The field of plasma etching is reviewed. Plasma etching, a revolutionary extension of the technique of physical sputtering, was introduced to integrated circuit manufacturing as early as the mid 1960s and more widely in the early 1970s, in an effort to reduce liquid waste disposal in manufacturing and achieve selectivities that were difficult to obtain with wet chemistry. Quickly, the ability to anisotropically etch silicon, aluminum, and silicon dioxide in plasmas became the breakthrough that allowed the features in integrated circuits to continue to shrink over the next 40 years. Some of this early history is reviewed, and a discussion of the evolution in plasma reactor design is included. Some basic principles related to plasma etching such as evaporation rates and Langmuir–Hinshelwood adsorption are introduced. Etching mechanisms of selected materials, silicon, silicon dioxide, and low dielectric-constant materials are discussed in detail. A detailed treatment is presented of applications in current silicon integrated circuit fabrication. Finally, some predictions are offered for future needs and advances in plasma etching for silicon and nonsilicon-based devices.

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Plasma etching: Yesterday, today, and tomorrow

A zero-dimensional, semi-empirical model is used to describe the plasma chemistry in an argon plasma jet flowing into humid air, mimicking the experimental conditions of a setup from the Eindhoven University of Technology. The model provides species density profiles as a function of the position in the plasma jet device and effluent. A reaction chemistry set for an argon/humid air mixture is developed, which considers 84 different species and 1880 reactions. Additionally, we present a reduced chemistry set, useful for higher level computational models. Calculated species density profiles along the plasma jet are shown and the chemical pathways are explained in detail. It is demonstrated that chemically reactive H, N, O and OH radicals are formed in large quantities after the nozzle exit and H2, O2(1Δg), O3, H2O2, NO2, N2O, HNO2 and HNO3 are predominantly formed as ‘long living’ species. The simulations show that water clustering of positive ions is very important under these conditions. The influence of vibrational excitation on the calculated electron temperature is studied. Finally, the effect of varying gas temperature, flow speed, power density and air humidity on the chemistry is investigated.

https://iopscience.iop.org/article/10.1088/0022-3727/46/27/275201/pdf

Kinetic modelling for an atmospheric pressure argon plasma jet in humid air

Aims/hypothesis
Exercise enhances insulin-stimulated glucose transport in skeletal muscle through changes in signal transduction and gene expression. The aim of this study was to assess the impact of acute and short-term exercise training on whole-body insulin-mediated glucose disposal and signal transduction along the canonical insulin signalling cascade.

https://link.springer.com/content/pdf/10.1007%2Fs00125-006-0457-3.pdf

Exercise training increases insulin-stimulated glucose disposal and GLUT4 (SLC2A4) protein content in patients with type 2 diabetes.

In this review paper, we discuss the current status of the physics of charged particle swarms, mainly electrons, having plasma modelling in mind. The measurements of the swarm coefficients and the availability of the data are briefly discussed. We try to give a summary of the past ten years and cite the main reviews and databases, which store the majority of the earlier work. The need for reinitiating the swarm experiments and where and how those would be useful is pointed out. We also add some guidance on how to find information on ions and fast neutrals. Most space is devoted to interpretation of transport data, analysis of kinetic phenomena, and accuracy of calculation and proper use of transport data in plasma models. We have tried to show which aspects of kinetic theory developed for swarm physics and which segments of data would be important for further improvement of plasma models. Finally, several examples are given where actual models are mostly based on the physics of swarms and those include Townsend discharges, afterglows, breakdown and some atmospheric phenomena. Finally we stress that, while complex, some of the results from the kinetic theory of swarms and the related phenomenology must be used either to test the plasma models or even to bring in new physics or higher accuracy and reliability to the models. (Some figures in this article are in colour only in the electronic version)

https://iopscience.iop.org/article/10.1088/0022-3727/42/19/194002/pdf

Measurement and interpretation of swarm parameters and their application in plasma modelling

Since the discovery of leptin, the adipocyte and its products have been the subject of intensive research. Thus, it has been demonstrated that adipose tissue plays a central role in energy homeostasis, behaving as an endocrine organ that expresses molecules involved in regulation of metabolism; alterations in the expression or activity of those molecules have a fundamental role in pathologies such as obesity and insulin resistance. However, little is known about the role played by another tissue, skeletal muscle, which may have similar functions regarding metabolism control. Indeed, some molecules expressed in this tissue have recently been shown to modulate adipose metabolism. The present review considers the metabolic interrelationships and cross-talk of signals derived from both skeletal muscle and adipose tissue. It is suggested that cytokines derived from both tissues may have an important role in maintaining an adequate ratio of skeletal muscle to fat and thus may play an important role in the control of body weight. IL-15 (a cytokine highly-expressed in skeletal muscle), TNF-alpha, and leptin could play a decisive role in the suggested "conversation" between adipose tissue and skeletal muscle.

Cross-talk between skeletal muscle and adipose tissue: a link with obesity?

Increases in RC delay times in interconnect wiring for microelectronics as feature sizes decrease have motivated investigations into the use of low-dielectric constant insulators, and in particular, porous silicon-dioxide (PS). Profile evolution and maintenance of critical dimensions during plasma etching of PS are problematic due to the exposure of open pores. To investigate these issues, reaction mechanisms for fluorocarbon plasma etching of SiO2 in C2F6, CHF3, and C4F8 chemistries have been developed and incorporated into the Monte Carlo Feature Profile Model which was modified to address these two-phase systems. The reaction mechanism was validated by comparison to experiments by others for etching of PS and solid SiO2 (SS). We found that the etch rates for PS are generally higher than that of SS due to the inherently lower mass fraction. Mass corrected etch rates of PS can be larger or smaller than those for SS depending on the degree of pore filling by polymer and the degree of ion activated chemica...

Integrated feature scale modeling of plasma processing of porous and solid SiO2. I. Fluorocarbon etching

To achieve shorter RC-delay times in integrated circuits low-dielectric-constant (low-k) materials are being investigated for interconnect wiring. Porous silicon dioxide (PS) is one such material. To address scaling issues during fluorocarbon plasma etching of PS, a feature profile model has been integrated with a plasma equipment model. To focus on issues related to the morphology of porous materials, the PS was treated as stoichiometric SiO2. The model was validated by comparison to experiments for PS etching in CHF3 plasmas sustained in an inductively coupled reactor. We found that etch rates (ER) for PS are generally higher than for SiO2 due to the inherent smaller mass density, although ER do not necessarily scale linearly with pore size or porosity. Mass-corrected ER can be either larger or smaller than that of solid SiO2. For example, in polymerizing environments, at high porosities and large pore radii, there is a reduction in ER due to pore filling with polymer. Profile scaling parameters, such a...

Fluorocarbon plasma etching and profile evolution of porous low-dielectric-constant silica

C-C4F8-based plasmas are used for selective etching of high aspect ratio (HAR) trenches in SiO2 and other dielectrics for microelectronics fabrication. Additives such as Ar and O2 are often used to optimize the process. Understanding the fundamentals of these processes is critical to extending technologies developed for solid SiO2 to porous SiO2, as used in low-dielectric constant insulators. To investigate these issues, reaction mechanisms developed for etching of solid and porous SiO2 in fluorocarbon plasmas and for etching of organic polymers in O2 plasmas have been incorporated into a feature profile model capable of addressing two-phase porous materials. The reaction mechanism was validated by comparison to experiments for blanket etching of solid and porous SiO2 in Ar∕c-C4F8 and O2∕c-C4F8 plasmas using inductively coupled plasma reactors. We found that the blanket etch rates of both solid and porous SiO2 had maxima as a function of Ar and O2 addition to c-C4F8 at mole fractions corresponding to an o...

Etching of porous and solid SiO2 in Ar∕c-C4F8, O2∕c-C4F8 and Ar∕O2∕c-C4F8 plasmas

Electron temperatures in low-pressure (<10s mTorr) inductively coupled plasma (ICP) reactors operating at 10s MHz do not significantly vary during the radio frequency (rf) cycle. There can be, however, considerable modulation of electron-impact source functions having high-threshold energies due to modulation of the tail of the electron energy distributions (EEDs). In many instances, it is convenient to use cycle-averaged values for these quantities in models due to the computational burden of computing and storing spatial and time-dependent EEDs. In this paper an “on-the-fly” (OTF) Monte Carlo technique is described to address these time-dependent plasma parameters. The OTF method directly computes moments of the EEDs during advancement of the trajectories of the pseudoparticles, thereby reducing computational complexities. The method can also be used to directly calculate the harmonic components of excitation, which can subsequently be used to reconstruct the time-dependent source functions. The OTF tec...

/pdf/harmonic-content-of-electron-impact-source-functions-in-1gyhaa8h4c.pdf

Harmonic content of electron-impact source functions in inductively coupled plasmas using an “on-the-fly” Monte Carlo technique

The adoption of low dielectric constant materials as inter-level dielectrics in microelectronics fabrication will ultimately depend on process integration. Porous SiO2 (PS) is one candidate material. Cleaning of residual polymer from trenches following etching using fluorocarbon plasmas and the deposition of a continuous barrier layer are critical processes for integration of PS as inter-level dielectrics. To investigate these issues, reactions mechanisms for plasma stripping of fluorocarbon polymer using oxygen containing plasmas and deposition of metal barrier coatings into PS trenches were developed, and incorporated into a feature profile model. The reaction mechanism was validated by comparison to experiments for blanket plasma etching of polytetrafluoroethylene using Ar–O2 chemistries. Plasma stripping of fluorocarbon polymers from solid SiO2 (SS) trenches was found to be less efficient at higher aspect ratios. Stripping was also less efficient from PS trenches having large average pore radius and h...

Integrated feature scale modeling of plasma processing of porous and solid SiO2. II. Residual fluorocarbon polymer stripping and barrier layer deposition

Arvind Sankaran

Papers

Integrated feature scale modeling of plasma processing of porous and solid SiO2. I. Fluorocarbon etching

Fluorocarbon plasma etching and profile evolution of porous low-dielectric-constant silica

Etching of porous and solid SiO2 in Ar∕c-C4F8, O2∕c-C4F8 and Ar∕O2∕c-C4F8 plasmas

Harmonic content of electron-impact source functions in inductively coupled plasmas using an “on-the-fly” Monte Carlo technique

Integrated feature scale modeling of plasma processing of porous and solid SiO2. II. Residual fluorocarbon polymer stripping and barrier layer deposition