RU2119692C1 - Method for chemical deposition of thin silicon-dioxide films - Google Patents

Abstract

FIELD: microelectronics; manufacture of multilayer very large- scale integrated circuits. SUBSTANCE: method involves oxidation reaction of silicon hydrides under flow conditions at low pressure with inflammation region extended towards lower temperatures (down to 35 C) and pressures using chemically active material such as long-living intermediate product of oxidation reaction proper, dichlorosilane being used as fuel. EFFECT: reduced deposition temperature of thin uniform films homogeneous and stoichiometric in their composition. 3 dwg

Description

Silicon dioxide films are widely used in the VLSI manufacturing technology, obtained a) by oxidation of silicon at 1200 ^° C in the presence of various additives, b) in the oxidation of monosilane by oxygen in the presence of an inert gas at a temperature of at least 400 ^° C [1], c) in the reaction monosilane oxidation with nitrous oxide in the afterglow zone of the plasma at temperatures not lower than 200 ^o C [2]. Despite the various technological methods used in the implementation of these methods, the methods listed above use either high temperatures or a high-frequency discharge, which is unacceptable when working with compounds whose electron mobility decreases sharply with increasing temperature, as well as in high-frequency electric and magnetic fields ( A ³ B ⁵ , A ² B ⁶ , high temperature superconductors).

The closest to the proposed technical essence and the achieved result is a method for producing silicon dioxide films, based on the expansion of the ignition region of combustible mixtures with external initiation and using the reaction of branched chain oxidation of dichlorosilane at a temperature of 130 ^o C in a reactor cooled to 0 ^o C and a pressure of 250 Pa under quasistatic conditions with a single ignition, while ignition is initiated by a pulsed local energy source remote from the substrate [3].

 In the prototype method, single-ignition deposition is used, which fundamentally limits the thickness of the resulting films and, accordingly, the possibility of their use as protective and dielectric layers in microelectronics technology. The use of a heated metal spiral as a source of physical stimulation can lead to the inclusion of extraneous impurities adsorbed on the metal in the material of the deposited film and the deterioration of its electrophysical characteristics.

 Two methods are known in the literature for expanding the ignition region of combustible mixtures at low pressures — the physical initiation described above [3] and the use of chemically active additives [4]. In the technology of microelectronics, physical stimulation methods are usually used, since sorption and side reactions of chemically active additives lead to a deterioration in the mechanical and electrophysical properties of the resulting films [5]. In this invention, the initiation of a chemical additive is used, the intermediate product of the working reaction used being used as the latter, therefore, the above-mentioned negative phenomena are excluded.

This invention uses the fact that we established that an Si-O bond-containing compound is formed as an intermediate product of low-temperature oxidation of dichlorosilane. It was shown that this compound interacts with other active particles (chain carriers) of the oxidation process, leading under certain conditions to expand the ignition region of mixtures of dichlorosilane with oxygen to 15 ^o C. This is a quadratic reaction (second kinetic order) in the concentration of intermediate particles, and if it leads to an increase in the number of chain carriers, then according to [4] the ignition region should expand, which is observed experimentally. Thus, a significant expansion of the ignition region can be achieved by adding an intermediate product to the Si - O working mixture. The accumulation of this product, which is relatively long-lived (life time of about 100 s), is carried out in a buffer volume, igniting the initial combustible mixture in it with a thermal pulse source. After several initiated ignitions, the buffer volume is connected to the reactor in which the deposition substrate is located and through which the initial mixture is continuously pumped at the desired pressure. An oscillating mode of self-ignition arises, which transfers to stationary combustion, which is accompanied by the deposition of a uniform and uniform silicon dioxide film. The observed complex pattern of oscillations is consistent with that expected in the presence of a quadratic chain branching reaction.

The novelty of the invention is determined by the following features:
a) the use of chemical initiation, devoid of the disadvantages associated with the negative effects of chemisorption and adverse reactions of chemically active impurities;
b) elimination of the source of physical stimulation from the deposition zone, which avoids chemisorption in the film material of the impurities contained in it, and their effect on the mechanical and electrophysical properties of the resulting film.

These techniques can avoid the simultaneous location in the reactor of the source of physical initiation and the surface to be coated, as well as lower the deposition temperature (to 35 ^o C) and the total process pressure (to 0.6 Torr) due to the expansion of the ignition region.

 Example. A cylindrical flow reactor for the deposition of thin films with a height of 200 mm and a diameter of 150 mm is made of quartz and equipped with a removable cover, flanges for introducing gases, measuring temperature and pressure, introducing electrical contacts and pumping. At the bottom of the reactor is a heater with a diameter of 100 mm and a height of 20 mm made of Teflon. A chromel-alumel thermocouple with a junction diameter of 0.1 mm is connected to a hole on the side of the heater, connected to a temperature setter to control the temperature of the heater. A silicon wafer (KEF-4.5 (100) with a diameter of 76 mm) is placed on the heater. A thin thermocouple with a junction diameter of 0.04 mm is placed 1 mm from the surface of the plate at its edge (so as not to disturb the uniformity of deposition), the signal from which is fed to a recording device (recorder or oscilloscope. The working gas mixture enters both the reactor and the spherical buffer volume of 70 mm in diameter, equipped with a pressure sensor and made of quartz. A pulse heater, consisting of several turns of nichrome wire, is placed in the side input of the buffer volume. The latter is cut off from the reactor by an electromagnetic valve ohm

The deposition procedure is as follows. In the reactor, previously evacuated to 10 ^-2 mm Hg, set the flow of the working gas (30% SiH ₂ Cl ₂ + O ₂ ) at a pressure of 0.6 - 0.9 mm Hg 3 mmHg are injected into the buffer volume. Art. the working gas is ignited by a pulse heater and the solenoid valve is opened. If the reaction does not start, the valve is closed and the initiation is repeated. The onset of deposition is evidenced by the occurrence of periodic temperature oscillations (FIG. 1), which turn into stationary combustion, accompanied by deposition, the speed of which is about 5 nm / min (0.6 mm Hg, 35 ^° C).

Films with a thickness of up to 0.6 μm have a spread in thickness <6%, porosity of 1-2 cm ^-2 . Figure 2 shows the IR spectrum of the coating with a thickness of 0.14 μm obtained at 35 ^o C. It can be seen that along with the intense absorption band of the Si - O - Si bond at 1050 cm ^-1 , very weak Si - H bond bands are observed (2150 cm ^-1 ) and Si - OH (3400 cm ^-1 ), undesirable in microelectronics technology. Obtained at various temperatures (35 ^o C - a, 45 ^o C - b, 55 ^o C - c), the films were investigated by the method of ESCA (figure 3). The chemical state of silicon atoms was determined by the energy position of the Si2p level, which for this method is E = 103.2 eV (for pure silicon E = 98.9 eV). The values of E for our samples were 103.5 ± 0.3 eV for Si2p. This means (see Fig. 3) that the silicon atoms Si2p and Si2s (155 eV) in the films are valence bound to oxygen atoms (536 eV) and are in a valence state close to stoichiometric SiO ₂ . The stoichiometric composition of the films is also indicated by the fact that the spectral lines of Si2p and O atoms, recorded with a 50-fold stretch in abscissa relative to FIG. 3, have a strictly symmetrical bell-shaped shape. There is no broadening of these lines toward lower binding energies, i.e. the resulting films do not contain non-stoichiometric SiO _x fragments (0 <x <2). Thus, the films obtained by the claimed method are stoichiometric in composition and practically do not contain undesirable Si - H and Si - OH bonds.

The claimed method does not require complex and expensive instrumentation. The characteristics of thin-film coatings obtained by the claimed method are promising for the application of these coatings in the technology of compounds A ³ B ⁵ and A ² B ⁶ and high-temperature superconductors as interlayer or passivating protective coatings.

Sources of information
1. Sugano T., Ikoma T., Takeishi E. Introduction to microelectronics. M .: Mir, 1988, 380 p.

 2. Lucovsky G., Kim S.S., Tsu D.V., Parsons G.N., Fitch J.T. Formation of silicon-based heterostructures in multichamber integrated processing thin film deposition systems. SPIE, 1989, v. 188. Multichamber and in siti Processing of Electronic Mat., P. 140-150.

 3. Rubtsov N.M., Azatyan V.V., Nagorny S.S., Temchin S.M., Lukashev A.S., Merzhanov A.G. A method for producing thin films of silicon dioxide. Patent RU 2040072, H 01 L 21/316, 1995. Bull. 20. ISMAN USSR, Institute of Physics of the Academy of Sciences of the USSR. 1987. A.S. 1338717.

 4. Semenov N.N. About some problems of chemical kinetics and reactivity. M.: Publishing House of the Academy of Sciences of the USSR, 1986, 686 p.

 5. Kern W. Deposited dielectrics fol VLSI. Part II, Semicond. Int. 1985, v. 5, N3, p. 122-140.

Claims (1)

The method of chemical deposition of thin films of silicon dioxide by carrying out the oxidation reaction of inorganic silicon hydrides in a working mixture containing dichlorosilane and oxygen at low pressure in a branched-chain ignition mode, characterized in that a pre-synthesized intermediate product of the used working reaction containing Si - O-bonds at 35-38 ^o C.

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