Diamond and Related Materials 11(2002) 509–512
0925-9635/02/$ - see front matter䊚 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 5 - 9 6 3 5 Ž 0 1 . 0 0 6 7 2 - 0
Diamond deposition on Si
(111) and carbon face 6H–SiC (0001)
substrates by positively biased pretreatment
Te-Fu Chang*, Li Chang
Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, Taiwan 300, ROC
Abstract
The growth of textured diamond films on Si (111) and carbon face 6H–SiC (0001) has been achieved by positive
bias-enhanced-nucleation in microwave plasma chemical vapor deposition.A bias voltage of q100 to q300 V, 3% CH concentration4
in bias step, and 0.33% CH concentration in growth step were used to synthesize diamond films on Si and carbon face 6H–SiC.4
Highly oriented diamond films were observed by scanning electron microscopy and X-ray diffraction patterns.Cross-sectional transmission electron microscopy showed that the interface between diamond and Si substrate was smooth, while it was rough between diamond and SiC.It also showed that diamond films were directly grown on both substrates.䊚 2002 Elsevier Science B.V. All rights reserved.
Keywords: Diamond films; CVD; 6H–SiC; Bias
1. Introduction
Diamond, which has many excellent properties, such as wide band gap, high thermal conductivity and high hole mobility, is a promising semiconductor material for high temperature and high power electronic devices.For the purpose of electronic usage of diamond films, it is necessary to synthesize heteroepitaxial diamond films via diamond growth techniques.Microwave plasma chemical vapor deposition (MPCVD) coupled with a
bias enhanced nucleation (BEN) method is one of the
many important techniques used to obtain heteroepitax-ial diamond films without any mechanical pre-treatment. The BEN method can significantly increase the nuclea-tion density of diamond which is necessary for heter-oepitaxial growth of diamond.Jiang and Klages first reported w001x-oriented diamond films epitaxially grown on Si(001) by applying negative BEN w1x.Since then, the negative BEN method in MPCVD has been widely used by many researchers to obtain heteroepitaxial diamond films on various substrates w1–6x.On a Si(111) substrate, Yugo et al. w7x and Schreck et al. w8x reported that heteroepitaxial diamonds can also be grown by applying a negative bias in MPCVD.However, no report
*Corresponding author.Tel.: q886-3-5712121, ext.55373; fax: q 886-3-5724727.
E-mail address: [email protected](T.-F. Chang).
has shown that diamond grows on a Si(111) substrate
by positive d.c. bias pre-treatment. Positive BEN, which applies positive voltage to a substrate, can also increase the nucleation density of diamond in MPCVD w9x. Therefore, it is promising that a positive bias could provide another method of obtaining heteroepitaxial diamond films.
It has often been observed that a b-SiC interlayer forms between diamond and Si.Stoner et al.reported the formation of an interfacial layer of b-SiC and amorphous carbon on Si during negative bias treatment
w2x.Stoner and Glass also demonstrated that locally
epitaxial diamond films could be successfully obtained on SiC w3x.Due to the structural similarity of b-SiC(111) and 6H–SiC(0001), it is possible to form a
heteroepitaxial diamond films on 6H–SiC (0001).Pre-vious work by Chang et al.reported that heteroepitaxial diamond nucleation on Si face 6H–SiC is possible by negative biasing w10,11x.Li et al.also reported that textured diamond films could be successfully grown on 6H–SiC in hot-filament CVD w12,13x.Under positive bias conditions, diamond growth on both of the sub-strates has not been reported.Hence, it is of interest to deposit diamond on a 6H–SiC substrate for comparison with the results on Si.Here, we have demonstrated that textured diamond films could grow on Si(111) and the
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Fig.1.SEM images showing(111) textured diamond films grown on (a) Si (111) and (b) carbon face 6H–SiC (0001) substrates deposited
for 2.5 h growth. Bias voltage of q300 V.
Fig.2.(a) SEM images and (b) XRD pattern showing N111M texture
of diamond film deposited with positive biasing at q200 V on Si
(111) substrate for 20 h growth.
carbon face 6H–SiC(0001) substrates by positive BEN in MPCVD.
2. Experimental details
Commercially available carbon face 6H–SiC(0001) and Si(111) were selected as the substrates.Si wafers were used of the grade used for IC production.The carbon face 6H–SiC(0001) wafer, which was 1.5 inches in diameter, used for optical-electronic devices, was provided by Sterling Semi-Conductor Co.Ltd.Both substrates were received with a mirror-like polished surface.The sample size of carbon face 6H–SiC was then prepared as 3=10 mm by cutting and the size of the p-type Si(111) sample was 10 mm .The substrates2 were dipped in HF for 1 min to remove oxides, and ultrasonically cleaned with acetone for 5 min to remove contamination, followed by ultrasonically cleaning in de-ionized water before inserting into the MPCVD reactor.A tubular MPCVD reactor made of quartz, 50 mm in diameter, was used to deposit diamond.After reactant gases(mixture of CH and H ) flowed into the4 2 quartz tube, a 2.45-GHz microwave with 500 W power was input to excite the plasma, and the pressure was fixed at 20 torr.The substrates were put on a 2-cm Mo holder acting as an anode and grounded during positive
d.c. bias pre-treatment while a counter electrode made of a 2-cm diameter Mo disk was negatively biased.The distance between the two electrodes was 3 mm in the bias step and 5 mm in the growth step.The correspond-ing applied bias voltage on the substrate was in the range of q100 to q300 V.CH concentrations during4 the bias step were 3% and the biasing period was fixed for 20 min.After biasing, all samples received the same growth conditions with a CH concentration of 0.33%4 for 2.5–20 h with the bias switched off.
3. Results and discussion
The methane concentrations of 3% in bias step and 0.33% in growth step were chosen to obtain textured
(111) diamond films.Bias voltage in the range q100
V to q300 V was applied during the bias pre-treatment period.After 2.5 h growth, no continuous diamond film was formed with q100 V bias.SEM micrograph in Fig. 1a shows the morphology of a diamond film grown on Si(111) substrate for 2.5 h with biasing at q300 V.It is clearly seen that the diamond surface exhibits strong
(111) facets in triangle shape, indicating that the
dia-mond has a (111) texture.The nucleation density estimated from SEM images is approximately 1.3=109
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T.-F. Chang, L. Chang / Diamond and Related Materials 11 (2002) 509–512
Fig.3.(a) Cross-sectional TEM micrograph showing diamond
dep-osition on Si(111) substrate with biasing pretreatment at q200 V. (b) The corresponding selected area electron diffraction pattern.
Fig.4.(a) Cross-sectional TEM micrograph of diamond deposited
with positive biasing at q200 V on carbon face 6H–SiC(0001)
sub-strate.(b) The corresponding selected area electron diffraction pattern.
cmy2.No significant difference can be observed from diamond films deposited on Si substrates with biasing at q200 V, which also reveals a highly oriented (111) surface.This implies that diamond nucleation is enhanced if the bias voltage is applied above a threshold value, similar to the cases with negative bias.Fig.1b
shows diamond grown on the carbon face of
6H–SiC(0001) for 2.5 h with biasing at q300 V.The diamond film also has a similar morphology of (111)
texture to that on Si.Compared with Fig.1a, diamond grains on the carbon face of 6H–SiC are relatively smaller than on Si.The nucleation density estimated from Fig.1b is 1.5=10 cm9 y2, slightly higher than on Si.The SEM image and X-ray diffraction(XRD) pattern
of a diamond film grown on Si substrate for 20 h with biasing at q200 V are shown in Fig.2a,b, respectively. The texture of the diamond film is improved over that with shorter growth periods, as shown in Fig.1a.The strong (111) peak of diamond can be seen in the XRD
pattern, indicating that the diamond film has (111)
preferred orientation.
The TEM micrograph in Fig.3a shows the interfacial region between diamond and Si from a sample deposited with bias voltage of q200 V.The interface between diamond and Si is relatively smooth, suggesting that the etching on the Si surface is, if any, insignificant during bias step.In Fig.3b, in a selected-area diffraction(SAD) pattern, only the diamond (111) ring can be seen in addition to Si diffraction spots, implying that the
for-mation of a SiC crystalline interlayer was absent in our films.On the diamond (111) ring, strong diffraction
spots are also seen around Si (111) spots, suggesting
that there may be a significant number of diamond particles oriented in w111x directions.The oriented dia-mond nuclei may then develop a(111) texture.Detailed
examination of interface in TEM image shows that diamond is directly grown on Si (111) over the whole
area.This is different from the result of diamond deposition on Si (001) in which an amorphous carbon
interlayer was formed during the positive bias stage
w14x.The reason is currently not known until further
studies are carried out.
The TEM micrograph in Fig.4a shows diamond growth on carbon face 6H–SiC (0001) with a bias voltage of q200 V.The diamondySiC interface is very
rough compared with the diamondySi interface.The
roughness is most likely caused by the poor conductivity of SiC, so that electron bombardment on the substrate would result in a charged effect.The corresponding SAD pattern in Fig.4b shows strong diamond (111)
spots, implying that a certain fraction of diamond grains may have oriented in parallel.Also, TEM shows that diamond is directly grown on carbon face 6H–SiC
512 T.-F. Chang, L. Chang / Diamond and Related Materials 11 (2002) 509–512
without any interlayer formation with positive BEN. Although the diamondySiC interface is rough, the
devel-opment of (111) texture of diamond is not affected in
the growth stage as shown in Fig.1b.
4. Conclusion
In conclusion, (111) oriented diamond films can be
deposited on Si (111) and carbon face 6H–SiC (0001)
by applying a positive bias voltage to the substrates in the nucleation stage.It is shown that the interface
between diamond and Si (111) was smooth under
positive bias conditions, while the interface of diamond with the carbon face of 6H–SiC(0001) was rough.The direct growth of the diamond films on both substrates without any interlayer was observed.
Acknowledgments
This work was supported by National Science Coun-cil, Taiwan, ROC under contract no.NSC 89-2216-E-009-033.
References
w1x X.Jiang, C.P.Klages, Diamond Relat.Mater.2(1993) 1112. w2x B.R.Stoner, J.T.Glass, Appl.Phys.Lett.60(1992) 698. w3x B.R. Stoner, G.-H.M. Ma, S.D. Wolter, et al., Diamond Relat.
Mater.2(1993) 142.
w4x B.R. Stoner, S.R. Sahaida, J.P. Bade, J. Mater. Res. 8(1993)
1334.
w5x C.J. Chen, L. Chang, T.S. Lin, F.R. Chen, J. Mater. Res. 10 (1995) 3041.
w6x R.Stockel, M.Stammler, K.Janischowsky, L.Ley, J.Appl.
Phys.83(1998) 5433.
w7x M.Schreck, R.Hessmer, S.Geier, B.Rauschenbach, B.
Strizker, Diamond Relat.Mater.3(1994) 510.
w8x S.Yugo, N.Nakamura, T.Kimura, Diamond Relat.Mater.7 (1998) 1017.
w9x M.Katoh, M.Aoki, H.Kawarada, Jpn.J.Appl.Phys.33 (1997) L196.
w10x L.Chang, T.S.Lin, J.L.Chen, Appl.Phys.Lett.62 (1993)
3444.
w11x L. Chang, J.E. Yan, F.R. Chen, J.J. Kai, Diamond Relat. Mater.
9(2000) 283.
w12x X.Li, Y.Hayashi, S.Lilov, S.Nishino, Jpn.J.Appl.Phys.
10B(1997) L1370.
w13x X.Li, T.Shirafuji, Y.Hayashi, S.Lilov, S.Nishino, Jpn.J.
Appl.Phys.36(1997) 6295.
