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NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Dedon, et al 1.

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Presentation on theme: "NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Dedon, et al 1."— Presentation transcript:

1 NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Dedon, et al 1

2 NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Dedon, et al 2

3 NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Dedon, et al 3 Perspective of Industrial Use of Arsenic U.S. industrial usage estimated at 150 tons in 1995 World reserves estimated at 11 million tons

4 NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Dedon, et al 4 Risk of Exposure to Arsenic Species in Ion Implantation 1. Replace tungsten filament. 2. Change the slit for the beam. 3. Scrub the implanter weekly. Change pump oil and clean the pump. house scrubber Chimney Change arsine tank every 3 weeks. Replace the catalyst every 2 years.

5 NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Dedon, et al 5 Chemistry of the Arsenic Species in the Fab Arsenic (As 0 ) A brittle, crystalline, silvery to black metalloid. Arsenic trioxide (As 2 O 3 ) Odorless, tasteless, white or transparent, amorphous or crystalline powder. Arsine (AsH 3 ) Colorless gas with garlic odor. Highly reactive : risk of explosion upon contact with air or when physically shocked. Accidental generation of AsH 3 : 6H + +2Al 0 + HAsO 2 -->AsH 3 +2H 2 O + 2Al 3+ (i.e. aluminum or galvanized buckets to transport arsenical slurry.) Removal of arsine in fab by the following chemical reactions Burn Box: 2AsH 3 + 3O 2 --> As 2 O 3 + 3H 2 O 4AsH 3 +3O 2 ---> 4As 0 + 6H 2 O Dry Scrubbing: 2AsH 3 + 3CuO ---> Cu 3 As + As 0 + 3H 2 O Cu 3 As + As 0 +3O 2 --> 3CuO + As 2 O 3 Wet Scrubbing: 4MnO AsH 3 --> As 2 O 3 + H 2 O + 4 MnO 2 + 4OH - 32MnO AsH 3 --> 3As 4 O H 2 O +32OH - +32MnO 2

6 NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Dedon, et al 6 Central and Peripheral Nervous System Neural degradation Peripheral neuropathy Kidneys Toxicity in acute exposure Suspected kidney carcinogen R ENAL FAILURE I S C AUSE O F D EATH in acute exposures Liver Suspected liver carcinogen Enlargement and toxicity Skin Suspected skin carcinogen High accumulation of As in skin Lungs Target of inhalation exposure P ROVEN Lu NG C ARCINOGEN Acute Effects Fatal at mg, toxicity at 1-50 mg Similar to AsH 3 except no RBC lysis Animal models are poor predictors Chronic Effects Meese’s lines; skin, hair accumlation Cancer of lungs, skin, kidney, bladder, and liver Low overall toxicity times more resistant than humans Generally non-carcinogenic except as tumor promoters H UMAN A NIMAL A RSENIC T OXICITY

7 NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Dedon, et al 7 Central and Peripheral Nervous System halucinations headaches neural degradation sensory loss Hemotologic RBC lysis ( ppm) Abdominal pain diarrhea vomiting unknown mechanism (GI toxicity?) Kidneys Hemoglobinurea Toxic to nephron R ENAL F AILURE I S C AUSE O F D EATH Liver Liver toxicity Altered hepatic function AsH 3 T OXICITY Fatal at 50 ppm (30 min) Around 750 reported exposures, 1/3 resulting in death Human and animal toxicity is very similar  predictive models Similar toxic effects seen in mice, rats, and hamsters RBC lysis at 3-12 ppm exposure Liver and spleen enlargement with long-term 5 ppm exposure Kidney toxicity at higher exposure Fatal at ppm H UMAN A NIMAL

8 NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Dedon, et al 8 The Main Route of Exposure to AsH 3 : Inhalation Larynx Trachea Bronchus Terminal brochiole AsH 3 Alveolar sac Pulmonary arteriole Bronchiole As? LUNGSALVEOLUS CROSS SECTION of ALVEOLA WALL RBC 7m7m Oxidation state of As in RBC is unknown but likely to be As 3+. Toxicity of As species to RBC is oxygen dependent in vitro. Arsine diffuses through the alveolar membrane into capillary lumen where it reacts with the Red Blood Cell (RBC). AsH 3 50 to 100 nm Threshold Limited Value (TLV) for AsH 3 is 5ppb. A B H

9 NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Dedon, et al 9 Inhalation of Arsenicals Bronchiole (1mm diameter) Terminal bronchiole Respiratory bronchiole Alveolar duct Alveolar sack (termination of alveolar duct) Particulate Arsenic (As 2 O 3, etc.) Particles deposit in lungs according to size > 6  m: trapped in nose 1-5  m: impact on bifurcations 1  m: reach terminal bronchioles <0.5  m: suspended in air; diffuse into alveoli Bronchial airways are coated with mucus that traps particles Trapped particles are cleared by ciliary action Gaseous Arsenic (AsH 3 ) Diffuse into alveoli Some direct toxicity to alveolar cells

10 NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Dedon, et al 10 The Primary Cytotoxic Target in Acute AsH 3 Poisoning: The Red Blood Cell Chemistry of RBC lysis (cell rupture): The first target of AsH 3 is the RBC. One site of reaction in the RBC is hemoglobin. Heme reacts with As species, and it is oxidized from oxyhemoglobin to methemoglobin. This reduces the O 2 carrying capacity of RBC. Reactions at other sites also result in protein denaturation (e.g. globin) and formation of insoluble precipates called Heinz bodies. These events lead to rupture of the RBC. Other possible contributions to RBC rupture: Production of H 2 O 2 and other reactive oxygen species when AsH 3 undergoes redox chemistry. Inhibition of RBC enzymes such as catalase and Na + /K +_ ATP ase. HEMOGLOBIN MOLECULE Globin Heme Red Blood Cell (RBC) consists of millions of hemoglobin molecules, and each hemoglobin is made up of protein called globin, and 4 hemes which carry oxygen. C

11 NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Dedon, et al 11 Renal failure is cause of death at acute exposures of AsH 3 and As in Direct toxicity of AsH 3 to proximal/distal tubule cells Direct toxicity of AsH 3 to glomerulus at high concentration Indirect toxicity of hemoglobin, Fe to nephron cells Renal failure induces loss of plasma contents (albumin, glucose, etc.) and electrolyte imbalance glomerulus collecting duct loop of Henle proximal tubule distal tubule The Most Common Cause for Fatalities in AsH 3 Poisoning: Kidney Toxicity D E F G

12 NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Dedon, et al 12 Life Cycle of Arsenic Species Outside the Fab Arsenic waste generated by U.S. semiconductor manufacturing: Laidlaw estimates the amount of As waste in solution generated by New England semiconductor industry is about 275 gallons per month, and it contains less than 5 ppm arsenic waste. Arsenic waste accounts for 1 % of their total chemical waste handling. Each Novapure solid scrubber may contain up to 4.6 kg of arsenic solid waste. Arsenic species in dry scrubbers Arsenic species in slurry Arsenic species in pump oil Arsenic species in wet scrubbers Solid Scrubbers are stabilized in Portland cement. No leaking of more than 5ppm. Buried in a land fill (e.g., Model City, N.Y.) Wet scrubbers contain permanganate (KMnO 4 ). Treated in Canadian facility where KMnO 4 is neutralized. Converted to solid waste to deposit in land fill. Solution waste is treated in a Dupont Waste Treatment Plant. Waste Handling Company, e.g., Laidlaw in New England

13 NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Dedon, et al 13 Chronic Exposure Possible chronic arsenic species exposure routes in ion implantation Arsenic species such as As 2 O 3 from cleaning and waste handling. Handling solid As 0 source. Toxicity Chronic exposure to toxic level of inorganic arsenic can have a cumulative damaging effect. Inorganic arsenic is classified as a human skin and lung carcinogen. Chronic loss of RBC can lead to anemia. Increased risk of diabetes and cardiovascular disease. Peripheral and central nervous system toxicity. Several studies reported that fab workers do not have increased levels of As in hair, urine, and blood samples.

14 NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Dedon, et al 14 Safety Measures Normal operation Workers wear smocks and gloves to prevent skin contact with arsenic species (solid and dust). Changing AsH 3 gas cylinders Workers wear self-contained respirators. The production floor is cleared. Cleaning the ion implanters Workers clean the chambers and walls with vacuums that contain high efficiency particulate air (HEPA) filters. Workers wear HEPA filter masks during operation. Trapping and retaining As species (The chemistry slide shows the reactions of these safety devices.) Burn boxes (AsH 3 gas is oxidized to As 2 O 3.) Dry scrubbers (AsH 3 is physically adsorbed onto high surface area catalyst.) Wet scrubbers (AsH 3 reacts with KMnO 4 to form As 2 O 3 and As 2 O 5.)

15 NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Dedon, et al 15

16 NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Dedon, et al 16 P UBLIC H EALTH A ND S AFETY Legislative Branch Mandates regulation of food, air, water, and workplace exposure Administrative Branch Implements mandates of congress through different departments -Toxic Substances Control Act -Food, Drug, and Cosmetics Act -Insecticide, Fungicide, Rodenticide Act -Resource Conservation and Recovery Act -Safe Drinking Water Act -Clean Air Act -Consumer Product Safety Act -Comprehensive Environmental Response, Compensation and Liability Act (Superfund)

17 NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Dedon, et al 17 Department of Health and Human Services - Food and Drug Administration (FDA) Force of law! Sets, regulates and enforces quality of foodstuffs and drugs - Center for Disease Control (CDC) National Institute for Occupational Safety and Health (NIOSH) Advisory authority only! Research safe workplace practices Department of Labor - Occupational Health & Safety Administration (OSHA) Force of law! Sets, regulates and enforces workplace exposure limits Independent Agencies - Environmental Protection Agency (EPA) Force of law! Sets, regulates and enforces waste disposal, Sets U.S. drinking water standards Independent Scientific Organizations -American Congress of Government Industrial Hygienists (ACGIH) Advisory authority only! Recommends safe workplace exposure limits

18 NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Dedon, et al 18 Regulation of Hazardous Chemicals Available scientific data is collected Data is studied by OSHA, NIOSH, EPA, and ACGIH to determine dose-response relationship Available data is ranked in order of human relevance - Large scale human chronic exposure data - Acute human exposure data - Large scale, long-term, multi-species animal data - Long-term, single species animal data - Acute animal exposure data Dose information is determined - NOAEL: No Observable Adverse Effects Level - LOEL: Limit of Observable Effects Level (commonly a 10% increase in liver weight) Dose is then extrapolated and modified for human exposure - Safety factors are introduced for threshold chemicals - Mathematical models are used for non-threshold chemicals

19 NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Dedon, et al 19 R EGULATION O F A RSENICAL C OMPOUNDS Arsine 750 documented human exposures Multi-species (rodent), acute and chronic exposure data available - NOAEL: ppm (90 day, 6 hr/day, 5 day/week exposure) - LOEL: 0.5 ppm (RBC lysis and turnover seen) Scaling factors (used by ACGIH for review of TLV) - Interspecies variability: 3x - Susceptible human populations: 10x - Subchronic exposure data: 10x Permissible Exposure Level (PEL) set by OSHA: 50 ppb (0.15 mg/m 3 ) Recommended ExposureLevel (REL) advised by NIOSH: 50 ppb (0.15 mg/m 3 ) Recommended Threshold Limit Value (TLV) advised by ACGIH: 50 ppb (0.15 mg/m 3 ) Exposures set as Time Weighted Average (TWA) over an 8 hour workday Ingested Inorganic Arsenic Extensive human epidemiological studies Animal experiments are inconclusive and poor models U.S. EPA regulates drinking water and hazardous waste disposal Drinking water limit set at 50  g/L in the U.S. Majority of U.S. drinking water <5  g arsenic/L Some areas (AZ) have ~50  g arsenic/L Airborne Inorganic Arsenic Proven human lung carcinogen Extensive human epidemiological data, few animal experiments Permissible exposure level (PEL) set by OSHA: 15 ppb (0.05 mg/m 3 ) Recommended exposure level (REL) advised by NIOSH and ACGIH: 3 ppb (0.01 mg/m 3 )

20 NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Dedon, et al 20

21 NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Dedon, et al 21 SDS vs. high pressure gaseous AsH 3 Regular AsH 3 F=fixed costs; P= operation costs; T=throughput, Y=yield, U=utilization SDS estimate Fixed costs (increase) -Equal to F + the cost of delivery system hardware and software + some other components Operation costs (similar) -Function of total time of workers, cost of materials, e.g., wafers, cost of arsine, electricity, etc. -Reduction in loss of workers time in changing AsH 3 because the lifetime of SDS increased approximately by a factor of 2. -Cost of AsH 3 per atom in SDS is 2 to 3 times higher then high pressure tank. -Other functions of operation costs remain unchanged. Utilization (increase) -More utilization of ion implanters as well as other machines because less time is spent on changing the AsH 3 cylinder. Throughput and yield are estimated to be the same as regular AsH 3 Example of Incorporating ESH into CoO Environmentally benign SDS may not impose a significant cost increased as compare to conventional AsH 3 sources.

22 NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing Dedon, et al 22 Conclusion Strategy for incorporating toxicology into semiconductor manufacturing process design: 1. Investigate a specific chemical in a specific process. 2. Identify routes of exposure. 3. Study the toxicity of that compound and its waste products. 4. Examine the current safety measures and waste handling methods. 5. Recognize alternative environmentally benign processes and resources. 6. Employ CoO to estimate the difference in costs between the conventional technology and environmentally benign technology.


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