Fabricating a Stacked Capacitor

The present invention relates to the field of integrated circuit fabrication. More specifically, the present invention relates to a structure and method for fabricating capacitors in integrated circuits.

The fabrication of high capacitance capacitors in integrated circuitry has proven problematic. The problem is caused by competing goals in the fabrication of the capacitors. To provide maximum capacitance, maximum interface area between the two plates of the capacitor is necessary. However, to maximize the number of components in an integrated circuit a minimum of surface area of the integrated circuit must be used to fabricate each component. Prior art techniques have used vertical plate structures to try to provide the necessary interface area between the capacitor plates while using a minimum of surface area of the integrated circuit. However, even these vertical structures do not provide adequate capacitance.

The described embodiments of present invention provides a structure, and method for fabricating that structure, which provides increased capacitance over the prior art while occupying a minimum of surface area of the integrated circuit. The present invention accomplishes this by interleaving multiple capacitor plates to provide increased capacitance while occupying the same surface area as a prior art capacitor which provides a fraction of the capacitance provided by the present invention. The present invention is fabricated by providing a capacitor stack which includes interleaved plates of material which may be selectively etched and which are separated by appropriate dielectric material. One portion of the stack is masked while one set of the interleaved plates is etched. The etched portion of the interleave plates is filled by a suitable dielectric and a contact is made to the remaining plates. A different portion of the stack is then exposed to an etch which etches the other set of interleaved plates. The area etched away is then filled with a suitable dielectric and a contact is made to the unetched interleaved plates. Thus a fully interleaved capacitor is provided using relatively simple fabrication techniques while still providing increased capacitance.

FIGS. 1A through 1G are side view schematic diagrams depicting the processing steps of this invention which provide one embodiment of the structure of this invention;

FIG. 2 is another embodiment of the present invention using a different plate contact scheme;

FIGS. 3A through 3F are processing steps of another embodiment of this invention to provide another embodiment of the structure of this invention; and

FIG. 4 is a side view schematic diagram depicting one embodiment of the invention including multiple interleaved plates.

FIGS. 1A through 1G are side view schematic diagrams depicting the processing steps of one embodiment of this invention used to fabricate a structure which is another embodiment of the present invention. As shown in FIG. 1A, dielectric layer 2 is formed on the surface of substrate 1 using techniques well known in the art such as chemical vapor deposition. Substrate 1 may be a crystalline silicon substrate so that other components well known in the art of integrated circuit manufacturing may be fabricated therein. Dielectric layer 2 may be any suitable dielectric such as silicon dioxide. Conductor layer 3 is formed on the surface of dielectric layer 2 using techniques well known in the art such as chemical vapor deposition. Conductive layer 3 is formed of a material such as molybdenum which may be selectively etched while not etching dielectric layer 2. Dielectric layer 4 is formed on the surface of conductive layer 3 using techniques well known in the art such as chemical vapor deposition. Dielectric layer 4 is a suitable dielectric such as silicon dioxide. Conductive layer 5 is formed on the surface of dielectric layer 4 using techniques well known in the art such as chemical vapor deposition. The material of conductive layer 5 is chosen so that conductive layer 5 may be selectively etched while not etching dielectric layers 2 and 4 and while not etching conductive layer 3. An example of such a material is doped polycrystalline silicon. Dielectric layer 6 is formed on the surface of conductive layer 5 using techniques well known in the art such as chemical vapor deposition to provide a nonconductive cap on the surface of conductive layer 5.

The present technique shows two conductive layers serving as capacitor plates. However, it is to be understood that the present method preferably provides multiple interleaved plates one on top of the other separated by dielectric material to provide increased capacitance. The depicted example is chosen as a relatively simple illustration of the technique of this invention. Referring now to FIG. 1B, photoresist layer 7 is formed on the surface of dielectric layer 6 and is patterned using techniques well known in the art. The pattern of photoresist layer 7 is used to etch dielectric layers 4 and 6 and conductive layers 5 and 3 as shown in FIG. 1B. The structure of FIG. 1B is then subjected to an etchant which selectively etches conductive layer 5 while not etching dielectric layers 2, 4, and 6 and not etching conductive layer 3. Such an etch may be a liquid etch such as hydrofluoric acid. Photoresist layer 7 may be partially etched as shown in FIG. 1C by this process.

As shown in FIG. 1D, dielectric layer 9 is then formed on the surface of the structure of FIG. 1C. Dielectric layer 9 is preferably formed using a conformal technique such as chemical vapor deposition which fills the space left by etching conductive layer 5. The structure of FIG. 1D is then subjected to an anisotropic etching process which provides substantially vertical etching to remove dielectric layer 9 as shown in FIG. 1E. The remaining structure includes dielectric plug 10 which insulates conductive layer 5 from the right edge of the stack of conductive and dielectric materials. The steps described with regard to FIGS. 1A through 1E are then performed to form the left side of the stack as shown in FIG. 1E. The difference between the method used to form the right side of the stack and the left side of the stack is that the selective etching step used to etch conductive layer 5 on the right side of the stack is performed using a different etching chemical which selectively etches conductive layer 3, for example dilute nitric acid, so that dielectric layer 12 may fill the etched portion of dielectric layer 3 as shown in FIG. 1F. Dielectric layer 12 and photoresist layer 11 are then anisotropically etched so that dielectric plug 13 remains as shown in FIG. 1G. Conductive contacts 14 and 15 are then formed on either side of the capacitor stack using techniques well known in the art as shown in FIG. 1G. Contact 14 provides contact to conductive layer 5 which functions as one plate of the capacitor. Contact 15 provides contact to conductive layer 3 which serves as the opposing plate of the capacitor. It is to be emphasized again that the stack could contain any number of conductors separated by dielectric material making contact to contacts 14 and 15 in an opposing manner. thus providing an interleaved capacitor on the surface of a substrate suitable for the formation of integrated circuit devices providing increased capacitance over the structures and techniques for forming capacitors used in the prior art.

Other materials may be used to fabricate conductive layers 3 and 5. For example, conductive layer 3 may be aluminum and conductive layer 5 may be tungsten. Conductive layer 3 may then be selectively etched using a chlorine plasma and conductive layer 5 may be selectively etched using a fluorine plasma.

FIG. 2 is a side view schematic diagram depicting another embodiment of the present invention which includes additional dielectric material formed on the surface of dielectric layer 2 thus providing a thicker dielectric layer and causing the surface of contacts 14 and 15 to be substantially coplanar. The structure of FIG. 2 minimizes the problems of step coverage and electromigration of conductive leads which may be formed on top of capacitor 20.

FIGS. 3A through 3G are side view schematic diagrams depicting the processing steps necessary to fabricate another embodiment of this invention. Cavity 40 is formed on the surface of substrate 30 using techniques well known in the art such as orientation dependent etching. Dielectric layers 32, 34 and 36 and conductive layers 33 and 35 are then formed on the surface of substrate 30 using a conformal deposition techniques such as chemical vapor deposition. Dielectric layers 32, 34 and 36 and conductive layers 33 and 35 are then etched back to be coplanar with the surface of substrate 30 using a technique such as photoresist fill and etch-back or other techniques well known in the art. Conductive layer 33 is then selectively etched on one side while mask 37 protects the other side of conductive layer 33. This provides the structure as shown in FIG. 3B. Dielectric layer 38 is then formed on the surface of substrate 30 using a technique well known in the art such as chemical vapor deposition. Dielectric layer 38 is then etched leaving dielectric plug 39 as shown in FIG. 3D. The left-hand side of the stack composed of dielectric layers 32, 34 and 36 and conductive layers 33 and 35, of conductive layer 35 is then selectively etched to provide the structure shown in FIG. 3D. Dielectric layer 41 is then deposited by using techniques well known in the art such as chemical vapor deposition to provide the structure as shown in FIG. 3E. Photoresist layer 40 is removed and dielectric layer 41 is then etched back to provide dielectric plug 42 as shown in FIG. 3F. Insulator layers 43 and 44 are then formed on the surface of substrate 30 using techniques well known in the art as shown in FIG. 3F. Conductive contacts 45 and 46 are then formed on the surface of the capacitor stack and insulator layers 43 and 44, thus providing an interleaved capacitor formed in a cavity in the surface of substrate 30. It is to be understood that other embodiments of the capacitor formed using the techniques described with regards to FIGS. 3A through 3F may provide more capacitor plates then conductive layers 33 and 35, thus providing a fully interleaved capacitor having multiple plates for increased capacitance. The structure described with regards to FIGS. 3A through 3F was chosen for illustrative purposes only and for simplicity of explanation.

FIG. 4 is a side view schematic diagram of another embodiment of the present invention. The shown embodiment includes multiple interleaved capacitor plates to provide additional capacitance over the normal two plate capacitor. Each additional plate increases the capacitance by an additive factor. For example, a three plate capacitor provides approximately twice (1+1) the capacitance of a two plate capacitor. A four plate capacitor provides three (1+1+1) times the capacitance of a two plate capacitor.

The present invention provides increased capacitance over techniques used in the prior art while occupying the same of similar surface area on the integrated circuit. Thus the present invention provides a more dense integrated circuit while providing the high levels of capacitance necessary for circuit operation of certain circuits.