Silicon Integrated Circuits. Advances in Materials and Device Research PDF
Preview Silicon Integrated Circuits. Advances in Materials and Device Research
Applied Solid State Science ADVANCES IN MATERIALS AND DEVICE RESEARCH Editor: Raymond Wolfe AT&T BELL LABORATORIES MURRAY HILL, NEW JERSEY Supplement 1 Magnetic Domain Walls in Bubble Materials A. P. Malozemoff and J. C. Slonczewski Supplement 2 (in three parts) Silicon Integrated Circuits Edited by Dawon Kahng Silicon Integrated Circuits Parte Edited by Dawon Kahng AT&T BELL LABORATORIES MURRAY HILL, NEW JERSEY 1985 ACADEMIC PRESS, INC. (Harcourt Brace Jovanovich, Publishers) Orlando San Diego New York London Toronto Montreal Sydney Tokyo COPYRIGHT © 1985, BY ACADEMIC PRESS, INC. ALL RIGHTS RESERVED. NO PART OF THIS PUBLICATION MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM OR BY ANY MEANS, ELECTRONIC OR MECHANICAL, INCLUDING PHOTOCOPY, RECORDING, OR ANY INFORMATION STORAGE AND RETRIEVAL SYSTEM, WITHOUT PERMISSION IN WRITING FROM THE PUBLISHER. ACADEMIC PRESS, INC. Orlando, Florida 32887 United Kingdom Edition published by ACADEMIC PRESS INC. (LONDON) LTD. 24-28 Oval Road, London NW1 7DX ISSN 0194-2891 ISBN 0-12-002960-X PRINTDE IN THE UNITDE STATS EOF AMERAI C 85 86 87 88 9 8 7 6 5 4 3 2 1 List of Contributors Numbers in parentheses indicate the pages on which the authors' contributions begin. G. K. CELLER, AT&T Bell Laboratories, Murray Hill, New Jersey 07974(1) W. FICHTNER, AT&T Bell Laboratories, Murray Hill, New Jersey 07974 (119) SEITARO MATSUO, Atsugi Electrical Communication Laboratory, Nippon Telegraph and Telephone Public Corporation, Atsugi-shi, Kanagawa 243-01, Japan (75) Τ. E. SEIDEL, AT&T Bell Laboratories, Murray Hill, New Jersey 07974 (1) vii Preface It has been twenty years since the first MOS transistors were demonstrated using the Si0 -Si system. This system is unique in that thermal Si0 films 2 2 possess high dielectric strength and its interfaces contain manageable amounts of interfacial states, both conditions being essential to a successful MOS transistor. In conjunction with Si planar technology, the MOS-based integrated circuits are impacting our daily lives on a scale not encountered since the Industrial Revolution. The MOS circuit performance has steadily improved with the advent of fine-line lithography and is expected to surpass that of bipolar transistor circuits. The Applied Solid State Science serial publication has followed these exciting developments through judicious selection of review articles, although they have been somewhat disjoint. The time is now ripe for presenting a package of reviews, in the form of supplementary volumes to the publication, on the current status of MOS device physics, which has shown remarkable maturity during the past five years, and of device processing technology, which is still undergoing almost daily improvement. The first supplementary volume begins with a chapter by John R. Brews. This chapter develops the most complete theory to date of long-channel MOS transistors on good physical foundations. Important device parameters are derived in closed form, mostly compact enough to aid circuit simulations, based on sound approximations with clearly defined validity. The chapter closes with an examination of short channel effects that indicate the future direction in research. The chapter has been written in a tutorial spirit and should prove an excellent text for students in undergraduate and graduate school, as well as a guide to practicing scientists and engineers. The first volume also contains two more chapters designed to introduce readers to emerging, next-generation integrated circuits. One is a review article by Yoshio Nishi and Hisakazu Iizuka covering the recent efforts to develop nonvolatile semiconductor memories. An ideal memory stores data per manently, yet permits fast access using a minimum of energy, and is physi cally compact. It appears that silicon technology is evolving to finally create such an ideal memory. The readers should find this chapter both illuminating and exciting. The final chapter of the first volume, by Alfred C. Ipri, reviews ix χ PREFACE the current status of silicon-on-sapphire (SOS) technology. This article assesses the future of SOS technology, which is presently at a crossroad. Long-held promises of higher circuit performance are being challenged by the evolving VLSI and non-SOS circuits on the one hand and lingering materials problems associated with silicon-sapphire interfaces on the other. Hopefully, this chapter prepares those who wish to work toward resolving the difficulties and attaining the promised land in the near future. The main applications of MOS integrated circuits have been in low-power circuitry (i.e., memories and logic circuits). Recent movements toward high power integrated circuits promise to carve out another major domain. The second volume, therefore, deals with the special considerations needed to achieve high-power Si-integrated circuits. The first chapter of this volume, by Richard B. Fair, lays foundation for the most important operations needed for the high-power circuitry, namely, impurity diffusion and oxida tion. This chapter treats these related phenomena in light of the most recent understanding of crystal defects under thermal equilibrium in silicon. The second chapter, by B. Jayant Baliga, systematically develops essential high- power device physics and associated technology. This chapter should serve the needs of practicing scientists and engineers for immediate applications. Again, it is written in a tutorial tone and should be appropriate as a text. The third volume contains topics on ever-evolving processing technology. Since Si-integrated circuits are matured commercial entities, new techno logical innovations rather than new physics tend to play a major role. It is felt appropriate, therefore, to review in this volume some of the most prom ising new approaches along with the new understanding of processing-related areas of physics and chemistry. The first chapter, by G. K. Celler and Τ. E. Seidel, is on the transient thermal processing of silicon. The second, by Seitaro Matsuo, is concerned with the use of electron cyclotron resonance plasmas in two important materials processing techniques: reactive ion-beam etching and plasma deposition. The third, by W. Fichtner, deals with the exploding area of VLSI processing and process simulation. The Editor wishes to thank the contributing authors for their arduous efforts and personal sacrifices that made the publishing of this volume possible. Finally, the Editor acknowledges AT & Τ Bell Laboratories, some facilities of which were used in editing these volumes, and especially the editorial skill rendered by Ms. Denise McGrew. Dawon Kahng APPLIED SOLID STATE SCIENCE, SUPPLEMENT 2C Transient Thermal Processing of Silicon G. Κ. CELLER AND Γ. £. SEIDEL AT&T BELL LABORATORIES MURRAY HILL, NEW JERSEY I. Introduction 2 II. Adiabatic Annealing 4 4 1. Introduction 2. Absorption of Photons and Electrons 4 3. Equipment 10 4. Microstructure and Dopant Incorporation 11 5. Amorphization of Si and Other Rapid Regrowth Phenomena . .. 18 6. Summary 22 III. Thermal Flux Annealing 23 7. Equipment 23 8. Diffusion Profiles 25 9. Defects in Beam-Annealed Si 26 10. SPE Rate Measurements 28 IV. Isothermal Rapid Annealing 32 11. Equipment and General Uses 32 12. Temperature Determination and Stress Effects 35 13. Dopant Activation 40 14. Dopant Diffusion (Boron and Arsenic) 44 15. Defect Removal 53 V. Related Rapid Thermal Processes 55 16. Fast Evaluation of Implantation 55 17. Shallow Junctions for ICs 55 18. Grain Boundary Diffusion 56 19. P-GlassFlow 58 20. Suicide Formation 58 21. Aluminum Contact Sintering 59 22. Recrystallization of Si on Insulator 60 23. Laser Gettering of Impurities 64 VI. Summary 66 References 67 1 Copyright © 1985 by Academic Press, Inc. All rights of reproduction in any form reserved. ISBN 0-12-002960-X 2 G. Κ. CELLER AND Τ. Ε. SEIDEL I. Introduction Very large scale integration (VLSI) of semiconductor devices has become a reality. Its needs are the driving force for developing new processing technologies. Typical processes for fabrication of semiconductor devices can be grouped into three categories: (1) pattern definition by lithography, (2) introduction of electrically active impurities (doping) and deposition of conducting or insulating films, and (3) heat treatments for oxidations, dif fusions, sintering, reflowing, suicide formation, and for annealing of defects introduced by any of the preceding processes. Although great advances have been achieved over the years in the fields of lithography, doping, and film deposition, the delivery of heat has not changed significantly since the early days of the semiconductor industry. It usually involves insertion of a stack of silicon wafers held in a quartz boat into a resistively heated quartz tube. The heating rates are a function of the inser tion speed and the number of wafers in the boat. The wafers start heating from the edges and it takes several minutes to reach the final temperature and even heat distribution. If wafers were inserted rapidly, the temperature gradients would be sufficient to cause wafer slip and bow, and boat rollers could scatter particles onto silicon surfaces. To avoid these problems wafers are heated and cooled slowly over several minutes and absorb much more thermal energy than is necessary for annealing. An additional disadvantage of con ventional heat treatments is the lack of any provision for localized heating of selected areas or layers. For example, since most semiconductor devices are formed in the top l-3-μηι surface layer of 500-^m-thick silicon wafers, it would often suffice to heat this top layer only, something that cannot be done in a tube furnace. As devices become smaller, it becomes more important to control precisely the spatial extent of the electrically active layers. By selecting a suitable acceleration energy, the stopping range of implanted ions can be controlled quite accurately. This advantage of depth control is largely compromised by thermal diffusion of impurities during furnace annealing and during other high-temperature processing steps. For that reason VLSI devices necessitate development of "low-temperature" processing. Rapid annealing encompasses several methods of reducing the heating cycles. They range from laser annealing with nanosecond pulses of light to rapid isothermal heating over several seconds. The rapid annealing processes can be divided into three groups: (1) adiabatic, (2) thermal flux, and (3) rapid isothermal annealing. This classifica tion, first proposed by Hill,1 is illustrated in Fig. 1. In adiabatic annealing, TRANSIENT THERMAL PROCESSING OF SILICON 3 the energy is deposited right at the surface, within the top \-μτη layer, in a time too short to allow any appreciable heat loss by diffusion into the mate rial. Consequently, the near-surface layer is melted while the rest of the sample remains at room temperature. All irradiations with energy beam pulses shorter than 10" 7 sec fall into this category. In thermal flux annealing, the thermal diffusion length is comparable to the wafer thickness. Heat is diffused into the bulk at a substantial rate and temperature gradients span the wafer thickness. Heating with scanned electron and laser beams falls into this category and so does flashlamp irradiation. During rapid isothermal annealing the entire wafer reaches a uniform temperature. This requires a heating time of at least 1 sec. Conventional furnace heating is of course isothermal as well. The difference lies in the fact that the entire chamber is isothermal in a standard furnace, whereas in rapid isothermal heating wafers absorb most of the radiation and the walls of the enclosure are usually at a lower temperature. In this chapter we review annealing with directed-energy beams and rapid isothermal annealing. Section II is devoted to adiabatic annealing with laser and electron beams. Pulsed melting provides a unique tool for the study of very rapid solidification phenomena, some of which are discussed. Thermal flux annealing is reviewed in Section III. It allows diffusionless DEPTH Fig. 1. Definition of three heating regimes—adiabatic, thermal flux, and rapid isothermal. 1 (From Hill. Copyright North-Holland Physics Publishing, Amsterdam, 1981.) 4 G. Κ. CELLER AND Τ. Ε. SEIDEL solid-phase regrowth of ion-implanted layers. In this section we also present some novel measurements of solid-phase regrowth rate. Section IV describes rapid isothermal annealing, from equipment and temperature measurement considerations to diffusion profiles and defect removal. Section V includes several applications stemming from rapid annealing and semiconductor processing with directed-energy beams. II. Adiabatic Annealing 1. INTRODUCTION In the mid-1970s Russian scientists were first to report that silicon amorph- ized by ion implantation recovered its crystallinity when irradiated with a short, high-intensity pulse from a ruby or Nd:glass laser.2-4 In the process the implanted impurities were incorporated into silicon lattice and became electrically active. Since the effect of irradiation was similar to that obtained in conventional furnace annealing of ion implants, the term laser annealing was coined. Over the next several years laser annealing has been studied in great detail and the concept of laser annealing has been broadened to encompass almost any thermal processing of semiconductors with lasers.5 In this section we primarily consider removing implantation damage and activating impurities using short laser pulses; we also discuss the limiting case of an extremely fast solidification. Crystalline recovery with longer, millisecond irradiation is discussed in Section III. 2. ABSORPTION OF PHOTONS AND ELECTRONS In adiabatic annealing, a pulse from a Q-switched laser is focused on an implanted Si target to supply an energy density in excess of 1 J/cm2 to the surface layer. Since pulses are 10"7-10"9 sec long, the power density has to be in the 108-W/cm2 range. Lasers with sufficient energy for short-pulse annealing include ruby, Nd:glass and Nd:YAG, excimer lasers, C0 and 2 alexandrite lasers. For better absorption in silicon, the output of Nd lasers is often shifted from infrared wavelengths into visible by frequency doubling. Some representative lasers and their uses are listed in Table I. The thickness of a heated layer is a function of the optical absorption depth a-1 and of thermal diffusivity D = K/Cp. The latter determines a charac v teristic thermal diffusion length d = (2Di )1/,2 where κ is the thermal con p ductivity, C is the specific heat per unit mass (joules per gram per degree v
The list of books you might like
