Presented by

Karan Sahni

A20345017

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Substrate surface effect on the structure of cubic

BN thin films from synchrotron-based X-ray

diffraction and reflection

X.M. Zhang, W. Wen, X.L.Li, X.T. Zhou

published on Dec 2012

PHYS 570

Instructor : Carlo Segre

ABSTRACT

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Cubic BN (cBN) thin film prepared by Mass ion beam deposition technique

(MSIBD) on Si substrate with different surface roughness were studied By

synchrotron-based grazing incidence X-ray diffraction (GI-XRD) and X-

ray reflectivity (XRR) measurements.

BN film composed of two phases: cubic phase (cBN) and hexagonal phase

(hBN). Cubic phase content of the thin films is dependent on the roughness of

their substrates and smooth substrate surface is helpful for the nucleation of

cBN phase.

cBN phase is mostly grown in the near surface region of the films and there is

a hBN interlayer at the film-substrate interface.

INTRODUCTION Cubic boron nitride has a structure similar to diamond and is also a super hard

material after diamond.

cBN can be used in many electronics applications since it has the widest optical

band gap among all III-V compound semiconductor and it can be doped for both

n and p type conductivity, which is still a challenge for diamond.

hBN has a structure very similar to graphite and is a sp2 bonded phase

commonly formed during the synthesis of cBN films whereas amorphous BN

(aBN) phase and turbostratic BN(tBN) phases can be formed by the cBN films

synthesized by the techniques such as sputtering, laser ablation and PECVD.

Synchrotron radiation X-ray has lots of advantages such as high flux, high

collimation, low emittance, and wide tunability in energy/wave length.

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EXPERMENTAL

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cBN films were grown on four pieces of p-type Si(001) substrates by MSID

method. To study the effects of the cBN thin film on the roughness of the

substrate ,four substrate with different surface roughness are chosen:

a) Sample A – mirror polished

b) Pre-scratched by diamond powders with diameter of .25µm, 1µm, and

3µm(sample B,C and D respectively).

The deposition was carried out at a pressure of 10-8 mbar by alternately deposit

11B+ and 14N+ ions which have a energy of 150eV and current densities of

25µA/cm2, and the temperature of the substrate is 250˚C.

The samples were characterized by GI-XRD then film were investigated by

synchrotron based XRR and SEM.

Boron Nitride Thin film

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Beam line Specification

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The GIXRD and XRR test were out at BL14B1 beamline of shanghai

Synchrotron radiation facility(SSRF), the wavelength of the X-ray is

.124nm(energy 10Kev).

The storage ring energy of SSRF is 3.5 GeV.

BL14B1 is a bending magnet beamline with the photon flux of about 4x1011

photons per second.

The data were collected by a NaI scintillation detector.

The GI-XRD data were analyzed by the program JADE 5, and XRR data was

analyzed by program parratt 32.

The SEM test was carried out by a LEO 1530 VP type microscopy.

Grazing angle X-Ray Diffraction

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Result and discussion

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XRD patterns of each sample

with grazing incident angle 1˚

The intensity of hBN (002) peak increase, while the intensity of the cBN

peak decrease, with the roughness of the substrate get larger.

GI-XRD patterns of samples A and B at different angles

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GIXRD for sample 3 and 4

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X-Ray Reflectivity

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The profile of the reflected X-ray curve is determined

by three factors:

a) A higher the electron density makes the total angle

bigger

b) A smoother surface makes the slope of the curve

smaller,

c) The thicker film makes the fringes closer if both the

surface and interface are smoother enough.

XRR for sample A and B

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SEM Images

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CONCLUSION

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BN films were grown on four Si(001) substrate in which one is

unprocessed and other three are polished by diamond powder with

different sizes to obtain different substrate surface roughness. The

cBN phase content of the films depends on the roughness of their

substrate and the smooth Si substrate surface is helpful to obtain

cBN thin film with high quality. Synchrotron based GI-XRD and

XRR are proved to be powerful techniques to analyze the

structure of cBN thin films and even can give more information

than FTIR technique.

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