1. Field of the Invention
This invention relates to the polishing of silicon wafers in preparation for their use in the production of integrated circuit chips.
2. Discussion of Related Art
Silicon wafers for the semiconductor industry must possess a high degree of surface perfection before they can be useful in the device fabrication process. These surfaces are universally produced by polishing the wafer with a polishing slurry. Polishing slurries generally consist of a composition which contains a concentration of submicron particles. The part, or substrate, is bathed or rinsed in the slurry in conjunction with an elastomeric pad which is pressed against the substrate and rotated such that the slurry particles are pressed against the substrate under load. The lateral motion of the pad causes the slurry particles to move across the substrate surface, resulting in wear, or volumetric removal of the substrate surface. Ideally, this process results in the selective erosion of projecting surface features so that when the process is completed a perfect plane surface is produced down to the finest level of detail.
The silicon polishing process as practiced in industry consists of two or more steps. In the first, or coarse polish step, gross defects remaining from wafer sawing and shaping operations are removed. The wafer surface appears smooth and specular but still contains numerous minute defects. These defects are removed by subsequent final polish steps which remove little material from the surface but act to polish away the surface defects. The present invention relates to these polishing processes.
Photoelectrochemical etching of semiconductor materials has been routinely carried out to provide holes and trenches in the semiconductor material. For example, U.S. Pat. No. 4,482,443, describes photoelectrochemical etching of N-type silicon using an alcohol based solution of hydrofluoric acid as the electrolyte.
It is known that silicon may be removed from the surface of a silicon wafer by photoelectrochemical action. This process has been used for many years to construct holes and trenches on silicon wafers and to make a porous silicon surface structure. If one could use the removal of silicon by photochemical action to provide a planarized surface, this would allow one to forego a standard polishing process with slurry particles and polishing pads and, therefore, provide a cleaner surface for subsequent processing of the wafer.