OHT: A Key Component of Automation
The OHT vehicle’s passengers are “wafers”. In semiconductor manufacturing, wafers are thin round slices of a mono-crystalline silicon ingot, which serve as major components in the fabrication of integrated circuits. A single wafer will undergo hundreds of physical and chemical steps before becoming a completed product and it is essential to keep delivering these wafers to the equipment more efficiently. To facilitate this, OHT devices are used to deliver wafers automatically to each stage in the production process. After the wafers are loaded into a special container, called a “FOUP” (Front Opening Unified Pod), the OHT vehicles move them around complex routes along the overhead rails.
OHT vehicles travel along a number of different routes and often encounter other vehicles at points where the rails cross or fork. To ensure a steady and collision-free flow, each OHT vehicle and crossing point have their own sensors. When these sensors detect more than two OHT vehicles in a designated section, the OHT devices can automatically slow down to guarantee safe transportation. Among the many technologies adopted by the semiconductor manufacturing facility, this is a good example of the simultaneous utilization of its software and hardware capabilities.
What is more, just as the dashboard of a car displays real-time gauges and alerts, the OHT system has many sensors that monitor the condition of its machine parts, offering diagnostics on parts that need to be inspected or replaced.
The use of automated OHT equipment contributes to enhancing production efficiency, like a well-designed transport system guarantees the smooth flow of traffic across a city. The OHT vehicles can travel on average up to 5m/s (18km/h) along straight tracks and up to 1m/s (3.6km/h) along curved tracks.
Information about OHT vehicles is delivered wirelessly to a central server installed in an integrated control system, which builds up a complete picture of every machine’s movements in the semiconductor manufacturing facility, much like a traffic control center overseeing the traffic flow of an entire city. The integrated control system monitors not only the overall flow of OHT vehicles but also the real-time information on the wait times of each individual vehicle. The system also makes sure vehicles move along designated pathways within their scheduled times. In addition, the system determines the fastest route for each vehicle and can even control the movements of a specific vehicle.
In many aspects, the OHT system offers clues about the future offered by self-driving cars. It carries its passengers faster and more efficiently without drivers. By developing these autonomous vehicles, Samsung Electronics will continue to build and operate smarter semiconductor manufacturing facilities.