Effect of gas pressure on ion energy at substrate side of Ag target radio-frequency and very-high-frequency magnetron sputtering discharge

The effect of gas pressure on ion energy distribution at the substrate side of Ag target radio-frequency (RF) and very-high-frequency (VHF) magnetron sputtering discharge was investigated. At the lower pressure, the evolution of maximum ion energy (E) with the discharge voltage (V) varied with the excitation frequency, due to the joint contribution of the ion generation in the bulk plasma and the ion movement across the sheath related to the ion transit sheath time τi and RF period RF. At the higher pressure, the evolution of E-V relationships do not vary with the excitation frequency, due to the balance between the energy lost through collisions and the energy gained by acceleration in the electric field. Therefore, for the RF and VHF magnetron discharge, the lower gas pressure can have a clear influence on the E-V relationship.

Breakthrough of Sublimation Drying by Liquid Phase Deposition

Damage-free drying becomes increasingly difficult with the scaling of semiconductor devices. In this work, we studied a new sublimation drying technology for 3nm node and beyond. In order to investigate the collapse factor by conventional sublimation drying, we observed the pattern with cryo-SEM and revealed that the collapse occurred when the liquid film on the substrate solidified. Based on this result, we considered that it was important to deposit a solidified film uniformly from the substrate side to suppress collapse. Two key process parameters were evaluated to achieve the uniform formation of the solidified film. One is interfacial free energy and the other is film thickness of solution just before solidification. By optimizing two key parameters, it was successfully demonstrated to suppress pattern collapse of challenging devices. In this paper, we report on a new drying method: sublimation drying by LPD (Liquid-phase deposition).

Исследование влияния легирования на переходные слои анизотипных гетероструктур на основе GaInAsP и InP, полученных методом МОС-гидридной эпитаксии

In the study of doped anisotypic heterostructures with layers of Ga(1-x)In(x)P(1-y)As(y) grown on InP substrates with a buffer layer of InP by MOC-hydride epitaxy, the presence of transition regions was detected in the Ga(1-x)In(x)P(1-y)As(y) layer on the substrate side for individual samples, across which the arsenic content (y) increased from the interface with the InP layer to the surface of the structure by the amount of (Δy) up to 0.15, and the content of elements of the third group (x) remained constant.

Interactions between a subset of substrate side chains and AAA+ motor pore loops determine grip during protein unfolding

Most AAA+ remodeling motors denature proteins by pulling on the peptide termini of folded substrates, but it is not well-understood how motors produce grip when resisting a folded domain. Here, at single amino-acid resolution, we identify the determinants of grip by measuring how substrate tail sequences alter the unfolding activity of the unfoldase-protease ClpXP. The seven amino acids abutting a stable substrate domain are key, with residues 2–6 forming a core that contributes most significantly to grip. ClpX grips large hydrophobic and aromatic side chains strongly and small, polar, or charged side chains weakly. Multiple side chains interact with pore loops synergistically to strengthen grip. In combination with recent structures, our results support a mechanism in which unfolding grip is primarily mediated by non-specific van der Waal’s interactions between core side chains of the substrate tail and a subset of YVG loops at the top of the ClpX axial pore.

Imaging of Chemical Reactions Using a Terahertz Chemical Microscope

This study develops a terahertz (THz) chemical microscope (TCM) that visualizes the distribution of chemical reaction on a silicon-based sensing chip. This chip, called the sensing plate, was fabricated by depositing Si thin films on a sapphire substrate and thermally oxidizing the Si film surface. The Si thin film of the sensing plate was irradiated from the substrate side by a femtosecond laser, generating THz pulses that were radiated into free space through the surface field effect of the Si thin film. The surface field responds to chemical reactions on the surface of the sensing plate, changing the amplitude of the THz pulses. This paper first demonstrates the principle and experimental setup of the TCM and performs the imaging and measurement of chemical reactions, including the reactions of bio-related materials.

High-Temperature Reliability of Wire Bonds on Thick Film

In a harsh environment, wire-bonded interconnects are critical for overall reliability of microelectronic assemblies. Aluminum is the dominating metallization of the die wire bonding pads and aluminum wires are used to achieve monometallic bonding system on die side. On the substrate side, a monometallic connection is not readily available and typically involves expensive aluminum thin-film deposition or labor-intensive bonding tabs. Nickel-palladium-gold galvanic or electro-less plating stacks are also used to improve bondability and reliability of non-monometallic Al wire bonds on the substrate side. However, these plating stacks do not perform well after excursions above 330°C that are needed for the attachment of die and passives prior to wire bonding. At these temperatures, both palladium and nickel diffuse through the gold and form surface oxides that degrade wire bondability. In monometallic wire-bonding schemes, in addition to aluminum wires gold wires within same assembly are often also needed, for example, when some die is only available with gold-plated bond pads, or to connect substrates to gold-plated pins of hybrid housings. A universal substrate metallization, compatible with aluminum wire and gold wire, is therefore desirable. Thin-film substrates produced by sequential deposition and etching of gold metal, barrier metals, then aluminum metal is a good working solution, but it can be as much as ten times more expensive than other types of substrates. Printed thick-film metallization, a well-established technology, have been widely used for hybrid substrates. Silver-based thick films are inexpensive and capable of accepting aluminum and gold bonds. However, the silver-aluminum bonds are seldom used because of intermetallic formation and subsequent degradation triggered by multiple factors like temperature, humidity, and the presence of halogens. Pd and Pt are often added to the Ag thick films to decrease this effect, but potential usability and the reliability of these formulations in extreme temperature environments is not well researched. For this study, samples of Pt/Ag thick-film metallization were printed on Al2O3 substrates, and 25-um and 250-um aluminum wires and 50-um gold wires were wedge bonded in daisy chain to the substrate. The test vehicles were subjected to high-temperature testing at 260°C and 280°C. Thermal cycling tests from −20°C to 280°C were also performed. Mechanical and electrical characterizations of the wire bonds were conducted periodically. These tests included resistance and pull-strength measurements. Failure analysis of the bond joints was performed to understand the results of the tests. The 250-um Al wire and 25-um Al wire showed no significant changes until a critical time-at-temperature was reached. After reaching this temperature, the wire/substrate interface resistance rapidly increased to values as high as 40 Ohms for the 25-um Al wires. However, the pull strength remained within standard throughout the tests of up to 1200 hours. The relationship between time to failure and the temperature is presented in the paper. There was a four times life increase of bonds with every 20°C. With gold wires, no dramatic increase of bond resistance was observed, only a slight increase with time. The pull strength of Au wires remained stable throughout the time at high temperature. The tested Ag/Pt thick film metallization was found to be compatible with bonding of the gold wires and the aluminum wires for high-temperature applications up to an Arrhenius equivalent of 800 hours at 260°C. Additionally, Parylene HT coating was vapor-deposited on one set of 250-um Al wire-bonding samples. This set of samples demonstrated doubling of its useful life as compared to the uncoated samples.