The boat is slowly pushed into the furnace using the pushrod. This slow, start-and-stop movement ensures that the wafers heat uniformly. If this is not done, the wafers will heat unevenly and their non-uniform expansion can lead to stresses so large that it will actually damage the crystal structure of the Si.
The boat stops in the central "sweet-zone of the furnace where the temperature is most uniform and well controlled. Typical oxidation temperatures exceed 1000°C.
