Boquan Li

X-ray photoelectron spectroscopy and grazing incidence X-ray reflectivity study of silicon nitride thin films

Abstract Silicon nitride thin films were deposited by rf magnetron sputtering with various gas flow conditions (N 2 /Ar). The effect of gas flow conditions on the structure and compositions of the films was investigated. X-ray photoelectron spectroscopy indicated that the binding energy of the Si 2p state successively shifted to higher energy while the binding energy of the N 1s state showed no change with the increase of the N 2 /Ar ratio. The films deposited under conditions of N 2 /Ar ratio below 0.5 were silicon-rich while the films formed with the N 2 /Ar ratio more than 0.5 were nitrogen-rich. Nearly stoichiometric Si 3 N 4 films can be obtained at the N 2 /Ar ratio of 0.5. Grazing incidence X-ray reflectivity showed that the nearly stoichiometric Si 3 N 4 film had a higher density (3.17 g/cm 3 ) while the silicon-rich or nitrogen-rich resulted in a decrease in film density. The surface roughness of these films lies almost in the same level.

Suppressing the surface roughness and columnar growth of silicon nitride films

The growth and structure evolution of silicon nitride films prepared by radio frequency magnetron sputtering at low pressure were investigated for thickness changes. Grazing-incidence X-ray reflectivity, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy were used to study the structure, surface roughness and composition, respectively, of the films. It was found that with an increase in thickness from 5 to 830 nm, the silicon nitride films have a similar surface structure and their surface roughness only slightly increases. The surface roughness of all the silicon nitride films is only a little more than 0.2 nm, much less than previously reported results. AFM measurement of the fractured film surface indicated that thin silicon nitride films with a thickness below approximately 300 nm have a dense, smooth and uniform structure, and columnar structures gradually appear only in thick films. These results are mainly attributed to the special design of the sputtering system and the energetic particle bombardment of the growing surface, by which the surface roughness and columnar growth were suppressed.

High resolution thickness and interface roughness characterization in multilayer thin films by grazing incidence X-ray reflectivity

Abstract Grazing incidence X-ray reflectivity (GIXR) is a powerful technique for investigating surfaces and multilayers. Three different material systems, GaAs/AlAs, SiO 2 /Si, and Si 3 N 4 /Si multilayers, were studied by GIXR. Structural parameters such as thickness, density and roughness of these multilayers were successfully determined with high accuracy. Sub-nm resolution was achieved for both thickness and roughness measurements. In addition, GIXR was found to be more sensitive to surface roughness than underlayer interface roughnesses.

An ultrahigh vacuum sputtering system with offset incidence magnetron sources onto a rotating substrate

An ultrahigh vacuum sputtering system with offset incidence magnetron sources has been designed and developed to deposit thin films and multilayers with excellent film thickness uniformity, precise control over layer thickness, and surface and interface roughness. The unique feature of the system is that the sputtering guns are aligned at 35° oblique incidence onto a rotating substrate with a 60 mm offset from the substrate center, which make full use of the best linearity of the plasma flux at the substrate, and therefore, deposit extremely uniform thin films. Other features include, computer-controlled deposition process, capability of heating the substrate to 1100 °C, and in situ monitoring of thin-film quality with reflection high-energy electron diffraction. The performance of the sputtering system is demonstrated, and a characterization of multilayers deposited by the system using a grazing incidence x-ray reflectivity and high resolution electron microscope is also presented.

XRR and XPS studies of SiO2 thin films formed by r.f. magnetron sputtering

Grazing-incidence x-ray reflectivity has been exploited to study as-grown SiO 2 thin films deposited on Si(100) substrates by radio-frequency (r.f.) magnetron sputtering under various substrate temperatures and gas flow conditions. Results indicate that an increase of substrate temperature from room temperature to 763 K only slightly decreases the surface roughness. Comparatively, the surface morphology is strongly controlled by the gas flow conditions during deposition. The surface roughness increases almost linearly from 0.51 to 2.38 nm as the argon gas flow is increased from 8 to 50 sccm. The chemical state and composition of the films were analysed by XPS.

Temperature dependence of SiO2/Si interfacial structure formed by radio-frequency magnetron sputter deposited SiO2 thin films on Si(111)

X-ray reflectivity has been used to characterize the interfacial structure of as-grown SiO2 layers deposited on Si(111) substrates by rf magnetron sputtering under different substrate temperatures. Results indicate that there exists a higher-density interfacial layer between crystalline Si and the amorphous SiO2 overlayer. As the substrate temperature was increased from 200 to 620 °C, the density of the interfacial layer increased from 2.37 to 2.67 g/cm3, and the thickness of the interfacial layer also increased slightly.

The structural nature of multilayers on Si(100) formed by ion-beam sputter deposition

multilayers on Si(100) were prepared by ion-beam sputter deposition. By using a grazing incidence x-ray reflectivity technique, the layer thickness and interfacial roughness of the multilayers were quantitatively characterized. In particular, the differences in structural features between the on interface and the on interface, as well as the possible inhomogeneity of the layers, were successfully revealed. The x-ray reflectivity results are consistent with the high-resolution electron microscopy observations. The process of the growth of the multilayers is also discussed.

Structural characterization of radiofrequency magnetron sputter deposited SiO2 thin films

The SiO2 thin-film structure deposited by radiofrequency (rf) magnetron sputtering was found to depend on whether the native oxide on the Si(111) was removed or not. X- ray reflectivity (XRR) data show that, when deposited on a clean Si(111) surface, the SiO2 thin film consistently has a two-layer (an overlayer and an interface layer) structure. The interfacial structure depends on the deposition temperature. The film deposited at room temperature has a lower-density interface layer. With increase of the substrate temperature, the density and the thickness of the interface layer also increase. In contrast, when deposited on Si(111) with a native oxide layer, the deposited films have varying structures. At lower temperatures, the XRR data can be fitted with a one-layer model. At higher temperatures, the films consist of two or three layers, including one lower-density top layer, a normal SiO2 layer and a higher-density interface layer. The layer thickness, surface and interface roughness of the two-group samples were also compared and discussed.

Dependence of structural features on substrates in Co/Cu multilayers

Metallic multilayers with giant magnetoresistance (GMR) effect is an active research field. GMR is governed by several physical parameters. In this paper, one of the most important parameters, surface and interface roughness is investigated. The Co/Cu multilayers on Si(111) and Si(100) with a Cr buffer layer were grown by electron beam evaporation in one run. Auger depth profiling, grazing incidence X-ray reflectivity and Atomic Force Microscopy clearly demonstrate the structural difference in the two Co/Cu multilayer samples. The multilayers on Si(111) have smoother surface and interfaces, while the multilayers on Si(100) have rougher surface and interfaces, which originates from the different surface roughness of the Si(111) and Si(100) substrates, 0.36 and 0.68 nm respectively. The surface evolution of the multilayers during deposition is also discussed.

Gas flow effects on the structure and composition of SiN x /Si/SiN x films prepared by radio-frequency magnetron sputtering

The structure and composition of SiN x /Si/SiN x films were investigated by means of x-ray reflectivity, x-ray photoelectron spectroscopy, and atomic force microscopy. The three-layer films were prepared by radio-frequency magnetron sputtering under the condition of constant nitrogen flow and the argon flow. It was found that the deposition rate and surface structure of the silicon nitride films were mainly determined by the nitrogen flow rather than the argon flow. But the composition of the silicon nitride films was controlled by the gas flow ratio (F Ar /F N2 ) used during sputtering.