The present invention is directed, in general, to a CMP process and, more specifically, to a novel CMP endpoint detection process.
As integrated circuits become more and more dense, the width of interconnect layers that connect transistors and other devices of the integrated circuit to each other is reduced. As the width decreases, the resistance increases. Accordingly, many companies are looking to switch from a traditional aluminum interconnect to other type interconnects. Copper and tungsten interconnects, among others, are a few of the more advanced interconnects that are currently being used. Unfortunately, both copper and tungsten are very difficult to etch in a semiconductor process flow. Therefore, damascene processes have been proposed to form these interconnects.
A typical damascene process consists of forming an interlevel dielectric 12 over a semiconductor body 10, as shown in
Today's CMP processes attempt to be gentle to the substrate surface, and for this reason, often use metal polish distributed across two or more tables, or “platens”, and thus polishing surfaces. In this typical scenario, the first platen uses a high down force (HDF) process to remove bulk portions of the metal layer 20, and the second platen uses a slow, gentle, lower down force (LDF) process to polish the remaining metal layer 20 until all areas of the substrate surface are clear of the metal layer 20, resulting in the metal plug 21. The problem typically encountered is how to balance the time between platens by removing a target amount of bulk metal layer 20 on the first platen, and then gently remove the remaining metal layer 20 on the second platen, all the while doing so in a controllable and repeatable manner. Prior art methods have generally been unable to balance the time between the platens in a controllable and repeatable manner, such that an optimal metal plug 21 may be manufactured.
Accordingly, what is needed in the art is a novel CMP endpoint detection process that does not experience the drawbacks of the prior art CMP processes.
To address the above-discussed deficiencies of the prior art, the present invention provides a method for polishing a layer of material, a method for manufacturing a damascene interconnect structure, and a method for manufacturing an integrated circuit. The method for polishing a layer of material, among other steps, includes obtaining a substrate having a layer of material located thereover, and polishing the layer of material using a polishing surface. The step of polishing the layer of material may include subjecting the layer of material to a first polishing process using a first endpoint detection method, the first polishing process removing a portion of the layer of material, and subjecting remaining portions of the layer of material to a second polishing process using a second different optical endpoint detection method.
As previously indicated, the present invention further includes a method for manufacturing a damascene interconnect structure. The method for manufacturing the damascene interconnect structure includes, without limitation, forming a layer of conductive material within an opening and over an upper surface of a dielectric layer, and polishing the layer of conductive material to form an interconnect plug. The polishing of the layer of conductive material, again without limitation, may include subjecting the layer of conductive material to a first polishing process with a polishing surface and using a first endpoint detection method, the first polishing process removing a portion of the layer of conductive material, and subjecting remaining portions of the layer of conductive material to a second polishing process with the polishing surface and using a second different optical endpoint detection method.
The foregoing has outlined preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention.
The invention is best understood from the following detailed description when read with the accompanying FIGUREs. It is emphasized that in accordance with the standard practice in the semiconductor industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. Reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
Prior Art
Referring initially to
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The layer of conductive material, in a step 240, may be subjected to a first polishing process with the first polishing surface. In accordance with the principles of the present invention, the first polishing process uses an endpoint detection method to remove a portion of the layer of conductive material. In many embodiments the first polishing process removes a substantial portion of the layer of conductive material. The endpoint detection method used in step 240, in an exemplary embodiment, is an eddy current endpoint detection method. The eddy current endpoint detection method is particularly useful when used in conjunction with a high down force (HDF) process advantageously used in step 240. Those skilled in the art appreciate that other detection methods are within the scope of the present invention.
Thereafter, in a step 250, remaining portions of the layer of conductive material may be subjected to a second polishing process with the first polishing surface. In accordance with the principles of the present invention, the second polishing process uses a second different optical endpoint detection method to remove all or a part of the remaining portions of the layer of conductive material. In an exemplary embodiment, the optical endpoint detection method allows the second polishing process to stop prior to completely removing the entire layer of conductive material, thereby leaving a film of conductive material remaining over the dielectric layer. While less likely, another embodiment might exist wherein the second polishing process accurately and completely removes all of the remaining portions of the layer of conductive material. This embodiment would most likely be used in conjunction with a two platen CMP tool.
In the embodiment wherein the film of conductive material remains over the dielectric layer after the second polishing process, the dielectric layer having the film of conductive material thereover may be moved to be located over a second different polishing surface. This might occur in the optional step 260. Thereafter, in an optional step 270, the film of conductive material may then be subjected to a third polishing process using the second different polishing surface. In accordance with one embodiment, the third polishing process could use an optical endpoint detection method to determine when to terminate the third polishing process. In another embodiment, the optical endpoint detection method could be a similar process to that used in step 250. Nevertheless, other optical endpoint detection methods could be used. After completing step 270, the process could then stop in a finish step 275, or repeat itself by returning to step 205 with a new dielectric layer having an opening therein.
Nevertheless, it goes without saying that certain steps neither discussed nor shown could be conducted prior to the finish step 275. One example is the conventional removal (e.g., polishing) of any remaining barrier/adhesion layer located over an upper surface of the dielectric layer. This step might be conducted after step 270, however, prior to the finish step 275. A number of other steps might also exist.
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Conventionally formed over the substrate 310 and within the opening therein may be a barrier/adhesion layer 320. The barrier/adhesion layer 320 is typically desired to help the layer of material 330 easily adhere to the substrate 310. The barrier/adhesion layer 320 is also typically desired wherein the layer of material 330 comprises a material that might be detrimental to devices that might be located proximate thereto. For example, in instances wherein the layer of material 330 comprises copper, the barrier/adhesion layer 320 might comprise tantalum/tantalum nitride. In the instance wherein the layer of material 330 comprises tungsten, the barrier/adhesion layer 320 might comprise titanium/titanium nitride/tungsten nitride.
As shown in
Similar to the material composition of the layer of material 330, the thickness (t0) of the layer of material 330 may vary greatly. It is important, however, that the layer of material 330 substantially fill the opening in the substrate 310. Depending on the size of the opening in the substrate 310, as well as the thickness of the substrate 310 itself, the initial thickness (t0) of the layer of material 330 should range from about 200 nm to about 2000 nm, and more particularly about 500 nm to about 1000 nm. The present invention should, nonetheless, not be limited to such thicknesses.
The method for forming the layer of material 330 may take on a number of different processes and techniques and remain within the scope of the present invention. For instance, in one embodiment of the invention the layer of material 330 is formed by electroplating the layer of material 330 within the opening and over the upper surface of the substrate 310 using a conventional seed layer formed over the barrier/adhesion layer 320. In an alternative embodiment, however, the layer of material 330 is deposited within the opening and over the upper surface of the substrate 310 using a conventional physical vapor deposition (PVD) or chemical vapor deposition (CVD) process. Other known or hereafter discovered process could also be used.
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Unique to the present invention, a first endpoint detection method is associated with the first polishing process to determine when and if the first polishing process should terminate. While a number of different endpoint detection methods exist and could be used, an exemplary embodiment of the present invention uses an eddy current detection method. As those skilled in the art appreciate, the eddy current method works by generating and measuring an eddy current created within the layer of material 330 to determine the thickness of the layer of material 330 being polished. In this embodiment, the first polishing process would continue until a desired amount of change in the eddy current measurement is detected. It is believed that the desired amount of change in the eddy current measurement indicates that the polished layer of material 420 is about 300 nm thick. While the eddy current method has been discussed in somewhat detail, other endpoint detection means could nevertheless be used for the first endpoint detection method, and remain within the purview of the present invention.
What results after polishing the layer of material 330 using the first polishing process is a polished layer of material 420. The polished layer of material 420, as indicated in
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While not being limited to such, the second polishing process, in an exemplary embodiment, is designed to remove all but a film of material 510. To accurately and reproducibly leave only this film of material 510, the second polishing process often uses a low down force (LDF) process. For example, depending on a number of different criteria, the LDF process typically uses a down force ranging from about 0.5 psi to about 2 psi. Again, those skilled in the art understand that this down force may vary, and thus the values given should not be used to limit the scope of the present invention.
Unique to the present invention, a second different optical endpoint detection method is used with the second polishing process to determine when and if the second polishing process should terminate. While a number of different optical endpoint detection methods may exist, an exemplary embodiment of the present invention uses a reflectance based endpoint detection method, such as that found on the ISRM tool that may be obtained from Applied Materials, Inc. Nonetheless, any known or hereafter discovered optical endpoint detection method or tool might be used, as long as it remains within the principles of the present invention.
The film of the material 510, as indicated in
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Unique to the present invention, a third endpoint detection method is associated with the third polishing process to determine when and if the third polishing process should terminate. While a number of different endpoint detection methods exist and could be used, an exemplary embodiment of the present invention uses an optical endpoint detection method. In one advantageous embodiment, the optical endpoint method used in the third polishing process is substantially similar to that used in the second polishing process.
In certain embodiment a portion of the barrier/adhesion layer 320 will remain over an upper surface of the substrate 310. In these instances, another polishing process (not shown) may be required to remove any remaining barrier/adhesion layer 320. Those skilled in the art understand the conventional processes that might be used to remove any remaining barrier/adhesion layer 320. What results after polishing the film of material 510 using the third polishing process and removing any remaining portions of the barrier/adhesion layer 320 is a completed interconnect 720. The interconnect 720 of the embodiment of
The present invention provides a number of advantages over that which might be provided by conventional methods. For example, the present invention provides continuous endpoint monitoring during the entire polishing process, which does not leave any “blind” times during which the material layer (e.g., conductive layer) is polished according to time only. Additionally, the present invention provides a method for ensuring a continuous, thin film of material covering the substrate as it transitions from the first polishing surface to the second polishing surface (e.g., from the second polishing process to the third polishing process). This, in turn, provides a reasonable degree of comfort when conducting the final polish that it may be precisely accomplished without either over or under polishing.
As illustrated in the table 800 of
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Although the present invention has been described in detail, those skilled in the art should understand that they could make various changes, substitutions and alterations herein without departing from the spirit and scope of the invention in its broadest form.