SAFETY IN THE MICROELECTRONICS FABRICATION CLEAN …The MSDS program is a federally mandated program that requires the manufacturer of a potentially hazardous material to fully explain

SAFETY

IN THE

MICROELECTRONICS

FABRICATION

CLEAN ROOM

John Hudak

Original: August 1995

PDF version with updates provided by Tim LaFave Jr. (December 2001)

John HudakMicroelectronics Clean Room Facilities Manager & Faculty Associate (ECE)

Office: Cameron 286Phone: 704-687-3967Fax: 704-687-3183E-mail: [email protected]

With a Bachelors of Science in Electrical Engineering (Wilkes University, Wilkes-Barre, PA),John Hudak has over 25 years of experience in the clean room fabrication of microelectronic devicesand integrated circuits. He has worked on various devices including schottky diodes, BJTs, FETs,solar cells, RF and microwave transistors and hybrid circuits, CATV and cellular hybrid amplifiers.He joined the University of North Carolina – Charlotte as a research engineer in July, 1994 withthe task of assembling the microelectronics fabrication clean room located in the C.C. CameronApplied Research Center.

In November, 1998, John became a faculty associate in the Department of Electrical and Com-puter Engineering.

Safety in the Microelectronics Fabrication Clean Room

1 Introduction

Semiconductor processing and the fabrication of microelectronic devices involves a wide range ofextremely hazardous materials, gases, and chemicals. It is extremely important that all users of theUNC-Charlotte microelectronics clean room understand and respect the dangerous nature of theprocesses involved in making a microelectronic device or semiconductor. This booklet will providea basic introduction to the hazards and safety procedures required in a microelectronics clean room.More comprehensive safety information is available from the UNC-Charlotte safety office.

A key part of any safety program includes an understanding of the MSDS program. MSDSstands for Material Safety Data Sheet. The MSDS program is a federally mandated program thatrequires the manufacturer of a potentially hazardous material to fully explain the hazards and safehandling of the material. In the MSDS program all chemicals and gases are considered materials.

This MSDS sheet is a comprehensive overview of the safe handling of the material and must beprovided by the manufacturer to any and all users. A notebook of the MSDS sheets for the itemsused in the microelectronic clean room is available in the lab manager’s office. In addition one canbe obtained from the manufacturer at any time. A sample MSDS is included in the back of thisbooklet. The MSDS sheet should be referred to whenever there is a question about the material.

An understanding of the contents of this booklet is required before students can work in themicroelectronics clean room.

2 General Clean Room Rules

Always enter the clean room wearing the proper attire. Working in a clean room requires specialgarments. A hair cover or hood is worn to cover the hair. A face mask covers the nose and mouth.A coat or coveralls covers the body. Shoe covers or boots cover the feet. Gloves cover the hands.Safety glasses protect the eyes. These garments are intended to minimize the contamination ofthe clean room by the human body. Because of the danger from chemical spills, no open shoes orsandals are allowed. Shorts are not allowed unless you wear a full coverall. Clean room garmentsare for contamination control and offer only limited protection from hazardous materials. Specialprotective equipment is required when handling hazardous materials.

No smoking, eating, or drinking is allowed in the clean room. No unnecessary books or papersare allowed. Pencils are not used in the clean room.

When entering the lab for the first time, note the location of the safety shower, eye wash, firstaid kit, fire extinguishers, and chemical spill control kit.

Do not work alone. Generally, the lab manager will be available to oversee the activity in theclean room. Permission of the lab manager is required for use of the microelectronics clean roomafter hours.

Do not touch any equipment or apparatus without approval or prior instruction. If a mistakeis made or equipment is not functioning properly, notify the lab manager.

Always report injuries promptly. Be alert at all times, the clean room is a hazardous area.In case of a fire, exposure to a hazardous chemical or gas, or any injury that requires immediatemedical attention, dial 911.

The clean room must be kept“clean”. This includes keeping the areas neat and tidy, puttingback everything in its original place after use, and avoiding clutter.

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The lab is equipped with automatic fire alarms and sprinklers. In the event of a fire, evacuatethe lab immediately. If the fire alarm has not yet sounded activate the fire alarm manually. Knowthe location of the fire alarm. The nearest alarm is located just outside the clean room by thecopier room at the top of the stairs. Do not try to extinguish a fire unless you have been trainedto do so.

3 Deionized Water

The clean room is supplied with deionized (DI) water. All conductive ions, salts, metals, andchemicals are removed from the water to provide contamination-free water for processing operations.While this water is not hazardous it should not be used like regular city water. Do not drink DIwater. It has no taste since everything that adds taste to the water has been removed. In addition,since bacteria-killing chlorine has been removed there is a chance that harmful bacteria might bepresent.

4 Electrical Safety

Much of the equipment used in semiconductor processing uses high voltage electrical power. Duringnormal operation there is very little chance of a problem. However, the danger from an electricalshock increases if safety interlocks are bypassed or the equipment is operated without its protectivecasing. Unless under the direct supervision of the lab manager or professor, no equipment is to beoperated with open cabinets, bypassed safety interlocks, or partially assembled.

If equipment must be worked on, electrical power to it must be disconnected prior to any workbeing done.

Some of the equipment used in processing uses RF and microwave energy which could bedangerous if not properly operated. Again, no equipment should be used that is not completelyassembled and approved for use.

5 Compressed Gas

Most gas handling in the microelectronics clean room will be done by the lab manager or otherqualified personnel. However, some basic understanding of compressed gas handling is necessary.

All cylinders of compressed gases should be handled as potential sources of high energy. Theyshould never be moved from place to place without the valve protection caps in place. They mustbe securely fastened at all times. This means secured with a chain or strap when stationary and aspecial gas handling hand truck with chain when moving cylinders from place to place. A rupturedvalve can cause a compressed gas cylinder to shoot off like a missile with high speed and force.

When opening a new cylinder be careful. The initial force may cause a gas line to rupture orleak. Always stand to the side and away from the valve opening when first opening a gas cylinder.Fresh cylinders can have several thousand pounds of pressure within the cylinder.

Never completely empty a cylinder. Leave about 25 psi (pounds per square inch) remainingin the cylinder. This prevents any sediment that might be in the bottom of the tank from beingintroduced into the gas distribution system. When a gas cylinder is near empty, mark the cylinder“EMPTY” or “MT”.

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Several different gases are used in the lab. Nitrogen is the most common, and is used as aclean dry purge gas and as a cover or operating gas for most equipment. Compressed air is usedto operate valves of some equipment. Argon is used as a process gas. Oxygen, and occasionallyhydrogen, are used in the formation of silicon dioxide layers. Several special gas mixes may bein operation in the lab. They are used for special processing applications. MSDS sheets will beavailable for all gases in use in the lab.

All compressed gases should be considered hazardous. Inert gases like nitrogen and argon canbe dangerous because they are under high pressure and can displace the oxygen in a closed areacausing asphyxiation. The presence of high concentrations of oxygen will increase the risk of fire.Hydrogen is highly flammable. Most of the specialty gas mixtures are flammable and/or toxic.Always treat a gas leak, however minor, as hazardous and notify the lab manager immediately.

Gases are piped throughout the clean room to supply the various pieces of processing equipment.Know the location of the nearest shut-off valve should a problem or leak occur.

Do not store incompatible gases together without special precautions. Oxygen, or mixes con-taining oxygen, should not be stored near flammable gases.

When installing new gas lines always leak check the system with nitrogen before introducingthe process gas.

Regulators to control the output pressure of a compressed gas cylinder are designed to preventcross-use. Each regulator has a unique thread connection that will only mate with the compressedgas cylinder it was designed for. This connection is called a CGA connector and is universallyaccepted. Thus, the regulator for inert gases, like nitrogen and argon, will only work on compressedcylinders of inert gases. Likewise, oxygen and hydrogen have their own respective CGA connections.Some regulators have an extra purging section to allow purging of the system during a cylinderchange. A complete list of CGA connections and their related gases is available from the labmanager. Never modify a regulator by changing the CGA connection. The internal components ofthe regulator may not be compatible with the new gas resulting in catastrophic failure.

Liquid nitrogen (LN2) is used in the lab. Liquid nitrogen is liquefied nitrogen gas. It is liquefiedby dropping it’s temperature to about −200◦C. As it warms it returns to its gaseous state. Alarge spill of liquid nitrogen can have the same affect as a rapid release of compressed nitrogen gas,displacing the oxygen in a closed area and possibly causing asphyxiation. Liquid nitrogen is alsoextremely cold, and even a small amount on your skin can cause a severe reaction. Never touch orimmerse anything in liquid nitrogen.

6 Chemicals

All chemicals in the lab are considered hazardous. Know the hazards and precautions required ofeach chemical before use. When in doubt refer to the chemical’s MSDS.

Never return a used chemical to the original container. Never mix chemicals unless a specificformula is provided. Some chemicals are explosive or react violently when mixed. Always labelthe container with the chemical name. Many of the chemicals used in the lab look the same in abeaker.

Strong chemicals must be neutralized before disposal. The lab manager, or other trained per-sonnel, will handle all chemical disposal. Do not pour any chemicals down the drain.

Wear protective equipment when handling chemicals. Chemical resistant gloves, an apron withsleeves, and face shield are required. Remember that the light-weight clean room gloves available in

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the change room are not chemically resistant and should not be substituted for the heavier chemicalresistant gloves. Chemical gloves should always be checked for pinholes before use.

All chemicals are to be used under the chemical hoods. They are specially designed with chem-ical resistant materials and provide a fume exhaust to prevent fumes from reaching the personnelarea. Do not bend over to get a better look as you mix chemicals. This puts your face too close tothe chemicals. Always take advantage of the face shield on the chemical bench when available. Beespecially careful around the chemical work areas. Various things as valves, timers, apparatus, andcontainers may have been touched by someone with a hazardous chemical on their gloves resultingin some chemicals remaining.

If a chemical spills, use the spill kits located in the lab to contain and neutralize the chemical.There are specific kits for each class of chemicals. Wear protective equipment when handling allspills. Call the lab manager for all spills.

If a chemical comes in contact with the skin immediately flush the skin with water for a minimumof 20 minutes. If your clothing is affected, remove it immediately, this is no time for modesty. Havesomeone bring a fresh lab coat to cover up. Get professional medical attention. Special neutralizersalve is available for HF exposure (see section 9).

If a chemical comes in contact with your eyes immediately flush with water using the eye washstation. You must force the eyelids open continuously to allow the water to flush the eye. Getprofessional medical attention.

If using a hot chemical, always let it cool before handling.Know each class of chemicals and their specific hazards.

7 Solvents

Several solvents are used in the lab. They are used for cleaning and dissolving photoresist. Theyinclude methanol, acetone, trichloroethylene, and propanol. Solvents are stored in a separatecabinet away from the other chemicals.

Most solvents are highly flammable and should be kept away from any heat source. This includesovens. Solvents should never be put into an oven.

Solvents should only be used under exhausted hoods. Solvents vaporize easily and should notbe inhaled.

Used solvents can be disposed of in an appropriate container. Chlorinated solvents like trichloroethy-lene are kept separate from the other solvents to help in disposal and reclaim. Empty bottles shouldbe left for the lab manager or other trained personnel to dispose of.

Solvents will dry out your skin and remove the natural oils from it. They will also dissolve thelight-weight clean room gloves.

8 Photoresist

Photoresist is an amber colored organic material used to define the patterns necessary to fabricatemicroelectronic and semiconductor devices. The most common photoresist in the lab is manufac-tured by Shipley (e.g. Microposit 1813 and Microposit 1400).

Photoresist is light-sensitive. It must only be used in the yellow lighted areas. It can be storedoutside of these areas if it is in a dark bottle. It is soluble in acetone.

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Generally photoresist is not very hazardous but, like any chemical, should be treated withrespect. It is very difficult to remove from clothing or skin once it is exposed to white light.

9 Corrosives

Corrosives includes acids, bases, and oxidizing agents. Corrosives are used extensively in the cleanroom. They are the cause of most injuries and must be treated with the greatest care and respect.They must be transported in special containers. Full protective equipment is required when usingthem.

Typical acids used in the clean room are sulfuric acid, nitric acid, hydrochloric acid, hydrofluoricacid, phosphoric acids, and acetic acid. BOE and PAE etchants are made up of various percentagesof acids. Sulfuric and nitric acid are also considered oxidizing acids. Always pour acids into water,not vice versa.

Hydrofluoric acid (HF) is particularly dangerous. HF differs from most acids in that it notonly causes surface burns but also rapidly penetrates the skin, even in dilute solution, and causesdestruction of underlying tissue and even bone by extracting ions of calcium. The effects of HFexposure may not be felt for hours. Any potential exposure to HF must be reported immediatelyso that neutralizing agents can be provided. HF will etch glass and must not be used in glasscontainers.

Phosphorus oxychloride is a liquid used to form n-type regions in silicon. On exposure to water(or water vapor in the air) it produces hydrochloric and phosphoric acids. Do not introduce waterto a spill. Avoid the fumes. Soak up spills in an absorbent compound.

Typical bases used in the clean room include ammonium hydroxide and photoresist developerssuch as Shipley Microposit developers 351 and 354. The basic component of photoresist developersis sodium hydroxide. Bases can cause severe burns just like acids.

Hydrogen peroxide is considered an oxidizing agent and can cause severe reactions. Lab towelsused with hydrogen peroxide must be rinsed well before disposal. Towels soaked in hydrogenperoxide can spontaneously combust.

10 Other Materials

Other materials may be in use in the clean room at various times. When necessary individual safetyinstructions will be provided by the lab manager.

11 Summary

The microelectronics clean room can be a scary and intimidating place. But knowledge, care, andunderstanding can make it a safe and exciting place as well as a great learning experience. Thisbooklet will get you started working in the microelectronics clean room. The lab manager and otherexperienced personnel will train you in the safe use of the lab. Ask questions if you are unsure ofhow to handle a material or process, it is all part of the learning experience.

The safety of the people working in the clean room is top priority.

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Figure 1: MSDS For Sulfuric Acid (Page 1 of 7)

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SAFETY IN THE MICROELECTRONICS FABRICATION CLEAN …The MSDS program is a federally mandated program that requires the manufacturer of a potentially hazardous material to fully explain

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