The present invention generally relates to substrate processing technology and more particularly to a substrate processing method of forming a high-K dielectric-film on a substrate.
With the progress in the technology of device miniaturization, production of ultra-fine semiconductor devices having a MOS transistor with a gate length of less than 0.1 μm is becoming possible.
To improve the operational speed of such ultra-fine semiconductor devices further by way of reduction of gate length of the MOS transistor, there is a need of reducing the thickness of the gate insulation film according to scaling law. For example, in the case of using a conventional silicon oxide film as the gate insulation film, it is necessary to reduce the thickness of the gate insulation film to 1.7 nm or less. However, when the thickness of the oxide film is decreased like this, there occurs an increase of gate leakage current through the oxide film by tunneling effect, and there is caused deterioration of device characteristics such as increase of electric power consumption, and the like.
Thus, it has been studied conventionally to use a high-K dielectric film such as the film of Ta2O5, ZrO2, HfO2 or Al2O3, and the like, for the gate insulation film, in place of the conventional silicon oxide film. However, such a high-K dielectric film has the properties very much different from those of the silicon oxide film used conventionally in the semiconductor technology, and there remain numerous problems to be solved in order to establish the technology of using such a high-K dielectric film as the gate insulation film.
Contrary to this, a silicon nitride film is the material that has been used in the conventional semiconductor process and has various advantageous features such as large specific dielectric constant of twice as large as that of a silicon oxide film. Further, a silicon nitride film has the capability of blocking diffusion of dopant elements in the gate electrode into the silicon substrate effectively. Thus, silicon nitride is thought as being a promising material for the gate insulation film of the next generation high-speed semiconductor devices.
Conventionally, a silicon nitride film has been formed by a plasma CVD process. However, such a CVD nitride film generally shows poor interface characteristics and the user thereof for a gate insulation film has been thought inappropriate. Because of this, there has been no attempt conventionally to use a nitride film for the gate insulation film.
On the other hand, there has been a proposal recently about the technology of converting the surface of a silicon oxide film to an oxynitride film by introducing a nitrogen gas or a mixture of a nitrogen gas and a hydrogen gas or a gas containing nitrogen such as NH3 into microwave-excited rare gas plasma of Ar, Kr, He and the like, to form N radicals or NH radicals. (Katsuyuki Sekine, Yuji Sato, Masaki Hirayama and Tadahiro Ohmi, J. Vac. Sci. Technol. A17(5), September/October 1999, pp.3129-3133; Takuya Sugawara, Toshio Nakanishi, Masaru Sasaki, Shigenori Ozaki, Yoshihide Tada, Extended Abstracts of Solid State Devices and Materials, 2002, pp.714-715). The oxynitride film thus formed has interface characteristics comparable to or superior to that of a silicon thermal oxide film, and thus, the oxynitride film is thought as being a promising material for the gate insulation film of the next generation high-speed semiconductor devices. Further, there is proposed a plasma nitridation technology that directly converts the surface of a silicon substrate by a nitriding processing by using such microwave plasma. Further, there is the technology of plasma oxidation that directly oxidizes a silicon substrate surface by introducing a gas containing oxygen into the foregoing rare gas plasma.
In the case of conducting a plasma nitridation processing subsequently to oxidizing processing in the same apparatus, on the other hand, there appears a problem in that oxidization occurs simultaneously to the nitridation due to the residual oxygen, which has been introduced into a processing apparatus previously for the oxidation processing or for other processing and remaining in the processing ambient, and there occurs an increase of thickness of the gate insulation film formed by such a nitridation processing. When such increase of the film thickness occurs, the desired improvement of operational speed of the semiconductor device according to the scaling low is not attained. This problem of increase of film thickness of the gate insulation film becomes particularly serious when the nitridation processing is conducted for long time in order to cause more diffusion of the introduced nitrogen atoms in the thickness direction of the film or in the case in which the thickness of the base oxide film is small. (Takuya Sugawara, et al., op. cit.; C. C. Chen, M. C. Yu, M. F. Wang, T. L. Lee, S. C. Chen, C. H. Yu and M. S. Liang, 2002 7th International Symposium on Plasma and Process Induced Damage, pp.41-44).
Further, even in the case the oxidation processing and the nitridation processing are conducted in different apparatuses, a similar problem of increase of film thickness of the gate insulation film by oxidation can be caused also when water is adsorbed to the substrate. In such a case, water is transported from the oxidation processing apparatus to the nitridation processing apparatus together with the substrate to be processed.