Butene sulfone

The most radiation-stable poly(olefin sulfone) is polyethylene sulfone) and the most radiation-sensitive is poly(cyclohexene sulfone). In the case of poly(3-methyl-l-butene sulfone) there is very much isomerization of the olefin formed by radiolysis and only 58.5% of the olefin formed is 3-methyl-l-butene. The main isomerization product is 2-methyl-2-butene (37.3% of the olefin). Similar isomerization, though to a smaller extent, occurs in poly(l-butene sulfone) where about 10% of 2-butene is formed. The formation of the olefin isomer may occur partly by radiation-induced isomerization of the initial olefin, but studies with added scavengers73 do not support this as the major source of the isomers. The presence of a cation scavenger, triethylamine, eliminates the formation of the isomer of the parent olefin in both cases of poly(l-butene sulfone) and poly(3-methyl-1-butene sulfone)73 indicating that the isomerization of the olefin occurred mainly by a cationic mechanism, as suggested previously72. 

The high sensitivity of poly(olefin sulfone)s to chain scission by radiation was first discovered for poly(l-butene sulfone) and poly( 1-hexene sulfone) by Brown and O Donnell79,80. 

The G values for S02 and butene production from the irradiation of poly (1-butene sulfone) are shown in Figure 3 as a function of temperature from... 

Figure 3. Temperature dependence of the yields (G values) of S02 and butene from 7 irradiation of poly (1 -butene sulfone).

There is evidence that both ionic and free radical species are involved in the degradation and depolymerization of poly (olefin sulfone) s by high energy radiation (70). Thus, the yields of olefins from poly (1-butene sulfone) at 30 °C (the sample was heated to 70 °C during removal of the gaseous products) are shown in Table II. The butene is not solely 1-butene, but comprises significant proportions of all three isomers, 1-butene, 2-butene and isobutene. 

Table II. Yields of Butene Isomers from the Radiolysis of Poly (1-Butene Sulfone) at 30 °C...

Properties of Poly butene Sulfone Foam. Many properties of polybutene sulfone foam are similar to those of polystyrene foam. Mechanical properties are a little lower for the same foam density, but the bulk density of polybutene sulfone is 1.37 compared with 1.05 for polystyrene. Figure 6 shows that mechanical properties vary in the same ratio as density The insulating properties of polybutene sulfone foam are very good, somewhat better than polystyrene foam (Figure 7). Polybutene sulfone has a good solvent resistance as shown in Table I. In particular, styrene, benzene, and toluene do not attack polybutene sulfone but attack polystyrene. 

A Expanded polystyrene B Expanded poly butene sulfone... 

The Incorporation of a weak link In the main chain of a olefin sulfone copolymer such as poly - 1 -butene sulfone Is a recent example of po mers with high G value and high sensitivity 10 coul/sq. cm. 

We have found that poly(l-butene sulfone) with p-pyridine N-oxide as a sensitizer yielded positive tone polymer patterns in thermal development after UV light exposure through a conventional photo-mask with a cut-off wavelength of 300 nm. Poly(l-butene sulfone) was mixed with... 

The mass spectroscopic analysis of the gases formed in thermal development of the UV exposed poly(l-butene sulfone)/pyridine N-oxide revealed only 1-butene and S02 as the products, which indicated depolymerization of the polymer initiated by energy transfer form the sensitizer. These photosensitized poly(olefin sulfones) are not suitable for dry etching processes, and they are not reactive ion etching resistant. Resists made of poly(olefin sulfones) and novolac resins which will be described next are CF plasma etch resistant with reasonable photosensitivities. 

Figure 1. Dry developed images of poly(l -butene sulfone)/p-nitropyridine N-oxide.

Infrared studies of the radiation-induced degradation of PMPS by Bowden et al. (19) supports the oligomerization process and also shows that the oligomers can be removed by post-exposure baking. These effects have not been seen for other poly (olefin sulfone)s (2.3). Figure 8 and Figure 9 show the yield versus dose curves for irradiation of poly(l-butene sulfone) and poly (cyclohexene sulfone) respectively (20). No comparable shift of the S02/olefin ratio towards unity is observed in the radiolysis of these polymers. 

Figure 8. Yield (moles/kg) versus radiation dose (Mrad) for poly(l-butene sulfone). S02, and 1-butene, for irradiations at 0 and 50 °C.

The use of poly(olefin sulfones) in resist applications was first demonstrated by Bowden and Thompson at Bell lahoratories. They prepared them hy radical copolymerization of (liquid) SO2 with a whole range of olefins, at reaction temperatures deliberately kept low because of the low ceiling temperatures of poly(afk-ene sulfones). For poly(butene sulfone), Tc 64°C. The resulting copolymers possess a regular 1 1 alternating composition. 

Poly(l-butene sulfone) resist has been widely used in photomask manufacture since the 1970s and 1980s because it affords resolution down to about 500 nm (on the mask). It is marketed under the commercial name PBS and was extremely successful during this time. However, the performance of the resist in terms of etch resistance, resolution, and critical dimension linearity and uniformity was found to be inadequate as the industry migrated to much smaller critical dimensions that required dry etch processing of the photomask Cr. ... 

The most important commercial exploitation of this phenomenon has been the development of positive radiation resists for use in the semiconductor industry. A number of methacrylates and butene sulfones have been developed for these applications (42-44). Another important class of materials which undergo large-scale degradation of the main chain are the aliphatic polysulfones. For example, in 1981 Bowmer and O Donnell (45) examined the 5delds of a number of aliphatic polysulfones as a fimction of temperature and discussed these results in terms of the change in the equilibrium between polymerization and depolymerization as the ceiling temperature is approached. This aspect of radiation chemistry has had far-reaching consequences for our modem society. 

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