The outstanding properties of SiO2, which include high resistivity, excellent dielectric strength, a large band gap, a high melting point, and a native, low defect density interface with Si, are in large part responsible for enabling the microelectronics revolution. The Si/SiO2 interface, which forms the heart of the modern metal–oxide–semiconductor field effect transistor, the building block of the integrated circuit, is arguably the worlds most economically and technologically important materials interface. This article summarizes recent progress and current scientific understanding of ultrathin (<4 nm) SiO2 and Si–O–N (silicon oxynitride) gate dielectrics on Si based devices. We will emphasize an understanding of the limits of these gate dielectrics, i.e., how their continuously shrinking thickness, dictated by integrated circuit device scaling, results in physical and electrical property changes that impose limits on their usefulness. We observe, in conclusion, that although Si microelectronic devices...

Ultrathin (<4 nm) SiO2 and Si-O-N gate dielectric layers for silicon microelectronics: Understanding the processing, structure, and physical and electrical limits

The physics and technology of a relatively new, short‐time, thermal processing technique, namely rapid isothermal processing (RIP), based on incoherent sources of light for the fabrication of semiconductor devices and circuits, are reviewed in this paper. Low‐cost, minimum overall thermal budget, low‐power consumption, and high throughput are some of the attractive features of RIP. The discussion of RIP, in the context of other thermal processes, history, operating principles, different types of RIP systems, various applications of RIP using single processing steps, and novel applications of RIP, including in situ processing and multistep processing, is described in detail. Current trends are in the direction of RIP‐dominated silicon integrated circuit fabrication technology that can lead to the development of the most advanced three‐dimensional integrated circuits suitable for applications such as parallel processing and radiation hardening. RIP is not only a superior alternative to furnace processing, but it is also the only way to perform certain crucial steps in the processing of compound semiconductor devices such as high‐mobility transistors, resonant tunneling devices, and high‐efficiency solar cells. Development of more accurate temperature measurement techniques and theoretical studies of heat transfer and other fundamental processes are needed. Dedicated equipment designed for a specific task coupled with in situ processing capabilities will dominate the future direction of RIP.

Rapid isothermal processing

Ion beam induced surface and interface engineering

The growth of ultrathin oxide films by the thermal oxidation of Si(100) at 1020--1170 K and in ${10}^{\mathrm{\ensuremath{-}}1}$--${10}^{\mathrm{\ensuremath{-}}3}$ Torr ${\mathrm{O}}_{2}$ pressure has been studied by high-resolution medium-energy ion-scattering spectroscopy (MEIS). To develop a fundamental understanding of very thin oxide film growth, we utilize sequential isotopic exposures ${(}^{18}$${\mathrm{O}}_{2}$ followed by $^{16}\mathrm{O}_{2}$). MEIS readily distinguishes $^{18}\mathrm{O}$ from $^{16}\mathrm{O}$ and the depth distribution for both species can be determined quantitatively with high accuracy. Our results show that the traditional phenomenological models for silicon oxidation cannot be applied to the initial oxidation. For very thin oxide films (15--25 \AA{}), we find overlapping isotope depth profiles in the film. For thicker films (g40 \AA{}), we find that several key aspects of the Deal-Grove model (oxygen diffusion to the Si-${\mathrm{SiO}}_{2}$ interface and oxide formation at and/or near that interface) are consistent with our results. We also observe $^{18}\mathrm{O}$ loss from the surface after reoxidation in $^{16}\mathrm{O}_{2}$. The complex oxidation behavior during the initial oxidation is likely to be a combination of interfacial, near-interfacial, and surface reactions.

Growth mechanism of thin silicon oxide films on Si(100) studied by medium-energy ion scattering.

Ion-beam-induced epitaxial crystallization and amorphization in silicon

High-resolution transmission electron microscopy (HRTEM) and ellipsometry techniques have been employed to measure thicknesses of silicon oxide, grown at 800°C in dry oxygen, in the thickness range of 2–20 nm. While the oxide growth data measured from TEM obey a nearly linear behavior, those obtained from ellipsometry are seen to vary nonlinearly. The interface structure as function of the increasing oxide thickness was studied using HRTEM. At these oxidation temperatures, the earlier reported variations of roughness at the interface on the oxide thickness for oxides grown at 900°C are not seen. Attempts aimed at correlating the high-resolution transmission electron micrographs with some physical parameters like the refractive index and the dielectric breakdown lead to considerations of the importance of the effect of protrusions of silicon atoms of 1 mm size into SiO2 layers on the interface properties. These findings lead to explanations of some key features concerning the refractive index and density of thin SiO2.

Silicon oxidation and Si-SiO2 interface of thin oxides

In light of the recent discovery [11,12] that heavy ion irradiation initiates a morphological instability in the amorphous phase of Ge which erupts to form surface craters, previous studies of ion beam mixing in the metal/Ge system [2,4] are re-examined. Correlated ion scattering/channeling and cross-section electron microscopy are utilized to study the Au/Ge and Al/Ge systems under a variety of mixing conditions. Implications for both the crater formation and ion beam mixing mechanisms are discussed.

Morphological instabilities and ion beam mixing in Ge

We have investigated ion‐beam and laser mixing of Ni overlayers on silicon carbide substrates using cross‐section and analytical techniques of electron microscopy, and ion scattering and channeling techniques. The thickness of the overlayers was varied from 200 to 500 A on both crystalline and polycrystalline substrates of silicon carbide. The thickness of the ion‐beam mixed region was found to increase with increasing dose of the implanted ions. The laser mixing was obtained only within a critical window of the pulse energy density (1.15±1.25 J cm−2) of a ruby laser (wavelength 0.693 μm, and pulse duration 28×10−9 s). The structure of the mixed region was found to be amorphous, with occasional presence of crystalline nickel silicide (Ni2Si) islands. The laser‐mixed SiC specimens showed a considerable improvement (>35%) in their fracture strength.

Ion‐beam and laser mixing of nickel overlayers on silicon carbide

High-resolution imaging of ion-implantation damage and mechanism of amortization in semiconductors

In light of the recent discovery that heavy ion irradiation initiates a morphological instability in the amorphous phase of Ge which erupts to form surface craters, previous studies of ion beam mixing in the metal/Ge system are re-examined. Correlated ion scattering/channeling and cross-section electron microscopy are utilized to study the Au/Ge and Al/Ge systems under a variety of mixing conditions. Implications for both the crater formation and ion beam mixing mechanisms are discussed.

D. Fathy

Papers

Silicon oxidation and Si-SiO2 interface of thin oxides

Morphological instabilities and ion beam mixing in Ge

Ion‐beam and laser mixing of nickel overlayers on silicon carbide

High-resolution imaging of ion-implantation damage and mechanism of amortization in semiconductors

Morphological instabilities and ion beam mixing in Ge. Revision