Chuanhong Fan

Improvement of the reliability of TSV interconnections by controlling the crystallinity of electroplated copper thin films

The degradation process of the crystallinity of electroplated copper thin films, which are used for interconnections and micro bumps for 3D integration, during electromigration and stress-induced migration tests was observed clearly by applying an EBSD method. The grain boundary diffusion was the main reason for the degradation of the crystallographic quality in both grain boundaries and grains. The reliability of the interconnections was improved drastically by minimizing the lattice mismatch between the electroplated copper and its base material for electroplating. The large mismatch deteriorated the crystallographic quality of the electroplated copper thin films and thus, increased the shrinkage rate of the films caused by the annealing. The electronic resistivity of the crystallinity-controlled films decreases effectively, and their lives during electromigration test improved drastically. In addition, the residuals stress in the films annealed at 400°C decreased to the stress lower than their yielding stress, and therefore, no stress-induced migration was observed. These results clearly indicate that the control of the crystallinity of metallic interconnection is indispensable for assuring their long-life reliability.

Improvement of the crystallinity of electroplated copper thin films for highly reliable 3D interconnections

The degradation process of the crystallographic quality of copper thin films, which are used for interconnections and micro bumps for 3D integration, during electromigration and stress-induced migration tests is dominated by the diffusion along grain boundaries and the diffusion constant of copper varies drastically depending on the crystallinity of the films. The degradation process was visualized clearly by applying an electron back-scatter diffraction method. The copper atoms in the electroplated copper thin films migrated mainly in the area with low crystallinity, in other words, the area with high defect density. Since the crystallinity of the films was found to be dominated by the lattice mismatch between copper and the seed layer material used for electroplating, the integrity of the interface structure was improved by minimizing the lattice mismatch. It was validated that the introducing the thin layer with fine grains and random orientation is effective for minimizing the lattice mismatch and thus, improving the crystallographic quality of the electroplated copper thin-film interconnections.

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

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.© 2013 ASME

Improvement of the Reliability of Thin-Film Interconnections Based on the Control of the Crystallinity of the Thin Films

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 discussed experimentally.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 significantly depending on their crystallinity. The crystallinity also changed drastically as functions of electroplating conditions and the annealing temperature after electroplating.Although the electro migration (EM) resistance of the annealed interconnection is improved, the stress-induced migration (SM) is activated by a high residual tensile stress after annealing caused by the strong constraint of the shrinkage of the film during recrystallization. To improve its electrical reliability without heat treatment after the electroplating, the effects of the seed layer under the interconnections on the crystallinity of the electroplated film was 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 improves the crystallinity. Therefore, both introducing the Ru seed layer in addition to decreasing the current density during electroplating is effective for developing highly reliable copper interconnections.Copyright

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

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.Copyright

Effect of the lattice mismatch between copper thin-film interconnection and base material on the crystallinity of the interconnection

Electroplated copper thin films have become indispensable for the interconnections in next-generation semiconductor devices because of its low electric resistivity and high thermal conductivity. Since the electrical properties of the electroplated copper thin films vary drastically depending on their micro texture, the effect of the base layer material (a copper diffusion preventing layer and an electroplating seed layer) on the crystallinity of the electroplated copper thin films was investigated quantitatively in order to assure and improve the performance and reliability of electroplated copper thin-film interconnections.

413 Effect of the Lattice Mismatch between Copper Thin-film Interconnection and Base Material on the Crystallinity of the Interconnection

Electroplated copper thin films have become indispensable for the interconnections in next-generation semiconductor devices because of its low electric resistivity and high thermal conductivity. Since the electrical properties of the electroplated copper thin films vary drastically depending on their micro texture, the effect of the base layer material (a copper diffusion preventing layer and an electroplating seed layer) on the crystallinity of the electroplated copper thin films was investigated quantitatively in order to assure and improve the performance and reliability of electroplated copper thin-film interconnections.