Active solid-state devices (e.g. – transistors – solid-state diode – Specified wide band gap semiconductor material other than... – Diamond or silicon carbide
Reexamination Certificate
2001-01-16
2002-07-23
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Specified wide band gap semiconductor material other than...
Diamond or silicon carbide
C257S328000, C257S506000
Reexamination Certificate
active
06423982
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a diamond interconnection substrate and a manufacturing method therefor, and more particularly to those applicable to a high-power electronic circuit substrate including a high power microwave circuit, which is a diamond circuit substrate, also serving as a heat sink, having multi-layer interconnections.
2. Description of the Background Art
Diamond is a material having the highest thermal conductivity of all materials, in a high temperature range between a room temperature and 200° C. Such a property is considered to be important for a heat sink required for lowering temperature of electron devices having, year by year, higher performance and greater heat-releasing values. Conventionally, when utilized as a high-performance heat sink, diamond may be provided with an interconnection of only one layer formed on the surface of the diamond. Thus, a conventional diamond interconnection substrate has attained only one layer of interconnection.
However, when a number of elements are formed on the diamond substrate, the interconnections may cross with each other in the only one interconnection layer. Further, miniaturization of a device may possibly make an interconnection thinner, which will require the interconnection to be electrical power resistant.
Currently, ceramics and conductors are used for circuit substrates, and a combination of simultaneously calcinable Al
2
O
3
/W, AlN/W or the like are selected as materials therefor. Some circuit substrates are designed to utilize CuW material, a low-temperature calcinated substrate and so forth, to be divided into a heat radiating portion and a multi-layer interconnection portion. Further, a multi-layer interconnection substrate of BeO is being contemplated in a field where both a highly thermal conductive material and a multi-layer interconnection technique are required.
However, such a circuit substrate had problems in that the thermal conductivity is lower compared to that of diamond, its structure is more complicated and its manufacturing process is troublesome.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a technique by which multi-layer interconnections can be realized using a diamond substrate with the highest thermal conductivity of all materials, in a packaging field for high power microwave and milliwave communications requiring a high thermal conductivity and a multi-layer interconnection technique.
A diamond interconnection substrate according to the present invention includes diamond, and a conductive layer constituted by a presence of metal elements having a thickness of at least 10 nm and a concentration of at least 10
20
cm
−1
in the diamond. More effectively, the conductive layer is constituted by the presence of metal elements having a thickness of at least 100 nm and a concentration of at least 10
21
cm
−3
.
To solve the problems described above, the diamond interconnection substrate of the present invention utilizes diamond having a thermal conductivity of approximately 2000 W/mK for the substrate, in which interconnections are provided within the diamond by implanting metal ions into the diamond substrate with a high energy level and a high dose.
Diamond is constituted by carbon atoms, each of which being a light element, and, different from Si and so forth, ions can enter very deeply into the diamond when implanted at a high speed. Further, fast ions (on the order of MeV) have a property in which a scattering cross section is small as long as the ions are at the high speed, so that they hardly collide with elements in a diamond crystal. Hence, the ions pass through the crystal without damaging the crystal. However, the scattering cross section is increased and the ions are rapidly stalled once the ions are decelerated in a substance, so that concentrated implantation is possible in a very narrow region.
Further, use of a mask enables forming of interconnections that are patterned together. That is, the interconnections can be formed with excellent controllability in depth and plane directions. It is also possible to attain a density value in the diamond very close to a density of metal, with a practical implant dose. This means that transfer of a substance, other than simple doping of elements into the diamond is possible.
Further, in a case that a conventional substance is used as a substrate material, when ions are implanted, energy of implanted elements may locally increase temperature and pressure of the material originally constituting the substrate, which may destroy the material. On the other hand, diamond has a high thermal conductivity such that it is hard to be heated to a high temperature, and also is very strongly bonded so as not to be destroyed.
Therefore, implantation of fast metal ions into the diamond substrate can produce an electrical interconnection area or areas within the diamond.
The diamond may be a monocrystal or a polycrystal, and either will have almost the same effect. Further, the effect described above can be attained even if an impurity is present in the diamond, since no doping is performed.
Further, interconnections are provided within the diamond, so that no gap can be formed between the diamond and the interconnections, and thus the interconnections cannot be corroded nor oxidized by acid or a severe environmental atmosphere. Thus, corrosive metals of alkali metals or alkaline earth metals may be utilized for the interconnections. It is understood that refractory metals of W, Mo, Nb, Pt and Ir may also be used. Lighter elements such as Li and Na of the metal elements can be implanted deeper, thereby causing less damage to the diamond.
Further, since the diamond substrate has a high thermal conductivity, heat of the metal interconnection is readily dissipated, so that even a low melting metal material has an electrical power transmission capability.
Preferably, the diamond interconnection substrate includes a plurality of conductive layers, the plurality of conductive layers being disposed at different depth positions with various distances from a surface of the diamond.
This can realize a multi-layer interconnection structure, facilitates arrangement of interconnections, and also realizes integration.
Preferably, in the diamond interconnection substrate, the plurality of conductive layers are electrically connected with each other in the diamond.
This allows each conductive layer to be electrically connected with each other.
Preferably, the diamond interconnection substrate further includes at least one electrode formed on the surface of the diamond, and at least one of the plurality of conductive layers is electrically connected to the at least one electrode.
This enables the conductive layers to be electrically connected to other circuit elements through the electrode.
Preferably, in the diamond interconnection substrate, the metal elements constituting the conductive layer are metal elements of at least one species selected from a group consisting of Cu, Ag, Au, Pt, Mg and Al.
Thus, a material can be selected as appropriate, and a low-melting/low-resistant material can be used to form the interconnections.
A method of manufacturing a diamond interconnection substrate according to the present invention includes the step of ion implanting metal elements with energy of at least 1 MeV and a dose of at least 10
16
cm
−2
into diamond to form a conductive layer constituted by at least one metal element.
According to the manufacturing method of the diamond interconnection substrate of the present invention, the conductive layers that are to be interconnections can be formed within the diamond as described above, by ion implantation with the high energy (at least 1 MeV) and the high dose (at least 10
16
cm
−2
).
Preferably, in the method of manufacturing a diamond interconnection substrate, the ion implanting is performed a number of times by varying implantation depths of the metal elements into the diamond.
Implantation at different imp
Imai Takahiro
Matsuura Takashi
Nishibayashi Yoshiki
Fasse W. F.
Fasse W. G.
Japan Fine Ceramics Center
Nelms David
Nguyen Thinh T
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