1. Field of the Invention
The present invention relates to a capacitor in a semiconductor device and a manufacturing method thereof, and more particularly, to a capacitor including a perovskite series dielectric film and a manufacturing method thereof.
2. Description of the Related Art
As integration of semiconductor devices progresses, the area occupied by capacitors is increasingly reduced. Thus, various approaches have been made to obtain high and stable capacitance in a relatively small area. These approaches include a method of using dielectric films in the metal oxide series such as tantalum oxide (Ta2O5), aluminum oxide (Al2O3), and titanum oxide (TiO2), or dielectric films in the perovskite series such as BST((Ba, Sr) TiO3), SBT((SrBi2Ta2O9), and PZT((Pb,Zr)TiO3). These dielectric films have dielectric constants of tens to hundreds times higher than conventional dielectric films made of conventional silicon nitride or silicon oxide film or composite film thereof have.
Among them, using BST as a dielectric film in dynamic random access memory (DRAM) or ferroelectric RAM (FRAM) has been continuously pursued. However, in the case of BST, when it is deposited as a thin film for a capacitor in high integrated semiconductor devices, there is a limitation in reducing the thickness of the film due to poor leakage current characteristics. This limits high integration of semi conductor devices using BST as a dielectric film of a capacitor.
Accordingly, regardless of the causes of poor leakage characteristics of BST dielectric film, methods of reducing the leakage current of a BST dielectric film capacitor are under study. For example, a method of forming buffer layers has been proposed by U.S. Pat. No. 5,471,364. In this case, the buffer layers are made of low dielectric constant materials formed between a BST dielectric film and an upper electrode or a lower electrode but that exhibit good leakage current characteristics. In addition, the buffer layers are thinner than the BST dielectric film. Furthermore, another method is proposed by U.S. Pat. No. 5,731,220 to reduce leakage currents. In this method, a small amount of erbium (Er) is added to a BST precursor solution with the molar ratio of the erbium to titanium in the BST precursor solution between 0.01-0.05 to deposit a BST film.
A method of interposing buffer layers, however, has a problem in that forming a dielectric film of a relatively low dielectric constant results in a reduction in the overall capacitance. Furthermore, a method of adding a small amount of Er has many problems in mass production because the process is complicated. Also, changes in capacitance characteristics resulting from changes in process variables are difficult to predict. Additionally, in U.S. Pat. No. 5,731,220, only the importance of reducing the leakage currents by addition of ER has been described, but the implementation of the invention has not been successful because the mechanism for such reduction is not clearly identified.
Accordingly, there is a need to improve the method of depositing a perovskite series dielectric film, e.g., a BST film, to avoid the problems described above, for example, reduction in overall capacitance, complicated process steps, and unpredictable changes in capacitor dielectric characteristics caused by changes in process conditions, particularly, during actual mass production.
To solve the above problems, the present invention provides a capacitor having a perovskite series dielectric film, in which the leakage current characteristics are improved.
In addition, the present invention provides a simplified method of manufacturing a perovskite series dielectric capacitor which improves the leakage current characteristics of the dielectric film.
Accordingly, the present invention reduces leakage currents by containing CuXO or copper in a perovskite series dielectric film. That is, a capacitor according to the present invention includes a perovskite series dielectric film disposed between upper and lower electrodes made of conductive material, wherein the perovskite series dielectric film contains CuXO or copper. The CuXO or copper is preferably contained in the grain boundary of the perovskite series dielectric film.
More preferably, the perovskite series dielectric film is a barium strontium titanate (BST) film or a PZT film.
Also, the present invention provides a method of manufacturing a perovskite series dielectric film capacitor, including penetrating the perovskite series dielectric film with CuxO or copper. According to a method of manufacturing a general perovskite series dielectric film capacitor, after depositing a conductive material on a substrate to form a lower electrode and depositing a perovskite series dielectric film on the lower electrode, a conductive material is deposited on the perovskite series dielectric film to form an upper electrode. The method of manufacturing the perovskite series dielectric film capacitor according to the invention has steps similar to the method of manufacturing the general perovskite series dielectric film capacitor, further including unique steps of depositing CuxO (x=1 or 2) on the perovskite series dielectric film to form a CuxO film, and performing a heat treatment on the substrate to permit CuxO or copper of the CuxO film to penetrate the perovskite series dielectric film.
In this case, the CuXO film may be formed sufficiently thin that substantially all CuXO or copper penetrates the perovskite series dielectric film to leave substantially no residue on the perovskite series dielectric film after the heat treatment. This is for preventing a reduction in the overall capacitance caused by CuxO film having a relatively low dielectric constant compared to the perovskite series film. Furthermore, the heat treatment is performed before, after, or both before and after forming the upper electrode.
It is believed that the prevention of leakage current flowing through a grain boundary of a columnar crystal structure of the perovskite series dielectric film is made possible by permitting CuXO or copper to penetrate the grain boundary of the perovskite series dielectric film.