Improving Silicon Wafer Processing with High Temperature Quartz Tanks

Because silicon wafer processing uses acids and bases, the process requires tanks that are impervious to aggressive chemicals. Quartz tanks are stable and do not take part in wet process chemical reactions, even at the high temperatures reached during some of the process steps. Modutek’s quartz tanks use pure flame-polished quartz to reduce impurities that might contaminate the chemical reactions. To keep the temperature at the setpoint, Modutek has added precise temperature controls. As a result, Modutek’s quartz tanks represent an ideal way to implement wet process wafer fabrication steps.

Quartz Tanks Improve Output by Reducing Contamination

The output quality of wet process semiconductor manufacturing is directly affected by contamination during silicon wafer processing. When microscopic particles adhere to wafer surfaces, wafer etching can be disrupted and the semiconductors produced by the manufacturer can be defective or of poor quality. A major concern during silicon wafer processing is the reduction of the particle count on the surface of each wafer.

The high-purity semiconductor grade quartz used in Modutek’s tanks is made up of a crystal lattice containing tightly-held atoms of silicon and oxygen. These elements remain locked in the lattice while the wet process chemical reactions of wafer cleaning, stripping, and etching take place. This ensures that the quartz tanks act as neutral containers and don’t add contaminants or particles to the wafers.

After processing a wafer through one of the many steps of semiconductor manufacturing, a wafer has to be clean and almost completely free of particles. When Modutek’s quartz tanks are used for processing, potential particle contamination from the tanks is significantly reduced. The tanks are based on over 30+ years of bath design and feature a seamless, sloped flange construction. This is especially important for semiconductor manufacturing as industry trends have been moving toward tighter packing and reduced structure sizes. This means even a single small particle can block an etched path or result in a defective structure. By reducing particle counts, Modutek’s quartz tanks improve manufacturing results.

Quartz Tanks with Tight Temperature Control for Improved Etching Precision

The exact shape and location of etched structures in the silicon are critical for the correct functioning of the final semiconductor device. Etching speed determines the shapes of the etched structures in the silicon and the speed is controlled by the chemical concentration and the reaction temperature. The chemical concentration is set at the beginning of the process steps for most of the processes, but the temperature can be used to control the etching speed.

Modutek’s quartz tanks are designed to keep the temperature at exactly the setpoints required for the process and to deliver the anticipated etch speed. The bath temperature can be controlled precisely up to 180 degrees centigrade and the tanks feature a quick temperature rise of up to 2 degrees centigrade per minute with an accuracy of plus/minus 1-degree centigrade.

Heating is even and the fast rate of temperature increase improves throughput. The high accuracy allows precise prediction of etching distances and reliable repeatability of the process when different batches are manufactured. Tank design provides high reliability and safety with a view to a low total cost of ownership.

Using the Right Quartz Tanks Improves Processing and Overall Output Quality

As a leading semiconductor equipment manufacturer, Modutek works with customers to design processing equipment that will help them meet manufacturing requirements. Modutek’s recirculating and constant temperature quartz tanks improve silicon wafer processing by reducing contaminating particle counts and ensuring precise control of etching. The reduced particle counts and the reliable production of required etched shapes reduce defects and rejects in manufactured devices. Contact Modutek for a free consultation and quote on selecting the right equipment to support your manufacturing requirements.

How Megasonic Cleaning Improves Silicon Wafer Manufacturing

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.