Deep-UV sensitivity

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 7. Deep UV sensitivity curves of SPP positive node (A) compared with that of SPP negative mode (B). In positive mode, a 0.4 izm thick SPP layer was exposed to deep UV and then dip-developed in a 1.6 wt% TMAH solution for 60 s at 25 °C. In negative mode, SPP was exposed to deep UV followed by a flood exposure using near UV radiation and then dip-developed in a 0.7 wt% TMAH solution for 60 s at 25 C.

The deep-UV sensitivity of PMMA, >1 Jem-2 (40), is also far from adequate to allow its use as a production scale UV resist. This is primarily due to the lack of... 

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. 

Photosensitizers can also be used to great advantage in multilevel photoresists. A typical system incorporates a long wavelength uv or visible light photosensitized resist on the top level and a deep uv sensitive resist on the bottom. Both resists may be based on cationic photoinitiators or one may be of this type while the other may be a conventional resist material. 

Fig. 156 Deep UV sensitivity curves of thermal development of poly(4-trimethylsilyl)-phthalaldehyde containing 1.2 and 4.8 wt% TPSOTf [334]...

Figure 4. Deep UV sensitivity curve of tertiary alcohol resist containing 4.75 wt% PhjS -SbFg...

Figure 12. Deep UV sensitivity curves of secondary alcohol resist containing 1.5 wt% PhjS -OTf.

A comparative study of polystyrene (PS) with bis(perfluorophenyl) azides 1-2 and the corresponding non-fluorinated bisazides 3-4 as deep-UV resists is reported. Inclusion of as low as 1.2 wt-% of 1 in PS led to 70% retention of thickness after photolysis and development. PS containing 2.4 wt-% of 1 is > 100 times more sensitive as a deep-UV negative resist than PS itself. The presence of 1 in PS also increased the contrast of the resist. On a molar basis, 1 was about 10 times as effective as non-fluorinated bisazide 3 in cross-linking PS while 2 was about 6 times as effective as 4. PS containing 2.4 wt-% of 1 was found to have a deep-UV sensitivity of 5-10 mJ cm and resolution of about 0.5 /tm. 

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