The present invention relates to a polishing slurry that may be used in the step of manufacturing semiconductor devices. The invention more specifically relates to a polishing slurry that may be advantageously used to polish mainly a barrier layer formed from a metallic barrier material and an interlayer dielectric film in planarization carried out in the step of forming interconnections in semiconductor devices.
In the development of semiconductor devices typified by semiconductor integrated circuits (hereinafter referred to as “LSI devices”), the trend toward smaller sizes and higher processing speeds has created a need in recent years for higher density and higher integration by the adoption of miniaturization and multilayer constructions of interconnections. Various techniques are being used to this end, including chemical mechanical polishing (hereinafter referred to as “CMP”). CMP is an essential technique for carrying out, for example, the surface planarization of a film to be processed (e.g., an interlayer dielectric film), plug formation, and buried metal interconnect formation, and this technology is used to carry out substrate planarization, to remove surplus metal thin film during the formation of interconnections and to remove surplus barrier layer on the dielectric film.
CMP generally involves attaching a polishing pad onto a circular platen, impregnating the surface of the polishing pad with a polishing slurry, pressing the front side of a substrate (wafer) against the pad, and rotating both the platen and the substrate while applying a predetermined pressure (polishing pressure) from the back side of the substrate so as to planarize the front side of the substrate by the mechanical friction that arises.
In the manufacture of semiconductor devices such as LSIs, fine interconnections are formed in multiple layers, and when interconnections of metals such as copper are formed in each layer, films of barrier metals such as Ta, TaN, Ti and TiN are formed in advance in order to prevent the wiring material from diffusing to the interlayer dielectric film while improving the adhesion of the wiring material.
In order to form each interconnection layer, CMP of a metal film (hereinafter referred to as “metal film CMP”) is carried out in one stage or multiple stages to remove surplus wiring material deposited by plating or other method. Then, CMP for removing metallic barrier materials (barrier metals) exposed at the surface by the metal film CMP is usually carried out. However, the metal film CMP suffers from problems such as dishing (excessive polishing of interconnection portions) and also erosion.
In order to suppress such dishing, it is required, in the barrier metal CMP following the metal film CMP, to finally form interconnection layers having reduced irregularities due to, for example, dishing and erosion by adjusting the polishing rate in the metal interconnection portions and the polishing rate in the barrier metal portions. In other words, in cases where the barrier metal and the interlayer dielectric film are polished at a relatively lower polishing rate than the metal wiring material, the interconnection portions are polished more quickly to cause dishing, resulting in erosion. It is desirable for the barrier metal and the insulating layer to be polished at a reasonably high rate in order to prevent these defects. The foregoing dishing very often occurs in the metal film CMP, and the dishing having occurred in the metal film CMP can be reduced by polishing the barrier metal and interlayer dielectric film in the barrier metal CMP at a higher polishing rate than the metal wiring material. Such a high polishing rate will bring about an increased throughput of the barrier metal CMP.
The metal polishing slurry used in CMP typically includes an abrasive (such as alumina, silica, ceric oxide or zirconia) and an oxidizer (such as hydrogen peroxide, persulfuric acid, hypochlorous acid or nitric acid). It is believed that polishing takes place with oxidization of the metal surface by the oxidizer and removal of the resulting oxide film by the abrasive.
However, CMP conducted by using such polishing slurry containing the solid abrasive is associated with the risk of scratches formed by the polishing (scratches), excessive polishing of the entire polishing surface (thinning), deformation of the polished metal surface in the shape of a dish (dishing), and excessive polishing of the insulator between metal interconnections and dish-shape deformation of a plurality of metal interconnection surfaces (erosion).
Various studies as described below have been made for such polishing slurry containing a solid abrasive.
Specifically, a CMP polishing agent and a polishing method for the purpose of polishing at a high rate while hardly causing polishing scratches (see, for example, JP 2003-17446 A), a polishing composition and a polishing method with which the cleaning property was improved in CMP (see, for example, JP 2003-142435 A), and a polishing composition for preventing polishing abrasive particles from agglomerating (see, for example, JP 2000-84832 A) have been proposed.