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For the last several generations of CMOS technology, copper has been used widely as an interconnect material in the back end of the line (BEOL). [1] [2] [3] As the current nodes technology are decreasing continuously, several copper scaling challenges appeared such as the Cu barrier thinning, the copper electromigration... [4] [5] Hence, cobalt and ruthenium are proposed as replacement materials. Recently, Co has made inroads in microelectronics, specifically on-chip metallization, serving as a capping layer for Cu to diminish electromigration but also provide a better conductivity for line width inferior to 10 nm [6] [7] [8]. In this very challenging context, the control of Co surface oxidation process is strategic. Conformal Co seed characteristics (i.e electronic conductivity), preceding the following filling chemistry, are partially related to its surface oxide. Its understanding, then its control, will be determinant to access to a perfect and reliable filling of the nodes. To collect quantitative information, we carefully investigate the behavior of a pure Co metallic surface which is exposed to air oxidation. For this purpose, we have used a 400nm thick Co layer electrochemically plated using Kari© aveni acidic chemistry. The Co layer is electrochemically deposited on Co seed (3nm) /Ta/TaN barrier/Tetraethyl orthosilicate (TEOS). The latter, with its native oxide, is introduced in ultra-high vacuum (UHV) of a XPS Nexsa ThermoFisher spectrometer. Then, a totally deoxidized Co surface is obtained with a argon beam sputtering. The initial free oxide bulk metallic Co is then checked by XPS. Starting from this surface, we explore again by XPS, consequences of different air exposure times using the entrance prepation chamber of the spectrometer. According to the time air-exposure, the kinetic of the oxide growth mechanism can be evaluated. Our work shows clearly that the metallic Co surface evolves very quickly to an ultra-thin ( Moreover, a simulation of behaviors of this oxide surface coverage immersed in acidic solution will be proposed to understand how an ultra-thin Co seed layer interacts in Co filling solution. For both cases (air-exposure and cobalt filling solution) the results comparison and a discussion will be proposed . References [1] D. Edelstein et all"IEEE IEDM Tech. Digest," p. 773, 1997. [2] S. Venkatesan et all "In Electron Devices Meeting," p. 769, 1997. [3] S. Tyagi, et all, "In Electron Devices Meeting,," p. 567, 2000. [4] H.-J. Cho, et all "VLSI Technology, IEEE Symposium," p. 1, 2016. [5] S. Y. Wu et all "Electron Devices Meeting (IEDM)," p. 2, 2016. [6] V. P. Graciano et all Journal of The Electrochemical Society, vol. 166, p. 3246, 2019. [7] J. H.-C. Chen et all 2016 IEEE International Interconnect Technology Conference / Advanced Metallization Conference (IITC/AMC);," p. 12, 2016. [8] C. Adelmann et all "Interconnect Technology Conference/Advanced Metallization Conference (IITC/AMC);," p. 173, 2014. Figure 1

The constant shrinking of critical dimensions in logic manufacturing is driving a change in integration of interconnects. While copper has been the material of choice for the past few decades, it is currently facing a serious challenge from other materials like cobalt. The focus of this paper is three-fold. First, we compare the reactivity of both materials in different media. Next, we confirm that kinetics of native oxide formation when exposed to atmosphere is an order of magnitude slower for copper than for cobalt and that, in the case of cobalt, the presence of an oxide is not avoidable in the industry conditions. And finally, we investigated the compatibility of plating solutions manufactured by aveni for cobalt and copper deposition. Both solutions reveal that, not only do they etch the native oxide of a cobalt seed, but they also preserve the integrity of the underlying metallic cobalt layer. This is highlighted by the fact that no oxide is detected at the interface between the deposited metal and the seed after deposition. We therefore provide evidence of the compatibility of aveni plating solution with a wide array of integrations for next generation interconnects such as copper extension with direct-on-cobalt integration or full cobalt integration.

International audience

Nowadays, Through Silicon Vias (TSV) with High Aspect Ratio (HAR > 8:1) are seriously mandatory in the 3D Integrated Circuits in order to maintain semiconductor performance trends into new technological advances. Consequently, successful integration of HAR TSVs requires solving key challenges in terms of technical (layer continuity, step coverage, adhesion) and industrial (scale-up to 300mm diameter wafer) developments. In this paper, one proposes to discuss those questions by means of the integration of an electrografting (eG) seed layer on a high conformal, but low conductive MOCVD TiN copper diffusion barrier. On the one hand, one studies the impact of different electrochemical parameters on eG Seed layer properties. On the other one, the encountered difficulties are presented and solutions are proposed to integrate eG Seed layer at a large scale i.e. on a specific industrial 300mm diameter wafer plating chamber.

Copper electrodeposition for on-chip interconnection has been widely described in the semiconductor industry. Most copper plating chemistries currently used for copper interconnects are acidic, involving special additives that provide bottom up fill of the narrow structures[1]. However, as copper interconnects continue to be scaled down in order to improve device performance within a minimum area, conventional acidic bath chemistries have shown limitations, due to the non-uniform coverage of the copper seed layer obtained with physical vapor deposition (PVD). In fact, acidic copper plating baths require a perfectly continuous copper seed layer in order to achieve void-free filling, which is mainly due to poor nucleation density of the acidic bath on resistive under layers (e.g., the barrier layer). Several years ago, a cobalt liner was widely studied as an additional layer to promote copper seed layer coverage on the barrier layer by improving copper wetting[2,3]. It resulted in a thin, continuous and conformal copper layer that facilitates the repair of discontinuities and the formation of a robust seed layer favorable to void-free copper filling. Also, geometry shrinking created high line resistance and the trend toward copper line failure. Interface quality between the copper and dielectric barrier then appeared to be vital, justifying again the introduction of a cobalt layer to ensure chip reliability, especially electromigration. Nevertheless, next generation interconnects will tend to adopt new integration schemes with increased copper volume inside the features in order to decrease RC delay. Additionally, aggressive critical dimensions (CD) will require a greater suppressing effect of the copper plating chemistries to avoid premature closure of the trenches / vias. In order to achieve void-free filling of advanced node copper interconnects, novel and innovative plating chemistries have to be developed. The conventional acidic three-component bath (accelerator, suppressor, and leveler) used for decades must be reinvented in order to improve the suppressing effect and bottom up efficiency, and to prevent any pinch-off during the gap fill of very aggressive and narrow trenches ( [1] P.C. Andricacos, C.Uzoh, J.O. Dukovic, J. Horkans, and H. Deligianni, IBM, J. of Res. And Dev., vol. 42, 1998, 567. [2] T. Nogami, et al., ‘CVD Co and its application to Cu damascene interconnections’, Interconnect Technology Conference (IITC), 2010, 1. [3] T. Nogami et al., ‘CVD-Co/Cu(Mn) integration and reliability for 10 nm node’, Interconnect Technology Conference (IITC), 2013,1

This paper reports the analysis of 4-mercaptoaniline (p-HSC6H4NH2) functionalized platinum nanoparticles by X-ray photoelectron spectroscopy (XPS). The spectra are recorded on mixed Langmuir-Blodgett (LB) films containing fatty acid and platinum particles in proportion 50/50. The LB films are deposited on gold layer made by thermal evaporation on glass substrate. The quite good stability of the nanomaterial under X-ray exposure is reported from one minute to two hours thirty. A line profile is conducted on seventeen points of a LB film to check the good homogeneity of the deposition. The elemental composition of the nanoparticule core-shell structure is reported for platinum sulfur and nitrogen. Then, the evolution of the Pt 4f core level intensity compared to the Au 4f signal coming from the burried gold electrode is established as a function of film thickness. From this analysis the effective electron attenuation length of Pt 4f photoelectrons and the effective value of platinum atom density are determined. Further exploitation of these data leads to an averaged interparticle distance in the nanocomposite. Comparison of these results with those recorded from X-rays reveals a quite good aggreement and validates the XPS intensities treatment.

In this work, the nano-scratch test is used to characterize the interfacial adhesion of amorphous SiCN thin films deposited by plasma enhanced chemical vapour deposition on Cu/Si substrates. The experimental results show that the critical load F c is directly related to the rupture of the SiCN/Cu interface. A strong linear dependence of F c to the SiCN thickness independently to the adhesion is also put in evidence. A three-dimensional finite element model of the test is then built. The results show a clear relation between the stresses into the coating and the cracking and buckling of the film observed experimentally. We then discuss how the interfacial tensile stresses can explain the increase of F c with the film thickness.

This paper reports on the study of the evolution of 4-mercaptoaniline (p-HSC6H4NH2) functionalized platinum nanoparticles in solution by coupling the Langmuir–Blodgett technique and X-ray photoelectron spectroscopy (XPS). The spectra are recorded on mixed LB films containing fatty acid and platinum particles in proportion 50/50. Several samples built from fresh and aged solutions of particles are analyzed. Comparison of the Pt 4f, S 2p and N 1s regions in each case points to the time dependant chemical evolution of the functionalized particles involving at once platinum, thiolate and amine components. The particle aging in solution is reported during several months, until the complete flocculation of the functionalized platinum nanoparticles. Using the compared XPS analysis of the LB layers obtained from the different particle solutions, unstability of the storage looks then clearly related to the chemical evolution of the bifunctional organic crown.

International audience; 4-mercaptoaniline functionalised platinum particles of 2 nm diameter were synthesised and over-grafted with 2-thiophenecarbonyl chloride. The derivative particles were dispersed in DMSO and gave long term stable suspensions. The Langmuir-Blodgett technique was then used to build up stable Langmuir-Blodgett films and the electrochemical behaviour of these ultra-thin films towards oxygen reduction was investigated in an acidic medium. It revealed direct activity without any previous activation treatments despite of the presence of the organic shell at the particle surface. Furthermore, XPS experiments revealed that the organic crown was not significantly destroyed on prolonged cycling. The results open a way to study original and versatile platinum-based nanocomposites.

After many years of developments, 3D Integrated Circuits have emerged as a potential key enabler for maintaining semiconductor performance trends. Through Silicon Vias (TSVs) sit at the foundation of the 3D-IC revolution for extending semiconductor integration into a new phase. Integrated device manufacturers and fabless design houses need small, high-density, fine-pitch vias for improving signal integrity and Si real-estate savings, without possibility to wait for very thin wafer processing and handling technologies to become a mainstream. Deep TSVs with Aspect Ratio (AR) greater than 10:1 elegantly fulfill those requirements. But they cannot be manufactured with acceptable yield/cost using traditional dry processes for liner, barrier and seed deposition. Conventional dry techniques show basic shortcomings and impose high capital investments. Beyond that, physical limitations of directional dry techniques prevent the deposited layer from reaching good step coverage or even continuity inside the vias, which is required to perform void-free gap filling with electroplated copper. To overcome those limitations, alternative wet solutions based on electrografting (eG) and chemical grafting (cG) technologies were developed. These latter are two fundamental molecular engineering technologies, delivering high-quality films (continuous, adherent and uniform) for high aspect ratio (HAR) TSVs. This paper will focus on the integration of eG copper seed as a mature solution for TSVs with HAR, to overcome PVD Copper limitations in those dimensions. Electrografting is based on surface chemistry formulations and processes. It is applied to conductive and semi-conductive surfaces, and enables self-oriented growth of thin coatings of various materials, initiated by in-situ chemical reactions between specific precursor molecules and the surface. Contrary to electro-deposition which requires a potential supply throughout deposition to fuel the redox processes, electrografting is an electro-initiated process which requires a charged electrode only for the grafting step, but not for the thickening. As eG is mainly a cathodic process, it can generally be applied to various metallic and semiconducting surfaces without any concern over oxide formation. In a first approach, electrografting was used for polymer deposition on various conductive and semi conductive substrates. In this case, the grafting occurs via a direct electron transfer from the cathode to the electro-active monomers in solution (Figure 1). Mechanisms of radical polymerization show that polymer electrografting is an electro-induced grafting process followed by a purely chemical propagation step (polymerization). The first electro-induced step is crucial to form the chemical bond between the polymer and the surface. A specific organic precursor (B) is used both to form a first primer grafted layer and to initiate the polymerization of the vinyl monomer (A) in solution. The termination step of the polymerization leads to the grafting of macromolecular chains (-[A-A-A]n-B) onto the first primer grafted layer. Based on the polymer electrografting concept, formulation and processes have been developed to graft metal layers onto various type of conductive and semi-conductive surfaces. In opposite, for instance, to copper electrodeposition which has to be performed on conductive layer to avoid terminal effect induced by resistive copper diffusion barrier layers, copper electrografting technology can interestingly be achieved on highly resistive substrates. A bath containing specific organics and copper has previously been developed to deposit the Cu seed layer. It has been shown that electrografted copper seed can directly be applied to various dry-deposited diffusion barriers (Ta, TaN, Ti, TiN, TiW) without any adhesion promoter in between. This paper deals with the integration of eG Seed layer on a conformal MoCVD TiN copper diffusion barrier on 8:1 aspect ratio TSVs. First, detailed mechanism of the electrografting process will be discussed. Secondly, the influence of the electrical barrier resistivity (PVD TiN, Ni vs MoCVD TiN) on the plating properties into the via will be presented for both experiments done at coupon level and up scaled in an industrial 300mm diameter wafer reactor. Plating differences will be considered in term of growth initiation and step coverage for these two experimental configurations. Fine tuning of the process parameters at the 300mm scale will then be examined to achieve a conformal, uniform and adherent copper seed layer in order to successfully respond to the high AR copper filling challenge in the TSV applications. Finally, void-free filling, integration in a conventional 3D process flow and electrical characterizations on high aspect ratio TSV middle daisy chains are ongoing. As a perspective to decrease the cost of TSV metallization, the entire wet metallization process flow including isolation, copper diffusion barrier, copper seed and copper fill steps will be developed at the end of this paper.

This paper reports on the original and promising electrocatalytic properties of thiol-capped platinum nanoparticules toward O2 reduction in acidic medium. The nanoparticles were initially functionalized by 4-mercaptoaniline, and were further derivatized with 2-thiophenecarbonyl chloride leading to high stabilization of the organic crown. Ultrathin films of these particles were built up by the LB technique on gold. Their electrochemical behavior was studied. These assemblages were also characterized by X-ray photoelectron spectroscopy before and after oxygen reduction experiments. An electrocatalytic activity was established without any activation treatment. Our results show that the organic crown of the nanoparticles does not prevent their electrochemical activity