1. 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

2. 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

4. Batch Processing Used in Manufacturing
Electronic materials
Specialty chemicals
Metals
Ceramics
Polymers
Food and agricultural materials
Biochemicals
Multiphase materials/blends
Coatings
Composites

5. Representative processing steps in a semiconductor wafer fab
(Deposition, Patterning, Etching, Doping, etc)

6. Unit operations in microelectronics manufacturing are characterized by:
Physical/chemical complexity
Inability to measure directly many process variables
High sensitivity to process changes
Multiple inputs/multiple outputs

7. CD Variation Effects in Pattern Transfer
Wafer
Reticle
Stepper
Etch CD
Defects
Edge Roughness
Proximity Effects
Aberrations
Lens Heating
Focus
Leveling
Dose
Power
Pressure
Flow rates
Flatness
Reflectivity
Topography
Refractive Index Thickness
Uniformity
Viscosity
Contrast
Temperature
Uniformity
Time
Delay
Time
Temperature
Dispense Pattern
Rinse
Amines
Humidity
Pressure
Resist
PEB
Develop
Environment

8. Silicon Integrated Circuit Technology Roadmap

9. Comparative Economics
Revenue/Capital1
Chemical & Petrochemical 22.4
Pharmaceutical
Semiconductor
Capital productivity is a major driving force for semiconductors
_______________
1From 1997 US Census Bureau

10. Why Control Critical Dimension (CD)?
Small changes in CD distribution = Large $ values lost
Higher speed
Gate CD (nm)
210
230
250
270
Zero Yield
(High leakage)
(Low conductance)
3s = 12nm
3s = 36nm
290

11. Figure 19.1 The five levels of process control and optimization in
manufacturing. Time scales are shown for each level.

12. Control Hierarchy in Batch Processing
Sequential control to step the process through a recipe
Logic control to deal with device interlocks
Within-the-batch control to make set point changes and reject disturbances
Run-to-run control to meet final quality constraints
Batch production control to maximize utilization of equipment and minimize cycle time

13. Batch Mixing Tank-Operations Sequence
Introduce liquid A until level reaches LH2
Close A valve, open B valve and start mixer
When level reaches LXH2, stop flow of B and the mixer and open discharge valve (VN9)
Discharge product until level reaches LL2, then close the discharge valve.

14. Figure 22.7

15. Graphical Description of Batch Sequence
Information flow diagram
Sequential function chart
Binary logic diagram
Ladder logic diagram

16. Figure 22.8

17. 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

19. 1000C
Temperature
Time sec Figure 3. Definition of bring-in (Rapid Thermal Processing)

20. 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)

21. 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

22. 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

23. 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

24. Results – Increased Cpk

25. Reduction in STI Rework with RtR
Fab 25 STI Rework Rate
0.00%
1.00%
2.00%
3.00%
4.00%
5.00%
6.00% 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41
1998 Work Week
Percent Rework
Manual Implementation
of APC Algorithm
Automated Implementation
Standard SPC Charting
Process Control

26. Figure 22.19 Batch control system – a more detailed view

27. Characteristics of batch scheduling and planning problems (Pekny and Reklaitis)
DETERMINE
What
Product amounts: lot sizes, batch
Sizes
When
Timing of specific operations, run
lengths
Where
Sites, units, equipment items
How
Resource types and amounts
GIVEN
Product requirements
Horizon, demands, starting and
Ending inventories
Operational steps
Precedence order
Resource utilization
Production facilities
Types, capacities
Resource limitations
Types, amounts, rates

28. 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

29. Figure 22.17 Multiproduct batch plant

30. Multi-Product Processing Overview
Fab Tool
Multi-product / Single Process
Process 1 A B B A A B
Fab Tool
Single Product / Multi-process
Process 1 A A A A
Process 2
Fab Tool
Multi-product / Multi-process
Process 1 A B B A A B
Process 2

31. Metrology Variations Correct Metrology Ordering Process
Incorrect Metrology
Ordering
Incorrect Metrology
Ordering