Case Study: Occupational Exposure Monitoring in Semiconductor Manufacturing

As part of their commitment to comply with Health and Safety Legislation, a semiconductor manufacturing company requested Sysco Environmental Ltd to conduct an assessment of occupational exposure to hazardous substances, with a focus on volatile components and some ancillary processes.
The primary objectives of the study were to measure the atmospheric concentrations of solder rosin, aldehydes, and volatile organic compounds within the working environment, establish the daily personal exposure of employees at risk, and advise on suitable risk control measures. While heavy metals remain a primary concern in the industry, this study specifically targeted the volatile components and related processes.

Main Exposure Hazards in Semiconductor Manufacturing Industry

The semiconductor manufacturing industry is highly complex, involving numerous chemical processes that present various industrial exposure risks to workers. Among these, heavy metals such as cadmium, zinc, and arsenic are of significant concern due to their toxicity and potential health effects. This overview focuses on these heavy metals and other hazardous chemicals commonly encountered in semiconductor manufacturing.

Cadmium is used in semiconductor manufacturing primarily in the form of cadmium sulphide (CdS) and cadmium selenide (CdSe) for certain types of photovoltaic cells and as a stabiliser in some plastic components. Cadmium exposure can occur through inhalation of dust or fumes and through dermal contact. Chronic exposure to cadmium is associated with severe health effects, including kidney damage, bone demineralisation, and respiratory issues. Cadmium is also classified as a human carcinogen, with long-term exposure linked to lung cancer.

Zinc is used in the semiconductor industry for zinc oxide (ZnO) thin films, which are utilised in various electronic devices and sensors. Although zinc is an essential trace element, excessive exposure can lead to health problems. Inhalation of zinc oxide fumes, often produced during high-temperature processes such as soldering, can cause metal fume fever, characterised by flu-like symptoms including fever, chills, and muscle aches. Chronic exposure can result in more severe respiratory conditions and skin irritations.
 
Arsenic is used in the semiconductor industry in the form of gallium arsenide (GaAs) for the production of integrated circuits and light-emitting diodes (LEDs). Arsenic exposure primarily occurs through inhalation of dust and fumes. Acute exposure can cause gastrointestinal symptoms, while chronic exposure is linked to skin lesions, cardiovascular diseases, and various cancers, including lung, skin, and bladder cancers. Arsenic is classified as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC).

Crystalline silica is used in the fabrication of semiconductor wafers. Workers can be exposed to respirable silica dust during wafer cutting, grinding, and polishing processes. Chronic inhalation of silica dust can lead to silicosis, a debilitating lung disease, and increases the risk of lung cancer.
Hydrofluoric acid is used for cleaning and etching silicon wafers. Exposure to HF can occur through inhalation of vapours or direct skin contact. HF is highly corrosive and can cause severe burns, respiratory damage, and systemic toxicity affecting the heart and bones due to its ability to penetrate deep tissues and release fluoride ions.

Various organic solvents such as acetone, isopropanol, and n-methyl-2-pyrrolidone (NMP) are used in semiconductor manufacturing for cleaning and degreasing. These solvents can be harmful if inhaled or absorbed through the skin. Chronic exposure to organic solvents can cause neurological damage, liver and kidney damage, and skin dermatitis.
Photoresists and their developers are used in the photolithography process to create circuit patterns on semiconductor wafers. These chemicals can contain toxic and carcinogenic compounds. Inhalation or dermal exposure can lead to respiratory issues, skin sensitisation, and increased cancer risk.

Other metals such as lead, chromium, nickel, and copper are also used in various stages of semiconductor manufacturing. These metals can pose significant health risks including neurological damage, respiratory issues, skin disorders, and increased cancer risk with chronic exposure.
 

Mitigation and Safety Measures Applied to Control Exposure Risk in Semiconductor Manufacturing

 
To mitigate the risks associated with hazardous chemical exposure in the semiconductor manufacturing industry, facilities must implement a range of comprehensive safety measures. These measures are essential for ensuring the health and safety of workers and maintaining compliance with regulatory standards.
 
One of the primary strategies to minimise airborne exposure to hazardous substances in semiconductor manufacturing is the use of engineering controls. Local exhaust ventilation (LEV) systems, specifically designed for semiconductor fabrication processes, fume hoods, and enclosed chemical handling processes are crucial in capturing and containing harmful fumes and particulates at their source. For example, LEV systems at soldering stations effectively extract solder rosin fumes and metal particulates, while enclosed etching and cleaning processes prevent the release of volatile organic compounds (VOCs) and other hazardous chemicals. These systems prevent contaminants from spreading throughout the cleanroom environment, thereby reducing the risk of inhalation and contact exposure.
 
Providing appropriate personal protective equipment is another critical component of a comprehensive safety plan in semiconductor manufacturing. Workers should be equipped with respirators specifically rated for protection against fumes and vapours from chemicals such as hydrofluoric acid and arsine gas, as well as gloves and protective clothing resistant to chemical permeation. Proper use and regular maintenance of PPE are vital to ensuring its effectiveness in protecting workers during processes such as photolithography and chemical vapour deposition.
 
Regular air monitoring and health surveillance programs are indispensable for detecting early signs of overexposure to hazardous substances in semiconductor manufacturing. Continuous monitoring of airborne contaminant levels, such as cadmium, zinc, and arsenic, ensures they remain within safe limits. Health surveillance, including biological monitoring, involves regular medical examinations and biological tests to track the absorption of hazardous substances in workers’ bodies. For instance, periodic blood and urine tests can monitor levels of heavy metals and solvents, providing early detection of potential health issues and enabling prompt corrective measures.
 
Continuous training and awareness programs are essential for fostering a safety-conscious culture among workers in the semiconductor industry. Employees must be educated on the specific hazards associated with chemicals used in semiconductor manufacturing, such as photoresists, solvents, and dopants, and the importance of adhering to safety protocols. Training should cover the correct use of engineering controls and PPE, emergency procedures for chemical spills, and the identification and reporting of unsafe conditions. Regular refresher courses help reinforce these practices and ensure that safety knowledge remains current, particularly as new materials and processes are introduced.
 
As an important control measure in semiconductor manufacturing, biological monitoring involves assessing the levels of hazardous substances within the bodies of workers. This can include tests for metals like cadmium, zinc, and arsenic, as well as exposure to other toxic compounds used in semiconductor fabrication. By monitoring biological samples such as blood and urine, health professionals can detect the presence and concentration of harmful substances, providing crucial data for managing exposure risks and ensuring the long-term health of workers.
 
In conclusion, the semiconductor manufacturing industry involves exposure to various hazardous chemicals, particularly heavy metals like cadmium, zinc, and arsenic. Addressing these risks requires the implementation of stringent safety measures, including robust engineering controls tailored for semiconductor processes, effective personal protective equipment, continuous monitoring and surveillance programs, and comprehensive training and awareness initiatives. Additionally, incorporating biological monitoring as a control measure is essential for assessing and managing the health impacts of chemical exposure. These combined efforts are vital for protecting workers' health and ensuring a safe and compliant working environment in semiconductor manufacturing.
 

Our Project Conclusion

 
The air sampling results indicated that employees are unlikely to be exposed to levels of solder rosin, aldehydes, and volatile organic compounds above Workplace Exposure Limits (WELs). The detected workplace contaminants associated with soldering and drossing operations were not found to be hazardous to health. However, part of the general ventilation system was identified as non-operational, necessitating repairs to ensure an adequate fresh air supply and effective dilution of workplace contaminants.
 
The air monitoring results suggest that employees' exposure levels to solder rosin, aldehydes, and volatile compounds are within safe limits. The combination of general ventilation and localised extraction effectively controls workplace contaminants. While the accumulation of process-related odours was minor and non-hazardous, repairs to the general ventilation system are recommended to enhance air quality management. The use of respiratory protective equipment (RPE) is not required for normal operations but is advised during maintenance and cleaning (drossing) operations to prevent short-term high exposure situations. A formal health surveillance program is not deemed necessary; however, regular training on the safe use of hazardous substances and control measures is essential.
 
Although heavy metals were not the primary focus of this project, the results provided invaluable information for managing broader health and safety risks. Understanding the exposure levels and implementing appropriate controls for volatile components and ancillary processes contributes to a safer working environment. This comprehensive approach ensures that both specific and general occupational health risks are adequately addressed, promoting overall workplace safety in the semiconductor manufacturing industry.