Improving industrial processes

Ross Yu, & Enrique Aceves, Linear Technology


Wireless sensor networks keep semiconductor wafer fab running efficiently

The problem

Critical to the manufacturing of semiconductor wafers is the meticulous, precision deposition of many layers of chemical materials to form the thousands, to millions, and in some cases, billions of transistors that make up a wide variety of complex integrated circuits (ICs). During the fabrication process of these ICs, different chemical gases are precisely metered at every step with usage varying widely as dictated by the different processes. For the most part, these steps are highly automated (see Figure 1). What is not automated, interestingly, is the simple keeping of adequate supply of these gases.

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Figure 1 – Improving Manufacturing Efficiency - Semiconductor companies use real-time monitoring to squeeze more efficiency out of the manufacturing process.

At Linear Technology’s Silicon Valley fab near San Jose, California, over 175 specialty gas cylinders are used in the wafer manufacturing process. These gas cylinders are closely monitored to ensure uninterrupted supply. Any unplanned interruption of gas supply would result in hundreds of thousands of dollars of wafer scrappage, revenue loss and create unacceptable delay in product shipments to customers. To avoid downtime, technicians manually log the pressure of each gas cylinder in the fab three times a day. This manual process is prone to human error and is expensive to maintain.

Previously, this manual datalogging was used because communications wiring is deemed expensive and impractical in the fab. Cylinders are located throughout the facility, and for most of the cylinders, there are no AC power outlets or Ethernet jacks nearby. The building is constructed of concrete walls for safety and seismic (earthquake) reasons, making it cost-prohibitive to install new wires. Furthermore, a large construction project to install power and communications wires would disrupt the manufacturing process, causing factory downtime.

Wireless mesh network solves the problem

In order to solve the wiring problem without disrupting the fabrication process,

a 32 node SmartMesh IP wireless mesh network is initially deployed to monitor the pressure of each gas tank in the closet (see Figure 2). Every node is powered by a pair of lithium AA L91 batteries to provide for approximately 8-year running life on normal operation. So no additional wiring and no unnecessary downtime is required to install the network, and only infrequent periodic maintenance is required to change out the batteries.

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Figure 2 – Gas Closet in Semiconductor Manufacturing Facility – Wireless nodes must perform reliably among pervasive metal and heavy concrete construction.

Despite the concrete construction and prevalence of metal structures in the fab, the network has proven to be highly reliable. As of this write-up, the network has been up continuously for over 83 days, and has transmitted over 26 million data packet readings with only 1 packet lost, which translates into >99.99999% reliability. This is 100 times better than the stringent “5 nines” reliability expected of high availability communication networks and computer systems. This level of network reliability ensures the factory to sustain maintenance free as well as to allow for adverse changes in the factory and RF environment.

In the gas closet, each cylinder is measured for both tank pressure and regulated pressure and these readings are communicated to a central monitoring system via the SmartMesh® wireless 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 and trend lines to predict regular schedules for cylinder replacement (see Figure 3) needs.

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Figure 3 – Predicting Toxic Gas Usage with Software Analytics – Real-time gas usage readings are wirelessly sent to plant software which predicts gas replenishment schedules and helps in capacity planning.

In addition, low-pressure thresholds are set to alert facility technicians should cylinders reach advanced warning levels prior to the scheduled replacement. Alerts are displayed on the control room monitor and via Internet messaging to both facility technician and plant management on a 24/7 basis.

Data analytics drive improved efficiency

By using real-time gas consumption rates, technicians can 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, this 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 optimize fab capacity growth as the need arises.

“The efficiency gains have more than justified the installation of the SmartMesh gas cylinder monitoring network. As a result, we plan to expand this wireless mesh system across the entire plant to gain further efficiency in our operations,” stated Alex McCann, Chief Operating Officer of Linear Technology.

For semiconductor wafer processing facilities, optimizing uptime and increasing operational efficiency results in increased production output, improved yield and reduced down time. SmartMesh IP wireless mesh networks enable non-disruptive installation to retrofit a running fab and monitor its gas cylinder usage. The wireless nodes fit within existing space confines and work reliably in the metal and concrete structure, while relaying real-time readings to plant management software. This data enables quick and accurate gas usage estimation, ensuring timely replenishment, reducing downtime and wasted gas. Data points are logged and used to aid capacity planning.

Dust networks

Linear Technology’s Dust Network products are chips and pre-certified PCB modules complete with wireless mesh networking software. When embedded into customers’ sensor and gateway products, the resulting wireless connections achieve >99.999% data reliability and ultra-low power consumption, enabling sensors to be placed in challenging Industrial Internet of Things (IoT) environments – anywhere. Dust Networks’ products are field proven, with over 50,000 customer networks deployed in 120 countries.