environmental health and safety concerns with group iii-v ... · general industry (29 cfr 1910)...

Environmental Health and Safety Concerns with Group III-V Compound Semiconductor Wafers

Joseph Barsky, MS, CIH – Principal Industrial Hygienist

1 EHS Concerns with Group III-V Compound Semiconductor WafersJuly 14, 2015

Introduction:

Basics of Industrial Hygiene Anticipation

- Chemical and Physical Hazards- Heath Hazards and Routes of Entry

Recognition- Identifying Potential Heath Hazards

Evaluation- Measuring Exposure Concentrations

Control- Exposure Control Concepts


Industrial Hygiene Focus on Arsenic

Person having a degree in engineering, chemistry, physics, health physics, nursing, medicine, or related field, by virtue of special studies, training, experience, and/or certification has acquired competence in IH.Industrial Hygienists look at: Health issues rather than just Safety. Illnesses in addition to Injuries.

Industrial Hygienists are concerned with Three Types of Hazards?

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Industrial Hygienist:

EHS Concerns with Group III-V Compound Semiconductor WafersJuly 14, 2015

Hazard Recognition

The FIRST group and the one that comes to mind for most people is Chemical Hazards.EXAMPLES INCLUDE:

Solvents/Paints: flammable, toxic to highly toxic

Welding Fumes: heavy metals, toxic to highly toxic

Carbon Monoxide: invisible and odorless gas, toxic

Simple asphyxiants: such as nitrogen purge, argon or other inert gases that can replace safe levels of oxygen in breathing air, sometimes done to prevent flammable vapors or corrosion of parts.

Compressed gases: flammable, corrosive, toxic, pyrophoric (self-ignition on short exposure to air)

Combustible dusts of polymers or metals: may cause a fire or explosion, may be water reactive, toxic. Any finely divided metal 420 μm (microns) or smaller in diameter (material passing a U.S. No. 40 standard sieve). When wetted they may release flammable hydrogen gas.

Chemical hazards introduced to the process from customer items being processed such as items which may contain arsenic, lead, chromium, and other chemicals.

Ozone: toxic gas used intentionally or generated as a byproduct during UV exposure.

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Types of Hazards

EHS Concerns with Group III-V Compound Semiconductor WafersJuly 14, 2015

Chemical Effects

Local - Damage to the part of the body that comes in contact with the substance. Systemic - Chemical is absorbed by the body and attacks a target organ.

Most chemicals that produce systemic toxicity do not cause a similar degree of toxicity in all organs but usually produce the major toxicity to one or two organs. Many illnesses are not obvious because they take so long to develop(latency period). Acute - Happens soon after exposure, usually of short duration

- Irritants - reversible inflammation at the site of contact

- fiberglass insulation, ammonia, acid mists- Corrosive - a visible destruction by chemical action

- Hydrofluoric acid, sulfuric acid, ammonium hydroxide and other semiconductor chemicals

The smaller amount of a substance it takes to produce the targeted effect, the more “toxic” the material.


Chemical Effects

Chronic - Health hazards occurring from long-term exposures - usually of long duration

- Sensitizers - allergies

- Carcinogens - cancers

- Target organ toxinsDISEASE EXPOSUREAsbestosis Asbestos - usually after 10-20 Years from thermal insulation

in furnaces and scrubber flanges or gasket materialsSilicosis Silica - usually after 10-20 Years from sand and rock

grinding/sandingLung Cancer Arsenic and hexavalent chromium - from welding stainless steel,

GaAs wafers or III/V compound semiconductor wafers - usually after 10 Years

Testicular Ethylene glycol ethers and their acetates (EGME, EGMEA)atrophy in photoresists - usually after 10 Years


PHYSICAL HAZARDS

The SECOND group is Physical Hazards.Examples Include: Noise Heat Stress Cold Stress Vibrations Ionizing Radiation

- X-ray, gamma (waves)- Alpha (particulate)- Beta (waves)

Non-Ionizing Radiation- UV/IR/Visible light- Lasers- Radiofrequency (RF)- Microwaves


BIOLOGICAL HAZARDS

The THIRD group is Biological Hazards.Examples Include: Bacteria Viruses Parasites Insects Animal wastes Bloodborne pathogens

Exposure can result in disease transmission


July 14, 20159 EHS Concerns with Group III-V Compound Semiconductor Wafers

Group III-V Compound Semiconductor Wafers

Arsine Gas and Arsenic

Composed of one element from column III, and one from column V, of the Periodic Table -- the so-called compound III-V semiconductors, such as GaAs, InP and GaN. These are often just a layer over a substrate that may be silicon or other. Many have thought that the Arsenic when embedded in the layer does not pose a potential hazard as it is embedded in the lattice or structure of the material. However, when heat is applied, we have found otherwise.

The quest for faster devices in the microelectronic industry has renewed interest in III-V materials such as InP, GaAs, and InGaAs as n-channel candidates because of their high electron mobility.

Arsenic and Arsine Gas General

July 14, 201510

Arsenic (As) occurs naturally in the environment as an element of the earth's crust.

Arsenic is combined with other elements such as oxygen, chlorine, and sulfur to form inorganic arsenic compounds.

Exposure to higher-than-average levels of arsenic occurs mainly in workplaces, near or in hazardous waste sites, and areas with high levels naturally occurring in soil, rocks, and water.

Exposure to high levels of arsenic can cause death.

Exposure to arsenic at low levels for extended periods of time can cause a discoloration of the skin and the appearance of small corns or warts.

Arsine gas (AsH3) or arsenic hydride is the gaseous form of arsenic used in semiconductor applications.

Workers have a right to a safe workplace. The law requires employers to provide their employees with safe and healthful workplaces.

EHS Concerns with Group III-V Compound Semiconductor Wafers

July 14, 201511 Environmental Health and Safety in the Work Place

Arsine Gas (AsH3)

• Highly poisonous, colorless, nonirritating, flammable gas

• Mild garlic odor at 0.5 ppm

• 2.5 times heavier than air

• Soluble in water

• Most acutely toxic form of arsenic

• Preferentially binds to blood hemoglobin

• Oxidizes to arsenic–dihydride intermediate and elemental arsenic (both toxic to blood)

• Direct and severe effect on the liver, spleen, kidneys, lungs, and other organs.

• Major route of toxicity in inhalation, 250 ppm instantly lethal.

• No antidote

• Known human carcinogen and suspected teratogen (birth defects)

Arsine Gas and Arsenic


OSHA

General Industry (29 CFR 1910)

1910 Subpart Z, Toxic and hazardous substances [related topic page]

1910.1018, Inorganic arsenic

Appendix A, Inorganic arsenic substance information sheet

Appendix B, Substance technical guidelines

Appendix C, Medical surveillance guidelines

OSHA Arsenic Standards

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Permissible exposure limits (PELs) were issued shortly after adoption of the Occupational Safety and Health (OSH) Act in 1970, and have not been updated since that time.

Threshold Limit Values (TLVs®) and Biological Exposure Indices (BEIs®) are determinations made by a voluntary body of independent knowledgeable individuals. They represent the opinion of the scientific community that has reviewed the data described in the documentation, that exposure at or below the level of the TLV® or BEI® does not create an unreasonable risk of disease or injury.

TLVs® and BEIs® are not standards. They are guidelines designed for use by industrial hygienists in making decisions regarding safe levels of exposure to various chemical substances and physical agents found in the workplace. In using these guidelines, industrial hygienists are cautioned that the TLVs® and BEIs® are only one of multiple factors to be considered in evaluating specific workplace situations and conditions.

TLVs® and BEIs® are health-based values established by committees that review existing published and peer-reviewed literature in various scientific disciplines (e.g., industrial hygiene, toxicology, occupational medicine, and epidemiology). Since TLVs® and BEIs® are based solely on health factors, there is no consideration given to economic or technical feasibility.


Occupational Exposure Limits

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Arsine gas CAS 7784-42-1 PEL = 0.05 ppm (50 ppb) or 0.2 mg/m3 8 hour TWA

In 2007, ACGIH changed the TLV for AsH3 from 0.05 ppm (50 ppb) to 0.005 ppm (5 ppb) 8 hour TWA based on Peripheral Nervous System and vascular system impairment, kidney and liver impairment.

NIOSH REL = 2 ug/m3 Ceiling in a 15 minute sample

Arsenic, inorganic compoundsCAS 7440-38-2 PEL = 10 ug/m3 8 hours TWA per 29 CFR 1910.1018. This was established in 1983 after OSHA’s risk assessment that it would reduce the risk of lung cancer by 98% from the prior limit which met the U.S. Supreme Court “significant risk” test.

Action Level of 5 ug/m3 8 hour TWA

PEL and TLV = 0.01mg/m3 8 hour TWA

~ = 3 ppb

Biological Exposure Indices TLV for elemental and inorganic compounds (excluding gallium arsenide and arsine): 35 ug As/L in urine, sampled at the end of the workweek.


Arsenic and Arsine Gas Occupational Exposure Limits


IH and OHS Services

With the Occupational Safety and Health Act of 1970, Congress created federal OSHA to ensure safe and healthful working conditions for working men and women by setting and enforcing standards and by providing training, outreach, education and assistance. States may develop their own federally approved plans (such as Cal/OSHA in

California). State programs must meet or exceed federal OSHA standards for workplace safety and health. 27 States have approved plans:

▪ Alaska▪ Arizona▪ California▪ Connecticut▪ Hawaii▪ Illinois▪ Indiana▪ Iowa▪ Kentucky▪ Maryland▪ Michigan▪ Minnesota▪ Nevada▪ New Jersey

▪ New Mexico▪ New York▪ North Carolina▪ Oregon▪ Puerto Rico▪ South Carolina▪ Tennessee▪ Utah▪ Vermont▪ Virgin Islands▪ Virginia▪ Washington▪ Wyoming

NOTE: The Connecticut, Illinois, New Jersey, New York and Virgin Islands plans cover public sector (State & local government) employment only.

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Arsine is the most acutely toxic form of arsenic and one of the major industrial causes of sudden extensive hemolysis (destruction of red blood cells). It has the ability to combine with hemoglobin within the red blood cell, causing destruction or severe swelling of the cell, rendering it nonfunctional. Inhalation of 250 ppm (800 mg/m3) of arsine gas is instantly lethal. Exposures of 25-50 ppm (80-160 mg/m3) for one-half hour are lethal, and 10 ppm (32 mg/m3) is lethal after longer exposures. The Mean Lethal Dose (MLD) is unknown for man.

The characteristic features of acute arsine poisoning are abdominal pain, bloody urine, and jaundice (yellow discoloration of the skin). Initial symptoms of arsine poisoning are headache, malaise, weakness, dizziness difficult breathing, abdominal pain, nausea, and vomiting, which are usually first noticed 2 to 24 hours after exposure. Bloody urine, light to dark red, is frequently noticed 4-6 hours after exposure to arsine and is often followed by jaundice 12-48 hours later. An unusual bronze discoloration of the skin can often be observed accompanying the jaundice. If the arsine exposure is severe, the products resulting from the breakdown of red blood cells and hemoglobin will clog the kidneys, causing a reduction in the amount of urine formed, sometimes to the point of complete blockage of urine formation. Other toxic effects of arsine include damage to the liver and heart, either by direct actions of arsine in the cells or due to the formation of arsenic.


Acute Arsine Toxicity


Once arsine is inhaled, it breaks down, releasing inorganic arsenic into the blood stream. The worker's risk of arsenic poisoning is therefore increased by the combination of inorganic arsenic exposure and the breakdown of arsine. A number of signs and symptoms are associated with arsenic poisoning. When ingested, arsenic compounds can cause nausea, vomiting and diarrhea within a few hours. Dermatitis may be observed after chronic ingestion but the typical signs include increased pigmentation, and thickening of the skin on the palms and soles of the feet. Changes in the heart's performance as measured by the electrocardiogram (ECG) have been reported after chronic arsenic intoxication. Observed ECG changes regressed after arsenic exposure ceased. Decreased numbers of red and white blood were reported in cases of chronic intoxication but these changes also regressed after arsenic ingestion ended. Lung and skin cancer has long been considered a consequence of arsenic exposure, however multiple cancers of the internal organs have also been reported.

Chronic Arsine Toxicity


A total of six unknown layer thickness of GaAs containing III-V 300 mm wafers were run in client’s thermal processor tool and IH samples were taken for potential off-gassing and solids deposition within the process chamber under a slight vacuum. This was in a regular fab floor with visqueen enclosure erected that had exhaust to prevent potential contamination of the surrounding fab. This ran for a bit over three hours. Three TLD-1 tools monitored the exhaust and tool area during the runs from 250 to 900 degrees C with regular and XPT tapes. The exhaust maxed out the TLD-1 XPT tape at 15+ ppb and alarm. On the second day, the chamber was opened after no cycle purges and 0.8 um mixed cellulose ester filters with air pumps were placed on the employees doing the chamber clean and wipe samples were taken inside the chamber and enclosure. The results indicated that no detectable arsine gas or arsenic particulates were measured at the personal breathing zones upon opening and wet cleaning of the System. High levels of arsine gas were measured in the sealed chamber exhaust only. High levels of arsenic particulate were measured deposited on the inside of the chamber (up to 10,000 micrograms per 100 cm2). Our established clearance level of acceptable residual contamination of 50 micrograms per 100 cm2 was not exceeded.

Case Study 1 Monitoring


A total of six 1600 to 2000 Angstrom layer of GaAs layer thickness III-V 300 mm wafers were run in client’s different thermal processor tool from Case Study 1 and IH samples were taken for potential off-gassing and solids deposition within the process chamber under a slight vacuum. This was in a regular fab floor with visqueen enclosure erected that had exhaust to prevent potential contamination of the surrounding fab. This ran for two days of different ramp recipes and holding and cool down recipes. A wafer was also re-run to see if it had finished off-gassing but it continued to do so. Three TLD-1 tools monitored the exhaust and tool area during the runs from 250 to 900 degrees C with regular and XPT tapes. The exhaust maxed out the TLD-1 SP tape at 150+ ppb and alarm. When the wafers were at 350 degrees C or above, they off-gassed significant levels of arsine in the chamber. On the third day, the chamber was opened after no cycle purges and 0.8 um mixed cellulose ester filters with air pumps were placed on the employees doing the chamber clean and wipe samples were taken inside the chamber and enclosure. The results indicated that no detectable arsine gas or arsenic particulates were measured at the personal breathing zones upon opening and wet cleaning of the System. High levels of arsine gas were measured in the sealed chamber exhaust only. High levels of arsenic particulate were measured deposited on the inside of the chamber. Our established clearance level of acceptable residual contamination of 50 micrograms per 100 cm2 was not exceeded.



A total of nine unknown thickness layer of As, Boron and Phosphorous implant doped customer wafers III-V 300 mm wafers were run in client’s Class IV 532 nm laser anneal tool and IH samples were taken for potential off-gassing and solids deposition within the open process area. This was in a laser regulated area of the regular fab floor. The areas were wiped clean in case prior wafers were run and baseline wipe samples were taken. This ran for about 11 hours with the different wafers. Four TLD-1 tools monitored the tool area during laser ablation regular and XPT tapes. The results indicated that no detectable arsine gas or arsenic particulates, diborane, or phosphine were measured at representative personal breathing zones and worst case directly above the point of operation.



AsH3 evolution observed during chemical mechanical polishing (CMP) of GaAs using aqueous solutions of hydrogen peroxide (H2O2) and silica slurries containing H2O2 by J. B. Matovu, et al. (ECS J. Solid State Sci. Technol. 2013 volume 2, issue 11, P432-P439)

The EHS concerns for As containing materials include the potential evolution of toxic arsenic (AsH3) gas, and the handling of arsenic contaminated slurry waste and used consumables (e.g., polishing pads).

While Matovu measured almost no evolution of the toxic arsenic gas (postulated by the solubility of the gas in water), the post-CMP slurry waste and consumables must be carefully handled because of the accumulation of the arsenic removed from the surface of the wafers.

For InP (which is less soluble in water), the major concern has been the generation of toxic phosphine gas during polishing.

Other III-V Arsenic Studies


Dry cleaning methods are not recommended for chamber cleans.

If parts are sent to an outside clean vendor, they must be warned in writing of the potential arsenic (or phosphine based on the wafer) contamination so they may provide adequate protection for their employees.

Again, these were only 6-9 wafers run, imagine the level of contamination inside the chamber after production running for 1 month or more to do a chamber clean.

TLD-1 tools after being subjected for high exhaust levels of arsine, needed to go back to Honeywell for service and re-calibration. They are not meant to be used for process exhaust with very high levels.

Due to 8 minute response time for the XPT Chemcassette® low level detection, the programmed temperature ramp was faster than the instrument response. If you only rely on this detector, employees may be exposed to significant levels prior to alarm. Use of both SP and XPT Chemcassettes® simultaneously is the safest option or XPT with Satellite MST detectors second best so if there is a large release, it will alarm within 1 minute.

Much more work to be done. If maintenance employees doing wet clean after many production wafers run, need to verify exposures stay below the Action Level or a regulated are may need to be established with all the warnings, showers and medical monitoring, etc. as required.

Case Study Lessons Learned


Two most often used means of area monitoring of the gas cabinet, exhaust or operator zone are Honeywell Analytics Hydride Chemcassettes® on TLD-1, SPM, CM4, System 16 and the Honeywell MST Satellite system. The regular hydride (SP) chemcassette and chemkey have a lower detection limit of 10 ppb level for the TLD-1 and SPM, 7 ppb for the System 16 and 5 ppb for the CM4 in 15 seconds response time. The XPT Tapes were developed for the lower levels needed and can see down to 0.5 ppb level on all but the CM4 which can detect down to 0.3 ppb but all take longer to read the sample at 8 minutes response time.

Honeywell Analytics MST Satellite arsine detectors (2 or 3 electrode) can see down to 0.03 ppm (30 ppb) level at less than 1 minute.

Again, the OEL TLV is 5 ppb.

Arsine Area Monitoring


With an OEL TLV at 5 ppb or OEL PEL at 50 ppb, tracer gas issues arise as the calibration gas concentration when using the Lagus Autotrac101 tool is 5 ppb. This is OK for PEL measurements but causes concerns about validity of sample limits of detection when trying to go to 25% and 1% of the OEL if using the TLV. SEMI S6 does not state that we need to use the lowest OEL, but that is the usual inclination of the Industrial Hygienist. As we said earlier, the TLVs do not take into account cost or if the level is reasonably achievable/detectable.

Within California, where use of SF6 for tracer gas has been banned as of last January, it’s replacement- Perfluorodimethylcyclobutane (PDCB) challenge chemical is not a gas at the higher concentrations needed to do arsine tracer gas to PEL levels. Lagus is still working on a solution to be able to provide this level of sensitivity. To date, within the USA- only California has this SF6 restriction.

This is a problem within the EU as well due to the F gas regulations as well restrictions on the electron capture detector radiation source.

Tracer Gas Challenges

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Documentation

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Sample OSHA Citation

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March 201426 EHS Consultation – Industrial Machinery26

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Questions/Comments?

Questions/Comments?

July 14, 201528

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environmental health and safety concerns with group iii-v ... · general industry (29 cfr 1910)...

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