IR Study on Room Temperature Atomic Layer Deposition of Aluminum Nitride Using Plasma Excited Ammonia

Abstract

Aluminum nitride (AlN) has been attracting much attention since it has a wide direct transition band gap of 6.3 eV and it is applicable for UV-LEDs. The AlN films have been deposited by chemical vapor deposition (CVD) and atomic layer deposition (ALD). These conventional processes were performed at a temperature of 300 °C and higher. To apply the AlN coating on flexible films, the low temperature deposition process has been demanded. To demonstrate the AlN deposition at RT, an RT-ALD of AlN using trimethylaluminum (TMA) as an Al precursor and plasma-excited ammonia are studied based on study on multiple internal reflection infrared spectroscopy (MIR-IRAS). An n-type Si substrate was used as a prism for MIR-IRAS. The size of prism was 10×45 mm2 and its resistivity was 1000 Ωcm. 45° bevels on each of the short edges were formed. The prism was set in a reaction chamber for the ALD. If the IR spectra before and after the processes are defined as Ir and I0, respectively, we can calculate the absorbance (Abs) from the equation, Abs = log10(Ir/I0). TMA was used as the Al precursor. In the nitridation step, ammonia and argon was mixed with a volume ratio of 7:3, followed by being excited through a quartz tube with an RF power of 250 W and a frequency of 13.56 MHz. The flow rate of the mixed gas was 10 sccm. Ammonia molecules in the mixture were dissociated to NH radicals and some fragments. Plasma excited ammonia was provided in the chamber. We observed the surface reaction to confirm TMA adsorption and examine if the plasma-excited ammonia generated nitride on the TMA adsorbed surfaces. Fig. 1 shows IR spectra were obtained from a TMA adsorbed surface with exposures from 1000 to 400000 L at RT. Peaks at 2933, 2894, and 2829 cm-1 correspond to C-H vibrations in TMA. The positive peak indicates that the TMA was adsorbed on the surface at RT. Fig. 2 shows IR spectra measured from plasma excited ammonia treated TMA saturated surface. Negative peaks at 2933, 2894, and 2829 cm-1 suggests that the nitride was generated there at RT. We also confirmed the presence of AlN on the prism by an Al 2p peak at 73.3 eV and a N 1s peak at 398.1 eV by X-ray photoelectron spectroscopy. These suggests that it is possible to deposit AlN at RT. Figure 1