Figure - available from: ECS Journal of Solid State Science and Technology
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Schematic process flow for the preparation of the wafers before adhesive bonding (1) to (5) and the subsequent parylene bonding (6). Note that the graphic is not to scale.
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Wafer bonding is a crucial process for fabricating microsystems. Within this study, the polymer parylene was used to establish a low-temperature adhesive wafer bonding process for wafers of 150 and 200 mm diameters. The bonding process was investigated for silicon and glass wafers with different additional coatings including silicon dioxide, silico...
Citations
... 50−52 In addition, parylene C can be produced as uniform films with thicknesses in the submicrometer range by room-temperature chemical vapor deposition. 53,54 Silicon is a typical material in MEMS/NEMS processes due to its toughness and reliability 55 and has a Young's modulus of 169 GPa. 56 In addition, silicon oxide, polysilicon, and silicon nitride can be fabricated more uniformly than polymeric materials. ...
... Utilizing the outstanding properties of Parylene, within previous studies, Parylene C (Poly[chloro-p-xylylene]) adhesive wafer bonding was established as a bonding process for biocompatible low temperature wafer bonding in industry scale, providing excellent mechanical and thermal stability as well as a good hermeticity of the bonds, and hence, process compatibility with most established microtechnologies. [2,3] Considering the established Parylene bonding process, the presented work focuses to provide a better understanding how the bonding conditions alter the material properties of Parylene as well as to extend the process flexibility and establish new variants. This includes wafer bonding at increased pressures in order to realize cavities with an adjustable pressure as well as bonding with Parylene N (Poly[p-xylylene]) and Parylene F (Poly[tetrafluoro-pxylylene]) instead of Parylene C in order to address different bonding temperature ranges, e.g. to enable the bonding of wafer stacks consisting of more than two wafers. ...
... Previous studies have proven that Parylene C does not get chemically altered during the established wafer bonding in vacuum using FTIR analysis. [2] However, other studies have revealed a dependency of the Young's modulus and the hardness on the thermal budget, which is assumed to be caused by recrystallization of the partially crystalline polymer. [5] Hence, free-standing Parylene C membranes of 5 µm thickness were fabricated according to the process and using the equipement given in the literature [2] and stored under the typical conditions of a bonding process, i.e. 30 min in vacuum at 260 °C, 280 °C, 300 °C, and 320 °C, respectively. ...
... [2] However, other studies have revealed a dependency of the Young's modulus and the hardness on the thermal budget, which is assumed to be caused by recrystallization of the partially crystalline polymer. [5] Hence, free-standing Parylene C membranes of 5 µm thickness were fabricated according to the process and using the equipement given in the literature [2] and stored under the typical conditions of a bonding process, i.e. 30 min in vacuum at 260 °C, 280 °C, 300 °C, and 320 °C, respectively. Changes in the crystallinity of the membranes were traced by X-ray diffraction. ...
Wafer to wafer and chip to wafer bonding technologies are a key enabling processes for the fabrication of microsystems. The presented paper focuses on the latest research results of Parylene adhesive bonding. Given the established wafer bonding processes based on Parylene C in vacuum, research on how the bonding process alters the Parylene material was performed using x-ray diffraction. Doing so, a significant increase of the crystalline fraction of Parylene was observed. In order to further develop the Parylene bonding beyond its state of the art, new process variants were successfully established with advanced features: Wafer bonding using Parylene C at increased pressure; Wafer bonding using Parylene N and Parylene F, respectively, to address a different bonding temperature range; as well as chip bonding using Parylene C in air.
... Parylene in general is primarily used as a sealing coating since it has great barrier properties. There are a lot of research papers to be found on parylene C, which is also the most used parylene type in the electronics industry [9][10][11][12][13][14][15][16]. On the other hand, a much lower number of papers are to be found on the parylene type AF4 (aliphatic fluorinate-4), which, especially in comparison to the other parylene types, stands out due to its high thermal stability (up to 550 °C) [17]. ...
Advanced packaging solutions require insulation and passivation materials with exceptional properties which can also fulfill the reliability needs of electronics devices such as MEMS, sensors or power modules. Since bonding (cohesive/adhesive) properties of packaging coatings are very important for reliable functioning of electronics devices, the bonding of aliphatic fluorinate-4 (AF4) parylene coatings was assessed in this work. As there is a lack of data regarding its bonding towards different substrates, pull-off tests of 1.6 and 2.5 µm thick AF4 coatings on silicon (Si) and glass (SiO2) substrates were performed. These showed a clear difference in the pull-off F/s curves between the AF4 coatings on Si and SiO2 substrates. This difference is parameterized by the pull-off energy, which will be presented in this work. To further understand the origin of the distinction in the pull-off energies between the AF4-Si and AF4-SiO2 samples and subsequently the cohesive/adhesive properties, mechanical and structural characterization was conducted on the AF4 coatings, where a clear difference in the E-modulus and crystallinity was observed. The Si and SiO2 wafers were shown to facilitate the CVD growth of the AF4 film distinctively, which likely relates to the divergent thermal properties of the substrates. Understanding of the cohesive/adhesive properties of AF4 coatings on different substrate materials advances the usage of the AF4 in electronics packaging technologies.
... An alternate process may be envisaged where the recrystallization may be done during bonding itself instead of prior to the bonding. Prior work [21] on the parylene-parylene utilized bonding at 260 • C for a near-hermetic bond. To compare our method with the previously reported results, paryleneparylene bonding done at 260 • C was used as the alternative. ...
... The non-patterned waferwafer bonding is prone to external local defects. These results are similar to results reported earlier by other groups [21,24] The mechanical strength of the parylene-parylene bond interface was investigated by determining the tensile and shear strength using a universal test machine (H5K5, Tinius Olsen), as shown in figures 7(c) and (d). Both sides of the bonded wafer were glued to a wooden specimen using Araldite epoxy resin. ...
This work reports a wafer-level vacuum packaging technique for MEMS using recrystallized parylene material as a bonding layer. The effect of thermal annealing on the crystallinity of the parylene surface was demonstrated. The low-temperature, stable, homogeneous, and defect-free recrystallized parylene is found as an excellent bonding material for hermetic packages, suitable for the packaging of MEMS sensors. The material's recrystallization improves its capabilities as a moisture and air barrier. The mechanical stability of the bond interface was also investigated by measuring the package's tensile and shear strength. In the absence of a vacuum bonding tool, a Ti getter was integrated into the cavity of the glass capping wafer to create the vacuum and test the hermeticity. The MEMS silicon Pirani gauge was used to monitor the pressure changes inside the sealed cavity. After the getter activation, it was observed that there was a decrease in the pressure from atmospheric pressure to 0.2 mbar for the first few days; after that, no noticeable change was observed. The hermeticity of the packaged device was examined, and the vacuum level inside the package remained the same for the last 70 days. The recrystallized parylene bonded micro package shows better hermeticity than the non-recrystallized parylene micro package.
... Poly-p-xylylen (Parylene) beschreibt eine thermoplastische Polymerfamilie, die eine einzigartige Kombination exzellenter Eigenschaften auszeichnet: Chemische Inertheit, Biostabilität und Biokompatibilität (nach ISO 10993), optische Transparenz, geringe Permeabilität gegenüber Wasser und Gasen sowie eine für Polymere vergleichsweise hohe thermische Beständigkeit. Gleichzeitig wird Parylene aus der Gasphase bei Raumtemperatur konform abgeschieden, was den Eintrag intrinsischer mechanischer Schichtspannungen vermeidet, sodass sich die hergestellten flexiblen Parylene-Substrate nicht aufrollen [1,2]. ...
... Der für die Herstellung des flexiblen potentiometrische pH-Sensors verwendete Prozess ist in Abbildung 1 schematisch dargestellt: Durch Vereinzeln eines 6"-Silizium-Wafers mittels Sägen wurden Chips gewonnen (1), auf die anschließend eine wasserlösliche Opferschicht pipettiert bzw. mittels Spincoating abgeschieden und getrocknet wurde (2). Im nächsten Schritt wurde eine etwa 10 µm dicke Schicht Parylene C aus der Gasphase mit Hilfe eines Plasma Parylene LC 300 RW (Plasma Parylene Systems GmbH) abgeschieden (3). ...
The polymer Parylene combines a variety of excellent properties and, hence, is an object of intensive research for packaging applications, such as the direct encapsulation of medical implants. Moreover, in the past years, an increasing interest for establishing new applications for Parylene is observed. These include the usage of Parylene as a flexible substrate, a dielectric, or a material for MEMS, e.g., a bonding adhesive. The increasing importance of Parylene raises questions regarding the long-term reliability and aging of Parylene as well as the impact of the aging on the Parylene properties. Within this paper, we present the first investigations on non-accelerated Parylene C aging for a period of about five years. Doing so, free-standing Parylene membranes were fabricated to investigate the barrier properties, the chemical stability, as well as the optical properties of Parylene in dependence on different post-treatments to the polymer. These properties were found to be excellent and with only a minor age-related impact. Additionally, the mechanical properties, i.e., the Young’s modulus and the hardness, were investigated via nano-indentation over the same period of time. For both mechanical properties only, minor changes were observed. The results prove that Parylene C is a highly reliable polymer for applications that needs a high long-term stability.
Traditional methods of wire bonding do not work well on liquid printed contact layers and soft substrate materials. Laser soldered wire bonding i.e. SB²-WB constitutes a novel approach to this problem as it works without the need for high pressures, temperatures or vibration [1]. In this work we qualify different conductive layers of printed, plated, and vapor coated materials containing Au, Cu and Ag with regard to their suitability for forming a stable and reliable interface with a SAC_305 laser jetted solder bump, which is the basis for the laser soldered wire bonding process (SB²-WB). As printing technologies, we have chosen stencil-and screen-printing, alternatively gold was deposited by sputtering and patterned by subsequent lithography and wet-chemical etching. As substrates, we selected Polyethylene-naphthalate (PET) Teonex Q51, Parylene and Glass. Au wire and Ag ribbon were used for forming the wire bonds. Investigations on printed layers have been focused on correlation between paste receipt, printing technology related layer thickness, paste-related post-treatment and compatibility to laser assisted solder ball bumping i.e., SB²-Jet. Using a shear-tester, the mechanical load-capacity of the formed solder joints was measured, and the corresponding fracture modes were inspected using an optical microscope. The characteristic of the interfacial layers, material bulk textures and other metallurgical properties was analyzed with SEM-FIB, EDX, X-ray and optical microscopy. Moreover, we demonstrated the forming of laser soldered wire bonds on two demonstrators showing different pad metallization, contact form and substrate bulk material. Finally, the future prospects of intended feasibility studies for laser soldered wire bonding, with structures consisting of paste and ink are highlighted.
