Diffusion and adhesion properties of Cu films on polyimide substrates

Copper thin films were prepared on polyimide (PI) substrates by physical vapor deposition (PVD) and chemical vapor deposition (CVD). Titanium nitride (TiN) diffusion barrier layers were deposited between the copper films and the PI substrates by PVD. Auger electron spectroscopy compositional depth profile showed that TiN barrier layer was very effective in preventing copper diffusion into PI substrate even after the Cu/TiN/PI samples were annealed at 300 °C for 5 h. For the as-deposited CVD-Cu/PI, CVD-Cu/TiN/PI, and as-deposited PVD-Cu/PI samples, the residual stress in Cu films was very small. Relatively larger residual stress existed in Cu films for PVD-Cu/TiN/PI samples. For PVD-Cu/TiN/PI samples, annealing can increase the peeling strength to the level observed without a diffusion barrier. The adhesion improvement of Cu films by annealing treatment can be attributed to lowering of the residual tensile stress in Cu films.     

Investigation of thermal stability of Mo thin-films as the buffer layer and various Cu metallization as interconnection materials for thin film transistor-liquid crystal display applications

Cu/Mo/Si multi-layer structures were fabricated to investigate diffusion behaviors and thermal stability between Cu and Mo. Physical vapor deposition (PVD), chemical vapor deposition, electroplating and electrolessplating were used to grow 100 nm thick Cu films as interconnection materials, and radio-frequency sputtering system was introduced to grow 37.5 nm thick Mo films as a buffer layer. All Cu/Mo/Si multi-layer specimens were annealed at 350 to 700 °C for 30 min. When the annealing temperature was over 600 °C, the Cu diffused through Mo into Si, and the Cu₃Si phase and Mo-Si intermetallic compounds formed at the Mo/Si interface. The diffusion mechanism is the grain boundary diffusion. The results indicate that Cu film deposited by PVD had best crystallinity, lower roughness, large adhesive energy and resistivity. The values of the resistivity, diffusion activity energy and large adhesive energy are 5.47 μΩ-cm, 0.948 eV and 2.46 N/m, respectively.     

Analysis of the oxidation kinetics and barrier layer properties of ZrN and Pt/Ru thin films for DRAM applications

ZrN and Pt/Ru thin films have been grown by an automated ion beam sputter-deposition system. Both materials were evaluated for use as barrier layers (ZrN) and bottom electrodes (Pt/Ru) in dynamic random access memory (DRAM) applications. The ZrN films had resistivities on the order of 250–300 μω cm. The ZrN films were (002) oriented and were rather smooth with an average surface roughness of ±17 Å. Analysis of the oxidation kinetics of the ZrN thin films reveals a thermally activated, diffusion-limited oxidation process with an activation energy of 2.5 eV in the temperature range of 500–650 ° C. This implies that there is an advantage in using ZrN as a barrier layer instead of TiN since the activation energy for oxidation of TiN is 2.05 eV. In addition, preliminary data suggest that a Pt/Ru double layer may be a promising bottom electrode and oxygen diffusion barrier for use in DRAMs with high-permitivity dielectrics.     

Deuterium post-metallization anneal of electrochemical-plated Cu film deposited on different barrier materials

In this paper, we report on electrochemical-plated (ECP) copper (Cu) film characterizations with different (Ta, TaN and TiN) barrier materials subjected to post-metallization-annealing (PMA) in deuterium (D₂) under various annealing conditions. For comparison, post-metallization-anneal of the ECP Cu film in pure nitrogen (N₂) and forming gas (20% hydrogen+80% nitrogen) were also performed. We used four-point probe to determine the sheet resistance. Scanning electron microscopy was used to examine the surface morphology of the after-annealed ECP Cu films. X-ray-diffraction (XRD) analysis was used to inspect the texture of the ECP Cu films before and after PMA. The deuterium distribution in the barrier layer was determined by using the secondary ion mass spectroscopy depth profile analysis. We found that under appropriate PMA conditions, the sheet resistance of ECP Cu films deposited on TaN barrier was the lowest after D₂ PMA when compared with those deposited on TiN and Ta barriers.     

Fracture prediction of dissimilar thin film materials in Cu/low-k packaging

For current semiconductor technology, interfacial crack in stacked thin films of Cu/low-k damascene integration is a critical reliability issue that needs to be urgently resolved. In addition to the measurement of 4-point bending test, how to precisely estimate the adhesion energy between dissimilar films through simulation, based on fracture mechanics is important while designing robust interconnect structures as well as developing next-generation low-k materials. Distinct from the former studies, this research proposes a novel tie-release crack prediction technique based on finite element calculations in order to consider the stress-induced impacts on the thermo-mechanical reliability of the microelectronic package with a low-k chip during the different cracking length of film interfaces. To ensure the correctness and feasibility of the presented technique, a plastic ball array (PBGA) package with stacked Cu/low-k interconnects is implemented as test vehicle to validate actual testing data of experiments and evaluate the variation of interfacial cracking energy while silicon chip becomes thinner. Through the combination of J-integral approach with the technique of global–local sub-modeling, all the predicted results for the forgoing referred cases reveal a good agreement with the physical behaviors of devices. Therefore, it can be concluded that the proposed methodology is highly reliable in estimating the occurrence opportunities of interfacial crack.     

Role of nanoscale Cu/Ta interfaces on the shock compression and spall failure of nanocrystalline Cu/Ta systems at the atomic scales

Molecular dynamics (MD) simulations are used to investigate the role of size and distribution of nanoscale Cu/Ta interfaces on the nucleation and evolution of defects during shock loading and spall failure of nanocrystalline (nc) Cu/Ta alloys. Cu/Ta interfaces are introduced through the embedding of Ta clusters in nc-Cu matrix. The phase stability of the embedded Ta clusters either as FCC or BCC clusters is first investigated and reveals that the FCC Ta clusters have a lower energy for diameters less than 4 nm, whereas the BCC Ta clusters have a lower energy for the larger diameters. The shock simulations are then carried out for Ta clusters with an average diameter of 1 and 3 nm and concentrations of 3.0, 6.3 and 10.0% to investigate the role of size and distribution of Cu/Ta interfaces (due to presence of clusters) on the nucleation and evolution of dislocations as well as the spall strength of the alloy. The MD simulations indicate that the Cu/Ta interfaces reduce the capability of nc-Cu to accommodate plasticity through nucleation of dislocations and create void nucleation sites during spallation. The MD simulations further reveal that the impact strengthening effects due to the presence of nanoscale Cu/Ta interfaces are strongly dependent upon the size and distribution of Ta clusters, as well as the grain size of Cu matrix. Smaller size of interfaces (cluster size), higher concentration of Ta (smaller spacing between interfaces) and larger matrix grain size render higher spall strengths of nc-Cu/Ta microstructures.     

Diffusion barrier property of TiN and TiN/Al/TiN films deposited with FMCVD for Cu interconnection in ULSI

Flow modulation chemical vapor deposition (FMCVD) with titanium tetrachloride (TiCl₄) and ammonia (NH₃) is effective for depositing titanium nitride (TiN) films with conformal morphology, good step coverage, low electrical resistivity, and low chlorine residual contamination. It means that FMCVD TiN film is a good candidate of diffusion barriers for copper interconnection technology in ULSI. But the diffusion barrier property of FMCVD TiN film against Cu diffusion has not been confirmed. So, firstly, we deposited Cu (100 nm)/FMCVD TiN (25 nm)/Si multilayer films and investigated the thermal stability of Cu/TiN/Si structure. Vacuum annealing was done at 400, 500, 550 and 600 °C. For films annealed for 30 min at 400 °C, Cu diffused through the TiN layer and formed copper silicides on the surface of Si substrates. Therefore, FMCVD films formed under such conditions are unsatisfactory diffusion barriers. To enhance the diffusion barrier property of FMCVD TiN films, we used sequential deposition to introduce a monolayer of Al atoms between two TiN films. Etch-pit tests showed that for TiN films with Al interlayer, Cu diffusion through the barrier occurred at 500 °C and that is 100 °C higher than TiN film without Al interlayer. Al atoms formed AlO_x with oxygen atoms present in the TiN films as impurities, and fill up the grain boundaries of TiN film, thereby blocking the diffusion of Cu atoms.     

Molecular dynamics study of diffusion and atomic configuration in layered structures for Al circuit interconnects

Diffusion at Al(1 1 1)/underlay-metal interfaces, which is a dominant factor of electromigration-induced open-circuit failures in Al interconnects, was investigated by molecular dynamics simulation. The author focused on interfaces between the (1 1 1) plane in Al and the plane of greatest atomic density in five kinds of metals that have high melting temperatures: Ti, Cr, Mo, W, and Ta. The calculated self-diffusion coefficients of Al atoms near the Al/Ti and Al/Cr interfaces were smaller than those near the other three interfaces. This result is consistent with experimental results by other works that showed that Ti and Cr are effective underlay metals for suppressing the diffusion in Al interconnects. This result on the self-diffusion coefficient was linked to the result on the atomic configurations. The configurations of Al atoms at Al/Ti and Al/Cr interfaces were close to that for bulk Al, while the configurations at the other three interfaces were significantly different from that for bulk Al. It was found that diffusion as well as atomic configuration at the Al/underlay-metal interface is determined by the lattice mismatch between the (1 1 1) plane in Al and the plane of greatest atomic density in the underlay metal. Received 11 May 1998     

Titanium nitride diffusion barrier for copper metallization on gallium arsenide

The diffusion properties of Cu, Cu/titanium nitride (TiN) and Cu/TiN/Ti metallization on GaAs, including as-deposited film and others annealed at 350-550 °C, were investigated and compared. Data obtained from X-ray diffractometry, resistivity measurements, scanning electron microscopy, energy dispersive spectrometer and Auger electron spectroscopy indicated that in the as-deposited Cu/GaAs structure, copper diffused into GaAs substrate, and a diffusion barrier was required to block the fast diffusion. For the Cu/TiN/GaAs structure, the columnar grain structure of TiN films provided paths for diffusion at higher temperatures above 450 °C. The Cu/TiN/Ti films on GaAs substrate were very stable up to 550 °C without any interfacial interaction. These results show that a TiN/Ti composite film forms a good diffusion barrier for copper metallization with GaAs.     

多弧离子镀TiN涂层结合力的影响因素

选择Ｗ６Ｍｏ５Ｃｒ４Ｖ２、３Ｃｒ２Ｗ８Ｖ和ＧＣｒ１５等材料研究了多弧离子镀ＴｉＮ涂层也基体的结合力。结果表明,基体表面粗造度越小、硬度越高,支与基体的结合力越好,涂层厚度以２．５～３．５μｍ为最佳,含Ｖ量高的基体和具有强烈ＴｉＮ（１１１）择优取向的除层结合力好。     

Investigations of failure mechanisms at Ta and TaO diffusion barriers by secondary neutral mass spectrometry

One of the most important processes in Cu metallization for highly integrated circuits is to fabricate reliable diffusion barriers. Recently, thin films made of refractory metals and their compounds have been widely used in solid-state electronics as barriers because of their good electric properties, favourable thermal properties and chemical stability. Thermal stability of Tantalum (Ta) and Tantalum-oxide (TaO_x) layers as a diffusion barrier in Si/Ta/Cu, Si/TaO_x/Cu and Si/Ta-TaO_x/Cu systems have been investigated. Si/Ta (10 nm)/Cu (25 nm)/W (10 nm), Si/TaO_x (10 nm)/Cu (25 nm)/W (10 nm) and Si/Ta (5 nm)TaO_x (5 nm)/Cu (25 nm)/W (10 nm) thin layers were prepared by DC magnetron sputtering. A tungsten cap layer was applied to prevent the oxidation of the samples during the annealing process. The samples were annealed at various temperatures (473 K-973 K) in vacuum. Transmission Electron Microscopy, X-ray diffraction, X-Ray Photoelectron Spectroscopy and Secondary Neutral Mass Spectrometry were used to characterize the microstructure and diffusion properties of the thin films. Our results show that at the beginning phase of the degradation of the Si/Ta/Cu system Ta atoms migrate through the copper film to the W/Cu interface. In the Si/TaO_x/Cu system the crystallization of TaO and the diffusion of Si through the barrier determine the thermal stability. The Ta-TaO bilayer proved to be an excellent barrier layer between the Si and Cu films up to 1023 K. The observed outstanding performance of the combined film is explained by the continuous oxidation of Ta film in the TaO_x-Ta bilayer.     

Cu丝上沉积Ti/TiN多层膜的研究

铜丝可用于尿毒症患者腹膜透析置管术中的替代导丝。为了减少或消除铜离子对生物组织的损害,增加铜丝表面的生物相容性,同时又保持铜丝较好的塑性变形能力,本文采用电弧离子镀工艺在铜丝上沉积Ti/TiN多层膜。研究结果显示,镀膜铜丝表面光亮呈金黄色。沉积膜有明显的周期性层状特征,TiN相和金属Ti相周期性交替分布。其中,TiN相具有(111)晶面择优取向。沉积膜与铜丝结合良好,弯曲时镀膜铜丝没有出现微裂纹和膜脱落现象。室温消毒液浸泡和高温蒸汽消毒处理后,镀膜铜丝表面没有变化。腹膜透析置管术中使用镀膜铜丝,患者腹膜炎发生率明显降低,镀制Ti/TiN多层膜的铜丝适合应用于腹膜透析手术。     

Substrate temperature dependence of electrical and structural properties of Ru films

Microstructures and resistivities of sputtered Ru films were investigated as a function of substrate temperature to obtain a single-layered Ru barrier without a Ta/TaN under layer. High resistivity Ru films with a high density of crevices, which enhances Cu diffusion along the crevices, were formed by the conventional sputtering process, i.e., sputtering at room temperature and annealing at 400 °C-700 °C for 30 min in Ar + 3%H₂. But, crevice-free and smooth Ru films with low resistivity, the same as that for the bulk phase, were formed when substrate temperature add sputtering was raised to 700 °C. Ru films formed by this process had (002) preferred orientation and then Cu (111) was formed by plating. This result corresponded to the tendency predicted by ab initio calculations.     

Adhesive B-doped DLC films on biomedical alloys used for bone fixation

The long-term failure of the total hip and knee prostheses is attributed to the production of wear particles at the articulating interface between the metals, ceramics and polymers used for surgical implants and bone-fixtures. Therefore, finding an adhesive and inert coating material that has low frictional coefficient should dramatically reduce the production of wear particles and hence, prolong the life time of the surgical implants. The novel properties of the non-toxic diamond-like carbon (DLC) coatings have proven to be excellent candidates for biomedical applications. However, they have poor adhesion strength to the alloys and biomaterials. The addition of a thin interfacial layer such as Si, Ti, TiN, Mo and Cu/Cr and/or adding additives such as Si, F, N, O, W, V, Co, Mo, Ti or their combinations to the DLC films has been found to increase the adhesion strength substantially. In our study, grade 316L stainless steel and grade 5 titanium alloy (Ti-6Al-4V) were used as biomaterial substrates. They were coated with DLC films containing boron additives at various levels using various Si interfacial layer thicknesses. The best film adhesion was achieved at 8% and 20% on DLC coated Ti-6Al-4V and grade 316L substrates, respectively. It has been demonstrated that doping the DLC with boron increases their adhesion strength to both substrates even without silicon interfacial layer and increases it substantially with optimum silicon layer thickness. The adhesion strength is also correlated with the hydrogen contents in the B-DLC films. It is found to reach its maximum value of 700 kg/cm² and 390 kg/cm² at 2/7 and 3/6 for CH₄/Ar partial pressures (in mTorr ratio) for Ti-6Al-4V and 316L substrates, respectively.     

Effects of nitrogen ion implantation and implantation energy on surface properties and adhesion strength of TiN films deposited on aluminum by magnetron sputtering

The performance of tribological coatings depends greatly on the adhesion strength between the coatings and substrates. In this work, we investigated the influence of the ion implantation energy of nitrogen on the adhesion and surface properties of TiN deposited on aluminum substrate. Aluminum samples were implanted with 15 keV, 30 keV and 40 keV nitrogen ions before TiN films were deposited using magnetron sputtering in a custom-designed multi-functional ion implanter. The adhesion properties of the implanted TiN films were assessed using nano-scratch tests and were observed to vary with the nitrogen ion implantation energy. Our frictional test results show that an appropriate ion implantation energy and dose can improve the frictional behavior of TiN films deposited on aluminum.     

Investigation on preparation and diffusion barrier properties of W-Ti thin films

An W-10 wt.%Ti alloy target was prepared by the W-Ti ball-milled powders, and W-Ti thin ?lms were deposited by dc magnetron sputtering on Si substrates. Then Cu/W-Ti/Si structures were prepared after Cu films were deposited on the W-Ti/Si structures. The results show that W-Ti alloy has a single phase structure with fine grain size. The structures of W-Ti thin films evolved from an amorphous film to a dual phase structure with bcc W and hcp Ti, followed by W-Ti solid solution with increasing sputtering powers. W-Ti thin ?lms can effectively block against Cu diffusion and maintain good adhesion strength with Cu ?lms at 600 °C. The failure mechanism of the crystal W-Ti films is related to the grain boundary which provides fast diffusion paths for Cu and Si atoms, while the amorphous W-Ti diffusion barrier layer is directly related to the thermal stress and interface reaction.     

Improved oxygen diffusion barrier properties of ruthenium-titanium nitride thin films prepared by plasma-enhanced atomic layer deposition

Ru-TiN thin films were prepared from bis(ethylcyclopentadienyl)ruthenium and tetrakis(dimethylamino)titanium using plasma-enhanced atomic layer deposition (PEALD). The Ru and TiN were deposited sequentially to intermix TiN with Ru. The composition of Ru-TiN films was controlled precisely by changing the number of deposition cycles allocated to Ru, while fixing the number of deposition cycles allocated to TiN. Although both Ru and TiN thin films have a polycrystalline structure, the microstructure of the Ru-TiN films changed from a TiN-like polycrystalline structure to a nanocrystalline on increasing the Ru intermixing ratio. Moreover, the electrical resistivity of the Ru0.67-TiN0.33 thin films is sufficiently low at 190 microomega x cm and was maintained even after O2 annealing at 750 degrees C. Therefore, Ru-TiN thin films can be utilized as a oxygen diffusion barrier material for future dynamic (DRAM) and ferroelectric (FeRAM) random access memory capacitors.     

Improvement of the properties and electrical performance on TiCl4-based TiN film using sequential flow chemical vapor deposition process

Sequential flow chemical vapor deposition (SFCVD), utilizing TiCl₄/NH₃ as reactants and immediate NH₃ treatment after film deposition, is applied to produce TiN barrier films in the contact process. Secondary ion mass spectroscopy results indicate that the SFCVD TiN film can effectively block the diffusion of WF₆ into the underlying Ti layer during W deposition. NH₃ treatment immediately after film deposition causes SFCVD TiN films to be less contaminated with carbon than TiN films that are formed by metallic organic compounds chemical vapor deposition (MOCVD) and to contain less chlorine residue than conventional TiCl₄/NH₃ CVD TiN layers even at a low reaction temperature. According to the resistance measurement of Kelvin contacts, the SFCVD process yields a lower resistance and a more uniform distribution than the MOCVD or CVD process. Transmission electron microscopic observations demonstrate that WF₆ can diffuse through the MOCVD TiN to react with the underlying Ti layer, causing a rupture at the Ti/TiN interface and poor W adhesion. The SFCVD TiN can serve as a sufficient diffusion barrier against WF₆ penetration during W CVD deposition.     

Improvement of the (1 1 1) texture and microstructures of Cu films by pulsed laser annealing

The improvement of the (1 1 1) texture and microstructure of Cu films on TiN/Si and TiN/SiO₂ substrates by pulsed KrF laser annealing as a function of the laser energy density, the deposition method of Cu films, and the orientation of TiN substrates is studied. Upon annealing at an energy density below 1.0 J cm^–2 the (1 1 1) texture of the evaporated Cu films increases with the energy density, whereas for the sputtered Cu films the (2 0 0) texture is promoted. The higher oxygen concentration in the sputtered Cu films may be responsible for the degradation of the Cu(1 1 1) texture. The enhancement of the Cu(1 1 1) texture is more evident for (1 1 1)-oriented TiN substrates than for (2 0 0)-oriented TiN substrates. The present study shows that pulsed laser annealing is superior to vacuum annealing in improving the (1 1 1) texture and microstructure of Cu films via the melt/solidification process.     

Effects of diffusion on interfacial fracture of gold-chromium hybrid microcircuit films

In this study, the effects of diffusion on gold-chromium film durability was determined from interfacial fracture energy measurements on laboratory samples aged to simulate long term service. The samples were prepared by sputter deposition of gold films and chromium adhesive layers on sapphire substrates. Some films were left in the as-deposited condition while others were given an accelerated age to drive the chromium off the interface and into the gold film. Stressed overlayers and nanoindentation were then used to induce interfacial delamination and blister formation from which interfacial fracture energies were determined using mechanics-based models. These tests showed that the fracture energies for interfacial failure of the as-deposited and annealed films occurred near 1.3 J m^–2 even when diffusion had driven all chromium into solution. These results clearly demonstrate that chromium in solution is as effective in promoting adhesion as continuous chromium adhesive layers.