ESR studies of thermally oxidized silicon wafers

We have performed ESR measurements on oxidized (111) silicon wafers and found two ESR centers. One, the previously known P_b center,was found to be a two level interface trap by corona bias studies. The other one, previously known as “damaged silicon” center was found to be a silicon center, probably related to the oxide growth process.     

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     

Modeling of Cu gettering in p- and n-type silicon and in poly-silicon

Based on experimental findings we set up calculations of numerical modeling of gettering efficiencies for Cu in various silicon wafers. Gettering efficiencies for Cu were measured by applying a reproducible spin-on contamination in the 10¹² atoms/cm² range, followed by a thermal treatment to redistribute the metallic impurity. Subsequently, the wafers were analyzed by a novel wet chemical layer-by-layer etching technique in combination with inductively coupled plasma mass spectrometry. We investigated p/p+ and n/n+ epitaxial wafers with different doping levels and different substrate-doping species. We have also investigated gettering efficiencies of phosphorus-diffused p- and n-type wafers. Heavilyboron doped silicon exhibited a gettering efficiency of ∼100%, while gettering by n+ silicon occurred for doping levels >3×10¹⁹ atoms/cm³ only. In another set of experiments we investigated the dependence of the gettering efficiency of p-type wafers with poly-silicon back sides for different cooling rates and Cu spiking levels. A strong dependence on both parameters was found. Cu gettering in p/p+ epitaxial wafers was modeled by calculating the increased solubility of Cu in p+ silicon compared to non-doped silicon taking into account the Fermi-level effect, which stabilizes donors in p+ silicon, and the pairing reaction between Cu and B. Calculated gettering efficiencies were in very good agreement with experimental results. Gettering in n+ silicon was similarly modeled in terms of pairing reactions and the Fermi-level effect. But, for n-type silicon, many experimental uncertainties existed; thus, we applied our expressions to solubility data of Hall and Racette to obtain the unknown parameters. The empirical calculations were in good agreement even with results on n/n+ wafers. For phosphorus-diffused wafers we had to consider an excess vacancy concentration of 1.2–5.5 times the equilibrium concentration to explain the experimental findings by the model. Gettering by poly-silicon back sides was simulated by solving the time-dependent diffusion equation with boundary conditions that take into account different surface reaction rates of silicon point defects. Using this advanced model, the experimentally measured gettering efficiencies were reproduced within the uncertainty of the measurement. Received: 3 September 2001 / Accepted: 4 September 2001 / Published online: 20 December 2001     

Ultrasound-assisted handling force reduction during the solar silicon wafers production

Surface adhesion between wet wafers poses great challenges for silicon wafer handling. It has been shown that both the shear and normal handling forces of the solar silicon wafers can be dramatically reduced by using the ultrasound energy. Approximately 20 and 5 times reduction in horizontal and vertical forces were achieved by as low power as 10 W, and a good agreement was found between the measured values and the predictions of a simple model for the effect of longitudinal vibration we developed.     

Experimental study of electrical properties at the Nd-doped Si-SiO2 interface

This paper presents the results of an experimental study designed to explore the electrical properties at the Nd-doped Si-SiO₂ interface. The Nd-doped silicon wafers and control silicon wafers (undoped) were annealed under different conditions of temperature, time and atmosphere. The electrical properties were measured using MOS test structures. The Nd-doped silicon wafers were analysed by electron spectroscopy (AES and ESCA). These results were compared with the Pd-, Rh-, La- and Gd-doped interfaces and briefly discussed in terms of the relevant action mechanisms of the negative electric effects.     

Ni reactions with surfaces: dependence of gettering efficiencies for Ni on crystal-growth conditions, back-side-gettering techniques, oxygen precipitates and thermal treatments

We have performed measurements on the gettering efficiencies for Ni in different silicon wafers. Gettering efficiencies were measured of wafers grown by different crystal-growth techniques, such as Czochralski-grown (CZ) and floating zone (FZ), as well as wafers containing crystal-originated particles (COPs) of different size and density. Lightly boron doped CZ wafers covered with an epitaxial layer were also evaluated. In another set of experiments, we compared different back-side-gettering techniques, like poly-silicon, stacking faults and He-implanted back sides and the dependence of back-side gettering on cooling rate and contamination level. Internal surfaces of oxygen precipitates were also investigated. The gettering test started with a reproducible spin-on contamination in the range around 10¹² atoms/cm² and was followed by a thermal treatment to redistribute the Ni impurity in the wafer. Subsequently, wafers were analyzed for their surface and bulk contamination by a novel layer-by-layer etching, stratigraphical technique in combination with inductively coupled plasma mass spectrometry. No detectable gettering effect of COPs was found. FZ wafers differed remarkably in their gettering behavior from CZ wafers, obviously due to differences in aggregated self-point defects. Most remarkably, the deposition process of an epitaxial layer changed the gettering behavior of p/p- wafers. Comparing the gettering efficiencies of different back sides, an extraordinarily high gettering efficiency of He-implanted voids can be anticipated, which was higher than the gettering efficiency of poly-silicon and stacking faults. High cooling rates at the end of the drive-in cycle and low contamination levels lowered the gettering efficiencies of back-side-gettering techniques, suggesting a diffusion-limited gettering process. Based on the dependence of the gettering efficiencies on different drive-in cycles, a surface reaction as a mechanistic initiation of the drive-in must be assumed. Oxygen precipitates exhibited a high gettering effect for Ni contamination. All experimental results are interpreted by available active surfaces in the gettering phases. Received: 30 May 2001 / Accepted: 16 June 2001 / Published online: 30 August 2001     

Effect of annealing temperature on determining trap depths of quartz by various heating rates method

The aim of this study is to determine the trap parameters (trap depth E, frequency factor s) of quartz using various heating rates method and also to investigate the effect of annealing temperature on determining trap depths. The method is based on the positions of the thermoluminescence peaks, obtained from the change in temperature of the peak at maximum caused by changing the heating rate at which the sample is measured. In the present work, powder quartz samples were annealed first at different temperatures before irradiation. Then samples irradiated to different doses were measured with a TL reader at different heating rates and the glow curves were recorded. In order to calculate the trap depth E and the frequency factor s, the glow parameter T_m was determined experimentally from the glow curve by measuring the shift of the maximum peak temperature depending on heating rate β. The calculation of trap parameters was repeated for each annealing temperature. Then the effect of annealing temperature on trap depths calculated by the various heating rates method was evaluated.     

InGaAsP/InP双异质结发光管频响特性的研究

本文研究了光纤通信用1.3μmInGaAsP/InP双异质结发光管的频响特性。结果表明:器件有源区掺杂浓度;有源层厚度;注入电流;光谱特性;P-n结特性等因素,对发光管的频响特性有重要影响。老化前有源区DSD的存在与否对频响无明显关系。     

Observation of ultracold ground-state heteronuclear molecules

We report the observation of translationally ultracold heteronuclear ground-state molecules in a two-species magneto-optical trap containing 39K and 85Rb atoms. The KRb molecules are produced via photoassociation and detected by multiphoton ionization. We had characterized their temperature and measured their formation rate constant. We believe that the two-species trap could be used as a reliable source of ultracold molecules to be captured by electrostatic, magnetic, or optical traps. This possibility will certainly motivate further investigation of quantum collective effects as well as high-resolution spectroscopy of the rovibrational level structure of cold heteronuclear molecular systems.     

Optical measurements of stress distributions in GaAs at low temperature

We have measured the stress distribution at He temperature on two epitaxial GaAs wafers which were compressed along one edge. The stress was determined non-destructively at different points on the wafer surface by using the line-splitting and the lineshifts of the photoluminescence spectra of the acceptor-bound excitons in comparison with calibration spectra at known uniaxial stress.     

Precipitation in silicon wafers after high temperature preanneal studied by X-ray diffraction methods

We have investigated oxygen precipitation in Czochralski silicon wafers focusing on influence of nucleation temperature and high temperature pre-anneal during common three step treatment. Thick Si wafers were studied mainly by x-ray diffraction in Laue transmission geometry using Mo x-ray tube, but were also compared to reciprocal space maps obtained in Bragg reflection geometry. The analysis of measured diffraction scans in Laue geometry was performed by means of Takagi equations and statistical dynamical theory of diffraction. From the simulated Laue diffraction curves we find the size of the individual defect area and the fraction of strain area volume in the wafer. The results obtained from x-ray diffraction were compared to loss of interstitial oxygen according to infrared absorption spectroscopy and the size of SiO₂ precipitate core was estimated. These techniques are in agreement with transmission electron microscopy images.     

Biaxial strains on thin silicon wafers

Abstract

Biaxial strains have been developed on thin silicon wafers by bending them under the action of external forces. In all devices used for bending, the amount of strains developed on the wafers was calculated from the radius of curvature measured at the center of the deformed surface, and from the shift in frequency induced by the biaxial strain on the silicon phonon line. The use of biaxial strain machines as practical devices for the study of the deformation potentials in thin films and superlattices is examined.     

Relaxation of green fluorescent protein chromophore anion observed by photodissociation in an electrostatic storage ring

The gas-phase absorption properties of the green fluorescent protein chromophore anion were studied using an electrostatic storage ring. The time sequence of neutral particles produced by photodissociation was detected following laser irradiation. The lifetimes of the photo-absorbed ions depended on their storage time in an ion trap before injection into the storage ring. The lifetime increased with the storage time and saturated, indicating a change in the population of rovibrationally excited states with respect to the storage time. Photodissociation neutral spectrum of the relaxed ions measured as a function of the laser wavelength was characterized by a narrow asymmetric shape, which was in good agreement with the photo fragment ion action spectrum reported recently.     

Hydrogen-induced boron passivation in Cz Si

Acceptor deactivation in the near-surface region of as-grown, boron-doped Si wafers was detected by in-depth profiles of the free-carrier density obtained by capacitance–voltage measurements. As this deactivation was only observed in wafers subjected to the standard cleaning procedures used in Si manufacturing, we ascribed it to boron passivation by an impurity introduced during the cleaning process. From the study of the free-carrier reactivation kinetics and of the diffusion behaviour of boron–impurity complexes, we have concluded that the impurity is possibly related to hydrogen introduced during the cleaning treatments. The characteristics of the deep level associated with this impurity have been analysed by deep-level transient spectroscopy. Received: 22 August 2001 / Accepted: 27 October 2001 / Published online: 29 May 2002     

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     

Dynamics of gold cluster systems

x surface of Si(111) wafers was studied as a function of annealing time at relatively low annealing temperatures (50 and 100 °C) by application of scanning force microscopy. A fast increase in cluster diameter and height as a function of annealing time was detected. After more than 3 h of annealing depletion zones and nucleation exclusion zones were observed. Received: 13 August 1998 / Published online: 10 February 1999     

Sheet resistance of LiNbO<Subscript>3</Subscript> wafers processed in radio-frequency plasma of hydrogen

Radio-frequency discharge of 13.56MHz in hydrogen was used for processing single domain crystalline LiNbO₃ wafers under an electrodeless capacitive coupling. At a pressure of 0.5 torr and RF input power of 250 W a surface layer of approx. 0.5 μm on the LiNbO₃ wafers was created in which the niobate structure was strongly injured. The Li concentration dropped almost to zero at the very surface and only niobium oxides remained there. After the surface modification the wafers lost their insulating properties and became electrically conducting. The sheet resistance was measured and revealed a semiconducting character. We discuss possible mechanisms of the charge carriers creation in the material during the plasma processing. The nuclear method NDP (Neutron Depth Profiling) has been used for the lithium depth profiling and the four-point probe technique for the sheet resistanace measurements.     

Work function, valence band and secondary ion intensity variations noted during the initial stages of SIMS depth profiling of Si and SiO2 by Cs

Work function, valence band and ²⁸Si⁻ secondary ion intensity variations from various Si substrates sputtered by 1 keV Cs⁺ at 60° were measured. Oxide free Si wafers and native oxide terminated wafers did not reveal any appreciable valence band variations close to the Fermi edge. Their work functions however, decreased substantially with an exponential trend noted between this and Si⁻ secondary ion intensities from the O free Si wafer. This is consistent with the electron tunneling model which assumes a resonance charge transfer process. Native oxide terminated wafers exhibited deviations from this exponential trend, while Si wafers with thicker oxides revealed the growth of sub-band features in the valence band spectra on sputtering with Cs⁺. These features, may partially, if not fully, explain the Cs⁺ induced enhancement effect noted on SiO₂ substrates where work function based models are not applicable.     

晶硅太阳电池中Fe-B对与少子寿命、陷阱浓度及内量子效率的相关性

以太阳电池级直拉单晶硅片为材料,利用瞬态微波反射光电导衰减仪研究了硅片分别经过单、双面扩散后Fe-B对与少子寿命τ、陷阱浓度及制备成电池的内量子效率（IQE）的相关性.对于单面扩散后的样品,Fe-B对浓度分布在较大程度上决定了少子寿命分布;对于双面扩散后的样品,Fe-B对浓度显著降低（在135×10¹¹ cm^-3左右）,已不及其他杂质和缺陷对少子寿命的影响.结合瞬态微波衰减信号和陷阱模型,对单、双面吸杂前后硅片的陷阱浓度进行数值计算,发现经过扩散 关键词： 少子寿命 陷阱浓度 内量子效率 Fe-B对