Through Glass Via Research Articles

Substrate Integrated Waveguide on Glass with Vacuum-Filled Tin Through Glass Vias for Millimeter-Wave Applications

This paper presents a novel approach to fabricate substrate integrated waveguides (SIWs) on glass substrates with tin (Sn) through glass vias (TGVs) tailored for millimeter-wave applications. The fabrication process employs a custom-designed vacuum suctioning system to rapidly fill precise TGV holes in the glass substrate, which are formed by wafer-level glass reflow micromachining techniques with molten tin in a minute. This method offers a very fast and cost-effective alternative for complete via filling without voids compared to the conventional metallization techniques such as electroplating or sputtering. An SIW with a 3-dB cutoff frequency of 17.2 GHz was fabricated using the proposed process. The fabricated SIW shows an average insertion loss of 1.65 ± 0.54 dB across the 20–35 GHz range. These results highlight the potential of glass substrates with tin TGVs for fabricating millimeter-wave devices.

Silicon dioxide (SiO2) solid blocking layer on through-glass via surface for efficient highly selective copper filling

Cu electrodeposition is utilized for filling through-glass via (TGV) to achieve the purpose of interconnection. However, Cu deposition is not only within the through-hole of TGV but also on the top and bottom surfaces of the through-hole. Therefore, additional chemical-mechanical-planarization (CMP) processes are required to remove the Cu overburden. To reduce the burden of CMP, this study proposes a method of making a SiO2 blocking layer (SBL) on the seed layers at the top and bottom of TGV before the filling process to inhibit excess Cu overburden deposition on the TGV surfaces during the filling process. We validated the effectiveness of the SBL through optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electrochemical measures. The Cu overburden typically requires removal through CMP processes after the Cu wiring. This study helps reduce the additional costs incurred during the TGV production process. The experimental results indicate that the proposed method is feasible, offering a new perspective for research on the selective filling of TGV.

Electroless silver plating on through-glass via (TGV) as an adhesive and conducting layer

The proposed method presents a scheme to modify the surface of the glass substrate using the piranha solution and to fabricate the conducting layer of the Through-glass Via (TGV) by the glucose-Ag electroless plating to achieve TGV metallization. The arithmetic mean deviation of the surface contours (Ra) for the substrates increases from 0.001 to 0.135. The contact angle of the substrates (unmodified and modified) is reduced to 6.4° and 12.2°, respectively. The sensitization process with SnCl2 and the activation process with silver ammonia solution are conducted using the glucose as the reducing agent to prepare the silver seed layer covered in the TGV through-vias with a high aspect ratio (9:1). The adhesion between the metal coating and the surface is measured by the 3M tape and chemical mechanical polishing (CMP). The metal coating adheres well to the surface-modified substrate without peeling off, which can satisfy the demands for the electroplating and CMP processes.

Localized surface roughening to improve adhesion of electroless seed layer in through-glass vias

This article reports the improvement of the adhesion of the electroless seed layer deposited on glass substrates used in creating through-glass vias (TGV) by localized surface roughening. Four glass substrates having varying roughness characteristics were prepared by electrochemical discharge machining (ECDM) and ultrasonic machining (USM). The electroless nickel seed layer was deposited directly on glass without any adhesion layer, followed by electrodeposited copper layers. In-depth surface topography and morphology analysis reveal the mechanism behind the improved adhesion during standard peel and cross-hatch adhesion tests, which were used to determine the interlayer adhesion.Localized roughening techniques generated specific microfeatures, i.e., microgrooves (in USM) or ridges (in ECDM), increasing the surface area. These features acted as interlocking/nucleation sites to hold the electroless nickel atoms, resulting in higher interfacial adhesion. USM-roughened samples exhibited stronger interfacial adhesion than their ECDM-roughened counterparts, which indicated that the interlayer adhesion depends on topography and the roughened surface's morphology. The surface with negative skewness and positive excess kurtosis promotes mechanical interlocking, offering a promising strategy for enhancing interlayer adhesion. Finally, conformal deposition in a 6 × 6 array of through-holes having an aspect ratio of ∼4 was also demonstrated.

Compact low-loss diplexer with stacked 2D and 3D structures using 3D glass-based advanced packaging technology

A compact low loss wideband diplexer is introduced by using stacked 2D and 3D structures through 3D advanced packaging and through glass vias (TGV). An inductor is designed by using stacked 2D and 3D structures to reduce the coupling effect between adjacent 2D inductors located in the same layer. It can greatly improve the Q factor yet minimize the chip size. This low loss, small size diplexer is developed by virtue of a modified topology and the proposed stacked 2D and 3D structures. The designed diplexer with a compact size of 1.6 mm × 0.8 mm × 0.25 mm is fabricated using 3D glass-based advanced packaging technology and measured by on-wafer probing. The measured results indicate that it achieves an insertion loss less than 0.8 dB and 0.9 dB and an isolation better than 20 dB and 17.5 dB in the bands of 0.699 GHz-0.960 GHz and 1.71 GHz-2.69 GHz, respectively. In comparison with the previously reported designs, the proposed diplexer shows the superior advantages of smaller size and lower insertion loss.

Eco‐friendly glass wet etching for MEMS application: A review

AbstractGlass is one of the most essential materials in various industrial fields. A representative application is as interposers in the semiconductor and display industries and microfluidic devices in the bio‐industry. Due to technological advancements, electric devices and various products are becoming lighter and smaller. Consequently, precision processing of the substrate is becoming increasingly important. One significant leading technology among these is through glass via (TGV) technology, which is attracting attention as a future alternative to through silicon via. In particular, TGV should be capable of microfabrication with a large aspect ratio and a consistent small hole size. TGV is typically fabricated using a wet etching process, so wet etching technology is a prominent focus in microfabrication. However, glass has isotropic properties, making achieving a high aspect ratio difficult. Traditionally, research on the wet etching method using hydrofluoric acid (HF) has been conducted. Nevertheless, HF etching has several disadvantages, including air pollution and human harm. Additional studies have been performed to address these issues. This review paper will cover the conventional HF‐based wet etching method and alternative HF etching processes (eco‐friendly materials). This technology would significantly help overcome the traditional problems associated with HF etching and fabricating precision‐processed glass in the semiconductor, display, and bio‐device industries.

Acoustic-streaming driven liquid filling patterns inside through-glass vias

Filling through-glass vias (TGVs) with liquid remains a significant challenge in IC packaging technology. This study presents an acoustic-streaming method to modulate the wetting behavior as well as the interfacial dynamics to fill the TGVs. We categorize the incomplete filling into three typical patterns: (a) neck wetting, (b) head and end wetting, and (c) bubble wrapping. Experimental results show that the ultrasonic driving at 522.5 kHz/160 V can effectively achieve ideal filling of these patterns in TGVs (aspect ratio of 1:2/1:3). The filling processes are elucidated from a new perspective: the liquid flow induced by acoustic streaming regulates the moving of contact line to complete wetting on sidewalls, while the acoustic wave impacts the gas–liquid interface to cause oscillations for pushing bubbles out. A Lattice Boltzmann model is constructed to reveal the mechanism. This method offers a viable and promising solution to promote liquid filling of TGVs.

Through glass via (TGV) copper metallization and its microstructure modification

The microstructure and uniformity of Cu metallization in the through glass via (TGV) structure were investigated through electron backscatter diffraction (EBSD) analysis system and finite element analysis (FEA) method. Two different direct current (DC) electroplating methods were employed for the TGV metallization, including single- and multiple-step electroplating methods. We found that the multiple-step electroplating process with appropriate current density (j)/plating time (t) can efficiently enhance the throwing power (TP) value (uniformity) of electroplated Cu in the TGV metallization. Moreover, the Cu electrodeposition via the multiple-step electroplating process possessed larger grain sizes and high fraction of high angle grain boundaries (HAGBs), including twin boundaries (TBs), which are very beneficial to the mechanical and electrical properties of Cu interconnects. Detailed analyses of the uniformity (i.e., TP), crystallographic microstructure (e.g., grain size), and mechanical characteristics (e.g., ductility) of electroplated Cu derived from single- and multiple-step electroplating process were discussed in this paper.

Ultrahigh Aspect Ratio Through Glass Vias Perforation Utilizing Selective Laser‐Induced Etching with Nanochannels

At present, perforation of high aspect ratio through glass vias (TGVs) is one of the primary factors limiting the development of glass interposers. Herein, it is based on a large number of experiments, combined with mechanistic analysis, to realize the perforation of ultrahigh/high aspect ratio fused silica TGVs using selective laser‐induced etching. First, the effect of the number of pulses as well as other laser parameters on the etching selectivity is systematically investigated. It is found that the formation of nanochannels in fused silica is crucial in determining the high selectivity. Subsequently, a model based on diffusion theory is proposed to mathematically explain the reasons for the high selectivity generation. Finally, the perforations of TGVs with diameters of 5.4–26.4 μm, aspect ratios of 11.7–61.3, and vertical sidewalls are achieved, at a laser treatment speed of ≈10 000 TGVs per minute. This research can serve as an essential reference for the manufacturing of TGVs with high aspect ratios and glass interposers with high interconnection density.

Fractures of low-k materials in a RF package with integrated passive device based on TGV

The radio frequency (RF) chips and passive devices integrated on the through-glass-via (TGV) substrate meets the demands of miniaturization, high performance and low losses in the application. The RF chip and integrated passive devices (IPDs) are interconnected electrically by a redistribution layer (RDL) on the TGV substrate with the isolation low-k materials. The low-k materials, however, are susceptible to fracture during the thermal process in packaging due to their weak mechanical properties. In this study, the fractures of the low-k material were studied by experiments and the finite element analysis (FEA) for a RF package with integrated passive device based on TGV. The mechanical properties of the low-k material used in the FEA were tested by fabricating freestanding low-k films using microfabrication techniques. Then the fracture behaviors of the low-k material in the package and its impact factors under thermal loadings were examined. The impact factors, such as the initial defect location, direction and length, were investigated by evaluating the stress intensity factors (SIFs) at the defect tips. The results revealed that the most hazardous location in the low-k material is the region below the micro-joint of RF chip. The vertical defects along thickness in low-k film are more likely to propagate than horizontal ones. The SIF value increases linearly with the defect length both in heating and cooling conditions.

P‐136: Process Optimization for Fabrication of 3D Through Glass Via (TGV) Inductor

Glass is a good candidate for substrate material of integrated passive device, due to its high resistivity and low dielectric loss. 3D through glass via (TGV) inductors can be formed with high radio‐frequency performance. This paper analyzes failure mechanisms of TGV inductors and proposes the method of process optimization.

Effect of heat treatment processes on the Cu-electrodeposited through glass vias (TGV) plate

Based on laser-induced deep etching technology and through-hole filling techniques, TGV interposers were successfully fabricated. The residual stress in the Cu overburden film directly affects the yield improvement after subsequent grinding of the interposer. Therefore, we studied the evolution of residual stress, microstructural changes, and micro-nano mechanical properties within the Cu overburden film after heat treatment at different temperatures. Residual stress analysis using the sin2Ψ method with an X-ray diffractometer (XRD) indicates that during the process of increasing temperature from 100°C to 200°C, the internal residual stress in the Cu overburden film changes from compressive stress to tensile stress. Furthermore, the maximum absolute value of the residual stress, 70.09 MPa, appears at room temperature, and the minimum absolute value of the residual stress, 15.59 MPa, occurs after the heat treatment process at 200°C. Electron backscatter diffraction (EBSD) microstructural analysis shows that the application of heat treatment can effectively accelerate static recrystallization (SRX), promote a higher proportion of high-angle grain boundaries (HAGB), and refine grain size. Additionally, a (001) preferred orientation at high residual stress states and a (111) preferred orientation at low residual stress states are observed. Nanoindentation test results indicate that the Cu overburden film treated at 100°C has the most potential for removal during the grinding process.

Scanning strategy-dependent etching rate in the formation of through-via holes by femtosecond laser-assisted etching

In this study, we used femtosecond laser-assisted etching (FLAE) to drill through glass vias (TGVs) in 0.3 mm thick non-alkali glass substrates. In FLAE, the focus of the femtosecond laser pulses is scanned to modify the material along a preprogrammed pattern, and the modified region is preferentially removed by chemical etching. We found that the scanning strategy affected the etching rate along the laser-modified lines. Among four types of scanning strategies tested, the strategy 〈du〉—that is, scanning in a downward direction followed by an upward direction—obtained the highest etching rate. In this case, the etching rate along the laser-modified line was approximately 10 times larger than that of the unmodified region.

Recent Progress of TGV Technology for High Performance Semiconductor Packaging

In recent semiconductor packaging, the adoption of through silicon via (TSV) technology has become crucial for the integration of 2.5 and 3D Si chips, and interposers. The TSV offers significant advantages including high interconnect density, shortened signal pathways, and improved electrical performance. However, challenges such as electrical loss, substrate warpage, and high manufacturing costs are associated with TSV implementation. In contrast, glass-based through-glass vias (TGVs) exhibit promising characteristics such as excellent insulation properties, cost-effectiveness, and variable coefficient of thermal expansion (CTE) values that mitigate warpage in stacked devices. Moreover, they facilitate miniaturization and support high-frequency applications. This paper provides an overview of recent advancements in glass substrate, TGV drilling techniques, functional layer depositions, and Cu-filling processes in semiconductor packaging evolution.

A Sensitivity-Enhanced Vertical-Resonant MEMS Electric Field Sensor Based on TGV Technology.

In order to enhance the sensitivity of wafer-level vacuum-packaged electric field sensors, this paper proposed a vertical-resonant MEMS electric field sensor based on TGV (Through Glass Via) technology. The microsensor is composed of the electric field sensing cover, the drive cover, and the SOI-based microstructures between them. TGV technology is innovatively used to fabricate the electric field sensing cover and the vertically-driven cover. The external electric field is concentrated and transmitted to the area below the silicon plate in the center of the electric field sensing cover through a metal plate and a metal pillar, reducing the coupling capacitance between the silicon plate and the packaging structure, thereby achieving the enhanced transmission of the electric field. The sensitivity-enhanced mechanism of the sensor is analyzed, and the key parameters of the sensor are optimized through finite element simulation. The fabrication process is designed and realized. A prototype is tested to characterize its performance. The experimental results indicate that the sensitivity of the sensor is 0.82 mV/(kV/m) within the electrostatic electric field ranging from 0-50 kV/m. The linearity of the sensor is 0.65%.

The Effects of Etchant on via Hole Taper Angle and Selectivity in Selective Laser Etching.

This research focuses on the manufacturing of a glass interposer that has gone through glass via (TGV) connection holes. Glass has unique properties that make it suitable for 3D integrated circuit (IC) interposers, which include low permittivity, high transparency, and adjustable thermal expansion coefficient. To date, various studies have suggested numerous techniques to generate holes in glass. In this study, we adopt the selective laser etching (SLE) technique. SLE consists of two processes: local modification via an ultrashort pulsed laser and chemical etching. In our previous study, we found that the process speed can be enhanced by changing the local modification method. For further enhancement in the process speed, in this study, we focus on the chemical etching process. In particular, we try to find a proper etchant for TGV formation. Here, four different etchants (HF, KOH, NaOH, and NH4F) are compared in order to improve the etching speed. For a quantitative comparison, we adopt the concept of selectivity. The results show that NH4F has the highest selectivity; therefore, we can tentatively claim that it is a promising candidate etchant for generating TGV. In addition, we also observe a taper angle variation according to the etchant used. The results show that the taper angle of the hole is dependent on the concentration of the etchant as well as the etchant itself. These results may be applicable to various industrial fields that aim to adjust the taper angle of holes.

Electrical characterization and performance analysis of coaxial through-glass vias

Electrical characterization and performance analysis of coaxial through-glass vias

Fabrication of through glass via (TGV) substrates using a pulse width modulated (PWM) vacuum suction system for molten solder filling

Fabrication of through glass via (TGV) substrates using a pulse width modulated (PWM) vacuum suction system for molten solder filling

Application of Through Glass Via (TGV) Technology for Sensors Manufacturing and Packaging.

Glass has emerged as a highly versatile substrate for various sensor and MEMS packaging applications, including electromechanical, thermal, optical, biomedical, and RF devices, due to its exceptional properties such as high geometrical tolerances, outstanding heat and chemical resistance, excellent high-frequency electrical properties, and the ability to be hermetically sealed. In these applications, Through Glass Via (TGV) technology plays a vital role in manufacturing and packaging by creating electrical interconnections through glass substrates. This paper provides a comprehensive summary of the research progress in TGV fabrication along with its integrations, including through via formation and metallization. This paper also reviews the significant qualification and reliability achievements obtained by the scientific community for TGV technology. Additionally, this paper summarizes the application of TGV technology in various sensors such as MEMS sensors and discusses the potential applications and future development directions of TGV technology.

Glass Package and Through Glass Via (TGV) for MEMS

Menlo Microsystems has introduced a glass-based MEMS switch that utilizes through glass via (TGV) technology. Created in the R&D labs at GE, these MEMS solutions combined with utilization of glass packaging, has enabled the creation of the highly reliable Ideal Switch™. It is the world’s smallest, most reliable, and efficient micro-mechanical switch that can be used for numerous applications, including power. Several advantages are gained by taking advantage of the low electrical loss of glass and hermetic TGV. The TGV technology enables >60% smaller package size relative to wirebond. Parasitics are reduced by >75% and devices have a wide operational bandwidth from DC to > 50 GHz. Devices can have dozens of switches in a small form factor that give reliable performance over billions of cycles. Leading up to the volume production of these devices, Menlo has helped drive the glass supply chain to an increased level of maturity. In this talk we will provide an overview of Menlo’s glass package for the Ideal Switch™ technology as well as discuss the growing maturity and emerging capabilities in the glass/TGV supply chain.