Unique Industrial HygieneUnique Industrial HygieneAspects in GalliumAspects in Gallium Arsenide Arsenide

Device ManufacturingDevice ManufacturingFacilitiesFacilities

Author: Anthony Jones

Presented by: Sarah Gibson

Outline• Gallium arsenide overview• Various operations – IH issues

–MOCVD–MBE–Plasma Etch–Saw and Grind–Wastewater treatment–Equipment decontamination

• Air and wipe sampling strategies• Training• OSHA’s inorganic arsenic standard• Summary

• Part of the “III-V” or compoundsemiconductor family

• Fused 48% Gallium and 52%Arsenic in wafer form

• Typical GaAs fabs use 4” or 6”wafers in manufacturing

• Wafers are stable at NTP

• GaAs has better semiconductingproperties for certain operationsover silicon substrates--differentproduct applications especiallywireless & optical communications

General GalliumGeneral Gallium Arsenide Arsenide ( (GaAsGaAs))InformationInformation

The Periodic Table

Group III Group V

General GalliumGeneral Gallium Arsenide Arsenide ( (GaAsGaAs))InformationInformation

The Periodic Table• Similar equipment used inprocessing

• Some differences in processingtechniques/applications

• Wastewater treatment (arsenic) isa major environmental concern.Local limits for devicemanufacturers vary. Wafergrowers have higher limits

• Discussion of lowering drinkingwater limit to 50 ppb or less

• Hazardous waste considerationsdue to arsenic content of wafers

• Crystal growing will not bediscussed in this presentation

Group III Group V

MetalorganicMetalorganic Chemical Vapor Chemical VaporDeposition (MOCVD) - GeneralDeposition (MOCVD) - General

• Used to grow thin epitaxial layers onGaAs substrates

• Many fabs contract EPI growth tofoundry operations

• Arsine (AsH3) and Phosphine (PH3) gasare used

• Several pyrophoric/toxic metalorganicsused as well: triethylgallium, triethylaluminum, triethylindium, others

• Potential inclusion in OSHA 1910. 119:Process Safety Management (PSM) ofHighly Hazardous Chemicals (ThresholdQuantity: 100 lbs for AsH3 and PH3)

• Frequent maintenance on internal reactorand abatement systems is needed

MetalorganicMetalorganic Chemical Vapor Chemical VaporDeposition (MOCVD)- MaintenanceDeposition (MOCVD)- Maintenance

• As and P particle trap removal

• As and P trap cleaning

• Hydride gas abatement systemmaintenance

• Hydride gas delivery andchangeout

• Preventative maintenance

• Reactor chamber access andprocess lines

MetalorganicMetalorganic Chemical Vapor Chemical VaporDeposition (MOCVD)- Particle TrapsDeposition (MOCVD)- Particle Traps

• Particle traps need frequentexchange and clean-out

• High [As] and white [P] are presentare in fine particulate and dry form

• Air sampling: Direct readinginstruments and OSHA compliance

• Spill containment (subfloor covers)

• Phosphorus fire response

• Respiratory protection and PPE

• Special training

MetalorganicMetalorganic Chemical Vapor Chemical VaporDeposition- Phosphorus Particle TrapsDeposition- Phosphorus Particle Traps

• Phosphorus (P) cold traps filterundeposited P before hitting the hydrideabatement systems. P is formed from PH3

• Clogging of trap exhaust lines/valves is aconcern

• P is in the white allotropic form, thus ispyrophoric and toxic (PEL = 0.1 mg/m3)

• A full trap can have up to several poundsof concentrated white P

• P ignition will create toxic phosphorusoxides. PH3 presence is also likely

• P trap cleanout requires a special cleaningand maintenance area with proper safetysystems. Copper sulfate recirculators arecommon

• Pyrophoric nature requires flame retardantPPE and air line respiratory protection

MetalorganicMetalorganic Chemical Vapor Chemical VaporDeposition- Arsenic Trap MaintenanceDeposition- Arsenic Trap Maintenance

• Cold traps filter undeposited As beforehitting hydride abatement systems

• Full trap can have up to several poundsof concentrated As in dried and fineparticulate form

• Cleanout may require soaking in mildchemical solution. AsH3 or other toxicAs oxides can be formed

• Soaking/cleaning must take place in abalanced chemical hood or glove box.Introduces a significant slug of As towastewater treatment system

• Respiratory protection and PPE

• Special training

• Used to grow ultra-thin epitaxialcrystals on substrate

• Process uses very high vacuum anda furnace heating element tovolatilize source materials

• Typically uses solid P, In, As, Gasource materials

• Increasing popularity inmanufacturing environments

• Several advantages over MOCVD

Molecular Beam Epitaxy(MBE)-Process

• Reactor access

• Potential hydride formation

• White phosphorus (P) traps

• Air sampling & PPE

• Local exhaust ventilation (carefulwith material of construction andP handling)

• Area contaminant control

Molecular Beam Epitaxy-General Maintenance IH Concerns

• White phosphorus (P) trapmaintenance

• Pyrophoric material

• Potential Phosphine andPhosphorus oxidation concerns

• Air sampling and PPE

• Special training

Molecular Beam Epitaxy-Trap Maintenance IH Concerns

Plasma Etch - GeneralPlasma Etch - General• Polymer or metal etch

processes

• Source via etch is alsocommon in GaAsmanufacturing

• Similar gases used as found inSilicon fabs: BCl3, Cl2, O2,perfluorocarbons, inerts

• Source via etches directly intoGaAs substrate throughbackside of wafer

• Etch chamber maintenancecleans are common andfrequent

Plasma Etch - MaintenancePlasma Etch - Maintenance• Source via etch is largest IH concern

since [As] is present in the chamberas a byproduct

• Wet cleans typically use DI water tophysically wipe internal chamber

• Opening chamber (humidity) andapplication of DI water will liberatechlorinated, fluorinated, and arseniccompounds (arsine generationpossible)

• Local exhaust is necessary asexposure control

• Extensive air sampling to documentexposure potential to typical etchclean gases as well as arseniccompounds (including arsine)

Plasma Etch - MaintenancePlasma Etch - Maintenance• Point of use water scrubbers will be

contaminated with arsenic compounds• Need to review preventative

maintenance practices on scrubbers• Clogging is a typical problem and

may require access/flangereplacement in tight spots

• Clean or soak flanges, etc. in achemical exhaust hood (halogenatedcompounds are concentrated and veryreactive). Ensure water is disposed ofproperly

• Local exhaust ventilation should beused (leave scrubber exhaust on!)

• Take air samples during maintenanceactivities

• PPE & Training

Saw Operations- GeneralSaw Operations- General• Centrifugal saws cut wafers

into die

• Large quantities of DI waterare used as a blade coolingmechanism as well as aparticle carrier fluid

• Typically, chemical additivesare not used in saw operations

• GaAs particulates generatedare typically >1 um with abulk weight distribution of >5um

• Saws generate ~20-25% ofarsenic load in waste stream

Saw Operations- MaintenanceSaw Operations- Maintenance• Preventative maintenance requires

access to contaminated areas of saws

• Saw blade exchange, chuckreplacement, and general cleaningnormally part of maintenance

• Dried arsenic particles of greatestconcern for exposure

• Air and wipe sampling strategyneeded to characterize exposurepotential during maintenance ANDhousekeeping

• PPE

• Training

WaferWafer Backgrind Backgrind- General- General• Centrifugal ceramics physically

grind the backside of wafers toreduce thickness

• Different devices requiredifferent wafer thickness

• Like saws, large quantities of DIwater are used to cool rotatingceramics as well as a particlecarrier fluid

• Typically, chemical additives arenot used in GaAs saw operations

• GaAs particulates are finer thansaws with <3 um particle size

• Grinders generate ~70% ofarsenic load in waste stream

WaferWafer Backgrind Backgrind- Maintenance- Maintenance• Like saws, preventative maintenance

requires access to contaminatedareas of grinders

• Ceramic exchange, chuckreplacement, and general cleaningnormally part of maintenance

• Technicians have direct contact withlarge concentrations of GaAs sludge

• Air and wipe sampling strategyneeded to characterize exposurepotential during maintenance ANDto monitor housekeeping

• PPE

• Training

Arsenic Wastewater TreatmentArsenic Wastewater TreatmentSystems- GeneralSystems- General

• Wastewater treatment systems usedto extract [As] out waste stream

• Ferric-Chloride most popular methodused

• High chemical usage: Ferricchloride inject, pH adjust (H2SO4,NaOH), coagulant additives, anti-bacterial chemicals

• Can be high concentrations of [As]in wastewater or other parts ofsystem

• Industrial centrifuges used to collectbulk of GaAs particles before hittingtreatment system

Arsenic Wastewater TreatmentArsenic Wastewater TreatmentSystems- Filter PressSystems- Filter Press

• Filter plates require frequentcleaning of arsenic laden ferrichydroxide cake

• “Filter Cake” is ionicallybound As in a ferric hydroxidematrix

• Filter cake can have up toseveral thousand ppm of [As]in the bound matrix

• PPE

• Training

• Housekeeping

Arsenic Wastewater TreatmentArsenic Wastewater TreatmentSystems- CentrifugeSystems- Centrifuge

• Industrial sized centrifugeused to remove suspendedGaAs particles before hittingthe wastewater treatmentsystem

• Large concentration of GaAscollected over time

• Removal of collection drumsand system maintenance

• Dried [As] a concern

• PPE, Training, & Labeling

Process Equipment DecontaminationProcess Equipment Decontamination• Must consider presence of As, AsH3, P, and PH3 in

decommissioned tools and abatement equipment

• Water from equipment decon may have high [As]

• Decontamination chemicals must be considered so as not tocreate toxic hydrides or oxide gases. Green Windex hasbeen effective

• Decon operations should be performed on designatedhazardous decontamination pads

• Air sampling

• PPE

• Training

Air Sampling StrategyAir Sampling Strategy

•Arsenic requires full shift air sampling perOSHA regulations

•NIOSH 7901 OR 7300 (arsenic)

•Proposed arsine TLV reduction from 50 ppb to3 ppb by ACGIH (NIOSH 6001)

•Since largest concern is with maintenance activities, it’s a goodidea to collect both short-term AND full shift samples (one forcompliance and one for characterization)

• Important to have a re-sample policy or plan

•Areas of arsenic/arsine potential: MOCVD, MBE, Saw/Grinder,Dry Etch, Decontamination Activities, Wastewater Treatment.

Wipe Sampling StrategyWipe Sampling Strategy

•A housekeeping plan is required underOSHA’s inorganic arsenic standard

•Should have a wipe sampling strategy orschedule to monitor adherence to thathousekeeping plan

•No OSHA standard exists for arseniccontamination

•Housing and Urban Development (HUD)standard for lead can be used as a referencefor contamination: 100ug/ft2 for floors, 500ug/ft2 for window sills and 800 ug/ft2 forwindow wells

GaAs FabGaAs Fab Training & Information Training & Information• All fab operators should have

basic orientation on GaAs

• Technicians or engineersperforming maintenance activitiesshould have detailed training onproperties and toxicology of As

• Specific training on MOCVDsystem including trapmaintenance and handling

• GaAs fab jobs that should haveadditional training: saw/grindertechnicians, MOCVDoperators/technicians/engineers,wastewater treatment technicians

OSHA’sOSHA’s Inorganic Arsenic Standard Inorganic Arsenic Standard

• 1910.1018 Inorganic Arsenic (Arsine exposure not applicable)• Initial 8-hour air sampling on every shift determines applicability of

several provisions of standard• Exceeding the PEL (0.01 mg/m3) requires the following provisions:

-Establishment and demarcation of a regulated area

-Notification to OSHA of regulated area, summary of operations,and plans to reduce employee exposures

-Written program with engineering plans/studies, monitoringschedule, to reduce exposures to below PEL throughengineering and work controls

-Additional air sampling required every 6 months

OSHA’sOSHA’s Inorganic Arsenic Standard Inorganic Arsenic Standard

• Exceeding the PEL (0.01 mg/m3) requires the following provisions.Some of the provisions may apply to exceeding the action level(0.005mg/m3):

-Respiratory protection requirements dependent on air samplingresults

-Establishment of hygiene facilities including change rooms,showers, lavatories, and lunch rooms

-Medical surveillance and training

OSHA’sOSHA’s Inorganic Arsenic Standard Inorganic Arsenic Standard

• The following provisions apply to ALL potential inorganic arsenicexposures:

-Initial air monitoring for every shift . Results must be below theaction level (0.005 mg.m3)

-Additional monitoring required upon change in operations whichmay result in new or additional exposure to arsenic

-Employee notification within 5 days of monitoring results

-A written housekeeping and maintenance plans to minimizedarsenic dispersion

-Specific verbiage on labeling arsenic shipping or storagecontainers (not applicable to GaAs wafers)

OSHA’sOSHA’s Inorganic Arsenic Standard Inorganic Arsenic Standard

• The following provisions apply to ALL potential inorganic arsenicexposures:

-Appropriate, freshly laundered (or new) PPE for employeeswith skin exposure potential

-Inform laundering services (in writing) of potentially harmfuland carcinogenic effects of exposure to inorganic arsenic

-Storage of PPE to prevent dispersion of inorganic arsenic

-Must ensure contaminated PPE/clothing is specifically labeledwith proper verbiage according to the standard

-Floors may not cleaned by compressed air, shoveling, orbrushing. Vacuums may be used for cleaning but mustminimize reentry of inorganic arsenic into the workplace(HEPA)

SummarySummary • Maintenance activities in GaAs fabs = largest exposure potential

• AsH3/PH3 usage and presence of [As] and [P] are the largest IHconcern and primary difference between Silicon and GaAs fabs

• MOCVD operations have additional concerns due to PH3 use

• MOCVD and MBE have white P as a hazardous byproduct

• Main areas of concern include: Saws/Grinders, MOCVD, MBE,Wastewater Treatment, Decontamination, and Dry Etch

• Compliance with OSHA’s arsenic standard must be consideredand documented. Air sample all potential exposures

• Special and detailed training for individuals performingmaintenance should be given and documented as a supplement togeneral hazard communication training