Elsevier

Thin Solid Films

Volume 518, Issue 13, 30 April 2010, Pages 3502-3505
Thin Solid Films

Deposition of amorphous carbon nitride films using Ar/N2 supermagnetron sputter

https://doi.org/10.1016/j.tsf.2009.11.051Get rights and content

Abstract

Amorphous carbon nitride (a-CNx) films were formed by supermagnetron sputter deposition using N2 and/or Ar gases. Supplying rf power with a substrate-holding electrode (bias sputter) and lowering the gas pressure were found to be effective at decreasing the optical band gap and increasing the hardness. Nitrogen concentrations of bias sputtered films were about 32–35 mass% (30–100 mTorr). The a-CNx films deposited for electron field emission showed a low-threshold electric field (ETH). With the decrease of gas pressure, admixture of Ar to N2 or the use of pure Ar, and the use of bias sputter, the ETH of a-CNx films largely decreased to 11 V/μm (30 mTorr Ar/N2 bias sputter).

Introduction

Field emission from carbon-based materials is of great technological and fundamental interest due to its possible application in display devices and in vacuum microelectronics. Amorphous carbon (a-C) film is of considerable interest due to its unique properties such as high hardness, low stress and chemical inertness. a-C films can be deposited by a variety of techniques. Commonly used techniques for growing a-C films include the plasma decomposition of hydrocarbon gas or the use of ion sources of different kinds [1], [2]. Besides plasma-enhanced chemical vapor deposition (PECVD), other techniques include laser ablation of graphite [3], filtered cathodic vacuum arc [4], hot-filament CVD [5], ion beam-assisted deposition [6], and magnetron sputter deposition [7]. Recent studies show that the unique properties of a-C films can be modified by incorporating nitrogen into the films. Because nitrogen addition can cause the reduction of the electrical resistivity and optical band gap width, nitrogen-incorporated amorphous carbon (a-C:N or a-CNx) has been proposed as a superior electronic material to amorphous carbon. In electron field emission, doping with nitrogen strongly influences the emission properties of amorphous carbon films [8]. Nitrogen is a very suitable atom as an n-type dopant because the atomic size is similar to C and the nitrogen atom is a donor in amorphous carbon film [9]. Supermagnetron plasma CVD has been used for the deposition of hydrogenated amorphous carbon nitride (a-CNx:H) films using hydrocarbon gas (i-C4H10) [10]; however, the supermagnetron sputter used in this study is suited to the deposition of a-CNx without hydrocarbon gas. By N2 or Ar/N2 magnetron sputter, a-CNx films with high N concentration (> 20 at.%) could be formed [11], [12]. Supermagnetron sputter is also a promising method for forming a-CNx films with higher N concentration than those of a-CNx:H films formed by supermagnetron plasma CVD (< 20 at.%) [13]. Supermagnetron sputter is also suited to high-performance sputtering of the target due to its nearly uniform erosion.

In this study, we deposited a-CNx films using supermagnetron sputter and investigated the physical and chemical properties of the resulting films. To examine the electron field emission characteristics, we applied the a-CNx films to a flat-face field emitter. The threshold electric field for field emission was measured as a function of gas pressure.

Section snippets

Experimental

For the deposition of a-CNx films, a supermagnetron sputter apparatus with two parallel magnetron electrodes was used (Fig. 1) [14]. Two different rf power sources with the same rf frequency (13.56 MHz) and a phase difference of 180° were supplied to two electrodes with respect to the grounded metal chamber. The lower electrode (i.e., substrate stage) was heated to 30 °C during a-CNx deposition. However, the substrate was heated by plasma heating in this experiment. Using intermittent sputter

Results and discussion

The DC self-bias voltage (VDC) of both the upper and lower electrode with respect to the ground potential was measured at upper and lower electrode rf powers (UPRF/LORF) of 200/15 W as a function of N2 and/or Ar gas pressure, as shown in Fig. 2. The VDC of the lower electrode decreased from − 57 V to − 80 V with the increase of gas pressure from 30 to 100 mTorr, almost independently of gas species. It seems that the ion-bombarding energy on the substrate increased slightly with the increase of gas

Conclusions

a-CNx films were deposited using N2 and/or Ar supermagnetron sputter at 200/15 W or 200 W/GND. The deposition rate and optical band gap increased with the increase of gas pressure (30–100 mTorr). The hardness decreased with the increase of gas pressure, and FT-IR absorption spectra showed increases of OH, NH and CH bonds with the increase of gas pressure, indicating that a-CNx films became polymer-like with the increase of gas pressure. The nitrogen concentration of a-CNx films deposited at 200/15 

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