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2001 | Buch

Fundamental Aspects of Silicon Oxidation

herausgegeben von: Yves J. Chabal

Verlag: Springer Berlin Heidelberg

Buchreihe : Springer Series in Materials Science

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Über dieses Buch

The idea for a book dealing specifically with elementary processes in silicon oxidation was formulated after a stimulating symposium that I organized at the American Physical Society meeting in March, 1998. The symposium, en­ titled "Dynamics of silicon etching and oxidation", explored the mechanisms governing silicon oxidation. With three experimental talks (Hines, Weldon and Gibson) and two theoretical presentations (Pasquarello and Pantelides), it provided a good cross-section of the recent efforts to characterize the in­ terfacial region of silicon oxide grown on silicon. The novelty of this work comes from the present experimental and theo­ retical advances that allow the investigation of the formation of ultra-thin silicon oxides. Although structural characterization of bulk silicon oxides and electrical characterization of thin oxides and their interfaces with silicon have produced an extensive body of work over more than forty years, a mechanis­ tic understanding of the initial oxidation processes has remained elusive. In the past, both the experimental and theoretical efforts have been thwarted by the complexity of dealing with the formation of a mostly amorphous oxide on a crystalline substrate. In this book we present a survey of the state-of-the-art methods, both ex­ perimental and theoretical, specifically dealing with the issue of amorphous dielectric growth. Each chapter critically reviews and cross-correlates infor­ mation provided by experimental techniques, such as microscopy, spectro­ scopy, or scattering, with results obtained using theoretical methods, such as ab initio electronic structure calculations, molecular dynamics, and Monte Carlo simulations.

Inhaltsverzeichnis

Frontmatter
1. Introduction
Abstract
The ages of civilization are denoted by the dominant material of the time; the Stone Age, the Bronze Age and Iron Age. We are now in the Silicon Age. The silicon transistor and development of the integrated circuit have produced a massive change not only in technology and economy, but also in culture and thinking, commensurate with the great materials revolutions of time.
Leonard C. Feldman
2. Morphological Aspects of Silicon Oxidation in Aqueous Solutions
Abstract
Aqueous etching of silicon is important to many processes in the microelectronics industry, including the cleaning of silicon wafers, the detection of dislocations and defects, and the fabrication of micromachined structures. In most of these processes, the anisotropy of the etchant is very important, because it controls the morphology of the etched surfaces. In some cases, the microscopic anisotropy or site-specificity of the etchant is of primary importance. For example, Ohmi et al.[1]have shown that atomic-scale roughness generated by RCA cleaning solutions, which are commonly used to clean silicon wafers, can degrade the performance of metal-oxide-semiconductor fieldeffect transistors (MOSFETs) subsequently fabricated on the cleaned wafer. To prevent this, highly anisotropic silicon cleaning solutions that produce atomically smooth Si(100) faces are highly sought after. Microscopic anisotropy also controls the performance of defect etchants, which are commonly used to quantify dislocation densities. These etchants apparently attack the strained bonds around each atomicscale dislocation and produce macroscopic etch pits that can be detected optically. For other purposes, atomicscale etchant anisotropy is less important than the macroscopic anisotropy — the face-specificity. For example, basic solutions etch Si(111) faces exceedingly slowly, so these etchants can be used to easily fabricate smooth, precisely oriented (111) facets for vee-grooves 2 , inkjet nozzles 3, or other micromachining applications 4.
Melissa A. Hines
3. Structural Evolution of the Silicon/Oxide Interface During Passive and Active Oxidation
Abstract
The dynamic events which occur at the silicon/oxide interface during oxidation are of fundamental importance both in developing models to explain oxidation kinetics and in understanding how interface structure influences the properties of microelectronic devices. Of particular interest is the evolution of interface roughness during oxidation. With modern gate oxides only a few atomic layers thick, any roughness at the silicon/oxide interface affects device performance significantly so that understanding and controlling interface morphology becomes necessary. Interface step behaviour is also important in understanding the mechanism of the oxidation reaction, helping to develop models for the reactivity of atoms at different sites and the order in which bonds are broken. Furthermore, the flow of surface steps during active oxidation (also referred to as etching) can be a powerful tool to modify surface morphology, as required in some interesting novel devices. So from both a practical and a fundamental point of view there is great interest in following the structural evolution of the silicon/oxide interface during oxidation.
F. M. Ross, J. M. Gibson
4. Oxidation of H-Terminated Silicon
Abstract
Recently, the densities, functions and operating speeds of integrated circuits driven by ever-increasing numbers of metal-oxide-semiconductor field-effect transistors (MOSFETs) have increased remarkably to produce not only ultrahigh-speed computers, but also many intelligent operating systems. This is largely a result of continuing progress in Si single-crystal growth and Si-related process and microfabrication technologies for integrated circuits. It is made possible by the stable electrical and thermal properties of Si-Si02 systems and the abundant silicon resources on the earth.
H. Nohira, T. Hattori
5. Layer-by-Layer Oxidation of Si(001) Surfaces
Abstract
The oxidation of Si surfaces is an important issue in the technological application of Si-based microelectronic devices such as metal-oxide-semiconductor field-effect transistors (MOSFETs). Over the past three decades, the excellent electrical properties of the SiO2/Si(001) system and its advantages in the fabrication processes have enabled us to continuously miniaturize Si-based devices. However, the semiconductor industry will soon demand ultrathin gate oxides that are less than 2 nm thick. Several research groups have recently demonstrated MOSFETs with ultrathin gate oxides and have reported problems with these devices [13]. The oxide thickness used for these devices corresponds to oxidation of less than ten monolayers of the Si(001) substrate, so we now face a fundamental physical limit of ultrathin SiO2 films [4]. In addition, while high dielectric-constant (high-K) materials, such as Si3N4, Ta2O5, and Al2O3 have been studied as alternative gate dielectrics for MOSFETs, the SiO2 interlayer between high-K materials and the Si substrate still strongly affects device performance [5, 6]. Therefore, an understanding of the initial oxidation process and the ability to control the oxidation reaction are indispensable for future device development.
H. Watanabe, N. Miyata, M. Ichikawa
6. Atomic Dynamics During Silicon Oxidation
Abstract
The rapid rate of development of the electronics industry is predicated on aggressive scaling rules for robust transistor design. In particular, each successive reduction in the size of the silicon based field effect transistor requires further thinning of the oxide layer which separates the polysilicon gate electrode from the channel. For integrated circuits in production now, this gate oxide has a thickness well below 50 Å. In this thickness regime, which is only an order of magnitude away from typical bond distances, a characterization of the Si(001)-SiO2 interface at the atomic scale is of critical importance. Knowledge of the atomic structure at this interface is intimately related to the understanding of the atomistic mechanisms that govern the oxidation process. In particular, the oxidation process used to fabricate integrated circuits yields a nearly perfect interface between amorphous silica and the silicon substrate for reasons that are still not well understood.
A. Pasquarello, M. S. Hybertsen, R. Car
7. First-Principles Quantum Chemical Investigations of Silicon Oxidation
Abstract
The development of accurate first-principles quantum chemical methods has made dramatic progress in the last two decades. The electronic structure theory of molecules has now reached a stage when calculations with chemically meaningful accuracy are feasible for a wide variety of systems [13]. Methods such as Hartree-Fock theory, coupled cluster theory, and gradientcorrected density functional techniques are widely used by a large number of research groups. Commercial software packages 4 have made the general availability of such methods to be almost universal. While traditional applications of quantum chemical methods were mostly for the study of molecules, such techniques are now finding increasing applications for the study of materials and surfaces. In this chapter, the applications of state-of-the-art quantum chemical methods to the study of chemical reactions on silicon surfaces are discussed.
Krishnan Raghavachari
8. Vibrational Studies of Ultra-Thin Oxides and Initial Silicon Oxidation
Abstract
Over the past two decades, infrared absorption spectroscopy (IRAS) has emerged as a preeminent technique for studying semiconductor surface and interface passivation [1]. For example, it has played a central role in identifying the nature of the HF induced passivation by hydrogen of Si surfaces [26] and, more recently, in describing the microscopic mechanism of surface oxidation [79]. In such studies not only can the nature of the surface termination (SiHx,(x=1–3), or SiOx,(x=0–2)) be determined, but the orientation of the various species can also be quantified, thus providing structural as well as chemical information. At present, IRAS exhibits sufficiently high sensitivity that it is possible to detect as little as 1% of a hydrogen monolayer. This effectively allows the characterization of minority surface species (steps, defects) as well as of the majority surface termination. In addition, the high spectral resolution afforded by IRAS can be utilized to distinguish subtle differences in chemical environment (due to the presence of dangling bonds, for example) and to unravel complex dynamical effects, such as coupling between isolated surface modes and the substrate phonons or electrons.
Y. J. Chabal, M. K. Weldon, K. T. Queeney, A. Estève
9. Ion Beam Studies of Silicon Oxidation and Oxynitridation
Abstract
In this chapter we discuss the use of ion beam methods to examine silicon oxidation and oxynitridation. Ion beam analysis, although usually performed ex-situ following growth, offers precise information about the composition and growth mechanism of films. We limit our work to an examination of methods involving ion beam energies E ≥ 50 keV. We discuss Rutherford backscattering spectroscopy (RBS), elastic recoil detection (ERD), medium energy ion scattering (MEIS), nuclear reaction analysis (NRA), and nuclear resonance profiling (NRP). SIMS and other lower energy methods are not reviewed; instead the reader is referred to reviews elsewhere [1,2]. For many isotopes SIMS has superior detection limits than RBS and NRA. It provides very high sensitivity (in some cases on the order of 0.001 atomic %) and can be performed rapidly [3,4]. For many of the applications discussed below, however, conventional SIMS techniques do not offer the depth resolution needed due to matrix effects and ion beam mixing.
W. H. Schulte, T. Gustafsson, E. Garfunkel, I. J. R. Baumvol, E. P. Gusev
10. Local and Global Bonding at the Si-SiO2 Interface
Abstract
The excellent electrical properties of the Si-SiO2 interface is the primary reason for the domination of Si-based microelectronics. No other semiconductor has a native oxide of such outstanding quality. Alternative dielectrics on any semiconductor only recently began to show promise. The Si-SiO2 interface has been studied extensively by a very wide array of experimental and theoretical techniques for more than 40 years. Yet, many of its key properties have remained a mystery. With little effort one can get an extremely abrupt and smooth interface by thermal oxidation (Fig. 10.1). Such behavior is surprising in view of the fact that oxygen has a high solubility in Si. At the high oxidation temperatures (> 900°C) oxygen is quite mobile in Si. Somehow, interdiffusion, which would cause a rough interface, should take place, but obviously it does not to any appreciable degree.
S. T. Pantelides, R. Buczko, M. Ramamoorthy, S. Rashkeev, G. Duscher, S. J. Pennycook
11. Evolution of the Interfacial Electronic Structure During Thermal Oxidation
Abstract
The narrowest feature on an integrated circuit is currently the gate oxide. At the end of the last century, gate oxides less than 20 Å were used in some commercial integrated circuits. Between 2004 and 2008, if silicon dioxide is still to be used, then the projected gate-oxide thickness will be less than 1 nm, or 5 silicon atoms across. At least two of those five atoms will be at silicon/oxide interfaces. The interfacial atoms have very different electrical and optical properties from the desired bulk silicon dioxide yet comprise a significant fraction of the dielectric layer. This fundamental problem has also become a very practical one. It is now technologically possible to produce metal oxide semiconductor field effect transistors (MOSFETs) with gates shorter than 50nm and SiO2 gate oxides less than 1.3nm thick [1]. Such a thin gate oxide is required to improve the drain-current response of the transistor to the applied gate voltage (allowing lower voltages to be used). Since power dissipation currently limits the scale of integration, lowering the power supply voltage becomes the key to increasing integration and improving IC performance. Therefore, the performance of the gate oxides is central to the improvement of very large-scale integrated circuits. Since a practical alternative to SiO2 (or its nitrogenated derivatives), providing a higher dielectric constant or a reduced leakage current, has not been identified yet [2], it is crucial to the future of large-scale integration to discover the practical limits on the thickness of the SiO2 gate oxide.
D. A. Muller, J. B. Neaton
12. Structure and Energetics of the Interface Between Si and Amorphous SiO2
Abstract
The unique role of silicon in semiconductor technology is due largely to the remarkable properties of the Si—SiO2 interface, especially the (001)-oriented interface used in most devices [1]. Although Si is crystalline and the oxide is amorphous, the interface has an extremely low density of dangling bonds or other electrically active defects. With the continual decrease of device size, the nanoscale structure of the silicon/oxide interface becomes more and more important. Yet the atomic structure of this interface is still unclear.
Yuhai Tu, J. Tersoff
Backmatter
Metadaten
Titel
Fundamental Aspects of Silicon Oxidation
herausgegeben von
Yves J. Chabal
Copyright-Jahr
2001
Verlag
Springer Berlin Heidelberg
Electronic ISBN
978-3-642-56711-7
Print ISBN
978-3-642-62583-1
DOI
https://doi.org/10.1007/978-3-642-56711-7