Electroplated Copper Thin Films Research Articles

Low-cycle fatigue testing and thermal fatigue life prediction of electroplated copper thin film for through hole via

A new fatigue test method was proposed for low-cycle fatigue lives of electroplated copper thin films for the through hole (TH) in a printed wiring board. And the low-cycle fatigue lives were investigated according to the proposed method. Furthermore, thermal stress analysis of the TH with the finite element method was performed to predict thermal fatigue life of the TH based on Manson-Coffin law for electroplated copper thin films obtained from the low-cycle fatigue test. Low-cycle fatigue damage in the electroplated copper thin film was occurring in the grain boundaries and the damage mechanism was found same as that for thermal fatigue damage in TH in the printed wiring board. And the fatigue life of TH predicted from the Manson-Coffin law at the maximum temperature of thermal fatigue test was good agreement with the thermal fatigue life obtained from the experimental result of thermal fatigue test.

160 Clarification of the relationship between the strength of a grain boundary and its quality in electroplated copper thin films

160 Clarification of the relationship between the strength of a grain boundary and its quality in electroplated copper thin films

Determination of Energy Release Rate Through Sequential Crack Extension

A method to determine the critical energy release rate of a peel tested sample using an energy-based approach within a finite element framework is developed. The method uses a single finite element model, in which the external work, elastic strain energy, and inelastic strain energy are calculated as nodes along the crack interface are sequentially decoupled. The energy release rate is calculated from the conservation of energy. By using a direct, energy-based approach, the method can account for large plastic strains and unloading, both of which are common in peel tests. The energy rates are found to be mesh dependent; mesh and convergence strategies are developed to determine the critical energy release rate. An example of the model is given in which the critical energy release rate of a 10-μm thick electroplated copper thin film bonded to a borosilicate glass substrate which exhibited a 3.0 N/cm average peel force was determined to be 20.9 J/m2.

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

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.

Improvement method of the crystallinity of electroplated copper thin films for next-generation interconnections of electronic devices

Improvement method of the crystallinity of electroplated copper thin films for next-generation interconnections of electronic devices

Prediction of recrystallization times in electroplated copper thin films

Room temperature recrystallization responses of blanket electroplated Cu thin films deposited under various conditions were monitored in real-time using synchrotron X-ray diffraction. Nominal control of electroplating parameters such as plating current, bath chemistry, and plating time was found to be insufficient to ensure repeatability of the 50% recrystallization time,τ50, from sample to sample even though the thickness variations between samples were insignificant. Real-time X-ray analysis of samples from numerous electroplating baths showed that, for a given seed deposition process, a reliable estimation of τ50 at room temperature can be obtained from the ratio of the integrated intensities of the 111 and 200 Cu reflections, I−111/I−200, of the electroplated film at time zero (immediately after plating). Among the plating parameters investigated seed-layer texture most influenced this ratio and, hence, the subsequent room temperature recrystallization behavior of the plated film.

半導体配線用めっき銅薄膜機械特性分布広がりのめっき下地依存性評価

半導体配線用めっき銅薄膜機械特性分布広がりのめっき下地依存性評価

138 めっき下地材質のめっき銅薄膜微細組織への影響

138 めっき下地材質のめっき銅薄膜微細組織への影響

143 次世代半導体配線用めっき銅薄膜機械特性分布広がり制御因子の解明

143 次世代半導体配線用めっき銅薄膜機械特性分布広がり制御因子の解明

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

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.

PS0021-294 めっき銅薄膜の微細組織制御方法の検討

The long-term reliability of electroplated copper thin-film interconnections varied drastically depending on their crystallinity. The crystallinity was mainly dominated by the seed layer material for electroplating because of the lattice mismatch between the seed layer material and copper. Even though tantalum is indispensable for a barrier of copper diffusion into silicon or oxide, the quality of thin copper films is rather low because there is a large mismatch in the lattice constant between tantalum and copper. Ruthenium is one of the most effective materials for improving the crystallinity of the electroplated copper thin films and the stability of the copper thin films electroplated on the ruthenium seed layer was very high during annealing up to 200℃.

OS1110 銅めっき薄膜配線におけるストレスマイグレーション支配因子の解明

In this study, the change of the crystallographic quality of electroplated copper thin-film interconnections due to stress-induced migration was investigated by using an EBSD (Electron Back Scatter Diffraction) method. This EBSD analysis clearly showed that the crystallinity of the annealed electroplated copper thin-film was degraded during the storage of the interconnection even at room temperature without any loading. This is due to the stress-induced migration caused by high tensile residual stress which occurred in the film after annealing. Molecular dynamics simulations showed that the diffusivity of copper atoms along grain boundaries with low crystallinity was enhanced significantly by high tensile residual stress. Therefore, the grain boundary diffusion accelerated by tensile residual stress is the main reason for the degradation of crystallinity the thin film interconnection after annealing.

323 めっき銅薄膜結晶品質のめっき下地依存性(フェロー賞対象講演II)

323 めっき銅薄膜結晶品質のめっき下地依存性(フェロー賞対象講演II)

PS10 薄膜銅配線の結晶粒界強度の経時劣化測定

Electric and mechanical properties of the electroplated copper thin film interconnections vary drastically depending on not only the size of grains but also the crystallographic characteristics of grain boundaries. In particular, the effect of the quality of grain boundaries plays very important role on the physical properties when the volume ratio of grain boundaries increases with the decrease of average grain size. In this study, in order to evaluate the damage due to the electro migration (EM) of electroplated copper interconnections, the tensile strength at grain boundaries in the interconnection was measured by the micro-tensile test method using Focused Ion Beam (FIB) technique. The micro-texture dependence of the tensile strength and the change in the strength of electroplated copper thin-film interconnections after the EM test were evaluated quantitatively.

101 めっき銅薄膜配線の結晶粒界品質と局所ジュール発熱

101 めっき銅薄膜配線の結晶粒界品質と局所ジュール発熱

314 高信頼めっき銅薄膜配線界面構造の検討(フェロー賞対象講演I)

314 高信頼めっき銅薄膜配線界面構造の検討(フェロー賞対象講演I)

OS0208 分子動力学法によるNI基超合金の高温微視組織変動支配因子の検討

OS0208 分子動力学法によるNI基超合金の高温微視組織変動支配因子の検討

Characterization of room temperature recrystallization kinetics in electroplated copper thin films with concurrent x-ray diffraction and electrical resistivity measurements

Concurrent in-situ four-point probe resistivity and high resolution synchrotron x-ray diffraction measurements were used to characterize room temperature recrystallization in electroplated Cu thin films. The x-ray data were used to obtain the variation with time of the integrated intensities and the peak-breadth from the Cu 111 and 200 reflections of the transforming grains. The variation of the integrated intensity and resistivity data with time was analyzed using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model. For both 111-textured and non-textured electroplated Cu films, four-point probe resistivity measurements yielded shorter transformation times than the values obtained from the integrated intensities of the corresponding Cu 111 reflections. In addition, the JMAK exponents fitted to the resistivity data were significantly smaller. These discrepancies could be explained by considering the different material volumes from which resistivity and diffraction signals originated, and the physical processes which linked these signals to the changes in the evolving microstructure. Based on these issues, calibration of the resistivity analysis with direct structural characterization techniques is recommended.

Improvement of Crystallographic Quality of Electroplated Copper Thin-Film Interconnections for Through-Silicon Vias

The relationship between the electrical properties and crystallographic quality (crystallinity) of electroplated copper thin-film interconnections was investigated. The crystallinity of the grains and grain boundaries of the interconnections was evaluated on the basis of the image quality (IQ) value obtained by electron back-scatter diffraction (EBSD) analysis. The electrical properties of the interconnections vary markedly depending on their crystallinity. The crystallinity also changed markedly as functions of electroplating conditions and the annealing temperature after electroplating. Although the electro migration (EM) resistance of the annealed interconnection was improved, stress-induced migration (SM) was activated by a high residual stress after annealing. To improve electrical reliability without heat treatment after electroplating, the effects of the seed layer under the interconnections on the crystallinity were investigated. As a result, the crystallinity was improved by changing the seed layer from Cu to Ru. In addition, the decrease in current density during electroplating also improved the crystallinity. Therefore, both introducing the Ru seed layer and decreasing the current density during electroplating are effective for developing highly reliable copper interconnections.

OS1204 ひずみ誘起粒界拡散に基づく電解めっき銅薄膜の劣化挙動

OS1204 ひずみ誘起粒界拡散に基づく電解めっき銅薄膜の劣化挙動