The characteristic life-times of radioactive isotopes can be used to label and identify defect levels in semiconductors which can be detected by photoluminescence (PL). This technique is illustrated with three examples: ZnS doped with radioactive 65Zn by neutron irradiation and GaAs doped with radioactive 111In by ion implantation. Finally we report that doping GaAs with radioactive 71As which decays to stable 71Ga can be used to create GaAs antisites in GaAs in a controlled way and to identify their levels.

The constant vibration mode and the constant excitation mode in noncontact atomic force microscopy were compared to investigate the force interaction between tip and surface. As a result, we found that the constant excitation mode is much more gentle than the constant vibration mode. We also succeeded in atomic resolution imaging on InP(110) surface not only in the noncontact region but in the contact region for the first time. Furthermore, we found the discontinuity of the force gradient curve on reactive Si(111)7×7 reconstructed surface. We proposed a model to explain the discontinuity with the crossover between the physical and chemical bonding interaction.

We have observed nuclear magnetic resonance (NMR) signatures from constituent Ga and As nuclei in single GaAs quantum dots formed by interface fluctuations in GaAs/AlGaAs quantum wells. Orientation of the nuclear spin system by optical pumping causes an Overhauser shift in the excitonic energy levels proportional to the degree of nuclear orientation. NMR was detected by monitoring changes in the combined Overhauser plus Zeeman splitting of an exciton localized in a single quantum dot as the RF frequency was swept through a nuclear resonance. The NMR signals originate from ∼105 nuclei in the quantum dot — (20 nm)3 volume - representing an increase in sensitivity of five orders of magnitude over previous optical NMR measurements and thirteen orders of magnitude over conventional NMR. The data were fit to Lorentzian lineshapes, giving 75As linewidths on the order of 20 kHz.

We present a new IR absorption technique of measuring the dissolved interstitial oxygen concentration [Oi] and its reduction Δ [Oi] due to oxygen precipitation of the heavily-doped silicon crystal with doping level of about 1019 atoms/cm3. The method consists of the three steps: bonding the silicon wafer to a thick FZ silicon substrate by heat-treatment, thinning the wafer, and measuring the height of the 1136-cm−1 absorption peak of Oi at a temperature below 5 K. For a heavily doped wafer and the heavily doped substrate of an epitaxial wafer, we demonstrate examples of measuring the initial [Oi] and Δ [Oi] due to heat-treatment. Using this method, we investigate oxygen precipitation characteristics of the wafer heavily doped with boron. We found that the enhanced oxygen precipitation due to heavy boron-doping is expected if we perform preanneal at temperatures below 700°C.

To inspect quality of the surface region (the depth < 0.5μm) of Si wafer, where devices are to be fabricated, a new measurement method named Optical Shallow Defect Analyzer (OSDA) is developed. This method is based on light scattering at two wavelengths having different penetration depths in silicon. The system measures the depth distribution and the size distribution of defects near the surface by comparing intensities of the two scattered lights. The depth resolution of 0.1 μm, the high measuring throughput (total 6“Φ surface area/1hr) and the minimum detectable defect size of 20 nm are achieved. The OSDA is a powerful measurement system for nondestructive quality check of silicon wafers. We first present the data of epitaxial grown-in defects in μm order thickness epitaxial layers about the defect densities, the size distribution and the depth distribution.

Mapping Low Angle Light Scattering method (MLALS) is proposed to study defect structure in materials used for solar cell production. Several types of defects are observed in Czochralski Si1−xGex (0.022<x<0.047) single crystals. Recombination activity of these defects is investigated. The possibility of contactless visualisation of grain boundary recombination in polysilicon is also demonstrated.

DLTS revealed that each plasma type (He and SiCl4) introduced its own characteristic set of defects. Some of the defects created during He processing and one defect introduced by SiCl4 etching had identical electronic properties to those introduced during high energy (MeV) He ion bombardment. SiC14etching introduced only two prominent defects, one of which is metastable with electronic properties similar to a metastable defect previously reported in high and low energy He-ion bombardment of Si-doped GaAs. IV measurements demonstrated that the characteristics of SBDs fabricated on He-ion processed surfaces were very poor compared to those of control diodes (diodes fabricated on surfaces cleaned by conventional wet etching). In contrast, the properties of SBDs fabricated on SiCl4 etched surfaces were as good as, and in some cases superior to, those of control diodes. SBDs fabricated on annealed (at 450°C for 30 minutes) He-processed samples exhibited improved but still poor rectification. In contrast, SBDs fabricated on annealed SiCl4 etched surfaces had virtually the same characteristics as those fabricated on unannealed SiCl4 etched samples.

Dry-etch damage, introduced by a low biased 92-MHz anode-coupled reactive ion etching (RIE), in MBE-grown undoped GaAs has been characterized by photoreflectance (PR) and photoluminescence (PL) measurements. PL spectra show emission peaks at 1.516 eV (excitons) and at 1.494 eV (D-A, B-A) before etching, whereas a new emission peak at around 1.488–1.490 eV appears after the RIE. The depth distribution of this new emission center, examined by PL measurements with a combination of step wet etching, has a Gaussian-shape with a l/e value of 56 nm. A very small number of nonradiative recombination centers are considered to be generated, because the integrated PL intensity including both emission peaks at 1.490 eV and at 1.516 eV is the same before and after the RIE. The surface recombination rate of the sidewall formed by the RIE is almost the same as that of the wet-etched surface. This low-damage etching has been applied to fabricate ultra-fine GaAs patterns to provide a nanometer-scale ridge structure with a cross-section 15-nm wide by 150-nm high. The low damage etching condition is also suitable for precise fabrication.

Reactivation of Si donors in Ar plasma-irradiated GaAs under reverse bias annealing (RBA) is substantially enhanced by Ar laser illumination. Reactivation occurs only in the surface layer and charge density overshoots its original donor density. These are identical to those observed by high temperature RBA without laser illumination. The activation energy of the reactivation rates is about 0.1 eV, whereas it is about 0.7 eV without laser illumination. The energy reduction is explained by charge state change of deactivators in terms of two hole capturing under minority carrier injection. These findings suggest that deep levels induced by complexes of Si donors with point defects should be present above midgap. The deep penetration mechanism of plasma-induced point defects is discussed, based on the present findings.

In this study 1016cm−3 n-type epitaxial GaAs was reactive-ion-etched (RIE) in a parallel plate type reactor as a function of rf power and gas pressure using a SiCl4 plasma. The sample matrix followed a 3 level 3 factorial statistical experimental design. Photoreflectance (PR) was employed to characterise the etch induced modification to the electronic band structure at the fundamental band-edge transition. Variable angle spectroscopic ellipsometry (VASE) and photoluminescence (PL) optical diagnostic techniques are also employed to characterise the plasma processed GaAs. PR results detail a decrease in the surface electric field (Fs) with etch severity arising from an RIE induced electron trap that increases in concentration with energetic ion sputtering. For the highest rf power densities PR further distinguishes between reactant desorption and adsorption limited etching regimes. VASE and PL data reveal the extent and degree of surface modification of the etched substrates. Atomic-Force-Microscopy showed the etched surfaces to have an average roughness, Ra of 15nm. Optical characterisation data are correlated with electrical measurements using fabricated Schottky barrier diodes for deep-level-transient spectroscopy (DLTS) as well as current-voltage and capacitance-voltage (CV) analysis. CV results detail a reduced surface carrier concentration after RIE while DLTS revealed the emergence of six electron trap defect levels. One of the two prominent RIE induced trap levels exhibited similar DLTS behaviour as that produced after ion bombardment of n-type (Si) GaAs.

The property of plasma induced defects in phosphorus doped CZ silicon has been investigated by reverse bias annealing (RBA). After CF4 plasma exposure, charge density at the surface decreased since plasma induced negatively charged defects inactivated phosphorus. With the increase of annealing time, inactivated phosphorus area moved into the bulk with reverse bias of −3V. Thus it is clearly observed that negatively charged defects drifted from the surface into the bulk. The thermal dissociation energy for phosphorus-defect complexes is estimated to be 1.22eV from the Arrhenius plot of dissociation rate. These defects are likely to be Si self interstitials or vacancies.

We have employed current-voltage (IV), capacitance-voltage (CV) and deep level transient spectroscopy (DLTS) techniques to characterise the defects induced in n-Si during RF sputter-etching in an Ar plasma. The reverse leakage current, at a bias of 1 V, of the Schottky barrier diodes fabricated on the etched samples was found to decrease with etch time reaching a minimum at 6 minutes and thereafter increased. The barrier heights followed the opposite trend. The plasma processing introduced six prominent deep levels below the conduction band of the substrate. A comparison with the defects induced during high energy (MeV) alpha-particle, proton and electron irradiation of the same material revealed that plasma-etching created the VO- and VP-centres, and V2-10. Some of the remaining sputter-etching-induced (SEI) defects have tentatively been related to those formed during either 1 keV He- or Ar-ion bombardment.

We found oxide defects originating in standard Czochralski silicon and proposed the sacrificial oxidation method to eliminate these defects in about 1979. Later, N2 annealing and H2 annealing methods were proposed successively, and these three elimination methods have been successfully introduced into actual fabrication lines for highly reliable integrated circuits. However, the origin of the defect was not clarified until recently. We combined copper decoration and TEM in order to observe the origin of the oxide defects and for the first time, observed octahedral void defects systematically at the oxide defects with standard Czochralski silicon. The sizes of the defects are typically 0.1–0.2 microns. These Si-crystalline defects are the origin of oxide defects and, at the same time, may be the origin of crystal originated particles. Recently, we have observed octahedral void defects in the bulk of the standard Czochralski silicon too. Some experimental findings suggest that some impurities on the side wall of the octahedral void defect induce dielectric breakdown of the gate-oxides.

Crystal-originated pits are known as the defects responsible for B-mode Time Zero Dielectric Break-down (TZDB) of the gate oxide grown on the surface of Si wafers. In order to clarify the breakdown mechanism, we have analyzed the structure of those defects formed at the surface of bare and oxidized wafers. In the latter case the analysis has been done both before and after gate oxide breakdown. Electric breakdown has been accomplished by Cu decoration method, recognized as an effective tool for unambiguous detection and positioning of the defects causing B-mode TZDB. As revealed by cross-sectional transmission electron microscopy (XTEM), crystal-originated pits at the bare wafer surface are polyhedral pits having about 5-nm-thick oxide layer on the inner walls. During gate oxidation the thermal oxide is growing faster on the pit walls than on the wafer surface, except for the pit comers where the oxide thinning has been observed. Resulting concave comers of the oxidized pits are suggested to be the weak spots where B-mode TZDB occurs.

We have developed a quantitative measurement method for the number density, size and morphology of grown-in defects in czochralski-grown silicon (CZ-Si) crystals with a bright-field infrared-laser interferometer (known as Oxygen Precipitate Profiler; OPP). Using this method we investigated the effect of crystal cooling condition during crystal growth on the formation of grown-in defects by growth holding experiments. The relation between gate oxide integrity (GOI) and grown-in defects was studied. It was revealed that the grown-in defects have octahedral shape and degrade the GOI performance. We estimate the density as well as cumulative volume of the grown-in defects and discuss the formation mechanism of them.

Grown-in defects detected by IR laser scattering tomography (LSTDs) in Czochralski-grown Si crystals were identified by transmission electron microscopy (TEM) with a special defect positioning technique. The basic structure of the LSTD was revealed to be a composite of two or three incomplete octahedral voids with the 100–300nm total size. The TEM images of the defect showed existence of 2∼4nm-thick walls surrounding the voids. These thin-walls are considered to be made of oxide, SiOx. These LSTDs are indeed dominant grown-in defect species in most of the commercial CZ-Si walers. The LSTD after 1200°C oxidation was also observed by TEM. The resulting image shows that the defect changed from void to filled oxide precipitate by the high temperature heat treatment. On the other hand, in very slowly pulled crystals with ∼0.4mm/min rate, interstitial type dislocation loops were observed as major defect species. Non-agitated Secco etching of these grown-in defects delineates “flow patterns” (FPs) or pits without the flow patterns. The FP forming property is shown to disappear by oxidation at temperature above 1150°C, while the defect itself remains stable. This implies that the grown-in defects lose their chemical properties to form FPs by the high-temperature oxidation. It is further revealed that the grown-in defects, which once lost the FP forming property by the high-temperature oxidation, can form FPs again by an intentional Cu contamination. Thus a possible FP formation factor is Cu decoration at the grown-in defect site. Defect formation model of the as-grown twin-type LSTD is also proposed.

In dislocated Cz-Si crystals, rows of flow patterns (FP) and Secco etch pits (SEP) (2–3 mm in length, along <110> direction) can be revealed by Secco etch without agitation. In this study, the crystal defects forming FP-SEP rows in dislocated Cz-Si crystals are investigated by transmission electron microscopy. Microdefects, 0.1 μm in size, are observed in a row along a FP-SEP row, <110> direction. These defects were identified as oxygen precipitates with or without dislocation loops (interstitial-type), and voids with oxidized interiors. We conclude that FP originate from interstitial-type dislocation loops, and SEP are due to oxygen precipitates or voids.

The origin of oxidation–induced stacking faults (OSF) and polyhedral cavities in as–grown Czochralski silicon (CZ–Si) crystals is discussed with comparison to the behavior of previously investigated grown–in oxide precipitates. The incorporation, diffusion and reaction in the vacancy, self–interstitial and oxygen ternary system are considered to discuss the origin of grown–in defects.

Defects on polished as well as hot SC1 treated silicon wafers were investigated with an Atomic Force Microscope (AFM) and Surface Scanning Inspection Systems (SSIS). Measurement with two SSIS of different type allows to identify most of the surface defects as non particulate scatterers. AFM of these defects reveals tiny pits or groups of pits. An almost linear relation is found between the geometrical lateral defect dimension and their average size in units of LSE (Latex Sphere Equivalent; an effective measure for the scattering cross section) as reported by one of the SSIS for the defects on wafers treated with hot SC1. Growth rates of about 40 nmLSE/h are observed for the defects during subsequent treatments of wafers with hot SC1. The LSE-size distribution of as-grown defects with a peak at about 105 and 110 nmLSE is obtained for two types of wafer by modeling the defect evolution during hot SC1 treatment. The number of surface flaws ≥ 0.12 μmLSE on a substrate is reduced by two orders of magnitude for epitaxial layers as thin as 1.5 μm.

This work demonstrates that positrons implanted into a 60 nm n-type polysilicon layer with large grains, can be pushed out of this layer by an externally induced electric field. In the case of a metal-oxide-silicon (MOS) system with a such a polysilicon gate, polysilicon-implanted positrons can be efficiently transported towards the SiO2/Si interface where they all are collected. This technique offers new and interesting possibilities to study defects at the SiO2/Si interface of technologically important MOS systems.