Complex machines in semiconductor manufacturing often have tough performance requirements for motion control. When traditional PLCor PC-based motion controllers fail to meet these requirements, machine builders turn to custom board development — a time-consuming and expensive process. Recent advances in embedded technologies have made it possible to use FPGA-based COTS platforms to not only meet those requirements, but also to get to market faster by using graphical system design.
When it comes to semiconductor wafer processing requiring high-speed servo update rates for piezo actuators, machine builders turn to designing their own motion controllers on a custom PCB. Not only is the development expensive in terms of time and cost, but the fixed personality of the motion controller makes the system inflexible for future redesigns or for accommodating variations in the motion control algorithms at run-time.
National Instruments reconfigurable I/O technology, coupled with LabVIEW SoftMotion technology, was used to design a machine for manufacturing semiconductors that consists of four chambers with different temperature and pressure settings for wafer manufacture. A system must be implemented to monitor and control the temperature and pressure in each chamber according to defined set points or according to a profile. An embedded control unit could be controlling the temperature and logging the average temperature once a minute to local storage while sending the current temperature data up to the host system for data logging. An operator may need to log into the system to view previous values up to a previous day’s worth of data. A process engineer who needs to load a new temperature profile for the chambers could do this by logging in at a higher access level than the operator.
National Instruments CompactRIO is a small, rugged industrial control and acquisition system powered by reconfigurable I/O FPGA technology. It incorporates a real-time processor and reconfigurable FPGA for standalone embedded or distributed applications, and hot-swappable industrial I/O modules with built-in signal conditioning for direct connection to sensors and actuators. CompactRIO embedded systems are developed using LabVIEW graphical programming tools.
CompactRIO combines a low-power-consumption real-time embedded processor with a high-performance FPGA chipset. The FPGA core has builtin data transfer mechanisms to pass data to the embedded processor for real-time analysis, post-processing, data logging, or communication to a networked host computer. The LabVIEW graphical system design platform combines off-theshelf hardware and LabVIEW real-time execution with algorithm design tools for simple to advanced control applications. The NI SoftMotion Development Module for LabVIEW provides virtual instruments (VIs) and functions to help build custom motion controllers that run using LabVIEW in combination with hardware such as CompactRIO. The module provides all of the functions that typically reside on a motion controller.
Wafer Measurement & Testing
Automation Works, Inc. was looking to automatically sort semiconductor wafers into categories based on physical and electrical characteristics such as thickness, bow, warp, total thickness variation (TTV), and type (N-type or P-type) in addition to matching the precision and repeatability of industry-standard equipment with greater throughput, flexibility, and user friendliness at much lower cost. They were able to achieve this by taking maximum advantage of National Instruments LabVIEW software, toolkits, and advanced analysis capabilities with tightly synchronized motion, vision, and data acquisition (DAQ) hardware products to create a PC-based system that sets a new standard for semiconductor wafer sorting.
To accommodate tight process step tolerances, wafers must be pre-sorted into narrow categories based on electrical and mechanical parametric values such as thickness, bow, warp, TTV, and type after semiconductor wafers are sawn from an ingot and before processing. Gigamat Technologies of Milpitas, CA — a manufacturer of sorting, polishing, and edge grinding equipment — undertook the task of developing the Model 200TRT, a new generation of automated, high-accuracy, high-throughput, full-scan wafer sorting machines with the help of AutomationWorks.
In semiconductor manufacturing, the push for greater efficiency and higher yield of silicon semiconductor material is never-ending. As circuit features shrink in size and global price competition intensifies, wafer processes push the physical and operational limits of equipment manufacturers. One result is increasingly narrow tolerances for incoming wafer physical and electrical parameters in delicate process steps, such as mask and etch.
Measuring the bow, warp, and TTV of a wafer requires performing a full dimensional measurement scan of the wafer top and bottom surfaces. This is not only technically challenging, but represents a significant increase in process time compared to simple, single-point measurements that were previously sufficient. For these measurements to be useful, they must match industry-standard benchtop instruments, which have the luxury of taking a great deal of time to ensure measurements are precise. Gigamat’s challenge was to automatically sort wafers from cassettes using full-scan measurements at high throughput rates, with industry-standard accuracy and repeatability.
The measurement process is comprised of two steps: wafer alignment and wafer measurement. Wafer alignment identifies the location and orientation of the wafer relative to a vacuum chuck on which it is held, and repositions the wafer exactly on the chuck center and with its primary fiducial precisely oriented. The second functional step in the measurement process is the performance of the full wafer scan. This step involves acquiring top and bottom distance measurements from many points across the surface of the wafer and performing analysis on them to derive results.
Wafer alignment was performed using three axes of motion and a linescan camera. A wafer was aligned by rotating it in the field of view of the camera. By synchronizing camera scans with chuck rotation, a 6-megapixel image of the wafer edge was composed in a single revolution, which took about one second. Because camera scans were synchronized with chuck position, they were independent of chuck velocity and could be acquired during chuck acceleration and deceleration ramps to save time. The wafer center, flat, and other features were identified from image data using LabVIEW vision, math, and advanced analysis tools. The wafer was then rotated and indexed in two short moves to bring it into perfect alignment for the measurement station.
A full measurement scan was performed by gripping a wafer from beneath with a rotational chuck and spinning it between top and bottom probes, which measured the distance to the wafer surface with a resolution of
NI LabVIEW running on a PC was the key to integrating all of the high-performance technologies required to make this project a success. Combining the hardware synchronization of PCI boards controlling eight NI motion axes with two NI DAQ boards and one vision board, the inherent multi-tasking and re-entrant execution capabilities and DAQmx task, timing, and triggering programming simplicity in LabVIEW gave engineers an ideal platform to rapidly implement, test, and validate multiple iterations of process code.
This article was written by Nipun Mathur, Motion Control Product Marketing Manager at National Instruments in Austin, TX. For more information, Click Here