Photoresist negative tone

A new family of perfluoroacrylate and methacrylate based positive and negative tone photoresist compositions activated at 193 run has been prepared by free radical homo-or co-polymerization of acrylate or methacrylate derivatives. Polymeric agents prepared in this manner had Mn s between 5,000 and 50,000 daltons and were readily soluble in organic solvents. 

Polymeric positive and negative tone photoresists activated at 193 nm were prepared using methacrylate monomers, (I-VI), and are illustrated in Table 1. 

Fig. 2 Typical exposure or characteristical curves, do is the maximum thickness of a resist layer (A) a negative tone photoresist (B) a positive tone photoresist.

CD Photoresists using step-wise photoreaction. Manufacturing process of silicon semiconductor integraed circuit by using negative-tone photoresist... 

Thermolysis of esters can be catalyzed through H+ 3. These protons may be created from several photo acid generators (PAG) through UV-irradiation (e.g. by photolysis of onium salts ). Due to the changes in solubility such systems work as negative tone photoresists. Furthermore this method can be used to build semiconducting structures in a nonconducting matrix. In this paper we present our first results of these experiments. 

Another example of a negative tone photoresist uses poly(vinyl cinnamate). The first step in the formation of an insoluble polymer is the esterification of poly (vinyl alcohol) (PVA) with cinnamate groups to yield poly(vinyl cinnamate) (Scheme 13.2). 

The alkene groups of the cinnamate moieties subsequently undergo a [2 -I- 2] cycloaddition reaction under irradiation (Scheme 13.3). This cycloaddition results in a cross-linked polymer suitable as a negative tone photoresist [4]. 

A well-known example of the chemically amplified process uses a t-Boc-sty-rene polymer. Exposure of this polymer in the presence of an acid catalyst results in the protecting t-Boc groups decomposing to carbon dioxide and isobutylene, both gases that subsequently leave the coating (Scheme 13.6). The de-protection reveals phenolic moieties, which are soluble in aqueous base. This material can thus function as a negative tone photoresist [16]. 

FIGURE 26.2 The photolithographic process sequence for positive and negative tone photoresists. (Reprinted by permission of CG.Willson, Introduction to Microlithography,Theory, Materials and Processing, AC5 Symposium Series219,Washington, D.C., 1983, p. 89.)... 

Figure 4.42. Molecular structures and photoinduced reactions of common photoresists. Shown are (a) the diazonaphthoquinone (DNQ) positive tone photoresist, and (b) the SU-8 epoxy-based negative tone photoresist.

To study this possibility, a thin film (ca. 200 nm) of Co-PFS on Si substrate was exposed to near UV radiation (k = 350-400 nm, 450 W) for 5 min. The exposed film was developed in THF before characterization. Co-PFS was found to be a negative-tone photoresist. This appears to be consistent with photo-initiated crosslinking mechanism of acetylenes in the presence of metal carbonyls. However, it is also possible to have crossUnking in Co-PFS as a result of decarbonylation of the Co-cluster. The thickness of the film before and after UV treatment was determined by eUip-sometry. A 200-nm-thick film of Co-PFS had a thickness of ca. 170 nm after expo-sme to UV radiation and solvent development. The decrease in thickness is probably a reflection of the decreased volmne of the polymer upon crosslinking. 

---