Geoffroy Auvert

CO2-laser-induced chemical vapour deposition of polycrystalline silicon from silane

Abstract Silicon dots have been deposited on silicon-coated quartz substrates by continuous wave CO2-laser-induced decomposition of silane. The deposited material was determined by micro Raman scattering to be polycrystalline silicon. The height of the silicon dots was measured as a function of output laser power and irradiation time. The growth rate of silicon dots having a gaussian profile was found to be proportional to silane pressure and laser power. The laser power required for silicon melting (1683 K) was measured under specific experimental conditions. The substrate temperature could be calculated for any laser power assuming a linear temperature dependence on this power. The growth rate of silicon dots was found to be proportional to the substrate temperature. The growth kinetics of silicon dots may be limited by the number of collisions between “cold” silane molecules and the heated zone of substrates. A reaction mechanism based on this assumption is proposed in this paper.

Deposition of micron-size nickel lines by argon-ion laser-assisted decomposition of nickel tetracarbonyl

Abstract Nickel lines were deposited from the decomposition of Ni(CO)4 on silicon/silicon-dioxide/silicon substrates locally heated by means of a focused CW argon-ion laser operating at several wavelengths around 0.5 μm. Growth kinetics, morphology and electrical resistivity of the nickel microstructures were investigated at various scanning speeds of the laser spot, laser beam powers and reactant gas pressures. Nickel lines as small as 1 μm in width were written. From the growth kinetics, the vertical deposition rate of nickel can be calculated. At low Ni(CO)4 pressures, typically below 0.3 mbar, deposition of flat-topped nickel lines occurs. The deposition rate is proportional to the Ni(CO)4 pressure and independent of the laser-induced temperature. At reactant gas pressures above 0.3 mbar, Gaussian nickel lines are obtained. The deposition rate is found to be independent of the Ni(CO)4 pressure and exhibits an activation energy of about 11.5 kcal mol-1. The measured electrical resistivity of the flat-topped lines is about 10 times higher than the bulk resistivity (7 μΩ·cm) while in the Gaussian regime this ratio falls below 1.5. The morphology and roughness of the deposited lines were investigated using both a scanning electron microscope (SEM) and an atomic force microscope (AFM). In the flat-topped regime, grains of about 100 nm are observed at the top of the nickel lines while in the Gaussian regime the surface is smooth.

Laser-induced deposition of one-micron-size polysilicon lines from mono and trisilane

Abstract High-resolution deposition of polysilicon lines has been performed on various silicon-silicon-dioxide-silicon multilayer substrates locally heated by means of a CW argon-ion laser emitting at several wavelengths around 0.5 μm in the presence of silane or trisilane gas. The deposition kinetics and the morphology of the silicon microstructures have been investigated as a function of laser beam power and gas pressure at various scanning speeds of the laser spot. Polysilicon lines between 1 and 2 μm in width have been written under specific processing conditions. These lines have been characterized using both a scanning electron microscope and a focused ion beam system. The deposition rate was found to be significantly faster with trisilane than with silane and limited by a thermally activated process occuring in the adsorbed layer.

Kinetics and mechanisms of CW laser induced deposition of metals for microelectronics

Abstract During the interaction of a high power CW laser beam with an absorbing surface in the presence of a reactive gas, local deposition of a metal can be achieved. The organometallic gas used for nickel deposition is nickel tetracarbonyl. The decomposition mechanism occurs in the absorbed layer via a thermally activated process. A gaseous molecule is first chemically adsorbed on the surface by exchanging two carbonyls. Then, due to the high local temperature, carbonyl groups desorb leaving free sites to be adsorbed by other molecules. Decomposition of nearly all impinging molecules may be achieved leading to a very high deposition rate. The theoretical highest rate is evaluated to be around 1mm/s at temperatures above 1200°C and at saturated vapour pressure of nickel tetracarbonyl. For tungsten deposition, by using pure tungsten hexafluoride, the local heating of a silicon surface leads to an etching due to the formation of a volatile complex preventing any tungsten deposition. In order to avoid this etching phenomena, hydrogen must be added. The rate limiting process is in this case, either the adsorption of hydrogen molecules on the growing tungsten surface or the decomposition of hydrogen molecules into two atoms as in a catalytic reaction. Therefore, as the surface is unsaturated in adsorbed hydrogen, the deposition rate of tungsten is smaller than that of nickel. A rate of 2 μm per second has been obtained at temperatures around 1300°C and for a hydrogen pressure close to atmospheric.

Realization of Hybrid Silicon core/silicon Nitride Shell Nanodots by LPCVD for NVM Application

We present the realization of hybrid silicon core/silicon nitride shell nanodots by Low Pressure Chemical Vapor Deposition (LPCVD) and their application as floating gate in Non Volatile Memory (NVM) devices. The LPCVD process includes three steps: nucleation using SiH4, selective growth of the silicon nuclei using SiH 2 Cl 2 and finally selective growth of silicon nitride using a mixture of SiH 2 Cl 2 and NH 3 around the silicon dot. The two first steps have already been described in literature. We will therefore focus on the selective growth of a nitride layer on silicon dots. Morphological characterization using Scanning Electron Microscopy (SEM) allows control over dots size – 5 to 10nm – and density – up to 1E12/cm 2 . High Resolution Transmission Electron Microscopy (HRTEM) shows a crystalline silicon core and an outer shell of amorphous silicon nitride. Energy Filtered TEM pictures confirm that the nitride layer is deposited only around the silicon dots and not on the oxide. Oxidation resistance of the silicon nitride shell is also investigated. A 2nm thick silicon nitride layer is an efficient barrier to an oxidation at 800°C in dry oxygen for 5 minutes. We thus have a very thin high quality stoechiometric nitride layer. Such a high quality nitride film can only be achieved using in-situ deposition i.e. on an oxide-free silicon surface. Finally, hybrid Si/SiN nanodots are integrated in a single memory cell with high-K interpoly dielectric. Electrical results show large threshold voltage shift of 6V. The use of silicon nitride shells on the silicon dots has therefore two main advantages: it provides both oxidation resistance and charge storage enhancement.

Deposition of Silicon Films by Photodissociation of Silane Under IR Laser Irradiation

In the field of semiconductor processing, a considerable amount of interest has been devoted to laser-induced deposition of silicon films [1]. For example, hydrogenated amorphous silicon (a-Si) films can be successfully deposited on quartz or glass substrates at temperatures below 400 °C [2–4]. The technique involves vibrational excitation of silane molecules by absorption of the P(20) CO2 laser line at 10.59 μm. Since the absorption of SiH4 molecules is known to be enhanced by buffer gases such as hydrogen and nitrogen, the deposition rate of a-Si films formed by irradiating SiH4-N2 mixtures is likely to be altered.

Kinetics of Laser-Assisted Chemical Vapor Deposition of Tungsten Microstructures

Tungsten microstructures (dots, strips and films) have been deposited via H2 reduction of WF6 on polycrystalline silicon-coated quartz substrates irradiated with a focused cw argon laser beam. The deposition rate of W dots, deduced from α-step measurements of the height of dots, was investigated as a function of irradiation time, composition of H2-WF6 gas mixtures and laser-induced surface temperature. At a laser-induced surface temperature ranging from 340° to 670°C with an H2 partial pressure varying from 50 to 700 Torr, the reaction order with respect to H2 was equal to one-half, whereas at higher temperatures (750°-950°C) and lower H2 partial pressures (20-80 Torr), the reaction order with respect to H2 was found to be one. The reaction mechanism of the H2 reduction of WF6 on substrates irradiated with the argon laser beam is discussed.

Absorption and decomposition of silane under infrared laser irradiation

Abstract Silane, dichlorosilane and gas mixtures were irradiated by a pulsed CO 2 laser beam operating at 10.59 μ m. The absorptance of pure gases and gas mixtures has been determined as a function of gas pressures. The effect of nitrogen and dichlorosilane on the silane absorption has been examined. Powdery silicon could be produced by photolysis of silane. The homogeneous decomposition threshold of silane (pure gas and in gas mixtures) has been investigated as a function of laser fluence and silane pressure. The mechanisms of the optical absorption and photolysis of silane are discussed.

Introduction to Direct Writing of Integrated Circuit

Integrated circuit fabrication steps employing localized-laser writing involves maskless and sequential processing of circuit layout. These steps are fundamentally different from those used in optical lithography but may be used for some process steps in device fabrication. The laser direct writing technique, sometimes called laser pantography, allows a rapid and discretionary interconnection network drawing of prefabricated gate-arrays and is suitable for either development of prototype circuits or filling low-volume custom orders of integrated circuits. It appears to be the most practical near-term application of this technology. Another application of the laser direct writing technique is the discretionary fabrication of high performance devices.

Laser Direct Writing for Device Applications

In silicon semiconductor technology, a one micron size probe is required for the modification of interconnection networks. The laser direct writing technique using a focused laser beam is a possible solution in the building of new connections in the circuit. The complete process is composed of three elementary laser - assisted steps: etching of the insulator, deposition of an insulator on conducting materials and deposition of a conductor on an insulator.