Abstract:
A new capacitor and a new method for fabricating the capacitor in an integrated circuit. The method uses fewer steps than those used in prior art processes. In accordance with the invention, trenches of differing depths are formed in a first insulating layer. One of the trenches is etched to expose a conducting layer formed under the insulating layer. Conductive material is deposited in the trenches to form a capacitor. The trenches are formed apart from each other.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is related to U.S. Pat. No. 6,080,625, entitled, “Dual-Polysilicon Structures In Integrated Circuits And A Method For Making Them”, which was filed on Aug. 26, 1998 and application Ser. No. 09/140,276, entitled, “A Method For Forming Dual-Polysilicon Structures Using A Built-In Stop Layer”, which was filed on Aug. 26, 1998. 
    
    
     TECHNICAL FIELD 
     This invention relates to integrated circuits and, more specifically, to capacitor structures in integrated circuits and a method for making them. 
     BACKGROUND OF THE INVENTION 
     Capacitors are used extensively in electronic devices for storing an electric charge. The capacitors essentially comprise two conductive plates separated by an insulator. The capacitance, or amount of charge held by the capacitor per applied voltage, is measured in farads and depends upon the area of the plates, the distance between them, and the dielectric value of the insulator. Capacitors are used in filters, in analog-to-digital converters (ADCs), in memories, and various control applications. Capacitors in integrated circuits are usually fabricated from polysilicon, metal to polysilicon, or metal to polycide structures. 
     In addition, in any fabrication process, simplicity is an advantage. Thus, a fabrication method which can achieve the same or better quality product with the same cost of materials while using fewer steps is highly preferred, especially if elimination of fabrication steps reduces labor costs and the need for expensive manufacturing equipment. A new structure built from materials already being used in the fabrication process is preferred since it reduces materials development efforts and the need for expensive manufacturing equipment. Thus, it would be desirable to provide a process to manufacture high quality capacitors in integrated circuits using a simple manufacturing process. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a new capacitor and a new method for fabricating the capacitor in an integrated circuit. The method uses fewer steps than those used in prior art processes. In accordance with the invention, trenches of differing depths are formed in a first insulating layer. One of the trenches is etched to expose a conducting layer formed under the insulating layer. Conductive material is deposited in the trenches to form a capacitor. The trenches are formed apart from each other. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The invention will be more fully understood from the following detailed description taken in connection with the accompanying drawing, in which: 
     FIGS. 1 to  3  illustrate an integrated circuit during successive stages of manufacture according to a first illustrative embodiment of the present invention; and 
     FIGS. 4 to  9  illustrate an integrated circuit during successive stages of manufacture according to a second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In accordance with the principles of the present invention, a new method for fabricating capacitors is characterized by a reduction in the number of steps required to build this type of structure. The process includes fabricating at least two trenches of differing depths and then forming conductive materials in the trenches to form a capacitor. Advantageously, this method may produce a structure with a planar or flattened topology. The individual steps of the new method utilize standard processing techniques. 
     The first illustrative embodiment is described below with reference to FIGS. 1 to  3 . Formed on the substrate  12  is an insulating layer  10 . Insulating layer  10  may be SiO 2  and may have a substantially uniform depth. The substrate is a conducting material such as tungsten, aluminum, copper, polysilicon, or other material suitable for use as a conductor and as is known to those skilled in this art. There may be one or more layers formed below the substrate  12 . The thickness of the insulating layer  10  varies based on the particular process and technology being used and the surface topology of the substrate  12 . At least one trench  14  is then formed by patterning the area to be etched using standard semiconductor photo-lithographic techniques and then etched (for example, chemically) to form the trench  14 . In particular, the trench  14  is etched to a depth equal to that of the insulating layer  10 . In other words, the trench  14  is etched to reveal the surface of the conducting material  12 . 
     Illustratively, trench  14  is formed by: 1) applying a layer of resist material on the insulating layer  10 ; 2) exposing the resist material to an energy source which passes through a pattern mask; 3) removing areas of resist to form the pattern in the resist; 4) etching the trench  14 ; and 5) removing the remaining resist material. The energy source may be an e-beam, light source, or other suitable energy source. 
     After formation of the first trench  14 , a second trench  20 , shown in FIG. 2, is formed in the insulating layer  10 . The second trench  20  has a depth that is less than the depth of the first trench  14 , and therefore has a base that sits above a remaining thickness of the insulating layer  10 . The second trench  20  may be formed using the process described above to form the first trench  14 . The depth d1 of second trench  20  or the thickness d2 of the insulating layer  10  remaining underneath the second trench  20  is dependent upon the desired characteristics of the structure being fabricated. The thickness d2 of the insulating layer  10  remaining underneath may be varied to change capacitance. Alternatively, the diameter D of the trench  20  may be increased or decreased to change capacitance or additional trenches  20  (or 120) may be formed and electrically connected. In other words, the total cross-sectional area of the trench  20  may be increased or decreased. In addition, multiple capacitors may be formed and interconnected as desired using this process. 
     Using standard processing techniques, a conductive layer  24 , shown in FIG. 3, is then formed in trenches  14  and  20 . The conducting layer  24  is a conducting material such as tungsten, aluminum, copper, polysilicon, or other conducting material suitable for use as a conductor as is known to those skilled in this art. After being deposited in a blanket fashion, the conducting layer  24  is processed to make the surface of the conducting layer  24  co-planar or substantially co-planar with the surface of the first insulating layer  10  to form plugs  241  and  242 . For example, this is accomplished by a conventional chemical-mechanical polishing (CMP) or other planarization techniques. 
     Subsequently, a second conducting layer  30 , shown in FIG. 3, is blanket deposited on the planarized surfaces of the insulating layer  10  and the first conducting layer  24 . The second conducting layer  30  is a conducting material such as tungsten, aluminum, copper, polysilicon, or other conducting material suitable for use as a conductor and as is known to those skilled in this art. The second conducting layer  30  is patterned as is described above and as is well known to form, for example, runners contacting the plugs  241  and  242  formed in trenches  14  ad  20 . 
     The process described above may be used to form metal-oxide-metal (MOM) capacitors. Alternatively, the process described above may be used to form metal to polysilicon or metal to polycide capacitors. In this embodiment, the substrate may be polysilicon or polycide and the first and second conducting layers are metals such as tungsten. 
     In the process described above, the conductive layers  24  and  30  may be formed at substantially the same time. For example, a conducting material may be blanket deposited over the insulating layer  10  and in trenches  14  and  20 . Then, the conducting material is patterned as is described above and as is well known to form, for example, runners and the plugs. In this way, processing steps may be eliminated. Further, the first and second conducting layers  24  and  30  may be formed of the same or different materials. In addition, the first conducting layer  24  may be formed from multiple layers of different or the same material. 
     A second illustrative embodiment is described below with reference to FIGS. 4-9 where an insulating layer  205  is formed on a substrate  200 . Insulating layer  205  may be SiO 2  and have a substantially uniform depth. The substrate  200  is a conducting material such as tungsten, aluminum, copper, polysilicon, or other conducting material suitable for use as a conductor as is known to those skilled in this art. There may be one or more layers formed below the substrate  200 . The thickness of the insulating layer  205  varies based on the particular process and technology being used as described above. 
     Subsequently, a stop layer  210  is formed on the insulating layer  205 . The stop layer  210  is, for example, TiN. The stop layer  205  is an etch stop layer as is described below. A second insulating layer  215  is formed on the stop layer  205 . The second insulating layer is, for example, SiO 2 . Next, a resist  220 , shown in FIG. 5, is formed on the second insulating layer  215  and patterned as is described above and as is well known in the art. The second insulating layer  215  is etched to form trench  120 , shown in FIG.  6 . The etch process is a selective etch process that etches the insulating layer  215  at a higher or substantially higher rate than the stop layer  210 . In other words, the stop layer  210  is resistant to the etch process used to etch insulating layer  215 . By using this process, the depth of trench  120  formed during the etch process may be precisely controlled. 
     Next, as is shown in FIG. 7, a second resist layer  230  is formed on the second insulating layer  215 . The second resist layer  230  is patterned as is described above and as is well known. The second insulating layer  215 , the stop layer  210 , and the first insulating layer  205  are etched using a process that selectively etches the materials of each layer to form trench  140 , shown FIG.  8 . In other words, stop layer  210  is not resistant to the etching process used to form trench  140 . After etching, the remaining portions of the second resist layer  230  are removed. The trench  140  is similar to the trench  14  shown in FIGS. 1-3 and trench  120  is similar to the trench  20  shown in FIGS. 1-3. Once trenches  140  and  120  have been formed, layers similar to layers  24  and  30  may be formed as described above in the first embodiment and shown in FIG. 9 to form a capacitor. 
     Finally, it is to be understood that although the invention is disclosed herein in the context of particular illustrative embodiments, those skilled in the art will be able to devise numerous alternative arrangements. Such alternative arrangements, although not explicitly shown or described herein, embody the principles of the present invention and are thus within its spirit and scope.