Customer Solutions
Control System for Automated Production of Semiconductors
Author(s):
Martin Brunner, Qualimatest sa
Industry:
Semiconductor
Product:
Compact FieldPoint, Data Acquisition, Distributed I/O, FieldPoint, LabVIEW, Motion Control, PXI/CompactPCI
The Challenge:
Creating a graphical user interface for an automated holographic mask aligner and developing the interface in a condensed time period while considering safety issues, such as emergency stop, general error handling and status lamps.
The Solution:
Developing a NI LabVIEWbased control system running on a network of one host PXI chassis, one real-time PXI module, and a FieldPoint module using data acquisition (DAQ) boards and NI FlexMotion motion boards.
Holographic Lithography
The principle of holographic lithography consists of recording a hologram from the pattern defined in a standard photo mask. We place the photo mask at a distance of ~100 mm from a holographic recording plate in contact with a prism. We then illuminate the mask with a laser beam while simultaneously illuminating the recording layer through the prism with a "reference" laser beam. We can then regenerate and print the pattern recorded in the hologram, or holographic mask, onto a semiconductor wafer by illuminating the holographic mask with a single laser beam.
System/Hardware Configuration
Besides developing the user interface, we were challenged to integrate all the hardware needed to fulfill our customer’s needs. We opted for a system of nine PCI/PXI boards on a host computer, six PCI/PXI boards on a real-time-based computer, and seven FieldPoint modules. We used MXI-3 technology to link two PXI chassis together and create a host system with 12 free PXI slots. We connected the FieldPoint modules and the real-time PXI chassis to the host computer via Ethernet/TCP-IP.
Machine Description
Loading/unloading substrate
To load a substrate, we open the front door of the machine and place the substrate on the loading platform and activate the air cushion. When we close the front door, the prealignment cycle starts. An internal robot transfers the substrate from the prealignment station onto the chuck. The transfer from the prealignment stage to the robot, for example, involves the monitoring of the robot’s vacuum level while slowly approaching the robot until it reaches a threshold level at which it clamps the substrate to the robot. Switching off the vacuum on the prealignment stage completes the transfer. On a security level, we need to monitor the position of the motor during the process so we do not exceed the
maximum position that could break the substrate.
Prealignment
Substrates are on an air-cushion during the manual loading procedure. For the prealignment, two retractable reference pins on two sides of the prealignment station align the substrate against a third pin in the opposite corner. The two motorized eccentric pistons push the substrate against the third pin, after which the air-cushion is switched off and the vacuum is switched on. Finally, the three pins are retracted.
Chuck and 8 degrees of freedom table
During the printing sequence, the substrate clamps to the chuck by vacuum. The chuck mounts at the top of an 8 d.o.f. table. Two axes are the X/Y directions that provide stepping movements, and three axes are for the vertical movements to achieve substrate/hologram leveling. Besides the motorized axes, piezo-actuators perform high-accuracy chuck positioning and dynamic autofocusing.
Autofocusing System
We measure and connect the gap between the hologram and the substrate in real time during the scanning exposure. So we can print a high-resolution pattern in focus over a large field. This process ensures that it stays constant within ±0.2 µm at the position of the beam. We achieve this with a "white light" interferometer in the PXI real-time chassis controlled feedback loop coupled with a piezo actuator system under the chuck.
Autoalignment system
Similar to the autofocusing system, we use three interferometers to monitor the X/Y/PHI position of the chuck. The PXI real-time module feedback loop monitors the three 32-bit signals and controls three piezo actuators.
Scanning stages
We use two motorized stage systems to perform the raster scanning to uniformly expose the plate - one for the UV beam, and one for the focus beam. We synchronize the stage systems, so the UV and focus beams align on the substrate during the whole exposure. We control the shutter of the UV laser within a loop running onboard the motion controller and open and close it depending on the position of the scanning stage. This loop runs on the motion controller in case of system failure to ensure that the shutter is closed after the scanning.
Microscopes/Alignment
To perform the alignment and magnification operation, four microscopes mounted on X/Y motorized stages look through the prism at the alignment marks in the hologram and on the substrate. Each microscope captures the image on a CCD camera and processes it with a vision board interfaced with the machine software. The position of the marks extracted from the video signals are processed and fed back to the multiaxes table to align the substrate marks with the hologram marks. If necessary, this sequence is repeated to maximize the alignments accuracy.
Software
Our graphical user interface had to be clear and user friendly for any operator using this machine. The preleveling and leveling brings the substrate from a starting gap of 0.5-1 mm to the working gap (120µm) by precisely moving the three motors placed underneath the chuck. The parallelism between the two planes must be exact. Because of the narrow working gap between the substrate and the hologram, we have to constantly monitor the position of the motor providing z displacements while using the leveling and preleveling functions. A contact between the substrate and hologram would be fatal to the machine because it would destroy the holographic mask and possibly break the substrate.
Conclusion
This project was a real challenge for us. Thanks to National Instruments, we managed to create a complex and reliable industrial system to fulfill our customer’s needs with a user-friendly interface suitable to any operator. Using LabVIEW was a real advantage because it provided a time-savings; therefore it was cost effective. It also provided easy connectivity to FieldPoint modules and easy hardware integration.
For more information, contact:
Martin Brunner
Qualimatest sa, 18, chemin des Aulx 1228
Geneva, Switzerland
Tel.: ++41 22 / 884 00 30
Fax: ++41 22 /884 00 40
E-Mail: info@qmt.ch
martin_burnner_pc_2002_semiconductor.pdf
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