Deposition of silicon oxynitride films by ion beam sputtering at room temperature

Silicon oxynitride films, possessing various compounds of SiO₂ and Si₃N₄, were deposited by ion beam sputtering at room temperature. This technique can easily and precisely control the refractive index and composition of the silicon oxynitride film. Properties of these films, such as the refractive index, the extinction coefficient, the surface roughness, and so on were measured in this study.     

Secondary ion species containing nitrogen atoms from plasma-enhanced chemical vapor deposited silicon oxide films on silicon

Secondary ion species from plasma-enhanced chemical vapor deposited (PECVD) SiO₂ films have been investigated using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Comparative studies of PECVD SiO₂ films prepared using a mixture of SiH₄/N₂O reaction gas at 400 °C with thermally oxidized SiO₂ films grown at 900 °C were carried out in the mid-range mass spectra from 95 to 165 amu. Small amounts of ion species containing nitrogen atoms, including Si₂O₂N⁺, Si₃O₂N⁺and Si₃O₃N⁺, were detected in the SiO₂ bulk from the PECVD SiO₂ films. Furthermore, large amounts of Si₃O₂N⁺ and Si₂O₃N⁻ were found at the interface between silicon and the SiO₂ films. Depth analysis showed that the intensity peak shapes of these ion species containing nitrogen atoms at the interface were closely coincident with those of Si₃O₃⁺ corrected by subtracting the influence of the SiO₂ matrix. The variation in the spectra of these ion species clearly indicates that two types of structures of oxynitride exist for the PECVD SiO₂ films in the SiO₂ bulk films and at the interface. These are likely produced by the reaction of reactive gas with SiO₂ and silicon surfaces where dangling bonds of silicon may exist in the different form.     

Electron and ion beam effects in auger electron spectrometry

In Auger Electron Spectrometry relatively high primary electron current density is usually used in order to obtain a good signal-to-noise ratio. As a consequence, a number of phenomena occurs, which can substantially modify—or even destroy—the sample, and impair the results of the analysis.

In this communication we report some observations on the electron and ion beam interaction on some of the insulating and conducting films used in the silicon device technology. Among the materials considered, silicon nitride and P-doped silicon dioxide are of primary interest, and will be treated in some detail; results on other films, both insulating (Al₂O₃, B-doped SiO₂, etc.) and conducting (Al-Si alloys) will also be reported.

The electron beam causes the oxides (B, Al, Si, P) to be reduced, as shown by the decrease of the height of the low energy, chemically shifted peaks (B_KVV, Al_LVV, Si_Lvv, P_Lvv) and by the contemporary increase of the height of the elemental peaks. In phosphorus doped glasses the electron beam also induces a strong surface P enrichment, followed by a P desorption. Silicon nitride was found to be quite stable against the e-b irradiation in “good” vacuum, but very sensitive to the e-b induced oxidation even at (total) pressure as low as 5 × 10¹⁰ torr. This is a very important fact to be taken into account when evaluating thin Si₃N₄ films, because it can change the apparent film stoichiometry.

Some metallic films are also preferentially oxidized by the electron beam; in Al/Si diluted alloy (0.1÷2% silicon) a strong surface silicon enrichment was found to take phase on small-grained thin films, but not on bulk material.

Our results show that much care has to be taken when performing or interpreting the AES data, and how to use, in some cases, the e-b irradiation effects to increase the sensitivity of the method.     

Radiation resistance of boron nitride and related ceramics to low-energy electron irradiation

The radiation resistance of heat-proof ceramics based on boron nitride (BN + Si₃N₄ and BN + SiO₂), which are proposed to be used as structural materials in space ion engines, to low-energy electron irradiation has been investigated.     

Electron-stimulated processes in boron nitride-based ceramics

The low-energy electron radiation resistance of boron nitride-based BN + Si₃N₄ and BN + SiO₂ ceramics proposed as a construction material for ion space engines was studied. It was shown that a reduced silicon phase is formed on the BN + Si₃N₄ ceramics surface in the high-temperature region (～900 K), which results from material thermal destruction. The BN + SiO₂ ceramics exhibits high thermal stability and is not prone to destruction due to electron-stimulated oxygen desorption (the cross section of this process does not exceed 10^?20 cm²). It is preferable to use such ceramics as a construction material. Based on the results obtained, some models were proposed that explain variations in the erosion rate of ceramic units of ion engines under electron and ion irradiation.     

Investigation of SiO2/Si3N4 films prepared on sapphire by r.f. magnetron reactive sputtering

Sapphire is a desired material for infrared-transmitting windows and domes because of its excellent optical and mechanical properties. However, its thermal shock resistance is limited by loss of compressive strength along the c-axis of the crystal with increasing temperature. In this paper, double layer films of SiO₂/Si₃N₄ were prepared on sapphire (α-Al₂O₃) by radio frequency magnetron reactive sputtering in order to increase both transmission and high temperature mechanical performance of infrared windows of sapphire. Composition and structure of each layer of the films were analyzed by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), respectively. Surface morphology and roughness of coated and uncoated sapphire have been measured using a talysurf. Flexural strengths of sapphire sample uncoated and coated with SiO₂/Si₃N₄ have been studied by 3-point bending tests at different temperatures. The results show that SiO₂/Si₃N₄ films can improve the surface morphology and reduce the surface roughness of sapphire substrate. In addition, the designed SiO₂/Si₃N₄ films can increase the transmission of sapphire in mid-wave infrared and strengthen sapphire at high temperatures. Results for 3-point bending tests indicated that the SiO₂/Si₃N₄ films increased the flexural strength of c-axis sapphire by a factor of about 1.4 at 800 °C.     

AlGaN/GaN-based HEMT on SiC substrate for microwave characteristics using different passivation layers

In this paper, a new gate-recessed AlGaN/GaN-based high electron mobility transistor (HEMT) on SiC substrate is proposed and its DC as well as microwave characteristics are discussed for Si₃N₄ and SiO₂ passivation layers using technology computer aided design (TCAD). The two-dimensional electron gas (2DEG) transport properties are discussed by solving Schr?dinger and Poisson equations self-consistently resulting in various subbands having electron eigenvalues. From DC characteristics, the saturation drain currents are measured to be 600?mA/mm and 550?mA/mm for Si₃N₄ and SiO₂ passivation layers respectively. Apart from DC, small-signal AC analysis has been done using two-port network for various microwave parameters. The extrinsic transconductance parameters are measured to be 131.7?mS/mm at a gate voltage of V _gs?= ?0.35?V and 114.6?mS/mm at a gate voltage of V _gs?= ?0.4?V for Si₃N₄ and SiO₂ passivation layers respectively. The current gain cut-off frequencies (f _t) are measured to be 27.1?GHz and 23.97?GHz in unit-gain-point method at a gate voltage of ?0.4?V for Si₃N₄ and SiO₂ passivation layers respectively. Similarly, the power gain cut-off frequencies (f _max) are measured to be 41?GHz and 38.5?GHz in unit-gain-point method at a gate voltage of ?0.1?V for Si₃N₄ and SiO₂ passivation layers respectively. Furthermore, the maximum frequency of oscillation or unit power gain (MUG = 1) cut-off frequencies for Si₃N₄ and SiO₂ passivation layers are measured to be 32?GHz and 28?GHz respectively from MUG curves and the unit current gain, ?O?h ₂₁??O?=?1 cut-off frequencies are measured to be 140?GHz and 75?GHz for Si₃N₄ and SiO₂ passivation layers respectively from the abs ?O?h ₂₁??O curves. HEMT with Si₃N₄ passivation layer gives better results than HEMT with SiO₂ passivation layer.     

X-ray reflectivity and photoelectron spectroscopy of superlattices with silicon nanocrystals

The structural properties and features of the chemical composition of SiO _x N _y /SiO₂, SiO _x N _y /Si₃N₄, and SiN _x /Si₃N₄ multilayer thin films with ultrathin (1–1.5 nm) barrier SiO₂ or Si₃N₄ layers are studied. The films have been prepared by plasma chemical vapor deposition and have been annealed at a temperature of 1150°С for the formation of silicon nanocrystals in the SiO _x N _y or SiN _x silicon-rich layers with a nominal thickness of 5 nm. The period of superlattices in the studied samples has been estimated by X-ray reflectivity. The phase composition of superlattices has been studied by X-ray electron spectroscopy using the decomposition of photoelectron spectra of the Si 2p, N 1s, and O 1s levels into components corresponding to different charge states of atoms.     

AES analysis of nitridation of Si(100) by 2–10 keV N+2 ion beams

Ion beam nitridation of Si(100) as a function of N⁺₂ ion energy in the range of 2–10 keV has been investigated by in-situ Auger electron spectroscopy (AES) analysis and Ar⁺ depth profiling. The AES measurements show that the nitride films formed by 4–10 keV N⁺₂ ion bombardment are relatively uniform and have a composition of near stoichiometric silicon nitride (Si₃N₄), but that formed by 2 keV N⁺₂ ion bombardment is N-rich on the film surface. Formation of the surface N-rich film by 2 keV N⁺₂ ion bombardment can be attributed to radiation-enhanced diffusion of interstitial N atoms and a lower self-sputtering yield. AES depth profile measurements indicate that the thicknesses of nitride films appear to increase with ion energy in the range from 2 to 10 keV and the rate of increase of film thickness is most rapid in the 4–10 keV range. The nitridation reaction process which differs from that of low-energy (< 1 keV) N⁺₂ ion bombardment is explained in terms of ion implantation, physical sputtering, chemical reaction and radiation-enhanced diffusion of interstitial N atoms.     

Embedded structure of silicon monoxide in SiO2 films

The structure of SiO_x (x = 1.94) films has been investigated using both X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). The SiO_x films were deposited by vacuum evaporation. XPS spectra show that SiO_1.94 films are composed of silicon suboxides and the SiO₂ matrix. Silicon clusters appeared only negligibly in the films in the XPS spectra. Si₃O⁺ ion species were found in the TOF-SIMS spectra with strong intensity. These results reveal the structure of the films to be silicon monoxide embedded in SiO₂, and this structure most likely exists as a predominant form of Si₃O₄. The existence of Si-Si structures in the SiO₂ matrix will give rise to dense parts in loose glass networks.     

Electron and ion beam effects in auger electron spectroscopy on insulating materials

Some insulating films—like SiO₂, P-doped SiO₂, B-doped SiO₂, K-silica glasses, SiaN₄, and alumina—are of primary interest in silicon device technology. In this work the main problems concerning the electron and ion beam interactions with these materials when performing Auger analyses are outlined. A few examples of radiation effects are provided. Among these, electron stimulated desorption as well as ion beam induced adsorption and oxide reduction are treated in some detail. General trends in avoiding charging problems with Auger Electron Spectroscopy are provided.     

Observing the effect of water vapor on post-irradiated surface morphology of SiO2 and Si3N4 insulators by atomic force microscopy

In this work, we investigated the effect of water-vapor treatment on the surface morphology of SiO₂ and Si₃N₄ insulators before and after Co⁶⁰ gamma-ray irradiation by using the atomic force microscopy (AFM) operated under non-contact mode. Before irradiation, no apparent surface morphology change was found in SiO₂ samples even they were water vapor treated. However, bright spots were found on post-irradiated water-vapor-treated SiO₂ sample surfaces but not on those without water-vapor treatment. We attributed the bright spots to the negative charge accumulation in the oxide due to charge balancing between hydroxyl (OH⁻) ions adsorbed on SiO₂ surface and electron-hole pairs (ehps) generated during irradiation since they can be annealed out after low temperature annealing process. On the contrary, no bright spots were observed on post-irradiated Si₃N₄ samples with and without water-vapor treatment. This result confirms that Si₃N₄ is a better water-resist passivation layer than SiO₂ layer.     

Characterization of ion species of silicon oxide films using positive and negative secondary ion mass spectra

Secondary ion species of silicon oxide films have been investigated using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Characterization of thermally grown SiO₂ films on silicon has been performed. A diagram showing secondary ion spectra of SiO₂ films in both positive and negative polarities indicates the pattern of change in polarities and intensities of ion species from SiO⁺ to Si₅O₁₁⁻. The ions mostly change from positive to negative polarity between Si_nO_2n−1 and Si_nO_2n. Ion peaks with the strongest intensities in the respective cluster ions correspond to the Si_nO_2n+1 negative ion. Intensities of ion species of Si_nO_2n+2 appear negligibly small. Ion species of Si₃O⁺, Si₃O₂⁺ and Si₃O₃⁺ have been found at the interface between silicon and SiO₂ films. The intensity patterns of these ion species compared to those of SiO₂ films indicate that most of these species are not emitted from the SiO₂ films, but likely from the SiO structures.     

Radiation damage effects on power VDMOS devices with composite SiO2–Si3N4 films

Total dose effects and single event effects on radiation-hardened power vertical double-diffusion metal oxide semiconductor (VDMOS) devices with composite SiO₂-–Si₃N₄ film gate are investigated. The relationships among the important electrical parameters of the samples with different thickness SiO₂-–Si₃N₄ films, such as threshold voltage, breakdown voltage, and on-state resistance in accumulated dose, are discussed. The total dose experiment results show that the breakdown voltage and the on-state resistance barely change with the accumulated dose. However, the relationships between the threshold voltages of the samples and the accumulated dose are more complex, not only positive drift, but also negative drift. At the end of the total dose experiment, we select the group of samples which have the smaller threshold voltage shift to carry out the single event effect studies. We find that the samples with appropriate thickness ratio SiO₂-–Si₃N₄ films have a good radiation-hardening ability. This method may be useful in solving both the SEGR and the total dose problems with the composite SiO₂-–Si₃N₄ films.     

离子束增强沉积制备p型氧化锌薄膜及其机理研究

采用离子束增强沉积方法在Si和SiO₂/Si衬底上制备In-N共掺杂ZnO薄膜(INZO)，溅射靶是用ZnO和2 atm% In₂O₃粉体均匀混合并压制而成，在氩离子溅射ZnO靶的同时，氮、氩混合离子束垂直注入沉积的薄膜.实验结果显示INZO薄膜具有(002)的择优取向，并且为p型导电，电阻率最低为0.9Ωcm.薄膜在氮气、氧气气氛下退火，对薄膜的结构和电学特性与成膜和退火条件的关系进行了分析. 关键词： 氧化锌薄膜 p型掺杂 离子束增强沉积     

Umladungsmessungen an Lithium-Ionen im Energiebereich von 3 bis 10 keV

An ion source is described where a beam of lithium ions is directly emitted from a platinum filament coated with the lithium mineralΒ-eucryptite. Charge exchange cross sections were measured in the energy range from 3 to 10 keV for the gases A, N₂, N₂O, H₂, O₂, CH₄, CCl₂F₂ and air. The results in this energy range agree with the adiabatic hypothesis of Massey. The uncharged particles were detected by means of a secondary electron emission detector. The secondary electron emission yield for a Cu-Be and a Ag-Mg surface by bombardment with lithium ions was measured.     

Ti-Si-N复合膜的界面相研究

为了揭示Ti_Si_N复合膜中Si₃N₄界面相的存在方式及其对薄膜力学 性能的影响 ，采用x射线衍射仪、高分辨透射电子显微镜、俄歇电子能谱仪和显微硬度仪对比研究了磁 控溅射Ti_Si_N复合膜和TiN/Si₃N₄多层膜的微结构和力学性能. 实 验结果表明 ，Ti_Si_N复合膜均形成了Si₃N₄界面相包裹TiN纳米晶粒的微结构. 其中低Si 含量的Ti_Si_N复合膜中Si₃N₄界面相的厚度小于1nm，且以晶体态 存在，薄膜 呈现高硬度. 而高Si含量的Ti_Si_N复合膜中的Si₃N₄界面相以非晶 态存在，薄 膜的硬度也相应降低. 显然，Ti_Si_N复合膜中Si₃N₄界面相以晶体 态形式存在 是薄膜获得高硬度的重要微结构特征，其强化机制可能与多层膜的超硬效应是相同的. 关键词： Ti－Si－N复合膜 界面相 微结构 超硬效应     

Advanced ion beam technology for versatile oxide thin film formation

Various oxide films, such as SnO₂, In₂O₃, Al₂O₃, SiO₂, ZnO, and Sn-doped In₂O₃ (ITO) have been deposited on glass and polymer substrates by advanced ion beam technologies including ion-assisted deposition (IAD), hybrid ion beam, ion beam sputter deposition (IBSD), and ion-assisted reaction (IAR). Physical and chemical properties of the oxide films and adhesion between films and substrates were improved significantly by these technologies. By using the IAD method, non-stoichiometry, crystallinity, and microstructure of the films were controlled by changing assisted oxygen ion energy and arrival ratio of assisted oxygen ion to evaporated atoms. IBSD method has been carried out for understanding the growth mode of the films on glass and polymer substrate. Relationships between microstructure and electrical properties in ITO films on polymer and glass substrates were intensively investigated by changing ion energy, reactive gas environment, substrate temperature, etc. Smooth-surface ITO films (R_rms ⩽ 1 nm and R_p−v ⩽ 10 nm) for organic light-emitting diodes were developed with a combination of deposition conditions with controlling microstructure of a seed layer on glass. IAR surface treatment enormously enhanced the adhesion of oxide films to polymer substrate. In the case of Al₂O₃ and SiO₂ films, the oxygen and moisture barrier properties were also improved by IAR surface treatment. The experimental results of the oxide films prepared by the ion beam technologies and its applications will be represented in detail.     

Analysis of intensities of positive and negative ion species from silicon dioxide films using time-of-flight secondary ion mass spectrometry and electronegativity of fragments

Intensities of positive and negative ion species emitted from thermally oxidized and plasma-enhanced chemical vapor deposited (PECVD) SiO₂ films were analyzed using time-of-flight secondary ion mass spectrometry (TOF-SIMS) and the Saha-Boltzmann equation. Intensities of positive and negative secondary ion species were normalized to those of ²⁸Si⁺ and ²⁸Si⁻ ions, respectively, and an effective temperature of approximately (7.2 ± 0.1) × 10³ K of the sputtered region bombarded with pulsed 22 kV Au₃⁺ primary ions was determined. Intensity spectra showed polarity dependence on both n and m values of Si_nO_m fragments, and a slight shift to negative polarity for PECVD SiO₂ compared to thermally oxidized SiO₂ films. By dividing the intensity ratios of negative-to-positive ions for PECVD SiO₂ by those for thermally oxidized SiO₂ films to cancel statistical factors, the difference in absolute electronegativity (half the sum of ionization potential and electron affinity of fragments) between both films was obtained. An increase in electronegativity for SiO_m (m = 1, 2) and Si₂O_m (m = 1-4) fragments for PECVD SiO₂ films compared to thermally oxidized films was obtained to be 0.1-0.2 Pauling units, indicating a more covalent nature of Si-O bonds for PECVD SiO₂ films compared to the thermally oxidized SiO₂ films.     

The comparison of reactive ion etching and plasma etching in a parallel-plate reactor

Reactive ion etching (RIE) and plasma etching (PE) of different materials (GaAs, Si₃N₄ SiO₂ and photoresist Microposit 1350 H) in freon 116 are compared in the present article. The importance of ion bombardment for the etching rate is evident from the experimental results. GaAs is etched only by RIE due to ion milling, the etching rates of Si₃N₄ and SiO₂ are 4 to 5 times higher by RIE than PE.