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Current Density Line Length Design Criterion for Multi-layered Interconnects

IP.com Disclosure Number: IPCOM000110048D
Original Publication Date: 1992-Oct-01
Included in the Prior Art Database: 2005-Mar-25
Document File: 2 page(s) / 72K

Publishing Venue

IBM

Related People

Ho, PS: AUTHOR [+2]

Abstract

This article describes a method of reducing electromigration damage in multi-metal interconnections. A design criterion is proposed for multi-layered wiring structures, in particular, a highly reliable local interconnect can be achieved using this criterion.

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This is the abbreviated version, containing approximately 52% of the total text.

Current Density Line Length Design Criterion for Multi-layered Interconnects

       This article describes a method of reducing
electromigration damage in multi-metal interconnections.  A design
criterion is proposed for multi-layered wiring structures, in
particular, a highly reliable local interconnect can be achieved
using this criterion.

      The advanced chip interconnects are often used with W as a
vertical interconnection between lines of Al, or Cu alloy to form the
multilayer metallization structure.  A flux divergence in such a
structure occurs at the Al or Cu/W interfaces to result in either
metal depletion or accumulation, depending on the electron flow
direction.  Such depletions or accumulations have been shown to be
the dominant electromigration failure mode in mutli-layered wiring
structures which use mixed metals for lines and studs.  However, the
electromigration mass transport rate is found to be dependent on
metal length.  In fact, it was found that no electromigration damage
would occur if the jxL is less than a threshold value (1-2), where j
and L are the metal line current density and length between two
studs, respectively.  We propose ground rules for interconnect wiring
design:  a) the design criterion states that the product of the
current density (j) and line length (L) should be as uniform as
possible.  The uniformity requirement will ensure a well-defined mass
depletion rate at the line/stud interface.  If the product of j and L
is less than the threshold value, there should be no
electromigration, and b) when larger values of jxL than the threshold
value are required, the line can be broken into sub-critical lengths
to satisfy the ground rule.

      This proposal is to set design limits on...