Thin Wafers Research Articles

Si Characterization on Thinning and Singulation Processes for 2.5/3D HBM Package Integration

As stacking technologies, such as 2.5D and 3D packages, continue to accelerate in advanced semiconductor components, the singulation and thinning of Si wafers are becoming increasingly critical. Despite their importance in producing thinner and more reliable Si chips, achieving high reliability remains a challenge, and comprehensive research on the effects of these processing techniques on Si chip integrity is lacking. In this study, the impacts of wafer thinning and singulation on the fracture strength of Si wafers were systematically compared. Three different grinding processes, namely fine grinding, poly-grinding, and polishing, were used for thinning, and the resulting surface morphology and roughness were analyzed using scanning electron microscopy and an interferometer. In addition, the residual mechanical stress on the wafer surface was measured using Raman spectroscopy. The fracture strength of Si wafers and chips was assessed through three-point bending tests. Singulation, including blade dicing, laser dicing, and stealth dicing, was evaluated for its impact on fracture strength. Among these processes, polishing for wafer thinning exhibited the lowest full-width half maximum and intensity ratio of Raman shifts (I480/I520), indicating minimal residual stress and surface defects. Consequently, Si wafers and chips processed through polishing demonstrated the highest fracture strength. Moreover, the 60 µm thick Si wafers and chips showed the highest fracture strength compared with those with thicknesses of 90 and 120 µm, possibly because of the increased flexibility, which mitigates stress. Among the singulation methods, stealth dicing yielded the highest fracture strength, outperforming blade and laser dicing. The combination of wafer thinning via polishing and singulation via stealth dicing presents an optimal solution for producing highly reliable Si chips for 2.5D and 3D packaging. These findings may be valuable in selecting optimal processing technologies for high-reliability Si chip production in industrial settings.

Fracture strength analysis of large-size and thin photovoltaic monocrystalline silicon wafers

Diamond wire slicing technology is the main method to manufacture the substrate of the monocrystalline silicon-based solar cells. With the development of technology, the size and thickness of monocrystalline silicon wafer are respectively getting larger and thinner, which cause an increase in silicon wafer fracture probability during wafer processing and post-processing. And the change of the sawing speed, saw wire diameter and abrasive size also affect the wafer’s surface characteristics, thereby affect its fracture strength. In this paper, monocrystalline silicon wafer with large size of 210 mm × 210 mm was taken as the research object, 4-point bending test was carried out on each series of silicon wafers. The load–displacement curves during bending test were collected, and the fracture stress values were calculated by finite element method. The characteristic fracture strength and Weibull modulus of each series of silicon wafers were obtained through the statistical analysis of the data using Weibull distribution function. The effect of the silicon wafer thickness, the position of the silicon wafer in the silicon brick (usage time of the saw wire varies), and the bending test direction on the fracture characteristics was analyzed. The results showed that the increase of thickness increase the characteristic fracture strength of silicon wafer. The characteristic fracture strength of the front wafers (sawn by the fresh wire) is the smallest, while the characteristic fracture strength of the middle wafers and the rear wafers (sawn by the worn wire) are similar. The characteristic fracture strength of bending in the direction of perpendicular to the saw marks is 2–3 times that of bending in the direction of parallel to the saw marks. The reason of the difference of characteristic fracture strength was analyzed based on the surface morphology, roughness, and the saw marks of silicon wafer. In this paper, the fracture characteristics of large size monocrystalline silicon wafer are studied to provide fracture data support for industry production. The mechanism and main effect factors of silicon wafer fracture are revealed, which provides directions for improving the sawing quality and reducing the fracture probability during wafer production process and post-processing.

Gelfoam Granuloma Mimicking Brain Abscess Following Decompressive Craniotomy

AbstractThe use of adjuvants in brain surgery has increased. Artificial adjuncts are being used in neurosurgery frequently. These foreign materials may result in a foreign body reaction inside the normal brain tissue surrounding the areas of pathology. This material may mimic an abscess or tumor in their presentation and masquerade the magnetic resonance (MR) or computed tomography (CT) image as recurrence, abscess, or granuloma. We present a case of a 42-year-old woman with a history of hypertensive basal ganglia bleeding who was operated on in an emergency. Decompressive craniectomy and clot evacuation were carried out. A thin layer of Gelfoam was applied in the operated area. After 4 weeks, she was planned for cranioplasty where an oval soft to firm yellowish lesion was found at the site of the previous cavity of the evacuated clot, which was sent for biopsy and it was confirmed as a Gelfoam granuloma. Meticulous use of hemostatic agents in the form of small surgical or thin waferlike gelatin sponges should be used intraoperatively. Large-size Gelfoam and artificial agents can lead to foreign body–like granulation tissue formation in normal brain tissue and several complications like hydrocephalous, meningitis, and seizures. Peculiarities in this case include the following: Gelfoam granuloma is a very rare complication following cranial surgery, it was mimicking like an abscess, and the size of Gelfoam used intraoperatively should be a thin wafer coating the raw surface or in the cavity.

Static and dynamic analyses and multi-objective optimization of wafer thinning machine’s design variables

In order to meeting the physical strength, heat dissipation and dimensional requirements of chips, the wafer surface needs to be thinned by wafer thinning machines. In the design of wafer thinning machine, the analysis and optimization of castings is an important and complex issue. In this study, the multi-objective optimization of wafer thinning machine’ s design variables are executed due to static and dynamic analyses. According to the analysis results, the design quality, amplitude and equivalent stress of the casting are optimized. The inner diameter of the ring, the height of the ring, the height of the middle groove, and the height of the groove on both sides are selected as the main design variables of the optimization. The results show that the static deformation of the optimized cast structure is 8% lower than the original structure, the overall mass is 4% lower, the operating frequency is 3.5% lower, higher stability, smaller mass and amplitude are obtained after optimization. The research has a great significance for the wafer thinning machines design, and provides theoretical guidance for the development of other lithography equipments.

Electrical and Structural Properties of Ohmic Contacts of SiC Diodes Fabricated on Thin Wafers

New generations of SiC power devices require to be fabricated on very thin substrates, in order to significantly reduce the series resistance of the device. The role of thinning process on the formation of backside ohmic contact has been investigated in this work. Three different mechanical grinding processes have been adopted, resulting in different amounts of defectivity and surface roughness values. An excimer UV laser has been used to form a Ni-silicide based ohmic contact on the backside of the wafers. The reacted layer has been studied by means of Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD) analyses, as a function of grinding process parameters and laser annealing conditions. The ohmic contact has been evaluated by measuring the Sheet Resistance (Rs) of silicided layers and the Vf at nominal current of Schottky Barrier Diode (SBD) devices, fabricated on 150 mm-diameter 4H-SiC wafers. A strong relationship has been found between the crystal damage, induced by thinning process, and the structural, morphological and electrical properties of silicided ohmic contact, formed by UV laser annealing, revealing that the silicide reaction is moved forward, at fixed annealing conditions, by the increasing of crystal defectivity and surface roughness of SiC.

Study of Prefabricated Crack Propagation on Monocrystalline Silicon Surfaces for Grinding Damage Analysis.

Crack generation and propagation are critical aspects of grinding processes for hard and brittle materials. Despite extensive research, the impact of residual cracks from coarse grinding on the cracks generated during fine grinding remains unexplored. This study aims to bridge this gap by examining the propagation law of existing cracks under indentation using the extended finite element method. The results reveal that prefabricated cracks with depths less than the crack depth produced on an undamaged surface tend to extend further without surpassing the latter. Conversely, deeper prefabricated cracks do not exhibit significant expansion. A novel method combining indentation and prefabricated cracks with fracture strength tests is proposed to determine crack propagation. Silicon wafers with varying damaged surfaces are analyzed, and changes in fracture strength, measured by the ball-on-ring method, are utilized to determine crack propagation. The experimental results confirm the proposed crack evolution law, validated by damage assessments across different grinding processes, which is suitable for crack damage. The findings demonstrate that residual cracks from coarse grinding are negligible in predicting the maximum crack depth during fine grinding. This research provides a crucial foundation for optimizing the wafer thinning process in 3D stacked chip manufacturing, establishing that changes in fracture strength are a reliable indicator of crack propagation feasibility.

Low loss ridge waveguides on the hybrid single crystalline silicon and lithium niobate thin films

The hybridization of silicon (Si) thin film and lithium niobate (LN) thin film with remarkable properties, including the excellent optical properties of LN, excellent electrical properties and mature processing advantages of Si, can provide an important material platform for integrated photonic applications. In this work, a 4-inch single crystalline Si thin film wafer was prepared using wafer bonding, grinding and polishing techniques on LN thin film substrate. The films were characterized by using high-resolution transmission electron microscopy (HRTEM). The interplanar spacings and strain of Si film were calculated by analysis of high-resolution X-ray diffraction (HRXRD). Si ridge straight waveguides were fabricated on the hybrid thin films, and the transmission loss was 1.2 dB/cm. The near-field mode distribution of the waveguide was investigated by combining FDTD (Finite-Difference Time-Domain) simulation and end coupling measurement.

Experimental Research on the Supply of Working Fluid for Fixed Diamond Wire Slicing Based on Ultrasonic Capillary Effect.

Thin wafers and thin wires are beneficial to the photovoltaic industry for reducing costs, increasing efficiency, and reducing the cost of electricity generation. It is a development trend in solar silicon wafer cutting. Thin wire cutting reduces the kerf between silicon wafers to less than 50 μm. Therefore, it is extremely difficult to supply cutting fluid to the cutting area. And this affects cutting performance. This paper proposes the use of the capillary effect produced by ultrasonic waves in fixed diamond wire slicing to improve the cutting fluid supply and reduce wafer adsorption. To explore the rules of ultrasonic capillary action between two plates and guide the industrial applications, the effects of the distance between parallel plates, the distance from the bottom of the parallel plates to the ultrasonic radiation surface, the non-parallelism between the plates, the temperature of the working fluid, the ultrasonic action time, and the type of working fluid on the liquid level rise height were studied. The conclusions can be used to guide the improvement of the supply of working fluid in fixed diamond wire slicing.

The influence of sub-surface damage microstructure on ultra-thin die flexural strength

In the semiconductor industry, where miniaturization is a key driver, mechanical properties of ultra-thin dies are increasingly important research topics. Sub-surface damage (SSD) is a common issue in wafer thinning processes, but there is a lack of research on the relationship between SSD microstructure and ultra-thin die strength. In this study, the influence of SSD microstructure on flexural strength was investigated through three-point bending tests of ultra-thin dies prepared by distinct wafer-thinning methods, coupled with SSD microstructure characterization. Flexural strength was highest for dies dry polished with N pad, intermediate for dies dry polished with M pad, and lowest for dies with fine grinding. We researched SSD microstructure by high-resolution transmitted electron microscope (HRTEM), revealing that it comprises amorphous regions, micro-cracks, and high-density distortion areas. The SSD of the fine grinding samples was thick and intermittent, with observable micro-cracks. Comparatively, the SSD structure from M pad polishing was uniform but thicker, whereas SSD from N pad polishing was thinner but exhibited greater variability. SSD thickness not only influences the average value but also dictates the distribution of flexural strength. This research enhances the understanding of SSD microstructure's impact on ultra-thin die flexural strength, providing valuable insights for optimizing wafer thinning processes to enhance die reliability.

Molecular Dynamics Analysis of Adhesive Forces between Silicon Wafer and Substrate in Microarray Adhesion

With the development of the electronics industry, the requirements for chips are getting higher and higher, and thinner and thinner wafers are needed to meet the processing of chips. In this study, a model of the adhesion state of semiconductor wafers in the stacking–clamping process based on microarray adsorption was established, the composition adhesion was discussed, the microarrays of different materials and pressures were experimentally studied, and a molecular dynamics model was established. The molecular dynamics analysis showed that the adhesion force was only related to the type of atom, and the applied pressure did not change the adhesion force. According to the simulation results, the tangential adhesion between the metal and the wafer is greater than that between the ceramic and the wafer, the adsorption force between the aluminum–magnesium alloy and the silicon wafer is shown in the normal direction, and the repulsion force between other materials and the silicon wafer is shown in the normal direction. During the pressure process, the metal is in the elastic deformation stage between the metal and the wafer, the wafer is plastically deformed in the silicon carbide ceramic and wafer, and the wafer is elastically deformed in the alumina ceramic and wafer. In this paper, the adhesion between the substrate and the wafer is studied, a method of constructing microarrays to enhance adhesion is proposed, and the tangential deformation of the array unit under pressure is studied, which provides theoretical support for increasing the adhesion by constructing microarrays.

Crack Catcher AI – Enabling smart fracture mechanics approaches for damage control of thin silicon cells or wafers

Silicon has been one among a few key technologically important materials especially in our modern world. Silicon, especially in its current most useful forms (thin layers), is a brittle material by nature. Thin silicon cells crack easily during manufacturing assembly. Every crack is a defect in any PV manufacturing lines, and if let to grow/propagate it will lead to reliability and quality issues with time. Nevertheless, the global silicon solar PV industry is aggressively reducing the cost of solar PV systems through cutting down the thickness of silicon solar cells. Cell cracks immediately lower PV module efficiency and can lead to premature aging of the entire module. The “Crack Catcher AI” was our research joint collaboration's entry in the Department of Energy (DOE)'s American-Made Solar Innovation competition in 2022 (Round 6) which later was selected as the national semifinalists and won an award announced by DOE in December 2022. It uses smart stress sensing and smart fracture prediction approaches utilizing fundamental fracture mechanics and big data analytics to reduce crack defects and enhance long-term durability/reliability of PV products/devices. Smart Stress Sensing uses a novel laser-based curvature methodology for fast in-line stress metrology in manufacturing lines. Smart Fracture Prediction uses Artificial Intelligence (AI) for defect control metrology and yield enhancement in PV production lines. It is based on monocrystalline silicon used in solar PV industries, but all scientific principles utilized and technological innovations developed in this article would be applicable as well for single crystal silicon semiconductor wafers.

From Rigid to Flexible: Progress, Challenges and Prospects of Thin c‐Si Solar Energy Devices

AbstractThe increasing adoption of solar energy as a renewable power source marks a significant shift toward clean, sustainable alternatives to conventional energy forms. A notable development in this field is the advancement of thin monocrystalline silicon (c‐Si) solar cells. Characterized by their lightweight, flexible nature, these solar cells promise to transform the renewable energy landscape with enhanced durability, adaptability, and portability. Amidst the growing demand for sustainable energy solutions, refining and evolving thin c‐Si solar cell technologies is crucial. This review comprehensively examines the latest progress in thin c‐Si solar energy conversion device technologies, offering an extensive overview of current methodologies for producing thin c‐Si films, advanced light trapping techniques, surface passivation strategies, and methods for managing thin wafers. It also explores the wide‐ranging applications of thin c‐Si solar cells. Furthermore, this article sheds light on the techno‐economic aspects, highlighting the intertwined challenges of commercializing these innovative cells. Through an in‐depth analysis of the latest advancements, this review serves as a valuable resource for researchers and industry experts, keeping them abreast of current trends and catalyzing further advancements in thin c‐Si solar cell technology.

High-efficiency green machining of single crystal 4H–SiC based on tribo-oxidation

High efficiency, high quality and green machining of single crystal silicon carbide (SiC) is an important issue in the third-generation semiconductor industry. In this paper, a novel machining method for single crystal SiC based on tribo-oxidation is proposed. The formula and preparation process of polysaccharide bonded soft abrasive tool were designed. Dry machining of C-face of 4H–SiC substrate was carried out with the prepared environmentally friendly abrasive tool sample. The material removal mechanism of the proposed machining method was preliminarily analyzed, and the material removal rate, surface roughness and subsurface residual stress were studied. The experimental results show that the maximum material removal rate of 4H–SiC can reach 1.03 μm/min with a corresponding average surface roughness of Sa 0.816 nm. The machined surface has no brittle flaw, and subsurface residual compressive stress exists with a maximum value of 58.9 MPa. The material removal mainly attributed to the active oxidation of SiC surface induced by the friction between alumina abrasives and SiC substrate. The proposed machining method has potential application value in thinning of SiC wafers.

Experimental and numerical study on thin silicon wafer CO2 laser cutting and damage investigation

Experimental and numerical study on thin silicon wafer CO2 laser cutting and damage investigation

Residual stress distribution of silicon wafers machined by rotational grinding based on molecular dynamics

Wafer rotational grinding is widely used to thin silicon wafers and the grinding-induced residual stress distribution is desired to be known. However, it is difficult to obtain it directly by measurement since the variation of residual stress values of different locations tends to be submerged in the fluctuations of measured values. In this study, molecular dynamics was employed to obtain the residual stress states of ground monocrystalline silicon of different crystal directions. The actual cutting directions of the abrasive grains were obtained as the tangential directions of the abrasive grain's traces on the silicon wafer surface relative to the crystal coordinate system. It was found that the actual cutting direction of an abrasive grain along a single grinding trace would change from the center to the edge of the silicon wafer since the grinding traces are curved lines. The residual stress state at a specific point on the wafer surface was obtained by mapping the residual stress values obtained by molecular dynamics to the actual cutting direction. The residual stress distribution map was obtained successfully and any point of the ground silicon wafer could be known. The location of maximum residual stress was found to deviate from the [1 1 0] crystalline direction on the ground wafer due to the change in the actual cutting direction relative to it.

Impact of Sub-μm Wafer Thinning on Latch-Up Risk in DTCO/STCO Scaling Era

Impact of Sub-<i>μ</i>m Wafer Thinning on Latch-Up Risk in DTCO/STCO Scaling Era

Thin silicon heterojunction solar cells in perovskite shadow: Bottom cell prospective

Perovskite/Silicon (Pero-Si) tandem with silicon heterojunction (SHJ) bottom cells is a promising highly efficient concept, which in the case of mass production will likely rely on the same wafer feedstock as the single junction Si solar cells. The thickness of these wafers is constantly decreasing for economic and sustainability reasons. We forecast that Si bottom cells for mass produced Pero-Si tandems will be based on wafers thinner than 100 μm. In our work we study challenges and opportunities related to this likely wafer thinning for the performance of the SHJ bottom cells operating in Perovskite shadow. We study SHJ cells prepared on 80 μm thick wafers in comparison to the reference cells based on 135 μm thick wafers addressing two issues: passivation and light management. Effects of passivating layer thickness, back reflector and antireflection coating are studied under AM1.5G standard test conditions, attenuated AM1.5G irradiance, and under Perovskite-filtered spectrum. We show that major wafer thickness reduction of 40% turns to only approx. 0.35%abs loss in the bottom cell efficiency. This minor loss can be reduced even further using highly technological ITO/MgF2/Ag back reflector and MgF2 anti-reflection coating. Our work shows that significant potential for Pero-Si tandems is waiting to be explored in the perovskite shadow from the SHJ bottom cell perspective.

Impact of non-linear heat source and magnetic field on the Carreau nanofluid Marangoni convective flow – a numerical investigation

ABSTRACT A recent study examines the features of a dusty Carreau nanofluid over a flat surface with allowance for mixed convection that is not linear and heat radiation. It also examines how these factors affect fluid movement due to temperature differences (thermal Marangoni effect). The change in surface tension levels causes Marangoni convection, which finds applications in scientific areas like making crystals, keeping soap bubbles steady, drying thin wafers and dry silicon. Similarity transformations have been incorporated to create ODEs from PDEs. The complex non-dimensional differential equations are then solved using a numerical method called shooting method (with RKF-45 approach). For the momentum and heat distribution analysis, physical parameters are expressed in detail. The findings show that the Marangoni flow makes heat move quicker. In the same way, there is a decrease in the fluid’s velocity due to magnetic effects.

Reverse Wafer Procedure for Ulnar Impaction Syndrome.

Ulnar impaction syndrome occurs when excessive load across the ulnocarpal joints results in pathologic changes, especially over the articular surface of the ulnar head and proximal ulnar corner of the lunate. The 2 main surgical options in ulnar impaction syndrome are ulnar shortening osteotomy and wafer procedure, whether open or arthroscopically, to decompress the ulnocarpal joint load. However, all of these techniques have their shortcomings and drawbacks. The current study demonstrates a novel technique to decompress the ulnocarpal joint load: the "reverse wafer procedure" for ulnar impaction syndrome. In this surgical technique, we resected the proximal ulnar side of the lunate instead of partial resection of the thin wafer of the distal ulnar head dome in the standard wafer procedure. This technique avoids iatrogenic central tear of triangular fibrocartilage and distal radioulnar joint portal arthroscopy, which is technically demanding while preserving the distal radioulnar joint.

Cleaning and Particle Challenges in the Temporary Bonding and Debonding Process

The demands of 5G, Internet of Things and other global technology trends, combined with the increasing cost of scaling down process nodes, have created a shift towards more integrated packaging requirements. The emergence of advanced packaging technologies, such as Fan-Out Wafer Level Packaging (FOWLP), 2.5D/3D IC packaging, and heterogenous integration, brings potential for smaller form factors with increased functionality and bandwidth [1]. Backside processing or thinning of the device wafer is often needed for enabling these technologies. This requires the device wafer be adhered to a rigid carrier wafer using a temporary bonding material (TBM) for mechanical support during handling and processing. Following carrier release, the TBM must be thoroughly removed and cleaned from the device wafer. Many of these adhesives are exposed to high-power lasers or elevated temperatures, making removal more challenging. Sub-micron particle level clean demands for temporary bonding material (TBM) removal are also reaching standards typically reserved for front-end-of-line (FEOL) processing. This is especially crucial in 3D processes such as hybrid bonding where feature and pitch sizes are nearing &lt;1 µm and insufficient cleaning can lead to failures in subsequent bonding processes [2]. Thus, careful consideration of all processing steps is necessary to meet stringent particle demands. This work investigates the removal of coated and baked TBM on silicon wafers, with an emphasis on processing conditions that obtain best particle results. Several chemistries were assessed at the beaker level by performing coupon-level studies and measuring surface properties. Based on these findings, studies with 300-mm wafers were performed using a customizable single-wafer processing tool.