Method for achieving an ultra-reliable thin oxide using a nitrogen anneal

In an integrated circuit fabrication process suitable for EEPROM devices, a method for forming a high-quality tunnel oxide upon a surface region of a semiconductor body over a heavily-doped N+ layer therein, comprising the steps of:

• forming a heavily-doped N+ layer in the semiconductor body;
• oxidizing the semiconductor body a first time, under an oxidizing ambient, subsequent to the N+ layer forming step, to form an oxide upon a surface region of the semiconductor body over the heavily-doped N+ layer;
• annealing the semiconductor body a first time, under a gettering ambient, subsequent to the first oxidizing step, to densify the oxide and to dope the oxide at its surface and for a portion thereinto near its surface with a gettering agent;
• oxidizing the semiconductor body a second time, under an oxidizing ambient, subsequent to the first annealing step, to thicken the oxide;
• and
• annealing the semiconductor body for a second time, under an oxidizing ambient containing nitrogen, subsequent to the second oxidizing step, thereby further thickening the oxide and forming a surface layer therein containing a concentration of nitrogen.

In an integrated circuit fabrication process suitable for EEPROM devices, a method for forming a tunnel oxide upon a first surface region of a semiconductor body over a heavily-doped N+ layer, and further for forming a gate oxide, of greater thickness than the tunnel oxide, upon a second surface region of the semiconductor body, comprising the steps of:

• growing a first oxide upon the first surface region of the semiconductor body over the heavily-doped N+ layer, and upon the second surface region of the semiconductor body;
• removing a region of the first oxide, to expose a surface of the semiconductor body over the heavily-doped N+ layer, and leaving a remaining region of the first oxide;
• oxidizing the semiconductor body to form a tunnel oxide on the exposed surface of the semiconductor body while re-oxidizing the remaining region of the first oxide to form the gate oxide;
• and
• annealing the semiconductor body a first time, under an oxidizing ambient containing nitrogen, to further thicken the tunnel oxide and gate oxide and to form a surface layer each therein containing a concentration of nitrogen.