Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – Insulated gate formation
Reexamination Certificate
2002-03-04
2003-05-06
Chaudhuri, Olik (Department: 2823)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
Insulated gate formation
C438S660000, C438S683000, C438S762000, C438S768000
Reexamination Certificate
active
06559041
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing a semiconductor device, and more specifically it relates to a semiconductor device which has a low-resistance ohmic contact that is suitable for use in high-speed device operation, and which enables the achievement and maintenance of a high-quality barrier property and high immunity to leakage current at this ohmic contact part, and to a method of manufacturing such a semiconductor device.
2. Description of the Related Art
In recent years, with ever-increasing levels of integration in semiconductor devices, there is an increasing tendency toward the short channel effect, that is, a decrease in the gate threshold voltage value, caused by the intrusion of a doped diffusion layer, which is used to separate various source and drain regions, below the gate and, to suppress this phenomenon, there is an increased need to make the junction depth of the ohmic contact part that is formed on the source and drain regions thin.
Therefore, an inevitable problem to be overcome is that of forming a contact boundary surface that is even sharper and more uniform than in the past. Metals such as titanium, cobalt, and nickel, which form suicides are coming into use for the purpose of forming self-aligning contacts.
A solid-phase siliciding reaction, however, is usually non-uniform, resulting in circular metal crystals and disturbance to the crystal structure of the diffusion layer, this leading to the tendency for leakage currents to occur.
Additionally, the silicide itself reacts easily with aluminum, the main metal that is used to form the contact wire, and particularly in the case of a non-uniform silicide film having many grain boundaries, a barrier film is necessary in order to be able to tolerate manufacturing processes at temperatures above 600° C.
It is difficult to achieve a uniform epitaxial suicide film on a silicon (100) substrate that i~ usually used for semiconductor devices. For the case of the cobalt silicide contact of the past, as taught in the Japanese Unexamined Patent Publication (KOKAI No. 3-67334, Japanese Unexamined Patent Publication (KOKAT) No. 9-69497, Japanese Unexamined Patent Publication (KOKAI) No. 9-251967, and Japanese Unexamined Patent Publication (KOKAI) No. 10-45416, there is disclosure of forming a film (100 to 150 &mgr;&OHgr;-cm) from the crystal phase of high-resistance CoSi or the like, by means of a first heat treating (at around 450° C.), after which heat treating at 600° C. or higher is done to form a film (14 to 17 &mgr;&OHgr;-cm) from low-resistance crystal phase CoSi
2
.
However, in a method which passes through a silicide crystal phase such as that of CoSi, which has a small amount of Si, the film formed is a CoSi
2
(100) film, thereby making it difficult to achieve a uniform epitaxial film.
One reason for siliciding proceeding non-uniformly is existence of various silicides that have different compositions and crystal structures.
With almost all of the metals that form silicides, at a siliciding reaction at a relatively low temperature, the heat of formation is small, and in contrast to the formation of a silicide phase having a small amount of silicon, at relatively high temperatures the heat of formation is large, this being replaced by a thermodynamically stable silicide phase having a large amount of silicon.
In the case of cobalt silicide, the participating phases are a CoSi crystal phase with a crystallization temperature of 450 to 500° C. and a CoSi
2
crystal phase with a crystallization temperature of 600° C. or higher, and in the thermal step of the phase change from the CoSi crystal phase to the CoSi
2
crystal phase, a spatially random lattice is formed, so that the final silicide thin film that is obtained is a polycrystal.
For this polycrystalline cobalt silicide, inevitable interface roughening causes increase of leakage current, worsening of thermal stability of the contact structure and increase of resistance.
Accordingly, it is an object of the present invention to improve on the above-described drawbacks in the prior art, by providing a semiconductor device wherein a ohmic contact is formed of cobalt silicide that has a high degree of surface flatness and a high uniformity, thereby enabling the achievement of a low resistance in the contact part, a low reactivity with other metals such as aluminum, and maintenance of good barrier characteristics and immunity to leakage currents, this semiconductor device featuring high-speed operation and high reliability, as well as the ability to be integrated to a high degree.
It is a further object of the present invention to provide a method for manufacturing the above-noted semiconductor device.
SUMMARY OF THE INVENTION
In order to achieve the above-noted objects, the present invention adopts the following basic technical constitution.
Specifically, the first aspect of the present invention is a semiconductor device that is provided with an ohmic contact made of a single-crystal CoSi
2
film on a silicon surface (100).
The second aspect of the present invention is a method for manufacturing a semiconductor device, this method having a step of performing hydrogen termination processing of a silicon (100) surface, a step of forming a cobalt film on the silicon surface (100) that was hydrogen termination processed, a step of causing thermal diffusion of the above-noted cobalt, so as to form an amorphous cobalt silicide film on the surface part of the silicon, this having an atomic number in Co:Si ratio of 1:1.5 to 1:2.5, and a step of performing heat treating of the above-noted amorphous cobalt silicide film so as to form an ohmic contact part that is made of a single-crystal CoSi
2
film.
A semiconductor device according to the present invention adopts the technical constitution described above, a feature of which is the provision of an ohmic contact part that is made of single-crystal CoSi
2
film on a silicon (100) surface, the effect being a flattening on a molecular level of the surface of this ohmic contact part and the achievement of a high uniformity, this enabling the achievement of a low-resistance contact part.
In addition, there is no reactivity with other metals such as aluminum, and maintenance of good barrier characteristics and immunity to leakage currents, giving this semiconductor device improved high-speed operation, high reliability, and the ability to be integrated to a high degree.
The provision of an ohmic contact made of a single-crystal CoSi
2
film on the silicon (100) surface is a new technology according to the present invention and, as discussed above, according to an invention by the inventor(s), with technology such as taught in Japanese Unexamined Patent Publication (KOKAI) No. 3-67334, Japanese Unexamined Patent Publication (KOKAL) No. 9-69497, Japanese Unexamined Patent Publication (KOKAI) No. 9-251967, and Japanese Unexamined Patent Publication (KOKAI) No. 10-45416, because the CoSi
2
film that forms the ohmic contact is a polycrystal, it is not possible to achieve the special effect of the present invention.
Furthermore, in the present invention the fact that the CoSi
2
film is a single-crystal film, in the usual meaning of the term, means that ideally the crystal orientation within the crystal is the same in all parts and that there are intrinsically no grain or other boundaries.
In actuality, however, if an electron beam is shone in the [100] direction using transmission electron beam diffraction, there is substantially a 99% or greater observation of diffraction spots on the CoSi
2
(100) surface that corresponds with the silicon (100) surface.
In the case of a polycrystal CoSi
2
film of the past, the ratio of the diffraction spots between the (100) surface and, for example, the normally observed (110) surface, is approximately 1:1, as could be calculated, for example, from the diffraction intensity.
From the electron beam diffraction image as well, it is possible to observe a polycrystal condition in w
Chaudhuri Olik
Hayes & Soloway P.C.
NEC Corporation
Nguyen Khiem
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