Chapter - Batch Processing, PPT, Chemical Engineering, Semester, Engineering - Computer Science Engineering (CSE) PDF Download

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

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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

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Batch Processing Used in Manufacturing

• Electronic materials

• Specialty chemicals

• Metals

• Ceramics

• Polymers

• Food and agricultural materials

• Biochemicals

• Multiphase materials/blends

• Coatings

• Composites

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

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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

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CD Variation Effects in Pattern Transfer

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Silicon Integrated Circuit Technology Roadmap

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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

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Why Control Critical Dimension (CD)?

• Small changes in CD distribution = Large $ values lost

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Figure 19.1  The five levels of process control and optimization in

manufacturing.  Time scales are shown for each level.

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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

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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.

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Figure 22.7

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Graphical Description of Batch Sequence

• Information flow diagram

• Sequential function chart

• Binary logic diagram

• Ladder logic diagram

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Figure 22.8

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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

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Figure 3.  Definition of bring-in (Rapid Thermal Processing)

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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)

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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

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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

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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.

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Results – Increased C_pk

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Reduction in STI Rework with RtR

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Figure 22.19  Batch control system – a more detailed view

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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

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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

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Figure 22.17  Multiproduct batch plant

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Multi-Product Processing Overview

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Metrology Variations