AVS 50th International Symposium
    Manufacturing Science and Technology Monday Sessions
       Session MS-MoA

Invited Paper MS-MoA7
Sub-100 nm Copper Wiring Challenges and Solutions

Monday, November 3, 2003, 4:00 pm, Room 309

Session: Challenges in Advanced Materials and New Processes for Semiconductor Manufacturing
Presenter: A. Rosenfeld, Applied Materials
Authors: M. Xi, Applied Materials
M. Yang, Applied Materials
W.-F. Yau, Applied Materials
J. Dukovic, Applied Materials
A. Rosenfeld, Applied Materials
N. Maity, Applied Materials
Correspondent: Click to Email
With the emergence of sub-100 nm Cu-low k BEOL technology, copper-electroplating faces a new set of challenges. The combination of shrinking dimensions (coupled with an increase in aspect ratio) and increased current density, necessitate innovation in process and hardware development that can provide acceptable process integration results. Furthermore, the ever-shortened development cycle requires proliferation of new innovations into predictable and repeatable production-worthy processes in minimal development and qualification cycle time. The Cu metallization process is performed in two steps. First, thin metallic layers of barrier material (such as TaN or Ta) and Cu seed is deposited into the vias and lines that define the interconnect. Next, Cu electroplating is used to fill the interconnect structures. The function of the barrier material is to prevent Cu diffusion into the surrounding dielectric, while the Cu seed enables the electroplating fill. The key requirement for both barrier & seed layers is conformal step coverage in sub 100nm features. As such, ionized PVD technology is required to achieve the desired step coverage. To address this requirement, a novel magnetron source was developed that enables high metal ionization with a flat target. The flat target design enables low defects and low cost of ownership for the Cu Barrier-Seed process. Moving to 65 nm and below, the PVD films could be substituted by ultra-thin conformal ALD films, particularly for the barrier process. This will enable lower interconnect resistance and further reduce cost of manufacturing, by reducing the cost of consumables for both the barrier deposition and the barrier CMP processes. To address the needs of sub 100nm copper plating, a novel electroplating system featuring a small volume plating bath with individual electrolyte circulation is was developed. Conventional large volume electroplating bath systems is are adequate for 130nm productions needs, but shows limitations in the area of consistent gap fill and defect performance for sub 100nm applications. In addition, a large bath system lacks the flexibility to change chemistry quickly, which slow down the development and optimization of new processes to meet the new requirements. Root cause of the inconsistent gap fill is correlated to organic by-product build up. In one experiment, the total organic content of a large bath system is measured throughout the life of the bath. The result shows that gap fill consistency is compromised when the total organic content is above 550ppm. In contrast, the small volume plating system allows periodic dumping and refilling of the plating bath after processing a small number of wafers, such as 200 wafers. This provides two key advantages. First, incoming wafers are exposed to fresh plating solution. This minimizes the gap fill inconsistency caused by aging and breakdown of the organic additives mentioned above. Second, by dumping and refilling the small bath after a small number of wafers are processed, different chemistry can be introduced and tested efficiently, from one bath to the next. This can provide significant time and chemical savings for process development and optimization. In addition, the individual electrolyte circulation design allows different plating cells within a plating system to process with different chemistries. This design enables sequential processing, or multi-step plating within a single plating system. The advantage of multi-step plating is demonstrated with experimental results showing dramatic reduction in as plated mounding.