SAFETY
IN THE
MICROELECTRONICS
FABRICATION
CLEAN ROOM
JOHN HUDAK
AUGUST 1995
INTRODUCTION
Semiconductor processing and the fabrication of microelectronic devices involves a wide range of extremely hazardous materials, gases, and chemicals. It is extremely important that all users of the UNCC microelectronics clean room understand and respect the dangerous nature of the processes involved in making a microelectronic device or semiconductor. This booklet will provide a basic introduction to the hazards and safety procedures required in a microelectronics clean room. More comprehensive safety information is available from the UNCC safety office.
A key part of any safety program includes an understanding of the MSDS program. MSDS stands for Material Safety Data Sheet. The MSDS program is a federally mandated program that requires the manufacturer of a potentially hazardous material to fully explain the hazards and safe handling 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 be provided by the manufacturer to any and all users. A notebook of the MSDS sheets for the items used in the microelectronic clean room is available in the lab manager’s office. In addition one can be obtained from the manufacturer at any time. A sample MSDS is included in the back of this booklet. 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 the microelectronics clean room
GENERAL CLEAN ROOM RULES
Always enter the clean room wearing the proper attire. Working in a clean room requires special garments. 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 of the clean room by the human body. Because of the danger from chemical spills, no open shoes or sandals are allowed. Shorts are not allowed unless you wear a full coverall. Clean room garments are for contamination control and offer only limited protection from hazardous materials. Special protective equipment is required when handling hazardous materials.
No smoking, eating, or drinking is allowed in the clean room. No unnecessary books or papers are 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, first aid kit, fire extinguishers, and chemical spill control kit.
Do not work alone. Generally the lab manager will be available to oversee the activity in the clean room. Permission of the lab manager is required for use of the microelectronics clean room after hours.
Do not touch any equipment or apparatus without approval or prior instruction. If a mistake is 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 immediate medical attention, dial 911.
The clean room must be kept “clean”. This includes keeping the areas neat and tidy, putting back everything in its original place after use, and avoiding clutter.
The lab is equipped with automatic fire alarms and sprinklers. In the event of a fire evacuate the lab immediately. If the fire alarm has not yet sounded activate the fire alarm manually. Know the location of the fire alarm. The nearest alarm is located just outside the clean room by the snack room at the top of the stairs. Do not try to extinguish a fire unless you have been trained to do so.
DEIONIZED WATER
The clean room is supplied with deionized water (DI Water). All conductive ions, salts, metals, and chemicals 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 DI water. It has no taste since everything that adds taste to the water has been removed. In addition, since the chlorine has been removed there is a chance that harmful bacteria might be present.
ELECTRICAL SAFETY
Much of the equipment used in semiconductor processing uses high voltage electrical power. During normal operation there is very little chance of a problem. However, the danger from an electrical shock increases if safety interlocks are bypassed or the equipment is operated without their protective cases. Unless under the direct supervision of the lab manager or professor, no equipment is to be operated 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 work being done.
Some of the equipment used in processing uses RF and Microwave energy. Again, no equipment should be used that is not completely assembled and approved for use.
COMPRESSED GASES
Most gas handling in the microelectronics clean room will be done by the lab manager or other qualified 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. They should never be moved from place to place without the valve protection caps in place. They must be securely fastened all times. This means a chain or strap when stationary and a special gas handling hand truck with chain when moving cylinders from place to place. A ruptured valve 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 or leak. 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) remaining in the cylinder. This prevents any sediment that might be in the bottom of the tank from being introduced into the gas distribution system. When a gas cylinder is near empty, mark the cylinder “EMPTY” or “MT”.
Several different gases are used in the lab. Nitrogen is the most common and is used as a clean dry purge gas and as a cover or operating gas in most equipment. Compressed air is used to operate valves of some equipment. Argon is used as a process gas. Oxygen and sometimes hydrogen are used in the formation of silicon dioxide layers. Several special gas mixes may be in operation in the lab. They are used for special processing applications. MSDS sheets will be available for all gases in use in the lab.
All compressed gases should be considered hazardous. Inert gases like nitrogen and argon can be dangerous because they are under high pressure and can displace the oxygen in a closed area causing asphyxiation. The presence of high concentrations of oxygen will increase the fire risk. 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 through out 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 containing oxygen should not be stored near flammable gases.
When installing new gas lines always leak check the system with nitrogen before introducing the process gas.
Regulators to control the output pressure of a compressed gas cylinder are designed to prevent cross use. Each regulator has a unique thread connection that will only mate with the compressed gas cylinder it was designed for. This connection is called a CGA connector and is universally accepted. Thus the regulator for inert gases like nitrogen and argon will only work on compressed cylinders of inert gases. Likewise oxygen has its own CGA connection. Hydrogen would also have a specific CGA connection. Some regulators have an extra purging section to allow purging of the system during a cylinder change. A complete list of CGA connections and their related gases is available from the lab manager. Never modify a regulator by changing the CGA connection. The internal components of the regulator may not be compatible with the new gas resulting in catastrophic failure.
Liquid nitrogen or LN2 is used in the lab. Liquid nitrogen is liquefied nitrogen gas. It is liquefied by dropping it’s temperature to about -200oC. As it warms it returns to its gaseous state. A large spill of liquid nitrogen can have the same effect as a rapid release of compressed nitrogen gas, displacing the oxygen in a closed area and possibly causing asphyxiation. Liquid nitrogen is also extremely cold and even a small amount on your skin can cause a severe reaction. Never touch or immerse anything in liquid nitrogen.
CHEMICALS
All chemicals in the lab are considered hazardous. Know the hazards and precautions required of each chemical before use. When is doubt refer to the MSDS.
Never return a used chemical to the original container. Never mix chemicals unless a specific formula is provided. Some chemicals are explosive or react violently when mixed. Always label the container with the chemical name. A lot of the chemicals used in the lab look the same in a beaker.
Strong chemicals must be neutralized before disposal. The lab manager or other trained personnel will handle all chemical disposal. Do not pour any chemicals down the drain .
Wear protective equipment when handling chemicals. Chemical resistant gloves, apron with sleeves, and face shield are required. Remember that the light weight clean room gloves available in the change room are not chemically resistant and should not be substituted for the heavier chemical resistant 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 chemical resistant materials and provide a fume exhaust to prevent fumes from reaching the personnel area. Do not bend over to get a better look as you mix chemicals. This puts your face too close to the chemicals. Always take advantage of the face shield on the chemical bench when available. Be especially careful around the chemical work areas. Valves, timers, apparatus, containers, etc. may have been touched by someone with a hazardous chemical on their gloves resulting in 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 all spills. Call the lab manager for all spills.
If a chemical comes in contact with the skin immediately flush with water for a minimum of 20 minutes. If your clothing is affected, remove immediately, this is no time for modesty. Have someone bring a fresh lab coat to cover up. Get professional medical attention. Special neutralizer salve is available for HF exposure (see section on acids).
If a chemical comes in contact with your eyes immediately flush with water using the eye wash station. You must force the eyelids open continuously to allow the water to flush the eye. Get professional medical attention.
If using a chemical hot, always let it cool before handling.
Know each class of chemicals and their specific hazards.
SOLVENTS
Several solvents are used in the lab. They are used for cleaning and dissolving photoresist. They include methanol, acetone, trichloroethylene, and propanol. Solvents are stored in a separate cabinet away from the other chemicals.
Most solvents are highly flammable and should be kept away from any heat source. This includes ovens. Solvents should never be put into an oven.
Solvents should only be used under exhausted hoods. Solvents vaporize easily and should not be inhaled.
Used solvents can be disposed of in the appropriate container. Chlorinated solvents like trichloroethylene are kept separate from the other solvents to help in disposal and reclaim. Empty bottles should be 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 the light weight clean room gloves.
PHOTORESIST
Photoresist is an amber colored organic material used to define the patterns necessary to fabricate microelectronic and semiconductor devices. The most common photoresist in the lab is manufactured by Shipley and has names like Microposit 1813 and Microposit 1400.
Photoresist is light sensitive. It must only be used in the yellow lighted areas. It can be stored outside of these areas if it is in a dark bottle. It is soluble in acetone.
Generally photoresist is not very hazardous but should be treated with respect like any chemical. It is very difficult to remove from clothing or skin once it is exposed to white light.
CORROSIVES
Corrosives includes acids, bases, and oxidizing agents. Corrosives are used extensively in the clean room. 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 using them.
Typical acids used in the clean room are sulfuric acid, nitric acid, hydrochloric acid, hydrofluoric acid, phosphoric acids, and acetic acid. BOE and PAE etchants are made up of various percentages of 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 not only causes surface burns but also rapidly penetrates the skin , even in dilute solution, and causes destruction of underlying tissue and even bone by the extraction of calcium. The effects of HF exposure may not be felt for hours. Any potential exposure to HF must be reported immediately so that neutralizing agents can be provided. HF will etch glass and must not be used in glass containers.
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 water to a spill. Avoid the fumes. Soak up spill in absorbent compound.
Typical bases used in the clean room include ammonium hydroxide and photoresist developers such as Shipley Microposit developers 351 and 354. Photoresist developers basic component is sodium hydroxide. Bases can cause severe burns just like acids.
Hydrogen peroxide is considered an oxidizing agent and can cause severe reactions. Lab towels used with hydrogen peroxide must be rinsed well before disposal. Towels soaked in hydrogen peroxide can spontaneous combust.
OTHER MATERIALS
Other materials may be in use in the clean room at various times. When necessary individual safety instructions will be provided by the lab manager.
SUMMARY
The microelectronics clean room can be a scary and intimidating place. But knowledge, care, and understanding can make it a safe exciting place and a great learning experience. This booklet will get you started working in the microelectronics clean room. The lab manager and other experienced personnel will train you in the safe use of the lab. Ask questions if you are unsure of how 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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