Jasmine Petry

Characterization of ALCVD-Al2O3 and ZrO2 layer using X-ray photoelectron spectroscopy

The atomic layer chemical vapor deposition (ALCVD) deposited Al 2 O 3 and ZrO 2 films were investigated by ex situ X-ray photoelectron spectroscopy. The thickness dependence of band gap and valence band alignment was determined for these two dielectric layers. For layers thicker than 0.9 nm (Al 2 O 3 ) or 0.6 nm (ZrO 2 ), the band gaps of the Al 2 O 3 and ZrO 2 films deposited by ALCVD are 6.7 ± 0.2 and 5.6 ± 0.2 eV, respectively. The valence band offsets at the Al 2 O 3 /Si and ZrO 2 /Si interface are determined to be 2.9 ± 0.2 and 2.5 ± 0.2 eV, respectively. Finally, the escape depths of Al2p in Al 2 O 3 and Zr 3p3 in ZrO 2 are 2.7 and 2.0 nm, respectively.

Surface preparation and interfacial stability of high-k dielectrics deposited by atomic layer chemical vapor deposition

The effects of various interface preparations on atomic layer chemical vapor deposition (ALCVD) deposited Al2O3 and ZrO2 dielectrics properties were investigated by X-ray photoelectron spectroscopy (XPS), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), medium energy ion scattering (MEIS) and transmission electron microscopy (TEM). H-terminated Si, SiO2 and SiOxNy surfaces were used as substrates upon which the dielectric was deposited. Thermal annealing of SiO2 in NH3 forms an oxynitride; subsequent deposition of a ZrO2/Al2O3 bi-layer stack resulted in a capacitor structure with an equivalent oxide thickness (EOT) of ˜ 0.8 nm and a leakage current of 3 × 10-4 A/cm2 at - 1 + Vfb. This is in contrast to capacitor structures grown on H-terminated Si where high leakage was found. The growth of additional interfacial SiO2 during processing, a critical problem in nano-electronic device applications, is temperature dependent with ZrO2 exhibiting a higher oxygen permeability than Al2O3. Use of a polysilicon cap was shown to be effective at blocking oxygen absorption and transport through the high-k dielectrics, with stability up to 1100 °C.

Composition and Growth Kinetics of the Interfacial Layer for MOCVD HfO2 Layers on Si Substrates

To boost MOS transistor performance, thickness of the gate dielectric is continuously scaled down. This results in an increase of gate tunneling leakage current, which at some point prevents further downscaling. Desired parameters of alternative materials to SiO 2 are a higher dielectric constant (high-k materials), stability, and compatibility with silicon. A general observation for one of the prime candidates. HfO 2 , is formation of an interfacial layer between the silicon and the high-k material that limits scalability because of its low k-value. Hence, a thorough study of the formation of this layer and its contribution to the equivalent oxide thickness is of utmost importance. We studied the composition and growth kinetics of the interfacial layer formed during the deposition of HfO 2 by metallorganic chemical vapor deposition using O 2 and tetrakis-diethylamidohafnium as precursor. We found the composition and thickness of the interfacial layer to be dependent on the deposition parameters as well as on the starting surface. The layers composition is hafnium silicate-like and its thickness increases as a function of deposition time and temperature. It is therefore controlled by deposition of the HfO 2 layer.

Impact of incorporated Al on the TiN/HfO2 interface effective work function

First principles calculations of the impact of Al incorporation on the effective work function of a TiN/HfO2 interface are presented. The undoped interface has a midgap effective work function. We find that Al in the metal and Al substituting for O in the dielectric make the effective work function more n-type. More importantly, Al substituting for Hf in the oxide near the interface—the energetically stable position for most growth conditions—increases the effective work function, making it more p-type. Furthermore, the shift of the work function increases with increasing the Al concentration at the interface. The calculated results are consistent with experimental data.

Thermal stability and scalability of Zr-aluminate-based high-k gate stacks

It is demonstrated that a narrow composition range exists in the ZrAl/sub x/O/sub y/ mixed oxide system between 25 and 50 mol% Al/sub 2/O/sub 3/, where the crystallization temperature exceeds 950/spl deg/C and at the same time the k-values remain larger than 12. In this composition range, enhanced thermal stability for better integration of the ZrAl/sub x/O/sub y/ gate dielectric in a conventional poly-Si device process is observed. It is also shown that thin interfacial oxides strongly enhance the electrical stability while allowing for thickness scaling down to /spl sim/1 nm, providing gate leakage current reductions of two to three orders of magnitude.

On the data interpretation of the C-AFM measurements in the characterization of thin insulating layers

The interpretation of the conductive atomic force microscopy (C-AFM) results is discussed in the framework of the characterization of the high-k layers as gate oxide. Because the high-k layer is deposited on an interfacial layer, at high gate voltage, the C-AFM current maps do not reflect the high-k properties but rather the interface. Moreover, in the point contact mode, the surface of the equivalent capacitor as well as the voltage and current ranges used with the C-AFM are different from the one used in common IV. The interpretation of macroscopic measurements can therefore not be transposed to the C-AFM results. More specifically, the shift towards lower voltage of the backward curve is ascribed to the creation of a conducting path at high voltage.

TOF-SIMS as a rapid diagnostic tool to monitor the growth mode of thin (high k) films

Abstract For deep submicron technologies it is of crucial importance to grow ultra-thin (

Nanoscale post-breakdown conduction of HfO/sub 2//SiO/sub 2/ MOS gate stacks studied by enhanced-CAFM

An enhanced conductive atomic force microscope has enabled a measurement of the conduction through a HfO/sub 2//SiO/sub 2/ gate stack until breakdown (BD) in a single measurement, with nanometer resolution. Before the stack BD, the current-voltage characteristic shows several conduction modes. After BD, switchings between different conduction states were observed, showing that BD is a reversible phenomenon.

Breakdown spots of ultra-thin (EOT < 1.5 nm) HfO2/SiO2 stacks observed with enhanced—CAFM

Abstract In this work, the (gate) current versus (gate) voltage ( I – V ) characteristics and the dielectric breakdown (BD) of an ultra-thin HfO 2 /SiO 2 stack is studied by enhanced conductive atomic force microscopy (ECAFM). The ECAFM is a CAFM with extended electrical performance. Using this new set up, different conduction modes have been observed before BD. The study of the BD spots has revealed that, as for SiO 2 , the BD of the stack leads to modifications in the topography images and high conductive spots in the current images. The height of the hillocks observed in the topography images has been considered an indicator of structural damage.

Effect of N2 annealing on AlZrO oxide

In the path to the introduction of high-k dielectric into integrated circuit components, a large number of challenges has to be solved. Subsequent to the film deposition, the high-k film is exposed to additional high-temperature anneals for polycrystalline Si activation but also to improve its own electrical properties. Hence, concerns can be raised regarding the thermal stability of these stacks upon annealing. In this study, we investigated the effect of N2 annealing (700 to 900 °C) of atomic layer chemical vapor deposition AlZrO layers using x-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOFSIMS), transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) spectroscopy. The effect of the Si surface preparation [H–Si, 0.5 nm rapid thermal oxide (RTO), Al2O3] on the modification of the high-k oxide and the interfacial layer upon annealing was also analyzed. Compositional changes can be observed for all temperature and surface preparations. In par...