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E-beam induced x-ray mask repair with optimized gas nozzle geometry

: Thiemann, M.; Brünger, W.H.; Kohlmann, K.T.

Microelectronic engineering 13 (1991), No.1-4, pp.279-282
ISSN: 0167-9317
International Conference on Microlithography: Microcircuit Engineering (ME) <16, 1990, Leuven>
Conference Paper
Fraunhofer ISIT ()

The deposition of tungsten by decomposing a W(CO) sub 6 precursor gas under a focussed electron beam is a promising technique for X-ray mask repair. A lateral resolution of 0,2 mym and a dot growth rate of 16 nm/s had been demonstrated in a simple experiment using a gas pressure cell inside a scanning electron microscope (1). For automated mask handling our SEM is now equipped with a gas nozzle arrangement (Micrion Corp.) with temperature controlled W(CO) sub 6 reservoir inside the vacuum system. With the common gas nozzle opening of 500 mym in diameter (2), the temperature of the reservoir could not be raised beyond 50 degree C because the corresponding gas flow deteriorated the vacuum in the system to a maximum allowed pressure of 1 - 10 high -5 mbar. At these conditions the resulting W deposition rates did not reach the values of the gas pressure cell experiment reported in (1). To increase the axial flux at constant total flux, the angular distribution of molecules leaving the gas nozzle was characterized for different nozzle geometries by calculation and experiment. Figure 1 shows growth rates of e-beam deposited dots versus the distance form the nozzle end to the mask surface was adjusted to 50 mym by a specially designed micromanipulator. A more direct measurement of the angular distribution of molecules leaving the nozzle was performed with a new micromechanical sensor using a thin Si cantilever which is bent under the impact of molecules (Fig.2). The carbon content of W-deposits has been investigated by Auger measurements for different conditions of molecular flux and current density of electron beam. As can be seen in Fig.1 best growth rates of 19 nm/s were found with the 80 mym wide conical gas nozzle which has less resistance to flow compared to the straight nozzle geometry. These findings demonstrate that the previously reported growth rates of gas pressure cell experiments can be reached or surpassed by gas nozzle arrangements with proper geometry.