1. Field of the Invention
The present invention relates to a polishing method and a polishing agent used in a semiconductor element manufacturing method, more specifically to a polishing method and a polishing agent used in a step for smoothing the surface of a substrate, especially, smoothing an interlayer insulation film, a step of forming a buried metal wiring portion, a step of forming a buried element separation film, or a step of forming a buried capacitor, or the like.
2. Description of the Related Art
With regard to current ultra-super-large-scale integrated circuits, there is a trend towards reducing the sizes of a transistor and other semiconductor elements and increasing the mounting density. Accordingly, various micro processing techniques are being studied and developed, and the design rule is already set to an order of a sub-half micron.
One of the techniques being developed in order to satisfy the strict requirement of the micro processing is a CMP (chemical mechanical polishing) technique. This technique is essential to the manufacturing process of a semiconductor, in particular, when smoothing an interlayer insulation film, forming a plug, forming a buried metal wiring portion, separation of a buried element, forming a buried capacitor and the like.
FIGS. 1A to 1E are cross sections of an interlayer insulation film, illustrating a step of smoothing the film by use of a CMP technique. First, as shown in FIG. 1A, a silicon oxide film 2 is formed on a silicon substrate 1 a ratio of whose protruding portions occupies 50% of the entire surface, and a first Al wiring portion 3 having a width of 0.3 xcexcm and a height of 0.4 xcexcm is formed on the silicon oxide film 2 by a general lithography method and a general etching method. Next, as shown in FIG. 1B, a silicon oxide film 4 having a thickness of 1.3 xcexcm is formed by a plasma CVD method, and then an abrasion process is carried out so as to smooth the silicon oxide film 4. Various changes in cross-sectional shape of the film are illustrated in FIGS. 1C to FIG. 1E. FIG. 1C shows a cross sectional shape of the film in the case where the abrasion process is completed at an ideal position, whereas FIGS. 1A and 1E each show a cross sectional shape in the case where the abrasion process is excessively carried out.
With the conventional abrasion technique, the abrasion rate changes along with an elapse of time, and therefore it is very difficult to stop the processing at an ideal position as shown in FIG. 1C. Further, in the case where there is a wide space between Al wiring portions, that is, when the silicon oxide film 4 is wide, the center portion of the silicon oxide film has priority to other portions in abrasion, thus causing a so-called dishing.
In the case where the abrasion is excessively carried out as shown in FIG. 1D, the pressure resistance between a second Al wiring portion (not shown) formed on the silicon oxide film 4 and the first Al wiring portion 3 is deteriorated. Further, the abrasion is excessively carried out as shown in FIG. 1E, the first Al wiring portion 3 is in some cases disconnected.
In order to solve the above-described drawbacks, it has been proposed a technique in which an anti-abrasion film 5 made of a material such as Si3N4, having an abrasion rate lower than that of a to-be-polished member (in this case, silicon oxide film) is formed on the wide silicon oxide film 4 as shown in FIG. 2 (Jap. Pat. Appln. KOKAI Publication No. 5-315308). However, this technique entails a problem in which the selection rate (the abrasion rate of the Si3N4 film/the abrasion rate of the silicon oxide film) cannot be set high, thus increasing the number of steps of forming, removing and the like of the anti-abrasion film 5.
The present invention has been proposed in consideration of the above problems, and the object thereof is to provide an abrasion method of polishing a desired protruded portion at high efficiency without causing dishing.
According to the first aspect of the present invention, there is provided a polishing method comprising the steps of: forming a film to be polished, having a depressed portion and a protruding portion on a surface of a substrate; and polishing the film to be polished by relatively moving the substrate and a polishing table, while pressing the substrate having the film to be polished, onto a polishing cloth of the polishing table and supplying a polishing solution containing polishing grains, between the film to be polished and the polishing cloth; wherein an average distance between a surface of the depressed portion of the film to be polished and a surface of the polishing cloth during polishing is set larger than an average diameter of the polishing grains.
According to the second aspect of the present invention, there is provided a polishing method comprising the steps of: forming a film to be polished, having a depressed portion and a protruding portion on a surface of a substrate; and polishing the film to be polished by relatively moving the substrate and a polishing table, while pressing the substrate having the film to be polished, onto a polishing cloth of the polishing table and supplying a polishing solution containing polishing grains, between the film to be polished and the polishing cloth; wherein a frictional coefficient between the film to be polished and the polishing solution during polishing is larger than a frictional coefficient between the polishing cloth and the polishing solution.
According to the third aspect of the present invention, there is provided a polishing method having the steps of: forming a film to be polished, having a depressed portion and a protruding portion on a surface of a substrate; and polishing the film to be polished by relatively moving the substrate and a polishing table, while pressing the substrate having the film to be polished, onto a polishing cloth of the polishing table and supplying a polishing solution containing polishing grains, between the film to be polished and the polishing cloth; wherein an organic compound having a molecular weight of 100 or more, and containing at least one hydrophilic group selected from the group consisting of COOM1 (M represents an atom or a functional group which can form a salt when substituted with a hydrogen atom of a carboxyl group), SO3H (sulfo group) and SO3M2 (M2 represents an atom or a functional group which can form a salt when substituted with a hydrogen atom of a carboxyl group) is added to the polishing solution.
According to the fourth aspect of the present invention, there is provided a polishing method comprising the steps of: forming a film to be polished, having a depressed portion and a protruding portion on a surface of a substrate; and polishing the film to be polished by relatively moving the substrate and a polishing table, while pressing the substrate having the film to be polished, onto a polishing cloth of the polishing table and supplying a polishing solution containing polishing grains, between the film to be polished and the polishing cloth; wherein a content of an organic compound in of the polishing solution supplied is varied during polishing.
Further, there are provided a polishing solution in which polishing grains are dispersed into a dispersion medium, and a polishing agent containing an organic compound having a molecular weight of 100 or more and containing at least one hydrophilic group selected from the group consisting of COOM1 (M represents an atom or a functional group which can form a salt when substituted with a hydrogen atom of a carboxyl group), SO3H (sulfo group) and SO3M2 (M2 represents an atom or a functional group which can form a salt when substituted with a hydrogen atom of a carboxyl group) added to the polishing solution.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
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