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Fig 1.) Stratus’ patent-pending ShearPlate technology creates programmable fluid agitation less than 2 mm from the surface of the wafer, resulting in the thinnest, most uniform diffusion layer in the industry -- as much as four times narrower than competing technologies.

Fig 2.) Comparison of Stratus boundary layer thickness with traditional horizontal fountain cell system.

Electro-Deposition of Metals

For the first time, wafer fabs can enjoy the process and cost advantages of thin boundary layer electro-deposition. The Stratus high throughput electro-deposition system integrates the wafer quality and process advantages of vertical orientation with the economic advantages of parallel processing. The Stratus is designed specifically for long deposition time processes for applications such as gold and solder wafer bumping, redistribution layers, integrated passives, and various MEMS layers.

Wafer bumping, integrated passives, redistribution layers, and MEMS applications are fundamentally different from copper damascene electro-deposition in ways that make thin boundary layer deposition the preferred choice:

• Layers are thick and deposition times are long, typically 5-60 minutes.
• Deposition rate and uniformity benefit from a thinner and more uniform boundary layer.
• Resist structures require vigorous agitation to ensure wetting and to avoid bubble entrapment.
• Multiple metal layer structures are becoming more common.

Economical electro-deposition of these resist patterned structures requires a two-pronged approach:

1. Obtain the highest possible deposition rate for a given metal system by making the fluid boundary layer thin and uniform. Stratus' new Shear Plate technology provides a boundary layer 1/5 of that in fountain systems without the radial non-uniformity inherent in rotating wafer fountain cells.¹
2. Use an architecture that minimizes the cost of expensive wafer handling automation while allowing parallel processing of many wafers. Stratus' vertical line architecture provides dual wafer processing in 20 cm wide deposition modules wherein the number of modules may be adjusted for a particular application to match the 40 wph of the system front end.

A single Stratus production system can have the throughput of two horizontal fountain cell systems!

Industry-leading seal and contact ring eliminates deposition uniformity variations, thus increasing wafer and device yield.

¹Diffusion Boundary Layer Studies in an Industrial Wafer Plating Cell (PDF), Journal of The Electrochemical Society, 152 (5) (2005)

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