Transcript Eric Williams

The 1.7 kg Microchip
Eric Williams, United Nations University
Robert U. Ayres, INSEAD
Miriam Heller, NSF
1
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?
2
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.
3
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.
4
Key Processes
１．Wafer Fabrication
2. Quartz to Silicon wafers
3. Semiconductor-grade
chemicals
4. Assembly
6
1
Wafer Fabrication
Inputs:
grams
.01
14
.23
31
45
Elemental gases:
(N2,He,Ar,H2,O2)
grams
556
cm 2
Silicon wafer: 1
=
.16 grams
Electricity:
1.5 kWh
Direct fossil fuels: 1 MJ
Water:
20 liters
Fabricated wafer: .16-.94 cm2
Wafer
Fabrication
Chemicals:
Dopants
Photolith.
Etchants
Acids/bases
Total
Outputs:
Wastewater: 17 kg
Solid Waste: 7.8 kg
Air emissions : -
7
Material inputs to semiconductor fabrication (anonymous firm data)
Chemical input :
Compare data sources
1
Aggregate chemical input/emission
9
Energy use in fabrication
1
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)
10
Water use in fabrication
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
58
1
Take “typical” figure as 20 liters/cm2
11
From quartz to wafers
2
Stage
Elect energy
input/kg silicon
Silicon
Yield
Data sources
Quartz + carbon →
silicon
Silicon →
trichlorosilane
Trichlorosilane →
polysilicon
13 kWh
90%
50 kWh
90%
250 kWh
42%
Harben, 99; Dosaj, 97
Jackson, 96
Takegoshi, 94;
O’Mara et al, 90
Tsuo et.al, 98; O’Mara,
90;Takegoshi, 94
Polysilicon →
single crystal ingot
250 kWh
50%
Takegoshi, 94
Single crystal ingot →
silicon wafer
Process chain to
produce wafer
240 kWh
56%
Takegoshi, 94;
Lammers and Hara, 96
2,130 kWh
9.5%
Production of silicon wafers requires around 160 times
The energy required for “industrial” grade silicon 12
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.
3
13
Assembly
4
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
14
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.
15
Energy use for different stages in
life cycle of 32 MB DRAM chip
56.1
60
50
40
27.1
30
20
5.8
total
use
assembly
materials
0.17
assembly
process
2.3
fabrication
0
5.8
chemical
production
10
15.0
silicon
chain
Energy (MJ per chip)
Breakdown of life cycle energy use in production
and use of 1 2-gram memory chip
16
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
17
Secondary materialization
Measure material and energy intensity:
secondary materialization index (SMI):
Weight of secondarymaterials consumed
SMI 
Weight of final product
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
18
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.
19
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.
20
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 ….)
21
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.
22
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.
23
Item
Electricity 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
7.7
113
140
CRT manufacturing/assembly
Bulk materials - control unit
NA
NA
765
Bulk materials - CRT
NA
NA
795
NA
140
Silicon wafers
39
Computer assembly
60
119
335
32
338
453
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
IO analysis
Electronic materials/chemicals (excluding wafers)
Semiconductor fab. equipment
24
8850
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.
25
Thank
You
Eric Williams
[email protected]
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