Substrate surface effect on the structure of cubic BN thin films from synchrotron-based X-ray diffraction and reflection

Transcription

1 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 Presented by Karan Sahni A

2 ABSTRACT 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. 2

3 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. 3

4 EXPERMENTAL 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 11 B + and 14 N + ions which have a energy of 150eV and current densities of 25µA/cm 2, and the temperature of the substrate is 250 C. The samples were characterized by GI-XRD then film were investigated by 4 synchrotron based XRR and SEM.

5 5 Boron Nitride Thin film

6 Beam line Specification 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 4x10 11 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. 6

7 Grazing angle X-Ray Diffraction 7

8 Result and discussion XRD patterns of each sample with grazing incident angle 1 8 The intensity of hbn (002) peak increase, while the intensity of the cbn peak decrease, with the roughness of the substrate get larger.

9 GI-XRD patterns of samples A and B at different angles 9

10 10 GIXRD for sample 3 and 4

11 X-Ray Reflectivity 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. 11

12 12 XRR for sample A and B

13 13 SEM Images

14 CONCLUSION 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. 14

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