Elastic Interface for Wafer Bonding Pressure Distribution
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Solution Overview
Problem
Existing wafer bonding techniques using deformable graphite pads fail to uniformly distribute pressure across imperfect or out-of-flat wafers, leading to non-uniform bonding, increased scrap rates, and contamination issues due to debris shedding.
Innovation Solution
An elastic interface with staggered raised features and a mesh design is used to distribute bonding force uniformly across the wafer assembly, employing materials like spring steel or beryllium copper alloy for reliable and long-lasting performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If a deformable graphite pad is used to distribute bonding force, then pressure distribution is improved, but the pad bottoms out with large wafer non-uniformity and has limited lifetime
Solution Approach 1:
The patent changes the material parameter from graphite to elastic material (such as silicon rubber or polyurethane) with elastic modulus between 0.01 and 1 GPa. This parameter change enables the material to provide sustained elastic recovery, preventing bottoming out and extending lifetime while maintaining pressure distribution uniformity across wafers with up to 50 microns non-uniformity
Solution Approach 2:
The patent uses composite structures including an elastic material substrate with an array of protrusions and recesses. This composite design combines the compliance of elastic materials with the force-distributing geometry of the protrusion-recess pattern, achieving both uniform pressure distribution and extended operational lifetime
2Force
If a graphite pad is used for force distribution, then bonding force transmission is improved, but debris is shed causing contamination
Solution Approach 1:
The elastic interface is designed as a disposable component that can be easily replaced. Although individual interfaces have limited life, their low cost and ease of replacement make them economically viable. The material composition (silicon rubber or polyurethane) is selected to minimize debris generation compared to graphite pads
Solution Approach 2:
The patent changes the material composition from graphite to elastic polymers (silicon rubber or polyurethane) that do not shed debris. This material parameter change eliminates the contamination problem while maintaining effective bonding force transmission through the elastic deformation mechanism
3Strength
If maximum pressure is applied to bond imperfect wafers, then bonding strength is improved, but non-uniform bonding and cracking occur
Solution Approach 1:
The elastic interface acts as a cushioning element placed beforehand between the pressure chuck and the wafer assembly. It absorbs and distributes the bonding pressure uniformly across the wafer surface, preventing localized stress concentrations that would cause cracking or non-uniform bonding, while still transmitting sufficient force to achieve strong bonds
Solution Approach 2:
The patent uses a thin elastic film or sheet with protrusions and recesses that flexes under bonding pressure. This flexible structure conforms to wafer non-uniformities and distributes pressure evenly across the entire wafer surface, enabling uniform bonding without cracking even when applying maximum necessary pressure
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
The elastic interface ensures consistent and reliable bonding across the entire wafer surface, reducing scrap rates and extending the tool's lifetime while preventing contamination, with manufacturing costs potentially lower than traditional graphite pads.
Implementation Method 1
an elastic interface having raised features which may be used in a wafer bonding tool. The elastic interface may comprise a first surface and a second surface, with the raised features on the first surface disposed in a staggered position with respect to the raised features on the second surface
Data Source
AI summary
An apparatus for bonding a lid wafer to a device wafer includes an elastic interface having a first surface and a second surface. Relieved areas may be created in the elastic interface by removing at least some of the elastic material of the interface, leaving a mesh with nodes. Raised areas may be disposed on the nodes in staggered positions on the first surface relative to the second surface. The bonding pressure deflects the raised features on the first surface in one direction and the raised features on the second surface in another direction. The restoring force of the mesh transmits the pressure through the interface and to a lid wafer and a device wafer, to bond the lid wafer to the device wafer.