Si 위에 성장된 SiC 박막의 반응 Kinetics 연구

남기석, 1김광철, 2서영훈

전북대학교 화학공학부, 1전북대학교 반도체과학기술학과, 2(주)아남반도체

The Reaction Kinetics in the Growth of SiC Thin Film on Si

Kee Suk Nahm, Kwang Chul Kim1), and Young Hun Seo2)

School of Chemical Engineering & Technology and

1)Department of Semiconductor Science & Technology,

Chonbuk National University, Chonju 561-756, Rep. of Korea

2)Anam Semiconductor, Inc. Buchun, 420-712, Rep. of Korea

Introduction

Silicon carbide (SiC) is a wide bandgap semiconductor and has superior electrical properties compared to those of Si, GaAs and InP for applications in high power, high temperature, high frequency, and short wavelength devices[1]. In recent years, some research groups have reported that the 3C-SiC/Si structures are very effective to fabricate high temperature-microelecromechnical system (MEMS)[2]. The previous works [3, 4] have mostly reported the successful growth of high quality 3C-SiC on Si using single or two source precursors. However, the kinetic study should be carried out to fully understand the growth process of high quality 3C-SiC film from tetramethylsilane(TMS). The kinetic data are also very important for the design of CVD reactor for the growth of high quality SiC films.

In this work, the growth mechanism of SiC films on Si has investiagted experimentally and theoretically. The structure, chemical composition, and surface morphology of the grown SiC films were measured at different growth conditions using various analytic techniques. Gaseous species in the reactor were also analyzed with a quadrupole mass spectrometer (QMS) during the deposition. A comprehensive discussion on the mechanism of void formation was also performed on the basis of the experimental results.

Results

Ⅰ. Effect of substrate temperature

We varied the substrate temperature from 800 to 1200 ℃ to investigate the effect of substrate temperature on the growth of SiC films. The flow rates of TMS and H2 were fixed at 0.3 and 200 sccm, respectively, and the growth was carried out for 10 minutes at the gas pressure of 1.2 Torr. In contrast to the fact that the formation of voids is observed in the silicon side of a SiC film grown at 1100 ℃ as was seen in Fig. 1(a), single crystalline void-free SiC films are grown in three dimensional structure at substrate temperatures of 800, 900, and 950 ℃, as typically shown in Fig. 1(b) for 900 ℃. However, it is interesting to see that the SiC films with better crystallinity grow at low temperatures. This phenomena is closely related to the low growth rate of SiC film.

Ⅱ. Effect of TMS flow rate

To investigate the effect of TMS concentration in the feeding mixture, SiC films were grown for 10 minutes at 1100 ℃ with varied TMS flow rates of 0.3 to 10 sccm under a constant H2 flow rate of 200 sccm. cross-sectional transmission electron microscopy (XTEM) photographs and transmission electron diffraction (TED) patterns showed that voids are detected in SiC film grown at a TMS flow rate of 0.3 sccm, while void-free films grow at the TMS flow rates above 3 sccm. This indicates that void-free SiC films might grow at higher TMS flow rates. It is interesting to observe that the thickness of SiC film grown at 0.3 sccm (89 mm) is thicker than that at 3 sccm (40 mm). TED patterns revealed that the crystallinity of SiC films deteriorates with increasing TMS flow rate. At low TMS flow rates single-crystalline SiC films are grown, while polycrystalline SiC films are grown at high TMS flow rates. At low TMS flow rates, a SiC films with better crystallinity grows because the supply rates of Si and C atoms are slower than the migration rates of the atoms needed to achieve good crystallinity.

Ⅲ. Effect of gas pressure in the reactor:

We have investiagted the effect of the gas pressure on the growth of SiC films. The SiC films were grown for 15 minutes at gas pressures of 1.7 and 12 Torr. The experiments were carried out at a temperature of 1100 ℃ and flow rates of 100 sccm of H2 and 0.5 sccm of TMS. The thickness of the SiC film decreases from 286 nm at 1.7 Torr to 73 nm at 12 Torr. Meanwhile, voids are observed to be formed on the Si side of the SiC/Si interface for both the samples, and the average size of voids decreases with the increased pressure.

Ⅳ. Gas analysis of decomposition of tetrametylsilane

In order to study the chemical species of tetrametysilane decomposed at the growth temperature, the partial pressures of typical chemical species observed in QMS spectra are depicted as a function of the temperature as shown in Fig. 2 (a) and (b). It is clearly observed that with increasing the temperature, the partial pressures of hydrocarbon related species increase, while those of silicon related species decrease. The partial pressures of methyl radical (CH3·) and CH4 increase significantly at the temperatures above 1100 ℃, as shown in Fig. 2(a). CH4 seems to be formed by the reaction of CH3· with hydrogen. Figure 2(a) also includes the data for the partial pressures of C2H2, C2H3·, and C2H4. This indicates that CH3· plays a significalt role in the growth of SiC films. On the other hand, the partial pressures of Si related species, Si(CH3)n (n=1-3) and SiHn (n=1-3), drastically decrease with the temperature and completely decompose at higher temperatures into Si atom and hydrocarbon gases including H2, as shown in Fig. 2(b).

Ⅴ. The growth mechanism of SiC films on Si

The initial growth mechnism of SiC film on Si substrate was investigated using atomic scale calcuation. The tight binding method of the density functional theory was employed to clearly show how CH3·  radicals and Si atoms participate into the growth reaction of SiC films. The CH3· radical adsorbed on hydrogen treated cleaned Si surface as a carbon source because the number and diffusivity of CH3· radical are much higher than those of other hydrocabon gases. The CH3· radical adsorbed on Si surface is energetically very stable. At high temperature, however, the adsorbed CH3· radical decomposes into CHx (x<3) species, or comes under the attack by another CH3· in the atmosphere of abundant CH3· to produce the adsorbed CHx (x<3) species and CH4 gas, and subsequently CHx bond is brocken by reacting with Si atom to liberate H2 gas, leaving the formation of SiC bond. Gaseous Si atom are absorbed at hollow bridge site on C-terminated surface by surface migration or by direct arriving.

References

[1] P. Liaw and R. F. Davis, J. Electrochem. Soc., 132(3), 642 (1985).

[2] M. Mehregany, C. A. Zorman, N. Rajan and C. H. Wu, Proceedings of the IEEE,

86(8), 1594 (1998).

[3] Kwang Chul Kim, Kee Suk Nahm, Eun-Kyung Suh, and Young Gyoo Hwang,

J. Cryst. Growth, 197, 841 (1999).

[4] Y.H. Seo, K.C. Kim, H.W. Shim, K.S. Nahm, E.K. Suh, H.J. Lee, D.K. Kim,

and B.T. Lee, J. Electrochem. Soc., 145(1), 292(1998).

(a)                                      (b)

Figure. 1. Cross-sectional TEM micrographs and TED patterns of 3C-SiC films              grown at (a) 1100 and (b) 950 ℃.

(a)                                       (b)

Figure 2. Dissociation of (a) hydrocarbon related species (m/e=15, 16, 26, 27, 28)

and (b) Si related species (m/e=29, 31, 43, 44, 45, 72, 73, 74) as a

function of temperature at 1500 sccm H2 flow rate and 1.0 sccm TMS

flow rate in QMS analyzer.

Fig. 3. FT-IR Spectrum for SiC films grown on Si substrates as a function of

TMS flow rate : (a) 0.5, (b) 1.0, (c) 3.0, and (d) 5.0 sccm