Potential Hazards of Semiconductor Equipment (I) - Oxidation, Cleaning and
Photoresist Coating
Oxidizing equipment
The manufacture of integrated circuits involves a series of processes that may be
repeated many times before the circuit is complete. Typically, the first step in
semiconductor device manufacturing involves oxidation of the wafer surface to
grow a thin layer of silicon dioxide (SiO2). This oxide is used to provide both an
insulating layer and a passivation layer.
●The most common oxidation method is thermal oxidation, which can be
divided into "dry" oxidation or "wet" oxidation. The wafer is loaded into a quartz
furnace tube and then heated to approximately 1200°C.
○ In dry oxidation, a thin oxide layer grows in an atmosphere containing oxygen
and hydrogen chloride at near atmospheric pressure.
○Thicker oxide layers require higher pressures and the use of steam (wet
oxidation). Wet oxidation is performed by exposing the wafer to a mixture of
oxygen and hydrogen in a furnace tube. Water vapor is formed when hydrogen
and oxygen react.
The following are potential hazards of oxidation.
●Flammable gas (fire)
●Toxic waste gas
● Potential hazards of toxic exhaust gases from radio frequency (RF) and
infrared (IR) radiation
●Employees may be exposed to corrosive exhaust gases, including hydrogen
chloride. Gases such as hydrogen chloride are irritating and corrosive to the
eyes, skin, and mucous membranes. Exposure to high concentrations can cause
laryngitis, bronchitis, and pulmonary edema.
Cleaning equipment
Frequent cleaning of particles and contamination-free wafer surfaces is
required. The main cleaning methods are:
●Wash with deionized water and detergent.
●Solvents: Isopropyl alcohol (IPA), acetone, ethanol, terpenes.
• Acids: HF, H 2 SO 4 and H 2 O 2 , HCl, HNO 3 and mixtures.
●Caustic soda: NH 4 OH
The following are potential hazards of cleaning.
Solvent
●Acid and caustic solutions
Potential hazards of acid and caustic solutions
●Employees may be exposed to acids and corrosive solutions used in the
cleaning process.
o Typical acids may include mixtures of HF, H2SO4, H2O2, HCl, and HNO3.
o The caustic solution mainly comprises NH 4 OH.
Photoresist coating equipment
After the silicon dioxide layer is formed, the wafer is coated with a light-sensitive
material called "photoresist."
●There are two types of photoresists: positive and negative. Positive
photoresists weaken when exposed to light, while negative photoresists
strengthen. Most semiconductor processes use positive photoresist.
●Photoresist is applied by delivering a small amount of liquid to the center of
the wafer, which is then spun at high speed to spread the material across the
entire surface in a thin, even coating. Sometimes the wafers are primed with the
adhesive hexamethyldisilazane (HMDS). Diglycol ethers have been the most
commonly used solvents for carrying HMDS, although some manufacturers have
switched to alternative solvents such as toluene, n-butyl acetate, acetone, and
1,1,1-trichloroethane.
The following are potential hazards of photoresist coating.
●Photoresist chemicals
Solvent
●Mechanical
Potential Dangers of Photoresist Chemicals
●Employees may be exposed to photoresist chemicals.
Possible solutions
●Resolve all skin exposure issues.
● Provide adequate ventilation to reduce airborne concentrations.
● Provide appropriate personal protective equipment to prevent eye and skin
contact.
● Use respiratory protection when necessary to further reduce exposure and
protect employees.
●Design and use specialized processing, material handling, and storage
equipment to properly contain acids and corrosive materials. Consider normal
use and emergency situations.
● Install emergency facilities (e.g., face and eye wash stations) to provide
immediate treatment and therapy in the event of accidental contact.
Source: U.S. OSHA Silicon Component Manufacturing Equipment