Semiconductor device manufacturing: process – Chemical etching – Combined with the removal of material by nonchemical means
Reexamination Certificate
2001-04-10
2003-05-13
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Chemical etching
Combined with the removal of material by nonchemical means
C438S687000
Reexamination Certificate
active
06562719
ABSTRACT:
PRIORITY TO FOREIGN APPLICATIONS
This application claims priority to Japanese Patent Application No.P2000-242750.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to polishing of a metal film, and in particular, to a method of polishing in an interconnect-fabrication process for producing semiconductor devices.
2. Description of the Background
In recent years, with rapid progress and development in the techniques available to produce semiconductor integrated circuits, such as large scale semiconductor integrated circuits (hereinafter referred as “LSI”), with greater integration and improved performance characteristics, new techniques for fabrication have been developed. One of these techniques is chemical-mechanical polishing (hereinafter referred as “CMP”), which is a technique frequently used in processes such as LSI manufacturing—in particular, CMP is used in the flattening of an inter-layer insulating film, the formation of metal plug, and the formation of buried interconnect layer in the process to form a multi-level interconnection. This technique is disclosed, for example, in U.S. Pat. No. 4,944,836.
Further, attempts have been made in recent years to utilize copper (Cu) alloy with low resistance as the material for interconnection, rather than the aluminum (Al) alloy used in the past, with the purpose of producing high-performance LSIs. However, for Cu alloy, it is difficult to carry out fine fabrication based on dry etching methods, which methods have been frequently used for the formation of Al alloy interconnects. For this reason, the “damascene” method has been primarily adopted, wherein a Cu alloy thin film is deposited on an insulating film formed with grooves fabricated thereon, and the Cu alloy thin film other than that buried in the grooves is removed by CMP, and buried interconnect is thereby prepared. This technique is disclosed, for example, in JP-A-2-278822. It is generally practiced to place a barrier metal film, such as a titanium nitride (TiN) film, a tantalum (Ta) film or a tantalum nitride (TaN) film, of several tens of nm in thickness, for the purposes of improving adhesive properties and of providing Cu diffusion barrier between the Cu alloy thin film and the insulating film.
In the past, the polishing solutions used in CMP, for metal films such as the Cu alloy commonly used for interconnects, generally contained abrasive power and oxidizer (oxidizing chemicals) as the main components. The basic CMP mechanism is oxidization of the surface of a metal film by the oxidizing action of the oxidizer, and the mechanical removal of the oxides by the abrasive powder. This technique is disclosed, for example, in “The Science of CMP” (edited by Masahiro Kashiwagi; published by Science Forum Co., Ltd.; Aug. 20, 1997, p.299)
Abrasive powders, such as alumina abrasive powder or silica abrasive powder, of several tens to several hundreds of nm in grain diameter, are known in the art. Most types of abrasive powder for metal CMP that are commercially available are alumina type powders.
As the oxidizer, hydrogen peroxide (H
2
O
2
), ferric nitrate (Fe(NO
3
)
3
), and potassium periodate (KIO
3
) are generally used. These are described, for example, in “The Science of CMP” (pp.299-300). Among these substances, hydrogen peroxide has been more frequently used in recent years, due to the fact that it does not contain metal ions.
However, when interconnects and/or plugs are fabricated using the polishing solution, which contains an abrasive powder for conventional type metal CMP as the main component, the following problems occur:
(1) Development of dishing (depression on interconnect) and erosion (corrosion and scraping of the insulating film on the peripheral portion of the interconnect);
(2) Development of scratches (polishing scratches);
(3) Delamination;
(4) The need to remove abrasive powder by ishing after CMP;
(5) High cost for abrasives;
(6) High cost for abrasive supply system and iste liquid processing system; and
(7) Dust in clean room originated from CMP system.
The above problems are caused by the fact that CMP is performed using abrasive powder. In the conventional CMP methods, however, the abrasive powder is needed to quickly remove oxide layers formed by the oxidizer. If abrasive powder is not added, it is not possible to reach a polishing rate (i.e. a polishing speed) that is suitable for practical use.
In contrast, JP-A-11-135466 discloses a method for polishing metal film using a polishing solution not containing abrasive powder, and for fabricating a buried interconnect structure. According to this method, using a polishing solution containing an oxidizer, a substance to turn the oxides to water-soluble, water and, if necessary, an anti-corrosive substance (for forming inhibition layer), the surface of the metal film is mechanically scrubbed, and a buried metal interconnect can be prepared on the surface. For example, a Cu interconnect is produced using an abrasive-free polishing solution, which contains hydrogen peroxide, citric acid, and benzotriazole (hereinafter referred as “BTA”).
The problems (1) to (7) described hereinabove may be solved when the above abrasive-free polishing solution method is used, while a acceptable polishing rate (speed) under normal polishing conditions of 80-150 nm/min is maintained. Even when high polishing load of 300 g/cm
2
or more is applied, the polishing rate reaches the saturation level and does not go beyond 200 nm/min, and thus it is not possible to increase the throughput beyond this limit. In the case wherein a commercial alumina polishing solution is used, a polishing rate as high as 300-500 nm/min may be reached by applying a high polishing load. In this case, however, the problems of scratches and delamination become more serious.
On the other hand, a number of different approaches to these difficulties are available. One such approach is presented in JP-A-7-94455, which discloses a phosphoric acid aqueous solution as one of abrasive polishing solutions for Cu (see Example 4 of the above publication). It is described therein that the ratio of polishing rate of Cu to the insulating film can be increased up to 14.5 by using the abrasive polishing solution containing phosphoric acid of 3% concentration (see
FIG. 5
of the above publication, wherein the Cu content is 100%). However, using experimentation, it is very difficult to attain a polishing rate of 50 nm/min. or more under practical polishing condition (i.e. polishing load of 500 g/cm
2
or less; rotational speed of platen at 90 rpm or less) by the simple combination of abrasive powder and phosphoric acid aqueous solution. If the abrasive powder is removed, the polishing rate is less than 20 nm/min. Therefore, although the ratio of polishing rate is high using this abrasive polishing solution, it is not possible to carry out polishing with a sufficient throughput and high accuracy (without developing erosion).
In the abrasive polishing solution for tungsten CMP disclosed in JP-A-10-265776, phosphoric acid or organic acid is used as a stabilizer. In this case, the stabilizer is a chemical to suppress and control the reaction between a catalyst (ferric nitrate) added in the polishing solution, and the oxidizer (hydrogen peroxide). According to experimentation, an etching rate for Cu of this polishing solution is more than 100 nm/min, and, using this solution, it is possible to polish Cu film, but a Cu interconnect is eliminated by the etching. This polishing solution is specifically directed to tungsten CMP and is not generally applicable for Cu-CMP. Thus, using the teachings of JP-A-10-265776, it is not possible to achieve high-speed polishing of Cu by simultaneously adding phosphoric acid and organic acid (in particular, lactic acid) to the polishing solution not containing abrasive powder.
A polishing solution for Cu-CMP is disclosed in JP-A-11-21546. This polishing solution includes abrasive powder, an oxidizer (e.g. urea—hydrogen peroxide), a chemical to form complex salt (e.g. ammonium oxalate or organic acid such
Hom-ma Yoshio
Kondo Seiichi
Sakuma Noriyuki
Dang Phuc T.
Hitachi , Ltd.
LandOfFree
Methods of polishing, interconnect-fabrication, and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Methods of polishing, interconnect-fabrication, and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Methods of polishing, interconnect-fabrication, and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3040074