Film Deposition in IC Fabrication

Metal Contacts/Connections

Electrodes

Masks

Wire insulation

Device encapsulation

Low stress

Adherent

Uniformity, no pin holes

Conformal step coverage

Thermal & electrical stability

Vapor pressure of metals

RF Sputter System

Magnetron Sputter Deposition

Sputter Deposition Systems

E

DC Sputter Deposition

Voltage ratio in RF sputtering: VC/VA = (AA/AC)n

Chemical Vapor Deposition (CVD)

Low-pressure CVD (LPCVD)Plasma-enhanced CVD (PECVD)

Different thin film textures

Single crystal Poly-crystalline

Poly-crystalline columnar Nano-crystalline

amorphous

Step Coverage of Deposited Films

High surface mobility + non-directional flux conformal step coverage

Electromigration EffectsVoid Pile-up

Electron wind and field-driven atomic migration

Bamboo-structured wireElectromigration-resistant

SiO2 Films for masking & protection

SiH4 + O2 SiO2 + 2H2 or SiH4 + N2O SiO2 + 2N2 + 2H2

by APCVD or LPCVD at ~ 450ºC, SiH4 diluted in H2

with Si(C2H5O)4 (TEOS), more stable to handle

Si(C2H5O)4 + 12O2 SiO2 + 8CO2 + 10H2O, APCVD or LPCVD at ~ 700ºC

SiO2 films by PECVD at 300-350ºC, low compressive stress.

Applications of deposited SiO2 films:

Field oxide for MOS and HV devices (deposited on thermal SiO2)

Fill-in of the isolation walls/wells

Isolation between multi-layer metal connections

Diffusion and implantation masks

Final encapsulation layer

Other Films for masking & protection Phosphosilicate glass (PSG)

adding P2O5 to improve the quality of SiO2

mixing PH3 or (CH3O)3P in oxidation gases

2PH3 + 4O2 P2O5 + 3H2O

or 2(CH3O)3P + 10O2 P2O5 + 6CO2 + 10H2O

Effect of P2O5: reduce tensile stress in SiO2 (to 0 at ~ 20% P2O5)

TCE() matching with substrate (P2O5 raises )

improve film texture (denser, void-free) effective diffusion barrier to Na

Si3N4 (and SiOxNy) more stable than SiO2, excellent barrier

to Na, B and Ga migration, mask for oxidation

3SiH4 + 4NH3 Si3N4 + 12H2 (PNH3 : PSiH4 ~ 150)

LPCVD at ~900ºC, high tensile stress, t < 1000Å PECVD at ~300ºC, low stress, high H incorporation

RF sputtering of Si in N2 discharge: 3Si + 4N Si3N4

Pit Formation of Al Contact with Si

High solubility of Si in Al (~1%)

Al spikes

Silicide Contacts

5.8

135.314.57

10.510.41343205.342

Resistivity of metal

Phase Diagram and Formation Sequence of Silicide

Oxidation of Silicide