Electroplated Copper Thin-film Interconnections Research Articles

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.

Dominant Factors of Electromigration Resistance of Electroplated copper Thin-film Interconnections

Dominant Factors of Electromigration Resistance of Electroplated copper Thin-film Interconnections

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℃.

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

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

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)

146 銅薄膜配線のエレクトロマイグレーション損傷過程の可視化と信頼性向上

146 銅薄膜配線のエレクトロマイグレーション損傷過程の可視化と信頼性向上

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.

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.

107 めっき銅薄膜配線伝熱特性の結晶品質依存性(フェロー賞対象講演II)

107 めっき銅薄膜配線伝熱特性の結晶品質依存性(フェロー賞対象講演II)

J061031 半導体薄膜配線材料のナノスケール結晶品質の評価に基づく信頼性設計

With the high integration and the high speed operation of LSIs in recent years, interconnection material has rapidly changed over from conventionally used aluminum alloy to electroplated copper to improve the elevtronic performance of the LSIs. However, it was found that both the electronic characteristics and reliability of th electroplated copper thin films were rather low comparing with those of bulk copper. In this study, the authors clarified that the degradation of the electronic performance of the electroplated copper interconnections is caused by low crystallinity of the interconnectins and the grain boundary diffusion in the films is accelerated by the low crystallinity. The change of the crystallinity was observed by using an EBSD (Electron Back-scattered Diffraction) method. It was found that the crystallinity of the interconnection varied drastically depending on the electroplating conditions and seed layer material. Based on the results, the authors proposed a new design guideline for highly reliabile electroplated copper thin film interconnections.

228 微視結晶組織制御による銅めっき薄膜配線の強度・信頼性向上技術(学生賞IV,一般講演)

228 微視結晶組織制御による銅めっき薄膜配線の強度・信頼性向上技術(学生賞IV,一般講演)

J031053 めっき銅薄膜配線のストレスマイグレーション支配因子の解明([J03105]電子情報機器,電子デバイスの強度・信頼性評価と熱制御(5))

J031053 めっき銅薄膜配線のストレスマイグレーション支配因子の解明([J03105]電子情報機器,電子デバイスの強度・信頼性評価と熱制御(5))

606 めっき銅薄膜配線のストレスマイグレーション耐性(OS6-1 シリコン貫通ビア技術と強度信頼性)

606 めっき銅薄膜配線のストレスマイグレーション耐性(OS6-1 シリコン貫通ビア技術と強度信頼性)