Handbook of Silicon Wafer Cleaning Technology

Karen Reinhardt, Werner Kern

• Publisher: William Andrew
• Year: 2008
• eBook ISBN: 9780815517733
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Industrial Engineering
• Index: Technology & Engineering

The second Edition of the Handbook of Silicon Wafer Cleaning Technology is intended to provide knowledge of wet, plasma, and other surface conditioning techniques used to manufacture integrated circuits. The integration of the clean processes into the device manufacturing flow will be presented with respect to other manufacturing steps such as thermal, implant, etching, and photolithography processes. The Handbook discusses both wet and plasma-based cleaning technologies that are used for removing contamination, particles, residue, and photoresist from wafer surfaces. Both the process and the equipment are covered. A review of the current cleaning technologies is included. Also, advanced cleaning technologies that are under investigation for next generation processing are covered; including supercritical fluid, laser, and cryoaerosol cleaning techniques. Additionally theoretical aspects of the cleaning technologies and how these processes affect the wafer is discussed such as device damage and surface roughening will be discussed. The analysis of the wafers surface is outlined. A discussion of the new materials and the changes required for the surface conditioning process used for manufacturing is also included.- Focused on silicon wafer cleaning techniques including wet, plasma, and other surface conditioning techniques used to manufacture integrated circuits- As this book covers the major technologies for removing contaminants, it is a reliable reference for anyone that manufactures integrated circuits, or supplies the semiconductor and microelectronics industries- Covers processes and equipment, as well as new materials and changes required for the surface conditioning process- Editors are two of the top names in the field and are both extensively published- Discusses next generation processing techniques including supercritical fluid, laser, and cryoaerosol

PART I

INTRODUCTION AND OVERVIEW

1 Overview and Evolution of Silicon Wafer Cleaning Technology

Werner Kern

Werner Kern and Associates, Lakewood, NJ, USA

1.1 Introduction

The preparation of ultraclean Si (silicon) surfaces by cleaning and surface conditioning for the manufacturing of integrated circuits (IC) has undergone considerable changes since we published the first edition of this book in 1993. The driving forces for these changes have been the ever-increasing requirements for producing advanced Si devices with improved performance, reliability, and cost. The feature sizes of these circuits have been scaled down to below 100 nm and the device structure may incorporate multilevel metallization layers with Cu (copper) and special dielectric materials.

The earlier Si wafer cleaning processes have evolved from aqueous-chemical (the so-called “wet chemical“) to alternative dry cleaning processes for metallized device wafers. These processes include gas-phase procedures, such as plasma reactions for stripping organic photoresist masking layers and their residues. The application of cryogenic aerosols and supercritical fluids for removing particle contaminants for applications where aqueous chemistry cannot be used is being investigated.

The understanding of surface contamination and defectivity and the role of particle adhesion, deposition, measurement, and removal have been substantially advanced during the past 14 years. The same is true for the ancillary analytical and control aspects, including the elucidation of the chemical composition of Si and SiO₂ surfaces, the measurement of the effects of electrically active contaminants, and the instrumental analysis of ultra-trace surface impurities.

While it is the purpose of this book to have experts of the various fields address these exciting developments in depth, the objective of the present chapter is to broadly review the advances achieved specifically in Si wafer cleaning technology and to outline chronologically its evolution from the 1950s to the present. Some portions of the basic material presented in the first edition of this book have been retained, but are updated and expanded to reflect the new developments. Wet-chemical processes are still the most widely used method for Si wafer cleaning in the semiconductor industry today. Therefore, special emphasis is placed in treating wet-processes in this chapter. Dry-cleaning processes will be briefly surveyed with references to the pertinent chapters in this book.

1.2 Importance of Clean and Conditioned Wafer Surfaces

The importance of clean substrate surfaces in the fabrication of semiconductor microelectronic devices has been recognized since the dawn of solid state device technology in the 1950s. It is now well known that the device performance, reliability, and product yield of Si circuits are critically affected by the presence of chemical contaminants and particulate impurities on the wafer or device surface. Effective techniques for cleaning Si wafers before thermal treatment such as oxidation, after patterning by etching, after ion implantation, and before and after film deposition are now more important than ever before because of extreme sensitivity of the semiconductor surface and the nanometer sizes of the device features. As a consequence, the preparation of ultraclean Si wafers has become one of the key technologies in the fabrication of ULSI (ultra-large scale integration) Si circuits.

The term “ultraclean” may be defined in terms of the concentration of both chemical contaminants and particles on the wafer surface. The International Technology Roadmap for Semiconductors (ITRS) [1, 2], shown in Tables 1.2-1-1.2-4, specifies metrics that define the impact on yield based on contamination and defectivity for both front end of line processing (Table 1.2-1 and 1.2-2) and for complete interconnect surface preparation (Table 1.2-3 and 1.2-4).

Table 1.2-1 Front End Processing Surface Preparation Technology Requirements (1): Near-Term Processes

Table 1.2-2 Front End Processing Surface Preparation Technology Requirements (1): Long-Term, Processes

Table 1.2-3 Interconnect Surface Preparation Technology Requirements (2): Near-Term Processes

Table 1.2-4 Interconnect Surface Preparation Technology Requirements (2): Long-Term Processes

For the 32-nm node the total metallic impurities should be, for example, less than 0.5 × 10¹⁰ atoms/cm². Particles larger than 0.11 μm in size should be fewer than approximately 0.1/cm², which translates to fewer than 30 particles per 300-mm wafer. These extremely low numbers are impressive indeed! The reason for such stringent specifications is the fact that the overall device quality is critically affected by trace impurities. Each of the hundreds of processing steps in the fabrication of advanced Si circuits can contribute to contamination. With each advancing year, the node size has been decreased to allow a more densely packed array of device features, while the device chip size has been increasing to accommodate a larger number of circuits. At the same time the permissible maximum concentrations of chemical surface impurities have been lowered. The size of particle contaminants and their density per unit area have also been specified to decrease. Therefore, the demands of surface purity are becoming continually greater and more critical, but are also more difficult to attain.

The term “surface conditioning” may need some clarification. In recent years one has become to realize that the process of cleaning may do more than just remove impurities from the surface. It can prepare the surface chemically for the next process step. For examp...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Foreword
• Preface to the Second Edition
• Preface to First Edition
• PART I: INTRODUCTION AND OVERVIEW
• PART II: WET CHEMICAL PROCESS
• PART III: DRY CLEANING PROCESSES
• PART IV: ANALYTICAL AND CONTROL ASPECTS
• PART V: DIRECTIONS FOR THE NEAR FUTURE
• Book Editors and Chapters Authors
• Index
• Materials Science and Process Technology Series