Synthesis and characteristics of Sn-doped SiO2via plasma-enhanced atomic layer deposition for self-aligned patterning

Abstract

Sn-doped SiO2 thin films as a spacer for self-aligned patterning were deposited by plasma-enhanced atomic layer deposition and their characteristics were evaluated. This doping research was conducted to improve the mechanical properties of SiO2 films, which have been conventionally used as a spacer material. Because pure SiO2 films have a low Young's modulus, the pattern is stretchable and may collapse as the patterning size decreases. The ratio of the SnO2 and SiO2 deposition cycle was varied from 15(SiO2):1(SnO2) to 3(SiO2):1(SnO2) to modify the film characteristics. X-ray reflectivity (XRR) and time-of-flight secondary ion mass spectrometer analyses revealed whether Sn was doped in SiO2 or became a nanolaminate. The x-ray photoelectron spectroscopy analysis showed that a greater amount of Sn in the SiO2 thin film resulted in a binding energy shift toward the lower binding energy Si2p and Sn3d peaks, and more Si-O-Sn chemical bonding, which increased the number of stiffer ionic bonds as the SnO2 cycle ratio was increased. Therefore, Young's modulus measured by using a nanoindenter increased from 39.9 GPa for SiO2 films to 90.9 GPa for 3(SiO2):1(SnO2) films. However, the hardness results showed a different tendency due to the not well-distributed nanolaminate film structure showing a tendency to decrease and then increase as doping increases. Moreover, the growth rate and film density were evaluated by XRR. The growth per cycle (GPC) of SiO2 was 1.45 Å/cycle and the GPC of SnO2 was 1.0 Å/cycle. The film density of SiO2 was 2.4 g/cm3 and the film density of SnO2 was 4.9 g/cm3. Also, the GPC and film density values of the Sn-doped SiO2 films were in between the values of pure SiO2 and SnO2. The dry etch rate was also measured by reactive ion etching using CF4 plasma with 150 W for 1 min.