Bonding Pad Structure with Via Plug-Free Central Region
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Solution Overview
Problem
Low-k and ultra low-k dielectric materials used in inter-metal dielectric layers are susceptible to cracking and delamination during the wire-bonding process due to insufficient strength, leading to pad lifting issues.
Innovation Solution
A bonding pad structure with a bondable metal pad layer on top of IMD layers, covered by a passivation layer and via plugs in an annular region around the central area, avoiding interconnection structures under the pad to prevent aluminum segregation and enhance bonding strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If low-k and ultra low-k dielectric materials are used for IMD layers to reduce RC delay and parasitic capacitances, then signal transmission performance is improved, but the strength and integrity of the dielectric material decreases, leading to cracking and delamination during wire bonding
Solution Approach 1:
The patent applies local quality by creating a via plug-free central region directly beneath the bonding pad, while maintaining via plugs in the annular region. This localized structural modification concentrates mechanical support where needed (at the pad center) without compromising the overall low-k dielectric benefits for signal transmission in other areas.
Solution Approach 2:
The patent employs composite materials by combining low-k dielectric layers with a protective cap layer (such as silicon nitride or silicon oxide) over the bonding pad region. This composite structure provides both the low RC delay benefits of low-k materials and the mechanical strength needed to prevent pad lifting during wire bonding.
2Reliability
If via plugs are formed throughout the pad forming region to provide electrical connections, then electrical connectivity is improved, but the mechanical stress during wire bonding causes delamination and pad lifting
Solution Approach 1:
The patent segments the pad forming region into two distinct zones: a central region without via plugs and an annular region with via plugs. This segmentation allows the central area to remain free of mechanical discontinuities that would cause delamination, while the annular region provides necessary electrical connections through via plugs.
Solution Approach 2:
The patent extracts via plugs from the central region of the bonding pad, removing the harmful elements (via plugs) from the critical area where they cause delamination. The via plugs are retained only in the annular region where they provide electrical connectivity without compromising pad integrity.
3Adaptability or versatility
If interconnection structures are placed under the bonding pad to provide electrical pathways, then electrical functionality is improved, but aluminum segregation occurs and bonding strength decreases
Solution Approach 1:
The patent extracts interconnection structures (via plugs) from the central region beneath the bonding pad, eliminating the source of aluminum segregation and bonding weakness. Electrical functionality is maintained through via plugs in the annular region and alternative current paths through the IMD layers.
Data Source
AI summary
A bonding pad structure includes a semiconductor substrate having thereon a plurality of inter-metal dielectric (IMD) layers comprising at least a topmost IMD layer; a bondable metal pad layer disposed on a surface of the topmost IMD layer within a pad forming region; a passivation layer covering a periphery of the bondable metal pad layer and the surface of the topmost IMD layer; and a plurality of via plugs disposed in the topmost IMD layer within an annular region of the pad forming region, wherein the via plugs are not formed in a central region of the pad forming region.