Lab in the clean room is not only dangerous, but also uncomfortable and dull. We have a Class 1000 clean room (no more than 1000 particles per cubic foot of air) and our protocol isn't as strict as at a commercial plant, where they would have a Class 10 or Class 1 clean room. I'm amazed that people at the big plants can stand it for any length of time. Then again, if they want out, all they have to do is break protocol and they're fired on the spot.
Protocol is the set of procedures one must follow in order to keep particles out of the clean room: bunny suits, hair nets, hoods, face shields, air showers, sticky mats at the doors to pull particles off the soles of your shoes. You can't take a pencil into the clean room, because a pencil works by rubbing particles onto paper. You have to use special paper. You have to use approved pens. If there is too much sodium in the ink, the particles released when you pull the cap off the pen will put sodium into the wafers, which will then have their electrical properties compromised by having too many ions.
Our protocol is sticky mats, booties, hair nets, safety glasses, latex gloves, and jump suits. Despite reality, it is assumed that all persons using the clean room are giants, so I get stuck with a huge jump suit, booties that flap around the soles of my shoes, safety glasses that rest painfully halfway down my nose (I have to use the big safety glasses to fit on over regular glasses since we aren't allowed to wear contact lenses), and big wrinkly gloves with squeaky air bubbles. I wonder if the petite researchers have their own personal gear that fits.
Many of the guys in my lab section (I'm the only one without the Y chromosome) are pretty big, however, and so I find myself spending most of the lab period looking at their backs as we gather around the rinse bench to wash our wafers. The washing process consists of dipping a basket of wafers in various toxic baths and standing around for several minutes while they soak. There's really only room for two people to work at the bench and I don't mind letting the foolhardy youths pour and mix the toxic chemicals because I've had more than enough physical trauma in the past six months, thankyouverymuch. The two boys who mess with the HF, hydrogen peroxide, and so on have to wear, over their protocol gear, face shields, rubber aprons, and big pink rubber gloves.
The rinse bench is back in the section of the clean room with yellow lights. This is where the resist is put on the wafers, and the wafers are exposed and developed (sort of like a photographic process, but not). The resist is light sensitive. You put resist on the wafer, expose the wafer to a certain pattern, the resist is cured in that pattern, you rinse off the uncured resist, do things to the wafer, then take off the rest of the resist so that the pattern of the things you did remains on the wafer. Lather, rinse, repeat. Eventually you get microchips.
Another particle attenuation method is air circulation. The air turns over in the clean room six times per minute and is filtered. Vertical laminar flow, in which air comes straight down through the ceiling and is vented out around the base of the walls, pulls particles down and out of the room. The ceiling is translucent and the fluorescent light is diffused so you don't get much in the way of shadows. Except in the yellow light area, the light is really bright and white. The fans make a lot of noise too. Between the weird light, the white noise, and the protocol gear, it's kind of a sensory deprivation experience.
Eventually our wafers are clean and dry. They are transferred back to their cassette for safekeeping till next week.
672 words | February 1, 2005 07:38 PM | Ivory tower