Patent Application
20080078420
Embodiments of the present invention will be described in detail with reference to accompanying drawings.
In the prior art, for example, an ultrasonic cleaning apparatus has an ultrasonic cleaning module, two scrubbing modules which are both assisted with a deionized water cleaning means and a chemical agent cleaning means respectively, and a drying module. In the cleaning process, there is a wafer in each of the modules. Supposing the time of ultrasonic cleaning in the ultrasonic cleaning module is 30 s, and the time of cleaning in the scrubbing module adjacent to the ultrasonic cleaning module is set to 60 s. Once a wafer with defect particles on its surface is loaded into the ultrasonic cleaning module, the ultrasonic cleaning begins immediately. After 30 s, the ultrasonic cleaning is completed. However, there is another wafer being scrubbed in the scrubbing module adjacent to the ultrasonic cleaning module. Since the heater in the ultrasonic cleaning module has a very short service life and may be damaged easily if it operates continuously for a long time, usually the wafer is held for 30 s in the ultrasonic cleaning module so as to prolong the service life of the ultrasonic cleaning module; only when the scrubbing of the wafer in the scrubbing module adjacent to the ultrasonic cleaning module is completed, the wafer in the ultrasonic cleaning module may be transferred to the scrubbing module and is placed into the scrubbing process. Then, the scrubbing and drying processes are implemented in the preset cleaning sequence and times.
However, after the wafers are cleaned and dried with the method in the prior art, it is found that there may still be defect particles on wafer surfaces.
Through further investigation, it is found that the defect particles existing on the surface of a wafer after the cleaning process in the prior art are adhered to the wafer surface again during the time the wafer is held in the ultrasonic cleaning module after ultrasonic cleaning. This is because there are defect particles removed from wafers in the ultrasonic cleaning module after those wafers are cleaned in the ultrasonic cleaning module. During the time the wafer is held in the ultrasonic cleaning module after ultrasonic cleaning, some defect particles will adhere to the wafer surface again.
Therefore, some embodiments of the present invention provides a method for cleaning the surface of a wafer after a Chemical Mechanical Polishing (CMP) of the wafer. The method includes the following processes: performing an ultrasonic cleaning on the wafer for time T1; cleaning with a chemical agent and deionized water for n times for time T2, T3, . . . , Tn+1, respectively, with n being a an integer; drying the wafer for time Tn+2; supposing the maximum value among T2, T3, . . . , Tn+2 is Tmax, in the case that T1<Tmax, the ultrasonic cleaning process includes the following procedures: loading a wafer into an ultrasonic cleaning module and holding the wafer static and ultrasonic no power for time T′ (T′=Tmax−T1); cleaning the wafer by the ultrasonic cleaning for time T1; after the ultrasonic cleaning, cleaning the wafer with the chemical agent and deionized water immediately.
It is undoubtedly that the bigger the “n” value is (i.e., the more the cleaning times are), the fewer the number of residual defect particles on the wafer surface after cleaning will be, and the higher the yield will be. However, in the industrial manufacturing process, in view of the requirement for process time and cost, “n” is preferably an integer≦3 in the embodiments of the invention, and more preferably n=2; for some wafers that have achieved better cleaning result in the ultrasonic cleaning process, preferably n=1. In some of the embodiments described below, n is equal to 1 or 2.
As shown in
In order to remove the defect particles on the wafer surface or inlaid in the wafer in the ultrasonic cleaning process, the ultrasonic cleaning module contains a chemical agent, which is chosen depending on the polishing solution used in the CMP process. For example, if the polishing solution contains silicon dioxide particles, usually a chemical agent containing ammonia is chosen for cleaning. The time T1 of ultrasonic cleaning may be set to 10 s-60 s, and preferably 35 s-45 s.
After the ultrasonic cleaning, the wafer is loaded into the deionized water and chemical agent cleaning module immediately; the time T2 of cleaning with a chemical agent and deionized water is set to 5 s-110 s, and preferably 20 s-90 s, in which the time of cleaning with chemical agent is 0 s-70 s, and the time of cleaning with the deionized water is 5 s-40 s. In the case that almost all defect particles on the wafer surface are removed after the ultrasonic cleaning, the wafer then may be cleaned merely with the deionized water; in that case, the time of cleaning with the chemical agent is 0. If there are defect particles on the wafer surface which cannot be removed by the ultrasonic cleaning, the wafer should be cleaned with the chemical agent first in the subsequent cleaning processes. The chemical agent may be chosen depending on the category and characteristic of the defect particles existing on the wafer surface. For example, if the defect particles existing on the wafer surface have negative charges, the chosen chemical agent should contain positive charges so as to remove the defect particles existing on the wafer surface by chemical cleaning. After the chemical cleaning, the chemical agent on the wafer surface is removed with pure deionized water in the same deionized water and chemical agent cleaning module. Next, the wafer is baked in the drying module for 5 s-20 s at 20° C.-40° C. to remove the moisture on the wafer surface.
Now a complete embodiment is described. A first wafer is loaded into an ultrasonic cleaning module and held with the application of ultrasonic power for 55 s. Then the ultrasonic cleaning module is started and cleans the wafer for 35 s; next, the first wafer is transferred to a deionized water and chemical agent cleaning module immediately and cleaned for a total of 90 s with a chemical agent and deionized water, in which the time of cleaning with the chemical agent is 60 s, and the time of cleaning with the deionized water is 30 s. Next, the first wafer is transferred to a drying module and baked for 20 s at 20° C. Subsequently, the first wafer is taken out from the drying module. After the first wafer is transferred to the deionized water and chemical agent cleaning module, a second wafer is loaded into the ultrasonic cleaning module, and similarly, the second wafer is held without the application of ultrasonic power in the ultrasonic cleaning module for 55 s. Then the ultrasonic cleaning module is started and cleans the second wafer for 35 s. Due to the fact that the first wafer stays in the deionized water and chemical agent cleaning module is 90 s, the second wafer may be transferred into the deionized water and chemical agent cleaning module immediately after the second wafer is cleaned in the ultrasonic cleaning module. The second wafer may be transferred into the drying module when the cleaning of the second wafer is completed, since the first wafer has been taken out from the drying module at that time. Through the above processes, multiple wafers may be cleaned in succession. In addition, those processes avoid the procedure that a wafer is held in the ultrasonic cleaning module for a period after the ultrasonic cleaning, and thereby prevent the defect particles in the ultrasonic cleaning module from contaminating the surface of the wafer again.
As shown in
The time T1 of ultrasonic cleaning is set to 10 s-60 s, and preferably 35 s-45 s. The chemical agent used in the ultrasonic cleaning is chosen according to the same principle as that used in Embodiment 1. The time of cleaning with the chemical agent and the deionized water for the first time is set to 5 s-110 s, and preferably 20 s-90 s, in which the time of cleaning with the chemical agent is 0 s-70 s and the time of cleaning with the deionized water is 5 s-40 s. The cleaning chemical agent and the cleaning time for the cleaning process with the chemical agent are chosen in the same way as that in Embodiment 1.
In order to achieve better cleaning effect and remove the defect particles still adhering to the wafer surface after the wafer is cleaned with the chemical agent and deionized water for the first time, the cleaning with chemical agent and deionized water is performed for the second time for time T4. The time T4 is 5 s-110 s and preferably 20 s-90 s, in which the time of cleaning with chemical agent is 0 s-70 s and the time of cleaning with deionized water is 5 s-40 s. The chemical agent should be chosen also depending on the category and amount of defect particles on the wafer surface. For example, if the defect particles on the wafer surface are alkaline particles, an acidic chemical agent with pH<7 is chosen as the cleaning chemical agent. After cleaning with the chemical agent, the residual acidic chemical agent on the wafer surface is removed with the deionized water. Next, the wafer is dried by baking for 5 s-20 s at 20° C.-40° C., so as to remove moisture on the wafer surface.
Now a complete embodiment is described. First, a first wafer is loaded into an ultrasonic cleaning module and held without application of ultrasonic power for 20 s. Then, the ultrasonic cleaning module is started and cleans the wafer for 40 s. Next, the wafer is transferred to a first deionized water and chemical agent cleaning module immediately and cleaned for total 50 s, in witch the time of cleaning with a chemical agent is 20 s and the time of cleaning with deionized water is 30 s. Afterwards, the wafer is transferred into a second deionized water and chemical agent cleaning module and cleaned for the second time for 60 s in which the time of cleaning with the chemical agent is 40 s and the time of cleaning with the deionized water is 20 s. Then, the wafer is transferred to a drying module and baked for 10 s at 30° C.; then, the wafer is taken out from the drying module. After the first wafer is transferred to the first deionized water and chemical agent cleaning module, the second wafer is loaded into the ultrasonic cleaning module. Similar to the treatment on the first wafer, the second wafer is held static and ultrasonic is held no power for 20 s first, and then the ultrasonic cleaning module is started and cleans the second wafer for 40 s. Since the first wafer stays in the first deionized water and chemical agent cleaning module for 50 s, the second wafer may be transferred to the first deionized water and chemical agent cleaning module immediately after being cleaned in the ultrasonic cleaning module. At that time the first wafer has been transferred into the second deionized water and chemical agent cleaning module, and a third wafer is loaded into the ultrasonic cleaning module, and so on. With the technical scheme provided in the embodiment of the present invention, any wafer will not stay in the ultrasonic cleaning module after being cleaned in the ultrasonic cleaning module. Therefore, the technical scheme may prevent the defect particles in the ultrasonic cleaning module from contaminating the surface of the wafer again.
In accordance with another aspect of the present invention, after being subjected to ultrasonic cleaning, defect particles adhering to a wafer surface or inlaid between semiconductor structures such as tungsten plugs cannot be removed completely merely with deionized water or a chemical agent, and they have to be further cleaned with a brush. Therefore, in an embodiment of the present invention, there is also provided a method for cleaning the surface of a wafer after a Chemical Mechanical Polishing (CMP) of the wafer. The method includes the following processes: performing an ultrasonic cleaning on the wafer for time T1; scrubbing the wafer for n times for time T2, T3, . . . , Tn+1 (“n” is an integer), respectively; drying the wafer for time Tn+2; suppose the maximum value among T2, T3, . . . , Tn+2 is Tmax, in the case that T1 is less than any one of T2, T3, . . . , Tn+2, the ultrasonic cleaning process includes the following procedures: loading the wafer into an ultrasonic cleaning module and holding the wafer without the application of ultrasonic power for T′ (T′=Tmax−T1); performing the ultrasonic cleaning on the wafer for time T1; after the ultrasonic cleaning, scrubbing the wafer immediately. The ultrasonic cleaning is performed for time T1, and the scrubbing is performed for n times for time T2, T3, . . . , Tn+1 (“n” is an integer) with the assist of a chemical agent and deionized water cleaning; drying for time Tn+2.S supposing the maximum value among T2, T3, . . . , Tn+2 is Tmax, in the case that T1<Tmax, the ultrasonic cleaning process includes the following procedures: loading the wafer into the ultrasonic cleaning module and holding the wafer without the application of ultrasonic power for time T′ (T′=Tmax−T1); performing the ultrasonic cleaning on the wafer for T1, and then scrubbing the wafer immediately.
As shown in
In this embodiment, the time T1 of ultrasonic cleaning is set to 10 s-60 s, and preferably 35 s-45 s. After the ultrasonic cleaning, the wafer is transferred into the scrubbing module. The time T2 of scrubbing is set to 5 s-110 s, and preferably 20 s-90 s. At the beginning of scrubbing, a chemical agent is chosen depending on the category and amount of the defect particles on the wafer surface. After being cleaned with the chemical agent for 0 s-70 s, the wafer is cleaned with the deionized water for 5 s-40 s till the entire scrubbing process is completed. The chemical agent is chosen according to the same principle as that used in Embodiment 1. Next, the wafer is dried by baking it for 5 s-20 s at 20° C.-40° C. so as to remove moisture on the wafer surface.
In a preferred embodiment, a wafer is held without the application of ultrasonic power in an ultrasonic cleaning module for 35 s; then, the wafer is cleaned by ultrasonic cleaning for time T1=45 s; next, the wafer is scrubbed with the assistance of a chemical agent and deionized water cleaning for time T2=80 s, in which the time of chemical agent cleaning is 50 s and the time of deionized water cleaning is 30 s. After the cleanings, the wafer is dried for 5 s at 40° C. to remove moisture on the surface of the wafer.
As shown in
In Embodiment 4, the time T1 of ultrasonic cleaning is set to 10 s-60 s, and preferably 35 s-45 s. After the ultrasonic cleaning, the wafer is transferred into the scrubbing module. The time T2 of scrubbing is set to 5 s-110 s, and preferably 20 s-90 s. At the beginning of the scrubbing, the chemical agent is chosen depending on the category and amount of the defect particles on the wafer surface. After being cleaned with the chemical agent for 0 s-70 s, the wafer is cleaned with the deionized water for 5 s-40 s till the entire scrubbing process is completed. The chemical agent is chosen according to the same principle as that used in Embodiment 1. Next, the scrubbing is performed for the second time. At the beginning of the scrubbing, the chemical agent is chosen depending on the category and amount of the residual defect particles on the wafer surface. After being cleaned with the chemical agent for 0 s-70 s, the wafer is cleaned with the deionized water for 5 s-40 s. Finally, the wafer is dried by being baked for 5 s-20 s at 20° C.-40° C., in order to remove moisture on the wafer surface.
In a preferred embodiment, a wafer is held without the application of ultrasonic power in an ultrasonic cleaning module for 25 s. Then, the wafer is cleaned with ultrasonic cleaning for time T1=25 s. Next, the wafer is scrubbed for the first time with the assist of a chemical agent and deionized water cleaning for time T2=50 s, in which the time of cleaning with chemical agent is 10 s and the time of cleaning with deionized water is 40 s. Subsequently, the wafer is scrubbed for the second time with the assistance of a chemical agent or deionized water cleaning for T3=40 s, in which the time of cleaning with chemical agent is 15 s and the time of cleaning with deionized water is 25 s. After the cleaning, the wafer is dried by being baked for 15 s at 25° C., in order to remove moisture on the wafer surface.
With any of the technical schemes in the above embodiments 1-4, the residual defect particles on a wafer surface or between semiconductor devices and structures after CMP may be removed effectively. Specific effects are shown in
Though the present invention is described above in preferred embodiments, it is noted that those skilled in the art may make modifications and variations, without departing from the basic principle of the present invention; any of those modifications and variations shall fall into the protected scope of the present invention defined by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 200610116851.8 | Sep 2006 | CN | national |
