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High Density Cross-Point Cell in an Interleaved Sense Amplifier Layout

IP.com Disclosure Number: IPCOM000040321D
Original Publication Date: 1987-Oct-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 2 page(s) / 78K

Publishing Venue

IBM

Related People

Scheuerlein, RE: AUTHOR

Abstract

This article describes a high density cross point cell structure with segmented metal bit lines used in an interleaved sense amplifier layout. (Image Omitted) Many high density cross-point cells utilize a wide diffused bit line BL, as shown in Fig. 1, resulting in a cell area larger than necessary. Cell length along the word line (WL) axis is limited by the proximity of passing diffused bit lines. Also, the polysilicon (Poly) WL to diffused bit line (BL) overlap causes the WL to be lengthened, which impacts the word line RC time constant. By reducing the BL diffused area to a short segment between cell trenches and introducing a contact for a metal BL, as shown in Fig. 2, the cell area can be made smaller by shrinking the cell size along the WL axis.

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High Density Cross-Point Cell in an Interleaved Sense Amplifier Layout

This article describes a high density cross point cell structure with segmented metal bit lines used in an interleaved sense amplifier layout.

(Image Omitted)

Many high density cross-point cells utilize a wide diffused bit line BL, as shown in Fig. 1, resulting in a cell area larger than necessary. Cell length along the word line (WL) axis is limited by the proximity of passing diffused bit lines. Also, the polysilicon (Poly) WL to diffused bit line (BL) overlap causes the WL to be lengthened, which impacts the word line RC time constant. By reducing the BL diffused area to a short segment between cell trenches and introducing a contact for a metal BL, as shown in Fig. 2, the cell area can be made smaller by shrinking the cell size along the WL axis. The WL length is also decreased by reducing the WL to diffused BL overlap, resulting in a lower word line RC time constant. Section A-A shows a cell BL contact structure. The WL polysilicon definition mask is opened near the BL diffusion between trenches and etched down to recess the BL contact below the top of the BL diffusion. A reoxidation of the WL polysilicon increases the thermal oxidation thickness on the edge of the BL diffusion near the trench wall. A low temperature reflow of borophosphosilicate glass (BPSG) is used to planarize the surface. The faster etch characteristics of the glass will cause the contact hole etch to penetrate only slightly into the therm...