Interconnect Bonding Pads With Reentrant Profiles to Prevent Voids
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Solution Overview
Problem
The challenge in semiconductor manufacturing is to simultaneously achieve robust metal-to-metal and dielectric-to-dielectric bonding between semiconductor dies while accommodating thermal expansion during the bonding process, which is often hindered by improper recess depth control of bonding pads, leading to voids and degraded bonding.
Innovation Solution
The use of reentrant shaped bonding pads with reduced contact area, featuring pillar portions or mesa-shaped vertical profiles, allows for effective metal-to-metal and dielectric-to-dielectric bonding by aligning thermally expanded surfaces, accommodating height variations, and enhancing bonding strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bonding pads are made with standard flat profiles, then manufacturing is simpler, but thermal expansion during bonding causes misalignment and voids
Solution Approach 1:
The bonding pad is given a reentrant curved profile where the distal surface is recessed relative to the proximal surface, creating a concave shape. This curvature allows the distal surface to be recessed into the bonding pad body, accommodating thermal expansion and mechanical interlocking during the bonding process, thereby preventing void formation and improving bonding integrity.
2Reliability
If bonding pads are recessed to accommodate thermal expansion, then bonding reliability improves, but manufacturing precision requirements increase
Solution Approach 1:
The reentrant profile is formed in advance during the bonding pad fabrication process, creating a pre-recessed structure before bonding. This preliminary shaping ensures that when thermal expansion occurs during bonding, the pad material already has the correct geometry to accommodate expansion without requiring precise real-time control of recess depth during the bonding operation itself.
3Strength
If bonding pads have larger contact area, then bonding strength is higher, but void formation increases due to thermal expansion
Solution Approach 1:
Instead of increasing the lateral contact area of the bonding pad, the solution moves to the vertical dimension by creating a reentrant profile with a recessed distal surface. This allows the bonding interface to accommodate thermal expansion in the vertical direction while maintaining adequate lateral contact area for bonding strength, effectively separating the functions of contact area and expansion accommodation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach ensures strong and reliable bonding between semiconductor dies by precisely controlling the recess depth of bonding pads, reducing void formation and improving overall bonding integrity.
Implementation Method 1
annealing the second semiconductor die in contact with the first semiconductor die such that a metallic material of at least one of the first metallic bonding structures and the second metallic bonding structures expands to fill the openings in the first dielectric capping layer to bond at least a first subset of the first metallic bonding structures to at least a first subset of the second metallic bonding structures
Data Source
AI summary
A bonded assembly includes a first semiconductor die that includes first metallic bonding structures embedded within a first bonding-level dielectric layer, and a second semiconductor die that includes second metallic bonding structures embedded within a second bonding-level dielectric layer and bonded to the first metallic bonding structures by metal-to-metal bonding. One of the first metallic bonding structures a pad portion, and a via portion located between the pad portion and a first semiconductor device in the first semiconductor die, the via portion having second tapered sidewalls.