Fixed charge in Cr-metallized MOS capacitors

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Abstract
Flat‐band voltages, surface‐state densities, and Fowler‐Nordheim tunneling characteristics were measured in MOS capacitor structures with oxide thicknesses ranging from 30 to 400 Å. The oxides were grown in dry oxygen on p‐silicon; the metallization was gold on top of chrome. The results show the silicon‐silica interface to be independent of oxide thickness down to a value of at most 40 Å. They also suggest the existence of charge not only at the silica‐silicon interface but also at the metal‐silica interface. The charge near the metal has the characteristic of a double layer. Right next to the interface it is negative and of magnitude 1019 electron charges/cm3. It goes to zero some 75 Å into the oxide and then increases to reach a maximum positive value on the order of −1018 electron charges/cm3. Approximately 150 Å into the oxide it goes to zero. The surface charge at the silicon‐silica interface was as in previous investigations found to be positive and, at flat band, on the order of −3×1011 electron charges/cm2.