Real-time Profile Control Research Articles

Integrated magnetic and kinetic control of advanced tokamak plasmas on DIII-D based on data-driven models

The first real-time profile control experiments integrating magnetic and kinetic variables were performed on DIII-D in view of regulating and extrapolating advanced tokamak scenarios to steady-state devices and burning plasma experiments. Device-specific, control-oriented models were obtained from experimental data using a generic two-time-scale method that was validated on JET, JT-60U and DIII-D under the framework of the International Tokamak Physics Activity for Integrated Operation Scenarios (Moreau et al 2011 Nucl. Fusion 51 063009). On DIII-D, these data-driven models were used to synthesize integrated magnetic and kinetic profile controllers. The neutral beam injection (NBI), electron cyclotron current drive (ECCD) systems and ohmic coil provided the heating and current drive (H&CD) sources. The first control actuator was the plasma surface loop voltage (i.e. the ohmic coil), and the available beamlines and gyrotrons were grouped to form five additional H&CD actuators: co-current on-axis NBI, co-current off-axis NBI, counter-current NBI, balanced NBI and total ECCD power from all gyrotrons (with off-axis current deposition). Successful closed-loop experiments showing the control of (a) the poloidal flux profile, Ψ(x), (b) the poloidal flux profile together with the normalized pressure parameter, βN, and (c) the inverse of the safety factor profile, , are described.

Application of Real-Time Cu Thickness Profile Control in Cu CMP

In this paper, a real-time profile control (RTPC) system in Cu CMP is introduced. The system mainly contains two parts: 1). Real-time metal thickness monitoring based on electromagnetic induction of eddy current in conductive metal layer; 2). Real-time new polishing pressure computing and adjusting for desired metal thickness profile. The RTPC system has been applied in bulk Cu removal step of Cu CMP. The result showed that the Cu thickness profile after bulk Cu removal was flatter and its WIW uniformity was improved by greater than 35% while WTW uniformity could be improved by greater than 65%.

CMP Process Control for Advanced CMOS Device Integration

New CMP steps are required to define the structures for new integration schemes for high-k metal gate and FinFET. The performance and yield of these new devices directly depend on CMP control of film thickness variation. As a consequence, CMP requirements are becoming increasingly stringent. This paper highlights the new process control technologies which enable efficient and cost-effective solutions for the new CMP steps, including FullVision® endpoint & in situ profile control (ISPC) for dielectric and poly CMP, and real-time profile control (RTPC) for aluminum, tungsten, and copper CMP.

Process development of high-k metal gate aluminum CMP at 28nm technology node

The replacement metal gate (RMG) height range and defectivity (fall on particle, Al residue, corrosion and micro-scratch) performance controls are very challenging for high-k metal gate (HKMG) RMG chemical mechanical polishing (CMP) processes. In this study, a robust aluminum metal CMP (Al-CMP) process development was investigated to meet the criteria of RMG at 28nm technology node. The Al metal gate height loss post-Al-CMP was found to increase with increasing the total area and pattern density of metal gates. Adding at least one extra ghost metal gate dummy structure on both sides of each metal gate and optimizing the metal gate dummy structure can effectively eliminate the metal gate height loss. Furthermore, implementing a real-time profile control (RTPC) end-point detecting system with lower down force polishing condition can further reduce the Al metal gate height loss and range levels. The defectivity issues of the microscratches and fall on particles can be fixed by using a soft pad with chemical wafer buff process on the final Al-CMP polishing step.

High K Metal Gate Aluminum CMP Challenges and Solutions

Because the gate height is critical to transistor performance, controlling gate height precisely and uniformly is the primary challenge for the replacement metal gate aluminum CMP process. A real-time profile control (RTPC) method was combined with a laser-based endpoint system to achieve within-wafer and wafer-to-wafer gate height uniformity requirements. To meet another challenge in Al CMP, defect performance was improved by 20X via consumables selection and process optimization.

Cu CMP Edge Uniformity Improvement Studies for 32 nm Technology Node and Beyond

AbstractStudies of the wafer edge uniformity step by step, from hard mask deposition, reactive ion etch, electroplating to post Cu CMP had been done using scanning electron microscopy (SEM) measurements, showed that the major wafer non-uniformity comes from the Cu CMP step. Improvement of Cu CMP edge uniformity had been achieved through engineering of platen 1 using real time profile control as well as CMP head zone pressure adjustment and platen 3 slurry optimizations

CMP for Copper TSV Applications

AbstractThrough-silicon via (TSV) 3-D packaging and integration present many new opportunities and challenges for metals CMP applications. For front-side TSV polishing, challenges include the removal of large amounts of copper overburden, dishing control during copper clearing steps, and removal of large amounts of barrier metal and dielectric layers while still maintaining control over topography and defectivity. Additionally, the choice of barrier material can have significant impact on polishing in terms of the mechanical reliability regarding adhesion between the barrier metal and underlying dielectric layers. This paper will address many of these challenges with an emphasis on innovative technologies for superior process and endpoint controls, such as real-time profile control for thick copper films up to 6μm or more in thickness and automatic endpoint controls for barrier removal and dielectric stopping. The paper will also discuss some salient challenges for back-side TSV polishing, including the handling and polishing of bonded wafer pairs and strategies to minimize handling and polishing damage to the potentially fragile thinned device wafer. Additionally, the development of slurries with highly tunable copper-to-dielectric selectivity will be critical for enabling a wide range of final topographies, depending on requirements for subsequent bonding steps.

Simulations of Reversed Shear Configuration in EAST

The reversed shear (RS) mode is one of the advanced configurationsbeing considered in EAST. Predictive simulations of EAST reversedshear configuration are carried out using an 1.5D equilibriumevolution code. In order to have the desired monotonic q-profileduring a tokamak discharge, a successful preparation phase isrequired. In our simulation, the plasma current is ramped up from100 kA to a flat-top maximum of 1.0 MA for four seconds. AnICRH power of 1 MW is applied until the plasma shape is formed atthe moment of 4 s, and then the power is raised to 3 MW. ALHCD power of 3.5 MW is applied from 1s to optimize the plasmacurrent density profile. A series of simulations are performed tostudy the influence of the time of applying the auxiliary heating onthe plasma parameters. Based on these simulations, a scheme isproposed and tested for the control of the safety factor profile,which is very useful in real time profile control in tokamakexperiments.

Advanced data handling for plasma profile control in JT-60

A real-time profile control system based on PCI-bus modules has been installed in the existing plasma control system (PCS) to control high performance plasmas. In profile control, pre-programmed profile reference data, which are two-dimensional, must be manipulated as the other mono-dimensional pre-programmed reference data such as plasma current in the discharge parameter set-up and in the post-discharge data archiving process, to re-use of the existing man–machine communication tools. An preprogram algorithm number was introduced to allow the change not only of control gains but also of control algorithm during a discharge, providing flexibility and extensibility to cope with future requirements coming from control studies that are now in progress. This system has been successfully applied to safety factor profile control by lower hybrid radio frequency heating system.

Predictive transport simulations of real-time profile control in JET advanced tokamak plasmas

Predictive, time-dependent transport simulations with a semi-empirical plasma model have been used in closed-loop simulations to control the q-profile and the strength and location of the internal transport barrier (ITB). Five transport equations (Te, Ti, q, ne, vΦ) are solved, and the power levels of lower hybrid current drive, NBI and ICRH are calculated in a feedback loop determined by the feedback controller matrix. The real-time control (RTC) technique and algorithms used in the transport simulations are identical to those implemented and used in JET experiments (Laborde L. et al 2005 Plasma Phys. Control. Fusion 47 155 and Moreau D. et al 2003 Nucl. Fusion 43 870). The closed-loop simulations with RTC demonstrate that varieties of q-profiles and pressure profiles in the ITB can be achieved and controlled simultaneously. The simulations also showed that with the same RTC technique as used in JET experiments, it is possible to sustain the q-profiles and pressure profiles close to their set-point profiles for longer than the current diffusion time. In addition, the importance of being able to handle the multiple time scales to control the location and strength of the ITB is pointed out. Several future improvements and perspectives of the RTC scheme are presented.

A model-based technique for integrated real-time profile control in the JET tokamak

This paper describes a new technique which has been implemented on the JET tokamak to investigate integrated real-time control of several plasma profiles simultaneously (such as current, temperature and pressure) and reports the results of the first experimental tests. The profiles are handled through their projection on a suitable basis of functions according to the Galerkin scheme. Their response to three actuators (heating and current drive powers injected in the plasma) is linearized in an experimentally deduced multi-input multi-output model. The singular value decomposition of this model operator allows us to design a distributed-parameter real-time controller which maximizes the steady state decoupling of the multiple feedback loops. It enables us to control several coupled profiles simultaneously, with some degree of fuzziness to let the plasma evolve towards an accessible non-linear state which is the closest to the requested one, despite a limited number of actuators.The first experiments using these techniques show that different current and electron temperature profiles can be obtained and sustained by the controller during a closed-loop operation time window. Future improvements and perspectives are briefly mentioned.

Integrated scenario in JET using real-time profile control

The recent development of real-time measurements and control tools in JET has enhanced the reliability and reproducibility of the relevant ITER scenarios. Diagnostics such as charge exchange, interfero-polarimetry, electron cyclotron emission have been upgraded for real-time measurements. In addition, real-time processes like magnetic equilibrium and q profile reconstruction have been developed and applied successfully in real-time q profile control experiments using model based control techniques. Plasma operation and control against magnetohydrodynamic instabilities are also benefiting from these new systems. The experience gained at JET in the field of real-time measurement and control experiments operation constitutes a very useful basis for the future operation of ITER scenarios.

JET progress towards an advanced mode of ITER operation with current profile control

The recent progress of the EFDA-JET facility in advanced tokamak (AT) scenario research is reviewed, emphasizing the relevance for the advanced mode of ITER operation. In particular, the key role played by the current density profile from the low-performance prelude phase, to trigger an internal transport barrier (ITB), to the high-performance steady state, to maintain the regime, is illustrated by the recent results obtained on JET with reversed magnetic shear targets. The mitigated ELMy edge behaviour, as well as the neoclassical nature of the particle transport in highly non-inductive ITB discharges, is also reported and discussed. Finally, the first demonstrations of real-time profile control of ITB discharges open the way towards high-performance steady-state AT discharges, provided that current density and pressure profiles are controlled.