Low-temperature annealing and hydrogenation of defects at the Si–SiO2 interface

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Abstract
Characteristic defects at the Si–SiO2 interface are strongly influenced by specific low-temperature treatments. Annealing aluminum thin films on thermal oxides removes both characteristic interface states and the interfacial paramagnetic defect center. However, the anneal processes occur at significantly different temperatures. Since the spin center has been previously identified as a trivalent silicon defect bonded to three silicon atoms at the interface, it appears that this defect center is not directly responsible for the characteristic interface states. Hydrogen is generally believed to be involved in the removal of interface states, although the microscopic processes have not been established. The effect of hydrogen was investigated by using deuterium as a readily traceable isotope which simulates hydrogen chemistry. Anneals in atomic deuterium annihilated the interface spin center. The physical presence of deuterium in the SiO2 layer was established with secondary ion mass spectrometry, which revealed an accumulation of deuterium at the Si–SiO2 interface for deuteration temperatures in the investigated range of 25 to 230°C; postdeuteration anneals above 500°C (in vacuum) were required for its removal. Annihilation of the spin center is therefore explained by the conversion of trivalent silicon defects to nonparamagnetic Si–D bonds.

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