I have a love-hate relationship with the cleanroom. I love making cool devices to play with, and I kind of love the whole process of getting gowned up and being part of the small, elite club of cleanroom workers. However, I have an on-going battle with it to get decent results, and I positively HATE the short breaks of waiting 3-5 minutes. I mean really, truly, loathe them. This, therefore, is an excerpt from the chronicles of my love-hate what-the-heck-am-I-doing-here life in the cleanroom.
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Timers (11/15/11)
Have I mentioned how much I hate waiting in the cleanroom? I really hate it. It would be one thing to have to wait an hour on something – I can go talk to people, catch up on some reading, degown and go do some other work, anything to disengage my brain from the monotony of waiting. Even a break of 10 minutes is enough to walk away and think about something else than the fact that I am just waiting. On the flip side, I really enjoy being so busy that I can’t get bored. There is something very satisfying about getting home and sitting down and finally letting the brain think about whatever it wants instead of maintaining the constant focus I’ve forced it into all day. Unfortunately, a fab process rarely affords me these luxurious wait times or exciting busy times, and instead forces me into 3-5 minute wait times that sap my soul away.
Let’s discuss today as a case study of all that is wrong with the cleanroom world of waiting. My first item on the agenda: clean my wafers. This is a 20 minute endeavor of first sonicating in acetone for 5 min, then in IPA for 5 min, then in water for 5 min, then in water AGAIN for 5 min. I was fresh in the cleanroom and could handle the short 4 min breaks for the first 15 minutes. By the start of the second water sonication, I was ready to gnaw my arm off at the shoulder to escape the cleanroom. So I took a picture of the timer. Yay, it’s almost done, only 2 min left to wait! I sent the picture to Fernanda to pass the time and spread the crazy around a little. Then I realized the ultrasonicator had shut off at some point during the 5 min, and I had no clue when, so I had to start the 5 minutes of torture over. God, do I really have to wait another 5 min for this thing to finish?
Next on the list is the Gods-forsaken plasma asher. This machine is one of many that is decidedly out to get me. First, most people pump it WAY down when they leave it. Some people pump it down less so, so when I set it to purge, it could be 30 seconds or 3 minutes before it opens. I usually start off hopeful, but by the time it finally opens I am usually gently tapping my forehead against it, pulling slightly at the door, and begging it under my breath to open already. At this point, I get the overwhelming excitement and joy of loading my wafers. After that breathless minute of pleasure, I set the machine to high vac and get to wait for it to pump down. This doesn’t take very long, so I usually leisurely fill out the machine log before having nothing to do but to stare at it for about 30 more seconds while it finishes up its task at hand. At about 25 seconds, I said “screw it, 0.5 torr is low enough today!” and started up the ashing.
This is one of the most exciting parts of the using the plasma asher, so let me describe it in detail. First, I flip a switch to say that I’d like to choose oxygen plasma (the other option is CF4). Then, I get to turn the dial off to the right of this switch to inform the machine that yes, indeed I am serious about choosing oxygen plasma.[1] This next step is critical: I have to hit the “Off” button. If I don’t, the power won’t turn on when I hit the “On” button. Don’t ask me how I know this.[2] But before I hit the “On” button, I must turn the power dial all the way to 0. After I’ve hit the “On” button, I get to turn the dial up and watch for the reflected power to drop, indicating that I have a plasma and things are going well. This happens at about 150 V. Then I get to start the timer. All this takes me about 5 seconds. Total. Tops. And it’s the most exciting thing about running this machine.
The next 5 minutes are sheer agony. This is the one machine with an analog timer, which means I get to physically watch each millisecond of my fleeting life stripped away from me as the second hand turns. I maintain my composure for the first 42 seconds of this assault, then photograph the offending timer and send it to Fernanda.
Somehow, I hold it together enough while the clock counts away another two minutes and 55 seconds before I lose it again and take another picture of the timer.
I send this to Fernanda, too, expending a further 5 seconds of the waiting, leaving me a remaining one minute and 17 seconds to wait.
About 15 seconds later I decide that 4 minutes ashing is just as good as 5 minutes ashing, leading me to another exciting time on the plasma asher. First I hit the “Off” button, giving me a tingling feeling inside that my time with this blasted machine is almost over. Then I turn the dial from O2 to off. I flip the O2 switch to off. I wait for the high vac to evacuate the chamber, and leisurely turn the power dial all the way off while I do so (about 3 seconds). This is enough time, I figure, to remove enough of the O2, and I flip the vacuum switch to off and the purge switch to on. I wait a couple of seconds (maybe 5?) before I get impatient and flip open the handle so the door will automatically open when the chamber is purged.
About 5 years later (maybe 30 seconds) I start to get really impatient. I tug on the handle. It’s still stuck, there’s still a vacuum in the chamber. I rest my forehead against the door and slowly count down another 5 years (another 5 seconds), and tug again. It’s still stuck. I bang my forehead against the door and beg it to open, then count down another 5 years (about 3 seconds this time) before tugging again. It’s still stuck!! Okay, if it wants to play this game, two can play it. I walk away and sing half of Queen’s Bohemian Rhapsody in my head. I walk back up the plasma asher and give the handle another gentle tug. It’s STILL stuck. I wail in frustration, and apparently not just in my head this time because Anita looks over and says, “What’s wrong, is it misbehaving again?” and I have to admit that, “No, Anita, the asher is working just fine, I’m just impatient.” Her kind words about the virtues of patience wash right over me.
Just when I am starting to seethe with impatience and frustration (and contemplating all the exciting methods of completely destroying the plasma asher), Cliff distracts me across the room by showing me pictures of his adorable baby girl on his iPhone. When I get back to the asher 5-10 minutes later, it is finally open and someone I probably know but can’t recognize in their cleanroom getup (only his eyes show) tries to tell me how inappropriate it is to leave the asher unattended on purge because it wastes nitrogen gas and costs the lab money. I could’ve kissed him through our facemasks because finally my torment with the plasma etcher was over.
[1] Again, the only other option is CF4. I wonder what would happen if I gave the plasma asher conflicting information? I am afraid to find out, it might hunt me down in my sleep.
[2] Okay, fine, I’ll reveal the source of this information this time: it’s on a handwritten sign next to the “On” button. Sometimes I fantasize about being a rebel and hitting the “On” button WITHOUT hitting the “Off” button, but like I mentioned in the previous footnote, I’m a little concerned about the bedtime ramifications of angering this machine.
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