N.D. Theodore

Passivation of Cu via refractory metal nitridation in an ammonia ambient

Cu-(27at.% Ti) and Cu-(26at.% Cr) alloys codeposited on silicon dioxide substrates were isochronally annealed for 30 min at 400–700 °C in a flowing NH3 ambient. In the Cu-Ti alloy, Ti segregates to the free surface to form a TiNx(O) layer and also to the alloy-SiO2 interface to form a Ti5Si3TiOw bilayer structure. Therefore the resulting structure is an almost completely dealloyed Cu layer located between a surface oxygen-rich Ti nitride and Ti-silicide/Ti-oxide bilayer interfacial structure. In the Cu-Cr alloy system, Cr seems to migrate only to the free surface to form a CrNx passivation layer. A 45 nm Al film was deposited after nitridation, whereupon a second anneal was performed to evaluate these nitride layers as diffusion barriers. The Cr-nitride diffusion barrier is stable up to 600 °C compared with Ti nitride that fails at 500 °C. The Cu-Cr nitrided samples also showed an overall lower sheet resistance.

Segregation of Cu in Cu(Ti) alloys during nitridation in NH3

Abstract Cu(Ti 27 at.%) alloys on SiO2 were reacted in NH3 for 30 min over the temperature range 400–700 °C. Rutherford backscattering spectrometry in conjunction with high resolution transmission electron microscopy were utilized to investigate reaction products. At 400–450 °C, Ti is observed to segregate to the free surface to react with NH3, forming an Ti oxynitride layer. Above 500 °C, Ti segregates to both the free surface and to the alloy/SiO2 interface, leaving relatively-pure Cu layer. Reaction between Ti and SiO2 results in a TiO Ti 5 Si 3 bilayer structure. By use of high spatial resolution energy dispersive X-ray spcctroscopy, the presence of a Cu-containing layer at the TiO Ti 5 Si 3 interface is observed. This layer may also contain Ti, Si and/or O. We propose a mechanism for Cu segregation to this interface which requires Cu diffusion across TiO and subsequent dissociation of Ti5Si3. Thermodynamic calculations support this mechanism.

Influence of interfacial copper during the dealloying and nitridation of Cu-Ti films

Abstract Cu(Ti 27 at.%) alloy and Cu(90 nm)/Ti(20 nm) bilayer films were deposited on thermally grown silicon-dioxide and dealloyed under thermal treatment at temperatures 400–700 °C for 30 min in an ammonia ambient. During annealing Ti segregated to both the free surface and the alloy/SiO 2 interface. At the interface the Ti dissociated the SiO 2 and reacted with the freed Si and O to form a TiO/Ti 5 Si 3 structure. High-resolution energy dispersive X-ray technique revealed the presence of interfacial copper between the Ti-silicide and Ti-oxide layers. The interfacial copper did not reduce the reaction temperature. Nevertheless it was associated with the enhanced dissociation of SiO 2 . The data suggested that in the presence of the interfacial copper, the rate of oxide consumption is increased by a factor of 3 to 4. The enhancement of the oxide consumption was observed at temperatures between 450 and 600 °C. It is believed that the higher reaction rate is due to a catalytic effect exhibited by the interfacial Cu when it exists in the form of Cu 2 O.

A Study of Tungsten-Titanium Barriers in Silver Metallization

This work investigated the viability of tungsten-titanium barrier layers for silver metallization. Reactive sputtered W-Ti was deposited on a Si wafer followed by an Ag thin film over layer. These samples were then annealed in vacuum at temperatures up to 700 °C. Characterization of these samples included using x-ray diffractometry, Rutherford backscattering spectrometry, scanning transmission microscopy, secondary ion mass spectroscopy, transmission electron microscopy, and four point probe analysis. The results indicated that the metal/diffusion barrier stack was stable up to 600 °C. Silicon started moving into the tungsten-titanium film at temperatures above 600 °C. Movement of Si resulted in local Si voiding. These results showed the promise of W-Ti as an effective barrier layer for silver metallization for process temperatures below 600 °C.

Low temperature oxidation of silicon after copper ion implantation

Silicon oxide films (> 1 {micro}m) were grown at room-temperature after low-energy copper-ion implantation of Si(100) substrates. The structural properties of the silicon oxide layer and the implanted silicon were characterized by Rutherford backscattering spectrometry and transmission-electron microscopy. During room temperature oxidation a portion of the implanted copper resided on the surface and a portion moved with the advancing Si/SiO{sub x} interface. This study revealed that the oxide growth rate was dependent on the amount of Cu present at the moving interface. The resulting oxide formed was approximately stoichiometric silicon dioxide.

Influence of Interfacial Copper on the Ti-SiO 2 Reaction During Nitridation of Cu-Ti Films

Cu(90 nm)/Ti(20 nm) bilayers and Cu(Ti 27 at.%) alloy films were deposited on SiO 2 and annealed in an NH 3 ambient at temperatures 400–700° C for 30 min. During annealing Ti segregated to both the free surface and the alloy/SiO 2 interface. At the surface Ti reacted with NH 3 to form TiN, whereas at the interface the Ti reacted with the SiO 2 to form a TiO/Ti 5 Si 3 structure. High resolution energy dispersive x-ray analysis revealed the presence of interfacial Cu between the Ti-silicide and Ti-oxide layers at temperatures greater than 450°C. Using Cu-Ti alloy films enhanced the Si0 2 consumption rate by a factor of 3-4 compared to that of pure Ti. It is suggested that the interfacial Cu is responsible for the increased rate. It is plausible that an interfacial Cu 2 O component has a catalytic effect on the Ti- SiO 2 reaction.