Jean Horkans

Damascene Copper electroplating for chip interconnections

Damascene Cu electroplating for on-chip metallization, which we conceived and developed in the early 1990s, has been central to IBMs Cu chip interconnection technology. We review here the challenges of filling trenches and vias with Cu without creating a void or seam, and the discovery that electrodeposition can be engineered to give filling performance significantly better than that achievable with conformal step coverage. This attribute of superconformal deposition, which we call superfilling, and its relation to plating additives are discussed, and we present a numerical model that represents the shape-change behavior of this system.

Film thickness effects on hydrogen sorption at palladium electrodes

Abstract Hydrogen sorption at thin film evaporated Pd electrodes is quite different from that at bulk Pd. Diffusion of dissolved hydrogen in the thin films is slow. The grain size of the evaporated films is small, and the large number of grain boundaries present a high resistance to hydrogen diffusion. Thin films sorb a greater quantity of hydrogen than bulk Pd. Annealing of the evaporated films, due to an increase in grain size, results in hydrogen sorption behavior resembling that of bulk Pd and a decrease in the charge due to sorbed hydrogen. The dependence of sorption charge on Pd morphology could be explained by segregation of sorbed hydrogen at grain boundaries.

Alloying of a Less Noble Metal in Electrodeposited Cu Through Underpotential Deposition

Underpotential deposition of Pb or Sn on Cu can be used to produce electroplated Cu-Pb and Cu-Sn alloys, with small amounts of alloyed Pb and Sn, from acid solutions that do not contain complexants. Such alloys are of interest as possible on-chip wiring for very large scale integration ; the content of alloying agent must be kept small in order to maintain a low resistivity. The primary requirement for the formation of the alloys is that the deposition process occur in the range of underpotential deposition (UPD) ; this requirement can be met in solutions of methane sulfonic acid (MSA). Both Pb(II) and Sn(II) depolarize Cu deposition from MSA ; the Sn(II) is the weaker depolarizer. Thus, in the absence of other additions to the Cu(II)/MSA solution, electrodeposition proceeds in the UPD range in the presence of Pb(II), producing a Cu-Pb alloy, but positive to the UPD range in the presence of Sn(II), producing pure Cu. The deposition potential can be manipulated by addition agents in solution. A direct relationship exists between the potential and the amount of incorporated Pb or Sn for all solution compositions and plating conditions, provided that the solution does not contain strongly adsorbing species that interfere with the UPD process. The minor component has been shown to be incorporated in the metallic state, even though the deposition potential is positive to its reversible potential.

Integrated, variable-reluctance magnetic minimotor

The use of lithography and electroplating to fabricate variable-reluctance, nearly planar, integrated minimotors with 6-mm-diameter rotors on silicon wafers is described. The motors consist of six electroplated Permalloy® horseshoe-shaped cores that surround the rotor. Copper coils are formed around each core. The Permalloy and copper electroplating baths, electroplating seed layers, and through-mask plating techniques are similar to those used to fabricate inductive thin-film heads. High-aspect-ratio optical lithography or X-ray lithography was used to form the various resist layers. The rotors were fabricated separately, released from the substrate, and then slipped onto the shaft, which was plated as part of the stator fabrication process. The fabrication processes for stator and rotor are described in this paper, and initial minimotor operation data are presented.

A rotating ring-disk stripping technique used to study electroplating of Sn-Pb from methane sulfonic acid solutions

A rotating ring-disk stripping technique has been used to analyze Sn-Pb alloys plated from methane sulfonic acid solutions with and without a proprietary additive and to construct associated current-potential curves. The deposition of both pure Sn and pure Pb was polarized by the additive, but the polarization was much greater for Pb. For alloys plated without the additive, the potential dependence of the partial currents iSn and iPb was essentially the same as that of the pure metals. The alloy compositions were very different from the solution ratios Sn(II):Pb(II) and could be either tin-rich or lead-rich compared to the solution. In the presence of the additive, on the other hand, the alloy compositions approximated the solution compositions of the metal ions; both Pb and Sn deposition were polarized in the alloy compared to deposition of the pure metals, but the extent of polarization caused by the codepositing metal was much greater for Sn. The electrodissolution of Sn-Pb alloys in HCI shows a complex oscillatory behavior, which is produced by the selective dissolution of Sn but which may also be sustained by the formation and redissolution of sparingly soluble surface films. The oscillatory behavior disappears at low dissolution current and low rotation rate, which favor a higher surface concentration of the dissolving metals. Composition determinations are essentially the same under conditions with and without oscillations.

Corrosion of Thin-Film Storage Media: A Review

The computer, one of the most important technological innovations of the 20th century, is rapidly decreasing in size while increasing in power. Small, powerful computers require small, high-capacity devices for permanent storage of data. The particulate disk, which has served in generations of computers, is not capable of meeting the projected density requirements and is being replaced by higher capacity thin-film disks and optical disks. The new kinds of disks, however, have less environmental stability than particulate disks. Thus, a stable disk is being replaced by a more vulnerable disk just as computers are being moved from controlled environments into the uncontrolled environments of homes, offices, and plants.

Polarographic methods of monitoring addition agents in the electroplating of Sn-Pb solders

The electrochemical techniques typically used to monitor organic addition agents in electroplating baths work poorly in Sn-Pb solder plating baths. These electrochemical monitoring methods are based on the principle that additives act through their effects on the kinetics of the metal-deposition reaction, and thus the reaction Mn+ + ne- → M can be used as a probe to determine the additive concentration. The heavy metal ions in solder plating baths readily poison probe electrodes, however, and thus electrochemical methods on solid electrodes are irreproducible and unreliable in these systems. A polarographic technique, which uses a renewable Hg drop electrode, can be used for the quantitative analysis of addition agents in solder plating solutions, even though the chemical identity of these species may not be known to the user of the plating solution.