Cleaning Slides with Plasma

Plasma Cleaner

[Ben Krasnow] hacked together a method of cleaning sides using plasma. His setup uses a mechanical vacuum pump to evacuate a bell jar. This bell jar is wrapped with a copper coil, which is connected to an RF transmitter. By transmitting RF into the coil, plasma is created inside the bell jar.

Plasma cleaning┬áis used extensively in the semiconductor industry. Depending on the gas used, it can have different cleaning effects. For example, an oxygen rich environment is very effective at breaking down organic bonds and removing hydrocarbons. It is used after manual cleaning to ensure that all impurities in the solvents used for cleaning are fully removed. According to [Ben], it’s possible to get a surface atomically clean using this process, and even remove the substrate if the energy levels are too high.

These machines are usually expensive and specialized, but [Ben] managed to cook one up on his bench. After the break, check out a video walk through of [Ben]’s plasma cleaner

35 thoughts on “Cleaning Slides with Plasma

    1. So use fluorocarbon polymers of polyhexafluoropropylene oxide lubricant AKA perfluoropolyether (PFPE), perfluoroalkylether (PFAE) or perfluoropolyalkylether (PFPAE) in your properly rated vacuum pump. Oxygen etching is commonly done in industry.

      1. Well, to be fair, just because Oxygen etching is routinely used in industry (it definitely is) doesn’t mean that Ben has the correct hardware to use it. If he was etching with O2, he should be using an oil-free vacuum pump. Uri is correct in suggesting an explosive hazard, particularly in areas where pure O2 can mix with oil. That’s why you can’t even use standard regulators with O2 bottles.

        On the other hand, Ben mentions the use of O2 but doesn’t actually use pure Oxygen in the experiment. I may be mistaken, but believe he is using room-air or argon, which both work very well for cleaning and are safe.

    2. This is all being done under a vacuum. There is no explosion issue involved here. The amount of oxygen involved is extremely low.

      As to the vacuum pump oils, the reason they are so expensive is because of their low vapor pressure (ability to get to a very low vacuum) and their inertness (won’t breakdown with all the chemical garbage that condenses in the pump oil)

      1. Yes, you are technically correct that there is no real explosion hazard in the chamber itself. The danger is that pumping oxygen out through the backing pump for the diffusion pump creates an explosion hazard near the seals. So it’s not a question of the diffusion pump oil stability, but the stability of the vacuum grease used for the seals and the oil used in the roughing pump. Yes the diffusion pump oil is formulated to resist breakdown or burnup, but only at the normal operating pressure for the diffusion pump (~10E-6 Torr). The pressures used to plasma clean are actually quite high (1E-2 to 1E-1 Torr) compared to the normal operating pressure for a diffusion pump.

          1. This is true for inside the chamber — but otherwise total flow rate is more of a determining factor. If the pumping speed is a constant 10 L/s, many more moles of gas are pulled through the pump at 1e-1 torr operating pressure than at 1e-6 torr.

          2. The difference in the operating pressures are admittedly a moot point. If Ben was doing O2 plasma cleaning (which he is not), he would be leaking a decent amount of oxygen into the chamber. That pure O2 would pose an explosion risk, with the danger occurring between the foreline of the diffusion pump and the exit of the roughing pump.

  1. This is incredible. I worked with a plasma cleaning machine many years ago. The specialized lubricating oil for the vacuum pump cost $15,000 per gallon – in 1995. The boss was pretty unhappy with me the day I accidentally lost a cleaning rag into the pump… (we were able to remove it without damage to the machine)

  2. Ben did an amazing job here, and most of this project can be done for relatively cheap. However, I get stuck with the RF power supply. A good supply is upwards of $1000. Anyone have any suggestions on how to roll your own or find a used one for cheaper?

    1. Wiki page mentioned “The plasma is created by using high frequency
      voltages (typically kHz to >MHz) to ionise the low pressure gas”, (note:
      starts at kHz not MHz). The few turns of coil for excitation reminds me
      of the primary of a Tesla coil. BTW mine is at 600kHz.

      There is Class E Tesla coil that are doing MHz. 4MHz is common, but I
      have seen 10MHz in google. The RF driver design is definitely worth look
      at for a starting point.

      1. It’s tricky to say, but I don’t think this would work. RF frequencies are required (10’s of MHz) to couple the energy into the gas in the vacuum chamber. A CW Tesla coil is high voltage AC, but doesn’t nearly approach the required frequencies.

        1. Most CB’s can be tweaked to 10-15 watts. A HF linear amp can be had for about a dollar a watt. or an old ham radio that will deliver about 100 watts can be found on ebay. (look for an old CW set) The most important piece of equipment you will need will be the antenna tuner so you don’t blow the finals (transistors) with lots of reflected power.

    2. I’ve seen something similar to this done in a microwave. It was done as part of the manufacturing process to make microfluidics devices from a silicon-based polymer.

      I’m unfamiliar with the exact details, since it wasn’t my project, but I’m sure it’s been described in the scientific literature.

  3. Hah, I missed that name at the top of the article, then I came to “according to [Ben].” *Of course* this is a Ben Krasnow project, heh. He seems to find (seemingly?) simple ways to do a lot of things I wouldn’t have thought were possible for a hobbyist. I love watching his videos.

  4. I’d be more concerned about all the stray RF… I’m not seeing much in terms of shielding, and the cumulative impact of this project (if undertaken by someone without a strong background in the matter) would have health concerns.

    As a general note, a growing pet peeve of mine is that those of us who have the technical background sufficient to allow us to execute such projects safely fail to make a strong enough point of the necessary safety/technical precautions when making instructional videos/presentations. Here’s to more (reasonable, of course) safety awareness in 2014!

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