Arthur J. Learn

Electromigration effects in aluminum alloy metallization

An investigation of electromigration-induced failure in aluminum alloy films, with the major emphasis on aluminum-copper-silicon, was conducted. Flash evaporation was utilized for alloy deposition and yielded aluminum-copper films having electromigration resistance comparable to that of such films prepared by other techniques. Results for aluminum-copper-silicon and aluminum-copper were similar indicating the passive role of silicon in the presence of copper. Additions of four weight percent copper resulted in near-optimum electromigration resistance. In addition, hot-substrate deposition was beneficial in attaining greater lifetime. For films deposited on unheated substrates, or having lower copper contents, heat treatment seriously degraded electromigration resistance. Heat treatment effects were considered to be a consequence of copper redistribution. Lifetime decrease at large copper contents and possible saturation at large thicknesses were interpreted in terms of clustering of CuAl2 precipitates. The superior reliability of copper-alloyed metallization when compared with aluminum or aluminum-silicon was clearly demonstrated. Lifetime improvement could be accounted for by the increased activation energy for the failure process in the aluminum-copper alloys.

Effect of structure and processing on electromigration‐induced failure in anodized aluminum

The effect of barrier and porous anodizations, either singly or sequentially, on the electromigration resistance of aluminum films was characterized. Samples were tested for current densities in the 4×105−2×106‐A/cm2 range and temperatures between 150 and 280°C with the median failure time being used as a basis for comparison of lifetimes. An initial barrier anodization was found to be necessary in order to consistently enhance lifetime. The addition of a porous layer as well led to the best result—an increase in lifetime by a factor of 23 at 227°C. All lifetime increases were attributable to increased activation energy for the electromigration‐failure process. An increase of 0.14 eV was obtained for the double anodic structure. Results for structures having a barrier layer adjacent to aluminum were considered in terms of surface sealing of the aluminum and/or response to mechanical constraints of the overlayer. Direct porous anodization resulted in preferential oxidation at grain boundaries, thereby wide...

Effect of Redundant Microstructure on Electromigration‐Induced Failure

Aluminum films with grain boundaries staggered throughout the film thickness, and hence with nonoverlapping sites for electromigration‐induced failure, were prepared by vacuum deposition in layered or extremely fine‐grained form. Mean lifetimes before the occurrence of electrical opens were an order of magnitude larger than those for control films having non‐redundant grain structure. Heat‐treatment effects which reduced lifetimes to values comparable to control lifetimes were interpreted in terms of either a lifetime minimum for grain size ∼ 0.6 μ or disruption of the layered structure.

Growth of borosilicate and borophosphosilicate films at low pressure and temperature

Abstract Boron- and phosphorus-doped silicon dioxide films grown at low pressure and temperature were characterized. A synergistic effect is observed in that the presence of either dopant enhances the incorporation of the other. The oxide growth rate is increased through the addition of either dopant. The incorporation efficiency of each dopant increases with decreasing growth temperature. Growth rates increase with increasing temperature and exhibit activation energies of 0.35 eV and 0.18 eV for boron-doped and boron—phosphorus-doped oxide respectively. The addition of boron to phosphorus-doped oxide reduces the magnitude of the compressive room temperature stress. The etch rate and reflow properties of the films are similar to those of films, having the same dopant levels, deposited at atmospheric pressure.

Aluminum alloy film deposition and characterization

Abstract A flash evaporation system which utilizes a mechanism for feeding alloy wire onto a heated bar was used for the deposition of aluminum-silicon, aluminum-copper and aluminum-copper-silicon. The effect of deposition conditions and processing procedure on film composition and microstructure was determined. Particular attention was given to the film surface topography and the possible influence of deposition conditions, alloy composition, substrate type, thickness, annealing time and temperature and addition of oxide overlayers. Resistivity, and possible shorting of junctions in silicon as a consequence of silicon dissolution in the metallization, were considered as a function of alloy composition. Metal continuity over steps in the substrate was tested as a function of deposition temperature. These studies yielded recommendations, regarding the general use of alloy metallization on silicon devices and its specific use in two-level metallization configurations, which include: deposition at temperatures down to 275°C and at evaporation rates of about 0.4 g/min; the use of initial layer thickness down to 0.7 μ; post-deposition processing for aluminum-copper or aluminum-copper-silicon not to exceed 525°C; the addition of 1% silicon to prevent junction penetration; and the addition of 4% copper to lend adequate electromigration resistance and inhibit hillock growth during high temperature processing.

Effects of ion implantation on charges in the silicon--silicon dioxide system

Structures consisting of thermally grown oxide on silicon were implanted with boron, arsenic, or argon ions. For argon implantation through oxides, an increased fixed oxide charge (Qss) was observed with the increase being greater for 〈111〉 than for 〈100〉 silicon. This effect is attributed to oxygen recoil which produces additional excess ionized silicon in the oxide of a type similar to that arising in thermal oxidation. Fast surface state (Nst) generation was also noted which in most cases obscured the Qss increase. Of various heat treatments tested, only a 900 °C anneal in hydrogen annihilated Nst and allowed Qss measurement. Such Nst apparently arises as a consequence of implantation damage at the silicon–silicon dioxide interface. With the exception of boron implantations into thick oxides or through aluminum electrodes, reduction of the mobile ionic charge (Qo) was achieved by implantation. The reduction again is presumably damage related and is not negated by high‐temperature annealing but may be c...

Effects of oxidation and nitrogen annealing on ion‐implantation‐induced interface states in the silicon–silicon dioxide system

Experiments designed to determine the effects of oxidation and nitrogen annealing on interface states created by argon implantation through thermally grown silicon dioxide films are described. Although these states could be inactivated by a 900 °C hydrogen anneal, they reappeared after short nitrogen or oxygen treatments at 1000 °C. Only oxidations which consumed at least 500 A of the implantation‐damaged silicon surface completely eliminated the states. The oxidation rate of the implanted structures was found to be increased relative to that of the unimplanted controls.

Limitations on high-temperature processing of aluminum-copper metallization

Disruptive alteration of the structure of heat-treated aluminum-copper metallization either containing or contacting silicon is reported. Effects are attributed to eutectic formation in the aluminum-copper-silicon system. Processing temperatures less than 525°C are recommended for aluminum metallization containing copper.