For this study, Ti/Si and Ta/Si structures were implanted with two doses of nitrogen 10<sup>15</sup> ions/cm<sup>2</sup> (low dose) and 10<sup>17</sup> ions/cm<sup>2</sup> (high dose) at 10KeV and 20KeV energy. Characterization was performed by Sheet resistance measurement and X-Ray diffraction (XRD) techniques. Results shows that implantation of 10<sup>15</sup> ions/cm<sup>2</sup> dose of nitrogen does not cause any nitridation, while in case of high dose implanted samples formation of tantalum nitride phase was observed. Nitride layers formed this way was used as diffusion barrier layers for copper metallization in Silicon based integrated circuits.
Ta(N) film was synthesized by implanting the nitrogen ions in Ta films employing Plasma Immersion Ion implantation (PIII) technique. Silicon wafers coated with Ta were implanted with nitrogen at two different doses. Nitrogen ions implanted in the film render it to become Ta(N), which in effect hinders the grain boundary diffusion. The ion implantation was carried out for two doses 10<sup>15</sup>ions/cm<sup>2</sup> and 10<sup>17</sup>ions/cm<sup>2</sup> corresponding to low and high dose regime. Thereafter a copper layer was deposited on the samples to produce Cu/Ta(N)/Si structure. To evaluate the barrier properties of Ta(N) these samples were annealed up to 700°C for 30 minutes. Sheet resistance, X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) measurements were carried out to investigate the effect of annealing.
Plasma immersion Ion Implantation technique has been used to modify the diffusion barrier properties of titanium (Ti) metal layer against copper diffusion. Ti coated silicon wafer were implanted with doses viz. 10<sup>15</sup>ions/cm<sup>2</sup> and 10<sup>17</sup>ions/cm<sup>2</sup> corresponding to low and high dose regime. High dose of implantation of nitrogen ions in the film render it to become Ti(N). Cu/Ti(N)/Si structures were formed by depositing copper over the implanted samples. Diffusion barrier properties of Ti(N) was evaluated after annealing the samples up to 700 degrees C for 30 minutes. Sheet resistance, X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) measurements were carried out to investigate the effect of annealing. Low dose implanted Ti layer does not show any change in its diffusion barrier properties and fails at about 400 degrees C. The failure of diffusion barrier properties of low dose implanted samples is attributed to the chemical reaction between titanium and copper films. The high dose implanted layer stops the diffusion of Cu metal through it even at high annealing temperature. The enhancement in its diffusion barrier properties is supposed to be due to nitridation of titanium film which increases the activation energy involved for its chemical reaction with copper metal film.
Silicon wafers of p and n-types of 1 to 10 ohm-cm resistivity were implanted with nitrogen ions employing Plasma Immersion Ion Implantation (PIII) technique. Implantation were carried out at three doses corresponding to low (approximately 10<SUP>13</SUP> /cm<SUP>2</SUP>), moderate (approximately 10<SUP>15</SUP> /cm<SUP>2</SUP>) and high (approximately 10<SUP>17</SUP> /cm<SUP>2</SUP>) dose regimes. Metal-silicon devices were fabricated using conventional semiconductor processing techniques. One set of the samples was annealed in forming gas ambient. Electrical characterization was done on all the devices. Change in reverse and forward current was observed with dose of implanted ions. The barrier height of the n- type sample decreases with increase in implanted ion dose, where as in the case of p-type silicon, barrier height was found increasing with dose. At high doses the top layer of both n and p-type silicon become nitrogen rich and exhibits optical properties different from that of unimplanted silicon as measured by ellipsometry. With the nitrogen rich layer, the device behaved like metal-insulator-silicon structure whose electrical characteristics have been studied. Sputtering effects of the nitrogen ions during implantation were also studied.