Si Ion Implantation Research Articles

Ion beam synthesized luminescent Si nanocrystals embedded in SiO 2 films and the role of damage on nucleation during annealing

Si nanocrystals in thermal oxide films (∼ 250 nm) were fabricated by 100 keV Si ion implantation followed by high temperature annealing. Two different doses were compared after annealing at 1050 °C for 2 h. A sample implanted with a dose of 1 × 10 17 cm − 2 shows a broad photo luminescence peak centered around 880 nm after annealing. A dose of 5 × 10 16 cm − 2 yields a considerable blue shift of about 100 nm relative to the higher dose as well as a reduction in intensity. Transmission electron microscopy study reveals a difference in the microstructure of the SiO 2 films. Nanocrystals are clearly identified in the middle of the film for the highest dose, but not for the lower dose. The difference is discussed in terms of concentration dependent nucleation rate and differences in defect concentration. It is argued that the latter effect has a strong effect on the depth distribution of nanocrystals.

RTA effects on the formation process of embedded luminescent Si nanocrystals in SiO 2

It is well known that Si ion implantation into SiO 2 and subsequent high temperature anneals induce the formation of embedded luminescent Si nanocrystals. In this work, the potentialities of rapid thermal annealing to enhance the photoluminescence as well as those to induce low temperature formation of luminescent Si nanocrystals have been investigated. Ion implantation was used to synthesize specimens of SiO 2 containing supersaturated Si with different concentrations. The implanted samples were rapidly annealed only for a few minutes. After that, in some cases before that, the samples were annealed for a few hours using a conventional tube furnace to induce Si precipitation. Photoluminescence spectra were measured at various stages of anneal processes. The luminescence intensity is strongly enhanced with a rapid thermal annealing prior to a conventional furnace anneal. The luminescence intensity, however, decreases when rapid thermal annealing follows conventional furnace annealing. It is found that the order of heat treatment is an important factor in intensities of the luminescence. Enhancement is found to be typical for low dose samples. Moreover, the visible photoluminescence is found to be observed even after conventional furnace anneal below 1000 °C, only for rapidly thermal annealed samples. Based on our experimental results, we discuss the mechanism for the enhancement of the photoluminescence, together with the mechanism for the initial formation process of Si nanocrystals.

Dissociation of Si+ ion implanted and as-grown thin SiO2 layers during annealing in ultra-pure neutral ambient by emanation of SiO

We have observed a very inhomogeneous dissociation of stoichiometric and non-stoichiometric thin SiO2 layers (thermally grown on Si substrates) during high temperature annealing at a low partial pressure of oxygen. During this process some silicon of the (100)Si substrate and, in case of Si ion implantation, and additionally, excess Si is consumed. The SiO2 dissociation has been studied by electron microscopy and Rutherford backscattering spectrometry. Large holes (>1 μm) in non-implanted oxide layers have been observed which evolve probably from defects located at the Si∕SiO2 interface. For Si implanted SiO2 additionally the formation of voids within the oxide during annealing has been observed preferably at the position of the implanted Si excess. Oxygen vacancies are possibly emitted from Si∕SiO2 interfaces into the oxide and migrate through SiO2 with long-range distortions of the oxide network. In that way the hole and void formation in the oxide can be explained by oxygen-vacancy formation, migration and silicon-monoxide (SiO) emanation. As a driving force for growth of the large holes we identified oxygen diffusion from the Si∕SiO2 interface to the bare Si surface. This surface is a sink of oxygen diffusion due to the emanation of volatile SiO, whereas the Si∕SiO2 interface serves as an oxygen source. The predicted mechanism is consistent with the geometry of the holes in the SiO2 layer.

CMOS-Compatible All-Si High-Speed Waveguide Photodiodes With High Responsivity in Near-Infrared Communication Band

Submicrometer silicon photodiode waveguides, fabricated on silicon-on-insulator substrates, have photoresponse from <1270 to 1740 nm (0.8 AW <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> at 1550 nm) and a 3-dB bandwidth of 10 to 20 GHz. The p-i-n photodiode waveguide consists of an intrinsic waveguide 500times250 nm where the optical mode is confined and two thin, 50-nm-thick, doped Si wings that extend 5 mum out from either side of the waveguide. The Si wings, which are doped one p-type and the other n-type, make electric contact to the waveguide with minimal effect on the optical mode. The edges of the wings are metalized to increase electrical conductivity. Ion implantation of Si <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> 1times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> at 190 keV into the waveguide increases the optical absorption from 2-3 dBmiddotcm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> to 200-100 dBmiddotcm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and causes the generation of a photocurrent when the waveguide is illuminated with subbandgap radiation. The diodes are not damaged by annealing to 450 degC for 15 s or 300 degC for 15 min. The photoresponse and thermal stability is believed due to an oxygen stabilized divacancy complex formed during ion implantation

Nanogram amounts of selected rare earth elements measured by AMS

Results are presented from a series of measurements on nanogram quantities of selected rare earth elements. The work was performed at the NRL trace element AMS facility using a multi-cathode cesium-sputtering negative-ion source. The possibility to simultaneously inject, transmit and analyze a relatively broad mass range is a unique feature of our AMS system. The detection system, placed in the focal plane of the split-pole magnetic spectrograph, consists of a combination of position-sensitive microchannel plate and ion-implanted Si detectors. The small amounts of rare earth elements to be measured were chemically extracted from the surface of metallic samples. Calibration curves were built using standards containing 3 and 10ng of the material of interest. Extensive studies were performed to develop a method of normalizing the data by adding known amounts of a given element to the samples and to the standard material. Dedicated software was written to allow for event-by-event data acquisition as well as for data reduction. Results are shown for samples containing from less than 100pg to almost 10ng of material with uncertainties of the order of 15%. Further upgrades of the experimental method are underway.

Nanocavities induced by neon Plasma Based Ion Implantation in silicon

Nanocavities formed by neon Plasma Based Ion Implantation (PBII) in Si have been studied in comparison with conventional ion implantation (CI). Interstitial-type defects are also investigated. To avoid amorphisation, neon implantations were performed at 250°C with a fluence of ≈5×1016cm−2. Using PBII a rather uniform layer of cavities is observed from the surface while a three layer structure is present using the CI. However, the mean diameter of cavities is smaller due to the interaction with the interstitial-type defects. After annealing at 800°C, bubbles grow and extended defects identified as {113} defects are formed.

Scanning probe measurements on luminescent Si nanoclusters in SiO 2 films

Embedded Si nanocrystals in SiO 2 have a large current interest due to the prospects for practical applications. For most of these it is essential to characterize and ultimately control the nanocrystal size, size distribution and spatial distribution. Here we present a study of Si nanocrystals and clusters in SiO 2 studied by atomic force microscopy (AFM). Since it is an indirect method, it requires several other methods to establish a reliable description of the structure of the samples. We here compare the AFM results with photoluminescence (PL) and transmission electron microscopy (TEM). Si nanocrystals in thermal oxide films (∼ 250 nm) were fabricated by 100 keV Si ion implantation at a dose of 1 × 10 17 cm − 2 followed by high temperature annealing. AFM micrographs were taken after different etching times of the oxide and compared to TEM measuerements of the nanocrystal size and distribution. The correlations observed strongly indicate AFM signatures connected to the nanocrystals. We have analyzed and modeled the etch sectioning technique. Comparisons with the experiments let us conclude that the sectioning technique has some memory effect, but yields a distribution of nanocrystals with depth. A dose of 5 × 10 16 cm − 2 yields a PL blue shift of about 100 nm relative to the higher dose. No nanocrystals are observed with TEM in this latter case. However distinct signatures can be observed with AFM and is tentatively attributed to the presence of non-crystalline Si-rich nanoclusters.

Lamp annealing effects on the formation process of implanted silicon nanocrystals in SiO2

Si ion implantation into SiO2 and subsequent high temperature anneals induce the formation of embedded luminescent Si nanocrystals. The potentialities of rapid thermal annealing to enhance the photoluminescence as well as those to induce low temperature formation of luminescent Si nanocrystals have been investigated. Si ion implantation was used to synthesize specimens of SiO2 containing supersaturated Si with different concentrations, from 4 to 16% in excess. The implanted samples were rapidly annealed only for a few minutes. After that, in some cases before that, the samples were annealed for a few hours using a conventional quartz tube furnace to induce Si precipitation. Photoluminescence spectra were measured at various steps of anneal processes. The luminescence intensity is strongly enhanced with a rapid thermal annealing prior to a conventional furnace anneal. The luminescence intensity, however, decreases when rapid thermal annealing follows conventional furnace annealing. It is found that the order of heat treatment is an important factor in intensities of the luminescence. Enhancement is found to be typical for low dose samples. Moreover, the visible photoluminescence is found to be observed even after conventional furnace anneal below 1000°C, only for rapidly thermal annealed samples. Based on our experimental results, we discuss the mechanism for the enhancement of the photoluminescence, together with the mechanism for the initial formation process of luminescent Si nanocrystals.

Variation of ion-irradiation induced strain as a function of ion fluence in Si

Strain in Si induced by ion irradiation at temperatures of 200–400°C has been measured at room temperature. Quantitative analysis of the strain distribution produced by 750-keV Si ion implantation in Si substrates was characterized by double-crystal X-ray diffraction (DCXRD). Strain in the Si surface layer was determined by modeling the DCXRD rocking curve using the program Rocking curve Analysis by Dynamic Simulation (RADS) where a generated strain profile is iteratively fitted to the measured rocking curve.The strain was tensile, resulting from a vacancy excess, and measured as a function of irradiation temperature and ion fluence. For a given temperature, strain increased as a function of ion fluence until a strain maximum was attained and then relaxed via dislocation formation. The maximum strain attainable decreased with an increase in irradiation temperature as consistent with thermally activated dislocation formation.

Implantation and Sputtering of Ge and Si Ions into SiO2 Substrates using Electric Fields for Acceleration and Optimisation of Laser-produced Ion Streams used for Modification of Semiconductor Materials

AbstractLaser plasma has been proved to be a potential source of multiply charged ions which could support the growing demands for high-current ion beams. To optimize efficiency of the ion implantation technology selection of proper laser beam characteristics is very important and should be investigated. With LIS, several variables can and must be controlled. The properties of ions (current densities, the ion charge state, angular and energy distributions) depend on target material and the laser energy, pulse duration and intensity on the target surface. So, the characteristics of laser-produced ion streams should be determined with the use of precise ion diagnostic methods.Based on the preliminary results for acceleration of ions produced with the use of a repetitive laser system at IPPLM the special electrostatic-acceleration system has been designed and prepared. This device permits to accelerate ions having charge states of 1+ to energies up to ∼40 keV. The movable target holder was located inside the cylindrical box connected with a high-voltage source (up to 50 kV at 50 mA). The accelerated Ge and Si ions was implanted to SiO2/Si substrates and analyzed.This contribution is concerned mainly on the analysis and optimization of laser-produced Ge and Si ion streams as well as on investigation of the direct implantation of these ions into SiO2 substrates. Targets were irradiated with the use of repetitive (up to 10 Hz) laser with energy up to 700 mJ in one pulse, at radiation intensities of ∼1011 W/cm2. The ion stream parameters were measured using the time-of-fight method. The depth of ion implantation was determined by X-Ray Photoelectron Spectroscope (XPS). After the implantation the samples were annealed in different temperatures in range of to create nanocrystal structures and then analyzed by means of Raman Spectroscopy, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The work has been performed within SEMINANO project supported by EC (within 6FP).

Oxide-nitride-oxide Dielectric Stacks with Embedded Si-nanoparticles Fabricated by Low-energy Ion-beam-synthesis

AbstractThis work reports on the formation of Si-nanocrystals within silicon nitride layers by low-energy Si ion implantation. Electrical characterization of oxide/Si-nanocrystal-nitride/oxide dielectric stacks demonstrates regions of negative differential resistance at low-fields. In addition, the memory characteristics in terms of charge trapping, write/erase response and retention properties of the dielectric stacks were recorded. The results indicate the large potential of the low-energy ion beam synthesis method in nitride memory technology.

Dielectric functions of densely stacked Si nanocrystal layer embedded in SiO2 thin films

A densely stacked silicon nanocrystal layer embedded in a SiO2 thin film is synthesized with Si ion implantation. The dielectric functions of the nanocrystal layer are determined with spectroscopic ellipsometry. The dielectric functions show a significant suppression as compared to that of bulk crystalline Si. Thermal annealing leads to an evolution of the dielectric functions from the amorphous towards crystalline state. For an insufficient annealing, the dielectric functions present a single broad peak, being similar to that of amorphous Si. However, a sufficient annealing leads to the emergence of the two-peak structure which is similar to that of bulk crystalline Si. In addition, the dielectric functions increase with annealing with a trend towards bulk Si.

Multiscale modeling of radiation damage and annealing in Si

The fabrication of small Si devices brings up complex physical mechanisms, whose modeling requires a multiscale approach. We illustrate the case of ion implantation and annealing in Si. Ab initio calculations and molecular dynamics simulations provide defect energetics and the physical basis for defect formation and annihilation mechanisms. Binary-collision approximation for ion implantation combined with kinetic Monte Carlo simulation for annealing is used to define the range of validity of some approximations used in continuum models.

Electrically detected magnetic resonance in ion-implanted Si:P nanostructures

The authors present the results of electrically detected magnetic resonance (EDMR) experiments on ion-implanted Si:P nanostructures at 5K, consisting of high-dose implanted metallic leads with a square gap, in which phosphorus is implanted at a nonmetallic dose corresponding to 1017cm−3. By restricting this secondary implant to a 100×100nm2 region, the EDMR signal from less than 100 donors is detected. This technique provides a pathway to the study of single donor spins in semiconductors, which is relevant to a number of proposals for quantum information processing.

Enhanced room temperature ferromagnetism in Co- and Mn-ion-implanted silicon

The authors report on ferromagnetism at room temperature in cluster-free, cobalt- and manganese-ion-implanted crystalline silicon. Through magnetic and structural analysis it is shown that the ion-implanted Si consists of two layers of Co- and Mn-containing silicon: (1) an amorphous Si layer on the surface and (2) single crystalline Si beneath. The amorphous layer shows very little magnetism by itself but seems to be responsible for partially canceling out or masking the ferromagnetism in the crystalline Si. The authors also observe that etching of the amorphous Si layer dramatically enhances the measured magnetism by as much as 400%.

Ion beam synthesis and characterization of yttrium silicide in Si(111)

Thin YSi2−x layers are formed by 195 keV Y ion implantation in Si(111) substrates to a dose of 2×1017 Y+/cm2 at 500 °C followed by annealing in nitrogen atmosphere at different temperatures for 1 h. The investigation of the phase composition is carried out by Rutherford backscattering spectrometry (RBS), whereas the structural characterization is accomplished by means of both X-ray diffraction (XRD) pole figure and cross-sectional transmission electron microscopy (XTEM). The results show that the YSi2−x layers grown on the Si has the epitaxial relationship of YSi2−x (0 0 0 1)//Si(111) and YSi2−x [1 1 − 2 0 ]//Si [110].

Formation of planar optical waveguide by multi energy Si ion implantation into Nd:YVO 4 crystal

The planar waveguides have been fabricated in Nd:YVO 4 crystals by single and multi energy Si ion implantation. Optically polished Nd:YVO 4 samples were implanted at room temperature by 2.6 MeV Si ions and multi energy (3.0 MeV, 2.6 MeV and 2.2 MeV) Si ions, to the dose of 6 × 10 14 ions/cm 2. The prism-coupling method was carried out to measure the dark modes in the Nd:YVO 4 crystal waveguides by using a model 2010 prism coupler. In both waveguides 3 modes were observed before annealing and after annealing the effective refractive index of all these modes gets smaller. The two waveguides show much similarity in prism-coupling results. Reflectivity Calculation Method was applied to fitting the single energy ion implanted waveguide refractive index profile. TRIM'98 (Transport of Ions in Matter) code was used to simulate the damage profile in Nd:YVO 4 by a single and multi energy ion implantation, respectively. It is found that the electronic energy loss in ion implantation may play an important role in Nd:YVO 4 waveguide formation.

Luminescence from silicon nanoparticles in SiO2: atomic force microscopy and transmission electron microscopy studies

Si nanocrystals in thermal oxide films (∼250 nm) were fabricated by 100 keV Si ion implantation at various doses followed by high temperature annealing. After annealing a sample implanted with a dose of 1×1017 cm−2 at 1050°C for 2 h, a broad photoluminescence peak centred around 880 nm was observed. A dose of 5×1016 cm−2 yields a considerable blue shift of about 100 nm relative to the higher dose. Transmission electron microscopy and atomic force microscopy (AFM) are used to characterize the microstructures in the SiO2 film. The limitations of these techniques for the study of the nanostructures are addressed in this paper and it is suggested that AFM combined with etching can yield a structural spectroscopy with very good sensitivity.

Selective etching in LiNbO 3 combined of MeV O and Si ion implantation with wet-etch technique

The selected etching in lithium niobate (LiNbO 3) crystals is carried out by two different ion implantation and differential wet etching. The LiNbO 3 samples are cleaned and partially masked with photoresist in lithographic procedure firstly, followed by 1.5 MeV O + or Si + ion implantation at a dose of 1×10 15 ions/cm 2 at room temperature. It is found that the ion implanted region can be etched more easily than that protected by photoresist mask using mixture of hydrofluoric and nitric acids at room temperature. The surface morphology of the etched samples is examined using surface profilometer and SEM. Ridge structures are formed by the ion implantation and the subsequent selective wet etching. The results show that this technique may be suitable for fabrication of high quality ridge waveguides.

Depth Profiling of Charging Effect of Si Nanocrystals Embedded in SiO2: A Study of Charge Diffusion among Si Nanocrystals

Si nanocrystal (nc-Si) embedded in SiO2 thin film is synthesized with low-energy Si ion implantation. Depth profiling of the charging effect of the nc-Si is determined from X-ray photoemission measurement. It is observed that there is a strong correlation between the depth profile of the charging effect and the nc-Si depth distribution. The charging effect is found to decrease with the increase of nc-Si concentration and to vanish when a densely stacked nanocrystal layer is formed. The phenomenon is attributed to the charge diffusion among the nanocrystals. The charge diffusion in the nanocrystal layer may have an important implication for nanocrystal flash memory. When such a layer is used as the charge-storage layer in the memory cells, the stored charges could be lost due to the rapid charge diffusion among the nc-Si if a single defect exists in the tunneling oxide, causing a reliability problem in data retention.