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19 Wafer finishing 10

19 Wafer finishing 10 - Finishing and Packaging This...

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Planarization – flattening of topography Wafer thinning – to improve heat flow Packaging– connections to the outside world and final test Finishing and Packaging This lecture covers planarization and back-end processes such as wafer thinning and packaging…
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Specs for planarization λ ( nm 29 436 365 248 193 NA=0.65 0.51 0.43 0.29 0.23 DoF (microns) DoF This is the TOTAL vertical budget across the whole image field (~ 25 mm sq) Resist < 1 μ m Substrate Solutions: Define image on top surface of resist only, or… Planarize wafer to half DoF spec ! ( 29 2 2 NA DoF λ ± =
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n-well p-well p-substrate Metal 1 Fox Topography without planarization DoF budget More metal layers = bigger problem So planarize! - Etchback or - CMP Mountainous !
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Planarization - etchback n-well p-well p-substrate Fox 1. Coat surface with resist or SOG 2. Surface across wafer is flat 3. Etch with a very non-selective etch (e.g. ion milling) to this level to take off peaks and get flat surface What’s this? Spin casting gives a self-planarized surface
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Planarization - etchback Advantages Disadvantages Use available materials Milling is slow Use available tools Tools are expensive Process is ‘familiar’ Selectivity can change Fine control over Z Contaminant effects Uniformity across wafer Conclusion: May be used as an incidental part of a process but CMP has taken over
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Planarization - CMP Chemical - Mechanical - Polish We have a long “grinding & polishing” technology history: 1. Lens grinding 2. Wafer preparation 3. Thin finished wafer for better thermal performance of die Grind Lap Polish optically flat (< λ /4)
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CMP Equipment Rotating platten Wafer assemblies Slurry on surface Load Pressure equalization Slurry on surface Wafer Check out CMP references!
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CMP process Number of particles Particle size
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19 Wafer finishing 10 - Finishing and Packaging This...

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