Customer Solutions

LabVIEW Helps Fabrication Process of Next Generation Microprocessors

Author(s):

James Kring, CAl-Bay Systems

Industry:

Semiconductor

Product:

Data Acquisition, LabVIEW, Motion Control

The Challenge:

Integrating a multi-axis motion and high-speed data acquisition system with deterministic hardware triggered events, while providing both a user-friendly interface and remote operation capabilities via an Ethernet network.

The Solution:

Using a PC-based system that incorporates National Instruments motion control, data acquisition, and network-ready LabVIEW to develop an integrated test, measurement, and control system as part of a distributed fabrication process.

Introduction
Moore’s Law speculates that the numbers of transistors on a microchip will double every 18 months. Extreme Ultraviolet Lithography (EUVL) is leading the race to push Moore’s Law to its current physical limitations. By using smaller wavelengths of light in the chip lithography process, smaller traces can be etched into a semiconductor wafer. This will allow chips to be produced with nanoscale circuitry, meaning microprocessors with a billion transistors. Each transistor on the chip can be as small as 40 atoms in width.

The EUVL process, shown in figure (1), uses a mirror coated with a non-reflective negative image, or mask, of a microprocessor circuit. An EUV light source, which produces light peaking at 134 Angstroms, is used to illuminate the mask. A magnified image of the circuit on the mask is projected onto the semiconductor wafer, burning away conductive material and leaving a microprocessor circuit.

The mask mirror is a critical component in the EUVL process. It must have high reflectivity at exactly 134 Angstroms to reflect enough light to burn the circuit into the wafer. Mask mirrors, also known as multi-layers, consist of 40 molybdenum and silicon layer-pairs sputtered onto a substrate. The spacing between alternating layers creates a constructive interference, or reflection, of light at a specific wavelength as given by the Bragg equation l = 2dSinq; where l is wavelength of light reflected, d is the spacing between layer-pairs, and q is the angle of incident light. In the EUVL application the multi-layer spacing of the mask mirror is tuned to be reflective at 134 Angstroms, the same wavelength of the light source.

Lawrence Livermore National Labs (LLNL) is one of the only producers of EUVL mask mirrors. To test these mirrors, LLNL called upon EUV Technology (www.euvl.com), a small silicon valley based company, to build the first reflectometer that was small enough to be placed in a clean room and able to meet LLNL’s testing requirements. EUV Technologies partnered with Cal-Bay Systems to develop the reflectometer’s control and data acquisition system.

This small reflectometer, known as a laser plasma reflectometer (LPR), uses a laser-induced gold plasma as its EUV light source. It is and is one of the keys to bringing EUVL out of the lab and into the semiconductor fab for large-scale chip production. Previously, EUVL mask mirrors were tested for reflectivity using a particle accelerator ring known as a synchrotron as an EUV light source. A synchrotron costs hundreds of millions of dollars and is the size of a football field. Test time had to be scheduled months in advance, took a setup time of 1 hour, and had a turnaround time of eight hours. EUV Technology’s LPR, shown in figure (2), occupies only 1.5 square meters, easily fits into a clean room, has a test setup time of ten seconds, and can test the mirrors in five minutes. The EUV Technologies LPR is even a candidate for the 2001 R&D 100 award.

Reflectometer System Requirements
The research and development of any complicated first generation system requires a flexible set of tools. The LPR’s laser must be fired in synchrony with data acquisition and motion control for precise measurements to be made. Two stepper motors and five servomotors are used to position various filters, EUV light monochromator, a gold target, and the mask mirror. Digital timing signals must be generated to trigger cascading events such as flashing the laser lamp, firing the laser, and acquiring analog data. Motorized micrometers and New Focus, Inc. Picomotors are used to align optical components with nanometric precision to focus the laser and EUV light. Analog voltages from optical power sensors must be read to acquire the reflectivity data. System interlocks had to be checked to ensure that the system was in a safe operating state. Finally, the system had to communicate with other production tools over an Ethernet network.

Hardware
We chose National Instruments data acquisition and motion control hardware because of their advanced triggering features and the ability to synchronize events via the Real Time Systems Integration (RTSI ä ) bus. We used the National Instruments PCI-6052E multifunction data acquisition card to create several precisely spaced timing signals that cause the laser to fire and analog signal acquisition to occur. We achieved the seven axes of coordinated motion with the two PCI-7344 FlexMotion control cards and we used a FlexMotion stepper and servomotor power drives to drive them. The entire control system runs on a rack-mounted industrial PC and is housed in a 19 in. industrial-rack enclosure.

Software
We Chose NI LabVIEW as the software development environment because of its ease of use, flexibility, network-ready functionalities, and tight integration of motion control and data acquisition. We used the LabVIEW data acquisition and motion control example programs to quickly prototype a solution to the complex hardware timing issues. After the prototyping software was written, we developed an operator interface, which allowed scanning optical power levels vs. any motion axis. This provided characterization information that allowed the LPR to be fine-tuned. This was an invaluable feature. Having all of the motion control functions available in LabVIEW via FlexMotion allowed the code to be modular and flexible. Finally a network interface was developed to allow remote operation of the device by other tools in the fabrication system.

The data displayed in the LabVIEW user interface shown in figure (3) is a wavelength scan. This data is acquired and then analyzed for peak value, FWHM, and centroid. This analysis data is then used for Statistical Process Control (SPC) of the multi-layer sputtering in real time as the next mirror is made.
As the LPR’s physical and functional design evolved, the LabVIEW graphical code was quickly modified to meet the new needs of the system; motion control axes were added and removed, scanning methodology changed, subsystems and interlocks evolved, calibration and characterization methods were refined. Having all of the hardware routines developed in LabVIEW allowed all the flexibility we required.

Conclusion
LabVIEW and National Instruments hardware proved to be an excellent platform for developing a successful system in a highly experimental R&D environment such as this. The flexibility and features of National Instruments software and hardware p roducts addressed all of our system needs and made the system a success. In the next generation of the system, we plan to incorporate additional National Instruments hardware such as PXI and FieldPoint. The National Instruments hardware and software combination enabled the development of this key technology that will help bring mass production of billion transistor microchips closer to reality. This should allow the chip industry to push Moore’s law to its current physical limits.

 

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