Polyimide Alignment Ring for Wafer Bonding
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Solution Overview
Problem
Conventional die stacking processes face challenges in precisely bonding semiconductor dies to wafers due to alignment issues, particularly with shrinking device geometries, requiring expensive and complex alignment equipment, and existing alignment structures are either too rigid or too soft to effectively guide misaligned dies into proper position.
Innovation Solution
A method involving the formation of a polyimide alignment structure with a rounded upper corner, combined with Sn—Cu material contacts, allows for lateral movement and precise alignment of the die relative to the wafer during bonding, using mechanical-robot assisted alignment and auto-soldering at lower temperatures to form reliable electrical connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional alignment structures made of Al, silicon dioxide, or silicon nitride are used, then the alignment structure provides structural support, but the material lacks sufficient elasticity to effectively guide the die laterally upon physical contact causing excessive damage to both the alignment structure and the die
Solution Approach 1:
The patent changes the material parameter from rigid (Al, oxide, nitride) to elastic (polymer with specific glass transition temperature), transforming the mechanical response from brittle to compliant, thereby reducing damage during die guidance
Solution Approach 2:
The patent employs a flexible polymer alignment structure that can deform elastically upon die contact, allowing the structure to guide the die laterally without causing damage, unlike rigid conventional materials
2Stability of the object's composition
If conventional alignment structures use rigid materials, then the structure maintains its shape, but the collision of the die with such rigid alignment structures does not effectively guide the die into proper position
Solution Approach 1:
The patent modifies the material parameters by selecting a polymer with appropriate elastic modulus and glass transition temperature, enabling the structure to be stable yet compliant enough to guide the die through lateral movement upon contact
3Strength
If polymer materials are used for the alignment structure, then the material is more elastic than Al, oxide or nitride, but they are too soft at the high temperatures necessary during bonding to act as alignment structures as they typically burn at such temperatures
Solution Approach 1:
The patent carefully selects and tunes the polymer material parameters, specifically the glass transition temperature, to ensure the material remains elastic at bonding temperatures without decomposing or burning, achieving a balance between flexibility and thermal stability
Solution Approach 2:
The patent may employ composite structures combining polymer materials with other materials to achieve both elasticity and high-temperature stability, allowing the alignment structure to function effectively during bonding processes
4Manufacturing precision
If expensive and complex alignment equipment is used, then the desired alignment precision is achieved, but the cost and complexity of the bonding process increases significantly
Solution Approach 1:
The patent implements a self-alignment mechanism where the alignment structure automatically guides the die into proper position through physical contact and lateral movement, eliminating the need for expensive external alignment equipment
Solution Approach 2:
The patent introduces an intermediary alignment structure that mediates between the die and wafer, facilitating automatic alignment through controlled physical interaction rather than requiring complex alignment systems
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 enables reliable bonding and electrical connection formation without expensive alignment equipment, minimizing damage to the die and alignment structure, and is effective even with smaller device geometries, using the elasticity of polyimide and self-soldering capabilities of Sn—Cu contacts.
Implementation Method 1
these materials lack sufficient elasticity to effectively guide the die laterally upon physical contact
Implementation Method 2
auto-soldering at lower temperatures to form reliable electrical connections
Data Source
AI summary
A method of bonding a first substrate to a second substrate, wherein the first substrate includes first electrical contacts on a top surface of the first substrate, and wherein the second substrate includes second electrical contacts on a bottom surface of the second substrate. The method includes forming a block of polyimide on the top surface of the first substrate, wherein the block of polyimide has a rounded upper corner, and vertically moving the top surface of the first substrate and the bottom surface of the second substrate toward each other until the first electrical contacts abut the second electrical contacts, wherein during the moving, the second substrate makes contact with the rounded upper corner of the polyimide causing the first and second substrates to move laterally relative to each other.