Distribution and Apparent Source Geometry of Electron-Beam-Heated Evaporation Sources

Abstract

The distribution and apparent source geometry were determined for aluminum evaporation from a 12-kW 270° electron beam gun. The distribution was measured as a function of deposition rate for rates from 1000 to 50 000 Å/min, 20 cm from the hearth. These measured distributions and those from other workers can be described not by a simple cosine relation, as has been assumed, but by a relation of the form (1-A) cosn θ+A, where θ is the angle from the vertical. The coefficient A is the normalized magnitude of an isotropic component, and n is a rate-dependent beaming exponent. The apparent source geometry was measured using a pinhole camera technique. These measurements show the evaporant to originate from the area defined by the visual beam impact point at low-to-moderate rates, and additionally from a larger virtual source at high rates or when a hearth linear is used. The run-to-run stability of the evaporant distribution was also determined.