LJ04 CZ FZ Processes Aug2010

7/31/2019 LJ04 CZ FZ Processes Aug2010

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August 2010S. K. Bhatnagar 1

CZ and FZProcesses

Dr. S. K. Bhatnagar

Professor and Head,

R & D Center for Engg. and Science,

J. E. C. Kukas


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Mono-crystal Silicon Growth

Crystal PullingCZ Method

Floating Zone Method


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August 2010S. K. Bhatnagar 3h103


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Surface Tension

Weight of the liquid silicon pulled up is supported

by the surface tension of the melt.For 300 mm diameter wafer and 1 mm pulledmelt, weight = 165 gm

Weight of 1 meter long crystal = 165 Kg.

It is important that the pulled liquid solidifiesquickly and does not melt again.

The temp. gradient across the pulled crystal shouldbe very large.


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Czochralski (CZ) crystal growth

It involves the crystalline solidification of

atoms from a liquid phase at an interface.

The process consists of the following steps:

1. A fused silica crucible is loaded with a

charge of undoped EGS together with a

precise amount of diluted silicon alloy.

2. Evacuate the growth chamber.

3. Back-fill with inert gas prevent

atmospheric gases from entering the

chamber.


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Czochralski (CZ) crystal growth

4. Heat Crucible to 1421o C to melt Silicon.

5. Introduce seed crystal in molten silicon.

Seed crystal is slim ( 5 mm dia) and 100300

mm long with precise orientation6. The seed crystal is then withdrawn at a very

controlled rate.

7. The seed crystal and the crucible are rotatedin opposite directions while this withdrawal

process occurs.


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Crystal Growing Theory

Every impurity has a solid solubility in Siliconand a different equilibrium solubility in the

melt.

Segregation Coefficient k0 = Cs / ClCs , Cl = equilibrium concentrations of the

impurity in the solid and melt near the

interface


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Distribution of impurity in the grown crystal

Freezing Relation

Where


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h104


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August 2010S. K. Bhatnagar 11q410


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Pull Rate and Growth Rate


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Float Zone Cystal Growth

S. K. Bhatnagar 13


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August 2010S. K. Bhatnagar 14S. K. Bhatnagar 14q411b


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August 2010S. K. Bhatnagar 15S. K. Bhatnagar 15h105


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The FZ Process consists of the following steps:

1. A polysilicon rod is mounted vertically inside a chamber,

which may be under vacuum or filled with an inert gas.2. A needle-eye coil that can run through the rod is

activated to provide RF power to the rod, melting a 2 cm

long zone in the rod. This molten zone can be maintained

in stable liquid form by the coil.

3. The coil is then moved through the rod, and the molten

zone moves along with it.

4. The movement of the molten zone through theentire length of the rod melts the polysilicon and

solidifies it into a single crystal.

S. K. Bhatnagar 17


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Alternative

Alternatively the coil can be kept stationary

and the rod can be moved up or down

through the coil.


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August 2010S. K. Bhatnagar 19S. K. Bhatnagar 19Wafers from the ingot


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August 2010S. K. Bhatnagar 20S. K. Bhatnagar 20Thank You


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Schematic of a Float Zone

System for growing large

diameter boules


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August 2010S. K. Bhatnagar 22S. K. Bhatnagar 22


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Mark identificationsFig:q422


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August 2010S. K. Bhatnagar 26S K Bhatnagar 26

LJ04 CZ FZ Processes Aug2010

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