cracker valve and plasma control process for reactive sputtering with selenium & sulphur · 2015....

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Cracker valve and plasma control process for reactive sputtering with Selenium & Sulphur Dr. Iván Fernández- Martínez, Ambiörn Wennberg Fernando Briones Raquel Gonzalez, Pedro Melgar Victor Bellido-González, Dermot Monaghan, Benoit Daniel, Joseph Brindley , Gencoa Ltd, UK

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  • Cracker valve and plasma control process for reactive sputtering with Selenium & Sulphur

    Dr. Iván Fernández-Martínez, Ambiörn Wennberg

    Fernando Briones

    Raquel Gonzalez, Pedro Melgar

    Victor Bellido-González, Dermot Monaghan, Benoit Daniel, Joseph Brindley , Gencoa Ltd, UK

  • Other activities include on-site process implementation, training and tuning

    GENCOA current products cover 3 sputtering related areas

    Reactive gas controller & endpoint detector

    Linear ion sources

    planar & rotatable Magnetron Sputter

    Cathodes and Magnetic Systems

  • • Introduction to reactive sputtering • Existing CIGS processing routes and one system concept • Feedback control and cracker design •Reactive sputtering of sulphur and selenium based layers with Cu, In & Zn target materials • Conclusions

    NREL

    Structure of presentation

  • Reactive Sputtering is highly unstable, but advanced control makes widespread

    production process in many sectors

    Reactive gas input

    To pumps

    Layer creation

    Sp

    utter T

    arg

    et

    Process Sensors

    Process controller

  • Objective is to bring established high volume flexible process

    to delivery of calcogens for CIGS layers

    Key technology requirement in order to implement this is the delivery of the solid Se & S species to the reactive process environment at high speed - in the vapor phase - main topic of this presentation.

  • The attraction of the reactive sputtering route has been recognised and

    several companies have sought success

    Mo

    CIG(S,Se)

    CdS or ZnS

    ITO , AZO Solyndra, Miasole, Daystar have all pursued and implemented the reactive sputtering method, but due to technical and commercial challenges all have failed.

    Older more established technologies of evaporation and sputtering with a 2nd stage selenization and sulphurization have won out – FOR NOW!

  • But it is accepted that the existing technologies cannot approach the

    theoretical maximum efficiencies of 30%

    In order to achieve the higher efficiencies total flexibility to readily change layer compositions and layer combinations with a reliable process is required.

    A pure sputter based approach can achieve this so long as the current challenges of the Se and S delivery are overcome. I ‘believe’ that the biggest technical challenge that faced Solyndra, Daystar and possibly Miasole, was lack of good control of the Se and S gas combined with lack of a fast feedback and precise dosing method.

  • Cracker zone - Up to 850°C Homogeneous gas delivery Corrosion resistant parts

    Evaporation zone – RT to 550°C Temperature control ±0.1°C Corrosion resistant parts Large capacity deposit

    Hermetic fast actuating valve

    • Fluxes from 20 msec • Flux rate up to 15 Hz • complete flux shut-off

    Principle of the gas delivery units – pulsed cracker valve – patent pending

  • Operation principle: pulsed mode

    0 1 2 3 4 5 6 7 8 90

    20

    40

    60

    80

    100

    120

    Se

    flu

    x (

    A/s

    ec

    )

    Pulsing frequency (Hz)

    20ms

    40ms

    100ms

    Aperture time

    Time OFF

    Flux ON

    Time ON

    Flux OFF

  • Test setup – 2 x planar magnetrons 0.5m long with MF power

    Effusion cell cracker for reactive gas injection

  • Response of the valve and target condition with varying pulse widths

    Time OFF

    Flux ON

    Time ON

    Flux OFF

    100ms : 1Hz

    400ms : 1Hz

    Valve actuator

    Target voltage response

  • Video of plasma appearance with Se pulse gas input

  • Plasma optical emission spectrum with pure copper (inlaid graph) & with Cu

    combined with Sulphur (main graph)

    Cu I

    510.5 nm

    515.3 nm

    521.8 nm

    200 400 600 800 10000

    2x104

    4x104

    6x104

    Inte

    nsity (

    a.u

    .)

    Wavelength (nm)

    500 520 540

    6x103

    1x104

    2x104

    Inte

    nsity (

    a.u

    .)Wavelength (nm)

  • Having a fast and stable Se & S delivery system completes the cycle required for

    total control of the process

    SENSOR INPUTS

    ACTUATOR OUTPUT

    REACTIVE GAS INJECTION

  • Hysteresis ramps: P.E.M.

    0 500 1000 1500 20000

    2

    4

    6

    8

    10

    Va

    lve

    fre

    qu

    en

    cy (

    Hz)

    Time (s)

    0

    20

    40

    60

    80

    100S

    en

    so

    r (%

    )

    Fully poisoned

    ‘Metal’

    Sulphur flow (valve duty cycle)

    Transition regime

    λ Sensor (CCD)= 510.8nm (Cu)

  • Hysteresis ramps: P.E.M. & target voltage, displays classic reactive sputtering

    behaviour which indicates needs feedback control

    0

    20

    40

    60

    80

    100

    Se

    nso

    r (%

    )

    500 1000 1500 2000 25000

    2

    4

    6

    8

    10

    Va

    lve

    fre

    qu

    en

    cy (

    Hz)

    Time (s)

    Fully poisoned

    Sulphur flow

    (valve duty cycle)

    Sensor (CCD)= 510.8nm (Cu)

    570

    600

    630

    660

    690

    Ta

    rge

    t p

    ote

    ntia

    l (V

    )

    0 500 1000 1500 20000

    2

    4

    6

    8

    10

    Va

    lve

    fre

    qu

    en

    cy (

    Hz)

    Time (s)

    Sulphur flow

    (valve duty cycle)

  • 0

    20

    40

    60

    80

    100

    SetPoint (%)

    Sensor (%)

    Sensor

    (%)

    720 740 760 780 800 820 840

    0

    20

    40

    60

    Actu

    ato

    r (%

    )

    Time(s)

    Actuator (%)

    Example of Selenium flow adjustment via feedback control of the pulsed

    cracker valve by plasma emission sensing of Se

  • Active feedback control – changing set-points and controlling compositions at

    different levels to demonstrate control

    20

    40

    60

    80

    SetPoint (%)

    Sensor (%)

    Sensor

    (%)

    300 400 500 600 700 800

    0

    20

    40

    Actu

    ato

    r (%

    )

    Time(s)

    Actuator (%)

    80% 60% 40% 80%

    SetPoint

    Cu rich S poor

    Cu poor S rich

  • -15 -10 -5 0 5 10 150

    100

    200

    300

    400

    500

    600

    700

    800

    Position (cm)

    Cu+S

    Th

    ickn

    ess (

    nm

    )

    -15 -10 -5 0 5 10 150

    25

    50

    75

    100

    S

    Cu

    C

    om

    po

    sitio

    n (

    at

    %)

    Position (cm)

    Thickness and composition distribution for a Copper Sulphide

    combination of materials

  • Example of reactively sputtered CuInGaSe2 structure - No serious

    layer or cell development to be performed

  • 300 350 400 450 500

    Inte

    nsity (

    a.u

    .)

    Wavelength (nm)

    Zn

    Cu

    In

    Zn In Cu

    Plasma emission spectrums for In, Cu & Zn in the presence of Sulphur

  • In / S

    10

    20

    30

    40

    50

    60

    70

    80

    90

    100

    Se

    nso

    r (%

    )

    500 1000 1500

    0

    2

    4

    6

    8

    Va

    lve

    fre

    qu

    en

    cy (

    Hz)

    Time (s)

    550

    600

    650

    700

    750

    800

    Ta

    rge

    t p

    ote

    ntia

    l (V

    )

    λ Sensor (CCD) = 451.7nm (In) Target potential

    Hysteresis ramps: P.E.M. & target voltage for the Indium & Sulphur system

  • In

    Indium target (In) + Sulphur (S) – target displays classical

    transition mode appearance

  • In2S3 deposition

    In2S3 In2S3:V 20 40 60

    0

    200

    400

    Co

    un

    ts (

    a.u

    .)

    2

    (103)

    (203)

    (206)

    (318) (103)

    Tetragonal -In2S3 on glass at 250ºC

  • 20

    40

    60

    80

    Se

    nso

    r (%

    )

    λ Sensor (CCD) = 307.4nm (Zn)

    Target potential

    Zn / S

    400 800 1200

    0

    3

    6

    Va

    lve

    fre

    qu

    en

    cy (

    Hz)

    Time (s)

    600

    640

    680

    Ta

    rge

    t p

    ote

    ntia

    l (V

    )

    Hysteresis ramps: P.E.M. & target voltage for the Zinc & Sulphur system

  • The control process is good and rotatable magnetrons are better for

    cleanliness and productivity

    • A rotating target is self-cleaning so is an easier process to control compared to planar type targets

    • Rotating targets offer higher rates and longer lifetimes

    • CuGa, CuIn, CuInGa, In, Zn rotatable targets are readily available

  • • A fast feedback process for reactive sputtering of several layers in a CIGS cell has been shown

    • CuInGa, Zn, In elements can be combined with both S and Se with a high degree of control and in varying combinations

    • This technology makes the highly developed graded structures possible that will be required to improve cell efficiency

    • The 2nd stage selenization / sulphurization can be removed

    • A single stage purely sputtered cell is readily achievable with non-reactive and reactive sputtering

    General Conclusions

    References attributed to Niki et al, Prog. Photovolt. Res. Appl. 2010 18 453-466

  • Employment opportunities exist at Gencoa for people with good

    scientific backgrounds or with plasma knowledge.

    Victor Bellido-González

    Dermot Monaghan

    Benoit Daniel

    Joseph Brindley

    Fernando Briones

    Ambiörn Wennberg

    Ivan Fernandez

    Thank you for listening and acknowledgments

    Raquel Gonzalez, Pedro Melgar