After a semester of processing wafers to build PMOS devices, it's now time for us to test the wafers and see if they actually work. I'm a member of the Tuesday lab group, but I'm attending the Monday lab because I'll be out of town tomorrow.
"That's cheating," the King of Comedy says after I justify my presence to him.
"No, it's not."
Once enough of the real Monday lab people show up, with various interruptions from others (including the Out-Holder who drops in to ask about developer, because the new developer he's using is totally stripping all the resist of the wafers, thus undoing all that lithography), we begin. Because the test equipment is delicate, participation in this lab involves watching the professor take measurements and hearing a few anecdotes about odd, observed effects that turned out to be nifty tunneling devices and other accidental discoveries.
"Like Otto Tittslinger, who invented the brassiere," the KoC puts in.
To the tune of neaner-neaner I sing, "You watch chick films."
"Hey, Beaches is, like, my favorite movie. I even have the soundtrack," KoC says.
"How old are you?" I demand. "That movie came out in 1990." (1988, actually. I just checked.)
"I'm very mature for my age," he says.
Now that gets a laugh.
"So anyway, the resistance of Wafer 4 is 800 ohms per square, which is consistent with it having the longer drive-in, but then Wafer 2 that had the fifteen minute drive-in had the same… Huh. Let's take some more measurements." The professor puts another wafer on the probe.
We all dutifully record the measurements. Some wafers have a lot of variance: 300 ohms per square in one spot, 900 in another, with these spots being rather close together. Then it's time to measure the devices on another delicate test device. We start by checking the resistance of some of the resistors.
The professor says, "Okay. Now this resistor is a ten square resistor and we measured 500 ohms per square for this wafer, so what should the resistance be?"
"5000 ohms."
"It's 47 kilo-ohms," someone reads from the screen.
Students pace around the lab and grumble under their breaths. It's really amusing how they thought that somehow this was all going to work. Where did they intern that stuff works on the first try?
"Let's try it again with the light off." The professor touches the switch. The light is to help position the probes on the contacts, but reacts with the silicon enough to mess up the readings.
"132 mega-ohms."
"Woo! Light-sensitive resistors!"
"Nobel Prize!"
The professor is shaking his head. "No. I think I'm going to have to check these probes out. I think there must be something wrong, either with the probes or maybe the contacts are misaligned. Anyway, for your lab notebooks, you should all do the calculations to figure out what the values should be."
The KoC gets serious. "Professor. This whole semester's been a lie, hasn't it?"
498 words | April 18, 2005 09:53 PM | Ivory tower