Robotic Vacuum Chamber

At Persimmon, I owned the design of a vacuum chamber to validate the operation and heat transfer characteristics of a new linear wafer handling robot.

This chamber was needed to evaluate the effects of vacuum on the robot’s ability to remove heat. At low pressures, convection is severely limited and heat transfer occurs mostly through radiation and conduction through the linear rails. The system needed to be able to achieve high vacuum (<10^-6 Torr) and have temperature controlled cold plates to replicate conditions in the fab.

In order to reduce material costs, the chamber was reworked from an existing chamber. I was able to reuse the stand and cover, but a new baseplate and significant changes to the walls were required. The baseplate design was very similar to what I worked on for the customer unit, however, this configuration was bottom-mounted instead of resting inside the customer’s chamber. Because of these differences, it was important to ensure that all of the tested components (wireless communication and power coupling, mock transfer modules, linear motor, etc.) operated in the same way. One of the challenges was packaging these features, while avoiding or incorporating the existing chamber geometry.

The positioned robot inside the vacuum chamber. Cold plates are shown on either side of drive. This robot has 5 degrees of freedom: extension of both arms, rotation, height, and movement along the chamber.

Coldplate shown with cover removed. The coldplate considers of a bent stainless steel tube.

To allow the robot to operate indefinitely, the electronics and motors needed to be cooled. In this design, energy leaves the robot mostly in the form of radiation from the “tub” walls to the coldplates. After exploring several concepts, the final design consisted of formed tubing epoxied into a machined aluminum plate. While having a higher thermal resistance than machined channels, this design was chosen since sealing would be more robust. The outer surface of the plate was anodized to increase the emissivity and cooling capacity. The epoxy was selected to be relatively thermally conductive, have low outgassing, and to have a viscosity that would be easy to apply without voids.

Aside from the engineering aspect of the project, the design, procurement, and assembly needed to be managed to meet the required schedule. The project had over a hundred parts, many of which were machined, welded, or formed. I worked with purchasing and our vendors to ensure everything was ordered in time to meet the required delivery. This including making a tracking spreadsheet to monitor what was ordered and any schedule changes. I also tracked completed tasks so I could coordinate between other members of my team (i.e. cables or electrical work) and secure their time.

The chamber being inspected at a local machine shop

Assembling the baseplate, while waiting for all components to arrive

As well as communicating with vendors throughout the manufacturing process, I also visited and inspected some of the more complex parts. Because it was a rework of an existing part, the chamber walls had some issues. For example, a pair of tapped holes was drilled longer than specified in the original documentation. The extra length caused one of the o-ring grooves to break through around one of the process modules. I worked with the supplier to resolve the issue. Since this was a crucial sealing surface I emphasized the importance of deep, airtight welds. To maintain a smooth transition and surface finish, we decided to remachine the groove after welding.

Assembly:

I was involved with several steps of the assembly process including:

The spindle, which houses the 3 theta motor stages and the z-axis.
The drive, which encloses the the spindle and electronics from vacuum
Install of robotic arms on to the drive
Optical feedthroughs for communication
Power feedthroughs to wirelessly power the robot
The baseplate, which supports the linear rails, linear motor, and power couplings
The cooling system including chiller, plumbing, and cold plates
The chamber baseplate, walls, and covers
The vacuum system (roughing pump, turbopump, valves, instrumentation, etc.)

At each step, the critical performance criteria (leak checking, bearing runout, etc.) were measured to validate correct assembly.

After assembly and troubleshooting of the cooling and vacuum systems, we were able to achieve the required vacuum level (10^-6 Torr) and control the surface of the cold plates within 1 deg C. The applications team took over and validated operation of the robot in low and high vacuum. The results were satisfactory and allowed us to make design improvements on the beta prototype.

Challenges/Takeaways:

VACUMM DESIGN (I.E. VIRTUAL LEAKS, MATERIAL CONSIDERATIONS, FEEDTHROUGHS)
COOLING SYSTEM DESIGN (GALVANIC CORROSION, TUBE BENDING, EPOXY SELECTION, ECT.)
TROUBLESHOOTING CHILLER AND PUMP
MANAGING PARTS AND SUPPLIERS
VACUUM SYSTEMS AND INSTRUMENTATION
ASSEMBLY OF LARGE EQUIPMENT
RETROFITTING AN EXISTING COMPONENT

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