Polysilicon encapsulated localized oxidation of silicon

Abstract

A reduction in defects and lateral encroachment is obtained by .[.utilizing a high pressure oxidation in conjunction with.]. an oxidizable layer conformally deposited over an oxidation mask. .[.The.]. .Iadd.In one embodiment, the .Iaddend.use of high pressure oxidation provides for the formation of LOCOS oxide without the formation of defects. Any native oxide present on the substrate surface is removed by using a ramped temperature deposition process to form oxidizable layer and/or a high temperature anneal is performed to remove the native oxide at the substrate surface. In this embodiment, any oxide which can act as a pipe for oxygen diffusion is removed. Therefore, nominal or no lateral encroachment is exhibited. .Iadd.Alternately, lateral encroachment can be controlled by intentionally growing an oxide layer on the substrate surface. .Iaddend.

We claim: 
     
       1. A method of fabricating isolation oxide, comprising the steps of: providing a semiconductor substrate;   forming a buffer layer on the substrate;   forming an oxidation resistant layer on the buffer layer;   removing selected portions of the oxidation resistant layer and the buffer layer to expose portions of the substrate;,   controlling an amount of oxide encroachment by forming an oxide layer on the exposed portions of the substrate and controlling the thickness of the oxide layer; conformally forming an oxidizable layer after the step of forming an oxide layer to overlay the oxide layer and the oxidation resistant layer; and   oxidizing the oxidizable layer and the exposed portions of the substrate to form the isolation oxide in the portions of the substrate covered by the oxide layer, wherein oxidation is performed at high pressure.   
     
     
       2. The method of claim 1 further comprising the step of removing portions of the buffer layer to form a recess under the oxidation resistant layer before the step of conformally forming an oxidizable layer. 
     
     
       3. The method of claim 1 further comprising the step of anisotropically etching the oxidizable layer to leave a portion of the oxidizable layer bounding the buffer layer and the oxidation resistant layer. 
     
     
       4. The method of claim 1 wherein the oxidation resistant layer is comprised of silicon nitride or oxynitride. 
     
     
       5. The method of claim 1 wherein the step of oxidizing completely consumes the oxidiazble layer converting the oxidizable layer to a silicon dioxide. 
     
     
       6. A method of fabricating isolation oxide, comprising the steps of: providing a semiconductor substrate;   forming a buffer layer on the substrate;   forming an oxidation resistant layer on the buffer layer;   removing selected portions of the oxidation resistant layer and the buffer layer to expose portions of the substrate;   removing portions of the buffer layer to form a recess under the oxidation resistant layer;   controlling an amount of oxide encroachment by forming an oxide layer on the exposed positions of the substrate and controlling the thickness of the oxide layer;   conformally forming an oxidizable layer after the step of forming an oxide layer to overlay the oxide layer and the oxidation resistant layer, and to substantially fill the recess in the buffer layer; and   oxidizing the oxidizable layer and the exposed portions of the substrate to form the isolation oxide in the portions of the substrate covered by the oxide layer, wherein oxidation is performed at high pressure.   
     
     
       7. The method of claim 6 further comprising the step of anisotropically etching the oxidizable layer to leave a portion of the oxidiazble layer bounding the buffer layer and the oxidation resistant layer. 
     
     
       8. The method of claim 6 wherein the oxidation resistant layer is comprised of silicon nitride or oxynitride. 
     
     
       9. The method of claim 6 wherein the step of oxidizing completely consumes the oxidizable layer converting the oxidizable layer to a silicon dioxide. 
     
     
       10. The method of claim 1 wherein the oxidizable layer is comprised of amorphous silicon, polysilicon, or silicon-rich dioxide. 
     
     
       11. The method claim 6 wherein the oxidizable layer is comprised of amorphous silicon, polysilicon, or silicon-rich dioxide. .Iadd. 
     
     
       12.  A method of fabricating isolation oxide layer, comprising the steps of: providing a semiconductor substrate;   forming a buffer layer on the substrate;   forming an oxidation resistant layer on the buffer layer;   removing selected portions of the oxidation resistant layer and the buffer layer to expose portions of the substrate;   controlling an amount of oxide encroachment by forming an oxide layer on the exposed portions of the substrate and controlling the thickness of the oxide layer;   conformally forming an oxidizable layer to overlie the oxide layer and the oxidation resistant layer; and   oxidizing the oxidizable layer and the exposed portions of the substrate to form the isolation oxide layer. .Iaddend. .Iadd.13. The process of claim 12 further comprising the step of removing portions of the buffer layer to form a recess under the oxidation resistant layer prior to conformally forming an oxidizable layer. .Iaddend. .Iadd.14. The process of claim 12 further comprising the step of removing native oxide on the exposed portions of the substrate prior to forming an oxide layer. .Iaddend. .Iadd.15. The process of claim 12, wherein the oxidizable layer comprises a material selected from the group consisting of polysilicon, amorphous silicon, and silicon-rich silicon dioxide. .Iaddend.