Low dielectric constant materials (low-k) are used as interlevel dielectrics in integrated circuits. This paper concerns the etching process of these materials in high density plasma with the aim to provide some insights concerning the etch mechanisms. Materials studied are methylsilsesquioxane (MSQ) polymers, either dense (SiOC) or containing 40% of porosity (porous SiOC). Amorphous hydrogenated silicon carbide (SiC) material, used as hard mask and/or etch stop layer, is also investigated. Etch is performed in an inductively coupled reactor using fluorocarbon gases, which have proven to be very successful in the etch of conventional SiO2. First, etching with hexafluoroethane (C2F is performed. Although etch rates are high, etch selectivities with respect to SiC are weak. So, oxygen, argon, and hydrogen are added to C2F6 with the aim of improving selectivities. The best selectivity is obtained for the C2F6/H2 (10%–90%) mixture. To understand etch rate and selectivity variations, plasma analyses by optical emission spectroscopy are correlated to surface analysis using X-Ray Photoelectron Spectroscopy (XPS). In general, atomic fluorine concentration in the plasma explains the etch rate, while the presence of a fluorocarbon layer on the surface is well correlated to the selectivity. To ensure that the etch process does not affect materials properties, and particularly their dielectric constant, bulk analysis by Fourier Transformed Infra-Red spectroscopy and images by Scanning Electron Microscopy have also been carried out.
Abstract The effect of radio frequency bias pulsing on porous SiOCH, SiCH and SiO 2 etching using inductively coupled fluorocarbon plasmas was investigated. It was found that pulse frequency had only a small influence on material etch rates. However, pulse duty cycle, defined as the time during which a bias is applied over the total period, clearly modified etch rates and selectivities. Indeed, etch selectivities between porous SiOCH and SiCH or SiO 2 were considerably improved when the duty cycle was decreased. This enhancement was associated with relatively high porous SiOCH etch rates, and pattern transfers under low duty cycle conditions proved to be successful. To better understand the pulse process, surface analysis was also realised. According to XPS analysis, the material surface structure was found to be similar after etching in continuous or in pulsed mode. However, fluorocarbon species on material surfaces were fluorine richer after etching in the pulsed mode. magnified image
Organic and inorganic silicon dioxide films have been deposited by means of an atmospheric pressure microplasma jet. Tetramethylsilane (TMS), oxygen, and hexamethyldisiloxane (HMDSO) are injected into argon as plasma forming gases. In the case of TMS injection, inorganic films are deposited if an admixture of oxygen is used. In the case of HMDSO injection, inorganic films can be deposited at room temperature even without any oxygen admixture: at low HMDSO flow rates [<0.1 SCCM (SCCM denotes cubic centimeters per minute at STP),<32 ppm], the SiOxHz films contain no carbon and exhibit oxygen-to-silicon ratio close to 2 according to x-ray photoelectron spectroscopy. At high HMDSO flow rates (>0.1 SCCM,>32 ppm), SiOxCyHz with up to 21% of carbon are obtained. The transition from organic to inorganic film is confirmed by Fourier transform infrared spectroscopy. The deposition of inorganic SiO2 films from HMDSO without any oxygen admixture is explained by an ion-induced polymerization scheme of HMDSO.
The inactivation of spores of Bacillus atrophaeus and of Aspergillus niger using beams of argon ions, of oxygen molecules and of oxygen atoms is studied. Thereby, the conditions occurring in oxygen containing low pressure plasmas are mimicked and fundamental inactivation mechanisms can be revealed. It is shown that the impact of O atoms has no effect on the viability of the spores and that no etching of the spore coat occurs up to an O atom fluence of 3.5 × 1019 cm−2. The impact of argon ions with an energy of 200 eV does not cause significant erosion for fluences up to 1.15 × 1018 cm−2. However, the combined impact of argon ions and oxygen molecules or atoms causes significant etching of the spores and significant inactivation. This is explained by the process of chemical sputtering, where an ion-induced defect at the surface of the spore reacts with either the incident bi-radical O2 or with an incident O atom. This leads to the formation of CO, CO2 and H2O and thus to erosion.
En micro-electronique, la performance des circuits integres est limitee par l'augmentation des delais d'interconnexions. Une solution est de remplacer le dielectrique d'interniveaux conventionnel (SiO2) par un materiau a plus faible constante dielectrique (low-k). Cette etude concerne la gravure de materiaux low-k SiOCH et SiOCH poreux, et la gravure de la couche barriere SiCH et du masque dur SiO2. La selectivite de gravure des low-k par rapport a SiCH et SiO2 est un critere important a obtenir. De plus, l'etape de gravure ne doit pas modifier considerablement la constante dielectrique du materiau. Enfin, la gravure de motifs doit etre anisotrope. Pour atteindre ces objectifs, un meilleur controle du procede de gravure et une meilleure comprehension des mecanismes de gravure sont souhaites. La gravure des materiaux est realisee en plasma fluorocarbone (CHF3) additionne ou non de H2 ou Ar, dans un reacteur a couplage inductif (ICP), dans lequel le substrat est polarise negativement. Ce procede a ete modifie en appliquant une polarisation pulsee au substrat (1 Hz a 10 kHz). Dans cette configuration, l'energie des ions est pulsee. L'influence des conditions de pulse (frequence, et rapport cyclique rc=TON/T) sur la gravure des materiaux SiOCH poreux, SiOCH, SiCH, SiO2, et Si est etudiee. En particulier, en diminuant le rapport cyclique, ce procede pulse fournit d'excellents resultats concernant la gravure selective de SiOCH poreux vis a vis de SiCH et SiO2. Pour optimiser le procede de gravure, une meilleure comprehension de l'interaction plasma-surface, et par suite des mecanismes de gravure, est indispensable. Pour cela, des analyses de surface (XPS, ellipsometrie spectroscopique, MEB) sont correlees a des analyses du plasma (spectrometrie de masse, spectroscopie d'emission optique, sonde de Langmuir, sonde plane). En particulier, durant cette these, le diagnostic de sonde plane a ete developpe. Il permet une mesure precise du flux d'ions, qui peut alors etre mesure en temps reel en plasma polymerisant, electronegatif et instable. En comparant ces differents diagnostics, nous concluons que les mecanismes de gravure en polarisation pulsee sont similaires a ceux en polarisation continue. Toutefois, le procede de gravure differe. Aussi, pour comprendre ce procede, un modele decrivant les vitesses de gravure en fonction de la tension de polarisation a ete developpe. En resume, lorsque aucune tension n'est appliquee (phase OFF), un film fluorocarbone se depose a la surface des materiaux. Puis, a l'application d'une tension (phase ON), une energie des ions superieure a celle obtenue en polarisation continue est necessaire pour graver ce depot puis graver le materiau. De plus, la gravure du materiau en polarisation pulsee s'opere a travers un film fluorocarbone plus riche en fluor par rapport au mode continu : La gravure des materiaux en est amelioree. Le modele, tenant compte de cet etat de surface, decrit alors correctement les seuils et vitesses de gravure des differents materiaux en polarisation pulsee.
Summary form only given. There has been much interest in inductively coupled plasmas for semiconductor processing and for integrated optic applications. We are concerned with several processes using Inductively Coupled Plasma, such as deep silicon oxide etching using fluorocarbon gases (CF/sub 4/, C/sub 2/F/sub 6/, CHF/sub 3/) and their mixtures with methane (CH/sub 4/) or hydrogen (H/sub 2/), low-k etching using fluorocarbon gases mixed with oxygen (O/sub 2/) or nitrogen (N/sub 2/) and resist etching in oxygen, fluorocarbon or SF/sub 6/ plasmas. Our main aims are to develop, understand and optimize these processes. When considering etching, a fundamental process parameter is the ion flux impinging the substrate, as well as the Electron Energy Distribution Function (EEDF). We use Langmuir probe diagnostic to measure these two parameters. Most of the gases used are polymerizing gases and deposition on the probe tip is a major problem to be addressed to obtain reliable probe measurements. Furthermore, all the gases studied (except nitrogen) have a common point, their strong electronegativity, that leads to another problem to be faced. Actually, we have observed strong plasma oscillations when using electronegative gases. This kind of plasma instabilities were attributed to a periodic capacitive to inductive discharge jump because of a periodic negative ion creation. As a consequence of the plasma oscillations, probe acquisitions are disturbed and do not allow to determine plasma electrical characteristics. Hence, time resolved probe measurements must be employed in order to follow electron and ion densities variation during instability. In this work we present our first studies concerning time resolved probe measurements during instabilities. First, we have identified for the different gases used, the instability window (source power versus pressure). We show for example that C/sub 2/F/sub 6/ plasmas present oscillations over a very large range of power and pressure. Second, for non polymerizing gases, we have measured time resolved electron and ion densities during plasma oscillations.
The authors present the design, realization and characterization of photonics integrated circuits made up of organosilicon (SiO x C y H z ) materials called HexaMethylDiSilOxane plasma polymers (pp-HMDSO), elaborated by plasma enhanced chemical vapour deposition (PECVD). Such a versatile technique offers the noticeable advantage to allow the control of respectively; the value of the refractive indices, the thickness of each layer while entailing a lower stress, as the gas proportion of precursors (HMDSO) and plasma conditions are conveniently adjusted. The cladding and core layers of such waveguides have been elaborated into the same reactor thanks to the same precursors with relevant changes regarding the plasma parameters. Then, various integrated photonics devices have been realized, from planar and single-mode rib waveguides to more complex structures like S-bends, Y-junctions, and Mach Zehnder interferometers (MZI). Such structures prove to yield a good single-mode confinement for both polarisations. Moreover optical losses ascribed to pp-HMDSO structures have been respectively evaluated to 5.6 dB.cm 1 and 11.5 dB.cm 1 for TE 00 and TM 00 optical modes. Hence, pp-HMDSO and PECVD appear as quite promising techniques for devising ultra-integrated components like microresonators, and many another functional devices
