1. Field of the Invention
The present invention relates to a thin-film vapor deposition apparatus, and more particularly to a thin-film vapor deposition apparatus suitable for depositing in a vapor or gas phase a thin film of a high dielectric constant such as barium/strontium titanate.
2. Description of the Prior Art
In recent years, there have been increasing efforts in the semiconductor industry to increase the degree of integration of integrated circuits. Such efforts are directed to, among others, the research and development of DRAMs (Dynamic Random-Access Memories) ranging from present megabit storage capabilities to future gigabit storage capabilities. For producing such DRAMs, it is necessary to provide devices having large storage capabilities. In an attempt to produce dielectric thin films for use in such large storage capability devices, researchers have been shifting their attention from silicon oxide films and silicon nitride films whose dielectric constants are 10 or less to more promising thin film metal oxide materials including tantalum pentoxide (Ta.sub.2 O.sub.5) whose dielectric constant is about 20, and barium titanate (BaTiO.sub.3), strontium titanate (SrTiO.sub.3), and mixtures of barium/strontium titanate whose dielectric constants are about 300.
However, the vapor deposition of a thin film of such a high dielectric constant material prevent a manufacturing problem in that the rate of film deposition is lower than that of conventional thin films. Japanese laid-open patent publication No. 7-58036 discloses a thin-film vapor deposition apparatus which has been proposed to solve such a problem. The disclosed thin-film vapor deposition apparatus has a reaction chamber which develops therein an atmosphere different from the ambient atmosphere, a susceptor rotatably disposed in the reaction chamber for supporting a substrate on which a thin film will be formed, a levitating mechanism having a magnetic bearing for lifting the susceptor, and an actuator mechanism for rotating the susceptor at high speed. The susceptor is levitated by the levitating mechanism with magnetic bearings. Since a no contact-type bearing is used to support the susceptor, the rotational speed of the susceptor can be increased freely insofar as it is permitted by the strength of the susceptor to withstand centrifugal forces applied thereto. The susceptor is specifically rotatably supported by a motor, which is combined with magnetic bearings, having a solid rotor. The susceptor has a heater and a chuck mechanism, and also includes a slip ring for supplying electric energy thereto.
The vapor deposition of a thin film of a high dielectric constant material is characterized in that a material gas in a vapor phase should be kept in a very narrow, high temperature range. When the above conventional thin-film vapor deposition apparatus is employed to deposit a thin film of a high dielectric constant material, if there are undue temperature irregularities in the reaction chamber, then the material tends to be separated out, contaminating the reaction chamber, or resulting in an wasteful consumption of the material and a lowered yield.
Furthermore, since the susceptor and the heater rotate integrally with each other, the motor is subject to a large load and cannot easily be controlled. The heater is apt to deteriorate soon and its maintenance cycle is short because the heater is exposed at all times to the atmosphere in the reaction chamber. The solid rotor is heavy for its required level of mechanical strength, and cannot easily be controlled because it is likely to vibrate in a certain vibration mode. Inasmuch as the slip ring for supplying electric energy is liable to wear quickly, it tends to cause a failure and make the supply of electric energy unstable.
In the conventional thin-film vapor deposition apparatus, the temperature of the atmosphere in the reaction chamber and the temperature of the substrate have to be strictly controlled separately from each other. Since the reaction chamber incorporates temperature control means for separately controlling the temperatures, the reaction chamber is relatively complex in structure, leaving a comparatively low degree of freedom as to the designing of a feed path for loading and unloading substrates and a robot arm for guiding a substrate through the feed path to place the substrate on or remove the substrate from the susceptor.
In the conventional thin-film vapor deposition apparatus, furthermore, because the substrate is heated through the susceptor, the temperature of the substrate cannot quickly be changed. Consequently, even when the temperature of the substrate is detected as being improper, the temperature of the substrate cannot quickly be controlled to its appropriate value. As a result, desirable reactive conditions may not be established.