Evaluation of the Impact of Abnormal Grains on the Performance of Sc0.15Al0.85N-based BAW Resonators and Filters

ScxAl1-xN is a promising piezoelectric material for radio frequency communication applications with excellent electro-acoustic properties. However, the growth of abnormally oriented grains is widely observed in the Sc doped AlN films deposited by sputtering. In this work, for the first time, the impact of the abnormal grains in the Sc0.15Al0.85N films on the performance of bulk acoustic wave resonators and filters is systematically evaluated by both simulations and measurements. The correlation between the device performance and the abnormal grain parameters, including the density, dimension, crystal orientation, growth height, and the total volume of the abnormal grains, is evaluated and quantified. Simulation results show that the total volume of all abnormal grains in the whole device is the most critical factor among the parameters. Abnormal grains with randomly distributed parameters and around 6% total volume of the film can degrade the effective coupling coefficient of the resonator from 13.6% to 11%, leading to a 10.6% decrement of the filter bandwidth. Wafer-level device characterizations and measurements are performed, and the results are consistent with the simulations. This study provides a practical method for predicting the performance of the resonators and filters with abnormal grains, and a guideline for film quality evaluation.

Automated Measurement and Analysis of Sidewall Roughness (SWR) Using 3D-AFM

As the semiconductor device architecture develops, from planar field-effect transistor (FET) to FinFET and toward gate all around (GAA), it is more needed to measure 3D structure sidewall precisely. Here, we present a 3D-atomic force microscopy (3D-AFM) by Park Systems Corp., a powerful 3D metrology tool to measure SWR of vertical and undercut structures. First, we measured 3 different dies repeatedly to calculate reproducibility in die level. Reproducible results were derived with relative standard deviation under 2%. Second, we measured 13 different dies, including the center and edge of the wafer, to analyze SWR distribution in wafer level and reliable results were measured. And all analysis was performed using a novel algorithm including auto flattening, sidewall detection, and SWR calculation. In addition, SWR automatic analysis software was implemented to reduce analysis time and to provide standard analysis. The result suggests that our 3D-AFM based on tilted Z scanner enabled an advanced methodology for automated 3D measurement and analysis.

Wafer-Level 3D Integration Based on Poly (Diallyl Phthalate) Adhesive Bonding

Three-dimensional integration technology provides a promising total solution that can be used to achieve system-level integration with high function density and low cost. In this study, a wafer-level 3D integration technology using PDAP as an intermediate bonding polymer was applied effectively for integration with an SOI wafer and dummy a CMOS wafer. The influences of the procedure parameters on the adhesive bonding effects were determined by Si–Glass adhesive bonding tests. It was found that the bonding pressure, pre-curing conditions, spin coating conditions, and cleanliness have a significant influence on the bonding results. The optimal procedure parameters for PDAP adhesive bonding were obtained through analysis and comparison. The 3D integration tests were conducted according to these optimal parameters. In the tests, process optimization was focused on Si handle-layer etching, PDAP layer etching, and Au pillar electroplating. After that, the optimal process conditions for the 3D integration process were achieved. The 3D integration applications of the micro-bolometer array and the micro-bridge resistor array were presented. It was confirmed that 3D integration based on PDAP adhesive bonding is suitable for the fabrication of system-on-chip when using MEMS and IC integration and that it is especially useful for the fabrication of low-cost suspended-microstructure on-CMOS-chip systems.

Low Temperature Hydrophilic SiC Wafer Level Direct Bonding for Ultrahigh-Voltage Device Applications

SiC direct bonding using O2 plasma activation is investigated in this work. SiC substrate and n− SiC epitaxy growth layer are activated with an optimized duration of 60s and power of the oxygen ion beam source at 20 W. After O2 plasma activation, both the SiC substrate and n− SiC epitaxy growth layer present a sufficient hydrophilic surface for bonding. The two 4-inch wafers are prebonded at room temperature followed by an annealing process in an atmospheric N2 ambient for 3 h at 300 °C. The scanning results obtained by C-mode scanning acoustic microscopy (C-SAM) shows a high bonding uniformity. The bonding strength of 1473 mJ/m2 is achieved. The bonding mechanisms are investigated through interface analysis by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). Oxygen is found between the two interfaces, which indicates Si–O and C–O are formed at the bonding interface. However, a C-rich area is also detected at the bonding interface, which reveals the formation of C-C bonds in the activated SiC surface layer. These results show the potential of low cost and efficient surface activation method for SiC direct bonding for ultrahigh-voltage devices applications.

Systematic identification of crosstalk and bandwidth upper limit in highly cascaded Mach-Zehnder lattice optical filters

Crosstalk among channels in wavelength division multiplexing (WDM) filters must be suppressed to enhance receiver sensitivity in direct-detection-based optical communication systems. We present a systematic method to identify the maximum crosstalk and upper limit of the transmission spectrum bandwidth of a highly multi-staged Mach-Zehnder interference (MZI) lattice optical filter with a number of cascade N (N=1,2,…,∞). The scattering matrix including the wafer-level-measurement-based coupling coefficients of directional couplers is used to calculate the transmittance from the input to each output channel and the result is exactly extrapolated to infinite N. This method can be used to design, characterize, and evaluate $N$-cascaded MZI lattice optical filters that must meet strict WDM specifications.

Large-size (1.7 × 1.7 mm2) β-Ga2O3 field-plated trench MOS-type Schottky barrier diodes with 1.2 kV breakdown voltage and 109 high on/off current ratio

We fabricated high forward and low leakage current trench MOS-type Schottky barrier diodes (MOSSBDs) in combination with a field plate on a 12 μm thick epitaxial layer grown by halide vapor phase epitaxy on β-Ga2O3 (001) substrate. The MOSSBDs, measuring 1.7 × 1.7 mm2, exhibited a forward current of 2 A (70 A cm−2) at 2 V forward voltage and a leakage current of 5.7 × 10–10 A at −1.2 kV reverse voltage (on/off current ratio of > 109) with an ideality factor of 1.05 and wafer-level specific on-resistance of 17.1 mΩ · cm2.