Investigation of RF sputtered PSG films for MEMS and semiconductor devices

In this work, we report the preparation of phospho-silicate-glass (PSG) films using RF magnetron sputtering process and its application as a sacrificial layer in surface micromachining technology. For this purpose, a 76 mm diameter target of phosphorus-doped silicon dioxide was prepared by conventional solid-state reaction route using P₂O₅ and SiO₂ powders. The PSG films were deposited in a RF (13.56 MHz) magnetron sputtering system at 200-300 W RF power, 10-20 mTorr pressure and 45 mm target-to-substrate spacing without external substrate heating. To confirm the presence of phosphorus in the deposited films, hot-probe test and sheet resistance measurements were performed on silicon wafers following deposition of PSG film and a drive-in step. As a final confirmatory test, a p-n diode was fabricated in a p-type Si wafer using the deposited film as a source of phosphorus diffusion. The phosphorus concentration in the target and the deposited film were analyzed using energy dispersive X-rays (EDAX) tool. The etch rate of the PSG film in buffered HF was measured to be about 30 times higher as compared to that of thermally grown SiO₂ films. The application of RF sputtered PSG film as sacrificial layer in surface micromachining technology has been explored. To demonstrate the compatibility with MEMS process, micro-cantilevers and micro-bridges of silicon nitride were fabricated using RF sputtered PSG as a sacrificial layer in surface micromachining. It is envisaged that the lower deposition temperature in RF sputtering (<150 °C) compared to CVD process for PSG film preparation is advantageous, particularly for making MEMS on temperature sensitive substrates.     

Characterization of sputtered tungsten nitride film and its application to Cu electroless plating

In this study, W and tungsten nitride films were fabricated by reactive sputtering in a N₂/Ar atmosphere, the native oxide growth on the surface of the tungsten nitride films was investigated by X-ray photoelectron spectroscopy (XPS). It was found that tungsten nitride films were the mixture of W and W₂N sputtered in atmospheres of 3 mTorr argon and at the N₂ partial pressure from 0.1 to 2.0 mTorr. The ratio of W and W₂N in films was changed with the nitrogen partial pressure in sputtered chamber. Surface oxidations of the W film and tungsten nitride films advanced with time. Electrochemical measurement shows that all reduction-oxidation (redox) potentials of tungsten and tungsten nitrides were lower than that of copper film in electroless copper solution. And so, electroless-plated copper could be deposited on the surface of tungsten nitride films when the substrates were immersed into electroless copper plating solution without any pretreatment. Tungsten nitride films are appropriate for ULSI Cu interconnections using electroless Cu deposition.     

Electrical characterization and morphological properties of AlN films prepared by dc reactive magnetron sputtering

Aluminum nitride (AlN) films were deposited by dc reactive magnetron sputtering on p-Si-(1 0 0) substrate in Ar-N₂ gas mixtures. The effects of nitrogen concentration and sputtering power on AlN films deposition rate, crystallographic orientation, refractive index, and surface morphology are investigated by means of several characterization techniques. The results show that AlN films reasonably textured in (0 0 2) orientation with low surface roughness can be obtained with the deposition rate as high as 70 nm/min by the control of either target power or N₂ concentration in the gas mixture. Increasing the dc discharge power, Al atoms are not completely nitridized and the Al phases appear, as well as the AlN phases. MIS (Metal-Insulator-Semiconductor) structures were fabricated and electrically evaluated by I-V (current-voltage) and C-V (capacitance-voltage) measurements at high frequency (1 MHz). The results obtained from C-V curves indicate that charges at the dielectric/semiconductor interface occur, and the dielectric constant values (extracted under strong accumulation region) are compatible with those found in literature.     

Thickness dependence of the structural and electrical properties of copper films deposited by dc magnetron sputtering technique

This paper addresses the influences of film thickness on structural and electrical properties of dc magnetron sputter-deposited copper (Cu) films on p-type silicon. Cu films with thicknesses of 130-1050 nm were deposited from Cu target at sputtering power of 125 W in argon ambient gas pressure of 3.6 mTorr at room temperature. The electrical and structural properties of the Cu films were investigated by four-point probe, atomic force microscopy (AFM) as well as X-ray diffraction (XRD). Results from our experiment show that the grain grows with increasing film thickness, along with enhanced film crystallinity. The root mean square (RMS) roughness as well as the lateral feature size increase with the Cu film thickness, which is associated with the increase in the grain size. On the other hand, the Cu film resistivity decreases to less than 5 μΩ-cm for 500 nm thick film, and further increase in the film thickness has no significant effects on the film resistivity. Possible mechanisms of film thickness dependent microstructure formation of these Cu films are discussed in the paper, which explain the interrelationship of grain growth and film resistivity with increasing Cu film thickness.     

Evaluation of a novel unfluorinated copper precursor for chemical vapor deposition

A kinetics of the chemical vapor deposition (CVD) of copper using novel unfluorinated precursor, copper(I)(N(1(dimethylvinylsiloxy)-1-methylethano)-2-imino-4-pentanoate), namely Cu-KI5, was studied. Since its great thermal stability, Cu-KI5 allowed high source temperature to provide high vapor pressure, for example Cu-KI5 has a vapor pressure of 0.2-2.2 Torr at the temperature range of 100-140 °C. Furthermore, copper could be deposited by direct reduction from Cu-KI5 instead of disproportionation. By using formic acid (HCOOH) as a reducing agent, copper films were deposited on ruthenium substrate at temperature range of 150-350 °C. The activation energy was 48.9 kJ/mol in surface reaction limited region (<210 °C) and 1.9 kJ/mol in diffusion limited region (>210 °C) at the total pressure of 5 Torr. Secondary ion mass spectroscopy (SIMS) analysis showed that CVD copper film of high purity (>99.99%) was deposited at 250 °C. The as-deposited copper films grown at 150-300 °C exhibited strong 〈111〉 preferred orientation. The minimum resistivity of the copper film was 1.77 μΩ cm obtained at the deposition temperature of 250 °C. In the surface reaction limited region, kinetic data extracted from experiments enabled 2-D computational simulation to predict copper deposition into trench structures. Simulation results showed excellent step coverage, which was larger than 90% for aspect ratio of 10:1. Cu-KI5 is a promising Cu-CVD precursor for the fabrication of ultra large scale integration (ULSI) or through silicon via (TSV) copper interconnects.     

Properties of magnetron sputtered hydrogenated amorphous silicon

Hydrogen concentrations and bonding configurations were studied in hydrogenated amorphous silicon (a-Si:H) films deposited at 50‡C using the magnetron mode of sputtering with partial hydrogen concentrations between 0 and 90 percent in flowing argon. Hydrogen content within the films was determined from nuclear reaction analysis, and the chemical bonding of hydrogen was determined from infrared absorption of as-deposited, thermally annealed, and ion-bombarded films. Hydrogen/silicon ratios in the films increase to a maximum of 0.31 with increasing hydrogen in the deposition system. Ion backscattering shows ∼ 6 at.% argon trapped in the films, but no oxygen was detected by either ion backscattering or by sputter-Auger analysis. The wag and bend modes for Si-H in the films are typical of sputter-deposited a-Si:H; however, the stretch mode region is atypical with absorption near 2000 cm^−l dominating even for H/Si ratio of 0.27. From results of thermal annealing and post-deposition ion bombardment, it is concluded that argon ion bombardment during deposition produces enhanced absorption near 2000 cm^-1 in these a-Si:H films deposited by magnetron sputtering. This work was sponsored in part by the U. S. Department of Energy, under Contract DE-AC04-76-DP00789 and the U. S. Army Research Office, Contract DAA29-79-C-0026. U. S. Department of Energy facility.     

DC Magnetron-Sputtered Mo Thin Films with High Adhesion,Conductivity and Reflectance

The main challenge in the deposition of molybdenum thin films for high efficiency in copper indium gallium selenide (CIGS) modules lies in gaining an adherent coating without compromising conductivity and reflectance characteristics. In this study, Mo thin films were deposited on soda-lime glass by DC magnetron sputtering at different deposition power (55, 100, 200 and 300 W) and with high working gas pressure (2 and 4 Pa). Analytical techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and Hall effect were employed to analyze the structure, morphology and electrical resistivity of the deposited films. Ultraviolet–visible (UV–Vis) spectrometry was performed to measure the reflectance and a cross-hatch adhesion tape test was employed to determine the adhesion behavior of deposited films. With higher sputtering power and reduced gas pressure, an increase in the crystallite size of the deposited films was observed. Films deposited at higher gas pressure were found with tensile stresses and higher adhesion with the substrate. The van der Pauw method reveals an increase in conductivity at high power and low gas pressure. Improved reflectance was achieved at moderate sputtering power and low gas pressure.     

Characteristics of ZnO thin films prepared by radio frequency magnetron sputtering

We investigated in this study structural and nanomechanical properties of zinc oxide (ZnO) thin films deposited onto Langasite substrates at 200 °C through radio frequency magnetron sputtering with an radio frequency power at 200 W in an O₂/Ar gas mixture for different deposition time at 1, 2, and 3 h. Surface morphologies and crystalline structural characteristics were examined using X-ray diffraction, scanning electron microscopy, and atomic force microscopy. The deposited film featured a polycrystalline nature, with (1 0 0), (0 0 2), and (1 0 1) peaks of hexagonal zinc oxide at 31.75°, 34.35°, and 36.31°. As the deposition time increased, the ZnO film became predominantly oriented along the c-axis (0 0 2) and the surface roughness decreased. Through Berkovich nanoindentation following a continuous stiffness measurement technique, the hardness and Young’s modulus of ZnO thin films increased as the deposition time increased, with the best results being obtained for the deposition time of 3 h. In addition, surface acoustic wave properties of ZnO thin films were also presented.     

生长功率对HgCdTe薄膜微观结构以及表面形貌影响

实验采用射频磁控溅射生长了HgCdTe薄膜,并利用台阶仪、XRD、原子力显微镜等现代分析手段对HgCdTe薄膜的生长速率、物相、表面形貌进行了研究。实验结果表明,随着溅射功率增大,其生长速率成线性增大,当溅射功率低于30w时,薄膜XRD衍射图谱上没有出现任何特征衍射峰,只是在2θ=23°附近出现衍射波包,材料具有明显的非晶态特征,当溅射功率高于30w时,XRD表现为多晶结构;AFM和SEM分析表明生长速率对HgCdTe薄膜表面粗糙度、形貌、形成机理等有直接影响,随着生长速率提高,薄膜表面粗糙度逐渐增大,且薄膜逐渐形成“迷津”结构。     

Effect of power variation on microstructure and surface morphology of HgCdTe films deposited by RF magnetron sputtering

Mercury cadmium telluride films were grown by the RF magnetron sputtering technique at different sputtering powers.In experiment,X-ray diffraction (XRD) and atomic force microscopy (AFM) have been used to characterize the microstructure of HgCdTe films.The experimental results showed that when the growth power increased,the growth rate of HgCdTe films increased; when the growth power was less than 30 W,the HgCdTe film deposited by RF magnetron sputtering was amorphous; when the growth power was more than 30 W,the films exhibited polycrystalline structure.Films deposited at different growth rates were found to have characteristically different formations and surface morphologies; as observed through AFM,the surface morphology is composed of longitudinal islands forming a maze-like pattern in the high deposition rate.AFM analysis also illustrated that a significant reduction in the areal density of large islands and characteristically smoother films was achieved using a low deposition rate.     

氧化铁镍薄膜的制备与表征

首先提出射频反应磁控溅射中薄膜沉积速率同O2流量和溅射功率关系的理论计算模型;其次根据这一理论计算模型,在O2/Ar气氛中,利用射频反应磁控溅射制备氧化铁镍薄膜;最后分别采用台阶仪、X射线衍射(XRD)、X射线光电子能谱(XPS)、电子扫描镜(SEM)和电化学工作站对薄膜进行了表征,并分析了在制备过程中O2含量、工作压强和溅射功率对薄膜的沉积速率、结构、组分和表面形貌的影响.实验验证了所提出的理论计算模型以及Ni3 的存在;得到了膜厚与晶型以及工作压强与形貌的关系;电化学测试结果为:在电流密度为8 mA/cm2时的过电势为284 mV.     

Properties of transparent conductive ZnO:Al thin films prepared by magnetron sputtering

Middle-frequency alternative magnetron sputtering was used to deposit transparent conductive ZAO (ZnO:Al) thin films with ZAO (98 wt%ZnO+2 wt%Al₂O₃) ceramic target on glass and Si wafers. The influences of the various deposition parameters on the structural, optical and electrical performances of ZAO films have been studied. The structural characteristics of the films were investigated by the X-ray diffractometer and atomic force microscope, while the visible transmittance, carrier concentration and Hall mobility were studied by UV-VIS and the Hall tester, respectively. The lowest resistivity obtained in the work was 4.6×10⁻⁴ Ω cm for the film with average transmittance of 90.0% within the visible wavelength range and sheet resistance of 32 Ω, which was deposited at 250 °C and 0.8 Pa.     

Effect of annealing on the structural, optical and electrical properties of ITO films by RF sputtering under low vacuum level

Indium tin oxide (ITO) thin films were prepared by RF sputtering of ceramic ITO target in pure argon atmosphere at a high base pressure of 3×10⁻⁴ mbar without substrate heating and oxygen admittance. The use of pure argon during deposition resulted in films with high transparency (80-85%) in the visible and IR wavelength region. The films were subsequently annealed in air in the temperature range 100-400 °C. The annealed films show decreased transmittance in the IR region and decreased resistivity. The films were characterized by electron microscopy, spectrophotometry and XRD. The predominant orientation of the films is (2 2 2) instead of (4 0 0). The transmission and reflection spectra in the wavelength range 300-2500 nm are used to study the optical behaviour of the films. The optical transmittance and reflectance spectra of the films were simultaneously simulated with different dielectric function models. The best fit of the spectrophotometric data was obtained using the frequency-dependent damping constant in the Drude model coupled with the Bruggeman effective medium theory for the surface roughness. It has been found that the sputtering power and the chamber residual pressure play a key role in the resulting optical properties. This paper presents the refractive index profile, the structure determined from the XRD and the electrical properties of ITO films. It has been found from the electrical measurement that films sputtered at 200 W power and subsequently annealed at 400 °C have a sheet resistance of 80 Ω/□ and resistivity of 1.9×10⁻³ Ωcm.     

Large area silicon epitaxy using pulsed DC magnetron sputtering deposition

Pulsed DC magnetron sputtering is used for the deposition of large area crystalline (200 mm) silicon 100 nm thin films. p doped Si substrates are flashed (T_s = 900 °C) under high vacuum (5 × 10⁻⁶ Pa) for removing native oxide and restoring surface crystallinity. Subsequent boron-doped Si homoepitaxy is obtained at substrate temperature below 500 °C for pulse frequency of 150 kHz.     

Si基GaN薄膜的制备方法及结构表征

分别采用射频磁控溅射、热壁化学气相沉积(CVD)、电泳沉积法制备GaN薄膜。利用扫描电镜(SEM)、荧光光谱仪对样品进行结构、形貌和发光特性的分析比较。射频磁控溅射方法中,把SiC中间层沉淀到Si衬底上,目的是为了缓冲由GaN外延层和Si衬底的晶格失配造成的应力。结果证实了SiC中间层提高了GaN薄膜的质量。热壁化学气相沉积法制备GaN晶体膜时,选择H2作反应气体兼载体,有利于GaN膜的形成。电泳沉积法显示所得样品为六方纤锌矿结构的GaN多晶薄膜。结果表明:溅射法制备的GaN薄膜结晶效果好;CVD法制备时GaN薄膜应用范围广;电泳沉积法操作方便、简单易行。     

Texture enhancement of Al films on Ti underlayers by radio-frequency bias sputtering

The influence of sputtering pressure and radio-frequency (RF) bias power on the texture of Al/Ti thin films has been investigated. The Al/Ti thin films were deposited sequentially onto thermally oxidized Si wafers in a direct-current (DC) magnetron system. The RF bias was applied during Ti deposition. The texture of Al thin films was quantified by θ–2θ scans and rocking curves of x-ray diffraction (XRD). The Al thin films deposited on bias-sputtered Ti underlayers showed an epitaxial growth and strong (111) texture. The Al (111) texture improved with decreasing sputtering pressure and increasing RF-bias power. The Al/Ti texture was also enhanced when the SiO₂/Si substrate surface was RF plasma cleaned prior to Ti deposition. The Al (111) texture was closely related to Ti (0002) texture. The mechanism of Ti-texture improvement by applying bias sputtering was explained based on the ion-bombardment effect.     

Atomic layer deposition of titanium nitride from TDMAT precursor

TiN was grown by atomic layer deposition (ALD) from tetrakis(dimethylamino)titanium (TDMAT). Both thermal and plasma enhanced processes were studied, with N₂ and NH₃ as reactive gases. Using an optimized thermal ammonia based process, a growth rate of 0.06 nm/cycle and a resistivity of 53 × 10³ μΩ cm were achieved. With an optimized plasma enhanced NH₃ process, a growth rate of 0.08 nm/cycle and a resistivity of 180 μΩ cm could be obtained. X-ray photo electron spectroscopy (XPS) showed that the difference in resistivity correlates with the purity of the deposited films. The high resistivity of thermal ALD films is caused by oxygen (37%) and carbon (9%) contamination. For the film deposited with optimized plasma conditions, impurity levels below 6% could be achieved. The copper diffusion barrier properties of the TiN films were determined by in-situ X-ray diffraction (XRD) and were found to be as good as or better than those of films deposited with physical vapor deposition (PVD).     

铜薄膜的直流磁控溅射制备与表征

根据薄膜的形成机理,用直流磁控溅射方法制备出了表面结构平滑、致密的Cu薄膜.实验中,采用纯度＞99.9%的铜靶,工作气压保持在2.7 Pa不变,玻璃衬底温度随环境温度变化.用X射线衍射仪(XRD)、扫描电镜(SEM)研究了薄膜的织构、晶粒尺寸和表面形貌.结果表明,随着溅射功率增大,薄膜织构减弱;溅射功率增大和溅射时间增加均可使薄膜的晶粒尺寸增大,在溅射功率≤100 W时获得的薄膜晶粒细小,有裂纹缺陷;溅射功率为150 W,溅射时间为30 min时,薄膜表面结构平滑、致密,晶粒尺寸相对较大.须进一步改进工艺参数,如衬底温度等,从而制备出表面结构平滑、致密、晶粒细小的薄膜.     

Annealing effects on the formation of semiconducting Mg2Si film using magnetron sputtering deposition

Semiconducting Mg2Si films were synthesized on silicon (11 1) substrates by magnetron sputtering deposition and subsequent annealing in an annealing furnace filled with argon gas,and the effects of heat treatment on the formation and microstructure of Mg2Si films were investigated.The structural and morphological properties were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM),respectively.The results show that the crystal quality of Mg2Si films depends strongly on the annealing temperature,the annealing time and the deposited magnesium film thickness.Annealing at 400 ℃ for 5 h is optimal for the preparation of Mg2Si film.XRD and SEM results show that magnesium silicide film with various orientations is formed on the silicon surface because of the interdiffusion and reaction of magnesium with substrate silicon atoms,and the evolution of surface features on growing films is very dependent on the annealing temperature and time.     

Effects of substrate temperature on electrical and structural properties of copper thin films

This paper addresses the effects of substrate temperature on electrical and structural properties of dc magnetron sputter-deposited copper (Cu) thin films on p-type silicon. Copper films of 80 and 500 nm were deposited from Cu target in argon ambient gas pressure of 3.6 mTorr at different substrate temperatures ranging from room temperature to 250 °C. The electrical and structural properties of the Cu films were investigated by four-point probe and atomic force microscopy. Results from our experiment show that the increase in substrate temperature generally promotes the grain growth of the Cu films of both thicknesses. The RMS roughness as well as the lateral feature size increase with the substrate temperature, which is associated with the increase in the grain size. On the other hand, the resistivity for 80 nm Cu film decreases to less than 5 μΩ-cm at the substrate temperature of 100 °C, and further increase in the substrate temperature has not significantly decreased the film resistivity. For the 500 nm Cu films, the increase in the grain size with the substrate temperature does not conform to the film resistivity for these Cu films, which show no significant change over the substrate temperature range. Possible mechanisms of substrate-temperature-dependent microstructure formation of these Cu films are discussed in this paper, which explain the interrelationship of grain growth and film resistivity with elevated substrate temperature.