Robert H. J. Fastenau

On the low-temperature nucleation and growth of bubbles by helium bombardment of metals

Abstract A model for the nucleation and growth of helium bubbles at low temperatures is described. The model characteristics are based on recently published results of helium desorption experiments and on atomistic calculations, which indicate that mass transport is achieved by punching out and migration of self interstitials. Simulations are performed up to a helium content of 30 at % resulting in the prediction of the bubble density, bubble volume, fraction of helium in bubbles and point defect concentration. The results show good agreement with experiment and a possible mechanism of blistering is discussed.

Electron beam point spread function determination with a confocal scanning laser microscope

The confocal scanning laser microscope (CSLM) was utilized for the measurement of electron beam resist features in over‐exposed and normally exposed patterns. Using Fizeau interference, a well defined criterion for the location of resist sidewalls was obtained. Measurement of resist feature sizes in over‐ and normal exposed patterns, in combination with an accurate determination of the dose required to clear the substrate of positive resist, is shown to be very suitable for an accurate determination of the point spread functions in electron beam lithography. The point spread functions for 20 and 50 kV exposure of 0.5 and 1.0 μm thick resist layers were obtained for a variety of substrate materials; Si and GaAs wafers, an ‘‘x‐ray‐wafer’’ and Cr masks. Also the effect of resist tone on the point spread function was evaluated.

Scanning photon and scanning electron metrology on photomasks

Resist and chromium features on electron beam generated photomasks ranging from 0.4 to 10. μm were measured with a classical scanning slit optical microscope, a confocal scanning laser microscope and a low -voltage scanning electron microscope. The scanning slit microscope was used in a calibrated way. The results obtained with those instruments are compared mutually and with the designed values. The accuracy of the measurements is evaluated using a model for electron beam exposure of resist in order to explain trends observed in the measurements. The results show that these systems can be used for mask metrology of sub -micron features with mutual differences of about 10 nm. The resolution limit of the optical systems appeared to be 0.4 μm.