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Lecture 9

Ion – surface interactions

References:

1) L.C. Feldman, J.W. Mayer (1986) Fundamentals of Surface and Thin Film Analysis.

2) Y. Wang, M. Nastasi (2010, or previous edition) Handbook of Modern Ion Beam Materials Analysis.

3) The Stopping and Range of Ions in Matter (SRIM), http://www.srim.org/

4) SIMNRA, 6.0; http://home.rzg.mpg.de/~mam/

Part I

• Why Ions? Ion-solid interactions

• Stopping and Range of Ions in Matter (SRIM)

Part II Application of ion beams:

- Sputtering

- Rutherford backscattering spectrometry (RBS), elastic recoil detection

- Secondary Ion Mass Spectrometry (SIMS)

- How to fabricate via ion implantation

Part I: Ion-solid interactions

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(1) elastic scattering

(2) fast recoils arising from elastic scattering

(3) steering effects due to the crystalline

structure of target atoms

(4) inelastic processes: energy loss as a

function of depth

(5) nuclear reactions

(6) interference of elastic scattering and

nuclear interaction amplitudes, which leads to

so-called resonant scattering

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3

Elastic Collisions

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M2

Z4,M4

M1

E0

θ

E0=0

E1

M2

M1

E2 z1

Z2

(Eq.3) sinsin0

(Eq.2) coscos

(Eq.1) 2

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2

1

2

1

2211

22111

2

22

2

11

2

1

vMvM

vMvMvM

vMvMvM

3

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Advantages of Ion Beams

• Can be used for material modification and analysis

• Mass Specific

- Kinematic factor

• Cross sections are very well known

• Good depth resolution

• Penetrating (can access buried interfaces)

• What about substrate?

- can use channeling and blocking effects

2

21

1

22

1

2

2

1

cossin

MM

MMMEE o

Lecture 15 6

Ion channeling and blocking

• Si(111) Si (diamond structure)

• Si(111) – side view

)110( )112(

)110(

)112(

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Kinematic Factor, k

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From Eq. 2 and 3, eliminating first, then v2, one finds the ratio of particle

velocities, and we can show that the energy of projectile (M1) after collision can

be found by the following relationship:

2

12

1

2/122

1

2

201

cossin

MM

MMMEE

2

12

1

2/122

1

2

21 cossin

MM

MMM

E

Ek

o

Ratio of E1 and E0 is called kinematic factor:

Plot of the kinematic factor, k, vs

scattering angle for H+ scattering

from various targets

k

Stopping and Ranging of Ions in Matter (SRIM)

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When an ion collides with electron clouds in the solid, it does not loose much

energy and its direction of motion is hardly change, in a contrast with

electrons colliding with electrons

18keV e- and 1800 keV He+ striking a Si3N4 layer with a SiO2 substrate

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SRIM

http://www.srim.org/ Download SRIM-2013

SRIM Setup Window

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Calculated Ion Trajectories

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2MeV He+ in Si 50keV He+ in Si 50keV Au+ in Si

2MeV He+ in Si

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Simulating sputtering conditions

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When you set up the SRIM, you can select, with a small menu at the top

right corner, the type of SRIM calculation options.

One option is to include the calculation of surface sputtering.

So activate this option and find the sputter-yield of Ne+ of silicon for your

ion energy.

If the sputter-yield is close to 1, you will remove a lot of silicon atoms

Find out sputter yield dependence as a function of:

• Energy

• Incident angle

• Mass of the element

Simulating SIMS conditions

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