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NITRIDED SiO2 FILM AS A NEW OXIDATION MASK MATERIAL

IP.com Disclosure Number: IPCOM000039308D
Original Publication Date: 1987-May-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Ray, AK: AUTHOR

Abstract

In the conventional local oxidation of silicon (LOCOS) process, a stacked structure consisting of 500 o Si3N4/100 o SiO2 is used as an oxidation mask. The Si3N4 film acts as the mask and the SiO2 film as a pad layer to minimize stress induced on silicon substrates. The stress results in defect formation in Si substrates. However, the presence of a pad oxide leads to the formation of a "bird's beak" due to lateral diffusion of oxidant through the pad oxide. During a typical field oxidation step only 20 - 30 o of the Si3N4 top layer is oxidized. So only 80 - 100 o dense, pinhole-free Si3N4 film should be enough as an oxidation mask. The thinner the Si3N4 film, less would be the stress induced on the silicon substrates.

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NITRIDED SiO2 FILM AS A NEW OXIDATION MASK MATERIAL

In the conventional local oxidation of silicon (LOCOS) process, a stacked structure consisting of 500 o Si3N4/100 o SiO2 is used as an oxidation mask. The Si3N4 film acts as the mask and the SiO2 film as a pad layer to minimize stress induced on silicon substrates. The stress results in defect formation in Si substrates. However, the presence of a pad oxide leads to the formation of a "bird's beak" due to lateral diffusion of oxidant through the pad oxide. During a typical field oxidation step only 20 - 30 o of the Si3N4 top layer is oxidized. So only 80 - 100 o dense, pinhole-free Si3N4 film should be enough as an oxidation mask. The thinner the Si3N4 film, less would be the stress induced on the silicon substrates. But it is difficult to deposit 80 - 100 o pinhole-free Si3N4 film by conventional CVD (chemical vapor deposition) techniques. In this article, nitrided SiO2 film is employed as a new oxidation mask material. First, about 200 o thick thermal SiO2 film is grown on silicon substrates. Then a controlled amount of nitrogen is incorporated in the SiO2 film by varying nitridation time at a nitridation temperature, typically 1000oC. The result of nitridation in NH3 at 1000oC is shown in the drawing. Nitrided SiO2 films with nitrogen NITRIDED SiO2 profile (marked (a)) is ideal as an oxidation mask. The nitrogen-rich layer at the top surface acts as a blocking layer for oxygen diffusion, and the nitrogen rich...