Post Metal Etch Residue

Post Metal Etch Residue - Al Layer

Material Name: Aluminium
Record No.: 42
Primary Chemical Element in Material: Al
Sample Type: Layer
Uses: Etching
Etchant Name: None
Etching Method: Dry etching
Etchant (Electrolyte) Composition: No data
Procedure (Condition): No data
Note: After the TEOS hard mask was patterned, the remaining metal stack was etched on Alliance 9600PTX. Figure 5(a) shows the cross-sectional SEM micrograph of Al interconnect etched using high CHF3 (15 sccm) flow rate during the ME step in the starting etch baseline; the Al profile was tapered and notch-free. Subsequently, the defect inspection in die-to-die mode revealed the defect adder density around 3.98 defects/cm2 in average, in which the major defect type is post metal etch residue (78% of total defect adders). Upon SEM review, the residues are found to be concentrated near the semi-iso Al-damaged sidewall and do not appear to be randomly distributed. From the analysis of EDS spectrum (see Figure 6) attained from a representative residue adder, the defect contains Al, F, Cu, Si, and Cl atoms. The data indicate that the residues are related to the attack of the Al (0.5% Cu) sidewall by Cl atoms, and too much CHF3 addition in the ME step could passivate the surface of Al resulting in poor capability to remove the Al-containing residues. As expected in Figure 5(b), the extent of Al residue was decreased with decreasing CHF3 additive gas (6 sccm) in the ME step; the ratio of Al residue to total defect adders was suppressed from 78% to 2.7%. The reduction of the CHF3 flow rate in the ME step can effectively improve the post metal etch residue issue, but it will also result in less passivant on the metal sidewall to protect the Al bottom corner from the attack of Cl atoms. As shown in Figure 5(b), a slight bottom notching was observed on the Al corner. Therefore, there is a tradeoff between Al notching elimination and residue removal.

Reference: Hong-Ji Lee, Che-Lun Hung, Chia-Hao Leng, Nan-Tzu Lian, Ling-Wu Young, Tahone Yang, Kuang-Chao Chen, and Chih-Yuan Lu, Etch Defect Characterization and Reduction in Hard-Mask-Based Al Interconnect Etching, International Journal of Plasma Science and Engineering, Volume 2008, Article ID 154035, pp. 1-5.

Figure 1: (a) SEM micrograph of Al profile etched using 15 sccm of CHF3 during the ME step. The major defect type is post metal etch residue (78% of total defect adders). (b) The ratio of post metal etch residue to total defect adders was decreased to 2.7% at the lower CHF3 flow of 6 sccm; however, there is a slight Al bottom notching observed from physical profile.Defect density (Do) was expressed as means ± standard deviation (sigma) in counts/cm2. Each etch condition was tested on three wafers.