(1) Field of the Invention
This invention relates generally to the field of integrated circuits (ICs) fabrication, and more particularly, to a process of forming metal wires without the concerns of electrical short problem.
(2) Description of the Prior Art
In order to form compact and high density devices, multiple layers of conductors and insulators are stacked within the limited area in IC fabrication. It tends to have steep and complicated topography on the wafer surfaces. As the size of the contact hole is reduced, metals are not well filled in the contact hole during the metal contact process, therefore, there occurs a problem that the contact resistance is increased or even became open circuit. In general, aluminum, which has high conductivity, is widely used as a metal conductor in the metal contact process. However, aluminum cannot satisfactorily fill inside the contact hole of small size due to its poor step coverage characteristics. As a solution to solve such problem, first inside the contact hole is filled by a metal of excellent step coverage characteristics, and then metal wiring is formed by an aluminum deposition and patterning. Tungsten is mainly used to fill the contact hole because of its excellent step coverage characteristics. Tungsten is an high resistant metal with a high melting point and has the advantage in that is has excellent thermal stability with silicon and also has low electrical specific heat.
Referring now to FIGS. 1(a) to 1(b), there are top views of the metal short illustrations according to the conventional contact hole process. First, electrical elements such as MOSFETs are fabricated on a P-type semiconductor silicon wafer. Then, an insulating layer is formed over the entire wafer. Next, the insulating layer is partially etched to form metal contact windows by the conventional lithography and plasma etching techniques. A TiN barrier layer and a tungsten metal layer are then sequentially deposited overlaying the insulating layer and filling into the metal contact windows. Next, chemical mechanical polishing (CMP) process is performed to remove the metal and TiN barrier layers exposed outside the contact windows. As the spacing between two metal wires 1 continuously shrinking (about 0.17 .mu.m in today's technology), TiN barrier residues 3 are very difficult to be removed completely by CMP. Therefore, these TiN barrier residues 3 will short 5 the metal wiring, particularly around narrow comer area 7 as shown in both FIGS. 1(a) and 1(b), thereby, degrading the reliability of the integrated circuit devices.
This invention reveals an improved process of tungsten plug etching for contact windows to eliminate the above mentioned metal wiring short problem.