This invention relates to a semiconductor device containing a capacitor wherein a metal oxide of tantalum pentoxide, and the like, is used as dielectrics and a method for manufacturing thereof.
In semiconductor devices having LSI such as dynamic random access memory (DRAM), etc., the capacitor area is reduced with higher integration. Thus, there is studied application of metal oxide dielectrics such as tantalum pentoxide (Ta2O5) having high permittivity of several tens in place of the silicon oxide which has been used as capacitor dielectric film. Further, in gigabit generation semiconductor devices wherein the minimum processing size is 0.15 μm or less, it is necessary to form a dielectric film by using a CVD (chemical vapor deposition) method on a surface of deep hole or concave in order to enhance capacitance, even if metal oxide dielectrics having a higher permittivity are used.
High dielectric Ta2O5's applied so far can be summarized as follows.
1) In a capacitor using MIS (metal-insulator-semiconductor)-Ta2O5 film, the permittivity increases to 40 at most depending on conditions of CVD method and heat treatment. It is estimated that the crystal phase transfers to a δ phase, but this is not identified precisely.
2) MIM (metal-insulator-metal)-Ta2O5 film has a large permittivity of from 40 (formed by CVD) to 80 (formed by sputtering) depending on film preparation and heat treatment conditions. It is estimated that the crystal phase transfers to a δ phase, but this is not identified.
3) Ta2O5 film obtained by adding TiO2 or Al2O3 and heat-treated at about 1400° C. has a high permittivity of 126 at most. The crystal phase is monoclinic H′ phase or a mixture, respectively.
However, the high dielectric Ta2O5's mentioned above have problems mentioned below, respectively.
First, in the case of MIS-Ta2O5 formed on a silicon nitride film, the permittivity is higher than a typical value of 25 of the L phase, but retains at about 40. Next, in the case of Ta2O5 formed on Pt by a sputtering method, the permittivity is as high as 75 or more, but the preparation temperature is as high as 550° C. Considering application to devices, for example, in order to form a Ta2O5 film uniformly on inner walls of a deep hole by using a CVD method, it is required a technology to form the film at a temperature of 500° C. or less. In the case of forming high dielectric Ta2O5 on Ru, a heat treating temperature of 750° C. or higher is necessary. Considering application to device processes, technology of reducing to the temperature of 700° C. or less is required. In addition, properties of these MIM and MIS capacitors are largely dependent on preparation conditions and heat treating conditions, and lack in reproducibility. As to the addition of TiO2 and Al2O3, since high temperature heat treatment of 1400° C. is necessary, application to the device processes is impossible.