Cylindrical Cu Pillar Preforms for Semiconductor Interconnects
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Solution Overview
Problem
The existing method of forming Cu pillars by plating faces challenges in achieving high height/diameter ratios, leading to slower growth, unstable shapes, voids, and reduced productivity, making it difficult to produce Cu pillars with a height/diameter ratio of 2.0 or more, especially when trying to increase the height beyond conventional 50 to 60 µm, which is undesirable for applications like mold-underfill in semiconductor devices.
Innovation Solution
Forming Cu pillars as cylindrical preforms from materials melted and rolled into fine wires, allowing for the adjustment of components and alloying, which are then connected to semiconductor chip electrodes, enabling higher height/diameter ratios and increased productivity without the limitations of traditional plating methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If Cu pillars are formed by plating in deep holes with small diameters to achieve high height/diameter ratios, then the pillar height increases, but the plating solution supply becomes insufficient leading to slower growth and deteriorated throughput
Solution Approach 1:
The patent applies preliminary action by pre-forming Cu pillars outside the semiconductor chip using a plating process, then transferring them to the chip. This separates the pillar formation from the chip processing, allowing pillars to be formed in optimal conditions without the constraints of deep hole plating on the chip, thereby improving both height achievement and production throughput
2Length of moving object
If Cu pillars are formed by plating in deep holes with small diameters to achieve high height/diameter ratios, then the pillar height increases, but the Cu pillars become finer in diameter than targeted and the shapes become unstable
Solution Approach 1:
The patent forms Cu pillars in advance on a separate substrate with optimized plating conditions, achieving precise diameter control and stable cylindrical shapes. These pre-formed pillars are then transferred to the semiconductor chip, eliminating the shape instability and diameter variation problems that occur when attempting to plate directly in deep holes on the chip
3Length of moving object
If Cu pillars are formed by plating in deep holes with small diameters to achieve high height/diameter ratios, then the pillar height increases, but voids form in the deposited Cu and the quality deteriorates
Solution Approach 1:
The patent performs the plating process in advance on a dedicated substrate where plating solution can be supplied adequately, preventing void formation in the deposited Cu. The quality-controlled pillars are then transferred to the chip, ensuring high reliability without the quality deterioration that occurs in deep hole plating
4Length of moving object
If the height of Cu pillars is increased to 200 µm or more for mold-underfill applications, then the applicability for mold-underfill improves, but the time required for production is lengthened
Solution Approach 1:
The patent produces Cu pillars of any required height, including 200 µm or more, in advance on a separate substrate using optimized plating processes. This preliminary formation allows tall pillars to be created efficiently without the time penalty of extended plating on the chip, as the pillars are pre-formed and then transferred in bulk to the semiconductor chip
Solution Approach 2:
The patent segments the manufacturing process into distinct stages: pillar formation on a separate substrate, and subsequent transfer to the chip. This segmentation allows the pillar formation to be optimized independently for high throughput, while the chip processing is not delayed by the time-consuming plating process
Data Source
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AI summary
The present invention has as its theme the provision of Cu pillars on a semiconductor chip and electrical connection of the same during which able to enlarge a height/diameter ratio of the Cu pillars, improve the productivity, and raise the height of the Cu pillars and thereby improve the reliability of the Cu pillars compared with the method of forming Cu pillars by plating. The present invention solves this problem by forming the material for the Cu pillars as cylindrical preforms in advance and connecting these cylindrical preforms to electrodes on the semiconductor chip to form Cu pillars. Due to this, it becomes possible to make the height/diameter ratio of the Cu pillars 2.0 or more. Since electroplating is not used, the time required for production of the Cu pillars is short and the productivity can be improved. Further, the height of the Cu pillars can be raised to 200 µm or more, so these are also preferable for moldunderfill. The components can be freely adjusted, so it is possible to easily design the alloy components to obtain highly reliable Cu pillars.