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Diffusion (Buried) Strap Self-Aligned to the Storage Trench for High Density DRAM Trench Cells Using a Spacer Technique

IP.com Disclosure Number: IPCOM000112629D
Original Publication Date: 1994-Jun-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 113K

Publishing Venue

IBM

Related People

Rajeevakumar, TV: AUTHOR

Abstract

For high density trench DRAM cells, a surface strap or a diffusion strap may be used for contacting the storage node to the access device. For making a diffusion strap, traditionally, the collar oxide and/or the capacitor dielectric films are removed from the trench surface to form a window for outdiffusing the dopants from the trench poly fill. Figs. 1 and 2 illustrate the conventional method of forming the diffusion (buried) strap. It is not easy to remove the oxide and nitride residues from the trench surface with a RIE step alone. Wet etch in hot phosphoric acid to remove nitride degrades the exposed silicon and capacitor dielectric. So it is desirable to have a method to form the diffusion strap without the above-mentioned problems.

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Diffusion (Buried) Strap Self-Aligned to the Storage Trench for High
Density DRAM Trench Cells Using a Spacer Technique

      For high density trench DRAM cells, a surface strap or a
diffusion strap may be used for contacting the storage node to the
access device.  For making a diffusion strap, traditionally, the
collar oxide and/or the capacitor dielectric films are removed from
the trench surface to form a window for outdiffusing the dopants from
the trench poly fill.  Figs. 1 and 2 illustrate the conventional
method of forming the diffusion (buried) strap.  It is not easy to
remove the oxide and nitride residues from the trench surface with a
RIE step alone.  Wet etch in hot phosphoric acid to remove nitride
degrades the exposed silicon and capacitor dielectric.  So it is
desirable to have a method to form the diffusion strap without the
above-mentioned problems.

      The proposed scheme uses a spacer technique to etch a clean
silicon surface for diffusion.  The proposed scheme and associated
processing steps are explained in detail below.

The trench is etched, and capacitor dielectric is formed, followed by
poly recess and oxide collar formation.  The pad films are pad oxide,
silicon nitride, polysilicon, and silicon nitride, as shown in Fig.
3.

      The trench is again filled with poly, planarized and recessed
as shown in Fig. 4.  The top nitride layer may be used as the polish
stop/etch stop.

      The top nitride layer is now removed sele...