Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having insulated gate
Reexamination Certificate
1997-12-11
2001-10-02
Whitehead, Jr., Carl (Department: 2822)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having insulated gate
C438S003000, C438S396000
Reexamination Certificate
active
06297085
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains to a method for manufacturing a ferroelectric capacitor (particularly, the capacitor of a semiconductor memory cell having a lead zirconate titanate (PZT) film) and a method for manufacturing a ferroelectric memory device.
BACKGROUND OF THE INVENTION
For example, an ONO film formed by sequentially laminating SiO2, Si3N4, and SiO2 is used as an insulating film (dielectric film) for forming the capacitor of a dynamic RAM memory cell.
However, since the effective specific inductive capacity of the ONO film is as low as about 5, under the area restriction, a complicated shape is required to make the capacitor's dielectric film thinner and to expand the area when the film is used for a memory with a capacity of 256 Mb or larger. As a result, the process becomes very complicated.
On the other hand, the ferroelectric material with a perovskite crystal structure becomes noticeable as a material to be used in the future to form the insulating film of the capacitor for dynamic RAM because it has a very high specific inductive capacity ranging from a level of several hundred to several thousand.
The sol-gel method, CVD (chemical vapor deposition) method, sputtering method, etc., can be used to form the PZT film represented by Pb(Zr, Ti)O3 in the ferroelectric material. Among these methods, the sputtering method is the most appropriate one for mass production because it can uniformly form a film on an extensive flat portion without being affected by the roughness of the substrate.
However, when the PZT film is formed using the sputtering method, the density of the formed PZT crystallized nuclei on the substrate is low, and PbO evaporates in the formed film because of the low crystallinity. Consequently, it is relatively difficult to obtain a PZT capacitor with good electrical characteristics.
Platinum (Pt) is ordinarily used as the electrode substance for the PZT capacitor. However, since Pt is unable to reduce the silicon oxidized film, it cannot be directly adhered to the film. Therefore, after a Ti bonding layer with a thickness of about 50 nm is formed on the silicon oxidized film, Pt is deposited using the sputtering method or the electron beam heating deposition method.
When the PZT film is formed on said Pt using the sol-gel method, Ti diffuses through the Pt grain boundary to form TiO2 at the Pt-PZT boundary. Said TiO2 acts as the crystal nucleus when the PZT film is formed. In the sputtering method, however, since the evaporation of PbO is severe, it is difficult to form a PZT film better than that formed using the sol-gel method.
On the other hand, it is known that an electrode made of an oxidizing metal, such as iridium (Ir), or an electroconductive oxide, such as iridium oxide (IrO2), can be used to improve the polarization fatigue characteristics property of the PZT capacitor. However, when these substances are present on the substrate, the effect of forming nuclei by means of Ti diffusion cannot be realized even when a Ti layer is formed.
The purpose of this invention is to provide a method that can be used to form a high-quality ferroelectric film by forming good nuclei when using the sputtering method to manufacture a PZT capacitor or other ferroelectric capacitors using Ir or other electrode substances in addition to Pt for the electrode.
SUMMARY OF THE INVENTION
This invention provides a method for manufacturing a ferroelectric capacitor characterized by the following facts: this method is used to manufacture a ferroelectric capacitor comprising a first electrode made of iridium, etc., a ferroelectric film made of lead zirconate titanate, etc., and formed on the first electrode, and a second electrode made of iridium, etc., and formed on the ferroelectric film; this manufacturing method has the following steps:
a step in which at least one type of constitutive metal element (such as titanium) of the aforementioned ferroelectric film or its oxide is deposited on the aforementioned first electrode to form a metal or metal oxide film (such as a titanium film);
a step in which the oxide of a metal element (such as the oxide of lead: PbO), which is a type of constitutive metal element of the aforementioned ferroelectric film and is different from the aforementioned metal or metal oxide film, is deposited on the aforementioned metal or metal oxide film;
a step in which an oxide film (such as lead titanate: PbTiO3) consisting of the deposited metal oxide (such as lead oxide) and the metal (such as titanium) of the aforementioned metal or metal oxide film, is generated on the aforementioned first electrode;
a step in which the generated oxide film is used as the crystal nucleus, and in which the constitutive material (such as lead zirconate titanate: Pb(Ti, Zr)O3) of the aforementioned ferroelectric film is deposited on the oxide film to form the aforementioned ferroelectric film; and
a step in which the aforementioned second electrode is formed on the ferroelectric film. This invention also provides a method for manufacturing a ferroelectric memory, characterized by the fact that it includes a step in which a ferroelectric capacitor is formed in a memory cell using the aforementioned manufacturing method.
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Aoki Katsuhiro
Fukuda Yukio
Murayama Ikuko
Nishimura Akitoshi
Numata Ken
Jr. Carl Whitehead
Kempler William B.
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
Vockrodt Jeff
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