蒙特卡罗模拟电子束光刻中30、50和100keV电子束入射在层结构样品中的能量耗散剖面

本文利用蒙特卡罗模拟给出了电子束光刻中 30、50、100 keV 电子束垂直入射到厚衬底硅上的薄膜(0.4m)电子抗蚀剂聚甲基丙烯酸甲酯聚合物(PMMA)中的能量耗散剖面,模拟了理想点源和高斯圆束点源电子束情况下的膜中的径向散射和能耗,包括来自衬底的背散射,计算的电子数为三万到五万个。     

An exposure model for electron-sensitive resists

We present a mathematical model for the exposure of electron-sensitive resists where an electron beam is incident normal to a substrate coated with a thin layer of resist. We include both the scattering of the incident electrons as they penetrate the resist and the electrons backscattered from within the resist and from the substrate. The calculations yield contours of equal absorbed energy density, and these are interpreted as the contours which bound the resist after development. The absorbed energy density is found as the sum, for all electrons, of the product of the energy absorbed per unit length of trajectory and the flux density of electrons at the point in question. We first calculate the absorbed energy density for an electron beam of vanishingly small cross section (an incident delta function) and then convolve that result with a beam of Gaussian current-density distribution to obtain the reSult for a single beam location. For poly(methyl methacrylate) resist, we study the achievable dot resolution, as a function of the incident charge, for various incident energies-and substrates. Since our main interest is in computer-controlled resist exposures in which patterns are generated as a succession of dots, we calculate the absorbed energy density contours for a line generated in that manner. Detailed comparison is made with the experimental results of Wolf et al., by fitting a single point on one contour at one beam energy to account for the unknown developer sensitivity. The resulting contours predict the undercutting effect experimentally observed for the 5-20-keV beam energies studied. The developed shape and linewidth are found to be nonlinear functions of the incident charge per unit length. Experimental data for the linewidth at 20 keV are presented and compared with theory.     

Hole trapping in E-beam irradiated SiO2 films

Low energy (25 kV) electron beam irradiation of MOS capacitors is shown to produce neutral hole traps in thin ‘radiation hardened’ SiO₂ films. These traps are found in an uncharged state after irradiation and are populated by passing a small hole current, generated by avalanche breakdown of then-type silicon substrate, through the oxide. From the time dependence of the observed trapping, a capture cross-section between 1 × 10∼⁻¹³ and 1 × 10⁻¹⁴ cm² is deduced. The trap density is found to depend on the annealing conditions and incident electron beam dosage. The density of traps increases with incident electron beam exposure. Once introduced into the oxide by the radiation the traps can be removed by thermal anneals at temperatures above 500° C. Parallels between electron and hole trapping on these neutral centers are strong evidence for an amphoteric uncharged trap generated by ionizing radiation.     

A controlled radiation source and electron/X-ray flux ratios in an electron beam metal evaporator

The use of ionizing radiation (X-rays, electrons and ions) in semiconductor processes is becoming more pervasive as device dimensions decrease. One such source of ionizing radiation is an electron beam (EB) metal evaporator. It has, in fact, been used earlier as a mixed X-ray/electron source to simulate ionizing radiation processes in device fab-rication sequences. In those studies, it was not known, however, what fraction of the energy striking a specimen was due to electrons, and what fraction was due to X-rays. In the present paper, application of an electron beam evaporator as a controlled, essen-tially monochromatic ionizing radiation source is described. Using a 0.5 mil thick Be foil, and knowing its mass absorption coefficient for X-rays at the wavelengths involved, the percentage electron and X-ray fluxes as a function of hearth beam current for a set of accelerating voltages was estimated. In addition, the absorption coefficient of an in-expensive, expendable, polymeric foil (pellicle) used in place of Be for actual experi-mental studies was evaluated. The 2.85 μm thick pellicle was found to transmit 87% of the incident Al K_α radiation, and to exhibit a mass absorption coefficient of 303 cm²/ g. The electron flux percentage from an aluminum hearth at a distance of 205 mm, was found to be 26% for a range of hearth electron beam currents between 2.5 x 10^-2A and 7.5 x 10^-2A, at an accelerating voltage of 6 kV. For a 10 kV accelerating voltage the electron percentage was found to be 35% between 2.5 x 10^-2A and 7.5 x 10^-2A. X-ray fractions were 74% and 65%, respectively. The radiation system can be used to pro-vide exposures in the 5 x 10⁴ rad(SiO₂) to the 2 x 10⁸ rad(SiO₂) range for Insulated Gate Field Effect transistors, in about an hour-long experiment.     

Electronic properties of diamond for high-power device applications

The generation and transport of impact-ionized electrons in diamond are investigated using secondary electron emission spectroscopy. By studying secondary electron emission from diamond surfaces having a negative electron affinity (NEA), the total transmitted intensity and the full energy spectrum of the internal electrons are revealed in the measurements. Electron yield and energy distribution measurements from C(100) and CVD diamond samples are analyzed as a function of incident beam energy and information is obtained on both the internal gain and electron energy distribution following impact ionization as well as the effects of the transport process on the internal electron distribution. High internal gain and efficient electron transport are inferred from an analysis of the very high yields measured from both samples. In fact, by fitting calculated yield curves to the measured yield data, we deduce a lower limit on the electron escape depth of 5 μm and 1.3 μm in the C(100) and CVD diamond samples, respectively. Energy spectra measured from the diamond samples contain an intense, low-energy peak whose energy position and width are independent of incident beam energy. Based on an analysis of the energy distribution data, a model of the impact-ionization process in diamond is presented.     

Influences of Uncaptured Electron on Energy Conversion of Photon Compton Scattering in High Power Laser-mplasma

Using the single particle theory and the non--flexibility collision model of electron and photon,the influence of the uncaptured electrons on the energy conversion efficiency of multi--photon nonlinear Compton scattering in the extra stationary laser--plasma is investigated. It shows that in extra stationary laser—plasma, the uncaptured electrons make the Ato of the scattering frequency of the multi--photon Compton fall down with the increases of the incident radiation electron speed, the materials of the incident collision of electron and photon, and the number of the photons which work with the electrons at the same time. Under the modulation of the uncaptured electrons to the laser field, the energy conversion efficiency between electrons and photons will fall down with the increase of the electron incident radiation speed, using the low--power electrons for incident source, the loss can be efficiently reduced.     

Well-width dependence of the phase coherent photorefractive effect in ZnSe quantum wells

We report on the well-width dependence of the phase coherent photorefractive (PCP) effect in ZnSe/ZnMgSe single quantum wells (QWs) using 90 fs light pulses. The experiments are performed in a four-wave-mixing configuration at temperatures between 25 and 65 K. The ZnMgSe/ZnSe QWs with 10, 5 and 3 nm well width were grown on GaAs substrate using molecular beam epitaxy. With decreasing QW thickness we observe a reduction of the PCP diffraction efficiency. This is attributed to the higher electron energy in small QWs due to the quantum size effect, which leads to a reduced equilibrium density of captured electrons in the QW. With increasing temperature the PCP signal further decreases which is attributed to thermal activation of the QW electrons back to the GaAs substrate.     

电离效应对EBCMOS中电子倍增层增益的影响研究

采用蒙特卡罗模拟方法研究了电子轰击互补金属氧化物半导体(EBCMOS)成像器件中高能电子轰击半导体时产生的电离效应对电荷收集效率和电子倍增层增益的影响。分析了入射电子能量、p型衬底层掺杂浓度、电子倍增层和钝化层厚度对电荷收集效率和增益的影响。结果表明,增加入射电子能量(小于4 keV)、减小电子倍增层和钝化层厚度、降低掺杂浓度等是提高电荷收集效率和电子倍增层增益的有利途径,可为获得高增益的EBCMOS器件提供理论支撑。     

Influences of Uncaptured Electron on Energy Conversion of Photon Compton Scattering in High Power Laser-plasma

Using the single particle theory and the non-flexibility collision model of electron and photon, the influence of the uncaptured electrons on the energy conversion efficiency of multi-photon nonlinear Compton scattering in the extra stationary laser-plasma is investigated. It shows that in extra stationary laser-plasma,the uncaptured electrons make the Δω of the scattering frequency of the multi-photon Compton fall down with the increases of the incident radiation electron speed,the materials of the incident collision of electron and photon, and the number of the photons which work with the electrons at the same time. Under the modulation of the uncaptured electrons to the laser field, the energy conversion efficiency between electrons and photons will fall down with the increase of the electron incident radiation speed, using the low-power electrons for incident source, the loss can be efficiently reduced.     

Resonant interaction of electrons with an rf electric field in asymmetric double-barrier structures

Analytical expressions for the electron wave functions, the low-signal, high-frequency conductance, and the widths of the energy levels (minibands) in a asymmetric double-barrier structure with thin barriers are obtained under conditions of coherent electron tunneling strictly along the centers of the energy levels and with the electron energies deviating from exact resonance. It is shown that an electron transmittance equal to 1 and a substantial increase in the integrated (taking into account the energy distribution of the electrons incident on the structure) rf conductance of the structure can be obtained by choosing the appropriate arrangement of the minibands of the structure relative to the conduction band bottom of the semiconductor materials to the left and right of the structure. Fiz. Tekh. Poluprovodn. 31, 1077–1082 (September 1997)     

电子束曝光中低能电子散射的模拟

介绍了Pendry弹性散射截面,描述了电子在固体中的散射过程,包括散射步长、散射角、方位角和散射点处能量的确定,并将Pendry截面和Monte Carlo计算方法应用到电子散射过程中。分别改变入射电子束能量、抗蚀剂厚度和衬底材料,模拟了能量不超过5keV的低能电子束在PMMA抗蚀剂中的散射轨迹。模拟结果表明,低能电子束曝光同样可应用于较高分辨率的表面成像技术工艺。通过对模拟结果和电子束曝光实验比较分析,可以进一步完善散射模型,为更深入开展电子束曝光技术的应用研究创造有利条件,同时也为开发低成本的低能电子束曝光系统提供了理论依据。     

The effect of crossed fields on the velocity distribution of hollow electron beams

An analysis of the effect of radial electric and longitudinal magnetic fields on the axial velocity distribution of electrons in a hollow beam was carried out on a simplified model. Two results, both consistent with experimental observations, were obtained. First, the longitudinal velocity spread (or equivalent temperature) increases with distance from the axis. Second, the retarding potential at which all electrons are collected also increases with distance from the axis; this indicates that the energy of the slowest electrons at the beam edge is decreased as a result of the crossed fields. The radial electric field, which is greatest near the beam edge and zero on the axis, converts some of the longitudinal energy of the electrons into rotational energy. This kind of scattering is analyzed by a perturbation method whereby the transverse motion of the incident beam is considered harmonically bound by the magnetic field. The spectrum of the energy absorbed in the rotational mode is shown to be velocity dependent and thus to give rise to distortion in the Maxwellian distribution of the incident beam.     

Efficient electron beam condensing for low-energy microcolumn lithography

Low-energy electron beam lithography has been performed with a microcolumn by adopting a new technique that condenses the electron beam efficiently. To increase the probe current while keeping the kinetic energy of electrons sufficiently low, the negative or positive bias has been applied to the accelerator electrode, which reduces the divergence of the electron beam and hence makes more electrons pass through the microcolumn. With this technique, the probe current more than 1 nA has been achieved, which is large enough for the practical application of microcolumn lithography even when the kinetic energy of electrons is as low as 160 eV. The results of microcolumn lithography by using the condensed electron beam with a low-energy of 160 and 327 eV are also presented.     

Chemical beam etching of InP in GSMBE

Etching of InP using a beam of PC1₃ is demonstrated in a standard gas source molecular beam epitaxy machine. The principle of an atomic layer accurate end-point detection technique usingin-situ reflection high energy electron diffrac-tion is described and used to study the kinetics of PCl₃ etching. The etch rate is found proportional to the PCI₃ fluence and weakly dependent on the substrate temperature. The morphology of etched surfaces and the etch rate uniformity is compatible with the regrowth of high quality InGaAsP active structures and with the realization of etch and regrowth sequences controlled at the nm scale. Etch profiles at mask edges are defined by nearly perfect crystallographic facets with a very limited mask undercut (≈100 nm) due to the beam nature of the etching technique.     

Monte Carlo方法模拟低能电子束曝光电子散射轨迹

建立了一个适用于描述低能电子散射的物理模型 ,利用 Monte Carlo方法对低能电子在多元多层介质中的散射过程进行模拟 .低能电子弹性散射采用较严格的 Mott截面描述 ,为了节约机时 ,利用查表与线性插值方法获得 Mott截面值 ;低能电子非弹性散射能量损失采用 Joy修正的 Bethe公式计算 ,并对其加以改进 ,引入多元介质平均电离电位、平均原子序数、平均原子量概念 ,利用线性插值方法给出光刻胶 PMMA对应的 k值 .对电子穿越多层介质提出一种新的边界处理方法 .在此基础上运用 Monte Carlo方法模拟高斯分布低能电子束在 PMMA-衬底中的复杂散射过程 .     

Characteristics of negative electron beam resists, ma-N2410 and ma-N2405

We have characterized the electron beam lithography (EBL) properties of the new negative tone resists, ma-N2410 and ma-N2405. These negative resists reacts under low electron dose values from 10 to 140 μC/cm², tested using 10, 20, 28 keV electron beam. There was negligible loss of pattern height, which was attributed to the combined dose of the incident electron beam and the backscattered electrons. Experimental tests were performed under various EBL writing conditions of dose value, developing time, line-width and resist thickness. Our investigation showed that these new commercially available resists have high resolution and high contrast with non-chemical amplification, useful for micro-fabrication application.     

Deposition Characteristics of AlN Thin Film Prepared by the Dual Ion Beam Sputtering System

In this experiment, a radio frequency dual ion beam sputtering (DIBS) system was used to prepare aluminum nitride (AlN) films with a bottom Al electrode on a Si (100) substrate. After systematic testing of the processing variables, a high-quality film with preferred c-axis orientation was grown successfully on the Si (100) substrate with an Al target under 700 eV energy flux, N₂/(N₂ + Ar) ratio of 55%, and 4 × 10⁻⁴ torr in vacuum. The characteristics of the deposited AlN thin films were studied by x-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), secondary ion mass spectrometry (SIMS), and electronic spectroscopy for chemical analysis (ESCA). The surface roughness was also measured. It was found that AlN films prepared by DIBS at room temperature are better than those prepared at 300°C, and those prepared with an Al target are better than those prepared with an AlN target. The inferiority of AlN films prepared with AlN targets is due to the AlN bond being broken down by the ion beam source.     

Theoretical study of electron wave diffraction caused by transversepotential grating-effect of incident angle

The electron wave diffraction caused by a transversally periodic structure is analyzed when the electron is incident upon the grating at an angle. Using these results, diffraction characteristics of electrons equilibrating at a finite temperature are derived. The dependence of the diffraction efficiency on the electron energy at 4 K shows the same sharp trend as at 0 K. Although the sharpness of the dependence is reduced somewhat, the switching characteristics of the diffraction are still preserved at 77 K. The diffraction of the electron beam of a finite width is also studied     

Characteristics of surface states at the insulator-semiconductor interface in the thin-film electroluminescent structures based on ZnS:Mn

Distributions of the density of occupied surface electron states at the cathode interface between the insulator and phosphor in thin-film electroluminescent emitters are simulated in relation to the energy on the basis of experimental data. The dependences of the above distributions on the conditions of excitation of emitters are obtained. It is shown that these distributions shift to deeper levels of surface states as the frequency of excitation voltage is decreased and the pause between two neighboring switched-on states of emitters is increased, which corresponds to the cascade mechanism of relaxation of electrons captured by surface states. The coefficient of cascade capture of electrons prior to relaxation ((4−5) × 10⁻¹² cm²/s), instantaneous lifetime of electrons prior to relaxation (0.2–0.25 s), cross section for capture of electrons to deeper levels of surface states (in excess or on the order of (6.7−8.3) × 10⁻²¹ cm²), largest values of the densities of occupied surface states at the cathode boundary from which electron tunnel (∼2.5 × 10¹³ cm⁻²), and energy density of above-specified surface states (7 × 1014 cm⁻² eV⁻¹) have been determined. The values of the quasi-equilibrium Fermi level at the surface in the course of the activity of electroluminescent emitters varies in the range from 0.9 to 1.35 eV, depending on conditions of excitation.     

The growth of GaAs,AIGaAs, InP and InGaAs by chemical beam epitaxy using group III and V alkyls

The growth kinetics of chemical beam epitaxy (CBE) were investigated with the growth of GaAs, AIGaAs, InP, and InGaAs. Results obtained with epilayers grown by using trimethylarsine (TMAs) and triethylphosphine (TEP) instead of arsine (AsH3) and phosphine (PH₃) were reviewed with some additional results. The CBE grown epilayers have similar optical quality to those grown by molecular beam epitaxy (MBE). Superlattices of GaAs/AlGaAs with abrupt interfaces have been prepared. Since trimethylindium (TMIn) and triethylgallium (TEGa) used in the growth of InGaAs emerged as a single mixed beam, spatial composition uniformity was automatically achieved without the need of substrate rotation in the InGaAs epilayers grown. Lattice-mismatch Δα/α< 1 x 10^-3 have been reproducibly obtained. For epilayers grown with high purity TMAs source, room-temperature electron mobility as high as 9000 cm²/V sec and concentrations of ˜7 x 10¹⁵ cm^-3 were produced. In general, the electron mobilities were as good as those obtained from low-pressure metalorganic chemical vapor deposition. (MO-CVD). Unlike MBE, since the In and Ga were derived by the pyrolysis of TMIn and TEGa molecules at the heated substrate surface, respectively, oval defects observed in MBE grown epilayers due to Ga splitting from Ga melt were not present in CBE grown epilayers. This is important for integrated circuit applications. Unlike MO-CVD, the beam nature of CBE allows for selective area growth of epilayers with well-defined smooth edges using mask shadowing techniques. Typically, growth rates of 2-5μm/h for InP, 2-6μm/h for GaAs and AIGaAs, and 2-5μm/h for InGaAs were used.