Study on further reducing the epitaxial silicon temperature down to 250 °C in low-energy bias sputtering

Abstract

The epitaxial silicon growth temperature has been reduced to as low as 250 °C by optimizing the ion bombardment condition in low-energy bias sputtering process. Independent and precise control of ion bombardment energy and ion flux density incident on a growing film surface is most essential to realize very low temperature epitaxy. It has been experimentally shown that the deficit in energy for epitaxial growth by reducing the substrate temperature is able to be compensated for by increasing the total energy dose on a film surface by low-energy ion bombardment. Increase in the impact energy of individual ions, however, results in the formation of high-density defects in the film. Therefore, the right direction to enhance the total energy deposition by ion bombardment is to increase the ion flux density while keeping the ion impact energy at an optimum value. As a result of such optimization, epitaxial growth of silicon has become possible at a temperature as low as 250 °C. The etch pit density in this low-temperature growth film is less than 3×103 cm−2, the detection limit of our experiments. The carbon and oxygen concentrations in a grown film as measured by secondary ion mass spectroscopy increase with the background pressure, and these impurity concentrations are correlated to the crystallinity of the film. From these observations, the profound effect of contamination on the reduction of silicon epitaxial temperature is demonstrated.