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SPACER FOR IMPROVED LOCAL OXIDATION PROFILE

IP.com Disclosure Number: IPCOM000025758D
Original Publication Date: 1987-Oct-31
Included in the Prior Art Database: 2004-Apr-04
Document File: 4 page(s) / 154K

Publishing Venue

Xerox Disclosure Journal

Abstract

An oxide formation called a "bird's beak" ordinarily forms along the edge of a field oxide being grown in a semiconductor substrate such as silicon, because the profile of the field oxide is not as steep as desired. This beak limits the packing of devices on the substrate, so that the shorter the beak, the more devices can be packed into a given area. In addition, if the field oxide profile were steeper, isolation between devices would be better.

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XEROX DISCLOSURE JOURNAL

SPACER FOR IMPROVED LOCAL OXIDATION PROFILE U.S. C1.427/93 Russel Martin

Proposed Classification

Int. C1. B05d 5/12

F/G. I

F/G. 2

Volume 12 Number 5 September/October 1987 251

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SPACER FOR IMPROVED LOCAL OXIDATION PROFILE (Cont'd)

An oxide formation called a "bird's beak" ordinarily forms along the edge of a field oxide being grown in a semiconductor substrate such as silicon, because the profile of the field oxide is not as steep as desired. This beak limits the packing of devices on the substrate, so that the shorter the beak, the more devices can be packed into a given area. In addition, if the field oxide profile were steeper, isolation between devices would be better.

Conventional techniques for limiting beak size and producing a steeper profile include LOCOS, SILO, SWAMI, recessed SILO, and so forth. Each of these techniques uses a combination of oxide and nitride layers to prevent beak growth by preventing oxygen from reaching the adjacent active substrate surface area of the field oxide. Nitride layers may be used to provide stiffness to seal the active substrate surface area, while pad oxide layers may be used to relieve stress between the nitride and the substrate. If the surface is very tightly sealed, however, the field oxide profile can be so steep that crystalline defects occur for certain geometries. This can occur, for example, for geometries between those suitable for SILO with thermal nitride or SWAMI. Because the geometry for which SILO is suitable is somewhat larger than that for which SWAMI is useful, neither SILO nor SWAMI is satisfactory for intermediate geometries, because each causes this type of crystalline defects.

Fig. 1 shows substrate 10 with oxidation layers 12, 14 and 16 forming a stack on top of which is a layer of photoresist 18, as would occur after field mask etch in the SILO technique. SILO layers 12 and 16 are nitride and layer 14 is oxide. The SILO oxidation stack has an edge abutting region 20 where the field oxide is to be formed, as would the oxidation stack in the LOCOS techniqu...