A study on film thickness control of vertical flow showerhead reactor for RF plasma deposition

Recently, as DRAM device scale is decreasing, multi-patterning and ACL(Amorphous Carbon Layer) process steps are increasing for DRAM manufacturing[1]. This change needs to improve film thickness uniformity to hold a CD(Critical Dimension) uniformity. A showerhead structure is widely adopted in a RF(Radio Frequency) plasma reactor for the thin film deposition such as the ACL and PEALD(Plasma Enhanced Atomic Layer Deposition) SiO
2
layer. The gas distribution of the showerhead is one of the critical factors to determine the deposition uniformity [2,3,4,7,8]. In this paper, we focused on the influence of a hole open area ratio in the showerhead structure for the film thickness distribution within the wafer. During the ACL deposition, precursor goes through muti-hole patterned distribution plate inside the showerhead, and the showerhead structure without the distribution plate could be used in the PEALD process. In both cases, it is possible to change the gas distribution within the showerhead volume through the hole open area ratio variation of gas distribution plate or showerhead. Mass flow rate distribution of gas to be injected to wafer determines the film growth rate on wafer according to the film material. The gas distribution of the process volume was analyzed according to the hole open area ratio of the showerhead, and the distribution plate. The experiments were performed with various hole open area ratios of the showerhead configuration for the same process recipe. The ACL deposition was applied to the distribution plate which had different open area ratios, and the PEALD SiO
2
layer was applied to the showerhead. The results indicated that the film deposition shape could be controlled and the film thickness uniformity was improved for not only ACL deposition but also PEALD SiO
2
layer by the hole open area ratio optimization of the showerhead structure.