Photodiodes in epitaxial laterally overgrown silicon for image sensors in 3D-technology

Abstract

The incorporation of image sensors with parallel signal-processing components would increase image-processing speed dramatically. With the arrangement of the sensor elements in a separate silicon layer above the signal-processing circuits, the fill factor would be optimized as well. In this paper we report the fabrication of silicon photodiodes for application in such a three-dimensional integrated image sensor. The silicon for the sensor elements is grown with selective epitaxy, starting at seed windows (etched openings on an oxidized silicon surface). In the course of the chemical vapour deposition (CVD) process, the silicon grows laterally over the surrounding silicon dioxide, even at larger steps. The silicon crystals are polished for height reduction and planarization. Photodiodes with defined thickness and hexagonal shape determined with a plasma oxide layer are produced and various parameters measured. The photodiodes have their maximum responsivity in the visible range. Stacking faults originating at the border of the seed windows cause distinct leakage currents. Investigations of the cleaning procedure and the edge geometry of the seed windows to reduce these crystal defects are under study.