Effect of N2-Anneal Temperature on Silicon Nitride Film: (I) Time-Dependent Dielectric Breakdown and ESR Evaluations

Abstract

Silicon Nitride (SiN) film has been used as insulating material in many electronic devices such as capacitors and memories . In this report, the effect of N2 anneal temperature on charge break down (Qbd) of LP-CVD SiN film was electrically evaluated using the time-dependent dielectric breakdown (TDDB) test method, and the variation and the density of defects which exist in SiN film, in the oxide layer between SiN and Si substrate, and at the surface of Si substrate, were investigated using an Electron Spin Resonance (ESR) to reveal the defect behavior related to the trigger of Qbd.SiN metal-insulator-metal (MIM) capacitors were fabricated to evaluate TDDB. A 54 nm dielectric layer of SiN film was deposited at 700 degree-C, using a mixture of dichlorosilane（SiH2Cl2）and ammonia (NH3) gasses, by a LP-CVD vertical furnace. For the lower and upper electrode, a 400 nm polycrystalline silicon films were deposited using a LP-CVD. In order to evaluate the effect of anneal temperature on SiN film breakdown frequency, these samples were annealed in nitrogen atmosphere at temperatures between 700 and 1150 degree-C for 1 hour, using a vertical furnace.Breakdown voltage was measured with a current-voltage tester (HP4071A, Hewlett Packard) for each SiN MIM capacitor. The breakdown frequency was defined as the ratio of failed capacitors to tested capacitors. For the TDDB measurements, a constant current stress of 1.33 A/cm2 was applied to the MIM capacitors with the area of 0.00375cm2, 0.0075cm2, 0.015cm2 and 0.03cm2. For each area, 100 chips were made from one wafer and measured.In Fig.1, SiN film breakdown frequency increases toward a peak at around the N2 anneal temperature of 900 degree-C, then decreases at 1000 degree-C, and at more than 1100 degree-C, the frequency increases again drastically at 1150 degree-C.SiN films for ESR study were fabricated on Si wafer in the same LP-CVD process, and annealed in nitrogen atmosphere at temperatures between 700 and 1150 degree-C for 1 hour, using a vertical furnace.The ESR measurements were performed at room temperature using an X-band spectrometer (JES-RE1X). To improve the signal-to-noise ratio of an ESR signal waveform, we set the accumulation number of magnetic-field (H) sweep about 300 times. Mn2+/ MgO hyperfine lines were used for the g marker, and spin densities were determined by using the standard of known spin content.In Fig.2, Dangling bond density at silicon interface (Pb center) has a peak at 900 degree-C, and those in SiO2 (E’ center) and SiN film (K center) increase with increasing temperature from 1000 to 1150 degree-C. The former phenomena of Pb center coincides with the peak of SiN film breakdown frequency at 900 degree-C, and the latter one of E’ center and K center coincides with the tendency of increasing Qbd frequency at more than 1000 degree-C. Figure 1