One bad accident could conceivably bring an end to the ECE 344 lab. Its excellent 20+ year safety history depends largely upon student preparedness, so the best thing you can do in the interest of safety is understand what you will be doing BEFORE you come to lab.
Here is some information which should help you stay out of danger.
The chemicals required for IC fabrication are hazardous. The student is well advised to develop a healthy respect (if not fear) for the chemicals in the lab. Below is a brief listing of most of the chemicals in the lab. More detailed safety information can be found in the safety and MSDS (Material Safety Data Sheet) files in the top drawer of the filing cabinet in the lab. Please take a look at them when you have a chance (e.g., during a diffusion furnace operation).
NOTE: When using acids or organic solvents, ALWAYS wear gloves, goggles, and a face shield. Work under a fume hood.
Chemicals : Acetone, Isopropyl alcohol (IPA), Ethyl alcohol,
Methyl alcohol, Trichloroethane (TCA)
Use : Cleaning, organic solvents.
Handling : The above chemicals will irritate the skin if
not washed off as soon as possible. If you use
gloves (especially plastic gloves) in handling the
above solvents, check them for holes before
handling acids. All the above liquids have low
boiling points and evaporate quickly when left
standing in the open.
Chemical : HF (Hydrofluoric acid)
Use : Dissolve SiO2 (and other glasses).
Handling : ALWAYS USE GLOVES. HF, unlike other acids,
does not burn immediately. HF is absorbed through
the skin and dissociates into H and F ions. The
F ions bind with Ca in the blood stream, which
can cause cardiac fibrillation.
After handling HF, always rinse your hands
carefully (even if you use gloves). Make a
special effort to rinse underneath the fingernails
- a burn here really smarts. If you spill HF on
yourself, rinse the affected part in water
immediately (although there is controversy
about washing). Have someone report to your TA
immediately while you are rinsing.
Chemical : HN03 (Nitric acid)
Use : Oxidize silicon.
Handling : Use gloves. Nitric acid leaves a tell-tale
yellow mark when it contacts the skin. If you see
yellow marks developing, wash the affected area _
small burns are seldom painful.
Chemical : H2SO4 (Sulfuric acid)
Use : Inorganic and metallic solvent.
Handling : USE GLOVES. Concentrated sulfuric acid is a
powerful acid. Have respect for it. If it
contacts the skin, the affected part quickly
blisters.
Chemical : H202 (Hydrogen peroxide)
Use : Oxidizing agent, passivation.
Handling : Use gloves. This is concentrated stuff, not
the household variety.
Chemical : Deionized water
Use : Solvent, rinsing. Deionized water is used for
rinsing such things as tweezers, beakers, and
other lab equipment. In high purity work it is
often used in the cleaning of semiconductor
wafers. Please do not use it to clean your hands.
(use tap water).
NOTE: We call deionized water DI
Chemical : AZ 5214 Photoresist
Use : Photomasking (positive type).
Handling : Use under gold light to avoid polymerization.
Use adequate ventilation. Avoid contact with
skin.
Chemical : MIF 327 Developer
Use : Develops positive resists after exposure to UV.
Handling : Use adequate ventilation. Avoid contact with
skin.
Chemical : Phosphoric Acid, H3PO4, Mixed 1:1:1 with HNO3
and DI for "aluminum etch"
Use : Removes Al from Si in unmasked areas.
Handling : Use gloves and goggles; heat only under hood
(70 C).
Chemical : "Hot Oxide Etch" [6NH4F(40%): 1 HF]
Use : Etches unmasked oxide layer on Si wafer.
Handling : Same as HF.
Chemical : HMDS (Hexamethyldisilazane)
Use : To improve the adherence of the photoresist to the
oxidized wafer.
Handling : Avoid contact with skin.
The remaining chemicals on this list are available in the
lab, but not used in the current experiments.
Chemical : "6/l/l ETCH," HNO3/HF/CH3COOH
Use : Slow but high quality Si wafer preparation.
Chemical : "l3/l/l ETCH," HNO3/HF/CH3COOH
Use : Very slow but excellent, chemical-mechanical Si
etch.
Chemicals : "4/l ETCH," HNO3/HF
Use : Fast but imperfect etch (used for very thorough
etch of alloyed device material where "wetting" is
important but planar quality is not).
Handling : Quench all etches above with CH3COOH in a
roughly equal volume; add half, decant, add
remainder, decant, quench thoroughly (three times)
with DI. Always keep material submerged (all Si
out of air) until ALL etch has been decanted in
fifth quench. As with any chemical containing HF,
use gloves and goggles, care when swirling the
beaker, and wash as per "HF Handling" above.
Also, stir gently all pre-prepared etches before
use to insure good mixing (GLOVES). Fill the etch
tubs with only enough etch to cover the wafers;
they should never come anywhere near completely
full unless specified in the text.
The fume hoods are designed for safety. Such materials as HF and trichloroethane give off fumes which are potentially dangerous. Always work with these chemicals at a fume hood - make sure the vent fan is ON. There are LED indicators and streamers to help you know if the proper fan is on. We have labeled waste containers for most of the chemicals used in ECE 344, but if chemicals must be dumped down the sink, always flush with plenty of tap water. This will keep the plumbers at home. Most drains are either plastic base or metallic base. You will be working with both organic and inorganic solvents and thus only sufficient flushing will keep the pipes intact. Used organic solvents are to be stored beneath the developer hood in bottles labeled with the contents and the word "waste", used acids go in the carbouy labeled "waste acids" in the acid hood (the lid must be left a bit lose except during transportation). Avoid pouring anything but water down the drain.
NOTE: Only expensive Teflon has no known solvent.
The following instructions will be posted as a sign at the ACID HOOD.
There are certain DO's and DON'TS, tips and tricks associated with working with furnaces. Some are obvious, some are not so obvious.
Use care at all times (both for your sake and the sake of your wafer). If you move a wafer, carry it in your wafer carrier with the lid ON. If you MUST carry it in tweezers, cup your other hand under the wafer. In the event that it slips from the tweezers, it will fall into your hand rather than onto the floor. Two inch wafers are fragile! Previous students have broken their wafers by swishing them in a rinse tank or even simply squeezing too hard with their tweezers.
THINK SAFETY - Eyes and fingers must be protected. They cannot be (easily) replaced.
Cleanliness is of great importance in the fabrication process. Contaminants introduced during the process can degrade or destroy device performance. Therefore, it is important that processing equipment or chemicals are never touched with the bare hands, (i.e., diffusion furnaces, push rods, boats, etc.) Not only do the bare hands contain dirt and oils, but also sodium which can easily destroy FETs. Always handle the wafer with clean tweezers. A good rule to remember is to never touch anything with your bare hands that will come in contact with the wafer. Always consult the instructor if any mistakes are made in processing. Always consult your instructor at the beginning of the period for any special processing instructions. Often the instructor will call a short meeting at the beginning to make such announcements to everyone at once.
Photoresist should not be left on wafers overnight. Do not begin a photoresist operation unless you are confident you can finish it. At the beginning of the semester a PR patterning process will take a little over an hour. Later, it will go more quickly.
Always wipe your feet well on each rug as you enter the complex. Leave most of your stuff outside the cleanroom. Bring only your lab manual, notebook, and a pen into the lab. Use the shoe cleaner before entering the gownroom. Wait outside if there are already three persons in the gownroom. Don your tyvek coveralls and cap while on the "dirty" side of the bench. If you do not wear glasses, put on a pair of safety glasses or goggles. Contact lenses are unnecessarily risky because they can hold chemicals against your eye. Please do not use them when you come to lab. Put on the booties as you step onto the "clean" side of the bench. Never step on the dirty side of the gownroom with booties on. As you enter the cleanroom, take a couple of steps on the tacky mat to remove lint from the booties. Never ever enter the wet lab without gloves and a face shield (and glasses).
It is of the utmost importance that processing instructions be performed carefully, step by step, as outlined. Of equal importance is the requirement of absolute cleanliness. Industrial fab labs often spend as much or more on "clean" as on the equipment in the lab. In this laboratory, however, we must be satisfied with observing basic precautions. Always clean tweezers in the vapor degreaser before use. When a rinse with DI water is called for, rinse thoroughly with copious quantities of water. Any strange stains or spots which may develop on the wafer should be called to the attention of the lab instructor for analysis and treatment.
To fight pollution and cost overruns, use all chemicals sparingly; i.e., never scrimp on cleanliness, but avoid excess.
Read instructions carefully, think about what must be done, and then do it with care. It is imperative that you read the instructions through completely before coming to lab. Watch for changes, corrections, or addenda. These will normally be posted in the Network Newsgroup: uiuc.class.ece344. This manual is revised frequently, but last minute changes may be added during the course of the semester. This is particularly true now that the manual is available on the World Wide Web.