Exposure Assessment Among US Workers Employed in Semiconductor Wafer Fabrication

Research advance of occupational exposure risks and toxic effects of semiconductor nanomaterials

In recent years, semiconductor nanomaterials, as one of the most promising and applied classes of engineered nanomaterials, have been widely used in industries such as photovoltaics, electronic devices, and biomedicine. However, occupational exposure is unavoidable during the production, use, and disposal stages of products containing these materials, thus posing potential health risks to workers. The intricacies of the work environment present challenges in obtaining comprehensive data on such exposure. Consequently, there remains a significant gap in understanding the exposure risks and toxic effects associated with semiconductor nanomaterials. This paper provides an overview of the current classification and applications of typical semiconductor nanomaterials. It also delves into the existing state of occupational exposure, methodologies for exposure assessment, and prevailing occupational exposure limits. Furthermore, relevant epidemiological studies are examined. Subsequently, the review scrutinizes the toxicity of semiconductor nanomaterials concerning target organ toxicity, toxicity mechanisms, and influencing factors. The aim of this review is to lay the groundwork for enhancing the assessment of occupational exposure to semiconductor nanomaterials, optimizing occupational exposure limits, and promoting environmentally sustainable development practices in this domain.

Lymphohematopoietic cancer mortality among Korean semiconductor manufacturing workers

BACKGROUND

We aimed to examine the lymphohematopoietic cancer mortality in a cohort of workers at a semiconductor manufacturing company in South Korea according to their jobs.

METHODS

A retrospective cohort was constructed using the personnel records of semiconductor manufacturing workers who were employed in a semiconductor company in South Korea in 1998-2012. Data on their vital status and causes of death were obtained from the National Statistical Office of South Korea. The standardized mortality ratios (SMRs) of lymphohematopoietic cancer were calculated.

RESULTS

A total of 288 deaths were reported, of which 22 were caused by lymphohematopoietic cancer, among 65,782 workers in 878,325 person-years. The SMRs for lymphohematopoietic cancer were 0.78 (95% confidence interval [CI] = 0.39-1.40; the number of observed cases [Obs] = 11) among male workers and 1.71 (95% CI = 0.85-3.06; Obs = 11) among female workers. Among female operators, excess deaths due to lymphohematopoietic cancer (SMR = 2.59, 95% CI = 1.24-4.76) and leukemia (SMR = 2.92, 95% CI = 1.26-5.76) were observed. However, they were not observed among office workers, facility managers, utility managers, or process managers.

CONCLUSION

Female operators involved in the semiconductor wafer fabrication process had higher risk of mortality from lymphohematopoietic cancer.

Nanoscale Bilayer Mechanical Lithography Using Water as Developer

Sustainability has become a critical concern in the semiconductor industry as hazardous wastes released during the manufacturing process of semiconductor devices have an adverse impact on human beings and the environment. The use of hazardous solvents in existing fabrication processes also restricts the use of polymer substrates because of their low chemical resistance to such solvents. Here, we demonstrate an environmentally friendly mechanical, bilayer lithography that uses just water for development and lift-off. We show that we are able to create arbitrary patterns achieving resolution down to 310 nm. We then demonstrate the use of this technique to create functional devices by fabricating a MoS₂ photodetector on a polyethylene terephthalate (PET) substrate with measured response times down to 42 ms.

Case-control study of brain and other central nervous system cancer among workers at semiconductor and storage device manufacturing facilities

OBJECTIVE

This study evaluated the relationship between brain and other central nervous system cancer ('CNS cancer') and exposures at two semiconductor and electronic module manufacturing facilities and at a storage device manufacturing facility.

METHODS

The case-control study, nested in a cohort of 126 836 employees, compared 120 CNS cancer cases and 1028 matched controls with respect to employment in 10 process groups and estimated cumulative exposure to 31 known or possible carcinogens.

RESULTS

CNS cancer was associated with module manufacturing operations at two facilities. Module manufacturing is a process that begins with production of ceramic substrates followed by attachment of completed semiconductor chips and metal-containing circuitry resulting in a high performing electronic device. Positive associations with the highest tertile of estimated cumulative exposure were found for several chemicals, including 2-butoxyethanol, cyclohexanone, ortho-dichlorobenzene, cadmium, molybdenum, trichloroethylene and vinyl chloride.

CONCLUSIONS

Results suggested positive associations between CNS cancer and specific operations and chemicals experienced in the semiconductor and electronic module manufacturing industry. However, lack of external support for these findings precludes a causal interpretation, and the observed associations may have been due to chance.

Occupational Characteristics of Semiconductor Workers with Cancer and Rare Diseases Registered with a Workers' Compensation Program in Korea

Background

The aim of this study was to describe the types of diseases that developed in semiconductor workers who have registered with the Korea Workers' Compensation and Welfare Service (KWCWS) and to identify potential common occupational characteristics by the type of claimed disease.

Methods

A total of 55 semiconductor workers with cancer or rare diseases who claimed to the KWCWS were compared based on their work characteristics and types of claimed diseases. Leukemia, non-Hodgkin lymphoma, and aplastic anemia were grouped into lymphohematopoietic (LHP) disorder.

Results

Leukemia (n = 14) and breast cancer (n = 10) were the most common complaints, followed by brain cancer (n = 6), aplastic anemia (n = 6), and non-Hodgkin lymphoma (n = 4). LHP disorders (n = 24) accounted for 43%. Sixty percent (n = 33) of registered workers (n = 55) were found to have been employed before 2000. Seventy-six percent (n = 42) of registered workers and 79% (n = 19) among the registered workers with LHP (n = 24) were found to be diagnosed at a relatively young age, ≤40 years. A total of 18 workers among the registered semiconductor workers were finally determined to deserve compensation for occupational disease by either the KWCWS (n = 10) or the administrative court (n = 8). Eleven fabrication workers who were compensated responded as having handled wafers smaller than eight inches in size. Eight among the 18 workers compensated (44 %) were found to have ever worked at etching operations.

Conclusion

The distribution of cancer and rare diseases among registered semiconductor workers was closely related to the manufacturing era before 2005, ≤8 inches of wafer size handled, exposure to clean rooms of fabrication and chip assembly operations, and etching operations.

Retrospective Exposure Assessment for Semiconductor and Storage Device Manufacturing Facilities

OBJECTIVE

The aim of this study was to develop exposure estimates for a case-control study of central nervous system cancer in semiconductor and storage device manufacturing workers.

METHODS

Over 700,000 records on sample measurements were obtained. Mean exposure intensity was estimated for 31 established/suspected carcinogens (agents of interest) in 10 primary exposure groups over three manufacturing eras. We assigned confidence ratings, based on number/type of measurements, to each estimate.

RESULTS

Mean exposures decreased by an order of magnitude over the three manufacturing eras and were below applicable occupational exposure limits for 22 of 31 agents of interest. For 25 agents, at least 70% of the exposures were estimated with high confidence.

CONCLUSION

This is the largest comprehensive study of exposures in the semiconductor/storage device industry and the first to include cumulative exposure estimates and measures of confidence in the exposure estimates.

Review for Retrospective Exposure Assessment Methods Used in Epidemiologic Cancer Risk Studies of Semiconductor Workers: Limitations and Recommendations

This article aims to provide a systematic review of the exposure assessment methods used to assign wafer fabrication (fab) workers in epidemiologic cohort studies of mortality from all causes and various cancers. Epidemiologic and exposure–assessment studies of silicon wafer fab operations in the semiconductor industry were collected through an extensive literature review of articles reported until 2017. The studies found various outcomes possibly linked to fab operations, but a clear association with the chemicals in the process was not found, possibly because of exposure assessment methodology. No study used a tiered assessment approach to identify similar exposure groups that incorporated manufacturing era, facility, fab environment, operation, job and level of exposure to individual hazardous agents. Further epidemiologic studies of fab workers are warranted with more refined exposure assessment methods incorporating both operation and job title and hazardous agents to examine the associations with cancer risk or mortality.

Evaluation of Hazardous Chemicals with Material Safety Data Sheet and By-products of a Photoresist Used in the Semiconductor-Manufacturing Industry

Background

The photolithography process in the semiconductor industry uses various chemicals with little information on their constitution. This study aimed to identify the chemical constituents of photoresist (PR) products and their by-products and to compare these constituents with material safety data sheets (MSDSs) and analytical results.

Methods

A total of 51 PRs with 48 MSDSs were collected. Analysis consisted of two parts: First, the constituents of the chemical products were identified and analyzed using MSDS data; second, for verification of the by-products of PR, volatile organic compounds were analyzed. The chemical constituents were categorized according to hazards.

Results

Forty-five of 48 products contained trade secrets in amounts ranging from 1 to 65%. A total of 238 ingredients with multiple counting (35 ingredients without multiple counting) were identified in the MSDS data, and 48.7% of ingredients were labeled as trade secrets under the Korea Occupational Safety and Health Act. The concordance rate between the MSDS data and the analytical result was 41.7%. The by-product analysis identified 129 chemicals classified according to Chemical Abstracts Service No., with 17 chemicals that are carcinogenic, mutagenic, and reprotoxic substances. Formaldehyde was found to be released from 12 of 21 products that use novolak resin.

Conclusion

We confirmed that several PRs contain carcinogens, and some were not specified in the toxicological information in the MSDS. Hazardous chemicals, including benzene and formaldehyde, are released from PRs products as by-products. Therefore, it is necessary to establish a systematic management system for chemical compounds and the working environment.

Comprehensive Evaluation of Hazardous Chemical Exposure Control System at a Semiconductor Manufacturing Company in South Korea

The goal of this study was to evaluate the hazardous chemical exposure control system in a semiconductor manufacturing company and recommend an appropriate exposure surveillance system for hazardous agents. We reviewed compliance-based chemical exposure data compiled between 2012 and 2014 by the study company. The chemical management system, characteristics of chemical use and hazardous gas monitoring system were also investigated. We evaluated the airborne isopropyl alcohol (IPA) and acetone generally used as cleaning solvents, volatile organic compounds and metals levels using internationally recommended sampling and analytical methods. Based on the results of past working environment measurement data and of our investigation, the overall current exposure to chemicals by semiconductor workers during routine production work appears to be controlled below occupational exposure limits. About 40% of chemical products used were found to contain at least one unidentifiable trade-secret substance. There are several situations and maintenance tasks that need special attention to reduce exposure to carcinogens as much as possible. In addition, a job-exposure matrix as a tool of surveillance system that can examine the exposure and health status of semiconductor workers according to type of operation and type of job or task is recommended.

Potential risk factors for haematological cancers in semiconductor workers

BACKGROUND

There has recently been increased interest in cancer incidence in electronics workers.

AIMS

To determine the cancer incidence ratio in electronics workers and the potential factors affecting the risk for development of cancer.

METHODS

Epidemiological study performed in electronics workers who were employed between 1999 and 2008 in South Korea. Cancer incidence ratio was analysed with respect to departments, divisions, job titles, gender, age, hepatitis B and C virus infection and work duration. We compared the incidence of haematological cancer in this cohort with that expected in the general population.

RESULTS

The study population was 56283. Overall, the standardized incidence ratio (SIR) for haematological cancer was 0.85. In particular, the SIR for leukaemia was 0.86 and for non-Hodgkin lymphoma (NHL) was 0.93, which were not statistically significant. The SIR for NHL was significantly increased [SIR 5.23, 95% confidence interval (CI) 1.31-20.95] in female office workers. We also found that the SIR for NHL was significantly increased in female workers who tested positive for hepatitis virus infection (SIR 7.69, 95% CI 1.08-54.60).

CONCLUSIONS

The raised SIR for NHL among female workers was due to potential risk factors such as hepatitis virus infection although additional research and an ongoing, long-term, prospective epidemiological cohort study is needed.

A model to systematically employ professional judgment in the Bayesian Decision Analysis for a semiconductor industry exposure assessment

Bayesian Decision Analysis (BDA) uses Bayesian statistics to integrate multiple types of exposure information and classify exposures within the exposure rating categorization scheme promoted in American Industrial Hygiene Association (AIHA) publications. Prior distributions for BDA may be developed from existing monitoring data, mathematical models, or professional judgment. Professional judgments may misclassify exposures. We suggest that a structured qualitative risk assessment (QLRA) method can provide consistency and transparency in professional judgments. In this analysis, we use a structured QLRA method to define prior distributions (priors) for BDA. We applied this approach at three semiconductor facilities in South Korea, and present an evaluation of the performance of structured QLRA for determination of priors, and an evaluation of occupational exposures using BDA. Specifically, the structured QLRA was applied to chemical agents in similar exposure groups to identify provisional risk ratings. Standard priors were developed for each risk rating before review of historical monitoring data. Newly collected monitoring data were used to update priors informed by QLRA or historical monitoring data, and determine the posterior distribution. Exposure ratings were defined by the rating category with the highest probability--i.e., the most likely. We found the most likely exposure rating in the QLRA-informed priors to be consistent with historical and newly collected monitoring data, and the posterior exposure ratings developed with QLRA-informed priors to be equal to or greater than those developed with data-informed priors in 94% of comparisons. Overall, exposures at these facilities are consistent with well-controlled work environments. That is, the 95th percentile of exposure distributions are ≤50% of the occupational exposure limit (OEL) for all chemical-SEG combinations evaluated; and are ≤10% of the limit for 94% of chemical-SEG combinations evaluated.

Leukemia and non-Hodgkin lymphoma in semiconductor industry workers in Korea

Reports of leukemia and non-Hodgkin lymphoma (NHL), cancers known to have a similar pathophysiology, among workers in the semiconductor industry have generated much public concern in Korea. This paper describes cases reported to the NGO Supporters for the Health and Rights of People in the Semiconductor Industry (SHARPs). We identified demographic characteristics, occupational, and disease history, for 17 leukemia and NHL cases from the Giheung Samsung semiconductor plant, diagnosed from November 2007 to January 2011. Patients were relatively young (mean = 28·5 years, SD = 6·5) at the time of diagnosis and the mean latency period was 104·3 months (SD = 65·8). Majority of the cases were fabrication operators (11 workers among 17) and 12 were hired before 2000. Six cases worked in the etching or diffusion process. The evidence to confirm the causal relationship between exposures in the semiconductor industry and leukemia or NHL remains insufficient and a more formal, independent study of the exposure-disease relationship in this occupation is needed. However, workers should be protected from the potential exposures immediately.