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].

How Megasonic Cleaning Technology Improves Silicon Wafer Yields

How Megasonic Cleaning Technology Improves Silicon Wafer YieldsSilicon wafer cleaning is a key process during semiconductor manufacturing that becomes especially critical for smaller microcircuit geometries on 300 mm (approx. 12 inch) silicon wafers. Sub micron particles must be removed from the wafer substrate during processing without damaging the delicate microcircuit structures. Any particles that remain may result in defective semiconductor components or output of low quality.

A process incorporating Megasonic Cleaning technology at higher megahertz frequencies can help remove tiny particles and contaminants without damaging or altering the surface of the wafer. The selection of appropriate frequencies and power levels is important for effective cleaning results. Modutek has partnered with leading ultrasonic cleaning system provider Kaijo Corporation to incorporate Kaijo’s high frequency Megasonic Cleaning technology into the Modutek wet bench process equipment. These wet benches can combine chemical cleaning processes such as SC1 with megasonic cleaning in the megahertz range to remove a high percentage of 0.1 to 0.4 micron particles. Depending on cleaning times and temperatures, cleaning efficiencies of over 99 percent can be achieved.

How Megasonic Cleaning Works

In megasonic cleaning systems, a megasonic frequency generator produces high-frequency sound waves in a liquid via a transducer immersed in a liquid bath. The sound waves are compression waves that generate high pressure at their peaks and low pressure in their troughs. Cavitation bubbles appear in the low-pressure troughs and collapse in the high-pressure peaks. This bubble action in the cleaning liquid removes contaminants from exposed surfaces.

Low ultrasonic frequencies in the range of 20 to 40 kHz produce comparatively large, very energetic bubbles whose collapse can cause cavitation damage to delicate surfaces. For semiconductor cleaning applications, megasonic frequencies in the MHz range generate much smaller, less energetic bubbles. Their gentle cleaning action does not damage the wafer surface while still cleaning effectively.

At the same time, the bubbles agitate the cleaning solution, reducing boundary layers and promoting cleaning solution access to small surface features such as crevices and complex shapes. Using megasonic cleaning in silicon wafer manufacturing improves the effectiveness of the chemical cleaning solution by removing small sub-micron particles through the action of energetic bubbles.

Modutek Megasonic Cleaning Systems

Modutek has been in partnership with Kaijo Corporation to improve the cleaning performance of their wet benches by incorporating the use Kaijo’s Megasonic Cleaning technology. Kaijo Corporation is a world leader in megasonic and ultrasonic cleaning systems and Modutek incorporates the Quava megasonic cleaning system generator into their wet bench equipment for this application.

Modutek’s Megasonic Cleaning System that utilizes Kaijo’s megasonic generator operates at 950 kHz in the standard version. Frequencies of 200 kHz, 430 kHz, 750 kHz and 2 MHz are also available for cleaning applications that require a more or less robust cleaning action. The Megasonic Cleaning System can operate at power levels of 600, 900 or 1200 W.

Modutek has incorporated Megasonic Cleaning into their wet benches in either indirect or direct bath designs. Indirect Megasonic Cleaning can operate at temperatures of up to 140 degrees centigrade while the direct design places a Teflon-coated transducer directly into the tank and can operate at up to 70 degrees centigrade. Both designs offer optimal sub micron particle removal without cavitation damage to the silicon wafers at the standard 950 kHz frequency.

Decision makers at semiconductor manufacturing facilities can use Modutek’s wet benches that incorporate the use of megasonic cleaning technology to improve yields. Cleaning times are reduced while cleaning effectiveness is higher and lower chemical consumption can contribute to better cost control. Improved removal of small sub-micron contaminants and particles can reduce wafer defects and produce better quality output. If you need to improve wafer processing quality and yields and want a free consultation or quote on using wet bench stations that incorporate megasonic cleaning technology, call Modutek or email [email protected].