Chap3. Silicon Oxidation 1

Chap. 3. Silicon Oxidation

:

- silicon dioxide(SiO2)

-

- SiO2 file

Why silicon in modern integrated circuit ?

Ge : 1950 (silicon energy gap=1.12 eV, Ge energy gap=0.6 eV)

() , Silicon

Si : 1960

() , (O2) SiO2 .

Silicon dioxide

: thermal growth . high quality, dopant mask, selective etching mask etc.

: MOSFET gate oxide, capacitor , , PMD, IMD, spacer etc.

(MOSFET) : SiO2 film

Chap3. Silicon Oxidation 2

MOSFET 3-D (SEM) MOSFET (SEM)

3.1 Thermal oxidation process

silicon wafer oxide

(thermally growth) : quality film .

-

PECVD

thermal oxidation furnace

: 800~1200, gas flow rate: ~ liter/min., temp. range: 1, ramp-up &

down .

Chap3. Silicon Oxidation 3

3.1.1 Oxidation Kinetics

Chemical reaction of Dry & wet oxidation ( )

:

:

silicon silicon 44% .

(100nm SiO2 44nm silicon .)

* SiO2

Basic structural unit Basic structural unit of silicon dioxide.of silicon dioxide.

22--dimensional Quartzdimensional Quartz

22--dimensional dimensional --oxideoxide

amorphous SiO2 vacancy

diffusion

.

Chap3. Silicon Oxidation 4

* Simple oxidation model

(, D; , x: )

(, k: surface reaction rate constant)

,

, growth rate

( x(0)=d0 ) ,

(d0)

( ,

; time coordinate shift to account for the initial oxide layer)

, given oxidation time

Chap3. Silicon Oxidation 5

. ( )

.

(, root .)

compact form

(,

)

,

Dry wet B/A

B/A (linear rate constant)

, activation energy()

2eV .

() Si-Si bond

1.83 eV/molecule .

(111) (100) go B/A

(111) bond .

Chap3. Silicon Oxidation 6

Dry wet B(parabolic rate constant)

Dry oxidation Wet oxidation

Dry oxidation Wet oxidation remark

slowfaster than dry

(5~10 times)

,

thin & high

quality required

oxide

(e.g. gate oxide)

thicker oxide

(FOX, PVX,

masking layers)

gate oxide

wet

.

Gate oxide

anneal .

Parabolic rate constant

(B)

: 1.24 eV ()

: 0.71 eV ()

()

fused silica O2 1.18 eV

fused silica H2O 0.79 eV

Parabolic rate constant

wafer orientation .

Chap3. Silicon Oxidation 7

(!) simple oxidation model oxide ( ) ,

thin oxide simple oxidation model .

Chap3. Silicon Oxidation 8

3.1.1 Thin oxide growth

Thin oxide ( ) : reproducibility, Uniformity etc.

For thin oxide growth

Low temp oxidation ( )

ULSI . (typical oxidation temp. ~850 )

dilution ( N2 + O2 , Ar + O2 etc.)

high quality thin oxide .

composite oxide film : thermal + LPCVD oxide

thermal cycle .

thin oxide growth anneal . (N2, N2O, Ar anneal)

dry oxidation thin oxide growth ( ) simple oxidation

model .

* Thin oxidation model

model

, term .

, .

(, ; initial oxide thickness when time is extrapolated to zero .)

3.2 Impurity redistribution during oxidation ( )

silicon silicon dioxide .

Segregation coefficient (k) :

SiO2 Si , .

Impurity diffusion through SiO2 escape to the gaseous ambient

Oxide growing Si/SiO2

Chap3. Silicon Oxidation 9

4 :

oxide (k < 1), oxide (k > 1)

Case (a) : Oxidation of Boron doped silicon, k ~ 0.3

Case (b) : H2 anneal of Boron doped silicon,

H2 oxide B oxide B

Case (c) : Oxidation of Phos. doped silicon, k ~ 10

oxide Ph. silicon .

Case (d) : k oxide oxide silicon

Ga (k ~ 20)

Chap3. Silicon Oxidation 10

3.3 Masking properties of silicon dioxide

Selective masking : SiO2 layer IC

* Pre-deposition / drive-in (high temperature anneal )

Oxide , .

, . (typically 0.5 ~ 1.0 um)

Ga Al IC (As, Ph, B, Sb) silicon oxide

10 .

Si3N4 (silicon nitride) oxide .

Chap3. Silicon Oxidation 11

3.4 Oxide quality

IC MOSFET .

factor .

oxide oxide (charge) oxide/silicon trap .

(interface trap charge, fixed oxide charge, oxide trapped charge, mobile ionic charge)

interface trap charge (Qit) :

Si/SiO2 . Si-SiO2 , state silicon

. Si wafer orientation . 1/10 Qit

. Qit H2 anneal (~450 ) .

: ~1010 /cm2, : ~1011 /cm2

Fixed oxide charge (Qf) :

Si/SiO2 3nm . positive charge. //orientation

. Oxidation ionic silicon Si/SiO2 silicon

bond .

: ~1010 /cm2, : ~5 1010 /cm2

*IC Qf Qit wafer .

Oxide tranpped charge (Qot) :

SiO2 . electron bombardment X-ray

. IC Qot anneal .

Chap3. Silicon Oxidation 12

Mobile ionic charge (Qm) :

sodium alkali . 100 , e-field oxide

. (e.g. MOSFET VT )

IC sodium ion 6% HCl .

oxidation rate .

3.5 Oxide thickness characterization

Profilemeter

Ellisometer : IC . (~ 100 x 100um2)

.

C-V : . Large area capacitor pattern .

Chap3. Silicon Oxidation 13

* Oxide color

Chap3. Silicon Oxidation 14

3.6 Process Simulation :

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