Darryl W Hertz and Richard M Holland Ebasco Environmental Services

1.0 INTRODUCTION

Many electronic companies in the State of California create a substantial volume of arsenic waste through the processing or manufacture of gallium arsenide (GaAs) microchips. Since the concentration of arsenic in wastewaters or sludges usually exceeds disposal limits for sewer and municipal landfills, these wastes are quite often treated and disposed to a Class I hazardous landfill. This practice is undesirable environmentally and economically as a long-term mechanism for waste disposal.

The Hewlett-Packard Company (HP) currently operates a gallium arsenide (GaAs) microelectronics chip manufacturing facility in San Jose, California. In the manufacturing process a solution of hydrofluoric acid is produced which contains significant levels of arsenic as well as non-hazardous constituents. The hydrofluoric acid solution is currently neutralized with lime which yields a calcium fluoride sludge containing high levels of arsenic. Other electronics companies utilize little or no treatment and haul the entire waste volume to a treatment storage and disposal facility (tsdf). In 1985, HP produced 887,500 gallons of hydrofluoric acid wastewater and 25,219 gallons of calcium fluoride sludge.

Phase I of this project reviewed various processes to reduce, recycle and/or treat arsenic-laden wastes in a manner such that costs and disposal to the land are significantly reduced. The methods evaluated at various manufacturing stages included, but were not limited to, separation, precipitation/fixation, ion exchange, and arsine generation. The information from Phase I was suitable for the design of a pilot scale treatment facility.

Current findings from Phase II indicate that filtration of gallium-arsenide particulates from wastewater streams prior to entering Hewlett Packard's Hydrofluoric (HF) wastewater treatment facility will result in the following benefits:

o Potential income of approximately $100,000 from the sale of treatment facility solids (Calcium Fluoride - CaF2)

o ¿35,000 per year in disposal cost savings o $5,000 per year in revenue from increased GaAs recycling o HP's maintenance and health and safety management costs should be reduced by $15,000 per year

2.0 MANUFACTURING PROCESS AND WASTE STREAM CHARACTERIZATION

2.1 DESCRIPTION OF GALLIUM ARSENIDE MICROCHIP MANUFACTURING PROCESS

A brief description of the major steps required to produce GaAs microchips at Hewlett Packard's San Jose facility follows.

Ingot Growing

Elemental forms of gallium and arsenic, plus small quantities of dopant material — silicon, tellurium or chromium — are reacted at elevated temperatures to form ingots of doped single-crystal GaAs.

The bulk polycrystalline GaAs compound is normally formed by the reaction of As vapor with Ga metal at elevated temperatures in sealed quartz ampoules as shown in Figure 2.1-1. One process gaining favor is the commercial production of bulk single-crystal GaAs as shown in Figure 2.1-2. Here, the bulk GaAs is melted and the single crystal is slowly pulled out. The single-crystal GaAs ingot must be sandblasted and cleaned to remove exterior oxides and contaminants.

WAFER PROCESSING

Ingot Cropping

The ends or tails of the single-crystal ingot are removed using a water-lubricated single-bladed diamond saw, with various coolants added to the water.

Wafer Slicing

Gallium arsenide ingots are wax mounted to a graphite beam and sawed into individual wafers through the use of automatically operated inner diameter (ID) diamond blade saws. This operation is done wet with the use of lubricants and generates a gallium arsenide slurry.

Lapping

Wafers are wax mounted to the lapper using a hot plate, and are lapped on a machine exerting a set rotational speed and pressure. A lapping solution is fed onto the lapping surface and constitutes a slurry of aluminum oxide, glycerin and water. After a brief lapping period, the wafers are dismounted on a hot plate, rinsed in a soap solution and wiped dry.

Figure 2.1-1 SEALED QUARTZ AMPOULE GaAs GROWTH SYSTEM

1390.

1160.

790-

Distance

Figure 2.1-2 LIQUID ENCAPSULATED CZOCHRALSKI (LEC Cz) INGOT GROWTH SYSTEM 174

Reactor Czochralski

Polishing

The wafers are then physically mounted to a mechanical polishing machine, using a sodium bicarbonate, 5% chlorine, water and colloidal silica slurry.

EPITAXIAL GROWTH

The single-crystal GaAs wafers are used as substrates for the growth of very thin layers of the same or other III-V compounds having the desired electronic or optical properties. Such crystal growth, in which the substrate determines the crystallinity and orientation of the grown layer, is called epitaxy, and a variety of epitaxial growth techniques are used in III-V display and device production.

Reactor Load and Unload

The degreased and polished wafers initially receive a PRE-EPI etch and clean step. This involves a sequential wet chemical dipping operation utilizing sulfuric acid, hydrogen peroxide and water; a de-ionized water rinse; and finally, an isopropyl alcohol clean/dry.

The etch cycle is performed at the end of the growth cycle and on new quartz reactors to clean the interior surface of impurities.

Reactor Cleaning

After each growth cycle, the reactors must be opened, the wafers removed, and the lower portion of the reactor physically cleaned. The lower quartz reactor and the bottom plate (base plate) are scraped clean using a metal tool, and the particulate material (mixture of GaAs, GaAsP, arsenic oxides and phosphorus oxides) is collected in a metal container positioned below the vertical reactor.

DEVICE FABRICATION

The GaAs wafer with an epitaxially grown layer of GaAsP on the upper surface proceeds into the device fabrication processing sequence.

Wet Etching

Various mixtures of wet chemical acid solutions are used in plastic baths in locally exhausted etch stations. The primary acids In use are sulfuric hydrofluoric, hydrochloric and phosphoric. As in silicon processing, hydrogen peroxide used with sulfuric acid and ammonium hydroxide (NH4OH) provides a caustic etch.

Backlapplng

Backlapping is done to remove deposited materials from the backside of the wafer. The wafers are wax mounted to a lapper plate and wet lapped with a colloidal silica slurry.

2.2 CHEMICAL CHARACTERIZATION OF WASTE STREAMS

In order to begin any waste reduction endeavor, a complete evaluation of the chemical process must be completed. This evaluation requires the total cooperation of the facility's management, operations supervisors, operators and maintenance personnel. Hewlett Packard's San Jose facility management and staff have exemplified total cooperation in this evaluation and have made arsenic waste redaction an achievable goal.

Identification of all possible sources of arsenic required education of the investigators by means of written literature, lectures by Hewlett Packard's staff, and demonstrations and explanations by HP's process operating supervisors and staff. This education is one of the prime areas where HP demonstrated the kind of cooperation and knowledge of their facility and process that made the chemical characterization with respect to arsenic a rather comprehensive one.

Figure 2.2-1 illustrates how arsenic wastewater flows through that facility. The first three arsenic sources were thought to be minor and composed of soluble arsenic. These waste streams flow directly to the HF preholding tank and are not involved in the Slurry Recovery process. Sample acquisition for these sources required the operator to perform the wash process in a container with graduations on the sides for volume measurement. Samples were taken after the processes were completed. Arsenic analysis was done on the measured wash solution and with this analysis and the number of ingots or wafers cleaned or etched, a total arsenic contribution was calculated.

Measurements of streams 16 and 17 were made for the same reasons as streams 11 and 12. That is, for evaluation of particle size distribution and slurry recovery process evaluation. It was found that inlet fluid composition was highly dependent on which wafer manufacturing operations were being performed at the time. This obstacle led, in part, to the decision to use GaAs weight loss data on file rather than base the evaluation on such non-steady state sampling data.

Chemical analysis of the HF Treatment System Sludge Cake (#18) indicates that this material is considered to be extremely hazardous solely because of its arsenic content. Waste Extraction Tests (WET) indicate that this arsenic is in an extremely inert form and that even in its elevated concentration it produces a WET test result with a non-hazardous leachate. Our conclusion is that a 50 percent reduction in arsenic content in the sludge cake would produce a solid material classified as non-hazardous by the State of California except for fluoride content.

Arsenic analysis of the other waste streams at HP's facility completed the chemical characterization. Results are listed in Table 2.2-1 and illustrated in Figures 2.2-2, 2.2-3 and 2.2-4. Figure 2.2-2 indicates the sources and amounts of the average monthly arsenic weights that are produced at HP's San Jose facility (Table 2.2-1 data column 2). The most important point here is that nearly all (about 94%) of the arsenic that flows to the HF Treatment System is from the Slurry Recovery process and is essentially all solid GaAs particles. The remainder is entirely soluble arsenic from the cleaning and etching processes.

Figure 2.2-3 presents information tabulated in Table 2.2-1 (data column three) and illustrates the relative amounts of arsenic produced from each source with respect to GaAs solids currently recycled off site and arsenic disposed of as a hazardous waste in the sludge cake from the HF Treatment system. Daily liquid flowrates are indicated on Figure 2.2-4 and In Table 2.2-1. Here, the most important conclusion to be drawn is that a waste stream with a flowrate of approximately eight (8) gallons per day of GaAs-laden liquid overflowing to the HF Treatment System is responsible for about 94 percent of the arsenic in the sludge cake solids.

In summary, arsenic solids (GaAs) represent at least 94% of the arsenic contamination found in the sludge cake produced from the HF Treatment process. These solids are produced from physical sawing, grinding and polishing operations and are present in the overflow liquid from the Slurry Recovery process. Removal of these solids from this water flowing to the HF Treatment process by a filtration technique appears to be the most direct and simple process from a chemical engineering point of view. Although filtration is possible, a review of other

Figure 2.2-1

GALLIUM-ARSENIDE MICROCHIP MANUFACTURING ARSENIC WASTEWATER FLOW DIAGRAM

Figure 2.2-1

GALLIUM-ARSENIDE MICROCHIP MANUFACTURING ARSENIC WASTEWATER FLOW DIAGRAM

Waste Reduction Table

TABLE 2.2-1 ARSENIC PROCESS WASTEWATER DATA SUMMARY

Percent Arsenic

Arsenic to HF Treatment Total Arsenic Soluble Arsenic

Stream Liquid Flowrate Rate System and Concentration Percent Concentration

Number Stream Source (GPD) (lb/MO) Recycled Solids (mg/L) Solids (mg/L)

1.

Ingot Cleaning

0.6

0.03

0.04

<0.1

2.

Wet Etching

0.66

0.93

<0.1

3.

Furnace Cleaning

<0.1

0.02

0.03

<0.1

4.

Ingot Grinding

166.0

51.43

72.76

5.

Ingot Cropping

10.2

1.43

2.02

6.

Wafer SIi cing

11.81

16.71

7.

Wafer Profiling

0.60

0.84

8.

Lappi ng

0.77

1.09

9.

Pol i shi ng

0.23

0.32

10.

Backlapping

3.70

5.23

11.

Coolant Side Circulating Liquid

1.0

18

12.

Non-Coolant Side Circulating Liquid

13.

Overflow to HP System

7.8

11.09

15.69

1.1

15

14.

Preholding Tank Output

5,000

11.80

16.69

15.

Holding Tank Output

5,000

11.80

16.69

1.0

20

16.

Coolant Side Inlet Fluid

1.3

20

17.

Non-Coolant Side Inlet Fluid

6.9

210

18.

HF System Sludge Cake

10.85

16.69

19.

Acid Wastestream

155,000

1.18

0.0

20.

Slurry Recovery Solids

0

58.88

83.31

21.

Wastewater to Sewer System

170,000

2.13

-

0.05

<0.1

0

22.

Building 90 HF and Wastewater

0.0

<0.05

<0.1

<0

23.

Building 91 HF and Wastewater

0.0

<0.5

<0.1

Figure 2.2-2

GALLIUM-ARSENIDE MICROCHIP MANUFACTURING ARSENIC PROCESS WASTE FLOW DIAGRAM ARSENIC PRODUCTION RATES

CO M

HF & WASHWATER 23

INGOT CLEANING

0.03 lb/mo

WET ETCHING

0.66 lb/mo

FURNACE CLEANING 3

0.02 lb/mo

0.71 lb/mo

RECYCLE

INGOT GRINDING

51.43 lb/mo

INGOT CROPPING

1.43 lb/mo

WAFER SLICING

11.81 lb/mo

WAFER PROFILING 7

0.60 lb/mo

COOLANT

SIDE SLURRY RECOVERY

RECYCLE

LAPPING

0.77 lb/mo

LAPPING

CHEMICAL/

0.23 lb/mo _

PHYSICAL POLISHING "

3.70 lb/mo

BACK LAPPING 10

3.70 lb/mo

NON-COOLANT SIDE SLURRY RECOVERY

11.09 lb/mo OVERFLOW TO HF SYSTEM

11.80 lb/mo

58.88 lb/mo .wDRIED GaAs "" SOLIDS

0.0 lb/mo

HF

-►

SLUDGE CAKE

TREATMENT

FROM

SYSTEM

FILTER PRESS

0.95 lb/mo

0.95 lb/mo

ACID WASTE STREAM

1.18 lb/mo

NEUTRALIZATION SYSTEM

BUILDING 90 & 91

2.13 lb/mo

TO SEWER SYSTEM

3 us

Figure 2.2-3

GALLIUM-ARSENIDE MICROCHIP MANUFACTURING ARSENIC WASTE WATER FLOW DIAGRAM PERCENT ARSENIC TO HF TREATMENT SYSTEM AND RECYCLED SOLIDS

0.0% _

HF AND WASHWATER

Figure 2.2-3

GALLIUM-ARSENIDE MICROCHIP MANUFACTURING ARSENIC WASTE WATER FLOW DIAGRAM PERCENT ARSENIC TO HF TREATMENT SYSTEM AND RECYCLED SOLIDS

BUILDING 90

HF AND WASHWATER

TO SEWER SYSTEM 21

BUILDING 90 & 91

18

FROM FILTER PRESS

NEUTRALIZATION SYSTEM

NEUTRALIZATION SYSTEM

BUILDING 90 & 91

TO SEWER SYSTEM 21

CO U1 00

Figure 2.2-4

GALLIUM-ARSENIDE MICROCHIP MANUFACTURING ARSENIC WASTE WATER FLOW DIAGRAM DAILY LIQUID FLOWRATES

Figure 2.2-4

GALLIUM-ARSENIDE MICROCHIP MANUFACTURING ARSENIC WASTE WATER FLOW DIAGRAM DAILY LIQUID FLOWRATES

arsenic removal processes is important. In order to choose the best system for arsenic recovery, a working knowledge of arsenic chemistry is required. This knowledge, along with information regarding potential arsenic removal processes, should be considered before correct engineering design of the wastewater treatment system can be Initiated. Detailed discussions of both areas follow.

2.3 IDENTIFICATION OF POTENTIAL TREATMENT PROCESSES

The primary goal in hazardous waste reduction in a chemical process facility is to accomplish the task without impacting the process itself and to, if possible, generate a saleable product that has been generated from the waste reduction "treatment".

Table 2.3-1 lists each potential arsenic removal process evaluated in this study along with major evaluation criteria with respect to HP's GaAs processing facility. Because effective liquid solid separation was required, filtration was selected as the process of choice.

Filtration can be an extremely efficient means of separating solid particles from liquid streams. This process has been in use for many years under almost every type of chemical and physical environment. Figure 2.3-1 lists just some of the many types of filters available and their main selection criteria. For most liquid flow streams, filtration efficiency can be designed to whatever level is desired. For HP, a design efficiency of only 60 percent or better is required to eliminate the solid hazardous waste problem with respect to arsenic. Because of the ambient temperature and pressure conditions in the wastewater streams, design became dependent on the particle distribution of the solids present. In this case, a large portion of sub-micron particles were confirmed. Although successful installation of effective filtration equipment should be a matter of routine engineering practice, concern for significant wastestream changes cannot be Ignored.

Operational characteristics of the required filtration equipment, like other liquid-solid separation processes, should be relatively simple in operation and offer excellent reliability with full automation. This hands-off operation would reduce health and safety concerns to an absolute minimum.

Potential costs to HP for filtration equipment should be among the lowest of treatment processes because of: l) high efficiency; 2) minimal operating and maintenance costs (i.e., no chemical addition or residence time constraints); 3) total automation capability; and 4) the favorable ambient conditions (low temperature and pressure) for filtration.

3.0 RESULTS OF PILOT TESTING OF WASTE REDUCTION SYSTEM

Pilot testing procedures for the available filtration equipment focused primarily on the parameters most Important to the application to HP's facility GaAs wastewater cleanup (i.e., filtration efficiency, long-term backwash capability, and cycle time). Four filtration equipment vendors were selected to provide equipment for pilot testing. These vendors had long-standing reputations for providing not only quality equipment, but also service expertise necessary to evaluate system problems that occur during initial and long-term operation.

Testing procedures were established for each vendor selected for on-site demonstration of filtration equipment. These procedures were based on the need for testing data to properly complete the final equipment specifications and purchase justification.

TABLE 2.3-1

COMPARISON OF POTENTIAL ARSENIC TREATMENT PROCESSES

Arsenic Removal Process

Form of Possible

Arsenic Applicability

Most to

Effectively Hewlett

Treated Packard

Potential

Waste Reduction Efficiency for Hewlett Packard

Operational Characteristics for Hewlett Packard

Potential Health and

Safety Concerns

Potential Costs for HP Relative to Other Listed Procedures

Overall Potential Effectiveness in Reducing Hazardous Waste

1. Liquid - Solid Separation

- Fi 1tration Sol id

- Centrifugation Solid

- Settl ing Sol id

Yes Yes Yes

Excellent Excellent Good

Excellent Excellent Excellent

Low Low

Low Low Low

Excel lent Excellent Good

Preci pi tati on

- Sodium Sulfide

- Ferric Hydroxide

Soluble Soluble Soluble

No No No

Low Low Low

Not Applicable Not Applicable Not Applicable

Moderate Low

Moderate Moderate Moderate

Minimal Minimal Minimal

Coagulati on

- Ferric Sulfate

- Ferric Chloride

Soluble Soluble

No No

Low Low

Not Applicable Not Applicable

Low Low

Moderate Moderate

Minimal Minimal

Solidification

Solid

No

Low

Costly

Low

High

- Ion Exchange Resins

- Activated Carbon

- Activated Alumina

- Bauxi te

Soluble Soluble Soluble Soluble

No No No No

Low Low Low Low

Not Applicable Not Applicable Not Applicable Not Applicable

Low Low Low Low

High High High High

Minimal Minimal Minimal Minimal

Arsine Generation

Soluble

No

Low

Not Applicable

Extreme

High

SELECTION OF SEPARATION PROCESS BY PARTICLE SIZE & CONTAMINATION LEVEL

Filtration Process

Particle Size in Microns 0.0001 0.01 0.1 1 10 100

Contaminant Level* % Solids In Feed

0.01 0.1 1.0 10 100

BAG TYPE (Liquid)

CARTRIDGE

-HOLLOW PAPER

-MEMBRANE

-PLEATED MEDIA

-SINTERED METAL

-YARN WOUND

-MOLDED

-WOVEN WIRE

CENTRIFUGE

CYCLONE

FILTER PRESS

FLAT BED

ION EXCHANGE

LEAF

REVERSE OSMOSiS STRAINER VACUUM DISK VACUUM DRUM (Precoat)

1 1 1 1 1 1

1 1 1 1

1 1

1 1

o

1-1-1

oil 1

1 1 -1 1

—1 1

--h

—1—

1 1 -1-1-

—J—1—1—1—

—m 1

1 1

1

-J-1—1

1

o 1 1

H-1-1

O 1

—1-h-

—t—

Filtration Range

R.O.

Ultra

Microfiltration

O Contaminant Level Should Be Minimized By Prefiltration With More Economical Method

*0.1%=1000PPM

The purpose of demonstrating the pilot-scale operations of this filtration equipment was to provide definitive answers to the following design criteria that all would impact the final design:

o Removal efficiency of GaAs particles in wastewater o Overall equipment performance o Compatibility with the wastewater corrosion resistance o Purchase, operating and maintenance costs o Health, safety and environmental concerns

In addition, the following parameters required data for final specification.

Filter Equipment o Filter media type and pore size o Equipment Size o Materials of Construction o Backwash efficiency and frequency

Filter Press o Optimal differential pressure o Solids loading capability o Optimum operating pressure o Need for automation systems o Utility requirements o Press cake capacity o Overall equipment size o Materials of construction o Closing mechanism design o Maximum operating pressure o Cake dewatering cycle o Cake removal procedure o Need for automation systems o Utility requirements

In order to adequately assess whether the filter manufacturer's filter element was performing in the pilot test apparatus, a comparison of the filter elements performance data was made with published data.

This evaluation of filtration equipment available from these four vendors has resulted in a more realistic engineering design for GaAs solids removal equipment. The final specifications for the equipment will allow future manufacturing process changes to occur without seriously Impacting the system and represents an economically and environmentally sound method for substantially reducing arsenic waste generation where the particulate form Is involved.

This short-term pilot-scale evaluation was accomplished by testing various filtration units under the same set of process conditions. Not only did this work result in a final equipment specification, but revealed significant wafer fabrication process changes. The conclusions of this process design project are listed below:

1. Arsenic waste generation at HP's facility can potentially be reduced by almost 30,000 Kg (33 tons) per year by the installation of filtration equipment.

2. The potential cost savings to HP from installation of filtration equipment to remove GaAs solids prior to the waste water entering the HF treatment system are:

o Potential income of $100,000 per year from sale of the HF treatment solids if free from significant GaAs contamination.

o Increased revenues of at least $5,000 from GaAs direct recycling.

o Potential savings of at least j35,000 per year in HF treatment solids disposal costs.

o Reduced maintenance and health and safety management costs of about $15,000 per year from improved handling of hazardous GaAs solids.

3. Filtration equipment followed by a filter press is an effective process in separating GaAs solids from the HP arsenic wastewater.

4. Substantial submlcron GaAs solids were confirmed in the wafer fabrication waste stream that were not evident during the initial study.

5. Successful removal of GaAs submlcron particles using filtration will probably require the use of a chemical pretreatment.

6. Significant increases in total liquid flowrate requiring filtration were revealed that were not evident during the initial study.

7. The technology of arsenic waste reduction via filtration for removal of particulate arsenic from wastewater streams should be easily transferable to other semiconductor firms as well as to any other industry where heavy metal solids are produced.

The technology to be applied for removing arsenic solids is considered state-of-the-art. A flow diagram of the installed system is depicted in Figure 3-1. The arsenic removal system will be located within HP's slurry room as Indicated in Figure 3-2. This was the same location where pilot studies were carried out.

4.0 REFERENCES

1. Envirosphere Company, The Reduction of Arsenic Wastes in the Electronics Industry, Final Report. Prepared for the California Department of Health Services Toxic Substances Control Division, Alternative Technology Section, Grant No. 86-T0178, June, 1987.

2. Envirosphere Company, Process Design to Reduce Arsenic Wastes in the Electronics Industry, Final Report. Prepared for the California Department of Health Services Toxic Substances Control Division, Alternative Technology Section, Grant No. 86-T0113, June, 1988.

3. Perry, R.H., Chilton, G.H. Fifth Edition, Chemical Engineers' Handbook, Section 19, McGraw-Hill Book Company, New York, 1973.

4. Wade, R. et. al. Semiconductor Industry Study. State of California Department of Industrial Relations, Division of Occupational Safety and Health, 1981.

5. Sax, N.I. - Dangerous Properties of Industrial Materials - Sixth Edition

- Van Nostrand Reinhold Ginhold Company, New York, 1984.

6. Treybal, R.E., Mass Transfer Operations, Third Edition, McGraw-Hill Book Company, New York.

7. Schweitzer, P.A. Handbook of Separation Techniques for Chemical Engineers, McGraw-Hill Book Company, New York, 1979.

GALLIUM-ARSENIDE FILTRATION s

FLOW DIAGRAM ?

to g

Produce Technology Gaas Ingots

Figure 3-2

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