Fabrication of beam resonators from hot-wall chemical vapour deposited SiC

doi:10.1016/j.mee.2008.11.016

Microelectronic Engineering

Volume 86, Issues 4–6, April–June 2009, Pages 1194-1196

https://doi.org/10.1016/j.mee.2008.11.016 Get rights and content

Abstract

Single crystal and polycrystalline 3C–SiC have been grown in a hot-wall chemical vapour deposition reactor on 100 mm diameter p-type boron-doped (1 0 0) Si wafer. The crystal structure of the films has been determined by X-ray diffraction. Moreover, cantilever resonators have been fabricated from the two grown 3C–SiC films using a one-step dry etch and release process. The designed beam length has been varied between 50 and 200 μm. Resonant frequencies in the range between 110 kHz–1.5 MHz and 50–750 kHz have been obtained for single crystal and polycrystalline SiC devices, respectively. Furthermore, the experimental resonance frequencies have been used to calculate Young’s Modulus E for both types of SiC. The single crystal SiC has shown a relatively high Young’s Modulus (446 GPa) and should be an optimal material for RF–MEMS applications.

Introduction

Silicon carbide (SiC) micro electromechanical systems (MEMS) are promising devices for high efficiency radio frequency (RF) applications [1], [2]. Among the unique material properties of SiC, the high value of Young’s Modulus and the relatively low mass density permit SiC to achieve higher resonant frequencies compared to other materials [3]. In addition, the mechanical strength, high thermal conductivity and the high sublimation point of SiC make it an extremely robust material suitable for harsh environment applications. In the past decade, significant progress has been made in the growth of SiC wafers, however, the epitaxial growth on silicon (Si) and dry etching techniques need still further developments to improve the quality and reliability of SiC MEMS [4].

In this work, single crystal and polycrystalline 3C–SiC have been grown on Si wafers. X-ray diffraction has been employed to characterise the epi-layers. In addition, the grown SiC films have been used to fabricate cantilever resonators with different beam lengths. The resonators have been actuated mechanically and Young’s Modulus has been calculated for both epi-layers from the measured resonant frequencies.

Section snippets

Growth of the 3C–SiC films

Both single crystal and polycrystalline 3C–SiC films have been grown in a hot-wall chemical vapour deposition reactor (CVD) [5] on 100 mm diameter p-type boron-doped (1 0 0) Si wafer without rotation of the wafer. Hydrogen purified through heated palladium cells, mixed with 2% of Ar has been used as carrier gas while silane (SiH₄) and propane (C₃H₈) have been used as precursor gases. The Si/H₂ ratio has been fixed at 0.024% and the C/Si ratio between 0.8 and 1. Prior the SiC growth, before and

Characterisation of the 3C–SiC films

After the growth process, the epi-layers have been assessed with a Nomarski optical microscope in reflection mode. The nucleation of the single crystal layer has been observed to be more homogeneous compared to the polycrystalline one. Furthermore, by reflectance technique in the visible range, an average epi-thickness of 1.4 and 2.3 μm have been measured for the polycrystalline and single crystal layers, respectively, leading to a typical growth rate in a 3–4 μm/h range.

The crystal structure of

Summary

Single crystal and polycrystalline 3C–SiC films have been grown in a hot-wall CVD reactor. The films structure has been investigated by XRD analysis showing a high crystal quality for the single crystal film. Both SiC epi-layers have been used to fabricate cantilever resonators with different lengths. The resonators have been actuated mechanically and the measured natural resonant frequencies have been used to calculate Young’s Modulus E of both materials. For the single crystal and the

References (12)

P.M. Sarro
Sensor. Actuator.
(2000)
R. Cheung
Silicon Carbide Micro Electromechanical Systems for Harsh Environments
(2006)
Di Gao, M.B.J. Wijesundra, C. Carraro, C.W. Low, R.T. Howe, R. Maboudian, Transducers ’03, 12th International...
J.M. Melzak
IEEE MTT-S Dig.
(2003)
A. Henry et al.
Chem. Vap. Depos.
(2006)
L. Jiang et al.
J. Appl. Phys.
(2003)

There are more references available in the full text version of this article.

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This paper reports on the measurement of the thermal coefficient of Young's modulus of both single crystal silicon and 3C silicon carbide over the temperature range spanning 200–290 K. The thermal coefficients were determined by monitoring the change of resonance frequency of micro-cantilevers as their temperature was reduced. The thermal coefficient of Young's modulus, 1/E · δE/δT was measured to be −52.6 ± 3.45 ppm/K for silicon and −39.8 ± 5.99 ppm/K for 3C silicon carbide, agreeing well with theoretical predictions, and also with experimental values that have been previously published for temperatures above 273 K. This work has therefore expanded the temperature range over which the thermal coefficient of Young's modulus has been measured to below 273 K and towards the temperatures required for low-temperature military and space applications.
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However, for Micro-Electro-Mechanical-Systems (MEMS) applications, due to its unique mechanical and physical properties, 3C-SiC is emerging as an alternative to mainly used materials like silicon and silicon nitride. Among the different silicon carbide polytypes, 3C-SiC is favored according to its capability to be grown on cheap and large diameter silicon substrates [3,4]. For example, such a material is an ideal candidate for cantilever elaboration used for micromechanical sensors and for Atomic Force Microscopy (AFM) probes.
The recent achievement of a continuous silicon monocrystalline thin film on 3C-SiC epilayers deposited on silicon substrates has opened the field for new microstructures. In this work, this original hetero-structure is the basis for the elaboration of an entire cantilever for atomic force microscopy. The hetero-epitaxially grown silicon layer is used to define the tip of the cantilever fabricated from the 3C-SiC epilayer deposited on silicon. The complete cantilever is elaborated by plasma etching using a nickel mask. The use of a full dry etching process is very promising as it is independent of the crystalline orientation of the silicon epilayer contrary to process based on wet etching solutions. Moreover, based on such hetero-structure, new MEMS devices can be considered.
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Fabrication of beam resonators from hot-wall chemical vapour deposited SiC

Abstract

Introduction

Section snippets

Growth of the 3C–SiC films

Characterisation of the 3C–SiC films

Summary

Sensor. Actuator.

Silicon Carbide Micro Electromechanical Systems for Harsh Environments

IEEE MTT-S Dig.

Chem. Vap. Depos.

J. Appl. Phys.