| AVS 62nd International Symposium & Exhibition | |
| Thin Film | Wednesday Sessions |
| Session TF+SS-WeM |
| Session: | ALD Surface Reactions and Precursors |
| Presenter: | Jaime DuMont, University of Colorado at Boulder |
| Authors: | J.W. DuMont, University of Colorado at Boulder Y. Lee, University of Colorado at Boulder S.M. George, University of Colorado at Boulder |
| Correspondent: | Click to Email |
Sequential exposures of Al(CH3)3 [trimethylaluminum (TMA)] and HF can lead to either AlF3 atomic layer deposition (ALD) or Al2O3 atomic layer etching (ALE). The observation of AlF3 ALD or Al2O3 ALE depends on temperature and pressure. AlF3 ALD occurs at lower temperatures and higher pressures. Al2O3 ALE of an initial Al2O3 film occurs at higher temperatures and lower pressures. The AlF3 ALD or Al2O3 ALE were investigated using in situ Fourier transform infrared (FTIR) spectroscopy and quartz crystal microbalance (QCM) measurements.
The FTIR analysis observed AlF3 ALD or Al2O3 ALE by measuring the absorbance gain of Al-F stretching vibrations in AlF3 or the absorbance loss of Al-O stretching vibrations in Al2O3. At lower temperatures, the HF exposures react with the underlying Al2O3 surface to form AlF3 and HF molecules on the surface. TMA molecules subsequently react with HF on the surface to yield AlF(CH3)2 surface species. AlF(CH3)2 is then converted to AlF3 with the next HF exposure producing AlF3 ALD. At higher temperatures, the HF exposures react with the underlying Al2O3 surface to form AlF3 and fewer HF molecules absorb on the surface. TMA then accepts fluorine from AlF3 to form AlF(CH3)2 which desorbs from the surface and leads to etching of the initial Al2O3 film.
The effect of pressure was also explored by adjusting the N2 carrier gas flow from 0-150 sccm to vary the background pressure from 30 mTorr to 1.6 Torr. These FTIR experiments revealed that the transition from AlF3 ALD to Al2O3 ALE occurred at higher temperatures for higher background pressures. The higher pressures apparently produce a “cage effect” and increase the lifetime of the AlF(CH3)2 surface species that leads to AlF3 ALD. The QCM experiments measured an AlF3 ALD growth rate that progressively decreased at higher temperatures and went negative at >250°C when TMA and HF etched the AlF3 or Al2O3 films.