Introduction
Electro Static Chuck (ESC) is based on the force of attraction between charged plates of a capacitor. For designing ESCs, the ESC can be regarded as a capacitor with a conductive plate (The Lower Electrode), an insulating layer (Coating on the Electrode), and another conductive plate (The Wafer).

To maximize the clamping force out of few factors, the insulating. Material needs to have as high a dielectric constant as possible. Polyimide as insulating source is widely applied for the industry. Although it has shown some weaker points at manufacturing sites such as lifetime, handling attention for cleaning ESC and process of assembling chamber.

To alternate these difficulties, Ceramic Coated ESC has been developed without a minimal change of present procedure.

Polyimide vs. Ceramic Coating
Adopting of a dielectric material is considered by electrical properties, the workability to a thin quality film, and the ability to clamping force under high voltage.

The following table shows the properties of some typical insulating sources.

Property
Quartz
Sapphire
Polyimide
Alumina (Ceramic)
Dielectric Constant
3.8
7.5 - 10.5
3.4
9 - 10
Thermal Conductivity
1.46
42
0.1 - 0.35
35
Thermal Melting Temperature
1100
1800
320
1800

The higher the dielectric constants, the thicker the insulating layer can be. The thicker insulator makes the ESC's lifetime last longer.

Capability of absorbing the heat from plasma operating is one of ability of elements to reduce the "Shorts" from contamination on the surface of ESC.


Polyimide ESC
Polyimide has been quite an adequate material for the dielectric layer to manufacturing of ESC's.

However, Polyimide ESC has suffered from following difficulties on operating sites.
  • Separation between polyimide film and pedestal around edge rim - causing from losing adhesive's ability. Figure 1 - B
  • Exposure of aluminum around edge rim from worn-out of thin coating over pedestal body - causing from cleaning & plasma. Figure 1 - C
  • Vulnerable material to heat and physical impacts from normal handling procedures needs a great attention for contamination free between a wafer and ESC and installing or carrying. Figure 1 - A
  • Space between polyimide and edge rim causes an unstable temperature transferring from pedestal to wafer. Figure 1 - D




    Ceramic Coated ESC
    Plasma aided ceramic spraying method was chosen for the durable lifetime and handling of ESC under harsh environments.

    Following are changes made from the conventional polyimide ESC's.
  • Thicker layers - The higher dielectric constant can make the top layer thicker for the adequate clamping force.
  • Protected edge rim - The rim is coated with 10 times thicken than the conventional ESCs.
  • Solid material - Ceramic in nature is resistant to heat and physical contact under normal procedure.
  • High thermal conductivity - With full coverage of top surface, cooling. The wafer is much effective for stable and uniform temperature control from edge to center.




    Benefits of Ceramic Coated ESC
  • - Achieves uniform and stable wafer temperature control.
  • - Improves etch uniformity near the edge of the wafer.
  • - Extends lifetime of ESC for 3 - 5 times longer.
  • - Reduces "Shorts" caused from contaminations and scratches which might happened during installing, carrying and cleaning.
  • - Eliminates worn-outs of edge rim.
  • - Operates under the present recipe without any alterations.

    Test Results
    Testing Equipment
    Applied Materials: LTD.
    Centra 5200 Poly MXP

    Testing ESC
    1. Polyimide ESC
    2. Ceramic Coated ESC


    Helium Pressure & Leaking Test
  • As results, helium leakage of Ceramic ESC was a bit less than the polyimide's. Otherwise, both of ESCs were mostly identical in rest of them.
  • Dechucking time of ceramic ESC was 2 seconds longer compared to 5 seconds of polyimide's.

    HE PRESS
    HE FLOW
    HE LEAK
    ESC VDC
    CERAMIC
    POLYIMIDE
    CERAMIC
    POLYIMIDE
    CERAMIC
    POLYIMIDE
    4
    5.6
    7.4
    0.3
    0.4
    1588
    1576
    6
    9.3
    12.9
    0.6
    0.5
    1588
    1576
    8
    13.9
    19.8
    0.7
    0.9
    1588
    1576
    10
    19.7
    28
    1.1
    0.8
    1588
    1576
    12
    34.3
    37.3
    0.8
    1
    1588
    1576
    14
    43.1
    48
    1.4
    1
    1588
    1576




    HIGH VOLTAGE
    HE FLOW
    HE LEAK
    ESC VDC
    ESC A
    CERAMIC
    POLYIMIDE
    CERAMIC
    POLYIMIDE
    CERAMIC
    POLYIMIDE
    CERAMIC
    POLYIMIDE
    400
    19.9
    21.2
    1.3
    2.2
    423
    423
    47
    47
    600
    19.7
    20.8
    1.3
    1.9
    623
    623
    70
    70
    800
    19.6
    20.5
    0.7
    1.4
    823
    811
    82
    82
    1000
    19.5
    20.2
    0.4
    1.2
    1011
    1000
    105
    105
    1200
    19.5
    20
    0.4
    1.1
    1200
    1200
    129
    129
    1400
    19.5
    19.8
    0.4
    0.8
    1400
    1400
    141
    141
    1600
    19.3
    19.6
    0.2
    0.5
    1588
    1576
    164
    164
    1800
    19.2
    19.5
    0.1
    0.6
    1788
    1776
    176
    176




    TIME (MIN)
    ESC VDC
    ESC A
    HE FLOW
    HE LEAK
    1
    1011
    105
    19.5
    0.6
    2
    1011
    105
    19.4
    0.3
    3
    1011
    105
    19.3
    0.3
    4
    1011
    105
    19.3
    0.3
    5
    1011
    105
    19.3
    0.3
    6
    1011
    105
    19.2
    0.2
    7
    1011
    105
    19.2
    0.2
    8
    1011
    105
    19.2
    0.2
    9
    1011
    105
    19.2
    0.2
    10
    1011
    105
    19.2
    0.2




    Process Test
  • Poly Etching rate for Uniformity
  • Non-Pattern poly wafer

    Results
  • Uniformities of the both ESCs' are almost similar to each other. The 2 second longer dechucking time of ceramic ESC's made some differences on etching results.


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