1 Introduction

1.1 What is Metrology?

1.2 Measurements and Metrology

1.3 Metrology in Daily Life

1.4 Applications in Modern Manufacturing

1.5 Standards and Traceability

1.6 Metrology Standards Related to IC Manufacturing

1.7 Measurement Methods and Process

     1.7.1 Operator, measurement system, and measurement target

     1.7.2 Manual measurement versus automatic measurement

1.8 Applications of Industrial Metrology

References

2 Metrology Fundamentals: Measurement System Characterization and Calibration Using Traditional Definitions

2.1 Introduction

2.2 Precision

2.3 Long-Term Stability

2.4 Accuracy

2.5 Linearity

2.6 Tool-to-Tool Matching: Multiple Measurement Systems

2.7 Classifying Components of Uncertainty

2.8 Measurement Errors and Measurement Uncertainties

     2.8.1 Random errors

     2.8.2 Systemic errors

     2.8.3 Tool-to-tool variations

2.9 Uncertainties and Risks

2.10 Are These Traditional Metrics Enough?

References

3 Fundamental Metrology: Redefining Measurement System Analysis

3.1 Introduction

3.2 A Metrologist�s Core Activities

3.3 Roadmap and Specifications

3.4 Standards

3.5 Monitor Samples and Process Stressed Artifacts (PSAs)

3.6 Test Vehicle Variability, Metrology-Induced Sample Damage, and Sample Stability

3.7 Reference Measurement System

3.8 Precision

     3.8.1 Precision example

3.9 Calculating Precision in the Presence of Measurement-Induced Damage or Sample Changes over Time

3.10 Mandel Regression

3.11 Accuracy

     3.11.1 Accuracy example

3.12 TMU: An Alternative Definition for Clarification

     3.12.1 Mandel analysis: the building block for new matching terms

3.13 Matching

     3.13.1 Matching example 1

     3.13.2 Matching example 2

3.14 Sustaining/Stability/Statistical Process Control (SPC)

     3.14.1 Using TMP and FMP methodology to calculate SPC control-chart limits

     3.14.2 Mean control-chart-limit calculations for each tool

     3.14.3 Mean control-chart-limit calculations for the fleet

     3.14.4 Control-chart-limit setup example 1

     3.14.5 Control-chart-limit setup example 2

     3.14.6 Leveraging FMP to determine the root cause to allow the fleet to meet the requirements

3.15 Sampling Plan: Catch-All Major Variations

3.16 Random Sampling

3.17 Systematic Sampling

3.18 Summary

References

4 Metrology in the Semiconductor IC Industry

4.1 Pervasiveness of Metrology

4.2 Metrology�s Impact on Time to Market

4.3 Value of Metrology

4.4 Metrology Target Design: an Element of Overhead

4.5 Chip Scaling and an Introduction to Some Key Metrology Toolsets

4.6 Vision System and Recipes

4.7 Toolset Recipe Portability Monitoring

4.8 Large Fleet Sizes: Fleet Management

4.9 IC Process Development and Control

4.10 Metrology in IC Manufacturing Process Control

References

5 Metrology Toolsets in IC Manufacturing: Optical Metrology

5.1 Optical Film Characterization: Thickness and Composition

5.2 Scatterometry (OCD)

5.3 Overlay

References

6 Metrology Toolsets in IC Manufacturing: Charged-Particle Metrology Systems

6.1 Electron-based Systems

6.2 CD-SEM and Sample Interactions

6.3 Key Fundamental Challenges of the CD-SEM

6.4 SEM-based Overlay Measurements

References

7 Metrology Toolsets in IC Manufacturing: Additional Metrology Systems

7.1 X-Ray Metrology

7.2 In situ and Integrated Metrology

7.3 Critical-Dimension Atomic Force Microscope (CD-AFM)

References

8 Limitations of Metrology Techniques and Hybrid Metrology

8.1 Introduction

8.2 Hybrid Metrology: Synergies of Multiple Techniques

8.3 Types of HM Implementation

References

9 Metrology in Mask Making

9.1 Mask CD Measurements

9.2 Mask Inspection

References

10 Perspectives on Future Challenges and Considerations

10.1 Measurement Tooling Challenges

10.2 Fault Detection and Control

10.3 Virtual Metrology

10.4 Waferless Recipe Writing

10.5 The Blurry Line between Metrology and Defect Inspection

10.6 Line-Edge Roughness and 3D Metrology

10.7 Contour Metrology

10.8 Lab-to-Fab and New Technology Trends

References

Preface

We contemplated writing a book about IC manufacturing metrology for years. Each of us in parallel recognized a gap that existed in the field of metrology and inspection. Until now, metrology (not to be confused with meteorology) had no book from the perspective of an engineer in a manufacturing and development environment in the modern IC industry. The closest we could find was a chapter called "Metrology Methods in Photolithography," written by Laurie J. Lauchlan, Diana Nyyssonen from IBM Microelectronics, and Neal Sullivan from DEC, within a book titled Handbook of Microlithography, Micromachining, and Microfabrication, Vol. 1 (SPIE Press, 1997). The other significant text comes from Alain Diebold, in a book titled Handbook of Silicon Semiconductor Metrology (CRC Press, 2001). Numerous other books, especially statistical books, briefly mention metrology in the context of gauge studies, precision-to-tolerance ratios (also called the gauge maker's rule), and repeatability and reproducibility.

The three of us combined have been working in semiconductor IC fabs for more than two decades, specializing in metrology in semiconductor manufacturing. This book allows us to share our learning, understanding, and experiences with our fellow engineers and managers. As in other disciplines, metrology is constantly improving, enhancing, and developing to meet ever-increasing needs in today�s high-technology manufacturing. In IC fabs, people refer to metrology equipment as process equipment tools or a fleet of tools. We will use that term in this book to mean metrology equipment or systems. Photomasks, masks, and reticles are all used to describe the photomasks used in IC manufacturing, interchangeably. Many acronyms in IC fabs are used in this book; please refer to the List of Acronyms for their exact meanings.

The contents of the book are organized not only for metrology engineers but also for other process engineers and fabmanagers to better understand metrology data and the uncertainties associated with those data. It also serves as a textbook for students and researchers who are interested in metrology in general or as a reference book on fundamentals and latest developments in the IC industry. The first two chapters introduce metrology at its most basic level. The first half of Chapter 1 defines metrology, its origin, and its purpose regardless of the field of practice. The second half of the chapter discusses measurement methods and the measurement process and includes descriptions of operator, machine, and what is being measured along with the evolution of manual and automated measurements. It closes with a discussion on applications of industrial metrology. Chapter 2 explores metrology fundamentals as they pertain to traditional measurement system characterization and calibration. The word "traditional" is used because this is an area where much has changed since the 1997. Chapter 3 discusses the need to improve upon the traditional forms of measurement system characterization and calibration. Many newer concepts are introduced here in the areas of system matching, long-term stability monitoring, and accuracy. Chapter 4 focuses on a particular industrial application of metrology--the semiconductor industry--that has the tightest metrology requirements in the world. It explores areas such as the pervasiveness and value of metrology, target design, and process control. Chapter 5 features optical metrology measurement techniques such as ellipsometry and scatterometry. Chapter 6 presents charged-particle measurement techniques, with a primary focus on scanning electron beam metrology. Chapter 7 explores other measurement techniques not used inline in 1997, such as x-ray and in-situ metrology. Chapter 8 discusses the limits of metrology and the evolution of hybrid metrology. Hybrid metrology development and implementation is another major change. Chapter 9 discusses metrology in mask making, emphasizing the differences as compared to wafer metrology. The final chapter closes with trends, perspectives on future metrology challenges, and other considerations not covered in the other chapters.

Example Excel spreadsheets are provided in the accompanying CD in the area of measurement uncertainty analysis--specifically, precision, matching and relative accuracy. These files complement the textbook material and help readers understand the metrology concepts better (as well as leverage these spreadsheets in their own work, as needed).

Although there is a significant focus on the semiconductor industry, many of the concepts can be easily applied to other industrial fields. The metrology field has grown significantly over time, especially in the areas of semiconductor manufacturing. With this growth comes an increasing need for metrology expertise. This book is intended to introduce a new generation to metrology while also helping current practitioners. Almost every other major semiconductor discipline, such as lithography and etch, is taught in academia; there is very little metrology material taught currently, and we hope this book helps spark increased academic interest.

Bo Su
Eric Solecky
Alok Vaid
August 2015