David J. Coumou

Insertion, Deletion Codes With Feature-Based Embedding: A New Paradigm for Watermark Synchronization With Applications to Speech Watermarking

A framework is proposed for synchronization in feature-based data embedding systems that is tolerant of errors in estimated features. The method combines feature-based embedding with codes capable of simultaneous synchronization and error correction, thereby allowing recovery from both desynchronization caused by feature estimation discrepancies between the embedder and receiver; and alterations in estimated symbols arising from other channel perturbations. A speech watermark is presented that constitutes a realization of the framework for 1-D signals. The speech watermark employs pitch modification for data embedding and Davey and Mackays insertion, deletion, and substitution (IDS) codes for synchronization and error recovery. Experimental results demonstrate that the system indeed allows watermark data recovery, despite feature desynchronization. The performance of the speech watermark is optimized by estimating the channel parameters required for the IDS decoding at the receiver via the expectation-maximization algorithm. In addition, acceptable watermark power levels (i.e., the range of pitch modification that is perceptually tolerable) are determined from psychophysical tests. The proposed watermark demonstrates robustness to low-bit-rate speech coding channels (Global System for Mobile Communications at 13 kb/s and AMR at 5.1 kb/s), which have posed a serious challenge for prior speech watermarks. Thus, the watermark presented in this paper not only highlights the utility of the proposed framework but also represents a significant advance in speech watermarking. Issues in extending the proposed framework to 2-D and 3-D signals and different application scenarios are identified.

Watermark Synchronization: Perspectives and a New Paradigm

Synchronization is one of the most challenging elements of a watermarking system. In this paper, we survey and classify methods employed for watermark synchronization and highlight some inherent difficulties in synchronization that arise due to the nature of multimedia signals. We then propose a framework that addresses these hurdles in practical applications. Our framework utilizes feature-based embedding in concert with error correction codes capable of handling not only substitutions caused by various perturbations but also insertion and deletion events caused by erroneous feature estimates. We present a practical scheme for speech watermarking based on the framework. Experimental results show that the proposed methodology indeed enables synchronization in scenarios where a mismatch in estimated features between embedder and receiver would otherwise cause synchronization loss. We explore connections of the framework with recent theoretical analyses of watermark synchronization.

Ion Energy Distribution Skew Control Using Phase-Locked Harmonic RF Bias Drive

The energy distribution of ions accelerated through a radio frequency sheath and incident on a plasma-facing material significantly influences material interaction with the plasma and can impact manufacturing at the nanoscale. Ion energy distributions are controlled through appropriate mixing of drive frequencies, which has been shown to control distribution width. This paper presents a modification to multifrequency drive for ion energy control by exploiting a digital frequency and phase controller that enables modification of the higher order moments of the distribution, specifically, controlling the skew of the distribution. By modulating the sheath with two frequencies where one frequency is the harmonic of the other and controlling the relative phase of these two waveforms incident on the plasma-facing surface, skew control is achieved. A simple empirical model is presented to describe this method, as well as experimental validation of the model and demonstration of skew control in a parallel plate capacitively coupled reactor.

Control of ion energy distributions using phase shifting in multi-frequency capacitively coupled plasmas

Summary form only given. Anisotropic etching for microelectronics fabrication is accomplished by energetic ion bombardment in chemically enhanced sputtering. One challenge is being able to control the ion energy-angular distributions (IEADs) onto the surface of the wafer to selectively activate desired processes, which is advantageous for maintaining the critical dimension (CD) of features. Capacitive coupled plasmas (CCPs) powered by non-sinusoidal waveforms and or using multiple frequencies are strategies employed to provide flexible control of IEADs which produce high selectivity and uniformity. Varying relative voltages, powers and phases between multiple frequencies that differ by integer multiples have demonstrated potential control mechanisms for the IEADs and optimization of etching profiles. In this paper, we report on computational and experimental investigations of lEAD control in a dual-frequency CCP where the phase between the frequencies is used as a control variable. The rf frequency and its harmonic frequencies are both applied to the wafer substrate. Both symmetric and asymmetric CCPs are studied. The Hybrid Plasma Equipment Model (HPEM) was employed to predict plasma properties and obtain the harmonic contributions to the power applied to the same electrode. The ion and radical fluxes incident onto the surface are used as input to the Monte Carlo Feature Profile Module (MCFPM) with which profiles are predicted. The operating conditions are 5-100 mTorr in Ar and Ar/CF4/O2 gas under different frequency mixing and phase of integer multiple frequency drives. We find that by changing the phase between the applied rf frequency and its second harmonic, the Electrical Asymmetric Effects (EAE) is significant and can shift the dc self-bias.[I] When changing phases between the rf and its higher harmonics, the EAE becomes less effective and ion energy distributions spike at specific energies. Computed results for lEADs are compared with rf phase locked harmonic experimental results measured by Radio Frequency Ion Energy Analyzer.

Watermark Synchronization for Feature-Based Embedding: Application to Speech

We propose a novel framework for synchronization in feature-based data embedding systems. The framework is tolerant to de-synchronizing errors in feature estimates, which have hitherto crippled feature-based embedding methods. The method uses a concatenated coding system comprising of an outer q-ary LDPC code and an inner insertion-deletion code to recover from both de-synchronization caused by feature estimation discrepancies between the transmitter and receiver; and errors in estimated symbols arising from other channel perturbations. We illustrate the framework in a speech watermarking application employing pitch modification for data-embedding. We show that the method indeed allows recovery of watermark data even in the presence of de-synchronization errors in the underlying pitch-based embedding. The resilience of the method is also demonstrated over channels employing low bit rate speech encoders

Uniformity control with phase-locked RF source on a high density plasma system

Summary form only given. Semiconductor device manufacturing continues to achieve decreased feature sizes with a corresponding density increase along device area and volume. The consequence of manufacturing semiconductor devices with a higher level of integration remains a vexing challenge to achieving repeatable target yields, minimizing plasma induced damage, and optimizing process throughput all while gaining the technological advantage to reach the next high-performance node. We present control mechanisms to improve the fidelity of plasma density and the control of ion energies for a high-density plasma source. For a high-density plasma source, plasma generation is associated with the coupling of RF power to the plasma discharge through a coil antenna arrangement. The RF bias, coupled to a substrate, creates the ion energies utilized for material-etch processing associated with high-volume semiconductor manufacturing. Our fundamental technique is based on a frequency-and-phase locking controller. For the RF source, this frequency-and phase locking enables precise control of the electromagnetic field emissions from the antenna coil. By amplitude and relative phase manipulation of a dual-RF power supply scheme providing the excitation for the source coil arrangement, the constructive-deconstructive interaction of the coil fields enables the finest control of plasma density and uniformity along the wafer area. We further exploit the frequency-and-phase locking capability with the bias RF power delivery system to control the width and skew of the ion energy distribution function (IEDF). The coupling of these RF power delivery systems to a high-density plasma source formulates a systematic control of plasma parameters, ameliorating the state of thin-film manufacturing capability closer to the elusive atomic layer etch facility necessary to achieve future semiconductor nodes.

Coherent feedforward impedance correction and feedback power regulation in a plasma processing RF power delivery system

A breadth of advanced manufacturing technologies utilize plasma based material processing. A central system to plasma processing schemes is the RF power delivery and associated components. In a conventional RF power delivery system, the RF power supply performs power regulation for a desired power leveling quantity, and an impedance tuning network operates autonomously to match the dynamic and nonlinear plasma impedance to the transmission line impedance. We centralize these controllers to the RF power supply and remove systematic redundancy, coupling our feedforward controller with the conventional power feedback controller. With our RF power delivery control scheme, next generation plasma tool requirements for thin-film manufacturing is achievable with performance gains to commensurate with a lower system cost.

Feedforward power distortion correction in RF power delivery systems for plasma processing systems

Many critical technologies rely and will continue to rely on processes that utilize plasma based material processing. Plasma processing is a cornerstone technology for the semiconductor industry, and plays a critical role in the continued adherence of technology advances to the now famous Moores Law. Paramount to the continuum of plasma processing advances for thin-film manufacturing are reliable and repeatable RF power delivery systems used for RF plasma discharges. In conventional RF power delivery systems, the RF power supply performs local control to regulate power for the required power level. An impedance tuning network resides between the RF power supply and the RF discharge. In a manner analogous to the RF power supply, this impedance tuning network, with dual actuators for load and tune compensation, adjusts variable impedance devices (i.e. variable capacitors) with motor-controlled actuators to adapt the network for maximum power transfer from the RF source to the plasma discharge. When power transfer is not at a maximum, some portion of the power is reflected by the load back to the RF source. We consider this power loss a distortion that requires a correction to achieve an optimal power transfer condition. Our centralized control approach is economical and achieves the vexing performance objectives necessary for advancing thin-film manufacturing. In our scheme, power regulation is also conducted with autonomous feedback control in the power supply. An RF sensor in the power supply serves a dual purpose of (1) coupling feedback to the power controller, and (2) providing a quantitative power distortion measurement of the RF power delivery system. We centralize control and remove systematic redundancy with a feedforward controller, also in the RF power supply, to correct the power distortion by adjusting elements in the impedance tuning network. We demonstrate the primary instantiation of our feedforward controller with a frequency-agile RF power supply. By adjusting frequency, power distortion in the RF power delivery system is corrected. Our feedforward framework is a significant and substantial departure from the industry practice of using heuristic methods for impedance tuning to overcome RF power distortion. We demonstrate fast frequency tuning operation that is required by short-cycle thin-film processes and RF pulsing applications.

Leveraging small scale electron density oscillations in RF plasmas to simplify hairpin resonator probe measurements

Summary form only given. Hairpin resonator probes have several design criteria that must be met in order for them to be an effective plasma diagnostic; one of the most important criteria is that they have a very high quality factor, typically Q > 100 or better.1 This criteria is so that the measured resonance can be resolved despite the presence of other chamber resonances and is able to be resolved when loading effects from secondary resonators, electron collisions, and transmission line poles contribute to the electrical characteristics of the probe. Even at these high Q-factors extraction of the resonant frequency can be difficult, particularly for larger industrial systems. An analysis method for low pressure RF driven plasmas will be presented that can greatly simplify the extraction of resonant frequency data for a modestly high Q resonator. By leveraging the large δZ/δω of the high Q circuit compared to the lower δZ/δω characteristics of interfering influences such as transmission line effects and chamber loading, the small oscillations in resonance frequency generated by density oscillations on the RF time scale are used to more easily differentiate resonance probe characteristics from other masking electrical characteristics. Results will be presented for experiments conducted on a 300mm inductively coupled plasma reactor used for semiconductor processing. Both parametric study of electron density as a function of process parameters and comparison to other diagnostics such as ion flux probes and field measurements will be presented. Additionally, standard reflection and transmission measurement techniques will be compared side by side with the δZ/δω measurement technique outlined here to demonstrate the improvement in resonant frequency identificaton and extraction over a large process window.

Experimental results for uniformity and IEDF control with phase-locked RF source and bias on an inductively coupled plasma system

Summary form only given. A vexing challenge for inductively coupled plasma sources is the uniformity effect of gas flow, pressure regulation, and RF field emissions from the top coil antenna and its coupling with the electrode bias. These three entities can impair symmetrical flow and adversely impinge pattern etching across the wafer. We focus our effort on controlling the amplitude and phase relation of a dual coil driven antenna and thereby the EM field emission uniformity. Industry has long countered this challenge by affecting the electric field with a various approaches: (1) a permanent magnet assembly around the periphery of the substrate, (2) coil geometry arrangement, (3) RF source pulsing, (4) controlling the ratio of the coil currents, or (5) non-similar frequency assignments to the coils of the antenna structure. With EM field simulations, we previously showed by amplitude and relative phase manipulation of the RF excitation for the source coil arrangement, the controllability of the constructive-deconstructive interaction of the coil fields to positively affect plasma density and associated uniformity along the wafer area.1 We demonstrate this uniformity by measuring the ion flux along the bias diameter. We further explore the quantitative benefits of tailoring ion energy distribution functions with the phase interaction between the RF powered bias and the source RF power delivery system. The RF bias, coupled to the substrate, produces ion energies utilized for pattern-etch processing associated with high-volume semiconductor manufacturing. Our fundamental technique is based on a frequency-and-phase locking controller with plurality instantiations in the source RF power delivery system and the bias RF power supply. With precise control of the electromagnetic field emissions, our systematic control of plasma parameters yields enhancements toward uniformity improvement commensurate with IEDF generation, all necessary improvements for next generation plasma processing systems.