Many methods have already been provided to form electric connection elements in vias, that is, holes or openings, through all or part of the thickness of a silicon substrate.
The surface of the via is generally coated with an insulating layer, typically made of silicon oxide, enabling, in particular, to insulate the substrate connection element.
Conventionally, the forming of the connection element comprises a step of depositing a barrier layer on the silicon oxide layer, followed by a step of depositing a third copper seed layer, coating the barrier layer, followed by a step of electrolytic deposition of a thicker copper layer, for example filling the entire via. The barrier layer particularly has the function of preventing a possible copper diffusion through the silicon oxide layer, which could cause a short-circuit between the electric connection element and the substrate. The barrier layer should further enable the copper seed layer to bond to the via walls. In certain cases, a specific bonding layer may be provided between the barrier layer and the seed layer to fulfill this function.
The steps of depositing the barrier layer and the copper seed layer are generally carried out by vapor deposition, for example, by CVD (“Chemical Vapor Deposition”), or by ALD (“Atomic Layer Deposition”), or by PVD (“Physical Vapor Deposition”).
A disadvantage of existing electric connection element manufacturing methods is that they are poorly adapted to the forming of connection elements in vias having a high form factor, that is a high depth-to-width (or diameter) ratio, for example, greater than 10. In practice, in such vias, it can be observed that the barrier layer and/or the copper seed layer do not very uniformly deposit over the entire surface of the via. In vias having a high form factor, interruptions of the barrier layer and/or of the seed layer, capable of resulting in malfunctions, may in particular be observed, for example, close to the bottom of the via.
Another disadvantage of existing methods is the high cost of the equipment used to carry out the steps of vapor phase deposition of the barrier layer and/or of the copper seed layer.