Clean room robot with precious cargo
Robots moving parts from A to B may sound like a routine procedure. It is a very different matter, however, when they are handling wafers in the back-end area, since at this stage, a single wafer can be worth as much as 10,000 euros. SÜSS MicroTec relies on the high-precision Stäubli TX60L cr robot to ensure ultra-safe handling of these precious cargos.
Asia virtually has a stranglehold on the semiconductor market, yet the SÜSS MicroTec Group is able to compete in the same league where wafer processing is concerned, with customers all around the world who value the company’s expertise. The SÜSS MicroTec Group has over sixty years of experience in the design and manufacture of process solutions for micro-structural applications. The range of solutions comprises all stages in wafer processing: coating, baking, developing, aligning and bonding of wafers.
Solutions from SÜSS MicroTec are deployed across a wide range of manufacturing processes for domestic and/or industrial applications, including memory chips, cameras for cell phones and tire pressure sensors. One member of the Group is SÜSS MicroTec Lithography GmbH, with production facilities in Garching and Vaihingen an der Enz. The Vaihingen factory specializes in lithographic processes for wafer handling in the back-end area and offers a comprehensive product portfolio of coaters and developers, ranging from inexpensive laboratory equipment to highly efficient production systems for 300mm wafers.
One hundred percent control of the processes plus fast, precise and reliable handling of the wafers with negligible breakage rates in the ppm range have won over customers around the world. Stefan Lutter, Product Manager (Coaters) at SÜSS MicroTec: "Another reason for our strong market position, particularly in Asia, is our high degree of flexibility. As a German manufacturer of special machines, we have a very high level of competence in the customization of equipment, whereas our Asian competitors focus primarily on the construction of purely standard plant."
Innovative coater and developer systems featuring robotic handling
Even in standard configuration, the systems are designed to be very flexible, as exemplified by the ACS 300 Gen2 modular coating and development cluster. The system can be used without mechanical modification for the processing of 200mm and 300mm wafers. The main application areas are, first and foremost, in sophisticated coating processes, in wafer level packaging applications and in 3D integration. Compact design and two loading modules mounted directly on the base frame ensure optimum operating cost efficiencies. The ultra-precise Stäubli TX60L cr (i.e. clean room) robot undertakes all handling tasks within the system. In the back-end area, clean room requirements range from ISO 3 to ISO 4 and are easily met by the clean room version of the TX60L.
The ACS300 Gen2 is composed of a base frame and four different module slots. These can be equipped with different modules, i.e. coater and developer, as well as with heating and cooling plate stacks. In addition, a frame extension is available which can accommodate two additional heating and cooling plate stacks. This makes it possible to configure the plant either for coating or for developing purposes only, or as a combined system for both coating and developing. The user-friendly in-house control system facilitates straightforward operation of the plant – the operator simply assigns certain "recipes" to each module, detailing the wafer’s route through each particular station.
The ACS 300 Gen2 is a back-end system through which wafers pass during the final handling stages. The wafers have become extremely valuable at this point, because some 90 percent of the production steps have already been completed; consequently, very high demands are put on the SÜSS MicroTec equipment in terms of reliability, repeatability, uptime and safe handling. "It is extremely serious when a wafer breaks in our system," adds Lutter. "After all, its value can range from 1,000 to 10,000 euros, depending on version and type. Such a wafer can produce anything from 1,000 to 10,000 chips which are used in computers, mobile phones, and LEDs. So at this stage of production, you simply do not want any rejects, nor can you afford them. This puts correspondingly high demands on the robot's performance."
Six-axis machine instead of 3-link robot
SÜSS consistently uses the six-axis Stäubli TX60L cr robot in its modern ACS 300 Gen2 coater. That the compact articulated-arm robot is the machine of choice rather than the classic 3-link robot that is commonplace in the industry clearly lies in the Stäubli robot's performance, as Rainer Targus from SÜSS MicroTec's research and development department explains: "There is a considerable gain in flexibility with the six-axis machine as compared to a 3-link robot that has freedom of movement in only three planes. The TX60L in particular with its long arm can reach quite a distance. This greater working area enables the modules to be arranged much more flexibly within the system. The Stäubli robot with its much higher payload capacity also scores in comparison with the 3-link manipulators, which quickly becomes the deciding factor, taking into account the extreme accelerations in conjunction with the weight of gripper and wafers." In addition, the TX60L has higher placement accuracy within its reach and greater repeatability when compared to 3-link systems, which is an essential feature in wafer edge bead removal.
The robot has plenty to do in the plant because, with the exception of manual loading, all the remaining steps are fully automated. The operator loads the plant by inserting a cassette that contains 25 wafers, known as a Front Opening Unified Pod (FOUP) in the jargon of the industry. A load port module opens the FOUP and scans the contents. The system detects the number of wafers and their exact location. Information concerning the number of wafers to be processed is communicated to the plant's control system. Intelligent, self-optimizing scheduling is the controller's key feature. After the operator has inputted the job settings and the "recipes", the system controller determines of its own accord the optimum time management for the complex sequence of tasks without any human intervention.
Processing can now begin; it is time for the Stäubli TX60L cr to get down to work. The robot picks the wafer from the cassette and moves to a centering station where, by means of image processing, the exact position of the disk in the gripper is determined. The image processing unit now sends data concerning the amount of deviation from the optimum coordinate values that it has detected to the robot's controller so that the wafer can be placed, precisely centered, in the assigned module. The robot is, of course, also tasked with inserting and retrieving the wafer at all four process modules in the plant and with placing the finished wafer back into the FOUP.
Placement accuracy of ± 50 microns
Stefan Lutter: "The robot has to be ultra-precise when placing wafers in the process modules. With the high-precision Stäubli TX60L, we are able to realize our stated goal of an absolute placement accuracy of ± 50 microns in the modules." This is due in no small part to the patented JCM drive technology of the Stäubli robot. The high path accuracy of the robot is also a major benefit when picking and inserting wafers in cassettes and modules. Without the slightest hint of a tremble, the robot handles the costly wafers in an exemplary manner and with total reliability. Wafer breakage is consequently excluded from the process.
Cycle times for the system vary considerably depending on the task in hand. Module times are the limiting elements for certain "recipes" and sequences. The robot's cycle time is the determining factor in other tasks. Rainer Targus: "In both cases we benefit from the ultra-fast cycle times of the Stäubli robot which works with the utmost precision despite the high acceleration values involved, safely avoiding damage to the wafer."
That only six-axis robots produced by Stäubli are used nowadays in the innovative ACS300 Gen2 clusters built by SÜSS MicroTec is anything but a coincidence. Stefan Lutter: "We carefully scrutinized and compared robots manufactured by various companies. There is only one robot that meets our specification for this application which demands the optimum combination of range, speed, accuracy and reliable handling. That is the reason why we opted for Stäubli."
For further information, please contact:
Stäubli Tec-Systems GmbH
Head of Marketing
Phone: +49 (0)921 88 32 12
Fax: +49 (0)921 88 34 44
About Stäubli: Textile machinery, connectors and robotics
Stäubli is a mechatronics solution provider with three dedicated divisions: textile machinery, connectors and robotics. Employing more than 4,000 people, Stäubli is an international group based in Pfäffikon (Switzerland) with offices in 25 countries and agency representation in 50 more.