Thermodynamics in Chip Processing II

mistaureolinΜηχανική

27 Οκτ 2013 (πριν από 3 χρόνια και 9 μήνες)

78 εμφανίσεις

Thermodynamics in Chip
Processing II

Terry A. Ring

CVD


Materials Deposited


Dielectrics


SiO2, BSG


Metals


W, Cu, Al


Semiconductors


Poly silicon (doped)


Barrier Layers


Nitrides (TaN, TiN), Silicides (WSi
2
, TaSi
2
, CoSi,
MoSi
2
)

Deposition Methods


Growth of an oxidation layer


Spin on Layer


Chemical Vapor Deposition (CVD)


Heat = decomposition T of gasses


Plasma enhanced CVD (lower T process)


Physical Deposition


Vapor Deposition


Sputtering

Critical Issues


Adherence of the layer


Chemical Compatibility


Electro Migration


Inter diffusion during subsequent processing


Strong function of Processing


Even Deposition at all wafer locations

CVD of Si
3
N
4

-

Implantation
mask


3 SiH
2
Cl
2

+ 4 NH
3

Si
3
N
4

+ 6 HCl + 6 H
2


780C, vacuum


Carrier gas with
NH
3

/
SiH
2
Cl
2
>>1


Stack of wafer into furnace


Higher temperature at exit to compensate for gas
conversion losses


Add gases


Stop after layer is thick enough

CVD of Poly Si


Gate conductor


SiH
4


Si + 2 H
2


620C, vacuum


N
2

Carrier gas with
SiH
4
and dopant precursor


Stack of wafer into furnace


Higher temperature at exit to compensate for gas
conversion losses


Add gases


Stop after layer is thick enough

CVD of SiO
2



Dielectric


Si0C
2
H
5

+O
2

SiO
2

+ 2 H
2


400C, vacuum


He carrier gas with vaporized(or atomized)
Si0C
2
H
5

and O
2

and B(CH
3
)
3

and/or P(CH
3
)
3

dopants for BSG
and BPSG


Stack of wafer into furnace


Higher temperature at exit to compensate for gas
conversion losses


Add gases


Stop after layer is thick enough

CVD of W


Metal plugs



3H
2
+WF
6



W + 6HF


T>800C, vacuum


He carrier gas with
WF
6


Side Reactions at lower temperatures


Oxide etching reactions


2H
2
+2WF
6
+3SiO
2



3SiF
4

+ 2WO
2

+ 2H
2
O


SiO
2

+ 4HF


2H
2
O +SiF
4


Stack of wafer into furnace


Higher temperature at exit to compensate for gas conversion
losses


Add gases


Stop after layer is thick enough

Chemical Equilibrium

CVD Reactor


Wafers in Carriage
(Quartz)


Gasses enter


Pumped out via
vacuum system


Plug Flow Reactor

Vacuum

CVD Reactor


Macroscopic Analysis


Plug flow reactor


Microscopic Analysis


Surface Reaction


Film Growth Rate

Macroscopic Analysis


Plug Flow Reactor (PFR)


Like a Catalytic PFR Reactor


F
Ao
= Reactant Molar Flow
Rate


X = conversion


r
A
=Reaction rate = f(C
A
)=kC
A


C
i
=Concentration of Species, i.


Θ
i
= Initial molar ratio for species i to
reactant, A.


ν
i
= stoichiometeric coefficient


ε = change in number of moles


Combined Effects

Contours = Concentration

Reactor Length


Effects

SiH
2
Cl
2
(g) + 2 N
2
O(g)


SiO
2
(s)+ 2 N
2
(g)+2 HCl(g)

How to solve? Higher T at exit!

Deposition Rate over the
Radius

r

C
As

Thiele Modulus
Φ
1
=(2kR
w
/D
AB
x)
1/2

Radial Effects

This is bad!!!

Combined Length and Radial
Effects

Wafer 20

Wafer 10

CVD Reactor


External Convective Diffusion


Either reactants or products


Internal Diffusion in Wafer Stack


Either reactants or products


Adsorption


Surface Reaction


Desorption

Microscopic Analysis
-
Reaction Steps


Adsorption


A(g)+S

A*S


r
AD
=k
AD

(P
A
C
v
-
C
A*S
/K
AD
)


Surface Reaction
-
1


A*S+S

S*S + C*S


r
S
=k
S
(C
v
C
A*S

-

C
v
C
C*S
/K
S
)


Surface Reaction
-
2



A*S+B*S

S*S+C*S+P(g)


r
S
=k
S
(C
A*S
C
B*S

-

C
v
C
C*S
P
P
/K
S
)


Desorption: C*S<
----
> C(g) +S


r
D
=k
D
(C
C*S
-
P
C
C
v
/K
D
)


Any can be rate determining! Others in Equilib.


Write in terms of gas pressures, total site conc.

CMP


What is CMP?


Polishing of Layer to
Remove a Specific
Material, e.g. Metal,
dielectric


Planarization of IC
Surface Topology

Scratching Cases


Rolling Indenter


Line Scratches


Copper Only


Copper & ILD


Chatter Scratches


Uncovery of Pores

CMP Tooling


Rotating Multi
-
head
Wafer Carriage


Rotating Pad


Wafer Rests on Film of
Slurry


Velocity=
-
(Wt

Rcc)

[Rh

(Wh

Wt)]



when Wh=Wt
Velocity = const.

Slurry


Aqueous Chemical Mixture


Material to be removed is soluble in liquid


Material to be removed reacts to form an oxide layer
which is abraded by abrasive


Abrasive


5
-
20% wgt of ~200
±
50nm particles


Narrow PSD, high purity(<100ppm)


Fumed particle = fractal aggregates of spherical primary
particles (15
-
30nm)

Pad Properties


Rodel Suba IV


Polyurethane


tough polymer


Hardness = 55


Fiber Pile


Specific Gravity = 0.3


Compressibility=16%


rms Roughness = 30μm


Conditioned

Heuristic Understanding of
CMP


Preston Equation(Preston, F., J. Soc. Glass Technol., 11,247,(1927).


Removal

Rate

=

K
p
*V*P



V

=

Velocity,

P

=

pressure

and

K
p

is

the

proportionality

constant
.


CMP Pad Modeling


Pad Mechanical Model
-

Planar Pad


Warnock,J.,J. Electrochemical Soc.138(8)2398
-
402(1991).








Does not account for Pad Microstructure


CMP Modeling




Numerical Model of Flow under Wafer


3D
-
Runnels, S.R. and Eyman, L.M., J. Electrochemical Soc.
141,1698(1994).


2
-
D
-
Sundararajan, S., Thakurta, D.G., Schwendeman, D.W.,
Muraraka, S.P. and Gill, W.N., J. Electrochemical Soc.
146(2),761
-
766(1999).

Copper Dissolution



Solution Chemistry


Must Dissolve Surface
Slowly without Pitting


Supersaturation

Oxidation of Metal Causes
Stress


Stress,

i

= E

i

(P
-
B

i



1)/(1
-


i
)


P
-
B
i

is the Pilling
-
Bedworth ratio for the oxide