Dielectric Properties of Ultra Dense (3 g/cm3) Silicon Nitride Deposited by Hot Wire CVD at Industrially Relevant High Deposition Rates

Abstract

AbstractFor silicon nitride (SiNx) deposited at 3 nm/s using hot wire chemical vapor deposition (HWCVD), the mass-density reached an ultra high value of 3.0 g/cm3. Etch rates in a 16BHF solution show that the lowest etch rate occurs for films with a N/Si ratio of 1.2, the ratio where also the maximum in mass density occurs. The thus found etch rate of 7 nm/min is much better than that for PECVD layers, even when made at a much lower deposition rate. The root-mean-square (rms) roughness measured on 300 nm thick SiN1.2 layers is only about 1 nm, which is advantageous for obtaining high field-effect mobility in thin-film transistors. SiN1.2 films have succesfully been tested in “all hot wire” thin film transistors (TFTs). SiNx films with various x values in the range 1.0 < × <1.5 have been incorporated in metal-insulator-semiconductor structures with n-type c-Si wafers to determine their electrical properties from C-V and I-V measurements. We analyzed the behavior of the static dielectric constant, fixed nitride charges and trapped nitride charges as function of N/Si ratio. I-V measurements show that the HW SiNx films with N/Si ≥ 1.33 have high dielectric breakdown fields that exceed 5.9 MV/cm. For these films we deduce a low positive fixed nitride charge density of 6.2-7.8 × 1016 cm-3 from the flat band voltage and from the small hysteresis in the backward sweep we deduce a low fast trapped charge density of 1.3-1.7 × 1011 cm-2. The dielectric constant ε for different compositions is seen not to change appreciably over the whole range and amounts to 6.3 ± 0.1. These high-density SiNx films possess very low tensile stress (down to 16 MPa), which will be helpful in for instance, plastic electronics applications. HWCVD provides high quality a-SiNx materials with good dielectric properties at a high deposition rate.