Brief History

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Around twenty years ago, P&S Galvasols had the chance to recover and implement a formulation, based on potassium gold sulphite, in order to fulfil the needs of the growing demand of the dental field, where electroformed pure gold caps were required. Several years later, after a series of deposition trials at different working condition, the process revealed to be suitable for many other applications where a pure, smooth and ductile gold deposit was required.

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Current Status

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On the other hand, the semiconductor manufacturing companies were still having some

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• Technical problems related to the process management

• Environmental issues, due to the presence of toxic metals with the commonly used sodium sulphite based, pure gold electrolytes

 

Current Issues

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Technical

• Too alkaline pH photoresist attack carbon in the gold layer deposited on wafer structures

• voids!

• Working at °C and CD far below optimum range, to reduce the above issue, was bringing to a consistent decrease of wafer throughput.

 

Environmental

• The presence in the electrolyte of toxic materials, not so easily detectable in the environment and in humans, was accepted only because of lack of alternatives

 

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Observations

 

After a series of tests with GEEFORM 2024-SKS, carried out in a fountain plating tool very closely reproducing the working condition of a “cup-plating” unit, P&S found that

• no photo-resist attack was present on wafers;

• optimum t °C and CD could be used;

• deposit micro-roughness, hardness and resistivity were within the required values

• In addition, no carcinogenic, toxic or harmful material being present, the gold plating solution was also 100% RoHS compliant.

 

Main Electrolyte Features

 

• Neutral pH solution

• Mainly potassium sulphite based

• No harmful, toxic, dangerous or carcinogenic element contained

• Interconnected flexibility of working parameters (gold concentration, temperature and

current density)

• Easy to manage and simple to control

• Hardness can be changed from 110 to 250 Hv, depending on specific application needs

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Operation Flexibility

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Depending on requirements, the electrolyte can be made-up

 

• With higher gold concentration (up to 30 g/l) , in order to operate with current densities up to 3.0 A/dm2, thus substantially increasing the number of wafers produced per time unit;

• with different ratios between sulphite salts, to change the deposit hardness, if required

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Standard Process Operating Condition

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Gold deposit characteristics of wafer application

 

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Advantages found in wafer plating trials

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• High deposition rate at optimum temperature value

• No resist etching at all, thanks to neutral pH

• High wafer throughput, thanks to high CD possible

• Increased bath working life (poor organic pollution)

• Reduced micro-mask effect in the deposited metal

• Very good thickness distribution on the wafer

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Summary

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• GEEFORM 2024-SKS is an innovative, sulphite based, high efficiency electroplating process, especially designed to produce stress-free and finegrained, high purity gold deposits.

• Deposits obtained from GEEFORM 2024-SKS show a much better surface texture and thickness distribution compared to all others sulphite based electrolytes.

• The neutral pH of GEEFORM 2024-SKS enables the electrolyte to be perfectly compatible with mostly all types of photosensitive masking polymers used in semiconductor manufacturing and other selective plating applications.

• Even with extended contact time at typical plating temperatures of 52°C, there is no under-etching or chemical attack of the resist.

In wafer plating, its excellent chemical stability and resistance to contamination, under standard working condition, results in a high degree of performance and long working life of the product (around 10 MTOs).

• The absence of any dangerous, harmful or toxic substance (thallium, arsenic, cyanides, ammonia, etc.) in the solution makes it an attractive process even at logistic level, eliminating most of the risks on transport, warehousing and spent solution handling, and reducing related costs

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Conclusions

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• GEEFORM 2024-SKS is a unique, innovative pure gold plating process, designed for high productivity of electronic components, particularly suitable for wafer and packaging.

• The characteristics of its chemistry (stable, long life and green) make it a high throughput process, able to effectively reduce wafer fabrication costs.

• GEEFORM 2024-SKS is also the highest expression of environmentally safe chemistry, absolutely eco-compatible and eco-sustainable, aligned with all the most ambitious projects of all leading semiconductor companies, more and more looking for GREEN AND COST REDUCING plating chemistry.

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IP and Patent

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• GEEFORM 2024-SKS process has a consistent technical background and P&S applied for an invention patent on September 2021, to protect the IP.

• After PCT application (October 2021), it has been published in December 2021. Some months ago the “inventive step” has been assigned and a procedural interview to the inventor has followed.

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