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A Batch Processing Module
Thomas F. EdgarDepartment of Chemical Engineering
University of TexasAustin, TX 78712
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
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
Batch Processing Used in Manufacturing
• Electronic materials• Specialty chemicals• Metals• Ceramics• Polymers• Food and agricultural materials• Biochemicals• Multiphase materials/blends• Coatings• Composites
Representative processing steps in a semiconductor wafer fab(Deposition, Patterning, Etching, Doping, etc)
Unit operations in microelectronics manufacturing are characterized by:
1. Physical/chemical complexity2. Inability to measure directly many
process variables3. High sensitivity to process changes4. Multiple inputs/multiple outputs
CD Variation Effects in Pattern Transfer
WaferFlatnessReflectivityTopography
Resist
ReticleCDDefectsEdge Roughness Proximity Effects
Refractive Index ThicknessUniformityViscosityContrast
PEB
TemperatureUniformityTimeDelay
AberrationsLens HeatingFocusLevelingDose
Stepper
Develop
PowerPressureFlow rates
TimeTemperatureDispense PatternRinse
Etch
Environment
AminesHumidityPressure
Why Control Critical Dimension (CD)?• Small changes in CD distribution = Large $ values lost
290
Higher speed
Gate CD (nm)
210 230 250 270
Zero
Yie
ld(H
igh
leak
age)
Zero
Yie
ld(L
ow c
ondu
ctan
ce)
3σ = 12nm
3σ = 36nm
Control Hierarchy in Batch Processing
1. Sequential control to step the process through a recipe
2. Logic control to deal with device interlocks3. Within-the-batch control to make set point
changes and reject disturbances4. Run-to-run control to meet final quality
constraints5. Batch production control to maximize utilization
of equipment and minimize cycle time
Figure 22.19 Batch control system – a more detailed view
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
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)
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
Silicon Substrate
STI STI
Poly Silicon
Gate Oxide
SiONTrimmed
Resist
Results – Increased Cpk
0
10
20
30
40
-1 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Normalized Deviation From Target
Freq
uenc
yPrior to APC Implementation
With Automated Run-to-Run Control
Metric Uncontrolled Controlled % ChangeMean Deviation From Target -0.201 0.045 -77%
Standard Deviation 0.254 0.188 -26%Cpk 1.05 1.7 +62%
Figure 22.17 Multiproduct batch plant
Characteristics of batch scheduling and planning problems (Pekny and Reklaitis)
GIVEN
Product requirementsHorizon, demands, starting andEnding inventories
Operational stepsPrecedence orderResource utilization
Production facilitiesTypes, capacities
Resource limitationsTypes, amounts, rates
DETERMINE
WhatProduct amounts: lot sizes, batchSizes
WhenTiming of specific operations, runlengths
WhereSites, units, equipment items
HowResource types and amounts
Multi-Product Processing Overview
Process 2
Fab Tool
Process 1
AB BBA A
Process 2
Fab Tool
Process 1
A A A A
Fab Tool
Process 1AB BBA A
Metrology Variations
0
0.5
1
1.5
2
2.5
3
3.5
4
A B C D E
Correct MetrologyOrdering
0
0.5
1
1.5
2
2.5
3
3.5
4
E D C B A
Incorrect MetrologyOrdering
0
0.5
1
1.5
2
2.5
3
3.5
4
C D A E B
Incorrect MetrologyOrdering
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
A B C D E
Process
Integration Across StandardChE Courses
• discrete logic in process operations• design for safe operation• measurement strategies (e.g., end point)• batch vs. semibatch (bioreactors)• use of fundamental (nonlinear) models• numerical methods, statistics• population balances• case studies