MeV-boron implanted layer, oxygen precipitates and poly-silicon back side combined in one silicon wafer: at what defect will Cu and Ni be gettered?

We have measured the gettering efficiencies for Cu and Ni of various silicon wafers, such as MeV-boron-implanted p- polished wafers treated with two different implantation doses of 3×10¹³ atoms/cm² B and 1×10¹⁵ atoms/cm² B, respectively. A third kind of wafer was covered with a poly-silicon back side and thermally pretreated before the gettering test to form oxygen precipitates in the bulk. The gettering test started with a reproducible spin-on spiking on the front side of the wafers in the range around 10¹² atoms/cm², followed by a thermal treatment to redistribute the metallic impurities in the wafer. Then the gettering efficiencies were measured by a novel wet chemical layer-by-layer etching technique in combination with inductively coupled plasma mass spectrometry. This led to “stratigraphical concentration profiles” of the metallic impurities in the wafer with typical detection limits of (5–10)×10¹² atoms/cm³. The concentration profiles were compared with concentration profiles found after testing the gettering efficiency of p/p+ epitaxial wafers. Almost 100% of the total intentional Cu spiking was recovered in the boron buried layer for both implantation doses. On the front surface and in the region between the front surface and the buried layer a Cu concentration ∼20 times higher than on/in p/p+ epitaxial wafers/layers was measured for the implanted specimen. The lower implantation dose led to higher Cu-concentration levels on the front surface compared to the higher implantation dose. The wafer containing a MeV-boron-implanted layer as well as oxygen precipitates and a poly-silicon back side exhibited a Cu distribution of 30/∼0/70%, respectively. Thus, the gettering by poly-silicon exceeded both the gettering effects by the buried layer and by the oxygen precipitates. Ni gettering in MeV-boron-implanted wafers exhibited other characteristics. The gettering efficiency of the buried layer was 65%, while the remaining Ni contamination was equally distributed between the front-side region and the wafer back side. A wafer containing a buried layer obtained by a 1×10¹⁵ atoms/cm³ B dose and oxygen precipitates exhibited 17% of the total Ni contamination in the boron layer, while ∼80% of the total Ni contamination was gettered by oxygen precipitates. In the case of buried layer/oxygen precipitates/poly-silicon back side the distribution was found to be 13/37/45%, thus exhibiting equal gettering strengths for oxygen precipitates and the poly-silicon back side for Ni contamination. The results were discussed in terms of segregation and relaxation-induced gettering mechanisms including different reaction rates. Received: 30 May 2001 / Accepted: 16 June 2001 / Published online: 30 August 2001     

Gettering of implanted Au in MeV?C implanted Si

The gettering behavior of 1 MeV?C implantation induced defects for Au (1.5 MeV, 2.2×10¹⁵ cm^-2), implanted into FZ Si(111), has been investigated using Rutherford backscattering spectrometry and cross-sectional transmission electron microscopy. The gettering efficiency of the C implanted layer has been studied as a function of C dose, annealing temperature and time. For a C dose of 2×10¹⁶ cm^-2, a 2 h anneal at 950 °C has been found to result in a gettering efficiency going beyond ?90%. Thermal stability of the gettered Au in the C implanted layer has subsequently been investigated over a temperature range of 950–1150 °C using isochronal annealing. The gettered amount has been found to be stable up to 1050 °C beyond which there is a release. We have observed nanovoids in the C implanted layer surrounded by ?-SiC precipitates along with patches of a-SiC. Up to about 1050 °C, these nanovoids act as efficient gettering centers beyond which they seem to release the trapped Au. Four distinct regimes in annealing temperature with different mechanisms for Au gettering have been observed.     

Comparison of different gettering techniques for Cu–p+ versus polysilicon and oxygen precipitates

We performed measurements of gettering efficiencies for Cu in silicon wafers with competing gettering sites. Epitaxial wafers (p/p+) boron-doped with a polysilicon back side allowed us to compare p+ gettering with polysilicon gettering. We further measured metal distributions in p+/p- epitaxial test wafers, with the p- substrate wafers pretreated for oxygen precipitation to compare p+ gettering with oxygen precipitate gettering. Our test started with a reproducible spin-on contamination in the 10¹² atoms/cm² range, followed by thermal treatment in order to redistribute the metallic impurity. Wafers were then analyzed by a novel wet chemical layer-by-layer etching technique in combination with inductively coupled plasma mass spectrometry. This led to “stratigraphical” concentration profiles of the impurity, with typical detection limits of 5–10×10¹² atoms/cm³. Twenty-five percent of the total Cu contamination in the p/p+/poly wafer was found in the p+ layer, whilst 75% was gettered by the polysilicon. Obviously, polysilicon exhibits a stronger gettering than p+ silicon, but due to the large distance from the front surface, polysilicon was less effective in reducing impurities from the front side of a wafer compared with p+ gettering. An epitaxial layer p+ on top of p- substrates with oxygen precipitates gettered 50% of the total Cu; while the other 50% of the Cu was measured in the p- substrate wafer with oxygen precipitates. Without oxygen precipitates, 100% of the spiked Cu contamination was detected inside the p+ layer. Gettering by oxygen precipitates thus occurs in the same temperature range as that where p+ silicon begins to getter Cu. Received: 3 September 2001 / Accepted: 17 October 2001 / Published online: 27 March 2002     

Gettering efficiencies for Cu and Ni as a function of size and density of oxygen precipitates in p/p- silicon epitaxial wafers

We have measured the gettering efficiencies for Cu and Ni in p/p-Si epitaxial wafers. The wafers were pretreated to obtain oxygen precipitates of different sizes and densities in the bulk. Gettering tests started with a reproducible spin-on spiking in the range of 10¹² atoms/cm², followed by thermal treatment to drive-in and redistribute the impurities in the wafer. Subsequently, the wafers were analyzed by a novel stratigraphical layer-by-layer etching technique in combination with inductively coupled plasma mass spectrometry. Gettering efficiencies for Ni did not depend on oxygen precipitate sizes and densities as long as ΔO_i was larger than 0.2×10¹⁷ atoms/cm³ and the bulk micro defect densities were detectable by preferential etching (10⁷ cm^-3). In these cases, gettering efficiencies were 96–99% for Ni, while wafers not containing any measurable BMDs exhibited no detectable gettering. Cu exhibited a more complex behavior because the total Cu contamination was found to be divided into two species, one mobile and the other immobile species. A dependence on BMD size and BMD density of the Cu distributions in the wafers was also detected. Gettering effects were increased with increasing BMD densities and sizes. For BMD densities <10⁹ cm^-3, Cu was not efficiently gettered by oxygen precipitates. Even for BMD densities >10¹⁰ cm^-3, gettering effects due to oxygen precipitates were one order of magnitude lower than in heavily boron-doped silicon. Received: 19 January 2001 / Accepted: 31 January 2001 / Published online: 20 June 2001     

The linkage between macroscopic gettering mechanisms and electronic configuration of 3d-elements in p/p+ epitaxial silicon wafers

We have measured the gettering efficiencies for Cr, Mn, Fe, Co, Ni and Cu in p/p+ epitaxial wafers. The gettering test started with a reproducible spin-on contamination on the front side of the wafers in the 10¹²–10¹⁴ atoms/cm² range, followed by thermal treatment to redistribute the metallic impurities in the wafer. The gettering efficiencies were measured by a novel wet chemical stratigraphic etching technique in combination with inductively-coupled plasma mass spectrometry. The residual bulk metal contamination was also measured by this method. This procedure led to global distributions of the 3d elements on the wafer’s front side, in the bulk of the wafer and on the wafer’s back side. Recovery rates were found to be 34%, 2.3%, 100%, 85%, 100% and 100% for Cr, Mn, Fe, Co, Ni and Cu, respectively. An impurity segregation effect in the wafer bulk was measured for Cu (100%) and Cr (34%), while no detectable segregation-induced gettering mechanisms were detected for the other elements in the applied concentration range. The segregation-induced gettering mechanisms were interpreted from the electronic structure of the metallic impurities. For segregation gettering by increased solubility in p+ silicon, the metallic species must form donors. Only Cu⁺ (3d ¹⁰) and Cr⁺ (3d ⁵) can form singly positively charged species that exhibit a spherical electronic distribution. It is well known from spinell structures that 3d ¹⁰ and, to a smaller extent 3d ⁵, are stable configurations in tetrahedral structures like the silicon lattice. Thus, we link the segregation-induced gettering mechanism in p/p+ epitaxial wafer to the electronic configuration of the 3d elements. Received: 19 January 2001 / Accepted: 31 January 2001 / Published online: 20 June 2001     

Integrity of ultrathin gate oxides with different oxide thickness, substrate wafers and metallic contaminations

The integrity of ultrathin gate oxides was investigated as a function of polished and epitaxial wafer surfaces with various gettering sites. After intentional contamination of wafers with 1×10¹¹ atoms/cm² and 5×10¹² atoms/cm² Cu and Ni by a spin-on technique of high reproducibility, we performed 0.18-μm low-thermal-budget CMOS process runs. Thermal oxides were grown with various gate oxides in the range of 5–17 nm. After a MOS-capacitor fabrication we applied a ramped current-density test to study the gate-oxide integrity. Generally, thinner gate oxides exhibited a much more robust behavior than thicker oxides. The gate-oxide integrity was strongly influenced by different gettering sites. Although a higher Ni contamination led to a higher number of gate-oxide failures, Cu contamination exhibited a higher impact on the gate-oxide integrity than Ni. Received: 12 September 2000 / Accepted: 21 September 2000 / Published online: 22 November 2000     

Ion implanted induced giant gettering of gold in silicon

Abstract

Ion implanted induced giant gettering of Gold in Silicon has been investigated by using ?111? Si wafer implanted with 10¹⁶ Ar⁺ ions/cm² at 280 keV. Some conditions of the appearance of giant gettering of Au in Si have been establi shed at different temperatures i.e. 500°C and 900°C: (i) annealing in vacuum, (ii) an “infinite” source of Au from a preannealed Au-Si film deposited by sputtering. On the basis of the experimental results a simple thermodinamic model explaining the giant gettering involving the mechanism of a liquid Au-Si phase has been developed.     

Au gettering by Ne and Ar implantation in silicon

The gettering efficiency for Au induced by Ne⁺ and Ar⁺ implantation has been studied. The depth distribution of gettered Au as a function of annealing temperature and dose of implanted Ne⁺ and Ar⁺ ions are presented. The experiment shows that the maximum efficiency of gettering occurs when the implantation doses are comparable with amorphization dose.     

Improved device performance in nonpolar a ‐plane GaN LEDs using a Ni/Al/Ni/Au n‐type ohmic contact

The authors report upon the increased light‐output power (P_out) via a reduction in the forward voltage (V_f) for nonpolar a ‐plane GaN LEDs using Ni/Al/Ni/Au n‐type ohmic contacts. The specific contact resistivity of the Ni/Al/Ni/Au contact is found to be as low as 5.6 × 10^–5 whereas that of a typical Ti/Al/Ni/Au contact is 6.8 × 10^–4 Ω cm², after annealing at 700 °C. The X‐ray photoelectron spectroscopy results show that the upward surface band bending is less pronounced for the Ni/Al contact compared to the Ti/Al contact, leading to a decrease in the effective Schottky barrier height (SBH). The V_f of the nonpolar LEDs decreases by 10% and P_out increases by 15% when the Ni/Al/Ni/Au scheme is used instead of the typical Ti/Al/Ni/Au metal scheme. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mixing of Au in Si induced by secondary and high-order recoil implantation

The mixing of Au in Si induced by secondary and high-order recoil implantation was investigated using 350 keV Ar⁺ and 350 keV Kr⁺ ions to fluences from 1?×?10¹⁶ to 3?×?10¹⁶ ions/cm² at room temperature. The thickness of the Au layer evaporated on Si substrate was ～2400 Å.The ranges of the Ar and Kr ions were chosen to be lower than the thickness of the Au layer in order to avoid the ballistic mixing produced by the primary knock-on atoms. Rutherford backscattering spectrometry (RBS) experiments were carried out to study the effects induced by Ar and Kr irradiation at the interface of Au–Si system. We observed that in the case of the irradiation with Ar⁺ ions, a broadening of the Au–Si interface occurred only at the fluence of 3?×?10¹⁶ Ar⁺/cm² and it is attributed to the surface roughening induced by ion bombardment. In contrast, the RBS analysis of a sample irradiated with 2?×?10¹⁶ Kr⁺/cm² clearly showed, in addition to the broadening effect, the formation of a mixed zone of Au and Si atoms at the interface. The mixing of Au in Si atoms can be explained by the secondary and high-order recoil implantation followed by subsequent collision cascades.     

Effect of the doping level on temperature bistability in a silicon wafer

The influence of the doping level on the effect of the temperature bistability in a silicon wafer upon radiative heat transfer between the wafer and the elements of the heating system is studied. Theoretical transfer characteristics are constructed for a silicon wafer doped with donor and acceptor impurities. These characteristics are compared with the transfer characteristics obtained during heating and cooling of wafers with the hole conduction (with dopant concentrations of 10¹⁵, 2 × 10¹⁶, and 3 × 10¹⁷ cm^?3) and electron conduction (with impurity concentrations of 10¹⁵ and 8 × 10¹⁸ cm^?3) in a thermal reactor of the rapid thermal annealing setup. It is found that the width and height of the hysteresis loop decrease with increasing dopant concentration and are almost independent of the type of conduction of the silicon wafer. The critical value of the impurity concentration of both types is 1.4 × 10¹⁷ cm^?3. For this concentration, the loop width vanishes, and the height corresponds to the minimal value of the temperature jump (～200 K). The mechanism of temperature bistability in the silicon wafer upon radiative heat transfer is discussed.     

Magnetic properties of dilute Co impurities in liquid Sn

The susceptibility of dilute Co impurities in liquid Sn is reported. It displays an almost linear increase from 1.8 × 10^?4 cm³/mole at 240°C to 4.5 × 10^?4 cm³/mole at 1000°C. These results are compared with other experimental information and are shown to be consistent with a recently proposed ionic impurity model if an interaction parameter is assumed to be temperature dependent.     

Neutron irradiation effects in Fe–Cu–Ni–Mn model alloys studied by measurements of magnetic minor hysteresis loops

We have measured magnetic minor hysteresis loops of neutron-irradiated Fe–Cu–Ni–Mn model alloys with variable combinations of Cu and Ni contents. It was revealed that minor-loop coefficients which are in proportion to internal stress decrease after neutron irradiation to a fluence of 0.44?×?10¹⁹?n?cm^?2 for all alloys. The decrease of the coefficients strongly depends on both Cu and Ni contents and is enhanced for alloys with high Cu and high Ni contents, in particular. The decrease of the coefficients during neutron irradiation was explained as due to preferential formation of Cu rich and/or Mn-Ni rich precipitates on dislocations which reduces internal stress of dislocations.     

在不同的退火温度下钴注入二氧化钛结构与磁性

选用能量为180 keV,温度为623 K,注入4×10¹⁶ cm^-2剂量的钴离子束注入TiO₂样品.在不同的退火温度下,用高分辨的扫描电镜、同步辐射X射线衍射、卢瑟福背散射/沟道实验和超导量子干涉仪,分别对样品进行结构与磁性的测试. SR-XRD和HRTEM测试结果表明: 在Co注入TiO₂后,形成了钴的体心立方(hcp)相和面心立方(fcc)相,且在TiO₂中,钴-纳米粒子也已经形成. 随着退     

CdS/CdTe薄膜太阳电池的深能级瞬态谱和光致发光研究

用深能级瞬态谱和光致发光研究了无背接触层的CdS/CdTe薄膜太阳电池的杂质分布和深能级中心.得到了净掺杂浓度在器件中的分布.确定了两个能级位置分别在E_V+0365 eV和E_V+0282 eV的深中心,它们的浓度分别为167×10¹² cm^-3和386×10¹¹ cm^-2,俘获截面分别为143×10^-14cm²和153×10^-16cm².它们来源于以化学杂质形式存在的Au和（或）Te_Cd^-复合体,或与氩氧气氛下沉积CdTe时的氧原子相关. 关键词： 深能级瞬态谱 光致发光 CdS/CdTe太阳电池     

Electrotransport d'impuretes dans Cu et Ni

The effective valency of ⁵⁹Fe, ⁵⁸Co and ¹²⁵Sb in Cu and ⁵⁹Fe, ¹²⁵Sb in Ni has been determined using the thin-layer technique. The impurities are observed to move to the cathode in Ni, showing that the scattering of the holes of the d band dominates s scattering in Ni. In the Cu matrix, the resistivities obtained at the saddle point are rather small. A tentative explanation is given in terms of a virtual bound level on the impurity.     

Materials modification at zirconium–silicon interface using swift heavy ions

The reactivity of the Zr/Si interface induced by swift heavy ion beams of Au has been investigated in the present work. Zirconium was evaporated on a clean silicon substrate in ultra high vacuum (UHV) at a pressure of 10^?8 Torr by the electron beam evaporation technique and the final layer was a thin film of Au to avoid oxidation of zirconium. The Zr/Si system was irradiated by 350 MeV Au²⁶⁺ ions at liquid nitrogen temperature at different fluences (0.46×10¹⁴, 1.85×10¹⁴ and 4.62×10¹⁴ ions/cm²). Rutherford back scattering (RBS) spectroscopy using 2 MeV He ions was used to monitor the Zr and Si concentration profiles and interdiffusion at the interfaces. The irradiation at the Zr/Si interface showed mixing. X-ray diffraction measurements confirmed the formation of the ZrSi₂ phase. Thermal spike formation and melting in the tracks was found to be the dominant process at the interfaces.     

High dose iron implantation into silicon and metals

High dose implantations of Fe into metals and semiconductors have been performed with beam energies up to 1 MeV at the UNILAC-injector at GSI. Unusual high concentrations of 70 atomic % for Si and 20 atomic % for Cu have been obtained, with doses of 10¹⁸ Fe/cm² in the case of Si and several 10¹⁷ Fe/cm² in the case of Cu. For Si the thickness of the layers were determined by Rutherford backscattering to be 4500 Å. These results are consistent with calculations, which show that these high concentrations are due to the reduction of the sputter yield at the relative high particle energies. Samples have been characterized using several complementary methods (Mössbauer Spectroscopy (MS), Rutherford Backscattering Spectroscopy (RBS), Auger electron Spectroscopy (AES). Scanning Electron Microscopy (SEM), X-ray diffraction (XRD)).     

Diffusion constant and surface states of positrons in metals

Positron lifetime spectra and angular correlation curves for seven fine-grained powders of Fe, Co, Ni, and W are analyzed. From the lifetime data, the positron diffusion constant in metals atT=300°K was found to beD ₊=(1.0±0.5)×10^?2 cm² sec^?1. Evidence is presented that positrons are trapped in metal surface states.     

Ion-beam induced mixing of Cu/Au bilayer thin film (kinematics and formation of solid solutions)

Ion-beam induced atomic mixing of Cu/Au bilayer thin film is studied using combined electrical resistivity measurements and Rutherford Backscattering Spectrometry (RBS). 400 keV Kr⁺ ion irradiation with fluences ranging from 3.3×10¹⁵ to 7.6×10¹⁶ ions/cm² at room temperature have been used. Ion beam mixing lead to a uniformly mixed metal alloy. The formation of Cu/Au solid solutions depends on the initial composition and on the fluence of irradiating ions. For an initial composition of Cu₄₂Au₅₈, a Cu-rich solid solution of composition Cu₇₂Au₂₈ is formed after irradiation with 7.6×10¹⁶ ions/cm². The kinematics of the intermixing process is also studied by in situ electrical resistivity measurements which confirmed the formation of the Cu/Au solid solutions.