Cz-Si Wafers Research Articles

Impurity engineering of Czochralski silicon used for ultra large-scaled-integrated circuits

Impurities in Czochralski silicon (Cz-Si) used for ultra large-scaled-integrated (ULSI) circuits have been believed to deteriorate the performance of devices. In this paper, a review of the recent processes from our investigation on internal gettering in Cz-Si wafers which were doped with nitrogen, germanium and/or high content of carbon is presented. It has been suggested that those impurities enhance oxygen precipitation, and create both denser bulk microdefects and enough denuded zone with the desirable width, which is benefit of the internal gettering of metal contamination. Based on the experimental facts, a potential mechanism of impurity doping on the internal gettering structure is interpreted and, a new concept of ‘impurity engineering’ for Cz-Si used for ULSI is proposed.

Rapid-thermal-anneal-based internal gettering for germanium-doped Czochralski silicon

The internal gettering (IG) effects involved with a rapid thermal anneal (RTA) in germanium-doped Czochralski silicon (GCz-Si) wafer have been investigated. It was found that germanium doping could enhance the oxygen precipitation in bulk while shrinking the denuded zone width near the surface through pre-RTA at high temperature plus low–high temperature conventional furnace anneals. Rapid cooling rate after RTA was clarified to be beneficial for oxygen precipitation for GCz-Si wafer. It was suggested that the germanium doping could increase the vacancy concentration in Cz-Si during RTA by forming the germanium–vacancy complexes. In contrast to that in Cz-Si wafer, the smaller-sized higher-density oxygen precipitates were presented in the nucleation anneals, then followed RTA pretreatment while more oxygen precipitates survived during ramping processes after nucleation anneals in the GCz-Si wafer. Enhanced heterogeneous nucleation and reduced critical radius of precipitates associated with the germanium–vacancy complexes have been proposed for the oxygen precipitation enhancement.

Influence of germanium doping on the mechanical strength of Czochralski silicon wafers

The mechanical strength in germanium-doped Czochralski silicon (GCz-Si) wafers has been investigated through the on-line warpage statistics analysis, indentation tests, and fracture structure measurements. It was found that the wafer warpage during manufacturing processes could be statistically suppressed by the germanium doping slightly. The enhancement effect of germanium doping on the mechanical strength in GCz-Si wafers could be shown obviously when the germanium concentration was higher than 1018cm−3. Meanwhile, the fracture strength for both the as-grown and the postannealed GCz-Si wafers might be greater compared to that of the conventional Czochralski (Cz-Si) wafers. Moreover, the generation and mobilization of the dislocations induced by indentation in Cz-Si wafers could be suppressed by the germanium doping. These phenomena are interpreted through a dislocation pinning-up effect associated with the smaller-sized higher-density oxygen precipitates formed in GCz-Si wafers.

Formation of insulating oxygen-containing layer on the silicon wafer surface using low-temperature hydrogenation

This experimental work demonstrated that the low-temperature (25 °C) hydrogen ion-beam treatment has led to the formation of an oxygen-containing nanolayer at the surface of standard commercial p- and n-type Czochralski-grown (Cz) Si wafers. The measurements of I–V and C–V characteristics have shown that this layer has insulating properties, its resistivity ≈5 × 1012 Ω cm. It was suggested that the formation of such an insulating layer might be related to the highly distorted region under the wafer surface due to the incorporation of high dose of hydrogen and its low diffusivity into the bulk at low-temperatures.

Study of nanopipes formed in silicon wafers using helium implantation by SEM, RBS and SIMS methods

A system of vertical pipes with 100 nm diameter was formed in standard 4.5 Ω cm n-type Cz Si wafers due to propagation of the defects, created in a buried helium-containing defect layer, towards the wafer surface and their oxidation during subsequent oxygen plasma treatment. The buried helium-containing layer was formed by ion implantation. Investigation of the formed structure by SEM, RBS and SIMS methods has revealed that (a) a length of nanopipes corresponds rather well to the projective range Rp of helium ions, and (b) the silicon wafer regions unoccupied by nanopipes retain the monocrystalline structure free of defects.

Radially non-uniform interaction of nitrogen with silicon wafers

Reproducible and pronounced ring-like structures have been revealed on both sides of commercial grade wafers after certain regimes of annealing in pure nitrogen atmosphere at 1200 °C. To minimize residual oxygen concentration during the annealing procedure, a furnace with a Si3N4 coated SiC reactor tube and high purity N2 flow were employed. Single-side polished Cz–Si wafers with a diameter of 200 mm, used in the experiments, were manufactured from silicon crystals free of oxidation-induced stacking fault rings.

Influence of Low-Temperature Argon Ion-Beam Treatment on the Photovoltage Spectra of Standard Cz Si Wafers

The main goal of this work is to investigate the influence of low-temperature argon ionbeam treatment on the electric and structural properties of a near-surface region of the standard commercial p-type Cz Si wafers, and to compare the effects of Ar+ and H+ ion-beam treatment. The measurements of thermo-EMF have shown that both Ar+ and H+ ion-beam treatment with the ion energy 200 eV and current density 0.15 mA/cm2 at a temperature of 30 oC during 30 min leads to the p-to-n −type overcompensation of the near-surface layer of silicon wafers. The measurements of photovoltage spectra have shown that (i) Ar+ and H+ treatments in like manner lead to the appearance of a photovoltage signal over a wide spectral region due to the formation of p-n-junction on the treated surface, and (ii) photosensitivity of the Ar+ ion-beam treated wafers in the ultraviolet (UV) spectral region (200-400 nm) is much greater as compared to the wafers subjected to H+ ion beam treatment in the same conditions. The main difference in the Ar+ and H+ ion-beam treatment effects is the formation of a thin (5-20 nm) oxygen-containing dielectric layer on the surface of hydrogenated samples and the absence of such layer in case of Ar+ ion-beam treatment.

SEM Investigation of Surface Defects Arising at the Formation of a Buried Nitrogen-Containing Layer in Silicon

The main goal of this work is to demonstrate the correlation between the density and type of surface defects arising during the formation of a buried nitrogen-containing layer in Si wafers, and the number of buried defects formed by different dose hydrogen preimplantation. Standard commercial 12 ⋅cm boron-doped and 4.5 ⋅cm phosphorous-doped Cz Si wafers were subjected to hydrogen ion implantation at room temperature with the energy 100 keV and doses 1⋅1015 - 4⋅1016 at/cm2. Then nitrogen was introduced into silicon from a DC plasma source at a temperature of 300 oС. Finally, all samples were subjected to 2 h vacuum annealing at 900 oС. The experiments have shown that the density and type of the surface defects depend significantly on the dose of hydrogen implantation, parameters of N+-plasma treatment, and conductivity type of silicon. Optimization of the above-mentioned parameters makes it possible to create the substrates containing a buried dielectric SixNy layer and having a practically defect-free surface.

Regular Dislocation Networks in Si. Part II: Luminescence

Regular dislocation networks formed as a result of the direct bonding of Cz-Si wafers with oxide remnants on the pre-bonding surfaces were investigated. Besides the dislocation network, oxide precipitates were detected at the bonding interface. The precipitate density across the network was ~5×1010 cm-2, except small irregularly distributed circular areas, several mm in diameter, where the density was remarkably lower (<5×108 cm-2). The dislocation network structure was not affected by the change in the precipitate density. Photoluminescence spectroscopy (PL) and light beam induced current (LBIC) mapping were applied for characterization of such dislocation networks. For the locations with high precipitate density, PL signal from dislocations and that from the band-to-band transitions were enhanced. On the other hand, the LBIC results indicated that oxide precipitates are active recombination centers and thus should suppress the observed radiative transitions. The controversy can be explained in the assumption that the D-band PL signal increases due to scattering of excitation light by the precipitates and due to related expansion of the excitation area of the dislocation network. The light reflection from the precipitate layer also enhances the detected band-to-band PL signal. The shape of PL spectra from the samples in the range of photon energies 0.75 – 1.15 eV was not influenced by the oxide precipitates.

Investigation of electric fields in B‐implanted Si by positron beam spectroscopy

AbstractBesides its conventional applications in defect characterization, variable‐energy positron annihilation spectroscopy can be employed to monitor internal electric fields in the depletion regions in semiconductor structures. In this work, electric fields were studied in pre‐amorphized Cz Si wafers (background dopant level ∼ 1015 cm–3) implanted with 0.5 keV B ions at a dose of 1015 cm–2, and then annealed isothermally at 800oC for times ranging from 1 to 2700 s. Differences in the S parameter with annealing time were observed in samples implanted (a) with B ions only and (b) with B followed by F ions at 10keV; these were attributed to different electric fields, which drift positrons back (a) to the surface, or (b) to a vacancy‐like defected layer. Fitting of the data revealed depletion regions of widths between 150‐350 nm centered at depths between 250‐350 nm, with electric field values in the range ‐9 x 106 to ‐3 x 106 Vm–1. The depth and width of the depletion regions increase significantly for annealing times greater than 100 s, attributed to B diffusion. The results are consistent with simple theoretical estimates, but the uncertainties on the latter are large. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Crystal-originated particles in germanium-doped Czochralski silicon crystal

Grown-in distribution and annealing behavior of crystal-originated particles (COPs) in Czochralski silicon (Cz-Si) wafer with germanium doping have been investigated. It was found that COPs with high density but small sizes were inclined to generate in germanium-doped Cz-Si (GCz-Si) wafer. The increase of boron atoms in Cz-Si crystal with the germanium doping could benefit the formation of COPs while the oxygen interstitials in GCz-Si wafer could enhance the generation of COPs with small sizes. Meanwhile, it was suggested that the germanium doping in Cz-Si would result in the poor thermal stability of COPs. It is proposed that the combination between germanium atom and vacancy could reduce the free vacancy concentration and the onset temperature for void generation, thus forming denser but smaller void. While the stress compensation induced by boron and germanium atoms could increase the vacancy fluxes in heavy-boron doped GCz-Si crystal, the presence of oxygen atom in GCz-Si would incline to benefit the formation of inner oxide walls of void, especially with small sizes. Furthermore, thinner oxide walls within void for GCz-Si crystal are considered to be charged for the easy annihilation by the germanium doping.

Denuded zone in Czochralski silicon wafer with high carbon content

The thermal stability of the denuded zone (DZ) created by high–low–high-temperatureannealing in high carbon content (H[C]) and low carbon content (L[C]) Czochralskisilicon (Cz-Si) has been investigated in a subsequent ramping and isothermal1050 °C annealing. The tiny oxygen precipitates which might occur in the DZ werechecked. It was found in the L[C] Cz-Si that the DZ shrank and the densityof bulk micro-defects (BMDs) reduced with the increase of time spent at1050 °C. Also, theDZs above 15 µm of thickness present in the H[C] Cz-Si wafers continuously and the density and total volumeof BMDs first decreased then increased and finally decreased again during thetreatments. Moreover, tiny oxygen precipitates were hardly generated inside the DZs,indicating that H[C] Cz-Si wafers could support the fabrication of integrated circuits.

From Smart-Cut to Soft-Cut: Mechanisms of Hydrogen Plasma Supported Layer Exfoliation in Silicon

Comparative investigations of silicon layer exfoliation within the Smart-Cut process and its progression at lower H+ implantation doses and subsequent H-plasma exposure (Soft-Cut) were done by µ-Raman spectroscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM) on (100)-oriented Cz Si wafers. Blister formation and evolution at various process temperatures were analyzed to clarify the mechanisms of layer exfoliation for both approaches. On base of the Raman analyses and supporting SEM and AFM measurements of samples prepared under various process temperatures, we identified the V2H6 defect complexes as the precursor of blisters for the Smart-Cut scenario. Under Soft-Cut conditions (100)-oriented platelets created during H-plasma exposure can be identified as the prevailing precursors of blisters.

Microstructure of flow pattern defects in boron-doped Czochralski-grown silicon

The morphology and microstructure of flow pattern defects (FPDs) in lightly boron-doped Czochralski-grown silicon (Cz-Si) crystals were investigated using optical microscopy and atomic force microscopy. The experimental results showed that the morphology of FPDs was parabola-like with several steps. Single-type and dual-type voids were found on the tip of FPDs and two heaves exist on the left and right sides of the void. All the results have proved that FPDs were void-type defects. These results are very useful to investigate FPDs in Cz-Si wafers further and explain the annihilation of FPDs during high-temperature annealing.

Thermal donor generation in Czochralski silicon particle detectors

In this report, the processing of thermal donor (TD) compensated detectors is described. Heat treatment of Czochralski silicon (Cz-Si) wafers between 400 and 600 °C leads to aggregation of interstitial oxygen atoms resulting in electrically active shallow levels in the silicon band gap. This process is known as TD formation. It depends on the temperature, the oxygen concentration in the silicon material and the presence of hydrogen in device manufacturing process. The oxygen concentration in silicon wafers grown by Magnetic Czochralski (MCz) method is sufficiently high in order that the concentration of TDs is comparable with the initial phosphorous or boron doping of high-resistivity Cz-Si. The TD formation has been studied by monitoring the detector full depletion voltage with respect to the heating time at 430 °C. The TD formation has been verified by Deep Level Transient Spectroscopy (DLTS) measurements. In addition, the annealing behavior of the irradiated samples at different temperatures is discussed. The TD formation in n +/p −/p + pad detectors has been observed not to influence the leakage current of the devices. Thus, the full depletion voltage of the detectors processed on p-type MCz-Si wafers can be modified by this method.

Effect of carbon doping on oxygen precipitation behavior in internal gettering processing for Czochralski silicon

The effect of carbon doping on oxygen precipitation behavior in internal gettering processing for Czochralski silicon (Cz-Si) has been investigated. Through high–low–high anneals in argon ambient, it has been shown that both good-quality denuded zone and high-density bulk microdefects (BMDs) could be formed in high carbon content (H[C]) Cz-Si wafer. Meanwhile, the density of BMDs in H[C] Cz-Si crystal was a little higher compared with that in the Cz-Si crystals with lower carbon content or without carbon doping. The concentration of substitutional carbon almost remained during the whole thermal cycles. Moreover, the [C i–O i]C(3) centers with low concentration were detected by infrared spectroscopy. Weak effect of carbon on oxygen precipitation in H[C] Cz-Si during internal gettering processing is considered. Based on the experimental results, H[C] Cz-Si crystal is suggested to be one of silicon materials used for larger scale integrated circuit fabrication.

In situ observation of substitutional and interstitial Fe atoms in Si after GeV-implantation: An in-beam Mössbauer study

Unstable isotopes of 57Mn ( τ 1 / 2 = 1.4 5 m ) are separated and implanted into FZ– and CZ–Si wafers using a RIKEN projectile nuclear fragment separator (RIPS). Subsequently, Mössbauer spectra of 57Fe in Si are measured at high temperatures up to 800 K, in order to study the charge states and the diffusion processes of interstitial and substitutional Fe atoms in Si matrix. The spectra consist of two singlets between 300 and 650 K, and only one singlet above 700 K. The isomer shifts of the singlets at 300 K are 0.809(13) and −0.042(38) mm/s, referring to the value of α-Fe. The values correspond to interstitial and substitutional Fe, respectively. Above 600 K, both the disappearance of the interstitial component and the simultaneous relaxation effects on the centre shifts are clearly observed. These dynamical behaviours can be interpreted as a reaction process of interstitial Fe atoms jumping into vacancies, which are accompanied by changes in the charge states. Above 650 K a line broadening of the singlet can be also seen, indicating an enhanced diffusion of the Fe atoms due to the excess vacancies.

Evolution of Hydrogen Related Defects in Plasma Hydrogenated Crystalline Silicon under Thermal and Laser Annealing

Boron doped [100]-oriented Cz Si wafers are hydrogenated with a plasma enhanced chemical vapor deposition setup at a substrate temperature of about 260 °C. In-situ Raman spectroscopy is applied on samples under thermal and laser annealing. It is found that different Si-H species have different stabilities. The most stable one is the Si-H bond at the inner surfaces of the platelets. The dissociated energy of Si-H bonds is deduced based on the first order kinetics. It is found that the hydrogen atoms which are released during annealing are trapped again by the platelets and passivate the silicon dangling bonds at the inner surfaces of the platelets or form H2 molecules in the open platelet volume, possibly relating to the basic mechanism of the hydrogen-induced exfoliation of the silicon wafer and the socalled “smart-cut” process.

P/sup +//n/sup -//n/sup +/ cz-Si detectors processed on p-type boron-doped substrates with thermal donor induced space charge sign inversion

We have processed pad detectors on high-resistivity p-type Cz-Si wafers. The resistivity of the boron-doped silicon is approximately 1.8 k/spl Omega/ cm after the crystal growth. The detector processing was carried out using the common procedure for standard n-type wafers, to produce p/sup +//p/p/sup -//n/sup +/ detector structures. During the last process step, i.e., sintering of aluminum electrode, the p-type bulk was turned to n-type through generation of thermal donors (TD). This way, high oxygen concentration p/sup +//n/sup -//n/sup +/ Cz-Si detectors were realized with low temperature process. The full depletion voltage of detectors could be tailored between wide range from 30 V up to close 1000 V by changing heat treatment at 400/spl deg/C-450/spl deg/C duration from 20 to 80 min. The space charge sign inversion (SCSI) in the TD generated devices (from p/sup +//p/sup -//n/sup +/ to p/sup +//n/sup -/(inverted)/n/sup +/) has been verified by transient current technique measurements. The detectors show very small increase of full depletion voltage after irradiations with 24 GeV/c protons up to 5*10/sup 14/ p/cm/sup 2/.

Revealing the structural disturbances in Czochralski silicon by high temperature–pressure treatment

High-resolution X-ray diffraction and topographic methods were used to characterize the structural defects in single crystalline Czochralski-grown silicon (Cz-Si) with various oxygen concentrations. Annealing under hydrostatic pressure (HP) was applied for revealing the defects existing in Cz-Si wafers. The high pressure–high temperature treatment of as-grown Cz-Si at 1127 °C under 1.1 GPa resulted in enhanced oxygen precipitation, mostly at the initially existing structural disturbances, while annealing under 10 7 Pa did not affect the defect structure in the sample. The visibility of defects after the treatment under high pressure can be related to HP-induced strain at the boundary between the defect and the Si matrix, to increased defect dimensions due to HP-stimulated oxygen precipitation and to decreased concentration of defects. Precipitation of oxygen on small structural inhomogeneities and agglomeration of small defects assist in revealing the structural disturbances pre-existing in Cz-Si.