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

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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)

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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

Wafer

FlatnessReflectivityTopography

Resist

Reticle

TemperatureUniformityTimeDelay

AberrationsLens HeatingFocusLevelingDose

CDDefectsEdge Roughness Proximity Effects

Stepper

TimeTemperatureDispense PatternRinse

Refractive Index ThicknessUniformityViscosityContrast

PEB Develop

PowerPressureFlow rates

Etch

AminesHumidityPressure

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

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Why Control Critical Dimension (CD)?• Small changes in CD distribution = Large $ values lost

290

Higher speed

Gate CD (nm)

210 230 250 270

Zer

o Y

ield

(Hig

h le

akag

e)

Zer

o Y

ield

(Low

con

duct

ance

)

3 = 12nm

3 36nm

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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

13

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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19

Time 10 sec

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

1000C

Temperature

0

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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.S ilicon S ubstra te

S T I S T I

P oly S ilicon

G ate O xide

S iO NTrim m ed

R esist

Linewidth

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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

Fre

qu

ency

Prior 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%

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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

Per

cen

t R

ewo

rk

Manual Implementationof APC Algorithm

Automated Implementationof APC Algorithm

Standard SPC ChartingProcess Control

26Figure 22.19 Batch control system – a more detailed view

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

DETERMINE

WhatProduct amounts: lot sizes, batchSizes

WhenTiming of specific operations, runlengths

WhereSites, units, equipment items

HowResource types and amounts

GIVEN

Product requirementsHorizon, demands, starting andEnding inventories

Operational stepsPrecedence orderResource utilization

Production facilitiesTypes, capacities

Resource limitationsTypes, 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 OverviewFab Tool

Process 2

Fab Tool

Process 1

Process 2

Fab Tool

Process 1

Process 1AB BB

A A A A

A A

AB BBA A

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Metrology Variations

0

0.2

0.4

0.6

0.8

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1.2

1.4

1.6

1.8

2

A B C D E

Process0

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1.5

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2.5

3

3.5

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A B C D E

Correct MetrologyOrdering

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0.5

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1.5

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2.5

3

3.5

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E D C B A

Incorrect MetrologyOrdering

0

0.5

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1.5

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2.5

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C D A E B

Incorrect MetrologyOrdering