Reflow Behavior Research Articles

Thermal reflow of plasma-polymerized fluorocarbon for nanochannels and particle encapsulation

Thermal reflow is an important property for thermoplastic polymers, which has been studied extensively especially for photoresists and electron beam resists in semiconductor industries. While the surface smoothening effect is beneficial to reduce the roughness of micro- and nanostructures, the drastic morphology change has been tested to be efficient to fabricate optical devices like microlens arrays. Plasma-polymerized fluorocarbon (PPFC) is a feasible polymer material, which can be achieved conveniently with standard plasma etching systems, however, there have been limited studies regarding its properties and applications apart from its usage as a passivation layer during reactive ion etching. In this study, the thermal reflow behavior of PPFC on various substrates will be presented, including planar surfaces, gratings and trenches. Importantly, the formation of buried micro- and nanochannels has been demonstrated, when PPFC is heated above its glass transition temperature on trench structures. This encapsulation dynamics is analyzed with regard to various parameters like temperature and duration of thermal treatment, trench widths and initial thickness of PPFC film. As a proof of concept, silicon nanorods have been encapsulated in the microchannels by the reflowed PPFC. The results have demonstrated strong potentials of PPFC for applications like micro- and nanofluidics, microcontainers and drug delivery. Because of its good chemical stability and biocompatibility, PPFC can also be expected to be used for various biological devices like brain-machine interfaces, neural probes, epidermal devices and biological implants.

Polymer Microlens 제작을 위한 Thermal Reflow 공정 해석

Polymer microlens manufacturing using thermal reflow was simulated and optimized by a numerical approach. Microlenses are used in various industrial fields, such as optical, semiconductor, and observation experiment equipment. Therefore, polymer microlens fabrication using an economical thermal reflow process is important for mass production and cost reduction. The feasibility of a thermal reflow process for microlens fabrication was analyzed in this paper by numerical methods. First, we refer to the previous studies and papers for the theoretical shape of the microlens. Second, for numerical simulation of the process above Tg (Glass Transition Temperature), we studied the multiphase flow simulation using a VOF method and adopted a Cross-WLF model to consider the rheological characteristics of PMMA. Finally, several parametric studies were carried out to compare the simulation profile and the theoretical lens shape in order to optimize the thermal reflow process. The numerical approach presented in this paper would enable a more efficient analysis and provide better understanding of reflow behavior to obtain the optimal process.

Analysis of the Loading Process of a Slider With Reflowed Lubricant in a Hard Disk Drive

As the recording density of hard disk drives has increased exponentially recently, the load/unload process can be affected severely by the nanolevel changes in the air-bearing surface (ABS) induced by the reflow behavior of perfluoropolyether molecules. In this paper, clean-up time and reflow time were first measured by using thermal flying controller measurements to check whether reflowed lubricant can affect loading performance. The measured clean-up time and reflow time were 120 s and 40 min, respectively. Because the clean-up time is so much longer than the loading process, almost all the reflowed lubricant remained on the bottom of the ABS during the loading process. Next, the lubricant behavior at rest was modeled and simulated theoretically by using a diffusion process. At rest, the time-dependent profiles of the reflowed lubricant were investigated. In addition, the ABS was modified with reflowed profiles at various time intervals and loading process was carried out with the modified ABS for various parameters such as reflow time and loading velocity. As a result, the slider–disk contact distinctly occurred during the loading process in the case with reflowed lubricant profiles. The simulation results were verified with the experimental results. Consequently, the effects of reflowed lubricant should be considered when designing the loading process of a slider to improve head–disk interface reliability.

Cost-Efficient Wafer-Level Capping for MEMS and Imaging Sensors by Adhesive Wafer Bonding.

Device encapsulation and packaging often constitutes a substantial part of the fabrication cost of micro electro-mechanical systems (MEMS) transducers and imaging sensor devices. In this paper, we propose a simple and cost-effective wafer-level capping method that utilizes a limited number of highly standardized process steps as well as low-cost materials. The proposed capping process is based on low-temperature adhesive wafer bonding, which ensures full complementary metal-oxide-semiconductor (CMOS) compatibility. All necessary fabrication steps for the wafer bonding, such as cavity formation and deposition of the adhesive, are performed on the capping substrate. The polymer adhesive is deposited by spray-coating on the capping wafer containing the cavities. Thus, no lithographic patterning of the polymer adhesive is needed, and material waste is minimized. Furthermore, this process does not require any additional fabrication steps on the device wafer, which lowers the process complexity and fabrication costs. We demonstrate the proposed capping method by packaging two different MEMS devices. The two MEMS devices include a vibration sensor and an acceleration switch, which employ two different electrical interconnection schemes. The experimental results show wafer-level capping with excellent bond quality due to the re-flow behavior of the polymer adhesive. No impediment to the functionality of the MEMS devices was observed, which indicates that the encapsulation does not introduce significant tensile nor compressive stresses. Thus, we present a highly versatile, robust, and cost-efficient capping method for components such as MEMS and imaging sensors.

Reflow behavior of Cu–Mn in LSI line patterns

The reflow behavior of sputter-deposited Cu–Mn alloy into narrow trench lines formed in a SiO2 dielectric layer was investigated. At a substrate temperature of 350 °C, Cu–Mn completely filled a trench of 50 nm width. The reflow was rate-controlled by mixed-mode diffusion. An interfacial layer was formed between Cu and SiO2 during this process, which was considered to improve wettability and enhance reflow filling. The reflowed Cu–Mn lines had a few grain boundaries, most of which are coherent twin boundaries.

Zn diffusion and reflow behaviour of Sn-9Zn and Sn-8.5Zn-0.5Ag-0.01Al-0.1Ga solders on a Ni/Cu substrate under IR reflow

Purpose – This paper aims to compare the reflow and Zn diffusion behaviors in Sn-Zn and Sn-8.5Zn-0.5Ag-0.01Al-0.1Ga (5E) solders during soldering on a Ni/Cu substrate under infrared (IR) reflow. The study proposes a model on the effect of various elements particularly Zn diffusion behavior in the solders on the formation of intermetallic compounds (IMCs). Design/methodology/approach – The melting activities of two solders near their melting points on copper substrates are visualized in an IR reflow furnace. Reflowed solder joints were analyzed using scanning electron microscope and energy dispersive X-ray spectroscopy. Findings – Reflow behaviors of the solders are similar. During melting, solder balls are first merged into each other and then reflow on the substrate from top to bottom. Both solders show a reduced amount of Zn in the solder. Theoretical calculations demonstrate a higher Zn diffusion in the 5E solder; however, the amount of Zn actually observed at the solder/substrate interface is lower than Sn-9Zn solder due to the formation of ZnAg3 in the solder. A thinner IMC layer is formed at the interface in the 5E solder than the Sn-Zn solder. Research limitations/implications – The present work compares the 5E solder only with Sn-Zn solder. Additional research work may be required to compare 5E solder with other solders like Sn-Ag, SnAgCu, etc. to further establish its practical applications. Practical implications – The study ascertains the advantages of 5E solder over Sn-Zn solder for all practical applications. Originality/value – The significance of this paper is the understanding of the relation between reflow behavior of solders and reactivity of different elements in the solder alloys and substrate to form various IMCs and their influence on the formation of IMC layer at solder/substrate interface. Emphasis is provided for the diffusion behavior of Zn during reflow and respective reaction mechanisms.

Reflow of Phosphorous Silicate Glass Layer Formed on Textured Si Surface in Crystalline Si Solar Cells

We have investigated the reflow behavior of phosphorus silicate glass (PSG) layer formed on textured Si surface using transmission electron microscopy and simulation. For conventional wet oxidation process, stress-dependent surface reaction and stress-dependent oxidant diffusion led to the oxidation retardation in both convex and concave regions of the textured Si surface, respectively. However, PSG film formed by POCl3-diffusion underwent reflow, resulting in the formations of thinner and thicker PSG films in convex and concave regions, respectively. Simulation results showed that the reflow of PSG films causes lateral thermal mismatch stresses to increase and decrease in convex and concave regions, respectively.

Diffusion of Cu and interfacial reactions during reflow of Sn–8.5Zn–0.5Ag–0.01Al–0.1Ga alloy on Ni/Cu substrate

Abstract

Reflow of supported sub-100 nm polymer films as a characterization process for NanoImprint lithography

In this paper, we address the reflow behavior of polymer thin films, focusing our effort on the accuracy of surface shape recognition. Although much work was already performed to control resist reflow during lens manufacturing for instance, our approach is significantly different since no contact line (substrate/polymer/atmosphere) needs to be considered. Here, a linear stability approach is successfully developed to describe the thin film evolution which is also compared with experiments. Polystyrene films, with thickness ranging from few tens of nanometers up to several hundred of nanometers were patterned with NanoImprint lithography technique. Atomic force microscopy measurements were used to characterize smooth or steep shapes, respectively. Mechanical measurements of earlier stages of pattern reflow were directly accessible without any assumption, contrary to the diffraction method usually employed. We show that by controlling the reflow process of any complex surface shape during the course of time, measurements of material parameters such as thin film viscosity, surface tension, or even Hamaker constant can be made possible.

A Study of Difference in Reflow Characteristics Between Electroplated and Sputtered Cu in a Dual-Damascene Fabrication Process for Silicon Semiconductor Devices

The difference in reflow characteristics between electroplated and sputtered Cu films during high-temperature high-pressure treatment was confirmed, and the basis for this difference was analyzed. Using test element groups containing a number of via holes, it was found that electroplated Cu films had much superior embedding characteristics compared with sputtered Cu films. This was confirmed by measurements of the stress–strain curves of these Cu films, which indicated that the strength at high temperature of the electroplated films was lower than that of sputtered films. Identification of lattice defects and analysis of the microstructure of these films were carried out by positron lifetime measurements and transmission electron microscopy, respectively. The results showed that a large quantity of vacancy clusters was present in the electroplated Cu films, and this increased to a maximum after isochronal annealing at 300°C. From the results, it was shown that Cu atoms in electroplated films with a large number of vacancy clusters diffuse rapidly at around 300°C, and this rapid diffusion contributes greatly to softening of the film and a promotion in reflow behavior. This study revealed that the reflow behavior of Cu films strongly depends on the presence of vacancy clusters within it.

Influence of Cu substrate surface oxides and heating rates during reflow on melting point of Sn–3.5Ag solder

Three types of copper substrates, fresh, aged (kept for years in open atmosphere) and acid washed aged, were investigated for the reflow behaviour of a solder using different heating rates. Melting point of the Sn–3.5Ag solder was lowered on the aged Cu substrate. Reduction was found to be higher in high heating rate and declined with the decrease in the heating rate. Melting point was lowered from 221 °C to 175 °C with the heating rate of 180 °C/min, but recovered to 210 °C when aged Cu substrate was washed with sulphuric acid. XPS depth profile revealed the presence of Cu 2O up to the greater depth in the aged substrate compared to the fresh and acid washed aged substrates. Study showed the relation of reduction in melting point with the depth of Cu 2O on the surface of aged Cu substrates. It was proposed that lower dissipation of heat generated in high heating rates by the oxidation of the flux carbon during reduction of high Cu 2O amount in aged carbon was responsible for the variations in melting points.

Diffusion Behavior of Zn During Reflow of Sn-9Zn Solder on Ni/Cu Substrate

Reflow behavior of Sn-Zn solder on Ni/Cu substrate was investigated in an infrared (IR) reflow furnace using different heating rates from 180 °C/min to 36 °C/min. Energy dispersive spectroscopy (EDX) studies of the reflowed samples showed increased diffusion of Zn from the solder to the intermetallic compound (IMC) layer with a decrease in heating rate. Higher interfacial activity and affinity of the Zn in the formation of the IMC with the lowering of the heating rate were further demonstrated by electron probe microanalyzer (EPMA) results. The Zn diffusion behavior was related to its higher reactivity and smaller size in comparison with Sn, phase separation during heating, and affinity of Zn to form Ni-Sn-Zn and Ni-Zn intermetallic compounds.

Advanced alloy for lead‐free solder balls

A new alloy for lead‐free solder balls is introduced combining the advantages of a smooth surface after production and a uniform reflectivity after the ball attach process. This property significantly simplifies the inspection process during ball grid array (BGA) processing. By adding small amounts of Indium and Lanthanum to the ternary eutectic SnAgCu‐alloy a pentary, virtually eutectic composition with a melting point of 214°C is realised. It is shown that the processability in terms of reflow behaviour and the shear strength of BGA spheres made of this alloy is comparable to or better than that of ternary SnAgCu‐balls.

The influence of weathering on scratches and on scratch and mar resistance of automotive coatings

Automotive coatings are expected to retain a good scratch resistance over years of service. On the other hand, scratches once arisen should disappear by reflow or should not become more visible during further use of the car. These expectations are a challenge to the paint manufacturer and are not easy to fulfil as our work will show. Seven car coatings were examined, each with different PU clearcoats. The coatings were treated under artificial weathering conditions before and after the scratch test. Scratching was carried out using laboratory car wash and Nano Scratch techniques. In comparison to other essential coating properties measured, the scratch and mar resistance was mainly affected by pre-weathering. Alterations in reflow behaviour, shape and size of single scratches were observed during post-weathering which included partly acid precipitation.

Automotive coating

Automotive coatings are expected to retain a good scratch resistance over years of service. On the other hand, scratches once arisen should disappear by reflow or should not become more visible during further use of the car. These expectations are a challenge to the paint manufacturer and are not easy to fulfil as our work will show. Seven car coatings were examined, each with different PU clearcoats. The coatings were treated under artificial weathering conditions before and after the scratch test. Scratching was carried out using laboratory car wash and Nano Scratch techniques. In comparison to other essential coating properties measured, the scratch and mar resistance was mainly affected by pre-weathering. Alterations in reflow behaviour, shape and size of single scratches were observed during post-weathering which included partly acid precipitation.

Planarization Processes and Applications: I. Undoped GeO2 ‐ SiO2 Glasses

The reflow behavior of undoped glass films deposited by plasma enhanced chemical vapor deposition using germane, silane. and oxygen has been studied in several annealing ambient atmospheres. Such films offer the potential for both trench etchrefill and interlevel dielectric applications. Film synthesis was carried out at 200°C using a dual coil inductively coupled plasma system. Oxide film composition was determined using energy dispersive X‐ray spectroscopy and Auger energy spectroscopy. Cross‐sectional scanning electron microscopy has been employed to study the flow behavior of glass films of varying compositions over silicon trenches. Reflow was studied over the temperature range from 600 to 1050°C. The lowest temperature at which complete planarization was observed was 750 and 850°C in steam and inert gas ambient atmospheres, respectively, for films containing approximately 85 mol % . Surprisingly, it was discovered that the steam anneals caused a decrease in the Ge composition of as‐deposited germanosilicate glasses. This offers the potential for establishing a reflow hierarchy, which may have application in the planarization of interlevel dielectrics for ultralarge scale integrated circuits. © 1999 The Electrochemical Society. All rights reserved.

Planarization Processes and Applications: II. B 2 O 3 / P 2 O 5 Doped GeO2 ‐ SiO2 Glasses

Plasma enhanced chemical vapor deposition of boron and phosphorus doped mixed glass films in a horizontal tube reactor using germane , silane , diborane , phosphine , and oxygen has been studied. The glass films offer the potential for both trench refilling and interlevel dielectric applications. Film synthesis was carried out at 200°C using a dual coil inductively coupled plasma system. Oxide film composition was determined using energy dispersive X‐ray spectroscopy and Auger energy spectroscopy. Cross‐sectional scanning electron microscopy was employed for studing the compositional dependency of the reflow behavior of the mixed , , , and glass films over silicon trenches under various ambient atmospheres. Reflow experiments were performed at temperatures ranging from 550 to 800°C in various gas ambient atmospheres. As result of the work, a low temperature (∼600°C) reflow process was developed resulting in fully planar dielectric films. This process may have application for planarization of interlevel dielectrics for ultralarge scale integrated circuits. © 1999 The Electrochemical Society. All rights reserved.

Lubricant replenishment on carbon coated discs

The replenishment of a lubricant on a carbon coated disc was characterized through theoretical modeling employing experimentally acquired diffusion coefficient data. To quantify the reflow behaviour of a lubricant film, a parameter, the critical reflow time, was defined as the time to replenish a depleted hole of 1 /spl mu/m diameter in a 2 nm thick lubricant film. The results based on solving 2D diffusion equations showed that the critical reflow time is a strong function of the endgroup polarity and molecular weight of a lubricant, as well as the H and N content in the carbon film. Based on these results, design criteria have been provided for enhanced wear durability of magnetic media.

Improvement of polarizable capacitance—voltage curves of MOS capacitors passivated with BN-and PbF 2-containing SiO 2B 2O 3GeO 2 glasses

Passivation of MOS (metal, oxide, semiconductor) devices requires glasses with reflow preferably below 750°C. The compositional dependence of PbF 2- and BN-containing SiO 2B 2O 3GeO 2 glasses with respect to their reflow behavior was studied. Glass flow points, which were below 750°C, decreased with increasing BN and PbF 2. The OH content as measured by the absorption coefficient around 3600 cm −1 decreased with increasing fluorides and nitrides in these glasses. In agreement with previously reported results, it was found that glasses with low polarizability and low-OH contents were favorable for device passivation particularly with regard to the recovery of capacitance—voltage ( C-V) curve shift ( ΔV g shift) and hysteresis. Possible mechanisms have been discussed using Poisson's equation and the -OH absorption coefficients.

Aluminum Reflow Behavior in Via-Hole Filling Investigated by Molecular Dynamics Simulation and Computer Graphics

We have performed molecular dynamics simulation to study the fine structure of Al thin layer and Al reflow behavior in a temperature range of 300 K-1400 K. We have shown that at 300 K the Al atoms on the insulator surface do not migrate toward the via-hole. With increasing the temperature, the mobility of all the Al atoms increased and the via-hole was completely filled with the Al atoms at 1400 K. This acceleration of Al reflow behavior due to the rise of the temperature is in qualitatively good agreement with the experimental result. Furthermore, we clarified the dynamic transformation process of an Al thin-layer on SiO2 surface to an Al plug filling in the via-hole on an atomic scale. Hence, the effectiveness and the applicability of the molecular dynamics method to investigate the Al reflow behavior related to the fabrication of an electronic device were strongly confirmed.