Session GR5: Diamond Like Carbon Deposition

Effect of pulse width on deposition of diamond-like carbon on high power pulsed magnetron sputtering

A diamond-like carbon (DLC) is an amorphous carbon containing both sp² bond and sp³ bond structures. Ion flux to substrate and ion energy around 100 eV is essential to increase the sp3 bond in the DLC film. An increase in the ion flux is expected by using high power pulsed magnetron sputtering (HPPMS) due to large plasma density. In this study, the effect of pulse width on deposition of DLC film on HPPMS under constant peak power density or constant average power density. The relationship between behavior of ion measured by energy-resolved mass spectrometry and film quality of DLC film was investigated.

The frequency of applied pulse to the carbon target was 400 Hz and no substrate bias voltage was applied. The gas flow rate of Ar was 5 sccm and the pressure was 0.5 Pa. The distance between the target and the orifice was 80 mm.

I_D/I_G ratio, evaluated by Raman scattering spectroscopy, decreased from 1.13 to 0.80 with decreasing the pulse width from 50 to 20 µs under the applied average power density of 1.97W/cm². On the other hand, I_D/I_G ratio was constant for any pulse width under constant peak power density of 1.5kW/cm². These results indicate that the peak power density is essential to characterize the film density of the DLC in comparison with average power density.   

Gas phase diagnostics on high power pulsed magnetron sputtering using double-pulse target-voltage

 A diamond-like carbon (DLC) is an amorphous carbon containing both sp² bond and sp³ bond structures. Ion flux to substrate and ion energy around 100 eV is essential to increase the sp³ bond in the DLC film. An increase in the ion flux is expected by using high power pulsed magnetron sputtering (HPPMS) with double-pulse target-voltage. In this study, the energy distribution of Ar⁺ and C⁺ was measured by energy-resolved mass spectrometry. The relationship between behavior of ion and film quality of DLC film was investigated.

 

 The HPPMS power supply was connected to the carbon target. The condition of first pulse was the frequency of 400 Hz, the pulse width of 25 μs and the peak power density of 1.5kW/cm². The applied voltage of second pulse was -600 V and the pulse width was 10 μs. The time interval between first and second pulses was varied from 20 μs to 50 μs. The pressure was 0.5 Pa and the gas flow rate of Ar was 5 sccm. The distance between the target and the orifice was 80 mm.

 

 The fluxes of Ar⁺ or C⁺ at time interval of 20 μs were 1.8 and 1.3 times higher than those of the single pulse, respectively. In addition, the fluxes of Ar⁺ or C⁺ decreased with increasing the time interval between the first and second pulses.   

Effect of xenon gas on deposition of diamond-like carbon film using high power pulsed magnetron sputtering

 A diamond-like carbon (DLC) is an amorphous carbon containing both graphite (sp2 bond) and diamond (sp3 bond) structures, and shows excellent material properties such as high hardness, low friction, and wear resistance. The DLC coatings have been applied to automobile parts, cutting tools and so on. Ion flux to substrate and ion energy around 100 eV is essential to increase the sp3 bond in the DLC film. In this study, the effect of Xe as the rare gas on film property of DLC film and its gas phase on high power pulsed magnetron sputtering using carbon target was investigated due to the ionization potential and mass in comparison with Ar.

 The peak current applying to the carbon target was 70A, the pulse width was 10µs, and the frequency was 400 Hz. The total gas flow rate of Xe/Ar mixture gas was 10sccm at a pressure of 0.5 Pa. Xe gas mixture ratio to Ar gas was varied from 0% to 100%.

 ID/IG ratio, which is due to disorder and graphite band, was evaluated by Raman scattering spectroscopy. ID/IG ratio was constant of 1.2 for any Xe gas mixture ratio. The flux and energy of carbon ions decreased with increasing Xe gas mixture ratio. Xe ion with high kinetic energy would contribute to the film density of the DLC because mass of Xe is three times larger than that of Ar.

    

Deposition of hydrogenated diamond-like carbon using high power impulse magnetron sputtering

Diamond-like carbon (DLC) shows high hardness and low friction, and has been applied in tribology field for sliding parts and machining parts. High power impulse magnetron sputtering (HiPIMS) realizes high ionization rate and production of high energy ions, resulting that the DLC film with high hardness more than 20 GPa can be obtained without substrate bias voltage. The deposition rate, however, was lower than DCMS due to high ionization rate and small duty ratio. In this study, hydrogenated DLC film was deposited by reactive HiPIMS using CH4 gas in order to improve deposition rate.

A negative voltage pulse with a voltage of 800 V, a frequency of 400 Hz and a pulse width of 10 μs was applied to the carbon target. The total gas flow rate (Ar+CH4) was 10 sccm, CH4 gas mixture ratio was 20% and the pressure was 0.5 Pa. The negative substrate bias voltage was varied from 100 to 700 V under constant target voltage. ID/IG ratio, which is due to disorder and graphite band, was evaluated by Raman scattering spectroscopy. ID/IG ratio decreased to be 1.0 with increasing bias voltage up to 400 V, and then increased with further increasing bias voltage. Higher substrate bias voltage has been required to improve ID/IG ratio in comparison with the sputtering condition of pure Ar gas.   

Optimization of hexagonal boron nitride deposition by micro hollow cathode discharge

Hexagonal boron nitride (h-BN) has attracted a lot of attention for electronic and optoelectronic applications, as an atomically flat insulator, with a structure very similar to graphene (1% mismatch). To deposit this material, our group uses a process based on a Micro Hollow Cathode Discharge (MHCD) in Ar/N₂ mixture with boron tribromide (BBr₃) as a boron precursor. We have shown the feasibility of h-BN deposition on large area Silicon substrates (2 inches) at relatively low temperature (800°C). To optimize and better understand the deposition process, the discharge has been characterized. In particular, we have used nanosecond Two-photon Absorption Laser Induced Fluorescence (ns-TALIF) to measure the nitrogen atom density, a key parameter in the deposition process. This diagnostic has a high spatial resolution (600 µm) and allows a mapping of the atomic nitrogen density in the discharge, from the MHCD to very near the substrate’s surface. TALIF measurements showed that the atomic nitrogen is produced inside the MHCD hole and can be transported over long distances (i.e. even up to the substrate) using a pressure differential between the two sides of the MHCD. To achieve the h-BN deposition, the substrate holder must be polarized, which further favors the plasma expansion towards the substrate. TALIF measurements confirm that the substrate holder polarization leads to a higher nitrogen atom density above the substrate.   

Evaluation of carbon bonding of DLC films using HF-HiPIMS method by Raman spectroscopy

A double-pulse high-power impulse sputtering (HiPIMS) method has deposited DLC films with higher hardness than conventional unipolar HiPIMS method. We have developed high frequency (HF)-HiPIMS method as a new power supply to improve the film properties of HiPIMS method. However, the carbon bonding of DLC films deposited by the HF-HiPIMS method has not been clarified. In this study, we report on the carbon bonding of DLC films using the HF-HiPIMS method by Raman spectroscopy. Raman spectra were deconvoluted into five active bonds (N, D, G⁻, G⁺, D’) using the Voigt function. The film density was measured by X-ray reflectometry (XRR). In this study, the discussion will focus on the relationship between film density and G⁻/G⁺ area rate. The film density was negatively correlated the G⁻/G⁺ area rate (r = −0.87). This G⁻/G⁺ area rate is related to the quantity of strained constituents in the films. Also, when the CH₄/Ar ratio is high, the quantity of strained constituents are high and the matrix sea (DLC) is sparse. It is considered that the DLC films are dense when the quantity of strained constituents are low. Therefore, the G⁻/G⁺ area rate decreased and the film density increased.

    

Single Crystal Diamond Growth by High-Flow Ar/CH4/H2 Modulated Induction Meso-Plasmas at Reduced Pressures

Single crystal diamond growth experiment was conducted using the power-modulated induction meso-plasma at reduced pressure condition. The induction meso-plasma was realized by improving the apparatus to achieve both reduced pressure and larger gas flow simultaneously. The influence of the flow rate of the source gas was investigated on diamond growth by exposure of the modulated induction meso-plasma. In addition, numerical thermofluid simulation was carried out for the modulated induction plasma at reduced pressures at different gas flow rates.

    

Deposition mechanism of hydrogenated amorphous carbon film by C3H6/H2 mixture gas plasma

Hydrogenated amorphous carbon (a-C:H) thin films as a hard mask for plasma etching were deposited by a plasma-enhanced chemical vapor deposition using C₃H₆/H₂. The residual compressive stress a-C:H films once decreased with increasing a hydrogen (H₂) flow rate ratio from 0.00 to 0.50, then it increased at the H₂ flow rate ratios above 0.50. As a result, the residual compressive stress showed the minimum value at a H₂ flow rate ratio of 0.5. According to Raman spectra, it was suggested that residual stress depends on the sp³ C-C contents in the a-C:H films. This is also consistent the maximum film density estimated using elastic recoil detection analysis (ERDA) and nuclear reaction analysis (NRA). On the other hand, the etching rates of a-C:H films deposited at H₂ flow rate ratios of 0.25 and 0.75 were similar, but their film densities were 2.03 and 1.85 g/cm³, respectively. This is suggested that not only the film density but also its structure contributes to the etching resistance.