- Email: [email protected]
Toward high-quality 3C–SiC membrane on a 3C–SiC pseudo-substrate
Materials Letters 160 (2015) 28–30
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Toward high-quality 3C–SiC membrane on a 3C–SiC pseudo-substrate Rami Khazaka a,b, Emilie Bahette a, Marc Portail b, Daniel Alquier a, Jean-François Michaud a,n a b
Université François Rabelais, Tours, GREMAN, CNRS-UMR7347, 16 rue Pierre et Marie Curie, BP 7155, 37071 Tours Cedex 2, France CRHEA, CNRS-UPR10, rue Bernard Gregory, 06560 Valbonne, France
art ic l e i nf o
a b s t r a c t
Article history: Received 8 June 2015 Received in revised form 13 July 2015 Accepted 15 July 2015 Available online 16 July 2015
The cubic polytype of silicon carbide is an interesting candidate for Micro-Electro-Mechanical-Systems (MEMS) applications due to its tremendous physico-chemical properties. The recent development of multi-stacked Si/SiC heterostructures has demonstrated the possibility to obtain a (110)-oriented 3C–SiC membrane on a 3C–SiC pseudo-substrate, using a silicon layer grown by low pressure chemical vapor deposition as a sacrificial one. However, the (110) orientation of the 3C–SiC membrane led to a facetted and rough surface which could hamper its use for the development of new MEMS devices. Then, in this contribution, an optimized growth process is used to improve the surface quality of the 3C–SiC membrane. The progress relies on the mastering of a (111) orientation for the SiC film, resulting in a smooth surface. Such an optimized structure could be the starting point for the achievement of new MEMS devices in medical or harsh environment applications. & 2015 Elsevier B.V. All rights reserved.
Keywords: 3C–SiC Micromachining LPCVD Micro-structure Membrane MEMS
1. Introduction Since three decades, the chemical vapor deposition of cubic silicon carbide (3C–SiC) on silicon substrates has been widely investigated for the achievement of electronic and mechanical devices [1–3]. However, by means of scanning spreading resistance microscopy, our groups highlighted the electrical activity of the extended defects in this material [4]. This result is a major concern for electrical device functioning as the current can flow preferentially through the defects, leading to a steep degradation of their electrical performance. Based on this statement, the elaboration of 3C–SiC-based electrical devices seems to be challenging since a drastic reduction of the electrical activity of the defects, or of their density, has not been achieved yet. Nevertheless, for Micro-Electro-Mechanical-Systems (MEMS) applications, silicon carbide presents physical and chemical properties (hardness, inertness, melting point, operative temperature etc.) perfectly appropriate. As an example, the unique mechanical properties of silicon carbide are huge benefits to achieve high-frequency resonant devices [5]. In addition, the silicon carbide biocompatibility is particularly suitable for bio and medical applications [6]. Recently, we succeeded to fabricate (110)-oriented silicon tips on 3C–SiC cantilevers, based on a Si/3C–SiC/Si heterostructure [7]. This study was also the basis for the elaboration of a (110)-oriented 3C–SiC/Si/3C–SiC/Si heterostructure, leading to an original 3C–SiC n
Corresponding author. Fax: þ33 2 47 42 49 37. E-mail address: [email protected] (J.-F. Michaud).
http://dx.doi.org/10.1016/j.matlet.2015.07.071 0167-577X/& 2015 Elsevier B.V. All rights reserved.
microstructure on a 3C–SiC pseudo-substrate [8]. To do that, the silicon epilayer was used as a sacrificial layer. This result was very promising for the achievement of new MEMS devices. For example, by using a thick 3C–SiC bottom epilayer, an entire etching of the silicon substrate can be considered, resulting in a 100% monocrystalline 3C–SiC structure. Then, thanks to the 3C–SiC physical properties, this kind of membrane could be the starting point to conceive MEMS devices involved in medical or harsh environment applications. However, the (110) 3C–SiC membrane obtained in the initial demonstration was facetted and rough, which could be detrimental for MEMS applications. The aim of this paper is to present recent notable improvements reached by our groups in order to obtain a smooth 3C–SiC membrane.
2. Experimental details The complete formation of the 3C–SiC-based membrane requires alternating growth and process stages. The improved process proposed here is based on the original process described in [8]. 2.1. Growth stage 1: formation of the Si/3C–SiC heterostructure on Si (001) substrate The Si/3C–SiC epilayers were grown on 2″ on-axis Si (001) substrate in a resistively heated hot wall reactor. Prior to the
R. Khazaka et al. / Materials Letters 160 (2015) 28–30
29
growth, a thin Si film is homo-epitaxied on the Si substrate to form a clean and non-oxidized surface to start the subsequent growth. The temperature and the pressure were respectively 1050 °C and 600 mbar. After the cleaning procedure, the temperature was decreased to 860 °C and the pressure was fixed at 200 mbar. At 860 °C, the propane (C3H8) was introduced to the chamber to start the carbonization of the Si substrate. The temperature was raised to 1075 °C under a 10 sccm C3H8 flux. The duration of the entire carbonization step was 5 min. Then, the temperature was increased to 1320 °C to start the 3C–SiC film growth using a 4 sccm flow of SiH4 and a 1.3 sccm flow of C3H8 as precursor gases and hydrogen (H2 ¼ 15 slm) as carrier gas. The duration of the growth was 60 min. After the 3C–SiC growth, the temperature was reduced to room temperature. To start the Si heteroepitaxy, the pressure was changed to 950 mbar, the H2 flux was set at 10 slm and the temperature was then increased to 900 °C to start the growth. The duration of this growth step was 20 min. Additional details on the growth parameters and the structural properties of this Si layer can be found elsewhere [9,10]. The thicknesses are respectively 5 mm and 300 nm for the 3C–SiC and the Si layers. 2.2. Technological stage 1: formation of silicon islands Consecutively to this growth step, a classical photolithography stage has been completed to obtain square silicon islands. For that, an Inductively Coupled Plasma (ICP) reactor (Corial 200IL) using a mixture of SF6, Ar and C2H4 has been used to obtain silicon patterns with vertical sidewalls. Then, the photoresist mask has been removed by means of an oxygen plasma followed by a Piranha cleaning aiming to eliminate organic contaminants. 2.3. Growth stage 2: 3C–SiC regrowth on the silicon islands This step consists of the heteroepitaxy of the 3C–SiC on top of the patterned Si epilayer which is oriented along the [110] direction. Firstly, the temperature was increased to 900 °C for a 950 mbar pressure then an annealing was performed for 20 min. The aim of this annealing is to prepare the surface of the Si epilayer. We note that a higher annealing temperature deteriorates the surface morphology [9]. After this “cleaning” procedure, the temperature was decreased to 860 °C and the pressure was fixed at 200 mbar. At 860 °C, the propane (C3H8) was introduced to the chamber to start the carbonization of the Si epilayer. The temperature was raised to 1150 °C under a C3H8 flux of 20 sccm. The duration of the entire carbonization step was 5 min. Then, the temperature was increased to 1320 °C to start the 3C–SiC film growth using a 1 sccm flow of SiH4 and a 0.5 sccm flow of C3H8 as precursor gases and hydrogen (H2 ¼15 slm) as carrier gas. The duration of the growth was 2 min. The thickness of the 3C–SiC epilayer is then around 200 nm. Under these conditions, the 3C– SiC layer is shown to be (111) oriented as attested by the 2θ ω X-Ray Diffraction (XRD) scan of the 3C–SiC/Si/3C–SiC/Si heterostructure shown in Fig. 1a. Then, for the first time, the possible growth of a (111) oriented 3C–SiC film on a (110) Si epilayer is demonstrated. The key parameter responsible on this orientation change seems to be the surface state prior to the subsequent 3C– SiC growth. Without the« cleaning » step, the final 3C–SiC film is (110) oriented as shown in Fig. 1b. This result highlights the importance of the surface state prior to the growth of the 3C–SiC film. 2.4. Technological stage 2: membrane formation The last step of the whole process consists in a wet etching of the silicon epilayer which acts as a sacrificial layer. To do that, the 2″ sample was first cleaved to longitudinally cut the defined
Fig. 1. 2θ ω XRD scan of the complete 3C–SiC/Si/3C–SiC/Si heterostructure where the final 3C–SiC epilayer is (a) (111) oriented, (b) (110) oriented. The insets depict the orientation of each layer.
structures and then immersed in a hydroxide potassium (KOH) solution. The resulting silicon etching leads to the release of the top 3C–SiC membrane. The final structure is presented in Fig. 2, for the (111) and (110) orientations.
3. Discussion In a previous work, we succeeded to elaborate, for the first time, a 3C–SiC micro-structure on a 3C–SiC pseudo-substrate by means of surface micromachining. However, the surface of the 3C– SiC membrane, which was (110) oriented, presented a rough and faceted surface. The aim of this letter is then to demonstrate that significant improvements are « easily » accessible. First, as the crystalline quality of the 3C–SiC/Si stack is directly related to the crystalline quality of the bottom 3C–SiC layer, we decided to grow a 5 mm-thick 3C–SiC for the first epilayer. In this case, as the crystalline quality of 3C–SiC films is improved with the increase of the thickness, it results in an improvement of the crystalline quality of all the successive epilayers [10]. In addition, with the same objective, we tried to improve the surface quality of the silicon epilayer as it acts as a substrate for the growth of the final 3C–SiC epilayer used to define the membrane of the structure. For that, we studied the influence of a thermal treatment aiming to prepare the Si epilayer surface for the consecutive 3C– SiC epilayer. We mention that the mechanical properties of the 3C–SiC membrane is directly linked to its crystalline quality. Thus,
30
R. Khazaka et al. / Materials Letters 160 (2015) 28–30
Fig. 2. Cross-section scanning electron microscopy images of a 3C–SiC micro-structure with a 3C–SiC membrane presenting (a) a (111) orientation and (b) a (110) orientation.
improving the material crystalline quality strengthen its mechanical properties which is desired for MEMS applications. The result of both approaches are clearly evident as, in all cases, the roughness of the final 3C–SiC membrane is significantly reduced in comparison with our previous results [8]. Indeed, the RMS roughness for 5 5 mm2 atomic force microscopy scans is limited to 18 nm for the (110) oriented 3C–SiC epilayer, with a 64 nm peak-to-peak value, whereas it drops to 9 nm for the (111) 3C–SiC epilayer, with a 38 nm peak-to-peak value. The difference in terms of roughness is explained by the crystal orientation of the 3C–SiC membrane which is (110) without cleaning and (111) consecutively to the « cleaning » procedure. Then, the (110) orientation which results to a faceted surface is more rough compared to the (111) orientation. Nevertheless, the 3C–SiC(111) growth on Si(110) suffers from the difference in symmetries between the three-fold symmetric 3C–SiC(111) and the mirror symmetric Si(110) which leads to the formation of the double positioning domains [11]. For the moment, the detailed mechanism responsible of this orientation switch is unclear but some complementary experiments are currently under investigation. Anyway, this switch is favorable for the final surface morphology of the 3C–SiC layer. In addition, as this result is repeatable, a smooth 3C–SiC membrane on a 3C–SiC pseudo-substrate can be « easily » obtained. These results are expected to pave the road for new MEMS devices based on this original heterostructure.
4. Conclusion Recently, we succeeded to achieve, for the first time, an innovative 3C–SiC micro-structure on a 3C–SiC pseudo-substrate. This result was attained by means of surface micromachining and using a silicon film as a sacrificial layer. However, the (110) 3C–SiC membrane was rough and faceted, which can hamper its use for the achievement of new MEMS devices. In this contribution, we demonstrate that a smooth 3C–SiC membrane can be obtained using a (111) 3C–SiC epilayer as, for this orientation, the surface is not faceted. The orientation of the 3C–SiC layer and, hence, of the membrane, seems directly linked to the growth process. Until now, the complete mechanism
involved to guide the 3C–SiC crystal orientation is still uncertain but the result is reproducible then, using the identified process, smooth 3C–SiC membranes on 3C–SiC pseudo-substrates can be “easily” obtained. Considering the properties of this material, the perspectives of such a structure could be massive, for example in medical field where the silicon carbide biocompatibility is a huge advantage. The SiC thermal properties combined with its chemical inertia could be also great benefits to design new MEMS devices, which could be subjected to harsh environments.
Acknowledgments The authors are grateful to Luan Nguyen for technical assistance. R.K. wishes to thank “Region Centre”and “Conseil General d’Indre et Loire” for their financial supports.
References [1] J.B. Casady, R.W. Johnson, Solid-State Electron. 39 (10) (1996) 1409. [2] P.G. Neudeck, Silicon Carbide Electronic Devices in Encyclopedia of Materials: Science and Technology, 2001. [3] O. Kordina, S.E. Saddow, Silicon Carbide Overview in Advances in Silicon Carbide Processing and Applications, Artech House, Inc, Boston, 2004. [4] X. Song, J.F. Michaud, F. Cayrel, M. Zielinski, M. Portail, T. Chassagne, E. Collard, D. Alquier, Appl. Phys. Lett. 96 (2010) 142104. [5] R. Boubekri, E. Cambril, L. Couraud, L. Bernardi, A. Madouri, M. Portail, T. Chassagne, C. Moisson, M. Zielinski, S. Jiao, J.-F. Michaud, D. Alquier, J. Bouloc, L. Nony, F. Bocquet, C. Loppacher, D. Martrou, S. Gauthier, J. Appl. Phys. 116 (2014) 054304. [6] S.E. Saddow, Silicon Carbide Biotechnology: A Biocompatible Semiconductor for Advanced Biomedical Devices and Applications, Elsevier Science, Amsterdam, 2011. [7] S. Jiao, J.F. Michaud, M. Portail, A. Madouri, T. Chassagne, M. Zielinski, D. Alquier, Mater. Lett. 77 (2012) 54. [8] J.F. Michaud, M. Portail, T. Chassagne, M. Zielinski, D. Alquier, Microelectron. Eng. 105 (2013) 65. [9] R. Khazaka, M. Portail, P. Vennéguès, M. Zielinski, T. Chassagne, D. Alquier, J. F. Michaud, Mater. Sci. Forum 821–823 (2015) 978. [10] R. Khazaka, M. Portail, P. Vennéguès, D. Alquier, J.F. Michaud, Acta Mater. (2015), http://dx.doi.org/10.1016/j.actamat.2015.07.052. [11] M. Nakamura, T. Isshiki, T. Nishiguchi, K. Nishio, S. Ohshima, S. Nishino, Mater. Sci. Forum 483–485 (2005) 181.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Toward high-quality 3C–SiC membrane on a 3C–SiC pseudo-substrate Rami Khazaka a,b, Emilie Bahette a, Marc Portail b, Daniel Alquier a, Jean-François Michaud a,n a b
Université François Rabelais, Tours, GREMAN, CNRS-UMR7347, 16 rue Pierre et Marie Curie, BP 7155, 37071 Tours Cedex 2, France CRHEA, CNRS-UPR10, rue Bernard Gregory, 06560 Valbonne, France
art ic l e i nf o
a b s t r a c t
Article history: Received 8 June 2015 Received in revised form 13 July 2015 Accepted 15 July 2015 Available online 16 July 2015
The cubic polytype of silicon carbide is an interesting candidate for Micro-Electro-Mechanical-Systems (MEMS) applications due to its tremendous physico-chemical properties. The recent development of multi-stacked Si/SiC heterostructures has demonstrated the possibility to obtain a (110)-oriented 3C–SiC membrane on a 3C–SiC pseudo-substrate, using a silicon layer grown by low pressure chemical vapor deposition as a sacrificial one. However, the (110) orientation of the 3C–SiC membrane led to a facetted and rough surface which could hamper its use for the development of new MEMS devices. Then, in this contribution, an optimized growth process is used to improve the surface quality of the 3C–SiC membrane. The progress relies on the mastering of a (111) orientation for the SiC film, resulting in a smooth surface. Such an optimized structure could be the starting point for the achievement of new MEMS devices in medical or harsh environment applications. & 2015 Elsevier B.V. All rights reserved.
Keywords: 3C–SiC Micromachining LPCVD Micro-structure Membrane MEMS
1. Introduction Since three decades, the chemical vapor deposition of cubic silicon carbide (3C–SiC) on silicon substrates has been widely investigated for the achievement of electronic and mechanical devices [1–3]. However, by means of scanning spreading resistance microscopy, our groups highlighted the electrical activity of the extended defects in this material [4]. This result is a major concern for electrical device functioning as the current can flow preferentially through the defects, leading to a steep degradation of their electrical performance. Based on this statement, the elaboration of 3C–SiC-based electrical devices seems to be challenging since a drastic reduction of the electrical activity of the defects, or of their density, has not been achieved yet. Nevertheless, for Micro-Electro-Mechanical-Systems (MEMS) applications, silicon carbide presents physical and chemical properties (hardness, inertness, melting point, operative temperature etc.) perfectly appropriate. As an example, the unique mechanical properties of silicon carbide are huge benefits to achieve high-frequency resonant devices [5]. In addition, the silicon carbide biocompatibility is particularly suitable for bio and medical applications [6]. Recently, we succeeded to fabricate (110)-oriented silicon tips on 3C–SiC cantilevers, based on a Si/3C–SiC/Si heterostructure [7]. This study was also the basis for the elaboration of a (110)-oriented 3C–SiC/Si/3C–SiC/Si heterostructure, leading to an original 3C–SiC n
Corresponding author. Fax: þ33 2 47 42 49 37. E-mail address: [email protected] (J.-F. Michaud).
http://dx.doi.org/10.1016/j.matlet.2015.07.071 0167-577X/& 2015 Elsevier B.V. All rights reserved.
microstructure on a 3C–SiC pseudo-substrate [8]. To do that, the silicon epilayer was used as a sacrificial layer. This result was very promising for the achievement of new MEMS devices. For example, by using a thick 3C–SiC bottom epilayer, an entire etching of the silicon substrate can be considered, resulting in a 100% monocrystalline 3C–SiC structure. Then, thanks to the 3C–SiC physical properties, this kind of membrane could be the starting point to conceive MEMS devices involved in medical or harsh environment applications. However, the (110) 3C–SiC membrane obtained in the initial demonstration was facetted and rough, which could be detrimental for MEMS applications. The aim of this paper is to present recent notable improvements reached by our groups in order to obtain a smooth 3C–SiC membrane.
2. Experimental details The complete formation of the 3C–SiC-based membrane requires alternating growth and process stages. The improved process proposed here is based on the original process described in [8]. 2.1. Growth stage 1: formation of the Si/3C–SiC heterostructure on Si (001) substrate The Si/3C–SiC epilayers were grown on 2″ on-axis Si (001) substrate in a resistively heated hot wall reactor. Prior to the
R. Khazaka et al. / Materials Letters 160 (2015) 28–30
29
growth, a thin Si film is homo-epitaxied on the Si substrate to form a clean and non-oxidized surface to start the subsequent growth. The temperature and the pressure were respectively 1050 °C and 600 mbar. After the cleaning procedure, the temperature was decreased to 860 °C and the pressure was fixed at 200 mbar. At 860 °C, the propane (C3H8) was introduced to the chamber to start the carbonization of the Si substrate. The temperature was raised to 1075 °C under a 10 sccm C3H8 flux. The duration of the entire carbonization step was 5 min. Then, the temperature was increased to 1320 °C to start the 3C–SiC film growth using a 4 sccm flow of SiH4 and a 1.3 sccm flow of C3H8 as precursor gases and hydrogen (H2 ¼ 15 slm) as carrier gas. The duration of the growth was 60 min. After the 3C–SiC growth, the temperature was reduced to room temperature. To start the Si heteroepitaxy, the pressure was changed to 950 mbar, the H2 flux was set at 10 slm and the temperature was then increased to 900 °C to start the growth. The duration of this growth step was 20 min. Additional details on the growth parameters and the structural properties of this Si layer can be found elsewhere [9,10]. The thicknesses are respectively 5 mm and 300 nm for the 3C–SiC and the Si layers. 2.2. Technological stage 1: formation of silicon islands Consecutively to this growth step, a classical photolithography stage has been completed to obtain square silicon islands. For that, an Inductively Coupled Plasma (ICP) reactor (Corial 200IL) using a mixture of SF6, Ar and C2H4 has been used to obtain silicon patterns with vertical sidewalls. Then, the photoresist mask has been removed by means of an oxygen plasma followed by a Piranha cleaning aiming to eliminate organic contaminants. 2.3. Growth stage 2: 3C–SiC regrowth on the silicon islands This step consists of the heteroepitaxy of the 3C–SiC on top of the patterned Si epilayer which is oriented along the [110] direction. Firstly, the temperature was increased to 900 °C for a 950 mbar pressure then an annealing was performed for 20 min. The aim of this annealing is to prepare the surface of the Si epilayer. We note that a higher annealing temperature deteriorates the surface morphology [9]. After this “cleaning” procedure, the temperature was decreased to 860 °C and the pressure was fixed at 200 mbar. At 860 °C, the propane (C3H8) was introduced to the chamber to start the carbonization of the Si epilayer. The temperature was raised to 1150 °C under a C3H8 flux of 20 sccm. The duration of the entire carbonization step was 5 min. Then, the temperature was increased to 1320 °C to start the 3C–SiC film growth using a 1 sccm flow of SiH4 and a 0.5 sccm flow of C3H8 as precursor gases and hydrogen (H2 ¼15 slm) as carrier gas. The duration of the growth was 2 min. The thickness of the 3C–SiC epilayer is then around 200 nm. Under these conditions, the 3C– SiC layer is shown to be (111) oriented as attested by the 2θ ω X-Ray Diffraction (XRD) scan of the 3C–SiC/Si/3C–SiC/Si heterostructure shown in Fig. 1a. Then, for the first time, the possible growth of a (111) oriented 3C–SiC film on a (110) Si epilayer is demonstrated. The key parameter responsible on this orientation change seems to be the surface state prior to the subsequent 3C– SiC growth. Without the« cleaning » step, the final 3C–SiC film is (110) oriented as shown in Fig. 1b. This result highlights the importance of the surface state prior to the growth of the 3C–SiC film. 2.4. Technological stage 2: membrane formation The last step of the whole process consists in a wet etching of the silicon epilayer which acts as a sacrificial layer. To do that, the 2″ sample was first cleaved to longitudinally cut the defined
Fig. 1. 2θ ω XRD scan of the complete 3C–SiC/Si/3C–SiC/Si heterostructure where the final 3C–SiC epilayer is (a) (111) oriented, (b) (110) oriented. The insets depict the orientation of each layer.
structures and then immersed in a hydroxide potassium (KOH) solution. The resulting silicon etching leads to the release of the top 3C–SiC membrane. The final structure is presented in Fig. 2, for the (111) and (110) orientations.
3. Discussion In a previous work, we succeeded to elaborate, for the first time, a 3C–SiC micro-structure on a 3C–SiC pseudo-substrate by means of surface micromachining. However, the surface of the 3C– SiC membrane, which was (110) oriented, presented a rough and faceted surface. The aim of this letter is then to demonstrate that significant improvements are « easily » accessible. First, as the crystalline quality of the 3C–SiC/Si stack is directly related to the crystalline quality of the bottom 3C–SiC layer, we decided to grow a 5 mm-thick 3C–SiC for the first epilayer. In this case, as the crystalline quality of 3C–SiC films is improved with the increase of the thickness, it results in an improvement of the crystalline quality of all the successive epilayers [10]. In addition, with the same objective, we tried to improve the surface quality of the silicon epilayer as it acts as a substrate for the growth of the final 3C–SiC epilayer used to define the membrane of the structure. For that, we studied the influence of a thermal treatment aiming to prepare the Si epilayer surface for the consecutive 3C– SiC epilayer. We mention that the mechanical properties of the 3C–SiC membrane is directly linked to its crystalline quality. Thus,
30
R. Khazaka et al. / Materials Letters 160 (2015) 28–30
Fig. 2. Cross-section scanning electron microscopy images of a 3C–SiC micro-structure with a 3C–SiC membrane presenting (a) a (111) orientation and (b) a (110) orientation.
improving the material crystalline quality strengthen its mechanical properties which is desired for MEMS applications. The result of both approaches are clearly evident as, in all cases, the roughness of the final 3C–SiC membrane is significantly reduced in comparison with our previous results [8]. Indeed, the RMS roughness for 5 5 mm2 atomic force microscopy scans is limited to 18 nm for the (110) oriented 3C–SiC epilayer, with a 64 nm peak-to-peak value, whereas it drops to 9 nm for the (111) 3C–SiC epilayer, with a 38 nm peak-to-peak value. The difference in terms of roughness is explained by the crystal orientation of the 3C–SiC membrane which is (110) without cleaning and (111) consecutively to the « cleaning » procedure. Then, the (110) orientation which results to a faceted surface is more rough compared to the (111) orientation. Nevertheless, the 3C–SiC(111) growth on Si(110) suffers from the difference in symmetries between the three-fold symmetric 3C–SiC(111) and the mirror symmetric Si(110) which leads to the formation of the double positioning domains [11]. For the moment, the detailed mechanism responsible of this orientation switch is unclear but some complementary experiments are currently under investigation. Anyway, this switch is favorable for the final surface morphology of the 3C–SiC layer. In addition, as this result is repeatable, a smooth 3C–SiC membrane on a 3C–SiC pseudo-substrate can be « easily » obtained. These results are expected to pave the road for new MEMS devices based on this original heterostructure.
4. Conclusion Recently, we succeeded to achieve, for the first time, an innovative 3C–SiC micro-structure on a 3C–SiC pseudo-substrate. This result was attained by means of surface micromachining and using a silicon film as a sacrificial layer. However, the (110) 3C–SiC membrane was rough and faceted, which can hamper its use for the achievement of new MEMS devices. In this contribution, we demonstrate that a smooth 3C–SiC membrane can be obtained using a (111) 3C–SiC epilayer as, for this orientation, the surface is not faceted. The orientation of the 3C–SiC layer and, hence, of the membrane, seems directly linked to the growth process. Until now, the complete mechanism
involved to guide the 3C–SiC crystal orientation is still uncertain but the result is reproducible then, using the identified process, smooth 3C–SiC membranes on 3C–SiC pseudo-substrates can be “easily” obtained. Considering the properties of this material, the perspectives of such a structure could be massive, for example in medical field where the silicon carbide biocompatibility is a huge advantage. The SiC thermal properties combined with its chemical inertia could be also great benefits to design new MEMS devices, which could be subjected to harsh environments.
Acknowledgments The authors are grateful to Luan Nguyen for technical assistance. R.K. wishes to thank “Region Centre”and “Conseil General d’Indre et Loire” for their financial supports.
References [1] J.B. Casady, R.W. Johnson, Solid-State Electron. 39 (10) (1996) 1409. [2] P.G. Neudeck, Silicon Carbide Electronic Devices in Encyclopedia of Materials: Science and Technology, 2001. [3] O. Kordina, S.E. Saddow, Silicon Carbide Overview in Advances in Silicon Carbide Processing and Applications, Artech House, Inc, Boston, 2004. [4] X. Song, J.F. Michaud, F. Cayrel, M. Zielinski, M. Portail, T. Chassagne, E. Collard, D. Alquier, Appl. Phys. Lett. 96 (2010) 142104. [5] R. Boubekri, E. Cambril, L. Couraud, L. Bernardi, A. Madouri, M. Portail, T. Chassagne, C. Moisson, M. Zielinski, S. Jiao, J.-F. Michaud, D. Alquier, J. Bouloc, L. Nony, F. Bocquet, C. Loppacher, D. Martrou, S. Gauthier, J. Appl. Phys. 116 (2014) 054304. [6] S.E. Saddow, Silicon Carbide Biotechnology: A Biocompatible Semiconductor for Advanced Biomedical Devices and Applications, Elsevier Science, Amsterdam, 2011. [7] S. Jiao, J.F. Michaud, M. Portail, A. Madouri, T. Chassagne, M. Zielinski, D. Alquier, Mater. Lett. 77 (2012) 54. [8] J.F. Michaud, M. Portail, T. Chassagne, M. Zielinski, D. Alquier, Microelectron. Eng. 105 (2013) 65. [9] R. Khazaka, M. Portail, P. Vennéguès, M. Zielinski, T. Chassagne, D. Alquier, J. F. Michaud, Mater. Sci. Forum 821–823 (2015) 978. [10] R. Khazaka, M. Portail, P. Vennéguès, D. Alquier, J.F. Michaud, Acta Mater. (2015), http://dx.doi.org/10.1016/j.actamat.2015.07.052. [11] M. Nakamura, T. Isshiki, T. Nishiguchi, K. Nishio, S. Ohshima, S. Nishino, Mater. Sci. Forum 483–485 (2005) 181.