Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1999-08-06
2001-02-27
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S626000, C438S627000, C438S653000, C438S654000, C438S660000, C438S668000
Reexamination Certificate
active
06194316
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for forming a Cu-thin film on a semiconductor substrate such as an LSI substrate and more particularly to a method for forming a Cu-thin film on a semiconductor substrate using a dispersion containing Cu ultrafine particles individually dispersed therein.
2. Prior Art
In the recent semiconductor industries, the distributing wires formed on a substrate have been increasingly finer and the number of layers formed thereon has also been increased in proportion to the requirements for LSI's having a higher integration density and ability of operating at a high speed. However, this results in a decrease in the pitch of wires and in turn impairs the capacity between neighboring wires and the resistance of the wires and a problem accordingly arises such as delayed signal transmission. To eliminate this problem, it has been required to use a wiring material having a low specific resistance and an interlayer insulating film having a low dielectric constant. For this reason, attempts have been made to use, as a material for distributing wires, Cu having a low specific resistance and excellent resistance to electromigration (EM) in place of Al alloys or the like conventionally used. As a method for forming a Cu-thin film, there has been developed a so-called damascene method which comprises the steps of depositing a Cu film in, for instance, wiring grooves, via holes and contact holes according to, for instance, the sputtering method, CVD method or plating method and then subjecting the Cu film to a chemical-mechanical polishing (CMP) treatment.
However, such a conventional Cu-thin film-forming method suffers from the following problems. In the sputtering method among the methods for depositing Cu-thin films on a substrate, there is in general a limit in the degree of step coverage and further the reflow temperature should be reduced in order to ensure the compatibility with the method to the formation of a low dielectric film, even when the sputtering method is used in combination with the reflow method. For this reason, it is difficult to accelerate the embedding or filling up of fine grooves through reflow. Additionally, this method also suffers from a problem in that it requires a high processing cost. On the other hand, the plating method requires the formation of a Cu-thin film, as the so-called seed layer, on a barrier layer and this in turn results in such a problem that the plating liquid remains in voids. Both of the foregoing film-forming methods are insufficient for the method for forming the Cu-thin film. In addition, these methods are insufficient in the ability to embed or fill up, for instance, grooves for distributing wires when the aspect ratio of the grooves or the like is high.
SUMMARY OF THE INVENTION
The present invention has been developed for solving the foregoing problems associated with the conventional techniques and it is accordingly an object of the present invention to provide a method for forming a Cu-thin film which can embed or fill up recessed portions, with Cu metal, on a semiconductor substrate possessing such recessed portions as wiring grooves, via holes and contact holes which have a high aspect ratio, without forming any void therein and which requires a low processing cost.
The foregoing object of the present invention can effectively be accomplished by providing a method for forming a Cu-thin film which comprises the steps of coating a dispersion containing Cu ultrafine particles individually dispersed therein (hereinafter simply referred to as “individual Cu ultrafine particle dispersion”) on a semiconductor substrate having recessed portions such as wiring grooves, via holes and contact holes, having an aspect ratio ranging from 1 to 30; firing the coated semiconductor substrate in an atmosphere which can decompose organic substances present in the dispersion, but never oxidizes Cu to form a Cu-thin film on the substrate; then removing the Cu film on the substrate except for that present in the recessed portions to thus level the surface of the substrate and to form Cu-thin film in the recessed portions.
The firing step is desirably carried out in vacuum or desirably at a pressure of not more than 10
−2
Torr, in the presence of an extremely small amount of O
2
or H
2
O or CO
2
. Moreover, the firing step is carried out at a temperature ranging from 150 to 500° C. for a time preferably ranging from 10 minutes to one hour. With regard to the firing temperature, if it is less than 150° C., the Cu-thin film is not sufficiently dried because of insufficient removal of the dispersion medium of the dispersion, while if it exceeds 500° C., the semiconductor element would thermally be damaged. The crystallization of the Cu metal thin film and the adhesion of the metal thin film to the inner walls of the recessed portions can be accelerated or improved if the coated substrate is heated in an atmosphere identical to that used in the firing step at a temperature ranging from 300 to 500° C. for a period of time preferably ranging from 15 to 30 minutes, after the foregoing firing step. Regarding the heating temperature, if it is less than 300° C., the metal thin film is insufficiently crystallized, while if it exceeds 500° C., the semiconductor element would thermally be damaged. In this connection, the method for coating the foregoing dispersion is not restricted to any specific one and may be a commonly used coating method such as a spin coating, dip coating or spray coating method. In addition, the foregoing leveling step is carried out by, for instance, the damascene method which makes use of the so-called CMP treatment.
The Cu-thin film-forming method according to the present invention may include a pre-treatment comprising the steps of, for instance, forming a barrier film of TiN, Ta, TaN, WN or the like on the surface of the substrate including the inner walls of the recessed portions such as wiring grooves, via holes and contact holes through a sputtering method such as a directional sputtering method or a CVD method and then forming a seed film of Cu thereon by a sputtering method such as a directional sputtering method or a CVD method.
The individual Cu ultrafine particle dispersion, which may be used in the Cu wire-forming method of the present invention comprises, for instance, an organic solvent which can be evaporated during the drying-firing step upon forming Cu-distributing wires on a semiconductor substrate, preferably an organic solvent capable of being evaporated at a temperature of not less than 150° C.; and metal Cu-containing ultrafine particles having a particle size of not more than 0.01 &mgr;m mixed with or dispersed in the organic solvent. In this dispersion, the metal Cu ultrafine particles are dispersed in the organic solvent while individually surrounded by or covered with the organic solvent and the dispersion has a viscosity of not more than 100 cP as determined at a temperature of 20° C.
Examples of such organic solvents preferably used in the present invention include &agr;-terpineol, mineral spirits, tridecane, dodecylbenzene or mixtures thereof. In addition, examples of the foregoing metal Cu-containing ultrafine particles usable herein are those comprising metal Cu particles, CuO particles or a mixture of Cu and CuO particles. The concentration of the metal Cu-containing ultrafine particles in the dispersion in general ranges from 5 to 70% by weight and preferably 15 to 50% by weight on the basis of the total weight of the dispersion. If the concentration of the particles exceeds 50%, the viscosity becomes too high, and if the concentration of the particles is less than 15%, the film thickness is too small. The metal Cu-containing ultrafine particles may comprise, in addition to Cu metal, at least one metal or metal-containing compound whose solubility in Cu is low and which is susceptible to the reaction with the basic material for a semiconductor substrate and thus, the adhesion thereof to the basic material may b
Imazeki Nobuya
Murakami Hirohiko
Oda Masaaki
Yamakawa Hiroyuki
Arent Fox Kintner & Plotkin & Kahn, PLLC
Gurley Lynne
Niebling John F.
Vacuum Metallurgical Co., Ltd.
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