Shou-Yi Chang

Structural and Thermodynamic Factors of Suppressed Interdiffusion Kinetics in Multi-component High-entropy Materials

We report multi-component high-entropy materials as extraordinarily robust diffusion barriers and clarify the highly suppressed interdiffusion kinetics in the multi-component materials from structural and thermodynamic perspectives. The failures of six alloy barriers with different numbers of elements, from unitary Ti to senary TiTaCrZrAlRu, against the interdiffusion of Cu and Si were characterized, and experimental results indicated that, with more elements incorporated, the failure temperature of the barriers increased from 550 to 900°C. The activation energy of Cu diffusion through the alloy barriers was determined to increase from 110 to 163 kJ/mole. Mechanistic analyses suggest that, structurally, severe lattice distortion strains and a high packing density caused by different atom sizes, and, thermodynamically, a strengthened cohesion provide a total increase of 55 kJ/mole in the activation energy of substitutional Cu diffusion, and are believed to be the dominant factors of suppressed interdiffusion kinetics through the multi-component barrier materials.

Nanoindentating Mechanical Responses and Interfacial Adhesion Strength of Electrochemically Deposited Copper Film

The nanomechanical responses and interface adhesion of electrochemically plated copper (Cu) film have been investigated for the evaluation of interconnect reliability. The hardness and elastic modulus of the Cu film were measured by nanoindentation test as about 2.1 and 120 GPa, respectively. A dislocation burst phenomenon was observed and revealed the initiation of plastic deformation of the Cu film. The converted true stress-strain curve provided a stress criterion of 9.3 GPa for the plastic yielding of the Cu film. Besides, the creep behavior was also analyzed under nanoindentation test and showed a power law expression with a creep stress exponent of about 22. Moreover, the interfacial adhesion strength and delamination behavior between the Cu film and silicon carbide (SiC) etch stop layer have been studied using a four-point bending test. During delamination, cracks irregularly propagated along the Cu/SiC interface with blocking by the ductile Cu film. The fracture energy release rate for the delamination of Cu/SiC interface was measured as around 2-10 J/m 2 , affected by SiC deposition condition and testing parameter.

Multiprincipal-Element AlCrTaTiZr-Nitride Nanocomposite Film of Extremely High Thermal Stability as Diffusion Barrier for Cu Metallization

To inhibit rapid Cu diffusion in interconnect structures, an effective diffusion barrier of high thermal stability is strongly demanded. Thus in this study a nitride nanocomposite film of equimolar five-element high-entropy alloy (AlCrTaTiZr)N was developed and deposited by reactive sputtering. Thermal stability of the (AlCrTaTiZr)N film and its barrier performance to the interdiffusion of Si and Cu were investigated under thermal annealing at 700-900°C. The (AlCrTaTiZr)N film, constructed of mixed crystalline and amorphous nanocomposite structure, was found to remain thermally stable at an extremely high temperature of 900°C with low electrical resistance. Neither interdiffusion between Si and Cu through the (AlCrTaTiZr)N layer nor formation of any silicides occurred. Severe lattice distortions caused by the addition of multiprincipal elements and the nanocomposite structure of nanocrystallites surrounded by an amorphous matrix without the existence of grain boundaries were expected as the dominant factors for the high thermal stability and superior diffusion resistance of the (AlCrTaTiZr)N film as an effective barrier material.

Structures and Characterizations of TiVCr and TiVCrZrY Films Deposited by Magnetron Sputtering under Different Bias Powers

In this study, TiVCr and TiVCrZrY films were deposited on Si substrates by magnetron sputtering with the application of radio-frequency substrate bias of different powers from 0 to 15 W. The crystal structures, microstructure, and mechanical, electrical, and optical properties under the effect of bias were characterized. Both the TiVCr and TiVCrZrY films constructed simple solid solutions from all alloyed elements. The TiVCr films possessed a body-centered cubic crystal structure with a pyramid-like surface, while the TiVCrZrY films had a hexagonal close-packed crystal structure with a domelike surface. The microstructure and properties of the films varied with bias power. As the bias power increased, the microstructure of the films obviously changed from a porous to a dense columnar feature, and the density of the voids existing between the columns decreased. Accordingly, the physical properties of the films were improved. The hardness of the TiVCr and TiVCrZrY films was enhanced to about 11 and 14 GPa, and the electrical resistivity was lowered to 80 and 100 μΩ cm, respectively.

Hydrothermal Growth and Interface Correlation of Highly Aligned ZnO Nanorod Arrays on UV-Activated Sol–Gel Transparent Conducting Films

In this study, aluminum-doped zinc oxide (AZO) transparent conducting films were deposited as seed layers by sol―gel method, followed by UV exposure and subsequent thermal curing at a low temperature of 300°C. Zinc oxide nanorod arrays were then hydrothermally grown on the seed layers at 70°C. By the activation of UV exposure, the 300°C cured AZO seed layers possessed an obvious crystallinity and a [002] texture. The well-aligned and vertical growth of high density zinc oxide nanorods with a [002] preferred orientation and strong photoluminescence was consequently accomplished on the UV-exposed seed layers. The zinc oxide nanorods were characterized as single crystals of typical wurtzite structure with a (002) lattice spacing of 0.26 nm. Highly [002] textured grains with small-angle misfits of lattice orientations in the UV-exposed seed layers dominated the aligned growth of the nanorod arrays.

Interface Chemistry and Adhesion Strength Between Porous SiOCH Low-k Film and SiCN Layers

In this study, the interface chemistry and adhesion strength between a porous SiOCH extra-low-dielectric-constant film and SiCN etch stop layers were investigated with different plasma treatments. An interlayer of ∼6 6 nm thick between the porous SiOCH film and SiCN layers was found to be composed of Si, N, C, and O. The SiOCH/SiCN interface was constructed by mixing bonds, including Si-C-N, Si-N-C, Si-O-C, Si-O 2 , etc. Under H 2 and NH 3 plasma treatments, a large amount of weak Si-CH 3 and SiO-CH 3 bonds were broken, and more Si-O related bonds of high binding energy formed at the interfaces. Moreover, under the accumulation of sufficient shear stresses around the indented regions during nanoindentation tests, interface delamination between the porous SiOCH film and SiCN layers occurred. The interface adhesion energy between untreated porous SiOCH film and SiCN layers was accordingly measured as 1.68 J/m 2 . After plasma treatments, especially NH 3 plasma, the adhesion strength was effectively improved to 2.13 J/m 2 .

Thermal Stability and Interface Diffusion Behaviors of Electrolessly Deposited CoWP and Cu Films

Amorphous CoWP films have been studied as a capping or diffusion barrier layer to reduce Cu electromigration. However, the interface characterizations between the CoWP and Cu films have not been clarified. Thus, in this study, CoWP and Cu films are deposited by electroless plating, and their thermal stability and interface diffusion behaviors are investigated. By the activation of nanoscaled Pd catalysts, a continuous amorphous CoWP layer is obtained with stable concentrations of 82.5 atom % Co, 5.5 atom % W, and 12.0 atom % P, and then a smooth crystalline Cu film is directly deposited on the CoWP layer. Under thermal annealing at 500°C, the CoWP layer remains an amorphous structure, and no obvious interdiffusion between the Cu and CoWP films is found. The electrical resistivity of the CoWP layer and CoWP/Cu bilayer decreases to the lowest values of 35 and 3.3 μΩ cm, respectively. However with increasing annealing temperature to 600°C, crystallization of the amorphous CoWP occurs, and much severe interdiffusion between the Cu and CoWP films is observed.

Effect of Plasma Treatments on the Interface Chemistry and Adhesion Strength Between Cu Metallization and SiCN Etch Stop Layer

In this study, the interface chemistry and adhesion strengths between Cu and SiCN etch stop layers have been investigated under different plasma treatments. From the examination of interface microstructures and the analyses of chemical compositions and bonding configurations, an oxide layer was found to exist at the untreated Cu/SiCN interface. After H 2 and NH 3 treatments, the amount of oxides was effectively reduced. Some Cu silicides formed during SiCN deposition, and Cu nitrides even formed under NH 3 plasma treatment. The adhesion strengths of the Cu/SiCN interfaces were measured by nanoindentation and nanoscratch tests under which interface delamination occurred around indented regions. The adhesion energy of the untreated Cu/SiCN interface was obtained as about 4.98 and 0.98 J/m 2 , respectively, by nanoindentation and nanoscratch tests. After H 2 and NH 3 plasma treatments, the adhesion energy was effectively improved to 5.90 and 5.99 J/m 2 by nanoindentation test, and to 1.74 and 2.58 J/m 2 by nanoscratch test, respectively, because of the removing of oxides and the formation of Cu silicides and nitrides at the Cu/SiCN interfaces.

Microstructure and tensile properties of Al0.5CoCrCuFeNi alloys produced by simple rolling and annealing

Abstract This study demonstrates that simply by rolling at ambient temperature, FCC type high entropy alloy Al0.5CoCrCuFeNi can be refined to have nanocrystalline structure and exhibits outstanding combination of strength and ductility. The yield strength and ultimate tensile strength are 1284 and 1344 MPa, respectively, in combination with an elongation of 7.6%. After a short annealing at 900°C for 10 min, the elongation is doubled to 15.3% with a trade-off around 20% in strength. This excellent combination of strength and ductility is attributable to the activation of quasi-dynamic recrystallisation during cold work and the limited grain growth during 900°C annealing.

Ultrathin ( AlCrTaTiZr ) N x / AlCrTaTiZr Bilayer Structures with High Diffusion Resistance for Cu Interconnects

In this study, (AlCrTaTiZr)N 0.7 and (AlCrTaTiZr)N 1 films with quinary metallic elements were developed as diffusion barrier materials for Cu interconnects. To improve the interface adhesion to Cu, an AlCrTaTiZr buffer layer was deposited on the barriers to form (AlCrTaTiZr)N 0.7 /AlCrTaTiZr and (AlCrTaTiZr)N 1 /AkCrTaTiZr bilayer structures. The as-deposited AlCrTaTiZr and (AlCrTaTiZr)N 0.7 films were amorphous structures, and (AlCrTaTiZr)N 1 possessed a nanocomposite structure. After annealing at 800°C, although Cu penetrated into the AlCrTaTiZr buffer layer, the diffusion of Cu was retarded by the (AlCrTaTiZr)N 0.7 and (AlCrTaTiZr)N 1 barriers. During annealing at 900°C, the interdiffusion of Si and Cu occurred through the (AlCrTaTiZr)N 0.7 /AlCrTaTiZr bilayer, and Cu silicides formed. However, the (AlCrTaTiZr)N 1 /AlCrTaTiZr bilayer remained stable. Neither the interdiffusion of Cu and Si through the (AlCrTaTiZr)N 1 /AlCrTaTiZr bilayer nor the silicide formation was identified, indicating the high diffusion resistance of the bilayer structure.