Method of manufacturing MOS transistors with gate electrodes formed in a packet of metal layers deposited upon one another
View Patent ↗Consistent with an example embodiment, a method of manufacturing a semiconductor device comprises MOS transistors having gate electrodes formed in a number of metal layers deposited upon one another. Active silicon regions having a layer of a gate dielectric and field-isolation regions insulating these regions from each other are formed in a silicon body. Then, a layer of a first metal is deposited in which locally, in a part of the active regions, nitrogen is introduced. On the layer of the first metal, a layer of a second metal is then deposited, after which the gate electrodes are etched in the metal layers. Before nitrogen is introduced into the first metal layer, an auxiliary layer of a third metal permeable to nitrogen is deposited an the first metal layer. Thus, the first metal layer can be nitrided locally without the risk of damaging the underlying gate dielectric.
1. A method of manufacturing a semiconductor device with MOS transistors comprising gate electrodes formed in a packet of metal layers deposited upon one another, in which method, on a surface of a silicon body on which border active regions of silicon and field isolation regions insulating these regions with respect to each other,
a layer of a gate dielectric is formed at the location of the active regions, after which a layer of a first metal is deposited wherein nitrogen is introduced at the location of a part of the active regions,
after which a layer of a second metal is deposited on the layer of the first metal, and
subsequently the gate electrodes are etched in the packet of superposed metal layers,
characterized in that before nitrogen is locally introduced into the layer of the first metal, an auxiliary layer of a third, nitrogen-permeable metal is formed on this layer,
characterized in that the nitrogen is locally introduced into the layer of the first metal by diffusion from a solid substance that contains an excess of nitrogen and is locally provided on the auxiliary layer.
2. A method as claimed in claim 1 , characterized in that a layer of TiN x , where x>1, is locally provided on the auxiliary layer as a layer of a solid substance containing an excess of nitrogen, after which a thermal treatment is carried out wherein nitrogen diffuses through the auxiliary layer into the layer of the first metal.
3. A method as claimed in claim 1 , characterized in that a layer of tantalum or molybdenum is deposited as the layer of the first metal, on which a layer of cobalt or nickel is deposited as the auxiliary layer.
4. A method as claimed in claim 2 , characterized in that a layer of tantalum or molybdenum is deposited as the layer of the first metal, on which a layer of cobalt or nickel is deposited as the auxiliary layer.