Scratches Formed on STI-Patterned Wafers

Scratches Formed on STI-Patterned Wafers

Material Name: No data
Record No.: 47
Primary Chemical Element in Material: No data
Sample Type: Wafer
Uses: Polishing
Etchant Name: None
Etching Method: Polishing
Etchant (Electrolyte) Composition: No data
Procedure (Condition): No data
Note: CMP is a complex interaction process between the wafer surface and the consumables. The CMP polishing pad is an important consumable among all other consumables, and has a dominating effect on the material removal rate. The structure and material properties determine the material removal rate and planarization ability. Usually, the polishing pad contains both pores and grooves, which help for better planarization. The pores of a pad act as a lake, store the slurry particles, and enhance the contact time between slurry particles and the wafer. Grooves provide a channel for efficient and uniform slurry distribution across the pad surface to the wafer surface. These parameters determine the slurry transportation and contact area at the pad/wafer interface. Choi et al. studied the synergistic role of pores and grooves of a pad in forming the scratches (especially chatter mark scratches) using three types of pads. Pad with only pores, only grooves, and both pores and grooves were investigated to understand its effect on scratch formation. Figure 1 shows the SEM images of scratch shapes formed on the STI patterned wafers polished using three types of pads. Different types of pads generated different types of scratches. Pad-3 (containing both pores and grooves) generated short chatter mark-shaped scratches compared with the other types of pads.
Figure 2 shows the effect of pad type on scratch ratio (percentage of scratches/defective die, i.e., the number of scratches formed on 100 defective dies) and removal rate during the STI CMP process. Scratch formation was found to be higher in the contact regime and lower in the lubricating regime. The contact regime exists when the pad contains only grooves [63], and the lubricating regime exists when the pad contains pores [64]. Optimum conditions were obtained in the presence of a lubricating regime with fewer scratch sources present on the pad. Also, the presence of grooves helps to discharge most of the scratch sources generated during the process away from the wafer–pad contact.
Reference: Tae-Young KWON, Manivannan RAMACHANDRAN, Jin-Goo PARK, Scratch formation and its mechanism in chemical mechanical planarization (CMP), Friction 1(4): 279–305 (2013).

Figure 1: SEM images of scratches formed on STI-patterned wafers after CMP using pads with (a) only grooves (pad-1), (b) only pores (pad-2), and (c) pores and grooves (pad-3).

Figure 2: (a) Scratch ratio on the STI-patterned wafer, and (b) MRR of blanket oxide wafer with ceria slurry as a function of pad type.