chemical storage, labeling, and handling · 4/1/2009 · chemical storage • chemicals must use...

R. B. Darling / EE-527 / Winter 2013

EE-527: MicroFabrication

Chemical Storage, Labeling, and Handling


Chemical Storage Principles• Chemical Storage in the Microfab Lab is based upon:

– Minimizing risk from chemical incompatibilities– Maintaining required purity of starting materials– Reducing cross-contamination– Reducing degradation mechanisms which limit shelf life– Segregating stock from waste

• Chemical grades are non-sequential, non-linear, and overlapping. – Chemical purity is measured by the maximum level of potential

impurities: • Qualitative: which impurities may be present• Quantitative: how much of each impurity may be present

– Example: 99% is not always more pure than 95% material. • It depends upon which impurities are present in the counts.


Chemical Grades and Purity - 1

• Commercial or Technical Grade– typically 85-90 % purity– rarely used in the laboratory

• Practical Grade– small step above technical grade– often contain intermediate compounds as part of the preparation

process

• United States Pharmacopoeia (USP) Grade– suitable for drug use– generally acceptable for chemistry lab work

• Chemically Pure (CP) Grade– almost as pure as reagent grade, but application determines

whether purity is adequate for the purpose



• Spectroscopic Grade– purity determined by optical absorption at particular wavelengths– usually around 99 % purity– used for IR, VIS, & UV spectrophotometry

• Chromatography Grade– minimum of 99 % purity with no single impurity over 0.2 %

• Reagent Analyzed or Reagent Grade– certified to have impurities below specific levels set by the

Committee on Analytical Reagents of the American Chemical Society (ACS)

– bottles are identified by a batch number– minimum standard for any chemical analysis work



• Electronic or Semiconductor Grade– specified to contain less than set levels of specific impurities:

• Na, K, Ca, Mg, etc.– common subdivisions are:

• Low-Sodium MOS Grade• Low-Sodium CMOS Grade – If in doubt, order this grade.

• Primary Standard Grade– at least 99.95 % purity– can serve as reference standards in analytical procedures

• Ultra-High Purity Grade– usually solids that have been successively refined– expressed as number of nines of purity, e.g. 5-9s = 99.999 % purity– often the highest available overall purity of a material


Chemical Labeling

• Primary Labeling– printed on containers by the manufacturer– specific information is set by Federal Lab Safety Standard (FLSS)– DOT labels are required for transport and storage

• Secondary Labeling– used for labeling smaller, secondary containers– must be done by user to provide point-of-use information– must contain:

• common or scientific name of chemical• name of person who is responsible for it• date at which container was filled• any specific precautions; minimum is NFPA 704M symbol• the best practice is to add precaution codes (A – Z)


DOT/United Nations Hazard Classes

– Class-1 Explosives Class A, B, C– Class-2 Compressed Gases Flammable, Nonflammable– Class-3 Flammable Liquids– Class-4 Flammable Solids– Class-5 Oxidizing Materials Oxidizers, Organic Peroxides– Class-6 Poisonous Materials Class A, B– Irritating Materials Domestic, Import/Export– Class-7 Radioactive Materials Class I, II, III– Class-8 Corrosive Materials– Class-9 Miscellaneous Hazards

• Each has standard international placards that must label any material for transportation


Common DOT Labels for Microfabrication

rare for microfablaboratories


NFPA 704M Labeling System

• National Fire Protection Association (NFPA)• Hazard Ratings; 0 to 4:

– 0 none– 1 slight– 2 significant– 3 severe– 4 extreme

• Example: H2SO4: 3

W2

0

Flammability (red)

HealthHazard(blue)

Reactivity(Stability)(yellow)

Special Symbols (white)Some manufacturers, e.g. Baker, use the fourth (white) position to indicate immediate contact hazard


Secondary Labeling Methods in the Lab

• Solvent wash bottles– Use the pre-labeled polypropylene squirt bottles and just refill then

when needed.

• Glass beakers– For long term use in the same process, use a Sharpie felt-tip

marker on the white labeling area, or create a tape label and apply this to the beaker. Tape labels will resist most chemicals, solvents will dissolve the Sharpie felt tip marks.

– For short term use, label a filter paper and place the beaker over top of it to identify it. (Laboratory version of a glass coaster.)

• Screw cap chemical bottles– Use a clean, new bottle and put a pressure sensitive label on it, or

use tape labels.


Secondary Labeling – Solvent Wash Bottles

• Use the pre-labeled bottles –nothing to label by hand!

• Be careful with their use: – Only light pressure will

discharge contents– Heat from a hand will often

cause pressure and discharge volatile solvents, e.g. acetone

– Unscrew the cap slightly to break the pressure, but still limit the evaporation rate

– Lift the bottle by the cap and discharge tube to avoid squeezing out the contents

ISOPROPANOL

13

0


Secondary Labeling – Beakers

ACETONE

ACETONE

adhesive label labeled filter paper


Secondary Labeling – Glass Jars

• Necessary elements of secondary label: – Primary composition– Primary hazard– Owner– Date

• Precaution codes are also very helpful.

acetone/PR

flammable!

R.B.Darling

2009/04/01


Chemical Precaution Codes for Secondary LabelingA Acid N Narcotic

B Base O Oxidizer

C Corrosive P Pyrophoric

D Dizziness & Drowsiness Q Heat Sensitive (Q = Heat)

E Explosive R Radioactive

F Flammable S Solid

G Compressed Gas T Toxic

H Hygroscopic U Ultrahigh Purity

I Irritant V Contents under Vacuum

J Etiological Agent (Jerms) W Water Reactive

K Carcinogenic X Asphyxiant (hands around neck)

L Liquid Y Vibration Sensitive

M Light Sensitive Z Static Sensitive (Zappable)Note that these are specific to the EE Micro Fab Lab and not universal.Spell these out – don’t just use the alphabet letters.


Chemical Storage

• Chemicals must use segregated storage because of potential for cross-reactivity and cross-contamination.

• Chemical Storage Classes for Microfabrication: – Compressed gases– Acids and bases– Flammable solvents– Oxidizers (H2O2, chlorates, phosphates)– Photosensitive chemicals (e.g. photoresist)– Dry chemicals (powders, granules, shot)– Heat sensitive chemicals (thermosetting adhesives, etc.)– Hygroscopic materials– Ultrahigh purity materials (e.g. wafers)


Storage Hazards• The biggest and most common hazard is storing

incompatible liquid chemicals in the same place: • Acids & bases, flammable solvents, and oxidizers must

each be stored separate from the others. • Each of these three has their own specific storage space. • Misplacing any two of these three together can produce a

potentially explosive situation!

Acids&

Bases

FlammableSolvents Oxidizers

A non-overlapping Venn diagram !!!


Laboratory Refrigerators• Many microelectronics materials are heat sensitive and need to be stored in

a refrigerator. • Special designated refrigerators are in the lab for this purpose.

– They are NOT for storing any foodstuffs under ANY conditions!• Materials that are usually stored under refrigeration:

– Hydrogen peroxide (H2O2) – a strong oxidizer!!!– Crystalbond® mounting resin– Apiezon W black mounting wax– Polyimide resins– Spin-on glasses (SOG) and spin-on dopants (SOD)– Some unusual photoresists, e.g. P2460– Thermosetting silver epoxy– Solder pastes

• Each of these materials must be warmed back to room temperature before use. Plan ahead since that can often take a few hours.


Dry Boxes

• Used for storing materials under conditions of reduced humidity.

• Dry nitrogen is used to purge the air from the dry boxes. – The dry box is not “dry” unless

this is done… • A dry nitrogen purge will usually

achieve < 5 % RH. • This is not adequate for truly

hygroscopic materials. • This is the most common storage

for wafers, furnace parts, vacuum deposition parts and materials, and some analytical supplies.

psi

drynitrogenpurge


Dessicators• Used for storing more highly hygroscopic materials. • Usually glass construction with a ground sealing flat. • Residual moisture is absorbed by CaSO4 crystals (Drierite). • Vacuum can be pulled to remove air and water vapor.

vacuum valve

cover

base

Drierite, CaSO4

perforated base plate

with moisture indicator

Drierite is added to the dessicator in an anhydrous form. “Indicating” drierite has a dye added which turns from blue to purple when moisture is absorbed. Drierite can be recycled by baking the water out and restoring it to a white (or blue) color of the anhydrous form.


Bottle Residue

• No bottle cap is ever perfect –some leakage always occurs.

• Always treat the outside of a bottle with the same precautions as its contents!

• Acid and base bottles very often accumulate crystal growth around their mouths. – This can be removed by careful

washing of the bottle, with the cap on!

• Always use acid gloves when handling acid bottles, even for just moving them.

Sulfuric Acid H2SO4

3 20

W


Returning Material to a Container

• One Rule: NEVER. • What comes out of a stock bottle NEVER goes back.

– If too much is poured out, NEVER return the excess back to the stock bottle.

– Instead, just pour it into the waste container for that chemical.

• This is true for all process chemicals, wet or dry, • But ABSOLUTELY ESSENTIAL for photoresist.

– Dried flakes of material falling back into a photoresist bottle will totally ruin the entire bottle for any future use!

– Returning any material back to a stock container will contaminate the stock, rendering it useless for any critical work that follows.

– Photoresist is always transferred with a pipette, never poured. – The mouth of the bottle and its cap must be kept spotlessly clean.


Photosensitive Materials

• Many photochemicals are used for image transfer or printing in microfabrication.

• Photoresist is by far the most common. • These chemicals are sensitive to normal room and outdoor light and

must be kept in bottles which are opaque to their sensitive part of the spectrum.

• Photoresist is normally kept in brown glass bottles as working secondary containers. A 50 mL or 100 mL size is usually best.

• All photoresist work is performed in the yellow-lighted photolithography room. The filters on these room lights are designed to produce illumination which does not expose photoresist.

• Note that inspection microscopes must also use a yellow or orange filter to keep the illuminator from exposing photoresist that has not yet been developed.


Bringing New Materials into the MicroFab Lab

• First check with the laboratory manager to insure that the chemical is compatible with other processes and equipment in the lab, and that an adequate storage location is available in the lab. Do not just assume this is the case!

• Unpack the new material in the gowning room, using the sink to wash off any packing material residue. Dry the container thoroughly before moving it further. Do not open the container in the gowning room.

• Label the container with your name and date. • Insure that the laboratory manager logs the new chemical into the

laboratory inventory. • Check with the laboratory manager to insure that the necessary

engineering controls and personal protective equipment is available for using the chemical in the MicroFab Lab.

• When your use of the new chemical is complete, it is your responsibility to arrange for the chemical to be removed or disposed of. Check with the laboratory manager on the specifics for this.


Waste Containers

• When a bottle of a new stock chemical is empty, the bottle is thoroughly washed, dried, and used as a waste container for the same type of chemical that it originally held.

• Waste containers are clearly marked with the word “WASTE” on their labels, along with the composition of what the waste is.

• Be certain to add waste only to a waste container whose composition matches what you are disposing. – This is absolutely critical! – When in doubt, start a new waste container. – Adding random wastes to the same container is the foremost way

to create an unintended chemical reaction, a fire, an explosion, or worse!


Sources for Chemical Information

• Material Safety Data Sheets (MSDS)• Chemical Abstracts Services (CAS)• Handbooks


Material Safety Data Sheets (MSDSs)

• Material Safety Data Sheets (MSDSs) are a Federally required piece of documentation that must accompany the transport or sale of any substance that could contain anything of a hazardous nature.

• Hard copies will normally be shipped along with the substance, but they can also be downloaded, usually as PDFs, directly from the manufacturer, who is responsible for making them available.

• MSDSs contain a lot of boiler plate legalese, and they do not contain detailed chemical property information for using the substance, but they do contain information on the known hazards of storing or handling the substance which are important.

• An important skill is being able to read an MSDS and understand the chemical hazard information that it contains.


Organization of an MSDS

• Product identification (CASRN, mfg. no., etc.)• Breakdown of ingredients• Physical property data (MP, BP, FP, AP, VP, SG, etc.)• Shipping description (as applicable)• Reactivity data (stability, incompatibilities, etc.)• Fire and explosion hazard data (UEL, LEL, fire extinguishants, etc.)• Toxicological properties and health data (TLV, LD50, LC50, etc.)• Preventative measures

– Personal protective equipment (PPE)– Storage and handling– Engineering controls (ventilation, alarms, etc.)– Spill or leak procedures

• First-aid measures• Additional information and sources used


Obtaining MSDSs

• From the manufacturer: – http://www.sigmaaldrich.com/united-states.html– others…

• From the UW MyChem: – http://mychem.ehs.washington.edu/– Login with your UW NetID and password. – The MyChem database is managed by UW Environmental Health

& Safety (EHS). – Limited to those substances which are in use or have been used on

campus. This is still quite extensive! – Students, faculty, and staff can access all of these MSDSs. – Laboratory managers can in addition access and maintain chemical

inventories for each laboratory. (A UW requirement!)


UW MyChem:


Chemical Abstracts Services (CAS)• The chemical properties of a substance depend upon more than just its

chemical composition – its grade, form, purity, microstructure, and method of manufacture also matter. – E.g. an iron bar behaves differently from a bottle of iron powder.

• Different materials have been cataloged by the Chemical Abstracts Services (ACS), a division of the American Chemical Society, to give more precise information on materials that takes these differences into account. The ACS monitors, indexes, abstracts, and adds to their registry nearly all of the chemicals and materials that are used in microelectronics and general inorganic and organic chemistry. The CAS maintains the most extensive, complete, and up-to-date database for chemical information.

• ACS Home Page: http://www.acs.org/• CAS Home Page: http://www.cas.org/ (A division of the ACS) • The CAS SciFinder service is the best method for accessing the CAS

databases, but it is a subscription service.


The CAS Registry

• The CAS Registry is the primary database for information on different substances. It contains: – Literature references to the substance, – Experimental and predicted property data, – Commercial availability, – Preparation methods, – Optical spectra, and – Regulatory information.

• Different substances are indexed with a CAS Registry Number (CASRN). – It is conventionally enclosed in square brackets, e.g. []. – This provides the most universal, unique identifier for a specific substance,

and these are frequently cited in the chemical literature. – The CAS Registry includes more than just pure substances; common mixtures

and solvent-solutes are also indexed, e.g. fuels, oils, alloys, buffer solutions, and spectroscopic standards.


CAS Registry Numbers - Examples

• HCl, Caledon Laboratories Ltd.: [7647-01-0]• HF, General Chemical Canada Ltd.: [7664-39-3]• H2SO4, General Chemical Canada Ltd.: [7664-93-9]• HNO3, Caledon Laboratories Ltd.: [7697-37-2]• KOH, Mallinckrodt Baker Inc.: [1310-58-3]• NaOH, Mobay Chemical Corp.: [1310-73-2]• Acetone, Sigma-Aldrich: [67-64-1]


Handbook Information

• CRC Handbook of Chemistry and Physics– The original classic– Limited in scope, but generally good for inorganics and pure

substances– Quite good for physical property data, e.g. MP, BP, heats of

evaporation, vapor pressures, dissociation constants, surface tensions, dielectric, magnetic, and optical properties, etc.

• Sigma-Aldrich Catalog-Handbook of Fine Chemicals– The best single volume handbook from a chemical manufacturer– Nicely indexed to match to the CAS registry numbers– Available for free upon request from Sigma-Aldrich!

• Numerous other specialty handbooks– McGraw-Hill Handbook of Thin Film Technology, etc.

chemical storage, labeling, and handling · 4/1/2009 · chemical storage • chemicals must use...

Documents