Method of making MOS transistor having improved oxynitride dielectric

DETAILED DESCRIPTION In accordance with the invention, a silicon oxide dielectric is grown in a nitrous oxide (N.
sub.
2 O) environment and then nitrided in an anhydrous ammonia (NH.
sub.
3) atmosphere to introduce a sufficient amount of nitrogen at the silicon/silicon oxide interface to provide resistance to boron penetration but with reduced electron traps induced from the nitridation as compared to pure silicon oxide which has been nitrided.
In fabricating the dielectric, a silicon surface is oxidized in an atmosphere consisting essentially of nitrous oxide (N.
sub.
2 O).
In preferred embodiments, a pure (e.
g.
, 99.
998%) nitrous oxide gas is employed at a temperature of approximately 900.
degree.
-1100.
degree.
C.
Ultrathin (approximately 60-65 .
ANG.
) gate dielectrics can be grown having a nitrogen rich layer at the silicon/silicon oxide interface.
Thereafter, the structure is placed in an atmosphere of NH.
sub.
3 at a temperature in the range of 800.
degree.
C.
-950.
degree.
C.
for a period of time between 30 seconds and 30 minutes; to introduce additional nitrogen atoms.
The structure is then annealed in a nitrogen gas (N.
sub.
2) atmosphere.
Results show that NH.
sub.
3 -nitrided N.
sub.
2 O-oxides have excellent electrical (low N.
sub.
f) and reliability properties (smaller charge trapping and suppressed interface state generation) comparable to N.
sub.
2 O oxides, with an additional advantage of significantly improved resistance to boron penetration.
The invention and objects and features thereof will be more readily apparent from the following description and appended claims when taken with the drawing.