Hydrogen passivation of defects and impurities in GaAs and InP

Hydrogen passivation experiments in GaAs and InP are discussed. For GaAs it is argued that the results of hydrogen passivation of shallow donors, shallow acceptors and deep centers in materials with different Fermi level positions as well as diffusion data for undoped or lightly doped GaAs are consistent with the assumption that hydrogen is neutral or amphoteric (at least at rather high temperatures of treatment). Some new interesting effects are reported such as improvement of GaAs homogeneity as revealed by microcathodoluminescence imaging and also hydrogen passivation of surface states in GaAs. Evidence is presented that hydrogenation in direct plasmas leads to damage region formation at the surface of the GaAs. A new method of hydrogenation is described that is free from that drawback. The marked improvement of Au/n-GaAs Schottky diodes I-V characteristics is reported after using this method. This new technique is also used to hydrogenate InP for which conventional methods encounter very serious problems. In InP the results of hydrogen passivation experiments on shallow donors and acceptors imply that hydrogen is a deep donor. An interesting effect of injection annealing at room temperature of hydrogen-donor complexes inn-InP is observed.     

Influence of background impurities on the formation of stacking faults in silicon wafers

The microhardness of silicon wafers containing stacking faults is investigated experimentally. The main findings are as follows: (1) Fast-diffusing background impurities (Fe, Au, Ni, Cu, etc.) make for the formation of these defects. (2) Stacking faults are manifested in a bimodal statistical distribution of microhardness made up of two normal distributions. (3) Wafer areas with stacking faults are characterized by higher microhardness.     

STUDY OF MORPHOLOGICAL DISTRIBUTION OF DEFECTS IN GaAs WAFERS BY INFRARED DIGITAL IMAGE PROCESSING

A new method is applied to characterize the defects in GaAs material(e.g.the absorption ofEL2 centres).The method consists of transmitting a laser beam(λ=1.1-1.5μm)through the GaAs wa-fer of 4—8 mm thickness and 50 mm diameter.The image is received by the TOSHIBA 8844 cameraand entered into the DATASUD computer image processing system.This image is displayed on amonitor permitting to observe the inhomogeneity(like cross,cells and volutes)of theEL2 and dislocation defects.This paper will introduce a specific image processing software for GaAs materi-al,called ZHIMAG(ZHang IMAGe)and its application to GaAs wafer.The software can bealso applied to any other types of image processing.     

Density functional theory calculations for estimation of gettering sites of C,H, intrinsic point defects and related complexes in Si wafers

Very recently, a C₃H₅ cluster ion implantation technique for proximity gettering has been reported with the low energy of around 10¹⁵/cm² dose without recovery heat treatments. The main feature of this technique is that the gettering efficiency is higher than that by C monomer implantation, even though irradiation defects are too small to clarify by TEM observation. In the present work, we evaluate the binding energies of metal atoms with candidate gettering sites of C, H, intrinsic point defects and related complexes in Si wafers induced by C₃H₅ cluster ion implantation or different methods, for example, H implantation etc. by using density functional theory calculations. In addition to C and H atoms, we consider donor P and O atoms contained in an n- CZ-Si wafer for use in a CMOS image sensor. The simplest complexes of substitutional/interstitial C (C_s/C_i), H_i, P_s, O_i, and incorporated intrinsic point defects (vacancy (V) and self-interstitial Si (I)) by C₃H₅ implantation were also considered. We found that C_s–I (= C_i), C_i–C_i, H_i–I, VH_n (n=1–3), and VO complexes are the best candidates for gettering sites. Gettering by C₃H₅ cluster ion implantation is more effective than that by C monomer implantation due to the formation of VH_n (n=1–3) and H_i–I complexes, which provides more effective gettering sites.     

Enhanced performance in the deteriorated area of multicrystalline silicon wafers by internal gettering

The deteriorated area of the multicrystalline silicon (mc‐Si) ingots grown by directional solidification, commonly known as the Red Zone, is usually removed before wafering. This area, characterized by poor minority carrier lifetime, is located on the sides, at the top, and the bottom of the mc‐Si ingots. In this study, the effect of internal gettering by oxygen precipitates and structural defects has been investigated on the bottom zone of a mc‐Si ingot. Nucleation and growth of oxygen precipitates as well as low temperature annealing were studied. Photoluminescence imaging, lifetime mapping, and interstitial iron measurements performed by μ‐PCD reveal a considerable reduction of the bottom Red Zone. An improvement of lifetime from below 1 µs to about 20 µs and a reduction of interstitial iron concentration from 1.32 × 10¹³ at/cm³ to 8.4 × 10¹⁰ at/cm³ are demonstrated in this paper. Copyright © 2013 John Wiley & Sons, Ltd.     

Process-induced stress and microcrack nucleation in GaAs wafers

Breakage of GaAs wafers during device fabrication leads to reduced yield and decreased quality control. Historically, wafer breakage that is not attributable to human or equipment errors has been assumed to be due to poor quality wafers. We present evidence that the probability of breakage during sub-micron GaAs device fabrication is a function of dielectric film edge stress, and not necessarily dependent on the magnitude of a critical flaw in the as-received wafer. X-ray residual stress measurements, x-ray topographic imaging, and three-point bend fracture measurements are used to determine the nature and origin of wafer breakage during those fabrication steps which induce large mechanical or thermal stresses. Our data show that the processing sequences that most influence wafer breakage are SiN passivation deposition and rapid thermal annealing implant activation. These processes are primarily responsible for large residual stresses developed in the near-surface layers of the GaAs substrate. For microelectronic applications, the existence of high film edge stresses nucleates microcracks, which further reduces fracture strength. The combined effects of high residual stress and low fracture strength make SiN passivated wafers more fragile (as compared to SiON passivated wafers), and therefore more likely to break during device processing.     

Phosphorus gettering of iron by screen‐printed emitters in monocrystalline Czochralski silicon wafers

In this paper, we demonstrate single‐sided screen‐printed emitters in thin monocrystalline Czochralski silicon (Cz‐Si) wafers with an improved gettering of iron compared with conventional double‐sided POCl₃ emitters. The phosphorus dopant pastes used have to be chosen carefully to provide a sufficiently low emitter sheet resistance and to avoid iron contamination. The iron concentration is determined in a non‐destructive way from the minority carrier lifetime obtained by quasi‐steady‐state photoconductance measurements, down to levels not yet demonstrated for screen‐printed emitters. In addition, the well‐known metastable boron–oxygen complexes in Cz‐Si have been transferred into a stable state by light‐induced degradation prior to these measurements. Copyright © 2012 John Wiley & Sons, Ltd.     

Stress analysis and bending tests for GaAs wafers

Wafer made from single crystal gallium arsenide (GaAs) are used as substrate materials in micro- and opto-electronic devices. During the various processes of manufacturing, the wafers are subjected to mechanical loads which may lead to fracture. The characterization of the fracture strength of the wafers need bending tests and a theoretical calculation of various stress distributions within the wafers.In this study we show that the nonlinear von Kármán theory may serve as an appropriate tool to calculate the stress distributions as functions of the external load, while the Kirchhoff theory has turned out to be completely inappropriate. Our main focus is devoted to (i) calculation of the contact area between the load sphere and the wafer, (ii) study of the influence of the anisotropic character of the material, (iii) study of the important geometric nonlinearity. Finally we compare the calculated and theoretical load–flexure relations in order to demonstrate the high accuracy of the von Kármán theory and its finite element implementation.     

Discrimination of particles and defects on silicon wafers

Angle-resolved light scattering measurements of particles and crystal originated particles (COP) point out ways for discriminating different types of defects on Silicon wafers. Particles and COP display a significantly different light-scattering behavior. Comparing the intensity of light scattered into the different solid angles of the two detection channels of the KLA-Tencor SP1 is sufficient for distinguishing particles from other defects. The share of particles identified correctly by SP1 data analysis depends on the defect size and on the wafer material and is >85%.     

Surface passivation of CdZnTe wafers

The chemical polishing process and the subsequent passivation process of CdZnTe wafers were studied. The treatment effects were tested through XPS analysis and I–V measurement. The chemical etching in 2%Br–MeOH solution may effectively remove the damaged layer and improve the ohmic contact between CdZnTe wafer and Au electrodes. CdZnTe wafers after Br–MeOH etching were passivated with five different passivants respectively. It was found that the surface leakage currents of all CdZnTe wafers passivated with different passivants were reduced by 1–2 orders. CdZnTe wafer passivated in NH₄F/H₂O₂ solution showed the best passivation efficiency because the enriched Te on the surface was fully oxidized to TeO₂, which results in the thickest oxide layer, the most stoichiometric surface and the least leakage current. The surface of CdZnTe wafer is Te-rich after passivated in NH₄F/H₂O₂ or H₂O₂ solution and Cd-rich after passivated in KOH or KOH/H₂O₂ solution.     

Correlation between oxide breakdown and defects in SiC wafers

A correlation between gate oxide breakdown in metal oxide semiconductor (MOS) capacitor structures and structural defects in SiC wafers is reported. The oxide breakdown under high applied fields, in the accumulation regime of the MOS capacitor structure, is observed to occur at locations corresponding to the edge of bulk structural defects in the SiC wafer such as polytype inclusions, regions of crystallographic misorientation, or different doping concentration. Breakdown measurements on more than 50 different MOS structures did not indicate any failure of the oxide exactly above a micropipe. The scatter in the oxide breakdown field across a 10 mm × 10 mm square area was about 50%, and the highest breakdown field obtained was close to 8 MV/cm.     

Round-robin test for flatness measurement of GaAs wafers

Due to the increased demand for GaAs substrates, improved physical characteristics such as warp, flatness, local thickness variation and other parameters are required. In the first of a 3-part series III–V Review continues its coverage of the round-robin testing of GaAs by Japanese substrate suppliers [1]. In this article we cover warp and bow, in part II next issue we report on total thickness variation (TTV) and total indication reading (TIR), and then in the concluding part we cover local thickness variation (LTV) and percentage local thickness variation (PLTV).     

Performance limiting micropipe defects in silicon carbide wafers

Reports on the characteristics of a major defect in mass-produced silicon carbide wafers which severely limits the performance of silicon carbide power devices. Micropipe defects originating in 4H- and 6H-SiC substrates were found to cause pre-avalanche reverse-bias point failures in most epitaxially-grown pn junction devices of 1 mm² or larger in area. Until such defects are significantly reduced from their present density (on the order of 100's of micropipes/cm²), silicon carbide power device ratings will be restricted to around several amps or less     

Enhanced gettering of iron impurities in bulk silicon by using external direct current electric field

Iron impurities in bulk silicon are found to getter efficiently at the polysilicon layer by an electric field during isothermal annealing. Experimental results show that iron concentration at the polysilicon layer increases to the level that becomes detectable by total reflection x-ray fluorescence (TXRF) spectroscopy. The improved gettering efficiency for iron is attributed mainly to the directional drift of ionic iron interstitials toward the polysilicon gettering sites, under the influence of the applied potential gradient, thus presenting a more effective method for reducing the iron content in silicon.     

Clustering of defects and impurities in hydrogenated single-crystal silicon

Data obtained to date on specific features of defect formation for hydrogenated single-crystal Si are analyzed. It was demonstrated that, in addition to other effects, interaction of H atoms with radiation defects and impurities leads to the formation of large clusters of three main types, namely, vacancy, interstitial, and impurity clusters. The main condition for formation of these clusters is the simultaneous presence of supersaturated solutions of H and defects in the sample. The interaction of H atoms with impurities and defects initiates the decomposition of the supersaturated solid solution of defects and impurities with the formation of precipitates. This leads to the formation of clusters, which are not observed in the absence of H. The mechanisms of formation and structure of clusters are discussed.