In the recent processes for production of semiconductor devices, the importance of processing technologies for density enhancement and miniaturization is ever increasing. The chemical mechanical polishing (CMP) technology, which is one of such technologies, now serves as a technology essential for the formation of shallow trench isolation, flattening of pre-metal insulating films or interlayer insulating films, and formation of plugs and embedded metal wirings, in the processes for production of semiconductor devices.
In the conventional processes for production of semiconductor devices, fumed silica polishing agents are generally investigated for the flattening of insulating films such as silicon oxide films, which are formed by a method such as a chemical vapor deposition (CVD; chemical layer growth) method or a spin coating method. Fumed silica polishing agents are produced by growing particles by a method of thermally decomposing silicon tetrachloride or the like, and adjusting the pH.
However, such silica polishing agents have a technical problem that the polishing rate is low. In the generation of a design rule of 0.25 μm or less, shallow trench isolation is being used for the isolation of devices within an integrated circuit.
In the shallow trench isolation, CMP is used to eliminate any excess silicon oxide film formed on the substrate, and in order to stop polishing, a stopper film to be polished at slower polishing rate is formed underneath the silicon oxide film. The stopper film is formed using silicon nitride or the like, and it is preferable that the polishing rate ratio between the silicon oxide film and the stopper film is large. Conventional colloidal silica-based polishing agents are such that the polishing rate ratio of the silicon oxide film and the stopper film is as small as about 3, and the polishing agents do not have a characteristic of being durable for the actual use in shallow trench isolation.
On the other hand, cerium oxide polishing agents are being used as glass surface polishing agents for photomasks, lenses and the like. The cerium oxide polishing agents have an advantage that the polishing rate is fast as compared with silica polishing agents or alumina polishing agents.
In recent years, polishing agents for semiconductor using high-purity cerium oxide polishing particles have been put to use. For example, the technology is disclosed in Patent Literature 1. It is also known to add additives in order to control the polishing rate of cerium oxide polishing agents and to enhance overall flatness. For example, this technology is disclosed in Patent Literature 2.
In recent years, further miniaturization is in progress with regard to the processes for production of semiconductor devices, and polishing flaws that occur at the time of polishing have been a problem. In regard to this problem, there has been an attempt to make the average particle size of the cerium oxide particles of such polishing agents using cerium oxide as described above small. However, when the average particle size is made small, the mechanical action is reduced, and therefore, there is a problem that the polishing rate is decreased.
In regard to this problem, a polishing agent using tetravalent metal hydroxide particles is under investigation, and this technology is disclosed in Patent Literature 3. This technology is intended to take advantage of the chemical action of the tetravalent metal hydroxide particles, while reducing the mechanical action as far as possible, and to thereby achieve a balance between the reduction of polishing flaws caused by the particles and the enhancement of polishing rate.