3D Die Stack Pad Structure for Heat Dissipation and Stable Bonding
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Solution Overview
Problem
As the number of stacked semiconductor dies in high-bandwidth memory increases, heat dissipation and bonding problems become significant challenges due to the limitations in pad structure design, leading to inefficiencies in thermal management and stability.
Innovation Solution
The semiconductor die stack structure incorporates a pad structure with an enlarged volume, featuring a front-side and back-side pad configuration that includes multiple layers and patterns to enhance heat dissipation and bonding stability, utilizing a staircase and reverse staircase design for the front-side and back-side pads, respectively, with unified metal layers for improved connectivity and thermal conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of stacked semiconductor dies is increased to improve memory capacity, then the memory capacity is improved, but heat dissipation becomes more difficult and bonding stability deteriorates
Solution Approach 1:
The pad structure transitions from a conventional two-dimensional planar configuration to a three-dimensional multi-layered structure with vertical stacking. The front-side pad includes multiple layers (first front-side pad layer, second front-side pad layer, third front-side pad layer) arranged vertically, and the back-side pad includes multiple layers (first back-side pad layer, second back-side pad layer, third back-side pad layer) arranged vertically. This dimensional transition increases the effective pad area and volume without increasing the horizontal footprint, thereby improving heat dissipation capacity and bonding stability while maintaining high memory capacity through vertical die stacking.
2Quantity of substance
If the number of stacked semiconductor dies is increased to improve memory capacity, then the memory capacity is improved, but bonding stability deteriorates
Solution Approach 1:
The pad structure employs a composite multi-layered configuration where front-side pad layers (including copper and barrier layers) are bonded to corresponding back-side pad layers. Each bonding interface consists of multiple material layers working together: copper layers for electrical conductivity, barrier layers for diffusion prevention, and adhesive layers for mechanical bonding. This composite structure at each bonding interface enhances overall bonding stability and reliability, enabling stable operation of high-capacity stacked memory devices.
3Ease of manufacture
If a conventional pad structure is used to simplify manufacturing, then the manufacturing process is simpler, but heat dissipation efficiency and bonding stability are insufficient
Solution Approach 1:
The pad structure is segmented into multiple discrete layers with distinct functions: first pad layers for electrical connection, second pad layers for mechanical bonding, and third pad layers for thermal management. Each layer can be independently optimized and manufactured using standard semiconductor fabrication processes such as sputtering, electroplating, and CMP. This segmentation allows the complex multi-functional pad structure to be manufactured through sequential application of conventional processes, maintaining manufacturing feasibility while achieving superior heat dissipation and bonding performance.
4Ease of manufacture
If a conventional pad structure is used to simplify manufacturing, then the manufacturing process is simpler, but bonding stability deteriorates
Solution Approach 1:
The pad structure incorporates preliminary bonding layers and adhesive layers that are formed in advance during the semiconductor fabrication process, before the actual die stacking and bonding operations. The first front-side pad layer, second front-side pad layer, and third front-side pad layer are pre-formed with appropriate thicknesses and material compositions to ensure optimal bonding performance. Similarly, back-side pad layers are pre-configured. This preliminary preparation of bonding interfaces with multi-layered structures ensures stable bonding when dies are stacked, while still using standard fabrication processes.
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 enhanced pad structure improves heat dissipation efficiency and bonding stability by increasing the surface area and volume of the pads, facilitating stable copper-to-copper bonding and reducing contact resistance, thereby addressing the thermal management and bonding issues in high-bandwidth memory systems.
Implementation Method 1
The enhanced pad structure improves heat dissipation efficiency and bonding stability by increasing the surface area and volume of the pads
Implementation Method 2
facilitating stable copper-to-copper bonding and reducing contact resistance
Data Source
AI summary
A semiconductor die stack structure includes a base die, a plurality of semiconductor die stack units, and bumps. Each of the plurality of semiconductor die stack units includes a lower semiconductor die and an upper semiconductor die. Each of the lower semiconductor die and the upper semiconductor die includes a body and a front-side pad structure. The front-side pad structure includes a front-side pad seed layer and a front-side pad pattern. The front-side pad pattern includes a first front-side pad portion, a second front-side pad portion, and a third front-side pad portion. The first front-side pad portion and the second front-side pad portion forms a staircase. The first front-side pad portion and the third front-side pad form a reverse staircase. The first front-side pad portion, the second front-side pad portion, and the third front-side pad include a same metal.