DIY Semiconductor fabrication using maskless lithography

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The goal of this project is to fab some working IC's in a relatively cheap, DIY-friendly manner.

Thanks to the work of folks like Jeri and Sam (see links), a road has been paved for amateurs to produce some simple, working transistors in their own home fab. I'm tackling this project largely as a learning experience; I don't really expect to one day fab an Intel 8080.

The project offers a lot of interesting things to learn: optics, microcontrollers, cartesian printer/plotter design, semiconductor fabrication, etc.

At best, I successfully fab a working transistor or simple circuit. At worst, I'll have built a high-resolution lithography machine which I can use to play with microfluidics or other large-feature projects.

The plan is roughly:

  1. Modify an LCoS pico projector to perform maskless photolithography using a 405nm laser
  2. Build a high-precision cartesian plotter for automated positioning and die exposure
  3. Work my way through IC fab and metallization
  4. Figure out wire bonding (either via an eBay machine or DIY)

Realistic goal is around 10µm. Theoretical limit of the system is ~600nm due to the 405nm laser wavelength, so I figure an order of magnitude higher is reasonable. It's also the process size of the Intel 4004 in 1971 which seems like a good goal :)

Why Maskless Lithography?

Mask generation is one of the most expensive parts of actual IC fabrication. High-quality photomasks are typically chrome-on-quartz, although cheaper/lower resolution photomasks can be created with regular soda-lime glass and photographic emulsion (e.g. a film negative... but on glass). You could probably even get away with actual film negatives, or laser-printed designs on acrylic.

Considering the target process size (1-10µm) was accomplished in the 1970's, emulsion-based photomasks is probably more historically accurate. :)

That said, there are a lot of challenges to sort out with a mask system (optics, mask production, etc). Many of these also apply to a maskless system using some kind of projector technology... so why not start there?

In addition, a maskless process opens some potentially interesting doors to play with, such as "easy" computational lithography, scanning lithography without having to move the mask, etc.

Why LCoS Pico Projector?

There are four main projection technologies at the moment: digital micromirror devices (DMD, aka DLP), liquid-crystal-on-silicon (LCoS), LCD, and laser. Laser projectors are rather expensive, so we can rule those out right away. Of the rest, LCoS tend to be available cheaply in small "pico projector" packages. There may be other advantages or disadvantages, but price was my main reason.

Why 405nm?

I've read that most photoresists are somewhat sensitive to light at 405nm, which corresponds to the "h-line" on mercury lamps. 405nm is violet light, and just on the edge of visible. Below 400 and you start to reach into UV, which is problematic to work with for many reasons. It requires better optical glass to deal with UV, any plastic in the light path will degrade, LCDs don't enjoy UV light, etc.

So the h-line seemed like a reasonable place to park my wavelength. Finally, you can buy 405nm lasers which will be more convenient to work with than a giant, hot mercury lamp.

IF, however, it turns out that photoresist does not respond to 405nm well, I may investigate "daylight resins" used in some SLA 3D printers. These resins cure with ~500nm (blue) light, and as long as I can find a solvent to dissolve them, may work as a replacement for proper photoresist.

How are you going to build the translation stage?

The plan is to use two aluminum CNC z-axis as the basis for the translation stage. These parts are extremely rigid, and geared with a leadscrew that provides 1mm movement per turn. Combined with some high-resolution encoded gear motors (8400 pulses per rotation), I'm hoping to eke out acceptably accurate positioning from the stage

  • Final light engine deconstruction

    polyfractal8 hours ago 0 comments

    Welp. The deed is done; the final components of the light engine have been removed and measured... and the housing was destroyed in the process.

    After removing and measuring the components, I started playing around with them and discovered a few interesting, unexpected things.

    Read more »

  • Let the modeling begin

    polyfractal4 days ago 0 comments

    I've decided to try "Option #2" with regards to the light engine's optical assembly; namely, pulling the components and designing a single, monolithic print to house everything (PCBs, light engine, microscope objective).

    Measured all the inter-element dimensions before I start pulling components, just to make sure I have a record of the "official" setup. I'm going to try removing the PCX lenses from the overall configuration so I don't think I'll need these dimensions, but it can't hurt to have. I also took down the PCB dimensions so I can build a proper housing instead of just using double-sided tape :)

    Time to dust off OpenSCAD and start modeling the enclosure!

  • Light engine teardown: redux

    polyfractal06/20/2017 at 15:20 0 comments

    I've been avoiding this step, but I think it's time: I need to replace the projector's LEDs with my 405nm laser. So time to open the projector back up and start dissecting it again.

    Read more »

  • In search of a better photoresist

    polyfractal06/19/2017 at 04:07 0 comments

    Not much to report from this last week, unfortunately. I printed a test enclosure for the lenses and a slide holder, then proceeded to test different exposure times with the photoresist.

    The goal was to find the shortest time on the projector so that I could evaluate if the projector is sufficient, or if I need to start working on integrating the laser.

    It was all sidetracked by problems with the photoresist. Or rather, developing the resist. Many consumer resists are developed in an alkaline solution, ranging from the relatively mild sodium carbonate through sodium metasilicate and ending at potassium or sodium hydroxide.

    I assumed this random photoresist from China would be similar. I assumed incorrectly :)

    Read more »

  • First photoresist development test

    polyfractal06/12/2017 at 02:15 0 comments

    I'm currently waiting on a shipment of chemicals to arrive so I can develop my photoresist-coated slides. But I just couldn't resist (har har har) doing a quick test to see if the projector and/or laser put out enough power to actually develop the resist.

    Tl;dr: they do :)

    Read more »

  • Photoresist spincoating tests

    polyfractal06/08/2017 at 18:09 0 comments

    Before any lithography can be done, I need to work out how to spincoat with photoresist. The photoresist I currently have is UV curable "solder mask" / "solder paint", which is used to mask off PCBs and resist solder adhesion everywhere except the pads.

    The first few attempts were a bit dicey, but I think I figured it out by the end.

    Read more »

  • Recreating an Achromat Microscope Objective

    polyfractal06/06/2017 at 13:13 0 comments

    So the idea of using a pico projector as a maskless lithography system seems sensible, except for one minor problem. Projectors making small images big, and we want the opposite. We need to convert the projector into a microscope-projector.

    Read more »

  • 3D Printed Optics Bench

    polyfractal06/05/2017 at 01:29 0 comments

    If you've ever played with lenses, you'll quickly recognize the need for some kind of optics bench. An Optics Bench is really just a fancy name for some kind of system to hold lenses precisely in line with each other, at adjustable distances.

    With a bench, you can easily setup multiple lenses, splitters, mirrors, etc to play around with compound systems.

    Optic benches are crazy expensive unfortunately. This is partially because they are precision devices meant to be used in experiments, and partly because they are relatively niche (experimenters, and students).

    There are numerous ways to create simple optic benches, but I opted for the 3D printed approach.

    Read more »

  • LCoS Light Engine

    polyfractal06/05/2017 at 01:09 0 comments

    Having received my pico projector, the first order of business was cracking it open to take a look at the light engine.

    Read more »

  • Spincoater from old HDD

    polyfractal06/05/2017 at 00:23 0 comments

    While waiting for components to arrive, I set to work on building a spincoater. Spincoaters are used to spread photoresist evenly on a silicon wafer (or anything else you need to coat, such as glass slides).

    They can be purchased on eBay for a reasonable sum. Proper spincoaters give precise speed, automated ramp up/down profiles, exact timing and vacuum chucks to hold the wafer.

    But for my purposes, simple DIY will probably be ok to start. There are tons of DIY plans on the internet, ranging from simply taping your wafer to the back of a fan, to using an old hard drive, to a full microcontroller project (from the ever-excellent Ben Krasnow)

    I opted for the HDD route since I have several laying around (I mean, who doesn't?).

    Read more »

View all 10 project logs

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Dylan Brophy wrote an hour ago point

I would love to see this project work well because I want to design my own chips.

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Cyberman wrote 06/20/2017 at 17:57 point

This is the coolest project! Is there any way to support your efforts?

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polyfractal wrote 7 days ago point

Thanks!  Right now, I think the best support is just to keep following updates and chime in if you have any knowledge/suggestions.  I'm going to quickly be hitting the edge of my knowledge, and expect to have a lot of open questions as things progress, especially once I start building the xy translation stage.  Having people around to discuss problems with is super helpful!

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Jarrett wrote 06/06/2017 at 17:21 point

Suddenly, I have a burning desire to learn optics and build a selective PCB exposure box.

Your project logs are great. Well written and accessible to the lay-person.

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polyfractal wrote 06/06/2017 at 20:19 point

Thanks! Glad you've enjoyed the logs so far. It's going to be a wild and bumpy ride as I learn everything, so I figured writing detailed logs would double as my lab notebook :)  I also personally find it easier to understand a topic after having worked through how to explain it.

I bet a PCB exposure box would be pretty straightforward! Creating a PCB-sized, in-focus image shouldn't require a ton of fiddling I don't think, since you're working with the projector's original intention to enlarge the image.  It could probably be done with the stock projection lens, but just from my playing around it'd be doable wit two achromat lenses at the right distance.

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