Method for manufacturing a semiconductor device comprising transistors each having a different effective work function
The disclosed technology generally relates a semiconductor device comprising transistors, and more particularly to a semiconductor device comprising transistors each having a gate stack with a different effective work function, and methods of fabricating such a device. In one aspect, the method of fabricating the semiconductor comprises providing at least two channel regions in the substrate and providing a dielectric layer on the substrate. The method additionally includes forming a plurality of gate regions by providing openings in the dielectric layer. The method further includes providing a gate dielectric layer in the openings and providing on the gate dielectric layer of each of the gate regions a barrier layer stack having different thickness along the different gate regions.
1. A method of manufacturing a semiconductor device comprising transistors each having a different work function arranged along a main surface of a substrate, the method comprising:
providing at least two channel regions in the substrate;
providing a dielectric layer on the substrate over the at least two channel regions;
providing openings through the dielectric layer to expose portions of each of the at least two channel regions, thereby defining corresponding gate regions inside the openings and over the at least two channel regions;
providing a gate dielectric layer on the exposed channel regions of each of the gate regions;
providing on the gate dielectric layer of each of the gate regions a barrier layer stack each having a different thickness,
wherein providing the barrier layer stack comprises:
providing a first barrier layer on the gate dielectric layer of each of the gate regions;
selectively removing the first barrier layer from a subset of the gate regions while leaving the first barrier layer in at least a complementary subset of the gate regions;
repeating at least once the processes of:
providing a subsequent barrier layer in each of the gate regions;
selectively removing the subsequent barrier layer from a respective subset of the channel regions, while leaving the respective subsequent barrier layer in a respective complementary subset of the channel regions, such that barrier layer stacks having different thickness along different gate regions are provided; and
providing a gate-filling stack of metal layers on the barrier layer stack in each of the gate regions.
2. The method according to claim 1 , wherein providing the barrier layer comprises repeating only once the processes of:
providing a subsequent barrier layer in each of the gate regions;
selectively removing the subsequent barrier layer from a respective subset of the channel regions, while leaving the respective subsequent barrier layer in a respective complementary subset of the channel regions.
3. The method according to claim 1 , wherein providing the barrier layer comprises repeating only twice the processes of:
providing a subsequent barrier layer in each of the gate regions;
selectively removing the subsequent barrier layer from a respective subset of the channel regions, while leaving the respective subsequent barrier layer in a respective complementary subset of the channel regions.
4. The method according to claim 1 , wherein the first barrier layer and the subsequent barrier layer comprise one or both of TiN and TaN.
5. The method according to claim 1 , wherein the first barrier layer and the subsequent barrier layer are formed of the same material.
6. The method according to claims 1 , wherein the first barrier layer and the subsequent barrier layer are formed of a different material.
7. The method according to claim 1 , wherein providing the gate-filling stack of metal layers comprises providing a metal selected from the group consisting of TiN, TiAl, Al, TiC, Co, W and combinations thereof.
8. The method according to claim 7 , wherein providing the gate-filling stack of metal layers comprises providing a metal layer formed of TiAl or Al and further comprises:
providing a TiN layer on the metal layer;
patterning the TiN layer above at least one gate region;
selectively removing the metal layer from at least one gate region by using the patterned TiN layer as a mask; and
providing a further metal layer of the gate filling stack of metal layers in the at least one gate region.
9. The method according to claim 8 , wherein patterning the TiN layer comprises resist patterning.
10. The method according to claim 1 , further comprising performing a flattening step on the substrate, up until a level defined by the dielectric layer.
11. The method according to claim 1 , wherein the exposed portions of the at least two channel regions define channel lengths smaller than 20 nm of the transistors.
12. The method according to claim 1 , wherein providing the first barrier layer or the subsequent barrier layer comprises depositing using atomic layer deposition (ALD).