Resist novolac-based

Etching resistance = novolac based positive photoresists... 

While "conventional positive photoresists" are sensitive, high-resolution materials, they are essentially opaque to radiation below 300 nm. This has led researchers to examine alternate chemistry for deep-UV applications. Examples of deep-UV sensitive dissolution inhibitors include aliphatic diazoketones (61-64) and nitrobenzyl esters (65). Certain onium salts have also recently been shown to be effective inhibitors for phenolic resins (66). A novel e-beam sensitive dissolution inhibition resist was designed by Bowden, et al a (67) based on the use of a novolac resin with a poly(olefin sulfone) dissolution inhibitor. The aqueous, base-soluble novolac is rendered less soluble via addition of -10 wt % poly(2-methyl pentene-1 sulfone)(PMPS). Irradiation causes main chain scission of PMPS followed by depolymerization to volatile monomers (68). The dissolution inhibitor is thus effectively "vaporized", restoring solubility in aqueous base to the irradiated portions of the resist. Alternate resist systems based on this chemistry have also been reported (69,70). 

Figure 3 shows the sensitivity curves for SPP (solid lines) compared with that of a novolac-based resist (dashed line). From these curves, we obtained the maximum clearing dose (Dq), the dose for 50% thickness remaining (D50), and lithographic contrast (7-value). These resist characteristics are summarized in Table I. 

A higher sensitivity of SPP can be obtained using a more dilute TMAH solution, but at the expense of lower contrast. A solution more dilute than 0.6 wt% cannot completely dissolve the resist. The SPP exhibited a higher sensitivity and contrast than the novolac-based resist. 

Figure 3. Sensitivity curves of SPP image reversal (solid line) after 20kV EB exposure compared with a novolac-based resist (dashed line). A 0.3 //m thick resist layer was exposed to EB followed by a flood exposure using near UV radiation and then dip-developed in an aqueous THAH solution for 60 s at 25°C. TMAH concentration A 0.65 wt%, B 0.70 wt%, C 0.80 wt%, D 1.2 wt%.

Materials DNQ was synthesized by esterification of o-cresol formaldehyde novolac resin (Mw=900) and of l,2-diazonaphthoquinone-5-sulfonyl chloride. The esterification rate was ca. 0.4. The novolac-based resist used in EB lithography to compare with SPP was... 

Interest in solution inhibition resist systems is not limited to photoresist technology. Systems that are sensitive to electron-beam irradiation have also been of active interest. While conventional positive photoresists may be used for e-beam applications (31,32), they exhibit poor sensitivity and alternatives are desirable. Bowden, et al, at AT T Bell Laboratories, developed a novel, novolac-poly(2-methyl-l-pentene sulfone) (PMPS) composite resist, NPR (Figure 9) (33,34). PMPS, which acts as a dissolution inhibitor for the novolac resin, undergoes spontaneous depolymerization upon irradiation (35). Subsequent vaporization facilitates aqueous base removal of the exposed regions. Resist systems based on this chemistry have also been reported by other workers (36,37). 

Novolac- or phenolic resin-based resists usually show no pattern deformation induced by swelling during development in aqueous alkaline solution. Examples of such resists are naphtho-quinonediazide/novolac positive photoresists, novolac-based positive electron-beam resist (NPR) (1), and azide/phenolic negative deep-UV resist (MRS) (2). Iwayanagi et al.(2) reported that the development of MRS proceeds in the same manner as the etching process. This resist, consisting of a deep-UV sensitive azide and phenolic resis matrix, is also sensitive to electron-beams. This paper deals with the development mechanism of non-swelling MRS and its electron-beam exposure characteristics. 

However, the photochemistry itself does not make a relief image. Rather it is used to modify the solubility of the polymeric binder. The diazoquinone compounds used in resists are referred to as dissolution inhibitors or photoactive components (PAC s). The addition of a diazoquinone molecule dramatically inhibits the dissolution rate of a thin film of a novolac resin. Upon exposure, the dissolution rate of the novolac based resist is considerably faster than the rate for the novolac alone. The accelerated dissolution rate may be caused by formation of acid eind its subsequent ionization during development or by enhauiced diffusion of the developer into the coating because of changes caused by the formation and fate of the nitrogen (2). 

The first attempt to design a conventional photoresist resistant to RIE made use of trimethylsilylphenol (36), However, efforts to prepare an aqueous-base-soluble novolac from this monomer were frustrated by the hydrolytic instability of the bond between the aromatic carbon and the silicon atom. These problems were overcome by insertion of a methylene spacer between the aromatic ring and the silyl substituent. Thus, trimethylsilyl-methylphenol may be terpolymerized with ere sol and formaldehyde to afford stable, etching-resistant, aqueous-base-soluble resins see structure) (37). Formulation with a diazonaphthoquinone inhibitor affords a UV-sensitive resist (120 mj/cm at 405 nm) that acts as an etching mask for subsequent... 

Poly (2-methyl-1-pentene sulfone) may be used as a dissolution inhibitor to effect e-beam sensitivity (38). Trimethylsilylalkoxyphenol is another monomer that has been used in the preparation of oxygen-etching-resistant no-volacs for resist applications (39). For all of the novolac-based systems studied to date, the hydrophobic nature of the silicon moiety limits the incorporation of silicon to —10 wt %. However, this level is sufficient to allow use of these resins as oxygen RIE masks. 

DUV exposure of poly( p-substituted styrenes), such as poly( p-chloro-styrene), poly( p-chloromethylstyrene), and poly( p-hydroxystyrene) [poly(p-vinylphenol)] (structure 3.11), in air leads to photocross-linking and photooxidation. Consequently, DUV hardening is applicable to resists based on these polymers as well as novolac-based resists (168, 169). 

Novolac Based Positive Electron Beam Resist Containing a Polymeric Dissolution Inhibitor... 

A novolac-based positive electron beam resist has been investigated for use in direct device... 

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