Search

Persistent surface morphologies in extruded polymer substrates can be generated in a first step by projecting a mask with argon ions and, secondly, by a consecutive exposure to solvent. In the first step, the polymer is locally cross-linked as a consequence of the interaction of the Ar-ions with -C-H-groups. During the second step, protrusions occur owing to swelling, which persist after removal of the solvent. The morphology of the protrusions can be tuned by choosing the right set of the experimental parameters, i.e. the ion dose, the size and distance of the holes in the mask, and their height by the duration of swelling.

The paper describes an electron beam lithography system for structures as small as 10nm and pattern samples produced on it. The system works with electron energies from 20keV down to 1keV. A special objective lens allows to realize probes of 5nm diameter for the lower energy range. Depending on how much energy is applied, the electrons will penetrate more or less deeply into the material. This may be used to create three-dimensional profiles in the resist. Provided in the system is a quasi-continuous path control to generate protracted curved structures with minimum edge roughness. Automatic marker detection algorithms and metric coordinate-control facilities enable the use of mix-and-match technologies.

The irradiation of polymer surfaces with ion beams leads to pronounced chemical and physical modifications when the ions are scattered at the atoms in the polymer chain. In this way, different products of decomposition occur. Here we show that by changing the ion fluence and the mass of the ion the local mechanical properties as Young's modulus of a polystyrene surface layer can be tailored. By annealing prestretched irradiated PS near the glass transition, surface rippling occurs in the irradiated areas only, which can be described with an elastic model. The moduli obtained from rippling periodicities and elastic model assumptions are in the range between 8 and 800 MPa at the glass transition and characterize the irradiated PS as rubberlike. From these values the network density and the molar mass of entanglement are quantified. The obtained network density equals the density of hydrogen vacancies generated through the scattered ions, as confirmed by simulations of the atomic scattering and displacement processes. The obtained molar mass of entanglement reveals that the PS locally was densely cross-linked. Our results show that even for nondiscrete layered polymer systems relevant polymer parameters can be derived from the well-known surface rippling without the need for costly chemical analysis.

We present a technique to fabricate polymer substrates with locally structured surfaces in the nanometer scale. By ion projection direct cross-linking the surface of a stretched polymer is locally cross-linked and afterwards annealed above the glass transition temperature to induce surface rippling. The rippling periodicity depends on the thickness of the cross-linked surface layer, formed through hydrogen vacancies, which are generated by the ion bombardment. We systematically studied the effect of the projectile mass on the hydrogen vacancy distribution in polystyrene (PS) samples. Simulations revealed a decreasing depth of the maximum hydrogen vacancy numbers by increasing projectile mass. This value can be correlated to the thickness of the cross-linked PS layer, which directly determines the ripple periodicity. An additional Au capping layer was used to further reduce the cross-linked layer thickness to a few nanometers. By this, defined structures with a ripple periodicity of 250 nm were fabricated. In addition, the technique allows inferring the Young’s modulus of thin cross-linked PS layers.

The electron beam induced metal deposition is a powerful technique to repair clear X-ray mask defects in the sub-μm range. The initial growth rate of dots deposited at 10 keV e-beam energy and 3 nA/μm 2 current density was 10 nm/sec. Dots of different heights were exposed to synchroton radiation. Dot growth times of 150 sec gave sufficient X-ray contrast for pattern transfer into HPR 204 resist. Mask repair is demonstrated on a test structure by closing clear defects and adding lines. The spatial resolution of deposited structures is ⩽ 500 nm with aspect ratios up to 6.