Advances in Materials Science and Engineering

Advances in Materials Science and Engineering / 2010 / Article

Research Article | Open Access

Volume 2010 |Article ID 892792 | https://doi.org/10.1155/2010/892792

Jingwei Song, Xiying Ma, Wang Zui, Chen Wei, Zhongpin Chen, "Fabrication of Si3N4 Nanocrystals and Nanowires Using PECVD", Advances in Materials Science and Engineering, vol. 2010, Article ID 892792, 4 pages, 2010. https://doi.org/10.1155/2010/892792

Fabrication of Si3N4 Nanocrystals and Nanowires Using PECVD

Academic Editor: Dao Hua Zhang
Received26 Oct 2009
Accepted09 Mar 2010
Published29 Jun 2010

Abstract

nanowires and nanocrystals were prepared on Si substrates with or without Fe catalyst using silane () and nitrogen () as reactive gases through plasma-enhanced chemical vapor deposition (PECVD) technology. With Fe catalyst, nanowires were developed, indicating that Fe catalyst played a role for molecules directionally depositing into strings. The density of the nanowires is closely related to the density of Fe catalyst. When the density of Fe ions on the substrate was decreased remarkably, a smooth superlong nanowire with 12 m in length was fabricated. Having analyzed the growth mechanism, a growth model for nanowires was developed. The growth of nanocrystallines was attributed to be a vapor-solid (V-S) deposition process.

1. Introduction

Silicon nitride () is a versatile material, which has been widely used in ceramic engines, microelectronics, nuclear power engineering, space science [13], and other fields due to its many excellent properties, such as high temperature resistance, high strength and modulus, and good chemical stability properties. Moreover, nanoscaled materials, quantum dots [46], nanotubes [7], nanowires [8, 9], and thin nanofilms [10] have superior photoelectric [11] and mechanical properties [12, 13] for the quantum confinement effects, and therefore, the improvement in device and nanocomposite performance can be predicted [14]. Various techniques, such as catalyst-assistant synthesis of a polysilazane [15], direct nitridation process [16], amorphous silicon nitride nanopowder nitridation [17], si-containing compounds carbothermal reduction-nitridation [18], chemical vapor deposition (CVD) [19], and plasma assisted chemical vapor deposition (PECVD) are used to prepare nanomaterials. Among these available techniques, PECVD has many advantages over others. A main reason is that the chemical groups in plasma has a very high energy, which can remarkably low the reaction temperature that is very useful for synthesis of both nanocrystals and nanowires. Another significant advantage is the capability of fast deposition high quality of nanocrystals and nanowires on large area substrates. Now it has been used increasingly to synthesize various semiconductor films [20]. In this paper, using PECVD we have fabricated nanowires and nanocrystals on Si substrates with or without Fe catalyst, respectively. By decreasing the number of Fe catalyst on Si substrates to a minute, single dispersed nanowires can be obtained. Based on the analysis of scanning electronic microscopy (SEM) and X-ray diffraction (XRD), we developed a growth model for nanowires and discussed the growth mechanism as well.

2. Experiment

The studied samples were prepared on n-type Si (100) wafers by using PECVD system. Two substrates were cleaned ultrasonically with a sequence of acetone, ethanol, and deionized water, and dried by blowing N2. One was directly placed in the vacuum chamber; the other was coated Fe catalyst by dipping into a weak solution of FeCl2 with some time and then put into the chamber as well. The reactive gases were silane diluted with nitrogen gas (10%Si + 90%) and Ar (99.999%), with a volume ratio of 1 : 4. Prior to the deposition, a pretreatment of the samples in hydrogen plasma was performed at about C for 10 minutes. At deposition, the substrate temperature was fixed between 400–C, the working pressure was kept in 40–50 Pa, and the plasma power was about 50 W under an applied bias of 800 V.

In the deposition, Si, , and Ar were initially decomposed to a mixture state of Si, H, N, Ar, , and under the large bias. This mixture state is referred to as a plasma state, in which the chemical groups consisted of atoms and molecules have very high energy. A new matter of SiN was compounded feasibly at low temperatures when Si and N atoms were combined together. With SiN molecules condensed continually on the substrates, nanocrystals or nanowires were developed. The decomposition and compound processes of the experiment can be described as the following chemical reactions:

The experiment was carried out for 1 hour. The samples were removed from the chamber when they cooled to room temperature. The morphology and structure of the samples were characterized by field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD).

3. Results and Discussion

Figure 1(a) shows a surface SEM image of the sample deposited on Si substrate free of Fe catalyst at temperature of C and pressure of 40 Pa. It can be seen that many cubic crystals are scattered homogeneously on the picture. The crystals take almost identical shape, that is, a normal tetrahedron structure, as clearly shown in the enlarged picture Figure 1(b). The tetrahedron structure shows that the deposited nanocrystals are characteristic of the typical diamond structure. The size of crystals also is nearly uniform, with a mean side length of 1 m. The X-ray diffraction pattern of the sample is shown in Figure 2. The diffraction peaks from 19.7, 22.0, 26.7, 32.9, 33.69, and correspond to (101), (110), (200), (102), (201), and (301) of crystals facets, respectively. The peaks of (101) and (110) are relatively wide for some amorphous particles attached on the crystals. It confirms that the crystals are polycrystals.

For Si substrate coated with Fe catalyst by dipping in a weak FeC solution for 48 hours, nanowires were developed, as shown in the SEM images of Figure 3. Many tree-like structures made up of thin branches are distributed on the picture. We referred to the thin branches here as nanowire, on which many newly nucleated nanoparticles attached. The diameter of the nanorires is basically uniform, with a size of 0.20 m; but the length is various, from 5 to 20 m. Figure 3(b) is a magnification picture, where the nanowires with many nanoparticles are clearly seen. We note that one of the nanowires broke off, wich might be caused by the unevenly stressing and large surface tension for it is too long.

nanowires and nanoparticles were grown on Si substrates with or without Fe catalyst under the same deposition conditions, indicating that Fe catalyst has a promote action for preferring orientationally growing, which plays a key role in the synthesis of nanowires. It has been reported that Fe ions have a directional action in the growing of nanotube and nanowires materials [21]. To explore the growth mechanism, we developed a growth model for nanowires, as shown in Figure 4. Fe ions have catalysis and play the centers of nucleation to accelerate the nucleation of that absorbed on Fe ions by Van der Waals attractive force. With a strong Van der Waals attractive force, ions can promote molecules growing in a preferred orientation by fixing and decreasing the mobility of them. With deposition, small nanowires are formed and finally developed into long nanowires. Through branching in various directions, many nanowires with tree-like structure are finally completed on the substrate.

Many nanoparticles and amorphous are attached on the nanowires, which make the nanowires not very well. The particles are caused by too many molecules nucleated on the nanowires due to a large number of Fe ions on Si wafers. To reduce the useless particles, we decreased the concentration of Fe ions by shorting the dipping time of Si wafer in FeC solution to 4 hours. In addition, to diminish the amorphous and to enhance the crystallization, the reactive pressure was decreased to 40 Pa and the temperature was increased to C. As shown in Figure 5(a), a smooth, single, superlong nanowire without any nanoparticles is developed on the substrate. Like a tree growing from a large root, the superlong nanowire grows from a large spherical cluster. The total length is about 12 m, and the diameter is about 0.25 m, but becomes thinner from the bottom to the top. Moreover, the nanowire broke off at its middle, just at the mass center of the nanowire. Thus the gap may be caused by the gravity and large surface tension because the nanowire protrudes out the substrate with a slope than lies on it. Figure 5(b) is another single nanowire picture taken from other place of the sample. It grows from a cluster and ends to another one, like a long bridge between two clusters. The nanowire twisted twice showing that there is a large stress existing during growth. Obviously, by decreasing the concentration of Fe ions and the reactive pressure, the density of nanowires is significantly decreased, and the useless nanoparticles and amorphous are hardly seen on the nanowires. As a result, superlong high quality nanowires are obtained.

Since there are no liquid droplets at the tips of nanowires, which were typically observed in vapor-liquid-solid (VLS) growth mechanism [22, 23], hence in our experiment the growth mechanism of nanocrystals can be assigned to a vapor-solid (V-S) process.

4. Conclusion

A superlong single nanowire without any useless particles has been synthesized on Fe coated Si substrate using PECVD system by optimize deposition conditions including temperature and pressure. Based on the observation of SEM) we developed a model for nanowires growing, and the growth mechanism is attributed to a vapor-solid (V-S) deposition process.

Acknowledgments

This work was supported in parts by the National Natural Science Foundation of China (no. 60776004, 60976071) and the scientific project of Shaoxing city (no. 2008R40G2180006).

References

  1. M. Herrmann, C. Boberski, G. Michael, G. Putzky, and W. Hermel, “Redistribution of the liquid phase during sintering of silicon nitride,” Journal of Materials Science Letters, vol. 12, no. 20, pp. 1641–1643, 1993. View at: Publisher Site | Google Scholar
  2. G. Ziegler, J. Heinrich, and G. Wötting, “Relationships between processing, microstructure and properties of dense and reaction-bonded silicon nitride,” Journal of Materials Science, vol. 22, no. 9, pp. 3041–3086, 1987. View at: Publisher Site | Google Scholar
  3. M. J. Hoffmann and G. Petzow, “Microstructural design of Si3N4 based ceramics,” in Materials Research Society Symposium Proceedings, vol. 287, pp. 3–14, Boston, Mass, USA, December 1993. View at: Google Scholar
  4. C. Livermore, C. H. Crouch, R. M. Westervelt, K. L. Campman, and A. C. Gossard, “The Coulomb blockade in coupled quantum dots,” Science, vol. 274, no. 5291, pp. 1332–1335, 1996. View at: Publisher Site | Google Scholar
  5. S. Tarucha, “Transport in quantum dots: observation of atomlike properties,” MRS Bulletin, vol. 23, no. 2, pp. 49–53, 1998. View at: Google Scholar
  6. A. J. Nozik and O. I. Mićić, “Colloidal quantum dots of III-V semiconductors,” MRS Bulletin, vol. 23, no. 2, pp. 24–30, 1998. View at: Google Scholar
  7. G. G. Tibbetts, “Vapour grown carbon fibers,” Carbon Fibres Filaments and Composites, Kluwer Academic Publishers, Amsterdam, The Netherlands, 1990. View at: Google Scholar
  8. Y. Cui and C. M. Lieber, “Functional nanoscale electronic devices assembled using silicon nanowire building blocks,” Science, vol. 291, no. 5505, pp. 851–853, 2001. View at: Publisher Site | Google Scholar
  9. W. Yang, Z. Xie, J. Li, H. Miao, L. Zhang, and L. An, “Ultra-long single-crystalline α-Si3N4 nanowires: derived from a polymeric precursor,” Journal of the American Ceramic Society, vol. 88, no. 6, pp. 1647–1650, 2005. View at: Publisher Site | Google Scholar
  10. D.-H. Xiang, M. Chen, Y.-P. Ma, and F.-H. Sun, “Adhesive strength of CVD diamond thin films quantitatively measured by means of the bulge and blister test,” Journal of University of Science and Technology Beijing, Mineral, Metallurgy, Material, vol. 15, no. 4, pp. 474–479, 2008. View at: Publisher Site | Google Scholar
  11. L. Zhang, H. Jin, W. Yang, Z. Xie, H. Miao, and L. An, “Optical properties of single-crystalline α-Si3N4 nanobelts,” Applied Physics Letters, vol. 86, no. 6, Article ID 061908, 3 pages, 2005. View at: Publisher Site | Google Scholar
  12. A. M. Morales and C. M. Lieber, “A laser ablation method for the synthesis of crystalline semiconductor nanowires,” Science, vol. 279, no. 5348, pp. 208–211, 1998. View at: Publisher Site | Google Scholar
  13. L.-W. Yin, Y. Bando, Y.-C. Zhu, and Y.-B. Li, “Synthesis, structure, and photoluminescence of very thin and wide alpha silicon nitride (α-Si3N4) single-crystalline nanobelts,” Applied Physics Letters, vol. 83, no. 17, pp. 3584–3586, 2003. View at: Publisher Site | Google Scholar
  14. G. Gundiah, G. V. Madhav, A. Govindaraj, Md. M. Seikh, and C. N. R. Rao, “Synthesis and characterization of silicon carbide, silicon oxynitride and silicon nitride nanowires,” Journal of Materials Chemistry, vol. 12, no. 5, pp. 1606–1611, 2002. View at: Publisher Site | Google Scholar
  15. W. Yang, Z. Xie, H. Miao, L. Zhang, H. Ji, and L. An, “Synthesis of single-crystalline silicon nitride nanobelts via catalyst-assisted pyrolysis of a polysilazane,” Journal of the American Ceramic Society, vol. 88, no. 2, pp. 466–469, 2005. View at: Publisher Site | Google Scholar
  16. H. Y. Kim, J. Park, and H. Yang, “Synthesis of silicon nitride nanowires directly from the silicon substrates,” Chemical Physics Letters, vol. 372, no. 1-2, pp. 269–274, 2003. View at: Publisher Site | Google Scholar
  17. H. Zhang, S. Zhang, S. Pan, and J. Hou, “Synthesis and characterization of several α-silicon nitride nanostructures,” Journal of the American Ceramic Society, vol. 88, no. 3, pp. 566–569, 2005. View at: Publisher Site | Google Scholar
  18. C. N. R. Rao, G. Gundiah, F. L. Deepak, A. Govindaraj, and A. K. Cheetham, “Carbon-assisted synthesis of inorganic nanowires,” Journal of Materials Chemistry, vol. 14, no. 4, pp. 440–450, 2004. View at: Google Scholar
  19. Q. Wei, C. Xue, Z. Sun et al., “Fabrication of large-scale a-Si3N4 nanotubes on Si(1 1 1) by hot-wall chemical-vapor-deposition with the assistance of Ga2O3,” Applied Surface Science, vol. 229, no. 1–4, pp. 9–12, 2004. View at: Publisher Site | Google Scholar
  20. D. Hegemann, H. Brunner, and C. Oehr, “Evaluation of deposition conditions to design plasma coatings like SiOx and a-C:H on polymers,” Surface and Coatings Technology, vol. 174-175, pp. 253–260, 2003. View at: Publisher Site | Google Scholar
  21. H. Dai, J. Kong, C. Zhou et al., “Controlled chemical routes to nanotube architectures, physics, and devices,” Journal of Physical Chemistry B, vol. 103, no. 51, pp. 11246–11255, 1999. View at: Google Scholar
  22. F. Gao, W. Yang, Y. Fan, and L. An, “Mass production of very thin single-crystal silicon nitride nanobelts,” Journal of Solid State Chemistry, vol. 181, no. 1, pp. 211–215, 2008. View at: Publisher Site | Google Scholar
  23. R. S. Wagner and W. C. Ellis, “Vapor-liquid-solid mechanism of single crystal growth,” Applied Physics Letters, vol. 4, no. 5, pp. 89–90, 1964. View at: Publisher Site | Google Scholar

Copyright © 2010 Jingwei Song et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


More related articles

 PDF Download Citation Citation
 Download other formatsMore
 Order printed copiesOrder
Views998
Downloads818
Citations

Related articles

We are committed to sharing findings related to COVID-19 as quickly as possible. We will be providing unlimited waivers of publication charges for accepted research articles as well as case reports and case series related to COVID-19. Review articles are excluded from this waiver policy. Sign up here as a reviewer to help fast-track new submissions.