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Substrate Plate Trench DRAM Cell with an Increased Background Doping (Halo) Surrounding the Strap Region

IP.com Disclosure Number: IPCOM000113888D
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 73K

Publishing Venue

IBM

Related People

Bronner, GB: AUTHOR [+4]

Abstract

Disclosed in this article is a method to solve the boron out-diffusion problem associated with the buried strap in a p-type Substrate-Plate Trench (SPT) DRAM cell [1]. The degradation of the pass transistor device characteristics caused by the boron out-diffusion is eliminated by forming a high concentration halo around the strap region. In addition, the node capacitance is increased by the halo (Hi-C) without increasing the bit-line capacitance.

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Substrate Plate Trench DRAM Cell with an Increased Background Doping
(Halo) Surrounding the Strap Region

      Disclosed in this article is a method to solve the boron
out-diffusion problem associated with the buried strap in a p-type
Substrate-Plate Trench (SPT) DRAM cell [1].  The degradation of the
pass transistor device characteristics caused by the boron
out-diffusion is eliminated by forming a high concentration halo
around the strap region.  In addition, the node capacitance is
increased by the halo (Hi-C) without increasing the bit-line
capacitance.

      In substrate plate DRAM cells, the capacitor node is made by
forming a deep trench in the silicon followed by triple dielectric
formation and fill by p + poly where the charge is stored [1].  A key
element is the strap formation between the capacitor node and the
transfer device (pFET) drain region (p + diffusion).  For scaled DRAM
cells, the highest density is achieved by forming a buried strap by
out-diffusion of boron from the p+ poly in the trench.  However, the
main difficulty with this process is the effect of deep p+ region
(&nearly. 0.2&mu.m) on the transfer device short channel effect.  To
eliminate this problem, the formation of an n-type halo which
surrounds the out-diffused p+ region is proposed (Figure).  This halo
can be formed by ion-implantation of phosphorous or arsenic into the
strap region in order to increase the n-type background concentration
to about 1E18 cm-3.  The increased background concentration reduces
the depletion width caused by the reverse bias of the deep,
out-diffused buried strap and therefore...