth loss. 

Earlier, (2) PMCA, -(CH2-C(C1)C02CH3 was reported to plasma etch at a rate greater than 1.8X Si02> and this was attributed to the weak C-Cl bond. PTCEMA has a PE etch rate ratio of 2.3, thus, the presence of the weak C-Cl bond at either the alpha-position or on the ester alkyl group apparently enhances the PE decomposition of these resists. To further study this phenomenona, the obvious system with both alpha-Cl and the trichloroethyl ester group, PTCECA, was synthesized and studied. As predicted, (see Table I) PTCECA and the 29/71 TCECA/MMA copolymer both etch faster than PMMA reference. These values are significantly larger than the desired less than one value. EBR-9, the Toray Japanese E-beam resist, is structurally similar to... 

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