Simplified Example of a LOCOS Fabrication ProcessLOCOS DefinedLOCOS –step 1Slide 4Slide 5Slide 6LOCOS –step 2Slide 8Slide 9Slide 10Slide 11LOCOS –step 3Slide 13Slide 14Slide 15LOCOS –step 4Slide 17Slide 18LOCOS –step 5Slide 20Slide 21LOCOS –step 6Slide 23Slide 24Slide 25LOCOS –step 7Slide 27Slide 28Slide 29LOCOS –step 8Slide 31Slide 32Slide 33LOCOS –step 9Slide 35Slide 36Slide 37LOCOS –step 10+Simplifications from complete processLOCOS Fabrication Illustration Prof. A. Mason Page 1Simplified Example of aLOCOS Fabrication ProcessProf. A. MasonElectrical and Computer EngineeringMichigan State UniversityLOCOS Fabrication Illustration Prof. A. Mason Page 2LOCOS 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 LOCOSLOCOS Fabrication Illustration Prof. A. Mason Page 3LOCOS –step 1Form N-Well regions•Grow oxide•Deposit photoresistLayout viewCross section viewp-type substrateNWELL maskNWELL maskoxidephotoresistLOCOS Fabrication Illustration Prof. A. Mason Page 4LOCOS –step 1Form N-Well regions•Grow oxide•Deposit photoresist•Pattern photoresist–NWELL Mask–expose only n-well areasLayout viewCross section viewp-type substrateNWELL maskNWELL maskoxidephotoresistLOCOS Fabrication Illustration Prof. A. Mason Page 5LOCOS –step 1Form N-Well regions•Grow oxide•Deposit photoresist•Pattern photoresist–NWELL Mask–expose only n-well areas•Etch oxide•Remove photresistLayout viewCross section viewp-type substrateoxideLOCOS Fabrication Illustration Prof. A. Mason Page 6LOCOS –step 1Form N-Well regions•Grow oxide•Deposit photoresist•Pattern photoresist–NWELL Mask–expose only n-well areas•Etch oxide•Remove photoresist•Diffuse n-type dopants through oxide mask layerLayout viewCross section viewp-type substraten-wellLOCOS Fabrication Illustration Prof. A. Mason Page 7LOCOS –step 2Form Active Regions•Deposit SiN over wafer•Deposit photoresist over SiN layerACTIVE maskACTIVE maskSiNphotoresistp-type substraten-wellLOCOS Fabrication Illustration Prof. A. Mason Page 8LOCOS –step 2ACTIVE maskACTIVE maskSiNphotoresistForm Active Regions•Deposit SiN over wafer•Deposit photoresist over SiN layer•Pattern photoresist–*ACTIVE MASKp-type substraten-wellLOCOS Fabrication Illustration Prof. A. Mason Page 9LOCOS –step 2ACTIVE maskSiNphotoresistForm Active Regions•Deposit SiN over wafer•Deposit photoresist over SiN layer•Pattern photoresist–*ACTIVE MASK•Etch SiN in exposed areas–leaves SiN mask which blocks oxide growthp-type substraten-wellLOCOS Fabrication Illustration Prof. A. Mason Page 10LOCOS –step 2ACTIVE maskp-type substraten-wellForm Active Regions•Deposit SiN over wafer•Deposit photoresist over SiN layer•Pattern photoresist–*ACTIVE MASK•Etch SiN in exposed areas–leaves SiN mask which blocks oxide growth•Remove photoresist•Grow Field Oxide (FOX)–thermal oxidationFOXLOCOS Fabrication Illustration Prof. A. Mason Page 11LOCOS –step 2ACTIVE maskp-type substraten-wellForm Active Regions•Deposit SiN over wafer•Deposit photoresist over SiN layer•Pattern photoresist–*ACTIVE MASK•Etch SiN in exposed areas–leaves SiN mask which blocks oxide growth•Remove photoresist•Grow Field Oxide (FOX)–thermal oxidation•Remove SiNFOXLOCOS Fabrication Illustration Prof. A. Mason Page 12LOCOS –step 3Form Gate (Poly layer)•Grow thin Gate Oxide–over entire wafer–negligible effect on FOX regionsgate oxideLOCOS Fabrication Illustration Prof. A. Mason Page 13LOCOS –step 3Form Gate (Poly layer)•Grow thin Gate Oxide–over entire wafer–negligible effect on FOX regions•Deposit Polysilicon•Deposit Photoresistgate oxidePOLY maskPOLY maskpolysiliconLOCOS Fabrication Illustration Prof. A. Mason Page 14LOCOS –step 3Form Gate (Poly layer)•Grow thin Gate Oxide–over entire wafer–negligible effect on FOX regions•Deposit Polysilicon•Deposit Photoresist•Pattern Photoresist–*POLY MASK•Etch Poly in exposed areas•Etch/remove Oxide–gate protected by polygate oxidePOLY maskPOLY maskLOCOS Fabrication Illustration Prof. A. Mason Page 15LOCOS –step 3Form Gate (Poly layer)•Grow thin Gate Oxide–over entire wafer–negligible effect on FOX regions•Deposit Polysilicon•Deposit Photoresist•Pattern Photoresist–*POLY MASK•Etch Poly in exposed areas•Etch/remove Oxide–gate protected by polygate oxideLOCOS Fabrication Illustration Prof. A. Mason Page 16LOCOS –step 4Form pmos S/D•Cover with photoresistPSELECT maskPSELECT maskLOCOS Fabrication Illustration Prof. A. Mason Page 17LOCOS –step 4Form pmos S/D•Cover with photoresist•Pattern photoresist–*PSELECT MASKPOLY maskPSELECT maskLOCOS Fabrication Illustration Prof. A. Mason Page 18LOCOS –step 4Form pmos S/D•Cover with photoresist•Pattern photoresist–*PSELECT MASK•Implant p-type dopants•Remove photoresistp+ dopantPOLY maskp+ dopantLOCOS Fabrication Illustration Prof. A. Mason Page 19LOCOS –step 5Form nmos S/D•Cover with photoresistPOLY maskNSELECT maskp+p+ p+nLOCOS Fabrication Illustration Prof. A. Mason Page 20LOCOS –step 5Form nmos S/D•Cover with photoresist•Pattern photoresist–*NSELECT MASKPOLY maskNSELECT maskp+p+ p+nLOCOS Fabrication Illustration Prof. A. Mason Page 21LOCOS –step 5Form nmos S/D•Cover with photoresist•Pattern photoresist–*NSELECT MASK•Implant n-type dopants•Remove photoresistn+ dopantPOLY maskn+ dopantp+p+ p+nn+ n+ n+LOCOS Fabrication Illustration Prof. A. Mason Page 22LOCOS –step 6Form Contacts•Deposit oxide•Deposit photoresistCONTACT maskp+p+ p+nn+ n+ n+CONTACT maskLOCOS Fabrication Illustration Prof. A. Mason Page 23LOCOS –step 6Form Contacts•Deposit oxide•Deposit photoresist•Pattern photoresist–*CONTACT Mask–One mask for both active and poly contact shownCONTACT maskp+p+ p+nn+ n+ n+CONTACT maskLOCOS Fabrication Illustration Prof. A. Mason Page 24LOCOS –step 6Form Contacts•Deposit oxide•Deposit photoresist•Pattern photoresist–*CONTACT Mask–One mask for both active and poly contact shown•Etch
View Full Document
Unlocking...