Oxidation/Diffusion

An eight-stack Bruce Model BDF-8 furnace bank is available for oxidation, annealing, pre-deposition and drive-in steps on wafers up to 100 mm in diameter. At present tubes for oxidation, implant annealing and drive-in, phosphorus predep and hydrogen metal sinter are operational.

The furnaces have central computer control of temperature through profile thermocouples permanently installed in the process zone. All gas sources are MFC controlled, and push and pull sequences are automated. Gettering with HCl gas is used before all oxidation cycles to control Na+ ionic contamination. With this precaution it is possible to produce gate oxides showing effectively no flatband shift in bias-temperature stress tests.

In a recent experiment gate oxides of 10 – 12 nm thickness were grown in pure oxygen at a temperature of 900° using the Bruce furnaces. With in- situ doped n+ polysilicon gates, these oxides gave a tightly-peaked breakdown distribution at 13 MV/cm, and fast surface state density below 1E10 cm-2.