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The feasibility of patterning a cured polymeric film of benzocyclobutene (BCB) using silicon nitride (SIN=) as an etch mask was investigated. Due to the carbon-and silicon-containing composition of BCB, a gas mixture with oxygen-and fluorine-containing components is required, which unfortunately also etches SIN=. Therefore, a reactive ion etching pro-~M cess with high selectivity between the etch rates of the BCB, CYCLOTENE 3022-46, and the SiNx was developed. We have investigated the dependence of the etch rates as a function of the CF~ content in the O2/CF4 gas mixture. The surface morphology and the angle of the etched BCB sidewall were determined using a scanning electron microscope. A process with 37.5% CF4 content was defined, exhibiting etch rates of 155 and 14 nm/min for the polymerized BCB and the SiNx, respectively. This yields a selectivity of 11: I. The morphology of the etched BCB surface is smooth. Depending on the shape of the SiN= etch mask, sidewall angles of the BCB structure between 70 ~ and 80 ~ were obtained. These inclinations allow an effective deposition of a contact metallization. For further technological processing, a residual dielectric SiN= film can be left on the structure when the BCB layer is etched.

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Zn diffusions from spin-on films have been carried out into n-InP/p+-InGaAs/n-InP heterostructures, which were grown by metalorganic vapor phase epitaxy for heterojunction bipolar transistors with Mg as a p dopant. After diffusion, Mg was completely substituted by Zn and enriched in the spin-on film. In the presence of Mg, the indiffusion of Zn is strongly enhanced. By varying doping levels and diffusion conditions, the underlying mechanism is studied and compared to recent experiments with Be-doped AlGaAs/GaAs heterostructures.