A simple method for the characterization of thin films during heat treatment

 In this paper, we propose a simple method to characterize thin film during heat treatment with a compact structure as a specimen. By detecting the variation of displacements of the structure, thereby, various kinds of information, such as thermomechanical properties, stress relieving, or microstructure variations of thin films during heat treatment, can be characterized from the record of the displacements of the structure. The measurement of displacements can be done directly under an optical microscope with the specimen placed in a heating stage. Based on this method, the specimen is free from substrate, no mechanical constraints imposed on the specimen, and the characterization can display local conditions on a wafer. To set an example, as-deposited polycrystalline silicon films with phosphorous doping on regular high temperature annealing between 550 and 1100 °C are used as a model system to demonstrate the effectiveness of the proposed method for characterizing variations of stress-levels as function of temperature and time during heat treatment. Received: 30 May 2001/Accepted: 29 August 2001     

NiCrAlY薄膜应变计的研制

采用射频磁控溅射法在Ni基高温合金拉伸件上制备NiCrAlY薄膜应变计。研究了热稳定处理对NiCrAlY薄膜结构、表面形貌的影响,并且测试了NiCrAlY薄膜应变计的电学与应变性能。结果表明：热稳定处理后 NiCrAlY 薄膜应变计由于在表面形成了一层 Al2 O3膜,具有抗高温氧化的特性,在室温～800℃范围内,应变计电阻同温度呈线性变化,电阻温度系数（ TCR）约为290×10－6/℃,室温下的应变计系数（ GF）为2.1。     

Pulsed-laser annealing, a low-thermal-budget technique for eliminating stress gradient in poly-SiGe MEMS structures

In this paper, we demonstrate eliminating the stress gradient in polycrystalline silicon germanium films at temperatures compatible with standard CMOS (Al interconnects) backend processing. First, we study the effect of varying the germanium concentration from 40% to 90%, layer thickness, deposition pressure from 650 to 800 mtorr and deposition temperature from 400 to 450/spl deg/C, on the mechanical properties of SiGe films. Then the effect of excimer laser annealing (248 nm, 38 ns, 780 mJ/cm/sup 2/) on stress gradient is analyzed. It is demonstrated that stress gradient can be eliminated completely by depositing Si/sub x/Ge/sub 1-x/(10%相似文献   

A study of the effect of the fabrication process on diffusion in a layered thin film

 A diffusion layer that is likely to be formed at the interfaces of the multi-layered thin film would affect its overall mechanical properties; the thinner the thin film, the more significant would be the effect. We measure the distribution of atoms and estimate the thickness of the diffusion layer at the vicinity of the interfaces among thin films of Al and SiO₂ and silicon wafer with the aid of Auger electron spectroscopy (AES). The effect of heat treatment after fabrication of the thin films on the diffusion is also investigated. Received: 28 December 1998/Accepted: 4 January 1999     

NEG thin films for under controlled atmosphere MEMS packaging

Non-evaporable getter (NEG) thin films for residual gases control in micro-electro-mechanical systems (MEMS) cavities after sealing are considered. For this study, several getters are deposited and analyzed in terms of sorption performances, microstructure and activation mechanism. Compared to single layer evaporated titanium reference, the addition of a chromium sub-layer is shown to decrease the activation temperature of the NEG. Moreover, when activated under 0.2 mbar of N₂, nitrogen diffusion in the titanium layer is enhanced by sub-layer addition. Effective pumping of nitrogen is monitored by residual gas analysis (RGA). Transmission electron microscopy investigation of as-deposited thin film getters reveals Ti layer microstructure modification due to platinum sub-layer addition. Furthermore, activation under nitrogen atmosphere is shown to induce microstructure modifications for both getters. X-ray photoelectron spectroscopy (XPS) and depth profiling monitoring of NEG activation under high vacuum conditions (10⁻⁸ mbar) shows the dissolution of the NEG surface oxide in the getter bulk, along with the formation of carbide and nitride compounds. These results are in good agreement with already published results on getter alloys.     

应用C-V测量研究铁电薄膜材料的电特性

通过分析钛酸铋铁电薄膜材料MFS结构的C－V特性曲线,发现经过快速退火工艺处理的钛酸铋铁电薄膜的剩余极化强度Pr提高,界面上固定电荷的分布和性质发生了变化。     

Elastic–plastic modeling of heat-treated bimorph micro-cantilevers

This paper models the residual stress distributions within micro-fabricated bimorph cantilevers of varying thickness. A contact model is introduced to calculate the influence of contact on the residual stress following a heat treatment process. An analytical modeling approach is adopted to characterize bimorph cantilevers composed of thin Au films deposited on thick poly-silicon or silicon-dioxide beams. A thermal elastic–plastic finite element model (FEM) is utilized to calculate the residual stress distribution across the cantilever cross-section and to determine the beam tip deflection following heat treatment. The influences of the beam material and thickness on the residual stress distribution and tip deflections are thoroughly investigated. The numerical results indicate that a larger beam thickness leads to a greater residual stress difference at the interface between the beam and the film. The residual stress established in the poly-silicon cantilever is greater than that induced in the silicon-dioxide cantilever. The results confirm the ability of the developed thermal elastic–plastic finite element contact model to predict the residual stress distributions within micro-fabricated cantilever structures with high accuracy. As such, the proposed model makes a valuable contribution to the development of micro-cantilevers for sensor and actuator applications.     

Fabrication and electrical properties of polymer-derived ceramic (PDC) thin films for high-temperature heat flux sensors

In this paper, we describe the fabrication of ceramic thin films for high-temperature heat flux sensors. The polymer-derived ceramic (PDC) thin films are prepared by using soft lithography on pre-ceramic polymer precursors followed by pyrolysis and heat treatment. Processing routes have been developed which lead to thin film resistance-thermal detectors (RTD) that have sufficient mechanical strength for handling and for use in thermal sensing. The effect of annealing temperatures on the electric resistivity of the PDC sensors was investigated. The electrical resistivity of the sensors was measured at different temperatures.     

Elastic–plastic modeling of heat-treated bimorph micro-cantilevers

This paper models the residual stress distributions within micro-fabricated bimorph cantilevers of varying thickness. A contact model is introduced to calculate the influence of contact on the residual stress following a heat treatment process. An analytical modeling approach is adopted to characterize bimorph cantilevers composed of thin Au films deposited on thick poly-silicon or silicon-dioxide beams. A thermal elastic–plastic finite element model (FEM) is utilized to calculate the residual stress distribution across the cantilever cross-section and to determine the beam tip deflection following heat treatment. The influences of the beam material and thickness on the residual stress distribution and tip deflections are thoroughly investigated. The numerical results indicate that a larger beam thickness leads to a greater residual stress difference at the interface between the beam and the film. The residual stress established in the poly-silicon cantilever is greater than that induced in the silicon-dioxide cantilever. The results confirm the ability of the developed thermal elastic–plastic finite element contact model to predict the residual stress distributions within micro-fabricated cantilever structures with high accuracy. As such, the proposed model makes a valuable contribution to the development of micro-cantilevers for sensor and actuator applications.

     

薄膜热膨胀系数测试技术研究

热膨胀系数是薄膜的重要热学性能参数,也是薄膜热应力和残余应力计算分析过程中的关键数据.文章基于热诱导弯曲原理,分别采用单基片法和双基片法对氮化钛(TiN)和铝(Al)薄膜的热膨胀系数进行测试,并着重对双基片法的测试误差和适用性进行了分析.研究结果表明,薄膜在不同材质基底上弹性模量的差异是影响双基片法薄膜热膨胀系数测试精度的重要因素.当不同材质基片上薄膜弹性模量差异较小时,双基片法测得的热膨胀系数与单基片法所获结果基本一致;而当不同材质基片上薄膜弹性模量相差较大时,双基片法将不再适用.此外,文章结合薄膜的形貌、结构和残余应力表征测试,对TiN和Al薄膜热膨胀系数与其块体材料的差异进行了分析,结果显示残余压应力会导致薄膜热膨胀系数增大,而残余拉应力则具有相反的效果.     

Highly reliable a‐IGZO TFTs on a plastic substrate for flexible AMOLED displays

We have successfully reduced threshold voltage shifts of amorphous In–Ga–Zn–O thin‐film transistors (a‐IGZO TFTs) on transparent polyimide films against bias‐temperature stress below 100 mV, which is equivalent to those on glass substrates. This high reliability was achieved by dense IGZO thin films and annealing temperature below 300 °C. We have reduced bulk defects of IGZO thin films and interface defects between gate insulator and IGZO thin film by optimizing deposition conditions of IGZO thin films and annealing conditions. Furthermore, a 3.0‐in. flexible active‐matrix organic light‐emitting diode was demonstrated with the highly reliable a‐IGZO TFT backplane on polyimide film. The polyimide film coating process is compatible with mass‐production lines. We believe that flexible organic light‐emitting diode displays can be mass produced using a‐IGZO TFT backplane on polyimide films.     

The development of a low-stress polysilicon process compatible withstandard device processing

When surface micromachined devices are combined with on-chip circuitry, any high-temperature processing must be avoided to minimize the effect on active device characteristics. High-temperature stress annealing cannot be applied to these structures. This work studies the effects of deposition parameters and subsequent processing on the mechanical properties of the polysilicon film in the development of a low-strain polysilicon process, without resorting to high-temperature annealing. The films are deposited as a semi-amorphous film and then annealed, in situ at 600°C for 1 h, to ensure the desired mechanical characteristics for both doped and undoped samples. This low temperature anneal changes the strain levels in undoped films from -250 to +1100 με. The best results have been obtained for an 850°C anneal for 30 min which is used to activate the dopant (both phosphorus and boron). No further stress annealing was used, and 850°C does not present problems in terms of thermal budget for the electrical devices. It is shown that these mechanical characteristics are achieved by forming the grain boundaries during subsequent low temperature annealing, and not during deposition. TEM (transmission electron microscopy) studies have been used to investigate the link between the structure and mechanical strain. This has shown that it is the formation of the grain boundary rather than the grain size which has a significant effect on strain levels, contrary to reports in the literature. Using the above-mentioned deposition process, a series of experiments have been performed to establish the flexibility in subsequent processing available to the designer. Therefore, by careful consideration of the processing, a low-temperature polysilicon process, which can be used to fabricate thin micromachined structures, has been developed     

Pulsed laser deposition of Y2O3 : Eu thin film phosphors

Thin films of Y₂O₃ : Eu cathodoluminescent (CL) phosphors were deposited using pulsed laser deposition using deposition temperature between 250°C and 800°C, O₂ pressures between residual vacuum (2×10⁻⁵ Torr) and 6 Torr, and post annealing up to 1200° for 1 h in air. The CL efficiency of the best thin film was about one third that of the starting powder. The brightness and efficiency of the thin films improved as the deposition temperature, O₂ pressure and post annealing temperature were increased, except that O₂ pressures above 600 mTorr did not significantly improve the CL properties. At deposition temperatures >600°C, the surface morphology changed from a smooth film to a nodular deposit for O₂ pressures >200 mTorr, with nodule dimensions ≈100 nm. Simultaneously, the CL properties improved dramatically because of enhanced optical scattering out of the thin film. Optical scattering was discussed in terms of anomalous diffraction. The CL properties also improved dramatically with high temperature post annealing. This effect was interpreted in terms of improved crystallinity and activation of the Eu. The low brightness and efficiency of thin films versus powder was affected by depletion of the Eu in the thin films owing to the deposition process.     

多晶硅薄膜残余应力在线测量技术

介绍了多晶硅薄膜中的残余应力对微结构性能的影响,分析了应力在线测量技术的必要性。说明了T型微检测结构的测试原理,并基于单T型结构设计出双T型检测结构。探讨了检测结构的制作工艺,加工出试验样片,用刻度显微镜测量出试验数据,推导出误差修正公式,结合M athCAD软件计算出应力值。在结论部分,指出了双T型检测结构能够提高测量精度,并给出了多晶硅薄膜残余应力在线测量技术的工艺实现方法。     

Residual stress influences on the sensitivity of ultrasonic sensor having composite membrane structure

Stress and sensitivity of arrayed ultrasonic sensors utilizing piezoelectric thin film (lead–zirconate–titanate film: Pb(Zr_0.52Ti_0.48)O₃) having composite membrane structure are demonstrated. Due to different thermal and elastic characteristics of each constitutive layer, a subsequent residual stress and deflection is generated on the resultant composite membrane. We present the influence of residual stress on the mechanical behaviors and sensitivities of a Si-based integrated sensor device. The design of sensor structure and the fabrication process especially relating to thermal treatment have significant effects on the stress state of the composite membrane, and the relationships among the stress states, deflections of membrane and sensitivities of sensor devices are considered. Tensile stress induced on the membrane consequently leads to sensitivity deterioration, while compressive stress improves sensitivity. Sensitivities of each sensor structure are expressed as the ratio of output voltage (V) to the acoustic pressure (P), and the variations of those are discussed relating to the residual stress states, PZT film properties and mechanical behaviors of each composite membrane.     

Properties and cathodoluminescence of Y2O2S:Eu thin films

Abstract— Europium‐activated yttrium oxysulfide thin films were fabricated by electron‐beam deposition of Y₂O₂S:Eu with consequent annealing in an H₂S/Ar gas mixture. Transformations in film composition and surface morphology as well as corresponding changes in the optical, photoluminescent, and cathodoluminescent properties were studied and will be discussed. It is shown that 248‐nm laser irradiation of heat‐treated films improves cathodoluminescence by as much as 30%, supposedly due to annealing. The developed phosphor films have a luminance comparable to that of annealed europium‐activated yttrium oxide films and improved color properties (CIE color coordinates: x = 0.624, y = 0.329), and are suitable for display and optoelectronics applications.     

Characterization of Polycrystalline Silicon-Germanium Film Deposition for Modularly Integrated MEMS Applications

The deposition of in situ boron-doped polycrystalline silicon-germanium (poly-SiGe) films in a conventional low-pressure chemical-vapor deposition reactor has been characterized using the design of experiments method. The dependencies of deposition rate, resistivity, average residual stress, strain gradient, and wet etch rate in hydrogen peroxide solution are presented. Structural layer requirements for general microelectromechanical system applications can be met within the process temperature constraint imposed by complementary metal-oxide-semiconductor (CMOS) electronics. However, residual stress and strain gradient requirements for inertial sensor applications will be difficult to meet with a single homogeneous layer of poly-SiGe that is about 2 mum thick. By correlating stress depth profile measurements with cross-sectional transmission electron microscopy images, we conclude that the large strain gradient is due to highly compressive stress in the lower (initially deposited) region of the film. For films deposited at very low temperature (near the range of amorphous film deposition), in situ boron doping enhances film crystallinity and reduces the strain gradient     

Optical micro-paddle beam deflection measurement for electrostatic mechanical testing of nano-scale thin film application to MEMS

The authors describe their design for a paddle-like cantilever beam sample to relieve non-uniform stress distribution in beam-bending tests of the mechanical properties of thin film applications to MEMS. We added the sample to a custom-designed system equipped with an electrostatic panel and optical interferometer. The system overcomes problems associated with using nano-indentation for testing, and reduces errors tied to the amount of contact force required to bend the beam. Accurate paddle cantilever beam deflection was obtained using a four-step phase-shifting process with a Michelson interferometer. Film strain was determined using a simple force equilibrium equation. Residual stresses were measured at −41.3 MPa for 150 nm silver film, −3.2 MPa for 150 nm gold film, and −16.8 MPa for 150 nm copper film. We observed residual stresses for copper films at different thicknesses. The results indicate high tensile stress forms during the early deposition stage for thin copper film due to grain coalescence, and a decrease in stress with an increase in film thickness. In copper films with thicknesses greater than 153 nm, lattice relaxation associated with the surface mobility of metallic atoms changed residual stress from tension to compression.     

Determination of Young’s modulus and residual stress of electroless nickel using test structures fabricated in a new surface micromachining process

This paper reportsin situ measurement of Young’s modulus and residual stress of electroless nickel films through the use of microfabricated nickel test structures, including electrostatic microactuators and passive devices. Th test structures are fabricated in a new surface micromachining process, termed “nickel surface micromachining”, using electroless plated nickel as the structural layer and polysilicon as the sacrificial layer. Subsequent to fabrication, lateral resonant-type electrostatic microactuators of different geometries are resonated by electrical excitation. Using the measured resonant frequencies and knowledge of the device geometry, the Young’s modulus of the film is determined. The passive electroless nickel microstructures deform upon completion of the fabrication process due to residual stress in the film Measurement of this deformation in conjunction with an appropriate mechanical model is used to determine the residual stress in the films.     

Oil thermal annealed nano‐structured indium tin oxide thin films for display applications

Indium tin oxide‐coated thin films (200 nm) are deposited on glass substrates by using R.f. sputtering technique. Here, we investigate the influence of new technique of treatment, which is called as “oil thermal annealing” on the nano‐structured indium tin oxide thin films at fixed temperature (150 °C) which improves adhesion strength, electrical conductivity and optical properties (transmittance) of the films. Oil thermal annealing is used to reduce inherent defects that may be introduced during the prepared thin film and cooling processes. Proposed technique is highly suitable for liquid crystal displays, solar cells and organic light emitting diodes, and many other display‐related applications.