One major challenge in plasma etching processes for integrated circuit fabrication is to achieve a good wafer-to-wafer repeatability. This requires a perfect control of the plasma chamber wall conditions. For silicon etching processes, which deposit SiO y Cl z layers on the chamber walls, this is achieved by cleaning the interior surfaces of the plasma chamber with an SF 6 -based plasma after each wafer is etched. However, x-ray photoelectron spectroscopy analysis of the reactor wall surfaces shows that the inner parts of the Al 2 O 3 chamber are strongly fluorinated (formation of Al-F bonds) during the SF 6 plasma. At the same time the AlF x layer is sputtered from some parts of the chamber (mostly from the roof, which is bombarded by high energy ions), and AlF redeposition is observed on other parts of the reactor body. Hence, the cleaning process of the reactor leaves AlF residues on the chamber wall on its own. This leads to several issues including flake off of Al x F y particles on the wafer and process drifts (due both to the progressive growth of AlF material on the SiO 2 windows and to the release of F atoms from the chamber walls during the etching process). This indicates that a strategy other than dry-cleaning the Al 2 O 3 chamber walls in fluorine-based plasmas should be found. In this paper we have investigated two different strategies. The first one consists of replacing Al 2 O 3 covering the chamber walls by another material for the chamber walls inner coating. In particular, we have investigated the surface modification of several types of organic polymers (Teflon, Parylene and carbon-rich polymers), when exposed to SF 6 -based plasmas. We show that these materials can be reset to their original condition after exposure to a dry-cleaning process because carbon containing polymers are slowly etched away by the SF 6 /O 2 plasma. This suggests that the replacement of the conventional Al 2 O 3 chamber wall material by a carbon-coated liner should be possible. Alternatively, we also propose a powerful strategy for conditioning and cleaning an Al 2 O 3 reactor, in which a thin carbon-rich layer is deposited on the reactor walls by a short plasma step prior to any etching process. After etching, the SiO y Cl z layer deposited on the carbon layer during a silicon gate etch step can be cleared with an appropriate plasma, and the carbon layer removed by an O 2 plasma, thus resetting the reactor walls to their initial state. Using this strategy the etching process always starts under the same chamber walls conditions (a carbon-rich wall) and is thus reproducible. At the same time, the issues associated with AlF deposits are prevented because the carbon-coated layer protects the Al 2 O 3 chamber walls, and there is no fluorine released into the plasma. Finally, we will show that the etching profiles of the silicon gates and the selectivity towards the thin gate oxides are excellent in the carbon-coated chamber. This strategy is thus promising for future metal gate etching applications.

Addition of yttrium in HfO 2 thin films prepared on silicon by metal organic chemical vapor deposition is investigated in a wide compositional range ͑2.0-99.5 at. % ͒. The cubic structure of HfO 2 is stabilized for 6.5 at. %. The permittivity is maximum for yttrium content of 6.5-10 at. %; in this range, the effective permittivity, which results from the contribution of both the cubic phase and silicate phase, is of 22. These films exhibit low leakage current density ͑5 ϫ 10 −7 A/cm 2 at −1 V for a 6.4 nm film͒. The cubic phase is stable upon postdeposition high temperature annealing at 900°C under NH 3 .

During plasma etching processes, organic or mineral layers are deposited on the chamber walls. In general, these layers cause large and uncontrolled shifts in the etch process, which is becoming a major issue in some of the plasma processes used in integrated circuit fabrication. The chemical nature of these layers and their deposition mechanisms remain poorly understood due to the lack of in situ surface diagnostics available to monitor the reactor walls. In this article, we present a simple technique using x-ray photoelectron spectroscopy (XPS) analyses to monitor the chemical composition of the layer deposited on a sample floating on top of a 200-mm-diam wafer where the layers deposited are identical to those deposited on the chamber walls. The principle of the technique is to stick a small Al2O3 sample onto the 200-mm-diam silicon wafer, with an air gap between the sample and the wafer. Providing that the air gap is thick enough, the Al2O3 surface will be electrically floating even when the silicon wafer is rf biased. During the etching process, the Al2O3 sample thus experiences exactly the same plasma conditions as the reactor walls. As the sample is physically clamped on the wafer, it can then be transferred under vacuum to an XPS analyzer, allowing quasi-in situ analyses of the deposited layers. The validity of the technique has been tested during silicon gate etching in HBr/Cl2/O2 plasmas, which are known to deposit silicon oxychloride layers on the chamber walls. The influence of CF4 addition in the plasma which has been recently introduced in gate etching manufacturing is also analyzed using the same technique. In a second step, we show that the presence of photoresist on the etched wafer profoundly affects the chemical nature of the layers formed on the chamber walls, mainly by significantly increasing the carbon concentration in the deposited layer.

We present a detailed study of the growth of Ge nanocrystals (NCs) on SiO2 by chemical vapor deposition. A two-step process was developed. First, Si nuclei are deposited on SiO2 using SiH4 as a gaseous precursor. Then, Ge NCs grow selectively on the Si nuclei previously formed. The density of the Ge NCs is adjustable in between 109 and 1012 cm−2. Their mean size varies between 5 and 50 nm. We have shown, combining grazing incidence x-ray diffraction and x-ray photoelectron spectroscopy, that pure Ge NCs are grown in a polycrystalline phase on a SiO2 surface.

Effects of Ge 2 Sb 2 Te 5 and GeTe oxidation on their phase-change properties were studied by optical measurements and Parallel Angle Resolved X-ray Photoelectron Spectroscopy (PARXPS). The influence of oxygen on the active material was depicted in order to explain variations of the phase-change properties. The surface analysis evidenced a two-steps oxidation involving the formation of germanium and antimony oxides then tellurium oxide. A smooth surface sputtering allowed physically distinguishing the different oxides on GeTe sample overlayer and gave information about oxidation mechanisms. A significant drift of crystallization temperatures and activation energies were observed after 12 months air exposure time that points out the influence of the phase-change materials oxidation on their active properties.

Effect of fluoroalkyl substituents on the reactions of alkylchlorosilanes with mold surfaces for nanoimprint lithography J.The adhesion between the fused silica mold and the resist remains a key issue in ultraviolet nanoimprint lithography ͑UV-NIL͒, especially in step and repeat processes. In this paper, we present results on antisticking layers ͑ASLs͒ of tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane ͑F 13 -TCS͒ deposited in vapor phase and of a commercial product, Optool DSX™, from Daikin Chemical, deposited in liquid phase. The antisticking properties and structural morphologies of the formed self-assembled monolayer are investigated using contact angle, Fourier transform infrared spectroscopy, and x-ray photoelectron spectroscopy ͑XPS͒ measurements. Obtained surface energies are as low as 10 mN/ m for both types of ASL. The stability of these formed layers during the UV-NIL process remains the main important issue. It was tested on an EVG ® step and repeat UV-NIL equipment using acrylate-based resists. After only 50 prints, we observed a high increase in the surface energy of the mold, which indicates a drastic degradation of the antisticking ͑ASL͒. XPS measurements show that fluorine is removed from the mold surface. This surface modification is attributed to free radicals created during the UV cure of the resist that easily cleaved fluorocarbon chains. This can be confirmed by the fact that the polar component of the surface energy was increased by a larger factor than the dispersive one. To overcome this problem, the acrylate-based resist was modified by the adjunction of a fluorine surfactant. To go further in the mold/resist interaction, we developed an original setup that directly measures the adhesion force. Almost no degradation of the organic ASL was observed in terms of surface energy and fluorine density after more than 50 prints when using a sufficiently high amount of surfactant in the resist.

No abstract

The controlled incorporation of dopants like copper into ZnO nanowires (NWs) grown by chemical bath deposition (CBD) is still challenging despite its critical importance for the development of piezoelectric devices. In this context, the effects of the addition of copper nitrate during the CBD of ZnO NWs grown on Au seed layers are investigated in detail, where zinc nitrate and hexamethylenetetramine are used as standard chemical precursors and ammonia as an additive to tune the pH. By combining thermodynamic simulations with chemical and structural analyses, we show that copper oxide nanocrystals simultaneously form with ZnO NWs during the CBD process in the low-pH region associated with a large supersaturation of Cu species. The Cu(II) and Zn(II) speciation diagrams reveal that both species show very similar behaviors, as they predominantly form either X 2+ ions (with X = Cu or Zn) or X(NH3)4 2+ ion complexes, depending on the pH value. Owing to their similar ionic structures, Cu 2+ and Cu(NH 3 ) 4 2+ ions preferentially formed in the low-and high-pH regions, respectively, are able to compete with the corresponding Zn 2+ and Zn(NH3)4 2+ ions to adsorb on the c-plane top facets of ZnO NWs despite repulsive electrostatic interactions, yielding the significant incorporation of Cu. At the highest pH value, additional attractive electrostatic interactions between the Cu(NH 3 ) 4 2+ ion complexes and negatively charged c-plane top facets further