Dielectric film and method for forming the same

Abstract

After an underlying layer, made of a single crystal metal material, has been formed on a semiconductor layer, part or all of the underlying layer is changed into a metal oxide layer by supplying oxygen thereto from above the underlying layer. Then, a ferroelectric or high-dielectric-constant film is further formed on the metal oxide layer. Since the film made of a metal material is formed on the semiconductor layer, a silicon dioxide film or the like is not formed easily. Thus, a dielectric film, which includes an underlying layer with a high dielectric constant and has a large capacitance per unit area, can be obtained. Various defects such as interface states in the semiconductor layer can also be reduced advantageously if these process steps are performed after a thermal oxide film has been formed on the semiconductor layer.

What is claimed is:  
     
         1 . A dielectric film comprising: 
 an underlying layer toned on a crystalline semiconductor layer and made of a metal material, the affinity of the metal material for oxygen being higher than affinity of a semiconductor material of the semiconductor layer for oxygen; and    a crystalline CeO 2  film toned on the underlying layer.    
     
     
         2 . The dielectric film of  claim 1 , wherein at least part of the underlying layer has been oxidized.  
     
     
         3 . The dielectric film of  claim 1 , wherein the metal material for the underlying layer is at least one material selected from the group consisting of Mg, Zr, Y, Ce, La and Bi.  
     
     
         4 . A dielectric film comprising: 
 an underlying layer formed on a crystalline semiconductor layer and made of a compound oxide containing a metal element and a semiconductor material for the semiconductor layer; and    a crystalline CeO 2  layer formed on the underlying layer.    
     
     
         5 . The dielectric film of  claim 4 , wherein the metal material for the underlying layer is at least one material selected from the group consisting of Mg, Zr, Y, Ce, La and Bi.  
     
     
         6 . A dielectric film comprising: 
 an underlying layer formed on a crystalline semiconductor layer and made of a crystalline metal oxide that substantially lattice-matches crystals of the semiconductor on the principal surface of the semiconductor layer; and    a crystalline CeO 2  layer formed on the underlying layer.    
     
     
         7 . The dielectric film of  claim 2 , wherein the metal material for the underlying layer is at least one material selected from the group consisting of Mg, Zr, Y, Ce, La and Bi.  
     
     
         8 . A dielectric film comprising: 
 an underlying layer formed on a crystalline semiconductor layer and made of at least one metal material selected from the group consisting of Mg, Zr, Y, Ce, La and Bi; and    a ferroelectric layer formed on the underlying layer.    
     
     
         9 . The dielectric film of  claim 8 , wherein at least part of the underlying layer has been oxidized.  
     
     
         10 . A dielectric film comprising: 
 an oxide layer formed on a crystalline semiconductor layer and made of an oxide of a semiconductor material for the semiconductor layer;    an underlying layer formed on the oxide layer and made of an oxide of a metal material; and    a ferroelectric layer formed on the underlying layer.    
     
     
         11 . The dielectric film of  claim 10 , wherein the metal material for the underlying layer is at least one material selected from the group consisting of Mg, Zr, Y, Ce, La and Bi.