1. CMOS Fabrication
EMT 251

2. Objectives To discussed the fundamentals of CMOS fabrication steps.
To examined the major steps of the process flow.
To overview the cross section view of a circuit

3. Chip making Process

4. Introduction
MOSFET
PMOS
NMOS
CMOS

5. MOSFET Metal Oxide Semiconductor Field Effect Transistor
Source
Drain
Gate
Metal Oxide Semiconductor Field Effect Transistor
Source (Arsenic, Phosphorous, Boron)
Drain (Arsenic, Phosphorous, Boron)
Gate (Aluminum, Polysilicon)
MOSFET

6. NMOS P-type substrate N-type dopant for Source & Drain
Inversion layer is formed to conduct electricity

7. NMOS P-type substrate N-type dopant for Source & Drain
Inversion layer is formed to conduct electricity

8. PMOS N-type substrate P-type dopant for Source & Drain
Inversion layer is formed to conduct electricity

9. PMOS N-type substrate P-type dopant for Source & Drain
Inversion layer is formed to conduct electricity

10. CMOS A combination of both NMOS & PMOS technology
Most basic example: inverter

11. PROCESS FLOW WELL FORMATION ISOLATION FORMATION TRANSISTOR MAKING
INTERCONNECTION
PASSIVATION

12. CMOS FABRICATION PROCESS well formation
Start with clean p-type substrate (p-type wafer)

13. CMOS FABRICATION PROCESS well formation
Grow epitaxy layer (made from SiO2) as mask layer for well formation

14. CMOS FABRICATION PROCESS well formation
Well will be formed here
By *photolithography and etching process, well opening are made
*photolithography and etch processes are shown in next slides

15. Photolithography (CED)
photoresist
Photoresist coating (C)
Masking and exposure under UV light(E)
Resist dissolved after developed (D)
Pre-shape the well pattern at resist layer
Si02
P-substrate
UV light
mask
Opaque area
P-substrate
Transparent area

16. etching Removing the unwanted pattern by wet etching Resist clean
Desired pattern formed
P-substrate
P-substrate

17. CMOS FABRICATION PROCESS well formation
Phosphorus ion
Ion bombardment by ion implantation
SiO2 as mask, uncovered area will exposed to dophant ion

18. CMOS FABRICATION PROCESS isolation formation
Thick oxide
Increase SiO2 thickness by oxidation at high temperature
Oxide will electrically isolates nmos and pmos devices

19. CMOS FABRICATION PROCESS transistor making
pmos will be formed here
nmos will be formed here
LOCOS (isolation structure)
By photolithography and etching process, pmos and nmos areas are defined

20. CMOS FABRICATION PROCESS transistor making
Gate oxide
Grow very thin gate oxide at elevated temperature in very short time

21. CMOS FABRICATION PROCESS transistor making
polisilicon
Deposit polisilicon layer

22. CMOS FABRICATION PROCESS transistor making
gate
Photolithography (photo) and etching to form gate pattern

23. CMOS FABRICATION PROCESS transistor making
Arsenic ion
photoresist
Photo process to define the nmos’s active (source and drain) area and VDD contact
Ion implantation with Arsenic ion for n+ dophant.
Photoresist and polisilicon gate act as mask

24. CMOS FABRICATION PROCESS transistor making
VDD contact
source
drain
Nmos’s Source and drain with VDD contact formation
Resist removal

25. CMOS FABRICATION PROCESS transistor making
Boron ion
photoresist
Photo process to define the GND contact and pmos’s active area (source and drain)
Ion implantation with boron ionto have p+ dophant
Photoresist and gate act as mask

26. CMOS FABRICATION PROCESS transistor making
GND contact
Pmos’s drain
Pmos’ source
Pmos’s source and drain formation with GND contact
Resist removal

27. CMOS FABRICATION PROCESS interconnection
SiO2
Deposit SiO2 layer through out wafer surface

28. CMOS FABRICATION PROCESS interconnection
contact
Photo and etching process to make contact

29. CMOS FABRICATION PROCESS interconnection
Metal 1
Metal 1 deposition throughout wafer surface

30. CMOS FABRICATION PROCESS interconnection
Photo and etching processes to pattern interconnection

31. Mask Layout

32. Mask Layout

33. Mask Layout

34. Mask Layout

35. A A’
oxide
p-substrate n+
N-well p+
Metal 1

36. Assignment B B’

37. GLOSSARY Photolithography (photo) Etching Diffusion Ion implantation
Process of transferring pattern on mask to photoresist layer on wafer surface (pre-pattern the chip)
Etching
Process of permanently removed the unwanted part of design on wafer surface to get the desired pattern
Diffusion
Process of introducing dophant layer by movement of dophant atoms from high concentration to low concentration area at high temperature
Ion implantation
Process of introducing dophant layer by bombardment of high energy dophant ion in high electric field chamber
Oxidation
Process of growing thick or thin SiO2 layer depend on oxide application
CMP
Process to physically grind flat to have a planar surface for better exposure at photo process.

38. THE END