EE-452 13 - 1 Czochralski (CZ) crystal growing Si is purified - - PowerPoint PPT Presentation

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• Si is purified from SiO2 (sand) by refining, distillation and

CVD.

• It contains < 1 ppb impurities. Pulled crystals contain O (~1018

cm-3) and C (~1016 cm-3), plus dopants placed in the melt.

Czochralski (CZ) crystal growing

Plummer

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Crystal seed Molten polysilicon Heat shield Water jacket Single crystal silicon Quartz crucible Carbon heating element Crystal puller and rotation mechanism

CZ Crystal Puller

Figure 4.10

Plummer

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• All Si wafers come

from “Czochralski” grown crystals.

• Polysilicon is

melted, then held just below 1417 °C, and a single crystal seed starts the growth.

• Pull rate, melt

temperature and rotation rate control the growth

lummer

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lummer

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Silicon Ingot Grown by CZ Method

Photograph courtesy of Kayex Corp., 300 mm Si ingot

Photo 4.1

lummer

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An alternative process is the “Float Zone” process which can be used for refining or single crystal growth.

Plummer

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Float Zone Crystal Growth

RF Gas inlet (inert) Molten zone Traveling RF coil Polycrystalline rod (silicon) Seed crystal Inert gas out Chuck Chuck

Figure 4.11

lummer

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• In the float zone process, dopants and other impurities are rejected

by the regrowing silicon crystal. Impurities tend to stay in the liquid and refining can be accomplished, especially with multiple passes. (See the Plummer for models of this process)

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Flat grind Diameter grind Preparing crystal ingot for grinding

Ingot Diameter Grind

Figure 4.20

Plummer

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Internal diameter wafer saw

Internal Diameter Saw

Figure 4.23

Plummer

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After crystal pulling, the boule is shaped and cut into wafers which are then polished on one side.

Plummer

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Wafer Notch and Laser Scribe

1234567890

Notch

Scribed identification number

Figure 4.22

Plummer

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Polished Wafer Edge

Figure 4.24

Plummer

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Chemical Etch of Wafer Surface to Remove Sawing Damage

Figure 4.25

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Wafer Dimensions & Attributes

Table 4.3

Diameter (mm) Thickness (µm) Area (cm2) Weight (grams/lbs) Weight/25 Wafers (lbs)

150

675 ± 20 176.71 28 / 0.06

1.5 200

725 ± 20 314.16 53.08 / 0.12

3 300

775 ± 20 706.86 127.64 / 0.28

7 400

825 ± 20 1256.64 241.56 / 0.53

13

Plummer

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88 die

200-mm wafer

232 die

300-mm wafer

Increase in Number of Chips

• n Larger Wafer Diameters

(Assume large 1.5 x 1.5 cm microprocessors)

Figure 4.13

Plummer

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Wafer Polishing