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SputteringSputtering

WW49/00

Eyal GinsburgEyal Ginsburg

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ContentsContents

Metallization structureMetallization structureUses for different layersUses for different layersStep CoverageStep CoverageSputtering: yield, conditioning, Sputtering: yield, conditioning,

methodsmethods

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Metallization StructureMetallization Structure

The semiconductor industry uses PVD The semiconductor industry uses PVD to deposit the metal that electrically to deposit the metal that electrically connects the various parts of the IC to connects the various parts of the IC to each other and to the outside world.each other and to the outside world.

There are four common structure in There are four common structure in metallization: metallization: contactscontacts, , viasvias, , plugsplugs and and interconnectsinterconnects..

Contact:Contact: A hole in the Si dioxide layer A hole in the Si dioxide layer that connect the transistors to the first that connect the transistors to the first metal layer.metal layer.

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Metallization Structure (Cont.)Metallization Structure (Cont.)

Via:Via: A hole in the Si dioxide layer that A hole in the Si dioxide layer that connect two metal layers.connect two metal layers.

Plug:Plug: A metal layer that fills either a A metal layer that fills either a contact or a via. Made of either contact or a via. Made of either tungsten (W) or aluminum (Al). tungsten (W) or aluminum (Al).

Interconnect:Interconnect: Metal layer. The IC has Metal layer. The IC has more than one layer of interconnects, more than one layer of interconnects, each layer has different name, starting each layer has different name, starting with the first layer deposited, “Metal with the first layer deposited, “Metal 1”, “Metal 2”, etc. 1”, “Metal 2”, etc.

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Contact / Via / Plug / InterconnectContact / Via / Plug / Interconnect

Silicon

Silicon Dioxide

Metal 1

Silicon Dioxide (ILD)

Metal 2

Silicon Dioxide (ILD)

Metal 3

Interconnects Via 2

Contact

Via 1

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Uses for Uses for different layersdifferent layers

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Glue Layer or Adhesion layerGlue Layer or Adhesion layer

Companies commonly use the WCVD Companies commonly use the WCVD process to fill contacts/vias with process to fill contacts/vias with tungsten. Unfortunately, if one uses tungsten. Unfortunately, if one uses WCVD to deposit W directly to SiOWCVD to deposit W directly to SiO22, , the W flakes and peels, producing the W flakes and peels, producing many particles. many particles.

Therefore, an intermediate layer is Therefore, an intermediate layer is deposited between the oxide and deposited between the oxide and WCVD. WCVD.

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Glue Layer (Cont. 1)Glue Layer (Cont. 1)

The most common process:The most common process:1.1. Deposit Ti layer onto silicon oxideDeposit Ti layer onto silicon oxide

2.2. Deposit TiN onto TiDeposit TiN onto Ti

3.3. Deposit WCVDDeposit WCVD

TiN

Ti

W

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W filled Contact/ViaW filled Contact/Via

Ti reduce contact resistanceTi reduce contact resistance– Reacts with Si to form Silicide.Reacts with Si to form Silicide.– Acts as Getter to reduce native oxide Acts as Getter to reduce native oxide

resistance (Ti reacts with oxygen at the resistance (Ti reacts with oxygen at the bottom of the hole).bottom of the hole).

TiN prevents W from peelingTiN prevents W from peeling– Stop WF6 from reacting with Ti or SiO2.Stop WF6 from reacting with Ti or SiO2.– Called glue or adhesion layer.Called glue or adhesion layer.

W carries current from Si to W carries current from Si to interconnect and called “plug”.interconnect and called “plug”.

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Figure: TiN Glue LayerFigure: TiN Glue Layer

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Aluminum - GeneralAluminum - General

Al-alloys thin films were selected for Al-alloys thin films were selected for the first 30 years of the IC industry.the first 30 years of the IC industry.

They continue to be the most widely They continue to be the most widely used materials, although copper. used materials, although copper.

Al has low resistivity (Al has low resistivity (=2.7=2.7-cm), -cm), and its compatibility with Si and SiOand its compatibility with Si and SiO22..

Al forms a thin native oxide (AlAl forms a thin native oxide (Al22OO33) on ) on its surface upon exposure to oxygen, its surface upon exposure to oxygen, and affect the contact resistance.and affect the contact resistance.

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Aluminum - General (cont. 1)Aluminum - General (cont. 1)

Al thin films can also suffer from Al thin films can also suffer from corrosion (ex. Al dry etch may leave corrosion (ex. Al dry etch may leave chlorine residues on Al surface and chlorine residues on Al surface and lead to formation of HCl and then lead to formation of HCl and then attack the Al).attack the Al).

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Aluminum interconnectsAluminum interconnects The material used in interconnects is not The material used in interconnects is not

pure aluminum, but an aluminum alloy. pure aluminum, but an aluminum alloy. Usually with Cu (0.5-2%), sometimes with Usually with Cu (0.5-2%), sometimes with Si.Si.

The Cu in Al-alloy slows the The Cu in Al-alloy slows the electromigration (EM) phenomenon. Si electromigration (EM) phenomenon. Si slows EM slightly, used in contact level to slows EM slightly, used in contact level to prevent spiking.prevent spiking.

Al-alloys decrease the melting point, Al-alloys decrease the melting point, increase the resistivity and need to be increase the resistivity and need to be characterized (ex. Dry etch). characterized (ex. Dry etch).

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Aluminum contactAluminum contactAluminum can be used to fill contacts. Aluminum can be used to fill contacts.

Unfortunately, with Al you encounter a Unfortunately, with Al you encounter a problem that don’t finds with WCVD: problem that don’t finds with WCVD: Si dissolves into Al at high temp Si dissolves into Al at high temp (>450(>450ºC) which cause a failure called ºC) which cause a failure called “spiking”. “spiking”.

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Al contact (Cont. 1)Al contact (Cont. 1)

To prevent it To prevent it – We placed a barrier layer : TiN or TiW.We placed a barrier layer : TiN or TiW.– And by using Al-Si alloy (which And by using Al-Si alloy (which

essentially predissolving Si into the Al). essentially predissolving Si into the Al).

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Aluminum contact – process flowAluminum contact – process flow11stst Ti layer reduces contact resistance Ti layer reduces contact resistance TiN layer stops Si from from diffusing TiN layer stops Si from from diffusing

into Al (Barrier layer)into Al (Barrier layer)22ndnd Ti layer helps Al form continues Ti layer helps Al form continues

film (wetting layer)film (wetting layer)Al fills contact and forms interconnectAl fills contact and forms interconnect

TiNTi

SiO2

Al

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Al filled contact - SEMAl filled contact - SEM

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Aluminum ViaAluminum Via

If you fill a via with Al, spiking is not a If you fill a via with Al, spiking is not a problem, since the Al dose not come problem, since the Al dose not come into contact with any Si. into contact with any Si.

Barrier layers are not necessary. Barrier layers are not necessary. Most applications do still use a layer Most applications do still use a layer

of Ti, because Al forms a much of Ti, because Al forms a much smoother film on top of Ti than on smoother film on top of Ti than on SiOSiO22 (Wetting layer). (Wetting layer).

Al fills Via and forms interconnect.Al fills Via and forms interconnect.

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Aluminum filled Via - SEMAluminum filled Via - SEM

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ARC LayerARC Layer In the photolithography step that In the photolithography step that

follows aluminum, the high reflectivity follows aluminum, the high reflectivity of Al can present large problem. The of Al can present large problem. The light can pass through the PR, reflect light can pass through the PR, reflect off of the Al and expose areas of PR off of the Al and expose areas of PR that should not be exposed. that should not be exposed.

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ARC Layer (Cont. 1)ARC Layer (Cont. 1)

Therefore we deposit a layer that Therefore we deposit a layer that stops the light from reflecting off of stops the light from reflecting off of the Al. the Al.

The layer is called an “Anti Reflective The layer is called an “Anti Reflective Coating” layer or ARC layer.Coating” layer or ARC layer.

Common PVD layers are TiN or TiW.Common PVD layers are TiN or TiW.TiN has a very low reflectivity at a TiN has a very low reflectivity at a

436nm wavelength, this is the same 436nm wavelength, this is the same wavelength that the resist is exposed wavelength that the resist is exposed to during photolithography.to during photolithography.

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TiN for TiN for Hillock SuppressantHillock Suppressant Hillock Suppressant is the second purpose Hillock Suppressant is the second purpose

for the TiN Arc layers.for the TiN Arc layers. Hillocks are a result of stress relief between Hillocks are a result of stress relief between

the underlying dielectric and the metal the underlying dielectric and the metal layers. This stress arises from the different layers. This stress arises from the different thermal expansion coefficients and can thermal expansion coefficients and can cause protrusions (hillocks) of the dielectric cause protrusions (hillocks) of the dielectric into the metal. into the metal.

This is undesirable since the metal is This is undesirable since the metal is thinner, it is more susceptible to EM. thinner, it is more susceptible to EM.

TiN has a compressive film stress, it aids in TiN has a compressive film stress, it aids in suppressing the hillocks.suppressing the hillocks.

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Hillock diagramsHillock diagrams

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Hillocks – SEM Hillocks – SEM

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Metal line – stack Metal line – stack

Usually the metal line contains 4-5 Usually the metal line contains 4-5 layers:layers:

Al - This layer makes the contacts with Al - This layer makes the contacts with the Tungsten plugs. It is the primary the Tungsten plugs. It is the primary current carrier. current carrier.

TiN Layer - Creates a barrier between TiN Layer - Creates a barrier between the Al/Cu and the Titanium layers the Al/Cu and the Titanium layers because of the increasing temperature because of the increasing temperature at a downstream process will increase at a downstream process will increase the rate of the reaction of Al with Ti. the rate of the reaction of Al with Ti.

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Metal stack (Cont. 1)Metal stack (Cont. 1)

Titanium Layer - Provides an alternate Titanium Layer - Provides an alternate current path (shunt) around flaws in current path (shunt) around flaws in the primary current carrier. And thus the primary current carrier. And thus improves electromigration improves electromigration characteristics.characteristics.

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Metal stack (Cont. 2)Metal stack (Cont. 2)

TiN ARC Layer - This is an TiN ARC Layer - This is an anti‑reflecting coating which aides anti‑reflecting coating which aides lithography to keep control of critical lithography to keep control of critical dimensions and to absorb light during dimensions and to absorb light during the resist exposure. It also functions the resist exposure. It also functions as a hillock suppressant.as a hillock suppressant.

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Last metal lineLast metal line

The Titanium layers is deposited first The Titanium layers is deposited first because the last metal layer must connect because the last metal layer must connect to the bond pads that connect the to the bond pads that connect the microprocessors to the outside world. The microprocessors to the outside world. The bond pads adhere poorly to Titanium, but bond pads adhere poorly to Titanium, but they adhere well to Al/Cu. they adhere well to Al/Cu.

The Al/Cu is deposited second.The Al/Cu is deposited second. There is no TiN buffer layer between There is no TiN buffer layer between

Titanium and Al/Cu layers because there Titanium and Al/Cu layers because there are no high temperature steps.are no high temperature steps.

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Last metal line (Cont. 1)Last metal line (Cont. 1)

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Step CoverageStep Coverage

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What is step coverage ?What is step coverage ? It is a measure of how well the film covers It is a measure of how well the film covers

topography.topography.

Definitions:Definitions:ttoo = field thk t = field thk tbb/t/too = bottom coverage = bottom coverage

TTbb = bottom thk t = bottom thk tcc = cusping thk = cusping thk

H/D = Aspect Ratio (A/R)H/D = Aspect Ratio (A/R)

Before deposition After deposition

tc

to

tb

H

D

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Step coverage issuesStep coverage issues

The Aspect Ratio dependence of step The Aspect Ratio dependence of step coverage is critical into the submicron coverage is critical into the submicron regime.regime.

Cusping can lead to voids.Cusping can lead to voids. Voids in metal films can cause problems:Voids in metal films can cause problems:

– Increased resistance.Increased resistance.– Trap impurities.Trap impurities.– Non-repeatable results.Non-repeatable results.– Decrease the cross sectional area that increase Decrease the cross sectional area that increase

electromigration (high current density).electromigration (high current density).

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Void formation - SEMVoid formation - SEM

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PVD Vs. CVDPVD Vs. CVD

PVDPVD Metal is transported from target to Metal is transported from target to

substrate.substrate. Deposition is “line of sight”.Deposition is “line of sight”. Poor step coverage (can be improved by Poor step coverage (can be improved by

increasing the surface-migration ability by increasing the surface-migration ability by raising the substrate temperature).raising the substrate temperature).

CVDCVD Chemical reaction.Chemical reaction. Excellent step coverage.Excellent step coverage.

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Step coverage trendsStep coverage trends Cause:Cause:

– Devices are getting smaller.Devices are getting smaller.– Aspect Ratio are getting higher.Aspect Ratio are getting higher.

Then:Then:– Planarization process bring vias with same Planarization process bring vias with same

depth.depth.– Contact to Metal 2 was allowed only through Contact to Metal 2 was allowed only through

Metal 1.Metal 1.– Vias with sloped sidewalls but have a conflict Vias with sloped sidewalls but have a conflict

with design rules. with design rules. Sputter Sputter CVD CVD Electroplating Electroplating

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SEM interconnectsSEM interconnects

Example of contact to Metal 2 was Example of contact to Metal 2 was allowed only through Metal 1.allowed only through Metal 1.

– Dielectric layers etched awayDielectric layers etched away

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Sputter Sputter deposition for deposition for

ULSIULSI

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Sputtering – GeneralSputtering – General

Sputtering is a term used to describe the Sputtering is a term used to describe the mechanism in which atoms are ejected from mechanism in which atoms are ejected from the surface of a material when that surface the surface of a material when that surface is stuck by sufficiency energetic particles.is stuck by sufficiency energetic particles.

Alternative to evaporation.Alternative to evaporation. First discovered in 1852, and developed as First discovered in 1852, and developed as

a thin film deposition technique by a thin film deposition technique by Langmuir in 1920.Langmuir in 1920.

Metallic films: Al-alloys, Ti, TiW, TiN, Metallic films: Al-alloys, Ti, TiW, TiN, Tantalum and Cobalt.Tantalum and Cobalt.

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Reasons for sputteringReasons for sputtering

Use large-area-targets which gives Use large-area-targets which gives uniform thickness over the wafer.uniform thickness over the wafer.

Control the thickness by Dep. time Control the thickness by Dep. time and other parameters.and other parameters.

Control film properties such as step Control film properties such as step coverage (negative bias), grain coverage (negative bias), grain structure (wafer temp), etc.structure (wafer temp), etc.

Sputter-cleaned the surface in vacuum Sputter-cleaned the surface in vacuum prior to deposition. prior to deposition.

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Sputtering stepsSputtering steps

1.1. Ions are generated and directed at a Ions are generated and directed at a target.target.

2.2. The ions sputter targets atoms.The ions sputter targets atoms.

3.3. The ejected atoms are transported to The ejected atoms are transported to the substrate.the substrate.

4.4. Atoms condense and form a thin Atoms condense and form a thin film.film.

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The billiard ball modelThe billiard ball model

There is a probability that atom C will There is a probability that atom C will be ejected from the surface as a result be ejected from the surface as a result of the surface being stuck by atom A.of the surface being stuck by atom A.

In oblique angle (45In oblique angle (45ºº-90-90º) there is º) there is higher probability for sputtering, higher probability for sputtering, which occur closer to the surface. which occur closer to the surface.

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Sputter yieldSputter yield

Defined as the number of atoms Defined as the number of atoms ejected per incident ion.ejected per incident ion.

Typically, range 0.1-3.Typically, range 0.1-3. Determines the deposition rate.Determines the deposition rate. Depends on:Depends on:

1.1. Target material.Target material.

2.2. Mass of bombarding ions.Mass of bombarding ions.

3.3. Energy of the bombarding ions.Energy of the bombarding ions.

4.4. Direction of incidence of ions (angle).Direction of incidence of ions (angle).

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Sputter yield (Cont. 1)Sputter yield (Cont. 1)

Sputter yield peaks at <90Sputter yield peaks at <90º.º.Atoms leave the surface with cosine Atoms leave the surface with cosine

distribution.distribution.

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Process conditionsProcess conditions

Type of sputtering gas. In purely Type of sputtering gas. In purely physical sputtering (as opposed to physical sputtering (as opposed to reactive sputtering) this limits to noble reactive sputtering) this limits to noble gas, thus Argon is generally the gas, thus Argon is generally the choice.choice.

Pressure range: usually 2-3 mTorr (by Pressure range: usually 2-3 mTorr (by glow discharge).glow discharge).

Electrical conditions: selected to give Electrical conditions: selected to give a max sputter yield (Dep rate).a max sputter yield (Dep rate).

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Sputter deposition film growthSputter deposition film growth

Sputtered atoms have velocities of Sputtered atoms have velocities of 3-6E5 cm/sec and energy of 10-40 eV.3-6E5 cm/sec and energy of 10-40 eV.

Desire: many of these atoms Desire: many of these atoms deposited upon the substrate.deposited upon the substrate.

Therefore, the spacing is 5-10 cm.Therefore, the spacing is 5-10 cm.The mean free path is usually The mean free path is usually

<5-10 cm.<5-10 cm.Thus, sputtered atoms will suffer one Thus, sputtered atoms will suffer one

or more collision with the sputter gas.or more collision with the sputter gas.

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Sputter dep. film … (Cont. 1)Sputter dep. film … (Cont. 1)

The sputter atoms may therefore:The sputter atoms may therefore:1.1. Arrive at surface with reduce energy Arrive at surface with reduce energy

(1-2 eV).(1-2 eV).

2.2. Be backscattered to target/chamber.Be backscattered to target/chamber.

The sputtering gas pressure can The sputtering gas pressure can impact on film deposition impact on film deposition parameters, such as Dep rate and parameters, such as Dep rate and composition of the film.composition of the film.

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Sputtering - methodsSputtering - methods

Reactive sputteringReactive sputteringRF sputteringRF sputteringBias sputteringBias sputteringMagnetron sputteringMagnetron sputteringCollimated sputteringCollimated sputteringHot sputteringHot sputtering

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Reactive sputteringReactive sputtering

Reactive gas is introduced into the Reactive gas is introduced into the sputtering chamber in addition to the sputtering chamber in addition to the Argon plasma.Argon plasma.

The compound is formed by the The compound is formed by the elements of that gas combining with elements of that gas combining with the sputter material (Ex. TiN).the sputter material (Ex. TiN).

The reaction is usually occurs either The reaction is usually occurs either on the wafer surface or on the target on the wafer surface or on the target itself.itself.

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Reactive sput. (Cont. 1)Reactive sput. (Cont. 1)

In case of TiN, the Nitrogen reacts In case of TiN, the Nitrogen reacts with the Ti on the surface of the target, with the Ti on the surface of the target, and then it is sputtered onto the wafer.and then it is sputtered onto the wafer.

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RF sputteringRF sputtering

DC sputter deposition is not suitable DC sputter deposition is not suitable for insulator deposition.for insulator deposition.

RF voltages can be coupled RF voltages can be coupled capacitively through the insulating capacitively through the insulating target to the plasma, so conducting target to the plasma, so conducting electrodes are not necessary.electrodes are not necessary.

The RF frequency is high enough to The RF frequency is high enough to maintain the plasma discharge. maintain the plasma discharge.

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RF sputtering (Cont. 1)RF sputtering (Cont. 1) During the first few complete cycles more During the first few complete cycles more

electrons than ions are collected at each electrons than ions are collected at each electrode (high mobility), and cause to electrode (high mobility), and cause to negative charge to be buildup on the negative charge to be buildup on the electrodes. electrodes.

Thus, both electrodes maintain a steady-Thus, both electrodes maintain a steady-state DC potential that is negative with state DC potential that is negative with respect to plasma voltage, Vrespect to plasma voltage, Vpp..

A positive VA positive Vpp aids the transport of the aids the transport of the slower positive ions and slow down the slower positive ions and slow down the negative electrodes.negative electrodes.

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RF sputtering (Cont. 2)RF sputtering (Cont. 2)

The induced negative biasing of the target The induced negative biasing of the target due to RF powering means that continuous due to RF powering means that continuous sputtering of the target occurs throughout sputtering of the target occurs throughout the RF cycle. the RF cycle.

But it is also means that this occurs at both But it is also means that this occurs at both electrodes.electrodes.

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RF sputtering (Cont. 3)RF sputtering (Cont. 3)

The wafer will be sputtered at the The wafer will be sputtered at the same rate as the target since the same rate as the target since the voltage drops would be the same at voltage drops would be the same at both electrodes for symmetric system.both electrodes for symmetric system.

It would thus be very difficult to It would thus be very difficult to deposit any material in that way. deposit any material in that way.

Smaller electrode requires a higher RF Smaller electrode requires a higher RF current density to maintain the same current density to maintain the same total current as the larger electrode.total current as the larger electrode.

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RF sputtering (Cont. 4)RF sputtering (Cont. 4)

By making the area of the target By making the area of the target electrode smaller than the other electrode smaller than the other electrode, the voltage drop at the electrode, the voltage drop at the target electrode will be much greater target electrode will be much greater than at the other electrode.than at the other electrode.

Therefore almost all the sputtering will Therefore almost all the sputtering will occur at the target electrode.occur at the target electrode.

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Bias sputteringBias sputtering In addition, sometimes sputtering of the In addition, sometimes sputtering of the

wafer is desirable. This is done by reversing wafer is desirable. This is done by reversing the electrical connections.the electrical connections.

One application would be for precleaning One application would be for precleaning the wafer before the actual deposition.the wafer before the actual deposition.

During this step, a controlled thickness of During this step, a controlled thickness of surface material is sputtered off the wafer, surface material is sputtered off the wafer, removing any contaminants or native oxide.removing any contaminants or native oxide.

A film can then be sputter deposited A film can then be sputter deposited immediately afterward without breaking the immediately afterward without breaking the vacuum. vacuum.

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Bias sputtering (Cont. 1)Bias sputtering (Cont. 1)

Useful for cleaning contact/vias.Useful for cleaning contact/vias.Sputter etching has serious problems Sputter etching has serious problems

as particles.as particles.

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Magnetron sputteringMagnetron sputtering Here magnets are used to increase the Here magnets are used to increase the

percentage of electrons that take part in percentage of electrons that take part in ionization events, and the ionization ionization events, and the ionization efficiency is increased significantly.efficiency is increased significantly.

A magnetic field is applied at right angle to A magnetic field is applied at right angle to electric field by placing large magnets electric field by placing large magnets behind the target.behind the target.

This traps the electrons near the target This traps the electrons near the target surface, and causes them to move in spiral surface, and causes them to move in spiral motion until the collide with an Ar atom.motion until the collide with an Ar atom.

Dep rate increases up to 10-100 times faster Dep rate increases up to 10-100 times faster than without magnetron configuration. than without magnetron configuration.

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Magnetron sput (Cont. 1)Magnetron sput (Cont. 1) Magnetron sputtering can be done in either Magnetron sputtering can be done in either

DC or RF modes, but the former is more DC or RF modes, but the former is more common.common.

Target erodes rapidly in the ring region Target erodes rapidly in the ring region resulting in a deep groove in the target face, resulting in a deep groove in the target face, which cause to non-uniformity film.which cause to non-uniformity film.

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Collimated sputteringCollimated sputtering

A small range of arrival angles during A small range of arrival angles during deposition can cause nonuniform film.deposition can cause nonuniform film.

However, if material is required to be However, if material is required to be deposited into of a deep contact/via, a large deposited into of a deep contact/via, a large angle distribution can cause problems (like angle distribution can cause problems (like little deposition at the bottom of the via, or little deposition at the bottom of the via, or cusping formation).cusping formation).

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Collimated sput. (Cont. 1)Collimated sput. (Cont. 1)

One way to improve this by having a One way to improve this by having a narrow range of arrival angles, while narrow range of arrival angles, while atoms arriving perpendicularly to the atoms arriving perpendicularly to the wafer. wafer.

This method called collimated This method called collimated sputtering (first proposed in 1992).sputtering (first proposed in 1992).

A hexagonal holes plate is placed A hexagonal holes plate is placed between the target and the wafer. between the target and the wafer.

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Collimated sput. (Cont. 2)Collimated sput. (Cont. 2)

As the sputtered atoms travel through the As the sputtered atoms travel through the collimator toward the wafer, only those with collimator toward the wafer, only those with nearly normal incidence trajectory will nearly normal incidence trajectory will continue to strike the wafer. continue to strike the wafer.

The collimator thus acts as a physical filter The collimator thus acts as a physical filter to low angle sputter atoms.to low angle sputter atoms.

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Collimated sput. (Cont. 3)Collimated sput. (Cont. 3)

70-90% 70-90% of atoms are filtered and therefore of atoms are filtered and therefore the Dep rate is significantly reduced.the Dep rate is significantly reduced.

In addition the collimator should be cleaned In addition the collimator should be cleaned and replaced, resulting additional downtime and replaced, resulting additional downtime of the tool = COST.of the tool = COST.

Suitable for contact and barrier layers Suitable for contact and barrier layers where lot of material is not needed to be where lot of material is not needed to be deposited.deposited.

Benefit with cover the bottom of Via’s. Benefit with cover the bottom of Via’s.

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Collimated sput. (Cont. 4)Collimated sput. (Cont. 4)The next figure shows the bottom The next figure shows the bottom

coverage of collimated sputtering coverage of collimated sputtering compared to conventional versus compared to conventional versus contact aspect ratio. contact aspect ratio.

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Hot sputteringHot sputtering

Hot sputtering is a method used to fill Hot sputtering is a method used to fill spaced during deposition as well as to spaced during deposition as well as to improve overall coverage.improve overall coverage.

The basic idea is to heat the substrate The basic idea is to heat the substrate to >450to >450ºC during deposition.ºC during deposition.

Surface diffusion is significantly Surface diffusion is significantly increased so that filling in spaces, increased so that filling in spaces, smoothing edges and planarization smoothing edges and planarization are accomplished, driven by surface are accomplished, driven by surface energy reduction. energy reduction.

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Hot sputtering (Cont. 1)Hot sputtering (Cont. 1)

Usually, a thin “cold” deposition is Usually, a thin “cold” deposition is done first with substrate at room done first with substrate at room temperature, which has better temperature, which has better adhesion to the underlying material. adhesion to the underlying material.

Then is followed by hot PVD Then is followed by hot PVD deposition. deposition.

Main drawbacks is the relatively high Main drawbacks is the relatively high temp. (reaction, thermal-budget, etc). temp. (reaction, thermal-budget, etc).

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Manufacturing methodsManufacturing methods

Thin filmThin film EquipmentEquipment Typical Typical reactionreaction

CommentsComments

AlAl Magnetron Magnetron sputtersputter

25-30025-300ººC – C – standardstandard

440-550ºC – 440-550ºC –

hot Alhot Al

Ti and TiWTi and TiW Magnetron Magnetron

TiNTiN Reactive Reactive sputteringsputtering

Ti + NTi + N22 (in (in plasma) plasma) TiN TiN

CuCu ElectroplatingElectroplating CuCu2+2+ + 2 + 2e-e- Cu Cu

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Where to Get More InformationWhere to Get More Information

S. Wolf, S. Wolf, Silicon Processing for the VLSI eraSilicon Processing for the VLSI era, , Vol 1-2.Vol 1-2.

Peter Van Zant, Peter Van Zant, Microchip FabricationMicrochip Fabrication.. Stephen A. Campbell, Stephen A. Campbell, The science and The science and

engineering of microelectronic fabricationengineering of microelectronic fabrication.. J. D. Plummer, M. D. Deal and P.B. Griffin, J. D. Plummer, M. D. Deal and P.B. Griffin,

Silicon VLSI technologySilicon VLSI technology.. J.L. Vossen and W. Kern, J.L. Vossen and W. Kern, Thin film Thin film

processing IIprocessing II..