Silicon based conductive material and process for production...

Details Silicon based conductive material and process for production... Silicon based conductive material and process for production...

2000-06-08

2003-01-14

Kopec, Mark (Department: 1751)

Compositions

Electrically conductive or emissive compositions

Metal compound containing

C423S324000, C423S344000

Reexamination Certificate

active

06506321

ABSTRACT:

TECHNICAL FIELD
This invention relates to a novel silicon-based conductive material in which the silicon is made to contain various elements in relatively large quantities, and more particularly to a novel silicon-based conductive material that allows substrates, chips, and the like to be made smaller and increases productivity by implanting phosphorus, boron, aluminum, or the like in a silicon substrate with:an ion beam in a pattern so that the required areas become conductive, wherein this silicon-based conductive material can be worked into a sheet or rod and utilized in connector terminals, contacts, and so forth, or can be made into fines and dispersed in a resin or glass to produce a conductive sheet material, for example, and is therefore suitable for any application that requires electrical conductivity.
BACKGROUND ART
Electrically conductive materials need to have a variety of characteristics. For example, in conductive wire applications, such as the wiring of semiconductor devices or various types of electronic and electrical devices, the electrical resistance must be low, corrosion resistance and mechanical properties need to be excellent, and connection must be easy. Copper and aluminum, as well as alloys such as copper alloys and aluminum alloys, have often been used for this purpose.
Depending on the package material, a variety of alloys have been employed for the lead frame materials of conductive sheets and strips, typified by semiconductor lead frame materials. Among those that have been used are Fe—Ni, Cu—Fe, Cu—Sn, and Cu—Zr systems.
Various alloy materials, such as those based on copper, carbon, silver, gold, or a platinum family metal, are used as contact point materials, which need to be conductive and resistant to arcing and wear.
Methods that have been- adopted for manufacturing conductive plastics, which are produced by imparting conductivity to a plastic (which is an insulator) and which are utilized for antistatic purposes, involve admixing carbon black, carbon fiber, or a metal powder or fiber into a resin.
The various electronic and electrical devices of today are more compact and lightweight because of higher packaging density, accomplished by putting resistors, capacitors, diodes, and transistors on a chip, but advances in chip-in-chip technology are making even higher packaging density possible, with the density of go-called printed wiring being increased (for example, copper foil of less than 20 &mgr;m is being used), and wire bonding is also becoming ultrafine.
Multilayer thin film circuits have been proposed in an effort to further advance chip-in-chip technology. A conduction thin film with a width of no more than 3 &mgr;m and a thickness of no more than 0.1 &mgr;m is formed, and three-dimensional wiring is achieved by through-holes in the insulating films between layers. Aluminum films are used for these conduction thin films, and copper films are increasingly being employed in CPU applications.
Metals and alloys are used for conductive wires, such as the wiring of semiconductor devices or various: types-of electronic-and electrical devices, and in addition to their use as multilayer thin film circuits, these materials. have also been used as sheets, strips, and wires so as to allow connection to a mounting substrate or semiconductor chip, but this has been an impediment to increasing fineness and density and obtaining a smaller and lighter product.
The inventors came to the conclusion that if the required conductivity could be ensured without using conductive wires or the like on the chip, as is the case with an ordinary silicon substrate or other such semiconductor device substrate then devices could be made thinner and smaller, a reduction in the number of parts could be achieved, and various devices could be packaged more compactly on a single substrate.
The electrical resistivity p of a semiconductor is generally held to be 10
−2
to 10
9
(&OHgr;·m). Silicon is a semiconductor with a diamond structure, and its electrical resistivity p is 2.3×10
5
(&OHgr;·m), but it can be made into a p- or n-type semiconductor by adding boron or phosphorus as impurities. Silicon can also be used over a wide range of temperatures, and as a semiconductor it allows current to be controlled, and is therefore widely used in devices today. This pn control is achieved by doping the silicon with only a tiny amount of impurities (about {fraction (1/10,000)}th), and it is known that pn control is impossible with doping in larger quantities.
Meanwhile, it is known that silicon is metallized when a large quantity of impurities is introduced. An article titled “Low-Temperature Magnetoresistance of a Disordered Metal” by T. F. Rosembaum and R. F. Milligan (Physical Review Letters, pp. 1758-1761, dated Dec. 14, 1981) reports on the magnetoresistance of metallic Si-P at 100 mK. It is reported that the critical density at a temperature of 3 mK is n
c
=3.74×10
18
cm
−3
, and the electrical resistivity p is 2×10
−2
(&OHgr;·m).
Also, salicide technology, in which a silicide layer is formed on the gate electrodes and diffusion layer surfaces of the source and drain, has been developed in an effort to lower resistance within an element in the manufacture of a MOSFET, and materials that have been studied include TiSi
2
, NiSi, and CoSi
2
.
None of the above-mentioned silicon semiconductors, metallic Si-P, or suicides had an electrical resistivity p that was any better than that of semiconductors (10
−2
(&OHgr;·m)), and could not be used as conductors for “carrying current.”
As mentioned above, however, system integration is possible if polycrystalline Si-TFT can be formed on a single glass substrate and various devices such as microprocessors formed on the surrounding substrate, but it is believed that packaging would be easier if conduction could be ensured with the very material used to form a film on the glass substrate, and particularly a silicon-based material other than a metal.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a silicon-based conductive material that is based primarily on semiconductor silicon, can be easily manufactured, is easy to handle, has an electrical resistivity at normal temperature of 10
−3
(&OHgr;·m) or less, which could not be achieved up to now, and furthermore attains the electrical resistivity that is commonly found in semiconductors (10
−6
(&OHgr;·m) or less), and can be provided in the required pattern within a semiconductor silicon substrate, or made into a substrate, rod, or wire, or can be made into fines and dispersed in a resin or glass to produce a conductive sheet material, and is therefore suitable for any application that requires electrical conductivity.
The inventors conducted various studies aimed at finding a material based primarily on semiconductor silicon and with which an electrical resistivity at normal temperature of 10
−3
(&OHgr;·m) or less, or even 10
−6
(&OHgr;·m) or less, could be attained, which was impossible in the past. In the course of this investigation, they turned their attention to the conventional belief that if various dopants were added to silicon alone, the energy state density decreased and the Seebeck coefficient would also go down steadily as the added amount was increased, that is, the belief that the decreases in energy state density and the Seebeck coefficient were a result of an increase in the band width of the impurity level in the band gap along with an increase in the carrier concentration (A. F. Joffe: Semiconductor Thermoelements and Thermoelectric Cooling, Infosearch, London, 1957).
In view of this, the inventors came to the conclusion that if the carriers are at a certain specific concentration, there is an electron correlation or hole correlation at work between the electrons or holes that are the carriers, and conversely that the energy state density of the carriers is higher through the segregation of the carriers in the semiconductor, that is to say that Anderson segreg

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