Elsevier

Applied Surface Science

Volume 252, Issue 13, 30 April 2006, Pages 4672-4677
Applied Surface Science

Growth and characterization of β-SiC films obtained by fs laser ablation

https://doi.org/10.1016/j.apsusc.2005.07.087Get rights and content

Abstract

We achieved the growth of cubic silicon carbide (SiC) films on (1 0 0)Si substrates by pulsed laser deposition (PLD) at moderate temperatures such as 750 °C, from a SiC target in vacuum. The as-deposited films are morphologically and structurally characterized by scanning electron microscopy (SEM), conventional and high-resolution transmission electron microscopy (TEM/HRTEM). The morphology of deposited films is dominated by columns nucleated from a thin nanostructured beta silicon carbide (β-SiC) interface layer. The combined effects of columnar growth, tilted facets of the emerging columns and the presence of particulates on the film surface, lead to a rather rough surface of the films.

Introduction

Semiconductor electronic devices and circuits based on silicon carbide (SiC) were developed for the use in high-temperature, high-power and/or high-radiation conditions under which devices made from conventional semiconductors cannot adequately perform. The ability of SiC-based devices to function under such extreme conditions is expected to enable significant improvements in a variety of applications and systems. These include greatly improved high-voltage switching for saving energy in electric power distribution and electric motor drives, more powerful microwave electronic circuits for radar and communications, sensors and controllers for cleaner burning, more fuel-efficient jet aircraft and automobile engines [1].

The excellent physical and electrical properties of silicon carbide, such as wide band gap (between 2.2 and 3.3 eV), high-thermal conductivity (three times larger than that of Si), high-breakdown electric field, high-saturated electron drift velocity and resistance to chemical attack, defines it as a promising material for high-temperature, high-power and high-frequency electronic devices [2], [3], as well as for opto-electronic applications [4], [5].

Silicon carbide occurs in many different crystal structures, called polytypes. Despite the fact that all SiC polytypes consist in carbon atoms covalently bonded with equal numbers of silicon atoms, each SiC polytype has its own distinct set of electrical semiconductor properties. While there are more than 100 known polytypes of SiC, only two of them are presently grown and commercially available in forms acceptable for the use as an electronic semiconductor. Both of them, denoted 4H–SiC and 6H–SiC, have hexagonal crystal structure. Another polytype, denoted 3C–SiC or beta silicon carbide (β-SiC) has cubic crystal structure and, with respect to use in electronic devices, offers significant benefits over conventional hexagonal SiC polytypes. Beta silicon carbide is considered an attractive candidate window material for adverse environments, due to its isotropic properties, i.e. cubic structure, low mass density and thermal expansion, high-thermal conductivity and flexural strength, thermal shock resistance, oxidation and rain erosion resistance potential [6].

There are no fully suitable substrates in order to grow epitaxial β-SiC films, but β-SiC epilayers have been grown in the past on (1 0 0)Si substrates, despite a 20% mismatch of lattice constants and 8% mismatch of thermal expansion coefficients between SiC and Si [7]. For device integration using SiC, it is desirable to grow the SiC films on silicon substrates below 1000 °C. Since Matsunami et al. [8] pioneered in 1981 the growth of single crystalline cubic SiC on (1 0 0)Si by chemical vapor deposition (CVD); this technique became the most frequently used method for the growth of SiC thin films. More recently, it has been demonstrated that crystalline SiC films can also be grown on Si substrates by pulsed laser deposition (PLD) [9], [10], [11].

The formation of SiC films by the condensation of vapors produced by laser ablation from solid SiC targets seems to be a promising alternative to many other methods, because the composition of the reacting species is limited to the elements silicon and carbon and because of some useful aspects of the process control, given for instance by the variability of the energy or the repetition rate of the laser pulses.

We report here new attempts to synthesize 3C–SiC layers by PLD from bulk SiC target in vacuum at moderate temperatures such as 750 °C.

Section snippets

Experimental details

The SiC depositions were carried out inside a high-vacuum stainless steel irradiation chamber [12]. Prior to deposition, the chamber was evacuated down to a residual pressure of 10−4 Pa. In the experiments, we used a Ti:Sapphire (λ = 800 nm, τFWHM  50 fs) laser source. The laser beam was directed at an incidence angle of 45° with respect to the normal to the target surface. We used as target a sintered SiC pellet. To avoid the drilling caused by the multipulse laser irradiation, the target was

Results and discussions

The typical surface morphology of the films revealed by SEM (Fig. 1) is characterized by the presence of rather round shaped particles (microdroplets), most of them not larger than 200 nm.

A plan-view TEM image and the corresponding SAED pattern of a film deposited at 750 °C and a laser beam fluence of 180 mJ cm−2 are presented in Fig. 2. The TEM image (Fig. 2a) confirms at a smaller scale the surface features imaged by SEM, showing locally that particles no larger than 100 nm are scattered across or

Conclusions

We succeeded to obtain adherent thin films of pure 3C–SiC by PLD from a sintered SiC target. The deposition conditions that we used (10−4 Pa, 750 °C) led to the formation of the cubic 3C–SiC phase on (1 0 0)Si substrates. The films are not fully crystallized, consisting in a nanostructured matrix incorporating well-defined crystalline grains with elongated shapes. A high density of {1 1 1} planar defects has been observed inside the crystalline grains, most probably formed by the dissociation of

Acknowledgements

Experiments were carried out at the Ultraviolet Laser Facility operating at I.E.S.L.-FO.R.T.H. and supported by the EU through the Research Infrastructures activity of FP6 (Project: Laserlab-Europe; contract no. RII3-CT-2003-506350).

This work was supported by the Ultraviolet Laser Facility operating at FO.R.T.H. under the Improving Human Potential (IHP)—Access to Research Infrastructures program (contract no. HPRI-CT-1999-00074).

C.G. and L.C.N. are grateful for the permission to use the Philips

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