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Robots perform in parallel
April 23, 2001
4 Min Read
Austin, TX -Time is money. So it's no surprise that high throughput was one of the key goals of Mattson, a division of Steag Electronic Systems, when designing its new wafer handling system. In particular, Mattson engineers were looking for a front-end input/output handling system to its wet bench tool that had a throughput of 400 300-mm wafers per hour. Their solution? An input/output tool from Berkeley Process Control (BPC; Richmond, CA) that allows four robots to operate in parallel, thereby eliminating any down time in the process.
This front-end wafer handling system for a wet bench consists of four robots, two slides, and one aligner for a total of 14 axes. Three BXi controllers networked together oversee the operation. Normally, a controller would be required for each mechanism (7 total), plus a PC with a 2-axis motion card.
Performing certain operations at the same time can be difficult to accomplish with conventional robot control systems, which operate as a central "brain" with sub-controllers connecting on each robot and other mobile devices connected in serial fashion. A central computer sends messages to each individual sub-controller, but leaves the central controller out of the communications loop. In other words, the left hand doesn't know what the right hand is doing-making it difficult to perform multiple tasks in parallel. Although information on their status can sometimes be squeezed out of the sub-controllers through a kind of game of 20 questions, this process eats up computing resources in a big way.
However, the latest generation of controllers by Berkeley Process Control places the functionality under one brain, thereby eliminating the independent nature of individual operations. Called the BXi motion and machine controller, it is an 8-axis distributed control element that is integrated with eight servo drives and allows individual controllers to be networked together as if they were one. The entire package-measuring a compact 8.6 x 3.2 x 9.8 inches, includes a 64-bit RISC scheduling computer, 56 digital I/Os, light curtain circuitry, and e-stop circuitry with force-guided contactors.
The key to the new controller is its increased computing power (almost ten times the previous generation) and the available bandwidth of system communication pathways (100 Mbit as compared to 10 Mbit Ethernet).
Through virtually instantaneous acquisition of data from system sensors and other I/Os, and its delivery to the "brain" powered by a 64-bit microprocessor, the controller can know the position of all individual elements at any given time. In other words, the system can now "see" where it once was blind.
Wafers in this input/output handling system move between different processing stages. An R-Z-Theta input robot (1) picks wafers one at a time from the input pod and places them on the wafer aligner (2). The R-Z-Theta robot then orients the wafer for hand-off to the twist-and-rotate robot, which places it into the wafer boat on the input slide. Once the wafer is centered and aligned, the R-Z-Theta input robot (3) picks it up and orients it. The twist-and-rotate robot (4) picks up the wafer and places it into the input wafer boat (5) that is indexed by the input slide.
In the input/output wafer handling system, which is a front-end to Mattson's wafer handling system, engineers networked 3 Bxi controllers, which oversee the operations of four robots, two slides, and one aligner-a total of 14 axes in all.
This constant and automatic feedback of operational data allows various tasks of the wafer handling system's ability to overlap without danger of a collision, which has an obvious impact on throughput. The ability of the controller to auto-calibrate in minutes also reduces setup time from hours or days to just minutes.
When vendors introduce new versions of their controllers, backward compatibility is always a question for design engineers. "Because it is based on the same architecture and design, the BXi controller is compatible with software written for our controllers dating back some 15 years," says BPC's Mario Lento, product specialist. "The only software tweaking required is a remapping of the internal I/O module."
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