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Simple Chemistry To Metallize And Etch Silicon Chips

December 3, 2023 by 5 Comments

We’ve been eagerly following [ProjectsInFlight]’s stepwise journey toward DIY semiconductors, including all the ups and downs, false leads, and tedious optimizations needed to make it possible for the average hacker to make chips with readily available tools and materials.

Next up is metallization, and spoiler alert: it wasn’t easy. In a real fab, metal layers are added to chips using some form of deposition or sputtering method, each of which needs some expensive vacuum equipment. [ProjectsInFlight] wanted a more approachable way to lay down thin films of metal, so he turned to an old friend: the silver mirror reaction. You may have seen this demonstrated in high school chemistry; a preparation of Tollen’s reagent, a mix of sodium hydroxide, ammonia, and silver nitrate, is mixed with glucose in a glass vessel. The glucose reduces the reagent, leaving the metallic silver to precipitate on the inside of the glass, which creates a beautiful silvered effect.

Despite some issues, the silvering method worked well enough on chips to proceed on, albeit carefully, since the layer is easily scratched off. [ProjectsInFlight]’s next step was to find an etchant for silver, a tall order for a noble metal. He explored piranha solutions, which are acids spiked with peroxide, and eventually settled on plain old white vinegar with a dash of 12% peroxide. Despite that success, the silver layer was having trouble sticking to the chip, much preferring to stay with the photoresist when the protective film was removed.

The solution was to replace the photoresist’s protective film with Teflon thread-sealing tape. That allowed the whole process from plating to etching to work, resulting in conductive traces with pretty fine resolution. Sure they’re a bit delicate, but that’s something to address another day. He’s come a long way from his DIY tube furnace used to put down oxide layers, and suffering through the search for oxide etchants and exploring photolithography methods. It’s been a fun ride so far, and we’re eager to see what’s next.

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Old Batteries Yield Thermite And Manganese

March 16, 2017 by 16 Comments

Some people collect stamps, some collect coins, some even collect barbed wire. But the aptly named [Plutonium Bunny] is an element collector, as in one who seeks a sample of as many elements on the periodic table as possible. Whatever, we don’t judge – after all, there are more than a few Hackaday readers who collect lots of silicon, right?

So what’s a collector to do when he gets to the 25th place on the periodic table? Easy – harvest manganese from alkaline batteries with a thermite reaction. There’s a surprising amount of manganese in depleted alkaline batteries, which of course are easy to come by in bulk. The chemistry of [Plutonium Bunny]’s process is pretty straightforward and easy to reproduce with common ingredients, but you’ll want to be careful with a few steps – chlorine gas is not something to trifle with. The basic idea is to solubilize and purify the manganese dioxide from the other materials in the battery cathodes, recrystallize it, and mix it with aluminum powder. The aluminum acts as the fuel, the manganese dioxide is the oxidizer, and once the satisfyingly exothermic reaction shown in the video below is over, the collector-grade elemental manganese can be chipped away from the aluminum oxide slag.

So once you’ve got a few manganese nuggets, what can you do with them? Not much really – it turns out the oxides recovered from the battery are far more useful for things like supercapacitors. But it’s still a neat trick.

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