Customer Solutions
Using NI-DAQ and LabVIEW to Construct a Prototype PC-Based Automated Optical Inspection System
Author(s):
Bernardino J. Buenaobra, National Institute of Physics -- University of the Philippines
Industry:
Semiconductor, University/Education
Product:
Data Acquisition, LabVIEW, Vision
The Challenge:
Building a PC-based imaging solution with the full functionality of an optical instrument, but without the use of a CCD camera; providing both visual capabilities and automated inspection tasks.
The Solution:
Combining optics and NI selected products to build a PC-based automated optical inspection system capable of imaging Integrated Circuit (IC) semiconductor sites.
Inexpensive Defect and Failure Analysis
Defect and failure analysis proves an expensive but necessary activity in semiconductor manufacturing. Using costly power microscopes for visual checks of an integrated circuit (IC) is common and generally provides good optical magnification. However, the use of these microscopes is somewhat limited in image generation and its inherently low contrast for sectioning details. This paper describes the building of a prototype optical inspection instrument using NI data acquisition products, control hardware, and instrumentation software.
We needed to build a PC-based design for solving imaging problems involving microscopic surface defects for visual inspections and failure analysis on IC semiconductor sites. We ended up implementing a system integration among selected National Instruments multifunction data acquisition hardware, a timer/counter board and a GPIB interface to an electro-optical system comprised of a laser diode controller with an optics and lens systems, a linear Piezoelectric actuator, and a set of nanometric displacement kinematic translation stages configured as a multiaxis scanning mechanism. A graphical user interface (GUI) developed in NI LabVIEW interacts with the user for an automated optical inspection system.
The prototype design depicts the electro optical system, which consists of an optical lens system that includes the kinematic translation stages, a laser diode source, and a controller with a GPIB interface. We conducted the X and Y-axis translation by pulsed friction type motors from New Focus Picomotor 8065 and 8095 stages, and we drove it by two 8801 Picomotor drivers. These accept finite pulse train and digital bit control for direction from a PCI-6602 32-bit counter/timer board. The Z-axis for depth control is a 15 um Thorlabs PZT driven by power amplifier that accepts a 0-10 VDC from a PCI-6024EDAC output. Optical feedback from the lens system is converted to current by a built-in power monitoring photodiode inside a 780 nm laser diode package. A Melles Griot 06 DLD105 Laser Diode Controller actually drives the device. Once we achieve optical alignment, the monitor current of the photodiode reaches its maximum, and laser diode junction voltage drops. Scanning the stage results in a varying amount of optical feedback and thus changes the current. This current then converts to voltage and is acquired as an analog input to XY-array definition inside the program in a start-stop manner, collecting data only when the motor scans along the X-axis.
Quick Diagnostics
This application requires a specially written program for testing the axial response of the imaging system to determine a key figure of merit in the design of an imaging system, called z-axial response. This curve is indicative of the resolving capability of the lens system to discriminate sites.
We used an NI DAQCard-1200 card-sized data acquisition on a mobile notebook computer to conveniently perform a quick diagnostic of the system, while equipping a desktop PC with a 12-bit PCI-6024E multifunction card. Additionally, we used an NI PCI-6602 as a pulsed motor controller and a GPIB controller combined with an imaging program written in LabVIEW to provide low-level signal acquisition, imaging, and instrument control. NI IMAQ Vision Builder provides offline image analysis.
Modular Programming with NI LabVIEW
The complexity of combining altogether on one program vision, motion control, data acquisition, instrument control, and file I/O management leads to a modular approach in programming in NI LabVIEW. We approached development of the modules from the bottom up; we then wrote the module codes and tested them for functionality.
The final code followed architecture that combines state machine diagrams and parallel loops synchronized in event occurrences, determined by timing involved in motor rotations and triggered acquisition and delay for array processing the image code.
At the GUI, operators have access to control of mechanical actuators and translation stages to position the target for a scanning job by inputting the number of pulses, correction factors, and offset at the beginning of the process. The GUI also provides capability to convert the data collected so we can save it as an image file in a spreadsheet format or a bit-mapped file at the end of the process automatically. We provide analog channels and a measure of magnitude for the signal by a time-domain graph and scaled array. The system also computes the mean and resolution of the image generated using a picture control palette in combination with NI IMAQ Vision utilities.
Through the use of NI tools, we quickly realized our goal of building a PC-based optical inspection instrument -- combining the resolving capabilities of a commercial power microscope with image capture and basic image processing, all without use of a CCD camera. We can develop flexibility for control and integrated image generation with synchronized motion control and triggered data acquisition into software prototypes rapidly using the NI LabVIEW graphical programming language. Commercial versions of automated optical inspection system capabilities would have proven costly, and we easily avoided them by designing with a National Instruments multifunction data acquisition card, timer/counter board, and instrumentation interface hardware.
For more information, contact
Bernardino J. Buenaobra
National Institute of Physics -- University of the Philippines
Tel: 632-434-4342
