Batch Processing – Definition,
Advantages, Disadvantages
• A sequence of one more steps (recipe) usually
carried out in more than one vessel and in a
defined order, yielding a finished product
• Production amounts are usually smaller than for
continuous processing
• Requires reduced inventories and shorter
response times
• Final product quality must be satisfied with each
batch (no blending)
• More emphasis on production scheduling in
batch processing
1
Other Advantages
• Batch time can be adjusted to meet quality
specs
• Repetition is conducive to continuous
improvement in product
• Slow dynamics permit real-time calculations
• Greater agility
2
3
Batch Processing Used in
Manufacturing
•
•
•
•
•
•
•
•
•
•
Electronic materials
Specialty chemicals
Metals
Ceramics
Polymers
Food and agricultural materials
Biochemicals
Multiphase materials/blends
Coatings
Composites
4
Representative processing steps in a semiconductor wafer fab
(Deposition, Patterning, Etching, Doping, etc)
5
Unit operations in microelectronics
manufacturing are characterized by:
1. Physical/chemical complexity
2. Inability to measure directly many
process variables
3. High sensitivity to process changes
4. Multiple inputs/multiple outputs
6
CD Variation Effects in Pattern Transfer
Wafer
Reticle
Flatness
Reflectivity
Topography
Refractive Index
Thickness
Uniformity
Viscosity
Contrast
Resist
CD
Defects
Edge Roughness
Proximity Effects
Temperature
Uniformity
Time
Delay
PEB
Stepper
Aberrations
Lens Heating
Focus
Leveling
Dose
Time
Temperature
Dispense Pattern
Rinse
Develop
Etch
Power
Pressure
Flow rates
Amines
Humidity
Pressure
Environment
7
Silicon Integrated Circuit
Technology Roadmap
8
Comparative Economics
Revenue/Capital1
Chemical & Petrochemical
22.4
Pharmaceutical
Semiconductor
19.6
6.8
• Capital productivity is a major driving force
for semiconductors
_______________
1From
1997 US Census Bureau
9
Why Control Critical Dimension (CD)?
• Small changes in CD distribution = Large $ values lost
Zero Yield
(Low conductance)
Zero Yield
(High leakage)
Higher speed
3s = 36nm
3s = 12nm
210
230
250
Gate CD (nm)
270
290
10
Figure 19.1 The five levels of process control and optimization in
manufacturing. Time scales are shown for each level.
11
Control Hierarchy in Batch
Processing
1. Sequential control to step the process through
a recipe
2. Logic control to deal with device interlocks
3. Within-the-batch control to make set point
changes and reject disturbances
4. Run-to-run control to meet final quality
constraints
5. Batch production control to maximize utilization
of equipment and minimize cycle time
12
Batch Mixing Tank-Operations
Sequence
1. Introduce liquid A until level reaches LH2
2. Close A valve, open B valve and start
mixer
3. When level reaches LXH2, stop flow of B
and the mixer and open discharge valve
(VN9)
4. Discharge product until level reaches
LL2, then close the discharge valve.
13
Figure 22.7
14
Graphical Description of Batch
Sequence
•
•
•
•
Information flow diagram
Sequential function chart
Binary logic diagram
Ladder logic diagram
15
Figure 22.8
16
Within-the-Batch Control:
Operational Challenges
• Time-varying process characteristics (no
steady state)
• Nonlinear behavior
• Model inaccuracies
• On-line sensors often not available
• Constrained operation
• Unmeasured disturbances
• Irreversible behavior
17
18
1000C
Temperature
0
Time
10 sec
Figure 3. Definition of bring-in (Rapid Thermal Processing)
19
Run-to-Run (RtR) Control
• Keeps batch process product on target by using
feedback to manipulate batch recipe for
consecutive batches
• Required due to a lack of in situ, real-time
measurements of product quality of interest
• Extremely useful where initial conditions or tool
states are variable and unmeasurable
• Supervisory controller determines optimal
setpoints for real-time control loops (typically
PID)
20
RtR Control
• Predominantly used in semiconductor and
batch chemical industries
• Can be viewed as discrete-time process
(k, k+1, k+2 … vs. t)
• Good for treating drifting processes (e.g.
reactor fouling)
• Run-to-run optimization can be performed
using process model
• Integrates with fault detection
21
Use of RtR Control
• Examples of events which can have slow
dynamics or infrequent step changes
-
-
equipment aging
periodic machine maintenance
changes in feedforward signal
- measure disturbance
major fault, such as instrumentation
degradation
22
Application: Resist etch process
•
The incoming pattern is masked
with linewidths greater than
required.
•
An additional step is added to the
etch process which etches the
resist pattern.
•
The resist etch step trims the
lines to the proper resist linewidth.
•
The rest of the etch transfers the
resulting mask pattern into the
polysilicon, creating the poly gate
structures.
Linewidth
SiON
Trimmed
Resist
Poly Silicon
STI
Gate Oxide
Silicon Substrate
STI
23
Results – Increased Cpk
40
Prior to APC Implementation
With Automated Run-to-Run Control
Frequency
30
20
10
0
-1
-0.9
-0.8
-0.7
-0.6
-0.5
-0.4
Metric
Mean Deviation From Target
Standard Deviation
Cpk
-0.3 -0.2 -0.1
0
0.1 0.2 0.3
Normalized Deviation From Target
Uncontrolled
-0.201
0.254
1.05
0.4
0.5
0.6
0.7
0.8
Controlled
0.045
0.188
1.7
0.9
1
% Change
-77%
-26%
+62%
24
Reduction in STI Rework with RtR
Fab 25 STI Rework Rate
6.00%
Standard SPC Charting
Process Control
Manual Implementation
of APC Algorithm
Percent Rework
5.00%
Automated Implementation
of APC Algorithm
4.00%
3.00%
2.00%
1.00%
0.00%
1998 Work Week
25
Figure 22.19 Batch control system – a more detailed view
26
Characteristics of batch scheduling and
planning problems (Pekny and Reklaitis)
DETERMINE
GIVEN
What
Product amounts: lot sizes, batch
Sizes
Product requirements
Horizon, demands, starting and
Ending inventories
When
Timing of specific operations, run
lengths
Operational steps
Precedence order
Resource utilization
Where
Sites, units, equipment items
Production facilities
Types, capacities
How
Resource types and amounts
Resource limitations
Types, amounts, rates
27
Welcome to the Real World!
• For a real lot in a real fab, there are:
–
–
–
–
–
–
–
–
Reworks
Different process equipment at previous steps
WIP ordering/processing
Equipment/Consumable material changes
Recipe changes/adjustments
Scheduled/Unscheduled maintenance
Multiple reticle instances
Engineering lots
28
Figure 22.17 Multiproduct batch plant
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Multi-Product Processing Overview
Fab Tool
A
B
B
A
A
B
Process 1
Fab Tool
Process 1
A
A
A
A
Process 2
Fab Tool
Process 1
A
B
B
A
A
B
Process 2
30
Metrology Variations
4
3. 5
3
Correct Metrology
Ordering
2. 5
2
1. 5
1
0. 5
Process
0
A
B
C
D
E
2
4
1. 8
3. 5
1. 6
1. 4
3
1. 2
2. 5
1
Incorrect Metrology
Ordering
2
0. 8
1. 5
0. 6
1
0. 4
0. 5
0. 2
0
0
A
B
C
D
E
E
D
C
B
A
4
3. 5
Incorrect Metrology
Ordering
3
2. 5
2
1. 5
1
0. 5
0
C
D
A
E
B
31