J. van de Ven

THE CHEMICAL OXIDATION OF HYDROGEN-TERMINATED SILICON (111) SURFACES IN WATER STUDIED IN SITU WITH FOURIER TRANSFORM INFRARED SPECTROSCOPY

The chemical oxidation of hydrogen‐terminated silicon (111) surfaces in water was studied in situ with Fourier transform IR spectroscopy in the multiple total internal reflection mode. On the basis of measurements of the absorbance of the Si‐H and Si‐O‐Si vibrations as a function of time it is concluded that reactions involving the oxidation of silicon hydride and the formation of silicon oxide are coupled. The decrease in the hydride coverage and increase in the oxide coverage are linear functions of ln(t). The time dependence of oxide growth is explained in terms of electrostatic and mechanical changes at the Si/water interface.

Anisotropic Photoetching of III–V Semiconductors I . Electrochemistry

The mechanism and influence of photogalvanic interactions during localized photoetching of III–V semiconductors have been investigated. Starting from the cyclovoltammograms and etching kinetics in the dark and under uniform illumination, the chemistry of the mixed dark/illuminated system is discussed. Both in terms of current‐potential curves and of band‐energy diagrams, it is demonstrated how a geometrical separation of partial hole and electron currents can lead to the strong enhancement of etch rates under localized illumination. Some illustrative experiments are discussed, quantitatively. In the present work in acidic and solutions are used as model systems, but in addition some results from other III–V compounds and etchants are presented.

Formation of stable and highly resistive anodic oxides on InP

When left in air, as‐grown anodic oxides grown under optimized conditions described in the literature have been found to age. It is shown that this is caused by a hygroscopic component in the outer indium‐rich layer of the oxide film. When oxalic acid is present in the forming electrolyte, this phenomenon is not observed: As‐grown oxides are stable and have a constant composition throughout their thickness. This paper discusses some of the properties of the oxide films, both as‐grown and annealed, and some aspects of the chemistry of their formation. This distinct behavior of oxalic acid can be attributed to the fact that it forms soluble complexes with In(III) in the relevant pH range.

Galvanic Effects in the Etching of Semiconductor p/n Structures

Galvanic cell formation during dissolution of semiconductor p/n structures in electroless and chemical etchants was studied with GaAs as a model system. Experiments were performed in a two-compartment cell in which etching of the p- and n-sides of the p/n sample could be investigated separately. The two sides could also be exposed to solutions of different composition and to different etching conditions. In particular, the role of illumination in galvanic cell formation was considered. Energy band diagrams and mixed-potential theory are used to explain and predict the etching properties of the p/n system.

Analysis of determining factors in the kinetics of anisotropic photoetching of GaAs

The possible factors which can determine the localized anisotropic photoetching of n‐GaAs are analyzed. Mass transport to and from the reaction zone is considered. It is shown that diffusion of the oxidizing agent can become limiting when photoetching is performed by illumination of a masked pattern. Photogalvanic effects, leading to a delocalized dissolution mechanism, play a vital role under almost all practical conditions. Heating effects and local photostimulation of the dissolution reaction are of minor importance.

Contour photoetching of n‐type semiconductors

In wet photoetching of semiconductors with a projected beam on a large surface the kinetics are limited by the dissolution of reaction products at high light intensities. The structures obtained after prolonged etching are of no practical use. For short etching times, however, it is shown that in specific etchants the contour of the projected beam can be etched, whereas the central part remains comparatively passive with an etch rate which is at least ten times lower. With this maskless method, narrow grooves can be produced which are interesting for isolation of specific areas of a wafer. The method is discussed and the mechanism explained in detail for n‐GaAs in H2O2/H2SO4 solutions. It is shown that the principle can be extended to other solutions and semiconductors.