Nitrogen Profile Engineering in Thin Gate Oxides

Abstract

In order to prevent boron penetration in PMOS transistors without degrading channel mobility, it is necessary to engineer the distribution of nitrogen introduced into the gate oxide. We have investigated methods of engineering this distribution using nitric oxide (NO) gas in an RTP system to thermally nitride ultra-thin gate oxides. In one approach, the gate oxide is simultaneously grown and nitrided in a mixture of nitric oxide and oxygen. For a 40 Å film, SIMS depth profiling shows that this process moves the nitrogen peak into the bulk of the oxide away from the oxide silicon interface. In another approach, an 11 Å chemical oxide produced by a standard pre-furnace wet clean is nitrided in NO at 800 deg. C. This film is subsequently reoxidized in either oxygen or steam. For an 1100 deg. C., 120 sec RTP reoxidation in oxygen, the final film thickness is 41 Å. The nitrogen has a peak concentration of 5 at. % and the peak is located in the oxide 25 Åfrom the oxide/silicon interface. Ramped voltage breakdown testing was carried out on MOS capacitors built using reoxidized NO nitrided films. They have breakdown characteristics that are equivalent to conventional furnace grown oxides. These films show considerable promise as gate dielectrics for CMOS technologies at geometries of 0.25um and below.