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.
|
