Nanotwinned copper (nt-Cu) has been attracting a great deal of attention in the past decades due to its excellent mechanical and electrical properties. In this study, a new approach, periodic-reverse (PR) waveforms, is adopted to electroplate nt-Cu films with highly ⟨111⟩ oriented columnar grain microstructures. We investigate the effect of the reverse current on the microstructures of ⟨111⟩-oriented nt-Cu films and their grain growth behavior. With proper reverse current parameters, we are able to obtain a nt-Cu film with a significantly thin transition layer, low amount of impurities, and low residual stress levels in comparison to a DC electroplated film. It is also discovered that the grain size after annealing of the nt-Cu film is related to its initial columnar grain microstructures, which can be tailored by the reverse current parameter. These results show that PR electroplating provides a promising approach in improving and controlling the microstructures and properties of nt-Cu films.

We reported that highly (111)-oriented nanotwinned gold can be fabricated by periodical-reverse electroplating. The as-deposited films are shown to have a strong (111) preferred orientation, increasing with the reverse current time. The ratios of I(111)/I(220) and I(111)/I(200) in X-ray diffraction signals indicates a strong (111) preferred orientation. Using the advantage of the fast surface diffusion of (111) plane compared to the other planes of gold, we performed direct bonding with different thicknesses. Grain growth was observed over two films’ interfaces to eliminate the bonding interface, when annealed at 250 °C for 1 h. Shear tests were performed to gain insight on the bonding quality. All the chips failed at either the silicon substrate or substrate-adhesion layer, showing possible higher strength than the tested maximum, 40.8 MPa.

We have reported a method of fabricating (111)-orientated nanotwinned copper (nt-Cu) by direct current electroplating. X-ray analysis was performed for the samples annealed at 200 to 350 • C for an hour. X-ray diffraction indicates that the (200) signal intensity increases while (111) decreases. Abnormal grain growth normally results from transformation of surface energy or strain energy density. The average grain size increased from 3.8 µm for the as-deposited Cu films to 65-70 µm after the annealing at 250 • C for 1 h. For comparison, no significant grain growth behavior was observed by random Cu film after annealing for an hour. This research shows the potential for its broad electric application in interconnects and three-dimensional integrated circuit (3D IC) packaging.

Nanotwinned copper (nt-Cu) films with ⟨111⟩ crystal orientation were electroplated on Si wafers by pulse plating, with original grain size of ∼1.4 μm. By patterning and annealing the nt-Cu film at 450–500 °C for 1 h, we can grow a large number of ⟨100⟩-oriented quasi-single crystal Cu lines that are 200 and 500 μm in length and 60 μm in width. We perform anisotropic grain growth on a Si substrate to fabricate quasi-single crystal Cu lines array of ⟨100⟩ crystal orientation. These large ⟨100⟩ Cu single crystals may have potential applications as interconnects in three-dimensional integrated circuit technology.

Fine grained and nanotwinned Au has many excellent properties and is widely used in electronic devices. We have fabricated $$\langle {110} \rangle $$ ⟨ 110 ⟩ preferred-oriented Au thin films by DC plating at 5 mA/cm2. Microstructure analysis of the films show a unique fine grain structure with a twin formation. Hardness tests performed on electroplated $$\langle {110} \rangle $$ ⟨ 110 ⟩ Au films show a hardness 47% greater than random and untwinned Au. We then achieved direct bonding between two Au $$\langle {110} \rangle $$ ⟨ 110 ⟩ surfaces operating at 200 °C for an hour in a vacuum oven. The highly-oriented $$\langle {110} \rangle $$ ⟨ 110 ⟩ nanotwinned Au films could be an ideal material in many gold products.