JP2007328136A - Copper alloy thin film for wiring and electrode of liquid crystal display and sputtering target for forming thin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a copper alloy thin film for forming a wiring and an electrode of a liquid crystal display wherein electric resistance of the wiring can be lowered and to provide a sputtering target for forming the thin film. <P>SOLUTION: The copper alloy thin film has a composition that 5 to 2,000 wt.ppm B(boron) is contained in pure copper (especially oxygen free copper having ≥99.99% purity) and the rest comprises Cu and inevitable impurities. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a copper alloy thin film for forming wirings and electrodes in a liquid crystal display device and a sputtering target for forming the thin film.

In general, a liquid crystal display device has a wiring formed of a metal thin film in a grid pattern on the surface of a glass substrate, and a TFT transistor is provided at an intersection of the grid wiring formed of a metal thin film in the grid pattern. The gate electrode is also formed of a metal thin film. The metal thin film may be formed of a metal such as pure copper and pure Al having excellent conductivity. However, the pure copper thin film is not preferable because it has extremely low electrical resistance but generates hillocks and voids when exposed to high temperatures. On the other hand, although a pure Al thin film has a low electrical resistance, it is not preferable because hillocks are generated when exposed to high temperatures. Therefore, at present, Al alloy thin films such as Al—Nd alloys or Al—Nd—Ti alloys, which generate little hillocks and voids even when exposed to high temperatures, although their electric resistance is slightly higher, are mainly used ( (See Patent Document 1 or 2).
JP-A-7-45555 JP-A-10-284493

  However, in recent years, liquid crystal display devices have become increasingly finer, so that the wiring formed on the glass substrate surface has become thinner and further, the liquid crystal display devices have become larger in size and wiring formed on the glass substrate surface. Is getting longer. For this reason, it is necessary to lower the electrical resistance of the wiring. However, the conventional thin film wiring made of an Al alloy such as an Al-Nd alloy or an Al-Nd-Ti alloy has a high electric resistance and is not suitable. I came.

Accordingly, the present inventors have developed a copper alloy thin film that generates less hillocks and voids even when exposed to high temperatures, while maintaining the characteristics that copper has a low electrical resistance, and uses this as a wiring in a liquid crystal display device. And research was done to apply to electrodes. as a result,
(A) A copper alloy thin film having a component composition containing B (boron) in an amount of 5 to 2000 wtppm in pure copper (particularly purity: 99.99% or more oxygen-free copper) has a lower electrical resistance than a conventional Al alloy thin film. Furthermore, there are few hillocks and voids even when exposed to high temperatures.
(B) The research result that the copper alloy thin film can be formed by sputtering using a target having the same component composition as the copper alloy thin film was obtained.

This invention was made based on the above research results,

(1) B: Copper alloy thin film for wiring and electrodes in a liquid crystal display device having a composition containing 5 to 2000 wtppm and the balance being Cu and inevitable impurities,
(2) B: It is characterized by a sputtering target for forming a copper alloy thin film for wiring and electrodes in a liquid crystal display device having a composition containing 5 to 2000 wtppm with the balance being Cu and inevitable impurities.

  In order to produce a target for forming the copper alloy thin film for wiring and electrodes of the liquid crystal display device of the present invention, first, an oxygen-free copper having a purity of 99.99% or more is used in a high-purity graphite mold in an inert gas atmosphere. In the molten metal obtained, the Cu-B master alloy containing B: 5 to 2000 wtppm is added to the obtained molten metal so that the balance is composed of Cu, and the obtained molten metal is added in an inert gas atmosphere. After casting and rapid solidification, cold rolling and annealing are repeated, and finally a strain relief annealing is performed to produce a sputtering target for forming a copper alloy thin film. The copper alloy thin film for wiring and electrodes in the liquid crystal display device of the present invention can be formed by joining the sputtering target for forming a copper alloy thin film thus obtained to a backing plate and sputtering under normal conditions.

In the liquid crystal display device according to the present invention, the B content is limited to 5 to 2000 wtppm in the copper alloy thin film for wiring and electrode and the sputtering target for forming the thin film, and B suppresses the generation of hillocks and voids in the pure copper thin film. However, if the content is less than 5 wtppm, the desired effect cannot be obtained, which is not preferable. On the other hand, if the content exceeds 2000 wtppm, the electrical resistance increases, which is not preferable.

  The copper alloy thin film for wiring and electrodes in the liquid crystal display device of the present invention is less likely to generate hillocks and voids even when exposed to high temperatures compared to the wiring and electrode copper alloy thin film made of pure copper, and is made of a conventional Al alloy. Since the electric resistance is lower than that of the wiring and the electrode, it has excellent effects such that the power consumption can be reduced even if it is used for the wiring and the electrode of the liquid crystal display device which has been refined and enlarged.

  Purity: 99.99 mass% oxygen-free copper was prepared, and this oxygen-free copper was melted at high frequency in a high-purity graphite mold in an Ar gas atmosphere to adjust the oxygen content. A Cu-1 mass% B mother alloy was added to the molten metal to adjust the components so as to obtain a molten metal having the component composition shown in Table 1, and the resulting molten metal was cast into a cooled carbon mold. After repeating rolling and annealing, finally the strain relief annealing is performed, and the surface of the obtained rolled body is turned to have the outer diameter: 300 mm × thickness: 5 mm, and the composition shown in Table 1 The present invention copper alloy sputtering target (hereinafter referred to as the present invention target) 1 to 12 and the comparative copper alloy sputtering target (hereinafter referred to as the comparison target) 1 to 2 were prepared. Further, a sputtering target (hereinafter referred to as a conventional target) 1 made of pure copper was prepared without adding an element to oxygen-free copper. Furthermore, a commercially available Al alloy target containing Nd: 3 atomic% and having the remainder composed of Al and inevitable impurities was prepared as the conventional target 2.

Further, an oxygen-free copper backing plate is prepared, and the present invention targets 1 to 12, the comparison targets 1 to 2 and the conventional targets 1 to 2 are superposed on the oxygen-free copper backing plate, and soldered with indium solder at a temperature of 200 ° C. By attaching, the present invention targets 1-12, comparative targets 1-2, and conventional targets 1-2 were joined to an oxygen-free copper backing plate to produce a target with a backing plate.

Using a target with a backing plate obtained by soldering the present invention targets 1-12, comparative targets 1-2, and conventional targets 1-2 to an oxygen-free copper backing plate,
Power supply: DC method,
Electric power: 4KW
Atmospheric gas composition: Ar,
Sputtering gas pressure: 0.67 Pa,
Distance between target and substrate: 80mm,
Sputtering time: 1 minute
A copper alloy thin film of the present invention (hereinafter referred to as the present thin film) 1 to 12 and a comparative copper alloy having a thickness of 300 nm on the surface of the glass substrate under the high output conditions and having the composition shown in Tables 2 to 5 Thin films (hereinafter referred to as comparative thin films) 1 and 2 and conventional copper alloy thin films (hereinafter referred to as conventional thin films) 1 and 2 were formed.

The obtained thin films 1 to 12, comparative thin films 1 and 2, and conventional thin films 1 to 2 were each subjected to heat treatment for 30 minutes at a temperature shown in Tables 2 to 5 in a vacuum atmosphere of 1 × 10 ⁻² Pa. After that, the surface of the thin film was observed with a 500 × optical microscope, and the presence or absence of hillocks and voids existing in the range of 100 μm × 200 μm was observed. The results are shown in Tables 2-5.
Furthermore, the specific resistances of the obtained present invention thin films 1 to 12, comparative thin films 1 to 2 and conventional thin films 1 to 2 were measured by a four-probe method, and the results are also shown in Tables 2 to 5.

From the results shown in Tables 1-5, voids are generated in the conventional thin film 1, but hillocks and voids are not generated in the present thin films 1 to 12 at 400 ° C. or lower. It can be seen that it is low. However, the comparative thin film 1 that contains less B than the conditions of the present invention is not preferable because hillocks and voids are generated. On the other hand, the comparative thin film 2 that contains much B deviates from the conditions of the present invention and has an increased electrical resistance. It turns out that it is not preferable.

Claims (2)

B: A copper alloy thin film for wiring and electrodes in a liquid crystal display device, comprising 5 to 2000 wtppm, with the balance being composed of Cu and inevitable impurities. B: A sputtering target for forming a copper alloy thin film for wiring and electrodes in a liquid crystal display device, comprising 5 to 2000 wtppm, and the balance being composed of Cu and inevitable impurities.