Boron contamination of surfaces in silicon microelectronics processing: Characterization and causes

Abstract

Boron contamination has been detected by secondary ion mass spectrometry at almost every surface and interface in silicon microelectronics structures. Areal densities for boron are typically 102–1013 atoms/cm2 and can cause counterdoping if the boron is distributed by an anneal into a lightly doped n-type region. Boron was quantified by encapsulating the surface of the layer of interest with an identical layer and thereby retaining matrix homogeneity across the interface where the original surface is located. The origin of boron was shown to be airborne contamination. Boron in the atmosphere and the borosilicate glass in the high efficiency particulate air filters used in clean room construction have been identified as contamination sources. Accumulation of boron on a polysilicon surface follows a relationship similar to that for oxide growth. Processing with hydrogen, buffered HF cleaning of the surface, or growth of a removable SiO2 layer will reduce or eliminate boron from the silicon surface.