Chemical mechanical planarization (CMP), a planarization process, is adopted to fabricate silicon wafers to produce globally planar wafer surface. CMP also enables the miniaturization of features, memory devices and other chips in ultra-large scale integration (ULSI). For twenty years, many research...
Chemical mechanical planarization (CMP), a planarization process, is adopted to fabricate silicon wafers to produce globally planar wafer surface. CMP also enables the miniaturization of features, memory devices and other chips in ultra-large scale integration (ULSI). For twenty years, many researchers have been studying this CMP process and have built up lots of theories about it. However, due to the continuous shrinkage of device size and appearance of new material, CMP technology became more complicated and various.
Copper (Cu) has been widely used for interconnection structure in integrated circuits because of its properties such as a low resistance and high resistance to electromigration compared with aluminum. Damascene processing for the interconnection structure utilizes 2-steps CMP. However 2-steps CMP consists of Cu CMP for removing overburden copper and barrier CMP for removing Ta/TaN/Ti layer. Such a 2-steps CMP process is a very dirty process that it leaves a lot of abrasive particles on the wafer surface, so, cleaning is required to remove abrasive particles after Cu CMP. The minimization of particle residue is required with each successive technology generation, and the cleaning of wafers becomes more complicated.
After the second step CMP, Cu and PETEOS (plasma-enhanced tetraethylorthosilicate) are exposed. To investigate the abrasive particles adhesion on Cu and PETEOS, the relative zeta potential among the colloidal silica abrasive, Cu and PETEOS was measured. The copper surface and colloidal silica abrasive has different sign of surface zeta potential, resulting in an attractive force between copper surface and the colloidal silica abrasive. However, the repulsive force exists between the PETEOS surface and colloidal silica abrasive because of same surface zeta potential sign. Hence, the abrasives on the copper surface is an important matter in the post Cu CMP cleaning.
To measure the adhesion force between Cu and abrasive, the lithography mode in Atomic Force Microscope(AFM) was used. Through the AFM scratch test, the force that induces to remove abrasive could be obtained. The abrasive particle was removed from 0.001 nN to 5000 nN without scratch on Cu surface.
A piezoelectric quarz sensor was used to detect dynamic friction during the buffing process. the buffing is performed under various conditions as a cleaning process. In each conditions, the friction force that was detected shows the friction characterization of boundary surface. According to increase of buffing velocity, abrasives removal was mainly induced by hydrodynamic drag force and pad rotating torque. The other case, the increase of buffing pressure, abrasives was remove by the impact between the pad and abrasives. Hydrodynamic drag force has weak abrasives removal efficiency, but it does not make scratch on Cu surface. Impact between the pad and abrasives has more effective cleaning ability than hydrodynamic drag force. but, it induced the scratch on the wafer in case of high friction force.
This paper studies the abrasive adhesion force on the Cu wafer and the cleaning efficiency of buffing process. It will be help us to understand about abrasives removal of wafer surface for post-Cu CMP cleaning.
Chemical mechanical planarization (CMP), a planarization process, is adopted to fabricate silicon wafers to produce globally planar wafer surface. CMP also enables the miniaturization of features, memory devices and other chips in ultra-large scale integration (ULSI). For twenty years, many researchers have been studying this CMP process and have built up lots of theories about it. However, due to the continuous shrinkage of device size and appearance of new material, CMP technology became more complicated and various.
Copper (Cu) has been widely used for interconnection structure in integrated circuits because of its properties such as a low resistance and high resistance to electromigration compared with aluminum. Damascene processing for the interconnection structure utilizes 2-steps CMP. However 2-steps CMP consists of Cu CMP for removing overburden copper and barrier CMP for removing Ta/TaN/Ti layer. Such a 2-steps CMP process is a very dirty process that it leaves a lot of abrasive particles on the wafer surface, so, cleaning is required to remove abrasive particles after Cu CMP. The minimization of particle residue is required with each successive technology generation, and the cleaning of wafers becomes more complicated.
After the second step CMP, Cu and PETEOS (plasma-enhanced tetraethylorthosilicate) are exposed. To investigate the abrasive particles adhesion on Cu and PETEOS, the relative zeta potential among the colloidal silica abrasive, Cu and PETEOS was measured. The copper surface and colloidal silica abrasive has different sign of surface zeta potential, resulting in an attractive force between copper surface and the colloidal silica abrasive. However, the repulsive force exists between the PETEOS surface and colloidal silica abrasive because of same surface zeta potential sign. Hence, the abrasives on the copper surface is an important matter in the post Cu CMP cleaning.
To measure the adhesion force between Cu and abrasive, the lithography mode in Atomic Force Microscope(AFM) was used. Through the AFM scratch test, the force that induces to remove abrasive could be obtained. The abrasive particle was removed from 0.001 nN to 5000 nN without scratch on Cu surface.
A piezoelectric quarz sensor was used to detect dynamic friction during the buffing process. the buffing is performed under various conditions as a cleaning process. In each conditions, the friction force that was detected shows the friction characterization of boundary surface. According to increase of buffing velocity, abrasives removal was mainly induced by hydrodynamic drag force and pad rotating torque. The other case, the increase of buffing pressure, abrasives was remove by the impact between the pad and abrasives. Hydrodynamic drag force has weak abrasives removal efficiency, but it does not make scratch on Cu surface. Impact between the pad and abrasives has more effective cleaning ability than hydrodynamic drag force. but, it induced the scratch on the wafer in case of high friction force.
This paper studies the abrasive adhesion force on the Cu wafer and the cleaning efficiency of buffing process. It will be help us to understand about abrasives removal of wafer surface for post-Cu CMP cleaning.
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