Elsevier

Applied Surface Science

Volume 301, 15 May 2014, Pages 28-33
Applied Surface Science

Effect of reactive magnetron sputtering parameters on structural and electrical properties of hafnium oxide thin films

https://doi.org/10.1016/j.apsusc.2014.01.155Get rights and content

Highlights

  • Structural and electrical characterization of HfOx and HfOxNy thin films.

  • Analysis of the influence of deposition process parameters on properties of films.

  • Investigation of the post-deposition annealing on HfOx and HfOxNy properties.

  • Experiment has been designed with use of Taguchi's orthogonal arrays.

  • The most favorable annealing temperature of HfOx and HfOxNy is 300 °C.

Abstract

The purpose of this work was to compare the structural and electrical properties of magnetron sputtered hafnium oxide (HfOx) and hafnium oxynitride (HfOxNy) thin films. A careful analysis of the influence of deposition process parameters, among them: pressure in the reactor chamber, Ar and O2 flow rate, power applied to the reactor chamber and deposition time, on electro-physical properties of HfOx and HfOxNy layers has been performed. In the course of this work we performed number of experiments by means of Taguchi's orthogonal arrays approach. Such a method allowed for the determination of dielectric layers properties depending on process parameters with relatively low amount of experiments. Moreover, the effects of post-deposition annealing on electrical characteristics of metal–insulator–semiconductor (MIS) structures with HfOx or HfOxNy gate dielectric and its structural properties have also been reported. Investigated hafnia thin films were characterized by means of spectroscopic ellipsometry (SE), electrical characteristics measurements, atomic force microscopy (AFM), X-ray diffraction spectroscopy (XRD) and Rutherford backscattering spectrometry (RBS).

Introduction

Ongoing development of the microelectronics, starting from the early 1960s of the 20th century, involves an increase in the integration degree of emerging semiconductor devices, as well as the increase of speed and functionality of integrated circuits (ICs). The scaling of complementary metal-oxide-semiconductor (CMOS) feature size has also caused a decrease of silicon dioxide (SiO2) gate oxide thickness into few nanometer regime. Semiconductor devices with such an ultra-thin SiO2 layer are characterized by unacceptably high leakage current resulting from tunneling current which leads to increased power consumption [1], [2]. In order to reduce the leakage current and capacitance of devices high-κ dielectric layers include HfO2, Al2O3TiO2, ZrO, CeO2 can be used as a substitution of ultra-thin silicon dioxide films [3]. From the point of view of applications in advanced microelectronic devices, hafnium oxide can be characterized by many important properties, such as: high dielectric constant (20–25), large band-gap (5.6 eV), amorphous or polycrystalline structure (depending on process temperature and fabrication method), compatibility with poly-silicon gate process, large conduction band offsets with Si and solid-sate thermodynamic stability on Si [3], [4], [5]. Hafnium oxide is one of the alternative dielectrics with high dielectric permittivity value that already has found applications in commercially available CMOS devices, i.e. as a gate dielectric in MOSFET devices [6], RRAM memories (Resistive Random Access Memory) [7] and for improvement of NVSM devices properties (Non-Volatile Semiconductor Memory) [8], [9]. Hafnium oxide is also used as a passivation layer in devices dedicated for special applications such as high temperature and high power electronics based on silicon carbide (SiC) [10], [11] or InGaAs/InP heterostructure bipolar transistors (HBT) [12]. HfOx is also one of the functional layers in gas sensors, in particular CO2 [13] or field-effect-transistor (FET) based sensors for the detection of deoxyribonucleic acid (DNA) hybridization [14]. Moreover, ISFET (Ion Selective Field Effect Transistors) sensor dedicated to pH, Na+, K, H+ is based on a silicon micromechanical transducers and in those application HfO2 acts as an sensitive layer [15]. HfOx is also an excellent layer from the point of view of applications as an antireflection coating. This is because of its superior properties such as thermal stability, relatively wide band-gap and transparent spectra range from the infrared to the ultraviolet [16]. The fabrication of HfOx films can be achieved using one of the well established for standard silicon-integrated-circuit deposition methods, i.e.: atomic layer deposition [9], reactive magnetron sputtering [17], plasma ion assisted deposition [18] or laser ablation [19]. Reactive magnetron sputtering is a low temperature deposition method which can be used for obtaining high quality thin films even on large area substrates. The method has also a number of other advantages including low cost manufacturing, capability for fabrication of thin oxide or nitride films from metallic target and easily controlled deposition process. In this work, the Taguchi design method was used to perform the series of technological experiments of hafnium oxide thin films deposition by means of reactive magnetron sputtering (RMS) method. Orthogonal experiment scheme (L934) [20] was designed and four critical parameters were taken into account: pressure in reactor chamber, sputtering power, oxygen partial pressure and deposition time. We also report on effects of post-deposition annealing on electrical characteristics of metal–insulator–semiconductor (MIS) structures with HfOx and HfOxNy gate dielectric and its structural properties.

Section snippets

Experimental

The hafnia films were deposited on 2-inch silicon 〈1 0 0〉 “p” substrates (1–10 Ω cm resistivity) cleaned just prior to the processing by Radio Corporation of America (RCA) method [21]. HfOx and HfOxNy thin films were fabricated in Plasmalab System 400 (Oxford Instruments Plasma Technology) at various process parameters: pressure in the reactor chamber, Ar and O2 flow rate, power applied to the reactive chamber and time (Table 1). Deposition temperature was 20 °C and argon flow was set at 25 ml/min.

Range analysis of sputtering parameters

The values of basic electro-physical properties evaluated from electrical characteristics (CV, JV) of studied MIS structures and ellipsometry measurements are presented in Table 2. Implementation of Taguchi's orthogonal arrays to optimize the RMS deposition of HfOx and to minimize the number of expensive technological experiments allowed us to achieve a number of trends of the influence of particular process parameter on various electro-physical properties of HfOx and MIS structures. In the

Conclusions

In this study the comparison of structural and electrical properties of magnetron sputtered hafnium dioxide and oxynitride thin films has been shown. A careful analysis of the influence of deposition process parameters (among them: pressure in the reactor chamber, Ar and O2 flow rates, power applied to the reactor chamber and deposition time) on properties of HfOx layers has been also performed. Presented results have shown that in the case of HfOx as well as HfOxNy gate dielectric, the most

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