Improvements of Self-Aligned Multi Patterning Spacer Technology by PEALD Sn-Doped SiO₂

Currently, EUV lithography begins to be adopted in a few patterning processes. But there is technical problem due to the low power of EUV light source and low hardness of EUV PR, self-aligned multi patterning (SAxP) have to be developed. SiO2 was chosen as a first spacer for self-aligned patterning. However, since SiO2 has low elastic modulus of 40GPa, spacer should be improved to prevent spacer collapse during further shrinkage of multi patterning. Therefore, SnO₂ is recently emerged as an alternative material. SnO2 has high modulus and good etch selectivity. But since there are problems of cost and etch issues, we have studied synthesis and characteristics of Sn-doped SiO2 as a spacer material.<br/><br/>Sn-doped SiO2 was mainly studied for optical applications using sol-gel or physical vaper deposition(PVD) such as sputtering. However, it is not a suitable for SAxP spacer deposition due to poor step coverage. Atomic layer deposition (ALD) is one of best method to solve above-mentioned problems. Due to self-limited ALD reaction, it has benefits such as excellent step coverage, uniformity, and thickness control. Also, Sn doping is easy to conduct through ALD super-cycles. Particularly, plasma enhanced ALD(PEALD) was utilized, which is driven by a high plasma energy, allowing low process temperatures to prevent thermal stress issue. As above, Sn-doped SiO2 has been deposited using PEALD.<br/><br/>In this study, we developed low-temperature Sn-doped SiO2 using BDEAS (Bis-Diethylamino Silane, H₂Si[N(C₂H₅)₂]₂), TDMA-Sn (Tetrakis(dimethylamido)tin(IV), [(CH₃)₂N]₄Sn) and O₂ reactant plasma as the Si, Sn precursor and reactant plasma. We studied about the effect of doping Sn in SiO2 film by varying the cycle ratio of SnO₂ and SiO₂and their film properties were evaluated. The ratio of the SnO₂ and SiO₂ deposition cycle was varied from 15(SiO₂) : 1(SnO₂), 9:1, 6:1, 4:1 to 3:1. Auger electron spectroscopy (AES) was utilized to measure the atomic concentration. As the SnO₂ cycle ratio increase, the amount of Sn in the SiO₂ thin film increase. The X-ray photoelectron spectroscopy (XPS) showed that the greater amount of Sn in the SiO₂ thin film, the binding energy of Si2p and Sn3d shift toward lower, and more Si-O-Sn chemical bonding are formed, which increased the number of stiffer ionic bonds. Therefore, the Young’s modulus measured by a nanoindenter increased from 39.9GPa at SiO₂ films to 90.9GPa at 3:1 film. However, the hardness results showed a different tendency showing decrease from 34GPa at 15:1 to 2.8GPa at 9:1 then increase to 7.9GPa at 3:1. This is because Sn is not well distributed in the SiO2 film due to the cyclic system of ALD and the low distribution energy of the low-temperature process, resulting in a bilayer structure of Sn-doped SiO2/SiO2/Sn-doped SiO2/SiO2 under the conditions of 15:1, 9:1 and 6:1. These results are compensated by X-ray reflectivity (XRR) and Time of Flight secondary ion mass spectrometer (TOF-SIMS) analysis. Moreover, the GPC of SiO₂ and SnO₂is 1.45Å/cycle, 1.0 Å/cycle. The values of the Sn-doped SiO₂ films are in between value of pure SiO₂ and SnO₂.