A silicon wafer has $100 \mathrm{~nm}$ of oxide on it and is inserted in a furnace at a temperature above $1000^{\circ} \mathrm{C}$ for further oxidation in dry oxygen. The oxidation rate
- is independent of current oxide thickness and temperature
- is independent of current oxide thickness but depends on temperature
- slows down as the oxide grows
- is zero as the existing oxide prevents further oxidation