IEDF distortion and resolution considerations for RFEA operation at high voltages

Plasma-enhanced atomic layer deposition (PEALD) has obtained a prominent position in the synthesis of nanoscale films with precise growth control. Apart from the well-established contribution of highly reactive neutral radicals towards film growth in PEALD, the ions generated by the plasma can also play a significant role. In this work, we report on the measurements of ion energy and flux characteristics on grounded and biased substrates during plasma exposure to investigate their role in tailoring material properties. Insights from such measurements are essential toward understanding how a given PEALD process at different operating conditions can be influenced by energetic ions. Ion flux-energy distribution functions (IFEDFs) of reactive plasmas typically used for PEALD (O 2 , H 2 , N 2 ) were measured in a commercial 200 mm remote inductively coupled plasma ALD system equipped with RF substrate biasing. IFEDFs were obtained using a gridded retarding field energy analyzer and the effect of varying ICP power, pressure and bias conditions on the ion energy and flux characteristics of the three reactive plasmas were investigated. The properties of three material examples-TiO x , HfN x and SiN x -deposited using these plasmas were investigated on the basis of the energy and flux parameters derived from IFEDFs. Material properties were analyzed in terms of the total ion energy dose delivered to a growing film in every ALD cycle, which is a product of the mean ion energy, total ion flux and plasma exposure time. The properties responded differently to the ion energy dose depending on whether it was controlled with RF substrate biasing where ion energy was enhanced, or without any biasing where plasma exposure time was increased. This indicated that material properties were influenced by whether or not ion energies exceeded energy barriers related to physical atom displacement or activation of ion-induced chemical reactions during PEALD. Furthermore, once ion energies were enhanced beyond these threshold barriers with RF substrate biasing, material properties became a function of both the enhanced ion energy and the duration for which the ion energy was enhanced during plasma exposure. These results have led to a better insight into the relation between energetic ions and the ensuing material properties, e.g. by providing energy maps of material properties in terms of the ion energy dose during PEALD. It serves to demonstrate how the measurement and control of ion energy and flux characteristics during PEALD can provide a platform for synthesizing nanoscale films with the desired material properties.

Section: Methodsmentioning

confidence: 99%

Energetic ions during plasma-enhanced atomic layer deposition and their role in tailoring material properties

Faraz

Arts

Karwal

et al. 2019

“…The ion flux energy distribution function (IFEDF) was measured using a commercial tool (Semion Sensor, Impedance Inc.). It is noted that the IFEDF is often used mistakenly as the ion energy distribution function (IEDF) and the detailed description of the relation between the IFEDF and the IEDF can be found in [50,51]. For the plasma treatment using the ICP, the Cu films were deposited on a SiO 2 /Si substrate using conventional RF sputtering with a pure Cu target (99.99%) at a working pressure of 1×10 −3 Torr and a growth rate of 1 Å s −1 .…”

Section: Methodsmentioning

confidence: 99%

Surface structurization and control of CuS particle size by discharge mode of inductively coupled plasma and vapor-phase sulfurization

Choi

Kim

Shahzad

et al. 2018

Copper sulfide (CuS) nanoparticle films with different nanoparticle sizes were fabricated using an inductively coupled plasma (ICP) and a vapor-phase sulfurization method. First, the ICP is applied to a thin copper film to obtain a copper nanoparticle film, based on the plasma-surface interactions through the ion bombardment on the film. The fabrication of the Cu nanoparticles revealed that their size and spatial distribution depend on the discharge mode of the ICP and plasma irradiation time. From the measurements of the plasma density, optical emission spectrum, and ion flux energy distribution function, it was found that the inductive mode of the ICP, compared to the capacitive mode of the ICP, is efficient at fabricating the uniform nanoparticle film due to the optimal plasma potential and high ion flux with narrow ion energy distribution. The Cu nanoparticles are then transformed to CuS nanoparticles through vaporphase sulfurization. For the hydrophobicity application of the CuS nanoparticle film, the contact angles of the CuS nanoparticle films were measured and compared with those of other thin films, such as SiO 2 and bulk CuS. The contact angle of the CuS nanoparticle film, fabricated through the plasma-surface interactions and sulfurization, was significantly higher than that of other thin films owing to the hydrophobic surface of the CuS with the nanoparticle structure.

“…Validation of the virtual IED sensor is carried out via the rf-compensated Retarded Field Energy Analyzer (RFEA), placed at the rf-biased electrode [22,23,[31][32][33][34]. The IEDs, obtained by the virtual sensor, are compared with the results of the direct RFEA measurements.…”

Section: Diagnosticsmentioning

confidence: 99%

‘Virtual IED sensor’ for df rf CCP discharges

Bogdanova¹,

Lopaev²,

Рахимова³

et al. 2021

Ion-assisted surface processes are the basis of modern plasma processing. Ion energy distribution (IED) control is critical for precise material modification, especially in atomic-level technologies such as atomic layer etching. Since this control should be done in "real time", it requires "real-time" feedback using fast process sensors. In the general case of an industrial plasma reactor, when direct IED measurement is not possible, the IED can be estimated using the concept of a "virtual IED sensor". In this paper, a similar "virtual IED sensor" is considered using an asymmetric dual-frequency (df) rf CCP discharge as an example. It is based on a fast calculation method of the IED at an rf-biased electrode. This approach uses the experimentally measured sheath voltage waveform and plasma density (or ion flux) as input data, and also includes Monte-Carlo simulation of ion motion in the sheath to take into account the effect of ion-neutral collisions. To validate this approach, experiments were carried out using various plasma diagnostics in several gases: argon and xenon as examples of plasma with atomic ions and nitrogen as an example of plasma with molecular ions. It is shown that in all cases it is possible to obtain an adequate IED estimation, close to the experimental one, in a reasonably short time ( tens of seconds when using a modern PC). The results obtained demonstrate the possibility of using a virtual IED sensor in real plasma processing.So, on the one hand, modern plasma processing requires the development of new plasma approaches and systems to ensure an appropriate level of control. On the other hand, this control requires the development of fast sensors.The dual-frequency (df) rf ICP and CCP discharges are widely used today in plasma surface treatment. The simultaneous use of high-frequency and low-frequency rf voltages is aimed at realizing separate control of ion flux and energy. This idea was presented in the works of Goto in the early 1990s [1,2]. Since then, these discharges have been extensively studied both experimentally and theoretically [3,4]. However, one of the main results of these studies is that the two frequencies are generally coupled and the desired functional separate control can only be achieved over a limited range of discharge parameters (frequencies, pressures, and input powers).The multi-frequency discharge excitation was also investigated [5] to reveal the role of the third frequency in controlling the IED shape [6]. In order to better control the ion energy, some new methods of rf discharge excitation have recently been developed. One of them is the excitation of a symmetric rf CCP discharge with two frequencies (the fundamental frequency and its second harmonic) with a phase shift between them. In this configuration, the dc self-bias voltage appears due to the electrical asymmetry effect (EAE) [7]. This voltage is adjusted by the phase shift value between the two frequencies and is used for additional control of ion energy. This idea was further developed in the so-call...