New SPM Process Provides 75% Improvement in Chemical Savings

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Earlier this year Modutek started implementing its new SPM process with automatic adjustment of the sulfuric peroxide mix concentration and the company now has benchmark results from real process applications. Normally the SPM mixture deteriorates continuously as the hydrogen peroxide turns to water and dilutes the concentration. The SPM mixture has to be completely replaced every eight hours or so at the outside. Costs are substantial for downtime during new mixture pour and for the replacement of the chemicals as well as for neutralizing and disposing of the corrosive mixture in an environmentally safe way. Trying to lengthen the period during which an SPM mixture can be used has been an ongoing process for many companies but without results that provide a safe and reliable alternative.

In the Modutek “Bleed and Feed” system, a “dirty” tank and a “clean” tank are used to continuously compensate for changes in the mixture concentration caused by the degradation of hydrogen peroxide. Periodically when needed, a programmable amount of mixture is drained from the dirty tank and another programmable amount of mixture is automatically transferred from the clean tank to the dirty tank. To compensate, an appropriate amount of sulfuric acid is added to the clean tank and both tanks receive enough hydrogen peroxide to restore the concentration. The “Bleed and Feed” process is designed to maintain the SPM mixture concentration automatically over extended periods.

Benchmark Results from a Real “Bleed and Feed” Application

One of Modutek’s customers that use their semiconductor manufacturing equipment now has real-life results from the use of the company’s “Bleed and Feed” SPM process improvements. The results show significant reductions in chemical use, downtime for re-pour and disposal volumes. Detailed results are based on a 2 6-inch carrier bath size with an 8-hour shift and are as follows:

  • Volume of sulfuric acid used reduced by 77%
  • Chemical disposal volume reduced by 75%
  • Acid neutralizer use reduced
  • Acid re-agent use and cost reduced
  • No downtime to drain and re-pour
  • System drains reduced from three times a day to once a week
  • Increased throughput
  • No original process result changes
  • Increased safety due to less operator interaction with dangerous chemicals

While other companies have tried to develop other SPM clean process improvements involving less chemical use, Modutek’s system is now proven to provide excellent results in real life applications and operate reliably.

Improved SPM Process in Custom Designed Systems

While Modutek has developed a greatly improved method for maintaining SPM process mixture concentrations and reducing chemical use, the new method can be applied in any custom-designed SPM process wet bench. Modutek designs and assembles wet bench products and semiconductor manufacturing equipment at their facility in San Jose, California and can supply systems that exactly meet its customers’ requirements.

Process engineers and facility managers concerned about the environmental impact of high toxic chemical use and the increasing costs of chemicals such as sulfuric acid can contact Modutek for a free quote or consultation to discuss solutions to these issues. Modutek can suggest wet bench systems and follow up with proposals from their complete line of wet bench products. If the SPM process is needed by a customer, Modutek now has the benchmark results on reduced chemical use and improved facility operation.

 

Changes to the SPM Process Improves Efficiency and Results

The sulfuric acid hydrogen peroxide mixture (SPM) process effectively strips and cleans wafers but suffers from instability due to the decomposition of the hydrogen peroxide. A heated bath improves performance but increases the rate at which hydrogen peroxide changes into water. Periodically spiking the mixture with extra hydrogen peroxide can restore the required concentration but affects the strip rate. As a result, the SPM mixture has to be changed frequently, leading to high costs for chemicals and frequent downtime on wet bench stations. Working closely with a local semiconductor manufacturer, Modutek has developed a “bleed and feed” process upgrade that addresses these problems and results in substantially longer mixture life and improved process results.

The SPM Process

A typical mixture for the SPM strip and clean process is one part hydrogen peroxide to three parts sulfuric acid. The sulfuric acid parts can go as high as 7 parts but once the process has started, if the concentration changes, the strip rate can change as well. The mixture is heated to 130 to 140 degrees centigrade to increase the strip rate. The higher the temperature, the faster the hydrogen peroxide decomposes to water, diluting the mixture.

To keep hydrogen peroxide in the mixture, more of the chemical is periodically added to the process, spiking the concentration back to its original level. Despite this, the mixture is normally usable for only a few hours at a time and typically has to be replaced several times a day. Replacing the mixture is costly and requires repeated downtime when processing has to wait for a new pour. In addition to the costs of the chemicals, there are treatment and disposal costs that are required to comply with environmental regulations.

Modutek’s “Bleed and Feed” Process Change

Modutek has developed a hydrogen peroxide spiking method that keeps the chemical mixture at a predictable concentration and avoids the requirement for frequent replacement. The method reduces consumption of the chemicals and lets the system run for extended periods without down- time.

Using a two-tank dirty and clean tank process, the “bleed and feed” method involves draining a programmable amount of mixture from the dirty tank prior to each process step. Another programmable amount is fed from the clean tank to the dirty tank. Then programmable amount of sulfuric acid is added to the clean tank and both tanks receive programmable amount of hydrogen peroxide.

When the entire mixture has to be replaced, normally about once every week, the system has a quick drain feature that reduces down time and gets the process up and running again quickly. The whole “bleed and feed” spiking method is PLC controlled and the periodic adding and spiking of chemicals allows the mixture to be used continuously for days at a time.

Benefits of the Modutek Process Change

In addition to savings related to the reduced use of chemicals, the new update improves overall efficiency and achieves better results. Instead of having to shut down the wet bench station every shift to pour new acid, the process can run for days and only requires a complete chemical change once per week. In addition, the process is cleaner and can deliver better cleaning and stripping performance.

Modutek is offering the SPM process upgrade on their new wet bench stations and can provide details regarding chemical use and performance. The company has the experience and expertise to help customers more effectively use the SPM and other processes to ensure they obtain the results they need. Call Modutek at 866-803-1533 for any questions you have with using either the updated SPM process or other wet processes needed for your application.

 

How the SPM Clean Process is Supported in a Wet Bench Process

How the SPM Clean Process is Supported in a Wet Bench ProcessSemiconductor manufacturing involves multiple processing steps which includes cleaning silicon wafers using wet bench technology. The SPM (sulfuric peroxide mix) clean process uses a solution of approximately 3 parts sulfuric acid to 1 part of hydrogen peroxide at about 130 degrees centigrade to strip organic material and photoresist from silicon wafers quickly and effectively.

Process engineers and facility managers using the SPM process in semiconductor fabrication have to make sure that the chemical ratio and temperature are maintained within safe limits and that the solution and wafers are contained safely in impervious baths. While the concentration may vary from 3 to 1 to a maximum of 7 to 1 and the temperature used may be as high as 140 degrees centigrade, once the solution operating values are chosen, the baths should be maintained at those concentration and temperature values to keep the strip rate uniform.

Modutek’s wet benches support the SPM process with manual, semi-automatic and fully automatic versions. Wet Bench stations are available in a wide variety of configurations as well as in custom designs. The fully automated stations use Modutek’s in house software for automatic process execution with high accuracy, reliability and repeatability. The semi-automated stations can achieve similar results with robotic controls at a lower cost. The manual stations have the same safety and process features without the cost of automation.

Quartz Recirculating Baths

To work well, the SPM solution has to be heated rapidly in a bath that can withstand high temperatures and that will not react with the aggressive chemicals. Heating has to be even and controlled within a narrow range. At high temperatures, hydrogen peroxide decomposes and the solution has to be spiked with more peroxide to maintain its concentration.

Quartz recirculating baths fulfill these requirements. The quartz can be manufactured in a pure enough form to withstand the temperatures and corrosion while the recirculation allows tight control of concentration with the adding of chemicals as required.

This spiking allows operators to use the solution for a longer period of time rather than discarding the solution when the concentration falls below acceptable levels. Re-using the sulfuric acid for as long as possible reduces costs and is desirable from an environmental point of view as well.

Modutek Series QFa Series Quartz Baths

Modutek’s Quartz Baths support the SPM clean process and satisfy key conditions for high safety and reliability as well as low cost of ownership. The tanks are made of semiconductor grade flame-polished quartz and are insulated with high density alumina silica fiber rated to 1260 degrees centigrade. The four-sided heating element promotes fast, even heating and the seamless sloped flange and the dual safety snap switch help ensure safe and convenient operation.

The quartz baths have an operating temperature range of 30 to 180 degrees centigrade and they feature a standard heat up rate of 2 degrees centigrade per minute. Operating temperature can be controlled to within plus/minus 1 degree centigrade and a liquid level sensor is available as an option.

Standard tanks are available in dimensions ranging from 7.75 to 21.5 inches inner side length and in square and rectangular formats. Depths range from 6.75 to 14.5 inches and available heaters are rated 2 to 6 KW. Modutek can design systems with custom vessel sizes to satisfy particular requirements.

Modutek’s wet bench stations and quartz baths are designed with low cost of ownership in mind while emphasizing features that reduce errors and improve reliability. Semiconductor manufacturers can achieve higher throughput and better output quality using the SPM process on the Modutek units. If you want a free consultation or quote on using quartz baths to support your wafer cleaning processes, call Modutek or email [email protected].