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Wireless sensor network streamlines semiconductor manufacturing

11 July 2016

Ross Yu and Enrique Aceves explain how a wireless real-time monitoring solution has been utilised to squeeze more efficiency out of the semiconductor manufacturing process.

Semiconductor wafer fabrication facilities (fabs) need to be carefully managed to maximise uptime, yield and throughput. Plant operations teams are constantly looking for new ways to squeeze even fractions of a percent more efficiency out of the manufacturing process. 

At Linear Technology Corporation’s Silicon Valley fab, over 175 specialty gas cylinders are used in the wafer manufacturing process. These gas cylinders need to be closely monitored to ensure uninterrupted supply. To avoid downtime, technicians manually log the pressure of each gas cylinder in the fab three times every day. This process is prone to human error and is costly to maintain. 

It is, typically, a manual process because communications wiring is costly and impractical in the fab. Cylinders are located throughout the facility, and there are often no AC outlets or Ethernet jacks nearby. For safety reasons the building will have concrete walls, making it cost-prohibitive and disruptive to the process to install new wires. 

A better solution
A better solution has been found by Linear Technology, through the use of its own low-power wireless mesh networking solution. A SmartMesh IP wireless mesh network has been deployed to monitor gas pressure in the gas bunker. Every node is powered by a pair of lithium AA L91 batteries for an approximate eight-year battery life, so no additional wiring was needed and no unnecessary downtime was required to install the network. Despite the concrete construction and prevalence of metal structures in the fab, the network has proven to be reliable. Since installation, the network has been up continuously for over 83 days, and has transmitted over 26 million data readings with >99.99999% reliability, which is 100 times better than the stringent ‘5 nines’ reliability expected of high availability communication and computer systems.

In the gas bunker, each cylinder is measured for both tank pressure and regulated pressure and these readings are communicated to a central monitoring system via the SmartMesh network. Each SmartMesh node is connected to a pair of cylinders and sends readings through the wireless mesh network to a web server across the building. In the control room, the fab’s site management software tools display real-time readings and automatically calculate run rates to establish regular schedules for cylinder replacements. In addition, low-pressure thresholds are set to alert facility technicians if cylinders reach low levels prior to the replacement schedule. Alerts are displayed on the control room monitor and via Internet messaging on a 24/7 basis.

By using real-time gas consumption rates, technicians are able to precisely predict when gas cylinders will need to be replaced, reducing waste from unused gas due to premature cylinder changes. The benefits extend beyond efficiencies in day-to-day operations. By centrally collecting gas usage data and making it readily available to plant management, the system enables trend analysis which further identifies opportunities to streamline plant operations by correlating readings with specific semiconductor fab processes and geometries. This helps to optimise fab capacity growth as the need arises. 

“The efficiency gains have more than justified the installation of the wireless gas cylinder monitoring network. As a result, we plan to expand this system across the entire plant to gain further efficiency in our operations,” said Alex McCann, chief operating officer at Linear Technology.

For semiconductor wafer facilities, optimising uptime and increasing operational efficiency results in increased production output. Installation must be non-disruptive, fit within existing space confines and work reliably in the metal and concrete structure.

Dust networks
Linear Technology’s Dust Network products are embedded chips and pre-certified PCB modules complete with intelligent wireless mesh networking software. When embedded into sensor and gateway products, the wireless connection achieves >99.999% data reliability and ultra-low power consumption, enabling sensors to be placed in challenging Industrial Internet of Things (IIoT) environments. 

Ross Yu is product marketing manager, Dust Networks Products at Linear Technology and Enrique Aceves is remote office facilities manager at Linear Technology.

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