November_EDFA_Digital

edfas.org ELECTRONIC DEV ICE FA I LURE ANALYSIS | VOLUME 23 NO . 4 8 colloidal silica was approaching its limit as a viable tech- nique to expose metal layers due to features approach- ing the size of the polishing media. Contamination and damage by 50 nm particles could destroy or block entire features on the surface. [15,16] The copper features at the M4-M1 size scale were observed to smear against colloidal silica after polishing. Smearing occurs when copper does not remove evenly during CMP due to its high ductility. Instead, the metal shears across the surface, redepositing in undesirable areas. This effect is more apparent at lower and thinner copper metal layers [17,18] and was observed during SEM mosaic imaging of these layers, where copper smeared and bridged individual features. Table 1: Summary of delayering approach for each layer in the 45 nm SPI device, with physical feature and layer measurements Layer GDSII feature material(s) Interlayer dielectric (ILD) matrix Smallest feature size, nm Layer thickness, nm Delayering approach Specific method M11 Aluminum SiO 2 4000 2225 CMP Diamond lapping film abrasive (DLF) V10 Tungsten SiO 2 3000 2500 N/A No GDSII identifiable features in ROI; not delayered M10-M9 Copper F-TEOS 800 1200 CMP Colloidal silica polish M8-M6 Copper Porous low k 144 255 CMP Colloidal silica polish M5 Copper SiCOH 100 175 CMP Colloidal silica polish M4-M1 Copper SiCOH 70 - 100 136 - 175 CMP Copper slurry polish V9-V8 Copper F-TEOS 360 - 800 1600 Wet Etch FeCl 3 solution V7-V5 Copper Porous low k 144 250 Wet Etch FeCl 3 solution V4-V2 Copper SiCOH 72 - 100 115 - 160 Wet Etch FeCl 3 solution V1 Copper SiCOH 72 115 Dry Etch XeF 2 + Backside P-FIB delayering Polysilicon Contact Tungsten SiO 2 60 250 Dry Etch + Wet Etch XeF 2 + Backside P-FIB Delayering + FeCl 3 solution Polysilicon Silicon SiO 2 40 65 Dry Etch XeF 2 + Backside P-FIB delayering Active Silicon N/A 150 80 Dry Etch XeF 2 + Backside P-FIB delayering Fig. 4 From L to R: The 45 nm node SPI delayered to a metal layer with ROI highlighted (red); a mosaic SEM image of ROI on said layer; a subregion of ROI showing extraction of layer features as vector-based polygons (green); and the final design reconstruction of entire ROI device stack with all layers of extracted polygons.