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.

Improvement of Thermal Conductivity of Electroplated Copper Interconnections by Controlling Their Crystallinity

2015 ◽  
Author(s):  
Masaru Gotoh ◽  
Ken Suzuki ◽  
Hideo Miura
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Thermal Conductivity ◽  
Thermal Properties ◽  
Grain Boundaries ◽  
Joule Heating ◽  
Seed Layer ◽  
Lattice Mismatch ◽  
Copper Thin Film ◽  
Electroplated Copper

Electroplated copper thin films are indispensable for the interconnections in the advanced electronic products, such as TSV (trough silicon via) structures, 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 grains and grain boundaries in the films. Porous or sparse grain boundaries cause the increase in electrical resistivity and the embrittlement of the films. Thus, the thermal conductivity of the electroplated copper thin films should be varied drastically depending on their micro texture based on Wiedemann-Franz law. Since copper interconnections are used for not only electrical conductor but also thermal heat conductor, it is important to clarify the relationship between the crystallinity and thermal properties of the films. In this study, the local distributions of the crystallinity and physical properties were investigated experimentally. As the result of the temperature distribution due to local Joule heating along an interconnection, it was suggested that the variation in the quality of the grain boundaries in the electroplated copper thin-films caused the non-uniformity of the resistivity and thus, Joule heating in the thin films. In this study, the effect of the seed layer material on the thermal properties of the electroplated copper thin film was investigated. When a Ru seed layer was deposited as a buffer layer between the electroplated copper thin film and the Ta diffusion barrier layer, both the crystallinity and uniformity of grain boundaries in the electroplated copper films were improved since lattice mismatch between copper and the seed layer metal was decreased. The improvement of the crystallinity increased the long-term reliability of the interconnections under the loads of electromigration and stress-induced migration.

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.

Effect of the Crystallinity on the Electromigration Resistance of Electroplated Copper Thin-Film Interconnections

2017 ◽  
Vol 139 (2) ◽  
Author(s):  
Takeru Kato ◽  
Ken Suzuki ◽  
Hideo Miura
Keyword(s):  
Thin Film ◽  
Activation Energy ◽  
Grain Boundaries ◽  
Joule Heating ◽  
Current Density ◽  
Constant Current ◽  
Maximum Temperature ◽  
Copper Thin Film ◽  
Electroplated Copper ◽  
Low Crystallinity

Dominant factors of electromigration (EM) resistance of electroplated copper thin-film interconnections were investigated from the viewpoint of temperature and crystallinity of the interconnection. The EM test under the constant current density of 7 mA/cm2 was performed to observe the degradation such as accumulation of copper atoms and voids. Formation of voids and the accumulation occurred along grain boundaries during the EM test, and finally the interconnection was fractured at the not cathode side but at the center part of the interconnection. From the monitoring of temperature of the interconnection by using thermography during the EM test, this abnormal fracture was caused by large Joule heating of itself under high current density. In order to investigate the effect of grain boundaries on the degradation by EM, the crystallinity of grain boundaries in the interconnection was evaluated by using image quality (IQ) value obtained from electron backscatter diffraction (EBSD) analysis. The crystallinity of grain boundaries before the EM test had wide distribution, and the grain boundaries damaged under the EM loading mainly were random grain boundaries with low crystallinity. Thus, high density of Joule heating and high-speed diffusion of copper atoms along low crystallinity grain boundaries accelerated the EM degradation of the interconnection. The change of Joule heating density and activation energy for the EM damage were evaluated by using the interconnection annealed at 400 °C for 3 h. The annealing of the interconnection increased not only average grain size but also crystallinity of grains and grain boundaries drastically. The average IQ value of the interconnection was increased from 4100 to 6200 by the annealing. The improvement of the crystallinity decreased the maximum temperature of the interconnection during the EM test and increased the activation energy from 0.72 eV to 1.07 eV. The estimated lifetime of interconnections is increased about 100 times by these changes. Since the atomic diffusion is accelerated by not only the current density but also temperature and low crystallinity grain boundaries, the lifetime of the interconnections under EM loading is a strong function of their crystallinity. Therefore, it is necessary to evaluate and control the crystallinity of interconnections quantitatively using IQ value to assure their long-term reliability.

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 the Lattice Mismatch Between Copper Thin-Film Interconnection and Base Material on the Crystallinity of the Interconnection

2013 ◽  
Author(s):  
Chuanhong Fan ◽  
Ryosuke Furuya ◽  
Osamu Asai ◽  
Ken Suzuki ◽  
Hideo Miura
Keyword(s):  
Thin Film ◽  
Seed Layer ◽  
Lattice Mismatch ◽  
Semiconductor Devices ◽  
Base Material ◽  
Diffraction Method ◽  
Copper Thin Film ◽  
New Material ◽  
Electroplated Copper ◽  
Electron Back Scattered Diffraction

In the present study, a new material, ruthenium whose lattice mismatch against copper is about 6%, was used as the seed layer of electroplated copper thin-film interconnections for semiconductor devices. The crystallinity of the copper thin-film interconnections was evaluated through an EBSD (Electron Back-scattered Diffraction) method and it is found that the crystallinity of them is improved drastically compared with those electroplated on the copper seed. The resistance and electro migration (EM) tolerance of the copper interconnections are also improved a lot compared with the interconnections electroplated on copper seed. Based on these results, a new guideline to design highly reliable electroplated copper thin-film interconnection has been established.

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.

Micro Texture-Induced Variation of Mechanical Properties of Electroplated Copper Thin Films

2007 ◽  
Author(s):  
Muneyuki Otani ◽  
Kazuhiko Sakutani ◽  
Kinji Tamakawa ◽  
Ken Suzuki ◽  
Hideo Miura
Keyword(s):  
Thin Films ◽  
Mechanical Properties ◽  
Grain Boundaries ◽  
Young’S Modulus ◽  
Young's Modulus ◽  
Bulk Material ◽  
Tensile Load ◽  
Columnar Structure ◽  
Grain Boundary Sliding ◽  
Electroplated Copper

The mechanical properties of copper thin films formed by cold-rolling and electroplating were measured using a tensile test and nano-indentation. Both the Young’s modulus and the tensile strength of the films were found to vary drastically depending on the microstructure of the films. The Young’s modulus of the cold-rolled film was almost same as that of the bulk material. However, the Young’s modulus of the electroplated thin film was about a fourth of that of the bulk material. The microstructure of the electroplated film was polycrystalline and a columnar structure with a diameter of a few hundred-micron. The strength of the grain boundaries of the columnar grains seemed to be rather week. Such a columnar structure with porous grain boundaries caused the cooperative grain boundary sliding. As a result, the effective elasticity of the film became rather low and the superplastic deformation of the film appearred under an uni-axial tensile load. In addition, there was a sharp distribution of Young’s modulus along the thickness direction of the film. Though the modulus near the surface of the film was close to that of the bulk material, it decreased drastically to about a half at the depth of 1 μm. There was also a planar distribution of Young’s modulus near the surface of the film.

Preparation of high-oriented molybdenum thin films using DC reactive magnetronsputtering

2017 ◽  
Vol 31 (07) ◽  
pp. 1750059 ◽  
Author(s):  
Zhengguo Shang ◽  
Dongling Li ◽  
She Yin ◽  
Shengqiang Wang
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Surface Roughness ◽  
Process Parameters ◽  
Gas Flow ◽  
Lattice Mismatch ◽  
Practical Significance ◽  
Process Time ◽  
Process Conditions ◽  
Influence Of Process Parameters

Since molybdenum (Mo) thin film has been used widely recently, it attracts plenty of attention, like it is a good candidate of back contact material for CuIn[Formula: see text]Ga[Formula: see text]Se[Formula: see text]S[Formula: see text] (CIGSeS) solar cells development; thanks to its more conductive and higher adhesive property. Besides, molybdenum thin film is an ideal material for aluminum nitride (AlN) thin film preparation and attributes to the tiny (−1.0%) lattice mismatch between Mo and AlN. As we know that the quality of Mo thin film is mainly dependent on process conditions, it brings a practical significance to study the influence of process parameters on Mo thin film properties. In this work, various sputtering conditions are employed to explore the feasibility of depositing a layer of molybdenum film with good quality by DC reactive magnetron sputtering. The influence of process parameters such as power, gas flow, substrate temperature and process time on the crystallinity and crystal orientation of Mo thin films is investigated. X-ray diffraction (XRD) measurements and atomic force microscope (AFM) are used to characterize the properties and surface roughness, respectively. According to comparative analysis on the results, process parameters are optimized. The full width at half maximum (FWHM) of the rocking curves of the (110) Mo is decreased to 2.7[Formula: see text], and the (110) Mo peaks reached [Formula: see text] counts. The grain size and the surface roughness have been measured as 20 Å and 3.8 nm, respectively, at 200[Formula: see text]C.

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