How Precise Control of the SPM Process Improves Processing Results

How Precise Control of the SPM Process Improves Processing ResultsWhile the SPM (Sulfuric acid Peroxide Mix) or Piranha process quickly removes organic contaminants such as photoresist, it is difficult to control. The cleaning action depends on both the temperature and the concentration of the mixture. Both vary if the process is left to carry on without intervention. Better controls can improve cleaning performance, reliability, and repeatability while increasing the lifespan of the mixture. Modutek has developed advanced controls that maintain temperature and concentration precisely at their desired levels to improve cleaning results.

The SPM Process Suffers from Decreasing Concentration and Slower Cleaning

The SPM mixture is typically about three parts sulfuric acid to one part hydrogen peroxide. The preparation of the mixture is highly exothermic. Once the mixture stabilizes, the wafer cleaning process occurs in a heated tank at 130 to 180 degrees centigrade. The hydrogen peroxide is unstable and decomposes to form water and oxygen. As the amount of water in the mixture increases and the concentration of hydrogen peroxide goes down, the cleaning effectiveness of the mixture deteriorates.

Small amounts of hydrogen peroxide are periodically added to the mixture to correct the problem of a decreasing hydrogen peroxide concentration. This spiking with hydrogen peroxide causes a sudden temperature increase due to the exothermic nature of the mixing process. While spiking solves the problem of a decreasing hydrogen peroxide concentration, the temperature can’t be kept constant. An SPM mixture that is not spiked is useful for about two hours, but spiking with hydrogen peroxide increases the lifespan of the mixture to about one day.

Modutek Has Developed Advanced Controls to Improve Process Results

Modutek’s “Bleed and Feed” process control strategy keeps the concentration of hydrogen peroxide and the mixture temperature within narrow limits. The temperature variations due to spiking and the need for spiking are eliminated. With concentration and temperature controlled accurately, the strip rate of the mixture remains constant and predictable. Reliable timing and repeatability of the process are excellent.

Modutek achieves these results by using a two-tank control system. The process tank is the “dirty” tank, while the second tank is the “clean” tank. At periodic intervals, a small amount of the mixture is drained from the dirty tank. It is replaced with a fresh mixture from the clean tank. The clean tank mixture is then replenished with new chemicals. A programmable controller controls the process, so the dosage intervals and the amount of mixture to be drained are adjustable and recorded by the programmable controller. As a result, once the process controls are optimized, the SPM wafer cleaning process can be run exactly the same way each time.

Modutek’s “Bleed and Feed” Reduces Costs and Provides Benefits

Customers who have switched to Modutek’s “Bleed and Feed” controls find that their costs are reduced, and the process line performance is better. Modutek’s control strategy reduces chemical use, and the mixture lasts longer when the temperature variations caused by spiking are eliminated. Downtime due to having to replace the bath chemicals is reduced as well. The risk of accidents from operators adding too much hydrogen peroxide or from spills is eliminated. In addition to savings from lower chemical purchases, reduced costs include lower chemical handling, storage, and disposal expenses.

Support for the “Bleed and Feed” Process

Modutek offers the “Bleed and Feed” process controls for the SPM process on new wet process stations. As one of the leading semiconductor equipment manufacturers, Modutek continues to work on improving its silicon wafer cleaning equipment to meet customer needs. Since Modutek designs and builds its equipment in-house, innovative features can be developed to support unique customer requirements. Wet bench processes are often specialized, and Modutek can utilize in-house expertise to customize equipment as needed. Innovation and customization make Modutek a valuable partner for wet bench technology.

How Quartz Tanks Provide High Reliability and Safety for Wafer Processing

How Quartz Tanks Provide High Reliability and Safety for Wafer ProcessingBecause quartz is an inert substance that does not take part in acid chemical reactions, quartz tanks are ideal containers for silicon wafer processing. The flame-polished quartz used in Modutek’s quartz tanks is impervious to the powerful acids used for processes such as SC1, SPM, and the Piranha process. Quartz tanks are designed to minimize particle contamination and to accurately control the temperature when required. As a result, quartz tanks deliver superior results for wet bench semiconductor fabrication.

Quartz Tanks Reliably Reduce Particle Counts

As semiconductor products require tighter packing of components, a reduced particle count becomes more important. The size of the microscopic structures etched into silicon wafers is reduced to such an extent that a single particle can distort the required shape. The resulting semiconductor chips can be defective or have reduced quality. Sometimes the performance could be better, or the lifespan is reduced. A low particle count is critical for achieving excellent quality output and a high yield from the semiconductor fabrication line.

Modutek’s quartz tanks reduce particle contamination to improve process results. The high-purity flame-polished quartz used in Modutek’s quartz tanks makes it chemically inert to most chemical compounds, including acids, water, and salt. Since the quartz crystal does not react with the chemicals used in semiconductor fabrication, contamination from the quartz tanks is eliminated.

The quartz tank design reduces particle contamination as well. Modutek’s quartz tanks are based on over 30 years of tank design experience to minimize particle contamination. The seamless design and sloped housing construction eliminate places where particles could become lodged. Actual results from real-world fabrication confirm that Modutek’s quartz tanks deliver low particle counts.

Accurate Quartz Tank Temperature Controls Produce Precise Results

For many wet bench processes, the etch rate depends on how the process is set up. The temperature, concentration, silicon wafer crystal lattice orientation, and possible doping of the silicon wafers all influence the etch rate. Except for the process temperature, they are all determined at the start of the process. The temperature, on the other hand, varies. It rises quickly at the beginning and can change as the etching progresses. Precise temperature control is required for reliable etching results.

The etch rate is critical for determining the shapes and details of the microscopic structures etched into the silicon wafer. If etching does not proceed at the right speed, the etched shapes may be too large or too small. The resulting semiconductor products won’t have the expected characteristics and may have to be discarded.

Modutek’s quartz tanks feature a rapid temperature rise to the temperature set point and precise control. The temperature can be set at up to 180 degrees Centigrade. The temperature rises at up to 2 degrees C per minute and is controlled with a precision of plus/minus 1 degree C. The rapid temperature rise helps achieve high throughput, and the tight temperature control provides excellent repeatability.

Quartz Tank Design Influences Output Quality

The quality of silicon wet etching results depends on low particle counts and accurate control of the process temperature. Modutek’s quartz tanks are designed with these two factors in mind. The tanks support wet bench processes such as SC1 and SPM and deliver consistent etching results. Reduced particle counts and excellent etch rate control are consistent during continuous manufacturing and across different batches.

Modutek Provides Safe and Reliable Equipment

Modutek works closely with customers to improve their wet processing manufacturing results, resolve problems and find solutions. Quartz tanks and other equipment that Modutek provides deliver high reliability and safe operation to support various wet processes. Contact us for a free quote and consultation to discuss your specific requirements.