Czochralski-grown Si Crystals Research Articles

Virtual experiments of Czochralski growth of silicon using machine learning: Influence of processing parameters on interstitial oxygen concentration

For a process development, it is crucial to know the influence of each process parameter on the process result. However, it is difficult to gauge the influence by experimentally changing only one parameter value owing to constraints of the combination of the parameter values and experimental costs. Machine learning models can predict results that will be obtained under conditions that have not been considered for the experiment. Utilizing a virtual experiment based on a machine learning model, we evaluated the influence of process parameters on the interstitial oxygen (Oi) concentration in Czochralski-grown Si crystals. A dataset for the parameter analysis was constructed, wherein the crucible rotation rate and/or Ar flow rate were systematically changed while maintaining the other parameters at the reference value of an experimental datum. Thereafter, the dataset was input into a neural network model that had been trained with 450 ingot data; consequently, the corresponding Oi concentration was obtained. The evaluated results were consistent with the scientific knowledge previously studied: Oi concentration increases with increasing crucible rotation rate and decreasing Ar flow rate. Furthermore, the two-parameter analysis illustrated a nonlinear relationship between the parameters quantitatively. These approaches demonstrating the Czochralski growth of Si in this study are useful in other crystal growth processes as well.

Determination of C concentration in P-doped n-type Czochralski-grown Si crystals by liquid N temperature photoluminescence after electron irradiation

We demonstrated the effectiveness of photoluminescence (PL) measurement at liquid N temperature after electron irradiation for the determination of the C concentration in P-doped n-type Czochralski-grown Si crystals. The disappearance of P-related lines simplifies the spectral analysis at 77 K, enabling us to estimate the C concentration from the G-line intensity ratio regardless of the difference in P concentration. The C concentration estimated by PL measurement at 77 K was in good agreement with those by measurement PL at 4.2 K and IR absorption. Unsusceptibility to the concentration of dopant impurities is a practical advantage of the PL measurement at 77 K over that at 4.2 K.

Determination of low carbon concentration in Czochralski-grown Si crystals for solar cells by luminescence activation using electron irradiation

We attempted the quantification of carbon concentration in Czochralski-grown Si crystals for solar cells by luminescence activation in the concentration range lower than the detection limit of IR absorption spectroscopy. A positive correlation was found between the relative intensity of the C-line and the substitutional carbon (Cs) concentration determined by IR absorption in the low 1015 cm−3 range. The detection limit was estimated to be approximately 5 × 1012 cm−3. We measured and compared the Cs concentrations in the wafers sliced from ingots grown under different conditions. The variations in Cs concentrations in the respective ingots were consistent with the segregation effect.

Spectroscopy and Topography of Deep-Level Luminescence in Photovoltaic Silicon

The aim of this paper is to identify the origin of a deep-level emission band with a peak at about 0.8 eV observed in photoluminescence from defective areas in multicrystalline Si crystals at room temperature. We compare the band with that in a plastically deformed float-zone and annealed Czochralski-grown Si crystals investigated in detail previously for microelectronic applications and point out the similarities in spectroscopic characteristics and in spatial distributions around dislocations. This prompted us to suggest that the 0.8-eV band consists of two dislocation-related components termed D a1 and D a2 at about 0.79 and 0.94 eV, respectively, and an oxygen-precipitation-related component Db at approximately 0.87 eV. Spatial variations of the three components around dislocation clusters forming small-angle grain boundaries reflect secondary defects or impurities trapped by the strain field around the dislocations, the intrinsic nature of the dislocations, and preferential oxygen precipitation on the dislocations, respectively. The presence of oxygen precipitates in a region emitting the strong Db component was confirmed by highly spatially resolved and highly sensitive secondary ion mass spectroscopy and by mapping of oxygen by luminescence activation using electron irradiation. Anisotropic properties expected for the dislocation-related D a1 component were detected by polarized luminescence imaging.

Vacancy formation energy in Czochralski-grown Si crystals determined by a quenching method

The vacancy formation energy in Czochralski-grown (Cz-) Si crystals was determined by applying a new quenching method. In this method, the optical absorption due to hydrogen atoms bound to vacancies is measured to estimate the vacancy concentration. In contrast with floating-zone grown Si crystals, one more optical absorption peak other than 2223 cm−1 peak was observed at about 2120 cm−1. The defects responsible for the 2120 cm−1 peak are proposed to be VOH4 and VO2H4, inferring from the Voronkov-Falster model on grown-in defects in Cz-Si crystals. The vacancy formation energy estimated from the quenching temperature dependence of the integrated intensity of the 2120 cm−1 peak is about 2.3 eV. After taking the contribution from vacancies generated in the perfect crystal part into account, the formation energy is determined to be approximately 1.5 eV. Such small formation energy compared to that (3.85 eV) in high-purity crystals is thought to be due to a strong interaction between a vacancy and an oxygen atom.

Analysis of Auger Recombination Characteristics in High Resistivity Si and Ge

The characteristics of the band-to-band Auger recombination in Czochralski-grown high resistivity Si and Ge single crystals have been studied using a contactless technique to measure excess carrier decay transients based on infrared absorption by free carriers. The measurements are performed using laser light excitation with wavelengths ranging from 1.2 to 2.5 µm to reduce inhomogeneity effects in the extraction of the Auger recombination parameters. A linear approximation of the initial excess carrier decay lifetime yields an approximate value of the Auger recombination coefficient in Ge γA,Ge ≈ 2×10-31 cm6/s, which is close to that in Si. These characteristics also indicate that the difference in Auger recombination coefficients for the ehh and eeh processes is small. A more detailed fitting procedure applied simultaneously on a series of experimental transients yields a more accurate value of (8±3)×10-31 cm6/s for the Auger recombination coefficient in Ge.

Interaction of copper atoms with radiation-induced defects in silicon

The annealing behavior of radiation-induced defects in Czochralski-grown n-type Si crystals doped with copper via high-temperature (600 and 650°) indiffusion has been studied using Hall effect measurements and deep level transient spectroscopy. The results indicate that radiation-induced vacancy-type defects (divacancies V2 and vacancy-oxygen complexes VO) are effective traps for copper atoms. The inter- action of Cu with VO and V2 reduces their annealing temperature and leads to the formation of electrically active centers at Ec − 0.60 eV and Ec − 0.17 eV, which are assumed to be Cu-VO and Cu-V2 complexes. The enhanced annealing of the radiation-induced vacancy-type defects in Si〈Cu〉 is due to the fact that these defects capture Cu interstitials released from neutral Cu-containing associates at temperatures above 150°C.

Radiation-induced defects in Czochralski-grown silicon containing carbon and germanium

Formation processes of vacancy-oxygen (VO) and carbon interstitial-oxygen interstitial (CiOi) complexes in electron-irradiated Czochralski-grown Si crystals (Cz–Si), also doped with Ge, are investigated. IR spectroscopy measurements are employed to monitor the production of these defects. In Cz–Si with carbon concentrations [Cs] up to 1 × 1017 cm−3 and Ge concentrations [Ge] up to 1 × 1020 cm−3 the production rate of VO defects as well as the rate of oxygen loss show a slight growth of about 10% with the increasing Ge concentration. At high concentrations of carbon [Cs] around 2 × 1017 cm−3 the production rate of VO defects is getting larger by ∼40% in Cz–Si:Ge at Ge concentrations around 1 × 1019 cm−3 and then at [Ge] ≈ 2 × 1020 cm−3 this enlargement drops to ∼13%, thus approaching the values characteristic of lesser concentrations of carbon. A similar behavior against Ge concentration displays the production rate of CiOi complexes. The same trend is also observed for the rate of carbon loss, whereas the trend for the rate of oxygen loss is opposite. The behavior of Ge atoms is different at low and high concentrations of this isoelectronic impurity in Cz–Si. At low concentrations most isolated Ge atoms serve as temporary traps for vacancies preventing them from indirect annihilation with self-interstitials. At high concentrations Ge atoms are prone to form clusters. The latter ones are traps for vacancies and self-interstitials due to the strain fields, increasing the importance of indirect annihilation of intrinsic point defects. Such a model allows one to give a plausible explanation for the obtained results. A new band at 994 cm−1 seen only in irradiated Ge-doped Cz–Si is also studied. Interestingly, its annealing behavior was found to be very similar to that of VO complexes.

Interactions of Cu and Ni Impurities with Vacancy-related Point Defects in Czochralski-grown Si Crystals

It has been inferred from DLTS measurements on electron-irradiated Si samples contaminated with copper and nickel that divacancies (V2) and vacancy-oxygen complexes (VO) are effective traps for mobile Cu and Ni interstitial atoms. Interactions of these impurities with VO and V2 result in the enhanced annealing out of the VO and V2 defects as well as in the formation of new electrically active centers. An enhanced annealing of the VO and V2 defects in Si:Cu crystals is accompanied by an appearance of electron traps with the energy levels at Ec - 0.60 eV and Ec - 0.17 eV. It is argued that these levels are related to acceptor levels of Cu-VO and Cu-V2 complexes. The stable configuration of the Cu-VO complex has been determined by means of quantum-chemical calculations. In Si:Ni crystals an energy level at Ec - 0.365 eV is related to a complex incorporating at least one Ni atom and a radiation-induced defect.

Micro-defects in Ge doped Czochralski grown Si crystals

With the reduction in size of the features of ultra large-scale integrated (ULSI) circuits, micro-defects such as voids in Czochralski (Cz) silicon (Si) crystals play more important roles in the reliability and yield of these devices. As one of the tetravalent atoms, the behavior of germanium (Ge) doped in Cz Si crystals has attracted considerable attention in recent years. In this presentation, recent processes in the study of voids in Ge doped Cz (GCZ) Si crystals are reviewed. The grown-in characteristics of voids in GCZ wafer, including flow pattern defects (FPDs) and crystal originated particles (COPs), suggested that Ge can suppress large voids resulting in denser and smaller voids. Meanwhile, it has been found that the density of voids can be decreased by Ge doping and they can be eliminated easily in GCZ Si crystals through high temperature annealing. It is therefore speculated that the gate oxide integrity (GOI) of semiconductor devices can be improved by Ge doping. The mechanism of the effect of Ge on voids is discussed to explain the experimental results.

Nitrogen effects on generation and velocity of dislocations in Czochralski-grown silicon

The dynamic properties of individual dislocations in nitrogen (N)-doped Czochralski-grown Si crystals with concentrations up to 6×1015cm−3 were investigated at temperatures of 650–950°C using the etch pit technique and compared with such characteristics of N-free Si crystals. The velocity of dislocations in motion in N-doped crystals was revealed to be unaffected by N doping. It was found that the generation of dislocations from a surface scratch was suppressed in N-doped Si and that the critical stress for dislocation generation increased with N concentration, which is interpreted as being due to dislocation immobilization caused by impurity segregation. N doping is concluded to be effective in the promotion of precipitation of oxygen impurity resulting in immobilization of dislocations.

Vacancy-related complexes in neutron-irradiated silicon

Electrically active defects induced by neutron irradiation in n-type Czochralski-grown (Cz)Si crystals have been studied by means of capacitance transient techniques. Theseneutron-induced defects are compared with those created by electron irradiation andself-ion implantation. Four electron traps with the activation energies for electronemission of 0.12, 0.16, 0.24 and 0.42 eV were observed after neutron irradiation inphosphorous-doped Cz Si crystals. It is inferred that the E(0.12) and E(0.16) traps arerelated to the single-acceptor states of the silicon self-interstitial–oxygen dimer complex(IO2i) and the vacancy–oxygen pair (VO), respectively. The E(0.24) trap is associatedwith the electron emission from the double-acceptor state of the divacancy(V2). However, an asymmetric peak with its maximum at around 220 K and an activationenergy for electron emission of 0.42 eV dominated the spectra. We used high resolutionLaplace DLTS to investigate the structure of E(0.42) and found that this signal iscomplex, consisting of contributions from several defects. From the annealingbehaviour, it was revealed that as some of these defects anneal out they aresources of vacancies evidenced by an increase in the concentration of VO andV2. It is suggested that some of the defects contributing to the E(0.42) peak are related tosmall vacancy clusters.

Thermal double donor annihilation and oxygen precipitation at around650 °C in Czochralski-grown Si: local vibrational mode studies

We have used local vibrational mode (LVM) spectroscopy to monitorthe formation of oxygen-related thermal double donors (TDDs) at450 °C and theirannihilation at 650 °C in carbon-lean Czochralski-grown (Cz-) Si crystals. A few samples were treated at650 °C under high hydrostatic pressure. It is found that the annihilation of TDDs at650 °C results not only in a partial recovery of the interstitial oxygen, but alsoin the appearance of a number of new O-related LVM bands in the range990–1110 cm−1. The positions of these lines and their shapes are identical to thoseobserved for Cz-Si irradiated with electrons or neutrons and annealed at600–700 °C. Since the lines appear upon annealing out ofV O3 and V O4 defects in irradiated samples, they are suggested to arise fromV Om (m>4) complexes. In both kinds of samples, pre-annealed and pre-irradiated,the new LVM bands disappear upon prolonged annealing at650 °C while enhanced oxygen precipitation occurs. TheV Om defects are suggested to serve as nuclei for oxygen precipitates developing at around650 °C. Highhydrostatic pressure is found to enhance further (up to 4–5 times) the oxygen precipitation process at650 °C in the samplespre-annealed at 450 °C.

Occupation site change of self-interstitials and group-III acceptors in Si crystals: Dopant dependence of the Watkins replacement efficiency

We studied the dependence of the Watkins replacement efficiency on the species of group-III impurities from the measurement of the concentration of $I{\mathrm{H}}_{2},$ a complex of one self-interstitial (I) and two H atoms. If the $I{\mathrm{H}}_{2}$ concentration depends on species of group-III impurities under the same irradiation dose, the smaller concentration means a greater replacement efficiency. Specimens were prepared from floating-zone-grown Si crystals and Czochralski-grown Si crystals doped with B, Al, Ga, and In. After hydrogenation, they were irradiated with 3-MeV electrons at room temperature. We measured the optical absorption of those specimens. The $I{\mathrm{H}}_{2}$ concentration was found to depend on the B concentration, becoming smaller as the B concentration became larger. It also depended on the species of group-III dopants. Hence the replacement efficiency of I and group-III impurities depended on the concentration and species of group-III dopants.

Effect of Dynamic Aging of Dislocations on the Deformation Behavior of Extrinsic Semiconductors

The Alexander-Haasen theory of deformation in semiconductor crystals with low dislocation density was generalized by taking into account the effect of dynamic aging of dislocation caused by the impurity drag. The generalized theory explains some qualitative distinctions of the elastic-plastic transition in Czochralski-grown Si crystals from that in crystals of higher purity. Particularly, this concerns the dependence of the height of the yield-point peak on the initial dislocation density and the weakening of the strain-rate sensitivity of the yield stress.

Defect‐impurity interactions in irradiated tin‐doped Cz‐Si crystals

Results of a combined infrared absorption (IR) and deep-level transient spectroscopy (DLTS) study of defects induced by irradiation with fast electrons in Sn-doped Czochralski-grown Si crystals are reported. Tin atoms were found to interact effectively with vacancy as well as with interstitial-type radiation-induced defects. Manifestations of stable tin-vacancy and tin-interstitial carbon atom complexes were observed in DLTS and IR absorption spectra. Defect transformations upon heat-treatments of the irradiated samples were studied. Tin atoms were found to be effective traps for mobile vacancy–oxygen (V–O) complexes. A local vibrational mode of a Sn–V–O complex has been identified.

Many optical absorption peaks observed in electron-irradiated n-type Si

The properties of many optical absorption peaks in electron-irradiated n-type Si crystals were studied. Specimens were prepared from various Si crystals. After chemical etching, they were irradiated with 3 MeV electrons at room temperature (RT). Their optical absorption spectra were measured with a Fourier transform infrared spectrometer at temperatures in the range of 7 K to RT with a resolution of 0.25 cm−1. Many optical absorption peaks were observed in the wave number range between 850 and 1600 cm−1 only in n-type (phosphorus-doped) Si crystals. Hence, they are due to donors. Such peaks were very weak in Czochralski-grown Si (Cz Si) crystals. This suggests that these peaks are due to complexes of phosphorus and vacancies since most vacancies in Cz Si form pairs (A center) with oxygen because of the very high concentration of oxygen in those crystals. They disappeared as the result of annealing at above 175 °C. Temperature dependencies of intensities of various peaks were studied.

Effect of dynamic aging of dislocations on the deformation behavior of extrinsic semiconductors

The Alexander-Haasen theory of deformation in semiconductor crystals with low dislocation density was generalized by taking into account the effect of dynamic aging of dislocation caused by the impurity drag. The generalized theory explains some qualitative distinctions of the elastic-plastic transition in Czochralski-grown Si crystals from that in crystals of higher purity. Particularly, this concerns the dependence of the height of the yield-point peak on the initial dislocation density and the weakening of the strain-rate sensitivity of the yield stress.

X-ray topographic observation of dislocation generation at the seed/crystal interface of Czochralski-grown Si highly doped with B impurity

Dislocation generation in the initial stage of Czochralski-grown Si crystals doped with B in various concentrations was observed by means of X-ray topography. Slip dislocations were generated due to the thermal stress at the dipping stage in the seed and in a crystal doped with B in the concentration lower than 1×10 18 cm −3. Misfit dislocations were generated and penetrated into the crystal when the difference of B concentration between the seed and crystal was higher than ≈8×10 18 cm −3.

Optical absorption peaks observed in electron-irradiated n-type Si

We found many optical absorption peaks in electron-irradiated n-type Si crystals. Specimens were prepared from various Si crystals. After chemical etching, they were irradiated with 3-MeV electrons at RT. Their optical absorption spectra were measured with an FT-IR spectrometer at temperatures in the range of 5 K and RT with a resolution of 0.25 cm −1. Many optical absorption peaks were observed in the wavenumber range between 950 and 1600 cm −1 only in n-type (phosphorus-doped) floating-zone grown Si crystals. Hence, they are due to donors. They were not observed in Czochralski-grown Si (CZ-Si) crystals. This suggests that these peaks are due to complexes of phosphorus and vacancies since most vacancies in CZ-Si form pairs (A-center) with oxygen because of very high concentration of oxygen. They disappeared by annealing at above 200°C.