| AVS 57th International Symposium & Exhibition | |
| Thin Film | Tuesday Sessions |
| Session TF1-TuM |
| Session: | ALD: Dielectrics for Semiconductors |
| Presenter: | L.C. Haspert, University of Maryland |
| Authors: | L.C. Haspert, University of Maryland P. Banerjee, University of Maryland L. Henn-Lecordier, University of Maryland G.W. Rubloff, University of Maryland |
| Correspondent: | Click to Email |
Thin film TiO2 is a relatively high permittivity material with applications in electronic and energy devices. However, TiO2 crystallizes easily, forming grain boundaries and creating current percolation pathways which increase leakage current and power consumption. Al-doped TiO2 (ATO) increases the thermal stability of TiO2, reducing leakage currents by suppressing phase transformation and limiting grain growth. To achieve the benefits of Al doping which retaining those of TiO2, structure-property relationships must be optimized as a function of processing parameters.
Raman spectroscopy (RS), a highly sensitive technique for observing the evolution of nano-crystalline phases - their time evolution, volume fraction, defect states and stresses, is employed here to characterize ATO films grown by atomic layer deposition (ALD) and their correlation with electrical performance. 25nm TiO2 thin films were deposited at 150ᵒC in a Beneq TFS500 cross-flow ALD reactor by sequentially pulsing TDMAT and water precursors. Aluminum doping was controlled from 0 to 15 at% by introducing a single TMA / water pulse sequence at pre-determined intervals of multiple TDMAT/water pulse sequences during oxide growth, producing reproducible compositions estimated from their TiO2 to Al2O3 pulse ratios. Following ALD the films were rapid thermal annealed (RTA) in an oxygen-rich environment ranging from 600ᵒC to 1000ᵒC from 5 to 300 sec.
The degree of crystallization was determined primarily through lineshape analysis of the Raman-active 144 cm-1 frequency mode. RS (and XRD) detected only the TiO2 anatase phase, even at annealing temperatures where rutile formation was expected. RS data clearly shows the crystallization of TiO2 with thermal anneal and that the crystallization onset shifts to higher temperatures with Al-doping while producing smaller grains. Pure TiO2 films show a dielectric constant of 28.5 with high leakage currents (up to 10-3 A/cm2). Annealed ATO films have a slightly lower dielectric constant (24) but leakage currents are dramatically reduced to ~ 1.0x10-7A/cm2. The clear correlation between the microstructure measured by RS and the electrical performance of ALD TiO2 and ATO thin films shows that RS can be a rapid, valuable monitor of thin film material nanostructure for correlation and optimization with electrical properties.
This work was supported by Laboratory for Physical Science, UMD