Typical requirements for measuring trace impurities in semiconductor production

The requirement to avoid pollution is simple: there should be no oxygen or moisture in the gases used in critical processes such as chemical vapor deposition or plasma etching.

Any analyzer or sensor selected for moisture or oxygen must have a detection level as low as ppb (LDL). Measurements need to be taken near the point of use to reduce the possibility of leakage after measurement, although gas quality can also be checked after storage.

Common oxygen control techniques in semiconductor manufacturing processes

Typically, zirconia and electrochemical sensors are used to measure trace amounts of oxygen in these applications.

The electrochemical oxygen sensing options are current/particle or Hertz battery. The advantages of these products are a low detection limit (LDL) of 100 ppt, small footprint, and ease of installation near each point of use. Both of these technologies are very reliable, with fast response times from low ppm readings to high ppm readings. The sensors used in cost-effective electrochemical analyzers are depleted and need to be replaced within 12 to 18 months, depending on the application and gas being measured. However, replacing sensors is very easy, does not require specialized knowledge, and is usually included in routine plans. Hatch batteries do not need to be replaced, but the electrolyte needs to be filled every few weeks.

For many customers, regular inspections of control equipment are a standard quality routine that will apply regardless of the type of equipment used. However, some people may think that this increases maintenance costs.

The advantage of zirconia oxygen sensing technology is its rapid response to changing conditions, whether from low ppm to high ppm or from high ppm to low ppm, and the sensor is non consumable. Unlike electrochemical sensors, exposure to air does not consume zirconia sensors.

The main disadvantage is the relatively high detection limit (about 0.01ppm O2), which makes them unsuitable for certain applications. Due to the high temperature of the sensor, any hydrocarbons will react with the oxygen on the sensor and give incorrect low readings.

Common humidity control techniques in semiconductor manufacturing processes

There are usually three techniques for measuring trace moisture in semiconductor manufacturing:

Due to the use of optical sensor technology, cavity ring down spectroscopy (CRDS) can provide accurate, stable, and fast measurements. According to the measured gas, the detection limit of the instrument has been reduced to 0.1 ppb. Due to relatively high costs, they are mainly used at central distribution points. If contaminated, maintenance work may be heavy and costly.

Quartz Crystal Microbalance (QCM). Although not as fast as CRDS, these analyzers have a detection limit of 0.05 ppmV and provide reliable long-term measurement and automatic calibration functions. Due to the size of the analyzer casing, despite significant cost advantages over optical technology, these analyzers are typically installed in a central position, such as at gas distribution points. Many models offer excellent life cost ratios and extended maintenance periods.

Ceramic impedance dew point transmitter. It has a high cost performance ratio and is a small part of the cost of other technologies. The sensor can measure as low as 1ppbV and is compact and easy to install at the point of use. To ensure consistent measurement results, recalibration is required once a year. However, this can be performed by the user or combined with other routine maintenance on the system. When a user participates in the manufacturer's sensor replacement program, their sensor will effectively receive a lifetime warranty.

The Importance of Sampling

Whether measuring oxygen or moisture, the correct sampling decision is equally important as choosing the right analyzer, as the speed and accuracy of measurement depend on all parts of the system, not just sensor technology. The type of sampling tube is important, and selecting appropriate accessories for low-level measurements is crucial. Ideally, electropolished stainless steel pipes with high integrity fittings should be used.

If you want to purchase a moisture or oxygen measurement system, be sure to consider sampling in the early decision-making stage and listen to expert advice as much as possible. Only the correct combination of analyzer and sampling system can provide optimal results, prevent premature damage, and ensure reliable and consistent measurement results.

summary

We hope this brief article will provide some insights into the precise measurement options for many trace amounts of moisture and oxygen currently available in the market for semiconductor manufacturing.

The wide range of technologies, analyzers, and brands in the market provides users with the opportunity to choose the right one for their application in terms of performance and budget. However, it is always a good idea to seek expert opinions before making a decision, especially for a system that measures multiple parameters, ensuring compatibility between technology and sampling components.