J. Semicond. > 2015, Volume 36?>?Issue 12?> 123006

SEMICONDUCTOR MATERIALS

Interface annealing characterization of Ti/Al/Au ohmic contacts to p-type 4H-SiC

Chao Han1, Yuming Zhang1, , Qingwen Song1, 2, Xiaoyan Tang1, Hui Guo1, Yimen Zhang1, Fei Yang3 and Yingxi Niu3

+ Author Affiliations

 Corresponding author: Zhang Yuming,Email:zhangym@xidian.edu.cn

DOI: 10.1088/1674-4926/36/12/123006

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Abstract: Ti/Al/Au ohmic contacts to p-type 4H-SiC in terms of a different annealing time and Ti composition are reported. At 1050℃, proper increase in annealing time plays a critical role in the Schottky to ohmic contact conversion. With the optimized annealing time, the contact with a high Ti content yields a lower specific contact resistivity(ρc) of 6.4×10-5 Ω·cm2 compared with the low-Ti contact. The annealed surface morphology and phase resultants were examined by scanning electron microscopy(SEM) and X-ray diffraction(XRD), respectively. For the better ohmic contact, element distribution and chemical states were qualitatively identified by X-ray photoelectron spectroscopy(XPS) depth analysis. In particular, the presence of C and a Si-related phase was discussed and associated with the change in the surface status of the as-grown epilayer of 4H-SiC during annealing. The results reveal that the out-diffused C and Si atoms, with an approximate atomic ratio of 1:1 in the contact layer, can combine to form an amorphous Si-C state. The polycrystalline graphite instead of an unreacted C cluster in the whole alloyed structure and an extra nanosize graphite flake on the outermost surface of the annealed contact were confirmed by Raman spectroscopy.

Key words: 4H-SiC, p-type, ohmic contact, titanium, aluminum, gold



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Fig1.  $I$--$V$ characteristics of the Ti (50 nm)/Al/Au contact before and after annealing at 1050 ℃.

Fig2.  Comparison of TLM data for Ti/Al/Au ohmic contacts with different Ti content after annealing at 1050 ℃ for 3 min.

Fig3.  SEM images of the annealed contacts. (a) Ti (50 nm)/Al/Au for 3 min. (b) Ti (20 nm)/Al/Au for 3 min. (c) Ti (50 nm)/Al/Au for 2~min.

Fig4.  EDS analysis of the Ti (20 nm)/Al/Au contact after annealing at 1050 ℃ for 3 min.

Fig5.  XRD spectra of the Ti (50 nm)/Al/Au contact after annealing at 1050 ℃ for 2 min.

Fig6.  (Color online) XRD spectra of the Ti/Al/Au contacts with different Ti content after annealing at 1050 ℃ for 3 min.

Fig7.  XPS profile of the top layer of the Ti (50 nm)/Al/Au structure after annealing at 1050 ℃ for 3 min.

Fig8.  Core-level photoelectron spectra of the annealed Ti (50~nm)/Al/Au structure at different sputtering time (in min). (a) C 1s. (b) Si 2p.

Fig9.  Raman spectra of the annealed Ti (50 nm)/Al/Au contact before and after removing the top layer.

Fig10.  Color online) XPS profile of the residual Ti (50 nm)/Al/Au structure after Raman measurement.

Fig11.  Core-level photoelectron spectral of the annealed Ti (50~nm)/Al/Au structure at different sputtering time (in min). (a) Ti 2p. (b) Al 2p. (c) C 1s. (d) Si 2p.

Fig12.  AFM images of the surface of the 4H-SiC sample (a) before metal deposition and (b) after metallization annealing and subsequent chemical etch.

Fig13.  SEM images of the surface of (a) Ti/Al/Au contact and (b) Ti/Al contact after chemical etching.

Table 1.   Summary of layer contacts (Ti is the first layer deposited on the surface of 4H-SiC)

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Table 2.   Element weight concentrations and atomic concentrations for the Ti (20 nm)/Al/Au contact shown in Figure 4.

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    Received: 28 April 2015 Revised: Online: Published: 01 December 2015

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      Chao Han, Yuming Zhang, Qingwen Song, Xiaoyan Tang, Hui Guo, Yimen Zhang, Fei Yang, Yingxi Niu. Interface annealing characterization of Ti/Al/Au ohmic contacts to p-type 4H-SiC[J]. Journal of Semiconductors, 2015, 36(12): 123006. doi: 10.1088/1674-4926/36/12/123006 ****C Han, Y M Zhang, Q W Song, X Y Tang, H Guo, Y M Zhang, F Yang, Y X Niu. Interface annealing characterization of Ti/Al/Au ohmic contacts to p-type 4H-SiC[J]. J. Semicond., 2015, 36(12): 123006. doi: 10.1088/1674-4926/36/12/123006.
      Citation:
      Chao Han, Yuming Zhang, Qingwen Song, Xiaoyan Tang, Hui Guo, Yimen Zhang, Fei Yang, Yingxi Niu. Interface annealing characterization of Ti/Al/Au ohmic contacts to p-type 4H-SiC[J]. Journal of Semiconductors, 2015, 36(12): 123006. doi: 10.1088/1674-4926/36/12/123006 ****
      C Han, Y M Zhang, Q W Song, X Y Tang, H Guo, Y M Zhang, F Yang, Y X Niu. Interface annealing characterization of Ti/Al/Au ohmic contacts to p-type 4H-SiC[J]. J. Semicond., 2015, 36(12): 123006. doi: 10.1088/1674-4926/36/12/123006.

      Interface annealing characterization of Ti/Al/Au ohmic contacts to p-type 4H-SiC

      DOI: 10.1088/1674-4926/36/12/123006
      • 1.

        School of Microelectronics, Xidian University, Key Laboratory of Wide Band-Gap Semiconductor Materials and Devices, Xi'an 710071, China

      • 2.

        School of Advanced Materials and Nanotechnology, Xidian University, Xi'an 710071, China

      • 3.

        State Grid Smart Grid Research Institute, Beijing 102211, China

      Funds:

      Project supported by the Key Specific Projects of Ministry of Education of China(No. 625010101), the Specific Project of the Core Devices(No. 2013ZX01001001-004), and the Science Project of State Grid(No. SGRI-WD-71-14-004).

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      • Corresponding author: Zhang Yuming,Email:zhangym@xidian.edu.cn
      • Received Date: 2015-04-28
      • Accepted Date: 2015-06-04
      • Published Date: 2015-01-25

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