l.mcturk aug 2002 motorola general business use motorola, the stylized m, and all other trademarks...

L.McTurk Aug 2002 Motorola General Business Use Motorola, the Stylized M, and all other trademarks indicated as such herein are trademarks of Motorola, Inc. ® Reg. U.S. Pat. & Tm. Off.

All other product or service names are the property of their respective owners. © Motorola, Inc. 2001. All rights reserved.

SPS Scotland

Introduction

Laurie McTurkMotorola , Quality, EKB, Scotland

Six Sigma Black Belt (1995)

Dennis WilsonMotorola, Process eng, MOS9, EKB, Scotland

Six Sigma Black Belt candidate



SPS Scotland

Contents

•Manufacturing Semiconductors

•Inline process control

•Maintaining good control limits with x,000 charts

•Trying to see ‘the wood for the trees’

•Managing ownership and driving continuous improvement



SPS Scotland

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3 2

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Objective is to turn Silicon wafers into ICsEach wafer can have ~300 to X,000 ICs

Yield is determined by how many wafers remain after all processes

+

What proportion of ICs function when tested (% good area of wafer).



SPS Scotland

Sequential process•Typically ~300 processes, 3 -4 weeks cycle time•Can be up to 600 processes

Electricalfunctionaltesting

Inline process measurement & control



Serial processing •All processes have the potential to scrap a batch.

IC verification is only possible after all inline processing is complete.

Inline process control must be maintained to avoid scrap product arriving at electrical verification.

Inline process control maintains optimum processing conditions leading to maximized production yield.



SPS Scotland

Process control

Each individual process must have • Process monitor

•Indicator of the completed IC performance • E.g Measured polysilicon gate dimension

•Transistor channel length •Speed of the circuit.

• Homogenous data stream•Use SPC to maintain control



SPS Scotland

Sample Plan

example 3 wafers,3 data sites per wafer

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2

3

1

2

31

2

3



Factory wide computer system Data entered into data collection files and subsequent control charts.

Data is charted by machine

Trends and shifts within the process are detected by applying WesternElectric control rules to the charts.

Out of limit rule violation results in immediate, automated equipmentshutdown, guarding against any further product risk.



Automated out of limit actions, however, are only useful if the imposed limits are accurate.

Limits too loose •Significant changes/excursions go undetected until fab completion

•possible scrap, reduced yield, etc.



Limits too tight false alarms/‘white noise’•poor productivity•over adjustment •increased variability •frustration from the front line operators



Western Electric control rules are probability based tests Some risk that a process is behaving differently from previous history.

Rule Test Warning/ActionWE1 1 Point GT upper control limit Auto ActionWE2 2 of 3 consecutive points GT CL+2 Sigma* WarningWE3 4 of 5 consecutive points GT Centerline +1 Sigma* WarningWE4 8 consecutive points above the Centerline WarningWE5 1 Point LT lower control limit Auto ActionWE6 2 of 3 consecutive points LT Centerline -2 Sigma* WarningWE7 4 of 5 consecutive points LT Centerline -1 Sigma* WarningWE8 8 consecutive points below the Centerline WarningWE9 15 consecutive points within Centerline +/- 1 Sigma* Warning

WE10 15 consecutive points outside Centerline +/- 1 Sigma* Warning



The Instability index

A tool to identify charts that are not performing according to the control limits and centrelines installed

Number of control rules violated within time period

Number of points collected within time period



The daily Istab report thus catches

Xbar charts with too wide control limits

Range, Std Dev, Particle charts with limits set too high



The Istab is at a minimum when •The fewest excursions occur•The control limits and centerlines are accurate•The process is stable

Off target &

Out of control

Off target &

wide limits

Stable process & accurate control limits



Using the Istab metric in this fashion promotes the use of accurate control limits and centerlines

FROM TO

Even on skewed distributions like particles, Ranges, Std.Dev



Two tier control rule system

•Engineering warning

Western Electric rules inside control limits (e.g. 8 points one side of the centreline) •minimizing production false alarms

•Automated immediate equipment shutdown on control limit violation

With accurate control limits and centrelines established

•Increase in Istab is an early warning of a change in the process•Control limit violation is likely to be due to a real process excursion•Less likely to be a false alarm.



Create a measure the measures to maintain process control

•Is the metric is being used to identify and rectify problems ?

•Derive a mean daily Istab per process group and per engineer•Chart file labels identify ownership by process section and by engineer

•Trend graph the mean of these Istabs for each day

•A 60 day rolling trend shows if process control is •Improving•Worsening•Stable

•Breaking the trend out by owner drives consistency across the factory

l.mcturk aug 2002 motorola general business use motorola, the stylized m, and all other trademarks...

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