13. Conditions of successful semiconductor
wafer fab
Robust technology (process and design) – follow the
Design for Manufacturability (DFM) rules
Efficient operation (from equipment layout to
automation system design, to daily operation etc.)
Built-in quality in the operation (quality degradation
wastes resources.)
Scrap
Downgrade
Lost yield
13
14. Operation cost
Operation can determine chip cost to a large extent.
Chip cost breakdown:
Wafer cost (equipment depreciation, labor, utility, fab
depreciation, raw materials, automation system)
Cost of quality (scrap, downgrade)
Yield (wafer, die, package)
Backend cost
Balance quality cost
14
16. Challenge 1 - dynamic
Every manufacturing operation is unique.
Manufacturing is dynamic that is constantly changing.
Managing manufacturing has large momentum, a decision
can change the course and make it difficult to turn around.
16
17. Challenge 2 - organizational
Manufacturing is a large organization > 5,000 people/ fab
Multi-fab manufacturing is even more complicated
Complicated organization – formal (department) and
informal organization (project, task force); many
disciplines
Indecision or conflict of directions waste resources.
A good operation requires precipitation of every member in
the factory with clear understanding of his daily, weekly,
monthly goals.
Goals for each member, each team/ task force/department
must be coherent.
17
18. Challenge 3 – systematic
Managing by system rather than managing by personal
judgment (mostly biased)
Personal judgment introduces many variations.
Consequences of these variations may not be traceable.
System based management decisions, based on the most
updated and accurate data, make the operation consistent,
independent of the personal decisions
Operation theory can help.
A good manufacturing system will reduce complex
operations into easy to follow goals at different levels
18
19. Challenges 4 – resources conflict
Production, engineering (equipment, process and
product), quality and R&D are often competing for
the same resources.
Priority setting
19
20. Challenges 5 - constrains
Manufacturing operation is not an isolated
operation. It has to exist and operate under the
business context.
Factory priority is often set by business priority
and financial requirements
20
21. Challenge 6 – escalating cost
Cost escalating because:
1. Equipment is more
expensive
2. Process becomes longer
3. Economic scale
becomes larger
21
23. Manufacturing efficiency
Productivity is measured by number of wafers
processed per day (DGR – daily going rate, or moves)
and inventory turn rate
Example: 60k/month capacity, 1,000 steps process
60k/mth *1,000 steps/30 days = 2,000 k moves per day
if each equipment can process 100 w/hr, and works 20
hours a day, we need 1,000 pieces of equipment
Turn = moves/ WIP or WIP = 2,000 k / turn
CT = total process steps/ turn
If turn =10, WIP = 200 k, CT = 1,000/10 = 100 days
Productivity = added value/ cost
23
29. Principle
Improve the efficiency of all resources (man, machine,
method, materials)
Organization
Tool management
Process management
WIP management
Improve the efficiency of their interaction
Operating Curve Management (OCM)
Resources synchronization
29
30. Tools and systems that can help
Production system (OCM, workflow)
Automation (factory, equipment, data)
ISO 9000
30
31. OCM (OPERATING CURVE MANAGEMENT)
31
Derived from
Queuing theory and
Operational Research
in the Industrial
Engineering
(raw process time)
32. OCM
Use operation techniques to reduce α and increases
capa
32
Wafer fab loading
33. How to improve α
To reduce α, one must reduce the variability in the line.
Achieve line balance using line control methodology:
WIP management
Accurately forecast WIP for bottleneck equipment
Establishalert for coming WIP too high or too low
Using dispatch rules to divert WIP flow
Priority setting consistent with reducing variability
Addressing bottleneck issues
Minimize disturbance
33
34. Cycle time
Flow factor (FF) is the normalized cycle time
Too long cycle time is bad:
Increase cost of WIP
Decrease quality
The curve (FF vs. UU) can be represented by
FF=α*[UU/(1-UU)]+1
Where FF is the flow factor [=CT/RPT] and UU is
the loading factor and α is the manufacturing
variability
34
35. Cycle time breakdown
Raw processing time
Queue time (waiting for tools, operator, WIP)
Hold time (waiting for engineers/ process)
Transport time
35
Raw Queue time Transport Hold
Process time time time
cycletime
FF = 1 +
40. Improve efficiency of human
resources
40
diffusion etch
photo
Thin film
operator
Eq eng
Proc eng
cell
department
A working cell involves operators, process engineers, equipment
engineers, integration. The communication and cooperation among
the working cell members are critical to the performance of the cell
42. Improve organization efficiency
Streamline workflow
Lean organization
System driven operation
Management by objectives
ISO 9000 compliance
42
43. Improve process efficiency
Process standardization
Process simplification
Yield improvement (excursion wafers require large
resources to manage)
Robust process design
Unnecessarily tight process spec reduces efficiency
without buying more quality or yield
43
44. Improve tool efficiency
“Tools” is the most expensive partner
Two components
For 40 w/m capacity fab making 32 nm DRAM product:
Depreciation ~ 60% of wafer cost
Maintenance ~ 14% of wafer cost
44
47. Reason for the economic scale
0
2
4
6
8
10
12
equipment 1 equipment 2 equipment 3 equipment 4
Excess capacity
Identifying and improving the capacity of bottleneck
equipment is a sure way to increase overall fab capacity
Bottleneck equipment
47
48. Factors determining depreciation
per unit output
Equipment purchasing price
Capacity balance
Fab utilization
Equipment utilization (including uptime and capacity
balance)
Throughput
48
49. Depreciation bench mark
The equipment of a fab with 60K/m for 15 nm
technology costs $ 6 B
6 years (72 months) depreciation
Depreciation cost per wafer: $6,000,000,000
/72/60,000=$1,389
The total wafer cost is around $2,315 (assuming
depreciation cost is 60%)
Wafer selling price $4,000
49
50. Equipment management
Equipment performance is defined by SEMI standards
SEMI E10 defines the equipment state of operation
SEMI E35 defines Cost of Ownership (COO)
SEMI E79 defines Overall Equipment Efficiency (OEE)
SEMI E58 defines Automated Reliability, Availability,
Maintainability Standard (ARAMS)
SEMI E124 defines Factory Level Productivity
50
52. Two major down times
Scheduled down
Make scheduled down effective
Unscheduled down
Reduce the frequency of unscheduled down
Minimize the time spent on unscheduled down
52
53. Scheduled down is the preventive maintenance
Daily, weekly, monthly, quarterly, yearly
How long takes to do maintenance
Effectiveness of scheduled down (If preventive
maintenance is done correctly, there should be no
unscheduled down.)
Review necessity of parts change
Bench mark different equipment of the same
equipment type
53
54. Unscheduled down time
Unscheduled down usually causes product damage. Its loss is
four folds-
Depreciationand maintenance
Productscrap, downgrade or rework
Extra resources to sort out damaged wafers, additional testing
and inspection
Delayed output
54
Step n Step n+1 Step n+2 Step n+3
Problem
happened
Problem
detected
Damaged
wafers
t2
t1
Metrology step
55. Minimize unscheduled down time
Unscheduled down maintenance requires two steps:
Diagnosis
Repair
Diagnosis time can be shortened by equipment
automation. EAP extracts all data from equipment in
real time.
Repair time can be shortened by proper maintenance
kit.
55
56. Monitoring tool performance
Compile trend charts for MTBF (Mean Time
Between Failure) and MTTR (Mean Time to Repair)
Compile trend chart data for the total equipment
maintenance cost (parts/ labor for both internal and
outsourcing)
Add maintenance cost to the equipment cost to
determine the cost of ownership
56
57. Predictive maintenance
Predictive maintenance is to monitor the equipment
status in real time. Any deviation will send alert to do
potential predictive maintenance.
Predictive maintenance requires extensive automation
(requires Fault Detection System).
57
59. WIP efficiency: Line balancing
To avoid capacity loss due to lack of WIP
According to OCM, too much WIP will slow down
cycletime.
The ideal WIP should be set up according to the daily going
rate of the equipment
In average, WIP should not spend more than 1 hour in
waiting before processing
Balance line has the same WIP turn rate at each process
step
59
60. How to do line balancing
Line balance improves α
Line balance is achieved by using effective WIP
dispatching
Both too much WIP and too little WIP are not
desirable
WIP arriving rate to an equipment should match its
throughput
Effective WIP dispatching needs to forecast WIP
distribution at least 3 hours ahead. This is done by
simulation with dispatch rules using the real-time WIP
distribution data
60
62. Make sure there is steady flow of
WIP from EQ 1 to EQ 2
EQ 1
EQ 2
AMHS
62
63. Wafer fab processes centered
around photomasking
photo
implant
diffusion
deposition
etching
oxidation
63
64. Dynamic capacity bottleneck
Many events create disturbance in line balance.
Unscheduled equipment down creates a
temporarily bottleneck.
This bottleneck is dynamic because it always
changes.
Many dynamic bottlenecks can happen at the
same time.
Identifying and resolving the dynamic bottlenecks
are the major task of the wafer fab operation.
64
65. How to find dynamic bottleneck
Determine WIP turn rate for each equipment or
process step
Turn rate = total moves in 24 hours/ average WIP
Rank turn rate
Process steps with smallest turn rates are dynamic
bottleneck
Priority of equipment maintenance should be given to
the dynamic bottleneck equipment
65
66. Daily management of WIP
日常在制品管理
66
bottleneck
bottleneck
This should be done by process steps, each equipment, equipment types and
equipment groups and process areas.
67. To improve line balance
Bottleneck equipment should be given highest priority for
maintenance
Relationship between line balancing and production
efficiency (α) should be carefully monitored
Manufacturing system should flash alert for the equipment
type with inventory turn trending down for prolong period
or below certain value
Using dispatching to avoid sending WIP to the
downstream bottleneck
Avoid equipment, operator and process recipe dedication if
possible
67
68. Gap Analysis
one shot view of operation status
68
Gap too large
FF too large
efficient production
In-efficient production
cycletime
Unused capacity
target
70. Link projects to performance index
Production
smoothness
index
Daily going rate
Production engineering department is responsible for line balance.
70
71. Loss of productivity due to quality
issue
Excursion
Wafer scrap, downgrade
Yield loss
New lots need to be issued
Engineering resources to debug the problem
Experiment
Equipment re-qualification
Process re-qualification
Quality problem is more than just quality. It is also a
productivity problem.
71
74. Schematics of automation system
74
AHMS: Automatic Materials handling System
MES: Manufacturing Execution System
PDM: Production Database Management
SPC: Statistical Process Control
APC: Advanced Process Control
RMS: Recipe Management System
EAP: Equipment Automation Program
PKD: Process Knowledge Database
EDA: Engineering Data Analysis
PKD
Qua
lity
sys
Customer
Service
sys
EDA
Data
Automation
EQ
automation
75. Advanced Process Control
•Fault Detection System (FDS)
•Statistical Process Control
•Process Recipe Management
•Run to Run Control
•Tool Preventive Maintenance
•Equipmentdown diagnsis
Tool
Equipment
Automation
Interface
Equipment Data Collection
New sensor :
plasma sensor
75
78. Real time process performance
monitoring
Tool Interface
Sensor signals
Filter
Qualified data
Database
Model
Process Performance
Disqualified data
Data adaptation
Discard
N
y
78
79. Yield enhancement system
79
A yield enhancement
system includes:
• data collection
• data analysis
• algorithm to determine
yield loss mechanisms
• corrective actions
80. Conclusion
There are many theories and applied techniques for
the manufacturing operation.
These theories and techniques need to be adapted to
fit different situations of each factory.
Sophisticated automation systems are required to
handle quickly changing production environment.
Modern wafer fab manufacturing system is a prelude
to the industry 4.0.
80