Iron Solubility in Boron-Doped Silicon and Fe Gettering Mechanism in p/p~+ Epitaxial Wafers

摘要

The dependence of the solubility of Fe on boron concentration in silicon at different temperatures has been measured by inductively coupled plasma mass spectrometry (ICP-MS) and graphite furnace atomic absorption spectroscopy (GF-AAS). Iron solubility was measured at 600, 700, 800, 900 and 1000 in silicon doped with 1.3xl0~(15), 4.5xl0~(18), 1x10~(19) and 6xl0~(19) boron atoms/cm~3. An enhancement of Fe solubility has been observed for boron concentration higher than 10~(18) atoms/cm~3 at 800 and lower temperatures. At all annealing temperatures a concentration maximum has been found at short time of annealing due to boundary phase formation. At temperatures higher than 800 this maximum concentration approaches the equilibrium concentration at extended annealing time. However, at 700 and 600 annealing the concentration maximum remains constant with longer annealing time. Based on this data we propose that, at high-temperature annealing, Fe contamination would be distributed uniformly in the p/p~+ wafer, irrespective of boron concentration. Upon reduction of the temperature in the cooling phase of high temperature annealing, Fe becomes supersaturated and, due to its solubility enhancement in highly boron-doped silicon p~+ substrates, a reduced Fe concentration in lightly boron-doped epi layers is established.