Patent Application
20120048296
1. Field of the Invention
The present invention relates to a cleaning method, and more particularly, to a cleaning method used after a CMP process to clearly remove the slurry used in the CMP process.
2. Description of the Prior Art
The chemical mechanical polishing (CMP) process is one of the most common and the most essential planarization processes to date. The CMP process aims to topographically planarize a thin film disposed on a wafer surface so as to ensure the wafer has a smooth surface. For fabrication of damascene metal connection wires, such as copper conduction wires, the CMP process is an irreplaceable process.
In general, CMP is a process that utilizes the reagent within slurry to react chemically with the front face of a wafer and produce an easily polished layer. Together with the abrasive action provided by the abrasive particles in the slurry above a polishing pad, the protruding portion of the easily polished layer is gradually removed. By repeating the foregoing chemical reaction and mechanical polishing steps, the surface of the wafer is planarized.
However, the slurry is highly corrosive and viscous and is easy to be retained on the surface of the copper. If the slurry is not removed after the CMP process, the slurry residues may cause a lot of problems such as the crater-defect when performing the lithography process, which will affect the quality of the wafer and thus decrease the yields of the wafer. Nevertheless, conventional post-CMP cleaning process dose not provide sufficient cleaning ability to remove the slurry. Consequently, a post-CMP cleaning process that can clearly remove the slurry on the wafer is still needed.
One objective of the present invention is to provide a cleaning method that can clearly remove the slurry and prevent the problems of crater-defect in conventional arts.
According to one embodiment of the present invention, a cleaning method for a wafer is provided. First, a first cleaning process is performed wherein the first cleaning process includes providing a cleaning solution having a first concentration. Next, a second cleaning process is performed, wherein the second cleaning process includes providing the cleaning solution having a second concentration. The second concentration is substantially greater than the first concentration. Next, a post-cleaning process is performed to provide dilute water.
By performing different cleaning steps with gradient concentrations, the cleaning process in the present invention can clearly remove unwanted stuff from the surface of the wafer to ensure the clearance of the wafer thereby improving the yields of the wafer.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
To provide a better understanding of the presented invention, preferred embodiments will be made in details. The preferred embodiments of the present invention are illustrated in the accompanying drawings with numbered elements.
Please refer to
Next, a pre-clean process is performed (step 304). In the pre-clean process, a cleaning solution is provided on the chemical mechanical polished wafer. The recipe of the cleaning solution can be adjusted according to different types of slurry used in the CMP processes. In the present embodiment, the cleaning solution includes organic amine, quaternary ammonium hydroxide or other suitable cleaning solutions that are able to remove the slurry, and should not be limited thereto. The cleaning solution is supplied unto the wafer, for example, by a delivery pipe, and then mixed with DI water which is supplied from another deliver pipe. The volume dilution ratio of the cleaning solution in the pre-clean process is substantially between 1:45 and 1:100. In one embodiment, about 2000 ml DI wafer and about 25 ml cleaning solution are mixed, leading to a 1:85 volume dilution ratio. In another embodiment, about 2400 ml DI wafer and about 25 ml cleaning solution are mixed, leading to a 1:95 volume dilution ratio. It is noted the pre-clean process is taken as a rinse process, so only the cleaning solution is applied to the wafer but no brush process is performed. That is, the brush does not contact the surface of the wafer during the pre-clean step. In the present embodiment, the pre-clean step is preformed for about 10 seconds.
Next, a first cleaning process is performed (Step 306). In the first cleaning process, the cleaning solution having a first concentration is provided on the surface of the wafer. In the present embodiment, the first concentration is substantially the same as the concentration used in the pre-clean process. In another embodiment, the first concentration of the cleaning solution is greater than the concentration used in the pre-clean process. The first cleaning process includes a brush process. That is, during the first cleaning process, the cleaning solution is supplied and the wafer is brushed simultaneously so as to clearly remove the slurry. In one embodiment, the brush process is performed during whole first cleaning process, and in another embodiment, the brush process is performed within a period of time during the first cleaning process. In the present embodiment, the first cleaning step (step 306) is preformed for about 20 seconds.
Subsequently, a second cleaning process is performed (Step 308). In the second cleaning process, the cleaning solution having a second concentration is provided on the wafer. It is one salient feature in the present invention that the second concentration in the second cleaning process is greater than the first concentration in the first cleaning process. That is, a lower concentration of cleaning solution is used first (the first cleaning process), and then a higher concentration of cleaning solution is used (the second cleaning process). In one preferred embodiment, the volume dilution ratio of the cleaning solution is about 1:45, which can be obtained by mixing about 2000 ml DI water and about 45 ml cleaning solution. In the second cleaning process, like the first cleaning process, the wafer is subjected to the brushing process, which can be performed during whole second cleaning process or only in a period of time. The second cleaning step (step 308) is preformed for about 30 seconds.
Lastly, a post-clean process is performed (Step 310). In the present embodiment, about 4000 ml DI water is provided on the wafer to thoroughly clean the wafer and remove the slurry. In the present embodiment, the wafer is subjected to the brushing process, which can be performed during whole post-clean process or only in a period of time. The post-clean step (step 310) is preformed for about 30 seconds.
According to the present embodiment, by using the cleaning process including the first cleaning process and the second cleaning process where a lower concentration (the first concentration) is used first and a higher concentration (the second concentration) is used subsequently, the slurry of the CMP process can be removed more clearly. Consequently, the defects caused by un-removed slurry can be alleviated. Moreover, the over-etching problem on the wafer in conventional arts which is resulted from directly using only one concentration of the cleaning solution (usually high concentration) can be prevented, thereby maintaining the smoothness of the layers on the semiconductor structure. As the pre-clean process which is performed before the first cleaning process and the second cleaning process provides the cleaning solution on the wafer without brushing the wafer, the slurry on the wafer is bathed within the cleaning solution for about 10 seconds, so the slurry can be removed more easily in the subsequent first cleaning process and second cleaning process, both of which include a brush process to remove away the slurry. After the cleaning process, the post-clean process is still subjected to the brush process to effectively remove the cleaning solution and the remainders. Further, the mixed cleaning solution has a pH value substantially between 12±0.3 (11.07˜12.03) during the post-CMP cleaning method in the present invention and pH value of the cleaning solution is not affected severely by the dilution ratio.
The first embodiment uses two separate cleaning processes with different chemical concentration to clearly remove the slurry. However, it is understood that, between the first cleaning process and the second cleaning process, more than one cleaning process can be performed. For example, please refer to
Through the cleaning process in the present invention, the defects such as crater defect caused from the un-removed slurry can be reduced. For example, in conventional arts, each wafer has an average about 10.175 defects caused by un-removed slurry. By using the cleaning process in the present invention, the defect number can be reduced to 2.54, leading to a 75% reduction in defect numbers. Accordingly, the cleaning process in the present invention can effectively decrease the defects caused from un-removed slurry, thereby increasing about 2% yield of the wafer.
In light of above, the present invention provides a cleaning method to solve the problems of crater defect or micro-scratch caused by the un-removed slurry. It is noted that the cleaning steps described above not only can be used in post-CMP process, but also is applicative in other cleaning process, such as the cleaning process after an etching process. By performing different cleaning steps with gradient concentrations, the cleaning process in the present invention can clearly remove unwanted stuff from the surface of the wafer to ensure the clearance of the wafer thereby improving the yields of the wafer.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.
