1. Field of the Invention
The present invention relates to a chemical mechanical polishing (CMP) process and fabricating methods of semiconductor structures. More particularly, the present invention relates to a complex CMP process and fabricating methods of a shallow trench isolation (STI) structure and an interconnect structure.
2. Description of the Related Art
In a semiconductor process, surface planarization is a very important issue for high-resolution lithography, because a rugged surface causes significant light scattering in the exposure step making the pattern transfer inaccurate. Since the CMP technology is the only solution for global planarization in VLSI circuits and even ULSI circuits, most of wafer-surface planarization processes are currently done through CMP.
Among various CMP machines, the fixed abrasive CMP (FACMP) machine is used more frequently now. A FACMP machine includes at least two polishing platens, while a wafer with a film to be polished thereon is first placed, by using a robot, on the platen having coarser abrasive thereon for coarse polishing, and then on the other platen having finer abrasive thereon for fine polishing. Though the planarity achieved by using the FACMP machine is higher, the polishing rate of the FACMP machine, which is merely about 8 wafers per hour, is lower than that of an ordinary non-fixed abrasive CMP machine. In addition, because the FACMP machine itself and the consumptive materials used therein are both expensive, the manufacturing process costs too much.
In view of the foregoing, one object of this invention is to provide a complex CMP process, which may utilize the combination of a FACMP machine and a non-fixed abrasive CMP machine for planarization to improve the polishing efficiency and thereby increase the throughput, as well as to lower the manufacturing cost.
Another object of this invention is to provide a method for fabricating an STI structure, which may use a FACMP machine together with a non-fixed abrasive CMP machine to planarize the STI insulating film for improving the polishing efficiency and the throughput of the process.
Still another object of this invention is to provide a method for fabricating an interconnect structure, which may use a FACMP machine together with a non-fixed abrasive CMP machine to planarize the conductive film for higher polishing efficiency and more throughput.
The complex CMP process of this invention is described as follows. A target film is coarsely polished using a first polishing platen in a first CMP machine. The remaining target film is then fine polished using successively a second polishing platen and a third polishing platen in a second CMP machine that is different from the first CMP machine.
In one embodiment of this invention, the first CMP machine is a non-fixed abrasive CMP machine, while the second CMP machine is a FACMP machine. The polishing rate to the target film on the first polishing platen is preferably higher than that on the second or third polishing platen, and the polishing rate on the second polishing platen may be substantially the same as that on the third polishing platen.
The method for fabricating an STI structure of this invention is described as follows. A semiconductor substrate is provided, and then a patterned hard mask layer is formed thereon. A trench is formed in the substrate using the patterned hard mask layer as an etching mask. An insulating film is then formed on the patterned hard mask layer and in the trench. Thereafter, the insulating film is coarsely polished using a first polishing platen in a first CMP machine. The remaining insulating film is then fine polished using successively a second polishing platen and a third polishing platen in a second CMP machine that is different from the first CMP machine to completely remove the insulating film on the hard mask layer. The patterned hard mask layer is then removed.
In one preferred embodiment of the above method, the first and the second CMP machines are respectively a non-fixed abrasive CMP machine and a FACMP machine. The polishing rate to the insulating film on the first polishing platen is preferably higher than that on the second or third polishing platen, and the polishing rate on the second polishing platen may be substantially the same as that on the third polishing platen. In addition, the abrasive used in the first CMP machine may include silicon dioxide (SiO2) particles, while that used in the second CMP machine may include cerium dioxide (CeO2) particles. The material of the hard mask layer may be silicon nitride (SiN).
The method for fabricating an interconnect structure of this invention is described as follows. A substrate is provided, and then a dielectric layer is formed thereon. An opening is formed in the dielectric layer, and then a conductive film is formed on the dielectric layer and in the opening. Thereafter, the conductive film is coarsely polished using a first polishing platen in a first CMP machine. The remaining conductive film is then fine polished using successively a second polishing platen and a third polishing platen in a second CMP machine different from the first CMP machine to completely remove the conductive film on the dielectric layer.
In one preferred embodiment of the above method, the first and the second CMP machines are respectively a non-fixed abrasive CMP machine and a FACMP machine. The polishing rate to the conductive film on the first polishing platen is preferably higher than that on the second or third polishing platen, and the polishing rate on the second polishing platen may be substantially the same as that on the third polishing platen. In addition, the conductive film may be a metal film, such as a copper film.
Accordingly, in a preferred embodiment of the complex CMP process of this invention, a non-fixed abrasive CMP machine is first used to coarsely polish the target film in high speed, and then a FACMP machine is used to fine polish the remaining target film with two polishing platens having substantially the same polishing rate. Therefore, not only a good planarity can be made via the fine polishing in the FACMP machine, but also the polishing time can be reduced to increase the throughput. Meanwhile, since the non-fixed abrasive CMP machine itself and the consumptive materials used therein are both cheaper, the manufacturing cost can be lowered.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.
Next, the substrate having the coarsely polished target film thereon is taken out from the first CMP machine and then loaded into a second CMP machine. The type of the second CMP machine is different from that of the first CMP machine, and is possibly a FACMP machine that has multiple polishing platens, for example, 4 polishing platens. In step 102, the remaining target film is fine polished first using a second polishing platen in the second CMP machine. The polishing rate to the target film on the second polishing platen is lower than that on the first polishing platen in the first CMP machine, but the surface planarity of the remaining target film is improved with the polishing step 102.
Subsequently, in step 104, the substrate is placed on a third polishing platen in the same second CMP machine, and then the remaining target film is polished using the third polishing platen. The polishing rates on the second and third polishing platens are substantially the same, which means their difference is within a small range.
It is particularly noted that since the requirement in planarity in the coarse polishing step 100 is lower, a non-fixed abrasive CMP machine having a much higher polishing rate and costing less is used to increase the polishing efficiency and lower the manufacturing cost. Thereafter, a FACMP machine having multiple polishing platens is used to perform the fine polishing steps 102 and 104, wherein each wafer is polished successively on a second polishing platen and a third polishing platen that has substantially the same polishing rate.
The reasons to polish one wafer successively on two polishing platens of the same type includes that the polishing efficiency of multiple wafers can be improved as considering the wafer transfer mechanism in the CMP machine. More specifically, the second and the third two polishing platens can be rotated at the same time, so that when a wafer is being polished using the third polishing platen, another wafer can be polished using the second polishing platen that was just used to polish the wafer. Therefore, not only the planarity is good due to the fine polishing in the FACMP machine, but also the polishing time is reduced to increase the throughput of the process. In the following embodiments of this invention, the above complex CMP process is applied to an STI process and an interconnect process, respectively.
Referring to
Referring to
Referring to
The abrasive used in the second CMP machine may be CeO2 particles, and the polishing rate usually ranges from 50 Å/min to 1500 Å/min, preferably from 200Å/min to 800 Å/min. The CeO2 abrasive has a higher polishing selectivity to an insulating material as compared with the SiO2 abrasive, and can make a surface non-uniformity as low as 3%, which is lower than the non-uniformity of 6% generally made by the SiO2 abrasive. Then, the patterned hard mask layer 202 is removed, as shown in
Referring to
Referring to
As mentioned above, in the preferred embodiment of this invention, a non-fixed abrasive CMP machine that costs less is first used to coarsely polish the target film in high speed, and then a FACMP machine is used to fine polish the remaining target film. Therefore, not only the planarity is good due to the fine polishing, but also the polishing time can be reduced to increase the throughput of the CMP process up to, for example, 18 wafers per hour. Meanwhile, since the non-fixed abrasive CMP machine itself and the consumptive materials used therein are both cheaper, the manufacturing cost can be lowered at the same time.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention covers modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.