Part I - Diffusion of Si in Al and Solid Phase Growth of Epitaxial Si Structures in Al. Part II - Investigation on the Si-Au Interface Effects and on the Phase Diagram of Si-Au-Cu

Citation

Sankur, Haluk (1975) Part I - Diffusion of Si in Al and Solid Phase Growth of Epitaxial Si Structures in Al. Part II - Investigation on the Si-Au Interface Effects and on the Phase Diagram of Si-Au-Cu. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/cvpy-tr40. https://resolver.caltech.edu/CaltechTHESIS:10282021-200925928

Abstract

Part I

Reactions between solid metal films and semiconductors are important in the reliability, operation of semiconductor devices and growth of semiconductor structures in solid state. In this work diffusion and precipitation of Si in Al films and growth of Si epitaxial structures in solid Al have been studied.

Diffusivity and solubility of Si in Al films of an integrated circuit structure have been investigated by means of electron microprobe analysis at temperatures between 360°C and 560°C. The Si solubility was found to be in essential agreement with values reported in the literature for bulk Al. The Si diffusivity was found to be enhanced with respect to bulk values and the activation energy for diffusion reduced by 42% from bulk value to 0.8 eV. The enhanced diffusivity and reduced activation energy are due to the presence of a large number of structural defects -- mainly dislocations -- in the evaporated Al film.

The thin Al films were also analyzed for the ultimate location of Si precipitation with the electron microprobe. Si in solution in Al becomes supersaturated and precipitates upon cooling from the dissolution temperature. Si in Al considerably less than a diffusion length from the substrate Si was found to regrow there. Elsewhere Si formed precipitates, preferentially near the free surface of the Al film.

In view of the results of the precipitation experiments, investigation of the growth of Si epitaxial structures in solid Al onto crystal Si substrates was performed by means of scanning electron microscopy. A variety of growth structures, such as mesas, faceted structures, thin vertical membranes, large plateaus were observed. The morphology of these structures depended on the amount of Si deposited in the Al film, annealing conditions, stresses in the metal film, crystalline orientation of the substrate surface.

Preferential growth was observed to occur at reentrant corners and small diameter oxide cuts. The probable cause for such preferential growth was indicated in pressure experiments which showed that regions in the solid Al under relatively less compression are favored locations for growth.

Part II

Interface conditions between a metal and a metal or semiconductor are known to affect solid state reactions there. In the present work dissolution reaction of crystalline and amorphous Si into evaporated Au films was studied with electron microprobe and scanning electron microscopy. The dissolution pattern was found to be nonuniform along the plane of the surface and dependent on the crystalline orientation of the Si substrate. The latter behavior was changed upon evaporation of a thin Pd layer between Au and Si, which greatly facilitated the dissolution reaction.

Investigation of Si dissolution in Au by electron microprobe analysis also indicated that Si solubility was below the sensitivity of this analysis technique. A study of Si-Au-Cu ternary solid solution was undertaken in view of the more extensive solubility of Si in Cu compared to that in Au. The analysis, which was performed by powder X-ray diffraction and micrography, indicated that a continuous ternary solid solution existed through most of the Cu-Au solubility range, and that it was in equilibrium with a phase, with cubic lattice structures. The solubility of Si deviated from the linear interpolation of binary solubilities and from a monotonically decreasing behavior going from Cu-rich toward Au-rich corner of the diagram.

Thesis Files