Epitaxial Wafers Research Articles

Elimination of OISF in large-size Si substrate for low warpage and crack-free GaN epitaxial wafer

The oxygen induced stacking fault (OISF) in heavy boron-doping Si substrates causes severe warpage and surface cracks of GaN epitaxial wafers, which will lower the production yield of GaN-based power devices. In this work, high-quality 8-inch Si substrates were fabricated by using rapid thermal annealing (RTA) to eliminate OISF. RTA at 1200 °C effectively eliminated OISF, then surface cracks of 8-inch epitaxial wafers were removed fully and its bow value was decreased markedly from 45.7 μm to 14.3 μm. Consequently, the yields of high electron mobility transistors based on GaN wafers were improved up to 97 %.

Study on the performance of InGaN-based micro-LED by plasma etching combined with ion implantation process

This study utilized blue-light epitaxial wafers and employed semiconductor processes such as maskless laser writing, dry etching, wet etching, passivation layer deposition, electron beam evaporation, and ion implantation to fabricate micro-light emitting diode (μLED) arrays with different pixel sizes but the same emitting area (900 μm²). The μLED arrays with single pixel sizes of 5 μm, 10 μm, and 15 μm were fabricated, with array numbers of 6×6, 3×3, and 2×2, respectively. This study proposes etching the material in the channel region while retaining a certain width for implantation, known as the sidewall ion implantation process, aiming to achieve better insulation characteristics by using ion implantation technology to insulate the sidewall regions. It involves ion bombardment of the defect areas generated after plasma etching and the use of a passivation layer for protection. The isolation characteristics of μLED arrays processed by sidewall implantation exhibited better electrical isolation than those of μLED arrays processed only by plasma. The light output power, external quantum efficiency, and wall-plug efficiency were all superior for the sidewall implantation process when the device was miniaturized to 5 μm. Overall, the sidewall implantation process combined with plasma dry etching effectively improved the light output characteristics, with the enhancement ratio increasing as the device was miniaturized.

Ultrasmall-sized light-emitting diodes fabricated by ion implantation based on GaN epitaxial wafers with fully activated or unactivated p-GaN.

A key challenge in realizing ultrahigh-resolution displays is the efficient preparation of ultrasmall-sized (USS) light-emitting diodes (LEDs). Today, GaN-based LEDs are mainly prepared through dry etching processes. However, it is difficult to achieve efficient and controllable etching of USS LED with high aspect ratios, and LED sidewalls will appear after etching, which will have a negative impact on the device itself. Herein, a method for preparing USS LED based on GaN epitaxial wafers is reported (on two types of wafers, i.e., with p-GaN fully activated and unactivated). F-ions are injected into the intentionally exposed areas on the two types of wafers to achieve device isolation. The area under the micro-/nano-sized protective masks (0.5, 0.8, 1, 3, 5, 7, 9, and 10 µm wide Ni/Au stripes) are the LED lighting areas. The LED on the p-GaN unactivated wafer (UAW) requires further activation. The Ni/Au mask not only serves as the p-electrode of LED but also Ni as a hydrogen (H) removing metal covering the surface of p-GaN UAW that can desorb H from a Mg element in the film at relatively low temperatures, thereby achieving the selective activation of LED lighting areas. Optoelectronic characterization shows that micro-/nano-sized LED arrays with individual-pixel control were successfully fabricated on the two types of wafers. It is expected that the demonstrated method will provide a new way toward realizing ultrahigh-resolution displays. Analyzing the changes in the current flowing through LED (before and after selective activation) on the F-injected p-GaN UAW, it is believed that depositing H removing metal on p-GaN UAW could possibly realize the device array through the selective activation only (i.e., without the need for ion implantation), offering a completely new insight.

Inverted V-shaped size-dependent emission wavelength shift in InGaN micro-LEDs with size down to 1 μm

The size-dependent emission wavelength shift of micro-scale light emitting diodes (micro-LEDs) has been frequently reported in recent publications, but its underlying physical mechanism has not yet been thoroughly elucidated. Here, we fabricate and characterize the red, green, and blue InGaN micro-LED mesas with different diameters down to 1 μm. As the size decreases, all the samples of different colors show an inverted V-shaped photoluminescence wavelength variation trend, first a red shift and then a blue shift, and the shifting range is larger for samples with longer wavelengths. Micro-Raman spectrum confirms that the stress was significantly released after scaling down the size from epitaxial wafer to 1 μm. The theoretical simulations show that the red and blue shifts are, respectively, attributed to the bandgap narrowing and the weakening of the quantum-confined Stark effect caused by strain relaxation, which dominate successively.

Early Detection of Bar-Shaped 1SSF before Expansion by PL Imaging

In this study, we investigated how bar-shaped 1SSF (Single Shockley-type stacking fault) in a chip of a SiC (Silicon Carbide) epitaxial wafer expanded with UV (ultraviolet) irradiation and observed it with PL (Photoluminescence) imaging and demonstrated early detection of bar-shaped 1SSF with an algorithm for automatic detection for the initial shape of bar-shaped 1SSF. Furthermore, we estimated that it was 83% how much UV irradiation time could be reduced.

Experimental Determination of Si Self-Interstitial Emission During Oxide Precipitation in Czochralski Silicon

We used the method of Torigoe and Ono [J. Appl. Phys., 121, 215103 (2017)] to investigate the kinetics of β, the number of self-interstitials emitted per precipitated oxygen atom, during oxide precipitation in Czochralski silicon. For this purpose, we used pp- epitaxial wafers with a buried highly B-doped epitaxial layer which were annealed with and without thermal pre-treatments at 950 °C. From the results we conclude that in the initial phase of oxide precipitation without thermal pre-treatment β is very high before it drops to low values. With a thermal pre-treatment at 800 °C for 2 h, the initial value of β is somewhat lower before the drop also occurs. If a nucleation anneal is carried out before the thermal treatment at 950 °C the β values are low from the beginning. All of these results confirm our previously published theoretical predictions experimentally. This work also shows that the crystal pulling process can affect the initial β value because grown-in oxide precipitate nuclei can reduce their strain by vacancy absorption. Therefore, high vacancy supersaturation during crystal cooling while oxide precipitate nucleate would lead to somewhat lower initial β values.

Non-destructive electroluminescence inspection for LED epitaxial wafers based on soft single-contact operation

Non-destructive and accurate inspection of gallium nitride light-emitting diode (GaN-LED) epitaxial wafers is important to GaN-LED technology. However, the conventional electroluminescence inspection, the photoluminescence inspection, and the automated optical inspection cannot fulfill the complex technical requirements. In this work, an inspection method and an operation system based on soft single-contact operation, namely, single-contact electroluminescence (SC-EL) inspection, are proposed. The key component of the SC-EL inspection system is a soft conductive probe with an optical fiber inside, and an AC voltage (70V pp , 100 kHz) is applied between the probe and the ITO electrode under the LED epitaxial wafer. The proposed SC-EL inspection can measure both the electrical and optical parameters of the LED epitaxial wafer at the same time, while not causing mechanical damage to the LED epitaxial wafer. Moreover, it is demonstrated that the SC-EL inspection has a higher electroluminescence wavelength accuracy than photoluminescence inspection. The results show that the non-uniformity of SC-EL inspection is 444.64%, which is much lower than that of photoluminescence inspection. In addition, the obtained electrical parameters from SC-EL can reflect the reverse leakage current (I s ) level of the LED epitaxial wafer. The proposed SC-EL inspection can ensure high inspection accuracy without causing damage to the LED epitaxial wafer, which holds promising application in LED technology.

Investigation of the Dislocation Behavior of 6- and 8-Inch AlGaN/GaN HEMT Structures with a Thin AlGaN Buffer Layer Grown on Si Substrates

Developing cost-effective methods to synthesize large-size GaN films remains a challenge owing to the high dislocation density during heteroepitaxy. Herein, AlGaN/GaN HEMTs were grown on 6- and 8-inch Si(111) substrates using metal–organic chemical vapor deposition, and their basic properties and dislocation evolution characteristics were investigated thoroughly. With the insertion of a 100 nm thin AlGaN buffer layer, bow–warp analysis of the epitaxial wafers revealed excellent stress control for both the 6- and 8-inch wafers. HR-XRD and AFM analyses validated the high crystal quality and step-flow growth mode of GaN. Further, Hall measurements demonstrated the superior transport performance of AlGaN/GaN heterostructures. It is worth noting that dislocations tended to annihilate in the AlN nucleation layer, the thin AlGaN buffer layer, and the GaN buffer layer in the initial thickness range of 200–300 nm, which was indicated by ADF-STEM. To be specific, the heterointerfaces exhibited a significant effect on the annihilation of c-type (b = <0001>) dislocations, which led to the formation of dislocation loops. The thin inserted layers within the AlGaN buffer layer played a key role in promoting the annihilation of c-type dislocations, while they exerted less influence on a-type (b = 1/3<112¯0>) and (a+c)-type (b = 1/3<112¯3>) dislocations. Within an initial thickness of 200–300 nm in the GaN buffer layer, a-type and (a+c)-type dislocations underwent strong interactions, leading to considerable dislocation annihilation. In addition, the EELS results suggested that the V-shaped pits in the AlN nucleation layer were filled with the AlGaN thin layer with a low Al content.

A Comparative Study of Methods for Calculating the Dislocation Density in GaN-on-Si Epitaxial Wafers.

A series of characterization methods involving high-resolution X-ray diffraction (HR-XRD), electron channel contrast imaging (ECCI), cathodoluminescence microscopy (CL), and atomic force microscopy (AFM) were applied to calculate the dislocation density of GaN-on-Si epitaxial wafers, and their performance was analyzed and evaluated. The ECCI technique, owing to its high lateral resolution, reveals dislocation distributions on material surfaces, which can visually characterize the dislocation density. While the CL technique is effective for low-density dislocations, it is difficult to accurately identify the number of dislocation clusters in CL images as the density increases. The AFM technique analyzes surface dislocation characteristics by detecting surface pits caused by dislocations, which are easily affected by sample and probe conditions. A prevalent method for assessing the crystal quality of GaN is the rocking curve of HR-XRD (ω-scan), which calculates the dislocation density based on the FWHM value of the curves. By comparing the above four dislocation characterization methods, the advantages and limitations of each method are clarified, which also verifies the applicability of DB=β29b2 for GaN-on-Si epitaxial wafers. This provides an important reference value for dislocation characterization in GaN-on-Si materials. The accuracy evaluation of dislocation density can truly and reliably reflect crystal quality, which is conducive to further optimization. Furthermore, this study can also be applied to other heterogeneous or homogeneous epitaxial materials.

High-Quality 4H-SiC Homogeneous Epitaxy via Homemade Horizontal Hot-Wall Reactor

In this paper, using a self-developed silicon carbide epitaxial reactor, we obtained high-quality 6-inch epitaxial wafers with doping concentration uniformity less than 2%, thickness uniformity less than 1% and roughness less than 0.2 nm on domestic substrates, which meets the application requirements of high-quality Schottky Barrier Diode (SBD) and Metal–Oxide–Semiconductor Field-Effect Transistor (MOSFET) devices. We found that increasing the carrier gas flow rate can minimize source gas depletion and optimize the doping uniformity of the 6-inch epitaxial wafer from over 5% to less than 2%. Moreover, reducing the C/Si ratio significantly can suppress the “two-dimensional nucleation growth mode” and improve the wafer surface roughness Ra from 1.82 nm to 0.16 nm.

Studying the suppression of quantum well intermixing in primary epitaxial wafers via oxygen ion bombardment

Studying the suppression of quantum well intermixing in primary epitaxial wafers via oxygen ion bombardment

Machine learning models in the process of metal organic chemical vapor deposition epitaxial manufacturing of Gallium Arsenide

Metal–organic chemical vapor deposition (MOCVD) is a vapor-phase epitaxial growth technique commonly used in industry and academia to manufacture high-quality Gallium Arsenide (GaAs) compound semiconductor materials. In the actual industrial GaAs MOCVD epitaxial production process, a large amount of process parameters, sensor data, epitaxial wafer testing data, etc. are generated. These epitaxial-growth big data have large sample size and high noise, making data mining increasingly difficult. Nevertheless, this indicates that these data contain abundant valuable information. Therefore, this study proposes a machine learning–based GaAs MOCVD growth model. By analyzing the GaAs epitaxial growth data generated during MOCVD of GaAs, a machine learning model is established to predict the optimal production process for epitaxial growth. By mining the relationship between variables and developing a predictive model for assessing the performance of epitaxial materials, important guidance can be provided for process parameter tuning of GaAs epitaxial growth, considerably reducing debugging costs and further improving the intelligence level of GaAs MOCVD epitaxial growth.

Investigation of Hydrogen Flux Influence on InGaP Layer and Device Uniformity

In this study, we conduct a comprehensive examination of the influence of hydrogen (H2) carrier gas flux on the uniformity of epitaxial layers, specifically focusing on the InGaP single layer and the full structure of the InGaP/GaAs heterojunction bipolar transistor (HBT). The results show that an elevated flux of H2 carrier gas markedly facilitates the stabilization of layer uniformity. Optimal uniformity in epitaxial wafers is achievable at a suitable carrier gas flux. Furthermore, this study reveals a significant correlation between the uniformity of the InGaP single layer and the overall uniformity of HBT structures, indicating a consequential interdependence.

Ammonia detection based on Pd/Rh-GaN and recognition of disease markers of nitrogen compounds assistant by deep learning

Bimetallic has received a lot of attention due to its excellent catalytic performance. Herein, bimetallic nanofilms were successfully modified on GaN epitaxial wafer by a co-reduction method in polyol solution, and different concentrations of Pd/Rh-GaN were obtained. Meanwhile, the morphology and structure of Pd/Rh-GaN were subjected to a series of measurements, and the gas sensors modified with bimetallic modification were also studied for gas sensitivity. The results of the gas-sensitive properties show that the Pd/Rh-GaN-0.25 sensor has outstanding gas-sensing performance with the highest sensitivity, the lowest limit of detection, and the fastest response/recovery time. In addition, we extended other bimetallic nanoparticles to Pd/Ru and Pt/Ru, and deep learning was combined with the sensor array to recognize three markers of nitrogen compounds (NH3, NO2, TMA) in Exhaled breath, achieving high precision recognition with up to 96 % accuracy. This work offers a new approach for the design and preparation of gas sensors for early warning of chronic kidney disease.

Influence of Carbon Source on the Buffer Layer for 4H-SiC Homoepitaxial Growth.

In this study, we systematically explore the impact of C/Si ratio, pre-carbonization time, H2 etching time, and growth pressure on the buffer layer and subsequent epitaxial layer of 6-inch 4H-SiC wafers. Our findings indicate that the buffer layer's C/Si ratio and growth pressure significantly influence the overall quality of the epitaxial wafer. Specifically, an optimal C/Si ratio of 0.5 and a growth pressure of 70 Torr yield higher-quality epitaxial layers. Additionally, the pre-carbonization time and H2 etching time primarily affect the uniformity and surface quality of the epitaxial wafer, with a pre-carbonization time of 3 s and an H2 etching time of 3 min found to enhance the surface quality of the epitaxial layer.

Influence of Growth Process on Suppression of Surface Morphological Defects in 4H-SiC Homoepitaxial Layers.

To address surface morphological defects that have a destructive effect on the epitaxial wafer from the aspect of 4H-SiC epitaxial growth, this study thoroughly examined many key factors that affect the density of defects in 4H-SiC epitaxial wafer, including the ratio of carbon to silicon, growth time, application of a buffer layer, hydrogen etching and other process parameters. Through systematic experimental verification and data analysis, it was verified that when the carbon-silicon ratio was accurately controlled at 0.72, the density of defects in the epitaxial wafer was the lowest, and its surface flatness showed the best state. In addition, it was found that the growth of the buffer layer under specific conditions could effectively reduce defects, especially surface morphology defects. This provides a new idea and method for improving the surface quality of epitaxial wafers. At the same time, we also studied the influence of hydrogen etching on the quality of epitaxial wafers. The experimental results show that proper hydrogen etching can optimize surface quality, but excessive etching may lead to the exposure of substrate defects. Therefore, it is necessary to carefully control the conditions of hydrogen etching in practical applications to avoid adverse effects. These findings have important guiding significance for optimizing the quality of epitaxial wafers.

Light Emission Characteristics in Nitride Semiconductor Nanowires Fabricated by Top‐down Method

Nanophotonic devices made from nitride semiconductors are promising for various applications, especially those utilizing ultraviolet‐visible light with low‐power consumption and high driving speed. Herein, nanowire structures are fabricated from a light‐emitting diode epitaxial wafer and demonstrates the effectiveness of wet etching in top‐down fabrication. Spontaneous emission from active layers and unanticipated lasing derived from a GaN layer in a single nanowire are observed by microphotoluminescence measurement. Lastly, the lasing mode through a 3D simulation of the eigenmodes in this nanowire structure is clarified.

Optimization of bulk microdefect performance in epitaxial silicon wafer

Bulk microdefects (BMDs) in epitaxial silicon wafers are pivotal for advanced node integrated circuits, offering enhanced mechanical strength and metal gettering capabilities. This study introduces two heat treatment procedures to optimize BMD density and radial uniformity in lightly doped wafers, addressing the challenges associated with large-diameter crystal growth and the thermal budget constraints of advanced node processes. We demonstrate that Rapid Thermal Annealing (RTA) at temperatures exceeding 1175 °C significantly improves BMD uniformity. A post-RTA stabilization step, when performed prior to epitaxial growth, enhances BMD density by retaining nuclei generated by RTA. Conversely, when the RTA with stabilization step follows epitaxial growth, a higher BMD density and larger BMD size are achieved. Light Scattering Tomography (LST) analysis confirms the optimal conditions for these treatments. The findings contribute to the semiconductor industry by optimizing wafer properties for high-performance ICs.

Research on the Influence of Carbon Sources and Buffer Layers on the Homogeneous Epitaxial Growth of 4H-SiC.

In this study, a 4H-SiC homoepitaxial layer was grown on a 150 mm 4° off-axis substrate using a horizontal hot wall chemical vapor deposition reactor. Comparing C3H8 and C2H4 as C sources, the sample grown with C2H4 exhibited a slower growth rate and lower doping concentration, but superior uniformity and surface roughness compared to the C3H8-grown sample. Hence, C2H4 is deemed more suitable for commercial epitaxial wafer growth. Increasing growth pressure led to decreased growth rate, worsened thickness uniformity, reduced doping concentration, deteriorated uniformity, and initially improved and then worsened surface roughness. Optimal growth quality was observed at a lower growth pressure of 40 Torr. Furthermore, the impact of buffer layer growth on epitaxial quality varied significantly based on different C/Si ratios, emphasizing the importance of selecting the appropriate conditions for subsequent device manufacturing.

Epitaxial silicon transition zone measurements by spreading resistance profiling and Fourier transform infrared reflectometry

AbstractSilicon epitaxy is an essential building block in the manufacturing of complementary metal‐oxide semiconductor (CMOS) devices. Accurate determination of epitaxial layer thickness is indispensable for a uniform and reproducible process. In this paper, we compare thickness values of the transition zone (TZ) in silicon epitaxial wafers obtained by two of Semilab's production‐compatible electrical and optical characterization techniques: Fourier‐transform infrared (FTIR) reflectometry and spreading resistance profiling (SRP). We demonstrate a high correlation between TZ thicknesses obtained from the optical modeling of FTIR reflectance spectra and SRP profiles. The dependence of TZ thickness change on the high‐temperature annealing steps is also examined. FTIR reflectometry thus offers a quick, contactless alternative for obtaining structural parameters of an epitaxial layer, and these values can be well matched to those given by SRP.