MOS Device Physics and Designs Chap. 5

Instructor: Pei-Wen LiDept. of E. E. NCU

1

Chap 5. MOS Fundamentals

u Ideal Structureu Energy Band Diagramu Bias Effectsu Capacitance-Voltage Characteristicsu Current-Voltage Characteristicsu Nonideal MOS u Gate Oxide Integrity

MOS Device Physics and Designs Chap. 5

Instructor: Pei-Wen LiDept. of E. E. NCU

2

Ideal Structure Definition

u MOS Capacitor

MOS Device Physics and Designs Chap. 5

Instructor: Pei-Wen LiDept. of E. E. NCU

3

Energy Band Diagram

u Individual energy band diagram

u Ideal Structure energy Band Diagram

MOS Device Physics and Designs Chap. 5

Instructor: Pei-Wen LiDept. of E. E. NCU

4

Block Charge Diagram

MOS Device Physics and Designs Chap. 5

Instructor: Pei-Wen LiDept. of E. E. NCU

5

Bias Effect

Ideal N-MOS Capacitor

MOS Device Physics and Designs Chap. 5

Instructor: Pei-Wen LiDept. of E. E. NCU

6

Bias Effect

Ideal P-MOS Capacitor

MOS Device Physics and Designs Chap. 5

Instructor: Pei-Wen LiDept. of E. E. NCU

7

C-V Characteristics

High- and low-frequency C-V characteristics of a pMOS capacitor

MOS Device Physics and Designs Chap. 5

Instructor: Pei-Wen LiDept. of E. E. NCU

8

AC Charge fluctuations inside an n-MOS C

VG < 0, Accumulation VG ≥ 0, Depletion

VG > 0, Inversion

MOS Device Physics and Designs Chap. 5

Instructor: Pei-Wen LiDept. of E. E. NCU

9

Oxide Thickness Effects

MOS Device Physics and Designs Chap. 5

Instructor: Pei-Wen LiDept. of E. E. NCU

10

Sweep Frequency Effects

MOS Device Physics and Designs Chap. 5

Instructor: Pei-Wen LiDept. of E. E. NCU

11

Nonideal MOS

u Metal-Semiconductor Workfunction Difference u Oxide Charge

– Mobile Ions– Trapped Oxide Charge– Fixed Charge– Interfacial traps

MOS Device Physics and Designs Chap. 5

Instructor: Pei-Wen LiDept. of E. E. NCU

12

Workfunction Difference

u Metal-Semiconductor workfunction difference induces a built-in potential (band bending) in MOS-C even when VG = 0.

u Vbi = φMS = φM - φS

MOS Device Physics and Designs Chap. 5

Instructor: Pei-Wen LiDept. of E. E. NCU

13

Work function as a function of doping conc. of semiconductor

MOS Device Physics and Designs Chap. 5

Instructor: Pei-Wen LiDept. of E. E. NCU

14

Barrier Height of Various Metals on MOS-Cs

MOS Device Physics and Designs Chap. 5

Instructor: Pei-Wen LiDept. of E. E. NCU

15

Oxide Charges

Four Major Charge/Traps in SiO2Mobile IonsTrapped Oxide ChargeFixed ChargeInterfacial traps

Arbitrary distribution of oxide charges

MOS Device Physics and Designs Chap. 5

Instructor: Pei-Wen LiDept. of E. E. NCU

16

Mobile Ions

u Arise from “Alkali-ion” contamination, such as Na+ and K+.u C-V curve shifts with bias-temperature.

∫−=

∆

ox

ooG dxxx

kV

0)(ion

1ions

mobileρ

ε

MOS Device Physics and Designs Chap. 5

Instructor: Pei-Wen LiDept. of E. E. NCU

17

Mobile Ions

u Two hypothetical ionic charge distributions involving the same total number of ions situated near the metal and near the semiconductor.

u Positive mobile ions within the oxide under (+) and (-) bias-temperature stressing.

u Specail fabrication procedures needed, such as RCA clean, Phosphorus or chlorine stabilization, and extremely clean environment.

MOS Device Physics and Designs Chap. 5

Instructor: Pei-Wen LiDept. of E. E. NCU

18

MOS stabilization procedures

MOS Device Physics and Designs Chap. 5

Instructor: Pei-Wen LiDept. of E. E. NCU

19

Fixed Charge

o

FG C

QV −=

∆

charge

fixedDue to excess ionic silicon that has broken away the silicon proper and is waiting to react in the vicinity of the Si-SiO2 interface when the oxidation process is abruptly terminated.

MOS Device Physics and Designs Chap. 5

Instructor: Pei-Wen LiDept. of E. E. NCU

20

Effects of oxidation process on fixed charge

MOS Device Physics and Designs Chap. 5

Instructor: Pei-Wen LiDept. of E. E. NCU

21

Interfacial Traps

u Interfacial traps are allowed energy states in which electrons are localized in the vicinity of Si-SiO2 interface. ⇒C-V curve distortion

MOS Device Physics and Designs Chap. 5

Instructor: Pei-Wen LiDept. of E. E. NCU

22

Interfacial Traps

MOS Device Physics and Designs Chap. 5

Instructor: Pei-Wen LiDept. of E. E. NCU

23

Physical Model of Interfacial traps

MOS Device Physics and Designs Chap. 5

Instructor: Pei-Wen LiDept. of E. E. NCU

24

Energy Distribution of Interface states

Annihilation of interface states by postmetallization H2annealing

MOS Device Physics and Designs Chap. 5

Instructor: Pei-Wen LiDept. of E. E. NCU

25

Induced Charge

u Radiation effects: a major concern of space and military.

∆VG Summary ( ) ( )o

SIT

o

MM

o

FMSGGG C

QC

QCQVVV φγ

φφ

−−−=−=∆S same

'