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Advanced Motion Control Network Boosts Performance of Wafer Handling System

BlueShift™ Technologies has introduced a game changer to the vacuum automation playing field. The QuickLink, with its innovative linear and linkable architecture, provides OEMs a competitive advantage against the conventional radial systems. The BlueShift advantage focuses on configurability allowing OEMs a common vacuum platform across tool generations as well as across process applications.

One of the greatest challenges in developing BlueShift’s QuickLink wafer handling system was designing a motion control system that could meet demanding requirements for expandability, resolution, stiffness and reliability at a competitive price. “We tried a motion control card using Firewire A, but could not make it work on more than one axis at a time,” said Chris Kiley, Vice President of Engineering for BlueShift Technologies. “A systems integrator suggested Danaher Motion’s XMP series motion controllers. We discovered that we could add up to 32 axes of motion simply by plugging them in. The XMP motion controller quality levels helped us exceed our competition in reliability by a factor of four. It meets our demanding repeatability and speed requirements with ease.”

An innovative approach to wafer handling Semiconductors are fabricated in miniaturized cleanrooms called cluster tools in which wafers are maintained in a vacuum environment while they are moved between processing stations by robots. Conventional cluster tools are arranged in a radial pattern with processing stations and load locks, for inserting and removing wafers, located around their circumference. As wafers have grown larger and semiconductor processing operations become more complex, the size of these cluster tools has continued to grow. Today the transfer chamber at the heart of the cluster tool can easily be 10 feet long by 6 feet wide, even before adding process chambers where the wafers are turned into valuable integrated circuits.

Designed to maintain very high levels of vacuum, transfer chambers are machined from very large pieces of aluminum that are expensive because they are at the limits of what can be produced. In producing these chambers, a single mistake might mean throwing out a $50,000 piece of aluminum. BlueShift’s linear geometry delivers substantial cost and performance advantages over the traditional radial design. Wafers pass along a line of process modules entering at one end and existing at the design. The linear transfer chambers are much smaller than radial chambers, which reduces both raw materials and machining costs and makes the new approach between 30% and 40% less expensive. The linkable design permits processing modules to be added as needed in a compact configuration, resulting in footprint reductions up to 40% compared with radial footprints and allowing the fab to optimize throughput by balancing the flow while eliminating bottleneck processing chambers. The use of building blocks makes it easy to configure wafer handling systems for high capacity and long process time, high throughput and short process time or increased vacuum isolation and contamination control.

Robotic motion control challenges

Robot design was critical to the QuickLink as it is to any wafer handling system. The reliability of the robot is a critical concern since if the robot goes down the entire fabrication process comes to a halt. High repeatability is critical to avoid damaging the wafer, while providing high throughput requires high speed. The modular design of the of the QuickLink vacuum robotic systems creates another important challenge. The QuickLink approach utilizes multiple robot transfer links that can be attached together to fit the fab’s current requirements and reconfigured at the fab if therequirements change. The modularity of this approach creates the need for modularity in the motion control system as well.

“Because these robots are designed to operate in a vacuum, they have to provide smooth and accurate motion with as few moving parts as possible,” Kiley said. “When these systems were originally designed there were no off-the-shelf motion control components that could meet these requirements. So the equipment manufacturers developed their own motion control systems. They now have tens of millions of dollars invested in the development and maintenance of these systems and large staffs of control engineers devoted to their development. The problem with this approach is that the motion control cards and amplifiers are typically only built in quantities of hundreds so there is no chance for manufacturing to gain the experience that could be used to improve their reliability. Manufacturing costs are obviously also much higher than off-the-shelf components produced in much higher quantities.”