Martin Kogelschatz

Influence of reactor walls on plasma chemistry and on silicon etch product densities during silicon etching processes in halogen-based plasmas

The absolute concentrations of SiClX (X = 0?2), SiFX (X = 1?2), SiClF, SiBr and SiO radicals were measured in an industrial silicon gate etching reactor with various halogen gas mixtures (HBr, Cl2, O2, CF4 mixtures). The influence of O2 gas flow in the HBr/Cl2 mixture, of the HB/Cl2 ratio, and of CF4 addition in HBr/Cl2 have been analysed systematically. These experimental results are the first quantitative information on the densities of silicon etch products in a high density Cl2-based plasma, and are useful to validate and improve numerical models. In addition, these results are correlated with the 200?mm diameter silicon wafer etch rate, and with the deposition rate of the layers deposited on the plasma chamber walls and with their chemical compositions. This allows us to discuss the production and loss mechanisms of silicon etching by-products during silicon etching processes. In Cl2-based plasmas, we show that the chamber walls are efficient for recycling silicon: SiCl2?4 radicals, initially produced from the etching of the wafer are ionized and dissociated by the plasma into reactive products Si, SiCl, Si+, SiCl+. These species can then undergo chemisorption on the reactor walls, where they can be either oxidized by O atoms from the plasma (leading to the formation and growth of SiOClX layers on the chamber walls) or be etched back into the gas phase by Cl atoms. Therefore, the deposition rate of SiOClX layers on the chamber wall results from a competition between these two reactions and is then limited by the amount of O atoms available. The other consequence of this competition is that reactor walls produce large amounts of SiCl2?4 radicals when the O2 flow is low. When CF4 is added to the plasma, the concentration of SiClX etch products decreases in favour of SiFX etch products. In addition, the presence of F atoms and CFX radicals and fluorine-based ions prevents the deposition of a SiOClX layer on the reactor walls.

Growth and characterization of gold catalyzed SiGe nanowires and alternative metal-catalyzed Si nanowires

The growth of semiconductor (SC) nanowires (NW) by CVD using Au-catalyzed VLS process has been widely studied over the past few years. Among others SC, it is possible to grow pure Si or SiGe NW thanks to these techniques. Nevertheless, Au could deteriorate the electric properties of SC and the use of other metal catalysts will be mandatory if NW are to be designed for innovating electronic. First, this articles focus will be on SiGe NWs growth using Au catalyst. The authors managed to grow SiGe NW between 350 and 400°C. Ge concentration (x) in Si1-xGexNW has been successfully varied by modifying the gas flow ratio: R = GeH4/(SiH4 + GeH4). Characterization (by Raman spectroscopy and XRD) revealed concentrations varying from 0.2 to 0.46 on NW grown at 375°C, with R varying from 0.05 to 0.15. Second, the results of Si NW growths by CVD using alternatives catalysts such as platinum-, palladium- and nickel-silicides are presented. This study, carried out on a LPCVD furnace, aimed at defining Si NW growth conditions when using such catalysts. Since the growth temperatures investigated are lower than the eutectic temperatures of these Si-metal alloys, VSS growth is expected and observed. Different temperatures and HCl flow rates have been tested with the aim of minimizing 2D growth which induces an important tapering of the NW. Finally, mechanical characterization of single NW has been carried out using an AFM method developed at the LTM. It consists in measuring the deflection of an AFM tip while performing approach-retract curves at various positions along the length of a cantilevered NW. This approach allows the measurement of as-grown single NWs Young modulus and spring constant, and alleviates uncertainties inherent in single point measurement.

Time-resolved measurements of Cl2 density in high-density plasmas and application

Absorption at 355 nm, with a pulsed frequency tripled yttrium-aluminum-garnet laser as light source, is used to monitor the time evolution of the Cl2 density in high-density inductively coupled plasmas. The detection limit over a 0.1 s acquisition time is about 0.2 mTorr of Cl2. This technique is well suited for monitoring chlorine density when studying elementary processes in Cl2 containing plasmas. Furthermore, it can be applied to control the process drift in industrial etch reactors resulting from the modification of the chamber walls conditions: by measuring the Cl2 density in a reference Cl2 plasma before etching a wafer, it can be determined if the chamber wall conditions are kept identical from one wafer to another.

Self-assembling study of a cylinder-forming block copolymer via a nucleation-growth mechanism.

Block copolymer materials form self-assembling structures at a nanometric scale, of interest in nanotechnology. The organization process of asymmetric poly(styrene-block-methyl methacrylate) (PS-b-PMMA) copolymer thin films is studied. In a first step it is demonstrated that two consecutive mechanisms lead to the formation of a well-ordered phase. The first mechanism is the local segregation of blocks, which leads to a metastable disordered cylinder phase (C(d)). The second mechanism is a transformation of the C(d) phase to a vertical cylinder phase via a nucleation-growth mechanism. The influence of film thickness and surface tension on the organization is also studied. Above the natural cylinder monolayer height, h(1), the kinetics of the cylinder organization strongly depends on the initial film thickness, and below h(1) the film splits into terraces. By varying the interactions between the substrate surface and the different blocks, a disordered phase can be formed instead of terraces.