The semiconductor integrated circuit (IC) industry has experienced rapid growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. However, these advances have increased the complexity of processing and manufacturing ICs and, for these advances to be realized, similar developments in IC processing and manufacturing are needed. In the course of integrated circuit evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased.
To enhance the performance of ICs, metal gate transistors have been used in recent years. However, conventional methods of forming metal gate transistors may be complex and expensive. For example, the NMOS and PMOS gates may require their own formation processes, which not only increase fabrication costs due to the added complexity, but may also lead to potential process defects and uniformity issues.
Therefore, while existing methods of fabricating metal gate transistors have been generally adequate for their intended purposes, they have not been entirely satisfactory in every aspect.