Separation By Implantation Of Oxygen Material Research Articles

Radiation hardness improvement of separation-by-implantation-of-oxygen/silicon-on-insulator material by nitrogen ion implantation

In our work, nitrogen ions were implanted into separation-by-implantation-of-oxygen (SIMOX) wafers to improve the radiation hardness of the SIMOX material. The experiments of secondary ion mass spectroscopy (SIMS) analysis showed that some nitrogen ions were distributed in the buried oxide layers and some others were collected at the Si/SiO2 interface after annealing. The results of electron paramagnetic resonance (EPR) suggested the density of the defects in the nitrided samples changed with different nitrogen ion implantation energies. Semiconductor-insulator-semiconductor (SIS) capacitors were made on the materials, and capacitance-voltage (C-V) measurements were carried out to confirm the results. The super total dose radiation tolerance of the materials was verified by the small increase of the drain leakage current of the metal-oxide-semiconductor field effect transistor with n-channel (NMOSFETs) fabricated on the materials before and after total dose irradiation. The optimum implantation energy was also determined.

Effect of ion-induced defects and oxygen concentration in annealing atmosphere on formation of buried oxide layer in SIMOX materials

Effects of ion-induced defects and oxygen concentration in annealing atmosphere on the formation of the buried oxide (BOX) layer in two-step implanted separation-by-implantation-of-oxygen (SIMOX) materials were investigated. It was found that the extra defects from the second-step oxygen implantation in the damage area promote the diffusion of oxygen in the annealing process. A thicker BOX layer can be obtained by increasing the concentration of oxygen in the annealing atmosphere after defect-induced by the oxygen implantation, which does not need longer annealing time compared to the normal annealing process. The formation mechanism of the BOX layer was discussed. Thus, the fabrication of the BOX layer in SIMOX material can be controlled by intentionally inducing the defects.

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

A modification of formulas used in SOI capacitors analysis and its application in total dose radiation

The capacitance-voltage (C-V) technique used to characterize the irradiation response of separation by implantation of oxygen (SIMOX) material was improved and then used in the analysis of the total-dose radiation effects of the silicon on insulator (SOI) capacitors. The capacitor samples were made up by using the etch-back technique to pull off several layers of fluorine ions (F+) implanted and non-implanted SIMOX materials. According to the results of deconvolution of C-V data of those samples, after irradiation, it indicated that the tolerane of SIMOX materials to total dose radiation was improved by F+ ions implanted into the buried SiO2 layer.

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.

Silicon-on-insulator material qualification for low-power complementary metal-oxide semiconductor application

To quantify silicon-on-insulator (SOI) material quality with limited or no processing requires an understanding of the correlations between material properties and device/circuit performance. We have developed robust procedures for on-line and off-line material qualification. Light point-defect detection, total reflectance X-ray fluorescence spectroscopy, atomic force microscopy, and wafer flatness measurements have been used to non-destructively qualify SOI wafers. Identification of defects has been performed by coupling scanning electron microscopy (SEM) /optical review and wet chemical etch procedures with surface defect mapping. Some of the most detrimental defects for separation by implantation of oxygen (SIMOX) wafers are caused by metal particle contamination introduced during implant. Off-line material characterization has been performed using transmission electron microscopy, SEM, Auger electron spectroscopy, secondary ion mass spectrometry, and wet chemical etch procedures. Buried oxide (BOX) and metal-oxide semiconductor (MOS) capacitors and MOS field effect transistors (MOSFETs) ( L drawn ≥ 0.2 μm) have been fabricated on 200 mm SOI wafers for correlation of material properties and device performance. BOX capacitors have been used to detect defects and contamination under the buried oxide and electrical defects in the buried oxide of SIMOX material. The defects and contamination under the BOX show spatial non-uniformities within wafers that can be correlated with similar non-uniformities during the implant process. Together, these results have assisted in defining a material qualification methodology for SOI that is well-aligned with low-power technology.

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>

A novel appproach to secondary defect reduction in separation by implantation of oxygen material

The effect of a preanneal Si implant after the initial O implant in the fabrication of separation by implantation of oxygen (SIMOX) material has been examined. In addition to studying the effect of the Si dose and implant temperature on the residual disorder, the Si implant energy was varied in order to elucidate the mechanism of secondary defect reduction in SIMOX material. Initial experiments showed that a low implant temperature (150 °C) and a moderate dose (5×1016 cm−2) of 4.2 MeV Si ions were the most successful in reducing the volume fraction of polycrystalline Si at the front Si/SiO2 interface. A systematic study of low-, medium-, and high-energy Si implantation with ion ranges less than, equal to, and greater than the initial O implant has been performed. The Si range and defect production per ion were shown to be most important in determining the final defect structure in SIMOX material formed by MeV O implantation in Si. Low- and medium-energy Si-implanted SIMOX material has a more homogeneous buried SiO2 layer and a less defected Si overlayer than virgin SIMOX (O-implanted Si which has not received a preanneal Si implant). The high-energy Si implant slightly reduced the defect density in the Si overlayer and planarized the back Si/SiO2 interface for SIMOX material formed at an implantation temperature of 300 °C but did not homogenize the buried SiO2 layer.

Paramagnetic defect centers in BESOI and SIMOX buried oxides

Electron paramagnetic resonance (EPR) and capacitance-voltage measurements have been combined to identify the chemical nature and charge state of defects in BESOI (bonded and etchback silicon-on-insulator) and SIMOX (separation by implantation of oxygen) materials. The four types of defect centers observed, charged oxygen vacancies, delocalized hole centers, amorphous-Si centers, and oxygen-related donors, are strikingly similar. In the BESOI materials, the radiation-induced EPR centers are located at or near the bonded interface. Therefore, the bonded interface is a potential hole trap site and may lead to radiation-induced back-channel leakage. In SIMOX materials, it is found that all of the defects in the buried oxide are due to excess Si. The results using poly-Si/thermal oxide/Si structures strongly suggest that it is the postimplantation, high-temperature anneal processing step in SIMOX that leads to their existence. The anneal leads to the out-diffusion of oxygen from the buried oxide, creating excess-Si related defects in the oxide and O-related donors in the underlying Si substrates. A relatively new class of defects in SiO/sub 2/, delocalized spin centers, are found to be hole traps in both SIMOX and BESOI materials.< <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.

Synthesis of Si1-xGex-on-Insulator by 74Ge+ Ion Implantation in a Simox Substrate

ABSTRACTA single crystalline Si1-xGex overlayer on insulator is realised by the implantation of germanium into a SIMOX (Separation by IMplantation of OXygen) substrate. Two SIMOX samples were implanted with 74Ge+ at elevated temperature (≈600°C), and subsequently annealed at different temperatures and anneal ambients. The microstructure, stoichiometry, and conductivity of the Si1-xGex over-layer were studied using transmission electron microscopy, Rutherford backscattering spectrometry/ion channelling and two-probe conductivity measurements. As a result of lattice reordering after final heat treatment, and despite high defect density observed in the XTEM microstructure, the measured conductivity of the over-layer is higher than of the starting SIMOX material. These results suggest a possibility of band-gap engineering by synthesis of Si1-xGex-on-insulator.

Photoconduction measurements of the charge trapping and transport in bond-and-etch-back buried oxides

The charge trapping and transport characteristics of bond-and-etchback buried oxides (BESOI) were investigated using a photoconduction current technique and total dose capacitance-voltage shift measurements. Results are compared with results previously obtained on standard SIMOX (separation by implantation of oxygen) materials. The photocurrent experiment was also performed on thermally grown oxides with an oxide layer similar in thickness to the BESOI and SIMOX material used in this study. Measurements were performed on the thermal oxides as a method of calibration for both the experimental and analytical methods that are applied to the photoconduction current technique. Large normalized photoconduction currents and large postirradiation midgap voltage shifts in the BESOI material were measured. Taken together, these results indicate that most of the electrons and the holes move through the BESOI oxide and significant fractions of the holes are trapped at the interfaces. These radiation response characteristics are also typical of non-radiation-hardened thermal oxides, and this leads to the further conclusion that techniques used to successfully harden thermal oxides may also be successful when applied to BESOI material.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Electron and hole trapping in irradiated SIMOX, ZMR and BESOI buried oxides

Shallow electron and deep hole trapping in the buried oxides of SIMOX (separation by implantation of oxygen), ZMR, and BESOI (bond and etchback silicon-on-insulator) material are examined. By irradiating the oxides with X-rays at cryogenic temperatures, 40-50 K, hole motion is frozen and electrons are trapped. The oxide charge is determined by C-V measurements. Following the cryogenic irradiation, the electrons are detrapped by field stressing (tunneling) or by annealing (thermal excitation). Hole trapping is examined by annealing after the trapped electrons are removed by field stressing. Substantial shallow electron and deep hole trapping distributed uniformly through the oxide is observed for all buried oxides that are processed above about 1100 degrees C. A comparison to thermal oxides grown at 850 degrees C and annealed at 1300 degrees C with and without a polysilicon capping layer shows that the top silicon layer significantly increases trap formation. These results indicate that the oxide defects responsible for the electron and hole trapping are produced by chemically reducing the oxide and producing defects such as Si-Si pairs.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

On the Formation of Ultrathin Simox Structures by Low Energy Implantation

ABSTRACTSilicon-on-insulator (SOI) wafers made by standard energy (150–200 keV) Separation by IMplantation of Oxygen (SIMOX) processes have shown great promise for meeting the needs of radiation-hard microelectronics. However, if SIMOX material is to become a competitive substrate material for manufacturing commercial integrated circuits, the cost of the SIMOX wafers must be greatly reduced. The low energy SIMOX (LES) process accomplishes the needed reduction in cost by producing ultrathin layers which require much lower ion doses. These ultrathin layers are necessary for the next generation of commercial ultra high density CMOS integrated circuits, and must be of very high quality to be utilized for commercial applications. In this paper we discuss characterization of ultrathin LES structures.

Low-Defect, High-Quality Simox Produced By Multiple Oxygen Implantation with Substoichiometric Total Dose

ABSTRACTThis work addresses the formation of Separation by IMplantation of OXygen (SIMOX) structures by multiple oxygen implantation into silicon and high temperature annealing. We observed no threading dislocation defects in the several plane view TEM and XTEM micro graphs of each of the samples implanted with a single dose of up to 8 × 1017 0+/cm2. We also demonstrated that with a multiple low-dose (3 to 4 × 1017 0+/cm2) oxygen implantation and high temperature annealing process, we are able to produce continuous and uniform buried SiO2 layers with a total dose of 1.1 × 1018 0+/cm2 (about 60% of the total dose for standard SIMOX). The density of defects is about 105/cm2. There are no silicon islands in the buried layer, no SiO2 precipitates in the silicon top layer, and the Si-SiO2 interfaces are sharp and smooth. SIMOX material with a high-quality Si top layer and a continuous buried layer has been produced with a total dose of 7 × 1017 0+/cm2 (40% of the total dose for standard SIMOX) and a two-step process. However, in this case there are a few Si islands present in the buried SiO2 layer.

Dislocation Reduction on Simox Substrates by Using Multiple Implants

AbstractA technique for dislocation density reduction in SIMOX (Separation by IMplantation of OXygen) substrates by using multiple implant and anneal cycles is described. This scheme produces SIMOX material with dislocation defect densities less than 1 x 105/cm2. This dislocation density value is three to four orders of magnitude lower than that of comparable single implant slices having the same total dose and anneal conditions.