Poly(butene-1 sulfone) : A highly sensitive positive resist

The positive electron resist poly(butene-1 sulfone) (PBS) has been reported previously. As with other electron resists, sensitivity has been shown to be dependent on a number of processing parameters such as accelerating voltage, developer, developer solvent, and polymer characteristics (namely, molecular weight, molecular weight distribution, etc.). Previous reports have involved resist samples and conditions resulting in sensitivities within the range of 4--6x10-6 C/cm2 at 10 kV. For certain uses, for example, on the Bell Laboratories electron beam exposure system (EBES), a sensitivity of better than 1x10-6 C/cm2 at 10 kV is desired for efficient operation. Recent studies involving samples of varying molecular parameters verify feasibility of sensitivities of 7--8x10-7 C/cm2 at 10 kV for carefully controlled molecular weight and molecular weight distribution. As expected, processing of PBS at this sensitivity requires careful attention to polymer dissolution mechanisms. An ideal developing system should dissolve the irradiated region while hardly swelling the unirradiated region. This requires a developing solvent to be kinetically poor but thermodynamically good. Swelling and loss of resolution can occur when these conditions are not fulfilled