Elsevier

Thin Solid Films

Volume 504, Issues 1–2, 10 May 2006, Pages 188-191
Thin Solid Films

Interface control in the laser MBE growth of hafnium oxide

https://doi.org/10.1016/j.tsf.2005.09.086Get rights and content

Abstract

High-k hafnium oxide thin films were deposited on p-type (100) silicon substrate by laser molecular beam epitaxy (LMBE) technique, and these ultrathin gate dielectric films were characterized by Auger electron spectroscopy (AES), capacitance–voltage (CV) and current–voltage (IV) measurements. In order to take full advantages of high dielectric constant of HfO2, the growth of low dielectric constant interfacial layer must be controlled as thin as possible in the deposition process under optimized conditions. The effect of the critical factor of oxygen partial pressure was studied in the range of 2 × 10 3 to 7 × 10 6 Torr while keeping other experimental parameters constant. It was found that by lowering down the oxygen partial pressure to an optimized level, the growth of the low-k interfacial layer was effectively suppressed. A two-step deposition method was adopted to further reduce the thickness of this interfacial layer. The interfacial reaction was better controlled by using this two-step deposition method, resulting in high quality ultrathin HfO2 films on Si with desired and improved dielectric properties.

Introduction

The aggressive scaling of CMOS transistors in recent years has necessitated the search for a suitable high-k gate dielectric to replace the conventional SiO2 that has a low dielectric constant of ∼ 3.9 [1]. A variety of high-k materials, such as HfO2, ZrO2, Al2O3, HfSixOy, HfOxNy and HfAlxOy, has been considered as the potential good candidates for alternative gate dielectrics [2], [3], [4]. Among these alternative high-k dielectric materials, HfO2 has been regarded as the most promising alternative gate dielectric to replace the currently used SiO2 for several reasons, such as its high dielectric constant of about 20–30, large energy band gap of ∼ 5.68 eV, and reasonably high tunneling barrier height of > 1 eV for both electrons and holes [2]. Various thin film fabrication techniques have been attempted to deposit the HfO2 thin films on silicon substrate, including metal organic chemical vapor deposition (MOCVD), atomic layer deposition (ALD), pulsed laser deposition (PLD), sputtering, etc. [5], [6], [7], [8], [9]. Since neither Hf nor HfO2 can effectively block the oxygen diffusion, oxygen ions in the processing environment or in the hafnium oxide thin film can easily reach the Si surface, interact with it, and form the undesirable low-k layer at the interface between the substrate and high-k HfO2 dielectric film. Therefore, in most cases, a considerably thick low–k layer usually exists at the HfO2/Si interface, which will largely increase the equivalent oxide thickness (EOT) and default the significance of scaling down for CMOS transistors [8], [9], [10]. In recent research development, numbers of methods or techniques have been tried by many researchers to suppress the formation of this low-k interfacial layer. Low temperature deposition is one of methods attempted [8], [11], however, also it generally results in a relatively low dielectric constant and the poor leakage current property. Thus, how to effectively suppress the formation of this low-k layer in the deposition process is a challenging issue in alternative high-k dielectric materials for Si CMOS and for nanoelectronics applications.

In this paper, we report our recent research work and experimental results on the ultrathin HfO2 films with EOT of 1.4 nm deposited by the laser molecular beam epitaxy (LMBE) technique and its high-k value of ∼ 20 by suppressing the formation of the interfacial low-k layer. The effect of oxygen partial pressure in LMBE chamber and a two-step deposition scheme on HfO2 film growth and properties are also presented and discussed.

Section snippets

Experimental

HfO2 films were deposited onto (100) p-type silicon wafers with resistivity of 1–10 Ω cm using the KrF excimer LMBE technique. The RCA-cleaned wafers were immediately loaded into the LMBE deposition chamber. During the deposition, the power density of the laser beam with wavelength of 248 nm was fixed at 1.8 J/cm2 and the laser pulse repetition rate was 2 Hz. Either Hf or HfO2 films were deposited by the ablation from a hafnium target with purity of 99.5%. The effect of oxygen partial pressure

Effect of oxygen partial pressure

As expected for growth of any oxide thin films, oxygen partial pressure plays a very important and critical role in depositing this high-k hafnium oxide film. Fig. 1 depicts the AES depth profiles of the four samples listed in Table 1. It is seen from Fig. 1 that with the decrease of oxygen partial pressure from 2 × 10 3 to 2 × 10 5 Torr, the thickness of the interfacial silicate layer between the silicon substrate and HfO2 is effectively reduced from 6.0 to 3.2 nm. Although the Auger electron

Summary

In this paper, we report our experimental approaches, such as variation of oxygen partial pressure and 2-stage deposition method, to effectively suppress and control the formation and growth of the low-k interfacial layer in the LMBE deposition of high-k HfO2 gate dielectric ultrathin films at the HfO2/Si interface. Experimental results show that the thickness of the interfacial layer depends strongly on the oxygen partial pressure in the LMBE chamber during the deposition process. With the

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