1. Field of the Invention
The present invention relates to an annealing furnace for processing the surface of an electronic device in the manufacturing process of the electronic device and, in particular, to a manufacturing apparatus and an annealing method of forming a thin insulating film by use of a heating lamp and to a manufacturing method of an electronic device.
2. Description of the Related Art
Large scale integrated (LSI) circuits have been becoming larger to improve their performance, and at the same time, finer elements have been advancing more rapidly than ever. When a metal-insulator-semiconductor field effect transistor (MISFET) is used, the electrical thickness of a gate insulating film is required to become thinner in correspondence to a decrease in a gate length to make the MISFET finer while controlling the threshold voltages thereof. Accordingly, a formation technique and optimization of thin gate insulating films have become extremely important. Especially, a technique of forming thin gate insulating films having an effective oxide thickness (EOT) of 2 nm or less is becoming increasingly important. Herein, EOT represents the thickness of the film converted into that of a silicon oxide (SiO2) film.
For example, a rapid thermal oxidation (RTO) or the like has been utilized as the method for forming ultra thin SiO2 or silicon oxy-nitride (SiOxNy, referred to as SiON hereinafter) films having an EOT of 2 nm or less on a semiconductor substrate such as silicon (Si), for example, (see U.S. Pat. No. 5,966,594 specification and Japanese Patent Application Laid-Open No. 6-349821). Moreover, for a method for forming an ultra thin insulating film with a thickness of 2 nm or less, an attempt has been made to use oxygen radical (O*) or oxygen ion at a low temperature of 500° C. or less.
If typical halogen lamps are used in the RTO, the temperature rises and falls slowly. Thus, it is difficult to form ultra thin insulating films with a thickness of 2 nm or less with great repeatability at a high oxidation temperature of, for example, approximately 1000° C. In addition, for SiON films which are formed by use of O* or oxygen ion at a low temperature, only insulating films which have high leakage current density of, for example, 100 A/cm2 under the condition of an EOT of 1 nm and an electric field of 4.5 MV/cm are obtained.
In a typical thermal oxidation process of Si substrates, first, a native oxide film on the surface of a Si substrate is removed by wet processing with dilute hydrofluoric acid (HF), ammonium fluoride (NH4F) or the like. However, a 0.5 nm to 1 nm thick native oxide film is formed in an atmosphere in advance of thermal oxidation. Although a Si substrate is installed in a lamp annealing apparatus in a shortest feasible time to prevent the formation of a native oxide film after wet processing, the 0.5 nm to 1 nm thick oxide film is formed by oxygen (O2), mixture gas of O2 and hydrogen (H2) or oxidation gas such as water vapor (H2O) in the atmosphere before the ambient temperature reaches the oxidation temperature.
The native oxide film, which is formed on the surface of the Si substrate, has inferior electrical characteristics. However, if the native oxide film is heated at, for example, 1050° C. or more, the electrical characteristics thereof are improved so that the characteristics are equivalent to those of a thermal oxide film. Thus, the thermal oxide film having good electrical characteristics can be formed in the RTO, but it is extremely difficult to control the thickness of the film to be 2 nm or less since the native oxide film is formed before the thermal oxidation process.