FIB Preparation of SiC Samples for Transmission
Electron Microscopy
M. Rawski1,2, J. Żuk1
Faculty of Physics, Marie Curie-Skłodowska University, Pl. M.C. Skłodowskiej 1, 20-031 Lublin, Polnad
2 Analytical Laboratory of Faculty of Chemistry, Marie Curie-Skłodowska University, Pl. M.C. Skłodowskiej 3, 20-031 Lublin, Poland
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ABSTRACT
ABOUT THE SAMPLE
Due to its unique properties, such as harsh environment resistivity, very high melting temperature and high heat conductivity
silicon carbide has recently been thoroughly investigated and is considered a very promising material for applications in high
power, high frequency and hostile environment electronics [1-2]. However, because of small values of diffusion coefficient for
the most of dopants, the most useful method of doping SiC is ion-implantation. Moreover, SiC is often used as a substrate for
growing high quality layers of other semiconductors such as ZnO [3], GaN [4], AlN [5] and graphene [6]. In all the abovementioned cases the quality of SiC crystal or layer is of utmost importance. Transmission Electron Microscopy is a very good
method for investigation of crystalline structure or defects. However, investigation of defects in layers (e.g. implanted) requires
cross-section samples, and because of the fact that SiC is a very hard material (about 9-9.5 in Mohs scale [7]) cutting crosssections and lamellas by Focused Ion Beam seems the best way to prepare such samples. In this work, the procedure of
cutting cross-section samples of ion-implanted 6H-SiC is described. Single-crystalline SiC samples doped with nitrogen during
gas-phase grow process were treated with FIB using Ga+ ion source. Platinum protective layer was selectively deposited with
ion beam and Gas Injection System to prevent surface etching. Ion energies used in the process were 16 keV and 30 keV for
deposition and etching respectively. All the systems were combined in the FEI Quanta 3D FEG Scanning Electron
Microscope.
The single-crystalline 6H-SiC samples were sequentially implanted with Al+ or N+ ions using
UNIMAS 79 implanter at the Institute of Physics at UMCS. The ion beam was at the angle 8o with
respect to the [0001] plane in order to avoid the channeling effect. The total fluencies were 91014
ions per cm2 and 81014 ions per cm2 for Al+ and N+, respectively. Sequential implantations were
performed in order to obtain quasi-rectangular shape of the dopant profiles. Current densities at the
target were kept below 0.2 A/cm2 and 0.1 A/cm2 for Al+ and N+ implantations, respectively. During all
hot implantations targets were heated to 500oC using Tectra Boraelectric HTR 1002 sample heater
in order to anneal damages produced by target irradiation. After implantation, samples were
annealed in argon for 10 minutes. Annealing temperatures were 1300oC and 1500oC.
[1] N. G. Wright, A. B. Horsfall, K. Vassilevski, Materials Today 11 16-21 (2008)
[2] C. D. Brandt et al., Silicon Carbide and Related Materials 1995 Institute Of Physics
Conference Series 142 659-664 (1996)
[3] J.Y. Lee, H.S. Kim, W. J. Lee, K. R. Ku, J. Cryst. Growth 312 2393-2397 (2010)
[4] A. Kuramata, K. Horino, K. Domen, Fujitsu Scientific & Technical Journal 34 (2) 191-203 (1998)
[5] S. Zuo et al., Crystal Growth of AlN: Effect of SiC Substrate. Materials Science inSemiconductor Processing (2012), doi:10.1016/j.mssp.2012.01.003
[6] M. Nagase, H. Hibino, H. Kageshima, et al., Nanotechnology 20 445704 (2009)
[7] M.T. Soo et al., Sensors and Actuators B 151 39–55 (2010)
SAMPLE PREPARATION PROCEDURE
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First step to obtain SiC x-cut is the deposition of
protective platinum layer. Deposition was carried out
with Ga+ ion beam and Gas Injection System (GIS).
Energy of Ga+ ions was 30kV and beam current was
10pA. For ion beam sensitive samples the deposition
should be made with the usage of electron beam to
avoid surface etching.
Next, two regular ’cross sections’ were etched with
5nA@30kV ion beam.
Further thinning of the x-cut was performed with
1nA@30kV and 0,1nA@30kV ion beams.
Pre-prepared lamella was almost cut out with
0,1nA@30kV ion beam. Only one small fragment
connecting lamella with the substrate was left.
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To lift out the lamella Omniprobe needle was inserted.
Etched region was 10x16 µm and its depth was 4 µm.
We can compare its size (small spot in the center) with
the GIS needle (right hand side) and Omniprobe needle
(left hand side) sizes.
Omniprobe needle was carefully brought nearer the
lamella until it touched the platinum layer and the
sample was soldered to the needle with platinum and
10pA@30kV ion beam. After soldering a small region
connecting sample and substrate was etched.
Cut and lifted out sample was transported by
Omniprobe needle near the copper Omniprobe lamella
carrier.
Also in this case the needle with sample had to touch
the carrier.
RESULTS
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Sample was soldered to the carrier with platinum layer
with 10pA@30kV ion beam and then connection with
the Omniprobe needle was etched with 0,1A@30kV ion
beam.
Lamella mounted to the copper Omniprobe carrier is
ready to final thinning.
Final thinning was performed with 0,1nA@30kV ion
beam and the sample surface was cleaned and
polished with 0,43nA@2kV ion beam. Energy of the ion
beam used in the last process was relatively small to
avoid damaging crystal properties of the sample
surface. Lamella prepared in such way is about 100nm
thick and is ready to be transported to the Transmission
Electron Microscope.
TEM picture of the cross-section of Al+ implanted
6H-SiC sample is presented. Highly defected
implanted layer is clearly seen beneath the Pt
protective layer and the sample surface. Thickness of
the implanted layer is about 500nm (length of the line).
The picture was taken with FEI Tecnai G2 TEM at the
Analytical Laboratory of Faculty of Chemistry at Marie
Curie-Skłodowska University in Lublin.