Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a divisional of U.S. patent application Ser. No. 10/093,114, filed Mar. 7, 2002 now U.S Pat. No. 6,617,666, the entire contents of which are incorporated by reference, and which is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2001-065253, filed Mar. 8, 2001, the entire contents of which are incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a semiconductor device with an MIM (Metal Insulating Metal) capacitor, and a process for manufacturing the semiconductor device. 
   2. Description of the Related Art 
   Semiconductor devices provided with Cu wiring of a damascene structure and MIM capacitors are now available. 
     FIG. 28  is a sectional view of a conventional semiconductor device. As shown in  FIG. 28 , a via hole  43  and a wire  44 , which are made of, for example, Cu, are provided in a film  41  of a low dielectric constant and a film  42  of a high dielectric constant. A Cu-diffusion-preventing film  45  is provided on the high dielectric film  42  and wire  44 , and a capacitor  49  is provided on a selected portion of the Cu-diffusion-preventing film  45 . The capacitor  49  is formed of a lower electrode  46 , a dielectric film  47  and an upper electrode  48 . An insulating film  50  is provided on the capacitor  49  and Cu-diffusion-preventing film  45 . The surface of the insulating film is flattened by CMP (Chemical Mechanical Polishing). 
   In such conventional semiconductor devices, it is desirable that the insulating film  50  be formed of a low dielectric film in order to reduce the parasitic capacitance between wires. 
   However, since the low dielectric film is a rough film, a crack may occur if the surface of the film is flattened. Therefore, it is very difficult to level, by CMP, the surface of an insulating film  50  formed of a low dielectric film. To avoid this, a high dielectric film could be used as the insulating film  50 , as thus would reduce the formation of cracks under CMP. 
   However, since the capacitor  49  is provided on a selected portion of the Cu-diffusion-preventing film  45 , there is a step corresponding to the thickness of the capacitor  49  between the area provided with the capacitor and the area without. To eliminate the step caused by the presence of the capacitor  49 , it is necessary to form an insulating film  50  in the area with no capacitor on the Cu-diffusion-preventing film  45 . Thus, as stated above, a high dielectric film or insulating film  50  is provided on the film  45  to surround the capacitor  49 . The provision of the high dielectric insulating film  50  to fill the step caused by the capacitor  49  inevitably increases the parasitic capacitance between wiring layers. 
   As described above, in the conventional semiconductor device, it is very difficult to level the surface of the insulating film  50  by CMP. 
   BRIEF SUMMARY OF THE INVENTION 
   According to a first aspect of the present invention, there is provided a semiconductor device comprising: a first insulating film comprising an opening; a capacitor formed at a selected position in the opening; a second insulating film formed at least in the opening; and a third insulating film formed on the second insulating film. 
   According to a second aspect of the present invention, there is provide a process of manufacturing a semiconductor device, comprising: forming a first insulating film; removing a selected portion of the first insulating film, thereby forming an opening; forming a capacitor at a selected position in the opening; forming a second insulating film at least in the opening; and forming a third insulating film on the second insulating film. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       FIGS. 1 ,  2 ,  3 ,  4 ,  5 ,  6 ,  7 ,  8  and  9  are sectional views illustrating the steps of a process for manufacturing a semiconductor device according to a first embodiment of the invention; 
       FIG. 10  is a plan view illustrating the semiconductor device according to the first embodiment of the invention; 
       FIGS. 11 ,  12  and  13  are sectional views illustrating the steps of a process for manufacturing another semiconductor device according to the first embodiment of the invention; 
       FIGS. 14 ,  15 ,  16 ,  17 ,  18 ,  19 ,  20 ,  21  and  22  are sectional views illustrating the steps of a process for manufacturing a semiconductor device according to a second embodiment of the invention; 
       FIGS. 23 ,  24  and  25  are sectional views illustrating the steps of a process for manufacturing another semiconductor device according to the second embodiment of the invention; 
       FIGS. 26 and 27  are sectional views illustrating another semiconductor device according to the first and second embodiment of the invention; and 
       FIG. 28  is a sectional view illustrating a conventional semiconductor device. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Reference will now be made in detail to the presently embodiments of the invention as illustrated in the accompanying drawings, in which like reference characters designate like or corresponding parts in all drawings. 
   In the embodiments of the invention, a “low dielectric film” means a film having a relative dielectric constant of about 4.0 or more, while a “high dielectric film” means a film having a higher relative dielectric constant than a low dielectric film. 
   [First Embodiment] 
   In a first embodiment of the invention, an opening is provided in an insulating film, i.e., a low dielectric film, and an MIM (Metal Insulating Metal) capacitor is formed in the opening. 
     FIGS. 1-9  are sectional views illustrating the steps of a process for manufacturing a semiconductor device according to the first embodiment. A description will now be given of the process for manufacturing the semiconductor device according to the first embodiment. 
   Firstly, as shown in  FIG. 1 , a high dielectric film  12  having a higher relative dielectric constant than a low dielectric film  11  is formed on the low dielectric film  11 . Subsequently, using a damascene process, a via hole  13  and a first wire  14 , which are made of, for example, Cu, are formed in the low and high dielectric films  11  and  12 . Thereafter, a Cu-diffusion-preventing film  15  made of, for example, SiN is formed on the first wire  14  and high dielectric film  12  by sputtering. An insulating film  16  as a low dielectric film is formed on the Cu-diffusion-preventing film  15 . The thickness of the insulating film  16  is formed to, for example, 270 nm. 
   Referring to  FIG. 2 , the insulating film  16  is coated with a resist film  17 , which is patterned by lithography. Using the patterned resist film  17  as a mask, the insulating film  16  is patterned by RIE (Reactive Ion Etching), thereby forming an opening  18 . Then, the resist film  17  is removed. 
   Referring to  FIG. 3 , a lower electrode film  19  made of, for example, TiN is formed in the opening  18  and on the insulating film  16  by sputtering, and a dielectric film  20  made of, for example, Ta 2 O 2  is formed on the lower electrode film  19 . Further, an upper electrode film  21  made of, for example, TiN is formed on the dielectric film  20 . The thicknesses of the lower electrode film  19 , dielectric film  20  and upper electrode film  21  are formed to, for example, 60 nm, 50 nm and 50 nm, respectively. 
   Referring to  FIG. 4 , the upper electrode film  21  is coated with a resist film  22 , which is patterned by lithography. After that, using the patterned resist film  22  as a mask, the upper electrode film  21  is patterned by RIE such that it remains in the opening  18 . Then, the resist film  22  is removed. 
   Referring to  FIG. 5 , the upper electrode film  21  and dielectric film  20  are coated with a resist film  23 , which is patterned by lithography. After that, using the patterned resist film  23  as a mask, the dielectric film  20  and lower electrode film  19  are patterned by RIE such that they have surface areas larger than that of the upper electrode film  21 , and remain in the opening  18 . As a result, an MIM capacitor  24 , composed of the lower electrode film  19 , dielectric film  20  and upper electrode film  21 , is formed in the opening  18 . Then, the resist film  23  is removed. 
   Referring to  FIG. 6 , a first interlayer film  25  is formed in the opening  18  and on the insulating film  16  by PECVD (Plasma Enhanced Chemical Vapor Deposition). The first interlayer film  25  is a high dielectric film form of SiO 2 , for example. However, the film  25  is not limited to a high dielectric film, as long as it is an insulating film that is formed at a low temperature and can be subjected to CMP. 
   Referring to  FIG. 7 , the first interlayer film  25  is flattened by CMP (Chemical Mechanical Polishing) until the surface of the insulating film  16  is exposed. At this time, it is desirable that a marginal interlayer portion X of about 500 Å to 1000 Å be left on the capacitor  24  so that the surface of the capacitor  24  will not be exposed. In other words, it is sufficient if the capacitor  24 , composed of the lower electrode film  19 , dielectric film  20  and upper electrode film  21 , is made thinner than the insulating film  16 . 
   Referring to  FIG. 8 , a second interlayer film  26  is formed on the first interlayer film  25  and insulating film  16 , and a third interlayer film  27  is formed on the second interlayer film  26 . The second interlayer film  26  is a low dielectric film such as an FSC (fluorine Spin Glass) film, while the third interlayer film  27  is a high dielectric film, formed of SiO 2 , for example. 
   Referring to  FIG. 9 , the first, second and third interlayer films  25 ,  26  and  27 , etc. are removed to form via holes and grooves for wires. Thereafter, a barrier metal layer (not shown) is deposited in via holes and wire grooves, and is plated with a Cu film. The barrier metal layer and Cu film are flattened by CMP, thereby forming via holes  28   a,    28   b  and  28   c  and second wires  29   a,    29   b  and  29   c.  The via hole  28   a  and second wire  29   a  are connected to the lower electrode film  19  on the capacitor  24 , the via hole  28   b  and second wire  29   b  are connected to the upper electrode film  21  on the capacitor  24 , while the via hole  28   c  and second wire  29   c  are connected to the first wire  14 . Subsequently, a Cu-diffusion-preventing film  30  is formed on the third interlayer film  27  and second wires  29   a,    29   b  and  29   c.    
     FIG. 10  is a plan view illustrating the semiconductor device according to the first embodiment of the invention. As shown in  FIG. 10 , the opening  18  is formed in the insulating film  16 , and the capacitor  24  is formed in the opening  18 . As a result, the capacitor  24  is surrounded by the insulating film  16 , and the first interlayer film  25  is formed in a clearance in the opening  18 .  FIG. 7  is a sectional view taken along line VII—VII of FIG.  10 . 
   In the above-described first embodiment, the first interlayer film  25  on the capacitor  24  is a film (e.g. a high dielectric film) that does not easily crack even if it is subjected to CMP. Accordingly, the surface of the first interlayer film  25  on the capacitor  24  can be flattened by CMP. 
   Further, since the opening  18  is formed in the insulating film  16  and receives the capacitor  24 , the insulating film  16  surrounds the capacitor  24 . Thus, the first interlayer film  25  as a high dielectric film is provided only in the opening  18 , which further reduces the parasitic capacitance between the wires. 
   Also, the second interlayer film  26  as a low dielectric film is mostly formed around the via holes  28   a,    28   b  and  28   c  and second wires  29   a,    29   b  and  29   c,  the parasitic capacitance between the wires can be further reduced. 
   Furthermore, the provision of the insulating film  16  around the capacitor  24  enables the step due to the capacitor  24  to be reduced. In other words, when the first interlayer film  25  is formed on the capacitor  24 , the shape of the capacitor  24  does not significantly influence the first interlayer film  25 . Accordingly, the surface of the first interlayer film  25  on the capacitor  24  can be more easily flattened than in the conventional case. 
   Also, since the insulating film  16  is a low dielectric film, the parasitic capacitance between the wires can be further reduced. 
   Moreover, the Cu-diffusion-preventing film  15  provided under the capacitor  24  prevents Cu from diffusing from the second wires  29   a,    29   b  and  29   c  and via holes  28   a,    28   b  and  28   c  into an element (not shown) located below and contaminating it. 
   Further, the margin X prepared for flattening the first interlayer film  25  by CMP prevents the surface of the capacitor  24  from being damaged, thereby enhancing the performance of the capacitor  24 . 
   The first interlayer film  25  may be an organic insulating film formed by coating. In this case, the surface of the organic insulating film can be substantially flattened when it is coated, and therefore, the leveling process using CMP shown in  FIG. 7  can be omitted. This means that a low dielectric film can be used as the first interlayer film  25 , which cannot be realized in light of the process of CMP in the prior art. Thus, the use of a coating-type film as the first interlayer film  25  can reduce the capacitance between the wires, as well as the number of required process steps. 
   In addition, if the surface of the first interlayer film  25  is sufficiently flattened by CMP in the process of  FIG. 7 , it is not necessary to level the first interlayer film  25  until the surface of the insulating film  16  is exposed. However, the thinner the remaining portion of the first interlayer film  25  as a high dielectric film, the lower the capacitance between the wires. In light of this, it is desirable to level the first interlayer film  25  until the surface of the insulating film  16  is exposed. 
   In the first embodiment, another Cu-diffusion-preventing film may be formed on the capacitor  24  to protect it. In this case, at first, the capacitor  24  is formed as shown in FIG.  5 . Subsequently, a Cu-diffusion-preventing film  31  is formed on the capacitor  24  and insulating film  16 , and the first interlayer film  25  is formed on the Cu-diffusion-preventing film  31 , as is shown in FIG.  11 . Then, the first interlayer film  25  is flattened by CMP until the surface of the insulating film  16  is exposed, as is shown in FIG.  12 . After that, the structure as shown in  FIG. 13  is formed by process steps similar to those of the first embodiment. In this structure, the Cu-diffusion-preventing film  31  on the capacitor  24  prevents Cu from diffusing from the second wires  29   a,    29   b  and  29   c  and via holes  28   a,    28   b  and  28   c  into the dielectric film  20  of the capacitor  24  and contaminating it. 
   [Second Embodiment] 
   In a second embodiment, the insulating film having the opening is a Cu-diffusion-preventing film. 
     FIGS. 14  to  22  are sectional views illustrating a process for manufacturing a semiconductor device according to the second embodiment. The process of manufacturing the semiconductor device of the second embodiment will be described. In this process, only steps differing from those of the first embodiment will be described. 
   Referring first to  FIG. 14 , a via hole  13  and a first wire  14 , which are made of, for example, Cu, are formed in low and high dielectric films  11  and  12 , as in the first embodiment. Thereafter, a Cu-diffusion-preventing film  15  made of, for example, SiN is formed on the first wire  14  and high dielectric film  12  by sputtering. The thickness of the Cu-diffusion-preventing film  15  is formed to, for example, 270 nm. 
   Referring to  FIG. 15 , the Cu-diffusion-preventing film  15  is coated with a resist film  17 , which is patterned by lithography. Using the patterned resist film  17  as a mask, the Cu-diffusion-preventing film  15  is patterned by RIE, thereby forming an opening  18 . Then, the resist film  17  is removed. 
   Referring to  FIG. 16 , a lower electrode film  19  made of, for example, TiN is formed in the opening  18  and on the Cu-diffusion-preventing film  15  by sputtering, and a dielectric film  20  made of, for example, Ta 2 O 2  is formed on the lower electrode film  19 . Further, an upper electrode film  21  made of, for example, TiN is formed on the dielectric film  20 . The thicknesses of the lower electrode film  19 , dielectric film  20  and upper electrode film  21  are set to, for example, 60 nm, 50 nm and 50 nm, respectively. 
   Referring to  FIG. 17 , the upper electrode film  21  is coated with a resist film  22 , which is patterned by lithography. After that, using the patterned resist film  22  as a mask, the upper electrode film  21  is patterned by RIE such that it remains in the opening  18 . Then, the resist film  22  is removed. 
   Referring to  FIG. 18 , the upper electrode film  21  and dielectric film  20  are coated with a resist film  23 , which is patterned by lithography. After that, using the patterned resist film  23  as a mask, the dielectric film  20  and lower electrode film  19  are patterned by RIE such that they have surface areas larger than that of the upper electrode film  21  and remain in the opening  18 . As a result, an MIM capacitor  24 , composed of the lower electrode film  19 , dielectric film  20  and upper electrode film  21 , is formed in the opening  18 . Then, the resist film  23  is removed. 
   Referring to  FIG. 19 , a first interlayer film  25  is formed in the opening  18  and on the Cu-diffusion-preventing film  15  by PECVD. The first interlayer film  25  is a high dielectric film formed of SiO 2 , for example. However, the film  25  is not limited to a high dielectric film, as long as it is an insulating film that is formed at a low temperature and can be subjected to CMP. 
   Referring to  FIG. 20 , the first interlayer film  25  is flattened by CMP until the surface of the Cu-diffusion-preventing film  15  is exposed. At this time, it is desirable that a marginal interlayer portion X of about 500 Å to 1000 Å be left on the capacitor  24  so that the surface of the capacitor  24  will not be exposed. In other words, it is sufficient if the capacitor  24 , composed of the lower electrode film  19 , dielectric film  20  and upper electrode film  21 ,is made thinner than the Cu-diffusion-preventing film  15 . 
   Referring to  FIG. 21 , a second interlayer film  26  is formed on the first interlayer film  25  and Cu-diffusion-preventing film  15 , and a third interlayer film  27  is formed on the second interlayer film  26 . The second interlayer film  26  is a low dielectric film such as an FSC film, while the third interlayer film  27  is a high dielectric film formed of SiO 2 , for example. 
   Referring to  FIG. 22 , via holes  28   a,    28   b  and  28   c  and second wires  29   a,    29   b  and  29   c  are formed, and then a Cu-diffusion-preventing film  30  is formed, as in the first embodiment. 
   The above-described second embodiment can provide the same advantages as the first embodiment. 
   Further, in the second embodiment, the opening  18  is formed in the Cu-diffusion-preventing film  15 . In other words, the Cu-diffusion-preventing film  15  is used instead of providing a film dedicated to the formation of the opening  18  therein (which corresponds to the insulating film  16  in the first embodiment). Accordingly, the second embodiment requires a smaller number of process steps than the first embodiment. 
   In the second embodiment, another Cu-diffusion-preventing film may be formed on the capacitor  24  to protect it. In this case, at first, the capacitor  24  is formed as shown in FIG.  18 . Subsequently, a Cu-diffusion-preventing film  31  is formed on the capacitor  24  and Cu-diffusion-preventing film  15 , and the first interlayer film  25  is formed on the Cu-diffusion-preventing film  31 , as is shown in FIG.  23 . Then, the first interlayer film  25  is flattened by CMP until the surface of the Cu-diffusion-preventing film  15  is exposed, as is shown in FIG.  24 . After that, the structure as shown in  FIG. 25  is formed by process steps similar to those of the second embodiment. In this structure, the Cu-diffusion-preventing film  31  on the capacitor  24  prevents Cu from diffusing from the second wires  29   a,    29   b  and  29   c  and via holes  28   a,    28   b  and  28   c  into the dielectric film  20  of the capacitor  24  and contaminating it. 
   As shown in  FIG. 26 , the Cu-diffusion-preventing film  15  as a high dielectric film and the insulating film  16  as a low dielectric film are provided, and the opening  18  may be formed in these films. 
   Also, as shown in  FIG. 27 , the Cu-diffusion-preventing film  31  may be formed on the capacitor  24  to protect it. 
   Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

Technology Category: 4