Abstract:
The subject matter described herein involves an improved etch process for use in fabricating integrated circuits on semiconductor wafers. The selectivity of the etch process for silicon carbide versus silicon oxide, organo silica-glass or other low dielectric constant type material is enhanced by adding hydrogen (H2) or ammonia (NH3) or other hydrogen-containing gas to the etch chemistry.

Description:
FIELD 
     The subject matter herein relates to fabrication of integrated circuits using a silicon carbide (SiC) etch stop layer. 
     BACKGROUND 
     In the fabrication of integrated circuits in and on a silicon wafer, particularly with copper (Cu) Damascene metallization processes, a silicon carbide (SiC) film, or layer, is commonly used as an etch stop, barrier or hard mask during plasma etching processes. The SiC film is relatively nonreactive to the plasma etch, which is typically used to remove silicon oxide, organo-silica-glass or other low k (dielectric constant) type materials that may be used in combination with the Cu Damascene metallization processes. Thus, the SiC film enables the plasma etch of the low k type material to stop at a desired depth or protects the underlying material from the plasma etch. 
     When it is necessary to remove the SiC film, an etch process is used that is relatively “selective” to the SiC. The SiC etch process typically uses CF4 (Carbon-Tetrafluorite), CHF3 (Trifluoromethane), CH2F2 (Difluoro-Methane ), CH4 (Methane) or the like as an etch chemistry. It is very difficult, however, to achieve a high selectivity to the SiC film that does not also affect the low k type material, thereby causing damage to, or erosion of, the low k type material. 
     It is with respect to these and other background considerations that the subject matter herein has evolved. 
     SUMMARY 
     The subject matter herein involves a new and improved etch chemistry for an improved SiC etch process that enhances, or increases, the selectivity of the etch process to the SiC film relative to the silicon oxide, OSG or other low k type material. In one particular embodiment, hydrogen (H2) or other hydrogen-containing gas is added to the prior art etch chemistry. Hydrogen has been found to facilitate the etching of the SiC film, while reducing the etch rate of the low k type material. In another particular embodiment, ammonia (NH3) is added to the prior art etch chemistry also to facilitate the etching of the SiC film and reduce the etch rate of the low k type material. In either embodiment, the selectivity of the etch chemistry to the SiC film is increased as compared to that for the low k type material. Thus, the SiC film can be more easily removed without damaging or eroding the low k type material. 
     A more complete appreciation of the present disclosure and its scope, and the manner in which it achieves the above noted improvements, can be obtained by reference to the following detailed description of presently preferred embodiments taken in connection with the accompanying drawings, which are briefly summarized below, and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The single FIGURE is a cross section of exemplary structures formed on a substrate of a semiconductor wafer on which the subject matter herein may be practiced. 
    
    
     DETAILED DESCRIPTION 
     A semiconductor wafer  100 , as shown in the FIGURE, typically includes a substrate  102  into and onto which various layers and structures of materials are formed and deposited by conventional means to form the desired integrated circuit chip. In particular, in the example shown, one or more silicon carbide (SiC) films, or layers,  104 ,  106  and  108  are deposited above the substrate  102 . Also, in this example, one or more low k (dielectric constant) type material films  110  and  112  (e.g. silicon oxide, organo-silica-glass “OSG,” etc.) are deposited between the SiC films  104 ,  106  and  108 , as shown. Additionally, an underlying metal layer  114 , such as copper (Cu), may be deposited under the first SiC film  104  and over various other layers  116  or structures formed in or deposited on the substrate  102 . With this initial exemplary structure, a Damascene metallization process can be used to form an electrical connection through the low k type material films  110  and  112  and the SiC films  104 ,  106  and  108  to the underlying Cu layer  114 . 
     In a Damascene metallization process, one or more insulating layers of material (such as the low k type material films  110  and  112  and the SiC films  104 ,  106  and  108 ) are deposited on top of the semiconductor wafer  100 , and trenches (such as removed regions  118  and  120 ) are etched into the insulating layers. Thereafter, a metal material (such as copper, etc.) is deposited across the top of the semiconductor wafer  100  and into the trenches (removed regions  118  and  120 ). The metal material is then chemical mechanical polished (CMP) to remove the excess metal material that covers the area beyond the trenches and form a relatively smooth top surface for the semiconductor wafer  100 . 
     For the exemplary structure shown, the deposition and removal processes are conventional, except for the improved SiC etch process described below. Also, a variety of other combinations of steps or procedures may be used to form the same or similar structures shown in this example. 
     After the various other layers  116  and structures, in the example, have been formed in or above the substrate  102 , an insulating layer  122  (such as silicon oxide, etc.) is typically deposited on top of the other layers  116 . A region of the insulating layer  122  is etched away, so that the underlying Cu layer  114  can be formed therein. Alternatively, the underlying Cu layer  114  may be deposited on top of the various other layers  116  and portions of the underlying Cu layer  114  may be removed, so that the insulating layer  122  may be formed therein. 
     For the exemplary structure shown, the first SiC film  104  is deposited on top of the underlying Cu layer  114  and the insulating layer  122 . The first SiC film  104  primarily serves as an etch stop for a subsequent etching of the first low k type material film  110 . The first low k type material film  110  is then deposited on top of the first SiC film  104 . The second SiC film  106  is deposited on top of the first low k type material film  110  to serve as an etch stop or barrier for a subsequent etching of the second low k type material film  112 . At this point, an etch mask layer (not shown) is deposited on the second SiC film  106  and patterned for the region  118 , so the portion of the second SiC film  106  within the region  118  can be etched away to expose a portion of the first low k type material film  110 . The SiC etch process may be the improved SiC etch process described herein, or since there is not yet an overlying low k type material that may be affected (e.g. damaged or eroded) by the SiC etch process, the SiC etch process may be conventional. The etch mask layer is removed, and the second low k type material film  112  is deposited on top of the second SiC film  106  and into the region  118  where the second SiC film  106  has been removed. The third SiC film  108  (used as a hard mask for subsequent processes) is optional and is deposited on top of the second low k type material film  112 . An etch mask layer  124  is deposited onto the third SiC film  108  and patterned for the region  120  to expose a portion of the third SiC film  108 . The portion of the third SiC film  108  within the region  120  is etched away to expose a portion of the second low k type material film  112 . Again, the SiC etch process may be the improved SiC etch process described herein, or since there is not yet an overlying low k type material that may be affected (e.g. damaged or eroded) by the SiC etch process, the SiC etch process may be conventional. Then the second low k type material film  112  is etched away in the region  120  exposing sidewalls  126  of the second low k type material film  112 . Upon reaching the second SiC film  106 , the etching of the second low k type material film  112  stops, except for the low k type material that was deposited in the region  118  where the second SiC film  106  was previously removed. If the first low k type material film  110  can be etched by the same process that removes the second low k type material film  112 , then the etch process may continue into the first low k type material film  110  in the region  118 . Otherwise, another etch process is used to etch away the portion of the first low k type material film  110  in the region  118  exposing sidewalls  128  of the first low k type material film  110 . The exposed portion of the second SiC film  106  at the bottom of the region  120 , thus, also serves as an etch barrier protecting the underlying portions of the first low k type material film  110  as the first low k type material film  110  is etched away in the region  118 . Upon reaching the first SiC film  104 , the etching of the first low k type material film  110  stops having exposed a portion  130  of the first SiC film  104 . 
     At this point, the portion of the first SiC film  104  below the region  118  is to be removed to expose the underlying Cu layer  114 , so that an electrical connection can be made thereto. In order not to erode or otherwise damage the exposed sidewalls  126  and  128  of the second and first low k type material films  112  and  110 , respectively, the improved SiC etch process described herein is used to etch away the exposed portion  130  of the first SiC film  104 . The improved SiC etch process will also likely remove the exposed portions of the second SiC film  106 . 
     After the exposed portion  130  of the first SiC film  104  is removed, a metal region, or other conductive region, (not shown) is generally formed in the regions  118  and  120  by an appropriate process, such as a Damascene metallization process. An appropriate conductive material (such as Cu, aluminum, etc.) is thus deposited into the regions  118  and  120 . Any excess of the conductive material outside of the region  120  is removed by a conventional chemical mechanical polishing process. 
     The improved SiC etch process adds hydrogen (H2) or ammonia (NH3) or other hydrogen-containing gas to the conventional SiC etch chemistry of CF4 (carbon-tetrafluorite), CHF3 (trifluoromethane), CH2F2 (difluoro-methane), CH4 (methane) or the like. The H2 or NH3 is added to the conventional SiC etch chemistry either in the etch chamber (not shown) in which the etching takes place or in the gas flow upstream of the etch chamber. The addition of H2 or NH3 to the etch chemistry improves, or increases, the selectivity of the etch chemistry to the SiC relative to the low k type material films  110  and  112  while maintaining control of the profile of the exposed portions of the SiC films  104 - 106 . In other words, the rate at which the exposed portions of the SiC films  104  and  106  are etched away is increased relative to the rate at which the exposed portions of the low k type material films  110  and  112  are eroded by the SiC etch process. 
     In an exemplary embodiment of the improved SiC etch process, a range for the preferred ratio for the carbon, fluoride and hydrogen (C:F:H) is 1:1:2 to 1:8:4 at a gas flow rate of about 50 to 100 sccm, a temperature of about −30° C. to 80° C., a pressure of about 5 mT to 300 mT and a power of about 200 to 1500 Watts. These parameters may result in an etch rate on the SiC films  104  and  106  of about 1000 to 3000 angstroms per minute. 
     The addition of hydrogen to the etch chemistry (by either H2 or NH3) enables greater control and variability of the C:F:H ratio than does the prior art, which uses only a single gas. Thus, the anticipated chemical reaction that etches away the proper material can be manipulated as desired to control the selectivity of the etch chemistry to the SiC relative to the low k type material. 
     Presently preferred embodiments of the subject matter herein and its improvements have been described with a degree of particularity. This description has been made by way of preferred example. It should be understood that the scope of the claimed subject matter is defined by the following claims, and should not be unnecessarily limited by the detailed description of the preferred embodiments set forth above.