Diffusion barrier properties of sputtered TaNx between Cu and Si using TaN as the target

TaN_x films sputtered from a TaN target were used as diffusion barriers between Cu thin films and Si substrates. Material characteristics of TaN_x films and metallurgical reactions of Cu/TaN_x/Si systems annealed in the temperature range 400–900 °C for 60 min were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, cross-sectional transmission electron microscopy, and sheet resistance measurements. We found that the deposition rate decreased with increasing bias. TaN, β-Ta, and Ta₂N phases appeared and/or coexisted in the films at specific biases. A step change in N/Ta ratio was observed whenever a bias was applied to the substrate. After depositing a copper overlayer, we observed that the variation percentage of sheet resistance for Cu (70 nm)/TaN_x (25 nm, x=0.37 and 0.81)/Si systems stayed at a constant value after annealing up to 700 °C for 60 min; however, the sheet resistance increased dramatically after annealing above 700 and 800 °C for Cu/TaN_0.37/Si and Cu/TaN_0.81/Si systems, respectively. At that point, the interface was seriously deteriorated and formation of Cu₃Si was also observed.     

Epitaxial growth of MgO/TiN multilayers on Cu

The growth of epitaxial MgO/TiN multilayer films on (001) Cu has been investigated. In particular, epitaxial structures were grown on (001) Cu layers that were epitaxial on (001) SrTiO₃. X-ray diffraction and reflection high-energy electron diffraction indicate that the multilayer structures are epitaxial on the (001) Cu surface. The motivation is the use of crystalline MgO/TiN multilayers as a diffusion barrier to both copper and oxygen. MgO/TiN multilayers are potentially useful as diffusion barriers for Cu interconnects on semiconductors as well as for superconducting wires based on the epitaxial growth of cuprate superconductors on biaxially textured copper.     

Diffusion barrier performance of amorphous W-Ti-N films in Cu metallization

W-Ti-N films were prepared on a Si wafer by reactive sputter-deposition, followed by a deposition of a Cu thin film by DC magnetron sputtering. The Cu/W-Ti-N/Si samples prepared were annealed at different temperatures under vacuum and then characterized using X-ray diffraction, scanning electron microscopy and auger electron microscopy. The sheet resistivity was determined by four point probe analysis. The results show that the amorphous W-Ti-N film is mainly composed of TiN and W and the crystallization temperature is above 800 °C. W-Ti-N thin films prepared have good thermal stability at 700 °C, but the Cu film tends to agglomerate when the temperature is above 700 °C. A failure mechanism of the diffusion barrier is proposed based on the thermal stress and interface reaction.     

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.     

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.     

集成电路Cu互连扩散阻挡层的研究进展

简要介绍了集成电路的发展趋势及其带来的相关问题和解决办法.综述了国内外对Cu互连扩散阻挡层的制备方法与工艺、阻挡层的选材、阻挡层薄膜的特性等最新研究的进展.评述了该领域的发展趋势及可能的影响因素.     

Mechanical measurement of the residual stress in thin PVD films

A practical mechanical bending plate method is proposed to calculate the residual stress present in thin physical vapour deposition films. A thin circular foil of stainless steel is coated with TiN, using an unbalanced magnetron sputtering technique. Sectioning of this foil into narrow strips leads to an easily measurable radius of curvature. With the help of calculations based on the finite element method it is shown that, if the width-to-length ratio is small, the analytical formula of Senderoff is valid. Above a certain width-to-length ratio, serious errors in calculated stress values are introduced using Senderoff. The second part of this paper describes the influences of the deposition parameters of TiN on the residual stress in the coating. An increase of the bias voltage results in a higher compressive stress, varying from −4.2 to −7.2 GPa. Experiments with different substrate materials show that the growth stress is independent of the substrate material. The total residual stress present in the coating increases with a higher magnetron current and a lower working gas pressure.

There was excellent agreement between the results of the proposed method and X-ray diffraction (Seemann-Bohlin).     

Effect of preparation conditions on properties of atomic layer deposited TiO2 films in Mo–TiO2–Al stacks

TiO₂ films were grown by atomic layer deposition on Mo electrodes in order to elucidate the dominating conductance mechanism and its dependence on the growth chemistry. TiCl₄ and Ti(OC₂H₅)₄ served as titanium precursors, and H₂O or H₂O₂ as oxygen precursors. The films grown at lower temperatures were amorphous. With increasing growth temperatures the crystallization first started in the TiCl₄–H₂O process. The films grown in this process were clearly leakier compared to the films grown from Ti(OC₂H₅)₄ and H₂O and from Ti(OC₂H₅)₄ and H₂O₂. In the Ti(OC₂H₅)₄-based processes, the application of H₂O₂ instead of H₂O resulted in the films with considerably lowered conductivity, although structural differences in these films were insignificant. Space–charge-limited currents were prevailing in all our amorphous Mo–TiO₂–Al packages. Measurements at different temperatures suggested quite high trap densities likely due to the presence of impurities and structural disorder, while the strong differences in conductivity seemed to be due to different densities of gap states.     

Diffusion during annealing of Al/Cu/Fe thin films

The Al-Cu-Fe system is interesting due to the existence of the quasicrystalline phase Al_62.5Cu₂₅Fe_12.5 as well as its approximant phases. A two-step procedure of thin film preparation is considered: deposition of a multilayer structure of individual elements and consequential annealing. To analyze the diffusion processes trilayers of individual elements were deposited by sputtering with a total thickness of about 400 nm. Afterwards, the samples were annealed in tube furnace in inert atmosphere. Rutherford backscattering spectrometry, Auger electron spectrometry and X-ray diffraction were used to quantify the depth profiles. The results point out to a three-stage process as a function of rising temperature: first Al and Cu form the γ-Al₄Cu₉ compound layer; second the aluminium spreads throughout the film with copper and iron mainly divided. The β-Al(Cu,Fe) phase is observed. Complete homogenization is followed afterwards.     

Preparation and properties of TiN and AlN films from alkoxide solution by thermal plasma CVD method

Single phase TiN and AlN films were prepared on a Si wafer from titanium tetra-etoxide and aluminum tri-butoxide solutions dissolved in ethanol and toluene, respectively, using an Ar/N₂/H₂ radio-frequency (r.f.) inductive thermal plasma chemical vapor deposition (CVD) method. The films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, measurement of electrical resistivity and Vickers microhardness. Factors affecting the formation of the films (lattice parameter, chemical composition, oxygen/carbon content, and deposition rate of the films) were examined in terms of the N₂ flow rate (2.5–4.5 slm), substrate temperature (300–700°C), feed rate of the solution (0.025–0.3 ml/min), and the mole ratio of the alkoxide solution (1:1–1:3). The optimum conditions for preparation of TiN films produced a film 0.2–3 μm thick with an oxygen content of 8 at.% and a free carbon content of 4 at.%, showing an electrical resistivity of 370 μΩ cm. The optimum conditions for AlN films produced a film 0.3 μm thick containing 14 at.% oxygen and 8 wt.% carbon. The deposition rate of the TiN film was determined to be 30–35 nm/min. The Vickers microhardness of the TiN and AlN films was found to be 10±1 and 13±3 GPa, respectively.     

The microstructure and mechanical properties of TaN/TiN and TaWN/TiN superlattice films

The microstructure and the microhardness of the TaN/TiN and TaWN/TiN superlattice films have been studied with X-ray diffraction, transmission electron microscopy and microhardness tester. The results showed that both TaN/TiN and TaWN/TiN superlattice films have a cubic crystal structure with an epitaxially grown mode of polycrystallinity. Lattice constants of superlattice films are between those of the constituent materials. The superhardness effect was found in TaN/TiN and TaWN/TiN superlattice films and the maximum hardness value was 40.0 GPa at a modulation period of 9.0 nm for TaN/TiN, and 50.0 GPa at a modulation period of 5.6 nm for TaWN/TiN. It is proposed that the lattice mismatch affects the microhardness value and the peak position of maximum hardness. The inhibition of dislocation motion by alternating stress fields of interfacial coherent strains is believed responsible for hardness anomalies.     

集成电路Cu金属化中的扩散阻挡层

阐述了集成电路Cu互连中的技术难题,重点讨论了Cu的扩散问题,综述了扩散阻挡层的研究发展进程,重点介绍了当今研究较多的难熔金属、难熔金属氮化物及其三元结构阻挡层的最新进展情况.研究表明,阻挡层的阻挡性能与制备工艺、薄膜组分及微观结构密切相关,其失效机制多为高温下阻档层晶化所产生的晶界为Cu扩散提供了快速通道,掺入Si或其它原子的难熔金属氮化物由于其较高的晶化温度和良好的阻挡性能正成为研究热点.     

Diffusion barrier capability of Zr-Si films for copper metallization with different substrate bias voltage

Efficiency of Zr-Si diffusion barriers in Cu metallization has been investigated. Amorphous Zr-Si diffusion barriers were deposited on the Si substrates by reactive magnetron sputtering with different negative substrate bias. The mass density of Zr-Si films increases with substrate bias voltage up to − 150 V. The deposition rate decreased with the negative substrate bias from 5.4 nm/min to 1.8 nm/min. XRD measurements show that the Zr-Si barriers have amorphous structure in the as-deposited state. The FE-SEM images show that the sizes of spherical granules on the Zr-Si film surface increase with increasing the substrate bias. The Cu/Zr-Si/Si structures were prepared and annealed in Ar ambient at temperatures varying from 500 to 650 °C for an hour. It is shown from the comparison study that the Zr-Si film deposited with − 150 V is better at maintaining good performance in Cu/Zr-Si/Si contact system than that of Zr-Si film deposited with − 50 V.     

Properties of thin TiN films deposited onto stainless steel by an in-line dry coating process

A new coil-coating pilot plant, capable of utilizing ion plating, sputtering and plasma-assisted chemical vapor deposition (PACVD) processes, independently or in series, was developed and optimum conditions for TiN, TiC, Al_xO_y, SiO_x and Cr coating were established. This paper is mostly concerned with the results of characterization (conducted in parallel by the authors′ two institutions) of TiN films deposited by ion plating or sputtering onto type-304 stainless steel strips. In particular, the dependence of the basic properties such as chemical composition, structure, adhesion, and color on the coating process are discussed with respect to anti-corrosion, anti-wear, and decorative applications. TiN coatings with a very attractive gold coloration were obtained; they performed well in wear testing, but did not show satisfactory corrosion resistance. However, it was found that the latter can be improved significantly by depositing a SiO_x, top layer by PACVD above the TiN coating. Thus the in-line dry coating processes are capable of producing highly functional steel surfaces with decorative color and high corrosion resistance.     

Influence of Ge addition on the morphology and properties of TiN thin films deposited by magnetron sputtering

Thin films of TM-X-N (TM stands for early transition metal and X = Si, Al, etc.) are used as protective coatings. The most investigated among the ternary composite systems is Ti-Si-N. The system Ti-Ge-N has been chosen to extend the knowledge about the formation of nanocomposite films. Ti-Ge-N thin films were deposited by reactive magnetron sputtering on Si and WC-Co substrates at T_s = 240 °C, from confocal Ti and Ge targets in mixed Ar/N₂ atmosphere. The nitrogen partial pressure and the power on the Ti target were kept constant, while the power on the Ge target was varied in order to obtain various Ge concentrations in the films. No presence of Ge-N bonds was detected, while X-ray photoelectron spectroscopy measurements revealed the presence of Ti-Ge bonds. Transmission Electron Microscopy investigations have shown important changes induced by Ge addition in the morphology and structure of Ti-Ge-N films. Electron Energy-Loss Spectrometry study revealed a significant increase of Ge content at the grain boundaries. The segregation of Ge atoms to the TiN crystallite surface appears to be responsible for limitation of crystal growth and formation of a TiGe_y amorphous phase.     

Epitaxial growth of SrTiO3 films with different orientations on TiN buffered Si(001) by pulsed laser deposition

Epitaxial SrTiO₃ (STO) films have been grown on TiN buffered Si(001) by pulsed laser deposition. The TiN layer was in situ deposited at 540, 640 or 720°C whereas the STO film was grown at a fixed temperature of 640°C. We have studied the effect of the growth temperature of TiN on the epitaxial relationship of STO/TiN heterostructures. It is found that for TiN grown at 540 or 640°C the epitaxial relationship is 001STO 001TiN, and for TiN grown at 720°C it changes to (101)STO (001)TiN and [ 01]STO [1 0]TiN (or [ 01]STO [110]TiN). This change of relationship is accompanied by a sharp reduction in the out-of-plane lattice constant of the TiN layer. Fourier transform infrared spectra show that the longitudinal optic modes are active for all the STO films, but the absorption peak associated with the transverse optic mode is observed only in the (101) oriented STO films.     

铜与硅之间W/Mo-N薄膜的扩散阻挡层性能

研究了铜与硅之间W／Mo-N薄膜的扩散阻挡性能。在Si(100)基片上利用反应溅射沉积一层Mo-N薄膜,然后再利用直流溅射在Mo-N上面沉积Cu／W薄膜。样品在真空下退火,并利用四点探针、X射线衍射分析、扫描电镜分析、俄歇电子能谱原子深度剖析等测试方法研究了Cu／W／Mo-N／Si的热稳定性及W／Mo-N薄膜对铜与硅的扩散阻挡性能。实验分析表明,Cu／W／Mo-N／Si结构具有非常好的热稳定性,在600℃退火30min仍未发生相变,并能有效的阻挡铜与硅之间的扩散。     

Formation of low-resistivity poly-Si and SiNx films by Cat-CVD for ULSI application

In this paper, bulk-Si metal–oxide–semiconductor field effect transistors (MOSFETs) are fabricated using the catalytic chemical vapor deposition (Cat-CVD) method as an alternative technology to the conventional high-temperature thermal chemical vapor deposition. Particularly, formation of low-resistivity phosphorus (P)-doped poly-Si films is attempted by using Cat-CVD-deposited amorphous silicon (a-Si) films and successive rapid thermal annealing (RTA) of them. Even after RTA processes, neither peeling nor bubbling are observed, since hydrogen contents in Cat-CVD a-Si films can be as low as 1.1%. Both the crystallization and low resistivity of 0.004 Ω·cm are realized by RTA at 1000 °C for only 5 s. It is also revealed that Cat-CVD SiN_x films prepared at 250 °C show excellent oxidation resistance, when the thickness of films is larger than approximately 10 nm for wet O₂ oxidation at 1100 °C. It is found that the thickness required to stop oxygen penetration is equivalent to that for thermal CVD SiN_x prepared at 750 °C. Finally, complementary MOSFETs (CMOSs) of single-crystalline Si were fabricated by using Cat-CVD poly-Si for gate electrodes and SiN_x films for masks of local oxidation of silicon (LOCOS). At 3.3 V operation, less than 1.0 pA μm⁻¹ of OFF leakage current and ON/OFF ratio of 10⁷–10⁸ are realized, i.e. the devices can operate similarly to conventional thermal CVD process.     

Fabrication of low-resistivity and gold-colored TiN films by halide chemical vapor deposition with a low [NH3]/[TiCl4] flow ratio

This work describes the preparation of titanium nitride (TiN) films on Si (111) substrates by atmospheric pressure halide chemical vapor deposition (AP-HCVD). Various TiN films were obtained by exploiting TiCl₄ + NH₃ gas chemistry with flow ratios [NH₃]/[TiCl₄] from 0.2 to 1.4, and deposition temperatures (T_d) from 600 to 900 °C. When T_d = 800 °C gold-colored films with electrical resistivities of under 100 μΩ cm were formed at almost all of the investigated [NH₃]/[TiCl₄] flow ratios. In particular, a lowest resistivity of about 23.7 μΩ cm, which is quite close to that of bulk TiN, was achieved using an [NH₃]/[TiCl₄] flow ratio of 0.3. Atomic force microscopy indicated that the root mean square surface roughness of that film was only about 5.1 nm. Under the same [NH₃]/[TiCl₄] flow ratio as above, X-ray diffraction analyses revealed the presence of a cubic TiN phase with a preferred orientation of (200) for T_d ≤ 800 °C, while additional (111) and (220) orientations emerged when the film was deposited at 900 °C. In conclusion, a low resistivity (< 100 μΩ cm) TiN film can be formed by AP-HCVD with very low [NH₃]/[TiCl₄] flow ratios 0.3-1.4.     

Morphology of TiN thin films grown on SiO2 by reactive high power impulse magnetron sputtering

Thin TiN films were grown on SiO₂ by reactive high power impulse magnetron sputtering (HiPIMS) at a range of temperatures from 45 to 600 °C. The film properties were compared to films grown by conventional dc magnetron sputtering (dcMS) at similar conditions. Structural characterization was carried out using X-ray diffraction and reflection methods. The HiPIMS process produces denser films at lower growth temperature than does dcMS. Furthermore, the surface is much smoother for films grown by the HiPIMS process. The [200] grain size increases monotonically with increased growth temperature, whereas the size of the [111] oriented grains decreases to a minimum for a growth temperature of 400 °C after which it starts to increase with growth temperature. The [200] crystallites are smaller than the [111] crystallites for all growth temperatures. The grain sizes of both orientations are smaller in HiPIMS grown films than in dcMS grown films.