Carlos Juan Sambucetti

Reduced electromigration of Cu wires by surface coating

Electromigration in on-chip Cu interconnections with a selective electroless metal coating, CoWP, CoSnP, or Pd, on the top surface of Cu damascene lines has been investigated. The 10–20 nm thick metal cap significantly improves electromigration lifetime by providing protection against interface diffusion of Cu which has been the leading contributor to metal line failure by electromigration.

Electrolessly deposited diffusion barriers for microelectronics

Electrolessly deposited materials were investigated as possible diffusion barrier layers for multilayer microelectronic structures. Attention was focused on selective deposition of barrier layers on various surfaces, the barriers capability to inhibit Cu diffusion, changes in Cu resistivity caused by barrier material diffusion into Cu, and adhesion between a polyimide film and the barrier layer. Electroless Co(P) was the most effective barrier to Cu diffusion at elevated temperature, even at Co(P) thicknesses as low as 500 A. Diffusion-barrier effectiveness of electrolessly deposited materials decreased in the following order: Co(P) > Ni-Co(P) ≃ Ni(P) > pure metals Co, Ni). Although a polyimide film bonded strongly to electrolessly deposited Ni(P) layers and only weakly to as-deposited Co(P), electroless Ni(P) significantly increased the Cu resistivity through interdiffusion. Polyimide adhesion to Co(P) was improved by oxidizing a Co(P) surface immediately after deposition to grow a passive film 50-75 A thick, yielding a surface to which the polyimide adheres strongly and reproducibly. A low-energy-beam, scanning electron microscopy/energy-dispersive X-ray analysis technique (SEM/EDX) was developed to measure the nonoxidized thin Co(P) barrier layer thickness.

Reduced Cu interface diffusion by CoWP surface coating

Electromigration in Cu interconnections with a 10-nm thick selective electroless CoWP coating on the top surface of Cu dual damascene lines has been investigated. The grain structures of the lines embedded in SiLK semiconductor dielectric ranged from bamboo-like to polycrystalline. CoWP coated structures exhibited a greatly improved Cu electromigration lifetime which was attributed to a reduction in Cu interface diffusion.

Pb-free solder alloys for flip chip applications

In addition to the environmental issue regarding the use of Pb-bearing solders in microelectronics applications, there is another issue associated with using Pb-bearing solders in interconnections, like flip chip solder interconnections in an advanced CMOS technology, that are near active circuits. In order to minimize the soft error rate due to alpha particle emission from Pb-bearing solder alloys, Pb-free solder alloys were studied as possible replacements for the Pb-based solders that are presently used in flip chip interconnections. A large number of solder compositions was selected for evaluation. Since all the candidate alloys were Sn-based, alternatives for the ball-limiting metallurgy (BLM) were also investigated. The physical, chemical, mechanical and electrical properties of the alloys were determined by thermal analysis, wettability testing, microhardness measurement, electrical resistivity measurement, interfacial reaction study and others. Test vehicles were also built with some selected Pb-free solder alloys with the proper BLM to evaluate integrity of the flip chip solder bump structure. Based on this study, a few candidate solder alloys were selected with a proper BLM barrier layer for flip chip applications.

Polymer/metal composite for interconnection technology

In this paper, we report on the the rheological, electrical and mechanical properties of paste which is composed of a thermoplastic polymer, solvent and silver particles, and the resulting polymer/metal composite (PMC) which forms after the solvent from the paste has dried. We will refer to the two states as paste and PMC. The paste properties indicate the applicability of the material for fine feature size interconnects such as required for flip-chip-attach. The adhesive and electrical properties of PMC demonstrates that this material will be suitable as an interconnect media in high performance applications. Furthermore, the system chosen is reworkable and the bonding process is volatile-free (i.e. the solvent may be completely removed prior to the bonding step).

Empirical Modeling and Response Surfaces for Electroless Co Deposition Process

The electroless deposition process was studied by statistical techniques. Two types of experiments were designed: the two-factor two-level factorial and the central composite rotatable five-factor five-level experiments. The two-factor factorial experiments were used to determine the effect of each individual variable and interactions between variables. It was concluded from the analysis of data that (i) the most significant factors are citrate, the Co 2+ complexing agent, pH, and temperature; and (ii) the most significant interactions are pH-citrate and pH-hypophosphite interactions. The central composite rotatable experiments were used to construct the second-order empirical model for the relationship between the Co deposition rate and five independent variables. The interpolation polynomial had 21 coefficients. The interpolation function was used to construct the 3-D response surfaces and 2-D response contours. Two types of response surfaces were found: simple maximum and rising ridge. The interpolation polynomial was used also to optimize the Co deposition process with respect to the minimized variability

Selective plating of nickel ceramic composite films for MEMS applications

A simple, selective and CMOS-compatible deposition method for nickel ceramic composite films has been demonstrated. Using an electroless plating technique, two types of nickel ceramic composite thin films, nickel-cordierite and nickel-iron (II, III) oxide, have been successfully deposited and characterized on silicon substrates. The incorporation of an appropriate amount of cordierite particles into a nickel matrix is shown to significantly reduce the thermal expansion mismatch between nickel and silicon, yet maintain the Youngs modulus, Berkovich hardness and electrical resistivity at approximately 167 GPa, 7.6 GPa and 9.4 /spl mu//spl Omega/-cm, respectively, values which correspond closely to electroless nickel. On the other hand, the addition of iron (II, III) oxide instead of cordierite can also increase the coercivity of electroless nickel up to 170 Oe, thereby significantly enhancing its ferromagnetic properties.

Highlights of the DARPA eletrically conductive adhesive FCA project. Quarterly report, April 1, 1996--June 30, 1996

The accomplishments are broken down into three different categories: materials development (polymer metal composite with increased bond strength), process development (reliability testing, bonding optimization evaluation, testing of bulk conductive adhesives, paste deposition process development), and equipment development (laboratory bonding equipment, cost estimation for flip chip attach methods).