A Soluble Polydiacetylene, P4BCMU, As a Negative Electron Beam Resist

The polydiacetylene with urethane substituents, P4BCMU, has been investigated under e-beam irradiation. A thin, ∼ (100nm), coating can be applied to a silicon wafer by spin coating from a solution in chloroform. E-beam exposure of around 20μC/cm2 renders the polymer insoluble and resistant to a CF4/O2 plasma etch and a RIE with freon 112. Features down to .2μm have been drawn and etched in this way. X-ray Photoelectron Spectroscopy indicates only a slight change in stoichiometry and suggests the irradiated polymer has tertiary amide characteristics. Fourier Transform Infra Red and Raman spectroscopies indicate that the unsaturated carbon bonds in the backbone of the polymer are not destroyed by e-beam irradiation. Rather the main changes occur in the N-H and the C=O (carbonyl) bonds of the urethane group.