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Bird's Beak-Free Recessed Oxide Isolation Process

IP.com Disclosure Number: IPCOM000061535D
Original Publication Date: 1986-Aug-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 66K

Publishing Venue

IBM

Related People

Pan, P: AUTHOR [+2]

Abstract

A process is shown for forming a bird's beak-free recessed oxide (ROX) isolation structure with an adjustable height topography above the silicon substrate surface. Stresses in a silicon substrate due to volume expansion during thermal oxidation creates silicon defects, one of which is a bird's beak. Other yield detractors include a non-uniform oxidation process due to etching of the silicon substrate and polysilicon layers, as well as the local oxidation of nitride layers. Process steps which will result in a large radius of curvature of the ROX corners, and an adjustable height topography above the silicon surface, are as follows: 1) Form a trench 10 with sloped sidewalls 11 in a silicon substrate 12, as shown in Fig. 1.

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Bird's Beak-Free Recessed Oxide Isolation Process

A process is shown for forming a bird's beak-free recessed oxide (ROX) isolation structure with an adjustable height topography above the silicon substrate surface. Stresses in a silicon substrate due to volume expansion during thermal oxidation creates silicon defects, one of which is a bird's beak. Other yield detractors include a non-uniform oxidation process due to etching of the silicon substrate and polysilicon layers, as well as the local oxidation of nitride layers. Process steps which will result in a large radius of curvature of the ROX corners, and an adjustable height topography above the silicon surface, are as follows: 1) Form a trench 10 with sloped sidewalls 11 in a silicon substrate 12, as shown in Fig. 1. The trench 10 is defined by a composite mask of silicon dioxide 13 and silicon nitride 14 on top of the silicon substrate 12. Ion implant the sloped sidewalls 11 and trench bottom 15 with boron ions to form region 16.
2) Deposit a layer of silicon 17, as shown in Fig. 2, and then reactive ion etch (RIE) the silicon 17 to form a silicon spacer 18, as shown in Fig. 3. 3) Grow a thermal oxide 19, as shown in Fig. 4. The desired thickness of the thermal silicon dioxide (SiO2) may be obtained by adjusting the thickness of the silicon spacer 18 and the oxidation time. The presence of the silicon spacer 18 will prevent the diffusion of oxygen into the layer of silicon dioxide 13 and prevent the formati...