Application of optics-geometrical method in short-range optical radar

The paper describes application of optics-geometrical method in short-range optical radar for measuring reflection characteristics of target and radiator’s angular energy distribution. The possibility of signal sampling in a base-type optical radar device using multi-element photoreceiver is studied as well as ways of improving precision of measurements with respect to linear coordinate up to ∼1 mm. A ratio between reflection coefficient of target’s surface and image coordinate in photoreceiver’s plane is determined. A working equation for calculating radiation pattern of radiator using the method of self-scanning of photoreceiver’s field of view with respect to its flare with precision ±0.5° with respect to angle coordinate is obtained.     

硅基高精度镍铬薄膜电阻的制备和性能表征

集成无源元件（IPD）技术可以将分立的无源元件集成在衬底内部,提高系统的集成度。为了获得高精度的薄膜电阻,采用多层薄膜电路工艺在硅晶圆上制备了不同线宽的镍铬薄膜电阻,利用显微镜和半导体参数测试仪对薄膜电阻的图形线宽及电学特性进行了表征及测试。结果表明,制备出的镍铬薄膜电阻线宽精度在±5%以内,电阻精度在±0.5%以内,具有稳定的电学特性。基于镍铬的高精度硅基无源集成电阻器在系统集成中有广泛的应用价值。     

Analysis of structural transformations and fluctuation effects in the nanosized nickel films in the vicinity of the melting point

The effect of heating temperature on the structure of the nickel films with an original thickness of 20 nm that are deposited on silicon-oxide substrate (the thickness of the thermally grown silicon oxide SiO₂ is about 1 ??m) is studied using the scanning probe microscopy. An increase in the temperature causes a decrease in the mean thickness of the Ni film from the original thickness h = 20 nm to 18 ± 2 nm at a temperature of 737 K and 15 ± 2 nm at a temperature of 752 K. The thickening of the film is interpreted with allowance for the heterogeneous melting. The voltage jumps across the film sample in the vicinity of the melting point under slow heating and constant current flow through the sample are interpreted. In particular, the primary fluctuations lead to a decrease in the nickel film thickness due to the formation of drops from the liquid layer on the film surface and, hence, significant positive fluctuations of the resistance (or voltage jumps across the sample). Irreversible variations in the properties of thin metal films upon heating below the melting point are interpreted.     

Simulation of a microprofile and electric field distribution in MIM structures

Simulation of etching of a microtip’s lower electrode and deposition of a dielectric film has shown that the film undergoes a strong thinning at lateral surfaces and at the microtip’s bases. It is demonstrated that, at a microtip density of 5 × 10⁸ cm⁻², the electric field’s strength at the base of the tip is 3.5 times that at its apex, which gives rise to additional emission centers.     

Facile chemical method of etching polyimide films for failure analysis (FA) applications and its etching mechanism studies

A new strategy has been developed for discovering a novel/facile way of etching polyimide film for FA application. The aromatic polyimide synthesized from pyromellitic dianhydride and 2,2′-dimethyl-4,4′-diaminobiphenyl in the presence of an acid catalyst. This polyimide film was used to study its physical attributes and the chemical etching rate which can be evaluated in microelectronic package application as dielectric film. Chemical etching rates of polyimide film by an alkaline etching solution with the presence of different kinds of etchants were studied by film-thickness measurement and UV absorption spectroscopy of dispersible etching residue. The etching rate of polyimide film in alkaline ethylenediamine solution is highest among the etching solution studied in the present experiment. If an external bias voltage was applied during etching, the etching rate was increased. The effect of temperature, solubility of the etchant was also discussed. The presence of a radical in the process of etching reveals that the etching reaction is a type of radical chain reaction. It was found that the deprocessing technique (drenched alkaline aqueous solution of ethylenediamine and then instantaneously combined with mix acid (2:1 Nitric 90% fuming to Sulfuric mix at 40 °C)) could be extended to remove polyimide in different package geometry and different thickness of film.     

Millimeter-wave measurements of the complex dielectric constant of an advanced thick film UV photoresist

The first measurement of the relative permittivity (ε_r) and loss tangent (tan δ) of EPON™ SU-8 advanced thick film ultraviolet photoresist is reported at frequencies between 75–110 GHz (W-band). The problems associated with such a measurement are discussed, an error analysis given, and values of ε_r=1.725±0.08 and tanδ =0.02±0.001 are determined.     

Measurement of high-dynamic temperature field using high-speed quadriwave lateral shearing interferometer

An approach to measure a high-dynamic two-dimensional (2D) temperature field using a high-speed quadriwave lateral shearing interferometer (QWLSI) is proposed. The detailed theoretical derivation to express the wavefront reconstruct principle of the proposed method is presented. The comparison experiment with thermocouples shows that the temperature field measurement using QWLSI has a precision of ±0.5 °C. An experiment for measuring the highdynamic temperature field generated by an electrical heater is carried out. A 200 frame rate temperature field video with 512 × 512 resolution is obtained finally. Experimental results show that the temperature field measurement system using a QWLSI has the advantage of high sensitivity and high resolution.     

Capacitance-voltage study of heterostructures with InGaAs/GaAs quantum wells in the temperature range from 10 to 320 K

Heterostructures with single strained InGaAs/GaAs quantum wells have been studied by measuring the capacitance-voltage characteristics in a wide range of temperatures and test signal frequencies. Based on the analysis of experimental capacitance-voltage characteristics, a temperature shift of the peak in the apparent profile of a majority carrier’s concentration is revealed and a quantitative model of this phenomenon is proposed. The effect of incomplete impurity ionization on the experimentally found quantum well’s charge is determined. It is established by numerical simulation and fitting of capacitance-voltage characteristics that the conduction band’s discontinuity for heterostructures with strained In _x Ga_{1 − x} As/GaAs quantum wells (x = 0.225) remains constant and equal to 172 ± 10 meV at temperatures from 320 to 100 K.     

The stability of α-Sn grown on CdTe by molecular beam epitaxy

We have examined the effect of the substrate orientation, thickness, growth rate, substrate temperature and inclusion of small amounts of Ge on the transition temperature of α-Sn films grown on CdTe. The transition temperature from α-Sn to β-Sn was determined by optical microscopy to be as high as 132° C. CdTe(ll0) is a somewhat better orientation than CdTe(100), and CdTe(lll)B appears to be totally unacceptable. The transition temperature from α-Sn to β-Sn depends on the film thickness; thinner films have a somewhat higher transition temperature than thicker films. The film quality can be increased by lowering the growth rate and raising the growth temperature to about 75° C. Since the transition from α-Sn to β-Sn starts at defects in the film, improving the film quality by lowering the growth rate and raising the growth temperature raises the transition temperature. Also by adding small amounts of Ge (∼2%) the transition temperature of films grown on CdTe can be significantly increased.     

In situ sensors for monitoring and control in molecular beam epitaxial growth of Hg1−xCdxTe

The current status of the implementation and refinement of two wafer state sensors forin situ monitoring and control during molecular beam epitaxial (MBE) growth of Hg_1−xCd_xTe will be reported. First a rapid scan spectral ellipsometer has been developed and employed for precisely measuring compositions of Hg_1−xCd_xTe alloys during growth. MBE films in the composition range x = 0.20 to 0.30 have been grown andin situ spectra taken at the growth temperature (180°C) and at room temperature. The MBE films were treated as single layers without the need to invoke any surface film (due to surface roughness, oxide, or of any different composition) as required for exsitu data. The least squares fit over the whole spectral range was used as a measure of the precision. The film composition was also determinedex situ by wavelength dispersive analysis of x-rays and by Fourier transform infrared (FTIR) spectrometry after verifying that there was no lateral variation. A precision of better than ±0.0015 has so far been demonstrated usingin situ spectral ellipsometry for Cd composition or CdTe mole fraction, x, measurements. This compares with ±0.003 for single wavelength ellipsometry. The composition of Hg_1−xCd_xTe films were also monitored during growth. A spectral pyrometer based on a FTIR spectrometer has also been developed for substrate temperature measurements during growth. The spectral pyrometer measures both the emission and reflectance to give the emissivity of a growing sample over a range of wavelengths spanning the peak of the grey body emission. From the reflectivity measurements, the thickness (in excess of 1 μm) of the growing film is also determined from the interference fringes. The spectral ellipsometer is only capable of measuring thicknesses up to C.a 5000°A (i.e. optically thin). Excellent agreement is obtained between thein situ (at growth temperature) andex situ (at room temperature) thickness measurements. The small discrepancy can be explained by the refractive index of Hg_1−xCd_xTe being 5% higher at the growth temperature than at room temperature. The combination ofin situ sensors now provides a means of continuously monitoring the composition and thickness of the growing Hg_1−xCd_xTe film.     

Supercooling studies and LPE growth of Hg1−xCdxTe from Te-Rich solutions

Hg_1-xCd_xTe liquid phase epitaxial (LPE) layers were grown from well-stirred large (100 g) Te-rich Hg-Cd-Te solutions by the dipping method. Supercooling below the liquidus temperature in Te-rich solutions was studied by differential thermal analysis (DTA) and film growth results. Although supercooling of 20 to more than 100° C was routinely measured in small (2 g) sample melts, supercooling in larger melts (>100 g) was erratic and smaller. Factors affecting the degree of supercooling were identified and a Hg-reflux was found to be a major cause of erratic melt behavior. The LPE reactor was modified to correct the Hg-reflux action and a visual technique was developed for in situ determination of the liquidus temperature. A limited amount of supercooling was found in the melt after reactor modification but it was difficult to maintain for extended durations before spontaneous nucleation occurred. Consequently, programmed cooling rather than isothermal LPE was employed to grow many of the films reported here. Hg_1−xCd_xTe epitaxial layers ofx = 0.2 to 0.25 were grown on (111)B oriented CdTe substrates by cooling the melts only 1–2° C below the previously measured crystallization temperature. The small amount of cooling minimized composition variation with film thickness. Excellent surface morphology was obtained when slow cooling rates of 0.02–0.05° C/ min were used. Cooling rates greater than 0.2° C/min created rough, pitted surface. Precise substrate orientation was important in reducing surface terracing. Composition and thickness uniformities of the epitaxial films were excellent as a result of substrate rotation. Run-to-run reproducibility of film composition was ±0.01 inx. Hall measurements showed carrier concentrations in the range 2–20 × 10¹⁴ cm⁻³ with photoconductive lifetimes of 0.5–3.0 dms forx = 0.20 to 0.25.     

Study of the laser-recrystallized film with a control of grain boundary location by using surrounding antireflection cap method

A modified technique for unseeded laser-recrystallization of poly-crystalline silicon films deposited on amorphous insulators has been developed whereby grain boundary location in the recrystallized silicon film can be controlled. In this technique, the silicon film is encapsulated with an antireflection cap with windows and then recrystallized by cw-Ar ion laser irradiation. Grain boundaries are removed from the silicon film at the place where the window is opened because of a temperature gradient due to a change in laserbeam absorption in the silicon film. The (100) texture is observed in the grain-boundary-free areas although the silicon shows (110) texture before the recrystallization. An SOI/ MOSFET has been fabricated in the recrystallized film. The channel regions of MOS-FET’s are aligned in the window regions. Field-effect mobility of 490 cm²/Vs is obtained for n-channel MOSFET’s. Source-to-drain leakage current of 5fA/μm is obtained at drain voltage of 5V and back-gate voltage of -100V for the W/L = 10 μ/2 μm MOSFET.     

Structures and physical properties of sputtered amorphous SiC films

Optical and electrical properties have been measured for amorphous SiC films prepared by rf sputtering in a pure Ar atmosphere with a sintered 6H-SiC target. The absorption edge E₀ determined from the relation of αhΝ = B(hΝ-E₀)² ranged from 1.45 to 1.80 eV depending on the film thickness and the substrate temperature. The room temperature electrical conductivity is in the range of 5.4×10⁻¹¹ and 1.4×10⁻⁵ Ω⁻¹cm⁻¹. The absorption edge decreases and the conductivity increases with increasing film thickness. The absorption edge shifts to shorter wavelengths (blue shift) and the conductivity decreases during annealing below 400‡C for 60 min, whereas the absorption edge shifts to the longer wavelength side (red shift) and the conductivity increases during annealing at 800‡C It is proposed that the two annealing processes cause structural changes in amorphous SiC films, one of which involves removal of defects or voids while the other involves rearrangement or rebonding of the component atoms.     

Developing an analytic methodology to accurately predict probing depth in integrated circuit structures

This work designs an analytic methodology for applying the probe-before-bump procedure to predict probing depth and proposes feasible probing design parameters to avoid excessive probing of the bump pad. Two kinds of multi-level wafers were used to implement the probing experiment, with a single touch down, and an overdrive of 70 μm, 100 μm, 130 μm, and 150 μm by using a vertical probe card. The Young’s modulus and hardness of the two multilevel structures are measured on which the first bump pads are produced by sputtering aluminum onto the SiO₂, while the second bump pads are produced by sputtering aluminum onto the copper, creating a pad metal of approximately 1-μm thickness by using the nanoindenter. The test results indicate that the Young’s modulus of the thin film material exceeds that of bulk material by 20–30 GPa. The difference between analytic and experimental probing depth ranges from 2.3% to 8.9%, revealing that the proposed novel analytic model is extremely accurate. Engineers or researchers can use the analytic methodology to accurately predict probing depth and acquire probing parameters that are accurate, cost effective, and efficient, thus eliminating the need to use focused ion beam (FIB) or other measurement instruments to determine the probing depth.     

Effect of nitridation on the electrical properties of W:Ti resistors

The electrical properties of tungsten-titanium (W:Ti) thin film resistors sputtered in an argon-nitrogen atmosphere were investigated. The resistivity ρ and the thermal coefficient of resistivity α were calculated as a function of film thickness and nitrogen content. A bulk resistivity of 70±4 μΩ-cm and the mean free path λ_o), of 0.8±0.1 μm were obtained for samples sputtered without nitrogen. The authors believe this to be the first report for the value of the λ_o in sputtered W:Ti. By appropriately controlling the nitrogen content during sputtering, it is possible to vary the value of α from positive to negative. It was found that α decreases with the nitrogen content and is zero at 0.5% N₂. This added degree of freedom in controlling α allows the integrated circuit designer to compensate the thermal effects within a circuit by customizing the resistor parameters without significant layout modifications.     

基于红外双光路的薄膜在线测厚系统的研究

红外测厚是薄膜在线测厚的主要方法之一,为了解决传统的红外测厚方法中尚存在的易受光源稳定性的影响、不适用于高速薄膜生产线等缺点,采用双光路参比测量的方法设计了一种双光路红外测厚系统,系统将光源的光分成测量路和参考路两路,并使用单个CCD同时收集两路光作为光强传感器。描述了系统的成像原理,讨论了系统对朗伯定律的适用性,最后通过对聚乙烯和聚四氟乙烯薄膜的标定实验论证了系统的精度。结果表明,该方法精度高、鲁棒性好,且能够有效避免光源不稳定带来的影响。     

Roll angle measurement with a large range based on the photoelectronic autocollimator

In this paper, we propose a roll angle measurement method with a large range based on the photoelectronic autocollimator. According to the corresponding relationship between the rotation position of the measured shaft and the spot position on the circular trajectory, the roll angle is calculated quickly and conveniently using a simple algorithm. Only a mirror, a coupler and a fine shaft are contained in the measurement system besides the photoelectronic autocollimator. Aiming at the terrible measurement error induced by the axis wobbly error, two measurement schemes are proposed, which are linking the fine precision shaft to the measured shaft for reducing the axis wobbly error and using the segment measurement to enlarge the radius of the circular trajectory. The experimental results show that the measurement error is decreased by ±0.38°. The roll angle error of the mechanism is ±0.14°, and the measurement precision is about ±2′. The proposed method can be widely used in the engineering fields.     

Analysis of the stress and interfacial reactions in Pt/Ti/SiO2/Si for use with ferroelectric thin films

The microstructure of the Pt/Ti/SiO₂/Si structure has been investigated by scanning and transmission electron microscopy. Pt films of 100 nm thickness deposited by sputtering or evaporation onto unheated substrates gave complete coverage of the underlying Ti layer and showed a granular and faceted structure with grains ∼20 nm in diameter. They did not exhibit hillocks or surface TiO_x formation. X-ray diffraction was used to examine the film stress through use of the sin²ψ method with bulk values for the elastic constants (v=0.39, E=162 GPa). The as-deposited sputtered film had a compressive stress of ∼540 MPa, while the evaporated films had tensile stresses of ∼630 MPa. The films then received a 400°C rapid thermal anneal (RTA) for 90 s and a subsequent RTA of 650°C for 30s. Further investigation of the film stresses and microstructure were made after each annealing step. After the low temperature anneal, the film stress for the sputtered film became tensile. Plan-view sections examined by transmission electron microscopy (TEM) showed that the as-deposited sputtered films were dense but became porous after annealing. Initially, the evaporated films had a less dense microstructure, but were more stable with annealing. Little change in the stress for the evaporated film was observed after this initial low temperature annealing step. Additional annealing of the evaporated and sputtered samples caused complete consumption of the Ti layer including some TiO_x formation from the underlying SiO₂ layer and marked interaction with the Pt; however, little change in the stress was found. The surface of the Pt film revealed larger grains, but otherwise remained unaffected. The underlying phase changes were minimized once the Ti layer had reacted with the Pt. Due to the ratio of the layers, Pt:Ti of 2:1, the surface of the Pt was unaffected.     

The near-field thermal microwave radiation response of a biological object to the local change of the lateral temperature distribution

A layer-by-layer method is theoretically developed for reconstructing the temperature distribution inside a biological object from the measured outgoing thermal microwave radiation energy flux. The measurement is carried out along the plane parallel to the heated object surface in the surface’s near-field area. The equation of the inverse problem is obtained. The equation couples the 2D spatial Fourier-component of Poynting’s outgoing radiation vector with the similar Fourier-component of the lateral temperature distribution along elementary inner layers parallel to the object surface. The obtained equation is solved for the case of a 1D periodic or local depth-uniform lateral temperature distribution inside an object. The effective half-width of the spatial-harmonic spectrum for the outgoing thermal radiation energy flux is shown to be estimated by the double wave number inside the object. At the same time, the spatial half-width of a biological object’s thermal-radiation response to a local change in the lateral temperature distribution is estimated as a half of the wavelength inside the object. This result justifies the antenna size conventionally applied in biomedical research.     

Chlorine-doped CdS thin films from CdCl<Subscript>2</Subscript>-mixed CdS powder

The CdS:Cl thin films have been prepared using thermally evaporated, CdCl₂-mixed CdS powder at 200°C substrate temperature. The percentage of CdCl₂ in the mixture varied from 0% to 0.20%. The electrical properties and the grain size of the deposited films were investigated. The results show that light doping, resistivity, carrier concentration, and mobility follow Seto’s model for polycrystalline material. However, with heavy doping, these properties undergo a saturation trend. The saturation behavior can be understood in terms of the rapid formation of the A-center complexes in the films. The deposited films were annealed at 250°C and 300°C. The resistivity of pure and lightly doped CdS films increased with annealing temperature, whereas carrier concentration and mobility in these films decreased. However, for the higher doping concentrations, the resistivity decreased, whereas carrier concentration and mobility showed improvement. These changes in electrical properties of the deposited films with annealing and doping concentration are attributed to a reduction in the lattice defect sites in CdS upon annealing. The experimental results are interpreted in terms of a modified version of Seto’s model for polycrystalline materials.