Elsevier

Current Applied Physics

Volume 23, March 2021, Pages 52-56
Current Applied Physics

Evolution of amorphous carbon films into nano-crystalline graphite with increasing growth temperature in plasma-enhanced chemical vapor deposition

https://doi.org/10.1016/j.cap.2020.12.012Get rights and content

Highlights

  • Amorphous carbon films were grown by plasma-enhanced chemical vapor deposition at different temperatures.

  • Relative abundance of sp2 bonds increased with increasing growth temperature.

  • Evolution of amorphous carbon films into nano-crystalline graphite with increasing growth temperature was observed.

  • Amorphous carbon films grown at lower temperatures provided better etching resistivity.

Abstract

Amorphous carbon films (ACFs) have recently emerged as one of the best candidates for etching-resistant hardmask materials in advanced semiconductor manufacturing processes. Etching resistivity of ACFs is known to be improved by controlling the relative abundance between sp2 and sp3 bonds. We have investigated the relative abundance between sp2 and sp3 bonds in several ACFs, fabricated by plasma-enhanced chemical vapor deposition at different temperatures, which were analyzed by using X-ray photoemission spectroscopy, Raman spectroscopy, and transmission electron microscopy. We found that the relative abundance of sp2 bond increased as the growth temperature was raised. Furthermore, the ACFs eventually evolved into nano-crystalline graphite with increasing growth temperature.

Introduction

Amorphous carbon materials have been used for wide applications such as solar cells, low friction device, and photoresist [[1], [2], [3]]. There are two types of bonds between carbon atoms, sp2 and sp3, in amorphous carbon materials. The sp2 bond with hexagonal structure is important for electrical and magnetic properties. For example, graphite consisting of the sp2 bond has very high conductivity. So amorphous carbon materials with highly abundant sp2 bonds have been used for magnetoresistance devices and electronic applications [4,5]. In contrast, the sp3 bond with tetrahedral structure is important for mechanical property because of its higher binding energy than the sp2 bond. Amorphous carbon materials with highly abundant sp3 bonds is known as diamond-like carbon (DLC). DLC can be fabricated to have enhanced mechanical hardness and thermal resistivity [6,7]. Since amorphous carbon materials are made up of both sp3 and sp2 bonds, they can have variety of electrical, mechanical, magnetic, and optical properties depending on the relative abundance between sp2 and sp3 bonds.

Recently, amorphous carbon films (ACFs) have been studied as a hardmask material because of their etching resistance [8,9]. Nowadays, advanced semiconductor manufacturing processes demand better etching-resistant photoresist than the existing ones, and ACF emerged as one of the best candidates. In the previous reports, etching resistivity of ACFs can be improved by controlling the abundance of sp2 bonds [8]. Fluorine, used in dry etching processes, generally penetrates sp2 bonds more easily as compared to sp3 bonds because the binding energy of sp2 bond is smaller than that of sp3 bond [8]. Thus, the relative abundance of sp2 bonds in ACF is a critical parameter in enhancing their etching resistivity. In fact, Lee et al. reported that the ACF deposited at low pressure has high abundance of sp3 bonds and strong etching resistivity [8].

In this study, we investigated relative abundance between sp2 and sp3 bonds in several ACFs fabricated by plasma enhanced chemical vapor deposition (PECVD) at different temperatures. The deposited ACFs were analyzed by using X-ray photoemission spectroscopy (XPS), Raman spectroscopy, and transmission electron microscopy (TEM). We found that the relative abundance of sp2 bonds increased as the growth temperature was raised. Furthermore, the ACFs eventually evolved into nano-crystalline graphite (NC-graphite) with increasing growth temperature.

Section snippets

Experiments

The ACFs were deposited on silicon substrate by PECVD with different growth temperatures ranging from 300 °C to 620 °C. Prophylene (C3H6) and Ar gases were used during the growth, and the thickness of the ACFs was as thin as 200 nm.

The Raman spectra were measured by single-grating spectrometer (Princeton Instruments, SP-2500i) with a CCD detector (Princeton Instruments, Spec-10) by using 532 nm laser as an excitation source. To avoid sample damage, the laser power less than 0.5 mW was used. A

Results and discussion

XPS analysis is useful to quantify relative abundance of sp2 and sp3 bonds in ACFs. C1s photoemission spectra from our samples were shown in Fig. 1, where the broad C1s peak consisted of contributions from sp2 (~284.7 eV), sp3 (~285.2 eV), C-O (~286.4 eV), and Cdouble bondO (~294 eV) bondings [10,12]. In order to analyze the relative abundance of sp2 and sp3 bonds in our ACFs, the XPS spectra were fitted with four Gaussian functions and the representative deconvolution of the C1s peak was shown in the

Conclusion

In summary, we have investigated amorphous carbon films, grown by PECVD with different growth temperatures ranging from 300 °C to 620 °C. XPS, Raman, and HR-TEM results confirmed that the relative abundance of sp2 bonds increased with increasing growth temperature and the ACFs eventually evolved into NC-graphite. From the perspective of etching resistivity, our results suggested that ACFs grown at lower temperatures would provide better etching resistivity because of higher abundance of sp3

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

This research was supported by the Chung-Ang University Graduate Research Scholarship in 2019 and by the Samsung Electronics' University R&D program (Research on hardmask materials for next-generation VNAND).

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    According to the cluster modes of amorphous carbon [34], The G peak position (G peak∼1581.92 cm−1) of our prepared films was in the transition stage from amorphous carbon (G peak∼1510 cm−1) to nanocrystalline graphite (G peak∼1600 cm−1), that is, the carbon layer in our prepared film exists in the form of amorphous carbon (a-C). Kim et al. [35] pointed out that the ID/IG ratio of a-C material was related to the sp2 bond content. The higher the ID/IG ratio is, the more the quantity of converging to nanocrystalline graphite in a-C is.

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