Metal material for electronic parts, electronic parts,...

Details Metal material for electronic parts, electronic parts,... Metal material for electronic parts, electronic parts,...

2000-07-11

2004-04-20

Wyszomierski, George (Department: 1742)

Alloys or metallic compositions

Silver base

Copper containing

C420S505000

Reexamination Certificate

active

06723281

ABSTRACT:

Metal material for electronic parts, electronic parts, electronic apparatuses, and method of processing metal materials
BACKGROUND OF THE INVENTION
The present invention relates to a metal material for electronic parts, electronic parts, electronic apparatuses, and method of processing metal materials. For example, the present invention can be applied to liquid crystal display panels, various semiconductor devices, wiring boards, chip parts, and the like. The present invention uses metal material, more specifically an alloy comprising Ag as a main component, 0.1 to 3 wt % of Pd, and a total of 0.1 to 3 wt % of elements such as Al, Accordingly, the present invention provides a metal material for electronic parts, electronic parts and apparatuses using this metal material, whereby the metal material is characterized by lower resistivity, higher stability, and more excellent processability than the prior art.
Conventionally, wires, electrodes, and contacts of electronic parts and apparatuses use metal materials such as pure metals including Cu, Al, Mo, Ta, W, Cr, and the like, and alloys including Al—Cu, Al—Cu—Si, Al—Pd, TaSi, WSi, and the like for forming wiring patterns.
For example, a transparent liquid crystal display panel constituting a flat panel display generally uses pure Al as a wiring material because of excellent etching characteristics and low electrical resistance. However, pure Al shows a melting point of as low as 660° C. Using pure Al as wiring material for liquid crystal display panels leaves the possibility of causing defects such as a hillock and a whisker during heat treatment at approximately 300° C. to 400° C. for a chemical vapor deposition (CVD) process after wiring film formation. Some types of liquid crystal display panels prevent these defects by using high-melting point materials for wiring such as Ta, Mo, Cr, W, and the like which are stable at a high temperature instead of pure Al.
A reflective liquid crystal display panel requires a high-reflectance layer which reflects transmitted light through liquid crystal cells. Such a high-reflectance layer or members for wiring patterns and electrodes functioning as a high-reflectance layer use pure Al, an Al-based alloy, pure Ag, an Ag-based alloy, Au, and the like. An electro-optical part (hereafter called an electro-optical part using micromirrors) uses micromirrors arranged on a silicon chip and displays images by means of optical modulation of each mirror. Such an electro-optical part uses pure Al for mirror members.
If there is provided a metal material which is characterized by lower electrical resistance, higher stability, and more excellent processability than metal materials used for conventional electronic apparatuses, using such a metal material for various electronic parts can improve performance and simplify manufacturing processes.
A transparent liquid crystal display panel uses Ta, Mo, Cr, W, and the like instead of pure Al in order to prevent defects. As shown in Table. 1, however, these materials have a disadvantage of larger resistivity than pure Al. If the transparent liquid crystal display panel becomes larger and provides higher resolution, the wire length for wiring patterns increases and wiring patterns become much finer, making it difficult to provide easy, reliable operations. For this reason, optimal wiring materials are unavailable for transparent liquid crystal display panels.
TABLE 1
RESISTIVITY
CHEMICAL
ANODIC
MATERIAL
[&mgr;&OHgr;cm]
RESISTANCE
OXIDATION
Mo
50
LOW
IMPOSSIBLE
Cr
12.9
GOOD
IMPOSSIBLE
Ti
55
EXCELLENT
IMPOSSIBLE
Ta
13.6
EXCELLENT
POSSIBLE
Al
2.7
LOW
POSSIBLE
Cu
1.7
LOW
IMPOSSIBLE
Ag
1.6
GOOD
IMPOSSIBLE
Au
2.3
EXCELLENT
IMPOSSIBLE
A reflective liquid crystal display panel and an electro-optical part using micromirrors allow wires and electrodes to serve as a high-reflectance layer. In this case, it is necessary to add requirements for a high-reflectance layer to wiring material characteristics for transparent liquid crystal display panels.
From the viewpoint of effectively reflecting incident light on the high-reflectance layer, pure Ag is an optimal material for high-reflectance layers because pure Ag provides the highest reflectance in a visible light wavelength region. However, pure Ag has weak corrosion resistance, not suitable for a wiring or electrode material. For this reason, optimal wiring materials are not always available also for reflective liquid crystal display panels and electro-optical parts using micromirrors.
In consideration of these points, the reflective liquid crystal display panel uses a barrier layer formed on, or on and below the high-reflectance film and the wiring electrode layer to improve corrosion resistance. However, increasing steps for forming barrier layers complicates the manufacturing process. Further, if the barrier layer is formed, its reliability remains unstable under high-temperature conditions.
As low-resistance wiring materials, Au, Cu, and Ag show lower resistivity than that of Al. However, Au is not easily available. Cu is characterized by poor corrosion resistance, provides degraded processability by etching, and presents difficult problems in fine processing. Ag excessively reacts on chloride, sulfur, and sulfide, offering problems in fine processing and corrosion resistance.
For example, Ag reacts excessively during a dry etching process by means of etching gas containing chlorine. As the etching process proceeds, Ag reacts on chlorine in the etching gas, generating AgCl on a boundary surface of the wiring pattern. This AgCl degrades electrical conductivity and thermal conductivity.
Here is an example in which Ag causes problems concerning corrosion resistance. When Ag is applied to a reflective liquid crystal display panel, there is a strong possibility of reacting on oxygen or a small amount of sulfur and the like on an interface by direct contact with a transparent conducting layer. Similarly to Al, it is necessary to form a barrier layer on the substrate layer or place the substrate layer between barrier layers in a sandwich structure.
In many cases, these liquid crystal display panels use a TFT (thin film transistor) comprising amorphous silicon or polycrystal silicon as a drive device. Presently, optimal electrode materials are unavailable from the viewpoint of drive devices.
Some of these drive devices simplify a manufacturing process by oxidizing metal material of electrodes and forming a gate insulating film between this electrode and a silicon active element. This is called an anodic oxidation method.
Of wiring materials shown in Table 1, Al and Ta can form gate insulating films. Especially, Ta can form an oxide insulating film which causes little defects such as pinholes and provides a high yield. However, Ta is characterized by high resistivity. When the anodic oxidation method is used, an electrode structure requires 2-layer wiring using Al with low resistivity, increasing manufacturing processes. When the 2-layer wiring is used, the resistivity of wiring patterns becomes same as that determined by Al.
In addition to application to the above-mentioned display devices, semiconductor devices such as DRAM, flash memory, CPU, MPU, and ASIC require a narrower wiring width due to high integration. The wiring length for wiring patterns is becoming longer due to increasing chip sizes and complicated wiring such as multilayer interconnection. These semiconductor devices also require wiring materials which are characterized by low resistivity, stable operations, and excellent processability.
Narrowing the wiring width and extending the wiring length increases the wiring resistance. Increasing the resistance also increases a voltage drop on wiring and decreases a drive voltage for elements. Further, the power consumption increases, causing a delay in signal transmission due to the wiring.
In addition to these semiconductor devices, electronic parts such as printed-wiring boards, chip capacitors, and relays use Cu and Ag for wiring, electrode, and contact materials. These materials also provide practically

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