Effect of Hydrogen Content and Bonding Environment on Mechanical Properties of Hydrogenated Silicon Films Deposited by High-Frequency PECVD Process

Jhuma Gope,C M S Rauthan,A Parashar,P C Srivastava,S Dayal,Sushil Kumar

doi:10.5402/2012/429348

Jhuma Gope, C M S Rauthan + Show 4 more

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https://doi.org/10.5402/2012/429348

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Abstract

The mechanical properties of hydrogenated silicon thin films deposited using high-frequency PECVD process were studied, which certainly have importance for optoelectronic devices particularly for getting stability and long operating lifetime in harsh conditions. Nanoindentation technique was used to measure the load versus displacement curves, hardness (H), elastic modulus (E), plastic resistance parameter (H/E), elastic recovery (ER), and plastic deformation energy (Ur), while laser scanning stress measurement setup was used to measure the intrinsic stress of these films. The concentration of bonded hydrogen in these films was found in the range of 3.6 to 6.5 at. % which was estimated using integrated intensity of IR absorption peak near 640 cm−1. Dependence of mechanical properties of these films on hydrogen content and bonding environment has been investigated. The film containing minimum hydrogen content (3.6%) shows the maximum elastic recovery (52.76%) and minimum plastic deformation energy (3.95×10−10 J). Surface roughness measured by AFM was found to decrease with the increase in hydrogen content in the film. The dependency of stress on the plasma frequency and applied power has also been discussed.

Highlights

The mechanical properties of amorphous and nano/microcrystalline silicon (a-Si : H and nc/μc-Si : H) thin films may play a significant role in the application of silicon-based devices such as solar cells, TFT, detectors, and on flexible substrates because it may affect the stability and operating lifetime of the devices
Nanoindentation technique was used to measure the load versus displacement curves, hardness (H), elastic modulus (E), plastic resistance parameter (H/E), elastic recovery (ER), and plastic deformation energy (Ur), while laser scanning stress measurement setup was used to measure the intrinsic stress of these films
It is known that 2000 and 2100 cm−1 modes in a-Si : H are assigned to the stretching vibration modes of SiH and SiH2, respectively, and the SiH2 bonds are mainly located in the internal surface of microvoids [13]

Summary

Introduction

The mechanical properties of amorphous and nano/microcrystalline silicon (a-Si : H and nc/μc-Si : H) thin films may play a significant role in the application of silicon-based devices such as solar cells, TFT, detectors, and on flexible substrates because it may affect the stability and operating lifetime of the devices. Nanoindentation technique is commonly used to measure the micromechanical properties such as hardness, elastic modulus and creep of thin films [2,3,4,5]. Measurement of intrinsic stress of films is important as excessive tensile stress may cause cracking, while excessive compressive stress may cause peeling of the deposited thin films [6] which limits their applications for various devices. The atomic concentration of hydrogen in the nc/μc-Si : H structure affects the density of films which could be important to correlate with the hardness and elastic modulus. The density of hydrogen in microcrystalline silicon (μc-Si : H) films is important as it passivates grain boundaries [7]

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