Metallization
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Metallization
---Dersun---
1
Contents • • • • • •
Definition Applications Typical material used in VLSI Metallization methods Metallic thin film measurement Future Trends ---Dersun---
2
Definition • Metallization A processes that deposit metal thin film on the wafer surface.
---Dersun---
3
Applications • • • •
Contact electrodes Interconnection Plug and connection Bonding pad
---Dersun---
4
Application: Contact Electrode Ti/TiN
TiN, ARC
TiSi2
Metal 1, Al•Cu W STI
n+
BPSG P-Well
n+
USG
p+
p+ N-Well
P-epi P-wafer ---Dersun---
5
Application: Interconnection
---Dersun---
6
Application: Plug and Connection SiN
Ti/TiN M1
Cu
CoSi2 FSG FSG
PSG STI
Ta or TaN
Cu
Cu
W W
n+
n+ USG P-Well P-Epi P-Wafer ---Dersun---
p+
p+
N-Well
7
Contents • • • • • •
Definition Applications Typical material used in VLSI Metallization methods Metallic thin film measurement Future Trends ---Dersun---
8
Metallization material: Criteria • • • • • • •
Low resistivity Good adherence and low stress Smooth for high resolution patterning Compatible with VLSI deposit and etch process High resistance to electro-migration Low diffusivity in Si and SiO2 Stable and no degradation in VLSI lifetime ---Dersun---
9
Four best conducting metal • The resistivities of best conducting metal – – – –
Silver Copper Gold Aluminum
1.6 µΩ⋅cm 1.7 µΩ⋅cm 2.2 µΩ⋅cm 2.65 µΩ⋅cm
• Aluminum was used for gate before mid-1970 • Al was the most commonly used metal in VLSI ---Dersun---
10
Most Common Used Material in Modern VLSI Metallization • • • • • • •
Aluminum and aluminum alloys Polysilicon and silicide Titanium (Ti) and titanium alloys (TiSi) Tungsten (W) Cobalt (Co) Copper (Cu) Tantalum (Ta) ---Dersun---
11
Common Conducting Thin Films in VLSI • • • • • • • •
Aluminum and Aluminum alloy Polysilicon and Poly-Silicides Titanium and Ti-silicide Cobalt and Co-Silicide Titanium Nitride Tungsten Copper Tantalum ---Dersun---
12
Some Facts About Aluminum × ° ´
Name Aluminum Symbol Al Atomic number 13 Atomic weight 26.981538 Discoverer Hans Christian Oersted Discovered at Denmark Discovery date 1825 Origin of name From the Latin word "alumen" meaning "alum" Density of solid 2.70 g/cm3 Molar volume 10.00 cm3 Velocity of sound 5100 m/sec Hardness 2.75 Electrical resistivity 2.65 µΩ cm Reflectivity 71% Melting point 660 C Boiling point 2519 C Thermal conductivity 235 W m-1 K-1 Coefficient of linear thermal expansion 23.1 10-6 K-1 Etchants (wet) H3PO4, HNO4, CH3COOH Etchants (dry) Cl2, BCl3 ---Dersun--13 CVD Precursor Al(CH3)2H
Typical Aluminum Deposition Equipment Wafers Aluminum Charge
Aluminum Vapor 10-6 Torr
To Pump
High Current Source ---Dersun---
14
Formation of Junction Spike • Al make direct contact with Si at source/drain • Si dissolves in Al and Al diffuses into Si • Junction spike – Aluminum spikes punctuate doped junction – Short source/drain with the substrate
---Dersun---
15
Junction Spike
Al p+
SiO2
Al
Al p+
n-type Silicon
---Dersun---
16
Prevention of Junction Spike • Method A: ~1% of Si in Al saturates it. • Method B: Thermal anneal at 400 °C to form Si-Al alloy after metallization.
---Dersun---
17
Mechanism of Al Electro-migration • • • • • •
Aluminum is a polycrystalline material Many mono-crystalline grains Current flows through an aluminum line Electrons constantly bombards the grains Smaller grains will start to move This effect is called electro-migration ---Dersun---
18
Electro-migration Effects • Electro-migration will tear the metal line apart and make the metal line narrower. • Narrow metal line cause higher current density – Aggravates the electron bombardment – Causes further aluminum grain migration – Eventually will break of the metal line
• Affect the IC chip reliability • Aluminum wires: fire hazard of old houses ---Dersun---
19
Prevention of Electro-migration • Alloy a small percent of copper with aluminum, can significantly improve electro-migration resistance of aluminum • Copper serves as “glue” between the aluminum grains and prevent them from migrating due to the electron bombardment • Al-Si-Cu alloy was used • Al-Cu (0.5%) is very commonly ---Dersun---
20
Conducting Thin Films • • • • • • • •
Aluminum and Aluminum alloy Polysilicon and Poly-Silicides Titanium and Ti-silicide Cobalt and Co-Silicide Titanium Nitride Tungsten Copper Tantalum ---Dersun---
21
Applications of Titanium Al-Cu
Ti
W PSG
TiSi 2
Ti
n+
---Dersun---
22
W Plug and TiN/Ti Barrier/Adhesion Layer Tungsten TiN/Ti
Oxide
---Dersun---
23
Contents • • • • • •
Definition Applications Typical material used in VLSI Metallization methods Metallic thin film measurement Future Trends ---Dersun---
24
Metallization Methods • Physical Vapor Deposition (PVD) --evaporation --sputtering • Chemical Vapor Deposition (CVD) • Electrochemical Plating Deposition (EPD) • Electroless Chemical Plating ---Dersun---
25
Physical Vapor Deposition(PVD) •Vaporizing solid materials •Heating(evaporating) or sputtering •Condensing vapor on the substrate surface •Very important part of metallization
---Dersun---
26
PVD Methods • Evaporation • Sputtering
---Dersun---
27
Evaporation Methods • Filaments • Flash hot plate • Electron beam
---Dersun---
28
Thermal Evaporator Wafers Aluminum Charge
Aluminum Vapor 10-6 Torr
To Pump
High Current Source ---Dersun---
29
Electron Beam Evaporator Wafers Aluminum Charge
Aluminum Vapor
Electron Beam
10-6 Torr
To Pump
Power Supply ---Dersun---
30
Sputtering Methods • • • • •
DC Diode — simplest and cheapest DC Triode RF Diode – for nonconductive film RF Triode DC Magnetron -- most commonly used • RF Magnetron ---Dersun---
31
DC Diode Sputtering -V Target Argon Plasma Wafer Chuck Wafer
Metal film ---Dersun---
32
Principle of Sputtering
Ar+ Momentum transfer will dislodge surface atoms off ---Dersun---
33
Collimated Sputtering • Used for Ti and TiN deposition • Collimator allows metal atoms or molecules to move mainly in vertical direction • Reach the bottom of narrow contact/via holes • Improves bottom step coverage
---Dersun---
34
Collimated Sputtering Magnets Target Plasma Collimator Film Via holes ---Dersun---
35
Inductive Coupled Sputtering • Ti, TiN, Ta, and TaN deposition • Ionize metal atoms through inductive coupling of RF power in the RF coil • Positive metal ions impact with the negatively charged wafer surface vertically • Improving bottom step coverage • Reduce contact resistance ---Dersun---
36
Inductive Coupled Sputtering −V Target Inductive Coils
Ionized Metal Plasma RF Via Hole
---Dersun---
37
Cluster Tool, Aluminum CVD/PVD Pre-clean Ti/TiN PVD TiN CVD
Wafer Loading Transfer Chamber
Transfer Chamber
Wafer Unloading
Al CVD
Cooldown Al-Cu PVD ---Dersun---
38
Endura® PVD System PVD Target PVD Chamber CVD Chamber ---Dersun---
39
Sputtering vs. Evaporator Sputtering
Evaporator
• Purer film • Better uniformity • Single wafer, better process control • Larger size wafer
• More impurities • Batch process • Cheaper tool
---Dersun---
40
Metallization Methods • Physical Vapor Deposition (PVD) --evaporation --sputtering • Chemical Vapor Deposition (CVD) • Electrochemical Plating Deposition (EPD) • Electroless Chemical Plating ---Dersun---
41
Properties of CVD Metallization • Good step coverage and gap fill capability – Can fill tiny contact holes to make connections between metal layers. – Widely used to deposit metal
• Poorer quality and higher resistivity than PVD metal thin films. – Used for plugs and local interconnections – Not applied for global interconnections ---Dersun---
42
Metal CVD Process Steps • Wafer into the chamber • Slip valve closes • Set up pressure and temperature, with secondary process gas(es) • All process gases flow in, start deposition • Termination of the main process gas. Secondary process gas(es) remain on • Termination of all process gases • Purge chamber with nitrogen • Slip valve opens and robot pull wafer out ---Dersun---
43
CVD Metallization Methods • Thermal CVD heat provides free energy needed for the chemical reaction • PECVD plasma enhanced CVD process • Typically used for W, WSix, Ti, and TiN • RF system is used for plasma dry clean of the process chamber ---Dersun---
44
PECVD Chamber RF Power
Process Gases
Process Chamber
Wafer
Heated plate To pump
---Dersun---
45
PVD vs. CVD • CVD: Chemical reaction on the surface • PVD: No chemical reaction on the surface • CVD: Better step coverage (50% to ~100%) and gap fill capability • PVD: Poor step coverage (~ 15%) and gap fill capability ---Dersun---
46
PVD vs. CVD • PVD: higher quality, purer deposited film, higher conductivity, easy to deposit alloys • CVD: always has impurity in the film, lower conductivity, hard to deposit alloys
---Dersun---
47
Metallization Methods • Physical Vapor Deposition (PVD) --evaporation --sputtering • Chemical Vapor Deposition (CVD) • Electrochemical Plating Deposition (EPD) • Electroless Chemical Plating ---Dersun---
48
Contents • • • • • •
Definition Applications Typical material used in VLSI Metallization methods Metallic thin film measurement Future Trends ---Dersun---
49
Metal Thin Film Measurements • • • •
Thickness. Stress Reflectivity Sheet resistance
---Dersun---
50
Summary • • • • • • • •
Mainly application: interconnection CVD (W, TiN, Ti) and PVD (Al-Cu, Ti, TiN) Al-Cu alloy is still dominant Need UHV for Al-Cu PVD W used as plug Ti used as welding layer TiN: barrier, adhesion and ARC layers The future: Cu and Ta/TaN ---Dersun---
51
---Dersun---
1
Contents • • • • • •
Definition Applications Typical material used in VLSI Metallization methods Metallic thin film measurement Future Trends ---Dersun---
2
Definition • Metallization A processes that deposit metal thin film on the wafer surface.
---Dersun---
3
Applications • • • •
Contact electrodes Interconnection Plug and connection Bonding pad
---Dersun---
4
Application: Contact Electrode Ti/TiN
TiN, ARC
TiSi2
Metal 1, Al•Cu W STI
n+
BPSG P-Well
n+
USG
p+
p+ N-Well
P-epi P-wafer ---Dersun---
5
Application: Interconnection
---Dersun---
6
Application: Plug and Connection SiN
Ti/TiN M1
Cu
CoSi2 FSG FSG
PSG STI
Ta or TaN
Cu
Cu
W W
n+
n+ USG P-Well P-Epi P-Wafer ---Dersun---
p+
p+
N-Well
7
Contents • • • • • •
Definition Applications Typical material used in VLSI Metallization methods Metallic thin film measurement Future Trends ---Dersun---
8
Metallization material: Criteria • • • • • • •
Low resistivity Good adherence and low stress Smooth for high resolution patterning Compatible with VLSI deposit and etch process High resistance to electro-migration Low diffusivity in Si and SiO2 Stable and no degradation in VLSI lifetime ---Dersun---
9
Four best conducting metal • The resistivities of best conducting metal – – – –
Silver Copper Gold Aluminum
1.6 µΩ⋅cm 1.7 µΩ⋅cm 2.2 µΩ⋅cm 2.65 µΩ⋅cm
• Aluminum was used for gate before mid-1970 • Al was the most commonly used metal in VLSI ---Dersun---
10
Most Common Used Material in Modern VLSI Metallization • • • • • • •
Aluminum and aluminum alloys Polysilicon and silicide Titanium (Ti) and titanium alloys (TiSi) Tungsten (W) Cobalt (Co) Copper (Cu) Tantalum (Ta) ---Dersun---
11
Common Conducting Thin Films in VLSI • • • • • • • •
Aluminum and Aluminum alloy Polysilicon and Poly-Silicides Titanium and Ti-silicide Cobalt and Co-Silicide Titanium Nitride Tungsten Copper Tantalum ---Dersun---
12
Some Facts About Aluminum × ° ´
Name Aluminum Symbol Al Atomic number 13 Atomic weight 26.981538 Discoverer Hans Christian Oersted Discovered at Denmark Discovery date 1825 Origin of name From the Latin word "alumen" meaning "alum" Density of solid 2.70 g/cm3 Molar volume 10.00 cm3 Velocity of sound 5100 m/sec Hardness 2.75 Electrical resistivity 2.65 µΩ cm Reflectivity 71% Melting point 660 C Boiling point 2519 C Thermal conductivity 235 W m-1 K-1 Coefficient of linear thermal expansion 23.1 10-6 K-1 Etchants (wet) H3PO4, HNO4, CH3COOH Etchants (dry) Cl2, BCl3 ---Dersun--13 CVD Precursor Al(CH3)2H
Typical Aluminum Deposition Equipment Wafers Aluminum Charge
Aluminum Vapor 10-6 Torr
To Pump
High Current Source ---Dersun---
14
Formation of Junction Spike • Al make direct contact with Si at source/drain • Si dissolves in Al and Al diffuses into Si • Junction spike – Aluminum spikes punctuate doped junction – Short source/drain with the substrate
---Dersun---
15
Junction Spike
Al p+
SiO2
Al
Al p+
n-type Silicon
---Dersun---
16
Prevention of Junction Spike • Method A: ~1% of Si in Al saturates it. • Method B: Thermal anneal at 400 °C to form Si-Al alloy after metallization.
---Dersun---
17
Mechanism of Al Electro-migration • • • • • •
Aluminum is a polycrystalline material Many mono-crystalline grains Current flows through an aluminum line Electrons constantly bombards the grains Smaller grains will start to move This effect is called electro-migration ---Dersun---
18
Electro-migration Effects • Electro-migration will tear the metal line apart and make the metal line narrower. • Narrow metal line cause higher current density – Aggravates the electron bombardment – Causes further aluminum grain migration – Eventually will break of the metal line
• Affect the IC chip reliability • Aluminum wires: fire hazard of old houses ---Dersun---
19
Prevention of Electro-migration • Alloy a small percent of copper with aluminum, can significantly improve electro-migration resistance of aluminum • Copper serves as “glue” between the aluminum grains and prevent them from migrating due to the electron bombardment • Al-Si-Cu alloy was used • Al-Cu (0.5%) is very commonly ---Dersun---
20
Conducting Thin Films • • • • • • • •
Aluminum and Aluminum alloy Polysilicon and Poly-Silicides Titanium and Ti-silicide Cobalt and Co-Silicide Titanium Nitride Tungsten Copper Tantalum ---Dersun---
21
Applications of Titanium Al-Cu
Ti
W PSG
TiSi 2
Ti
n+
---Dersun---
22
W Plug and TiN/Ti Barrier/Adhesion Layer Tungsten TiN/Ti
Oxide
---Dersun---
23
Contents • • • • • •
Definition Applications Typical material used in VLSI Metallization methods Metallic thin film measurement Future Trends ---Dersun---
24
Metallization Methods • Physical Vapor Deposition (PVD) --evaporation --sputtering • Chemical Vapor Deposition (CVD) • Electrochemical Plating Deposition (EPD) • Electroless Chemical Plating ---Dersun---
25
Physical Vapor Deposition(PVD) •Vaporizing solid materials •Heating(evaporating) or sputtering •Condensing vapor on the substrate surface •Very important part of metallization
---Dersun---
26
PVD Methods • Evaporation • Sputtering
---Dersun---
27
Evaporation Methods • Filaments • Flash hot plate • Electron beam
---Dersun---
28
Thermal Evaporator Wafers Aluminum Charge
Aluminum Vapor 10-6 Torr
To Pump
High Current Source ---Dersun---
29
Electron Beam Evaporator Wafers Aluminum Charge
Aluminum Vapor
Electron Beam
10-6 Torr
To Pump
Power Supply ---Dersun---
30
Sputtering Methods • • • • •
DC Diode — simplest and cheapest DC Triode RF Diode – for nonconductive film RF Triode DC Magnetron -- most commonly used • RF Magnetron ---Dersun---
31
DC Diode Sputtering -V Target Argon Plasma Wafer Chuck Wafer
Metal film ---Dersun---
32
Principle of Sputtering
Ar+ Momentum transfer will dislodge surface atoms off ---Dersun---
33
Collimated Sputtering • Used for Ti and TiN deposition • Collimator allows metal atoms or molecules to move mainly in vertical direction • Reach the bottom of narrow contact/via holes • Improves bottom step coverage
---Dersun---
34
Collimated Sputtering Magnets Target Plasma Collimator Film Via holes ---Dersun---
35
Inductive Coupled Sputtering • Ti, TiN, Ta, and TaN deposition • Ionize metal atoms through inductive coupling of RF power in the RF coil • Positive metal ions impact with the negatively charged wafer surface vertically • Improving bottom step coverage • Reduce contact resistance ---Dersun---
36
Inductive Coupled Sputtering −V Target Inductive Coils
Ionized Metal Plasma RF Via Hole
---Dersun---
37
Cluster Tool, Aluminum CVD/PVD Pre-clean Ti/TiN PVD TiN CVD
Wafer Loading Transfer Chamber
Transfer Chamber
Wafer Unloading
Al CVD
Cooldown Al-Cu PVD ---Dersun---
38
Endura® PVD System PVD Target PVD Chamber CVD Chamber ---Dersun---
39
Sputtering vs. Evaporator Sputtering
Evaporator
• Purer film • Better uniformity • Single wafer, better process control • Larger size wafer
• More impurities • Batch process • Cheaper tool
---Dersun---
40
Metallization Methods • Physical Vapor Deposition (PVD) --evaporation --sputtering • Chemical Vapor Deposition (CVD) • Electrochemical Plating Deposition (EPD) • Electroless Chemical Plating ---Dersun---
41
Properties of CVD Metallization • Good step coverage and gap fill capability – Can fill tiny contact holes to make connections between metal layers. – Widely used to deposit metal
• Poorer quality and higher resistivity than PVD metal thin films. – Used for plugs and local interconnections – Not applied for global interconnections ---Dersun---
42
Metal CVD Process Steps • Wafer into the chamber • Slip valve closes • Set up pressure and temperature, with secondary process gas(es) • All process gases flow in, start deposition • Termination of the main process gas. Secondary process gas(es) remain on • Termination of all process gases • Purge chamber with nitrogen • Slip valve opens and robot pull wafer out ---Dersun---
43
CVD Metallization Methods • Thermal CVD heat provides free energy needed for the chemical reaction • PECVD plasma enhanced CVD process • Typically used for W, WSix, Ti, and TiN • RF system is used for plasma dry clean of the process chamber ---Dersun---
44
PECVD Chamber RF Power
Process Gases
Process Chamber
Wafer
Heated plate To pump
---Dersun---
45
PVD vs. CVD • CVD: Chemical reaction on the surface • PVD: No chemical reaction on the surface • CVD: Better step coverage (50% to ~100%) and gap fill capability • PVD: Poor step coverage (~ 15%) and gap fill capability ---Dersun---
46
PVD vs. CVD • PVD: higher quality, purer deposited film, higher conductivity, easy to deposit alloys • CVD: always has impurity in the film, lower conductivity, hard to deposit alloys
---Dersun---
47
Metallization Methods • Physical Vapor Deposition (PVD) --evaporation --sputtering • Chemical Vapor Deposition (CVD) • Electrochemical Plating Deposition (EPD) • Electroless Chemical Plating ---Dersun---
48
Contents • • • • • •
Definition Applications Typical material used in VLSI Metallization methods Metallic thin film measurement Future Trends ---Dersun---
49
Metal Thin Film Measurements • • • •
Thickness. Stress Reflectivity Sheet resistance
---Dersun---
50
Summary • • • • • • • •
Mainly application: interconnection CVD (W, TiN, Ti) and PVD (Al-Cu, Ti, TiN) Al-Cu alloy is still dominant Need UHV for Al-Cu PVD W used as plug Ti used as welding layer TiN: barrier, adhesion and ARC layers The future: Cu and Ta/TaN ---Dersun---
51
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