Tag Archives: improving silicon wafer manufacturing

How Optimum Particle Reduction is Achieved in a Wet Bench Process

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When microscopic particles remain on the surface of silicon wafers during a wet bench process, the resulting semiconductor products may be of reduced quality or even defective. As semiconductor geometries and microscopic structures become smaller and are packed more densely on a silicon wafer, the presence of particles can influence the etch rate around the particle and compromise semiconductor fabrication. The smallest structures and conductor paths can be influenced by particles in the submicron size range and these particles are especially difficult to remove completely.

Modutek has developed innovative solutions that achieve particle reduction through reduced handling of wafers and excellent particle removal. The single chamber IPA Vapor Dryer and the use of megasonic cleaning deliver excellent results. The reduced particle count produces better yields and higher quality output. At the same time, Modutek’s solutions save money through the reduced use of chemicals.

The Single Chamber IPA Vapor Dryer Keeps the Particle Count Low

Modutek’s single chamber IPA Vapor Dryer incorporates rinsing and drying in a single system to save space, reduce costs, and minimize the handling of silicon wafers. The system initially rinses the wafers with de-ionized water and then introduces IPA vapor into the drying cabinet. The vapor comes from a one-gallon bottle that is located in the exhaust compartment for easy changing.

IPA vapor is introduced into the drying chamber from the top to ensure even distribution and reduce the amount of IPA required. When the IPA vapor condenses on the wafers, a surface tension gradient develops between the IPA and the remaining water. When water flows off the wafer surfaces it can remove the contaminating particles. The dry wafer surface doesn’t have any water marks and no particles are added.

One source of particles is the handling of wafers during transfers between stations. Reducing the number of transfers eliminates a source of particle contamination. Modutek’s Single Chamber IPA Vapor Dryer can handle an optional etching feature and drying in the same system. The wafers are rinsed and dried without transferring them to a new station. Since no additional particles are introduced during this process the particle count is kept to a minimum.

Megasonic Cleaning Effectively Removes Particles Without Toxic Chemicals

Megasonic cleaning relies on high-frequency sound waves in the cleaning solution to remove contaminating particles from wafer surfaces. Modutek has partnered with Kaijo Corporation, a world leader in megasonic cleaning systems to incorporate this technology in their wet bench equipment.

A megasonic generator feeds a high-frequency signal to a transducer immersed in the cleaning tank liquid. The transducer converts the signal into sound waves that travel throughout the tank. The sound waves generate microscopic cavitation bubbles that produce a scrubbing action to clean wafers. Particles on the surface of the wafer are dislodged and washed away.

The higher the megasonic frequency, the smaller the cavitation bubbles and the gentler the cleaning action. The microscopic structures etched into silicon wafers are very delicate and could be damaged with rough cleaning. Megasonic cleaning uses frequencies of 950 kHz and higher. The tiny bubbles of megasonic cleaning deliver gentle cleaning action without damaging fragile silicon structures.

Although megasonic cleaning works well with DI water or an SC1 process, adding a mild detergent or solvent can improve cleaning performance. Particles on silicon wafer surfaces often adhere to the surface and can be difficult to remove. Submicron particles may stay within a surface boundary layer, resisting removal. The microscopic bubbles can dislodge such particles, but the addition of solvents or detergents helps dissolve the bonds holding the particles to the surface and can improve particle removal.

Modutek Innovates to Help Meet Customer Challenges

Modutek works closely with customers to identify issues with wet process applications and continually works on developing new innovative solutions. The Single Chamber IPA Vapor Dryer and the megasonic cleaning process are innovations that help reduce particle counts while reducing chemical use and lowering costs. Modutek’s experience with wet processing equipment ensures customers will continually be able to improve their process performance results. Contact Modutek to schedule a free consultation to discuss your specific process requirements.

How Megasonic Cleaning Improves Silicon Wafer Manufacturing

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When silicon wafers are cleaned between manufacturing steps, it is critical to remove all contamination from the wafer surfaces. The remaining traces of process chemicals or microscopic particles can disrupt the etching process and result in defective or low-quality semiconductor devices.

Megasonic cleaning uses high-frequency sound waves in the cleaning tank to remove contaminants and particles from the silicon wafers. The technology can save time and money because it works quickly and does not require expensive chemicals. Silicon wafers cleaned with Megasonic cleaning are completely clean with a reduced particle count. As a result, the technology can improve the operation of semiconductor manufacturing lines for semiconductor fabricators and research labs.

Megasonic Cleaning Reduces the Use of Toxic Chemicals

The cleaning of silicon wafers after the completion of each semiconductor manufacturing step is accomplished by soaking the wafers in mixtures of chemicals including hydrochloric acid or sulfuric acid. In addition to the cost of the chemicals themselves, there are ongoing costs related to the storage, delivery, and disposal of these chemicals. The possibility of leaks and the disposal of the waste chemicals represent environmental hazards that are continuously being mitigated with tighter regulations. Reducing the use of aggressive chemicals can save money beyond their direct cost and can improve the environmental footprint of the semiconductor manufacturing facility.

With Megasonic cleaning, a frequency generator produces an electric signal in the MHz range that is transmitted to a transducer. The transducer that is immersed in the cleaning solution converts the signal to sound waves in the cleaning tank. The sound waves create microscopic cavitation bubbles that deliver a gentle scrubbing action against the surface of the silicon wafer. The cleaning intensity is strong enough to dislodge impurities and contaminants but will not damage the wafer surface or the microscopic structures that have been etched into it.

When Megasonic cleaning is used to replace some of the traditional cleaning steps, the use of chemicals is reduced. Megasonic cleaning uses plain water or water with the addition of mild detergents. The cost benefits and reduced environmental impact can be substantial, and the areas where Megasonic cleaning is used will have increased worker safety and reduced chemical exposure.

Megasonic Cleaning Can Deliver Improved Cleaning Performance

While acid baths work well for cleaning general contaminants from silicon wafer surfaces, ensuring low particle counts can be challenging. Contaminating particles can block etching and cause defects in the final semiconductor devices. As functions become more and more closely packed on the wafer and microscopic structures become smaller, a single particle can affect the etched shapes and current paths. A key factor for improving output quality and reducing defects is reducing particle counts to a minimum.

Microscopic particles can be difficult to remove from the surface of silicon wafers because they often develop a static charge that allows them to cling to the wafer. Chemicals can dissolve the substances that make the particle adhere to the wafer surface but the static charge often remains as an additional bond. With Megasonic cleaning, very small cavitation bubbles form and collapse in tune with the sound wave frequency in the MHz range. When a bubble collapses near the wafer surface, it emits a powerful jet that dislodges any particle still clinging to the surface. Wafers that have been cleaned with Megasonic cleaning systems have a lower particle count as well as a high degree of cleanliness.

Modutek Can Help with Megasonic Cleaning Integration

As a leading manufacturer of wet process semiconductor manufacturing equipment, Modutek can help customers integrate Megasonic cleaning into their wafer cleaning process. Modutek offers free consultation and can show customers how to realize the benefits of lower costs, better output quality, and improved yields.