Ti Barrier Layer Research Articles

Nanotwinning-assisted structurally stable copper for fine-pitch redistribution layer in 2.5D/3D IC packaging

The redistribution layer (RDL) is crucial for fanning out circuits and for 2.5D/3D IC packaging. As device density increases, RDL CD/pitch must shrink. During RDL circuit fabrication, the etching process is necessary to remove the exposed sputtered Cu seed layer and Ti barrier layer. Unfortunately, this process unavoidably etches and roughens the Cu surface of the RDL. As the post-plating resting time (q-time) increases, the Cu surface oxidizes, resulting in even worse surface roughness after etching. This roughness causes contact resistance and electromigration issues when the RDL linewidth shrinks. This paper presents a composite Cu structure that combines fine grains and nanotwins, which is structurally stable and can effectively resist surface damage even after extended periods, offering a promising solution for achieving finer RDL in advanced packaging technologies with a longer electromigration lifetime than regular coarse-grain lines.

Influence of Barrier Layers on ZrCoCe Getter Film Performance.

Improving the vacuum degree inside the vacuum device is vital to the performance and lifespan of the vacuum device. The influence of the Ti and ZrCoCe barrier layers on the performance of ZrCoCe getter films, including sorption performance, anti-vibration performance, and binding force between the ZrCoCe getter film and the Ge substrate were investigated. In this study, the Ti and ZrCoCe barrier layers were deposited between the ZrCoCe getter films and Ge substrates. The microtopographies of barrier layers and the ZrCoCe getter film were analyzed using scanning electron microscopes. The sorption performance was evaluated using the constant-pressure method. The surface roughness of the barrier layers and the getter films was analyzed via atomic force microscopy. The binding force was measured using a nanoscratch tester. The anti-vibration performance was examined using a vibration test bench. The characterization results revealed that the Ti barrier layer significantly improved the sorption performance of the ZrCoCe getter film. When the barrier material was changed from ZrCoCe to Ti, the initial sorption speed of the ZrCoCe getter film increased from 141 to 176 cm3·s-1·cm-2, and the sorption quantity increased from 223 to 289 Pa·cm3·cm-2 in 2 h. The binding force between the Ge substrate and the ZrCoCe getter film with the Ti barrier layer was 171 mN, whereas that with the ZrCoCe barrier layer was 154 mN. The results showed that the Ti barrier layer significantly enhanced the sorption performance and binding force between the ZrCoCe getter film and the Ge substrate, which improved the internal vacuum level and the stability of the microelectromechanical system vacuum devices.

Enhancement of the light output efficiency and thermal stability of AlGaN-based deep-ultraviolet light-emitting diodes with Ag-nanodot-based p-contacts and an 8-nm p-GaN cap layer.

The efficiency of AlGaN-based deep-ultraviolet light-emitting diodes (DUV LEDs) is limited by the high absorption issue of the p-GaN contact layer or poor contact properties of the transparent p-AlGaN contact layer. Enhancement of the light output efficiency and thermal stability of DUV LEDs with an emission wavelength of 272 nm was investigated in this work. Ag nanodots on an 8-nm p-GaN cap layer were used to form ohmic contact, and Al and Mg reflective mirrors were employed to enhance the light output power (LOP) of DUV LEDs. However, serious deterioration of LOP occurred after the high-temperature process for the LEDs with Al and Mg reflective mirrors, which can be attributed to the damage to the ohmic contact properties. A Ti barrier layer was inserted between the Ag/p-GaN and Al layers to prevent the degeneration of ohmic contact. The wall-plug efficiency (WPE) of DUV LEDs fabricated by the Ag-nanodot/Ti/Al electrode is 1.38 times that of LEDs fabricated by adopting a thick Ag layer/Ti/Al at 10 mA after a high-temperature process. The Ag-nanodot/Ti/Al electrode on thin p-GaN is a reliable technology to improve the WPE of DUV LEDs. The experimental and simulated results show that the ohmic contact is important for the hole-injection efficiency of the DUV LEDs when p-GaN is thin, and a slight increase in the contact barrier height will decrease the WPE drastically. The results highlighted the importance of thermally stable ohmic contacts to achieve high-efficiency DUV LEDs and demonstrated a feasible route for improving the LOP of DUV LEDs with a thin p-GaN cap layer and stable reflective electrodes.

Structural and morphological properties of contacts to a (111) orientation monosilicon substrate based on aluminum with a Ti and w – 10 % Ti barrier layer

The paper presents the results of studies on the formation of ohmic contacts to monosilicon from aluminum in the presence of a thin-film barrier layer based on titanium and tungsten.
 The purpose of reseach: to study the mechanism of solid-phase interaction in Al/Ti/Si and Al/Ti/SiOx/Si systems during the formation of contacts to (111) orientation silicon based on aluminum with a Ti and W 10% Ti barrier layer, their structural and morphological properties and ways to manage this mechanism. The study revealed relationships between the structure and properties of the films, which can lead to marriage or a decrease in the service characteristics of the IC due to a violation of the structure of the film composition.
 Methods and objects of research: It is shown that the difference in the behavior of thick and thin oxides is consistent with the thermodynamic data for bulk materials. In this case, the formation and final electrical properties of the silicidesilicon interface region depend on the presence of unavoidable impurities present during the deposition of the reacting metal.
 As a result of electron microscopic studies of the Al/WTi/Si system, it was found that the tungsten10 % (wt.) titanium barrier layer is reliably thermally stable up to a temperature of 773 K, regardless of the layer thickness (0.050.12 m).

Design and Development of Single-Qubit Ion Trap on Glass and Si Substrates With RF Analysis and Performance Benchmarking

This article presents the design and development of surface electrode ion traps on glass and Si substrates and their radio frequency (RF) characterizations and performance benchmarking. In this case, the ion trap on glass shows superior performances in all necessary criteria. In terms of RF characterizations, ion traps on glass have a ${Q}$ factor of greater than 900. This is significantly higher than the ${Q}$ factor of its silicon counterparts, which are around 20–300. Such a high ${Q}$ factor results in power spectral density (PSD) of greater than 10 W/MHz. On the other hand, ion traps on silicon produce PSD values of lower than 3 W/MHz. In terms of RF performance, the ion trap on glass shows insertion loss lower than 0.2 dB at 60 MHz. This is more superior to insertion loss values of ion traps on silicon, which are around 1–4 dB. The ion-traps metallization is developed using three metallization layers (0.1- $\mu \text{m}$ Ti barrier layer, 2.5–3.7- $\mu \text{m}$ Cu, and 0.3- $\mu \text{m}$ Au) on top of the dielectric. The on-chip resonance condition can be maintained upon packaging integration. The laser optical setup for ion trapping is verified to capture a single 88Sr+ ion.

Optimization Mechanisms of Microstructure and Mechanical Properties of SiC Fiber Reinforced Ti/Al3Ti Laminated Composite Synthesized Using Titanium Barrier

A novel structure-optimized SiC fiber reinforced metal-intermetallic-laminated composite (SiCf-Ti/Al3Ti) without intermetallic centerline defect has been fabricated by vacuum hot pressing using stacked fibers and foils as well as Ti barrier layer. Through microstructure characterization by SEM and EBSD, the mechanisms of centerline formation and structural optimization were investigated detailedly. The mechanical properties and fracture behaviors of the optimized and non-optimized SiCf-Ti/Al3Ti composites were studied via quasi-static compression tests. The experimental results indicated that the intermetallic centerline region existing at the mid-plane of Al3Ti layer in non-optimized composite mainly contains newly-formed Kirkendall voids and gathered metallic oxides. Additionally, owing to the similar moving trails of fibers, oxides and voids in molten Al during hot pressing, SiC fiber is always accompanied with centerline, which causes the poor bonding of SiCf/Al3Ti interface. Unlike that, due to the adding of Ti barrier layer, SiC fibers are separated from centerline and metallurgically bonded with Al3Ti intermetallic in the optimized composite. The compression testing results proved that the optimized SiCf-Ti/Al3Ti composite possesses superior strength and toughness compared with those of the non-optimized composite. Besides, the extending of cracks along centerline often leads to large-scale centerline splitting and untimely SiCf/Al3Ti interface debonding in non-optimized composite. Nevertheless, cracks formed in optimized composite tend to propagate at the interfacial zone between layers instead of cutting off Al3Ti layer along its mid-plane. Moreover, ascribed to the well-bonded SiCf/Al3Ti interface, SiC fibers play an important role in strengthening and toughening the optimized SiCf-Ti/Al3Ti composite by fiber bridging mechanism.

Electron scattering at Co(0001) surfaces: Effects of Ti and TiN capping layers

In situ transport measurements on epitaxial 7.6-nm-thick Co(0001)/Al2O3(0001) films with and without Ti and TiN capping layers during O2 exposure are used to investigate the effects of surface chemistry on electron scattering at Co(0001) surfaces. The Co sheet resistance Rs increases with increasing thickness dTi and dTiN of the Ti and TiN capping layers, saturating at 8% and 31% above the uncoated Co(0001) for dTi > 0.2 nm and dTiN > 0.1 nm, respectively. This increase is attributed to electron scattering into local surface states, which is less pronounced for Ti than TiN. In situ resistance measurements taken during a continuously increasing O2 partial pressure from 0 Pa to 40 Pa indicate a relatively steep 24% increase in Rs at an exposure of ∼50 Pa s, which can be attributed to Co surface oxidation that leads to atomic level roughness and a decrease in the electron scattering specularity p. Ti and TiN cap layers with dTi ≥ 0.5 nm and dTiN ≥ 0.13 nm exhibit no resistance change upon air exposure, indicating suppression of Co oxidation. These results indicate a promising Co–Ti interface with an electron scattering specularity of p = 0.4–0.5, which is retained during oxygen exposure, while, in contrast, electron scattering at the Co–TiN interface is completely diffuse (p = 0), suggesting that Ti barrier layers facilitate higher-conductivity Co interconnects than TiN barriers, as long as the Ti layer is sufficiently thick (dTi ≥ 0.5 nm) to suppress Co oxidation.

Heat-Resistant Microporous Ag Die-Attach Structure for Wide Band-Gap Power Semiconductors.

In this work, efforts were made to prepare a thermostable die-attach structure which includes stable sintered microporous Ag and multi-layer surface metallization. Silicon carbide particles (SiCp) were added into the Ag sinter joining paste to improve the high-temperature reliability of the sintered Ag joints. The use of SiCp in the bonding structures prevented the morphological evolution of the microporous structure and maintained a stable structure after high temperature storage (HTS) tests, which reduces the risk of void formation and metallization dewetting. In addition to the Ag paste, on the side of direct bonded copper (DBC) substrates, the thermal reliability of various surface metallizations such as Ni, Ti, and Pt were also evaluated by cross-section morphology and on-resistance tests. The results indicated that Ti and Pt diffusion barrier layers played a key role in preventing interfacial degradations between sintered Ag and Cu at high temperatures. At the same time, a Ni barrier layer showed a relatively weak barrier effect due to the generation of a thin Ni oxide layer at the interface with a Ag plating layer. The changes of on-resistance indicated that Pt metallization has relatively better electrical properties compared to that of Ti and Ni. Ag metallization, which lacks barrier capability, showed severe growth in an oxide layer between Ag and Cu, however, the on-resistance showed fewer changes.

Pt:Ti Diffusion Barrier, Interconnect, and Simultaneous Ohmic Contacts to n- and p-Type 4H-SiC

We report the initial results of using co-sputtered Pt:Ti 80:20 at. % composition ratio metallization as a diffusion barrier against gold (Au) and oxygen (O), as an interconnect layer, as well as forming simultaneous ohmic contacts to n-and p-type 4H-SiC. Having a single conductor with such combined multi-functional attributes would appreciably reduce the fabrication costs, processing time and complexity that are inherent in the production of SiC based devices. Auger Electron Spectroscopy, Focused Ion Beam-assisted Field Emission Scanning Electron Microscopy and Energy Dispersive Spectroscopy analyses revealed no Au and O migration to the SiC contact surface and minimal diffusion through the Pt:Ti barrier layer after 15 minutes of exposure at 800 oC in atmosphere, thus offering potential long term stability of the ohmic contacts. Specific contact resistance values of 7 x 10-5 and 7.4 x 10-4 Ω-cm2 were obtained on the n (Nd=7 x 1018 cm-3) and p (Na=2 x 1020 cm-3) -type 4H-SiC, respectively. The resistivity of 75 μΩ-cm was obtained for the Pt:Ti layer that was sandwiched between two SiO2 layers and annealed in pure O ambient up to 900 °C, which offers promise as a high temperature interconnect metallization.

Structure Stability of Electrodeposited Au-Cu Alloy Micro-Cantilever Evaluated By Long-Term Vibration Test for Applications As Movable Components in MEMS Devices

This study reports structure stability of micro-cantilevers composed of Au-Cu alloy for applications as moveable components in micro-electrical-mechanical system (MEMS) accelerometers. Au-based micro-components are developed to replace conventional Si-based components in a MEMS accelerometer to allow further miniaturization of the device [1]. However, the mechanical strength of Au is relatively low when compared with that of Si. The low mechanical strength raises concerns on structure stability of movable micro-components composed of Au-based materials, which could affect reliability and lifetime of the device. Electroplating is a promising technique in manipulating properties of the metallic materials for applications in MEMS. For instance, grain refinement effect often observed in electroplating can be employed to enhance the mechanical strength by the grain boundary strengthening mechanism [2]. In addition, alloy electroplating is a fascinating technique capable of controlling composition of the metallic material, and alloying the metallic material allows utilization of the solid solution strengthening mechanism to further enhance the mechanical strength [3]. By synergistic effects of the grain boundary strengthening and solid solution strengthening mechanisms, an ultra-high yield stress of 1.15 GPa [3] is reported for electroplated Au-Cu micro-specimens, which is comparable to fracture strength of Si. In order to apply the high-strength Au-Cu alloy as movable structures in MEMS devices, investigating the vibration fatigue is necessary to confirm the reliability and the lifetime. In this study, long-term vibration tests of micro-cantilevers fabricated by combining lithography and Au-Cu alloy electroplating were conducted to reveal effects of the vibration fatigue on structure stability of the Au-Cu alloy micro-cantilevers. Fabrication process of the micro-cantilevers is illustrated in Fig. 1. The Ti barrier layer and the Au seed layer were deposited by sputtering, and the layer thicknesses were both at 100 nm. The Au–Cu electrolyte used in this work was a commercially available electrolyte provided by MATEX Co. Japan, which contained 17.3 g/L of X3Au(SO3)2 (X = Na, K), 1.26 g/L of CuSO4, and ethylenediaminetetraacetic acid as the additive with pH at 7.5. The electroplating was carried out at 50 ◦C, and the current density was varied from 0.1 to 3 mA/cm2. A piece of Pt plate was used as the anode. Image of the Au-Cu alloy micro-cantilevers before the vibration test is shown in Fig. 2. Design-length of the micro-cantilever (l) was varied from 50 ~ 1000 μm, and design-width of the micro-cantilever (w) was ranged from 5 ~ 20 μm. Thickness of the Au-Cu alloy layer (t) was from 2.3 ~ 5.0 μm. The long-term vibration test was carried out under conditions of the cycle number in a range from 103 to 106, the frequency of 10.0 Hz, and the acceleration of 1.0 G (1 G = 9.8 m/s2). The structure stability was determined by evaluating height profiles of top surface of the micro-cantilevers before and after the vibration test by a 3D optical microscope. Height profiles of a micro-cantilever composed of 97.7 % Au with the length at 1000 μm, the width 20 μm, and the thickness at 3.9 μm before and after the vibration test are shown in Fig. 3. Fluctuations in the height before the vibration test, the 0 cycle result, were mainly results of the surface roughness. After 106 cycles of the vibration test, the micro-cantilever was still intact as observed from the optical microscope. The height profiles did not change much after the vibration. In order to quantify the structure stability, deflection at tip of the micro-cantilever was determined. The tip deflection merely changed 0.37 μm for the 1000 μm long micro-cantilever after 106 cycles of the vibration test. This result confirmed high structure stability in the electroplated Au-Cu alloy micro-cantilever and demonstrated the superiority of this Au-Cu alloy structure in applications as movable components in MEMS devices. [1] D. Yamane, T. Konishi, T. Matsushima, K. Machida, H. Toshiyoshi, K. Masu, Appl. Phys. Lett., 104 (2014) 074102. [2] H. Tang, C.-Y. Chen, T. Nagoshi, T.-F.M. Chang, D. Yamane, K. Machida, K. Masu, M. Sone, Electrochem. Commun., 72 (2016) 123–130. [3] H. Tang, C.-Y. Chen, M.Yoshiba, T.Nagoshi, T.-F.M. Chang, D.Yamane, K.Machida, K.Masu, M.Sone, Electrochemical Society, 164 (2017) 244–247 Figure 1

Controllable Electrical Contact Resistance between Cu and Oriented-Bi2Te3 Film via Interface Tuning.

The contact resistance between metals and semiconductors has become critical for the design of thin-film thermoelectric devices with their continuous miniaturization. Herein, we report a novel interface tuning method to regulate the contact resistance at the Bi2Te3-Cu interface, and three Bi2Te3 films with different oriented microstructures are obtained. The lowest contact resistivity (∼10-7 Ω cm2) is observed between highly (00l) oriented Bi2Te3 and Cu film, nearly an order of magnitude lower than other orientations. This significant decrease of contact resistivity is attributed to the denser film connections, lower lattice misfit, larger effective conducting contact area, and smaller width of the surface depletion region. Meanwhile, our results show that the reduction of contact resistance has little dependence on the interfacial diffusion based on the little change in contact resistivity after the introduction of an effective Ti barrier layer. Our work provides a new idea for the mitigation of contact resistivity in thin-film thermoelectric devices and also gives certain guidance for the size design of the next-level miniaturized devices.

A Measurement Method on Nanoscale Thickness of the Ti Barrier Layer of TSV Structure for 3-D IC

As the characteristic dimension of an integrated circuit (IC) continuously scales down, together with the requirements of low power consumption, multiple functionality, and cost effectiveness, the conventional IC transforms into a 3-D IC. Through-silicon via (TSV) is a promising and preferred way to realize the reliable interconnection for a 3-D IC. Thus, accurate measurement of the critical structural parameters plays an important role in securing the integrity and reliability of TSV. In this paper, a novel image-processing-based measurement method is proposed to measure the barrier layer thickness and step coverage of TSV. Since the thickness of the barrier layer is generally less than 100 nm, which is a drawback of the conventional SEM method, we used the material information from SEM as well as structural prior of TSV to infer the barrier layer thickness on nanoscale. In addition, we further achieved the step coverage of thin films in TSV using the proposed measurement method.

Improvement of mechanical properties of SiC(SCS-6) fibre-reinforced Ti3AlC2 matrix composites with Ti barrier layer

In this study, silicon carbide fibre-reinforced Ti3AlC2 matrix composites with a Ti barrier layer were prepared by hot-pressing at 1250°C and 1300°C. The microstructure of the composites was characterised by field-emission scanning electron microscopy. During consolidation, reactions of Ti with the fibres and the matrix led to the formation of an interfacial reaction zone between the fibres and the matrix and a matrix reaction zone within the matrix. Quantitative elemental distribution maps of both reaction zones were collected using energy-dispersive spectroscopy. The results revealed that the Ti layer effectively hindered the inward diffusion of Al from the matrix. In addition, the flexural strength of the composite was significantly improved with the addition of the Ti layer. Furthermore, noncatastrophic fracture behaviour was observed for the composites. The improvement of their mechanical behaviour is attributed to the added Ti layer, which prevented strength degradation of the fibres via a severe interface reaction.

Thermostable Ag die-attach structure for high-temperature power devices

This paper explores the possibility of using Ag paste containing silicon carbide particles (SiC-p) as a novel high-temperature die-attachment solution for the design of power devices. The bonding structure used in this research was composed of silicon dies and a direct bonded copper (DBC) substrate. A SiC-p/microporous Ag composite structure was prepared by sintering a Ag microflake paste containing 2 wt% sub-micron SiC-p under mild conditions (250 °C and 0.4 MPa for 30 min). In addition to the Ag paste, the surface metallization of the DBC substrate was also evaluated in this research. Ag metallization layers deposited by electroplating and sputtering were compared, along with samples also containing a titanium (Ti) diffusion barrier layer between Cu and Ag. The results indicated that the SiC-p-containing Ag sinter paste showed better stability in storage tests than the paste without SiC-p at the temperatures such as 150, 250 and 350 °C. Additionally, the Ti diffusion barrier layer played an active role in preventing the oxidation of Cu and inter-diffusion between Cu and Ag during use at high temperatures exceeding 250 °C. The joint bonded by SiC-p-containing Ag paste on DBC substrate with Ti barrier layer exhibited excellent stability up to 1000 h at 150 and 250 °C.

The role of the Ti and Mo barrier layer in Ti/Al metallization to AlGaN/GaN heterostructures at identical process conditions: a structural and chemical characterization

The composition and structure of TiAl-based metallizations have been investigated depending on the Ti and Mo barriers. The lowest contact resistivity of 4 × 10−6 Ω.cm2 for a Ti barrier and 7 × 10−6 Ω.cm2 for a Mo barrier is obtained at a Ti/Al ratio of 0.43 after annealing at 800 °C. The scanning transmission electron microscope (STEM) and energy dispersive spectroscopy (EDS) analyses reveal that Mo is not an effective barrier for the Au in-diffusion and Al out of diffusion during annealing. The intensive diffusion processes lead to the formation of the semimetal TiN compound at the interface and intermetallic phases of Au, Al, and Ti, the structure and composition of which depend on the barrier metal.

Study on the performance of Tungsten–Titanium alloy film as a diffusion barrier for iron in a flexible CIGS solar cell

A Tungsten–Titanium (W–Ti) diffusion barrier was prepared on an iron (Fe) substrate by means of magnetron sputtering with subsequent annealing at different temperatures. Rutherford Backscattering Spectrometry (RBS) was used to analyze the Fe distribution in the W–Ti layer. The diffusion constant D0=3.4×10−16m2/s and the activation energy Q=43kJ/mol of the Fe diffusing in the W–Ti layer were subsequently calculated based on Fick’s Second Law. The results demonstrated that a 291nm-thick W–Ti barrier layer can be used to block Fe from diffusing into a CIGS solar cell for 20years at a work temperature of 308K (35°C).

Adhesion strength of sputter deposited diffusion barrier layer coatings for the use in U–Mo nuclear fuels

Advanced designs for high-density U–Mo/Al nuclear fuel feature an interfacial barrier layer between the U–Mo fuel bulk and the Al cladding, which is intended to avoid the formation of an irradiation induced diffusion layer (IDL). Sputter deposition was suggested as a method to apply such interfacial barriers to the U–Mo/Al fuel system. We investigated the adhesion strength of sputter deposited Ti, Zr, Zry-4, Nb and Ta barrier layers of 15–20μm thickness in the U–Mo/Al system by pull-off tests. The adhesion strength is a measure for the robustness of a diffusion barrier layer against delaminating due to inner stresses. We found, that the adhesion strength of sputter deposited diffusion barrier layers is at least similar or even better compared to both the adhesion strength of barrier layers produced by the INL co-rolling process and the fuel-to-cladding adhesion strength achieved by the AREVA-CERCA C2TWP process.

Effects of surface treatment on the bonding quality of wafer-level Cu-to-Cu thermo-compression bonding for 3D integration

Various surface treatments are applied for surface oxide removal prior to wafer-level Cu-to-Cu thermo-compression bonding and the bonding quality is systematically analyzed in this work. Three methods are investigated: self-assembled monolayer (SAM) passivation, forming gas annealing and acetic acid wet cleaning. The surface conditions are carefully examined including roughness, contact angle and x-ray photoelectron spectroscopy (XPS) scan. The wafer pairs are bonded at 250 °C under a bonding force of 5500 N for a duration of 1 h in a vacuum environment. The bonding medium consists of a Cu (300 nm) bonding layer and a Ti (50 nm) barrier layer. The bonding quality investigation consists of two parts: hermeticity based on helium leak test and mechanical strength using four-point bending method. Although all samples under test with different surface treatment methods present an excellent hermetic seal and a robust mechanical support, the measurement results show that samples bonded after SAM passivation exhibit the best hermeticity and bonding strength for 3D integration application.

Effect of bonding temperature on hermetic seal and mechanical support of wafer-level Cu-to-Cu thermo-compression bonding for 3D integration

Hermetic seal and mechanical support of wafer-level Cu-to-Cu thermo-compression bonding with different bonding temperature are analyzed in this work. The investigation consists of two parts: hermetic seal study using helium bomb test and mechanical support study using four-point bending method. The wafer pairs are bonded at 250, 300 and 350 °C, respectively, under a bonding force of 5,500 N for a duration of 1 h in vacuum (~2.5 × 10−4 mbar). The bonding medium consists of Cu (300 nm) bonding layer and Ti (50 nm) barrier layer. Excellent helium leak rate, which is smaller than the reject limit defined by MIL-STD-883E standard (method 1014.10), and outstanding interfacial adhesion energy are detected for all samples. The cavities sealed at 300 °C present an excellent reliability of temperature cycling test up to 500 cycles. Cu-to-Cu thermo-compression bonding at low temperature (≤300 °C) presents an attractive hermetic seal and a robust mechanical support for 3D integration application.

Wafer-level hermetic packaging of 3D microsystems with low-temperature Cu-to-Cu thermo-compression bonding and its reliability

Low-temperature wafer-level Cu-to-Cu thermo-compression bonding and its reliability for hermetic sealing application have been investigated in this work. The volume of the encapsulated cavities is about 1.4×10−3 cm3 in accordance with the MIL-STD-883E standard prescribed for microelectronics packaging hermeticity measurement. The samples under test are bonded at 300 °C under a bonding force of 5500 N for 1 h in vacuum (∼2.5 × 10−4 mbar) with a 300 nm thick Cu diffusion layer and 50 nm thick Ti barrier layer which are deposited in an e-beam evaporator. The reliability test is accomplished through a temperature cycling test (TCT) from −40 to 125 °C up to 1000 cycles and a humidity test based on IPC/JEDEC J-STD-020 standard. In addition, an immersion in acid/base solution is applied to verify the corrosion resistance of the Cu frame for hermetic application. Excellent helium leak rate which is smaller than the reject limit defined by the MIL-STD-883E standard (method 1014.10) is detected for all the samples. These excellent helium leak rates show an outstanding bonding quality against harsh environment for hermetic encapsulation in 3D integration applications.