CZ Silicon Research Articles

Research on Abnormal State Detection of CZ Silicon Single Crystal Based on Multimodal Fusion.

The Czochralski method is the primary technique for single-crystal silicon production. However, anomalous states such as crystal loss, twisting, swinging, and squareness frequently occur during crystal growth, adversely affecting product quality and production efficiency. To address this challenge, we propose an enhanced multimodal fusion classification model for detecting and categorizing these four anomalous states. Our model initially transforms one-dimensional signals (diameter, temperature, and pulling speed) into time-frequency domain images via continuous wavelet transform. These images are then processed using a Dense-ECA-SwinTransformer network for feature extraction. Concurrently, meniscus images and inter-frame difference images are obtained from the growth system's meniscus video feed. These visual inputs are fused at the channel level and subsequently processed through a ConvNeXt network for feature extraction. Finally, the time-frequency domain features are combined with the meniscus image features and fed into fully connected layers for multi-class classification. The experimental results show that the method can effectively detect various abnormal states, help the staff to make a more accurate judgment, and formulate a personalized treatment plan for the abnormal state, which can improve the production efficiency, save production resources, and protect the extraction equipment.

Relationship between temperature gradient and growth rate during CZ silicon crystal growth

Temperature distribution in the growing crystal is the most important parameter that determines the grown-in-defects, growth rate, etc. There is a discussion either higher growth rate leads to larger thermal gradient or smaller thermal gradient. In this study, in order to make clear the reason of this discrepancy, the effects of growth rate on the shape of melt/crystal interface, and temperature distribution in growing crystal were investigated by numerical modeling. Firstly, as increasing the growth rate, the shape of melt/crystal interface becomes more concave. And temperature gradient along center axis on growing crystal increases as increasing the growth rate. On the other hand, temperature gradient along surface of growing crystal decreases as increasing the growth rate. To obtain higher growth rate, heat transfer should be enhanced. Along the center axis, heat transfer in vertical direction by heat conduction is dominant. Then concave interface shape and larger thermal gradient along center axis were obtained. In the periphery of grown crystal near the triple points, because of concave interface shape, heat transfer in radial direction, and radiative heat transfer from growing crystal become more important than heat transfer in vertical direction. Then smaller thermal gradient along the growing crystal surface was obtained. This surface temperature profile agrees well with Abe’s measurement results. It is cleared that higher growth rate leads to the higher heat transfer, and melt/crystal interface shape, and temperature distribution in growing crystal are determined by the balance of growth rate and heat transfer between heat conduction in vertical direction and heat conduction in radial direction combined with radiation heat transfer from crystal surface.

Optimizing CZ Silicon Crystal Growth: Algorithmic Approach for Defect Minimization

Optimizing CZ Silicon Crystal Growth: Algorithmic Approach for Defect Minimization

Numerical and experimental investigation on iron contamination of 200 mm semiconductor-grade CZ-Si by bubble-free layer of quartz crucible

The thickness of bubble-free (BF) layer of the quartz crucible is crucial for heat transfer during the crystal growth process of 200 mm semiconductor-grade CZ silicon. The effect of the BF layer thickness on the contamination of impurity Fe in the wafer was investigated through experimental and numerical simulations. The experimental results demonstrated that a crucible with a 3 mm BF layer (S1) exhibited a lower thermal conductivity (1.37 W/(K• m)) in comparison to a 6 mm BF layer (S2) with a thermal conductivity of 1.72 W/(K• m). Despite the S2 crucible requiring an additional 0.40 kW for thermal compensation, it resulted in a lower concentration of Fe impurities. Compared to S1, S2 crucible offered superior performance in stabilizing the distribution of O and C impurities, resulting in more uniform distribution and improved crystal quality. Simulations indicated that the utilization of S2 quartz crucibles had minimal effect on the velocity field of Ar gas but elevated the melt temperature, strengthened the Taylor-Proudman vortex beneath the crystal-melt interface and altered the flow direction of the secondary vortex. This study highlights the importance of crucible design in controlling the contamination of Fe impurities for the production of high-quality Si wafers.

Assessing the potential of TOPCon solar cells architecture using industrial n-type cast-mono silicon material

Cast-mono silicon material is interesting for its lower carbon footprint compared to Czochralski (Cz) monocrystalline silicon. However, solar cells fabricated using cast-mono (CM) silicon show lower performances. In this work, two routes to make cast-mono silicon advantageous over Cz silicon are considered. The first route is to further reduce carbon footprint of cast-mono silicon, by using Upgraded Metallurgical Grade silicon (UMG-Si) feedstock instead of Solar Grade silicon (SoG-Si) feedstock. TOPCon solar cells are fabricated using both feedstocks, and cast-mono growth technology, using industrial-type furnaces. Laboratory studies show that UMG-Si can result in efficiencies higher than solar cells made of SoG-Si when feeding the material to a CM crystallization process. But when compared to Cz, CM-UMG-Si TOPCon solar cells conversion efficiency values are still 0.5%abs lower. The second route is to take advantage of the TOPCon passivation layer (e.g., poly-Si) ability to getter metallic impurities, and thus improve the quality of cast-mono material. Several TOPCon sequences are tested and their effect on the carrier recombination properties of the device are studied. In the end, solar cells are fabricated and again, UMG-Si solar cells show better results than SoG-Si solar cells, with efficiency up to 22.65%, independently confirmed.

Effects of Nitrogen Doping on Pulling Rate Range of Defect-Free Crystal in CZ Silicon

We investigated the effect of nitrogen doping on the pulling rate range of defect-free crystal in silicon with a diameter of 200 mm. It was found that the pulling rate range of defect-free crystal in nitrogen-doped Czochralski silicon is wider and the pulling rate (defect free) is lower than it is in non-nitrogen-doped Czochralski silicon. Under the experiment, the pull rate was from 0.67 mm/min~0.58 mm/min to 0.65 mm/min~0.54 mm/min. To further confirm the above experimental analysis, a numerical simulation process of nitrogen-doped Czochralski and non-nitrogen-doped Czochralski in an industrial system was performed. The V/G value along the S/L interface was the same for both models, but the distribution of Cvi (concentration of vacancy–concentration of self-interstitial) for nitrogen-doped Czochralski crystal silicon was more uniform and flat in a nitrogen-doped single crystal. Furthermore, the nitrogen-doped Czochralski crystal silicon had a smaller void size and a higher oxygen precipitation density. The experimental results are in good agreement with the numerical simulation results.

Effect of metal impurities concentration on electrical properties in N-type Recharged-Czochralski silicon

The electrical properties of N-type Recharged-Czochralski (RCz) silicon solar cells are significantly affected by the concentration of metal impurities in the silicon materials. In this work, several N-type RCz silicon ingots were grown using feedstock with different impurities concentration, and the distribution of minority carrier lifetime was tested. It was discovered that a broader range of feedstock impurity concentrations resulted in high and stable minority carrier lifetime of the ingots. Solar cells made from these ingots had an average efficiency of over 24.57%. Meanwhile, the results of impurities segregation calculation and solar cells electroluminescence(EL) test were given. The results indicated that ring defects were the primary cause of differences in electrical properties among silicon ingots produced from feedstock with varying impurity concentrations. Further, the process window to produce high efficiency N-type Czochralski(Cz) silicon solar cells was broadened, and the production cost could be reduced.

Characterization of light induced degradation in PECVD silicon nitride passivated Cz silicon wafers using spectroscopic techniques

In this work we investigate the chemical species involved in the light induced degradation of plasma enhanced chemical vapor deposited (PECVD) hydrogenated silicon nitride (SiNx:H) passivated p-type and n-type samples under normal outdoor ambient conditions. The electrical characterization measurements along with Fourier Transform Infrared (FTIR) and photoluminescence (PL) spectroscopic techniques were utilized in this study. Significant reduction in effective minority carrier lifetime values and band to band PL intensities were noticed for both p-type and n-type samples after outdoor light soaking. The apparent defect density increased from 3.39 × 10−3 µs−1 to 1.68 × 10−2 µs−1 and 3.42 × 10−4 µs−1 to 3.46 × 10−3 µs−1, respectively for p-type and n-type samples after light soaking of 111 h corresponding to cumulative solar insolation of 95.7 kWh/m2. The changes in FTIR absorbance intensities of chemical species such as SiNyHa, SiNzHb, SiHm, SiO2i and SiOn after light soaking confirmed the role of oxygen in addition to hydrogen in both p-type and n-type samples. Spectroscopic PL analysis further validated the decrease in concentration of silicon-oxygen species and reduction in effective lifetime for n-type samples. We demonstrate that the chemical species contributing to light induced bulk and surface degradation can be identified by FTIR and PL spectroscopic techniques. This work would be beneficial for understanding, modeling and mitigating the degradation mechanisms in Cz silicon wafers passivated using PECVD dielectric films.

Determination of conduction type in high-resistivity silicon by combining spreading resistance profiling (SRP) with hydrofluoric acid treatment

The effect of hydrofluoric acid (HF) treatment on the surface electrical properties was observed in high-resistivity bulk silicon by the spreading resistance profiling (SRP) technique. It is found that the near-surface resistivity decreased in n-type silicon and increased in p-type silicon after HF treatment according to the SRP measurement. The variation of surface chemical elements and energy bands of HF-treated n-type and p-type (100) silicon has been characterized by x-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy measurements. The results indicate that the surface Fermi level is shifted toward the conduction band minimum after HF treatment. The surface energy band bending caused by the surface electronegative groups (–F and –OH) was investigated by the method of First-principles calculation. Based on these findings, a method combining the SRP measurement with HF treatment to determine the conduction type of high-resistivity silicon was proposed, which is critical for the development of high-resistivity CZ silicon crystal growth.

A simplified and masking‐free doping process for interdigitated back contact solar cells using an atmospheric pressure chemical vapor deposition borosilicate glass / phosphosilicate glass layer stack for laser doping followed by a high temperature step

AbstractIn this paper a simplified approach for the generation of laterally p‐ and n‐doped structures applicable for cost‐effective production of interdigitated back contact (IBC) solar cells is presented. We use a stack of doping glasses deposited by atmospheric pressure chemical vapor deposition (APCVD), consisting of borosilicate glass (BSG) and phosphosilicate glass (PSG) on Czochralski‐grown (Cz) silicon substrates. A laser process creates the p‐doped regions by local liquid phase diffusion of boron from the BSG layer into the underlying molten Cz‐Si substrate. Simultaneously, the BSG‐PSG stack is removed by laser ablation. In a subsequent high‐temperature step, phosphorus diffuses from the remaining PSG‐BSG layer into the crystalline silicon substrate under inert gas atmosphere, creating complementary to laser doped areas n+‐doped regions. By the use of APCVD, phosphorus and boron contents of the doping glasses can be adjusted freely to vary the resulting p‐ and n‐doped profiles. A higher boron content in the BSG layer enhances the diffusion of phosphorus through the BSG, especially at lower diffusion temperatures. The resulting doping profiles are characterized using electrochemical capacitance‐voltage measurements and the resulting sheet resistances using the four‐point probe method. The amount of minority dopant contamination in n‐ and p‐doped regions is investigated by secondary ion mass spectrometry. Furthermore, transfer length method (TLM)‐measurements indicate contactability of the generated doped regions.

Long-Term Stability of Novel Crucible Systems for the Growth of Oxygen-Free Czochralski Silicon Crystals

The replacement of the silica glass crucible by oxygen-free crucible materials in silicon Czochralski (Cz) growth technology could be a key factor to obtaining Cz silicon, with extremely low oxygen contamination < 1 × 1017 at/cm3 required for power electronic applications. So far, isostatic pressed graphite or nitrogen-bonded silicon nitride (NSN) crucible material, in combination with a chemical vapor deposited silicon nitride (CVD-Si3N4) surface coating, could be identified as promising materials by first short-term experiments. However, for the evaluation of their potential for industrial scale Cz growth application, the knowledge about the long-term behavior of these crucible setups is mandatory. For that purpose, the different materials were brought in contact with silicon melt up to 60 h to investigate the infiltration and dissolution behavior. The chosen graphite, as well as the pore-sealed NSN material, revealed a subordinated infiltration-depth of ≤1 mm and dissolution of ≤275 µm by the silicon melt, so they basically fulfilled the general safety requirements for Cz application. Further, the highly pure and dense CVD Si3N4 crucible coating showed no measurable infiltration as well as minor dissolution of ≤50 µm and may further acts as a nucleation site for nitrogen-based precipitates. Consequently, these novel crucible systems have a high potential to withstand the stresses during industrial Cz growth considering that more research on the process side relating to the particle transport in the silicon melt is needed.

Performance-driven semiconductor silicon crystal quality control

Aiming at the online monitoring of key variables during the growth process of Czochralski (Cz) silicon single crystal (SSC), this paper is aimed to propose a performance-driven hierarchical control strategy based on soft-sensing model. To this end, corresponding sub-models based on the mechanism model and industrial data are first established. Then, the two linear forms of them are combined to arrive at the mechanism- and data-driven hybrid variable weighted stacked autoencoder random forest (M-HVW-SAE-RF) soft sensing model. Among them, the stacked autoencoder (SAE) network is utilized to extract the deep features of the data, and the random forest (RF) is employed to realize the regression prediction of the target variable. Secondly, for the problem of model uncertainty, based on the identification for control (I4C) theory, a performance-driven hierarchical control strategy is established on the basis of the model predictive control-adaptive disturbance rejection control (MPC-ADRC). The main goal is to achieve the best output performance of the actual control system and to implement online monitoring of crystal size and V/G. Finally, based on the analysis of the production process data of the semiconductor industry, the effectiveness of the proposed control strategy is verified.

Low‐Temperature Photoluminescence Investigation of Light‐Induced Degradation in Boron‐Doped CZ Silicon

Light‐induced degradation (LID) in boron‐doped Czochralski grown (CZ) silicon is a severe problem for silicon devices such as solar cells or radiation detectors. Herein, boron‐doped CZ silicon is investigated by low‐temperature photoluminescence (LTPL) spectroscopy. An LID‐related photoluminescence peak is already found while analyzing indium‐doped p‐type silicon samples and is associated with the ASi–Sii defect model. Herein, it is investigated whether a similar peak is present in the spectra of boron‐doped p‐type CZ silicon samples. The presence of change in the photoluminescence signal intensity due to activation of the boron defect is investigated as well. Numerous measurements on boron‐doped samples are made. For this purpose, samples with four different boron doping concentrations are analyzed. The treatments for activation of the boron defect are based on the LID cycle. During an LID cycle, an additional peak or shoulder neither in the areas of the boron‐bound exciton transverse acoustic and nonphonon‐assisted peaks (BTA, BNP) nor in the area of the boron‐bound exciton transverse optical phonon‐assisted peak (BTO) is found. The defect formation also does not lead to a lower photoluminescence (PL) intensity ratio BTO(BE)/ITO(FE).

Electrical properties of oxygen precipitate-related defects in Czochralski silicon

Oxygen precipitate-related defects in Czochralski (Cz) silicon have been studied by electron-beam-induced current (EBIC) and deep-level transient spectroscopy (DLTS). The EBIC results present that oxygen precipitates combined with dislocations can strengthen carrier recombination. The DLTS data reveals two levels of T 1 (E v + 0.43 eV) and T 2 (E v + 0.26 eV), which are related to the oxygen precipitates and dislocations, respectively. Hydrogen can partly passivate the recombination activity of oxygen precipitates and dislocations, as well as their induced electronic states. The results are of interest for deeply understanding the electronic properties of oxygen precipitates and their induced dislocations in Cz silicon used in the semiconductor industry.

Mechanism to form ring-like distributed oxidation-induced stacking fault bands through relaxing thermal stress during stopping the growth in CZ silicon crystals

This paper aims to study the mechanism to form ring-like distributed oxidation-induced stacking fault (R-OSF) bands in CZ silicon. In this experiment, pulling crystals was stopped during the growth, and the crystals were held for predetermined periods contacting the melt while the seed rotation and converse crucible rotation were maintained. Then, the crystals were detached from the melt and cooled rapidly to freeze the defect distribution. In CZ crystals during the growth, high-temperature mass (crystalized silicon) is transferred upward from the growth interface with the crystal pulling. The top of the crystals is directly cooled by the cooling water chamber, while the peripheral part is heated by the radiation from the heater through the gap under the heat shield and the radiation from the melt surface. Thus, the temperature of the upper center part becomes lower than that of the peripheral part, and isotherms in the crystal form U-shape. When the growth is stopped, the crystals also stop raising the “high-temperature mass” from the growth interface. Thus, cooling rapidly proceeds from the center upper part to the growth interface, and the U-shape isotherms fall downward. When the temperature of a region along a U-shaped isotherm decreases to around 1000 ℃, and a temperature gradient exceeding a certain threshold also forms vertically to the U-shaped isotherm, a thermal stress (expansion stress) is applied from the high-temperature side part to the low-temperature center part. At this time, oxygen precipitates, the nuclei of the R-OSFs, are presumably generated there to relax the thermal stress. Although some researchers have presumed that the R-OSF band is a vacancies (Vs)/interstitials (Is) boundary formed at a temperature near the melting point, the results of this study contradict their presumption.

Annealing-temperature-dependent evolution of hydrogen-related donor and its strong correlation with X-photoluminescence center in proton-irradiated silicon

We have investigated the formation and decay of hydrogen-related donors (HDs) and irradiation-induced intrinsic defects. N-type m:Cz and FZ silicon wafers, which were irradiated with 2 MeV protons and subsequently annealed at 100–600 °C, were analyzed using spreading resistance profiling and photoluminescence (PL). HDs formed at 260 °C and then disappeared in two stages at 400–440 and 500–540 °C. This decay behavior indicates the existence of two types of HDs with different thermal stabilities. PL measurements showed interstitial silicon clusters (W and X center), a carbon–oxygen complex (C center), and exciton lines bound to unknown shallow centers. The origin of the HDs was investigated based on the correlation of the formation and decay temperatures between HDs and irradiation-induced defects. The predominant defects at the early stage of annealing, such as the C and W centers, are ruled out as candidates for the core defects of HDs because annealing above 260 °C is indispensable for the HD formation. In contrast, the X center was found to be thermally generated above 200 °C and disappeared at 580 °C. The similarity of the formation and decay temperatures between the X and HD centers suggests that HDs are associated with the formation of the interstitial silicon-related defects attached to hydrogen. Our results suggest that controlling the formation of interstitial silicon-related defects is important for realizing desirable doping profiles with high accuracy and reproducibility for power devices. Annealing above 400 °C exclusively provides thermally more stable HDs, leading to the realization of more rugged power devices.

Comprehensive characterization of efficiency limiting defects in the swirl-shaped region of Czochralski silicon

For Czochralski silicon (Cz-Si) solar cells, swirl-shaped regions in silicon wafers could lead to efficiency degradation, usually accompanied by hot spots and thermal breakdown. In this paper, comprehensive characterization methods including electroluminescence (EL), photo-induced current (LBIC), quantum efficiency (QE), cell efficiency, carrier lifetime, scanning electron microscope (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and deep level transient spectroscopy (DLTS) were used to investigate the formation and properties of the Swirl defects. It is found that there exists a strong correlation between the as-grown swirl defects and the degradation in cell performance. The Swirl defects cause an energy level of E v + 0.33 eV in silicon bandgap, with the capture cross section of 2.3 × 10 −15 cm 2 , which is consistent with the feature of silicon/oxide interface states. The swirl defects can further be evolved into stacking faults after annealing at 1050 °C for 16 h, and cause an additional energy level of E v + 0.42 eV with the capture cross section is 1.0 × 10 −14 cm 2 . These results suggest that oxygen precipitates are the vital component or precursor for the formation of swirl-shaped regions in Cz silicon wafers. • A comprehensive study of the nature of Swirl defects in the photovoltaic Czochralski silicon is obtained. • The direct evidence that Swirl defects are related to oxygen precipitates is provided by deep level transient spectroscopy (DLTS) measurements. • The influence of Swirl defects on solar cell performances and material properties is characterized.

Material evaluation for engineering a novel crucible setup for the growth of oxygen free Czochralski silicon crystals

For manufacturing of several high performance electronic devices, e.g. insulated-gate bipolar transistors (IGBT), single crystalline silicon crystals with high purity and minimum oxygen (in the range of 1015 at/cm3) concentration are required. Such silicon crystals are typically grown by the Floating Zone technique (Fz), as the more common and cheaper Czochralski technique (Cz) uses silica crucible, which leads always to a relatively high oxygen concentration in the silicon crystals (>1017 at/cm−3). Therefore, in this work potential materials were evaluated with respect to the development of a novel oxygen-free crucible system, which should enable a cost effective growth of oxygen free Cz silicon ingots. For that purpose different graphite materials as well as nitride bonded silicon nitride (NSN) were tested in contact with liquid silicon due to their infiltration behaviour and occurrence of crack formation. Functional silicon nitride (Si3N4) coatings were applied by powder based spray coating of reaction bonded silicon nitride (RBSN) and chemical vapour deposition (CVD) on graphite and NSN crucibles. Characterization of the crucible/coating systems before and after crystal growth experiments in a lab-scale casting furnace reveal information about morphology, infiltration behaviour and adhesion strength on the crucible. Further, investigations on the grown silicon crystals give information about impurity incorporation coming from the novel crucible systems. The results indicated, that especially graphite materials with low porosity and a high mechanical strength as well as NSN with polysilazane sealing in combination with a CVD Si3N4 coating have definitely a potential for application as crucible system in silicon growth processes.

Advanced approach for oxygen transport and crystallization front calculation in Cz silicon crystal growth

Modeling of oxygen transport during Czochralski (Cz) silicon crystal growth still is a big challenge due to oxygen evacuation from the melt free surface, affected by strong anisotropy of turbulent mass transport. To predict the crystal oxygen concentration and crystallization front geometry with reasonable accuracy usually a 3D unsteady LES or DNS approach is required which demands significant computation resources and time. We present a new steady turbulence model using the extended hypothesis for modeling the Reynolds stress tensor, which accounts for different mechanisms of Reynolds stresses anisotropy and can be used in fast 2D engineering calculations. Several 8″ silicon crystals were grown in EKZ 3500 furnace with varying operating parameters. Wafers have been cut from different parts of the crystals and analyzed using the Fourier-transform infrared spectroscopy (FTIR) for oxygen concentration in facilities of Fraunhofer CSP and iTechSolar. The comparison between experimental and calculated results, which include oxygen concentration and interface deflection, is discussed in details. Time-averaged Reynolds stress tensor components as well as the turbulent heat fluxes components are compared between unsteady LES and steady RANS approaches.

LeTID mitigation via an adapted firing process in p‐type PERC cells from SMART cast‐monocrystalline, Czochralski and high‐performance multicrystalline silicon

AbstractIn this work, we analyse passivated emitter and rear cells (PERC), based on wafers made from seed manipulation for artificially controlled defects technique (SMART) monocrystalline silicon, magnetically grown and conventional Czochralski (mCz and Cz) silicon, and high‐performance multicrystalline (hpm) silicon. All wafers were processed identically except for the hpm wafers, which received an acidic texture instead of random pyramids. The energy conversion efficiencyηof the SMART cells of 21.4 %is similar to the mCz cells (21.5 %) while being more thanhigher than for the hpm cells. Furthermore, we here show for the first time that light‐ and elevated temperature‐induced degradation (LeTID) is mitigated in hpm, Cz and SMART PERC cells without significant losses in initial efficiency by an adapted fast‐firing process, incorporating slower firing ramps that can be used in industrial production. The cells that are fired with these ramps show no significant efficiency loss () during LeTID testing at 75°C and 0.15 suns illumination for 1100 h, while the reference fast‐firing process results in efficiency losses ofdue to LeTID. For Cz cells that have been treated to regenerate the boron–oxygen defect prior to LeTID testing, the maximum degradation was reduced fromto.