Search

Co-sputtered Ru-Ta(N), Ru-W(N) and Ru-Mn composites are investigated in terms of their barrier properties against Cu diffusion. A wide range of stoichiometries is analyzed with regard to crystallization, barrier properties, resistivity, Cu adhesion and direct Cu plating behaviour. All films were annealed at 350^oC and 600^oC in forming gas for 1h and subsequently stressed at elevated temperatures and electrical fields (BTS, 250^oC, 2MV/cm, 30min). The leakage current was monitored during BTS to observe increased leakage due to Cu diffusion. The Cu ions that eventually have passed the barrier and drifted into the dielectric of the MIS test structure were detected and quantified using the triangular voltage sweep method. The addition of 10% W or Ta into a Ru film already leads to a highly improved barrier performance against Cu diffusion, comparable to TaN, as long as the temperatures involved are kept below 350^oC. Outstanding barriers were identified after 600^oC annealing and subsequent BTS, among them Ru"5"0W"5"0", Ru"5"0Ta"5"0 and Ru"9"5Mn"5. However, only Ru"9"0Ta"1"0 and Ru"9"5Mn"5 offer an excellent Cu adhesion and the possibility of direct Cu plating.

Electroplated Cu(Ag) alloy thin films are potential candidates for future electronic devices in terms of lifetime and reliability compared to copper as the state of the art interconnect material. In the present paper we focus on the microstructure of Cu(Ag) alloy films considering the grain evolution as well as silver incorporation and segregation. We show that Ag alloying addition prevents room temperature recrystallization. Thermally induced grain growth occurs mainly between 180 °C and 330 °C. Silver can be incorporated as solid solution into the Cu matrix by up to 0.8 at.% after annealing and even in higher concentrations in the as-deposited state, which is significantly above the equilibrium solubility limit. Precipitations are formed by the continuous mode and can be mainly found at the film surface but also inside the Cu(Ag) grains as ball-shaped particles. Based on our results a reliability improvement is expected by mechanical strengthening due to alloying effects while maintaining a low electrical resistivity and a {111} fiber texture.

Electromigration effects in interconnect metallizations cause a need for materials with superior resistance against electromigration failure but with adequate electrical properties. In principle, Cu(Ag) alloys are potential candidates to become an interconnect material of the next generation of microelectronic devices. Therefore, in the following paper the electroplating of such Cu(Ag) alloys from a sulfuric acid electrolyte solution with varying silver content in a home built deposition tool is presented. Besides the general deposition characteristics, the growth mode of the films and the deposition into trenches will be discussed. The investigations show that Cu(Ag) alloys can be deposited with adequate homogeneity of the film thickness by electroplating. Furthermore, the electrical resistivity is low enough to assure a use of these films for interconnect applications. However, distinct island growth and insufficient trench filling capabilities lead to the fact that the additive composition needs to be optimized for Cu(Ag) thin film electroplating.

Electromigration failure of copper interconnects in microelectronics evokes a need for materials with improved resistance against electromigration effects. Copper-silver alloy thin films are a promising material for the next generation of interconnects and were investigated with respect to their electromigration resistance. The investigations were done by atom drift experiments by means of Blech structures fabricated in single damascene technology with two different Ta-based liner systems. Electromigration induced atom drift could be demonstrated. The resistance against electromigration of Cu(Ag) films appears to be slightly higher than for pure Cu films. However, significant experimental errors are still present. Additionally, de-alloying effects were observed.

To increase the electromigration resistance of copper interconnects copper alloy systems are of interest. In the present paper electrical properties of Cu(Ag) films will be discussed with respect to heat treatment and in comparison to copper and other alloy systems. The investigations show that the electrical resistivity of Cu(Ag) films is very low in comparison to other copper alloy systems. Up to an alloy content of about 2 at.% Ag the International Technology Roadmap for Semiconductors criterion of 2.2 μΩcm (scattering by geometrical constraints neglected) can be fulfilled after heat treatment. The various components of the electrical resistivity will be discussed in detail. The investigations show that grain growth and the redistribution of silver and impurities dominate the electrical resistivity evolution.

The deposition of ultra thin Ta(N) films by ALD is a possibility to achieve conformal film thickness and suitable step coverage for microelectronic applications. Due to the sorption of a precursor molecule to the substrate surface, the chemical interface conditions are important. In the present study selected substrate pretreatments were investigated by in situ XPS and spectroscopic ellipsometry in reference to the amount of carbon containing contamination and oxygen and in reference to the ALD growth rate of Ta(N) films. Furthermore, surface roughness was measured by AFM and will be discussed in dependence on the individual pretreatment and the ALD Ta(N) cycle number.

Ta-N based thin films were grown by thermal atomic layer deposition (ALD) with an alternating supply of the reactant source TBTDET (tert-butylimidotris(diethylamido)tantalum) and NH3 (ammonia). The films were deposited using a newly designed and constructed atomic layer deposition prototype tool combined with several in situ metrology. It was observed that thin films were successfully deposited on a 300mm Wafer with a saturated growth rate of approximately 0.55i?/cycle at 270?C. The as deposited films resulted in the formation of Ta(C)N consisting of 38at% Ta, 32at% N and 10at% C. With in situ spectroscopic ellipsometry (SE) the growing behaviour of the film was investigated and compared to atomic force microscopy (AFM) images.

The modeling of residual stresses generally deals with the calculation of the thermal ones alone. In the present work, a model is proposed, where intrinsic residual stresses are calculated explicitly. It is based on the Tsui-Clyne model, which was modified in order to describe the deposition of n different deposited layers on the substrate with the same set of equations as in a mono-layer system. For that we introduced the notion of ''virtual substrate'' and ''effective parameters''. The calculated values are compared with experimental results obtained for the following systems: Ta/Si, Mo/Si, Al/SiO"x/Si and Pd/SiO"x/Si. The depositions were performed by electron beam evaporation onto Si and Si/SiO"x (100) substrates with varying film thickness.

The stress evolution in electrochemically deposited copper-silver alloy thin films during thermal cycling from RT up to 500 ^oC is presented. Stress-temperature behavior was studied by laser-optical substrate curvature measurements, and the results are compared with the behavior of pure copper films. It will be shown that Cu(Ag) reacts elastically to thermal stress loading up to 180 ^oC. The influence of the substrate on the @s(T) curves will be discussed. Furthermore, microstructure (e.g., grain size, single grain orientation) developing during thermal treatment has been investigated. It is shown that the microstructure of Cu(Ag) films is thermally stable after the first cycle.

In this article we present microstructural investigations of electrodeposited CuAg-alloy metallization thin films. The deposition was carried out on Si(100)/SiO2Ta/TaN/Cu-seed substrates at room temperature without any additives. It was found that the mean grain size decreases with increasing dc current density whereas a dependence on the Ag content was not observed. Additionally the crystalline structure and, particularly, the formation of CuAg-solid solutions and grain boundary segregation is discussed on the basis of XRD measurements. The Ag content within a supersaturated copper matrix increases with increasing dc current density.