1. Field of the Invention
The present invention relates to a method of forming a copper dual damascene structure, and more particularly to a method of forming a copper dual damascene structure, wherein a selectively deposited tungsten layer is formed on a silicide layer as a blocking layer of a copper contact.
2. Description of the Related Art
Conventional metal oxide semiconductor (MOS) contact technology commonly utilizes tungsten as a contact plug material. Tungsten has many advantages, such as the proper thermal expansion coefficient which is close to the one of silicon, the much less electromigration trend and the excellent step coverage ability. However, the high resistivity causes the increasing of the undesired RC time delay of the device used tungsten contacts and degrades the performance of the device. FIG. 1 shows a cross-sectional view of a conventional MOS device and tungsten contacts. As shown in FIG. 1, the MOS device comprises source/drain regions 104a and 104b formed in a silicon substrate 100 and between shallow trench isolations 102a and 102b, a gate oxide layer 106, a gate electrode 108, spacers 110a and 102b, and silicide layers 112a and 112b. A dielectric layer 114, tungsten contacts 116a and 116b, and metal lines 118a and 118b are also shown in FIG. 1.
Owing to the high resistivity of tungsten, the tungsten contacts 116a and 116b are gradually unsatisfactory for the demand of the high speed of modern integrated circuits.
Dual damascene structures are more and more used amid the manufacture of the semiconductor device in view of fewer processing steps of their formation. In the dual damascene structures, the metal lines and the contacts are formed simultaneously. Lately, copper is used as the material of the lead lines and the contacts to replace tungsten for its much lower resistivity. However, once copper is used as the contact material, the barrier layer which is either a tantalum/tantalum nitride layer or a titanium/titanium nitride layer may not block copper effectively, and copper is very likely to diffuse into the active regions of the device during the processing phase and cause the failure of the device. Therefore, it is necessary to provide a novel contact technology to solve the problems of the conventional one mentioned above, and the method of the present invention is just the one.