Electrical Characterization of n-Type Polycrystalline 3C-Silicon Carbide Thin Films Deposited by 1,3-Disilabutane

Abstract

X-ray diffraction, Hall effect probe, and four-point probe were used to characterize the n-type doping of polycrystalline 3C-SiC ͑poly-SiC͒ thin films. The films were deposited at 800°C on SiO 2 -isolated Si͑100͒ substrates by low-pressure chemical vapor deposition using 1,3-disilabutane single precursor and ammonia. Resistivity values as low as 30 m⍀ cm were achieved. A shrinkage in the SiC lattice constant from 4.360 to 4.345 Å was observed upon doping. The carrier concentration increased with doping from 9.2 ϫ 10 15 to 6.8 ϫ 10 17 cm −3 , while mobility decreased from 2063 to 400 cm 2 /V s. The temperature coefficient of resistivity was characterized in the range of 304-638 K and decreased in magnitude with temperature from −2.4 to − 1.3% K −1 for undoped and −0.17 to − 0.10% K −1 for the most conductive samples. The crystalline quality, carrier concentration and mobility, and energy barrier height at grain boundaries are discussed and correlated to the observed resistivity variation with doping.Silicon carbide ͑SiC͒ is a wide-bandgap semiconductor with many extraordinary properties and as such, it has attracted considerable attention for high-temperature and high-voltage electronics in the past two decades. 1 Recently, this material has also been pursued for microelectromechanical systems ͑MEMS͒ in harsh environments. 2 Compared to silicon ͑the prevalent MEMS structure material at present͒, SiC is more suitable for harsh environment applications due to its superior mechanical characteristics and chemical resistance. 3-5 For MEMS applications, the mechanical properties of SiC films, such as the residual stress and stress gradient through the film's thickness, are as important as the electrical properties. In addition, low growth temperatures and the possibility of deposition on various underlying films contribute to the development of SiC machining processes.SiC has numerous polytypes depending on the stacking sequences of Si-C bilayers in the direction perpendicular to the closest packed planes. 4H-SiC, 6H-SiC, and 3C-SiC are the most investigated polytypes, where the leading number indicates the repetition of Si-C bilayers with H and C representing hexagonal and cubic crystals, respectively. The growth processes and properties of singlecrystalline SiC have been extensively studied since the 1950s. Although single-crystalline SiC films have high crystalline quality, they can only be epitaxially grown on restricted substrates and at high temperatures over 1000°C. 6 There is a growing interest in the use of polycrystalline 3C-SiC ͑poly-SiC͒ as a MEMS structural material because it can be deposited on a variety of underlying films and at reduced temperatures. 4,7 Deposition of n-type poly-SiC films at 800°C on Si and SiO 2 -isolated Si substrates through conventional low-pressure chemical vapor deposition ͑LPCVD͒ has been recently demonstrated. 8 Due to the existence of grain boundaries, the dopant incorporation and carrier transport mechanism in polycrystalline semiconductors differ from those of their single-c...

Growth and characterization of nitrogen-doped polycrystalline 3C-SiC thin films for harsh environment MEMS applications

“…The model is based on the assumption that incorporation of N atoms may act to exclude excess C atoms forming C-C bonds, which exist in regions surrounding the SiC grains, and thus enhance the formation of a more crystalline Si-C network. In fact, an enhancement in crystallinity has been reported at moderate N-doping concentration in poly-3C films deposited by 1,3-disilabutane [4,18]. Our results are consistent with these earlier findings.…”

“…According to the authors, as the doping level reaches the 10 19 cm −3 range, the reduction in the lattice constant, a, with respect to the lattice constant of the undoped film, a o , falls in the range of a/a o ∼ 10 −4 . A similar lattice shrinkage has been experimentally reported for polycrystalline 3C-SiC film upon nitrogen doping [18]. The authors reported the lattice compression of about 3 × 10 −3 for the films with a carrier concentration of 6.8 × 10 17 cm −3 .…”

Robust Catalytic Gas Sensing Using a Silicon Carbide Microheater

“…The slight increase in power consumption can be offset through heater duty cycling, where the heater is turned on for only short time periods. The two microheaters have temperature coefficients of resistance that are opposite in sign, with the polysilicon resistance increasing with temperature (+350 ppm/K) and the SiC resistance decreasing with temperature (-700 ppm/K), which is comparable to previous work [11]. The sign of the microheater TCR is controlled by the competing effects of increased phonon scattering in the crystal grain (increasing resistance with temperature) and thermal activation of carriers through the grain interfaces (decreasing resistance with temperature).…”

Silicon Carbide Thin Films using 1,3-Disilabutane Single Precursor for MEMS Applications - A Review

“…Electrical properties were altered by changing the dopant precursor, NH 3 , flowrate. As the NH 3 flowrate was increased, resistivity decreased ( Figure 6), carrier concentration increased and mobility decreased (Figure 7) (22,23). Above ammonia fractions of 3% in the inlet gas mixture, the incremental increase in carrier concentration was no longer large enough to overcome the incremental decrease in mobility; hence, resistivity reached a constant, minimum value.…”

“…Increased ammonia flowrates led to increased amounts of nitrogen in the film ( Figure 3) and decreased crystallinity [16]. XPS analysis suggests that Si-N bonds predominated along with a reduction in Si-C bonds (21,22). Post-deposition annealing has been performed in order to activate more dopant atoms and reduce film resistivity.…”