SOP for bonding of PDMS to NPN

I’ve written a quick SOP document reflecting the procedure that resulting in successful permanent PDMS-NPN bonding. The procedure described in this document has not been optimized and may include unnecessary or otherwise sub-optimal steps. These steps reflect the steps that WERE taken to achieve a successful bond, not necessarily the steps that MUST be taken.

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1. Oxide layer formation — Rapid Thermal Processing (RTP)

   1. Place the silicon susceptor into the device and run the RTP device warmup recipe, which should take ~6-7 minutes to finish. Allow the device to cool to below 500C, and then carefully open the device and delicately remove the susceptor, placing it on a stable surface. Give it a moment to cool before proceeding.

   2. Place chips near the middle of the susceptor. Chips can be placed directly on the susceptor, but if oxide growth is desired on both sides of the chip, other (trash) chips can be placed underneath them as supports, such that both faces of the target chip are exposed to the atmosphere.

   3. Place the susceptor with chips back into the device and run the recipe labeled “O2 Anneal 700C 5min – Tejas.” As before, it should take ~6-7 minutes in total. Allow the system to cool to below 500C and delicately open the system, remove the susceptor, and remove the chips. Placing the chips in gelboxes after this step is not advisable, as they may stick.

2. Plasma activation — YES Plasma Oven

   1. Set the YES system chamber to 60C. NOTE: The YES temperature takes a very long time to change. Coordinate with other users in advance and set the temperature at least several hours before the process.

   2. Place the RTP-treated chips on an aluminum platen, bonding side up, into the YES system on the bottom shelf (arrange the shelves such that they are equally spaced — the floating shelf should be the bottom one) and shut the door. Run Recipe 10 for 600 seconds.

   3. When the recipe finishes, open the door and add to the bottom shelf the PDMS gaskets, also bonding side up, without removing the chips. Run Recipe 10 for 240 seconds.

3. Assembly

   1. Using two pairs of tweezers, one in each hand, and lift each gasket one-by-one. Invert them so that the bonding side is facing down, and carefully lower them onto the chip faces in the desired position. Gaskets can be peeled off and repositioned for a few minutes after they have been applied, but this is not optimal.

   2. Once all the gaskets have been applied to the chips, place the assemblies into an oven at 60C for 24 hours.

   3. Once the 24 hours have elapsed, remove the assemblies from heat and allow them to equilibrate to room temperature for at a few minutes. Test bonds by gently tugging with tweezers — ideal bonds should not give at all beyond the usual stretching of PDMS.

4. Process can be repeated from step 2 for other chip face if desired. It’s doubtful that the PDMS will survive the 700C conditions of the RTP, but the bonding survives plasma treatment just fine.

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Jim mentioned that he wanted to start an SOP section on the blog. When that happens, this will be moved there.