1 The 1.7 kg Microchip Eric Williams, United Nations University Robert U. Ayres, INSEAD Miriam Heller, NSF.

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The 1.7 kg Microchip

Eric Williams, United Nations University

Robert U. Ayres, INSEAD

Miriam Heller, NSF

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Motivations

Growth of IT industry: macro-economic scale and continued high growth (average annual growth of global semiconductor industry is 16% per year in recent decades) .

What are the environmental implications of this new industry? Are there general trends in relationship between high-tech economy and materials use/environment?

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Life cycle inventory of microchip

• Estimate life cycle inventory of energy and aggregate chemical use for production of common microchip.

• Energy use is good indicator of impacts on climate change and fossil fuel use. Aggregate chemical use is poor indicator of impacts on local soil, air, water systems.

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Guiding principles

Only use publicly available sources, fully report all data and assumptions used.

1. Critically compare different data sources for different processes.

2. Compare final results with those from other groups and deconstruct differences.

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Key Processes

１． Wafer Fabrication

2. Quartz to Silicon wafers

3. Semiconductor-grade chemicals

4. Assembly

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Wafer Fabrication 1

Waf

er

Fab

ricat

ion

Chemicals: gramsDopants .01 Photolith. 14 Etchants .23Acids/bases 31 Total 45

Fabricated wafer: .16-.94 cm2

Elemental gases: grams(N2,He,Ar,H2,O2) 556

Water: 20 liters

Electricity: 1.5 kWhDirect fossil fuels: 1 MJ

Silicon wafer: 1 cm2 = .16 grams

Inputs: Outputs:

Wastewater: 17 kg

Solid Waste: 7.8 kg

Air emissions : -

Material inputs to semiconductor fabrication (anonymous firm data)

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Chemical input :Compare data sources

Aggregate chemical input/emission

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Energy use in fabrication

Various sources suggest 1.4-1.6 kWh of electricity consumed per cm2 of wafer processed, 80-90% of total energy use is electricity. Data reflects aggregate of national industries.

Data sources: Census, JEIDA, Semiconductor Industry Association, Microelectronics and Computer Technology Corporation (MCC)

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Water use in fabrication

Take “typical” figure as 20 liters/cm2

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Data Source Water use

(liters/cm2)

Peters et. Al.

Semiconductor International, 98

18-27

Genova and Shadman

SEMATECH report, 97

5-29 (17)

MCC Life cycle study of workstation, 93

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From quartz to wafers 2

Production of silicon wafers requires around 160 timesThe energy required for “industrial” grade silicon

Stage Elect energy input/kg silicon

SiliconYield 

Data sources

Quartz + carbon → silicon

13 kWh 90% Harben, 99; Dosaj, 97Jackson, 96

Silicon → trichlorosilane

50 kWh 90% Takegoshi, 94; O’Mara et al, 90

Trichlorosilane → polysilicon

250 kWh 42% Tsuo et.al, 98; O’Mara, 90;Takegoshi, 94

Polysilicon → single crystal ingot

250 kWh 50% Takegoshi, 94 

Single crystal ingot → silicon wafer

240 kWh 56% Takegoshi, 94;Lammers and Hara, 96

Process chain to produce wafer

2,130 kWh 9.5%  

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Chemical inputs to fabrication

• Semiconductor grade chemicals/gases typically 99.999-99.9999% purity, requires substantial purification, for which no data was available.

• Data used reflects production of industrial grade chemicals (used Boustead database, other LCA databases same).

• Distillation processes are, in general, energy intensive.

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Assembly

Energy use: .34 kWh per cm2 of input silicon.

Material inputs: packaging material (epoxy, ceramic), lead frame (copper, aluminum), processing chemicals.

Data sources: MCC, JEIDA

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LCA of 32MB DRAM chip

Combine previous process data with information on wafer yields for 32MB DRAM chips (Semiconductor International, 1998): 1.6 cm2 of input wafer per chip.

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Energy use for different stages in life cycle of 32 MB DRAM chip

Breakdown of life cycle energy use in production and use of 1 2-gram memory chip

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Fossil fuel, chemical, and water use

For 1 memory chip, lower bounds are:• Fossil fuels consumed in production = 1,200

grams• Fossil fuels consumed in use = 440 grams• Chemicals “destructively” consumed = 72 grams• Water use is 36,000 grams per chip.

Total fossil fuel and chemical use to produce 2 gram memory chip 1.7 kg

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Secondary materialization

Measure material and energy intensity: secondary materialization index (SMI):

Secondary materials counted are only those obviously “destructively consumed”: fossil fuels and chemicals (water and elemental gases not included).

SMI index for various products:Microchip: 640

Automobile ： 1-2 Refrigerator: 2

product final of Weight

consumed materialssecondary of WeightSMI

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Why so different?

Despite trivial physical weight, “secondary” weight of chips is substantial.

Why such a dramatic figure?

Postulate: Because chips are exceedingly highly organized (low entropy) objects, the materials and energy required for processing is especially high.

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Entropy analysis

Estimate order of magnitude of entropy changes associated with final product and producing high-grade inputs:

• Mesoscopic order of microchip: use S=-k ln W and checkerboard model. Cell length = 1 μm Board length = die size = 1 cm. result:

Entropy (at room temp) = 9.5x10-20 J per memory chip

• Ultra-high purity water (tap water – 100 ppm impurities, fab water - 1 ppb). Use entropy of mixing: ΔS= -R [(1-x) ln (1-x) + x ln x ] (x = impurity concentration) result

Entropy change (at room temp) = 17 J/kg of pure water

Magnitudes of entropy change much lower than energy use - does not explain practical experience of high energy needed for pure materials.

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Third law of thermodynamics for purity as well as temperature?

Third law of thermodynamics (Nernst, 1906): it is impossible to reach absolute zero in a finite number of reversible steps

Analogous phenomenon for purity? Conjecture: energy efficiency of purification decreases as one approaches perfect purity.

Conjecture:• 100% purity is impossible (no perfect vacuum)

It follows that all purification processes have efficiency <1 and achieving higher purity with given process requires increasing # of steps (e.g. .9 x .9 x .9 ….)

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Secondary materialization

Many advanced materials/products are also low entropy. Does their proliferation imply increase in SMI of overall economy?

The possibility of this is called secondary materialization

Not known if significant, but suggests importance of life cycle materials studies to clarify. Need to carefully treat chemicals industry and purification/materials processing.

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Hybrid LCI for desktop computer

Analysis of energy use in production of desktop computer with 17-inch CRT monitor

Hybrid method that splits estimation into process and economic IO pieces.

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ItemElectricity use (kWh/unit)

Direct Fossil(MJ/unit)

Total Energy(MJ/unit)

Production

Process analysis

Semiconductors 170 298 909

Printed circuit boards 10.3 26.7 64

CRT manufacturing/assembly 7.7 113 140

Bulk materials - control unit NA NA 765

Bulk materials - CRT NA NA 795

Silicon wafers 39 NA 140

Computer assembly 60 119 335

IO analysis

Electronic materials/chemicals (excluding wafers) 32 338 453

Semiconductor fab. equipment 30.5 366 476

Passive components 9.1 127 160

Other parts assembly: disk drives, CD-ROM,etc. 16 273 330

Air and ground transport 3.8 459 473

Other processes 105 1920 2300

Total production 483 4039 7340

Use phase: home user (3 year lifespan) 420 0 1514

Total production + use phase 904 4039 8850

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Commentary

For desktop, production phase is 83% of total life cycle energy, very high share compared to other appliances such as refrigerator, which has 12% in production phase.

Combination of high energy intensity in production and short lifespan imply that lifespan extension is key approach that should be pursued in policy for managing impacts of IT equipment.

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ThankYou

Eric Williams

[email protected]