Study of basic mechanisms of semiconductor devices using ion beam induced charge (IBIC) collection

A change of wave form of current transients induced by a single heavy ion was investigated around a pn junction with 8 μm width and 10 μm length as a function of the ion incident position. Three pn junctions were made on a 3 μm thick Si epilayer (1 × 10¹⁶/cm³) grown on Si substrate and were in a line along an aluminum electrode with 10 μm spacing between the adjacent junctions. The elements of a pn junction array were irradiated with a 1 μm diameter 15 MeV C⁺ heavy ion microbeam spacing steps by 3 μm. At a bias voltage of − 10 V, 148, 91, and 54 fC were collected at the pn junction center, and at 3 μm and 4 μm from the edge of the electrode, respectively. Internal device structure was examined by IBIC (ion beam induced current) method by using a 2 MeV He⁺ ion microbeam. From the IBIC spectrum and the IBIC image, the charge collected from the open space by the diffusion process was observed in addition to the charge collected from the depletion layer of the pn junction.     

p-n结脉冲激光诱发电荷收集试验研究

测量了脉冲激光诱发半导体p-n结的瞬态脉冲电流,研究瞬态脉冲幅值和收集电荷与能量、偏压及入射位置的相关性。研究结果表明,瞬态脉冲信号幅值和收集到的总电荷随脉冲激光能量的增大而增多,与激光能量呈指数关系;收集电荷随偏压而增大;敏感区内的收集电荷数相差不大,远离敏感区的收集电荷明显减小。另外,将研究结果与重离子试验数据进行比对,两者有一定的相似性,但电荷收集脉冲幅值、脉冲波形有一定的差异。其结果为深入研究激光模拟单粒子效应技术奠定了基础。     

Submicron position-sensitive detector

A method has been developed to measure precisely the coordinates of charged particles incident between adjacent strips of a strip detector. The position sensitivity of an inter-strip gap has been studied by means of a pulsed laser beam and irradiation by -particles of a ²²⁶Ra-source. The capacitive division of charge generated by the incident particle depends on the position of its track. Its coordinates were determined by two-dimensional amplitude analysis of the charges collected by neighbouring strips. This method of coordinate determination applied to studies of spatial and energy distributions of electromagnetic as well as charged particle beams (including radioactive ion beams) of low intensity could provide the highest level of the precision limited by the track dimensions of charged particles, i.e. percents of a micrometer.     

Threshold LET for SEU induced by low energy ions [in CMOS memories]

Simulations to determine the threshold LET as a function of the length of the ion track are consistent with there being two regions of charge collection. In the top layer which contains the depletion region all the charge generated is collected in time to upset the device. In the next layer, 10% to 20% of the charge generated is collected and contributes to upsetting the device. This second layer of partial charge collection may significantly impact the accuracy of SEU predictions involving low-energy neutrons and protons. A simple method of including this contribution in calculations is proposed     

Medium-energy heavy-ion single-event-burnout imaging of powerMOSFETs

We present the first experimental determination of the SEB sensitive area in a power MOSFET irradiated with a high-LET heavy-ion microbeam. We used a spectroscopy technique to perform coincident measurements of the charge collected in both source and drain junctions together, with a nondestructive technique (current limitation). The resulting charge collection images are related to the physical structure of the individual cells. These experimental data reveal the complex 3-dimensional behavior of a real structure, which can not easily be simulated using available tools. As the drain voltage is increased, the onset of burnout is reached, characterized by a sudden change in the charge collection image. “Hot spots” are observed where the collected charge reaches its maximum value. Those spots, due to burnout triggering events, correspond to areas where the silicon is degraded through thermal effects along a single ion track. This direct observation of SEB sensitive areas as applications for, either device hardening, by modifying doping profiles or layout of the cells, or for code calibration and device simulation     

A time-dependent charge-collection efficiency for diffusion

The diffusion equation has some applications relevant to charge collection from ion tracks in silicon devices. Textbook solutions for the diffusion equation are available only for a few simple boundary geometries and special types of boundary conditions. A broader class of geometries was previously treated via a charge-collection efficiency function, but this applies only to total (integrated in time from zero to infinity) collected charge. The earlier work took advantage of the fact that Laplace's equation can be solved for a broad class of geometries. This paper extends the earlier work so that it applies to charge collected up to an arbitrary time. A time-dependent charge-collection efficiency function can be estimated for any geometry such that Laplace's equation has been solved. In particular, the analysis permits a comparison between diffusion calculations and a computer simulation of charge collection from an ion track. This comparison supports an earlier model in which charge collection, including a so-called “prompt” component, is driven by diffusion. The analysis applies to arbitrary track locations and directions. It also provides the option of treating a device geometry as two-dimensional in rectangular coordinates (if desired) while simultaneously treating the track as a line instead of a plane. Simulation codes having such flexibility regarding geometry are difficult to use, so the analysis makes the study of geometry effects accessible to a larger number of investigators     

The influence of spatial variations of diffusion length on charge collected by diffusion from ion tracks

Charge collected by diffusion from ion tracks in a semiconductor substrate may be influenced by the substrate diffusion length, which is related to recombination losses. A nonuniform spatial distribution of recombination centers results in a nonuniform diffusion length function. A theoretical analysis shows that, excluding some extreme cases, charge collection is insensitive to spatial variations in the diffusion length function, so it is possible to define an effective diffusion length having the property that collected charge can be approximated by assuming a uniform diffusion length equal to this effective value. Extreme cases that must be excluded are those in which a large number of recombination centers are confined to a narrow region near the substrate boundary.     

3D Position Information Extraction of Refilled Charge during Injection Process of Electron Storage Ring

The injection process of electron storage ring is a special transient process. The mismatch between the injector and the storage ring can be evaluated online by studying the 3D merging of refilled charge and stored charge. For the next-generation light source, it can lay a technical foundation for building a diagnostic system. The beam instrumentation group of the Shanghai Synchrotron Radiation Facility developed a 3D bunch-by-bunch diagnostic system based on button pick-up signal and high-speed acquisition boards to measure the beam transverse position and longitudinal phase. Extracting the 3D position information of the refilled charge during the injection process is the critical issue in this system. The charge-weighted average method was proposed to extract the transverse position and the proportional coefficient method was proposed to extract the longitudinal phase. The transverse betatron oscillation and longitudinal synchrotron oscillation of the refilled charge were analyzed. 3D position information of the refilled charge and several dynamic parameters of ring, such as longitudinal maximum oscillation amplitude, initial arrival time and synchrotron damping time, can be extracted during the user operation mode, which provides a strong toolkit for accelerator physics.     

电子储存环注入过程中补注电荷的三维位置信息提取

电子储存环的注入过程是特殊的瞬态过程，研究补注电荷和储存电荷的三维位置融合过程可在线评估注入器与储存环的匹配度，也可为下一代光源诊断系统的搭建奠定技术基础。目前，上海同步辐射光源束流检测组研发了一套基于纽扣电极拾取信号和高速采集板卡的三维逐束团诊断系统，可精确测量逐束团三维位置。注入过程中补注电荷的三维位置信息可通过电荷加权平均法和比例系数法分别提取。通过对补注电荷横向betatron振荡和纵向同步振荡的分析，可原位提取betatron振荡振幅、同步振荡振幅、初始到达时间、同步振荡阻尼时间等多个动态参数，不需提供特别的机器研究时间，为储存环动力学研究提供了有力工具。     

Computer investigation of ion beam optics for a Freeman type ion source system

The present work investigates the computer analysis of the ion beam properties produced by a Freeman type system. The extraction for such system is composed of four electrodes that permit to keep a fixed output energy by means of two accelerating gaps and one decelerating gap. The latter allows reducing the beam divergence angle. The combination of the acceleration/deceleration sections provides to keep a low beam emittance at the source outlet. The simulation of single charged argon ion trajectories for a plasma concave of curvature 4 mm was first studied with and without space charge effect using acceleration/deceleration extraction system with the aid of the SIMION computer program. The voltage applied to the accelerating electrode was optimized to accomplish the suitable ion trajectories without hitting the extraction electrode. Then, two additional studies were performed: the influence of the acceleration voltage and extraction voltage on the beam emittance and beam diameter; and the effect of the extraction gap width (distance between the plasma emission surface and the acceleration electrode) on the shape of the ion beam envelope and the position of the ion beam waist. Last, the influence of the space charge on the ion beam envelope was also investigated.     

利用加速器产生的中低能离子束进行离子原子碰撞研究

通过位置灵敏技术和飞行时间法,利用加速器产生的离子束研究中低能低电荷态Xq++B(X=C,O;q=1,2;B=Ne,Ar)的碰撞反应,分析研究了碰撞过程中的转移电离与单电子俘获。对于确定的电荷态,给出了转移电离与单电子俘获截面比值R随入射离子能量变化的规律与单电子电离随能量的变化规律之间的相互关系,同时通过实验数据分析、理论计算及模型对比给出R的峰位的近似表达式。     

Temporal and spatial study of differently charged ions emitted by ns-laser-produced tungsten plasmas using time-of-flight mass spectroscopy

Tungsten (W) is an important material in tokamak walls and divertors.The W ion charge state distribution and the dynamic behavior of ions play important roles in the investigation of plasma-wall interactions using laser-ablation-based diagnostics such as laser-induced breakdown spectroscopy and laser-induced ablation spectroscopy.In this work,we investigate the temporal and spatial evolutions of differently charged ions in a nanosecond-laser-produced W plasma in vacuum using time-of-flight mass spectroscopy.Ions with different charge states from 1 to 7 (W+ to W7+) are all observed.The temporal evolutions of the differently charged ions show that ions with higher charge states have higher velocities,indicating that space separation occurs between the differently charged ion groups.Spatially-resolved mass spectroscopy measurements further demonstrate the separation phenomenon.The temporal profile can be accurately fitted by a shifted Maxwell-Boltzmann distribution,and the velocities of the differently charged ions are also obtained from the fittings.It is found that the ion velocities increase continuously from the measured position of 0.75 cm to 2.25 cm away from the target surface,which indicates that the acceleration process lasts through the period of plasma expansion.The acceleration and space separation of the differently charged ions confirm that there is a dynamic plasma sheath in the laser-produced plasma,which provides essential information for the theoretical laser-ablation model with plasma formation and expansion.     

Guiding of argon ions through a tapered glass capillary

We report results from our recent experiments on guiding of Ar⁸⁺ ions through a single tapered glass capillary with an inlet diameter of 1 mm, an outlet diameter of 0.15 mm and a length of 45 mm. The profile width of the transmitted ion beam and the guiding power of the used glass capillary has been measured at a kinetic energy in the range of 8 keV up to 60 keV using a position sensitive detector. The charge up of the capillary and the evolution of the guiding effect is shown for a tilt angle of Ψ = 4°. The charge up of the inner walls of the tapered glass capillary causes a compression of the incident ion beam by a factor of 8. We found high guiding angles and small profile width of the transmitted ion beam in comparison to the transmission of highly charged ions through nanocapillaries in thin foils. A suppression of the transmission at small tilt angles and low kinetic energies has been observed.     

A fluorescent screen + CCD system for quality assurance of therapeutic scanned ion beams

A fluorescent screen + a charge coupled device (CCD) system were developed to verify the performance of scanned ion beams at the HIMAC. The fluorescent light from the screen is observed by the CCD camera. Two-dimensional fields, produced by the scanning process, i.e., the position and the size of the beam for each scan, represent of the important issues in scanning irradiation. In the developed system, the two-dimensional relative fluence and the flatness of the irradiation field were measured in a straightforward technique from the luminance distribution on the screen. The position and the size of the beams were obtained from centroid computation results of the brightness. By the good sensitivity and spatial resolution of the fluorescent screen + CCD system, the scanned ion beams were verified as the measurements at the HIMAC prototype scanning system.     

Ion irradiation effects on tungsten-oxide films and charge state effect on electronic erosion

We have studied electronic- and atomic-structure modifications of polycrystalline WO₃ films (bandgap of ∼3 eV) by ion irradiation. WO₃ films were prepared by oxidation of W films on MgO substrates and of W sheets. We find disordering or amorphization, the lattice expansion of ∼1.5% and bandgap increase of 0.2 eV after 90 MeV Ni ion irradiation at ∼3 × 10¹² cm⁻². A broad peak of optical absorption appears around 1.6 μm by ion irradiation. We also find that the erosion yield by high-energy ions with the equilibrium charge exceeds 10⁴ and that the erosion yield under ion impact with non-equilibrium charge (90 MeV Ni⁺¹⁰) is ∼1/5 of that with the equilibrium charge (89 MeV Ni⁺¹⁹). Effects of depth dependence of the ion mean charge on the erosion yields are discussed. The erosion yield by low-energy ions is also presented.     

Verification of three-dimensional charge transport simulations using ion microbeams

Optically targeted, ion microbeams provide a useful means of exposing individual structures within an integrated circuit to ionizing radiation. With this tool, calibrated, low damage, charge collection spectra can be measured from specific circuit structures without preceding ion damage to the structure or surrounding circuitry. This paper presents comparisons of calibrated, low damage, ion microbeam-based charge collection measurements and three-dimensional, charge transport simulations of charge collection for isolated n- and p-channel field effect transistors under conducting and non-conducting bias conditions.     

Equilibrium charge state distributions for boron and carbon ions emerging from carbon and aluminum targets

Equilibrium charge state distributions of boron and carbon ions through carbon and aluminum targets were measured with an energy range of 3-6 MeV. Comparisons of the data with relevant semi-empirical models for the equilibrium mean charge states and for the charge state distribution widths could provide valuable insight on the underlying mechanisms for a fast ion to lose or capture electrons. In-depth examinations of the experimental results in combination with semi-empirical models suggest that equilibrium charge state distributions are well represented by Gaussian distributions.     

Target dependence for low-Z ion charge state fractions

Equilibrium charge state fractions have been measured for 3-7 MeV lithium, boron and carbon ions passing through thin foils of copper, silver, and gold. The current results are combined with other low-Z ion data from the literature to give the relative influence of different target materials on charge exchange processes. The mean charge of the projectile, the functional form of the charge state distribution, and the charge state distribution width are parameters used to examine the effects of the electronic structure on charge exchange for various target-projectile combinations. Projectile shell structure is found to have a large influence on the widths of the charge state.     

igh statistics study of radiation damage on silicon microstripdetectors

This paper investigates the performance of silicon microstrip detectors after heavy irradiation. Full-size prototype sensors (53 × 64 mm²) designed for the CMS Tracker have been irradiated with protons and extensively studied in the laboratory and using a beam of minimum ionising particles operated at low temperature as foreseen for the Large Hadron Collider. We present results of large statistics measurements of collected charge, noise, position resolution, and hit finding efficiency for these irradiated detectors     

Determination of key parameters for SEU occurrence using 3-D fullcell SRAM simulations

A 3-D entire SRAM cell, based on a 0.35-μm current CMOS technology, is simulated in this work with a DEVICE simulator. The transient current, resulting from a heavy ion strike in the most sensitive region of the cell, is studied as a function of the LET value, the cell layout and the ion penetration depth. A definition of the critical charge is proposed and two new methods are presented to compute this basic amount of charge only using SPICE simulations. Numerical applications are performed with two different generations of submicron CMOS technologies, including the determination of the sensitive thicknesses