The effect of NO<Subscript>2</Subscript> adsorption on optical and electrical properties of porous silicon layers

The Raman spectra and current-voltage characteristics of porous silicon layers are studied before and after exposure to NO₂. It is shown that spherical nanocrystallites with the diameter of approximately 6–8 nm are present in the samples’ structure. The effect of NO₂ brings about a decrease in the resistance of porous Si by two-three orders of magnitude. An increase in the conductance of the structures at gas concentrations as high as 2000 ppm and a drastic decrease in this conductance if the concentration exceeds the above value are observed. This effect is explained in the context of the model that implies the formation of additional defects of the type of dangling silicon bonds at the Si/SiO₂ interface as a result of oxidation of the porous silicon surface. These defects are traps for holes and reduce the increase in the hole concentration.     

Impurity states in cobalt-doped silicon

Cobalt was diffused into p⁺ pn⁺ silicon structures at 900° and 1150°C for 2−4 hours followed by various quenching conditions. Four primary hole traps and two electron traps associated with cobalt in these devices were observed. The hole traps are labeled H1(E_v + 0.22 eV), H2(E_v + 0.29 eV), H3 (E_v + 0.40 eV) and H4(E_v + 0.45 eV) while the electron traps labeled E1 and E2 are located at E_c − 0.36 eV and E_c − 0.44 eV, respectively. The concentrations, thermal emission rates, and the capture cross sections for the majority carriers at these defects are reported. The behavior of these defects under heat treatment and the emergence of secondary defects, H5(E_v +0.22 eV) and H6 (E_v +0.34 eV), will be discussed.     

Electrical and optical properties of N-type Alx Ga1-x as grown by MO-VPE

Growth conditions and properties of Al_xGa_1-xAs (0.1 ≤ × ≤O.3) using metalorganic vapour phase epitaxy (MO-VPE) are investigated. N-type is achieved either by silicon or by selenium doping. Properties of the layers are evaluated by Hall effect, cathodoluminescence and photoluminescence. It is shown that selenium doping leads to luminescent material : when x = O.1, the efficiency is only a factor of 2 smaller than for GaAs. Deposition temperature is a critical parameter : increasing the growth temperature yields more luminescent Al_x Ga_1-x As. This work has been partly supported by the Délégation à la Recherche Scientifique et Technique (D.G.R.S.T.)     

Formation of radiation defects in high-resistivity silicon as a result of cyclic irradiation and annealing

Transformation of radiation-induced defects in p ⁺-n-n ⁺ structures fabricated from highresistivity n-type silicon subjected to cyclic irradiation and annealing is investigated. The kinetic behavior of the increase in the concentration of the C_i-O_i defects is analyzed as a function of the detector fabrication process. During the second irradiation cycle a transformation of the defects, which were formed as a result of annealing of the original radiation defects, is observed. The appearance of “hidden” sources of deep center formation is revealed. It is established that the presence of a higher oxygen concentration, which arises in the samples as a result of the extended silicon oxidation process, results in a more active complex-formation of carbon-containing defects in comparison with samples with reduced oxygen content. Fiz. Tekh. Poluprovodn. 31, 299–304 (February 1997)     

Application of defect spectroscopy to silicon processing technology

Established defect spectroscopies and silicon characterization techniques are successfully applied to device manufacturing quality control. Deep level transient spectroscopy, DLTS, and photoconducting decay recombination lifetime measurements routinely monitor epitaxial silicon. Fe and Mo are commonly observed contaminants. Processing tools, such as epitaxial reactors and ion-implantation machines, are regularly monitored for trace metals. Dislocations introduced by specific silicon processing steps are selectively studied with DLTS. Dislocation signatures are present in selectively grown epitaxial silicon as well as in shallow junctions created by BF₂ implantation. As a final example, defects introduced by reactive ion etching of silicon are examined by DLTS, photol-uminescence and spreading resistance profiling. The near surface displacement damage region is a source of interstitial defects which undergo recombination enhanced diffusion to depths as great as 1 μm. Measurements previously reserved for research are now being successfully employed as monitors and controls to improve the quality of silicon microelectronic manufacturing.     

Modification of the properties of porous silicon on adsorption of iodine molecules

Infrared spectroscopy and electron spin resonance measurements are used to study the properties of porous silicon layers on adsorption of the I₂ iodine molecules. The layers are formed on the p-an n-Si single-crystal wafers. It is established that, in the atmosphere of I₂ molecules, the charge-carrier concentration in the layers produced on the p-type wafers can be noticeably increased: the concentration of holes can attain values on the order of ～10¹⁸?10¹⁹ cm^?3. In porous silicon layers formed on the n-type wafers, the adsorption-induced inversion of the type of charge carriers and the partial substitution of silicon-hydrogen bonds by silicon-iodine bonds are observed. A decrease in the concentration of surface paramagnetic defects, P _b centers, is observed in the samples with adsorbed iodine. The experimental data are interpreted in the context of the model in which it is assumed that both deep and shallow acceptor states are formed at the surface of silicon nanocrystals upon the adsorption of I₂ molecules.     

A chromium-free etchant for delineation of defects in heavily doped n-type silicon wafers

Delineation of defects in the heavily doped n-type Czochralski silicon wafers by preferential etching is an issue not having been essentially solved. Herein, a chromium-free etchant based on HNO₃–HF–H₂O system, with an optimum volume ratio of V_HNO3%:V_HF%:V_H2O%=20%:45%:35%, has been developed. It can reveal well the defects such as dislocation and oxygen precipitation-induced bulk microdefects (BMDs) in the heavily doped n-type silicon wafers with resistivities even lower than 1 mΩ cm. Moreover, this etchant is appropriate to delineate the defects on (1 1 1), (1 1 0) or (1 0 0) surface of silicon crystal. Furthermore, the density of oxygen precipitation-induced BMDs in the heavily doped n-type silicon wafers derived from the preferential etching using this newly developed etchant correlates well with that derived from scanning infrared microscopy (SIRM) within its detection limit.     

Characterization of germanium implanted Si1−xGex layer

Characterization of a Si_1−xGe_x layer formed by high-dose germanium implantation and subsequent solid phase epitaxy is reported. Properties of this layer are obtained from electrical measurements on diodes and transistors fabricated in this layer. Results are compared with those of the silicon control devices. It was observed that the germanium implantation created considerable defects that are difficult to eliminate with annealing. These defects result in boron deactivation in the p-type regions of the devices, giving rise to larger resistance. Optimization of the device structure and fabrication process is discussed.     

Detection of paramagnetic recombination centers in proton-irradiated silicon

The method of spin-dependent recombination was used to record electron spin resonance (ESR) spectra of recombination centers in a thin (∼1 μm) surface layer of p-type silicon grown by the Czochralski method and irradiated by protons with energies of ∼100 keV. Spectra of excited triplet states of the oxygen + vacancy complex (A-centers) were observed along with complexes consisting of two carbon atoms and an interstitial silicon atom (C_S-Si_I-C_S complexes). The intensity of the ESR spectra of these radiation-induced defects was found to be largest at irradiation doses of ∼10¹³ cm⁻², and decreased with increasing dose, which is probably attributable to passivation of the radiation-induced defects by hydrogen. Fiz. Tekh. Poluprovodn. 33, 1164–1167 (October 1999)     

Dislocations structure investigation in neutron irradiated silicon detectors using AFM and microhardness measurements

The structure, microhardness and deformation character for silicon detectors were investigated following a neutron irradiation, using optical and atomic force (AFM) microscopes. The results of these investigations have given an important contribution to the understanding of silicon damage process by neutron irradiation. It was shown that in the interval of neutron fluences 9.9×10¹⁰≤Φ≤3.12×10¹⁵ n/cm², the shape of damage is accumulative (from small punctual to large defects). Abrupt changes of microstructure together with the electrical and mechanical properties [Bosetti M, Croitoru N, Furetta C, Pensotti S, Rancoita M, Rattaggi M, Redaelli M, Seidman A. Nucl Instr Methods B 1995;95:21; Croitoru N, Gambirasio A, Rancoita PG, Seidman A. Nucl Instr Methods B 1996;111:297; Croitoru N, Rancoita G, Rattaggi M, Rossi M, Seidman A. Nucl Instr Methods B 1996;114:120; Fretwurst N, Claussen N, Croitoru N, Papendick B, Pein U, Schatz H, Schultz T, Wunstorf R. Nucl Instr Methods A 1993;326:357; Croitoru N, Dahan R, Rancoita PG, Rattaggi M, Rossi G, Seidman A. Nucl Instr Methods B 1997;124:542], were found for Φ≥10¹⁴ n/cm². Different kinds of defects (dislocations and interstitials) and their complexes appeared under neutron irradiation. For all fluences the regions (“White” — “W”) with a microhardness smaller than in nonirradiated silicon were observed. Microhardness is larger in the regions where the concentration of dislocation loops is high. The “W” regions have a small number of the dislocations loops, and single punctual defects were seen there using atomic force microscope. The dislocation loops are placed in specific (“Black” — “B”) regions, which increase in size with the increase of neutron fluence due to a process of vacancies and interstitials accumulation.     

X-ray metrology for high-k atomic layer deposited HfxZr1−xO2 films

Hafnium-based dielectrics are the most promising material for SiO₂ replacement in future nodes of CMOS technology. While devices that utilize HfO₂ gate dielectrics suffer from lower carrier mobility and degraded reliability, our group has recently reported improved device characteristics with a modified Hf_xZr_1−xO₂ [R.I. Hegde, D.H. Triyoso, P.J. Tobin, S. Kalpat, M.E. Ramon, H.-H. Tseng, J.K. Schaeffer, E. Luckowski, W.J. Taylor, C.C. Capasso, D.C. Gilmer, M. Moosa, A. Haggag, M. Raymond, D. Roan, J. Nguyen, L.B. La, E. Hebert, R. Cotton, X.-D. Wang, S. Zollner, R. Gregory, D. Werho, R.S. Rai, L. Fonseca, M. Stoker, C. Tracy, B.W. Chan, Y.H. Chiu, B.E. White, Jr., in: Technical Digest - International Electron Devices Meet, vol. 39, 2005, D.H. Triyoso, R.I. Hegde, J.K. Schaeffer, D. Roan, P.J. Tobin, S.B. Samavedam, B.E. White, Jr., R. Gregory, X.-D. Wang, Appl. Phys. Lett. 88 (2006) 222901]. These results have lead to evaluation of X-ray reflectivity (XRR) for monitoring high-k film thickness and control of Zr addition to HfO₂ using measured film density. In addition, a combination of XRR and spectroscopic ellipsometry (SE) is shown to be a fast and non-intrusive method to monitor thickness of interfacial layer between high-k and the Si substrate.     

Electrical characterization of defects introduced during electron beam deposition of W Schottky contacts on n-type 4H-SiC

We have studied the defects introduced in n-type 4H-SiC during electron beam deposition (EBD) of tungsten by deep-level transient spectroscopy (DLTS). The results from current-voltage and capacitance-voltage measurements showed deviations from ideality due to damage, but were still well suited to a DLTS study. We compared the electrical properties of six electrically active defects observed in EBD Schottky barrier diodes with those introduced in resistively evaporated material on the same material, as-grown, as well as after high energy electron irradiation (HEEI). We observed that EBD introduced two electrically active defects with energies E_C – 0.42 and E_C – 0.70 eV in the 4H-SiC at and near the interface with the tungsten. The defects introduced by EBD had properties similar to defect attributed to the silicon or carbon vacancy, introduced during HEEI of 4H-SiC. EBD was also responsible for the increase in concentration of a defect attributed to nitrogen impurities (E_C – 0.10) as well as a defect linked to the carbon vacancy (E_C – 0.67). Annealing at 400 °C in Ar ambient removed these two defects introduced during the EBD.     

High growth rate process in a SiC horizontal CVD reactor using HCl

The results of a new epitaxial process using an industrial 6 × 2″ wafer reactor with the introduction of HCl during the growth have been reported. A complete reduction of silicon nucleation in the gas phase has been observed even for high silicon dilution parameters (Si/H₂ > 0.05%) and an increase of the growth rate until about 20 μm/h has been measured. Photoluminescence at room temperature and at 50 K was used for defects quantification and distribution. On these wafers grown using HCl high voltage Schottky diodes have been realized. The diodes were analyzed by current-voltage (I-V) characteristics.     

Influence of the substrate temperature and annealing on the 1.54-µm erbium photoluminescence of a-Si:H films obtained using a glow discharge

Effective Er photoluminescence is observed at room temperature in a-Si:H films doped with Er atoms through a gas phase using powdered Er(TMND)₃ as a source of Er ions. It is shown that the conditions for deposition of the films and their subsequent annealing influence the photoluminescence intensity and its temperature dependence. The observed behavior is attributed to restructuring of the amorphous silicon matrix within an Auger excitation mechanism involving defects. Fiz. Tekh. Poluprovodn. 33, 208–210 (February 1999)     

High quality silicon nitride deposited by Ar/N2/H2/SiH4 high-density and low energy plasma at low temperature

The high-quality PECVD silicon nitride has been deposited by high-density and low-ion-energy plasma at 400 °C and the effect of the process parameters, such as silane and nitrogen flow rate, pressure, on its structure and electrical properties has been investigated. The experimental results show that silane flow rate is the most sensitive parameter for determining deposition rate and N/Si atomic ratio of silicon nitride in the range of process parameters employed. The change of nitrogen flow rate leaded to slightly change in deposition rate, however, it effects significantly on the refractive index or densification of silicon nitride. With the addition of hydrogen gas in plasma, the hysteresis of C-V characteristics of MIS structure decreases from 0.4 to 0.1 V. The moderate increment of ion energy makes further reduction in the hysteresis of C-V characteristics of MIS from 0.1 V to below 0.05 V. The interface trap density of 6.2×10¹⁰ (ev⁻¹ cm^-2), deduced from the high frequency and quasistatic C-V characteristics of the MIS structure, is about the same as that of LPECVD silicon nitride deposited at the range of 750-850 °C. The stoichiometric silicon nitride of excellence electric and structural properties is obtained by Ar/N₂/H₂/SiH₄ high-density and low ion energy plasma.     

The effects of defects on electrical properties of Ag<Subscript>2</Subscript>S at phase transition

The temperature dependences of electrical conductivity σ(T) and the Hall coefficient R(T) in Ag₂S at the phase transition have been studied. Qualitative discrepancies in the changes in σ(T) and R(T) in the case of phase transition have been revealed; i.e., σ increases by several orders of magnitude while R decreases by a factor of 3–4. This is interpreted in the context of a model with two types of charge carriers and with variation in the band parameters and the concentration of defects formed at the phase transition taken into account.     

Carbon in silicon: Properties and impact on devices

The properties, origin and analysis of carbon in silicon and its influence on the electrical characteristics of devices are investigated and reviewed. The typical carbon concentrations in electronic-grade silicon are still some 10¹⁶ cm^?3. The small distribution coefficient (k₀ = 0.058) causes an inhomogeneous incorporation of carbon along the crystal axis and across the crystal diameter during crystal growth. Carbon concentrations exceeding about 5 × 10¹⁶ cm^?3 in float-zoned silicon can lead to the formation of process-induced defects in the fabrication of power rectifiers and thyristors. These defects which are frequently arranged in a swirl-like pattern strongly deteriorate the electrical characteristics of these devices. It is shown that carbon is involved primarily in the generation of the defect nuclei whereas the defects finally observed form via precipitation of oxygen and agglomeration of silicon interstitials. Reasons for the benign behavior of high carbon concentrations in the processing of integrated circuits are discussed. In powder device processing the formation of carbon-induced defects is safely avoided by application of silicon containing carbon less than 5 × 10¹⁶ cm^?3.     

Model of boron diffusion from gas phase in silicon carbide

Boron diffusion from the gas phase in silicon carbide is described on the basis of a two-component model. “Shallow” boron, i.e., boron at silicon sites, is a slow component with a high surface concentration. Its diffusivity is proportional to the concentration of positively charged intrinsic point defects, which are presumably interstitial silicon atoms. “Deep” boron, i.e., impurity-defect pairs of boron-carbon vacancy, is a fast component with lower surface concentration. The ratio between the surface concentrations of the components depends on the pressure of silicon or carbon vapors in the gas phase. The diffusion and interaction of components are described by the set of diffusion-reaction equations. The diffusion retardation observed on the concentration-profile tail is related to the capture of impurity-defect pairs and excess vacancies by traps of background impurities and defects.     

Very shallow boron junctions in Si by implantation and SOD diffusion obtained by RTP

Because of their very large integration capabilities and continuous scaling, the CMOS devices are the basic element in the current-integrated circuits. Their scaling up to sub-micrometric scale presents advantages like diminution of power consumption, faster devices and a larger level of integration. But the physics limitations begin to be important at these dimensions, anomalous effects like hot electrons, leakage currents and punch through, among others, appear. These effects can be reduced if, at the source/drain region, shallow junctions are obtained with junction depth (x_j) less than 200 nm. To achieve this goal, new junction fabrication methods, which include pre-amorphization [S.D. Kim, C.M. Park, J.C.S. Woo, Formation and control of box-shaped ultra-shallow junction using laser annealing and pre-amorphization implantation, Solid State Electron. 49 (2005) 131–135] are required. Other alternative techniques that do not require ion implantation [T. Uchino, P. Ashburn, Y. Kiyota, T. Shiba, A CMOS-compatible rapid vapor-phase doping process for CMOS scaling, IEEE Trans. Electron Devices 51(1) (2004) 14–19.], in order to prevent surface crystal damage and as a consequence the inhibition of boron interstitial clusters and {3 1 1} defects [R.T. Crosby, K.S. Jones, M.E. Law, L. Radic, Dislocation loops in silicon–germanium alloys: the source of interstitials, Appl. Phys. Lett. 87 (192111) (2005) 1–3.], which are the trigger of the “transient enhanced diffusion” (TED) process are used. In this essay, it is shown that rapid thermal process, allow the fabrication of very shallow junctions with a x_j less than 300 nm by using with high energies and high doses of boron/BF₂ ions implantation. By this way the slow dissolution of the dislocation loops, present at the end of range (EOR) of the implanted boron, allow this process. These obtained junctions are compared with those prepared by using the spin on doping (SOD) technique. The diffusion profiles obtained by both processes and their electrical properties are measured and compared for their application as S–D regions in a current CMOS process.     

Base doping and recombination activity of impurities in crystalline silicon solar cells

The optimisation of base doping for industrial crystalline silicon solar cells is examined with model calculations. Focus is on the relation between base doping and carrier recombination through the important impurities interstitial iron (Fe_i) and the metastable boron–oxygen (BO) complex. In p‐type silicon, the optimum base resistivity is strongly dependent on defect concentration. In n‐type silicon, recombination due to Fe_i is much lower and nearly independent of resistivity. Fe_i is likely representative for other transition metal impurities. In many real cells a balance between Fe_i or similar defects, and BO will occur. Copyright © 2004 John Wiley & Sons, Ltd.