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

2011 ◽  
Author(s):  
Naokazu Murata ◽  
Naoki Saito ◽  
Kinji Tamakawa ◽  
Ken Suzuki ◽  
Hideo Miura
Keyword(s):  
Thin Film ◽  
Brittle Fracture ◽  
Grain Boundaries ◽  
Fracture Mode ◽  
Electron Back Scatter Diffraction ◽  
Fracture Rate ◽  
Copper Films ◽  
Average Grain Size ◽  
Electroplated Copper

Both mechanical and electronic properties of electroplated copper films used for interconnections were investigated experimentally considering the change of their micro texture caused by heat treatment. The fracture strain of the film annealed at 400°C increased from about 3% to 15% and their yield stress decreased from about 270 MPa to 90 MPa. In addition, it was found that two different fatigue fracture modes appeared in the film. One was a typical ductile fracture mode and the other was brittle one. When the brittle fracture occurred, a crack propagated along weak or porous grain boundaries which were formed during electroplating. The brittle fracture mode disappeared after the annealing at 300°C. These results clearly indicated that the mechanical properties of electroplated copper thin films vary drastically depending on their micro texture. The electrical reliability of the electroplated copper yjin film interconnections was also investigated. The interconnections used for electromigration tests were made using by a damascene process. An abrupt fracture mode due to local fusion appeared in the as-electroplated interconnections. Since the fracture rate increased almost linearly with the square of the applied current density, this fracture mode was dominated by local Joule heating. It seemed that the local current concentration occurred around the porous grain boundaries. The life of the interconnections was improved drastically after the annealing at 400°C. This was because of the increase of the average grain size and the improvement of the quality of grain boundaries in the annealed interconnections. However, the stress-induced migration occurred in the interconnections annealed at 400°C. This was because of the high tensile residual stress caused by the constraint of the densification of the films during annealing by the surrounding oxide film. Therefore, it is very important to control the crystallographic quality of electroplated copper films for improving the reliability of thin film interconnections. The quality of the grain boundaries can be evaluated by applying an EBSD (Electron Back Scatter Diffraction) analysis. New two experimentally determined parameters are proposed for evaluating the quality of grain boundaries quantitatively. It was confirmed that the crystallographic quality of grain boundaries can be evaluated quantitatively by using the two parameters, and it is possible to estimate both the strength and reliability of the interconnections.

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.

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.

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 Thermal Conductivity of Electroplated Copper Thin-Film Interconnections by Controlling Their Micro Texture

2014 ◽  
Author(s):  
Pornvitoo Rittinon ◽  
Ken Suzuki ◽  
Hideo Miura
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Thermal Conductivity ◽  
Grain Boundaries ◽  
Diffraction Method ◽  
Electron Back Scatter Diffraction ◽  
High Resistivity ◽  
Copper Thin Film ◽  
Electroplated Copper ◽  
The Relationship

Copper thin films are indispensable for the interconnections in the advanced electronic products, such as TSV (Trough Silicon Via), fine bumps, and thin-film interconnections in various devices and interposers. However, it has been reported that both electrical and mechanical properties of the films vary drastically comparing with those of conventional bulk copper. The main reason for the variation can be attributed to the fluctuation of the crystallinity of grain boundaries in the films. Porous or sparse grain boundaries show very high resistivity and brittle fracture characteristic in the films. Thus, the thermal conductivity of the electroplated copper thin films should be varied drastically depending on their micro texture based on the Wiedemann-Franz’s law. Since the copper interconnections are used not only for the electrical conduction but also for the thermal conduction, it is very important to quantitatively evaluate the crystallinity of the polycrystalline thin-film materials and clarify the relationship between the crystallinity and thermal properties of the films. The crystallinity of the interconnections were quantitatively evaluated using an electron back-scatter diffraction method. It was found that the porous grain boundaries which contain a significant amount of vacancies increase the local electrical resistance in the interconnections, and thus, cause the local high Joule heating. Such porous grain boundaries can be eliminated by control the crystallinity of the seed layer material on which the electroplated copper thin film is electroplated.

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.

Crystallinity Control of Electroplated Interconnections for Improving Their Stability and Lifetime

2016 ◽  
Author(s):  
Jiatong Liu ◽  
Ken Suzuki ◽  
Hideo Miura
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Residual Stress ◽  
Grain Boundaries ◽  
Lattice Mismatch ◽  
Bulk Material ◽  
Chemical Properties ◽  
Mechanical Fracture ◽  
Copper Thin Film ◽  
Electroplated Copper

In a three-dimensional (3D) packaging systems, the interconnections which penetrate stacked silicon chips have been employed. Such interconnection structure is called TSV (Through Silicon Via) structure, and the via is recently filled by electroplated copper thin film. The electroplated copper thin films often consist of fine columnar grains and porous grain boundaries with high density of defects which don’t appear in conventional bulk material. This unique micro texture has been found to cause the wide variation of physical and chemical properties of this material. In the TSV structure, the shrinkage of the copper thin film caused by thermal deformation and recrystallization of the unique texture during high-temperature annealing is strictly constrained by surrounding rigid Si and thus, high tensile residual stress remains in the thin film after thermal annealing. High residual stress should give rise to mechanical fracture of the interconnections and the shift of electronic function of thin film devices formed in Si. Therefore, the residual stress in the interconnections should be minimized by controlling the appearance of the porous boundaries during electroplating for assuring the longterm reliability of the interconnections. As the lattice mismatch between Cu and its barrier film (Ta) is as larger as 18%, which is the main reason for the fine columnar structures and porous grain boundaries, it is necessary to control the underlayer crystallinity to improve the crystallinity of electroplated copper thin films. In this study, the effective method for controlling the crystallinity of the underlayer was investigated by improving the atomic configuration in the electroplated copper thin film. The result showed that by controlling the crystallinity of underlayer, crystallinity of electroplated copper thin films can be improved, the mechanical properties of thin films was improved and thus, stability and lifetime of electroplated copper interconnections can be improved.

Stress-Induced and Electro-Migration of Electroplated Copper Thin Film Interconnections Used for 3D Integration

2011 ◽  
Author(s):  
Naoki Saito ◽  
Naokazu Murata ◽  
Kinji Tamakawa ◽  
Ken Suzuki ◽  
Hideo Miura
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Residual Stress ◽  
Grain Boundaries ◽  
Current Density ◽  
Annealed Film ◽  
Applied Current ◽  
Copper Thin Film ◽  
Applied Current Density ◽  
Electroplated Copper

Electroplated copper thin films have started to be applied to not only interconnections in printed wiring boards, but also thin film interconnections and TSV (Through Silicon Via) in semiconductor devices because of its low electric resistivity and high thermal conductivity. Thus, the electrical reliability of the electroplated copper interconnections was investigated experimentally. Self-made electroplated copper thin film interconnections were used for the evaluation. Electroplating conditions are as follows. The thin film interconnections were made by damascene process for electromigration tests. The applied current density during the test was varied from 1 MA/cm2 to 10 MA/cm2. Abrupt fracture caused by the local fusion was often observed in the as-electroplated interconnections within a few hours during the test. Since there were a lot of porous grain boundaries in the as-electroplated thin films, the local high Joule heating should have caused the fusion at one of the porous grain boundaries. Actually, it was confirmed that the failure rate increased linearly with the square of the amplitude of the applied current density. However, the diffusion of copper atoms caused by electromigration was enhanced significantly when the film was annealed at 400°C. Many voids and hillocks were observed on their surfaces. This change of the fracture mode clearly indicates the improvement of the crystallographic quality of the annealed film. It was also observed that the stress-induced migration was activated substantially in the annealed film. Large voids and hillocks grew during the custody of the film even at room temperature without any application of current. This stress-induced migration was caused by the increase of residual tensile stress of about 200 MPa in the annealed film. It was also found that sulfur atoms segregated in the grown hillocks, though no sulfur atoms were found by EDX in the initial as-electroplated interconnections or other area in the annealed thin film interconnections. Thus, the hillock formation in the annealed interconnections was enhanced by the segregation of sulfur atoms. These sulfur atoms should have been introduced into the electroplated films during electroplating. Therefore, it is very important to control the micro texture, the residual stress and the concentration of sulfur in the electroplated copper thin film interconnections to assure the stable life, in other words, to eliminate their sudden brittle fracture and time-dependent degradation caused by the residual stress in the thin film interconnections.

Micro Texture Dependence of Mechanical Properties of Electroplated Copper Thin Films Used for Thin Film Interconnection

2009 ◽  
Author(s):  
Naokazu Murata ◽  
Kinji Tamakawa ◽  
Ken Suzuki ◽  
Hideo Miura
Keyword(s):  
Thin Films ◽  
Mechanical Properties ◽  
Fatigue Strength ◽  
Brittle Fracture ◽  
Grain Boundaries ◽  
The Other ◽  
Cycle Fatigue ◽  
Micro Structure ◽  
Columnar Grains ◽  
Electroplated Copper

Electroplated copper thin films have been used for interconnection of semiconductor devices. Both the mechanical and electrical properties of the films were found to be quite different from those of bulk material, and thus, the reliability of the devices is not so high as to be expected. The main reason for the difference was found to be their micro texture. When the films consist of fine columnar grains with weak grain boundaries, their mechanical properties show strong anisotropy and complicated fracture mode. Thus, the fatigue strength of the electroplated copper thin films was measured under uniaxial stress. The mechanical properties such as the yield stress, fracture elongation and Young’s modulus of each film were quite different from those of bulk copper due to their unique micro structure. The micro texture of each film was observed by using SEM (Scanning Electro Microscope) and SIM (Scanning Ion Microscope). The low-cycle fatigue strength varied drastically depending on their micro texture, while the high-cycle fatigue strength was almost same. The fracture surfaces were observed by SEM after the fatigue test. It was found that there were two fracture modes under the fatigue test. One was a typical ductile fracture, and the other was brittle one even under the fatigue load higher than its yield stress. The crack seemed to propagate in the grains when the ductile fracture occurred since typical striations and dimples were observed clearly on the fractured surfaces. On the other hand, the crack seemed to propagate along grain boundaries of columnar grains when the brittle fracture occurred. No striations or dimples remained on the fractured surfaces. One of the reasons for this brittle fracture can be explained by cooperative grain boundary sliding of the films which consist of fine columnar grains with weak grain boundaries. These results clearly indicated that the fatigue strength of the electroplated copper thin films varies depending on their micro structure. Since the initial micro texture was found to change significantly even after the annealing at temperatures lower than 300°C, the effect of the thermal history of them after electroplating on both their micro texture and fatigue strength was investigated quantitatively. Not only the average grain size, but also the crystallographic structure of the films changed significantly depending on their thermal history, and thus, the fatigue strength of the films varied drastically. It is important, therefore, to control the micro texture of the films for assuring their reliability.

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