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Advanced Instrumentation -- Nanodevice Fabrication : Stepper (Photolithography)

Once we have created nanoengineered spintronics materials using our automated sputter deposition systems, the PLD-TEON advanced multimode deposition system or other process techniques, we then need to fabricate and test devices from those materials. Preliminary tests can be done on devices patterned with masks during the deposition process, but later prototypes must be built on a smaller scale. We have a number of ways to accomplish this device nanofabrication.
ASML 5500 Photolithographic Stepper

A "stepper" is a photolithography machine used to expose a pattern on a wafer by shining light through a reticle (a glass plate containing a pattern etched in chrome, or other photolithographic mask). Since it cannot accurately expose the entire wafer at once, a stepper exposes an area of a smaller size and keeps repeating this until the whole wafer is covered. This process is called step and repeat. An eight inch wafer might need about 80 fields for full exposure. The stepper being used at Almaden uses ultraviolet light with a wavelength of 248 nanometers (nm).

8-inch wafer jig designed to hold multiple 1" wafers for exposure

ASML 5500 Stepper Project
Our most recent nano-fabrication project involves the use of an ASML 5500 248nm stepper for pattern generation on 1" wafers. The Almaden ASML stepper is an tool designed for working with 8" wafers, so our early work has involved developing a methodology for running 1" wafers in this tool. The method adopted involves the use of two 8" wafers, both polished to 500um thickness, which are bonded together for use in the 8" tool. One of the wafers has been laser cut with receptacles for 1" wafers (round and square wafers).

1-inch square wafer patterned in the Almaden ASML Stepper

This allows us to deposit materials on 1" wafers, coat those wafers with an appropriate anti-reflective coating and photoresist and then process the wafers through the 8" stepper tool.

Details of a 200 nanometer feature created on a 1-inch wafer in the Almaden ASML Stepper

To date we have succeeded in achieving feature sizes around 200nm using this method, as shown in these micrographs. The next stage of our process development will involve the production of sub-micron MTJs and nano-wires using this stepper tool.

  

Tools and Instrumentation
PLD-TEON MultiMode Deposition System
Automated Sputter Deposition Systems
Current in Plane Tunneling Measurement
Kerr Microscopy
Nanodevice Fabrication

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