Abrading – Flexible-member tool – per se
Reexamination Certificate
2001-02-21
2004-03-16
Rose, Robert A. (Department: 3723)
Abrading
Flexible-member tool, per se
C451S041000, C051S298000
Reexamination Certificate
active
06705934
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a polishing pad and to a method of polishing semiconductor substrates where this is employed and, furthermore, it relates to a polishing pad for mechanically planarizing the surface of the insulating layers and metallic interconnects formed on silicon or other such semiconductor substrates.
BACKGROUND ART
Year by year, the mounting densities of large scale integrated circuits (LSIs) typified by semiconductor memories have increased and, along with this, the widths of the interconnects on the large scale integrated circuits have narrowed and the number of superimposed layers has increased. Due to this increase in the number of superimposed layers, while not an issue in the past, unevenness of the semiconductor wafer main face, produced as a result of the layering, has become a problem. As a result, as described in, for example, Nikkei Microdevice, July 1994, pp 50-57, semiconductor wafer planarization using chemical mechanical polishing (CMP) techniques has been investigated with the object of dealing with the inadequate depth of focus at the time of light exposure brought about by the unevenness produced by layering, or with the object of improving interconnect densities by planarizing through-hole regions.
Generally speaking, CMP equipment comprises a polishing head which holds the semiconductor wafer, which is the material being treated, a polishing pad for carrying out the polishing treatment of the material being treated and a polishing platen which holds this polishing pad. In the semiconductor wafer polishing treatment, the wafer surface layers are made smooth by effecting relative motion between the semiconductor wafer and the polishing pad, and removing the projecting portions on the semiconductor wafer surface layers, using a slurry consisting of abrasive particles and chemical liquid. The polishing rate of a semiconductor wafer, for example in the case of a silicon oxide (SiO
2
) film formed on the main face of a semiconductor wafer, is roughly proportional to the relative speed between semiconductor wafer and polishing pad, and to the load. Thus, in order to carry out uniform polishing of each part of a semiconductor wafer, it is necessary to make the load applied to the semiconductor wafer uniform.
When insulating layers and the like formed on the main face of a semiconductor wafer are subjected to polishing, if the polishing pad is too soft then, the local planarity is adversely affected. For such reasons, at present a foamed polyurethane sheet of Shore A-type hardness not less than 90° is employed. However, with foamed polyurethane pads of high hardness, problems have arisen in that the degree of planarity varies between areas of different densities of unevenness of the insulating layers and the like, and a global step height is produced. There is also the problem that dishing (where the height of the central region of a metallic interconnect is lower than the edges) occurs when the width of Damascene-based metallic interconnects is large. Furthermore, there have also been problems in that the polishing agent is readily adsorbed and clogging tends to occur, or permanent set of the pad surface layer region is produced during the polishing, and so the polishing rate decreases.
OBJECTIVE OF THE INVENTION
The objective of the present invention lies in offering a polishing pad where, in the case of a polishing pad for mechanically flattening the surfaces of the insulating layers or metallic interconnects formed on a silicon substrate, the polishing rate is high, the global step height is low, dishing does not readily occur at the metallic interconnects, clogging and permanent set of the surface layer region do not tend to occur, and the polishing rate is stable.
DISCLOSURE OF THE INVENTION
The present invention has the following constitution.
“A polishing pad of micro rubber A-type hardness at least 80°, which contains polyurethane and polymer produced from a vinyl compound, and has closed cells of average cell diameter no more than 1000 &mgr;m and, furthermore, has a density in the range 0.4 to 1.1.”
BEST MODE FOR CARRYING OUT THE INVENTION
Below, the form for practising the invention is explained.
Firstly, the micro rubber A-type hardness referred to in the present invention denotes the value evaluated using a micro rubber durometer MD-1 produced by the Kobunshi Keiki Co. Ltd. The micro rubber durometer MD-1 enables hardness measurements to be carried out on thin/small items where measurement has been difficult with conventional durometers, and because it has been designed and manufactured as a spring-system rubber durometer A-type model scaled down to approximately ⅕, measured values which are in agreement with the spring-system rubber durometer A-type hardness are obtained. Since the polishing layer or hard layer thickness in the case of ordinary polishing pads extends less than 5 mm, evaluation is not possible with a spring-system rubber A-type durometer and so evaluation is carried out with this micro rubber durometer, MD-1.
For the polishing pad of the present invention, a micro rubber A-type hardness of at least 80°, and preferably at least 90°, is necessary. If the micro rubber A-type hardness is not at least 80°, the planarity of the local unevenness on the semiconductor substrate is unsatisfactory, so this is undesirable.
Since the polishing pad of the present invention has closed cells, it possesses elasticity in the thickness direction and even when slurry aggregates and polishing debris are sandwiched between the surface undergoing polishing and the polishing pad, scratching can be prevented. It is necessary that the closed cell diameter be no more than 1000&mgr;, as an average diameter, so that local unevenness is not brought about. No more than 500 &mgr;m is preferred, with no more than 30 &mgr;m still further preferred.
It is preferred that the polishing pad of the present invention has a density lying in the range 0.4 to 1.1. If the density is not at least 0.4, the local planarity is poor and there is a considerable global step height. If the density exceeds 1.1, scratching readily occurs. It is further preferred that the density lies in the range 0.6 to 0.9, with a density in the range 0.65 to 0.85 still more preferred.
The polyurethane in the polishing pad of the present invention is a polymer obtained from a polyisocyanate and a compound containing active hydrogen, specifically a hydroxy or amino group-containing compound with two or more active hydrogens. As examples of the polyisocyanate, there are tolylene diisocyanate, diphenylmethane diisocyanate, naphthalene diisocyanate, tolidine diisocyanate, hexamethylene diisocyanate and isophorone diisocyanate, but there is no restriction thereto. Polyols are typical of the polyhydroxy compounds, examples of which are polyether-polyols, polypropylene glycol, polytetramethylene ether glycol, epoxy resin-modified polyols, polyester polyols, acryl polyols, polybutadiene polyols, silicone polyols and the like. Of these, the polyurethanes obtained from a combination of tolylene diisocyanate or diphenylmethane diisocyanate, as the polyisocyanate, and polypropylene glycol or polytetramethylene ether glycol, as the polyol, are outstanding in their mouldability and are widely used, so are preferred.
The present invention is a polishing pad containing polyurethane and polymer produced from a vinyl compound, and which has closed cells. With a polyurethane, as the hardness is raised it becomes more brittle. Furthermore, while it is possible to raise the toughness and hardness merely using polymer from a vinyl compound, it has been difficult to obtain a homogenous polishing pad with closed cells. However, by incorporating polyurethane and polymer produced from a vinyl compound, it has been possible to produce a polishing pad of high toughness and hardness which contains closed cells.
In the present invention, a vinyl compound means a compound with a polymerizable carbon-carbon double bond. Specific examples are methyl methacrylate, ethyl methacrylate, propyl m
Hashisaka Kazuhiko
Oka Tetsuo
Shiro Kuniyasu
Morrison & Foerster / LLP
Rose Robert A.
Toray Industries Inc.
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