Arsenic Exposure in Gallium Arsenide Device Manufacturing: An Evaluation of Control Methods during MBE Maintenance
Ash, Sara
(University of California – Berkeley)
Topic Area: Specific Industrial Hygiene Topics
Objectives:
1. Review control options for arsenic exposure during maintenance operations on molecular beam epitaxy (MBE) systems, primarily assessing practical applicability of control methods in industry production versus an academic or small R&D setting.
2. Evaluate effectiveness of one or more control methods by conducting arsenic monitoring (using air and wipe samples) during a MBE maintenance task. These results could be compared to arsenic monitoring that I performed in August 2002 in UC Berkeley’s Electronics Research Laboratory during a maintenance task on MBE equipment.
Background:
MBE uses advanced thin-film growth techniques to grow semiconductor heterostructure layers by combining group III and group V elements. MBE technology is forecasted to expand because it produces compound semiconductor materials with high precision and purity that are used in cellular phones, fiber-optics, satellites, radar systems, and display devices (Veeco-Applied Epi, 2002). According to Global Information Inc., “The total market for MBE equipment, services, and materials is estimated to be $249.2 million in 2001, increasing to $1.05 billion in 2006 at an average growth rate of 33.3%” (GII, 2002). Gallium-Arsenide (GaAs) devices seem to be the most common MBE product and are the focus of this proposal because of the potential health hazards of worker exposure to arsenic, specifically during maintenance activities (Jones, 2001). Arsenic is a known lung and skin carcinogen regulated by Cal/OSHA. In 2000, American Xtal, a supplier of GaAs wafer substrates, was cited by Cal/OSHA for over $300,000 in penalties due to health and safety violations, particularly exposing workers to arsenic levels greater than the Cal/OSHA PEL (DIR, 2000). The high penalties were due to a new law, AB 1127, that became effective in California on January 1, 2000 to increase the effectiveness of Cal/OSHA’s enforcement efforts. Although arsenic is probably well-controlled in most facilities, there is still concern over the effects of low level occupational exposure in the semiconductor industry. A study of semiconductor workers in Taiwan recently found a significant decrease in white blood cell count compared to a control group of workers; arsenic was a listed potential source toxin in this plant, along with glycol ethers (Luo et al, 2002).
My evaluation of arsenic exposure in August 2002 as an intern for the UC Berkeley Office of Environment, Health and Safety, consisted of personal air monitoring on two workers, one area air sample on the benchtop under the MBE access port, and numerous surface wipe samples near the work areas and in a clean area of the laboratory. The MBE is being used lor the growth of Indium Gallium Aluminum Arsenide layers, including silicon and beryllium as dopant materials. On the day monitoring was conducted, the internal substrate heater was being replaced and other components within the MBE were transported to a fume hood and cleaned. Arsenic air concentrations were all well below the Cal/OSHA PEL of 0.01 mg/m3; but a number of wipe samples yielded concentrations near the semiconductor industry standard of 100 1lg/100 cm2 (ACGIH, 1989). Although there is not a regulated surface arsenic standard, hazardous surface dust may be inhaled, ingested via hand-to-mouth behavior, eating or smoking, or be tracked out of the laboratory on shoes or clothing. A study of low level arsenic exposure suggested that arsenic intake via ingestion rather than inhalation might play a significant role in observed elevated urinary arsenic levels among workers because measured air concentrations were very low, but high arsenic levels were found in wipe samples (Hwang, 2000). This may indicate that improved control methods should be implemented to reduce surface arsenic contamination and that maintaining air concentrations below Cal/OSHA standards is not adequate in controlling arsenic exposure.
Proposed Methods:
1. Conduct a literature review on subject of arsenic control in semiconductor industry , as well as control options from other industries, e.g. using glove bags designed for
asbestos work.
2. Conduct site visits to an industry facility and another academic or R&D facility.
3. Interview industry industrial hygienists regarding control methods.
4. Assess practical applicability of potential control options and choose feasible options.
5. Attempt to implement control at the UC Berkeley facility and conduct arsenic monitoring, if the opportunity arises (i.e. if a maintenance task is performed during timeframe of this scholarship).
Request for Industry Resources: In order to review arsenic control options and understand the set-up in industry production, I hope to visit a MBE production and/or R&D facility in the San Francisco Bay Area. Ideally I would be able to discuss arsenic exposure issues with environmental health and safety professionals familiar with the MBE systems.
References:
American Conference of Governmental Industrial Hygienist (ACGIH). Hazard assessment and control technology in semiconductor manufacturing, 1989. p. 167.
California Department of Industrial Relations (DIR). News Release, May 17, 2000. http://www.dir.ca. gov/DIRNews/2000/lR2000-09.html, accessed 10/25/02.
Global Information Inc. (GII). Ion implantation and MBE technologies to grow at 25% and 33% respectively on average per annum through 2006, released 6/19/02. http://www.the-infoshop.com/press/bc8038_en.shtml, accessed 1114102.
Hwang, YH. Monitoring of low level arsenic exposure during maintenance of ion Implanters. Arch Environ Health, 2000 Sept-Oct; 55(5):347-54.
Jones, Anthony. Unique Industrial Hygiene Concerns in Gallium-Arsenide (GaAs) Device Manufacturing facilities. Motorola, 2001. http://www.semipark.co.kr/tech data/downadd.asp?number=208, accessed 10/18/02.
Luo, JC; Hsieh, LL; Chang, MJ; Hsu, KH. Decreased white blood cells counts in semiconductor manufacturing workers in Taiwan. Occup Environ Med 2002 Jan; 59(1):44-8.
Veeco Applied Epi. General Information: MBE and MOCVD. http://www.epimbe.com/learning_center/general_info/cent_gen. htm, accessed 10/25/02.