Laser Diode Based Metrology Module

Project number: 
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Project description:
Design, build, and bench test a compact laser diode based metrology module that can illuminate a stream of water droplets and record the reflected signal from each droplet (or group of droplets) over a given time interval using a suitable solid state detector.
ASML in Rancho Bernardo, CA develops EUV (Extreme Ultra Violet, 13.6 nm radiation) lithography light sources for EUV lithography tools using LPP (Laser Produced Plasma) technology. EUV generation takes place inside a large diameter (>1.5 m) chamber by vaporizing/ionizing small liquid Sn (Tin) droplets at high repetition rates (50 kHz) using a powerful CO2 laser. The vaporized/ionized Sn droplets produce EUV radiation which is collected by a mirror and focused into a lithographic scanner. The scanning system exposes lithographic patterns on semiconductor wafers using the EUV light.
During EUV source operation, the Sn droplet stream passes through a light curtain (for example, a light curtain produced by a laser beam). The reflected light from the curtain is collected by a solid state detector whose signal is used to fire a powerful CO2 laser at the “proper time” to vaporize/ionize each Sn particle in the stream – thus producing EUV light.
Problem and Capstone Statement (using water droplets):
The detection of Sn particles and their position in space at a given time is critical to the operation of the LPP EUV source system. It is desirable to produce a metrology system using a diode laser and solid state detector that can be used to identify the position of small (~1 mm) moving targets - water droplets - in such a way that the light signals can be used to control the output of an external light source (an LED for example) which could in principal be used to fire an external laser or device.
The project task is to take this design and build a prototype using commercial off the shelf parts, supplemented by 3D printed or locally machined parts to deliver a unit that could be tested on a UoA test bench. The approximate size of the system (metrology unit) consisting of the water droplet dispenser, laser diode, and detector should fit inside a cube of no more than 2ft on each side – additional circuitry for collecting and displaying outputs need not be included in the contained metrology unit. Details of the firing sequence, and other details will be explored by the team during conversations with ASML leads.

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