Separation By Implantation Of Oxygen Wafers Research Articles

Low-Frequency-Noise Spectroscopy of SIMOX and Bonded SOI Wafers

Pseudo-MOSFET structures with metal source, drain, and guard electrodes are used to measure the low-frequency-noise characteristics of Separation by IMplantation of OXygen (SIMOX) and bonded silicon-on-insulator (SOI) wafers. The noise power spectra in the devices made from bonded SOI wafers are almost an order of magnitude lower than those made from SIMOX wafers. This is attributed to the lower interface trap density in the bonded wafers, which is extracted using the unified correlated model. The proposed method can be used to determine the 1/f noise characteristics of SOI wafers prior to circuit fabrication.

Fabrication of device-grade silicon-on-insulator material from appropriate matches of low oxygen implantation dose and acceleration energy

We report the formation of high-quality silicon-on-insulator materials using separation-by-implantation-of-oxygen (SIMOX) technology, with doses ranging from 1.8 to 13.5×1017 cm−2 at acceleration energies of 45–160 keV, and subsequently annealed at a high temperature of over 1300 °C in an oxygen and argon atmosphere for 5 h. The microstructure evolution of SIMOX wafers was characterized by Rutherford backscattering spectroscopy, transmission electron microscopy, modified enhanced Secco, Cu plating, and spectroscopic ellipsometry. The study reveals a series of good matches of dose–energy combination at acceleration energies of 45–160 keV with doses of 1.8–5.5×1017 cm−2, in which the SIMOX wafers have good crystallinity of the top silicon, a sharp Si/SiO2 interface, and a high-integrity buried oxide layer with a low pinhole density and few detectable silicon islands. Furthermore, the higher the oxygen dose, the higher the implanted energy required for the formation of a Si-island-free buried oxide layer. The mechanism of an appropriate dose–energy match is discussed.

Fabrication of Device-grade Separation-by-implantation-of-oxygen Materials by Optimizing Dose-energy Match

In this article, we report formation of separation-by-implantation-of-oxygen (SIMOX) silicon-on-insulator (SOI) materials with doses ranging from (2.5 to 13.5) × 1017 cm−2 at acceleration energies of 70–160 keV and subsequent annealing at temperatures over 1300 °C in oxygen + argon atmosphere for 5 h. The microstructure evolution of SIMOX wafers was characterized by Rutherford backscattering spectroscopy, cross-sectional transmission electron microscopy, high-resolution transmission electron microscopy, Secco, and Cu-plating. This study revealed a series of good matches of dose-energy combination at acceleration energies of 70–160 keV with doses of (2.5–5.5) × 1017 cm−2, in which SIMOX wafers had good crystallinity of the top silicon, sharp Si/SiO2 interfaces, high-integrity buried oxide layers with low pinhole density, and low detectable silicon islands. Furthermore, the higher the oxygen dose, the higher the implanted energy required for the formation of a buried oxide free from Si islands. The mechanism of the optimum dose-energy match is discussed.

Dose-energy match for the formation of high-integrity buried oxide layers in low-dose separation-by-implantation-of-oxygen materials

High-quality low-dose separation-by-implantation-of-oxygen (SIMOX) silicon-on-insulator (SOI) wafers have been fabricated from a series of good matches of dose-energy combinations. The results reveal that a wafer fabricated at an optimum dose-energy match has a superior SOI layer with a low threading dislocation density, a high-integrity buried oxide (BOX) layer with a minimal detectable silicon island density and a low pinhole density. This work introduces an approach to flexibly control the thickness of both SOI and BOX layers, allowing the fabrication of ultrathin SIMOX wafers with ultrathin SOI and BOX layers, and improving the throughput capacity by selecting good dose-energy matches. A possible mechanism is discussed.

The Effects of Surface Capping during Annealing on the Microstructure of Ultrathin SIMOX Materials

The effects of a protective capping layer on the microstructure of ultrathin separation by implantation of oxygen (SIMOX) materials formed by ion implantation were studied using transmission electron microscopy. A set of SIMOX wafers were implanted at 65 keV in a dose range of 1.5 to followed by a high temperature (1350°C) annealing with and without a protective cap. The lowest dose to form a continuous buried oxide (BOX) layer without Si islands at 65 keV is without a protective cap and with a protective cap. Above under both annealing conditions, the BOX layer formed continuously but with Si islands present. The uncapped samples show slightly lower density of Si islands. Oxygen from the annealing ambient can diffuse in the uncapped samples through the thin top Si layer, which helps the BOX layer grow laterally and lower the Si island density. The density of defects in the top Si layer is also slightly lower in the uncapped samples because of the ability of Si interstitials to incorporate into the surface and the effective annihilation of extended defects during the final annealing step. The top Si layers of the uncapped samples are thinner than those of the capped samples due to surface thermal oxidation. © 2001 The Electrochemical Society. All rights reserved

Nickel precipitation at nanocavities in separation by implantation of oxygen

The structures of nickel decorated cavities and Ni precipitates epitaxially grown in the nanocavity band in separation by implantation of oxygen (SIMOX) are studied. The nanocavities are generated in the silicon substrate of the SIMOX wafer by proton implantation followed by Ni implantation into the Si overlayer. Channeling Rutherford backscattering spectrometry results indicate that Ni implantation changes the crystalline Si overlayer into amorphous Si. After annealing at 1000 °C for 2 h, the amorphous Si evolves into a polycrystalline structure composed of NiSi2 and polycrystalline silicon. In the meantime, most of the nickel atoms diffuse through the buried oxide layer and are gettered by the nanocavity band. NiSi2 precipitates are observed both in the nanocavities and at the residual defects created by H implantation. The microstructure of the Ni precipitate depends on whether there are cavities nearby. Without cavities in the vicinity, dislocations are observed in the neighborhood of the precipitate, whereas no dislocation is detected around the precipitate when there are nanocavities in the neighborhood. The precipitation and gettering behavior can be explained by the gettering of Si interstitials to the microcavities and lowering of the nucleation barrier.

Comparison of Cu gettering to H+ and He+ implantation-induced cavities in separation-by-implantation-of-oxygen wafers

Well-defined bands of cavities have been formed beneath the buried oxide (BOX) layer of two sets of separation-by-implantation-of-oxygen (SIMOX) wafers by H+ and He+ implantation. The gettering of Cu impurities, which were implanted into the top Si layer at different doses (5×1013, 5×1014, and 5×1015/cm2), to the cavities has been studied by secondary ion mass spectroscopy and cross-sectional transmission electron microscopy. The results indicated that the cavities induced either by H+ or He+ implantation are effective gettering centers for Cu in SIMOX wafers, and up to 4×1015/cm2 Cu has diffused through the BOX layer and been captured by the cavities. The gettering efficiency of cavities increases with the decrease of Cu implantation doses and the increase of annealing temperatures. He+ ion implantation is found to be more suitable for cavity formation and impurity gettering than H+ ion implantation.

Diffusion of iron in the silicon dioxide layer of silicon-on-insulator structures

The redistribution of iron implanted into the oxide layer of silicon-on-insulator structures has been measured using the secondary ion mass spectroscopy technique after annealing at 900–1050 °C. Iron diffusion has been found to be much faster in the oxide prepared by the separation-byimplantation-of-oxygen (SIMOX) procedure compared to the thermally grown oxide in the bonded and etched-back structures. In the latter case, the Fe diffusivity exhibits a thermal activation with an energy of 2.8 eV, confirming the literature data on silica glass. In the SIMOX oxide, the diffusivity depends only weakly on temperature, indicative of an essentially activation-free diffusion mechanism. Gettering of Fe at below-the-buried-oxide defects in SIMOX wafers has been observed. No iron segregation has been detected at the SiO2–Si interfaces.

Nanocavities: an Effective Gettering Method for Silicon-on-Insulator Wafers

The 4×1016 / cm2 H+ and 9 × 1016 / cm2 He+ have been implanted into the silicon substrate of separation-by-implantation-of oxygen (SIMOX) wafers, respectively, followed by a 700°C annealing to form nanocavities beneath the buried oxide (BOX) layer. The SIMOX wafers were intentionally contaminated with Cu impurities by implanting different doses of Cu in the top Si layer. Secondary ion mass spectroscopy and cross-sectional transmission electron microscopy technologies have been employed to investigate the gettering effect of nanocavities to the Cu impurities. The cavities induced either by H+ or He+ implantation are effective gettering centers for Cu in SIMOX wafers. After annealing at 1000°C for 90 min, up to 4×1015 / cm2 Cu has diffused through the BOX layer and been captured by the cavities. The gettering efficiency of cavities increases with the decrease of Cu implantation doses. The nanocavities provide an attractive method for gettering transition metal impurities in SIMOX materials.

Gettering of Cu by He-induced cavities in SIMOX materials

Gettering of Cu impurities to He-implantation induced cavities in separation by implantation of oxygen (SIMOX) materials has been investigated by means of cross-sectional transmission electron microscopy and secondary ion mass spectroscopy. The cavities were introduced beneath the buried oxide layer (BOX) in SIMOX substrates by He + implantation (9×10 16/cm 2, 60 keV) and subsequent annealing. The results indicate that these cavities are strong gettering sites for Cu impurities which have been implanted into the top Si layer of SIMOX. After a 1000°C annealing, 80% of the initially implanted Cu impurities in the top layer have diffused through the buried oxide layer to be captured by the cavities. The gettering effect of these He-induced cavities is much stronger than the damage region beside the BOX. The buried oxide in SIMOX does not appear to prevent the movement of Cu at 1000°C. He + implantation-induced cavity has been demonstrated to be an attractive method to remove Cu impurities away from the top Si layer in SIMOX wafers.

A simple technique to measure generation lifetime in partially depleted SOI MOSFETs

This work presents a new, simple method of measuring the generation lifetime in silicon-on-insulator (SOI) MOSFETs. Lifetime is extracted from the transient characteristics of MOSFET subthreshold current. Using this technique, generation lifetime was mapped across finished SIMOX (Separation by IMplantation of OXygen) wafers and BESOI (Bonded and Etchedback SOI) wafers. BESOI material evaluated in this study had about seven times longer effective generation lifetime than SIMOX material and both the SIMOX and the BESOI are shown to have a lifetime variation of /spl plusmn/10% across four inch wafers.

Radiative properties of SIMOX

The first experimental results of the temperature dependent radiative properties of separation by implantation of oxygen (SIMOX) wafers, in the literature, have been reported in this study. These measurements have been performed in the temperature range of 17 to 800/spl deg/C and wavelength range of 0.8 to 20 /spl mu/m using a spectral emissometer. A modeling approach based on Multi-Rad, a matrix method of representing multi-layers, has been adopted to interpret the experimental data. Operating ranges of wavelength for pyrometry have been suggested for a reliable monitoring of temperature for processing SIMOX wafers.

Gettering of iron in silicon-on-insulator wafers

Gettering of Fe in silicon-on-insulator material has been investigated on both the bonded and separation by implantation of oxygen (SIMOX) platforms. Reduction of electrically active iron in intentionally contaminated and annealed wafers has been measured by deep level transient spectroscopy. These data, coupled with structural characterization techniques, such as transmission electron microscopy and preferential chemical etching, provide evidence that structural postimplantation damage below the buried oxide (BOX) in SIMOX wafers is an effective site for gettering of iron with the iron gettering efficiency varying with the SIMOX processing. Gettering was not observed in bonded wafers, and the lower BOX interface did not provide any iron gettering in either bonded or SIMOX wafers.

TEM Analysis of Defects in Simox Silicon-On-Insulator Material

Abstract Silicon-on-Insulator is the leading technology for VLSI fast speed processors and low voltage applications. SIMOX (Separation by Implantation of Oxygen) is a subset of SOI with a high quality top silicon layer onto which VLSI circuitry is placed. SIMOX processing begins with a high energy, high current implantation of a large dose of O+ ions to penetrate the wafer’s surface to form the buried oxide and top silicon layers. This implantation creates numerous precipitates and a large damage region. Therefore a multi-step anneal is used to improve the quality of the top silicon layer by significantly reducing precipitate and dislocation densities, to create smooth interfaces, and to remove any ion residual damage. Using TEM, this study traces the defect formations through the various processing steps, with the objective to arrive at device quality. The SIMOX wafers were implanted with an oxygen ion implant dose of 5xl017cm−2, and then subjected to multiple implantation and anneal steps, bringing the final oxygen ion dose to 1.5xl018cm−2[1].

Determination of interface recombination velocities and carrier lifetimes in SOI materials by a contactless optical modulation technique

A novel contactless dual-beam optical modulation (DBOM) technique has been employed for determining the interface recombination velocities and substrate carrier lifetimes in a SIMOX (Separation by IMplantation of OXygen) wafer. The DBOM method utilizes the optical modulation of the transmitted light intensity of an infrared (i.r.) probe beam ( hv < E g) modulated by a CW visible laser pump beam ( hv > E g) of different wavelengths (e.g., λ = 442 and 632.8 nm) via free-carrier absorption in the SIMOX wafer. The interface and bulk recombination velocities were determined by using pump beams of different wavelengths and incident angles. A theoretical model for the DBOM technique has been developed for extracting the interface recombination velocities and substrate lifetimes in the SIMOX wafers. The front-interface [Si film/buried oxide layer (BOX) interface] and back-interface (BOX/Si substrate interface) recombination velocities as well as the substrate carrier lifetimes were determined using this new technique. Mappings of the front- and back-interface recombination velocities and the substrate carrier lifetimes for several SIMOX wafers with different Si film thicknesses and oxygen implantation processes have been carried out.

A new contactless S-polarized reflectance technique for determining the Si film and buried oxide thickness in silicon-on-insulator materials

A new contactless dual-beam S-polarized reflectance (DBSPR) technique has been developed for measuring the top Si film and buried oxide thickness in a SIMOX (Separation by IMplantation of OXygen) wafer. Top Si film and buried oxide thicknesses of the SIMOX wafers ranging from 0.2 to 1.6 μm and 0.36 to 0.44 μm, respectively, were determined using this new technique. The DBSPR method is based on the S-polarized reflectances measured at oblique angle incidence using laser beam of different wavelengths ( λ = 442 and 632.8 nm). A theoretical model for the DBSPR technique has been derived for determining the top Si film and buried oxide thicknesses in the SOI wafers. A three-dimensional (3D) mapping of the top Si film and buried oxide thicknesses for several SIMOX wafers has been carried out, and the results were found in excellent agreement with values determined by the conventional reflection interference spectroscopy and ellipsometry methods.

The use of spectroscopic ellipsometry to predict the radiation response of SIMOX

We have studied SIMOX (Separation by Implantation of Oxygen) material using spectroscopic ellipsometry to determine the structure of the buried oxide and C-V measurements to determine the radiation response of the buried oxide. Our ellipsometric measurements indicate that the buried oxide is best described as a layer of stoichiometric SiO/sub 2/ which is more dense than bulk vitreous (v-) SiO/sub 2/. We find that the radiation response of the buried oxide is determined primarily by its density. We also find that small variations in the conditions used to prepare the SIMOX wafer can significantly affect the oxide density and its radiation response. The density of the buried oxide is also found to affect how it etches.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Manufacturing technology for 200mm SIMOX Wafers

Separation by IMplantation of Oxygen (SIMOX) has become the leading method for formation of high quality Silicon-On-Insulator (SOI) material. SIMOX material is currently being incorporated into technology designs for commercial ULSI CMOS applications. A critical issue for utilization of SIMOX for commercial applications is the availability of large diameter (>200mm) wafers in sufficient quantities. The need for large diameter wafers and the material quality requirements for ULSI CMOS applications present special issues for the design of implantation equipment used to fabricate the material. This paper discusses the design aspects of the Ibis 1000 implanter which allow the production of SIMOX wafers up to 300mm in diameter, and presents experimental results obtained using this machine.

Fabrication of ultrathin SOI by SIMOX water bonding (SWB)

Ultrathin silicon-on-insulator (SOI) layers of separation by implantation of oxygen (SIMOX) wafers have been transferred onto thermally oxidized silicon wafers by wafer bonding technology. Due to the technical availability and the complementary nature of SIMOX and wafer bonding approaches, SIMOX wafer bonding (SWB) solves some of the respective major difficulties faced by both SIMOX and wafer bonding for device quality ultrathin SOI mass production: the preparation of adequate buried oxide (including its interfaces) in SIMOX and the uniformly thinning one of the bonded wafers to less than 0.1 μm in wafer bonding. The effect of positive charges in the oxide on bondability of ultrathin SOI films and possible applications of SWB will also be outlined.

Ultrathin Low Energy Simox for Low Cost, High Density Applications

ABSTRACTSilicon-on-insulator (SOI) materials made by standard energy (150 to 200 keV) separation by implantation of oxygen (SIMOX) processes have shown great promise for meeting the needs of radiation-hard microelectronics. Since much smaller doses are required, low energy SIMOX (LES) reduces cost, improves radiation hardness, and increases the throughput of any ion implanter. The process can also produce high quality thin SIMOX structures that are of particular interest for fully depleted and submicron device structures. In this paper, we address the formation as well as the material and electrical characterization of LES wafers and compare them with standard SIMOX wafers.