System Overview

Performing the deposition in a controlled atmosphere is essential to generate films and structures with the appropriate characteristics. A decent vacuum ( ideally under 1e-6 torr ) and perhaps different low pressure reactive species (for examples O2 in the order of 1e-2 torr for oxides) must be alternated  in quick succession.

Usually high vacuum pumps such as turbomolecular pumps operate within a narrow range of conditions, and turning them on and off is a time consuming process. Therefore, is important to design a vacuum system with a set of valves which allow fast variations among different atmospheres.

This implementation took advantage of several components that I had available, which is far from ideal.

The Process Chamber

While most components where taken 'off the shelf', the mechanism chamber had several dimensional requirements (specially regarding the target-substrate distance and the different lasers focal lengths) that could only be met with a custom chamber. As those are very expensive, I had to manufacture it myself.

The cylindrical shape is quite standard due to it's ease of machining and good distribution of the pressure differential related efforts. I used a standard size for flanges, choosing ISO160 for their ease of use. I bought several Inner weld flanges from Aliexpress, as well as a 154mm OD x 2mm thick stainless steel pipe. Curiously I couldn't find any vendor from where I'm from, so I had to buy it abroad as well.

The chamber was machined to length in a lathe, and then the aperture for the flanges where milled.

The KF40 flanges, initially though as viewports and for plume diagnostics,  where bought from Aliexpress (they are fairly inexpensive) and then machined to provide the right fit to the main chamber:

The same process was made for the ISO63 flange intended initially as a coupling to an existing turbomolecular pump.

After making sure that the tolerances were acceptable, I proceeded to TIG weld the chamber together.

While definitively not very pretty welds, after a few adjustments they seemed to hold a decent vacuum :).

The process for the covers was quite similar: They also required custom apertures for the laser windows and manipulators. By mistake I bought KF160 instead of the proper ISO160 blind plates, but fortunately both standards are interchangeable.

After the holes where bored, cheap KF(40/25/16) flanges were welded in place.

Defining the process

To being able to flexibly fabricate the intended structures, the following process was devised:

One starts with a bare substrate, covered by the unmarked mask 'web' 
and a shutter between them. The target carousel is placed in such a way that it lets laser light pass through it. Either under vacuum or an unreactive gas, the apertures are defined.

When the apertures are cut, the shutter is removed and the proper atmosphere is set onto the chamber.  Then the proper deposition process is performed (either from a single target or a given combination).

Once the deposition step is completed, the mask web is moved until only unmarked tape covers the substrate.  This sequence may be repeated until the mask is completely consumed.

Evidently the shutter is required to protect the substrate from debris and laser ablation. It quite a compromise, as the distance between shadow mask and substrate heavily influences the achievable resolution.

As a solution, the mechanism is designed in such a way that whenever the shutter moves into place, it pushes the substrate stage onto a lower position. When the substrate is uncovered, the substrate stage  reciprocates back, with it's position determined by a simplified kinematic coupling.

Now such mechanism seems to have a fair bit of degrees of freedom: Target carousel, shutter, and mask roll movement is required. However, they move in a fairly well defined sequence, so in principle all movements could be partially coupled to one another in order to reduce the required actuation elements.

A First Iteration

The Prototype

While 3D printed components are usually not vacuum compatible (at least not as is), they were a great tool to test the ideas involved, and gradually start implementing the final pieces. Here are a couple of pictures of the process:

It was crucial to test the resistance of the tape after marking.

Actual Mechanism Fabrication

As the mechanism is mostly composed of planar 'plates' with different apertures, it's well suited for processing with laser cutters or waterjets. However, I wasn't very confident on my designs, so I rather chose to fabricate the whole assembly out of duraluminum stock.

I started from a 6' cylinder , and turned it on the lathe to the appropriate (149 mm) diameter.

After that, all the common perforations were made in a (relatively unsuccessful) attempt to keep al the plates and moving axis aligned. The common features between plates were machined as well:

After that, each plate was cut from the main block (a royal PITA)

And finished on the lathe:

Or given some extra details in the mill:

The process was repeated several times until the mechanism was completed:

The remaining components (rollers, target carousel, couplings) were machined with standard techniques (and in those cases it actually made sense to do so).

Evidently the manufacture could be simplified a lot using the proper tools to fabricate the plates, so I'm currently working on designing a mostly laser-cut version.