Infrared spectroscopy of oxide formation at silicon interfaces

We have studied the formation of oxide at the interface of two joined hydrophilic (oxide-terminated) Si(100) and Si(111) wafers, as a function of the annealing temperature. By using novel optical configurations, that allow probing of the 1000-4000 cm(-1) spectral region, we are able to conclusively demonstrate that the water trapped at the interface at room temperature leads to substantial additional oxide growth below 400 degrees C. At intermediate temperatures (400-800 degrees C), a further increase in the oxide signature is observed that is attributed to reaction of interface hydroxyl groups to form Si-O-Si bridges associated with closure of the formal interface between the two surfaces. Importantly, we find that there is significant inhomogeneity in both the oxide and bridging layer, even after annealing to 1100 degrees C. Comparison of data obtained using Czochralski and float-zone substrates indicates that partial loss of the interface oxide occurs for the latter at elevated temperature, due to dissolution into bulk interstitial sites.