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LOCOS Fabrication Illustration Prof. A. MasonPage 1 Simplified Example of a LOCOS Fabrication Process Prof. A. Mason Electrical and Computer Engineering.

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Presentation on theme: "LOCOS Fabrication Illustration Prof. A. MasonPage 1 Simplified Example of a LOCOS Fabrication Process Prof. A. Mason Electrical and Computer Engineering."— Presentation transcript:

1 LOCOS Fabrication Illustration Prof. A. MasonPage 1 Simplified Example of a LOCOS Fabrication Process Prof. A. Mason Electrical and Computer Engineering Michigan State University

2 LOCOS Fabrication Illustration Prof. A. MasonPage 2 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

3 LOCOS Fabrication Illustration Prof. A. MasonPage 3 LOCOS –step 1 Form N-Well regions Grow oxide Deposit photoresist Layout view Cross section view p-type substrate NWELL mask oxide photoresist

4 LOCOS Fabrication Illustration Prof. A. MasonPage 4 LOCOS –step 1 Form N-Well regions Grow oxide Deposit photoresist Pattern photoresist –NWELL Mask –expose only n-well areas Layout view Cross section view p-type substrate NWELL mask oxide photoresist

5 LOCOS Fabrication Illustration Prof. A. MasonPage 5 LOCOS –step 1 Form N-Well regions Grow oxide Deposit photoresist Pattern photoresist –NWELL Mask –expose only n-well areas Etch oxide Remove photresist Layout view Cross section view p-type substrate oxide

6 LOCOS Fabrication Illustration Prof. A. MasonPage 6 LOCOS –step 1 Form 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 layer Layout view Cross section view p-type substrate n-well

7 LOCOS Fabrication Illustration Prof. A. MasonPage 7 LOCOS –step 2 Form Active Regions Deposit SiN over wafer Deposit photoresist over SiN layer ACTIVE mask SiN photoresist p-type substrate n-well

8 LOCOS Fabrication Illustration Prof. A. MasonPage 8 LOCOS –step 2 ACTIVE mask SiN photoresist Form Active Regions Deposit SiN over wafer Deposit photoresist over SiN layer Pattern photoresist –*ACTIVE MASK p-type substrate n-well

9 LOCOS Fabrication Illustration Prof. A. MasonPage 9 LOCOS –step 2 ACTIVE mask SiN photoresist Form 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 p-type substrate n-well

10 LOCOS Fabrication Illustration Prof. A. MasonPage 10 LOCOS –step 2 ACTIVE mask p-type substrate n-well Form 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 FOX

11 LOCOS Fabrication Illustration Prof. A. MasonPage 11 LOCOS –step 2 ACTIVE mask p-type substrate n-well Form 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 SiN FOX

12 LOCOS Fabrication Illustration Prof. A. MasonPage 12 LOCOS –step 3 Form Gate (Poly layer) Grow thin Gate Oxide –over entire wafer –negligible effect on FOX regions gate oxide

13 LOCOS Fabrication Illustration Prof. A. MasonPage 13 LOCOS –step 3 Form Gate (Poly layer) Grow thin Gate Oxide –over entire wafer –negligible effect on FOX regions Deposit Polysilicon Deposit Photoresist gate oxide POLY mask polysilicon

14 LOCOS Fabrication Illustration Prof. A. MasonPage 14 LOCOS –step 3 Form 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 poly gate oxide POLY mask

15 LOCOS Fabrication Illustration Prof. A. MasonPage 15 LOCOS –step 3 Form 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 poly gate oxide

16 LOCOS Fabrication Illustration Prof. A. MasonPage 16 LOCOS –step 4 Form pmos S/D Cover with photoresist PSELECT mask

17 LOCOS Fabrication Illustration Prof. A. MasonPage 17 LOCOS –step 4 Form pmos S/D Cover with photoresist Pattern photoresist –*PSELECT MASK POLY mask PSELECT mask

18 LOCOS Fabrication Illustration Prof. A. MasonPage 18 LOCOS –step 4 Form pmos S/D Cover with photoresist Pattern photoresist –*PSELECT MASK Implant p-type dopants Remove photoresist p+ dopant POLY mask p+ dopant

19 LOCOS Fabrication Illustration Prof. A. MasonPage 19 LOCOS –step 5 Form nmos S/D Cover with photoresist POLY mask NSELECT mask p+ n

20 LOCOS Fabrication Illustration Prof. A. MasonPage 20 LOCOS –step 5 Form nmos S/D Cover with photoresist Pattern photoresist –*NSELECT MASK POLY mask NSELECT mask p+ n

21 LOCOS Fabrication Illustration Prof. A. MasonPage 21 LOCOS –step 5 Form nmos S/D Cover with photoresist Pattern photoresist –*NSELECT MASK Implant n-type dopants Remove photoresist n+ dopant POLY mask n+ dopant p+ n n+

22 LOCOS Fabrication Illustration Prof. A. MasonPage 22 LOCOS –step 6 Form Contacts Deposit oxide Deposit photoresist CONTACT mask p+ n n+ CONTACT mask

23 LOCOS Fabrication Illustration Prof. A. MasonPage 23 LOCOS –step 6 Form Contacts Deposit oxide Deposit photoresist Pattern photoresist –*CONTACT Mask –One mask for both active and poly contact shown CONTACT mask p+ n n+ CONTACT mask

24 LOCOS Fabrication Illustration Prof. A. MasonPage 24 LOCOS –step 6 Form Contacts Deposit oxide Deposit photoresist Pattern photoresist –*CONTACT Mask –One mask for both active and poly contact shown Etch oxide p+ n n+

25 LOCOS Fabrication Illustration Prof. A. MasonPage 25 LOCOS –step 6 Form Contacts Deposit oxide Deposit photoresist Pattern photoresist –*CONTACT Mask –One mask for both active and poly contact shown Etch oxide Remove photoresist Deposit metal1 –immediately after opening contacts so no native oxide grows in contacts Planerize –make top level p+ n n+

26 LOCOS Fabrication Illustration Prof. A. MasonPage 26 LOCOS –step 7 Form Metal 1 Traces Deposit photoresist p+ n n+ METAL1 mask

27 LOCOS Fabrication Illustration Prof. A. MasonPage 27 LOCOS –step 7 Form Metal 1 Traces Deposit photoresist Pattern photoresist –*METAL1 Mask p+ n n+ METAL1 mask

28 LOCOS Fabrication Illustration Prof. A. MasonPage 28 LOCOS –step 7 Form Metal 1 Traces Deposit photoresist Pattern photoresist –*METAL1 Mask Etch metal p+ n n+ metal over poly outside of cross section

29 LOCOS Fabrication Illustration Prof. A. MasonPage 29 LOCOS –step 7 Form Metal 1 Traces Deposit photoresist Pattern photoresist –*METAL1 Mask Etch metal Remove photoresist p+ n n+

30 LOCOS Fabrication Illustration Prof. A. MasonPage 30 LOCOS –step 8 Form Vias to Metal1 Deposit oxide Planerize oxide Deposit photoresist p+ n n+ VIA mask

31 LOCOS Fabrication Illustration Prof. A. MasonPage 31 LOCOS –step 8 Form Vias to Metal1 Deposit oxide Planerize Deposit photoresist Pattern photoresist –*VIA Mask p+ n n+ VIA mask

32 LOCOS Fabrication Illustration Prof. A. MasonPage 32 LOCOS –step 8 Form Vias to Metal1 Deposit oxide Planerize Deposit photoresist Pattern photoresist –*VIA Mask Etch oxide Remove photoresist p+ n n+

33 LOCOS Fabrication Illustration Prof. A. MasonPage 33 LOCOS –step 8 Form Vias to Metal1 Deposit oxide Planerize Deposit photoresist Pattern photoresist –*VIA Mask Etch oxide Remove photoresist Deposit Metal2 p+ n n+

34 LOCOS Fabrication Illustration Prof. A. MasonPage 34 LOCOS –step 9 Form Metal2 Traces Deposit photoresist p+ n n+ METAL2 mask

35 LOCOS Fabrication Illustration Prof. A. MasonPage 35 LOCOS –step 9 Form Metal2 Traces Deposit photoresist Pattern photoresist –*METAL2 Mask p+ n n+ METAL2 mask

36 LOCOS Fabrication Illustration Prof. A. MasonPage 36 LOCOS –step 9 Form Metal2 Traces Deposit photoresist Pattern photoresist –*METAL2 Mask Etch metal p+ n n+

37 LOCOS Fabrication Illustration Prof. A. MasonPage 37 LOCOS –step 9 Form Metal2 Traces Deposit photoresist Pattern photoresist –*METAL2 Mask Etch metal Remove photoresist p+ n n+

38 LOCOS Fabrication Illustration Prof. A. MasonPage 38 LOCOS –step 10+ Form Additional Traces Deposit oxide Deposit photoresist Pattern photoresist Etch oxide Deposit metal Deposit photresist Pattern photoresist Etch metal Repeat for each additional metal p+ n n+ p-type substrate

39 LOCOS Fabrication Illustration Prof. A. MasonPage 39 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


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