Harold R. Kaufman

Technology of ion beam sources used in sputtering

The technology of broad‐beam ion sources is reviewed from the viewpoint of the sputtering–deposition user. This review includes a short description of the development of discharge chambers, accelerator systems, and cathodes; the present alternatives for these components and the expected future improvements.

Ion Beam Divergence Characteristics of Three-Grid Accelerator Systems

A comprehensive experimental investigation of the geometrical and operating conditions which affect most strongly the ion beam divergence of three-grid accelerator systems is presented. Three-grid accelerator systems are shown to offer significant improvements in ion beam focusing over two-grid accelerator systems. These improvements are greatest for low net-to-total accelerating voltage ratios and small screen-to-accelerator grid separation ratios (i.e., high perveance grid sets). Ion beam focusing gains are negligible at a net-to-total accelerating voltage ratio near unity. Low decelerator grid impingement currents and low ion beam divergence angles require that the decelerator hole diameter be about 25% larger than the accelerator hole diameter, and also that the decelerator grid be spaced as close as is practically possible to the accelerator grid. The graphical results contained herein provide guidelines for the design of three-grid ion accelerator systems.

Ion beam texturing of surfaces

Textured surfaces, typically with conical structures, have been produced previously by simultaneously etching a surface and seeding that surface with another material. A theory based on surface diffusion predicts a variation in cone spacing with surface temperature, as well as a critical temperature below which cones will not form. Substantial agreement with theory has been found for several combinations of seed and surface materials, including one with a high sputter yield seed on a low sputter yield surface (gold on aluminum). Coning with this last combination was predicted by the theory for a sufficiently mobile seed material. The existence of a minimum temperature for the formation of cones should also be important to those interested in ion‐beam machining smooth surfaces. Elements contained in the environmental contaminants or in the sputtered alloys or compounds may serve as seed material.

Optimization of an electron‐bombardment ion source for ion machining applications

A new 10‐cm‐diameter ion source has been designed specifically for ion machining applications. This source employs technology and experience from the development of ion engines for electron space propulsion and generates a highly uniform beam of 500‐eV Ar+ at current densities exceeding 2 mA/cm2.

Ion Sources for Ion Machining Applications

Ion sources with beam diameters of 2.5, 10, and 20 cm have been developed for ion machining applications. All three of these sources use carbon grids to minimize accelerator grid sputtering. A new starting circuit Is also employed that uses only passive components for initiation of the discharge. The two larger sources use a flat multipole chamber with multiple cathodes to generate a very uniform beam. The multipole magnetic field is integrated into the anode, which greatly reduces the required number of insulating supports.

Thruster Technology Applied to a 30-cm Multipole Sputtering Ion Source

A 30-cm electron bombardment ion source has been designed and fabricated for micromachining and sputtering applications. This source has a multipole magnetic field that employs permanent magnets between permeable pole pieces. An average ion current density of 1 mA/cm with 500 eV argon ions was selected as a design operating condition. The ion beam at this operating condition was uniform and well collimated, with an average variation of ± 5% over the center 20 cm of the beam at a distance up to 30 cm from the ion source.