Cut Wafer Research Articles

Ensemble Meta-Learning-Based Robust Chipping Prediction for Wafer Dicing

Our previous study utilized importance analysis, random forest, and Barnes–Hut t-SNE dimensionality reduction to analyze critical dicing parameters and used bidirectional long short-term memory (BLSTM) to predict wafer chipping occurrence successfully in a single dicing machine. However, each dicing machine of the same type may produce unevenly distributed non-IID dicing signals, which may lead to the undesirable result that a pre-trained model trained by dicing machine #1 could not effectively predict chipping occurrence in dicing machine #2. Therefore, regarding the model robustness, this study introduces an ensemble meta-learning-based model that can evaluate many dicing machines for chipping prediction with high stability and accuracy. This approach constructs several base learners, such as the hidden Markov model (HMM), the variational autoencoder (VAE), and BLSTM, to form an ensemble learning. We use model-agnostic meta-learning (MAML) to train and test the ensemble learning model by several prediction tasks from machine #1. After MAML learning, we call the trained model a meta learner. Then, we successfully apply a retrieved data set from machine #2 to the meta learner for training and testing wafer chipping occurrence in this machine. As a result, our contribution to the robust chipping prediction on cross-machines can improve the yield of wafer dicing with a prediction accuracy of 93.21%, preserve the practical wearing of dicing kerfs, and significantly cut wafer manufacturing costs.

웨이퍼 핸들링을 위한 collet의 외관 비전 검사 장치 개발

In semiconductor manufacturing, small and precise tools such as collets are used during the assembly process to control and improve product quality. Monitoring the quality of the collet, such as its shape, size, and hole, is crucial for ensuring high reliability when picking up a cut wafer during the semiconductor packaging process. In this study, we propose a defect detection algorithm using image processing techniques. The application was implemented in a visual C++ environment, which enables motion control, image acquisition control, and the execution of image processing algorithms. The test and analysis of the collet inspection system yielded a defect detection rate of 99.3%.

Structural modification of diamond-wire-cut multicrystalline Si by Cu-catalyzed chemical etching for surface structuring

During the multicrystalline Si (mc-Si) solar cell production, metal-catalyzed chemical etching (MCCE) is an effective method for constructing texture surface on diamond wire sawing (DWS) cut mc-Si wafer. A dense Cu film was formed on silicon surface by Cu-MCCE, significantly restricting the etching process. In this work, FeCl3, MnO2 and H2O2, were selected to modify the structure of texture surface by one-step Cu-MCCE method. A wedge-shaped structure was formed when the concentration of FeCl3 and etching time are 0.2 mol/L and 15 min, and its reflectivity is 22.9%. A composite structure with shallow pits and nanopores was formed when the amount of MnO2 and etching time are 50 g/L and 20 min, and its reflectivity is 23.2%. An inverted pyramid structure was formed when the concentration of H2O2 and etching time are 3 mol/L and 15 min, and its reflectivity is 18.2%. The best conversion efficiency (η) of solar cell obtained is 19.0%, and, the depth-to-width ratio of texture structure is 1.33.

Studies on Schottky Barrier Diodes Fabricated using Single‐Crystal Wafers of β‐Ga2O3 Grown by the Optical Floating Zone Technique

β‐Ga2O3 is one of the most promising wide‐bandgap materials for optoelectronic applications as well as a conducting substrate for GaN‐based device technologies. Single crystals of undoped β‐Ga2O3 are grown by the optical floating zone technique utilizing compressed dry air as growth atmosphere. The properties of β‐Ga2O3 are highly anisotropic. Optimization of the processing recipe for wafers along different orientations suitable for device development is conducted. Structural, optical, and electrical properties of the wafers are determined. Efforts are made to fabricate Schottky diodes based on Pt/Ti/Au–β‐Ga2O3–Ti/Au device structures. Devices are fabricated on (−201) cut wafers. The device characteristics are discussed in detail.

Ar gas cluster ion beam assisted XPS study of LiNbO3 Z cut surface

XPS combined with profiling by Ar2500+ gas cluster ion beam (GCIB) sputtering has been used to obtain new refined data on the polarization and processing-dependent Li/Nb ratio for the surface of a LiNbO3 single crystal. The most suitable GCIB parameters (normal incidence, 10 keV energy) and irradiation dose (less than or equal to 2.7 × 1016 ions/cm2) have been determined and employed to perform high resolution depth profile analysis without cluster ion-induced Li/Nb changes. The Li/Nb profiles obtained for Z cut wafers with positive and negative faces revealed the presence of two distinct regions. The initial 0.3 nm-thick region had a low Li/Nb ratio due to machining and leaching and did not show a dependence on the polarity direction. The next profile region had a constant Li/Nb ratio, which depended on the crystal polarity. The Li/Nb ratio for the Z+ surface of a wafer and a cleaved sample exceeded the values for the Z– surface of a wafer by 1.2 times. This result confirms theoretical predictions of a different stoichiometry for Z+ and Z– terminations and indicates the ability of GCIB to reach the surface condition that is close to the perfect termination.

Single crystal growth of small-angle-grain-boundary-free Mg2Si via vertical Bridgman method

Mg2Si single crystal was grown via vertical Bridgman method using pyrolytic boron nitride (pBN) crucibles coated with boron nitride (BN). No stress was imposed from the liquid/ solid interface (molten Mg2Si/ BN-coated crucible surface) during the solidification leading to a small angle grain boundary free crystal. As a result of X-ray rocking curve measurement of the cut wafer, in-plane high crystallinity was confirmed and a sharp single peak with FWHM of 44–51 arcsec was measured. The typical electron concentration of grown crystal was 6.6 × 1017 cm−3 and Hall mobility was 280 cm2/Vs. The high electron concentration was attributed to the contamination of crystal by boron from BN coating source, confirmed by glow discharge mass spectroscopic (GDMS) analysis.

Study of the influence of treatment on the strength of undoped indium antimonide single-crystal plates

The method of plane-transverse bending was used to measure the strength of thin single-crystal plates of undoped InSb with a crystallographic orientation of (100). It was found that the strength of the plates (thickness ≤ 800 μm) depends on their processing. Using a full processing cycle (grinding and chemical polishing) allows to increase the strength of InSb plates by 2 times (from 3.0 to 6.4 kg/mm2). It is shown that the dependence of strength on processing for wafers with (100) orientation is similar to this dependence for wafers (111), while the strength of wafers (111) is 2 times higher. The contact profilometry method was used to measure the roughness of thin plates, which also passed successive processing steps. It was found that during a full cycle of processing, the roughness of InSb plates decreases (Ra from 0.6 to 0.04 μm), leading to a general smoothing of the surface roughness. The strength and roughness of the (100) InSb and GaAs wafers are compared. It was found that the strength of GaAs cut wafers is 2 times higher than the strength of InSb cut wafers and slightly increases after a full cycle of their processing. It was shown that the roughness of GaAs and InSb plates after a full cycle of surface treatment is significantly reduced: 10 times for InSb due to overall surface leveling and 3 times for GaAs (Rz from 2.4 to 0.8 μm) due to a decrease in the peak component. Conducting a full cycle of processing InSb plates can increase their strength by removing broken layers by sequential operations and reducing the risk of mechanical damage.

Phase Transformation in Germanium-on-Insulator (GeOI) Films Using Raman Spectroscopy and Nanoindentation

Germanium-on-insulator (GeOI) films fabricated using the SMART CUT wafer bonding and film exfoliation technology were investigated for the mechanical properties and induced phase transformations by using nanoindentation and Raman spectroscopy experiments. The hardness and modulus results of the GeOI films are significantly different from the published SOI literature and bulk germanium results obtained by Liu et al., 2020 [1] and SOI films results obtained by Miller et al., 2007 [2]. From our measured hardness results of 8 to 10 GPa for very thin single crystal Ge(100) films compared to 13.1 GPa for Bulk Ge (100), one can conclude that the thinning of crystalline Ge films leads to a considerable softening of the crystalline Ge resulting in less brittle robust films. Similarly, our measured modulus of 130 to 140 GPa for thin Ge (100) films compared to the reported bulk Ge (100) value of 157 GPa corroborates these research findings. The GeOI films are softer and more flexible as compared to bulk Ge hardness and stiffness properties. The Raman spectroscopy of the spherical indents indicate bands of metastable Ge phases @ 220 cm-1, 195 cm-1 and 184 cm-1 wavenumbers. Our results demonstrate that a spherical indenter impacted a wider area of contact and produced GeOI indented surfaces free of cracks and fracture. The spherical indenter tip kept the Ge top layer intact when compared to the Berkovich indenter tip during penetration. In contrast, the Berkovich indenter tip developed excessive fracture that resulted in displacing the Ge top layer sideways and exposed the Si substrate underneath revealing Raman spectra bands of metastable Si phases @ 350 cm-1, 399 cm-1 and 430 cm-1.Apart from the well documented electrical advantages of GeOI, the reported research on the nanomechanical properties reveals considerable softening and flexibility of the very thin exfoliated single crystal Ge films that promise added benefits and further implications for enhancing potential device application of GeOI wafers for process integration.1.] N. Liu, X-J Yang, Z. Yu, and L. Zhao, Trans. Nonferrous Met. Soc. China, 30, 181 (2020).2.] N. Miller, K. Tapily, H. Baumgart, G.K. Celler, F. Brunier, and A.A. Elmustafa, Mater. Res. Soc. Symp. Proc. Vol. 1021 © 2007 Materials Research Society, 1021-HH05-24. Boston, Massachusetts. (2007).

Effect of Microstructures With Different Depth-to-Width Ratios on Surface Reflectance and Si Solar Cell Performance

Metal-catalyzed chemical etching (MCCE) is an effective method for making texture surface on diamond wire saw (DWS) cut mc-Si wafer. In this work, microstructures with different depth-to-width ratios were obtained by MCCE on the surface of DWS cut mc-Si wafers. Simultaneously, the influence of etching time and the concentration of AgNO3 on etching depth, surface reflectance performance, and effect of reaming on the solar cell performance were studied. In total, 12 microstructures with different depth-to-width ratios ranging from 0.63 to 5.31 were prepared. The etching rate increased with the increase in concentration of AgNO3 and etching time. Moreover, the depth-to-width ratio significantly affected the reflectivity of silicon wafers. The relationship between them can be expressed by the fitting exponential function: y = 12.41 × x −0.733. The reflectivity obtained in the experiment ranged from 3.71% to 18.15%. After reaming, the performance of the mc-Si solar cells has been significantly improved, and η could reach up to 18.53%.

Challenges in Processing Diamond Wire Cut and Black Silicon Wafers in Large-Scale Manufacturing of High Efficiency Solar Cells

Texturing of diamond wire cut wafers using a standard wafer etch process chemistry has always been a challenge in solar cell manufacturing industry. This is due to the change in surface morphology of diamond wire cut wafers and the abundant presence of amorphous silicon content, which are introduced from wafer manufacturing industry during sawing of multi-crystalline wafers using ultra-thin diamond wires. The industry standard texturing process for multi-crystalline wafers cannot deliver a homogeneous etched silicon surface, thereby requiring an additive compound, which acts like a surfactant in the acidic etch bath to enhance the texturing quality on diamond wire cut wafers. Black silicon wafers on the other hand require completely a different process chemistry and are normally textured using a metal catalyst assisted etching technique or by plasma reactive ion etching technique. In this paper, various challenges associated with cell processing steps using diamond wire cut and black silicon wafers along with cell electrical results using each of these wafer types are discussed.

The Maximum Positive Curvature Recognition Method to Determine Etch Profiles in Wet Etching of Quartz on AT and BT Cuts

This paper presents a method to quickly determine the transient and stable profiles of trenches, cavities, and mesas formed by anisotropic wet chemical etching on AT and BT cut quartz wafers. Since most quartz orientations have low etch rates and both AT and BT cuts have no trigonal symmetry (unlike the Z cut), it is typically difficult to explain which sidewalls will appear on a given trench for a particular mask alignment on these cuts. By considering the complete etch rate distribution obtained from an etched quartz hemisphere we show that a maximum positive curvature recognition method can be used in order to determine a small number of key orientations, which will directly appear as the transient and stable sidewalls in the experimental trench profiles on both the AT and BT cuts. Similarly, the proposed method accurately explains the formation of complex facets on square cavities as well as on the top, middle and bottom regions of micro-needle arrays etched on the AT and BT cuts. This indicates that the etch profiles of any cut of the trigonal crystal can be determined by using the location of the proposed key orientations. [2017-0254]

Experiment study on electroplated diamond wire saw slicing single-crystal silicon

This paper conducted the slicing experiments of single-crystal silicon using a reciprocating electroplated diamond wire saw. The machined wafer topography and wire wear were observed by using scanning electron microscope (SEM). The influences of process parameters and cutting fluids on single-crystal silicon wafer surface roughness (SR), subsurface micro-crack damage (SSD) depth, total thickness variation (TTV) and warp were investigated. The bonded interface sectioning technique was used to examine the cut wafers SSD depth. Study results show that a higher wire speed and lower ingot feed speed can produce lower wafer SR and SSD; the lower warp of wafer needs lower wire speed and ingot feed speed; and low wafer TTV can be obtained by an appropriate matching relationship between wire speed and ingot feed speed. The synthetic cutting fluid has a better total effect to improve the wafer quality. The pulled-out of diamond abrasives is the main wear form of wire, which indicates that more research on improving the abrasives retaining strength on wire surface should be investigated in fixed-abrasive wire manufacturing process, in order to improve the wire life and wire saw machining process.

Nonstructural acousto-injection luminescence in metalized lithium niobate

We report the observations of nonstructural acousto-injection luminescence (NAIL) from tantalized LiNbO3 wafers. The samples under study are the X cut or Y cut wafers with the silver paste electrodes on opposite surfaces. The thickness is 1 to 2 mm and other linear dimensions are in the range of 2 to 25 mm. Experiments are done at room temperature in the MHz-frequency range. Mainly the fundamental shear ultrasound modes are excited in the samples. Experimentally are measured the spectra of NAIL, photo-luminescence spectra, acousto-electric properties, X Ray diffraction under NAIL. The NAIL and other effects appear above certain threshold amplitude of the acoustical strain that is about 10E-5. The involvement of the microstructural non-uniformity in the effects observed is experimentally identified by the photo-luminescence of point defects taken from different micro-regions of the samples. The data are explained in terms of the considerable acoustic stresses and piezoelectric fields that are capable injecting charge carriers from the metal contacts into a crystal.

Argon plasma inductively coupled plasma reactive ion etching study for smooth sidewall thin film lithium niobate waveguide application

Lithium Niobate (LN) exhibits unique physical properties such as remarkable electro-optical coefficients and it is thus an excellent material for a wide range of fields like optic communications, lasers, nonlinear optical applications, electric field optical sensors etc. In order to further enhance the optical device performance and to be competitive with silicon photonics, sub-micrometric thickness lithium niobate films are crucial. A big step has been achieved with the development of LN thin films by using smart cut technology and wafer bonding and these films are nowadays available in the market. However, it is a challenge to obtain the requirements of the high quality thin LN film waveguide. In this letter, we show smooth ridge waveguides fabricated on 700nm thickness thin film lithium niobate (TFLN). The fabrication has been done by developing and optimizing three steps of the technological process, the mask fabrication, the plasma etching, and a final cleaning wet etching step in order to remove the lithium niobate redeposition on the side walls. We have obtained single mode propagation with light overall losses of only 5dB/cm.

Nanomechanical Properties of Standard and Strained SOI Films Fabricated by Wafer Bonding and Layer Splitting

High demands for improved performance, better power consumption, and miniaturized devices prompted the migration to SOI technology. SOI fabrication process helps in achieving greater performance and offers less power consumption compared to the Bulk Si Process. In SOI fabrication technology, transistors are built on a Si layer grown on SiO2 (145 nm) insulating layer. The SOI is fabricated using the SMART CUT wafer bonding and layer splitting technology. The strained Si on insulator (sSOI) technology has recently been developed for high mobility channel devices [1-3]. Biaxial tensile strained Si layers grown on SiGe have attracted great attention for high performance CMOS devices. Strain engineering for mobility enhancement is an attractive option to improve CMOS device performance by introducing lattice strain into the Si channel. Epitaxial Si1-xGex and most recently Ge-free bi-axially strained sSOI are among the leading candidates for higher mobility channel material.In this paper, we have analyzed how the fabrication of very thin single crystal Si device films by wafer bonding and SMART CUTTM film exfoliation technique is affecting their nanomechanical properties in comparison to bulk Si. Although both the handle wafer and the bonded thin device layer are single crystal Si, it turns out that their nanomechanical properties differ considerably. Using nanoindentation, we measured the properties of (SOI-88nm) and bi-axially tensile strained Silicon-on-Insulator (sSOI 15, 70, and 100 nm) and benchmarked the results against bulk Si. The results of Figure 1 indicate that the hardness of these films vary significantly. The field emission scanning electron microscopy (FE-SEM) image of Figure 2 represents an sSOI film of 100 nm thick. References C. Mazure and A.J. Auberton-Herve, Proc. of 35th European Solid-State Device Research Conf. ESSDERC, p. 29 (2005)T. A. Langdo, M. T. Currie, Z.-Y. Cheng, J.G. Fiorenza, M. Erdtmann, G. Braithwaite, C.W. Leitz, C.J. Vineis, J. A. Carlin, A. Lochtefeld, M. T. Bulsara, I. Lauer, D.A. Antoniadis, M. Somerville, Solid-State Electronics, 48 , 1357 (2004).I. Cayrefourcq, A. Boussagol and G. Celler, in SiGe and Ge: Materials, Processing, and Devices , ECS Trans. 3, (7), 399 (2006)

New Laser Cutting Technology of Sapphire Wafers on Crystals

The work is devoted to development of new cutting technology of semiconductor wafers on crystals by a method of laser controlled thermocracking. There are results of numerical and experimental researches of the cut sapphire wafers on crystals for light-emitting diodes by means of two lasers (СО2 laser and UV laser).

Mechanical Strength of Silicon Wafers Cut by Loose Abrasive Slurry and Fixed Abrasive Diamond Wire Sawing

AbstractThis paper reports on the mechanical strength of polycrystalline silicon wafers cut by loose abrasive slurry and fixed abrasive diamond wire sawing processes. Four line bending and biaxial flexure tests are used to evaluate the fracture strength of the wafers. Fracture strength of the wafers depends on the location, size, and orientation of microcracks in the silicon wafer and the distribution and magnitude of applied stresses. Measurement of microcracks at the wafer edge and center shows that edge cracks are typically larger than center cracks. Fixed abrasive diamond wire sawn wafers are found to have a higher crack density but smaller average crack length. Wafer fracture in four line bending is found to be primarily due to the propagation of edge cracks while center cracks are found to be the primary cause of wafer failure in biaxial flexure tests. Fracture mechanics based analyses demonstrate that crack orientation plays a significant role in four line bending, but not in biaxial flexure. Correlations of the wafer fracture strength and critical crack length agree well with microcrack measurements. The fracture strength of diamond cut wafers is found to be comparable or superior to the strength of slurry cut wafers.

Effects of CMP Pad Conditioner Properties and Performance on Polishing Pad, Process and Wafer Removal Rate

The focus of this work is CMP pad conditioners and the impact of diamond shape, size, density and protrusion on pad cut rate, pad surface roughness and wafer removal rate. Conditioner properties such as diamond shape, density and protrusion were found to directly impact the pad cut rate and wafer removal rate. Conditioners with high variation in diamond protrusion and uneven diamond shapes exhibited high drop in pad cut rate and wafer removal rate over the test period. Conditioners with high and very aggressive diamonds led to uneven pad conditioning creating step like features on the pad. Diamonds show wearing off sharp edges and chipping of edges due to mechanical forces exerted on them during conditioning. Also diamonds on some of the tested conditioners were found to be missing or sheared off during conditioning due to the mechanical stress and weak bonding process.

Development of CMP Conditioner for Sub-50 nm Technology Nodes

Several key conditioner design parameters including diamond size, shape, and concentration were selected and optimized to tune wafer removal rate and pad cut rate for various types of CMP pads. Among various diamond types, two types of diamonds were selected for conditioner applications and numerous conditioners were manufactured to generate pad surface roughness on a regular polyurethane porous pad, hard porous pad, and hard solid pad. Furthermore pad cut rate stability curves and wafer removal rate were generated to correlate conditioner design with pad surface texture and wafer removal rate and defects. Experimental results revealed the effect of conditioner design on pad surface roughness was significant and wafer removal rate varied significantly depending on a specific set of conditioner and pad.

Comparison of Laser Chemical Processing and LaserMicroJet for structuring and cutting silicon substrates

This paper deals with the development of a new cutting method for thin silicon solar wafers with liquid-jet-guided lasers (LaserMicroJet®, LMJ, and Laser Chemical Processing, LCP). Several laser systems with different wavelengths were tested to find the optimum laser system and processing parameters in terms of efficient material removal and deep laser cutting. Water and potassium hydroxide were used as carrier liquids to enhance laser ablation. The ablation efficiency was defined as a target parameter and experimentally determined by performing single laser grooves. It is demonstrated that the ablation process of LMJ is mainly affected by silicon melting and then removing by the liquid-jet momentum for single laser grooves. Best result for deep laser grooves is achieved if evaporation dominates the ablation process. Better surface quality referred to laser-induced crystalline damage is presented for a cut wafer with LMJ in comparison to a standard multiwire slurry saw. This shows a great potential of wafering with liquid-jet-guided lasers although no optimal liquid media was used.