Wireless sensor network streamlines semiconductor fabrication facility operations
Semiconductor wafer fabrication facilities ("fabs") are carefully managed to maximize uptime, yield, and throughput. Plant operations teams are constantly looking for new ways to squeeze even fractions of a percent more efficiently out of the manufacturing process (see Figure 1).
At a Silicon Valley fab, more than 175 specialty gas cylinders are used in the wafer manufacturing process. These gas cylinders must be closely monitored to ensure uninterrupted supply. An unplanned interruption of gas supply would result in hundreds of thousands of dollars of wafer scrap, revenue loss, and 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.
This is typically done manually because communications wiring in the fab is expensive and impractical. Cylinders are located throughout the facility, and, for most of the cylinders, there are no ac outlets or Ethernet jacks nearby. The building is constructed of concrete walls for safety 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 and cause factory downtime.
Wireless mesh network as a work-around
To get around construction and downtime, a 32-mote wireless mesh network is deployed to monitor gas pressure in the gas bunker (see Figure 2). Every node is powered by a pair of lithium-ion (Li-ion) batteries for an approximate eight-year battery life; no additional wiring and no unnecessary downtime were required to install the network.
In spite of the metal structures and concrete construction, the fab’s network has proven to be extremely reliable. As of this write-up, the network has been up continuously for more than 80 days and has transmitted more than 26 million data readings with >99.99999% reliability. This 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 mesh network. Each mesh node is connected to a pair of cylinders and sends readings through the wireless mesh network to a web server across the building. The fab’s site management software tools in the control room display real-time readings and automatically calculate run rates to establish regular schedules for cylinder replacements (see Figure 3). 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 via Internet messaging on an around-the-clock basis.
Real-time data optimizes production, assets
By using real-time gas consumption rates, technicians can predict when gas cylinders will need to be replaced, which reduces waste from unused gas due to premature cylinder changes. The benefits extend beyond day-to-day operational efficiency. 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 mesh 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," said Alex McCann, chief operating officer (COO) of Linear Technology.
The wireless mesh network is designed to streamline manufacturing operations, monitor gas cylinder usage, and relay real-time readings to plant management software. This data enables quick and accurate gas usage estimation, which ensures timely replenishment, reducing downtime and wasted gas. Data points are logged and used to aid capacity planning.
For semiconductor wafer facilities, optimizing uptime and increasing operational efficiency result in increased production output. To achieve this, installation must be nondisruptive, fit within existing space confines, and work reliably in the metal and concrete structure.
Ross Yu, product marketing manager, Dust Networks Products, Linear Technology; Enrique Aceves, remote office facilities manager, Linear Technology. Edited by Eric R. Eissler, editor-in-chief, Oil & Gas Engineering, email@example.com.
- Data from the mesh network enables quick and accurate gas usage estimation, which ensures timely replenishment, reducing downtime and wasted gas.
- For semiconductor wafer facilities, optimizing uptime and increasing operational efficiency result in increased production output.
Wireless mesh networks can replace traditional, physical wires or cables, which will do away with construction or any associated downtime. Could your plant benefit from a wireless mesh network?
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