Property improvement of copper films with zirconium additive for ULSI interconnects

Thermal stability of Cu–Zr/Zr–Si/Si connect system was evaluated by a standard four-point probe (FPP) method, X-ray diffraction (XRD) and Auger electron spectroscopy (AES) analyses. And the Cu/Zr–Si/Si connect system was used as control experiment. XRD spectra for the Cu–Zr/Zr–Si/Si and Cu/Zr–Si/Si stacked films after annealing showed that the Cu–Zr/Zr–Si/Si specimen was stable up to 650 °C. However, the peaks of Cu silicide (Cu₃Si) appeared for Cu/Zr–Si/Si specimen after annealing at 650 °C. The formation of high resistivity Cu₃Si corresponding to the drastic increase in sheet resistance of copper film. The results observed by AES were consistent with those obtained from XRD measurements and demonstrated that Cu–Zr/Zr–Si/Si system had more thermal stability than that of the Cu/Zr–Si/Si system. The thermal stability of Cu–Zr/Zr–Si/Si specimen was obviously improved when Zr was introduced into Cu film.     

Characterization and Adhesion in Cu/Ru/SiO2/Si Multilayer Nano-scale Structure for Cu Metallization

In this study, we have characterized the microstructure, resistivity, and dynamic deformation behavior of Cu/Ru/SiO₂ and Cu/SiO₂ samples under scratch loading conditions. Cu/Ru/SiO₂ samples showed higher elastic recovery and hardness when compared to the Cu/SiO₂ samples. In the case of Cu/Ru/SiO₂ samples, Ru acts as a glue layer between the Cu and the SiO₂ substrate providing both strength and toughness against dynamic loading. Hence, the critical load for delamination is higher for Cu/Ru/SiO₂ samples compared to Cu/SiO₂ samples. Our results show that Cu/Ru/SiO₂ thin films present significant potential to be used in Cu metallization.     

Thermodynamic stability of Co/Cu multilayered nanostructures

In this paper, the Regular Solution Model (RSM) and the Cluster/Site Approximation (CSA) were used to study the unmixing as a function of the thickness of the Co/Cu metal layers. The results show that decreases in the thickness of the layers leads to a lowering of the demixing critical temperature.     

Cu—Ni—Si系引线框架用铜合金成分设计

研究了合金元素对ＣｕＮｉＳｉ 系列引线框架用铜合金性能的影响。发现合金中时效析出物具有与δＮｉ２Ｓｉ 相似的晶体结构,Ｎｉ 及Ｓｉ 元素含量对材料硬度和电导率有很大影响。当Ｎｉ 及Ｓｉ 元素含量增大时, 由于析出物数量增多, 材料硬度增加; 当Ｎｉ 与Ｓｉ 原子数之比小于２ 时, 材料电导率明显下降,这是由于过剩Ｓｉ 元素以固溶原子形式存在, 强烈损害材料电导率的结果。加入Ｚｎ 元素后, 保温过程中Ｚｎ 元素在合金与ＳｎＰｂ 共晶焊料界面处偏聚, 阻碍脆性金属间化合物层的形成, 在４２５ Ｋ 保温１ ０００ ｈ后, 铜合金与焊料间结合良好。     

Electrical properties of Al/conducting polymer (P2ClAn)/p-Si/Al contacts

Al/P2ClAn/p-Si/Al structure was obtained by the evaporation of the polymer P2ClAn on the front surface of p-type silicon substrate. The P2ClAn emeraldine salt was chemically synthesized by using propionic (C₂H₅COOH) acid. The current–voltage (I–V) characteristic of the structure was measured at room temperature. The capacitance–voltage–frequency (C–V–f) in terms of interface states over the frequency range of 10 kHz to 3 MHz has been investigated. The capacitance has decreased with increasing frequency, due to the interface states distribution. From the forward bias I–V plot for the sample, the ideality factor (n) and zero-bias barrier height (Φ_bp,0) were obtained as 4.84 and 0.787 eV, respectively. Under forward bias, the high value of the ideality factor and the dispersion in capacitance could be due to the interface state distribution, the interfacial insulator layer, the conducting polymer on the interface and inhomogeneity of the barrier height. The energy distributions and the relaxation times of the interface states were determined in the energy range of (0.387 − E_v) to (0.787 − E_v) eV.     

Ni segregation in the interfacial (Cu,Ni)6Sn5 intermetallic layer of Sn-0.7Cu-0.05Ni/Cu ball grid array (BGA) joints

Ni segregation in the interfacial (Cu,Ni)₆Sn₅ intermetallic layer of Sn-0.7Cu-0.05Ni/Cu BGA solder joints was investigated by using synchrotron micro X-ray fluorescence (XRF) analysis and synchrotron X-ray diffraction (XRD). Compared to Sn-0.7Cu/Cu BGA joints, Ni containing solder show suppressed Cu₃Sn growth in both reflow and annealed conditions. In as-reflowed Sn-0.7Cu-0.05Ni/Cu BGA joints, Ni was relatively homogenously distributed within interfacial (Cu,Ni)₆Sn₅. During subsequent annealing, the diffusion of Ni in Cu₆Sn₅ was limited and it remained concentrated adjacent the Cu substrate where it contributes to the suppression of Cu₃Sn formation at the interface between the Cu substrate and Cu₆Sn₅ intermetallics.     

Employment of a bi-layer of Ni(P)/Cu as a diffusion barrier in a Cu/Sn/Cu bonding structure for three-dimensional interconnects

This study explored the possibility of employing a bi-layer barrier of electroless-plated Ni(P)/thin Cu layers in a Cu/Sn/Cu bonding structure for three-dimensional interconnects. Our materials analysis revealed that the bi-layer barrier served effectively as a diffusion barrier and prevented full-scale materials interaction for temperatures higher than 300 °C. Such suppression of an intermetallic compound reaction and limiting Cu diffusion led to the formation of a rod-shaped Cu₆Sn₅ compound, rendering a unique microstructure of ductile Sn embedded with strong Cu₆Sn₅ rods. Our mechanical characterization using lap-shear testing and fracture analysis revealed that the sample with such a microstructure displayed a high bonding strength with some ductility, a desirable combination for high mechanical reliability.     

Effects of annealing and interlayers on the adhesion energy of copper thin films to SiO2/Si substrates

The adhesion of sputtered copper thin films was measured with a quantitative indentation technique utilizing refractory superlayers to trigger and promote delamination. Adhesion energies of the indentation-induced delaminations were analyzed in terms of the critical strain energy release rate. Two groups of films were investigated. Group I ranged in thickness from 225 to 1000 nm in both the as-deposited and annealed condition. Adhesion energies ranged from 2 to 15 J/m², with higher adhesion for the annealed condition. Group II films had nominal thicknesses of 430 and 1100 nm, some with 7–10 nm interlayers of either titanium or chromium. Adhesion energies of these films ranged from 4 to 30 J/m², increasing by a factor from 1.3 to 7.5, as a function of the interlayer presence and type, with the increase in energy due to a chromium interlayer exceeding that of titanium. Adhesion energies increased with film thickness for all films, with interlayers and annealing producing a larger increase. These quantitative results were compared to previous semi-quantitative and quantitative results, and shown to have comparable magnitudes and trends.     

Mechanical properties of polycrystalline copper and single-crystal LiF initial components for composite system Cu/LiF

The paper deals with an investigation of mechanical properties and deformation features of polycrystalline copper and single-crystal LiF under dynamic nano/microindentation. It is shown that the values of hardness and Young’s modulus depend on the magnitude of the applied load (P_max): when the load is increased, H and E decrease. General regularities of the indenter penetration process in a wide range of loads are revealed: the appearance of a “pop-in” effect at the initial stage of the loading process, the formation of more pop-in steps with the growth in load, and the formation of pileups around the indentations. Such a nature of deformation is the result of sequential activation of different dislocation mechanisms with indenter deepening. Along with a great similarity in the specificity of deformation, some differences are noted at the unloading stage. The results serve to compare the mechanical properties of Cu and LiF individual components with similar parameters of the “coating/substrate” composite systems (CS Cu/LiF) produced on their basis.     

Thermal stability of discontinuous precipitation in the Al-Zn-（Cu） system

The coarsening mechanism and kinetics of discontinuous precipitation (DP) in A1-Zn-(Cu) alloys were studied by means of optical microscopy, scanning electron microscopy, and X-ray diffraction analysis. The results show that the coarsening mechanism is different as the aging temperature varies. At a low temperature (150℃), the coarsening occurs through the dissolution and spheroidization of fme laminar structure of DP; at high temperatures (above 200℃), the discontinuous coarsening (DC) of DP microstructure mainly occurs, forming coarsening cells with a larger laminar distance. The growth velocity of coarsening cells rapidly reaches the maximum, and then decreases with the increase of time. The coarsening velocity of DP microstructure decreases due to the addition of Cu element.     

Thermal performance of sputtered Cu films containing insoluble Zr and Cr for advanced barrierless Cu metallization

Pure Cu films and Cu alloy films containing insoluble substances(Zr and Cr)were deposited on Si(100)substrates,in the presence of interfacial native suboxide(SiOx),by magnetron sputtering.Samples were vacuum annealed between 300℃and 500 ℃to investigate effects of Zr and Cr additions on the thermal performance of Cu films.After annealing,copper silicides were found in the Cu(Zr)films,while no detectable silicides were observed in Cu and Cu(Cr)films.Upon annealing,Zr accelerated the diffusion and reaction between the film and the substrate,and lowered the thermal stability of Cu(Zr)alloy films on Si substrates,which was ascribed to the‘purifying effect’of Zr on the Si substrates.Whereas,Cr prohibited the agglomeration of Cu films at 500℃and decreased the surface roughness.As a result,the diffusion of Cu in Si substrates for Cu(Cr)films was effectively inhibited.In contrast to the high resistivity of Cu(Zr)films,the final resistivity of about 2.76μΩ·cm was achieved for the Cu(Cr)film.These results indicate that Cu(Cr)films have higher thermal stability than Cu(Zr)films on Si substrates and are preferable in the advanced barrierless Cu metallization.     

Pd/Ge(or Si)/Pd/Ti/Au ohmic contacts to n-type InGaAs for AlGaAs/GaAs HBTs

Pd/Ge/Pd/Ti/Au and Pd/Si/Pd/Ti/Au ohmic contacts to n-type InGaAs were investigated for applications to AlGaAs/GaAs HBT emitter ohmic contacts. In the Pd/Ge/Pd/Ti/Au ohmic contact, a minimum specific contact resistivity of 1.1×10⁻⁶ Ωcm² was achieved by annealing at 425°C/10s, but the ohmic performance was slightly degraded with increasing annealing temperature due to the reaction between the ohmic contact materials and the InGaAs substrate. However, a non-spiking planar interface and relatively good ohmic contact (high-10⁻⁶ Ωcm²) were maintained after annealing at 450°C/10s. In the Pd/Si/Pd/Ti/Au ohmic contact, in spite of the lower barrier height of the metal-InGaAs junction, as-deposited contacts showed non-ohmic behaviors due to the presence of the insulating Si layer. However, the specific contact resistivity decreased remarkably to 4.3×10⁻⁷ Ωcm² by annealing at 425°C/10s. Minimum specific contact resistivity of 3.9×10⁻⁷ Ωcm² was achieved by annealing at 400°C/20s. RF performance of the AlGaAs/GaAs HBT was also examined by employing the Pd/Ge/Pd/Ti/Au and Pd/Si/Pd/Ti/Au systems as emitter ohmic contacts. Cutoff frequencies were 65.0 GHz and 74.4 GHz, respectively, and maximum oscillation frequencies were 51.3 GHz and 52.5 GHz, respectively, indicating very successful high frequency operations.     

Small-angle neutron scattering and differential scanning calorimetry studies on the copper clustering stage of Fe–Si–B–Nb–Cu nanocrystalline alloys

The kinetics of copper clustering and primary crystallization of FINEMET type alloys with the compositions Fe_74.5−xSi_13.5B₉Nb₃Cu_x and Fe₇₇Si₁₁B₉Nb_3−xCu_x have been studied by small-angle neutron scattering (SANS) and high-sensitivity differential scanning calorimetry (DSC) in order to explain the different optimized Cu contents, x, for obtaining the highest permeability in these two alloys. SANS results have shown that the alloys with the optimized Cu contents have the finest nanocrystalline microstructures. Kinetic analyses of Cu clustering prior to primary crystallization have shown that the number density of Cu clusters becomes highest at the crystallization stage of -Fe primary crystals in the alloy containing an optimized amount of Cu.     

Micro-patterning of Si(100) surfaces by ethanol cluster ion beams

The irradiation of Si(100) surfaces by ethanol cluster ion beams exhibited high-rate sputtering and low-damage formation. The sputtered depth increased with increase of the acceleration voltage for ethanol cluster ions, and the sputtering yield was a few hundreds times larger than that by Ar monomer ion beams. Also, the RBS channeling measurement showed that the irradiation damage was much less than that by Ar monomer ion irradiation. Furthermore, the AFM image showed that the surface roughness of the irradiated Si(100) surface was less than 1 nm. As well as the Si(100) surface, the sputtered depth of the photo-resist surface increased with increase of the acceleration voltage for ethanol cluster ions.Based on these results, micro-patterning with various sizes in a range of 3 μm to 100 μm was performed on the Si(100) surfaces by the ethanol cluster ion irradiation. Various kinds of photo-resist mask patterns such as circle, square and line patterns were made on a Si(100) surface by photo-resist technique. The SEM observation showed that micro-patterns were prepared on the Si (100) surface by the ethanol cluster ion irradiation.     

Crystallization process and thermal stability of Ge1Cu2Te3 amorphous thin films for use as phase change materials

The crystallization kinetics of amorphous Ge₁Cu₂Te₃ (GCT) films prepared by sputter deposition were investigated by differential scanning calorimetry under non-isothermal conditions. An exothermic peak due to crystallization was observed in the temperature range 230-270 °C. It was found that the local activation energy for crystallization is almost constant when the crystallization fraction is less than about 0.15 and then monotonically decreases with increasing crystallization fraction, which indicates that the crystallization of amorphous GCT films is a multi-step mechanism. The local Avrami exponent decreased from more than 5 to 1.7 with increasing crystallization fraction. It was demonstrated by the Ozawa method that GCT amorphous films show a higher thermal stability than Ge₂Sb₂Te₅ amorphous films, with an estimated failure time of over 70 years at 125 °C, which is well beyond the data retention requirements of the International Technology Roadmap for Semiconductors. In addition, the thickness change in GCT amorphous films accompanying crystallization was measured by atomic force microscopy. The GCT amorphous film was found to show a thickness increase of only 2.0% on crystallization, which is desirable to enhance the endurance of phase change random access memory devices.     

Effects of cold rolling parameters on sagging behavior for three layer Al−Si/Al−Mn(Zn)/Al−Si brazing sheets

The effects of intermediate annealing (IA) and the final cold rolling (CR) condition on the microstructure and sagging resistance during brazing were investigated using three layer clad sheets composed of the Al−7.5 wt.%Si alloy (filler, thickness: 10 μm)/Al−1.3 wt.%Mn based alloy (core, 80 μm)/Al−7.5 wt.%Si alloy (filler, 10 μm). Also, the effect of 1.2≈2 wt.% Zn addition into the core on the sagging resistance of the clad sheets was determined. It was revealed that all the clad sheets fabricated by the optimum condition (IA at 690 K and CR to 20≈45%) show excellent sagging resistance with a limited erosion due to the formation of a coarsely recrystallized grain structure in the core during brazing. It was also revealed that the recrystallization behavior of the Al−1.3 wt.%Mn based alloy is hardly affected by the addition of 1.2≈2 wt.%Zn during the brazing cycle. Therefore, the sagging resistance of the clad sheets is found to be governed not by the Zn content added in the Al−1.3wt.%Mn based core, but by the intermediate annealing and final cold rolling condition.     

SiC（Cu）／Fe复合材料制备工艺研究

采用非均相沉淀法制得Cu包裹SiC复合粉体，利用粉末冶金和常压烧结制备SiC（Cu）／Fe复合材料。利用Zeta电位仪、XRD，EDS以及SEM等手段对包裹粉体和烧结样品进行了分析。结果表明，采用非均相沉淀法可以得到Cu／SiC复合粉体。包裹后的粉体与原始SiC粉体的表面电位不同，达到了对SiC颗粒表面改性的目的。Cu作为过渡层改善了SiC／Fe的界面相容性，在1050℃烧结的样品只有微量的FeSi或Fe2Si生成，界面反应得到有效控制，获得化学结合的界面，温度过低不能烧结致密，温度过高出现大量缺陷。