Liquid crystal display device and process of manufacture

1. A liquid crystal display device, comprising:

a pair of substrates;

liquid crystal sandwiched between the pair of substrates;

a plurality of scanning signal lines formed on one of the pair of substrates;

a plurality of image signal lines which intersect the plurality of scanning signal lines in a matrix form;

a thin film transistor formed corresponding to each intersection between the plurality of scanning signal lines and the plurality of image signal lines;

a pixel electrode which is formed in a pixel region and connected to the thin film transistor;

a gate insulating film which substantially covers the plurality of scanning signal lines; and

a protective insulating film which covers the plurality of image signal lines and the thin film transistor;

wherein at least one of the plurality of scanning signal lines and the plurality of image signal lines are each formed of a laminated film including a first layer serving as a lower layer and a second layer which is formed on the first layer and serves as an upper layer;

wherein the first layer is formed of a copper film having a purity of at least 99.5%, and the second layer is formed of an alloy film containing copper as a main component and having a higher etching rate compared with an etching rate of the first layer, the alloy film containing at least one element selected from the group consisting of cerium, europium, hafnium, lutetium, manganese, magnesium, lead, terbium, thulium, and zinc; and

wherein the first layer and the second layer are collectively subjected to wet etching with an etchant having a pH smaller than 7.0, so as to form the laminated film including the upper layer of the second layer and the lower layer of the first layer into a forward tapered shape.

2. The liquid crystal display device according to claim 1 , wherein the second layer has a film thickness within a range of 10 nm to a value equal to or less than 10% of a film thickness of the first layer.

3. The liquid crystal display device according to claim 1 , wherein the forward tapered shape of the laminated film has a taper angle of 20° to 70°.

4. A liquid crystal display device, comprising:

a pair of substrates;

liquid crystal sandwiched between the pair of substrates;

a plurality of scanning signal lines formed on one of the pair of substrates;

a plurality of image signal lines which intersect the plurality of scanning signal lines in a matrix form;

a thin film transistor formed corresponding to each intersection between the plurality of scanning signal lines and the plurality of image signal lines;

a pixel electrode which is formed in a pixel region and connected to the thin film transistor;

a gate insulating film which substantially covers the plurality of scanning signal lines; and

a protective insulating film which covers the plurality of image signal lines and the thin film transistor;

wherein the plurality of scanning signal lines are disposed on a transparent conductive film containing indium oxide as a main component,

wherein the plurality of scanning signal lines are each formed of a laminated film including a first layer serving as a lower layer and a second layer which is formed on the first layer and serves as an upper layer;

wherein the first layer is formed of a copper film having a purity of at least 99.5%, and the second layer is formed of an alloy film containing copper as a main component, the alloy film containing at least one element selected from the group consisting of boron, bismuth, cerium, europium, germanium, hafnium, lutetium, manganese, magnesium, lead, silicon, terbium, thulium, vanadium, and zinc; and

wherein the first layer and the second layer are collectively subjected to wet etching with an etchant having a pH within a range of 1.8 to 7.0, so as to form the laminated film including the upper layer of the second layer and the lower layer of the first layer into a forward tapered shape.

5. A liquid crystal display device, comprising:

a pair of substrates;

liquid crystal sandwiched between the pair of substrates;

a plurality of scanning signal lines formed on one of the pair of substrates;

a plurality of image signal lines which intersect the plurality of scanning signal lines in a matrix form;

a thin film transistor formed corresponding to each intersection between the plurality of scanning signal lines and the plurality of image signal lines;

a pixel electrode which is formed in a pixel region and connected to the thin film transistor;

a gate insulating film which substantially covers the plurality of scanning signal lines; and

a protective insulating film which covers the plurality of image signal lines and the thin film transistor;

wherein at least one of the plurality of scanning signal lines and the plurality of image signal lines are each formed of a laminated film including a first layer serving as a lower layer and a second layer which is formed on the first layer and serves as an upper layer;

wherein the first layer is formed of a copper film having a purity of at least 99.5%, and the second layer is formed of an alloy film containing copper as a main component, the alloy film containing at least one element selected from the group consisting of aluminum, boron, beryllium, bismuth, cerium, europium, gallium, germanium, hafnium, lutetium, manganese, magnesium, lead, silicon, terbium, thulium, vanadium, and zinc; and

wherein the first layer and the second layer are collectively subjected to wet etching with an etchant having a pH of 7.0 or more, so as to form the laminated film including the upper layer of the second layer and the lower layer of the first layer into a forward tapered shape.

6. A method of manufacturing a liquid crystal display device comprising a pair of substrates, liquid crystal sandwiched between the pair of substrates, a plurality of scanning signal lines formed on one of the pair of substrates, a plurality of image signal lines which intersect the plurality of scanning signal lines in a matrix form, a is thin film transistor formed corresponding to each intersection between the plurality of scanning signal lines and the plurality of image signal lines, a pixel electrode which is formed in a pixel region and connected to the thin film transistor, a gate insulating film which substantially covers the plurality of scanning signal lines, and a protective insulating film which covers the plurality of image signal lines and the thin film transistor, the method comprising the steps of:

forming, on the one of the pair of substrates, a copper film having a purity of at least 99.5% which serves as a first layer constituting each of the plurality of scanning signal lines and an alloy film containing copper as a main component which serves as a second layer in a successive manner, for forming the each of the plurality of scanning signal lines and a gate electrode;

forming a film made of silicon nitride which serves as the gate insulating film, and forming a semiconductor layer by forming an amorphous silicon film and an n + -amorphous silicon film in a successive manner;

forming the plurality of image signal lines, a drain electrode, and a source electrode, which are each formed of a metal film;

forming a film made of silicon nitride serving as the protective insulating film, and opening a through hole in the protective insulating film and in the gate insulating film; and

forming a transparent conductive film to complete the pixel electrode;

wherein the laminated film of copper having the purity of at least 99.5% and the alloy film containing copper as the main component is collectively subjected to etching with an etchant having a pH in a range smaller than 7.0.

7. A method of manufacturing an in-plane-switching system liquid crystal display device comprising a pair of substrates, liquid crystal sandwiched between the pair of substrates, a plurality of scanning signal lines formed on one of the pair of substrates, a plurality of image signal lines which intersect the plurality of scanning signal lines in a matrix form, a thin film transistor formed corresponding to each intersection between the plurality of scanning signal lines and the plurality of image signal lines, a pixel electrode which is formed in a pixel region and connected to the thin film transistor, a gate insulating film which substantially covers the plurality of scanning signal lines, and a protective insulating film which covers the plurality of image signal lines and the thin film transistor, the method comprising the steps of:

forming, on the one of the pair of substrates, a transparent conductive film containing an indium oxide as a main component which serves as each of the plurality of scanning signal lines, a copper film having a purity of at least 99.5% serving as a first layer, and an alloy film containing copper as a main component serving as a second layer in a successive manner, for forming the each of the plurality of scanning signal lines, a gate electrode, a common signal line, and a common electrode;

forming a film made of silicon nitride which serves as the gate insulating film, and forming a semiconductor layer by forming an amorphous silicon film and an n + -amorphous silicon film in a successive manner;

forming the plurality of image signal lines, a drain electrode, and a source electrode, which are each formed of a metal film;

forming a film made of silicon nitride serving as the protective insulating film, and opening a through hole in the protective insulating film and in the gate insulating film; and

forming a transparent conductive film to complete the pixel electrode;

wherein the laminated film of copper having the purity of at least 99.5% and the alloy film containing copper as the main component is collectively subjected to etching with an etchant having a pH within a range of 1.8 to 7.0.

8. A method of manufacturing a liquid crystal display device comprising a pair of substrates, liquid crystal sandwiched between the pair of substrates, a plurality of scanning signal lines formed on one of the pair of substrates, a plurality of image signal lines which intersect the plurality of scanning signal lines in a matrix form, a thin film transistor formed corresponding to each intersection between the plurality of scanning signal lines and the plurality of image signal lines, a pixel electrode which is formed in a pixel region and connected to the thin film transistor, a gate insulating film which substantially covers the plurality of scanning signal lines, and a protective insulating film which covers the plurality of image signal lines and the thin film transistor, the method comprising the steps of:

forming, on the one of the pair of substrates, a copper film having a purity of at least 99.5% which serves as a first layer constituting each of the plurality of scanning signal lines and an alloy film containing copper as a main component which serves as a second layer in a successive manner, for forming the each of the plurality of scanning signal lines and a gate electrode;

forming a film made of silicon nitride which serves as the gate insulating film, and forming a semiconductor layer by forming an amorphous silicon film and an n + -amorphous silicon film in a successive manner;

forming the plurality of image signal lines, a drain electrode, and a source electrode, which are each formed of a metal film;

forming a film made of silicon nitride serving as the protective insulating film, and opening a through hole in the protective insulating film and in the gate insulating film; and

forming a transparent conductive film to complete the pixel electrode;

wherein the laminated film of copper having the purity of at least 99.5% and the alloy film containing copper as the main component is collectively subjected to etching with an etchant having a pH within a range of 7.0 to 14.0.