Abstract:
In order to form a first capacitor having a small capacitance and a second capacitor having a large capacitance on a substance with a minimum number of manufacturing steps, at least one of electrodes of the first capacitor and at least one of electrodes of the second capacitor are formed simultaneously.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present invention claims priority from Japanese Patent Application No.9-288467 filed Oct. 21, 1997, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a gallium-arsenide integrated circuit for use in a micro wave circuit and, particularly, to a technique for integrating a large capacitor formed of high dielectric constant material and a small capacitor formed of a dielectric material having relatively low dielectric constant. 
     2. Description of Related Art 
     In a gallium-arsenide (GaAs) integrated circuit for use in a micro wave circuit, a field effect transistor (FET), a large capacitor used for a power source or used as a coupling capacitor and a small capacitor necessary in matching circuits have been integrated. As a dielectric material between electrodes of a large capacitor, a thin film of SrTiO 3 (STO), BaTiO 3 , [Ba x Sr 1−x ]TiO 3 (BST), PbTiO 3  or [PbZr]TiO 3 (PZT), etc., whose relative dielectric constant is 100 or more is used. SiN x  having relative dielectric constant as low as about 7 is used as a dielectric material between electrodes of a small capacitor. 
     Japanese Patent Application Laid-open No. Hei 6-120425 discloses an integration of FET and capacitors. According to the disclosed technique, the FET is formed first and, then, the large capacitor is formed by using high dielectric constant material. 
     However, since, in the disclosed technique, the FET and the capacitor are formed separately, the number of manufacturing steps is increased. Further, in order to form the capacitor having different capacity, other manufacturing steps are required. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a semiconductor device which is an integrated circuit including capacitors having substantially different capacitances and a manufacturing method for manufacturing the semiconductor device with a smaller number of manufacturing steps. 
     According to a first aspect of the present invention, an upper electrode of a capacitor having small capacitance (referred to as “small capacitor”, hereinafter) and a lower electrode of a capacitor having large capacitance (referred to as “large capacitor”, hereinafter) are formed simultaneously. That is, after a film of low dielectric constant material is formed on a lower electrode of the small capacitor, the upper electrode of the small capacitor and the lower electrode of the large capacitor are formed simultaneously and a film of high dielectric constant material and the upper electrode are laminated on the lower electrode of the large capacitor. Thus, a semiconductor device in which the upper electrode of the small capacitor and the lower electrode of the large capacitor are formed as different regions of the same conductive film. It is enough that dielectric constant of the film of low dielectric constant material is lower than dielectric constant of the film of high dielectric constant material formed on the lower electrode of the large capacitor. The conductive film may be of a metal material or a conductive oxide material. 
     It is preferable to form an active elements on a substrate and form the lower electrode of the small capacitor simultaneously with the formation of electrodes of the active element. 
     In detail, at the time of formation of the electrode, for example, a gate electrode of the active element, the metal film is left on a portion of the substrate. The active element and the metal film are covered by an inter-layer film. An opening is formed in the inter-layer film such that a portion of the metal film is exposed. On the wafer, a dielectric film of a dielectric material having low dielectric constant (referred to as “low dielectric constant film”, hereinafter), a first conductive film, a dielectric film of a dielectric material having high dielectric constant (referred to as “high dielectric constant film”, hereinafter) and a second conductive film are formed in the order. The large capacitor is formed by processing the second conductive film, the high dielectric constant film and the first conductive film and the small capacitor is formed by removing the second conductive film and the high dielectric constant film correspondingly to the position of the metal film and processing the first conductive film. 
     According to a second aspect of the present invention, the dielectric material between the electrodes of the small capacitor has a double layer structure composed of a high dielectric constant film and a low dielectric constant film, the low dielectric constant film of the large capacitor is removed and the lower electrodes of the small and large capacitors are formed simultaneously and the upper electrodes of the small and large capacitor are formed simultaneously. That is, the lower electrode of the small capacitor and the lower electrode of the large capacitor are formed simultaneously and the high dielectric constant film and the low dielectric film are formed on these lower electrodes in the order. The low dielectric constant film in a region in which the large capacitor is to be formed is removed and the upper electrodes of the small and large capacitors are simultaneously formed on the low dielectric constant film in a region in which the small capacitor is to be formed and on the high dielectric constant film in the region in which the large capacitor is to be formed. Thus, the semiconductor device including the small and large capacitors having the simultaneously formed lower electrodes, the high dielectric constant film simultaneously formed as the inter-electrode dielectric layer, the low dielectric constant film formed in the inter-electrode layer of only the small capacitor and the upper electrodes formed simultaneously as the same conductive film. 
     It is preferable to form at least one active element and to form the lower electrodes of the small and large capacitors simultaneously with a formation of an electrode of the active element. 
     In detail, the active element is formed on the substrate, a metal film used to form the electrode of the active element is left on at least two portions of said substrate, the active element and the metal film are covered by an inter-layer film, openings are formed in the two regions of the inter-layer film to expose portions of the metal film, a second dielectric film having a high dielectric constant and a first dielectric film having a low dielectric constant are laminated, the first dielectric film is removed from one of the two regions, in which the large capacitor is to be formed, and the small capacitor and the large capacitors are formed in the region in which the low dielectric constant film exists and the large capacitor is formed in the region from which the low dielectric constant film is removed, by processing the conductive film. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent by reference to the following detailed description of the invention taken in conjunction with the accompanying drawings, in which: 
     FIGS. 1 a  to  1   e  are cross sections of a semiconductor device, showing manufacturing steps according to a first embodiment of the present invention; 
     FIGS. 2 a  and  2   b  are cross sections of a semiconductor device, showing manufacturing steps according to a second embodiment; and 
     FIGS. 3 a  to  3   e  are cross sections of a semiconductor device, showing manufacturing steps according to a third embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 a  to  1   e  are cross sections of a semiconductor device composed of a GaAs substrate and an FET, a small capacitor and a large capacitor formed on the substrate, showing manufacturing steps according to a first embodiment of the present invention. 
     According to the first embodiment of the present invention, the FET  12  having a gate electrode  12   a  and an ohmic electrode  12   b  is formed on the GaAs substrate  11  and, in forming the gate electrode  12   a  of the FET  12 , a metal film  13  is left on a portion of the GaAs substrate  11 , as shown in FIG. 1 a . In this embodiment, the gate electrode  1   2   a  and the metal film  13  are sputtered Au/WSi films. 
     Then, as shown in FIG. 1 b , the FET  12  and the metal film  13  are covered by a SiO 2  inter-layer film  14 , an opening is formed in the SiO 2  inter-layer film  14  to expose a portion of the metal film  13  and a low dielectric constant film  15  is formed on the whole wafer. In this embodiment, the low dielectric constant film  15  is a SiN x  film formed by plasma CVD. 
     Then, as shown in FIG. 1 c , a first conductive film  16 , a high dielectric constant film  17  and a second conductive film  18  are formed in lamination. The first conductive film  16  has a double layer structure having an upper Ti layer portion 20 nm thick and a lower Pt layer portion 70 nm thick and the high dielectric constant film  17  is of STO. The close adhesion between Ti and SiN x  is high and the reaction of Pt to STO is small. In this embodiment, the second conductive film  18  is a Pt of TiN film 100 nm thick. 
     Thereafter, as shown in FIG. 1 d , the second conductive film  18 , a large capacitor  20  is formed by processing the high dielectric constant film  17  and the first conductive film  16 . Simultaneously, the second conductive film  18  and the high dielectric constant film  17  are removed correspondingly to the metal film  13  and a small capacitor  19  is formed by further processing the first conductive film  16 . In this case, the first conductive film  16  forms an upper electrode of the small capacitor  19  and a lower electrode of the large capacitor  20 . 
     Then, as shown in FIG. 1 e , the large capacitor  20  is buried by an inter-layer film  21 . Then, through-holes are formed in respective portions of the inter-layer film  21  on the lower electrode (first conductive film  16 ) of the small capacitor  19  and the upper electrode (second conductive film  18 ) of the large capacitor  20  and through-holes are formed in the low dielectric constant film  15  and the inter-layer film, respectively, such that the gate electrode  12   a  of the FET and the lower electrode (metal film  13 ) of the small capacitor  19 , resulting in a wiring  22 . In the shown example, one of electrodes of the FET  12  is connected to the upper electrode of the small capacitor  19 , the lower electrode of the small capacitor  19  is connected to the lower electrode of the large capacitor  20  and the upper electrode of the large capacitor  20  is connected to other elements mounted on the same substrate. 
     FIGS. 2 a  and  2   b  are cross sections of a semiconductor device according to a second embodiment of the present invention, showing manufacturing steps subsequent to the manufacturing step shown in FIG. 1 d . In this embodiment, after the small capacitor and the large capacitor are formed, the wafer surface is flattened by burying them by an inter-layer film  23  as shown in FIG. 2 a  and, then, the wiring  22  is formed by forming through-holes in the positions of the respective electrodes of the FET, the small capacitor and the large capacitor, as shown in FIG. 2 b.    
     FIGS. 3 a  to  3   e  are cross sections of a semiconductor device having an FET, a small capacitor and a large capacitor, showing manufacturing steps according to a third embodiment of the present invention. 
     In this embodiment, the FET  32  having a gate electrode  32   a  and an ohmic electrode  32   b  is formed on the substrate  31  and, in forming the gate electrode  32   a  of the FET  32 , a metal film  33  is left on at least two regions of the substrate  31  for use as lower electrodes of the small and large capacitors, as shown in FIG. 3 a.    
     Then, as shown in FIG. 3 b , the FET  32  and the metal film  33  are covered by an inter-layer film  34 , an opening is formed in the inter-layer film  34  to expose a portion of the metal film  33 . 
     Then, as shown in FIG. 3 c , a high dielectric constant film  35  and a low dielectric constant capacitor  36  are laminated and the low dielectric constant film  36  in a region in which the large capacitor is to be formed is removed by dry-etching using a photo resist  37  as a mask. After the low dielectric constant film  36  is removed, the photo resist  37  is removed and a first conductive film  38  having thickness of 100 nm is formed as shown in FIG. 3 d.    
     Then, as shown in FIG. 3 e , the first conductive film  38 , the low dielectric constant film  36  and the high dielectric constant film  35  on other regions than the region in which the small and large capacitors are to be formed. Thus, a small capacitor  39  having the high dielectric constant film  35  and the low dielectric constant film  36  as a dielectric layer provided between the upper and lower electrodes and a large capacitor  40  having the high dielectric constant film  35  provided between the upper and lower electrodes are obtained. Finally, a wiring is formed in a similar manner to the steps shown in FIG. 1 e  or  2   b.    
     As described hereinbefore, according to the present invention in which at least one of electrodes of a first capacitor and at least one of electrodes of a second capacitor having dielectric constant different from that of the first capacitor are formed simultaneously, the manufacturing process can be simplified compared with the case where these capacitors are formed separately. Particularly, when a lower electrode of a capacitor and an upper electrode of another capacitor are formed simultaneously, the manufacturing process can be substantially simplified compared with the conventional manufacturing process.