Tag: Chemistry

How to Build a Computer 38: Epitaxy

 

Hello and welcome back to How to Build a Computer. If any of y’all are worried about my long absence, well, let that be a lesson to you: The bearded nogoodnik with the dimensional transportalponder does not have your best interests in mind. Sadly, the story is much less interesting than that; I ran out of processes that I either learned about in school or worked with on the job. I’m much less happy regurgitating textbooks than I am imparting actual experience. For instance, I don’t even know if “epitax” is a real verb, but I’m going to use it like such because it’s fun to say.

With the preliminaries out of the way, let’s take a look at the wonderful world of Epitaxy. From the Greek root it looks like we’re talking about a tax atop your other taxes, but however timely and relevant such a word might otherwise be that’s not what we’re working on. What we’re building here is a crystal on top of your other crystal. Recall way back from the start how wafers are sliced out of boules that are composed of one giant crystal. There’s some advantage to remember that that’s not a perfectly flat surface. Here, let me demonstrate:

Bakelite: The Beginnings of the Plastics Era

 

About 110 years ago, the plastics era (as we understand that term) began with a material called Bakelite named by its creator and inventor Leo Baekeland.

Leo Hendrick Baekeland was born on November 14, 1863, in Ghent, Belgium, to Karel and Rosalia Baekeland. His father was a cobbler while his mother worked as a housemaid. He was a bright young man who, encouraged primarily by his mother, read anything he could get his hands on.

Leo Hendrick Baekeland.

How to Build a Computer 37: CVD II, This Time It’s Personal

 

Last time, if you’ll recall, I discussed the basic idea of a chemical vapor deposition system, and described how you’d use it to deposit silicon onto your wafer. Today we’re following rather directly from that post, where we answer some important questions. Questions like “What if I don’t want to put down silicon? What other things can you offer me?” Well, for starters

SiCl4(g) + 2H2(g) + O2(g) —> SiO2(s) + 4HCl(g) ~900 C

How to Build a Computer 36: Chemical Vapor Deposition

 

No matter how much fun you’re having etching silicon, applying and stripping photoresist, or implanting ions, sooner or later you’re going to have to actually put down some lines. Gotta build a circuit eventually. Chemical Vapor Deposition (CVD) is one of the main ways this gets done. Let’s have a look at what we’re doing, shall we?

If I had known I was going to use this picture at least three times I might have put a little more effort into the sketching.

How to Build a Computer 35: Anisotropic Etching

 

Last time we talked about how to make tiny little holes in silicon using harsh acids. Wet etching is fine and all, but sometimes you just can’t make a feature small enough. You’re limited by the aspect ratio. That is, how wide it is versus how tall it is. A post hole has a high aspect ratio because it’s much deeper than it is wide. A strip mine is a pretty low aspect ratio hole. The difficulty with making high aspect ratio holes in your silicon is that your etchant is going to etch down, yes, but it’s also going to etch towards the sides.

Before we get into dry etching there’s one more trick for making an anisotropic (uh, it etches downward quicker than it goes sideways. Literally the word means not-the-same-in-all-directions.) wet etch. What happens if you do your etching with a strong base instead of a strong acid? As it turns out, and for no reason, I’ve managed to determine, a strong base will etch one crystal face preferentially.

How to Build a Computer 32: X-Rays

 

I think x-rays have had their dramatic potential shortchanged by the way they’re actually useful. You hear “gamma rays” and your mind is drawn to the Incredible Hulk and how he gained his bright purple shorts. Cosmic Rays? Space madness! But when your mind turns to x-rays you start thinking “dentistry.” Much less exciting.

Right. Computers. Today we’re going to spend one more post on Electron Microscopy, and another way these things are useful. This one is actually pretty straightforward from topics we’ve already covered. I’m sure y’all have been taking notes, and know immediately that I’m referring to Computers 5: Fundamental Chemistry, where I described the process of prodding electrons into giving up photons. I’ll save you the reread, even though jokes about New Jersey never get old. Here are the useful bits:

How to Build a Computer 15: Developing

 

No, this isn’t a story that’s still in progress, this is a process step. ‘Developing’ in this context means you’re chemically removing half your photoresist (either the stuff that was exposed in a positive photoresist or the stuff that wasn’t in a negative photoresist.) And no, it’s not about guys making software either. Look, if you’re going to stop us every single time the chance for a bad joke comes up… actually that’s pretty much the game plan. Carry on.

An exposed photoresist molecule. The cheese is carbon, the sausage is oxygen, and I’m thinking it’s high time to conduct some more chemistry, if you know what I mean.

How to Build a Computer 8: Organic Chemistry

 

I started with a discussion of the magic of photoresist, however (say it with me!) it got long-winded and I cut it down to the organic chemistry review. Next week photoresist. This week we’re going over some basic organic chemistry. Sounds fun, right? It’s going to be even more fun than that! You wait and see. We’re going to start small though, with methane.

You smell something? No? It’s probably just me.

How to Build a Computer 5: Fundamental Chemistry

 

I know I promised simple transistor uses last time. Thinking about it though, I’d rather go into a bit more detail about the electron golfing I described earlier. It’s a neat analogy, but it doesn’t cover some things you can do with diodes. Interesting things. Therefore we’re gonna dive in for a deeper understanding of chemistry, atoms, and cartoons. Let’s look at a model of an atom using common household objects:

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Member Post

 

Some non-physicts I know are excited by this graphene energy story. It seems to propose the possibility of perpetual subatomic friction of graphite-based materials which could endlessly supply energy and perhaps be scaled to suit a variety of applications. Is that correct?  It sounds too good to be true, so it probably is. Over the […]

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Member Post

 

My klutzy self has not been doing anyone any favors lately, whether what I’m breaking is computers or body parts. By falling off a stepladder, I neatly put the kibosh on having a few good days before Christmas to do the gift planning I’ve till now done earlier in the year. At first, nothing seemed […]

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Member Post

 

A fire consists of three essential elements: fuel, an oxidizer, and heat. The chemical reaction between the fuel and oxidizer is self-sustaining (as long as there is a steady supply of both) because it gives off enough heat to maintain the temperature above a necessary threshold. Looking more closely at the reaction between the fuel […]

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