Atomic Layer Deposition of Amorphous Hafnium-based Thin Films with Enhance Thermal Stabilities PDF Download

Author: Tuo Wang
Publisher:
ISBN:
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Languages : en
Pages : 280

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Book Description
The continuous scaling of microelectronic devices requires high permittivity (high-k) dielectrics to replace SiO2 as the gate material. HfO2 is one of the most promising candidates but the crystallization temperature of amorphous HfO2 is too low to withstand the fabrication process. To enhance the film thermal stability, HfO2 is deposited using atomic layer deposition (ALD), and incorporated with various amorphizers, such as La2O3, Al2O3, and Ta2O5. The incorporation is achieved by growing multiple ALD layers of HfO2 and one ALD layer of MO[subscript x] (M = La, Al, and Ta) alternately (denoted as [xHf + 1M]), and the incorporation concentration can be effectively controlled by the HfO2-to-MO[subscript x] ALD cycle ratio (the x value). The crystallization temperature of 10 nm HfO2 increases from 500 °C to 900 °C for 10 nm [xHf + 1M] film, where x = 3, 3, and 1 for M = La, Al, and Ta, respectively. The incorporation of La2O3, and Ta2O5 will not compromise the dielectric constant of the film because of the high-k nature of La2O3, and Ta2O5. Angle resolved X-ray photoelectron spectroscopy (AR-XPS) reveals that when the HfO2-to-MO[scubscript x] ALD cycle ratio is large enough (x> 3 and 4 for La and Al, respectively), periodic structures exist in films grown by this method, which are comprised of repeated M-free HfO2 ultrathin layers sandwiched between HfM[subscript x]O[scubscript y] layers. Generally, the film thermal stability increases with thinner overall thickness, higher incorporation concentration, and stronger amorphizing capability of the incorporated elements. When the x value is low, the films are more like homogeneous films, with thermal stabilities determined by the film thickness and the amorphizer. When the x value is large enough, the periodically-repeated structure may add an extra factor to stabilize the amorphous phase. For the same incorporation concentration, films with an appropriately high periodicity may have an increased thermal stability. The manner by which the periodic structure and incorporated element affect thermal stability is explored and resolved using nanolaminates comprised of alternating layers of [scubscript y]HfO2 and [xHf + 1M] x n, where y varied from 2 to 20, x varied from 1 to 2, and n varied from 4 to 22.