chemical vapor deposition cvd
TRANSCRIPT
CVD
MOS Transistor
CVD Thin Film Growth
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Atmospheric Pressure CVD
Atmospheric Pressure CVD
Atmospheric Pressure CVD
Horizontal type Barrel type
Atmospheric Pressure CVD
Low Pressure CVD
Low Pressure CVD
Laser Enhanced CVD
Plasma Enhanced CVD
Plasma Enhanced CVD
Plasma Enhanced CVD
Thin FilmDeposition
• Quality – composition, defect density, mechanical and electrical properties
• Uniformity – affect performance (mechanical , electrical)
Thinning leadsto ↑ R
Voids: Trap chemicals lead tocracks (dielectric) large contactresistance and sheet resistance(metallization)
AR (aspect ratio) = h/w ↑ with↓ feature size in ICs.
Examples
Poor step coverage with increasing AR
Thinning causesmetal resistance toincrease,generates heatand lead to failure
Chemical Vapor Deposition
Flat on thesusceptor
Cold wallreactor
Methods of Deposition:
Chemical Vapor Deposition(CVD):APCD, LPCVD, HDPCVDPhysical Vapor Deposition (PVD:evaporation, sputtering)
Atmospheric Pressure : APCVD
Cold wall reactors (walls not heated -only the susceptor)
Low pressure: LPCVD – batchprocessing.
Hot wallreactor
Atmospheric Pressure Chemical Vapor Deposition
Transport by forcedconvection
By diffusionthroughboundary layer Diffusion through the B. L
Desorption of by products
Transport of byproducts byforced convection
@ the surface (4): decomposition,reaction, surface migration attachmentetc.
(3) May be desorption which dependson a sticking coefficient (4)
Growth rate for Si depositionN=5•1022cm-3
Mole fraction of theincorporating species in the gasphase.
Partial pressure
Total concentration in the gas phase
CT = 1 * 1019 cm-3 5 * 1022
V = 0.14 µm/min
PG @ 1 torr
Ptotal = 1 atm = 760 torr
adsorption
transport
reaction
Steady state
Steps in deposition
As in Deal-Grovemodel for oxidation
Growth Kinetics
Determined by the Smaller of ks or hG Two limiting cases
1) Surface reaction ks << hG
Control: fast transport
slow reactionYk
N
Cv
S
T=
2) Mass transfer or gasphase diffusion hG << ks
YhN
Cv
G
T=
Fast reaction and slow transport.
Temperature uniformitymore important than thegas flow wafersvertically poly-Si
Put wafersflat toensure flowuniformity@ the Sisurface.
Epitaxy
APCVD
SiO2
(111) Si shows slower v – fewerattachment sites than in (100) Si
Ea ≈ 1.6 eV for all Si sources H desorption from the Si surface.
With H2 as a gas carrier
Light mass
heavy
Limited by transport
Both are linear with time (t)
SiH4 the fastest growth
kS limited deposition is VERY temp sensitive.hG limited deposition is VERY geometry (boundary layer) sensitive
Boundary Layer – Diffusion to the Surface
Gas moves with the constant velocity U.
Boundary layer (caused by friction ) increasesalong the susceptor, mass transfer coefficient hGdecreases, gas depletion caused by consumptionof the reacting species (concentrations decrease)
Growth rate decreases along the chamber
• Use tilted susceptor
• Use T gradient 5-25°C
• Gas injectors along the tube
• Use moving belt
Deposition of alloys DIFFICULT – variousreactions, kinetics (species, precursors)
Use PVD rather than CVD
B.L.
viscosity
gas density