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LOCOS Defined
• LOCOS = LOCal Oxidation of Silicon
• Defines a set of fabrication technologies where
– the wafer is masked to cover all active regions
– thick field oxide (FOX) is grown in all non-active regions
• Used for electrical isolation of CMOS devices
– Relatively simple to understand so often used to introduce/describe CMOS fabrication flows
– Not commonly used in modern fabrication
– other techniques, such as Shallow Trench Isolation (STI) are currently more common than LOCOS
Simplifications from complete process
• skipped several substrate doping steps
– channel implant to adjust threshold voltages
– surface implant to increase breakdown voltage
• no LDD, lightly-doped drain
• no deposition of contact interface materials
• metal patterning simplified
– more complex “lift-off” process often used
• no overglass (thick top dielectric) layer
• no bonding pad layer
• simplified use of dark/clear field masks and positive/negative photoresist