- Industry: Industrial Controls/Devices/Systems, Semiconductor
- Product: Data Acquisition, LabVIEW, Motion Control, Programmable Automation Controllers (PACs), Vision
- Challenge: Developing a highly automated wafer scriber that requires minimal service and engineering support.
- Solution: Using NI PAC platform with LabVIEW to develop the system.
The Need to Develop a Highly Automated Wafer Scriber
The initial mission of Micro Processing Technology, Inc (MPT) was to develop advanced computer control technology for the semiconductor equipment industry. In fact, MPT did this successfully for several years, selling hardware and software packages based on National Instruments products to companies to retrofit semiconductor manufacturing equipment.
In 2001, MPT began working on a project with SurvUs Company, an enterprise supplying high-level, wafer dicing services. The two companies saw a need for a highly automated wafer scriber that required minimal service and engineering support. As a result, the two companies developed the Model 24-7 High-Precision Scribe Dicing System (pictured).
After device fabrication completion on a semiconductor wafer, engineers must cut the wafer into individual circuits and devices. For most standard silicon devices, engineers carry out this dicing and singulation process using a very thin, diamond-coated saw blade. Some devices and circuits must be diced using other methods. Engineers fabricate some of these devices and circuits on thin material that is damaged by the saw vibrations. In addition, engineers fabricate other devices and circuits on very expensive starting materials, such as gallium arsenide or indium phosphide. The saw blade creates debris that harms other circuits and devices, such as MEMS and imaging devices. Engineers dice these and others using scribe dicing technology. In this process, the system draws a sharp diamond tip across the wafer surface between the circuits and devices along a crystallographic plane direction to form a scribe line with precise positioning and depth. The system then breaks and cleaves the wafer along this scribe line.
MPT engineers designed the high-precision scribe dicing system to run in an ultraprecise and reproducible manner, making it easy to set up and maintain scribe processes. They built the system with ultrahigh-precision linear bearings and linear motors. All system stages use 0.1 micron encoders. The scribe stage and force sensing and control stages use air bearings. The scribe stage can travel at velocities of up to 1 m/s. And the system uses closed-loop force control. The system will process up to 200 mm diameter wafers and is designed to require no customer maintenance. Factory technicians using remote computer diagnostics can resolve software and motion control issues. They resolve mechanical issues by replacing the system with one shipped overnight from the factory or warehoused on site. The scribe module weighs only 50 lbs and is shipped in a 24 x 25 x 28 in. container.
Creating the System
We wrote all system software using NI LabVIEW. The system performs motion control using NI-Motion software and an NI PCI-7356 motion control board. The system has six motion axes and an additional axis for the input from the force sensor. There are four linear motor and encoder stages in a gantry configuration with a vertical stage attached to the cross stage. In addition, there are two rotary stages. The system uses one to rotate a vacuum chuck that holds the wafer to be scribed and uses the other to change the scribe tip angle relative to the wafer surface. The force sensor is composed of an air bearing, a linear encoder, and high precision springs. When the system is in operation, the scribe tip position is controlled first to bring it to the wafer surface. The system then switches the feedback to this axis to the encoder on the force sensor for direct PID force control.
Engineers can upgrade NI motion controllers in functionality by loading the latest version of the NI-Motion driver software, which in turn updates the firmware onboard the controller. Initially, the ability to change the encoder assigned to an axis without stopping all axes on the board was not available in NI-Motion. Using an updated version of the driver, we could change the encoder assigned to an axis on the fly. Using the new feature, we increased the scribe force sampling rate from around 60 times a second to 4,000 times per second. Since the time for a typical scribe pass is less than a second, this improved force control is especially significant.
We used machine vision to position the scribe tip correctly between the devices on the wafer surface. This is done using NI vision software and two firewire cameras running on an NI PCI-8252 board. We used the first camera to determine the wafer location on the vacuum chuck. We mounted the second camera on a 12X zoom microscope. When viewed on a 17 in. LCD monitor portion, this configuration gives a maximum image magnification of about 800 times. With this high magnification, we can view the scribe tip positioning in the scribe street center to a precision of about 1 micron.
NI Products Reduce Development Time
Due to the National Instruments hardware and software ease of use, we completed the entire system development, including mechanical design, PC interface board, and control software writing with only three man-years of effort. Based on my experience developing other semiconductor manufacturing systems of similar complexity, this system would have taken in more than 20 man-years of design and development effort without using National Instruments PAC platform with LabVIEW.
Other ResourcesNi.com/motion
Motion Basics in 15 minutes Interactive Tutorial
Designing Your First Motion Control System - PowerPoint Presentation
Fundamentals of Motion Control - White Paper
10 Essential Technologies for High-Performance Motion Control - White Paper
Understanding NI SoftMotion Technology - 10-minute Interactive Tutorial
Create Custom Motion Controllers with NI SoftMotion Technology - White Paper
Soft Motion Technology Selection Guide