Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2000-12-01
2003-05-13
Fourson, George (Department: 2823)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S682000, C438S305000
Reexamination Certificate
active
06562716
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to technology for forming a cobalt silicide layer in a surface portion of a silicon layer formed on a semiconductor substrate, e.g., in a surface portion of a gate electrode composed of a polysilicon film or in a surface portion of an impurity diffused layer formed in a silicon substrate.
With the recent miniaturization of semiconductor devices, a semiconductor integrated circuit device has encountered various problems such as an increase in signal delay time caused by, e.g., an increase in the resistance of a contact or an impurity diffused layer and electric conduction between a gate electrode and the contact connecting to the impurity diffused layer caused by alignment offset.
As a method for solving the former problem, there has been proposed a salicide process as disclosed in, e.g., Japanese Unexamined Patent Publication No. HEI 7-86559, wherein a cobalt silicide layer is formed in a surface portion of a gate electrode or of an impurity diffused layer serving as a source or drain region in a MOS transistor.
A description will be given to a salicide process disclosed in Japanese Unexamined Patent Publication No. HEI 7-86559 as a first conventional embodiment. After a gate electrode composed of a polysilicon film is formed on a silicon substrate and an impurity diffused layer serving as a source or drain region is formed in the silicon substrate, a cobalt film and a titanium film are deposited successively over the entire surface of the silicon substrate. Then, a heat treatment is performed to cause a reaction between the cobalt and titanium films and the polysilicon film or the impurity diffused layer, whereby a cobalt silicide layer is formed in respective surface portions of the gate electrode and the impurity diffused layer. The titanium film is formed on the cobalt film with the view to lowering the surface energy of the cobalt silicide layer and thereby preventing agglomeration in a surface portion of the cobalt silicide layer.
The formation of the cobalt silicide layer in the surface portions of the gate electrode and the impurity diffused layer thus suppresses an increase in the resistance of each of a contact and the impurity diffused layer and thereby implements a higher-speed semiconductor integrated circuit device.
As a method for solving the latter problem, there has been proposed a self-aligned contact (SAC). In response to the miniaturization of a semiconductor device, the method forms an insulating film composed of a silicon oxide film on the upper and side surfaces of a gate electrode, deposits a liner film over the entire surface of the insulating film, deposits an interlayer insulating film composed of a silicon oxide film on the liner film, and forms, in the interlayer insulating film, a contact hole connected to an impurity diffused layer serving as a source or drain region. In accordance with the method, no electric conduction occurs between a metal film buried in the contact hole and the gate electrode since the insulating film is present on the gate electrode even if the contact hole is formed partly above the gate electrode.
To implement the self-aligned contact, however, the insulating film and the liner film should be deposited on the gate electrode. This causes the problem that a surface portion of the gate electrode cannot be silicidized during the formation of the self-aligned contact.
To solve the problem, Japanese Unexamined Patent Publication No. HEI 9-289249 proposes a method for a trade-off between the self-aligned contact and the salicide process.
A description will be given to a salicide process disclosed in Japanese Unexamined Patent Publication No. HEI 9-289249 as a second conventional embodiment. In the salicide process, a first offset oxide film is formed on the upper surface of a gate electrode, sidewalls are formed on the respective side surfaces of the gate electrode and the first offset oxide film, and the first offset oxide film is removed such that the gate electrode is exposed and a depressed portion is formed internally of the sidewalls. Then, a cobalt film is deposited all over and subjected to a heat treatment, whereby a cobalt silicide layer is formed in respective surface portions of the gate electrode and an impurity diffused layer. Subsequently, a second offset oxide film is formed on the cobalt silicide layer on the gate electrode to be buried in the depressed portion and a liner film and an interlayer insulating film are deposited successively all over. Thereafter, a contact hole connecting to the impurity diffused layer as a source or drain region is formed in the interlayer insulating film.
However, the salicide process according to the first conventional embodiment encounters a first problem that the vertical position of a top surface (upper surface) of the silicon layer lowers greatly in the direction of the depth of the substrate in the process in which a reaction occurs between Co atoms composing the cobalt film and Si atoms composing the polysilicon film serving as the gate electrode or the impurity diffused layer in the silicon substrate as the source or drain region (hereinafter the polysilicon film and the impurity diffused layer are collectively referred to as a silicon layer) to form the cobalt silicide layer. This is because the Si atoms in the silicon layer are consumed in a large quantity while a reaction occurs between the Co atoms composing the cobalt film and the Si atoms composing the silicon layer to form the cobalt silicide layer, so that the vertical position of the top surface of the silicon layer moves greatly in the direction of the depth of the substrate.
To provide the silicon layer which is sufficiently thick after the formation of the cobalt silicide layer, the silicon layer prior to the formation of the cobalt silicide layer should have a sufficient thickness. This causes the problem that a shallow pn junction cannot be obtained and hence miniaturization cannot be achieved. To obtain the shallow pn junction, on the other hand, the vertical position of the top surface of the silicon layer lowers in the direction of the depth of the substrate and the thickness of the silicon layer is reduced, which causes a junction leakage current.
The salicide process according to the second conventional embodiment allows both formation of the silicide layer in the surface portion of the gate electrode and formation of the self-aligned contact in the source or drain region. However, the salicide process according to the second conventional embodiment has the problem of an extremely large number of process steps since, after the first offset oxide film and the sidewalls are formed, the first offset oxide film is removed such that the depressed portion is formed internally of the sidewalls, the cobalt suicide layer and the second offset oxide film are formed successively, and then the liner film and the interlayer insulating film are deposited.
SUMMARY OF THE INVENTION
In view of the foregoing, a first object of the present invention is to prevent the vertical position of the top surface of the silicon layer from moving greatly in the direction of the depth of the substrate even if cobalt silicide is formed. A second object of the present invention is to form both of the suicide layer and the self-aligned contact without increasing the number of process steps.
(First Principle of Solution)
To attain the first object, the present inventors examined the mechanism of the formation of a cobalt silicide layer through a reaction between Co atoms composing a cobalt film and Si atoms composing a silicon layer and found a first principle of solution, which will be described below.
From a thermodynamic viewpoint, the mechanism of the formation of a cobalt silicide (to be precise, a monocobalt disilicide but hereinafter referred to as a cobalt silicide for the sake of convenience) through a reaction between Co atoms and Si atoms is the proceeding of the reaction of Co
2
Si (dicobalt monosilicide)→CoSi (monocobalt monosilicide)→CoSi
2
(monocobalt dis
Egashira Kyoko
Hashimoto Shin
Fourson George
García Joannie Adelle
Nixon & Peabody LLP
Studebaker Donald R.
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