Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2002-11-18
2004-07-20
Nguyen, Ha Tran (Department: 2812)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S530000, C438S600000, C438S601000, C438S752000
Reexamination Certificate
active
06764953
ABSTRACT:
The invention relates to an electronic device comprising a substrate having a first side, which substrate is provided at said first side with a first layer, which first layer comprises an electrically conducting portion and adjoining thereto an electrically insulating portion.
The invention also relates to a method of manufacturing an electronic device comprising the step of patterning a first layer in accordance with a chosen pattern, which first layer lies on a substrate and comprises an electrically conducting portion and an electrically insulating portion after patterning.
Such a device is known from U.S. Pat. No. 5,736,452. The first layer comprises a pattern of electrically conducting portions of aluminum which are separated from one another by electrically insulating portions of an electrically insulating material. The first layer in the device is manufactured in a usual manner, i.e. by the following steps: deposition of inter alia aluminum; provision of a layer of photoresist thereon; exposure of the photoresist in accordance with the chosen pattern through a photolithographic mask made for the purpose; development of the photoresist; removal by etching of the uncovered aluminum with any remaining photoresist thereon; removal of remaining photoresist from the etched aluminum; and deposition of the electrically insulating material on the etched aluminum.
It is a disadvantage of the known device that its manufacture is cumbersome.
It is a first object of the invention to provide an electronic device of the kind mentioned in the opening paragraph whose first layer is easy to manufacture.
It is a second object of the invention to provide a method of the kind mentioned in the opening paragraph in which the use of a photoresist is not necessary.
According to the invention, the first object is achieved in that:
the first layer comprises a material which is built up from at least a first and a second element,
the material has an amorphous state and a crystalline state,
the electrically insulating portion comprises the material in its amorphous state, and
the electrically conducting portion comprises the material in its crystalline state. Both the amorphous and the crystalline state of the material are utilized in the electronic device according to the invention. The material is present in its crystalline state in the electrically conducting portions of the first layer. The material in the amorphous state acts as an electrical insulation between the electrically conducting portions of the first layer. The material in its crystalline state has in fact a better electrical conductivity—i.e. a lower resistivity—than in its amorphous state. Preferably, the conductivity in the crystalline state is more than 10
4
times that in the amorphous state.
In its amorphous state, moreover, the material may act as an electrical insulation between conductor tracks outside the first layer, which conductor tracks are as yet not electrically interconnected. At any moment after the manufacture of the device according to the invention, a transition from the amorphous to the crystalline state may be achieved locally in the material. This gives rise to one or several electrically conducting portions which electrically interconnect the conductor tracks outside the first layer. The transition from the amorphous to the crystalline state may be achieved in a portion of the first layer through heating of this portion. The transition remains limited to the heated portion.
The first layer provided with the electrically conducting and the electrically insulating portions may be readily manufactured in that the first layer of the material is deposited in the amorphous state and is subsequently patterned through local heating of the material in accordance with the chosen pattern.
The first layer of the device according to the invention may lie directly on the substrate, or alternatively it may be present as an intermediate layer in the device, or at a surface of the device. The device is, for example, an integrated circuit, a display, a filter, an optoelectronic device, or a network of passive components.
Phys. Rev. Letters
21 (1968), 1450-1453 by S. R. Ovshinsky discloses a device comprising a material in which a transition from an amorphous state to a crystalline state of the material is utilized for switching and for making a memory unit. In the device according to the invention, crystalline and electrically conducting portions are present in a largely amorphous and electrically insulating layer. Whereas the material in the known device comprises at least the atoms of tellurium or arsenic, there is no need for this in the device according to the invention.
A number of materials are known from EP-A-0 644 537 in which a transition from an amorphous state to a crystalline state is achieved through irradiation with a laser beam. A difference in optical reflection is achieved thereby, which is utilized for data storage. It is not known or even suggested therein that such materials can be used in alternative applications on account of their difference in conductivity. Applications in which this difference in conductivity is utilized, such as the device according to the invention, are not demonstrated.
The material aluminum-germanium is known from Catalina et al.,
Thin Solid Films
167 (1988), 57-65. This article, however, does not show or suggest the use of the material in an electronic device. The article contains no suggestion on patterning of a first layer through local heating of the aluminum-germanium.
It was surprisingly found in experiments which led to the invention that several atoms may be chosen for the first element of the material, and that the second element may be chosen from gallium, germanium, and indium. If silicon is chosen as the second element, a slight drop in the resistivity is found, such as with Cr—Si, or the amorphous state is found to be instable, as is the case for Al—Si. Preferably, the proportional quantity of the second element in the material is at least 10%.
Examples of first elements are inter alia vanadium, cobalt, nickel, copper, zinc, gallium, aluminum, silver, tellurium, zirconium, titanium, molybdenum, antimony, arsenic, and tungsten. The first and the second element are different here. Preferably, the proportion of the first atoms type in the material exceeds 30%. Examples of first materials are Al—Ge, Ge—Te, Ga—Sb, and In—Sb.
The material may comprise a third element. The inclusion of the third element in the material may raise the resistivity in the amorphous state.
It is favorable when the first element of the material in the first layer is aluminum, and the second element is germanium, the germanium content being at least 20%. The crystalline state of the material aluminum-germanium has two phases: a phase of substantially pure crystalline aluminum and a phase of substantially pure crystalline germanium. Examples of favorable compositions of the aluminum-germanium are shown in Table 1.
A first advantage of aluminum-germanium as the material is that a conductivity was found for the material in its crystalline state which is only ten times smaller than that of pure aluminum. The inventors are of the opinion that this is caused by the presence of a substantial proportion of a crystalline phase of aluminum. A second advantage of the aluminum-germanium is that the crystallization temperature lies between 120 and 250° C. This is a temperature which can be readily achieved by local heating with a laser beam. At the same time, this temperature is high enough for preventing a spontaneous transition from the amorphous to the crystalline state. A third advantage is that the elements of aluminum and germanium are known per se in the manufacture of, for example, semiconductor devices. The purchase price of aluminum and germanium is comparatively low. A fourth advantage is that aluminum and germanium are easy to process. These substances are not toxic or reactive in combination with, for example, oxygen and water.
In a first embodiment of the device according to the invention, a fi
Boogaard Arjen
De Wild Willem Reindert
Huiberts Johannes Nicolaas
Liedenbaum Coen Theodorus Hubertus Fransiscus
Montree Andreas Hubertus
Nguyen Ha Tran
Zawilski Peter
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