The present invention generally relates to methods and control systems associated with chemical mechanical polishing processes. More specifically, the present invention relates to a method and control system for detecting harmonic oscillation in a chemical mechanical polishing process and, in response, taking steps to either: 1) reduce or eliminate the harmonic oscillation; or 2) counter the noise which is typically associated with harmonic oscillation in a chemical mechanical polishing process.
Manufacturing an integrated circuit, for example, is a multiple step process. Among the steps which are typically performed is a chemical mechanical polishing (CMP) process which is used to polish or planarize a wafer (e.g., copper, low k dielectrics and other films). As shown in
Sometimes, during a chemical mechanical polishing process, harmonic oscillation is experienced. Harmonic oscillation can be caused by the interaction of the down force on the wafer carrier, revolutions per minute (RPM) of the platen, and RPM of the polishing head and polishing table.
When harmonic oscillation manifests itself, typically there is a loud, high pitch noise (around 80–100 decibels). Tolerating the loud noise, especially for any substantial length of time, is uncomfortable for the typical employee. In many fabrications, there is a need (i.e., when a plurality of tools are running) to wear ear protection, typically either ear plugs or headsets. Wearing such ear protection is inconvenient and uncomfortable, as well as a hindrance to normal communication in the workplace, such as peer-to-peer, supervisor-to-employee and emergency communications. As such, the noise associated with harmonic oscillations in a chemical mechanical polishing process is a major drawback towards the goals of good communications, comfort and safety in the work environment.
The harmonic oscillation also sets up an oscillation, or resident vibration, in the complete polishing system. This, including the forces applied at the surfaces of the wafer, causes an oscillation or periodic increase on the forces on the films being polished. This is like a small “jack hammering” of the interconnect structure. For films which are not low k, this is not a problem (i.e., other than the occurrence of the noises and increased tool wear). However, if there is a low k film in the stack being polished, this oscillation in the forces is a major problem. One of the key problems with integration of low k films is the structural integrity of the film. The lower the k value of the film, the lower the structural integrity of the film. For this reason, harmonic oscillation, or any increase in the forces applied to the film, presents a major yield and reliability problem with regard to the structural integrity of low k films. When harmonic oscillation occurs during processing, there is a substantial increase in the localized forces on the surface of the wafer. Because this increase in forces is not consistent, it does not occur all the time or at the same points in the process. Therefore, harmonic oscillation can result in forces and stresses that are considerably greater than the process as characterized or qualified. This often causes one of the primary failure modes seen with integration of low k films: delamination, cracking and sheer-induced voiding. All of these results have an effect on die, reduced yield and potential reliability failures. The harmonic oscillation problem is especially prevalent with regard to large, rigid polishing tables.
Current, typical solutions to these problems include, for example: limiting the type of films being polished; reducing the down force being applied; and generally operating the polisher in a very sub-optimum set of conditions. Because harmonic oscillations normally occur in the polishing process, the processing parameters and film stack must have a lot of robustness. Harmonic oscillation limits the available choices in low k films, structures and processes.
An object of an embodiment of the present invention is to provide a method and control system for detecting harmonic oscillations in a chemical mechanical polishing process and reacting thereto.
Still another object of an embodiment of the present invention is to perform experiments and then react, based on results of the experiments, to harmonic oscillation as it occurs in a chemical mechanical process.
Briefly, and in accordance with at least one of the foregoing objects, embodiments of the present invention provide a method and control system for detecting harmonic oscillation in a chemical mechanical polishing process and reacting thereto, such as by taking steps to at least one of: 1) reduce or eliminate the harmonic oscillation; or 2) counter the noise which is associated with the harmonic oscillation.
One embodiment of the present invention provides a method wherein harmonic oscillation associated with the chemical mechanical polishing process is detected, and then one or more characteristics of the process are changed to reduce or eliminate the harmonic oscillation. For example, slurry flow can be increased, the down force pressure can be changed, or the rotational velocity of the wafer carrier or polishing table can be changed. Regardless, by reducing or eliminating harmonic oscillation during the process, films with reduced structure strengths including low k dielectric films can be used. In other words, the chemical mechanical polishing process need no longer require that robust films be used, because the films need not have to withstand the effects of harmonic oscillations, which would otherwise be experienced.
Another embodiment of the present invention provides a control system for reducing harmonic oscillation in a chemical mechanical polishing process, where the control system is configured to detect harmonic oscillation, and is configured to change at least one characteristic of the chemical mechanical polishing process to eliminate, or at least reduce, the harmonic oscillation which has been detected.
Other embodiments of the present invention provide a method and control system wherein harmonic oscillation associated with a chemical mechanical polishing process is detected, and then either an audio signal is generated and broadcasted to counter noise or a vibration signal is generated and coupled to the platen to counter the harmonic oscillation. By countering the noise, the quality of the work environment is improved and the harmonic vibration that damages the substrate is eliminated without other process changes.
Still yet other embodiments of the present invention provide a method and control system wherein harmonic oscillation is detected, and the noise associated with the harmonic oscillation is countered while the harmonic oscillation is either reduced or eliminated by changing one or more characteristics of the chemical mechanical polishing process.
The organization and manner of the structure and operation of the invention, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawing, wherein:
While the invention may be susceptible to embodiment in different forms, there are shown in the drawings, and herein will be described in detail, specific embodiments of the invention. The present disclosure is to be considered an example of the principles of the invention, and is not intended to limit the invention to that which is illustrated and described herein.
As shown in
Additionally, detection analysis can be completed to determine the harmonic spectrum associated with particles scratching of the surfaces. Many of the scratches show a characteristic chatter mark. This mark is associated with the velocity vector of the relative motion of the wafer surface against a stationary particle embedded in the polishing pad. These sets of conditions set up a unique frequency and associated harmonics that may be detectable by this type of system.
The methods and control systems described above detect harmonic oscillation in a chemical mechanical process and react by eliminating or reducing the harmonic oscillation and/or by countering the noise. By reducing or eliminating harmonic oscillation during a chemical mechanical polishing process, lower k dielectric films can be used. In other words, the chemical mechanical polishing process need no longer require that robust films be used, because the films need not have to withstand the effects of harmonic oscillations, which would otherwise be experienced. By countering the noise associated with harmonic oscillation, the work environment is improved.
Alternatively, harmonic oscillation can be countered using a vibration signal. Specifically,
While embodiments of the present invention are shown and described, it is envisioned that those skilled in the art may devise various modifications of the present invention without departing from the spirit and scope of the appended claims.
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Number | Date | Country | |
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20050181706 A1 | Aug 2005 | US |