edge exclusion

**Edge Exclusion Analysis** is a metrology practice that studies or deliberately excludes wafer edge regions from measurements due to inherent process variations at the periphery. ## What Is Edge Exclusion Analysis? - **Definition**: Excluding outer 2-5mm of wafer from yield calculations - **Reason**: Edge effects cause systematic deviations from center - **Standard**: SEMI specifies edge exclusion zones - **Application**: Die yield, film thickness, defect density ## Why Edge Exclusion Matters Process uniformity degrades at wafer edges due to gas flow, temperature, and electric field non-uniformities. Including edge data skews statistics. ```svg Wafer Uniformity Map: Center Edge ◄────────────────► ┌─────────────────────────┐ │ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ● │ │ ○ ○ ○ ○ ○ ○ ○ ○ ○ ● ● │ │ ○ ○ ○ ○ ○ ○ ○ ○ ● ● ● │ ← Edge exclusion │ ○ ○ ○ ○ ○ ○ ○ ○ ○ ● ● │ zone └─────────────────────────┘ ○ = In-spec data ● = Edge excludedTypical exclusion: 3mm from edge (300mm wafer) ``` **Edge Effects by Process**: | Process | Edge Issue | Typical Exclusion | |---------|-----------|-------------------| | CVD | Thickness roll-off | 3mm | | Photolith | Focus/dose variation | 2mm | | CMP | Over-polish | 3-5mm | | Etch | Loading effects | 2-3mm |

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