Batch Processing – Definition, Advantages, Disadvantages

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 Temperature Uniformity Time Delay Time Temperature Dispense Pattern Rinse Amines Humidity Pressure Refractive Index Thickness Uniformity Viscosity Contrast Resist PEB Develop Environment

8. Silicon Integrated Circuit Technology Roadmap

9. Comparative Economics Revenue/Capital1 Chemical & Petrochemical 22.4 Pharmaceutical 19.6 Semiconductor 6.8 • Capital productivity is a major driving force for semiconductors _______________ 1From 1997 US Census Bureau

10. Higher speed Zero Yield Zero Yield (High leakage) (Low conductance) 3s = 36nm 3s = 12nm 210 230 250 270 Gate CD (nm) Why Control Critical Dimension (CD)? • Small changes in CD distribution = Large $ values lost 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. Time 10 secFigure 3. Definition of bring-in (Rapid Thermal Processing) 1000C Temperature 0

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

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

27. 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 Characteristics of batch scheduling and planning problems (Pekny and Reklaitis)

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

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