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Retention Time And Soft Error Rate Improvement by Tailoring Well Doping in Trench Dram Cells

IP.com Disclosure Number: IPCOM000100952D
Original Publication Date: 1990-Jun-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 2 page(s) / 69K

Publishing Venue

IBM

Related People

Bertsch, JE: AUTHOR [+2]

Abstract

Three methods of creating doping gradients in the well of trench dynamic random-access memory (DRAM) cells are presented which result in electric field driving minority carriers away from the storage node and along the trench wall toward the substrate. Thus, increased retention time and reduced soft error rate is achieved.

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Retention Time And Soft Error Rate Improvement by Tailoring Well Doping in Trench Dram Cells

       Three methods of creating doping gradients in the well of
trench dynamic random-access memory (DRAM) cells are presented which
result in electric field driving minority carriers away from the
storage node and along the trench wall toward the substrate.  Thus,
increased retention time and reduced soft error rate is achieved.

      In all three figures a DRAM cell is comprised of well 10 in
substrate 12, trench storage node 14 having dielectric wall coating
16, recessed oxide (ROX) regions 18 and 20, gate conductor 22, bit
line 24, insulators 26, and source and drain diffusions 28 and 30.
Conductive strap 32 connects storage node 14 with diffusion 30.

      Referring to Fig. 1, dopant of the same type as the well is
deeply implanted in regions 31 and 34 after ROX device definition or
after definition of gate conductor 22 or immediately after source and
drain implantation in a MOSFET process.  To avoid bit line
capacitance impact, a mask may be added to implant region 34 only.

      The graph in Fig. 1 shows doping concentration increasing to
the left as a function of depth Y near the well wall indicated by the
dashed line in the cross section. The curve indicates relative doping
concentration after annealing is completed.

      Referring to Fig. 2, a second method is to apply a photoresist
mask after source and drain definition to expose only diffusio...