24September2017

Materials and Electronics Engineering

Studying the chemical composition and structure of hafnium, aluminium and lanthanum oxide films by X-ray photoelectron spectroscopy

Zhongli Li1, Yijian Liu1, Huijuan Geng1, AyraJagadhamma Letha2, Limin Sun3, Ying Wang1*, Huey-Liang Hwang1, 2*, Fedor A. Kyznetsov4, Tamara P. Smirnova4, Andrey A. Saraev5, Vasily V. Kaichev5, 6

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1Key Laboratory for Thin Film and Micro fabrication of Ministry of Education, Department of Micro/Nano Electronics, Shanghai Jiao Tong University, Shanghai 200240, P R China
2Department of Electrical Engineering and Institute of Electronics Engineering, National Tsing Hua University, Hsinchu 300, Taiwan
3Shanghai Jiao Tong University, Shanghai 200240, P R China
4Nikolaev Institute of Inorganic Chemistry, 630090 Novosibirsk, Russia
5Boreskov Institute of Catalysis, 630090 Novosibirsk, Russia
6Novosibirsk State University, 630090 Novosibirsk, Russia

Materials and Electronics Engineering 2015, 2:2

Publication Date (Web): October 2, 2015 (Article)

DOI:10.11605/mee-2-2

*Corresponding author. E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it. ; This email address is being protected from spambots. You need JavaScript enabled to view it.

 

Abstract

 


 Figure 1 The percentage of elements within the analysis area depending on ion sputtering time for films N1-N4.

In this paper, high-κ oxides films, Al2O3, HfO2, Al2O3/HfO2, Al2O3/La2O3 and HfO2/La2O3 stacked structures, were deposited on p-type Si wafers using plasma-enhanced atomic layer deposition (PEALD). The chemical composition and structure of the deposited high-κ films were investigated in detailed research by X-ray photoelectron spectroscopy. The layer by layer depth profiling and XPS analysis indicated that the synthesized stacked structures films are alloys, consist of Hf–Al–O, La–Al–O and Hf–La–O. And the analysis results suggested that the interfacial layer were most likely composed of Hf–Si–O for Al2O3/HfO2, La–Si–O for Al2O3/La2O3, Hf–Si–O and La–Si–O for HfO2/La2O3 rather than pure silicon oxide. It is also found that Hf and La was easier to react with Si to form silicate at the interface near Si. And the top surface is easy to absorb CO2 on the surface as a result of contact with air at normal conditions when La existed.


 

Keywords

Chemical composition, Lanthanum oxide film, X-ray photoelectron spectroscopy

 

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Introduction

    Surface passivation is of importance for a range of crystalline silicon (c-Si) based electronic devices, and in particular for nano scale CMOSFET and high-efficiency c-Si solar cells [1, 2]. Recently, high-κ oxides, such as aluminum oxide (Al2O3), and hafnium oxide (HfO2), have been widely employed as passivation layers in Si-based nano scale transistors. A suitable high-κ dielectric passivation layer can significantly increase the open circuit voltage, and improve the efficiency of the devices [3].

    So far, high-κ material research has been focused on Al2O3, HfO2, and lanthanum oxide (La2O3). Al2O3 has a relatively low dielectric constant (~9), larger band gap (~6.5 eV), stronger adhesion to many surfaces, excellent thermal stability, and a large band offset with a silicon substrate [4], which has been widely demonstrated to provide excellent passivation properties on Si surface. The most popular of these oxides is HfO2, HfO2 film has a relatively high dielectric constant (25~30) and a large band gap (~5.68 eV) with good thermal stability [5], which makes it suitable to passivate surface state. Apart from HfO2, another promising material is La2O3. It has a higher dielectric constant than HfO2 and a better thermodynamic stability on Si than Al2O3 [6]. However, HfO2 film and La2O3 film have been rarely used as passivation layers on Si surface. Besides, using the simple high-κ film as passivation layer, there are some drawbacks, such as high density of the oxide trap charge. So in order to further improve the interface property, stacked multilayer structures have been widely studied [7, 8], which do not require a strict composition ratio of two metal oxides but can combine the advantages of them.

    Several methods have been explored for the formation of high-κ films, such as molecular-beam epitaxy [9], PECVD [10], magnetron sputtering [11, 12] and atomic layer deposition (ALD) [3]. Among all the methods mentioned above, ALD process is a self-limiting growth method, where growth is achieved by alternatively pulsing precursors into the deposition chamber. And the process has many practical advantages, such as conformal coating, excellent uniformity, and composition and stoichiometry control, nano scale thickness control and the ability to grow uniform layers over a large substrate area [13]. ALD has been considered as a promising method for the layer-by-layer deposition of high-κ materials.

    To advance the current understanding on electronic structure of the high-κ dielectric materials system, Al2O3, HfO2, Al2O3/HfO2, Al2O3/La2O3 and HfO2/La2O3 stacked structures were grown on p-type Si (100) substrates using ALD method. We systematically investigated the chemical composition and structure of the deposited high-κ dielectric films by XPS. And the interface structures of the different prepared films were also compared.

Experiments

    The high-κ films were fabricated by ALD method on p-type silicon wafers (525 μm thick, 6 Ω-cm). Prior to film deposition, the Si wafers were ultrasonically cleaned with acetone and then thoroughly rinsed in deionized water. Finally, Si wafers were immersed into dilute HF (1:100) for 1 min to remove native SiO2 and to leave an H-terminated Si surface. Al2O3, HfO2, Al2O3/HfO2, Al2O3/La2O3 and HfO2/La2O3 films were deposited using hafnium precursor (Tetrakis(ethylmethylamino) hafnium(IV), TEMAH), aluminum precursor (Trimethylaluminium, TMA) and lanthanum precursor (La(iPr2-FMD)3) as precursors, H2O served as an oxygen source. The lative percentages of Al, Hf and La in the as-deposited films can be controlled by the ratio of the number of Al, Hf and La cycles. During deposition, Ar was employed as carrier and purge gas, the chamber temperature was held at 300 oC. The detailed process conditions for the depositions of samples were shown in Supplementary information.

    The compositions and chemical structures of the high-κ films were investigated using X-ray photoelectron spectrometer (XPS, SPECS Surface Nano Analysis GmbH, Germany). The core-level spectra were obtained using monochromatic Al Kα radiation (h* = 1486.74 eV) and a fixed analyzer passing energy of 20 eV under ultrahigh vacuum conditions. To carry out a layer-by-layer analysis, the etching of film surfaces by a focused Ar+ beam (2.4 keV, ~10 µA/cm2) was applied. According to the layer-by-layer analysis of SiO2/Si thin film, the rate of layers removing is ~0.5 nm/min at the given parameters. Relative concentrations of elements within the analysis area were determined from the integrated intensities of XPS peaks using the cross-sections according to Scofield [14]. To produce a detailed analysis, the resolution of spectra for individual components was performed.

Results and discussion

Films N1-N4:Al2O3/HfO2 stacked structures with different Al-Hf ratios

    The surveyed spectra of films N1-N4 taken for initial surfaces revealed the Hf (except for film N1), C, O, Al, Si as well as F lines, F being a random impurity. Fluorine could be adsorbed on the sample surface directly in the spectrometer chamber while registering XPS spectra. As practice shows, it is on this spectrometer that fluorine admixture is revealed while examining films and powders containing Al oxide. Other elements presence in the film structure was lower than the detection limit of XPS method. To determine the depth-profiling of elements, film spectra were registered after ion etching for 1, 2, 5 and 10 min. Atomic ratios [Al]/[Hf], [O]/[Hf+Al], [C]/[Hf+Al], [Si]/[Hf+Al], [CO3]/[Hf+Al] and [F]/[Al] detected during the layer-by-layer analysis were presented in Table 1. From Table 2, it could be seen that C and F were present only on the surface of the film, therefore, it was suggested that only the surfaces of the films were contaminated. Besides, for N2-N4, the ratios of [Al]/[Hf] appeared that substantial Hf enrichment occurred at the interface near Si. No matter what the content of Al and Hf in the samples was, the phenomena of Al deficiency near the Si surface still existed. It could be anticipated that Al has a high nucleation barrier on Si, leading to rich Hf during initial growth.

Table 1 The results of layer-by-layer analysis of films N1-N4.

table 1

    Figure 1 exhibited the changes in the percentage of elements within the analysis area of films N1-N4 (without C and Si) depending on the ion sputtering time. It could be seen that the concentrations of Al, Hf and O changed slightly with increasing sputtering time, which indicated that the as-deposited high-κ films were continuous with uniform dense layers and consisted of a continuous series of solid solutions formed during the co-deposition of two precursors containing Al and Hf.

Figure 1 The percentage of elements within the analysis area depending on ion sputtering time for films N1-N4.

Figure 1 The percentage of elements within the analysis area depending on ion sputtering time for films N1-N4.

    Table 2 exhibited the binding energy values of separate spectrum components Hf4f7/2, Al2p, O1s. Spectra C1s revealed another peak at 288.8-289.2 eV which could be attributed to carboxyl and/or carbonate groups, in addition to the peak at 284.8-285.1 eV corresponding to C-C bonds in hydrocarbon impurity [15, 16]. It was important to note that carbonate groups are mainly localized on the surface.

Table 2 Summary of binding energies of Hf4f7/2, Al2p, O1s, Si2p and C1s for the films N1-N4 with different sputtering times.

table 2

    Figure 2 shows the Al2p spectra of films N1-N4. The spectra are normalized to the total integrated intensity of corresponding Al2p and Hf4f7/2 spectra. The Al2p spectrum of the initial surface of the film N1 consists of a symmetric peak at 74.25 eV (the binding energy (Eb) was corrected to the C1s peak at 284.80 eV originating from the adventitious surface hydrocarbons. After ion etching, the binding energy was corrected to the Al2p peak at 74.25 eV). The binding energy was typical of aluminum in the Al3+ state in Al2O3 (Eb= 74.2-74.6 eV) [17-19]. The O1s binding energy was equal to 531.0 eV, which was also typical of Al2O3, this was consistent with the literature reporting the O1s binding energy of oxygen in Al2O3 is in the range of 531.0-531.6 eV [17-19]. The lower value of Al2p binding energy could be attributed to complex oxides (Hf–Al–O). According to the literature, the Al2p binding energies are in the range of 73.3-74.1 eV for Al in spinels (like Zn-Al-O) [20-22].

Figure 2 Normalized Al<em>2p</em> spectra of films N1-N4.

Figure 2 Normalized Al2p spectra of films N1-N4.

    An additional peak was observed at 72.5 eV in the Al2p spectra of the films N1 and N2 after ion etching for 10 and 5 min, respectively, which was due to the differential charging effect. The spectra of the films N2, N3 and N4 were calibrated according to the position of the Hf4f7/2 peak at 16.9 eV. In this case, the binding energy C1s for the sample N2 varied within a narrow range of 284.70-284.85 eV, indicating quite a high registration accuracy of the charging effect correction. For the samples N3 and N4 somewhat higher value of the C1s binding energy was observed within 285.05-285.09 eV.

    Figure 3 displays the normalized Hf4f spectra of the films N2-N4 obtained during a layer-by-layer analysis. Hafnium 4f-level is known to split into two sublevels, namely, Hf4f7/2 and Hf4f5/2 due to spin-orbital interactions. Accordingly, there appears Hf4f7/2–Hf4f5/2 doublet, its spin-orbital splitting being 1.66 eV, in Hf4f spectra of initial film surfaces. The position of Hf4f7/2 peak is 16.9 eV, which correspond to Hf in the Hf4+ state. It is in good agreement with the literature reports where the binding energy values of HfO2 are in the range of 16.3-17.1 eV [23, 24].

Figure 3 Normalized Hf<em>4f</em> spectra of films N2-N4.The blue peaks indicate doublets referring to Hf in hafnium silicide (HfSi<sub>x</sub>), red peaks indicate doublets referring to Hf in a complex oxide HfSi<sub>x</sub>O<sub>y</sub> forming an interface layer.

Figure 3 Normalized Hf4f spectra of films N2-N4.The blue peaks indicate doublets referring to Hf in hafnium silicide (HfSix), red peaks indicate doublets referring to Hf in a complex oxide HfSixOy forming an interface layer.

    After ion etching for 5 min, additional Hf4f7/2–Hf4f5/2 doublets with the Hf4f7/2 binding energies at 15.5 and 13 eV corresponding to hafnium in the Hf–Si–O interface layer and HfSix appeared in the Hf4f spectra [25]. The appearance of Hf–Si–O peak suggested the formation of hafnium silicate due to the interaction of HfO2 and Si. The narrow asymmetric peak in Hf4f spectrum in the field of lower binding energies closely corresponded to hafnium silicide, as the difference of binding energies and Hf4f7/2 is 84.5±0.1 eV for films N2-N4. The energy shift Si2p3/2 was defined by the differential charging effect of the surface. Compared with Al2p spectra, HfSix layer played a critical role in explaining the Hf4f XPS spectra.

    It should be noted that on fixing the position of Hf4f7/2 peak, the binding energies of Al2p shift monotonically from 74.25 eV to 74 eV when Hf existing. It actually reflected the nature of a local chemical environment of Al cations [26],which indicated that the prepared compound films under non-equilibrium conditions are not a mixture of HfO2 and Al2O3 phases. Moreover, for films N1-N4, the main oxygen peak also shifted to lower position with the Hf concentration increasing, which also indicated the formation of (HfO2)x(Al2O3)1-x alloys [27, 28]. Moreover, elemental Hf readily reacts with Si to form Hf silicide, while Al does not react with Si, and the presence of Al has no effect on silicate formation at the interface between the film and Si [29]. Thus, the XPS data directly confirmed the formation of Hf–Al–O films fabricated by ALD method, and the interfacial layer was a mixed compound of Hf–Si–O that was caused by the interfacial reaction during the film fabrication. The synthesized films were (HfO2)x(Al2O3)1-x alloys, but not a mixture of HfO2 and Al2O3 phases. 

Films N5 and N6: Al2O3/La2O3 stacked structures with different Al-La ratios

    There were La, C, O, Al and Si lines in the surveyed spectra of films N5 and N6 registered for initial surfaces. To determine the depth-profiling of element distributions film spectra were taken after ion etching for 1, 2, 5, and 10 min. The atomic ratios [La]/[Al], [O]/[La+Al], [C]/[La+Al], [Si]/[La+Al] and [CO3]/[La+Al] and [F]/[Al] detected during the layer-by-layer analysis are presented in TABLE III. The intensity of C1s and CO3line became below detection level after etching for 1 min, which indicated carbonate groups are mainly localized on the top surface layers, this was formed as a result of contact with air at normal conditions. Compared with the percentage of [CO3] in sampleN1, N5 and N6, it could be seen that the percentages of [C] and [CO3] increased with the percentage of La increasing, which indicated that the absorption of CO2 on the surface and the formation of lanthanum carbonate is very easy when La existed [30]. Besides, irrespective the content of Al and La in the samples N5 and N6, the ratio of [La]/[Al]in the depth profile revealed that substantial La enrichment occurred at the interface near Si, and Al element is deficient. The enrichment of La at the interface was expected to contribute significantly to that La was easier to nucleate than Al on Si, leading to rich La during initial growth [31], which is consist with the report that La2O3 reacted easily with Si to form (La2O3)x(SiO2)1-x.

Table 3 Layer-by-layer analysis results for the films N5 and N6.

table 3

    The Al, La and O depth-profiling of films N5 and N6 (without considering C and Si) is given in figure 4. It can be seen that the concentrations of Al, La and O change greatly with increasing the sputtering time. It is indicated that the Al and La in the as-deposited high-κ films are continuous, but not uniform. The binding energy values of individual components for La3d5/2, Al2p, O1s, Si2p3/2 and C1s spectra are presented in Table 4. The C1s   existed on the top surface.

Figure 4 Graphs of changing the element percentage within the analysis area depending on time of ion etching films N5-N6.

Figure 4 Graphs of changing the element percentage within the analysis area depending on time of ion etching films N5-N6.

   Table 4 The binding energies of La3d5/2, Al2p, O1s, Si2p3/2 and C1s for the films N5 and N6.

table 4

    Figure 5 exhibits the normalized Al2p spectra of the investigated films N5 and N6. The spectra are normalized to the total integrated intensity of corresponding Al2p and La3d5/2 spectra. The spectra were used to calibrate the scale of the binding energy (Eb= 74.0 eV). Compared with the binding energy of Al3+ state in Al2O3 (Eb= 74.2-74.6 eV), theAl2p binding energy for N5 and N6 shifted to a lower value of 74.00 eV when La existing. The lower value of Al2p binding energy can be attributed to complex oxides (La–Al–O), which indicated that the formation of La–Al–O films fabricated by ALD method, and the synthesized films were the (La2O3)x(Al2O3)1-x alloys, but not a mixture of La2O3 and Al2O3 phases.

Figure 5 Normalized Al<em>2p</em> spectra of films N5 and N6.

Figure 5 Normalized Al2p spectra of films N5 and N6.

    After ion etching for 5 min an additional peak at 72.5 eV was observed for film N5, its appearance was due to the differential charge effect. For sample N6, after ion etching for 10 min, Al element is not detected, which confirmed that Al did not exist in the interface, and substantial La enrichment occurred at the interface near Si, as mentioned previously.

    Figure 6 presents normalized La3d spectra of initial films N5 and N6 as well as those ones obtained after ion etching for 1, 2, 5 and 10 min. As a result of the spin-orbital interaction, La3d level is known to split into two sublevels leading to La3d5/2 - La3d3/2 doublet, its integrated intensities of components being 3:2. In turn, each component in La3d spectra of lanthanum being in the oxidized state, La3+ is accompanied by prominent lines of the so called “shake up” satellites. The spin-orbital splitting value (the value differences of binding energies La3d3/2 and La3d5/2) is ~16.9 eV. The literature provided La3d5/2 binding energy values for massive La2O3 in a wide range of 833.2-835.5 eV [32-34]. As for lanthanum carbonate and lanthanum hydroxides, the values of La3d5/2 binding energies are nearly in the same range of 835.0-835.5 eV [33, 35].

Figure 6 Normalized La<em>3d</em> spectra of films N5-N6.

Figure 6 Normalized La3d spectra of films N5-N6.

    According to results of the resolution for individual components the binding energies of the main line La3d5/2 was at 835.0 eV, the obtained value and the presence of “shake up” satellite indicated that lanthanum existed as La3+. It was also possible to state that there was no formation of lanthanum carbonates: there were no additional lines in La3d spectrum which could be attributed to lanthanum carbonate; moreover, after ion etching for 1-2 min, all surface carbonates were removed from film surfaces (zero intensity of C1s spectrum).

    The results of a series of analysis revealed that the prepared high-κ films were (La2O3)x(Al2O3)1-x alloys, but not a mixture of La2O3 and Al2O3 phases. In addition, the interfacial layer consisted of thinner compositionally graded La–Si–O silicate rather than pure silicon oxide. Furthermore, Al was highly deficient in the interfacial layer near Si.

Films N7-N10: HfO2/La2O3 stacked structures with different Hf-La ratios

    There were Hf, La, C and O lines in the surveyed spectra of films N7-N10 for initial surfaces. To determine the depth profiling distribution of the elements, film spectra were registered after ion etching for 1, 2, 5 and 10 min. The relative concentrations of elements detected during the layer-by-layer analysis are given in Table 5. The intensity of C1s and CO3line became below detection level after etching for 1 min, which indicated that carbonate groups are mainly localized on the top surface layer, as a result of contact with air at normal conditions. Compared with the percentages of [CO3] in the samples N7-N10, it could also be seen that the percentage of [CO3] increased with the percentage of La increasing, which confirmed that the absorption of CO2 on the surface and formation of lanthanum carbonate is very easy when La was present [30]. For sample N10, the ratio of [La]/[Hf] appeared that substantial La enrichment occurred at the interface near Si, however, this phenomenon did not exist for samples N8 and N9, the reason was maybe that both Hf and La were easy to nucleate on Si. And the content of La in sample N10 was higher, so La enrichment occurred and Hf element was deficient in the interfacial layer, which indicated that the interfacial layer consisted of La–Si–O and Hf–Si–O silicate rather than pure silicon oxide.

Table 5 The layer-by-layer analysis results of the films N7-N10.

table 5

    The Hf, La and O depth-profiling of films N7, N8, N9 and N10 (without considering C and Si) is given in figure 7. It could be seen that the concentrations of Al, La and O changed greatly with increasing the sputtering time. It was indicated that the Al and La in the as-deposited high-κ films were continuous, but not uniform. The binding energies of individual components for Hf4f7/2, La3d5/2, Al2p, O1s, Si2p3/2 and C1s spectra are given in Table 6. The binding energy located at ~531.0 eV corresponded to Hf-Si-O and La-Si-O bonds at the interface near Si. This result corresponded to the O1s spectra mentioned previously.

Figure 7 Graphs of changing the percentages of elements within the analysis area depending on the time of ion etching films N7-N10.

Figure 7 Graphs of changing the percentages of elements within the analysis area depending on the time of ion etching films N7-N10.

   Table 6 The binding energy values of Hf4f7/2, La3d5/2, Al2p, O1s, Si2p3/2 and C1s for the films HfO2-La2O3/Si.

table 6

    Figure 8 presents Hf4f spectra of surfaces of films N7-N10 obtained during the layer-by-layer analysis. The spectra are normalized to the total integrated intensity of appropriate Hf4f and La3d5/2 spectra. Hf4f doublet which is likely to refer to hafnium linked to lanthanum carbonate is marked by magenta color (N10). As for N7-N8 films, after 1 min ion etching (3 min for N9, 5 min for N10) Hf4f spectrum revealed additional doublets Hf4f7/2–Hf4f5/2, which corresponded to hafnium in the structure of Hf-Si-O interface layer, and no matter of the content of La, Hf-Si-O at the interface near Si always existed. On further ion etching, Hf4f spectrum showed a narrow asymmetric peak in the area of lower binding energies, which was certainly due to hafnium silicide HfSix, as the difference between the binding energies and Hf4f7/2is 84.6±0.05 eV for films N7-N10 [25]. In this case, the binding energy shift Si2p3/2 was determined by the effect of differential surface charging. An additional doublet was observed at17.9 eV which was likely to refer to Hf-La (ELa3d5/2 = 835.9 eV) for sample N10 in the case with the initial surface and after 1 min ion etching.

Figure 8 Normalized Hf<em>4f</em> spectra of films N7-N10.Blue peaks indicate doublets referring to Hf in hafnium silicide (HfSi<sub>x</sub>), red peaks indicate doublets referring to Hf in a complex oxide HfSi<sub>x</sub>O<sub>y</sub> forming an interface layer.

Figure 8 Normalized Hf4f spectra of films N7-N10.Blue peaks indicate doublets referring to Hf in hafnium silicide (HfSix), red peaks indicate doublets referring to Hf in a complex oxide HfSixOy forming an interface layer.

    Figure 9 exhibited normalized La3d spectra of surfaces of films N7-N10 after ion etching for 1, 2, 5 and 10 min, (3, 5, 15 min for N9). The spectra were normalized to the total integrated intensity of appropriate Hf4fand La3d5/2spectra. According to the results of the decomposition for individual components, the binding energies of the main line La3d5/2was at 834.7 eV, this value as well as the presence of “shake up” satellite showed lanthanum being La3+. It was also possible to state that there was no formation of lanthanum carbonates: there were no additional lines in La3d spectrum which could be referred to lanthanum carbonate. Moreover, after 1-2 minion etching, all surface carbonates were removed from film surfaces (zero intensity of C1s spectrum). This was consisted with the results mentioned previously. La3d spectra of the initial surface for film N10 revealed an additional La3d5/2 line and its corresponding “shake up” satellite. The given peak, high lanthanum content in the film and high [CO3]/[La+Hf] ratio testify that this peak refers to surface lanthanum carbonate.

Figure 9 Normalized La<em>3d</em> spectra of films N8-N10.

Figure 9 Normalized La3d spectra of films N8-N10.

    For the sample N7-N10, XPS analyses indicated that the prepared high-κ films were (La2O3)x(HfO2)1-x alloys, but not a mixture of La2O3 and HfO2 phases. And the interfacial layers of the films were composed of Hf-Si-O and La-Si-O silicate. And the top surface was easy to form lanthanum carbonate as a result of contact with air at normal conditions when La existed.

Conclusions

    Al2O3, HfO2, Al2O3/HfO2, Al2O3/La2O3 and HfO2/La2O3 films were successfully grown on p-type Si (100) substrates by ALD method, in which TEMAH, TMA and La(iPr2-FMD)3 were employed as precursor, and H2O served as an oxygen source. The results of a series of XPS analysis revealed that the prepared high-κ films are not a mixture of their corresponding element phases, but are alloys. The prepared Al2O3/HfO2 are directly (HfO2)x(Al2O3)1-x alloys, and the interfacial layer near Si was a mixed compound of Hf–Si–O. The synthesized Al2O3/La2O3 films were (La2O3)x(Al2O3)1-x alloys, and the interfacial layer consisted of thinner compositionally graded La–Si–O silicate rather than pure silicon oxide. Furthermore, the Al was highly deficient in the interfacial layer near Si. For samples HfO2/La2O3, XPS indicated that they were (La2O3)x(HfO2)1-x alloys, and the interfacial layers of the films were composed of Hf–Si–O and La–Si–O silicate. It was also found that Hf and La were easier to react with Si to form silicate at the interface near Si. And the top surface was easy to absorb CO2 on the surface as a result of contact with air at normal conditions when La existed.

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  10. P. Saint-Cast, D. Kania, M. Hofmann, J. Benick, J. Rentsch, and R. Preu, Very low surface recombination velocity on p-type c-Si by high-rate plasma-deposited aluminum oxide. Appl. Phys. Lett. 95, 151502 (2009). doi:10.1063/1.3250157
  11. R. Jiang, E. Xie, Z. Wang, Interfacial chemical structure of HfO2∕Si film fabricated by sputtering. Appl. Phys. Lett. 89, 142907 (2006). doi:10.1063/1.2358841
  12. C. V. Ramana, R. S. Vemuri, V. V. Kaichev, V. A. Kochubey, A. A. Saraev, V. V. Atuchin, X-ray photoelectron spectroscopy Depth Profiling of La2O3/Si Thin Films Deposited by Reactive Magnetron Sputtering. ACS Appl. Mater. Interfaces 3, 4370-4373 (2011). doi:10.1021/am201021m
  13. M. Leskelä and M. Ritala, Atomic layer deposition chemistry: recent developments and future challenges. Angew. Chem. Int. Ed. 42 (45), 5548-5554 (2003). doi:10.1002/anie.200301652
  14. J. H. Scofield, Hartree-Slater subshell photoionization cross-sections at 1254 and 1487 eV. J. Electron Spectrosc. Relat. Phenom. 8, 129-137 (1976). doi:10.1016/0368-2048(76)80015-1
  15. J. L. Hueso, A. Caballero, M. Ocana, A. R. Gonzalez-Elipe, Reactivity of lanthanum substituted cobaltites toward carbon particles. J. Catal. 257, 334-344 (2008). doi:10.1016/j.jcat.2008.05.012
  16. P. A. W. v. d. Heide, Photoelectron binding energy shifts observed during oxidation of group IIA, IIIA and IVA elemental surfaces. J. Electron Spectrosc. Relat.Phenom. 151, 79-91 (2006). doi:10.1016/j.elspec.2005.11.001
  17. J. V. D. Brand, P. C. Snijders, W. G. Sloof, H. Terryn, and J. H. W. D. Wit, Acid−Base Characterization of Aluminum Oxide Surfaces with XPS. J. Phys. Chem. B 108, 6017-6024 (2004). doi:10.1021/jp037877f
  18. J. Mendialdua, R. Casanova, F. Rueda, A. Rodriguez, J. Quinones, L. Alarcon, E. Escalante, P. Hoffmann, I. Taebi, and L. Jalowiecki, X-ray photoelectron spectroscopy studies of laterite standard reference material. J. Mol. Catal. A 228,151-162 (2005). doi:10.1016/j.molcata.2004.09.040
  19. N. Kosova, E. Devyatkina, A. Slobodyuk, and V. Kaichev, Surface chemistry study of LiCoO2 coated with alumina. Solid State Ionics 179, 1745-1749 (2008). doi:10.1016/j.ssi.2008.02.013
  20. M. Wei, H. Deng, X. Deng, C. Yang, and J. Structure and optical properties of AlxZn1−xO alloys by sol–gel technique. Res. Bull. 46, 755-759 (2011). doi:10.1016/j.materresbull.2010.12.010
  21. T. Wang, X. Diao, and P. Ding, Thermal stability of electrical properties of ZnO:Al films deposited by room temperature magnetron sputtering. J. Alloys Compd. 509, 4910-4915 (2011). doi:10.1016/j.jallcom.2011.01.210
  22. N. Huang, C. Sun, M. Zhu, B. Zhang, J. Gong, and X. Jiang, Microstructure evolution of zinc oxide films derived from dip-coating sol–gel technique: formation of nanorods through orientation attachment. Nanotechnology 22, 265612 (2011). doi:10.1088/0957-4484/22/26/265612
  23. M.H. Cho, Y. S. Roh, C. N. Whang, K. Jeong, S. W. Nahm, D.H. Ko, J. H. Lee, N. I. Lee, K. Fujihara, Thermal stability and structural characteristics of HfO2 films on Si (100) grown by atomic-layer deposition. Appl. Phys. Lett. 81 472-474 (2002). doi:10.1063/1.1487923
  24. O. Renault, D. Samour, J.-F.Damlencourt, D. Blin, F. Martin, S. Marthon, N. T. Barrett, P. Besson, HfO2/SiO2 interface chemistry studied by synchrotron radiation x-ray photoelectron spectroscopy. Appl. Phys. Lett. 81, 3627-3629 (2002). doi:10.1063/1.1520334
  25. S.W. Do, Y.H. Lee, Study of the characteristics of HfO2/Hf films prepared by atomic layer deposition on silicon. J. Kor. Phys. Soc. 50, 666-669 (2007). PACS numbers: 77.55.+f
  26. V. V. Kaichev, Yu. V. Dubinin, T. P. Smirnova, and M. S. Lebedev, A study of the structure of (HfO2) x (Al2O3)1−x /Si films by X-ray photoelectron spectroscopy. J. Struct. Chem. 52, 480-487 (2011). doi:10.1134/S002247661103005X
  27. T.P. Smirnova, L.V. Yakovkina, V.O. Borisov, V.N. Kichai,. V.V. Kaichev, and V.V. Kriventsov. Structure of HfO2 films and binary oxides on its base. J. Struct. Chem. 53, 708-714 (2012). doi:10.1134/S0022476612040130
  28. J. Zhu, Z.G. Liu, Y.R. Liu. Thermal stability and electrical properties of pulsed laser deposited Hf–aluminate thin films for high-k gate dielectric applications. J.Phys.D: Appl. Phys. 38,446-450 (2005). doi:10.1088/0022-3727/38/3/014
  29. M.-H. Cho, H. S. Chang, Y. J. Cho, D. W. Moon, K.-H. Min, R. Sinclair, S. K. Kang, D.-H. Ko, J. H. Lee, J. H. Gu and N. I. Lee. Change in the chemical state and thermal stability of HfO2 by the incorporation of Al2O3. Appl. Phys. Lett.84, 571-573 (2004). doi:10.1063/1.1633976
  30. F. Tang, C. Zhu, D. J. Smith and R. J. Nemanich, Low temperature growth of high-k Hf–La oxides by remote-plasma atomic layer deposition: Morphology, stoichiometry, and dielectric properties. J. Vac. Sci. Technol. A 30, 01A147 (2012). doi:10.1116/1.3665419
  31. A. D. Li, Q. Y. Shao, H. Q. Ling, J. B. Cheng, D. Wu, Z. G. Liu, N. B. Ming, C. Wang, H. W. Zhou, and B. Y. Nguyen, Characteristics of LaAlO3 gate dielectrics on Si grown by metalorganic chemical vapor deposition. Appl. Phys. Lett.83, 3540-3542 (2003). doi:10.1063/1.1622794
  32. Z. Boukha, L. Fitian, M. López-Haro, M. Mora, J. R. Ruiz, C. Jiménez-Sanchidrián, G. Blanco, J. J. Calvino, G. A. Cifredo, S. Trasobares, S. Bernal, Influence of the calcination temperature on the nano-structural properties, surface basicity, and catalytic behavior of alumina-supported lanthana samples. J. Catal. 272, 121-130 (2010). doi:10.1016/j.jcat.2010.03.005
  33. A. Galtayries, G. Blanco, G. A. Cifredo, D. Finol, J. M. Gatica, J. M. Pintado, H. Vidal, R. Sporken, S. Bernal, XPS Analysis and Microstructural Characterization of a Ce/Tb Mixed Oxide Supported on a Lanthana-modified Transition Alumina. Surf. Interface Anal. 27, 941-949 (1999). doi:10.1002/(SICI)1096-9918(199910)27:103.0.CO;2-Y
  34. M. Salavati-Niasari, G. Hosseinzadeh, F. Davar, Synthesis of lanthanum hydroxide and lanthanum oxide nanoparticles by sonochemical method. J. Alloys Compd. 509, 4098-4103 (2011). doi:10.1016/j.jallcom.2010.07.083
  35. J. S. Ledford, M. Houalla, A. Proctor, D. M. Gercules, L. Petrakis, Influence of lanthanum on the surface structure and carbon monoxide hydrogenation activity of supported cobalt catalysts. J. Phys. Chem. 93, 6770-6777(1989). doi:10.1021/j100355a039

 

Acknowledgements

This work was supported by National High-Tech R & D Program of China (863, No.2011AA050504), the National Natural Science Foundation of China (No.61274051), Ministry of Economic Affairs, Taiwan (No.102-EC-17-A-13-S1-173), and the Siberian Branch of the Russian Academy of Sciences in the frame of the Project No.9.

References

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  10. P. Saint-Cast, D. Kania, M. Hofmann, J. Benick, J. Rentsch, and R. Preu, Very low surface recombination velocity on p-type c-Si by high-rate plasma-deposited aluminum oxide. Appl. Phys. Lett. 95, 151502 (2009). doi:10.1063/1.3250157
  11. R. Jiang, E. Xie, Z. Wang, Interfacial chemical structure of HfO2∕Si film fabricated by sputtering. Appl. Phys. Lett. 89, 142907 (2006). doi:10.1063/1.2358841
  12. C. V. Ramana, R. S. Vemuri, V. V. Kaichev, V. A. Kochubey, A. A. Saraev, V. V. Atuchin, X-ray photoelectron spectroscopy Depth Profiling of La2O3/Si Thin Films Deposited by Reactive Magnetron Sputtering. ACS Appl. Mater. Interfaces 3, 4370-4373 (2011). doi:10.1021/am201021m
  13. M. Leskelä and M. Ritala, Atomic layer deposition chemistry: recent developments and future challenges. Angew. Chem. Int. Ed. 42 (45), 5548-5554 (2003). doi:10.1002/anie.200301652
  14. J. H. Scofield, Hartree-Slater subshell photoionization cross-sections at 1254 and 1487 eV. J. Electron Spectrosc. Relat. Phenom. 8, 129-137 (1976). doi:10.1016/0368-2048(76)80015-1
  15. J. L. Hueso, A. Caballero, M. Ocana, A. R. Gonzalez-Elipe, Reactivity of lanthanum substituted cobaltites toward carbon particles. J. Catal. 257, 334-344 (2008). doi:10.1016/j.jcat.2008.05.012
  16. P. A. W. v. d. Heide, Photoelectron binding energy shifts observed during oxidation of group IIA, IIIA and IVA elemental surfaces. J. Electron Spectrosc. Relat.Phenom. 151, 79-91 (2006). doi:10.1016/j.elspec.2005.11.001
  17. J. V. D. Brand, P. C. Snijders, W. G. Sloof, H. Terryn, and J. H. W. D. Wit, Acid−Base Characterization of Aluminum Oxide Surfaces with XPS. J. Phys. Chem. B 108, 6017-6024 (2004). doi:10.1021/jp037877f
  18. J. Mendialdua, R. Casanova, F. Rueda, A. Rodriguez, J. Quinones, L. Alarcon, E. Escalante, P. Hoffmann, I. Taebi, and L. Jalowiecki, X-ray photoelectron spectroscopy studies of laterite standard reference material. J. Mol. Catal. A 228,151-162 (2005). doi:10.1016/j.molcata.2004.09.040
  19. N. Kosova, E. Devyatkina, A. Slobodyuk, and V. Kaichev, Surface chemistry study of LiCoO2 coated with alumina. Solid State Ionics 179, 1745-1749 (2008). doi:10.1016/j.ssi.2008.02.013
  20. M. Wei, H. Deng, X. Deng, C. Yang, and J. Structure and optical properties of AlxZn1−xO alloys by sol–gel technique. Res. Bull. 46, 755-759 (2011). doi:10.1016/j.materresbull.2010.12.010
  21. T. Wang, X. Diao, and P. Ding, Thermal stability of electrical properties of ZnO:Al films deposited by room temperature magnetron sputtering. J. Alloys Compd. 509, 4910-4915 (2011). doi:10.1016/j.jallcom.2011.01.210
  22. N. Huang, C. Sun, M. Zhu, B. Zhang, J. Gong, and X. Jiang, Microstructure evolution of zinc oxide films derived from dip-coating sol–gel technique: formation of nanorods through orientation attachment. Nanotechnology 22, 265612 (2011). doi:10.1088/0957-4484/22/26/265612
  23. M.H. Cho, Y. S. Roh, C. N. Whang, K. Jeong, S. W. Nahm, D.H. Ko, J. H. Lee, N. I. Lee, K. Fujihara, Thermal stability and structural characteristics of HfO2 films on Si (100) grown by atomic-layer deposition. Appl. Phys. Lett. 81 472-474 (2002). doi:10.1063/1.1487923
  24. O. Renault, D. Samour, J.-F.Damlencourt, D. Blin, F. Martin, S. Marthon, N. T. Barrett, P. Besson, HfO2/SiO2 interface chemistry studied by synchrotron radiation x-ray photoelectron spectroscopy. Appl. Phys. Lett. 81, 3627-3629 (2002). doi:10.1063/1.1520334
  25. S.W. Do, Y.H. Lee, Study of the characteristics of HfO2/Hf films prepared by atomic layer deposition on silicon. J. Kor. Phys. Soc. 50, 666-669 (2007). PACS numbers: 77.55.+f
  26. V. V. Kaichev, Yu. V. Dubinin, T. P. Smirnova, and M. S. Lebedev, A study of the structure of (HfO2) x (Al2O3)1−x /Si films by X-ray photoelectron spectroscopy. J. Struct. Chem. 52, 480-487 (2011). doi:10.1134/S002247661103005X
  27. T.P. Smirnova, L.V. Yakovkina, V.O. Borisov, V.N. Kichai,. V.V. Kaichev, and V.V. Kriventsov. Structure of HfO2 films and binary oxides on its base. J. Struct. Chem. 53, 708-714 (2012). doi:10.1134/S0022476612040130
  28. J. Zhu, Z.G. Liu, Y.R. Liu. Thermal stability and electrical properties of pulsed laser deposited Hf–aluminate thin films for high-k gate dielectric applications. J.Phys.D: Appl. Phys. 38,446-450 (2005). doi:10.1088/0022-3727/38/3/014
  29. M.-H. Cho, H. S. Chang, Y. J. Cho, D. W. Moon, K.-H. Min, R. Sinclair, S. K. Kang, D.-H. Ko, J. H. Lee, J. H. Gu and N. I. Lee. Change in the chemical state and thermal stability of HfO2 by the incorporation of Al2O3. Appl. Phys. Lett.84, 571-573 (2004). doi:10.1063/1.1633976
  30. F. Tang, C. Zhu, D. J. Smith and R. J. Nemanich, Low temperature growth of high-k Hf–La oxides by remote-plasma atomic layer deposition: Morphology, stoichiometry, and dielectric properties. J. Vac. Sci. Technol. A 30, 01A147 (2012). doi:10.1116/1.3665419
  31. A. D. Li, Q. Y. Shao, H. Q. Ling, J. B. Cheng, D. Wu, Z. G. Liu, N. B. Ming, C. Wang, H. W. Zhou, and B. Y. Nguyen, Characteristics of LaAlO3 gate dielectrics on Si grown by metalorganic chemical vapor deposition. Appl. Phys. Lett.83, 3540-3542 (2003). doi:10.1063/1.1622794
  32. Z. Boukha, L. Fitian, M. López-Haro, M. Mora, J. R. Ruiz, C. Jiménez-Sanchidrián, G. Blanco, J. J. Calvino, G. A. Cifredo, S. Trasobares, S. Bernal, Influence of the calcination temperature on the nano-structural properties, surface basicity, and catalytic behavior of alumina-supported lanthana samples. J. Catal. 272, 121-130 (2010). doi:10.1016/j.jcat.2010.03.005
  33. A. Galtayries, G. Blanco, G. A. Cifredo, D. Finol, J. M. Gatica, J. M. Pintado, H. Vidal, R. Sporken, S. Bernal, XPS Analysis and Microstructural Characterization of a Ce/Tb Mixed Oxide Supported on a Lanthana-modified Transition Alumina. Surf. Interface Anal. 27, 941-949 (1999). doi:10.1002/(SICI)1096-9918(199910)27:103.0.CO;2-Y
  34. M. Salavati-Niasari, G. Hosseinzadeh, F. Davar, Synthesis of lanthanum hydroxide and lanthanum oxide nanoparticles by sonochemical method. J. Alloys Compd. 509, 4098-4103 (2011). doi:10.1016/j.jallcom.2010.07.083
  35. J. S. Ledford, M. Houalla, A. Proctor, D. M. Gercules, L. Petrakis, Influence of lanthanum on the surface structure and carbon monoxide hydrogenation activity of supported cobalt catalysts. J. Phys. Chem. 93, 6770-6777(1989). doi:10.1021/j100355a039

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Additional Info

  • Type of Publishing: JOUR - Journal
  • Title:

    Studying the chemical composition and structure of hafnium, aluminium and lanthanum oxide films by X-ray photoelectron spectroscopy

  • Author: Zhongli Li, Yijian Liu, Huijuan Geng, AyraJagadhamma Letha, Limin Sun, Ying Wang, Huey-Liang Hwang, Fedor A. Kyznetsov, Tamara P. Smirnova, Andrey A. Saraev, Vasily V. Kaichev
  • Year: 2015
  • Volume: 2
  • Issue: 2
  • Journal Name: Materials and Electronics Engineering
  • Publisher: Nicety Press Company Limited
  • ISSN: 2410-1648
  • URL: http://www.meej.org/volume-2/october-2015/item/372-studying-the-chemical-composition-and-structure-of-hafnium-aluminium-and-lanthanum-oxide-films-by-x-ray-photoelectron-spectroscopy
  • Abstract:

        In this paper, high-κ oxides films, Al2O3, HfO2, Al2O3/HfO2, Al2O3/La2O3 and HfO2/La2O3 stacked structures, were deposited on p-type Si wafers using plasma-enhanced atomic layer deposition (PEALD). The chemical composition and structure of the deposited high-κ films were investigated in detailed research by X-ray photoelectron spectroscopy. The layer by layer depth profiling and XPS analysis indicated that the synthesized stacked structures films are alloys, consist of Hf–Al–O, La–Al–O and Hf–La–O. And the analysis results suggested that the interfacial layer were most likely composed of Hf–Si–O for Al2O3/HfO2, La–Si–O for Al2O3/La2O3, Hf–Si–O and La–Si–O for HfO2/La2O3 rather than pure silicon oxide. It is also found that Hf and La was easier to react with Si to form silicate at the interface near Si. And the top surface is easy to absorb CO2 on the surface as a result of contact with air at normal conditions when La existed.

  • Publish Date: Friday, 02 October 2015
  • Start Page: 2
  • DOI: 10.11605/mee-2-2