Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Of specified material other than unalloyed aluminum
Reexamination Certificate
2002-02-28
2004-04-27
Vu, Hung (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Of specified material other than unalloyed aluminum
C257S763000, C257S764000, C257S765000, C257S766000, C257S770000, C257S773000
Reexamination Certificate
active
06727593
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-57376 filed on Mar. 1, 2001, Japanese Patent Application No. 2001-260644 filed on Aug. 30, 2001, Japanese Patent Application No. 2001-401293 filed on Dec. 28, 2001 and Japanese Patent Application No. 2001-378778 filed on Dec. 12, 2001; the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device and its manufacturing method, and more particularly to a semiconductor device with the reliability of connection by bonding or the like improved and its manufacturing method.
2. Description of the Related Art
Recently, with the increase of the integration degree and operation velocity of the semiconductor device, copper (hereinafter called as “Cu”) is used instead of aluminum (Al) or the like as a wiring material from the viewpoint of the reduction in resistance and high reliability of each wiring layer. The technology, which uses Cu as a wiring material, is increasing in importance for speed-up of the semiconductor device and the increase in stacked layers of a wiring structure with the advance of a microfabrication technology.
In the assembly process of a semiconductor device, a bonding step is performed to electrically connect each wiring layer of the semiconductor device and an outside conductive substance (e.g., a bonding pad of a package) via a metal wire or a conductive substance such as conductive bump. To perform the bonding step, a pad electrode layer and a metal wire or conductive bump of the semiconductor device are directly connected so to electrically conduct the respective wiring layers of the semiconductor device and the outside conductive substance. Specifically, the metal wire (e.g., gold (Au)) is directly bonded to the pad electrode layer or the conductive bump are formed on the pad electrode layer to make flip-chip connection.
Since the pad electrode layer is formed as apart of wiring on the top layer, the same material as the wiring layer of the semiconductor device is used. Therefore, Cu is conveniently used instead of Al or the like as a material for the pad electrode layer in the same way as the other wiring layer in view of reduction of the number of steps.
When a thermal treatment is performed with the top layer of the Cu wiring layer exposed to the atmosphere in order to form the pad electrode layer, the Cu wiring layer is readily oxidized from its surface to inside. Therefore, when Cu is used as a pad material, the bonding step cannot be performed while heating in the atmosphere by a conventional apparatus. In this case, the bonding step can be performed in a flow of nitrogen or hydrogen or in a non-oxidizing atmosphere or a reducing atmosphere with the surface of the pad electrode layer prevented from being oxidized, but it is necessary to make a major modification of the apparatus. In a step of heating treatment after the bonding, there is also a problem that a bonded part becomes defective because oxidation continues.
In connection with the above problems, Japanese Patent Laid-Open Application No. Hei 9-92649 JP-A discloses a method of forming an oxidation-resistant and corrosion-resistant protective layer on a copper wiring structure or a copper electrode pad structure (=copper pad electrode layer) within an opening.
It discloses a method of forming a copper-aluminum alloy layer (hereinafter called as “Cu—Al alloy layer”) on the surface of a Cu wiring layer by forming an aluminum film (hereinafter called as “Al film”) having a thickness of about 2% or less of that of the Cu film on a copper film (hereinafter called as “Cu film”) configuring wires and a pad electrode and on an insulating film around it and performing a thermal treatment. Thus, there is disclosed a method of improving the reliability of the wiring structure or the pad electrode structure by forming an alloy film of a metal containing Al and preventing the Cu wiring layer from being oxidized or corroded.
Japanese Patent Laid-Open Application No. Hei 9-92649 JP-A discloses a subsequent method of wet-etching to remove the unreacted Al film remained on the insulating film with diluted hydrofluoric acid or phosphoric acid and thermally treating the Cu wiring layer in a mixture gas of hydrogen and oxygen or hydrogen and steam. Here, the Cu wiring layer is thermally treated again to form a thin film containing Al and oxygen or a thin oxide film containing Al, Cu and oxygen on the surface of the Cu—Al alloy layer. Thus, the reliability of the Cu wiring or the Cu electrode pad structure can be improved.
It is necessary to minimize the thickness of the Cu alloy film in order to suppress the resistance value of the pad electrode layer (e.g., Cu) from increasing. Accordingly, it is thinkable that the metal film (e.g., Al) formed on the pad electrode layer is made to be thin as small as possible.
Therefore, Japanese Patent Laid-Open Application No. Hei 9-92649 JP-A needs make the Cu—Al alloy layer thinner as small as possible in order to suppress the resistance value of the Cu electrode pad structure (=Cu pad electrode layer) from increasing. Thus, it is conceivable that the Al film is formed in a thickness as small as possible on the Cu film configuring the electrode pad structure.
However, if the metal film (e.g., Al) formed on the pad electrode layer is excessively thin, the following problems occur.
For example, the metal film agglomerates to have a spherical shape on the periphery of the pad electrode layer (=wiring layer on the top layer), namely on the insulating film such as a passivation film by the thermal treatment in the process of forming the alloy film on the pad electrode layer, and the metal layer has an increased thickness (corresponding to a diameter of the sphere).
In this case, an unnecessary portion of the metal film remained on the insulating film around the pad electrode layer is removed by a wet etching process or a CMP method (=chemical-mechanical polishing method), etc., but there is a problem that the processing time becomes long and a practical process margin cannot be obtained.
After the electrode pad of the Cu wiring structure is formed, a silicon wafer is generally inspected before an assembly process is performed to connect to an outside conductive substance (e.g., package bonding pad) through a conductive substance such as a metal wire (e.g., gold (Au)) or conductive bump. Here, a probing needle is contacted to the pad electrode layer of each semiconductor chip to inspect in the atmosphere so that a judgment is made to select a good chip only. After the inspection, only the good chips are subjected to the assembly process.
In this case, there comes a scratch of certain depth in the pad electrode layer when the pad electrode layer is contacted by the probing needle because it has a sharp tip. Therefore, when the pad electrode layer has a structure that the protective layer is formed on the Cu wiring layer, the probing needle breaks through the protective layer to reveal the Cu wiring layer located below it, resulting in oxidation in the later assembly step. Therefore, there is also a problem that a metal oxide layer on the pad electrode layer is readily cut away by the probing needle, and the oxidation resistance of the pad electrode layer is degraded.
Before the assembly step, a thermal treatment may be performed to form an oxidizing protective layer again on the scratch caused by the probing needle so to protect the pad electrode layer. However, it is impossible to form the metal oxide layer again because a metal required to form the metal oxide layer as the protective layer is not enough contained in the Cu wiring layer located on a lower layer. In the assembly step, particularly in the bonding step or the like, a bonding strength and conductivity become defective when the metal wire or conductive bump are connected to such pad electrode.
Thus, to form the pad electrode
Hasunuma Masahiko
Kaneko Hisashi
Komukai Toshiaki
Nakao Mitsuhiro
Sakata Atsuko
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Vu Hung
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