Dopant gases

This content is from pages 482 to 484 of Workers' Guide to Health and Safety

Dopant gases are used to add layers (implant ions) to the wafer so the wafer will conduct electricity better. Arsine, diborane, and phosphine are the most commonly used dopant gases. Arsine gas comes from the element arsenic, diborane from boron, and phosphine from phosphorous.

As gases they are more dangerous than as solids because they can get on and inside you easily. Arsine, diborane, and phosphine gases are stored in containers that also contain their liquid forms. While most exposure occurs by breathing in fumes, a leak from a container can be liquid or gas.

Workers who load and unload wafers, replace gas cylinders, and clean and maintain the ion implantation machines can come into contact with dopant gases. So can other workers in the area.

If you accidentally swallow a dopant liquid, it can be released in your stomach as a gas and damage your digestive tract.

The charts include only some of the dopant gases that exist. See Learn about chemicals used in your factory and how to find information about other dopant gases. See the Index of chemical names to find alternative names for dopant gases.

Prevent or reduce exposure:

Use ventilation systems that extract fumes and replace or dilute dirty air with clean air. Machines need exhaust vents inside so that no gases escape (see Chapter 17: Ventilation).
Enclosed equipment that is remotely controlled reduces workers’ exposure where the possibility of an accident is greatest.
Wear protective equipment such as chemical goggles, gloves, chemical splash aprons, and respirators especially when in direct contact with gas cylinders and parts of the ion implanting machine, such as vacuum pumps and the ion source (see Chapter 18: Personal protective equipment).
Have an emergency plan that includes first aid treatment and protective equipment for spills, splashes, and accidental exposures. Keep necessary emergency supplies at the worksite, well stocked, and accessible to workers.
All dopants are extremely flammable and can explode. Areas where they are stored and used must be kept cool and the air must be monitored. The areas should also have alarms, fire extinguishers, and an emergency plan (see Chapter 11: Fire).

Dopant gases
	Arsine (arsenic hydride, hydrogen arsenide)	CAS No. 7784-42-1
	Diborane (boroethane, boron hydride, diboron hexahydride)	CAS No. 19287-45-7
	Phosphine (hydrogen phosphide, phosphorus hydride)	CAS No. 7803-51-2
WHAT ARE THEY? Dopants are colorless gases. Arsine and phosphine smell unpleasantly like garlic or rotten fish. Diborane has an unpleasant sweet smell. If you can smell them, you are being exposed to amounts high enough to harm you.
DO YOU WORK WITH THEM? Dopants are used in the electronics industry, in the process called “ion implantation” to make wafers conduct electricity better.
WHEN THEY COME IN CONTACT WITH YOUR BODY SKIN They may irritate your skin. In gas form they are not toxic to the skin, but if the liquid form touches you, it will burn quickly, even though the skin will feel cold and numb. Treat it quickly as a chemical burn. See First Aid EYES The fumes may irritate your eyes. The liquid form can cause severe eye burns. See First Aid. NOSE/LUNGS The fumes can irritate your nose, throat, and lungs, causing coughing and wheezing. Breathing in these gases can cause you to feel weak, dizzy, lightheaded, short of breath, and pass out. Some signs are similar to “metal fume fever,” which feels like a flu with a combination of these signs: headache, fever and chills, body aches, chest tightness, and cough. Higher exposures can also create a buildup of fluid in the lungs, called lung edema. See First Aid. MOUTH/BELLY A dopant gas can be released in your stomach and cause damage to your digestive tract and lead to abdominal pain, nausea, vomiting, and diarrhea. See First Aid and seek medical attention.
WHEN YOU ARE EXPOSED OVER TIME: All dopants can harm your liver, kidneys and the nervous system causing weakness, muscle cramps, and poor coordination in the limbs. Arsine kills red blood cells (hemolysis), which leads to anemia. Continuing to breathe arsine kills more red blood cells and can result in kidney failure. Skin and eyes that become yellow are danger signs and you should seek medical attention immediately. Arsine may cause skin, liver, kidney, lung, and bladder cancer. Diborane can harm your lungs and cause chronic bronchitis and breathing problems. Phosphine can harm your lungs and cause chronic bronchitis and breathing problems. High amounts of phosphine at once can cause heart and kidney failure. Skin and eyes that become yellow are danger signs and you should seek medical attention immediately.
IF YOU ARE AT RISK OF EXPOSURE: Use both neoprene and nitrile gloves, an apron, and eye/face protection when changing vacuum pump oils and gas containers (see Chapter 18: Personal protective equipment). This equipment must be well-cleaned or disposed of after use. Use a supplied-air respirator if you are cleaning the ion source, changing vacuum pumps, or doing other maintenance work on the machine, or if you are replacing gas containers.
SAFER SUBSTITUTES: Mono ethyl arsine is a less toxic substitute for arsine.