Measurement of ion density in a plasma torch using a plane probe

The plasma density of the flame of a plasma torch has been determined from the current to a plane probe using two theories. One includes only the ion flow motion; the other includes only the ion thermal motion. Comparison with spectroscopic results suggests that both motions should be included.     

Precise nanofabrication with multiple ion beams for advanced circuit edit

Gallium focused ion beam (Ga-FIB) systems have been used historically in the semiconductor industry for circuit edit. Significant efforts have been invested to improve the performance of Ga-FIB. However, as the dimensions of integrated circuits continue to shrink, Ga-FIB induced processes are being driven to their physical limits. A helium ion beam offers high spatial resolution imaging as well as precise ion machining and sub-10 nm nanofabrication capabilities because the probe size can be brought to as small as 0.25 nm. However, it is limited by its relatively low material removal rate. Recently, the new Zeiss Orion-NanoFab microscope provides multiple ion beams (He, Ne and Ga as an option) into one platform and promotes the further studies of He and Ne induced deposition and etching processes to compare with a Ga ion beam. Because of the mass difference between He, Ne and Ga ions, the interactions of ions with sample surface and precursor molecules result in different sputtering rates, implantation and deposition yields. This presentation gives an overview of our current studies using this new platform to deposit or mill nanostructures for circuit edit.     

A nonstationary probe that is self-consistently negatively charged and embedded in plasma

The dynamics of ions in a plasma layer adjacent to the conducting surface of an electrically insulated negatively charged probe is studied. Exact self-consistent analytical solutions to the nonlinear system of equations of ion hydrodynamics are obtained. The solutions satisfy nonstationary boundary conditions on the probe’s surface. The intensity of the electric field and the velocity, concentration, and density of the ion current are found as functions of the initial position of a particle and the distance to the probe’s surface. The rate of change in the probe’s charge is determined and it is shown that, with time, the parameters of the system considered approach their asymptotical values. For a spherical probe, the time dependence of the ion-current density, i.e., the probe’s transient response (which is an analogue of the current—voltage characteristic of the Langmuir probe with a constant negative bias), is obtained.     

A nonstationary cylindrical probe with a self-consistent negative electric charge in ionospheric plasma

The dynamics of a layer of ionospheric plasma ions is investigated. The layer borders the conducting surface of an electrically insulated negatively charged cylindrical probe. Self-consistent solutions to a nonlinear system of magnetohydrodynamics equations for plasma are obtained. The solutions satisfy non-stationary absorbing boundary conditions imposed on the probe’s surface and are expressed in quadratures. The electric-field intensity and the velocity, concentration, and density of the ion current are found, and the rate of the variation of the probe’s charge is determined. It is shown that, in time, the solutions to this system approach their asymptotic values. The time dependence of the ion current flowing to the probe is obtained; i.e., the probe’s transient response corresponding to the volt-ampere characteristic of a Langmuir probe with a negative bias is found.     

Experimental observations of gated field emitter failures

Intrinsic failure events in gated field emitters have been studied. The gate-emitter voltage, typically 140 V during operation, drops to 10-70 V at the onset of the failure. Measurements with a diagnostic probe indicate that plumes of ions and electrons are ejected into vacuum with the ion current typically 10% of the electron current. The arc voltage and the ion-to-electron current ratio are characteristic of a cathodic vacuum arc. For series resistors less than 1 kΩ, the arc is continuous, whereas for series resistors greater than 10 kΩ, the arc is intermittent     

Ion transport in encapsulants used in microcircuit packaging

Most semiconductor devices are encapsulated in epoxy molding compounds. These molding compounds contain ionic contaminants including chloride ions from epichlorohydrin used in the epoxidation of the resin and bromine ions incorporated into the resin as a flame retardant. Chloride ions are known to break down the protective oxide on the surface of aluminum metallization and accelerate corrosion. The encapsulant material is hydrophilic and will absorb moisture from the environment. When the absorbed moisture is combined with ions, there is an opportunity for electrolytic corrosion to occur on the metal surfaces of the device and package elements. However, the rate of corrosion in an encapsulated microcircuit may be expected to depend upon the rate of ion transport through the encapsulant. This paper evaluates two techniques for the measurement of ion diffusion in epoxy molding compounds used for microelectronic encapsulation. The data suggests that ion diffusion rates vary with molding compound formulation, the solution pH and the ion concentration. SEM-EDX analysis and TOF-SIMS analysis indicate that the mode of diffusion of ions in the encapsulants is primarily through the polymer resin matrix as opposed to diffusion at the interface of the resin and the filler particles. Calculated diffusion coefficients were slower than the literature values for moisture diffusion or the diffusion of gases. In fact, under basic conditions, the ions tend to diffuse through the molding compound almost as a front suggesting that the ions bind to the encapsulant and that the diffusion of ions in molding compounds can be modeled using a Type II non-Fickian model.     

A langmuir probe investigation of electron cyclotron resonance argon-hydrogen plasmas

We report on the physical attributes of an argon-hydrogen plasma and the effects that induced changes in these attributes have on the physical and electrical characteristics of the plasma itself. Changes in the plasma conditions of these argon-hydrogen plasmas due to variations in microwave power, DC biasing, gas concentrations, and pressures were measured. We determined that increasing the hydrogen flow increases the sheath potential of the plasma, thereby increasing the arrival energy of ions at the surface of a sample placed in the plasma. Even with the decrease in plasma density from an increase in hydrogen input flow, we found the ion current is maintained in the predominately hydrogen plasma and is likely compensated by the high velocity and long mean free path of the hydrogen. We also observed that increasing total pressure also results in hydrogen ions dominating the total number of ions reaching the Langmuir probe and therefore the sample during processing. Last, a model based on the ion/electron energy ratio was developed and used to determine the relative ion concentrations of hydrogen and argon ions.     

Electrostatic probe in a flowing continuum plasma

The transient behaviour of the current to a cylindrical probe in a flowing seeded flame plasma, after a large negative voltage is switched on the probe, is measured experimentally. The steady-state current in the flowing system is calculated from the transient behaviour at short times.     

Optimum neutralization of negative space charge in cylindrical andspherical diodes

Elevation of the space-charge-limited electron current in cylindrical and spherical diodes, brought about by the introduction of neutralizing positive ions between the electrodes, is considered. The ion distribution is chosen to belong to the particular mathematical class that enables one of the three successive integrals of Poisson's equation to be performed analytically. For the external cathode configuration, it is found that there is no upper limit to the electron current provided there is sufficient ion generation and provided the power supply can give sufficient current. These results are applied, for the enhancement of current, to the electron-beam-pumped excimer laser in cylindrical symmetry and a suitable means of generating the required ion production is suggested. In the internal cathode configuration the limited electron current can be increased severalfold by the introduction of ions. However, an upper limit is reached when the electric field is reduced to zero at some point between the electrodes     

Langmuir-probe measurement of ionisation density on a plasma jet

The current to a negative probe in an argon plasma jet shows a strong dependence on probe bias and is up to an order of magnitude less than the usual convection/diffusion saturation current. The current is also in surprisingly good agreement with the calculated sheath/convection current. The results are attributed to electron?ion recombination in the vicinity of the probe.     

Laser diagnostics of flames, combustion products, and sprays

Recently, numerous laser-based diagnostic methods have been developed to probe sprays and combustion processes. These diagnostic probes encompass spontaneous Raman spectroscopy, coherent Raman spectroscopy, laser fluorescence and absorption for temperature and species concentration measurements; laser Doppler velocimetry for fluid flow measurements; and particle sizing and vapor concentration in sprays by numerous optical methods. Specific examples will be presented of species concentrations and temperatures in flames. These results have been compared to theoretical calculations for these properties and in many cases show excellent agreement between experiment and theory. Moreover, the spatial resolution offered by these laser techniques allows one to determine how a flame is changed by the presence of an adjacent cooled, metal wall. Two new Raman spectroscopic methods are also described for the direct spectroscopic measurements in a flame of atomic oxygen-an important radical in flame chemistry. Finally, a two-wavelength absorption/scattering measurment is described whereby vapor concentrations inside sprays may be measured. This technique has been applied to measuring the vapor concentration in an axisymmetric n-heptane fuel spray.     

Ion transfer processes in an insulating layer containing traps

Abstrect A theory of ion transfer processes in an insulating layer containing a uniform distribution of traps throughout its volume is formulated. It is shown that free ions localized near the surface are held in a potential well created by repulsion from trapped carriers. Accordingly, the activation energy of the free-ion current is higher than the mobility activation energy and decreases as the voltage is increased, while detrapping takes place with a time delay. The temperature dependence of the depolarization current has two or three peaks, whose positions and profiles change with the voltage. A distinctive feature of the transfer of ions through an insulator containing traps is the “memory” of the electric field driving the carriers toward the surface prior to the start of the transfer process. Fiz. Tekh. Poluprovodn. 31, 43–48 (January 1997)     

离子阱中碳原子簇离子的碰撞反应

用激光溅射法产生并在射频离子阱中囚禁了碳原子簇离子，进而利用离子阱的质量选择存储和离子存储时间长等特点，研究了经过选择存储的碳原子簇离子在离子阱中的碰撞解离和碰撞缔合。根据碰撞解离的结果以及碰撞前后的焓变，分析了团簇离子发生碰撞解离的条件和吸热范围，以及团簇离子的囚禁工作点与碰撞活化的关系。在此基础上，进一步研究了团簇离子碰撞解离后的各碎片之间发生缔合反应的过程，探讨了计算有效碰撞截面的方法。     

伸杆对星载电场探测仪的影响研究

通过一定长度的伸杆使电场探头与卫星本体保持一定的距离,可以减小卫星本体鞘层对电场测量的影响。但卫星在运行时伸杆与电场探头之间可能存在电位差,从而为电场测量引入误差。该文利用卫星与等离子体相互作用模拟软件(SPIS)并结合法国DEMETER卫星的伸杆和电场探头模型,模拟了伸杆与探头之间不同电位差对电场探头收集电子流的影响,模拟表明当伸杆电位低于探头电位时,对电场测量影响较小,当伸杆电位高于探头电位时,对电场测量影响较大,且电位差越大,影响越显著。当等离子体浓度增大即德拜长度减小时,伸杆电位形成的鞘层减小,因此伸杆对电场测量的影响比低浓度时有所减小。     

A novel ion imager for secondary ion mass spectrometry

An area detector for a secondary ion mass spectrometry (SIMS) ion microscope and its performance are described. The operational principle is based on detecting the change in potential of a floating photodiode caused by the ion-induced secondary-electron emission and the incoming ion itself. The experiments demonstrated that 10¹-10⁵ aluminum ions per pixel can be detected with good linear response. Moreover, relative ion sensitivities from hydrogen to lead were constant within a factor of 2. The performance of this area detector provides the potential for detection of kiloelectronvolt ion images with current ion microscopy     

Ion implantation in semiconductors—Part I: Range distribution theory and experiments

Ion implantation in semiconductors provides a doping technique with several potential advantages over more conventional doping methods. Among the most important of these are: 1) the ability to introduce into a variety of substrates precise amounts of nearly any impurity element desired; 2) the ability to control doping profiles in three dimensions by modulating the energy, current, and position of the ion beam; and 3) the possibility of avoiding certain undesirable effects that accompany the high-temperature diffusion process. Ion implantation can also be used in conjunction with other fabrication techniques to produce device structures that no one process can produce simply by itself. Current research in the field is directed toward several problems that must be solved before the full impact of ion implantation on semiconductor technology can be soundly predicted. In particular, it is necessary to be able to predict the distribution profiles of the implanted ions accurately, to know which crystalline sites the implanted ions occupy, to know the nature of the damage centers that are introduced by the implantation process, and to determine the extent to which these defects can he removed by appropriate annealing procedures. Theoretical and experimental work pertinent to the problem of predicting impurity distribution profiles in ion-implanted material are reviewed here. A review of current research on the other problems listed will be given in Part II, together with the characteristics of a number of interesting semiconductor devices that have already been fabricated by ion implantation.     

Formation of nanosize structures on a silicon substrate by method of focused ion beams

The results of experimental studies of modes in which nanosize structures are formed on a silicon substrate by method of focused ion beams are presented. Dependences of the diameter and depth of the nanosize structures on the ion beam current and time of exposure to the ion beam at a point are obtained. It is demonstrated that the main factor determining the rate of ion-beam milling is the ion beam current. The results of the study can be used in the development of technological processes for the fabrication of components for nanoelectronics and nanosystems engineering.     

Macroscopic ion traps at the silicon-oxide interface

The drift kinetics of the mobile charge in SiO₂ films, its capture on ion traps localized at the Si-SiO₂ interface, and ion emission from these traps are investigated by measuring the capacitance-voltage characteristics, the dynamic current-voltage characteristics, and the thermally stimulated depolarization current of the insulator. The current components (peaks) associated with the emission of particles trapped on the interface during thermofield treatment are isolated in an explicit form. The charge of the surface ions is shown to be neutralized mainly by Si electrons, and the field dependence of the ion emission currents is characterized by an anomalous Schottky effect associated with opening of the ion-trap potential by the external field. The relationship between these traps and the potential inhomogeneities, i.e., potential wells for mobile particles, on the interface under consideration is discussed. It is noted that the mobile ions in the insulator can be used for interface potential inhomogeneity diagnostics. Fiz. Tekh. Poluprovodn. 32, 1439–1444 (December 1998)     

朗谬尔探针法测量横流CO_2激光器的电子密度

本文讨论了探针在流动等离子体中的鞘层变化,在厚鞘层情况下,用朗谬尔探针测量了在不同偏压和主放电电流下的离子电流,并计算出不同放电电流下的电子密度,给出了电子密度的顺流分布。     

SPICE Models of Fluorine-Ion-Irradiated CMOS Devices

CMOS image sensors are attractive for space applications due to their low-power and system-on-chip features. The typical active pixel sensor (APS) is composed of a photodiode and several transistors. Using Fluorine +7 ions with an energy of 17 MeV, the effects of radiation are investigated on photodiodes and transistors manufactured using a standard 0.35-mum CMOS process. Simulation results show that the range of these ions overlaps with the active region of the device. Thus, the proximity effect of the ions on the performance of the device can be important. The tested photodiode showed a leakage current increase after it was irradiated with fluorine ions. The ideality factor of recombination current is observed to increase up to 4. Moreover, an increase in leakage current and absolute threshold voltage was observed in fluorine-ion-irradiated nMOS and pMOS transistors. In this paper, behavioral SPICE models are developed to analyze the contribution of these components to an overall increase in dark current of a CMOS APS.