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SEMI E78-0998 Electrostatic Compatibility

October 19, 2000SEMATECH

Austin TX

Arnold Steinman M.S.E.E.Chief Technology Officer

ION SystemsLeader - SEMI ESD Task Force

asteinman@ion.com

• Problems Caused by Static Charge

• Static Charge Generation and Control

• SEMI E78-0998 Electrostatic Compatibility Guide

Typical Electrostatic Charges Found In Work Areas

Wafers 10 kVTeflon Wafer Carriers 5 kVReticle Carriers 35 kVAcrylic Covers 20 kVQuartz Ware 15 kVPellicles 20 kVGlass Windows 15 kV

Static Charge

Wafers

IntegratedCircuits

Reticles

Equipment

Contamination ESD Damage Process Interruptions

Static Charge

Reticles

Static Charge Effects in Semiconductor Manufacturing

Fq q

r= 1 2

4 02πε

for 1000 V surfaces, thegreatest force is electrostatic!

gravitational

aerodynamic

Electrostatic

What Happens When a Surface is Charged?

Contamination Study

Wafer at 0 Vclass 1 mini environment for 6 weeks

Wafer at 2000 Vclass 1 mini environment for 6 weeks

200 mm wafer in a Class 1 Mini-Environment

Electrostatic Discharge (ESD)Damages Devices

ESD Damage to Reticles

Induced Reticle Damage Due to Low Level ESD

Increasing number of induced ESD events >>>>

EMI produced by the ESD events

ESD Events CreateElectromagnetic Interference(EMI)

• Scrambled Program

Instructions

• Scrambled Data

• Confusing Error

Messages

• Microprocessor Lockup

• Phantom Particles

• Calibration Failures

• Apparent Software Bugs

• Triboelectric Charging

• Grounding for Conductors and Insulators

• Ionization

Charge generation:The Materials UsedEncourage Transfer:

Triboelectric Charging

P-Type Silicon

Human Hands

Quartz

Nylon

Aluminum

Chrome

Steel

Polyurethane

Polyethylene

Polypropylene

PVC (Vinyl)

Silicon

Mylar

Teflon

Positive+

Negative-

Contact and Separation are Required

Neutral Substrate Moves In

Contact of Dissimilar MaterialsAl2O3

Silicon

Charged Wafer Moves Out

Raising off of Ground Raises Voltage on Wafer

Sources of Static Charge:End effector moving a wafer

• Contact of Dissimilar materials • Pressure of contact• Separation after contact• Vibration• Friction between objects

Sources of Static ChargeCleaning Wafers

• Contact of Dissimilar materials • Pressure of contact• Separation after contact• Vibration• Friction between objects

Sources of Static Charge:Vacuum or electrostatic chuck

• Contact of Dissimilar materials • Pressure of contact• Separation after contact• Vibration• Friction between objects

Insulators vs. Conductors

• No current flows• Charge exists on islands• Both polarities can exist on one object• Charge trapped on the surface

+ + + + + + + + + + + ++ + + + + + + + + + + + + + + + + + + ++ + + + ++ + + + + ++ + + + + + + ++ + + + + ++ + +

• Charge drains to earth ground• Distributed over the object• Charge free to move

+ ++ + +

+- - -- -

Insulator Conductor

+ + + + + + + + + - - - - - - - - - - -

Insulator

Charged Air Molecules

++

+

+

+

+

+

+

+

+

+

+

+

+

+

++++++ +

+

++

Neutralizing Static Charge with Bipolar Air Ionization

An Effective ESD Prevention Program

• Ground all conductors– Pay close attention to moving

equipment parts

• Use static dissipative materials to replace insulators when possible

– Determine cleanroom compatibility

• Ground static dissipative materials

An Effective ESD Prevention Program

• Avoid readily charged materials when possible

– Teflon– Vinyl– Sheet protectors– Plexiglas

• Use Ionization to control static charge on process-essential insulators

– Oxide-coated Silicon– Teflon– Quartz– Polycarbonate– Glass– Kapton– Epoxy

SEMI E78-0998 GuideElectrostatic Compatibility

SEMI E78-0998 Electrostatic Compatibility:

Guide to Assess and Control Electrostatic Discharge (ESD) and Electrostatic Attraction (ESA) for Equipment

SEMI ESD Task Force

• Mission - “To minimize the impact on capital productivity due to the presence of static charge in semiconductor manufacturing environments.”

• Objective - To create a matrix of acceptable levels of static charge at the input and exit ports of production equipment for the purposes of:

– Eliminating equipment lock-up problems due to ESD events that produce EMI.

– Reducing the attraction of particles to charged surfaces.

– Reducing product and reticle damage due to ESD.

Equipment Manufacturer - “It’s not my problem”SEMI - “It’s a problem needing users and suppliers working together”

Estimating Static Charge Losses

Prevent ESD Damaged Reticles from Causing Die DefectsESD damages reticle after reticle inspection

Wafers per hour processed by stepper 30Dies per hour (assume 150 dies per 200 mm wafer) 4,500Time to inspection (next inspection after stepper) 4 hoursTotal number of damaged dies 18,000Finished Die Value (Selling Price) USD$10Estimated Static Losses per event USD$180,000Cost of static control program in photo area USD$180,000

Preventing one ESD damaged reticle pays back the investment!!

Problem - ESD damages reticles Static Control Effect - Reduce damage to reticles that occurs

during storage and handling in photolithography areas

ESD Task Force Issues

• Problems occur at different static charge levels.

• It is not possible to set standards for static charge control that interfere with semiconductor processing.

• The interior of production equipment is often inaccessible for static control.

• Set levels at the input and exit ports - an “exit charge specification”

Working Together - ESD DamageEnd User and Equipment Supplier

• End User - Determine most critical ESD damage model for devices or reticles

• End User - Use appropriate ESD simulator to establish damage threshold

• End User and Equipment Supplier - Agreement on E78 sensitivity level for ESD damage

• Equipment Supplier - Include appropriate static control methods. Verify that static level within equipment remains below sensitivity level.

• End User - Verify compliance with desired sensitivity level.

Test Method - ESD Damage

FARADAYCUP

WAFER OR RETICLE CASSETTES

WAFERS, RETICLES, OR ICs

LESS THAN 100 NANOCOULOMB

ALLOWABLE CHARGE LEVEL

1000

VOLTS

DEVICEUNDER

TEST

ESD

SIMULATORHBM, MM, CDM

100 NANOCOULOMBDISCHARGE IMMUNITY

WAFERRETICLE

IC

1. Determine Device DamageThreshold

2. Verify Charge Levels on Devices and Carriers after Processing in Equipment

Working Together-ContaminationEnd User and Equipment Supplier

• End User - Determine acceptable contamination levels based on industry roadmaps and product exposure times

• End User - Use E78 to determine acceptable electric field levels

• End User and Equipment Supplier - Agreement on E78 sensitivity level for contamination

• Equipment Supplier - Include appropriate static control methods. Verify that static level within equipment remains below sensitivity level.

• End User - Verify compliance with desired sensitivity level.

Contamination Control

E78-0998Guide

SensitivityLevel

EV/cm at2.5cm

N/Adefectsper cm2

velect

cm/secct

sec/cm3max t inClass 1

sec

Level 4 4000 0.016 0.21 0.0762 61

Level 3 400 0.016 0.021 0.762 610

Level 2 200 0.016 0.0105 1.524 1220

Level 1 100 0.016 0.00525 3.048 2440

N/A = Defect Density (shown for 0.25 micron technology)max t = Product Exposure Time (under Class 1 conditions)

Test Method - Contamination

1999

+ + + + + + + + + + + + + + + +

2.54cm(1”)

ElectrostaticFieldmeter(volts/cm)

+ + + + + + + + + + + + + + + +

ChargedSurface

Electric Field Lines

ChargedSurface

Measure Electric Field on Critical Surfaces After Processing

Working Together - EquipmentEnd User and Equipment Supplier

• End User - Estimate maximum static potentials in the production areas

• End User and Equipment Supplier - Agreement on E78 sensitivity level for equipment malfunctions

• Equipment Supplier - Include appropriate static control methods. Verify that static level within equipment remains below sensitivity level. Use appropriate ESD simulator to establish ESD immunity of equipment

• End User - Verify compliance with desired sensitivity level using appropriate ESD simulator

Equipment ESD Immunity -CE Requirements

Direct Discharge(4000 volts X 150 picofarads = 600 nC)

4000Volts

Air Discharge (8000 volts X 150 picofarads = 1200 nC)

8000Volts

10 cm

Test MethodsIEC 61000-4-2EN 50082-2

Test Method: Equipment Malfunction

4000

VOLTS

EQUIPMENTUNDER

TEST

ESD

SIMULATORIEC 1000-4

600 NANOCOULOMB

DISCHARGE IMMUNITY

FARADAY

CUP

WAFER OR RETICLE CASSETTES

WAFERS, RETICLES, OR ICs

LESS THAN 600 NANOCOULOMB

ALLOWABLE CHARGE LEVEL

1. Determine Equipment Malfunction Threshold

2. Verify Charge Levels on Devices and Carriers after Processing in Equipment

SEMI E78-0998 GuideRecommended Sensitivity Levels

ESD Control(nC)

Contamination(volts/cm)

EquipmentMalfunction

(nC)Level 4 100 4000 1200

Level 3 50 400 600

Level 2 10 200 300

Level 1 1 100 150

Worldwide Use of Static Control in in Wafer Fabs and Equipment

Manufacturers with static control in their equipment

• Applied Materials• KLA-Tencor• Watkins-Johnson• Gasonics• Coillard• Prometrix• Steag AST• Microtech• Semitool• Amecon• Nanometrics• ASM Europe• Tokyo Electron Labs• Submicron Systems• Thermco• Santa Clara Plastics• Asyst• Jenoptik• Silicon Valley Group • Recif• Fico• PRI Automation• Many others

End Users with static control in their factories

• Intel• Motorola• Texas Instruments• AMD• Analog Devices• IBM• Micron Technology• Hewlett Packard• Ericsson• ST Microelectronics• TSMC• Siemens• Philips• Toshiba• NEC• Samsung• UMC• Macronix• Wacker• MEMC• Photronics• DuPont• Many more

Make E78 Compliance Part of The Purchase Specification

• Purchase specifications are the final agreement between end user and equipment supplier

• Define the requirements for E78 compliance

• Define the requirements for testing to demonstrate compliance

Sample Specifications

• The static control system shall provide electrostatic charge control to meet the recommendations for Level 2 (or 1, 3, or 4 as agreed upon) contained in SEMI Standards document E78-0998.

• Compliance testing shall be done by the equipment manufacturer to demonstrate that the equipment meets the recommendations as contained in SEMI Standards document E78-0998.

• The static control system shall consist of the following items, applied as needed to assure compliance.

– Grounding of all conductive equipment parts

– Static dissipative materials to replace insulators within 30cm of product when feasible.

– Ionization sources to control static charge on process essential insulators or isolated conductors.

– Static control materials to be compatible with cleanroom contamination control and safety requirements.

Conclusions

• SEMI has issued E78-0998 to promote cooperation between users and equipment suppliers in solving static-related problems.

• Once proper materials have been chosen and everything has been grounded, ionizers are required

• Equipment suppliers will need encouragement (i.e., a purchase specification) to provide compliance

• The cost of static control is a small fraction of the cost of product losses and equipment downtime due to static charge.

• Do it Now! Sooner or later your customers will require static charge control.