Film properties of ALD HfO2 and La2O3 gate dielectrics grown on Si with various pre-deposition treatments

Abstract

In this article, we report film properties of HfO2 and La2O3 gate dielectrics grown on Si(100) substrate using atomic layer deposition (ALD) with various surfaces modified before film growth. The precursors used for HfO2 and La2O3 films are hafnium tetrachloride (HfCl4), lanthanum tris[bis(trimethylsilyl)amide] (C18H54N3LaSi6) and water. Pre-deposition treatments examined for HfO2 dielectric films include (1) surface nitridation using NH3, N2O, or NO, (2) substrate annealing in an oxidizing or reducing ambient, and (3) surface fluorination. These results were compared to those obtained using established approaches of growing HfO2 on an OH terminated surface produced chemically. Linear film growth was observed for the HfO2 with all pre-deposition treatments. Time-of-flight-secondary ion mass spectrometry (TOF-SIMS) and transmission electron microscopy (TEM) analysis indicated that all pre-treatments result in good film coverage with no interaction between HfO2 and silicon at the silicon substrate. The as deposited ALD HfO2 film is mainly amorphous, continuous, and relatively smooth on all pretreated Si surface. The thickness of a thin interfacial layer varies depending on the particular pre-treatments. Similar studies were also conducted for the growth of ALD La2O3. In this case, a significant interaction between La2O3 and silicon substrate was observed on films grown directly on chemical oxide. A rough interface between La2O3 and the silicon substrate is clearly seen in XTEM results. This interaction is more significant when the film is deposited at higher temperature. The XTEM images showed that the ALD La2O3 films are mostly amorphous. Results show that independent of surface pre-treatments, interactions between La2O3 and the silicon substrate occur for the deposition conditions explored here. Electrical characterization using evaporated platinum electrodes and mercury probe of the high-k film stacks have been carried out to determine the impact of the pre-treatments on the electrical properties of the films. Results indicated that ALD HfO2 films have higher dielectric constant, lower leakage and better flatband voltage stability during post deposition annealing compared to ALD La2O3 films. These results indicate that ALD HfO2 is a more promising candidate than ALD La2O3 due to superior thermal stability in contact with silicon.

Atomic Layer Deposition and Properties of Lanthanum Oxide and Lanthanum‐Aluminum Oxide Films

“…[7,8] The performance of La 2 O 3 dielectrics appeared to be rather unstable, compared to HfO 2 , when La 2 O 3 and HfO 2 were synthesized and examined under similar reactor conditions. [4] Lanthanum is also used as a component of mixed oxides, solid solutions, or binary phases, and is often mixed with alumina, forming mainly amorphous materials [9][10][11] with target stoichiometry corresponding to LaAlO 3 . In the crystalline form, LaAlO 3 is a layered, perovskite-type structure with alternate Al-O 2 and La-O layers comprising the lattice units.…”

“…[11,27] LaAlO 3 films can be processed by various techniques, such as molecular-beam epitaxy (MBE), [11,24,26,28] pulsed laser deposition, [27,29] magnetron sputtering, [15] or using 158 chemical methods such as alkoxide-based sol-gel chemistry, [16] thermolysis of hydrated nitrates, [18,23] gelation-precipitation techniques, [30] or metal-organic (MO) CVD. [8,[31][32][33] More recently, atomic layer deposition (ALD) has been examined as a low-temperature growth technique for synthesizing La 2 O 3 and LaAlO 3 films [1,4,7,[34][35][36] The lanthanum b-diketonate La(thd) 3 (thd = 2,2,6,6-tetramethyl-3,5 heptanedione) has been examined as a lanthanum precursor, [7,35] with ozone as an oxygen precursor, resulting in the growth of cubic La 2 O 3 at 300-350°C and higher temperatures. [7,35] Below 275°C, only [1,4] and also for the ALD of La-rich La x Al y O z films.…”

“…[1][2][3][4] The dielectric permittivity values of La 2 O 3 are in the range [20][21][22][23]. [1] Regarding transistor technology, gate current density values could be lower with La 2 O 3 compared to Al 2 O 3 and HfO 2 .…”

Limits of Optical and X-ray Metrology Applied to Thin Gate Dielectrics

“…1,4 Thin metal oxides on Si often contain a thin SiO 2 -like interfacial layer between the substrate and the film, whose thickness varies with process conditions. 3,6,7 It is desirable to determine both thicknesses (metal oxide film and interfacial layer) from XRR to avoid the need for destructive and time-consuming transmission electron microscopy (TEM) analysis, which also has limitations. Unfortunately, we were unable to meet this goal.…”

“…Figure 3 shows a typical XRR spectrum for 150 Å (nominal) HfO 2 on Si grown by atomic layer deposition. 3 The fit parameters are as follows: 2.4 Å substrate roughness, 135 Å metal oxide thickness with 9.6 g/cm 3 density (95% of bulk HfO 2 ), 4.1 Å surface roughness. Annealing this film at 1000°C for 30 s slightly increases the HfO 2 thickness, see Table 2.…”