S. M. Zyryanov

The mechanism of low-k SiOCH film modification by oxygen atoms

The interaction of oxygen atoms with three types of plasma enhanced chemical vapor deposition low-k SiOCH films is studied. The samples were treated by O atoms in the far plasma afterglow conditions in a special experimental system designed for this study. The experimental system allowed avoiding the effect of ions and vacuum ultraviolet (VUV) photons on surface reactions and controlling the oxygen atom concentration over the samples. Fourier-transform infrared spectroscopy, x-ray fluorescence, and atomic force microscopy techniques were used to analyze the changes occurring in low-k films. Monte Carlo model for O atom interaction with low-k material that includes penetration, recombination, and reactions with methyl groups was developed. It is shown that the surface recombination on the pore wall surface determines the profile and penetration depth of O atoms into the films. The reaction of O atoms with methyl groups has lower probability and therefore proceeds in the background mode.

Modification of organosilicate glasses low-k films under extreme and vacuum ultraviolet radiation

Degradation of chemical composition of porous low-k films under extreme and various vacuum ultraviolet emissions is studied using specially developed sources. It is shown that the most significant damage is induced by Xe line emission (147 nm) in comparison with Ar (106 nm), He (58 nm), and Sn (13.5 nm) emissions. No direct damage was detected for 193 nm emission. Photoabsorption cross-sections and photodissociation quantum yields were derived for four films under study. 147 nm photons penetrate deeply into low-k films due to smaller photoabsorption cross-section and still have sufficient energy to excite Si-O-Si matrix and break Si-CH3 bonds.

Recombination of O and H Atoms on the Surface of Nanoporous Dielectrics

The interaction of O and H atoms with SiOCH nanoporous low-dielectric-constant (low-k) films is studied in the far plasma afterglow in the absence of ion and photon fluxes on the surface. The loss probabilities of O and H atoms are directly measured by plasma-induced actinometry. Modification of low-k films during the experimental scans was studied by the Fourier transform infrared spectroscopy technique. The model of O- and H-atom recombination in nanoporous materials was developed to analyze the experimental data. It is shown that the main mechanism of the O and H loss is their surface recombination. The consumption of these atoms in the reactions with the carbon-containing hydrophobic groups has a minimal contribution. Thus, the surface recombination defines a damage depth in low-k films. It was shown that the oxygen atoms lead to the noticeable removal of CH3 groups. On the contrary, hydrogen atoms do not break Si-CH3 bonds, allowing the avoidance of plasma damage in the case of the hydrogen-plasma-based resist strip in appropriate conditions.

Surface recombination of oxygen atoms in O 2 plasma at increased pressure: I. The recombination probability and phenomenological model of surface processes

This work deals with the study of oxygen atom loss on a quartz surface in a glow discharge plasma in pure O2 at increased pressures (5?50?Torr). O atom loss probabilities are obtained from the radial distributions of oxygen dissociation degree measured by the actinometry method. It is shown that the applicability of the actinometry method at high pressures requires the knowledge of the spatial distribution of a reduced electric field for the correct calculation of the electronic excitation rates of oxygen and actinometer atoms. The analysis of the obtained data within the framework of a simple phenomenological model of the surface processes revealed that O atom surface recombination with physisorbed oxygen atoms and molecules (producing O2 and O3, respectively) is the main loss channel for oxygen atoms in O2 plasmas at increased pressures. The oxygen atom loss probability can noticeably grow in comparison with the case of low pressure due to the essential increase in the surface occupation degree by physisorbed atoms and molecules.

Surface recombination of oxygen atoms in O 2 plasma at increased pressure: II. Vibrational temperature and surface production of ozone

Ozone production in an oxygen glow discharge in a quartz tube was studied in the pressure range of 10?50?Torr. The O3 density distribution along the tube diameter was measured by UV absorption spectroscopy, and ozone vibrational temperature TV was found comparing the calculated ab initio absorption spectra with the experimental ones. It has been shown that the O3 production mainly occurs on a tube surface whereas ozone is lost in the tube centre where in contrast the electron and oxygen atom densities are maximal. Two models were used to analyse the obtained results. The first one is a kinetic 1D model for the processes occurring near the tube walls with the participation of the main particles: O(3P), O2, O2(1?g) and O3 molecules in different vibrational states. The agreement of O3 and O(3P) density profiles and TV calculated in the model with observed ones was reached by varying the single model parameter?ozone production probability on the quartz tube surface on the assumption that O3 production occurs mainly in the surface recombination of physisorbed O(3P) and O2. The phenomenological model of the surface processes with the participation of oxygen atoms and molecules including singlet oxygen molecules was also considered to analyse data obtained in the kinetic model. A good agreement between the experimental data and the data of both models?the kinetic 1D model and the phenomenological surface model?was obtained in the full range of the studied conditions that allowed consideration of the ozone surface production mechanism in more detail. The important role of singlet oxygen in ozone surface production was shown. The O3 surface production rate directly depends on the density of physisorbed oxygen atoms and molecules and can be high with increasing pressure and energy inputted into plasma while simultaneously keeping the surface temperature low enough. Using the special discharge cell design, such an approach opens up the possibility to develop compact ozonizers having high ozone yield at the low energy cost of O ? O3 conversion.

Removal of amorphous C and Sn on Mo:Si multilayer mirror surface in Hydrogen plasma and afterglow

Removal of amorphous carbon and tin films from a Mo:Si multilayer mirror surface in a hydrogen plasma and its afterglow is investigated. In the afterglow, the mechanism of Sn and C films removal is solely driven by hydrogen atoms (radicals). Probabilities of Sn and C atoms removal by H atoms were measured. It was shown that the radical mechanism is also dominant for Sn atoms removal in the hydrogen plasma because of the low ion energy and flux. Unlike for Sn, the removal mechanism for C atoms in the plasma is ion-stimulated and provides a much higher removal rate.

Experimental and theoretical study of dynamic effects in low-frequency capacitively coupled discharges,

A low-frequency capacitively coupled radio-frequency (rf) discharge in Ar excited at 1.76 MHz is studied both experimentally and theoretically. Experimental measurements of electron concentration, discharge voltage and current are presented for a wide range of rf input powers. The rf current shape is nonsinusoidal, close to the triangle one. The evolution of Ar(2p1) emission excitation function in the interelectrode gap during an rf cycle is measured using the phase-resolved optical emission spectroscopy technique. Theoretical study is based on the particle-in-cell Monte Carlo collision numerical simulation. Specific dynamic features of the low-frequency discharge are discussed. The important role of secondary electrons in discharge maintenance and power balance is shown. This study is crucial for understanding dual-frequency discharges with a corresponding value of low frequency.

Interaction of F atoms with SiOCH ultra low-k films. Part II: etching

The etch mechanism of porous SiOCH-based low-k films by F atoms is studied. Five types of ultra-low-k (ULK) SiOCH films with k-values from 1.8 to 2.5 are exposed to F atoms in the far downstream of an SF6 inductively coupled plasma discharge. The evolution of etching with an F dose was studied using various techniques of surface and material analysis such as FTIR, XPS, EDS and SE. It is revealed that the etch mechanism is connected with surface fluorination and formation of –CHxFy species on the surface due to H abstraction by F atoms from –CH3 groups. It is shown that the etching includes two phases. The first one is observed at the low F doses and is connected with chemical modification and etching of walls in the topmost pores, which finishes when the walls are fully etched. At the same time, the additional etching in the underlying pores due to F penetration forms the etch depth profile, after that the second etching phase starts. This phase is characterized by the higher etch rate due to the propagation of the etch depth profile further into the film. The preliminary treatment of pore walls inside porous channels effectively accelerates etching many times compared to non-porous material. The acceleration depends on the modification depth, which in turn is a function of pore structure and interconnectivity as well as the F atom reaction mechanism. The combined random walk (Monte-Carlo) & kinetics model developed to describe F penetration inside SiOCH films together with reactions of F atoms leading to –CHxFy depletion and opening SiOx bonds for F access allowed relating the increased etch rates with increasing the total number of F atom collisions inside interconnected pores. The etch mechanism of SiOCH films is found in many respects to be similar to the SiO2 etch mechanism on the elementary level, but as whole it is ruled by the SiOCH structure: porosity degree, pore size, pore interconnectivity as well as structural features of SiOx bonds.

Multi-step reactions mechanism for F atoms interactions with organosilicate glass and SiOx films

An ab initio approach with the density functional theory (DFT) method was used to study F atom interactions with organosilicate glass (OSG)-based low-k dielectric films. Because of the complexity and significant modifications of the OSG surface structure during the interaction with radicals and etching, a variety of reactions between the surface groups and thermal F atoms can happen. For OSG film etching and damage, we propose a multi-step mechanism based on DFT static and dynamic simulations, which is consistent with the previously reported experimental observations. The important part of the proposed mechanism is the formation of pentavalent Si atoms on the OSG surface due to a quasi-chemisorption of the incident F atoms. The revealed mechanism of F atom incorporation into the OSG matrix explains the experimentally observed phenomena of fast fluorination without significant modification of the chemical structure. We demonstrate that the pentavalent Si states induce the weakening of adjacent Si–O bonds and their breaking under F atom flux. The calculated results allow us to propose a set of elementary chemical reactions of successive removal of CH3 and CH2 groups and fluorinated SiO x matrix etching.

The effect of He plasma treatment on properties of organosilicate glass low-k films

The effect of low-pressure He plasma on properties of nanoporous organosilicate glasses low-k films with 24% and 33% open porosity is studied. The influence of ions, VUV radiation, and metastable atoms are extracted separately using a special experimental system designed for this purpose. The low-k films treated in He plasma were exposed to O or H atoms in the downstream of high-pressure O2 or H2 rf discharge. The changes in chemical composition and structure occurring in low-k films were measured before and after all treatments. The loss probabilities of oxygen and hydrogen atoms on the low-k film surface were measured for both treated and pristine films. It is shown that the film pretreatment in He plasma leads to the noticeable densification of the top surface layer up to complete sealing all the films studied. The sealing layer prevents O atoms from deep penetration to the film bulk and carbon extraction. The sealing mechanism related to the joint impact of low-energy ions and VUV photons with metasta...