“Automatic Control in Semiconductor Manufacturing: Challenges ...

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1 Νοε 2013 (πριν από 3 χρόνια και 9 μήνες)

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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

3

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:

1.
Physical/chemical complexity

2.
Inability to measure directly many
process variables

3.
High sensitivity to process changes

4.
Multiple inputs/multiple outputs

7

CD Variation Effects in Pattern Transfer

Wafer

Flatness

Reflectivity

Topography


Resist

Reticle

Temperature

Uniformity

Time

Delay

Aberrations

Lens Heating

Focus

Leveling

Dose


CD

Defects

Edge Roughness

Proximity Effects


Stepper

Time

Temperature

Dispense Pattern

Rinse

Refractive Index
Thickness

Uniformity

Viscosity

Contrast


PEB

Develop

Power

Pressure

Flow rates


Etch

Amines

Humidity

Pressure

Environment

8

Silicon Integrated Circuit
Technology Roadmap

9

Comparative Economics







Revenue/Capital
1



Chemical & Petrochemical


22.4



Pharmaceutical



19.6



Semiconductor





6.8



Capital productivity is a major driving force
for semiconductors

_______________

1
From 1997 US Census Bureau

10

Why Control Critical Dimension (CD)?


Small changes in CD distribution = Large $ values lost

290

Higher speed

Gate CD (nm)

210

230

250

270

Zero Yield

(High leakage)

Zero Yield

(Low conductance)

3
s
=
㴠12nm
=
3
s =
=
36nm
=
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

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.

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

18

19

Time 10 sec


Figure 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 C
pk

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%

1998 Work Week

Percent Rework

Manual Implementation

of APC Algorithm

Automated Implementation

of APC Algorithm

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

Process 2

Fab Tool

Process 1

Process 2

Fab Tool

Process 1

Process 1

A

B

B

B

A

A

A

A

A

A

A

B

B

B

A

A

31

Metrology Variations

Process

Correct Metrology

Ordering

Incorrect Metrology

Ordering

Incorrect Metrology

Ordering