Evaluation of the Crystallographic Quality of Electroplated Copper Thin-Film Interconnection Embedded in a Si Substrate

2013 ◽  
Author(s):  
Ryosuke Furuya ◽  
Osamu Asai ◽  
Chuanhong Fan ◽  
Ken Suzuki ◽  
Hideo Miura
Keyword(s):  
Thin Films ◽  
Electrical Properties ◽  
Defect Density ◽  
Bulk Material ◽  
Si Substrate ◽  
High Defect Density ◽  
Mechanical And Electrical Properties ◽  
Electroplated Copper ◽  
Interconnection Material

Electroplated copper thin films have started to be applied to the interconnection material in TSV structures because of its low electric resistivity and high thermal conductivity. However, the electrical resistivity of the electroplated copper thin films surrounded by SiO2 was found to vary drastically comparing with those of the conventional bulk material. This was because that the electroplated copper thin films consisted of grains with low crystallinity and grain boundaries with high defect density. Thus, in this study, both the crystallinity and electrical properties of the electroplated copper thin films embedded in the TSV structure was evaluated quantitatively by changing the electroplating conditions and thermal history after the electroplating. It was observed that many voids and hillocks appeared in the TSV structures after the high temperature annealing which was introduced for improving the crystallinity of the electroplated films. Therefore, it is very important to evaluate the crystallographic quality of the electroplated copper thin films after electroplating to assure both the mechanical and electrical properties of the films.

Improvement of Mechanical Reliability of 3D Electronic Packaging by Controlling the Mechanical Properties of Electroplated Materials

2013 ◽  
Author(s):  
Ken Suzuki ◽  
Hideo Miura
Keyword(s):  
Thin Films ◽  
Electrical Properties ◽  
Defect Density ◽  
Bulk Material ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Silicon Chips ◽  
Materials Used ◽  
Electroplated Copper ◽  
Interconnection Material

Three-dimensional (3D) integration of silicon microelectronic devices improves the electronic functions of devices and minimizes packaging density drastically. A through-silicon via (TSV) structure is indispensable for maximizing the density of interconnections among the stacked silicon chips. However, since the TSV structure is surrounded by silicon, and there is large mismatch in materials properties between metallic materials used for the TSV structure and silicon, thermal stress is essentially generated around the TSV structure during their fabrication process and operating conditions. Recently, electroplated copper thin films have started to be applied to the interconnection material in the TSV structure because of its low electric resistivity and high thermal conductivity. However, the electrical resistivity of the electroplated copper thin films surrounded by SiO2 was found to vary drastically comparing with those of the conventional bulk material. This was because that the electroplated copper thin films consisted of grains with low crystallinity and grain boundaries, in other words, abnormally high defect density. Thus, both the crystallinity and electrical properties of the TSV structure was investigated quantitatively by changing their electroplating conditions and thermal history after the electroplating. It was observed that many voids and hillocks appeared in the TSV structures depending on the electroplating conditions. It was also found that the stress-induced migration occurred after the high temperature annealing which was introduced for improving the crystallinity of the electroplated films. Therefore, it is very important to evaluate the crystallographic quality of the electroplated copper thin films after electroplating to assure both the mechanical and electrical properties of the films.

Micro Texture Dependence of Both the Mechanical and Electrical Properties of Electroplated Copper Thin Films Used for Interconnection

2010 ◽  
Author(s):  
Naokazu Murata ◽  
Naoki Saito ◽  
Kinji Tamakawa ◽  
Ken Suzuki ◽  
Hideo Miura
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Electrical Properties ◽  
Grain Boundaries ◽  
Fracture Mode ◽  
The Other ◽  
Copper Films ◽  
Mechanical And Electrical Properties ◽  
Electroplated Copper

Both mechanical and electrical properties of electroplated copper thin films were investigated experimentally with respect to changes in their micro texture. Clear recrystallization was observed after the annealing even at low temperature of about 150°C. The fracture strain of the film annealed at 400°C increased from the initial value of about 3% to 15%, and at the same time, the yield stress of the annealed film decreased from about 270 MPa to 90 MPa. In addition, it was found that there were two fatigue fracture modes in the film annealed at the temperatures lower than 200°C. One was a typical ductile fracture mode with plastic deformation and the other was brittle one. When the brittle fracture occurred, the crack propagated along weak or porous grain boundaries which remained in the film after electroplating. The brittle fracture mode disappeared after the annealing at 400°C. These results clearly indicated that the mechanical properties of electroplated copper thin films vary drastically depending on their micro texture. Next, the electrical reliability of electroplated copper thin film interconnections was discussed. The interconnections used for electromigration (EM) tests were made by damascene process. The width of the interconnections was varied from 1 μm to 10 μm. An abrupt fracture mode due to local fusion appeared in the as-electroplated films within a few hours during the test. Since the fracture rate increased linearly with the increase of square of the applied current density, this fracture mode was dominated by local Joule heating. It seemed that the local resistance of the film increased due to the porous grain boundaries and thus, the local temperature around the porous grain boundaries increased drastically. On the other hand, the life of the interconnections annealed at 400°C was improved significantly. This was because of the increase of the average grain size and the improvement of the quality of grain boundaries in the annealed films. The electrical properties of the electroplated copper films were also dominated by their micro texture. However, the stress migration occurred in the interconnections after the annealing at 400°C. This was because of the high residual tensile stress caused by the constraint of the densification of the films by the surrounding oxide film in the interconnection structures during the annealing. Finally, electroplating condition was controlled to improve the electrical properties. Both the resistance of electromigration and electrical resistivity were improved significantly. However, electromigration of copper atoms still occurred at the interface between the electroplated copper and the thin tantalum (Ta) layer sputtered as base material. Therefore, it is very important to control the crystallographic quality of electroplated copper films and the interface between different materials for improving the reliability of thin film interconnections.

Effect of Crystallographic Quality of Grain Boundaries on Both Mechanical and Electrical Properties of Electroplated Copper Thin Film Interconnections

2015 ◽  
Vol 137 (3) ◽  
Author(s):  
Naokazu Murata ◽  
Naoki Saito ◽  
Kinji Tamakawa ◽  
Ken Suzuki ◽  
Hideo Miura
Keyword(s):  
Electrical Properties ◽  
Grain Boundaries ◽  
Fatigue Fracture ◽  
High Crystallinity ◽  
Mechanical And Electrical Properties ◽  
Copper Interconnection ◽  
Electroplated Copper ◽  
Two Parameters ◽  
Low Crystallinity

Effects of crystallographic quality of grain boundaries on mechanical and electrical properties were investigated experimentally. A novel method using two parameters of image quality (IQ) and confidence index (CI) values based on electron back-scattering diffraction (EBSD) analysis was proposed in order to evaluate crystallographic quality of grain boundaries. IQ value was defined as an index to evaluate crystallinity in region irradiated with electron beam. CI value determined existence of grain boundaries in the region. It was found that brittle intergranular fatigue fracture occurred in the film without annealing and the film annealed at 200 °C because network of grain boundaries with low crystallinity remained in these films. On the other hand, the film annealed at 400 °C caused only ductile transgranular fatigue fracture because grain boundaries with low crystallinity almost disappeared. From results of measurement of electrical properties, electrical resistivity of copper interconnection annealed at 400 °C with high crystallinity (2.09 × 10−8 Ωm) was low and electron migration (EM) resistance was high compared with an copper interconnection without annealing with low crystallinity (3.33 × 10−8 Ωm). It was clarified that the interconnection with high crystallinity had superior electrical properties. Thus, it was clarified that the crystallographic quality of grain boundaries has a strong correlation of mechanical and electrical reliability.

Mechanical and Electrical Properties of Electroplated Copper Thin Films Used for Thin Film Interconnection

2010 ◽  
Vol 1249 ◽  
Author(s):  
Murata Naokazu ◽  
Kinji Tamakawa ◽  
Ken Suzuki ◽  
Hideo Miura
Keyword(s):  
Thin Films ◽  
Residual Stress ◽  
Electrical Properties ◽  
Grain Boundaries ◽  
The Other ◽  
Mechanical And Electrical Properties ◽  
Average Grain Size ◽  
Columnar Grains ◽  
Electroplated Copper ◽  
Electrical Reliability

AbstractMicro-texture dependence of both the mechanical and electrical properties of electroplated copper thin films was discussed experimentally considering the change of their micro texture caused by thermal history after the electroplating. Both the static and fatigue strength of the films changed drastically depending on the micro texture and it was found that there were two fatigue fracture modes in the films. One was a typical ductile intragranular fracture and the other was brittle intergranular one. The reason for the variation of the strength of the electroplated copper thin films was attributed to the variation of the average grain size and the characteristics of grain boundaries. In addition, the electrical reliability of the electroplated copper interconnections was discussed under electromigration tests. Though abrupt fracture mode due to the local fusion appeared in the as-electroplated films, the life of the interconnections was improved significantly after the annealing at temperatures high than 200°C. Typical change of the surface morphology of the film, i.e., the formation of voids and hillocks were observed on their surfaces after the annealing. This was also caused by the change of the micro texture from fine grains with porous grain boundaries to coarsened columnar grains with rigid grain boundaries. However, the stress-induced migration appeared in the annealed narrow interconnections, in particular. This was because of high tensile residual stress occurred in the film due to the constraint of the shrinkage of the films by rigid oxide around them. These results clearly indicated that the control of both the micro-texture and residual stress is indispensable for improving the reliability of the interconnectins.

Microtexture Dependence of Mechanical and Electrical Properties of Gold Thin Films Used for Micro Bumps of 3D Stacking Structures

2020 ◽  
Author(s):  
Genta Nakauchi ◽  
Shota Akasaki ◽  
Hideo Miura
Keyword(s):  
Thin Films ◽  
Mechanical Properties ◽  
Electrical Properties ◽  
Grain Boundaries ◽  
Indentation Test ◽  
Electron Back Scatter Diffraction ◽  
Effective Lifetime ◽  
Mechanical And Electrical Properties ◽  
Gold Thin Films ◽  
3D Stacking

Abstract The variation of their crystallinity, in other words, the order of atom arrangement of grain boundaries in electroplated gold thin films was investigated by changing their manufacturing conditions. Then, the effect of the crystallinity on both their mechanical and electrical properties was measured by using nano-indentation test and electromigration test. The crystallinity of the gold thin films was varied by changing the under-layer material used for electroplating. Also, the micro texture of gold thin films was evaluated by EBSD (Electron Back-Scatter Diffraction) and XRD (X-Ray Diffraction). It was clarified that the crystallinity of the electroplated gold thin films changed drastically depending on the crystallinity of the under-layer materials and electroplating conditions such as current density and temperature. This variation of the crystallinity should have caused wide variation of mechanical properties of the films. In addition, their mechanical properties such as Young’s modulus and hardness showed wide variation by about 3 times comparing with those of bulk gold. Similarly, the EM resistance of the electroplated gold bumps varied drastically depending on the ratio of porous grain boundaries and their crystallinity. Both the ratio and crystallinity also varied depending on the crystallinity of the under layer and electroplating conditions. The effective lifetime of the gold bumps was successfully predicted by considering both the crystallinity and residual stress of fine gold bumps. The lifetime varied more than 10 times as a strong function of the crystallinity of grain boundaries in the fine bumps. Therefore, it is very important to control the crystallinity of the under-layer for electroplating in order to control the distribution of the mechanical properties and reliability of the electroplated gold thin films.

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