Transport and structural modification during nitrogen implantation of hard amorphous carbon films

Abstract

Hard amorphous carbon (ta-C) films were implanted with 20 keV N+ ions with different fluences up to 6×1017/cm2 at different substrate temperatures. The nitrogen content of the films was monitored in situ using elastic recoil detection analysis. A characteristic temperature dependence is observed for the maximum achievable [N]/[C] composition ratio, with a drop of the saturation level from the room-temperature value of 0.35 to 0.17–0.12 above 150 °C. It is shown that the higher nitrogen retention at room temperature is correlated with the formation of N2-containing gas bubbles which are not present in samples implanted with high fluences at elevated temperatures. From residual-gas analyses it is found that nitrogen is reemitted from the films mainly as N2 when saturation occurs. Double-implantation experiments with spatially separated N14 and N15 implanted regions, respectively, indicate that the N–N molecule recombination observed at large implantation fluences occurs inside the films and not at the surface. Significant changes of the microstructure of the films are found with increasing implantation fluences. Inside the implanted near-surface region of several 10 nm thickness the density of the material decreases from 3.0 to about 1.7 g/cm−3. Graphitic clusters are identified in samples implanted up to saturation at 400 °C, using cross-section transmission electron microscopy. A basic approach to modeling the nitrogen saturation and release at large fluences is presented. Both nitrogen release and structural modification processes are interpreted as a tendency towards thermodynamic equilibrium which may constitute a strong driving force against the synthesis of nitrogen-rich hard C:N materials, compared to other nitride phases.

Influence of nitrogen and temperature on the deposition of tetrahedrally bonded amorphous carbon

“…We found that the nitrogen incorporation into a-C films decreases at higher deposition temperature, as also observed by other groups. 14,44,45 Recently it was also found that the nitrogen etch rate of ta-C decreases with increasing temperature. 46 This was explained by physisorbtion of N 2 at the growing film surface and then ion impingement would release CN and N into the gas phase.…”

Chemical sputtering of carbon by nitrogen ions

“…TRIM.SP predicts the correct magnitude and energy dependence. 4,5,11,15,19,20 In conclusion, particle-beam experiments in an ultrahigh vacuum chamber ͑MAJESTIX experiment͒ show that bombardment of a-C : H layers with N 2 + causes chemical sputtering. In contrast to the shown Ne results and our other experiments with noble gas ions, the yields calculated with TRIM.SP significantly underestimate the N 2 + erosion yields and predict a pronounced energy dependence.…”

“…14,15 A common observation in plasma-deposition experiments is that the deposition rate decreases with increasing nitrogen addition to the working gas and that the maximal achievable nitrogen fraction in the material is limited to about 30 to 40 at. 4,5,11,15,19,20 Chemical sputtering proceeds via formation of volatile HCN, CN, and C 2 N 2 . 2,16 Some authors speculated that this is due to the formation of volatile CN species during the interaction of energetic nitrogen ions with the carbon surface.…”

“…%. 4,5,15,19,20 Despite the large number of investigations, the energy dependence and sputtering yields of this process have not been investigated in detail. 17 Such a process is generally denoted as chemical sputtering.…”

Preparation of amorphous CNx thin films by pulsed laser deposition using a radio frequency radical beam source

“…Various deposition techniques have been adopted. They include dc and rf magnetron sputtering deposition, [5][6][7][8][9] ion beam and ion beam assisted deposition, 10-12 nitrogen implantation, 13 pulsed laser deposition, [14][15][16][17][18] and chemical vapor deposition. [19][20][21] Recently, we have prepared crystalline carbon nitride thin films with a high nitrogen content by the electron cyclotron resonance ͑ECR͒ sputtering deposition.…”