MCZ Silicon Research Articles

TCAD simulation of the mixed irradiated n-MCz Si detector: Impact on space charges, electric field distribution

In the mixed irradiations at HL-LHC, n- MCz Si as a detector material is reported as a prime applicant. To study the non-homogeneous distribution of space charges and electric field distribution in mixed irradiated p+n MCz silicon pad detectors, four-level numerical modeling of mixed irradiation induced deep traps using microscopic parameters obtained from experimental measurements were implemented in Synopsys T-CAD. These advanced damage model parameters were sufficiently tuned to reproduce the experimental data’s on the full depletion voltage and leakage current at 293K. In this paper, the influence of effective introduction rate of shallower donor deep trap E30 K has been determined using SRH theory calculations for experimental effective doping concentration f and the behavior of space charges and electric field distribution in the presence of deep traps are thoroughly investigated.

AC-coupled n-in-p pixel detectors on MCz silicon with atomic layer deposition (ALD) grown thin film

We report initial characterization of our novel sensor process solutions with AC-coupled n+/p−/p+ pixel detectors made on 150 mm diameter p-type Magnetic Czochralski silicon (MCz-Si) wafers. The pixels were segmented in a 52 × 80 dual column array and designed to be AC capacitive coupled. The resistive coupling between pixels, allowing quality assurance probing prior the flip chip bonding, was realized with thin film metal-nitride resistors fabricated by sputtering deposition. This approach allows us to omit punch-through resistor structures, which reduces the overall process complexity. Moreover, our previous studies have emphasized that applying ALD Aluminum Oxide (Al2O3) field insulator and passivation layer results in negative net oxide charge and thus additional p-spray or p-stop surface current termination structures are not necessary. Our focused application is a radiation-hard ALD AC-coupled pixel detector to be used in future particle physics experiments, such as the High-Luminosity Large Hadron Collider (HL-LHC), as well as photon counting applications. The pixel detectors were tested at Helsinki Institute of Physics (HIP) Detector laboratory and Ruđer Bošković Institute (RBI). We show measurement data of pixel detectors and other test structures. For the TiN resistors surrounding pixels, the resistance values were measured to be about 15kΩ. Data of electrical properties, full depletion voltage and leakage current are shown as well. Our Transient Current Technique (TCT) measurements indicated clear pixel segmentation with excellent homogeneity. For further study, AC-coupled sensors were hybridized to PSI46dig read out chips (ROC) by flip-chip interconnection technique and tested with a radioactive source.

Quality of n-Type Czochralski Silicon Crystals for Solar Cells Grown from the Melt in Liquinert Crucibles

For the application to advanced high-performance solar cells, we have developed n-type CZ monocrystalline silicon crystals whose lifetime values are almost equal to those of MCZ silicon. We analyzed this point in detail, using the Shockley-Read-Hall model. In our growth, liquinert silica crucibles having non-wettable properties for molten silicon were employed in a conventional CZ puller. The improved lifetime is likely due to reduced carbon impurity. The CZ growth technique with liquinert crucibles brings a novel approach to the new CZ technique because it can supply higher-quality silicon compared to silicon grown by conventional CZ technique.

Infrared defect dynamics: He irradiation induced complexes in high‐quality silicon crystal

The behavior of radiation‐induced complexes in MCZ silicon crystal after He irradiation was studied by highly sensitive and accurate infrared absorption spectroscopy. Samples from the same crystal that was used in the electron irradiation were employed. Many absorption lines with peak absorbance as small as 10−6 were successfully detected. Most of them were the same as those that had been observed in the electron irradiated samples and reported in the previous papers. Not only C‐rich type complexes such as CiOi and ICiOi, but also C‐lean type complexes such as I2O2i and IO3i were observed, in contrast to the electron case where only C‐rich type had been observed in the same crystal. Peak absorbances for the He case are about half of those in the electron case. The He dose was 5 × 1013 cm−2, 1/200 of the electron dose of 1016 cm−2. Thus, the complex production rate per particle in the He case was about 100 times as large as that for electrons. The production range in the He case was restricted to within 20 microns from the surface. This range amounted to about 1/100 of that observed in the electron case where complexes had been formed uniformly throughout the 2 mm thick sample. Also, therefore, the complex concentration in the layer was about 100 times higher than that in the electron case. The annealing behavior of complexes was essentially the same as that in the electron case with minor differences.

SU‐GG‐T‐374: Use of a Rad‐Hard Si Diode in Clinical Electron Beam Dosimetry

Purpose:The preliminary results obtained with a MCz silicon diode as online clinical electron beam dosimeter are presented in this work. Method and Materials: The diode was manufactured by Okmetic Oyj (Finland) and processed by the Microelectronics Center of Helsinki University of Technology in the framework of the CERN RD50 Collaboration. The n+‐p‐p+ junction device used (area of 25 mm2) was housed in a PMMA probe designed to operate without bias voltage in the direct current mode. During all measurements, the diode was held in a PMMA plate, placed at Zref and centered in a radiation field of 10 cm × 10 cm, with the SSD kept in 100 cm. The device's dosimetric response was evaluated for the 6, 9, 12, 15, 18 e 21 MeV electron beams from a Siemens KD2 Accelerator. The radiation induced current in the diode, for ach electron beam energy, was registered as a function of the exposure time during 60 s for a fixed 300 MU. To study the instantaneous repeatability of the MCZ diode, 5 consecutive current signals were registered for a same radiation dose around of 300 cGy. Measurements were performed with an average dose rate of 5.0 cGy/s for the electron beam energies of 6,9,12,15,18 and 21 MeV. Results: The results indicated a linear dose response for doses up to 93,28 Gy for electron beams energies of 6, 9, 12, 15, 18 e 21 MeV with very good instantaneous repeatability (CV better than 2,76 %). Conclusion: It worth noting that these results are preliminar and still remains to be investigated this energy dependence, the central axis depth dose response, the long term stability and the radiation hardness of this diode for absorbed doses higher than investigated in this work. All these studies are under way.

Infrared Absorption from Low Carbon Concentration, Low Dose, Annealed CZ Silicon

Complexes formed by low dose irradiation with electron (1015-16/cm2) and He (5x1012- 5x1013/cm2) in the relatively low carbon concentration (1016/cm3) MCZ silicon were investigated by highly sensitive and quantitative IR absorption analysis. CiOi and VO were the main complexes in all cases. The concentration of these complexes was about 1015/cm3, or 10% of included carbon in the highest case. Loss of almost equal amount of Cs was observed. The concentration of CiOiI was one order of magnitude lower. Upon annealing, these lines weakened and almost disappeared at 400 oC. There were some absorption lines introduced by the annealing. VO2 was strongest among them and CsOi related structure was also confirmed. There were absorption lines at 954.9 and 962.6 cm-1 appeared after annealing at 300 oC.

DLTS measurements of radiation induced defects in epitaxial and MCz silicon detectors

n-Type epitaxial silicon layers of different thickness and resistivity, grown on highly Sb doped CZ-substrate by ITME (Warsaw), and n-type MCz silicon supplied by Okmetic (Finland) were used for the processing of planar diodes at CiS (Erfurt). For the epi-diodes a standard as well as a diffusion oxygenation process was employed. Irradiations had been performed with 26 MeV protons at the cyclotron of the Karlsruhe University and with neutrons at the TRIGA reactor of the Ljubljana University. Microscopic investigations using the DLTS method were done. The correlation of the IO 2 i -defect and the oxygen concentration was studied by a depth-profile measurement. The annealing behavior of the IO 2 i -defect at different temperatures was investigated and the activation energy extracted.

Semiconductor detectors for high-luminosity environments

As the final touches are being put to the LHC detectors, the race is on to perfect technologies which could be used to confront the challenges of the ultra-high luminosities of the SLHC and International Linear Collider (ILC). These challenges include ever more hostile radiation environments, short signal shaping times and increasing emphasis on the highest possible granularity combined with the lowest possible mass. In the semiconductor detector field, dedicated studies have identified many mechanisms behind radiation damage and pointed the way towards the use of new techniques such as MCz silicon and p-type sensors. In the most extreme environments, completely new approaches, such as the use of diamond or 3D sensor detectors, will be essential. Pixel technology, which has been successfully employed to build large-scale vertex detection systems for the LHC, will be pushed towards higher density, lower mass and greater integration, to satisfy in particular the ILC requirements. We review the highlights of the current generation of semiconductor detectors and discuss some of the exciting prospects for future developments.

Study of radiation damage induced by 24 GeV/ c and 26 MeV protons on heavily irradiated MCz and FZ silicon detectors

The aim of this work is the development of radiation hard detectors for very high luminosity colliders. A growing interest has been recently focused on Czochralski silicon as a potentially radiation-hard material. We report on the processing and characterization of micro-strip sensors and pad detectors produced by ITC-IRST on n- and p-type magnetic Czochralski and float zone silicon. Part of the samples has been irradiated using 24 GeV/ c protons (CERN-Geneva), while another part has been irradiated with 26 MeV protons (FZK-Karlsruhe) up to a fluence of 5×10 15 1 MeV-neutron-equivalent/cm 2. All the samples have been completely characterized before and after irradiation. Their radiation hardness as a function of the irradiation fluence has been established in terms of breakdown voltage, leakage current and evaluating the more relevant mini-sensor parameter variation. Moreover, the time evolution of depletion voltage, leakage current and inter-strip capacitance has been monitored in order to study their annealing behavior and space charge sign inversion effects.

The LHCb VELO: status and upgrade developments

The VErtex LOcator (VELO) is the silicon microstrip vertexing and triggering sub-detector of the LHCb experiment. It consists of a series of forward disks with the active region extending to just 8 mm from the LHC beams. The current status of the VELO is presented. Due to the high radiation environment, the VELO may have to be replaced after some years, possibly with new materials. A candidate material is Czochralski silicon. We present here promising new results on the first test beam of a large, high resistivity Czochralski microstrip silicon detector read out with LHC speed electronics. The performance was studied before and after irradiation with high energy protons. A signal to noise of over 20:1 was obtained from the detector and significant charge collection efficiencies were measured at relatively modest voltages after a fluence of 4.3/spl times/10/sup 14/ 1 MeV neutron equivalents (n/sub eq/) per cm/sup 2/. Studies using the Transient Current Technique probed the electric field within MCz test detectors and proved that MCz silicon does not type invert up until a radiation level of at least 5/spl times/10/sup 14/ 24GeV/c p/cm/sup 2/. This would mean the VELO could possibly replace, in a potential upgrade, n/sup +/-on-n DOFZ sensors and the complicated processing involved, for standard p/sup +/-on-n processing with MCz.

Degradation of carrier lifetime in Cz silicon solar cells

The lifetime degradation induced by light illumination or carrier injection which is observed in Czochralski-grown silicon (Cz-Si) leads to a significant decrease of solar cell efficiency. Thus, the reduction of this effect has a high potential for the improvement of Cz-Si solar cells. In the present work both, the analysis of the underlying defect and its technological reduction are discussed. A clear correlation of the Cz-specific metastable defect with the oxygen and boron concentration in Cz-Si has been observed. Especially, recently performed lifetime measurements on oxygen-free boron-doped p-type MCz silicon and gallium-doped oxygen-contaminated Cz-silicon, both of which show no degradation, confirm this hypothesis. While the quantitative correlation between the defect concentration and boron is linear, the increase of the defect concentration induced by the interstitial oxygen concentration is superlinear, i.e. it follows a potential law of power approximately 5. Beyond the defect analysis, two different ways to reduce the metastable defect concentration are discussed. A proper material choice by substituting or reducing one of the major components of the metastable defect can completely avoid the degradation effect. The excellent performance of oxygen-free MCz-Si and gallium-doped Cz-Si is reflected in the achieved record efficiencies of 22.7% and 22.5%, respectively. In standard boron-doped oxygen-contaminated p-type Cz-Si a strong reduction of the metastable defect concentration can be achieved by a high-temperature process step resulting in an improvement of the stable bulk lifetime by a factor of 2–4.

24·5% Efficiency silicon PERT cells on MCZ substrates and 24·7% efficiency PERL cells on FZ substrates

This paper reports the recent improvements in the energy conversion efficiencies of solar cells on magnetically-confined Czochralski grown (MCZ) and float zone (FZ) silicon substrates at the University of New South Wales. A PERT (passivated emitter, rear totally-diffused) cell structure has been used to reduce the cell series resistance from higher resistivity substrates. The total rear boron diffusion in this PERT structure appears to improve the surface passivation quality of MCZ and some FZ substrates. Hence, higher open-circuit voltages were observed for some PERT cells. One of these cells on MCZ substrates demonstrated 24·5% energy conversion efficiency at Sandia National Laboratories under the standard global spectrum (100 mW/cm2) at 25°C. This is the highest efficiency ever reported for a MCZ silicon solar cell. The cells made on MCZ substrates also showed stable cell performance rather than the usually reported unstable performance for boron-doped CZ substrates. Also reported is a PERL (passivated emitter, rear locally-diffused) cell on a FZ substrate of 24·7% efficiency, which is the highest efficiency ever reported for any silicon solar cell. Copyright © 1999 John Wiley & Sons, Ltd.

24·5% Efficiency silicon PERT cells on MCZ substrates and 24·7% efficiency PERL cells on FZ substrates

This paper reports the recent improvements in the energy conversion efficiencies of solar cells on magnetically-confined Czochralski grown (MCZ) and float zone (FZ) silicon substrates at the University of New South Wales. A PERT (passivated emitter, rear totally-diffused) cell structure has been used to reduce the cell series resistance from higher resistivity substrates. The total rear boron diffusion in this PERT structure appears to improve the surface passivation quality of MCZ and some FZ substrates. Hence, higher open-circuit voltages were observed for some PERT cells. One of these cells on MCZ substrates demonstrated 24·5% energy conversion efficiency at Sandia National Laboratories under the standard global spectrum (100 mW/cm2) at 25°C. This is the highest efficiency ever reported for a MCZ silicon solar cell. The cells made on MCZ substrates also showed stable cell performance rather than the usually reported unstable performance for boron-doped CZ substrates. Also reported is a PERL (passivated emitter, rear locally-diffused) cell on a FZ substrate of 24·7% efficiency, which is the highest efficiency ever reported for any silicon solar cell. Copyright © 1999 John Wiley & Sons, Ltd.

Review of Growth Striations in CZ and MCZ Silicon Wafers

Review of Growth Striations in CZ and MCZ Silicon Wafers

CHARACTERIZATION OF MICRO-DEFECTS IN SILICON SINGLE CRYSTALS BY ANALYZING THE PENDELL?SUNG FRINGES

Based on the statistical theory of X-ray dynamical diffraction, a method to obtain the static Debye-Waller facter from section topographs is described. By analyzing the intensity distribution of the Pendelldsung fringes in the X-ray diffraction topograghs for heat treated CZ and MCZ silicon single crystals, the number density and the size of the oxygen precipitates which are smaller than X-ray topographic resolution are estimated. This quantitative analysis method provides a new means of studying the micro-defects.

Defects in MCZ Silicon with Various Oxygen and Carbon Contents

Defects in MCZ Silicon with Various Oxygen and Carbon Contents

Evaluation of interstitial oxygen along striations in CZ silicon single crystals with a micro-FTIR mapping system

Growth striations in CZ and MCZ silicon wafers were studied by the striation-etching method, spreading resistance measurements and the micro-FTIR mapping method. Microvariations in oxygen concentration were successfully measured using the micro-FTIR mapping system and the results were in good agreement with other results obtained by etching and resistance measurements. Two kinds of striations were observed in CZ and MCZ wafers with high oxygen concentration: weak striations at regular intervals and strong striations at irregular intervals. It was concluded that the former were related to the microsegregation of dopant impurities caused by remelting of the crystal during growth, while the latter were related to the fluctuation of oxygen concentration in the silicon melt.

Computer Simulation of Oxygen Segregation in CZ/MCZ Silicon Crystals and Comparison with Experimental Results

A computer model for the fluid flow and dopant transfer/segregation in Czochralski crystal growth (CZ) and in Czochralski crystal growth in an axial magnetic field (MCZ) is applied to the simulation of the oxygen source, transport, and segregation in CZ and MCZ silicon growth. To model the oxygen source, which is ablation of the silica crucible, the oxygen concentration at the melt/crucible interface is assumed to be at an equilibrium concentration which is dependent on temperature as described by Arrhenius kinetics. The oxygen sink is mostly evaporation of silicon monoxide from the melt‐free surface; a small percentage of the dissolved oxygen is incorporated into the growing crystal. Good agreement is established between the simulated oxygen radial profiles and experimental results in CZ/MCZ silicon growth, as well as in the comparison of the simulated ablation rate of the crucible with the experimental data reported to date.

EFFECT OF MAGNETIC FIELD ON THE PERFECTION OF MCZ SILICON

n-type and p-type MCZ silicon grown under different magnetic field strengths and different pulling rates compared with the CZ silicon were investigated by means of X-ray topography, micro-region infrared absorption, infrared microscopy, optical microscopy and spreading resistance, etc. The experimental results show that the MCZ method can provide high quality silicon crystals with a low oxygen concentration, uniform distribution of dopant and good thermal stability, leading to low thermal donor generation.

X-Ray Topography Studies of Oxygen Precipitates in MCZ Silicon

ABSTRACTX-ray section topography has been used to study the distribution and size of precipitates resulting from heat treatment of MCZ silicon. A low density of precipitates was found, enabling individual precipitate images to be studied. Images have been simulated by numerical solution of Takagi's equations and the magnitude of the strain field deduced by comparison with experiment. Excellent agreement has been found in the details of simulated and experimental images. The effective defect volume increased monotonically with annealing temperature. The effect of surface relaxation and long range curvature on the accuracy of determining the microscopic strain field by matching simulated and experimental images has been investigated.