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Self Aligned "Framed" Recessed Oxide Isolation Process

IP.com Disclosure Number: IPCOM000048147D
Original Publication Date: 1981-Dec-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 3 page(s) / 71K

Publishing Venue

IBM

Related People

Ho, AP: AUTHOR [+4]

Abstract

Recessed oxide isolation (ROI) is a commonly used dielectric isolation for present day semiconductor devices. However, formation of the "bird's beak" and "bird's head" structures at the lateral edges of the recessed oxide has negatively impacted the density and planarity of devices. The bird's beak and head in ROI can be minimized with an extra masking process in which a "narrow" stripe of Si(3)N(4) is deposited directly on the Si surface (Fig. 1A). This Si(3)N(4) frame prevents oxidizing species from diffusing under the Si(3)N(4), and hence formation of the bird's beak. This framed ROI process requires a second masking step with its lithographic alignment. The indefiniteness of the lithographic alignment imposes wider tolerance of lateral dimension in the integrated circuit layout.

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Self Aligned "Framed" Recessed Oxide Isolation Process

Recessed oxide isolation (ROI) is a commonly used dielectric isolation for present day semiconductor devices. However, formation of the "bird's beak" and "bird's head" structures at the lateral edges of the recessed oxide has negatively impacted the density and planarity of devices. The bird's beak and head in ROI can be minimized with an extra masking process in which a "narrow" stripe of Si(3)N(4) is deposited directly on the Si surface (Fig. 1A). This Si(3)N(4) frame prevents oxidizing species from diffusing under the Si(3)N(4), and hence formation of the bird's beak. This framed ROI process requires a second masking step with its lithographic alignment. The indefiniteness of the lithographic alignment imposes wider tolerance of lateral dimension in the integrated circuit layout. To reduce the need for the lithographic tolerances, a self aligned process, which forms a thin stripe of framed Si(3)N(4) (Fig. 1B), for ROI, is proposed.

The process described here provides an alternate self aligned process which results in forming a wider stripe of framed Si(3)N(4) (Fig. 1C) around the ROI windows. The wider stripe of framed Si(3)N(4) ensures the elimination of ROI bird's beak. The process is described by the following steps: 1. Standard semiconductor processing through EPI reoxidation

(thermal oxide).

2. Deposition of Si(3)N(4) and N+ polysilicon (Fig. 2A).

3. Photoresist exposed and developed with the ROI mask

and reactive ion etched (RIE) through polysilicon

nitride oxide layers to Si (EPI) surface. The sidewalls

are nearly vertical (Fig. 2B).

4. Strip photoresist.

5. Using buffered HF solution, undercut Si(3...