MOS Properties of Ultra Thin Oxides on Silicon

With some newly developed procedures it has become possible to grow ultra thin oxides on silicon in a series of steps operated at low temperature to achieve a good control of the interface properties. The growth mode is linear between 0.3 nm and 10 nm with a precision of one atomic layer (0.25 nm) pr. step. This includes the thinnest possible oxide-like layer that can be grown (0.3 nm) which has a non-uniform vertical chemical composition. The structural and chemical characterization of the oxides grown is done with synchrotron-induced photoemission, which also allows one to monitor the silicon band bending. To show the usefulness of these oxides for practical devices, the electrical properties of the interface and the charges in the oxide must be made accessible to measurements. An in-situ characterization is possible just after growth through photoemission, by depositing and contacting a metal (here silver) film on top of the oxide. In the conventional MOS capacitor model the silicon surface potential (band bending) with zero external bias should be equal to the negative of the flat band voltage. Deposition of silver is also used to detect if the oxide is not covering the surface uniformly, in which case there would be significant local variations in the band bending where silver gets in contact with clean silicon.