Growth of Lanthanum Silicate Thin Films by Liquid Injection MOCVD Using Tris[bis(trimethylsilyl)amido]lanthanum

Abstract

The rapid growth of the silicon-based microelectronics industry since the late 1980s has fuelled a demand for greater integrated circuit functionality and improved performance at lower cost. This requires an increased circuit density, which has been achieved by a continual reduction, or ªscalingº, in the dimensions of the field-effect transistor (FET), [1] the fundamental active device in the silicon integrated circuit (IC). Key elements enabling the scaling of the Si-based metal±oxide±semiconductor field-effect transistor (MOSFET) are the materials and electrical properties of the dielectric layer employed to isolate the transistor gate from the Si channel. For many years, amorphous SiO 2 has been the chosen dielectric layer, due to its stable, high quality, Si±SiO 2 interface, and excellent electrical isolation properties.[2] The rapid shrinking of the transistor feature size has forced the channel length and gate dielectric thickness to also decrease rapidly, but as the dimensions of the SiO 2 layer approach 20±30 , direct electron tunneling effects and high leakage currents present serious obstacles to future device reliability. The use of materials with a higher dielectric constant (k) than SiO 2 allows an equivalent capacitance to be achieved in a physically thicker insulating layer, and thicker layers should, in turn, provide reduced leakage currents. Therefore, there has been much recent research aimed at replacing the conventional SiO 2 gate dielectric with alternative high k dielectric oxides such as Al 2 O 3 , [3] Ta 2 O 5 , [4] TiO 2 , [5] ZrO 2 , [6] HfO 2 , [7] and La 2 O 3 , [8] and their related silicates.[2]Of these materials, lanthanum oxide, La 2 O 3 , has good potential due to its relatively high permittivity, [9] but unfortunately La 2 O 3 is chemically unstable in air, reacting with CO 2 to form La 2 (CO 3 ) 3 , [10] and adsorbing water to give LaO(OH) and La(OH) 3 by an extensive surface hydroxylation process. [11,12] This can result in oxygen vacancies and excess positive charge in the oxide film layer, leading to unwanted flat-band voltage shifts in the metal±oxide dielectric structure.[8] Some recent research efforts have therefore focussed on the deposition and properties of lanthanum silicate (LaSi x O y ) films. [13,14] Although LaSi x O y films have a lower permittivity than La 2 O 3 , they are more stable and are less likely to contain oxygen deficiencies.There have been a number of recent studies into the deposition of La-containing insulators for gate dielectric applications. For example, some of the highest capacitance metal±insulator±silicon structures have been fabricated by the deposition of metallic La followed by low temperature oxidation. [15] However, the precise nature of these films is uncertain due to the ready formation of lanthanum silicate at the silicon±LaO x interface. For instance, a significant concentration of Si (~10 at.-%) was observed in LaO x films deposited by atomic beam deposition on a Si(100) substrate, [8] whilst a La±Si±O alloy was observed to form at ...

Growth of Praseodymium Oxide and Praseodymium Silicate Thin Films by Liquid Injection MOCVD

“…An Arrhenius plot of this data, shown in Figure 5b, . [17] The PrSi x O y films also contain significantly higher levels of residual carbon (1.9 at.-% to 4.2 at.-%) than the LaSi x O y films (C not detected). The high levels of Si in the PrSi x O y films obtained at low growth temperatures (350 C), as well as the trends in the AES depth profiles (which demonstrate increasing Si concentrations towards the surface of the film), indicate that Si out-diffusion from the substrate is not an important factor.…”

MOCVD and ALD of High‐k Dielectric Oxides Using Alkoxide Precursors

“…[70] Simple 3 ]/3 tetraglyme to grow oxide films of La, [73] Pr, [74,75] Nd, [76] and Gd, [77] 3 ]/3 tetraglyme to grow thin films of praseodymium oxides on Si(100) over a wide range of substrate temperatures from 250 to 600°C. [74] XRD data for PrO x films deposited between 400 and 550°C in the presence of oxygen indicated that the layers were comprised predominantly of the b-Pr 6 O 11 phase.…”

The effect of Si surface nitridation on the interfacial structure and electrical properties of (La2O3)0.5(SiO2)0.5 high-k gate dielectric films

“…Moreover, some rare earth oxides, such as Sc 2 O 3 [5], Y 2 O 3 [6] and Pr 2 O 3 [12], are epitaxially grown on Si (1 1 1), which eliminates problems related to grain boundaries in polycrystalline films. Among rare earth oxides, La 2 O 3 is attractive due to its highest dielectric constant, but it is chemically unstable, as lanthanum hydroxide and carbonate are formed with exposure to ambient atmosphere [13], resulting in the unwanted flatband voltage shifts. Therefore several recent studies report preferential formation of lanthanum silicate films to improve the electrical and structural stabilities of La 2 O 3 [13,14].…”

“…Among rare earth oxides, La 2 O 3 is attractive due to its highest dielectric constant, but it is chemically unstable, as lanthanum hydroxide and carbonate are formed with exposure to ambient atmosphere [13], resulting in the unwanted flatband voltage shifts. Therefore several recent studies report preferential formation of lanthanum silicate films to improve the electrical and structural stabilities of La 2 O 3 [13,14]. Although detrimental to the permittivity, they are more stable and less apt to contain oxygen deficiencies.…”