Microwave ion source for ion implantation

Subject of Research. The paper presents the results of experimental study on the specific features of argon ion beam effect on a sapphire surface at small grazing angles. Mechanically ground and defective epipolished leucosapphire plates with 20 × 20 × 1.2 mm in size were used as experimental samples. The initial surface roughness of the polished samples was 0.250–1 μm and of the epipolished ones was 5–10 nm. Method. The ion beam deposition setup was used for research. It includes the ion source of CLAN-53M type with ion neutralizer. The ion source generates ion flux with energies in the range of 150–1500 eV, with an output ion current density up to 4 mA/cm2, with ion current from 10 to 80 mA. The studies were carried out at different technological parameters of ion-beam polishing: the ion energy and the angle between the sapphire surface and the ion beam axis α. Main Results. We have determined effects of sapphire surface morphology change both with preservation and change in the overall roughness level, and the effect of surface structuring during processing in two projections with the formation of flat peaks with a diameter of 2 μm. The experiment results have shown that the maximum efficiency (the highest value is a change in the arithmetic average surface roughness) during ion-beam polishing is observed at α equal to 15° and the ion beam energy of 400 eV. When α value changes from 25 to 30°, an oriented change of the surface morphology from the symmetrically ordered surface microrelief to an asymmetric one occurs. At the same time, the flat sides do not bleed much, and the effect of steep shadow smoothing of the local microrelief is observed with retention of the same general roughness level. After the sample surface processing with ion beam at the first stage of the experiment, it was re-processed at 90° angle relative to the previous treatment, which led to cross-spraying of the shadow sections and the design of gentle peaks with a diameter of about 2 μm (effect of the substrate surface structuring). Practical Relevance. After the ion-beam polishing of epipolished sapphire substrate samples, smoothing of the highest surface irregularities is observed, and the average arithmetic value of surface roughness has decreased from 5.7 nm to 0.9 nm for the polished sample.

With the development of Electron Cyclotron Resonance Ion Source (ECRIS), very high performance ECRIS nowadays have been set up one by one around the world, such as the GTS in Grenoble, SERSE in Catania, LECR3 in Lanzhou and etc, which can produce very intense Multiply Charged Ion (MCI) beam. But till now, the study of the extracted MCI beam from an ECRIS remains open. In this article, we present a theoretical and experimental study of the extracted MCI beam. In the theoretical part, the influences of the extraction system on the extracted ion beam quality are mainly analyzed. The aspects that have influences on the extracted ion beam quality have been analyzed. With the instruction of the analysis, the PBGUNS code is used to simulate the influences of some important aspects concerning the extraction system. The influences of the extraction system geometry design, magnetic field, and the space charge effect will be detailedly presented in this article. In the experimental part, with an Electric‐Sweep Scanner (ESS) emittance detection system, the influences on the extracted ion beam emittance of some typical parameters of ECRIS have been researched, such as the injected RF power, the RF frequency, the magnetic field and etc. The obtained results and the corresponding explanations are presented. Some of the results are well in accord with some empirical laws, but some other results seem to be disputed.

Production, acceleration and diagnostics of high intensity beams

A penning ionization gauge-type (PIG) ion source with one permanent magnet was designed and constructed for the installation of a MeV compact ion microbeam system. In the design of the ion source, the concept of the generation of high density small plasma confined by strong magnetic field in a small space was introduced to obtain a high brightness ion beam. As preliminary studies, the experiments of the separation of ion spices and ion beam brightness were performed on the generation of hydrogen ion beams. Our results show that diatomic hydrogen ion beams were mainly generated by the ion source. The ion beam brightness was experimentally evaluated to be 36.7 A/(m2srV), almost satisfying our goal.

The front end test stand (FETS) is a demonstrator for a future high intensity, high duty factor negative hydrogen (H') ion injector. With the radio-frequency quadrupole (RFQ) nearing installation, the ion source has been re-commissioned in preparation for long-term operation. The 3 MeV beam exceeds the radio-activation energy of common engineering materials, so radiation shielding has been erected. A new interlocking scheme has been signed-off which integrates the existing ion source high voltage area with the new shielding access points, to ensure that the machine can operate safely during beam production. The existing vacuum arrangement has been extended to in-clude the RFQ and medium energy beam transport (MEBT) line. A new programmable logic controller (PLC) has been built to operate the entire vacuum chain. The ion source high voltage equipment has been upgraded to minimise both spark rate and intensity. A collimating aperture and Faraday cup have been installed after the low energy beam transport (LEBT) section to ensure the beam is well aligned for injection into the RFQ. Re-commissioning the ion source has given a rugged shakedown of all these new systems before beam is required for the RFQ.

A new high current ion implanter "LUXiON" has been developed for semiconductor production. LUXiON implant several ion species to 300 mm silicon wafer by vertical long ion beam and horizontal mechanical scan wafer handling system. We describe the tool outline, beam result and implant results.

UltraCold Ion Beam Source. Focused ion beam (FIB) machines are largely used in the semiconductor industry mainly for imaging, milling and deposition of material, at the nanometer scale. To keep up with the trend of making smaller and smaller components, FIBs need to be continuously improved. A FIB is mainly made of an ion source and a focusing column. In this thesis, two concepts of ion sources are presented, modeled and discussed. The ultra-cold ion source (UCIS) is based on creating very cold ion beams (T <1 mK) by near-threshold photo-ionization of a laser-cooled and trapped atomic gas. In our experiment, 85Rb atoms are confined in a magneto optical trap built directly inside an accelerator structure. A spherical portion of the atom cloud is ionized with a 2-step ionization process and the bunched ions are accelerated by either a DC or a pulsed electric field. The liquid-metal ion source (LMIS) is the current state-of-art for focused ion beam technology, having a reduced brightness of 106 A/m2 sr eV. The reduced brightness characterizes the source and is proportional to the ion current and inversely proportional to the beam emittance (closely related with the source temperature). A high brightness is of importance as much as a low energy spread of the ion beam, since the latter is related with the focus ability of the beam. We have already shown that the UCIS can provide much lower energy spread (20 meV) than LMIS (˜ 4.5 eV), see Reijnders et al. (PRL, 2009), but not yet in combination with a high brightness as well. The energy spread is the limiting factor for the final achievable spot size in a FIB based on a LMIS. Chapter 3 and 4 present measurements of the source temperature and of the extracted current to complete the characterization of the UCIS. The ultra low temperature of the source permits collimated bunches to be created at low kinetic energy (down to few eV), which allows using time-dependent fields for accelerating and focusing. With this lens, a transversal ion temperature of (3±2) mK has been measured, as shown in chapter 3. This temperature is an upper limit since it is ten times higher than the expected value. The novel technique of focusing with time-dependent electric field is successfully applied to an ultra cold ion beam. In chapter 4, a dynamic model of the source describing its properties under pulsed operation has been developed and experiments validated it. A maximum average ion current of (13 ± 1) pA has been extracted from the UCIS and this is enough for imaging (1-100 pA are used). Those results correspond to a source reduced brightness of (8 ± 1) × 104 A/m2 sr eV with 0.9 eV energy spread. This result is 12.5 times lower than the brightness of a LMIS. An interesting pushing effect, due to the laser used to excite the atoms in the cloud, is described as well. Particle tracking simulations show that disorder induced heating has an important effect on the brightness, lowering its value by 1-2 orders of magnitude depending on the extracted current. Calculations and simulations of a different ion source, the atomic beam laser-cooled ion source (ABLIS), are presented in chapter 6. The follow-up project is based on a similar idea as an UCIS but aims for production of ion beams from a much higher initial atomic flux. The atoms originate from a Knudsen cell and, after being cooled and compressed transversally with laser cooling and trapping techniques, are photo-ionized and accelerated. The source size is reduced as well with respect to the UCIS. Realistic particle tracking simulations with 87Rb show that disorder induced heating is still very important, but in certain conditions, the so-called pencil-beam regime is reached and the disorder-induced heating does not deteriorate the brightness anymore. Depending on the extracted current, it is possible to reach a reduced brightness of 2 × 107 A/m2 sr eV with an ion current of 22 pA (corresponding to a final aperture diameter df = 1.6 µm) and an energy spread of 0.7 eV can be achieved. This source is likely capable of provide a high brightness and a low energy spread at the same time. The calculations are done assuming a purified 87Rb source. Eventually, it is possible to reach very high current (1 nA), making the ABLIS ideal also for milling applications with FIBs.

Epitaxial growth of β-SiC on Si (100) by low energy ion beam deposition

A new type of microwave ion source for a megaelectron volt ion implanter is designed to produce milliampere class multiply charged ion beams. This ion source has a single stage plasma chamber with both a mirror and an octopole magnetic field to produce milliampere class lower-charge-state ions efficiently. The extracted ion beam is mass separated, and a Kr2+ beam of 2.3 mA and an Ar2+ beam of 3.0 mA are obtained with absorbed microwave powers of 700 and 570 W, respectively. Combination of this new source with an ion accelerator should realize a milliampere class megaelectron volt ion implanter.

This thesis addresses the interaction of a supra-thermal ion beam with turbulence in the simple magnetized toroidal plasma of TORPEX. The first part of the thesis deals with the ohmic assisted discharges on TORPEX. The aim of these discharges is the investigation of the open to closed magnetic field line transition. The relevant magnetic diagnostics were developed. Ohmic assisted discharges with a maximum plasma current up to 1kA are routinely obtained. The equilibrium conditions on the vacuum magnetic field configuration were investigated. In the second part of the thesis, the design of the fast ion source and detector are discussed. The accelerating electric field needed for the fast ion source was optimized. The fast ion source was constructed and commissioned. To detect the fast ions a specially designed gridded energy analyzer was used. The electron energy distribution function was obtained to demonstrate the efficiency of the detector. The experiments with the fast ion beam were conducted in different plasma regions of TORPEX. In the third part of the thesis numerical simulations are used to interpret the measured fast ion beam behavior. It is shown that a simple single particle equation of motion explains the beam behavior in the experiments in the absence of plasma. To explain the fast ion beam experiments with the plasma a turbulent electric field must be used. The model that takes into account this turbulent electrical field qualitatively explains the shape of the fast ion current density profile in the different plasma regions of TORPEX. The vertically elongated fast ion current density profiles are explained by a spread in the fast ion velocity distribution. The theoretically predicted radial fast ion beam spreading due to the turbulent electric field was observed in the experiment.

Recent development of electron cyclotron resonance (ECR) ion sources in China is reviewed. Emphasis is put on high charge state ECR ion sources which have been mainly developed in China by Institute of Modern Physics (IMP). Presently two ECR ion sources built by IMP for highly charged ion beams are put into operation for cyclotrons and atomic physics research. The development of high charge state ECR ion sources at IMP has progressed with a new magnetic field configuration, better condition for extraction of highly charged ions, high mirror magnetic field, large plasma volume, and special techniques to provide extra cold electrons. These techniques greatly enhance the production of highly charged ions from IMP ECR ion sources. So far more than 185 eμA of Ar11+ and 50 eμA of Xe26+ were produced by the IMP ECR ion sources. The metallic ion beam production was tested and the first beam Ca11+40 was provided to the cyclotrons at IMP. The beam intensity of Ca11+40 could reach 130 eμA. The next part of this article will report the latest progress of 2.45 GHz ECR ion sources in China. A 2.45 GHz compact permanent magnet proton ion source was designed and constructed by IMP. A new microwave feeding system is applied on this ion source. The ion source is able to deliver 90 mA of mixed ion beam (H1++H2++H3+) after preliminary commissioning. The article also mentions a small 2.45 GHz ECR ion source which was built by Sichuan University and used for industry applications. The dependence of plasma density and electron temperature on radio frequency power, neutral gas pressure, and different microwave windows was measured by a Langmuir probe on this ion source.

The neutral beam heating system for the future international fusion experiment ITER will be based on radio-frequency driven ion sources delivering a large (≈1 × 2 m2) and homogeneous negative hydrogen or deuterium ion beam of several ten Amperes for several hundred seconds. The size scaling experiment ELISE (Extraction from a Large Ion Source Experiment) is an integral part of the R&amp;D road-map towards the ITER neutral beam heating system. Recently, 90% of the ITER target for the extracted current density was achieved in hydrogen for 600 s, increasing the pulse length over which such current densities can be achieved by a factor of more than ten. For ten second beam pulses the ITER target current density was achieved. These breakthrough results are made possible by using a steady-state capable high-voltage power supply together with an improved version of internal potential rods and a modified topology of the magnetic filter field.

Summary form only given, as follows. The most important developments in the field of ion sources at INFN-LNS, Catania, have been based on the generation of warm plasmas by means of microwaves at different frequencies. Indeed, we have built three different 2.45 GHz microwave discharge ion sources for different purposes, ranging from high efficiency ionization of light ions to high current proton beams production. A fourth multi-purpose compact 2.45 GHz microwave discharge sources, built with permanent magnets, is under construction. Different Electron Cyclotron Resonance Ion Sources (ECRIS) have been designed and built, at the operating frequency of 10, 14, 18 and 28 GHz as well as at intermediate frequency by means of a traveling wave tube microwave amplifier. The design of an innovative source to be operated at 28 GHz, named GyroSERSE, has been defined, with the aim to provide mA beams of highly charged heavy ions. The description of the different methods and tasks will be carried out, along with the preliminary results of the tests carried out with an hybrid ion source, consisting of a laser-generated plasma source coupled to the SERSE high performance ECRIS.

Simulation of the trajectories of negative hydrogen ion (H − ) beam in a 13 MeV PET cyclotron (DECY-13) w ere carried out by using the Runge-Kutta (RK4) approximation method and Scilab 5.4.1. The magnetic and electric fields were calculated using Opera - 3 d /T OSCA softwares at 1 mm resolution. The cyclotron is of a fourth-harmonics type, meaning that the acceleration occurs four times per cycle, with a radiofrequency (RF) field of 77.66 MHz frequency and 40 kV amplitude. The calculations and simulations show that the maximum distance between the ion source and the puller is about 6 mm, while the maximum width of the beam at 13 MeV is about 10 mm, and the initial phase between the RF field and the beam ranges from -10° to 10°, with a yield of about 10% of the beam from the ion source getting accelerated to 13 MeV. Received: 12 March 2015 ; Revised:30 June 2015; Accepted: 01 July 2015

The cathode-less microwave discharge ion engine generates plasmas in an ion source and a neutralizer in the method of the collision ionization by electron impact ionization, in which thermal electrons are energized by microwave electronic field without emanating from a cathode. The plasma generation mechanism on the microwave discharge ion source was modeled and formulated based on the global 0-dimensional Brophy’s models conserving particles and energy into the discharge and out of the plasma in the form of charged particles to the walls, beam and plasma radiation. In addition, the ion current of the wall loss in the ion source was measured in the laboratory so that the total amount of the ion production current and the ratio of the ion current contributing to the ion beam are determined.