Microstructure and Mechanical Properties of Electroplated Cu Thin Films

Abstract

Copper films of different thicknesses of 0.2, 0.5, 1 and 2 microns were electroplated on top of the adhesion-promoting barrier layers on <100> single crystal silicon wafers. Controlled Cu grain growth was achieved by annealing films in vacuum.The Cu film microstructure was characterized using Atomic Force Microscopy and Focused Ion Beam Microscopy. Elastic modulus of 110 to 130 GPa and hardness of 1 to 1.6 GPa were measured using the continuous stiffness option (CSM) of the Nanoindenter XP. Thicker films appeared to be softer in terms of the lower modulus and hardness, exhibiting a classical Hall-Petch relationship between the yield stress and grain size. Lower elastic modulus of thicker films is due to the higher porosity and partially due to the surface roughness. Comparison between the mechanical properties of films on the substrates obtained by nanoindentation and tensile tests of the freestanding Cu films is made.

Residual Stress and Microstructure of Electroplated Cu Film on Different Barrier Layers

“…Elastic modulus and hardness are the two properties that can be readily extracted from the nanoindentation loaddisplacement curve [11][12][13]. Results have been reported in previous studies [14]. Although films of the same thickness on Ta and TiW barrier layers have the same elastic modulus, the hardness of Cu films on Ta about 50 MPa lower than on TiW.…”

“…The grain size as well as the hardness in Cu films has been characterized and the results have been reported in our previous paper along with the analysis of the yield strength [14]. No significant differences in the mechanical properties are found for the films of the same thickness on two different barrier layers.…”

“…Upon cooling, the mismatch between the thermal expansion coefficients of the film and the substrate lead to an increase in tensile stress in the film. However, most of this stress is accommodated plastically [1,14,15]; otherwise complete elastic behavior upon cooling would result in residual stresses on the order of 800 MPa, which is not observed (Figure 2b). The final residual stress is about 200 MPa higher after the first heating/cooling cycle, as can be concluded from both post-annealing stress and stress-temperature measurements (Figure 2).…”

Method to determine thermoelastic material properties of constituent and copper-patterned layers of multilayer printed circuit boards

“…The black lines indicate the layer's CTE computed using various CTE values (viz. 17-29 ppm/K) of the ED copper, as the exact CTE value is unknown due to the variance of the plating process and the fact that the ED copper-plated layer is relatively thin [28,29]. As shown in the figure, the measured CTE values for all types of copper patterning lie within the computed range.…”

The Effect of TiO2Particulate Reinforcement on the Microstructure and Mechanical Properties of Binary Nano-Composite on Low Carbon Steel

“…Lately, major efforts to improve the wear, hardness and corrosion resistance of metallic zinc coating, can be traced towards its composites with different materials [11][12][13][14][15][16][17][18]. It is also identified, in particular, that the physical, mechanical and electrochemical properties of materials can be improved with the introduction of nano powders as the second phase particles within the material of interest [13][14][15][16][17][18]. Due to this improvement, composites and alloys such as Zn-Al2O3, Zn-WO3, Zn-Al and Zn-Ni have tremendously gained a wider range of applications in both marine and manufacturing industries recently as a better alternative for regular zinc plating [19][20][21][22][23][24][25].…”