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Aircraft Manufacturing and Assembly 51.4 Automated Assembly Systems/Examples 905

UT C-scan

image display

Fig. 51.17 Two types of automated ultrasonic inspection systems: independent tower system (right) and gantry system

(left) (courtesy of Boeing)

and squirter systems, where the transducer is located in

a nozzle that shoots water at a part from a short dis-

tance. The ultrasonic inspection can use one or more

transducers in a variety of combinations. The typical in-

spection uses either one transducer in pulse echo (PE)

mode, or two transducers, each aligned on opposite

sides of the part, for through transmission ultrasound

(TTU). Pitch-catch mode uses two transducers on the

same side of the part. For high throughputs using auto-

mated systems, the scanning robotics may handle arrays

of transducers that provide coverage of large areas of

material [51.16–27].

As aerospace structures become larger and more

complicated, overhead gantry systems or tower gantry

systems such as that illustrated in Fig.51.17 are used.

The overhead bridge scanning system can be used with

transducer manipulators with up to ﬁve axes of motion:

X, Y,andZ translations, rotation, and tilt. Using mo-

tion control software, the transducer can be oriented

normal to complex curved part surface during scanning.

Two transducer manipulators are employed for through

transmission imaging. The computer software can keep

the squirter transducers aligned and normal to the part

surface for complex geometric conﬁgurations. The part

geometries are taught by manual selection of a few data

points along a scan or using CAD surface data. In some

cases the systems will take pulse echo data from each

transducer on each side of the part and through trans-

mission data simultaneously. The tower scanner uses

independent machines on each side of the part to be

tested. The advantages of this conﬁguration include the

independent surface following from each side, the im-

proved reach in capability stiffness, and reduced ceiling

height. The ultrasonic testing (UT) data from a quality

surface following scanner includes 1-to-1 ﬂaw sizing on

complex curvature objects. The test part shown in the

tower system in Fig.51.17 is a landing gear pod fairing.

The UT C-scan image datashownin the lower-rightside

of the ﬁgure is the two-dimensional (2-D) ultrasonic

C-scan representation of the three-dimensional (3-D)

object, in which light areas indicate laminate and darker

areas indicate honeycomb core. Laminate inspections

are usually performed at 5MHz, while honeycomb is

commonly inspected with 1 or 2.25MHz ultrasound.

Inspection speeds depend on the data acquisition

rates. The data acquisition rate in X and the step size in

Y are determined by the minimum defect size that is to

be detected. Three data points are required for the mini-

mum defect size, such that 0.08in data space is used for

0.25in defect sensitivity. Many scanners and the asso-

ciated acquisition electronics can scan at up to 40in/s

while maintaining 0.04in data spacing in the scan di-

rection. Coverage of 25–50ft

/h is possible on many

parts.

51.4 Automated Assembly Systems/Examples

Conversion to digitally deﬁned parts is a key factor

that has enabled the widespread use of automation.

Aircraft assembly machines are custom-designed to

meet speciﬁc requirements, where the combination

Part F 51.4

906 Part F Industrial Automation

of tight engineering tolerances, the need to reduce

part variation, and large machine envelope drives

large and expensive machines. Despite the high initial

cost, the use of automation has been very success-

ful in addressing the needs to improve quality, reduce

costs, and improve ergonomics of aircraft fabrication

and assembly. Assembly systems are designed around

the type of structures to be assembled. For single

and very large panels, C-frame riveting/fastening ma-

chines are commonly used. The most suitable system

to assemble half-shells (fuselage barrels) is a ring

riveter, and ﬁnal aircraft assembly is performed man-

ually using advanced hand tools and, more recently,

newly developed, ﬂexible, adaptable, portable assembly

systems.

51.4.1 C-Frame Fastening Machine

Automated wing panel fastening machines are used

to build stringer stiffened wing panels by riveting

stringer-to-wing skins and fastening adjacent wing

panels together. Structurally, they are large C-frames

mounted on rails that travel the length of the wing.

Floor-mounted header tooling supports the temporarily

tacked together wing panel to ensure proper panel posi-

tioning forpermanent fastener installation.The C-frame

wraps around the wing skin and applies drilling and fas-

tener installation tools to both sides of the panel. For

accurate positioning, wing riveters obtain positional ac-

curacy from the stringers mounted on the underside of

the wing panel. A typical rivet installation cycle in-

volves positioning the machine to the proper location,

clamping the skin and stringer together, drilling a hole,

inserting a rivet, hydraulically squeezing a rivet, and

shaving the formed head. Then, an electronic vision

system veriﬁes ifthe shavedrivet meets theﬂushness re-

Fig. 51.18 Gemcor automated wing fastening system

quirement. Bolts are applied in a similar sequence, with

sealant beingapplied priorto boltinsertion, andthen the

nuts are installed and torqued.

A Boeing wing panel fastening system is shown in

production in Fig. 51.18. Typical production wing lines

have multiple wing assembly machines capable of op-

erating on multiple parallel rail systems with turntables

and interconnecting tracks allowing a machine to move

to work stations within the track network [51.4–8].

Machine Features

•

50000 lbs rivet upset capability to accommodate

7/16in-diameter 7050 rivets

•

Full servo programmable control including:

– High-speed upper head transfer

– High-speed drill and shave spindles

– High-speed servo buck

– High-speed servo lower head

– Servo clamp

•

Up to six upper head positions

•

Statistical process control (SPC) of fastener instal-

lation processes

•

Automatic fastener selection

•

Fastest machine cycle time in the industry

•

Standard slug squeeze process

•

Squeeze/squeeze III slug installation process

•

Vibratory insertion process for two-piece fasteners

in high interference ﬁt conditions

•

Torque-controlled nut runner

•

Lockbolt swage collar tooling

51.4.2 Ring Riveter

for Fuselage Half-Shell Assembly

System Description

This computer-controlled riveting/fastening machine is

being used to automatically join fuselage half-shells

made from single panels along longitudinal and radial

joints as shown in Fig.51.19. It consists of:

1. Outer ring, moving on longitudinal rails, carrying

a multifunction end-effector, which moves radially

on the inside of the machine ring structure

2. A roboticarm, moving on theﬂoor insidethe ring on

rails longitudinally, carrying a second multifunction

end-effector

3. A ﬂexible ﬁxture to support the half-shell during the

assembly operations

4. Machine controller, executing assembly sequence

programs generated using an ofﬂine programming

system [51.1–3].

Part F 51.4

Aircraft Manufacturing and Assembly 51.4 Automated Assembly Systems/Examples 907

Technical data

• Assembly of 180° half shells

• Machine size: L = 10–80m; W = 6–12m; H = 6–10m

• Fully automated process, CNC control

• Automatic work piece transfer

• Precision rivet/fastener head position

• Solid work piece clamping during run time

• Number of rivet/fastener cassettes = 16 or more

• Drill spindle rpm = 0 to 20000

• Spindle feed = 0 to 0.006 ipr

• Pneumatic hammer for interference fastener insertion

• Rivet installation rate = 4 to 10 rivets/min

• Fastener installation rate = 2 to 6 fasteners/min

• Off-line or teach-in programming

Fig. 51.19 Ring riveter assembly system (courtesy of Broetje)

Assembly Process

Single panels and all parts building the half-shell are

tacked together and half-shell stabilized on the ﬂexi-

ble ﬁxture is moved into the ring’s working envelope.

The multifunction end-effector moving on the out-

side of the half-shell, and the internal multifunction

end-effector, perform synchronous riveting/fastening

operations through the skin. The outside multifunction

end-effector uses a drilling module, a rivet fastener

feeding module, and a rivet upsetting tool; and the

internal multifunction end-effector uses a clamping

tool and rivet upsetting or sleeve installation tool

module, if two-piece fasteners are being installed. Pro-

cess parameters such as the clamping force generated

by internal and external end-effector bushings at the

drilling location areadjusted forstructural material(alu-

minum, titanium, composite) and stiffness. The drill

unit’s RPM and feed force are selected as a func-

tion of hole diameter, required hole tolerance (e.g.,

0.001in) and cutter material (e.g., carbide, PCD). The

position of all machine components (ring, robot, end-

effectors) is CNC controlled and a vision system built

into the outside multifunction end-effector provides

the operator with visual control and enables precision

position adjustments if required. The internal multi-

function end-effector can be quickly decoupled from

the robotic arm and replaced with the C-frame type

of multifunction end-effector for shear tie-to-frame

riveting operations. This multifunction end-effector lo-

cates a feature (hole or rivet) on the frame, using

a vision system, and communicates information to

the robot controller, which then positions the end-

effector to the proper location for clamping, drilling,

and rivet insertion/upsetting tasks. All process param-

eters are monitored and saved to a quality-assurance

data bank to verify and document process and part

quality.

51.4.3 Airplane Moving Line Assembly

System Description

In 1913 Henry Ford put the ﬁrst moving assembly

line ever used for large-scale manufacturing into use.

Fig. 51.20 Ford Motor Company moving assembly line

Part F 51.4

908 Part F Industrial Automation

Technical data

• Typical linear assembly line

• Line speed – 0.5" to 2"/min

• Guidance system – optical

or Hall-effect sensors

Fig. 51.21 Boeing 737 ﬁnal assembly line

Ford lowered the price of a car by producing them

at record-breaking rates with this new assembly pro-

cess. Today almost all automobile manufacturers use

moving lines to assemble their products for cost, qual-

ity, and ﬂow time reasons. In the past 5 years some

aerospace companies have moved away from tradi-

tional stationary dock assembly systems in favor of

the more efﬁcient moving assembly lines similar to

those used in the automobile industry. State-of-the-

art examples are the Ford production line at Flatrock,

MI,USA,showninFig.51.20 and the Boeing 737

ﬁnal assembly line in Renton, WA, USA, shown in

Fig.51.21.

Assembly Process

Major sections of commercial aircraft are assembled in

stationary ﬁxtures until they are structurally stable and

need little or no support from external tools. At this

point the aircraft is placed on a barge or carrier and

begins its ﬁnal assembly as it is towed by a motorized

automated tug. The tug attaches to the front of the barge

and pulls it forward under the power of a motor that

is computer controlled. Steering is accomplished by an

optical sensor that follows a white line along the ﬂoor.

Major subassemblies and components such as the

landing gear, interior systems, and passenger seats are

installed by mechanics as the airplane moves down the

assembly line. In addition, functional testing is per-

formed on the various systems in the airplane and the

engines are attached. The use of moving assembly line

can typicallyreduce the ﬁnal assemblytime by 50% and

signiﬁcantly reduce the number of days for this task.

The assembly time reduction is due to the application of

lean manufacturing techniques, which were introduced

into the aerospace industry in late 1999. Moving lines

help companiesachieve higherefﬁciencies because they

create a sense of urgency as well as streamlining and

standardizing assembly processes to eliminate waste

and nonvalue operations. Computer-controlled tugs set

the pace or takt time (the manufacturing time needed

to accomplish certain predetermined tasks). As the air-

plane moves past visible marks on the ﬂoor, teams of

mechanics install prekitted parts and tools using stan-

dard processes within the allotted time so that the next

team can continue adding value to the airplane as as-

sembly progresses [51.9–15].

51.5 Concluding Remarks and Emerging Trends

Aircraft fabrication and assembly technologies are un-

dergoing signiﬁcant changes driven by the need to

achieve performance and economic targets and only

a few predominant trends are discussed here. There is

a never-ending search for higher aircraft performance,

coupled with the desire to reduce the production la-

bor content, processing time, and cost. This requires

progressiveness and innovative use of exotic mater-

ials with improved speciﬁc mechanical properties (such

as carbon-ﬁber composites), and development of more

efﬁcient fabrication and assembly technologies for

metallic and nonmetallic structures. The move to more

composite aircraft mitigates some typicalproblems with

metallic parts (i. e., the shorter fatigue life and galvanic

corrosion inherent to aluminum alloys compared with

equivalent composite parts).

A majority of today’s manual high-level assem-

bly operations, such as joining fuselage barrels and

wing boxes, could be replaced in the future with

ﬂexible, adaptable, and affordable, semi-automated as-

sembly systems to perform clamping of parts using

electromagnets, drilling, and countersinking, and fas-

tener installation tasks.

One example offering potentially signiﬁcant im-

provements in assembly efﬁciency, is the friction stir

welding (FSW) process, developed for space launch

vehicle fabrication (for joining Delta II and IV alu-

minum panels to fuel tanks). This technology, once

Part F 51.5

Aircraft Manufacturing and Assembly References 909

thoroughly tested and approved, can be introduced into

commercial aircraft structural assembly, replacing to-

day’s time-consuming mechanical joining techniques.

The potential capability to produce high-level as-

semblies with composite structures helps to eliminate

several lower-level assembly tasks. This has been

achieved, as evidenced by the redesign of multipanel

aluminum fuselage barrels into a one-piece composite

barrel. Such moves call for development of innovative

structural conﬁgurations, and require mastering engi-

neering challenges associated with tooling, equipment,

processes, and inspection.

The emergence and growth of rapid prototyp-

ing/fabricationtechnology could revolutionizethe fabri-

cation/manufacturing of parts and assemblies. Parts will

be grown in a system that requires only the electronic

part geometry information and raw material in pow-

der form as inputs. Parts are currently created (grown)

by layered material deposition and particle fusion us-

ing lasers. These plastic net-shape, or near-net-shape,

metallic parts eliminate the need for a majority of the

material removalprocesses andreduce the material buy-

to-ﬂy ratios and manufacturing cost. This trend could

evolve into growing substructures or even complete

aircraft segments, eliminating all part fabrication and

assembly tasks.

The trend toward monolithic metallic and large-

scale integral composite structures will probably con-

tinue in the future, and will require the development of

advanced automated fabrication and assembly systems

to meet demands for improved aircraft performance at

minimal cost. The current trend is to machine or fabri-

cate components accurately with automated machines

and then use accurately machined features in the de-

tail parts as references to build larger assemblies. At

some point, as the structure increases in size, it becomes

cost prohibitive to use conventional automation to as-

semble large parts, so the fall-back position has been to

join or splice larger assemblies manually. To capture the

beneﬁts of automation with larger assemblies in the fu-

ture, a new generation of ﬂexible portable automation

is being developed. These lightweight portable systems

use the aircraft structure as their foundation and will

produce quality parts at an affordable cost.

References

51.1 C. Wick, J.T. Benedict, R.F. Veilleux: Tool and Manu-

facturing Engineering Handbook – Vol. 2: Forming

(SME, Dearborn 1984)

51.2 E.H. Zimmerman: Getting Factory Automation

Right: The First Time (SME, Dearborn 2001)

51.3 J.A. Schey: Introduction to Manufacturing Pro-

cesses (McGraw Hill, New York 1987)

51.4 M. Watts: High performance machining in

aerospace, Proc. 4th Int. Conf. Metal Cutt. High

Speed Mach. (Boeing, Seattle 2002)

51.5 M. Watts: Evolving aerospace machining processes,

4th Int. Conf. High Speed Mach. – Ind. Tool. Conf.

(Southampton 2001)

51.6 L. Hefti: Innovations in fabricating superplastically

formed components, First and Second Int. Symp.

Superplast. Superplast. Form. Technol. (ASM, Ma-

terials Park 2003) pp. 124–130

51.7 D. Sanders: A production system using ceramic die

technology for superplastic forming, Superplast.

Adv. Mat. ICSAM 2003 (Trans Tech, 2004) pp. 177–

182

51.8 GEMCOR: http://www.gemcor.com (2009)

51.9 PASER: Abrasive waterjet helps make composites

affordable for Boeing, http://www.ﬂowcorp.com/

waterjet-resources.cfm?id=251 (2008)

51.10 Boeing completes ﬁrst 787 composite fuselage

section, http://www.boeing.com/companyofﬁces/

gallery/images/commercial/787/k63211-1.html (2005)

51.11 R.A. Kisch: Automated Fiber Placement Historical

Perspective (Boeing, Seattle 2006),

http://www.ingersoll.com/ind/tapelayer.htm

51.12 Boeing reduces 737 airplane’s ﬁnal-assembly

time by 50 percent, http://www.boeing.com/news/

releases/2005/q1/nr_050127g.html (2005)

51.13 T.G. Gutowski: Advanced Composites Manufactur-

ing (Wiley, New York 1997)

51.14 S. Mazumdar: Composites Manufacturing: Mater-

ials, Product, and Process Engineering (CRC Press,

Boca Raton 2002)

51.15 F. Campbell Jr.: Manufacturing Processes for Ad-

vanced Composites (Elsevier, Amsterdam 2004)

51.16 R. Bossi, F. Iddings, G. Wheeler (Eds.): Nonde-

structive Testing Handbook, Vol. 4 – Radiographic

Testing, 3rd edn. (American Society for Nondestruc-

tive Testing, Columbus 2002)

51.17 R. Halsmshaw: Nondestructive Testing, 2nd edn.

(Edward Arnold, London 1991)

51.18 G.L. Workman, D. Kishoni (Eds.): Nondestructive

Testing Handbook, Vol. 7 – Ultrasonic Testing,3rd

edn. (American Society for Nondestructive Testing,

Columbus 2007)

51.19 ASM: ASM Handbook, Vol. 21 – Composites, Quality

Assurance (ASM, Metals Park 2001)

51.20

J. Summerscales (Ed.): Nondestructive Testing of

Fibre-Reinforced Plastics Composites,Vol.2(Else-

vier, New York 1990), pp. 107–111

Part F 51

910 Part F Industrial Automation

51.21 G.L. Workman: Robotics and nondestructive test-

ing – a primer, World Conf. Nondestruct. Test. (NDT)

(1985) pp. 1822–1829

51.22 P. Walkden, P. Wright, S. Melton, G. Field: Auto-

mated ultrasonic systems, World Conf. NDT (1985)

pp. 1822–1829

51.23 T.S. Jones: Inspection of composites using the au-

tomated ultrasonic scanning system (AUSS), Mater.

Eval. 43(6), 746–753 (1985)

51.24 M.K. Reighard, T.W. Van Oordt, N.L. Wood: Rapid

ultrasonic scanning of aircraft structures, Mater.

Eval. 49(12), 1506–1514 (1991)

51.25 Y. Bar-Cohen, P.G. Backes: Scanning aircraft struc-

tures using open-architecture robotic crawlers as

platforms with NDT boards and sensors, Mater.

Eval. 57(3), 361–366 (1999)

51.26 J.J. Gallar: Modular robotic manipulation in radio-

graphic inspection, Mater. Eval. 46(11), 1397–1399

(1988)

51.27 D. Mery: Automated radioscopic testing of alu-

minum die castings, Mater. Eval. 64(2), 135–143

(2006)

51.28 ASTM: ASTM E 1025-84, Standard Practice for Hole-

Type Image Quality Indicators Used for Radiography

Part F 51

911

Semiconducto

52. Semiconductor Manufacturing Automation

Tae-Eog Lee

We review automation requirements and tech-

nologies for semiconductor manufacturing. We

ﬁrst discuss equipment integration architectures

and control to meet automation requirements for

modern fabs. We explain tool architectures and

operational issues for modern integrated tools

such as cluster tools, which combine several pro-

cessing modules with wafer-handling robots. We

then review recent progress in tool science for

scheduling and control of integrated tools and

discuss control software architecture, design, and

development for integrated tools. Next, we discuss

requirements and technologies in fab integration

architectures and operation such as modern fab

architectures and automated material-handling

systems, communication architecture and net-

working, fab control application integration, and

fab control and management.

52.1 Historical Background ........................... 911

52.2 Semiconductor Manufacturing Systems

and Automation Requirements .............. 912

52.2.1 Wafer Fabrication

and Assembly Processes .............. 912

52.2.2 Automation Requirements

for Modern Fabs......................... 913

52.3 Equipment Integration Architecture

and Control.......................................... 914

52.3.1 Tool Architectures

and Operational Requirements .... 914

52.3.2 Tool Science:

Scheduling and Control............... 915

52.3.3 Control Software Architecture,

Design, and Development ........... 919

52.4 Fab Integration Architectures

and Operation...................................... 921

52.4.1 Fab Architecture and Automated

Material-Handling Systems ......... 921

52.4.2 Communication Architecture

and Networking ......................... 922

52.4.3 Fab Control Application

Integration................................ 922

52.4.4 Fab Control

and Management....................... 924

52.4.5 Other Fab Automation

Technologies ............................. 924

52.5 Conclusion ........................................... 925

References .................................................. 925

52.1 Historical Background

The world semiconductor market has been growing

fast and amounted to US$270billion in 2007. The

semiconductor manufacturing industry has kept mak-

ing innovations in circuit design and manufacturing

technology. Some key innovations include circuit width

reductions from 1.0μm in 1985 to60nm in 2005, 40nm

in 2007, and even down to 14 nm by 2020, and wafer

size increase from 200mm to 300mm wafers, and even

to 450mm or larger in the near future. Some fabs are

producing 1Gb random-access memory (RAM)byus-

ing 50 nm technology, which reduces the cost by about

50% compared with 60 nm technology. Such technol-

ogy innovations have led to higher circuit density,

increased circuit speed, and remarkable price reduction,

which also have created new demand and expanded the

market.

In 2007, 35 new wafer fabs began to ramp up world

monthly fab capacity by two million 200mm wafers,

Part F 52

912 Part F Industrial Automation

that is, a 17% increase. A modern fab construction

costs about US$ 2 billion. On the other hand, the semi-

conductor manufacturing industry has suffered strong

competition due to excessive capacity. Therefore, the

industry has tried to reduce costs, improve quality, and

shorten the manufacturing cycle time. Automation has

been the key for such manufacturing improvement and

business success. Consequently, there have been many

aggressive technology innovations and standardizations

for fab automation. We therefore need to review those

efforts, the state of art, and the future challenges for fab

automation.

In this chapter, we brieﬂy introduce semiconductor

manufacturing systems and automation requirements,

architecture and control for processing equipment and

material-handling systems, communication architecture

and networking, and software architecture for process

control, equipment control, and fab-wide control. We

explain academic research works as well as industrial

technologies and practices.

52.2 Semiconductor Manufacturing Systems

and Automation Requirements

52.2.1 Wafer Fabrication

and Assembly Processes

The semiconductor manufacturing process consists of

wafer fabrication and assembly. In the wafer fabrica-

tion process, multiple circuit layers (up to 30 or more)

are laid out on a wafer surface through the repetition

of identical sequences of process steps. Most fabrica-

tion process steps are chemical processes that oxidize

a wafer surface, coat photosensitive chemicals onto the

surface, expose it to a circuit image from a light source,

develop and etch the circuit pattern, deposit other chem-

icals onto it, diffuse and implant additional chemicals

on the etched pattern, and so on. Once a circuit layer

is formed, the wafer reenters the fabrication line to

form the next circuit layer. The total number of process

steps may amount to 480 or more. A wafer has several

hundreds of formed circuit devices. For strict quality

control, the formed circuits are measured by metrol-

ogy equipment frequently after some key process steps.

Based on the metrology results, some devices in a wafer

may be repaired, reworked or scrapped. Wafter yield

may be rather low, especially during the ramp-up stage

for the initial 3–6months. Wafers are transported and

loaded into processing tools using a carrier called a cas-

sette or pod that loads 25 wafers. A typical fab produces

40000 wafers each month. The fabrication cycle time is

several weeks or even a few months, depending on the

fab management performance. About 20000–100000

wafers may be in progress at any given time.

Once a wafer completes the fabrication processes,

devices on a wafer undergo intensive circuit tests called

electronic die sorting (EDS). Depending on the test

results, the devices are classiﬁed into different ﬁnal

products with speciﬁcations on clock speed, number of

effective transistors, and so on. A device that fails to

satisfy the speciﬁcation of a high-grade product is clas-

siﬁed into a lower-grade product. Such a sorting process

is also called binning. Some devices may be defective.

Due to the yield problem and binning, it is difﬁcult to

predict the number of ﬁnal products of each grade or

type.

Wafers that complete EDS are sent to an assembly

or packaging plant. The fabrication processes leading

to EDS and the assembly processes after EDS are

called front-end and back-end processes, respectively.

In the back-end processes, a wafer is sliced into indi-

vidual devices. The sliced devices undergo packaging

processes that include tape mounting, wire bonding,

molding, and laser marking. The packaged devices take

ﬁnal tests, where additional binning is carried out. The

back-end processeshave been regarded asrelatively low

technology with low value added and tend to be sub-

contracted. However, multichip packages (MCP)that

combine several chips together into a single package

are becoming increasingly popular due to growing de-

mand from the mobile-device industry. MCP or other

advanced packaging technologies such as wafer-scale

packaging and ﬂip chips increase the value and impor-

tance of the back-end processes. Hence, a number of

back-end processes still involve manual material han-

dling while the front-end processes have become highly

automated. Figure 52.1 summarizes the overall semi-

conductor manufacturing processes.

A process step is performed by a number of similar

or identical wafer processing tools. Due to strict quality

requirements, some wafer lots should be processed only

with a restricted set of tools. Different types of wafer

lots ﬂow concurrently through the fab. Therefore, the

fab can be viewed as a hybrid ﬂow shop. Reentrant job

Part F 52.2

Semiconductor Manufacturing Automation 52.2 Semiconductor Manufacturing Systems and Automation Requirements 913

Die

attach

Wire

bonding

Oxidation

Wafer

Deposition

Developing

Lithography

Coating

Etch

Back

lap

Saw Cure Mold

256mb mobile Dram

1Gb N and flsh

256mb mobile Dram

1Gb N and flsh

Plasma

Tape

mount

Final test

Assembly

EDS

(Electronic die sorting)

Fabrication

Assembly

MCP

Back-end

Front-end

Diffusion/implant

Fig. 52.1 Overall manufacturing processes

ﬂows for processing multiple circuit layers and random

yield make planning and scheduling complicated. A fab

consists of several hundreds of processing and inspec-

tion tools. The tools are grouped into bays, where each

bay consists of 10–20 processing tools. Each bay has

a stocker, where wafer cassettes are waiting for process-

ing or moving to the next bay.

52.2.2 Automation Requirements

for Modern Fabs

There are several drivers for fab automation. The

material-handling tasks in a fab are very large; for in-

stance, a fab that processes 40 000 wafers a month

requires 200 operators per shift just for moving

wafer cassettes [52.1]. Therefore, automated material-

handling systems (AMHSs) are used to reduce such

high human operator requirements. Other drivers for

material-handling automation include prevention of hu-

man’s handling errors such as wafer dropping, and

better tool utilization and reduced manufacturing cycle

time by fast and reliable material transfer [52.1]. The

keytechnological innovationsin the front-end processes

during the past decades are the continuing reduction of

circuit features for higher density and functionality, and

wafer size increase to 300mm for higher throughput.

These have led to signiﬁcant fab automation. Extreme

circuit shrinkage requires strict quality control and

higher-class clean rooms to reduce increased risk of

particle contamination. As human operators are a sig-

niﬁcant source of particle generation, the number of

operators needs to be reduced. Wafer size increase leads

to signiﬁcantly heavier weight of a wafer cassette be-

yond human operator’s adequate workload. Therefore,

in recent 300 mm fabs, wafer-handling operations have

been mostly automated. Control applications for equip-

ment and AMHSs from many different vendors should

be easily integrated. Design, scheduling, and control of

fully automated fabs are highly complicated and require

new concepts and ideas (Fig.52.2).

Traditionally, wafers in a cassette have been pro-

cessed in batch mode for most chemical processes such

as etching, deposition, etc. However, as the wafer size

increases and quality requirements become stricter due

to circuit shrinkage,it becomes difﬁcult tocontrol gasor

chemical diffusion on all wafer surfaces within a large

processing chamber to be uniform enough for strict

quality requirements. Therefore, single-wafer process-

ing (SWP) technology that processes wafers one by one

has been extensively introduced for most processes. In

order to reduce excessive moving tasks between SWP

chambers, several SWP chambers are integrated within

a closed environment together with a wafer-handling

robot. Such a system is called cluster tools.Aninte-

grated system of SWP chambers with multiple handling

robots is often called a track equipment or track sys-

tem. It can be considered as a combination of multiple

cluster tools. Cluster tools or track equipment have been

Part F 52.2

914 Part F Industrial Automation

Manufacturing execution

systems

Traditional clean room Minienvironment clean room

FMCS and HVAC

Life safety

Air Handling

CVD/PVD

Etch

Dice

Engineering

systems

Chemical distribution system

Package

Chase

Warehouse and

material handling

systems

Shipping

• Printed circuit

boards

Electronic assembly

Final test

Device attach/bond

Test Wafer probe

Oxidation

Class 100 area

Stocker

The open controller

and PLC and SLC

controllers

Operator interface

Industrial control

(Push buttons, pilot lights,

terminal blocks, relays,

contactors, switches)

Networks (Ethernet,

DeviceNet, Remote I/O,

Data Highway Plus,

ControlNet)

Reliance electric &

Allen Bradley drives

and motors and

Rockwell Automation

drive systems

Power monitoring software,

RSView32; Programming

Packages (RSQuality,

RSTrend, RSRecipe)

Process tool Process tool Process tool

Cassette handling system

Minienvironment

class 1

Minienvironment

class 1

Minienvironment

class 1

Vertical

furnace

Ion implant

photo litho

Office & business

systems

Water treatment

• PC workstations

• Consumer electronic

products

• Medical equipment

• Automobile electronic

systems

• Test and measurement

equipment

Gas dispensing system

Fig. 52.2 Semiconductor fabrication clean rooms (courtesy of Rockwell Automation, Inc.)

increasingly used formost processes. Dueto the internal

complexity and restrictions, they pose scheduling and

control challenges. First, their operations should be op-

timized to maximize throughput. Second, wafer delays

within a processing chamber after processing should be

controlled because residual gases and heat affect wafer

quality signiﬁcantly. Third, the tool controller should be

reliable and easily adaptable for different tool conﬁg-

urations and changing wafer ﬂow patterns or recipes.

Scheduling and control, and tool application integration

are not trivial.

Another important issue for fab automation is

standardization for reducing integration effort and per-

formance risk. Semiconductor Equipment and Material

International (SEMI), an international organization, has

developed extensive standards on architectural and in-

terface standards of material-handling hardware, com-

munication, and control software for fab automation.

The standards themselves are based on state-of-the-art

automation technologies; however, they should be con-

tinuously improved for higher operational goals and

changing automation requirements.

52.3 Equipment Integration Architecture and Control

52.3.1 Tool Architectures

and Operational Requirements

In a cluster tool, there is no intermediate buffer between

the process modules (PMs). A wafer, once unloaded

from a loadlock, can return to the loadlock only af-

ter it completes all required process steps and is often

cooled down at a cooler module, if any. This is because

a hot wafer returned to the wafer cassette at the load-

lock may damage other wafers there and a hot wafer in

progress should not be excessively cooled down before

processing at the next PM. A wafer loaded into a PM

immediately starts processing since the PM’s chamber

already has gases and heat. There are different cluster

tool architectures, as illustrated in Fig.52.3. Most tools

have radial conﬁgurations of chambers, where robot

move times between chambers are minimized. Linear

conﬁgurations are also considered to add or remove

chambers ﬂexibly. The robot has a single arm or dual

arms. The dual arms keep opposite positions. Dual-

armed tools are known to have higher throughput than

single-armed tools [52.2]. There are also tools with in-

termediate vacuuming buffers between chambers and

loadlocks [52.3] in order to save vacuuming and vent-

ing times at the chambers. Some new cluster tools use

multiple wafer slots in a chamber in order to improve

throughput above that of SWP tools by processing sev-

eral wafers together [52.4]. However, those new tool

architectures tend to increase scheduling complexity

signiﬁcantly.

Track equipment or systems are also widely used

for integrating several process steps. Photolithography

processes use track systems that supply steppers with

wafers coated with photosensitive chemicals and de-

Part F 52.3