How Quartz Tube Stations Work and the Benefits They Provide

Among the many processing steps involved in the manufacture of semiconductor components are high-temperature operations such as diffusion of materials into the silicon wafers. Quartz tubes are an ideal vessel for these process steps because the tubes can withstand the temperatures required and are inert enough to minimize contamination.

Typically, the silicon wafers are placed into a horizontal quartz tube large enough to hold the wafers and their supports. The quartz tube cleaning station can heat the contents up to over 1000 degrees centigrade. In a diffusion process, impurities such as phosphorus are introduced into the quartz tube.

Once the process is complete, the quartz tube is contaminated and has to be cleaned for the next batch of wafers. Complete and reliable cleaning is essential for the semiconductor manufacturing process because contaminating particles can cause defects in the semiconductor components or result in inferior product quality.

How Quartz Tube Cleaning Works

Quartz tube cleaning is a custom-designed process because the dimensions and cleaning requirements of quartz tube furnaces can vary widely. Quartz tubes are mechanically delicate, so they have to be handled with care. At the same time the cleanliness requirements are rigorous so that all traces of the contaminating material have to be removed. Finally, the rinsing and drying process must not introduce any new particles into the quartz tube. The cleanliness of the tube directly impacts the performance of the semiconductor manufacturing facility.

In horizontal quartz tube cleaning stations, the tube is inserted into the cleaning enclosure and cleaned with an acid spray. The acid dissolves and removes the contaminant from the high-temperature furnace. A subsequent rinse cycle removes all traces of the acid from the tube surfaces. A drying cycle can speed up drying without introducing particles into the cleaning enclosure. Mechanical handling of the tubes reduces the possibility of breakage due to human error and minimizes opportunities for the entry of contaminating particles. Safety interlocks, exhaust fans and safety shields protect operators from the hazardous chemicals.

Modutek’s Quartz Tube Stations Offer Numerous Benefits

A key factor in effective customization of quartz tube cleaning stations is that the supplier has to design and build the stations so that they can make the required adjustments. Modutek designs and builds all process, etching and cleaning components in house at the company’s San Jose, California facility. Equipment is customized exactly according to the requirements of the specific application.

In addition to providing customized equipment, Modutek can supply the degree of automation required by the customer. Cleaning process steps can be initiated manually or the whole cycle can be completely automated. Different steps can initially be run and timed manually and then, when optimum performance is reached, automated operation can be locked in.

Full automation reduces human error and keeps operators safe by allowing them to monitor the cleaning process remotely. Automated quartz tube cleaning stations will run the same cleaning job exactly the same way, with identical timing and dosages. Results from an automated system are predictable and uniform and the system can be programmed for the best possible results.

Modutek’s horizontal quartz tube cleaning stations are an excellent solution for semiconductor manufacturers. Rugged and reliable with one-piece construction up to ten feet long, the basic units offer many options for additional features. Once the requirements of the cleaning application are satisfied, Modutek can offer design add-ons such as holding tanks, automation features, a T/C sheath cleaner or a bottle washer. Modutek is a leading semiconductor equipment manufacturer that provides continuous product innovations and improvements along with the highest degree of customer service and support.

Reviewed and Approved by Douglas Wagner
President & CEO, Modutek Corporation

Why High Temperature Quartz Baths Are Required for Silicon Wafer Cleaning

Silicon wafers undergo many process steps during the manufacture of semiconductor components and cleaning the wafers properly is an important factor in successful fabrication. Process steps include etching and diffusion, both of which involve coating the wafer with masking material to guide the etching chemicals or diffusion targets. Once a step is completed, the masking chemicals have to be completely removed. If traces remain or if other impurities are introduced, the quality of the final semiconductor product will be affected.

Silicon wafers are cleaned with aggressive chemicals to remove organic masking material and other possible contaminants. As a result, the cleaning solution container has to be able to resist the action of corrosive chemicals while remaining inert without becoming a source of contamination itself. Baths made of quartz are highly stable, resist corrosion and can be designed and built to avoid contamination. Quartz baths are an ideal solution to the challenges of silicon wafer cleaning and the maintaining of high levels of wafer cleanliness.

How Quartz Baths Clean Silicon Wafers

Quartz baths provide a clean and safe container for the chemical reactions that are used in silicon wafer cleaning. Depending on the materials used, the quartz bath may simply hold the wafers and the cleaning chemicals, but some processes require heating, circulating the solution or the addition of chemicals. In each case, the control actions must be accurate, reliable and easily duplicated.

For example, materials such as hydrochloric acid, sulfuric acid and hydrogen peroxide may be used for cleaning the silicon wafers. Quartz is impervious to these strong chemicals and the quartz tanks remain unaffected while the acids clean the silicon wafers. With SPM clean, sulfuric acid and hydrogen peroxide are mixed and maintained at a constant temperature of about 130 degrees centigrade. Periodic spiking with hydrogen peroxide is necessary because it decomposes in the solution. The mixture cleans wafers rapidly but can’t attack the quartz bath container.

Using bath containers that are inert and don’t contaminate is important because the electrical and physical structures making up modern semiconductor components are extremely sensitive to contaminating particles. As these structures become smaller and more tightly packed on a wafer, even a single particle can interfere with the etching or the diffusion process. Such interference from particles reduces the yield of semiconductor components and affects the productivity of the semiconductor manufacturing facility.

The Benefits of Using Modutek’s Quartz Baths

Modutek has over 30 years experience in quartz bath design and manufacture so that the company’s baths fulfill all the basic requirements for semiconductor processing and deliver additional benefits. Modutek can provide standard units where they satisfy customer requirements but can also design and build custom systems for special applications.

Modutek’s QFa series high temperature re-circulating quartz baths are safe and reliable with a low total cost of ownership. The semiconductor grade quartz of the baths is flame polished to reduce contamination and the vessels are designed for an especially long service life. Particle addition from re-circulating flow is kept to a minimum and remote control is available. Tank sizes range from an inner measurement of 7.75 x 7.75 inches and 9 inches high to 21.5 x 11.5 inches and 10.5 inches high. Custom sizes are available as well.

The QFa baths have an integrated heater that provides an operating range of 30 to 180 degrees centigrade. The heaters produce a temperature rise of 2 degrees per minute and control accuracy is plus/minus 1 degree centigrade, these variables depending on the operating conditions. The wide temperature range, fast thermal response and accurate temperature control make the Modutek quartz baths ideal for silicon wafer cleaning. The high precision guarantees excellent repeatability of the process between batches and the fast heating rate reduces process times. Overall, Modutek’s quartz baths can help improve the semiconductor production performance of manufacturing facilities and research labs. For a free quote or consultation on selecting the right equipment for your manufacturing process contact Modutek at 866-803-1533.

Reviewed and Approved by Douglas Wagner
President & CEO, Modutek Corporation