Designer

Guillaume'

Project

This page presents a customized positioning device that is meant primarily for semiconductor wafers (size 4") but could be adapted to other sample types.

Concept

It is often needed to perform a measurement several times on the same sample, possibly after different processing steps. It can be required to perform the measurement at the exact same location, or in a different location, for instance in the case of destructive measurements. It is consequently important to place samples accurately on the measurement stage to be able to retrieve the location of the previous measurement. Sample positioning must often be performed on an already-existing measurement stage, and for that reason an external device should be used rather than a full-sized moveable stage that could interfere with the measurement.

The positioning device showed here has been developed for the Semilab PV2000 semiconductor characterization tool. The measurement stage is metallic and must be electrically conductive, and for that reason the positioning device has to be designed in a way that it does not support the sample.

The device consists in a primary rail that includes a rack and pinion to allow displacement in the X-direction. A secondary rail is attached to the rack and the sample clamp can move along this rail for displacement in the Y-direction.

The .stl and .scad files can be downloaded from the NIH repository: Files.

Estimated Cost

$1.33 = 1.14 € (PLA print)

$3.31 = 2.85 € (PP print)

The print in PLA is meant for prototyping and use in a standard laboratory. Price $25/kg PLA price.

Different materials must be used for cleanroom applications, for instance polypropylene. Price $49.99/800g PP price.

Estimated saving per replica

Prices of other positioning devices:

• Publication: Cossutta H, Taretto K, Troviano M. Low-cost system for micrometer-resolution solar cell characterization by light beam-induced current mapping. Measurement Science and Technology. 2014 Aug 29;25(10):105801.

--> could be an option, but 3D-printing it would be better (easy reproducibility) and no price estimate is given.

• Ali Express, Microscope Moveable Stage Caliper With Scale Attachable Mechanical Stage X-Y High-precision Vernier Biological.

--> relatively cheap at $11.74, but need to consider shipping expenses and shipping time. Those are not customized + possibly steel parts so no cleanroom compatibility.

• Edmund Optics stage

--> still needs to be customized, and rather expensive ($665).

• The PV2000 stage is actually motorized and the tool software could be upgraded to allow for single-measurements in a user-defined location. It is however a long process and no quote is available yet, but a reliable price estimate would be $5k-$10k (note that that would come with other useful features). Still, it would not allow accurate positioning of randomly-shaped samples.

Conclusion: At the moment, the most satisfactory solution (apart from 3D-printing the device) would be an upgrade of our tool that would be estimated at $5000 minimum. Assuming that the upgrade comes with 10 new features in total, the price per feature would be $500. The savings would thus be approximately $497 for one 3D replica.

Advantages of the 3D design

The 3D design provides several advantages compared to the tool upgrade:

• The positioning device is readily available
• Samples can be positioned accurately no matter their shape
• It can be tailored not only to our PV2000 tool but to any tool (for instance Sinton measurement tool)
• Similarly to the majority of 3D prints, it is cheaper than anything on the market

Current limitations

• Cleanroom compatibility of 3D-printed materials still needs to be investigated (possible metal contamination or dust).
• The wear of mechanical parts during device operation creates dust, which is not acceptable especially for cleanroom applications.

Further improvements to the design need to address the following issues (on 27 Oct. 2017):

• Some of the graduations do not print properly
• The height of the secondary arm and of the clamp still needs to be adjusted
• The height of the gear needs to be increased.
• Angle graduations need to be added to the clamp for positioning of wafer pieces

Parts

• 
  Primary rail support, gear and bolt
• 
  Primary and secondary rail
• 
  Sample clamp (for 4" wafer or pieces)
• 
  Full device (for 4" wafer or pieces), Files in the NIH repository

Directions

1) Download the .stl file or download the .scad file if you would like to modify the device by editing the source code: Link to the files.

2) Go directly to 3) if using the .stl file. If using the .scad file, you need to download the file "GE_calipers.stl" from thingiverse. Save the file on your computer and import it into the .scad file according to the instructions written it the beginning of the code.

3) Print the parts (sample clamp, primary and secondary arm, support for the primary rail, and gear and bolt) and mount them as shown in the photo. Use the gear to move the the primary rail and move the clamp along the primary rail.