Article

Characterization of In-Depth Cavity Distribution after Thermal Annealing of Helium-Implanted Silicon and Gallium Nitride

Authors:
Article

Characterization of In-Depth Cavity Distribution after Thermal Annealing of Helium-Implanted Silicon and Gallium Nitride

If you want to read the PDF, try requesting it from the authors.

Abstract

Single-crystalline silicon wafers covered with sacrificial oxide layer and epitaxially grown gallium nitride layers were implanted with high-fluence helium ions (2-6 x 10(16) cm(-2)) at energies of 20-30 keV. Thermal annealings at 650-1000 degrees C, 1 h were performed on the Si samples and rapid thermal annealings at 600-1000 degrees C, 120 s under N-2 were performed on the GaN samples. The as-implanted samples and the near-surface cavity distributions of the annealed samples were investigated with variable angle spectroscopic ellipsometry. In-depth defect profiles and cavity profiles can be best described with multiple independent effective medium sublayers of varying ratio of single-crystal/void. The number of sublayers was chosen to maximize the fit quality without a high parameter cross-correlation. The dependence of the implantation fluence, oxide layer thickness and annealing temperature on the cavity distribution was separately investigated. The ellipsometric fitted distributions were compared and cross-checked with analyses of transmission electron micrographs where the average surface cavity was determined sublayer by sublayer. The in-depth profiles were also compared with simulations of He and vacancy distributions.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... We have obtained good agreements in different studies. 63,96 Finally, it should be pointed out that the decreased penetration depth at direct interband transition photon energies is not only a problem, but it can also be utilized for depth scanning, when properly choosing the wavelength range used for the optical characterization (Fig. 3). By a systematic scan of the wavelength range, the penetration depth can be varied in a controlled way, which allows a model-independent direct depth scan. ...
Article
Full-text available
Indirect optical methods like ellipsometry or scatterometry require an optical model to calculate the response of the system, and to fit the parameters in order to minimize the difference between the calculated and measured values. The most common problem of optical modeling is that the measured structures and materials turn out to be more complex in reality than the simplified optical models used as first attempts to fit the measurement. The complexity of the optical models can be increased by introducing additional parameters, if they (1) are physically relevant, (2) improve the fit quality, (3) don't correlate with other parameters. The sensitivity of the parameters can be determined by mathematical analysis, but the accuracy has to be validated by reference methods. In this work some modeling and verification aspects of ellipsometry and optical scatterometry will be discussed and shown for a range of materials (semiconductors, dielectrics, composite materials), structures (damage and porosity profiles, gratings and other photonic structures, surface roughness) and cross-checking methods (atomic force microscopy, electron microscopy, x-ray diffraction, ion beam analysis). The high-sensitivity, high-throughput, in situ or in line capabilities of the optical methods will be demonstrated by different applications.
... The ellipsometric measurement of electrochemically etched thin films in silicon can be modeled using EMA with components of single-crystalline silicon and void, which can be extended by a fine-grained polycrystalline silicon reference if the typical crystallite sizes of the remaining porous Si skeleton are very small [37,79,80]. By fitting the volume fraction of void, the optical density and in turn the porosity can be determined, as demonstrated for void gradients caused by ion implantation [81,82]. The sensitivity also allows the determination of density gradients within the thin films. ...
Article
Full-text available
Re ection of light measured in a polarimetric, scatterometric and spectroscopic way allows the measurement of structures in a broad size range from large (meter) scales like photovoltaic panels down to small (nanometer) scales like nanocrystals. Optical metrology continues to be improved to measure those materials with increasing sensitivity and accuracy, typically in a form of thin �lms on high quality substrates. This review provides an overview of some recently developed or improved methods, e.g. divergent light source ellipsometry for the mapping of large surfaces for photovoltaic applications, Fourier scatterometry for the measurement of periodic structures with sizes comparable to the wavelength of illumination, as well as spectroscopy around the band gap photon energies to characterize nanostructures { without attempting completeness.
Article
Full-text available
Cavities created by He implantation with a dose of 5×1016 cm−2 and energy of 40 keV into single-crystalline silicon and annealing at 650–1000 °C for 15–60 min were characterized by multiple angles of incidence spectroscopic ellipsometry. Optical models of increasing complexity were developed assuming the cavity layer either to be homogeneous, or to have a Gaussian profile, or sublayers with independently fitted cavity ratios. Cavity profiles of different annealing conditions were compared and cross-checked by transmission electron microscopy. A strategy for the ellipsometric evaluation was proposed to reduce the computation time and the probability of getting in local minima using complex models with numerous parameters. High sensitivity on the angle of incidence was found, and the choice and the determination of the angle of incidence were discussed.
Article
Full-text available
We have developed optical models for the characterization of grain size in nanocrystal thin films embedded in SiO2 and fabricated using low pressure chemical vapor deposition of Si from silane on a quartz substrate, followed by thermal oxidation. The as-grown nanocrystals thin film on quartz was composed of a two-dimensional array of Si nanocrystals (Si-NC) showing columnar structure in the z-direction and touching each other in the x-y plane. The nanocrystal size in the z-direction was equal to the Si nanocrystal film thickness, changing by the deposition time, while their x-y size was almost equal in all the samples, with small size dispersion. After high temperature thermal oxidation, a thin silicon oxide film was formed on top of the nanocrystals layer. The aim of this work was to measure the grain size and the nanocrystallinity of the Si nanocrystal thin films, a quantity related to the change of the dielectric function. We used a definition for the nanorcystallinity that is related to the effective medium analysis (EMA) of the material. The optical technique used for the investigations was spectroscopic ellipsometry. To measure the above sample properties the thickness and composition of several layers on a quartz substrate had to be determined by proper modeling of this complex system. We found that the nanocrystallinity (defined as the ratio of nc-Si/(c-Si+nc-Si) decreases systematically with increasing the Si-NC layer thickness. Using this approach we are sensitive to the lifetime broadening of electrons caused by the scattering on the grain boundaries, and not to the shift of the direct interband transition energies due to quantum confinement.
Article
In this work, both ``Schottky to Schottky'' structure (STS) and pseudo-vertical Schottky barrier diode (pv-SBD) have been processed on GaN heteroepitaxially grown on sapphire or silicon by metal organic chemical vapor deposition (MOCVD) and characterized physically and electrically. Ni and Ti/Al were used to obtain respectively Schottky and Ohmic contacts using rapid thermal annealing (RTA). Adequate passivation steps and insertion of a resistive guard ring were also implemented in pv-SBD. The STS results, presented in this paper, evidence the impact of the substrate on the growth as well as all the progresses that have been done on GaN material quality. Furthermore, we demonstrate that high quality Schottky diodes can be obtained on GaN grown on sapphire by MOCVD. Indeed, ideality factors of 1.09 as well as a barrier height of 1.06 eV were obtained on pv-SBD devices that have a breakdown voltage over 600 V.
Article
We present here preliminary results on boron diffusion in presence of pre-formed voids of different characteristics. The voids were fabricated by helium implantation followed by annealing allowing the desorption of He prior to boron implantation. We show that under such conditions boron diffusion is always largely reduced and can even be suppressed in some cases. Boron diffusion suppression can be observed in samples not containing nanovoids in the boron-rich region. It is suggested that direct trapping of Si(int)s by the voids is not the mechanism responsible for the reduction of boron diffusion in such layers. Alternatively, our experimental results suggest that this reduction of diffusivity is more probably due to the competition between two Ostwald ripening phenomena taking place at the same time: in the boron-rich region, the competitive growth of extrinsic defects at the origin of TED and, in the void region, the Ostwald ripening of the voids which involves large supersaturations of Vs.
Article
High dose helium implantation leads to the formation of extended defects, such as cavities and dislocations that interact with impurities like metals and dopants, affecting their final profiles. The detailed mechanisms governing the boron segregation on these defects are still unclear. In this paper, we evidence that the boron diffusivity is decreased when boron is implanted between the surface and the He-induced defect layer. This layer acts as a sink for interstitials. Using “flat profile” experiments, we propose a simple trapping model of boron at the He-induced extended defects. Numerical modeling has been performed to extract the boron effective diffusion coefficient with regard to the defect band. This work emphasizes the impact of effective diffusivity variation on the boron gettering phenomenon and clarifies boron interaction with He-induced defects.
Article
In this paper, we shed light on the strong interaction between the cavity layer induced by helium implantation and boron. First, we present the impact of the He gettering step on a boron-diffused profile. In order to study the boron-cavity interaction, we used uniformly boron-doped wafers implanted with a high dose of helium and annealed using conventional furnace annealing as well as rapid thermal annealing. Then, to avoid any precipitation phenomena, conditions were chosen such that the boron solid solubility value was not exceeded. Our experimental results indicate a large trapping of boron within the cavity layer that occurs at the early stage of the annealing. A quantitative study of the gettered dopant fraction has been performed. These results enable us to have a better understanding of this interaction of the He-gettering step with boron atoms, which are of great interest for device applications.
Article
We have designed a set of experiments in which a controlled supersaturation of vacancies can be maintained constant during annealing of a boron implant. In presence of voids, a remarkable reduction of boron diffusivity is observed and, for low fluence B implantation, TED can be totally suppressed. We show that the presence of nanovoids in the B implanted region is not a prerequisite condition for the reduction of B diffusivity. Large voids located at more than 100 nm apart from the B profile still show the same effect. Small voids can also be used to increase the activation of boron. All these results are consistent with the hypothesis that, during annealing, vacancies are injected from the voids region towards the Is rich region in the implanted region where they massively recombine. Finally, we show that BICs cannot be simply dissolved by injecting vacancies into the region where they stand.
Article
Spectroscopic ellipsometry (SE), high-depth-resolution Rutherford backscattering (RBS) and channeling have been used to examine the surface damage formed by room temperature N and B implantation into silicon. For the analysis of the SE data we used the conventional method of assuming appropriate optical models and fitting the model parameters (layer thicknesses and volume fraction of the amorphous silicon component in the layers) by linear regression. The dependence of the thickness of the surface-damaged silicon layer (beneath the native oxide layer) on the implantation parameters was determined: the higher the dose, the thicker the disordered layer at the surface. The mechanism of the surface amorphization process is explained in relation to the ion beam induced layer-by-layer amorphization. The results demonstrate the applicability of Spectroscopic ellipsometry with a proper optical model. RBS, as an independent cross-checking method supported the constructed optical model.
Article
Among numerous metallic impurities gettering techniques, helium implantation that leads to the formation of both defect types (interstitial and vacancy type) has been investigated. The gettering efficiency has been demonstrated for metals like Au, Ni, Cu or Fe. Moreover, dopant gettering has also been observed on these defects. Boron is of particular interest for the realisation of ultra-shallow junctions. Its interactions with interstitial type defects are widely studied in the literature. In this paper, we will focus our attention on boron diffusion in presence of He induced defects. The boron diffusion, known to be driven by interstitial mechanism, can be largely affected by the presence of cavities, which are sinks for interstitials. In this work, n-type 〈1 1 1〉 Si wafers doped at 1 × 1014 B cm−3 were implanted with helium for various doses 1–5 × 1016 He+ cm−2 and energies 40–100 keV. Boron implantation was then performed at 5 keV for a dose of 2 × 1013 B cm−2. Secondary ion mass spectroscopy (SIMS), transmission electron microscopy (TEM), spreading resistance profilometry and simulation with PROMIS 1.5 code were used in order to study the defect band impact on boron diffusivity and electrical activity after classical thermal treatments. The impact of various parameters on boron diffusivity, such as defect density, distance between boron profile and defect band or annealing temperature is discussed in this work.
Article
The optical functions of several forms of thin‐film silicon (amorphous Si, fine‐grain polycrystalline Si, and large‐grain polycrystalline Si) grown on oxidized Si have been determined using 2‐channel spectroscopic polarization modulation ellipsometry from 240 to 840 nm (∼1.5–5.2 eV). It is shown that the standard technique for simulating the optical functions of polycrystalline silicon (an effective medium consisting of crystalline Si, amorphous Si, and voids) does not fit the ellipsometry data.
Article
100 keV Ar and Xe ions, as well as 40 and 60 keV Ge ions were implanted at room temperature into single-crystalline silicon. The used doses covered the range from slightly damaged to totally amorphized layers for the Xe, Ar and Ge ions, respectively. The relative damage was characterized using spectroscopic ellipsometry (SE) with the Bruggeman effective medium approximation combining the dielectric function of single-crystalline and ion implantation-amorphized silicon. The depth distribution of damage was described by the coupled half-Gaussian model and with an improved model, which describes the damage profile using sublayers with thicknesses inversely proportional to the slope of the profile. The SE results were cross-checked using Rutherford backscattering spectrometry (RBS). The damage peaks were determined from the SE and RBS measurements for different ions and different doses ranging from slight damage to total damage. Comparing the damage peaks (caused by the same doses) determined with SE and RBS, a systematic deviation can be observed: SE measures more damage than RBS for lower and less damage than RBS for higher doses.
Article
Helium was implanted into Cz 〈111〉 p-type silicon wafers at 40 keV for various doses between 1×1016 He+ cm−2 and 1×1017 He+ cm−2. Furnace Anneals were subsequently applied at temperatures ranging from 650 °C up to 1000 °C. The optical models for the as-implanted samples are based on the coupled half-Gaussian model developed by Fried et al. As point defects and cavities coexist in the as-implanted sample, the original model combining two half-Gaussian profiles was modified. Both the distributions of point defects and cavities were described by Gaussian profiles in the new model, each of them using two coupled half-Gaussians. The optical model allows the overlapping of the profiles of defects and cavities. A fitting procedure, called ‘multiple random search’, was applied to minimize the probability of getting in a local minimum. Using this new model, the measured spectra were well fitted, while there was no acceptable fit possible with conventional models. The annealed samples could be well described by cavity profiles only. Different models were investigated including Gaussian profiles or profiles with arbitrary distributions using independent volume fractions of cavities in the sub-layers. The results were crosschecked by transmission electron microscopy micrographs, showing a good agreement.
  • E Agocs
  • P Petrik
  • M Fried
  • A G Nassiopoulou
E. Agocs, P. Petrik, M. Fried and A. G. Nassiopoulou, Mater. Res. Soc. Symp. Proc. 1321 (2012) 367.
  • D Alquier
  • F Roqueta
  • L Ventura
  • F Cayrel
  • C Dubois
  • R Jérisian
D. Alquier, F. Roqueta, L. Ventura, F. Cayrel, C. Dubois and R. Jérisian, Jpn. J. Appl. Phys. 41(2002) 3625.
  • G E Jellison
  • M F Chrisholm
  • S M Gorgatkin
G. E. Jellison Jr., M. F. Chrisholm, S. M. Gorgatkin, Appl. Phys. Lett. 62 (1993) 3348.
  • D Alquier
  • F Cayrel
  • O Menard
  • A.-E Bazin
  • A Yvon
  • E Collard
D. Alquier, F. Cayrel, O. Menard, A.-E. Bazin, A. Yvon, E. Collard, Jpn. J. Appl. Phys. 51 (2012) 01AG08.
  • O Marcelot
  • A Claverie
  • M Gavelle
  • F Cristiano
  • F Cayrel
  • D Alquier
  • W Lerch
  • S Paul
  • L Rubin
  • H Jaouen
  • C Armand
O. Marcelot, A. Claverie, M. Gavelle, F. Cristiano, F. Cayrel, D. Alquier, W. Lerch, S. Paul, L. Rubin, H. Jaouen, C. Armand, Nucl. Instrum. Methods Phys. Res. B 257 (2007) 249.
  • F Cayrel
  • D Alquier
  • C Dubois
  • R Jérisian
F. Cayrel, D. Alquier, C. Dubois and R. Jérisian, Mater. Sci. Eng. B 124 (2005) 271.
  • F Cayrel
  • D Alquier
  • D Mathiot
  • L Ventura
  • F Roqueta
  • G Gaudin
  • R Jérisian
F. Cayrel, D. Alquier, D. Mathiot, L. Ventura, F. Roqueta, G. Gaudin and R. Jérisian, Nucl. Instrum. Methods Phys. Res. B 216 (2004) 291.
  • T Lohner
  • E Kotai
  • N Q Khanh
  • Z Toth
  • M Fried
  • K Vedam
  • N V Nguyen
  • L J Hanekamp
  • A Van Silfhout
T. Lohner, E. Kotai, N.Q. Khanh, Z. Toth, M. Fried, K. Vedam, N.V. Nguyen, L.J. Hanekamp, A. van Silfhout, Nucl. Instrum. Methods Phys. Res. B 85 (1994) 335.