Germanium-doped Czochralski Silicon Research Articles

Germanium-doped Czochralski silicon for photovoltaic applications

Germanium (Ge)-doped Czochralski (GCZ) silicon has been grown for photovoltaic (PV) applications. It is found that Ge doping improves the mechanical strength of CZ silicon, resulting in the reduction of breakage during wafer cutting, cell fabrication and module assembly. Boron–oxygen (B–O) defects that lead to the light-induced degradation (LID) of carrier lifetime are effectively suppressed by Ge doping. The decrease in the maximum concentration of B–O defects increases with an increase of Ge concentration. The efficiency of GCZ silicon solar cells and the power output of corresponding PV modules both exhibit smaller loss under sunlight illumination. The current work suggests that GCZ silicon should be potentially a novel substrate for thin solar cells with low LID effect.

Improvement in the mechanical performance of Czochralski silicon under indentation by germanium doping

The mechanical properties of germanium-doped Czochralski (GCz) silicon have been investigated using instrumented nanoindentation combined with an ultrasonic pulse-echo overlap technique. The GCz silicon samples showed higher Young’s modulus and hardness than germanium-free Czochralski silicon samples in nanoindentation tests. We believe this was caused by the enhanced phase transition from the Si-I phase to the stiffer Si-II phase in GCz silicon under contact load during indentation. This scenario was further confirmed by micro-Raman spectroscopy measurements.

Flow pattern defects in germanium-doped Czochralski silicon crystals

The distribution and etching rate of flow pattern defects (FPDs) in germanium- doped Czochralski (GCZ) silicon (Si) wafers with light and heavy dopants—either boron (B) or phosphorus (P)—have been investigated. In the lightly doped (both B and P) Czochralski (CZ) Si crystals, the FPD densities in GCZ Si decrease with the increase of Ge concentration. In the heavily B-doped GCZ Si crystals, the FPDs are denser compared with the heavily B-doped CZ Si, whereas the reverse is true in the heavily P-doped GCZ Si and CZ Si crystals. It is also shown that the etching rates in the lightly doped CZ Si crystals can be slightly enlarged by the Ge doping. It is proposed that, in lightly doped GCZ Si, Ge doping could consume free vacancies and thus form high-density but small-sized voids, while the stress compensation induced by B and Ge atoms could increase the vacancy concentration in heavily B-doped GCZ Si, leading to sparse and large-sized voids.

Effect of germanium on the kinetics of boron-oxygen defect generation and dissociation in Czochralski silicon

We have investigated the kinetics of boron-oxygen (B–O) defect generation and dissociation in germanium-doped Czochralski (GCZ) silicon. It is found that the activation energies for the B–O defect generation and dissociation in the GCZ silicon are around 0.63 eV and 1.52 eV, respectively, both larger than those in the conventional CZ silicon. The corresponding pre-exponential factors also are enhanced by two orders of magnitude due to Ge doping. It is believed that the Ge cannot only cause a higher energy barrier for oxygen-dimer (O2i) diffusion, due to its modulation on the crystal field in silicon lattice but also enhance the capture cross-section of Bs for O2i, as a result of Ge–B complex formation, as predicted by first-principle calculation. These results are significant for us to understand the mechanism of Ge influencing on the B–O defects in CZ silicon.

Effect of vacancies on oxygen precipitation in germanium-doped Czochralski silicon

The effect of vacancies introduced by rapid thermal annealing (RTA) on the oxygen precipitation in germanium-doped Czochralski (GCZ) silicon has been investigated. GCZ silicon is annealed at 650–1050 °C to facilitate the precipitation of oxygen. It is observed that the oxygen precipitation in silicon is enhanced by both the vacancies introduced during RTA pretreatment and the doping of germanium. Especially, we find that the enhancement effect of vacancies on the precipitation of oxygen is larger than that of germanium atoms. In contrast to non-RTA pretreatments, RTA pretreatments lead to less significant oxygen precipitation in GCZ silicon than in conventional Czochralski (CZ) silicon at temperatures ranging from 850 to 950 °C. The mechanism for the interaction between vacancies and germanium atoms in CZ silicon is elucidated.

High temperature nucleation of oxygen precipitates in Germanium-doped Czochralski silicon

Czochralski silicon (Cz-Si) doped with germanium (Ge) has recently drawn the attentions on the next generation of Cz-Si materials used for ultra large-scale integrated circuits. Oxygen precipitate, which is the most important micro-defect in Ge-doped Cz-Si (GCz-Si), domains the majority properties of bulk silicon. In this presentation, the behaviors of oxygen precipitation in GCz-Si at high temperatures have been studied. It was found that, compared with conventional Cz-Si, the higher-density but smaller-sized oxygen precipitates were formed in GCz-Si at extremely high temperature, which could be ascribed to the enhanced nucleation of oxygen precipitates by the Ge-doping. Meanwhile, compound morphologies of oxygen precipitates consisted of plate-like and polyhedral shapes were found in GCz-Si, which can probably be ascribed to the different levels of vacancy coalesced by the so-called Ge-related complexes in GCz-Si.

Internal gettering for germanium-doped Czochralski silicon: Treated by rapid-thermal-anneal based processing simulation

Intrinsic gettering (IG) in germanium-doped Czochralski (Cz) silicon wafer has been investigated through a processing simulation of dynamic random access memory fabrication involved with rapid-thermal-anneal (RTA). Compared with that of conventional Cz silicon, both the good quality defect-free denuded zone (DZ) with a slightly narrower width and the gettering region with a slightly higher density of bulk micro-defects (BMDs) could be generated in germanium-doped Cz (GCz) silicon during the device fabrication. These phenomena were interpreted through the generation of denser oxygen precipitates in GCz silicon than Cz silicon, which were considered to be ascribed to the enhancement of precipitate nucleation by the germanium doping. It is therefore believed that the germanium doping could improve the IG capability for Cz silicon wafer.

Copper Precipitation in Germanium-Doped Czochralski Silicon

Copper (Cu) precipitation behavior in p-type germanium-doped Czochralski (GCZ) silicon has been investigated by means of scanning infrared microscopy (SIRM) and optical microscopy (OM). It was revealed that compared with Cu precipitates in the form of etching pits (in OM image)/particles (in SIRM image) in conventional Czochralski (CZ) silicon, the Cu precipitates exhibited as the aggregated rods (in OM image)/star-like colonies (in SIRM image) within GCZ silicon. A mechanism of the effect of large grown-in oxygen precipitates on Cu precipitation is discussed. Moreover, it was found that the size or density of Cu precipitate colonies in GCZ silicon decreased with the decrease of annealing temperature or cooling rate, which is believed to be attributed to the reduced driving force for Cu precipitation.

Copper Precipitation in Germanium-Doped Czochralski Silicon

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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.

Enhanced Formation of Thermal Donors in Germanium Doped Czochralski Silicon Pretreated by Rapid Thermal Annealing

The thermal donor formation at 425oC - 450oC in Ge doped Czochralski (GCZ) silicon having about 1016 cm-3 Ge content pretreated by rapid thermal annealing (RTA) and conventional furnace annealing (CFA) has been investigated using low-temperature infrared spectroscopy (LT-IR). The measurements prove that lightly Ge doping can enhance the formation of thermal double donors in the initial stage of the low temperature annealing after RTA process. Ge induced additional grown-in oxygen precipitates during silicon ingot growth and the abundant self-interstitials during RTA may be the reason for the enhancement. However, after extending the annealing time at the low temperatures, the thermal donor concentration in the GCZ silicon is lower than that in the conventional CZ silicon. In final, the mechanism is also discussed.

Dissolution of oxygen precipitates in germanium-doped Czochralski silicon during rapid thermal annealing

The thermal stability of the oxygen precipitates in Czochralski silicon (Cz-Si) crystal with germanium doping has been investigated with rapid thermal annealing. It was found that the grown-in oxygen precipitates could be dissolved easily in germanium-doped Cz-Si (GCz-Si) than in conventional Cz-Si. After prolonged high-temperature thermal cycle, it was found that the germanium doping inclined to dramatically reduce the thermal stability of oxygen precipitates in Cz-Si crystal, either generated at low temperature (800 °C) or formed at high temperature (1000 °C). It is proposed that the germanium doping in Cz-Si could result in the oxygen precipitates with small size and plate shape, which reduce their thermal stability.

Investigation of intrinsic gettering for germanium doped Czochralski silicon wafer

The intrinsic gettering (IG) effects in a germanium-doped Czochralski (GCz) silicon wafer have been investigated through a processing simulation of dynamic random access memory making and an evaluation on IG capability for copper contamination. It has been suggested that both the good quality defect-free denuded zones (DZs) and the high-density bulk microdefect (BMD) regions could be generated in GCz silicon wafer during device fabrication. Meanwhile, it was also indicated that the tiny oxygen precipitates were hardly presented in DZs of silicon wafer with the germanium doping. Furthermore, it was found in GCz silicon wafer that the BMDs were higher in density but smaller in size in contrast to that in conventional Cz silicon wafer. Promoted IG capability for metallic contamination was therefore induced in the germanium-doped Cz silicon wafer. A mechanism of the germanium doping on oxygen precipitation in Cz silicon was discussed, which was based on the hypothesis of germanium-related complexes.

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.

Intrinsic gettering Based on rapid thermal annealing in germanium-doped Czochralski silicon

The intrinsic gettering (IG) effects under different thermal processes involved with rapid thermal annealing (RTA) in Czochralski (CZ) silicon wafers with germanium doping have been investigated. It has been shown that both good quality denuded zones and high-density bulk microdefect regions could be generated in germanium-doped CZ (GCZ) silicon wafers through thermal cycles of RTA treatments plus either low-high temperature two-step annealing or high temperature single-step annealing. Moreover, more oxygen precipitation was formed in GCZ silicon wafers in comparison with conventional CZ silicon wafers, indicating the enhancement of IG capability for CZ silicon wafers by the germanium doping. The phenomena have been considered to be ascribed to the increase of vacancy concentration associated with the presence of germanium, which results in the generation of Ge-V-related complexes in GCZ silicon wafers during RTA treatments.

Germanium-doped Czochralski silicon: Oxygen precipitates and their annealing behavior

Czochralski silicon (Cz Si) crystals with germanium (Ge) doping are considered to be of potential application for integrated devices. In this presentation, the influence of Ge doping of Cz Si crystals on oxygen precipitate thermal stability has been discussed. Compared with the conventional Cz Si, oxygen precipitates in Ge-doped Cz (GCz) Si was proposed to be poorer stable thermally during high temperature anneals, which is ascribed to the formation of smaller precipitates. Meanwhile, the oxygen precipitation was promoted in GCz Si wafers that received a high temperature pre-anneal treatment, which has been considered to be associated with the assumption of Ge-related complexes by the intended Ge doping.

Enhancement effect of germanium on oxygen precipitation in Czochralski silicon

Oxygen precipitation in germanium (Ge)-doped Czochralski (CZ) silicon has been investigated through a series of isothermal anneals at temperatures ranging from 550to950°C. It is found that the nucleation of oxygen precipitates can be enhanced in a wide temperature range and the onset temperature for precipitate nucleation can be increased by the germanium doping. Furthermore, it is also revealed that the oxygen precipitates with a higher density and smaller sizes can be formed in germanium-doped CZ silicon in comparison with those in conventional CZ silicon. These two phenomena are ascribed to the reduction in the critical radius for oxygen precipitation and the increase in the concentration of heterogeneous nuclei due to the germanium doping.

Germanium effect on oxygen‐related defects in Czochralski silicon

AbstractThe behaviours of germanium doped in Czochralski (CZ) silicon have attracted considerable attention in recent years. In this article, a review concerning recent processes in the study about oxygen related defects in germanium‐doped CZ (GCZ) silicon is presented. The formation of oxygen precipitates during CZ silicon growth can be improved by germanium, and the oxygen precipitation during thermal cycles can be enhanced, so that the internal gettering (IG) ability of GCZ silicon wafers for metallic impurities is improved. Meanwhile, the morphology of oxygen precipitates can be changed in GCZ silicon. Thermal donors (TDs) can be suppressed by germanium doping as the result of the reaction between germanium and point defects, while new donors (NDs) can be strongly enhanced in GCZ silicon because of a process associated with the nucleation enhancement of oxygen precipitates with germanium doping. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of light germanium doping on thermal donors in Czochralski silicon wafers

In this paper, the effect of light Germanium (Ge-) doping on thermal donors (TDs) in Czochralski silicon (CZ-Si) has been investigated by four-point probe and low-temperatures Fourier transform infrared (FTIR) spectrometer. After 650 °C, 30 min annealing to eliminate the grown-in TDs, conventional CZ-Si and germanium-doped CZ-Si (GCZ-Si) samples were further subjected to isothermal annealing at about 450 °C to generate TDs. It was found that Ge-doping suppressed the formation of TDs. Moreover, the low temperature FTIR absorption spectra of the TDs in GCZ-Si were found to agree quite well with that of TDs in CZ-Si, which was not the case for the heavily Ge-doped silicon. Therefore, it is considered that the light Ge-doping suppresses the formation of TDs but does not affect the microscopic structure of TDs.