Today, the majority of semiconductor manufacturing is done via advanced robotics and automation. It is not uncommon to go into a leading semiconductor manufacturing site, known as a fab, and find yourself easily outnumbered by a number of robots that you will encounter everywhere. Robots are at the heart of the semiconductor processing world. When you read about a semiconductor device’s node—22, 14, 10nm (under commercial development)[i]—you can understand how critical the processing placement of each and every silicon wafer is. Every semiconductor device starts as a piece of silicon (a wafer) and the processing placement—how these wafers are handled and placed into the various processing machines—is critical to the whole semiconductor manufacturing process. This level of precision can only be attained through the use of advanced robotics.
Having worked on many different types of industrial robots—SCARA, cylindrical, Cartesian, Articulated—used in semiconductor manufacturing, I can attest to the importance of choosing the right robot motors and ensuring that their speed and torque are optimized. Otherwise, the overall efficiency and productivity of the robot will be compromised.
In a semiconductor fab, there are robots that are confined to the interior of a host processing machine. When one of these robots fails, it impacts productivity for that machine only. Then, there are other robots on tracks that are in constant motion, moving lots of wafers (a lot is typically a group of twenty five wafers) throughout the fab. When one of these robots fails, it impacts the overall fab workflow process. Having the right robot design is paramount when the precision required of these machines is measured in half stepping (via a stepper motor), which results in a fraction of a degree of movement per half-step.
Regardless of the application, all robots (Figure 1) share some very important characteristics; they all must be reliable, precise in their movement, and predictable in their operation.
Figure 1: An industrial robot arm.
So how does an engineer go about choosing what motors to use when designing such robots? In a recent article by Bill Schweber he states that, “There are three primary parameters that designers consider when selecting a specific motor type and model: The minimum and maximum motor speed (and associated acceleration), the maximum torque the motor can deliver and the torque vs. speed curve, and the precision and repeatability of the motor’s operation (without using a sensor and closed-loop control).
Mr. Schweber touches on a lot of interesting aspects of robot motor selection with an engineering design approach. For example, you would think that the greater the resolution, the more precise the robot movement would be—the old adage of “more is better”—but the fact of the matter is that with precision (more resolution) comes less torque per microstep, a trade-off that needs to be considered if the final design requires a robot that needs to be precise, predictable and reliable.
To find out more, two of Bill’s articles are excellent resources:
Considerations in Choosing Motors for Robotics
Motors, Control Options Advance Robotic Opportunities
[i] Critical dimensions for the chips themselves, in nanometers.
Rudy Ramos brings 35+ years of expertise in advanced electromechanical systems, robotics, pneumatics, vacuum systems, high voltage, semiconductor manufacturing, military hardware, and project management. Rudy has authored technical articles appearing in engineering websites and holds a BS in Technical Management and an MBA with a concentration in Project Management. Prior to Mouser, Rudy worked for National Semiconductor and Texas Instruments..