|| SYNTHESIS OF NANOCRYSTALLINE HAFNIUM OXIDE THIN FILM BY SELF-ASSEMBLED MONOLAYER METHOD|
|| HfO2 thin films, OTS-SAMs, liquid phase deposition, pattern|
本文研究了一种低温水溶液中制备纳米晶态薄膜材料的新的合成方法。将自组装分子膜(Self-Assembled Monolayers, SAMs)技术与液相沉积技术(Liquid Phase Deposition, LPD)相结合，利用功能化自组装膜层对前驱体溶液的诱导作用，在玻璃基底表面制备出与基底结合紧密、结构致密均一的HfO2晶态薄膜及图案化薄膜。
With the decrease of the MOS devices size, the thickness of equivalent oxide of MOSFET lowers to nanometer magnitude, the electron tunneling is becoming serious enough to endanger the stability and reliability of devices. It is an urgent task now to seek a novel high-k dielectric material to substitute the traditional SiO2 gate dielectric in microelectronic industry. The Hf and oxide have currently become a hot point of study due to their high-k value and good thermal stabilization.
A new thin film synthesis method was investigated in this paper for preparing nanocrystalline thin films at the low temperature in an aqueous solution. By the combination process of Self-Assembled Monolayers (SAMs) technique and the Liquid Phase Deposition (LPD) method, the nanocrystalline titanium dioxide thin films were successfully deposited on the glass substrates modified by the self-assembled monolayers. The as-deposited hafnium oxide patterned thin films were uniform, dense, with excellent adherence.
Firstly, the growth and the process of octadecyl-trichloro-silane (OTS) self-assembled monolayers on the hydroxylated glass substrates were investigated in the present study. The characterization results of water contact angle, atomic force microscopy and scanning electron microscopy, indicated immersion time had the significant effects on the growth and surface structure of self-assembled layers on the glass substrates. As the deposition time increases the surface contact angle of OTS-SAMs became larger and the layers quality improved highly. After 1 minute deposition, OTS-SAMs have been formed on the whole substrate. After 20 minutes, the water contact angle turned larger sharply and got to maximum. The growing process tended to stable. There were no obvious changes after that. The layers were smooth and dense.
The OTS-SAMs were exposed to UV-light irradiation for functionalization. The test results of the surface water contact angle and Fourier-transform infrared spectroscopy (FT-IR) indicated irradiation time had a great effect on the hydrophile ability of the OTS-SAMs. The hydrophile ability would improve obviously with irradiation time increasing. After 30 minutes irradiation, the water contact angle had been less than 5°, indicating the surface of OTS-SAMs had been well hydroxylated.
At last, self-assembled monolayers with functional hydrophilic hydroxyl groups on the glass substrates were used as templates for the deposition of HfO2 thin films from aqueous solutions. The process and influence factors of HfO2 thin films prepared on OTS-SAMs were systematically investigated. The phase composition, microstructure and surface morphology of as-deposited HfO2 thin films were studied via XRD, SEM and AFM. The results indicated that HfO2 thin films could be fabricated under the following experiment parameters: the cubic-phase nanocrystalline HfO2 thin films successfully prepared were annealed at 600 °C for 2 hours in the air. The optimal experiment conditions were the precursor solution containing 5mmol/L Hf(SO4)2•4H2O and 0.3mol/L HCl, the deposition temperature at 70 °C. The surface of thin films was smooth, uniform and dense. It had good adherence with the substrate.
On the basis of the above-mentioned experimental results, the HfO2 thin films were further done with the pattern preparation. Different kinds of micro-patterns were created on the octadecyltrichlorosilane (OTS) self-assembled monolayers utilizing UV lithography with the cover of photomask, The HfO2 pattern films have been formed on silanol SAMs by the liquid-phase deposition (LPD) method. The test results of scanning electron microscopy (SEM), atomic force microscopy (AFM) and energy disperse spectroscopy (EDS) indicated the HfO2 pattern films with distinct patterns were successfully prepared. By UV sculpture, OTS self-assembled monolayers with patterns were prepared. Through the inducing deposition, the HfO2 pattern thin films were successfully prepared. The patterns on the surface of thin films were clear, the line edge roughness was small and they had the greater adherence with the substrate.