Post-CMP Brush Structure for Low-Water Wafer Cleaning
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Solution Overview
Problem
Current post-CMP wafer cleaning processes are highly water-intensive, leading to significant water usage in semiconductor fabrication, which strains natural resources and is not efficient, particularly due to the design limitations of conventional PVA brushes that couple pore percentage, pore size, and compressibility, affecting cleaning efficiency and requiring high DIW flow rates.
Innovation Solution
A composite brush design featuring a microporous core with a sleeve made of woven or knitted fabric with freestanding fibers or fiber loops, allowing optimized water flow and contact with the wafer surface, decoupling pore percentage from compressibility and reducing water usage while maintaining cleaning efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional PVA brush with high pore percentage is used, then water flow through brush is sufficient to prevent back diffusion of debris, but water consumption increases significantly
Solution Approach 1:
The brush is divided into multiple layers with different pore percentages. The lower layers (near the core) have higher pore percentage (80-90%) to ensure sufficient water flow and prevent back diffusion, while the upper layers (near the wafer contact surface) have lower pore percentage (40-60%) to reduce overall water consumption. This segmentation allows each layer to perform its specific function optimally.
Solution Approach 2:
Different regions of the brush are assigned different pore percentages based on their functional requirements. The core region requires high porosity for water supply, while the surface region benefits from lower porosity for reduced water usage and improved cleaning effectiveness. This local quality variation resolves the contradiction between water flow requirements and water consumption.
2Quantity of substance
If PVA brush with larger pore size is used, then water flow rate increases to maintain cleaning, but brush compressibility decreases affecting cleaning efficiency
Solution Approach 1:
The brush is segmented into layers with progressively varying pore sizes. Lower layers have larger pore sizes to facilitate water flow, while upper layers have smaller pore sizes to maintain compressibility and cleaning efficiency. This gradient structure allows the brush to achieve both adequate water flow and sufficient compressibility.
Solution Approach 2:
The pore size parameter is varied through the thickness of the brush rather than being uniform. By changing the pore size parameter from larger at the bottom to smaller at the top, the brush achieves optimal water flow in the lower regions while maintaining optimal compressibility in the upper regions for effective wafer cleaning.
3Quantity of substance
If reduction in pore percentage is implemented, then water flow and DIW usage decrease, but compressibility and cleaning efficiency are reduced
Solution Approach 1:
The brush is divided into multiple layers with progressively decreasing pore percentage from the core outward. This segmentation allows the overall brush to have reduced average pore percentage (lowering DIW usage) while individual layers maintain sufficient porosity for compressibility. The layered structure ensures that water flow requirements are met in lower layers while upper layers provide the necessary compressibility for cleaning.
Solution Approach 2:
The brush is constructed as a composite structure with multiple layers of PVA material having different pore percentages. This composite approach allows the brush to exhibit overall reduced water consumption characteristics while maintaining local regions with high compressibility for effective cleaning, thus resolving the contradiction between reduced DIW usage and maintained cleaning efficiency.
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 composite brush design significantly reduces DIW consumption while enhancing cleaning efficiency by optimizing water flow and contact dynamics, allowing for improved removal of particles and residues without compromising cleaning effectiveness.
Implementation Method 1
a microporous core with open cell pores forming microchannels through which the DIW flows from its inner surface to its outer surface
Implementation Method 2
The sleeve comprises a woven or knitted fabric with a plurality of freestanding fibers and/or fiber loops extending above the outer surface of the sleeve
Data Source
AI summary
A brush for post chemical/mechanical polishing cleaning of a semiconductor wafer is provided, the brush comprising a microporous core with open cell pores and an outer layer of a plurality of loop fibers formed on the outer surface of the microporous core, wherein the brush has a first core flow resistance R1, a second through surface flow resistance R2, and a third flow resistance R3 across the surface and wherein R3<R1<R2.