Dissolution, 4-hydroxystyrene-styrene

O-methylated PHOST [179]. This terpolymer was originally developed as a chemically amplified laser resist for circuit board application [180] and then as a single layer 193 nm positive resist [181], which will be described in more detail later. Another interesting three-component approach is the use of a N-acetal polymer as a dissolution inhibitor of poly(3-methyl-4-hydroxystyrene) [182]. A deep UV resist consisting of poly(3-methyl-4-hydroxystyrene-co-4-hydroxystyrene), poly(N,0-acetal), bis(arylsulfonyl)diazomethane, and a photobase was reported from Hoechst (currently Clariant). The function of the photobase is described later. A copolymer of 4-hydroxystyrene with styrene was also employed as a matrix resin. 

Figure 11.32 Dissolution rate curves for (a) an i-line DNQ/novolac resist, (b) a poly(hydroxystyrene)/melamine cross-linker resist (DUV 248-nm chemical amplification negative resist), and (c) poly(butylcarbonyloxy styrene-co-hydroxystyrene) (DUV 248-nm chemical amplification positive resist). The slope is the development rate log slope. ...

Copolymerization is the most important synthetic strategy available to tailor the physical, solution and mechanical properties of macromolecules. In this paper the synthesis of well defined random and block copolymers containing monomer units of very different polarity are described. Novel macromolecular architectures incorporating 4-hydroxystyrene, t-butylacrylate and styrene have been prepared to investigate the combined effects of macromolecular architecture and hydrophobicity on thin film aqueous base dissolution. 

Figure 7. Dissolution Rates of Random and Block Poly(4-hydroxystyrene -co-styrene) in 0.26 N TMAH...

Another very effective way to regulate the dissolution rate of photoresist polymers is copolymerization. Table 57.11 lists the physical properties of poly(4-hydroxystyrene-co-styrene) [35]. 

The copolymer architecture of poly(4-hydroxystyrene-co-styrene) was found to have insignificant effect on its dissolution rate (Fig. 57.5 Table 57.12) [36]. On the other hand, incorporation of inert styrene unit into poly(4-hydroxystyrene) drastically reduces dissolution rate. This method of incorporating inert unit has been employed to optimize the dissolution of base polymers for advanced DUV photoresists. 

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