Automated test wafer handling in semiconductor production

Test and calibration processes tie up a lot of resources in semiconductor production. Fabmatics has developed the Test Wafer Center (TWC) to reduce the associated complexity and increase efficiency. The TWC is a cleanroom system which automates the identification, sorting, and storage of test wafers. All tasks from robotics to IT integration are combined on a single end-to-end platform under the control of a Beckhoff CX series Embedded PC. Plant operators benefit from reduced set-up times, seamless traceability, and significantly greater overall plant efficiency.

The global semiconductor industry is experiencing unabated demand for microchips. Production facilities are subject to strict calibration and monitoring processes to ensure high quality and high yield in semiconductor manufacturing. “Test wafers”, which run through process stations to verify specified parameters, are used in this context. Regular wafers can only be processed once testing and calibration have been completed. Test wafers account for up to fifty percent of the wafers in circulation in modern semiconductor fabs. Logistics and administration are correspondingly complex. This is precisely where automation specialist Fabmatics comes in. The company has decades of automation experience in cleanrooms and supplies systems worldwide that automatically identify, transport, handle, and store wafer cassettes. The new TWC acts as a central hub for test wafers within intralogistics. It automates the kitting, intermediate storage, and re-sorting of test wafers in the cassettes to ensure just-in-time delivery to the process stations.

Minimizing risk through automation

The values handled in semiconductor production are considerable. “The value of a fully assembled wafer cassette quickly exceeds the acquisition costs of the mobile robot that transports it,” says Carsten Grunert, group leader product development at Fabmatics, getting straight to the point. “That’s why process reliability in the plant has top priority.” In many fabs, test wafers were previously provided manually or via fragmented subsystems that were difficult to integrate. “But the less manual intervention in the cleanroom, the fewer sources of error and contamination risks there are,” continues Michael Neumann, whose remit at Fabmatics includes specializing in PLC development. “Ultimately, integrated automation delivers an increased yield of functioning chips.” Damage caused by improper handling, contamination, or simple allocation errors can, therefore, quickly result in high financial losses and significant delays in the production process. In general, time is an extremely critical factor in semiconductor production. Especially after scheduled maintenance intervals, the process systems must be requalified by the test wafers as quickly as possible.

Central control for complex handling

To fully automate the process, Fabmatics has designed the TWC for 200 mm semiconductor fabs as an integrated system with compact dimensions of around 2.8 x 2 m. The system features up to 93 storage bins (equivalent to 2,325 wafers) and 14 material handling locations for wafer cassettes. The mechatronic core is formed by a six-axis robot for handling the cassettes and a SCARA robot that handles the delicate transfer of the individual wafers. On the automation side, Fabmatics relies entirely on PC-based control from Beckhoff. A fanless CX2043 Embedded PC acts as the central controller, bundling the entire control logic and communication as well as the integration of drive technology, image processing, and robotics on a compact hardware platform. The physical integration of the peripherals is decentralized via EK1100 EtherCAT Couplers and various EtherCAT Terminals from the EL series. EtherCAT junctions ensure a structured, fail-safe network topology. The hard real-time capability of the communication protocol enables highly dynamic synchronization of the robots with downstream processes. The TWC also integrates RFID readers for unique identification of the cassettes and camera-based systems for robot positioning.

IT convergence and software engineering

A major advantage of the Beckhoff architecture for Fabmatics is the integration of the TwinCAT 3 automation software. It transforms the embedded PC into a multitasking real-time controller with the complete configuration, PLC programming, and diagnostics located under one roof. Instead of linking isolated systems, Fabmatics programs the entire automation in a standardized development environment. This eliminates interface losses and simplifies plant design. Fabmatics also considers the integration of modern IT toolboxes to be essential. “To facilitate modern programming, code must be versionable today,” stresses Michael Neumann. “By integrating tools such as Git, TwinCAT provides a platform for working on control projects in parallel and across teams.” In addition, this solution makes the source code traceable, increases the reusability of function blocks, and increases general engineering efficiency. Functional safety is also seamlessly integrated with Fabmatics. The TWC uses TwinSAFE Terminals in combination with Safety over EtherCAT (FSoE) to transmit safety-related signals directly via the standard network. “The previously separate worlds of automation and safety technology are merging, eliminating the need for error-prone single-core wiring, reducing the space required in the control cabinet, and cutting costs,” says Carsten Grunert.

Facing new challenges together

The implementation of the automated Test Wafer Center is generating direct economic added value for semiconductor manufacturers. Just-in-time delivery of suitably configured test wafer batches eliminates manual search and sorting times. After maintenance work, the required calibration wafers are available at the process stations without delay, reducing downtime and stabilizing fab output. At the same time, fully automated handling reduces the error rate to a minimum. The seamless traceability of each wafer prevents mix-ups.

In this sense, the TWC demonstrates clearly how PC-based control technology is able to meet the high demands of the semiconductor industry and at the same time open up potential for process optimization. The collaboration between Fabmatics and Beckhoff is constantly evolving. “In addition to conventional control technology, we are also integrating more and more drive technology from Beckhoff in new applications,“ reveals Michael Neumann, “from the highly dynamic servo drives in the AX8000 series to the compact servomotor EtherCAT Terminals in the ELM72xx series and the associated motors.” Fabmatics is looking to the future with technologies such as AI-supported code generation, the use of digital twins, and advanced security concepts. “As Beckhoff is our preferred automation supplier, we will certainly be using the ever-evolving PC-based control modular system again for the challenges that lie ahead,” concludes Carsten Grunert.