Crystal Defects & Contamination Reduction

Contents

Defect in Silicon

• 0-D, 1-D, 2-D, and 3-D

Contamination reduction

• Level -1 Clean factories

• Level-2 Clean Wafer

• Level- 3 Gettering

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Defects in Silicon

0-D: Point defects

1-D: Line Defects

2-D: Area defects

3-D: Volume Defect / Precipitation

Defects Types

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Various crystal defects in a SC-Lattice

a. Interstitial Impurity

b. Edge-Dislocation

c. Self interstitial

d. Precipitate

e. Agglomeration of Self-Interstitial Atom

f. Substitutional atom widening the lattice

g. Vacancy

h. Agglomeration of vacancies

i. Substitutional Impurity Atom Compressing lattice

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Schottky Defect Frenkel Defect

Interstitial arriving from surface

Point (0D) Defects

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1D-Defects Edge Dislocation

Screw Dislocation

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2D and 3D Defects

(Plummer Fig. 3-4 p 98)

2D Defect

3D Defect

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Contamination Reductions

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Level -1 Clean factories (clean the environment around the wafer)

Level-2 Clean Wafer (need to remove the particulates that adhere to wafer surfaces)

Level- 3 Gettering (collects the metal atoms in the region of the wafer away from the active device)

Level-1 Clean factories

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Classes - 10000, 1000, 100, 10, 1

• Chemical gases and DI water used in the plant are potential sources of contamination. Need to be filtered on- site.

Advanced air filtration system to remove particles

Clean rooms

(clean the environment around the wafer)

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Level -2 Wafer Cleaning

Plummer

( This process removes the particulates that adhere to wafer surfaces)

Level -2 Wafer Cleaning

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Figure 4-16 Surface Analysis techniques used to identify and quantify contamination in IC manufacturing.

Plummer

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Level -3 Gettering

Gettering steps:

1- Elements to be gettered must be ‘freed’ from any trapping site.

2- They must diffuse to the gettering site

3- Must be trapped.

Damaged region will act as ‘ sink’ for unwanted region.

Capture defects at locations for away from the device region.

(This process collects the metal atoms in the region of wafer away from the active device)

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Level -3 Gettering

Oxygen diffuses interstitially in silicon with a diffusivity given by:

Figure 4-12 Process and time cycle for a typical intrinsic gettering process

Example

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Limits and Future Trends

• Volume of clean rooms is far larger than the wafers (Cost inefficient) – One alternate approach is SMIF (Standard Mechanical Interface)

boxes, work as sealed minienvironments for wafer processing – Other approach is “mini-clean rooms”

• RCA cleaning method uses large quantities of chemicals and DI (De-ionized) water at high temperatures resulting in large amount of chemical vapors. – One alternative is to use Ohmi’s process (ozonized ultrapure water is

used), fewer chemicals used as compared to standard RCA clean – Other alternate is dry or vapor phase cleaning procedures. Mutiple-

process steps are done in different chambers of one machine minimizing the contamination between cleaning and next step.

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Limits and Future Trends cont’d

• Tighter control on oxygen concentration in CZ wafers required.

• Role of carbon in oxygen precipitation process needs to be explored.

• Can the level of cleanliness be achieved to get away with the need of gettering?

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Summary

• Particles, cleaning and gettering are key-factors of design features for a particular product.

• Three steps to minimize contaminations

– To clean the environment

– Wafer cleaning

– Gettering (Extrinsic and Intrinsic)

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Thank you !

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