potential occupational health hazards in the microelectronics industry

8/3/2019 Potential Occupational Health Hazards in the Microelectronics Industry

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SHORTER COMMUNICATIONSScand j work environ health 9 (1983)42-46

Potential occupational hea lth hazards in the microelectronicsindustryby Joseph LaDou, MD1

LA DOU J. Potential occupational health hazards in the microelectronics industry. Scandj work environ health 9 (1983) 42-46. The microelectronics industry is a major user ofa wide variety of chemicals and other toxic materials. In the recent past semiconductormanufacturers have located in many countries and brought a new set of challengingclinical problems to occupational physicians. California,an area with a significant historyin the statistical study of health and safety in the microelectronics industry, presentssome evidence of potential health hazards in the semiconductor manufacturing process.The Semiconductor Industry Study done in California in 1981 explains the applicationof many toxic materials in the semiconductor manufacturing process, including a varietyof solvents, acids, and metals such as arsenic. The Study documents the extensive useof dopant gases, primarily arsine, phosphine and diborane. Further study is necessaryto assure the health and safety of microelectronics workers, particularly in the applica-tion of dopant gases.Key terms: arsine, diborane, dopant gases, occupational illness, phosphine, semiconduc-tor, systemic poisoning.

The microelectronics industry is rapidlybecoming a major industry throughout theworld. It began only 35 years ago withth e development of the transistor, a small,low-power amplifier which replaced thelarge, inefficient vacuum tube (5). Theindustry found large and ready markets inthe computer industry and for solid-stateintegrated circuits for consumer productsmade possible by the transistor. Todayth e industry produces a vast number ofelectronic circuits and devices for militaryand space agencies, the computer anddata communications industries, andindustrial and consumer applications.The initial development of microelec-tronic devices occurred primarily inCalifornia, which today continues tolead the industry in technological ad-vances and consumer applications. Theexplosive growth of this industry, stem-ming from a series of scientific discoveriesand rapid manufacturing process develop-ments, has resulted in a world market ofmore than USD 16 billion in sales andin a workforce of more than one-half

Department of Medicine, University ofCalifornia, School of Medicine, San Francisco,California, United States.Reprint requests to: Dr J LaDou, PeninsulaIndustrial Medical Clinic, 1197 E ArquesAvenue, Sunnyvale, CA 94086, USA.

million. The manufacture of semicon-ducto rs and related microelectronicdevices has been reviewed in the literaturealthough state-of-the-art techniques aremaintained in relative secrecy (2, 4, 6 , 8).

Sta tist ica l evidence of health hazardsTo date, the high technology manufac-turing techniques of this industry haveproduced some as yet unexplained healthand safety statistics in the state of Cali-fornia. These statistics are derived fromstate Workers' Compensation Insurancerecords from information supplied by themany hundreds of companies engagedin microelectronics manufacturing anddistribution. Although the electronicsindustry has traditionally had a lowercombined incidence of occupational ill-ness and injury than heavier industries,workers in semiconductor manufacturingin California have consistently exhibitedan unusually high incidence of occupa-tional illness, whereas they have showna low incidence of occupational injury.Table 1 compares the rate of injury andillness in California for all private indust ry,the electronics industry, and the semi-conductor segment of the electronicsindustry. The data indicate that th e elec-tronics industry has a higher rate of occu-


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Table 1. Occupational injury and illness rates for private-industry, electronics, and semiconductorworkers.8Injury and illness Occupational illnessincidence rate per incidence rate per100 full-time employees 100 full-time employees

1977 1978 1979 1980 1977 1978 1979 1980

Private industry 10.3 10.5 10.6 10.1 0.3 0.3 0.3 0.3Electronics industry 7.9 8.3 8.0 7.7 0.6 0.6 0.5 0.5Semiconductormanufacturing 7.6 9.1 8.0 7.6 1.3 1.3 0.8 1.3a Data summarized from California work injuries and illnesses, Department of Industrial Relations,

Division of Labor Statistics and Research, San Francisco, California, 1980, 1981 and 1982.pational illness than other industries andthat the semiconductor segment accountsfor a large part of the difference.

These findings may reflect the wide-spread use of toxic materials in the in-dustry, which has developed processapplications for many metals, chemicals,and gases in a wide variety of combina-tions and environmental settings. Onestatistical category of occupational illnesstermed "systemic poisoning" is increasingeach year among electronics workersengaged in semiconductor manufacturingin California. Table 2 compares the inci-

Table 3. Chemicals used #by42 companies manu-facturing semiconductors i n 1979.a

Solventslsopropanol (2-propanol)n-Butyl acetateFreonsXyleneAcetoneMethanolPetroleum distillatesTrichloroethylene1,1,l-Trichlorethane(methvl chloroform)dence of this illness among all manu- ~et hyi ene hloride'(dichloromethane)facturing workers and electronics workers. TetrachloroethyleneThe latter exhibit a large increase in this (perchloroethylene)category of occupational illness, primarily Ethylene glycolbecause of the high incidence among ethylsemiconductor workers. (2-butanone)HexamethyldisilazaneIt should be emphasized that systemic (10 %) (HMDS)poisoning includes a number of other Ethanol'disease possibilities and that the data $ $ : E ~ ~ ~ ~ ~ ~cited are derived from First Report ofInjury forms which seldom reflect a final Acids

AmountKilograms Liters

499,392348,106322,784280,884243,186196,10096,10186,07061.733

medical diagnosis in complex cases of Sulfuric acid 70,470 1,500,374toxic exposure. Thus, rather than accu- ~ $ $ : ~ ~ " ~ ~ ~ $ ~5,390 786,485rately indicating the incidence of systemic ~ h ~ ~ ~ h ~ ~ i ~cid 5,985 1,274,0317.560 122.444Table 2. Systemic poisoning as the percentage ofoccupational illness for manufacturing, elec-tronics, and semiconductor w0rkers.a

Manufacturing industry 17.8 19.0 19.2 19.2Electronics industry 29.8 31.4 35.5 38.8Semiconductormanufacturing 37.2 42.9 42.1 46.9a Data summarized from California work injuries

and illnesses, Department of Industrial Rela-tions, Division of Labor Statistics and Research,San Francisco, CA, 1980, 1981 and 1982.

~ m m on iumluoride 2,475 339,817Acetic acid 1,485 1,288,224Nitr ic acid 2,025 51 1,959Boric acid 360 37Citric acid 4 378Buffered oxide etch(hydrofluoric acid &ammonium fluoride) 88,947Fluoboric acid 302CausticsSodium hydroxide 243,045Ammonia 39,015Potassium hydroxide 16,051Ammonium hydroxide 3,658a Data summarized from pages 33-34 of thereport of Wade & Williams (11).


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poisoning, the data merely indicate anarea for suspicion about the semicon-ductor work environment.The semiconductor indus try studyIn 1980 the California Department ofIndustrial Relations asked 53 semicon-ductor companies to provide informationon their use of a large number of mate-rials. Forty-two companies responded.This small sampling of the hundreds ofsemiconductor manufacturers in Cali-fornia included many of the major com-panies in the industry. Consequently thequantities of chemicals shown in table 3are very probably indicative of the amountused overall in this segment of the elec-tronics industry.

Table 4 indicates the types and quan-tities of gases and liquids that have beenused widely in the manufacture of semi-

conductors in recent years. The occurrenceof health complaints among semicon-ductor workers parallels an increase indoping techniques i n which arsenic, phos-phorus, and boron are deposited on thesurface of silicon wafers either in diffu-sion furnaces or by ion implantation orother advanced techniques. Dopant gasesprovide the dopant ions required i n theseprocesses, and arsine (ASH,), phosphine( pH3) ,and diborane (B2H,)- the hydridesof arsenic, phosphorus, and boron - arebeing used increasingly in the semicon-ductor industry. These gases are usuallydiluted to a low concentration before thedoping, but some techniques now utilizehigher concentrations, which of courseincrease the potential for toxic exposure.Table 5 summarizes the use of these highlypoisonous gases, as well as other gasescommonly used, in the semiconductorindustry.

Table 4. Gases and liquids used by 42 companies manufacturing semiconductors in 1979."

GasesHydrogen chloride

Unspecified concentration (probablypure hydrogen chloride)5 % hydrogen chlorideSilaneUnspecified concentration (possible range1.5-100 % silane)1.5- 100 % (specified)PhosphineUnspecified concentration (possible range0.0005-100 % phosphine)0.0022- 10 %Ammonia (assumed 100 %)ArsineUnspecified concentration (possible range0.0005- 100 % arsine)0.002-2 %DiboraneUnspecified concentration (possible range0.0005- 1 % diborane)0.0023-1 %Boron trifluoride (assumed 100 %)Krypton 85 (assumed 100 %)LiquidsSilicon tetrachloride (assumed 100 %)Trichlorosilane (assumed 100 %)Boron tribromide (assumed 100 %)

Amount(1)

4,428,6802,756,355 (= 1,750,002 1 of pure silane)5,990,0564,652,7291,337,326 (= 66,030 1 pure phosphine)4,346,6941,815,6351,305,530510,105 (= 10,343 1 pure arsine)

750,705666,79383,912 (= 646 1 pure diborane)

a Data summarized from page 35 of the report of Wade & Williams (11).

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Table 5. Properties of gases used in semiconductor chemical vapor d e p o s i t i 0 n . aApproxi- &Hour

Pyrophoric mate permissible% i n air Lethal in a Lethal in a lrritant odor exposureFlammable (auto few minutes few hours level level levelGas (% in air) ignition%) (ppm) (ppm) (ppm) (ppm) (ppm) CommentsYes ?"C 250 6rsine (ASHI) - 1 0.05 Highly poisonousPhosphine (PH3) Yes 40- 50C 2.000 100 8 2 0.3 Highly poisonousDiborane (B2Hs) 0.8-88 % 37-52C 160? ? - 3 0.1 Highly poisonous.......................................................................................................................................................................................................................Ammonia (NHJ 15-28 % 650C 30,000 25 5 50 Reacts stronglywith chlorides

N i t r o ~ s xide Supports Non- ? - 100 10 - Anesthetic, possible(N D) combustion pyrophoric nerve damageNitrogenldinitro en Su pp o~ S Nan- ZOO? 60 10 5C...............................................................................................................etroxide WJN& cor j7~,u~o~, . . . . .~1y.~o~~.p. : ;~..................................-...........................................

No Non- Nonlethal -xygen (0,) - - -- Keep separate frompyrophoric reducers: supportsfierce combustionCarbon diox ide fCO2l NO Non- Asphyxiant 20.000 - - 5.000 Irritant.. - - . . pyrophoric............................................................................................................................................... .............................Silane (SiH,) Yes (0.5 % SiH,IH,) Nonlethal Nonlethal ? - 0.5 Forms fine silica dustDichlorosilane Yes (4 % SiH;IN,) and vigorous flameISiKCI,), trichlo ro- flameSilicon tetrachloride No(SiClJ

Decomposes to hydrogenchloride and silicondioxide in air................................................................................................................................................................_ ..............................................................

Hydrogen ((HZ) 4-80 % 585C Asphyxiant - Non- Non- - Store < 56.678 1 inirritant odorous buildingNitrogen (N2) No - Asphyxiant - Non- Non-trritant odorous........................ ......................... .. ........................................................................................................................................_ _......................................Hvdroaen chloride No - 1.300 1,000 10 1 5 Noxious(HCI) -Hydrogen fluoride No - 1OO? ? 30 ? 3 Noxious(HF)a Data summarized from page 146 of the report o f Wade 8 Williams (11)

DiscussionIt is a matter of concern that semicon-ductor manufacturers are using largequantities of the previously mentionedtoxic gases in a variety of manufacturingprocesses and in an even wider varietyof settings (1, 3, 6, 7 , 8) . The gases aredelivered in metal cylinders, and, althoughmany hundreds of companies frequentlyuse them, there are no uniform warninglabels or uniform codes of color demarca-tion on the cylinders. Plant engineersand safety professionals do not agree onhow the cylinders should best be handled.They must either be stored out of doorsor in the work area. where they are con-

Although semiconductor health andsafety personnel consider the use of ar-senic as a dopant to be an obvious healthhazard, the California Industrial RelationsDepartment survey indicates that gallium-arsenide is being used increasingly asa wafer material for higher speed micro-electronic devices (3 , 7 , 9, 10). This wideruse of arsenic was s tudied by state inves-tigators using industrial hygiene moni-toring, and some instances of airbornecontaminant levels in excess of thoseallowed for inorganic arsenic were dis-c l o ~ e d . ~Recommendations

nected to diffusion furnaces; ion im- The semiconductor industry representsplanters, or other devices by stainless a major challenge to the occupationalsteel gas lines. Some engineers feel thatthe cvlinders should be k e ~ t utside the 2 A review o f the 1981 Semiconductor In -plantwand ed into th e by gas lines, d u s t r y Study i s beyond the s c o p e of thewhile others argue that the safest method present Paper. T h o s e i n t e r e s t e d may obtaina copy of the report from CalOSHAis the 'ylinders into the work C o m m u n i c a t i o n s , 525 Golden Gate Avenue,areas and store them there. Third Floor, San Francisco, CA 94102, USA.


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physician. The industry and its productsare of very recent origin. Moreover, thetechnology often moves so rapidly thatnew materials and processes replace oldones before sufficient information isobtained on the health hazards of either.Consequently, in cases of worker illnessor injury in the semiconductor industry,occupational physicians should contactthe individual's place of employmentto determine from managers and super-visors the nature of the work and theconditions of the work environment.Finally occupational physicians involvedin the semiconductor industry wouldbe well advised to visit periodically thevarious manufacturing plants under theirpurview. The importance of further studiesof the health and safety of microelectronicsworkers is evident from this early ex-perience of the California semiconductorindustry.

AcknowledgmentsThe author is grateful to Ms KA Jonesand Mr AD Harmon of the Division ofLabor Statistics and Research, California

Department of Industrial Relations, fortheir technical assistance.References

Elliott DJ. Integrated circuit fabricationtechnology. McGraw-Hill Book Co, NewYork, NY 1982.Gise PE, Blanchard R. Semiconductorand integrated circuit fabrication tech-niques. Reston Publishing Company, Inc,Reston, VA 1979.Kazan B. Materials aspects of displaydevices. Science 208 (1980) 927-936.Meindl JD. Microelectronic circuit ele-ments. Sci am 237 (1977) 70-81.Noyce RN. Microelectronics. Sci am 237(1977) 63-69.Oldham WG. The fabrication of micro-electronic circuits. Sci am 237 (1977) 111-127.Panish MB. Molecular beam epitaxy. Sci-ence 208 (1980) 916-922.Penn TC. New methods of processingsilicon slices. Science 208 (1980) 923-926.Shank CV, Austin DH. Ultrafast phe-nomena in semiconductor devices. Science215 (1982) 797-801.Wade R, Williams M. Semiconductorindustry study. California Department ofIndustrial Relations, Division of Occu-pational Safety and Health, Taskforce onthe Electronics Industry, San Francisco,CA 1981, pp 33-34.

Received for publication: 10 November 1982

potential occupational health hazards in the microelectronics industry

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