Structural analysis of CuIn alloy films with XPS depth profiling by ion etching

1
Structural analysis of Cu-In alloy films with
XPS depth profiling by ion etching

• Shogo Sato, Takeo Nakano, and Shigeru Baba
• Dept. of Appl. Phys, Seikei Univ., Japan

2
Previous Results

• T.Nakano, T.Suzuki, N.ohnuki and S. Baba,
• Thin Solid Films 334 (1998) 192.
• When the film composition was near CuIn12 ,
  was observed X-ray diffraction (XRD) pattern,
  which indicated the C16 type crystal structure of
  CuIn2. Peaks of In metal phase were also observed
  in films where the composition of In exceeded
  67.5 at. .

• T.Nakano, H.Mizuhashi, and S. Baba, presented
• at the 1997 MRS Fall Meeting,Boston, MA, 1997
• The AFM observation of the morphology of the
  film elucidated droplet-like islands on the film
  surface, and the surface roughness increased
  rapidly for the compositional range beyond 67.5
  at. of In .

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Motivation

• We would like to report some atomistic behavior
  of indium in the Cu-In alloy system from the
  structural modification after the heat treatment.
  
• analyzed in an XPS apparatus with
  depth-profiling technique by sputter etching

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Process Flowchart
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Conditions

• Manufacturing film

Pressure Substrate Atomic concentration Evaporatio
n rate
10-4 Pa Mo 55.0, 60.0, 62.5, 65.0, 67.5, 70.0
at. 0.03 nm/s for both Cu and In

• Measurement

Pressure X-ray Measurement temperature Annealing
10-6 Pa MgKa(1253.6eV) -100? 120? 1hour
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XPS Spectra
Before Anneal
After Anneal
In 3d
In 3d
Cu 2p
Cu 2p
Mo 3d

• Cu signal is weak
• Surface is mostly covered with In, regardless of
  the In concentration.

• No strong signal from Cu
• Mo signal comes to appear.

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DATA Processing

• Obtained 0.2 eV step
• 5-point smoothing
• Savitzky-Golay method
• Satellite peak removal
• due to x-ray source
• Background subtraction
• Shirley method
• Normalization
• the sensitivy factor divided from the Handbook of
  Perkin-Elmer

X-ray Photoelectron Peaks
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Depth Profiling (67.5at.)
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Discussion (1)

• Before Anneal
• Indium is high at the surface.
• In decrease and the ratio of In/Cu becomes
  constant.
• Finally Mo is exposed, the ratio of In/Cu decays
  exponentially.
• A trace of In can be observed even after a long
  time when In is high.
• After Anneal
• The signals of Cu and In remain for long time.
• There is difference in compositional ratio of
  In/Cu.

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Island-shrink model
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Last part of the depth profile (after anneal)
a constant ratio of In/Cu

Mo is exposed before the sputter-etching.
island structure of Cu-In alloy
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Last part of the depth profile (after anneal)
a constant ratio of In/Cu

a convex nature clearly
island structure
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Last part of the depth profile (after anneal)
The compositional ratio of In/Cu varied in a
different manner with time.
island of CuIn2

islands of pure In
The different values of a in eq.(1). The mixture
of different quadratic functions were realized
eventually.
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Summary

• Depth profiles of sequentially deposited Cu-In
  films and those of before-and-after the heat
  treatment could be explained from the structural
  viewpoint.
• Films had a layered structure just after the
  deposition, while 3-D island structures were
  formed after the annealing.
• For films whose In contents were beyond CuIn2,
  extra In atoms formed islands of a different
  type.