JP2004363494A - Solid state image sensor and its fabricating process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid state image sensor in which multi-pixel and a large screen can be realized by reducing propagation delay, and to provide its fabrication process. <P>SOLUTION: Transfer electrodes 11 and 12 at a charge transfer section 3 are composed of polysilicon 4 and 5 in the same layer, and high melting point metal silicide 6 is formed on a part of the polysilicon 4 and 5 between light receiving sections 2 in the direction at least parallel with the charge transfer section 3 thus constituting a solid state image sensor 1. The solid state image sensor 1 is fabricated through a step for forming an opening in a part of an insulating film on the polysilicon films 4 and 5 between the light receiving sections 2 in the direction at least parallel with the charge transfer section 3, a step for forming a high melting point metal film and causing reaction between the high melting point metal film and the polysilicon films 4 and 5 below the opening through heat treatment to form high melting point metal silicide 6, a step for removing nonreaction high melting point metal film, and a step for forming an insulating film to cover the polysilicon films 4 and 5 and the high melting point metal silicide 6. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a solid-state imaging device and a method for manufacturing the solid-state imaging device.
[0002]
[Prior art]
A CCD solid-state imaging device is usually configured using polycrystalline silicon for a transfer electrode of a CCD transfer register.
[0003]
By the way, in a CCD solid-state imaging device, for example, when an attempt is made to realize a large-sized imaging device or a high-speed reading drive such as a high-speed frame rate, a sheet resistance of a transfer electrode is prevented in order to prevent propagation delay of a transfer clock supplied to the transfer electrode. Is required to be as low as possible.
[0004]
As a method of reducing the sheet resistance of the transfer electrode, for example, a method of forming the transfer electrode thicker, a method of using a low-resistance material such as a refractory metal silicide such as WSi as a material of the transfer electrode (for example, see Patent Document 1) , A method of connecting a shunt wiring made of an Al film or the like to a transfer electrode has been proposed.
[0005]
[Patent Document 1]
JP 2002-184968 A
[Problems to be solved by the invention]
However, any of the above-described methods for reducing the sheet resistance of the transfer electrode causes some problems.
[0007]
In the method in which the transfer electrode is formed to be thick, the step due to the transfer electrode becomes large, so that the sensitivity is reduced due to vignetting of the incident light.
Further, when patterning the transfer electrode formed of the second and subsequent electrode layers, overetching and unetched electrode layer are likely to occur.
For this reason, there is a problem that the gate insulating film is cut off due to over-etching, and a short circuit is caused due to the remaining etching.
[0008]
In the method of using a refractory metal silicide such as WSi as a material for the transfer electrode, the refractory silicide is not easily oxidized, so that a high-temperature process is required for the oxidation. In addition, it becomes difficult to form an interlayer insulating film by thermal oxidation. On the other hand, when an interlayer insulating film is formed by a method other than thermal oxidation, for example, a method of surrounding a transfer electrode with a nitride film, a separate process for forming the interlayer insulating film is required, which complicates the manufacturing process.
In addition, since the refractory metal causes an interface state on the substrate surface or a bulk intermediate level inside the substrate with respect to the silicon substrate, the refractory metal may enter the silicon substrate during the manufacturing process. As a result, white spots, white spots, and dark currents are generated in the manufactured solid-state imaging device.
[0009]
In the method of connecting the shunt wiring to the transfer electrode, the formation of the shunt wiring increases the step below the light-shielding film, so that there is a concern that the sensitivity may be reduced due to vignetting of incident light.
In addition, since it is necessary to ensure the withstand voltage between the shunt wiring and the light-shielding film, it is necessary to make the insulating film below the light-shielding film have a certain thickness or more, and this insulating film is also formed on the light receiving portion. Therefore, it is difficult to prevent the smear by reducing the distance between the light shielding film and the silicon substrate of the light receiving section.
[0010]
Therefore, in order to increase the number of pixels and increase the screen size, it is necessary to reduce the sheet resistance of the transfer electrode to suppress the propagation delay and to suppress the occurrence of the above-described problem.
[0011]
In order to solve the above-described problems, the present invention provides a solid-state imaging device capable of increasing the number of pixels and increasing the screen by reducing the propagation delay, and a method for manufacturing the solid-state imaging device. .
[0012]
[Means for Solving the Problems]
In the solid-state imaging device of the present invention, a charge transfer unit is provided on at least one side of one row of the light receiving units arranged in a line or a matrix, and the transfer electrodes of the charge transfer unit are formed of the same layer of polycrystalline silicon. A high melting point metal silicide is formed on at least a portion of the polycrystalline silicon between the light receiving portions in a direction parallel to the charge transfer portion.
[0013]
The method for manufacturing a solid-state imaging device of the present invention is a method for manufacturing a solid-state imaging device in which a charge transfer unit is provided on at least one side of one row of a light-receiving unit arranged in a line or a matrix. Forming a polycrystalline silicon film via an insulating film, patterning the polycrystalline silicon film, forming an insulating film covering the surface of the polycrystalline silicon film, and then forming an insulating film on the polycrystalline silicon film. A step of forming an opening in at least a portion between the light receiving sections in a direction parallel to the charge transfer section; and forming a high melting point metal film, and performing a heat treatment on the high melting point metal film and the polycrystalline silicon film below the opening. To form a refractory metal silicide, remove the unreacted refractory metal film, and form an insulating layer covering the polycrystalline silicon film and the refractory metal silicide. Those having also.
[0014]
According to the configuration of the solid-state imaging device of the present invention described above, at least the high-melting-point metal silicide is stacked and formed on the polycrystalline silicon, at least on a portion between the light receiving units in a direction parallel to the charge transfer unit. The portion between the light receiving portions has a structure in which a high melting point metal silicide is laminated on polycrystalline silicon, that is, a so-called salicide structure. With this salicide structure, the sheet resistance of the transfer electrode can be reduced. . Thereby, propagation delay in the transfer electrode can be suppressed.
In addition, since the refractory metal silicide is not formed directly on the gate insulating film but is formed on polycrystalline silicon, the refractory metal is less likely to enter the silicon substrate of the light receiving portion during manufacturing. .
Further, since the transfer electrode is formed of the same layer of polycrystalline silicon, the step due to the transfer electrode can be reduced, and the step of forming the refractory metal silicide can be simultaneously performed in each transfer electrode.
Therefore, the solid-state imaging device having a configuration in which the vignetting of the incident light due to the transfer electrode can be reduced, the range of the light incident on the light receiving unit can be widened, and the sheet resistance of the transfer electrode can be reduced to suppress the propagation delay, It becomes possible to manufacture in a relatively short process.
[0015]
According to the above-described method for manufacturing a solid-state imaging device of the present invention, after forming an insulating film covering the surface of the polycrystalline silicon film, the insulating film on the polycrystalline silicon film has at least a direction parallel to the charge transfer portion. Forming an opening in the portion between the light-receiving portions in step 1), forming a high-melting-point metal film, and reacting the high-melting-point metal film with the polycrystalline silicon film below the opening by heat treatment to form a high-melting-point metal silicide. Forming a high melting point metal silicide above the polycrystalline silicon film in this portion through an opening formed in at least a portion between the light receiving portions in a direction parallel to the charge transfer portion.
Then, by performing a step of removing the unreacted high-melting-point metal film, a transfer electrode having a structure in which a high-melting-point metal silicide is laminated on a polycrystalline silicon film, that is, a so-called salicide structure is formed. This makes it possible to manufacture a solid-state imaging device having a configuration in which the sheet resistance of the transfer electrode is reduced to suppress the propagation delay.
Also, at this time, since the refractory metal silicide is not formed directly on the gate insulating film but on polycrystalline silicon, it is necessary to suppress the refractory metal from entering the silicon substrate of the light receiving portion. Can be.
Further, in the step of forming an insulating layer covering the polycrystalline silicon film and the high-melting-point metal silicide, the transfer electrode is covered with the insulating layer, and is insulated from a light-shielding film, wiring, and the like to be formed thereafter.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
According to the present invention, a charge transfer portion is provided on at least one side of at least one column of light receiving portions arranged in a line or a matrix, and a transfer electrode of the charge transfer portion is formed of the same layer of polycrystalline silicon. And a solid-state imaging device in which a high-melting-point metal silicide is formed on at least a portion between light-receiving portions in a direction parallel to the charge transfer portion.
[0017]
Further, according to the present invention, in the solid-state imaging device, the refractory metal silicide is cobalt silicide.
[0018]
The present invention is a method for manufacturing a solid-state imaging device in which a charge transfer unit is provided on at least one side of one line of a light-receiving unit arranged in a line or a matrix, and a method of manufacturing the solid-state imaging device by interposing an insulating film on a silicon substrate. Forming a polycrystalline silicon film by patterning the polycrystalline silicon film, and forming an insulating film covering the surface of the polycrystalline silicon film. A step of forming an opening in a portion between the light receiving sections in a direction parallel to the transfer section, forming a high melting point metal film, and reacting the high melting point metal film with the polycrystalline silicon film below the opening by heat treatment. Forming a refractory metal silicide, removing an unreacted refractory metal film, and forming an insulating layer over the polycrystalline silicon film and the refractory metal silicide. A method for producing a body image pickup device.
[0019]
According to the present invention, in the method for manufacturing a solid-state imaging device, a cobalt film is formed as the high-melting-point metal film.
[0020]
FIG. 1 shows a schematic configuration diagram (plan view) of an embodiment of the solid-state imaging device of the present invention. FIG. 2 is a sectional view taken along line AA of FIG.
This embodiment shows a case where the present invention is applied to a CCD solid-state imaging device.
[0021]
In the solid-state imaging device 1, light receiving units 2 are arranged in a matrix, and a vertical transfer register 3 extending in a vertical direction (vertical direction in the drawing) V is provided on one side of each column of the light receiving units 2 as a charge transfer unit. Have been. A horizontal transfer register (not shown) is connected to one end of the vertical transfer register 3.
Each of the light receiving units 2 constitutes a pixel, and includes a photoelectric conversion unit (not shown) for converting light into electric charge and a charge accumulating unit for accumulating the converted electric charge.
[0022]
The vertical transfer register 3 is constituted by transfer electrodes 11 and 12 and a transfer channel (not shown) formed on the silicon substrate 21 thereunder for transferring signal charges, and serves as a charge transfer section having a CCD structure. I have.
[0023]
A gate insulating film (such as a silicon oxide film) 22 is formed between the transfer electrodes 11 and 12 and the silicon substrate 21 thereunder.
Further, a light-shielding film 8 is formed so as to cover the transfer electrodes 11 and 12. The light shielding film 8 has an opening 8A on the light receiving unit 2 so that light is incident on the light receiving unit 2.
[0024]
In the solid-state imaging device 1 according to the present embodiment, in particular, the transfer electrodes 11 and 12 of each vertical transfer register 3 are formed from the same layer (single layer) of the electrode layers, that is, from the first-layer polycrystalline silicon films 4 and 5. Make up.
The polycrystalline silicon films 4 and 5 can be formed, for example, by forming a non-doped polycrystalline silicon film and then doping impurities.
The polycrystalline silicon films 4 and 5 of the transfer electrodes 11 and 12 are insulated from each other by an insulating film (silicon oxide film or the like) 23 covering the surfaces thereof.
[0025]
Each of the polycrystalline silicon films 4 and 5 has a conductor portion extending in the horizontal direction (horizontal direction in the figure) H and an electrode portion protruding along the vertical transfer register 3. The conductor portion is arranged and formed at a portion between pixels in the vertical direction V.
The polycrystalline silicon film 4 is arranged on the upper side in the figure with respect to the light receiving section 2 and the electrode section protrudes downward.
The polycrystalline silicon film 5 is arranged on the lower side in the figure with respect to the light receiving section 2, and the electrode section protrudes upward.
The polycrystalline silicon films 4 and 5 vertically adjacent to each other in the figure are arranged such that the respective conductor portions and the respective electrode portions face each other with a narrow gap formed by the insulating film therebetween.
The transfer channel region of the vertical transfer register 3 is formed in the silicon substrate below the electrode portions of the polycrystalline silicon films 4 and 5.
[0026]
In the solid-state imaging device 1 according to the present embodiment, the transfer electrodes 11 and 12 further include a silicide film 6 made of a high melting point metal silicide such as cobalt (Co) silicide on each of the polycrystalline silicon films 4 and 5. It is formed by lamination.
That is, the transfer electrodes 11 and 12 having a so-called salicide structure are formed by stacking the polycrystalline silicon films 4 and 5 and the silicide film 6.
[0027]
As described later, the silicide film 6 is formed by forming a high melting point metal such as cobalt on the polycrystalline silicon films 4 and 5 and reacting them.
As a silicide film having a salicide structure, cobalt silicide is generally used, but other refractory metal silicides can also be used for the silicide film 6.
[0028]
By configuring the transfer electrodes 11 and 12 having the salicide structure in this manner, the sheet resistance of the transfer electrodes can be reduced, for example, by a factor of several as compared with the case where the transfer electrodes are formed only by the polycrystalline silicon films 4 and 5. To a degree.
The silicide film 6 is formed on a conductive line portion extending in the horizontal direction (horizontal direction in the drawing) H of the polycrystalline silicon films 4 and 5.
[0029]
In FIG. 2, reference numeral 24 denotes an interlayer insulating layer made of SiO ₂ or the like, and reference numeral 25 denotes an insulating layer including a passivation film and a flattening film.
Above the insulating layer 25, a color filter, an on-chip lens, and the like (not shown) are provided as necessary.
[0030]
According to the configuration of the solid-state imaging device 1 of the present embodiment described above, the polycrystalline silicon films 4 and 5 of the transfer electrodes 11 and 12 are formed by the same layer (single layer) of the electrode layer. As compared with a CCD solid-state imaging device in which a transfer electrode is formed by a multi-layered electrode layer, a step due to the transfer electrode is reduced.
Thereby, since the range of light incident on the light receiving unit 2 can be widened and the vignetting of the incident light by the transfer electrodes 11 and 12 can be reduced, the amount of incident light can be increased, and the sensitivity of the light receiving unit 2 can be improved. Can be planned.
Therefore, the solid-state imaging device 1 with high sensitivity can be realized.
[0031]
In addition, since the silicide film 6 is formed on the conductive wires of the polysilicon films 4 and 5 of the transfer electrodes 11 and 12 to form a salicide structure, the transfer electrodes are formed only by the polysilicon films 4 and 5. The sheet resistance of the transfer electrode can be reduced to, for example, about several times as compared with the case where is configured.
As a result, the transfer electrodes 11 and 12 can be reduced in resistance and the propagation delay can be suppressed, so that the solid-state imaging device 1 can easily realize a large number of pixels, a large angle of view (large size), and a high-speed reading. It becomes possible to do.
[0032]
When the silicide film is formed directly on the gate insulating film, the refractory metal of the silicide film may enter the silicon substrate of the light receiving portion by etching or the like at the time of patterning the silicide film.
On the other hand, in the solid-state imaging device 1 of the present embodiment, the silicide film 6 is formed on the polycrystalline silicon films 4 and 5 on the gate insulating film 22, and is formed directly on the gate insulating film 22. It has not been. The silicide film 6 having a salicide structure is usually patterned by wet etching as described later.
Therefore, according to the configuration of the solid-state imaging device 1 of the present embodiment, the refractory metal of the silicide film 6 does not easily enter the silicon substrate 21 of the light receiving section 2.
This prevents the generation of interface states and internal states on the surface of the silicon substrate 21 and realizes the solid-state imaging device 1 with less white scratches and dark current.
[0033]
Further, since the polycrystalline silicon films 4 and 5 of the transfer electrodes 11 and 12 are formed by the same (single-layer) electrode layer, each polycrystalline silicon film 4 and 5 is The step of forming the silicide film 6 by the reaction can be performed at a time.
If the transfer electrode having the salicide structure is a multi-layered electrode layer, since the conductive portions of the electrode layers of each layer overlap with each other, it is necessary to individually perform a silicidation reaction on each electrode layer. This complicates the manufacturing process.
Therefore, according to the solid-state imaging device 1 of the present embodiment, there is an advantage that the solid-state imaging device 1 in which the transfer electrodes 11 and 12 have a low resistance can be manufactured by a relatively short process. I have.
[0034]
The solid-state imaging device 1 of the present embodiment can be manufactured, for example, as follows.
[0035]
First, in the silicon substrate 21, the transfer channel region of the vertical transfer register 3 and the horizontal transfer register, the channel stop region, the semiconductor region serving as the photoelectric conversion unit and the charge storage unit constituting the light receiving unit 2, the field of the peripheral circuit unit, and the like are stored. , Respectively, by ion implantation of impurities.
Further, a gate insulating film 22 made of an oxide film, a silicon nitride film or the like is formed on the surface of the silicon substrate 21.
[0036]
Next, by forming a polycrystalline silicon film on the gate insulating film 22 and patterning the same, a plan view is shown in FIG. 3A and a cross-sectional view is shown in FIG. Then, polycrystalline silicon films 4 and 5 are formed.
[0037]
Next, an insulating film (oxide film or nitride film) 23 that covers the polycrystalline silicon films 4 and 5 from the top and side surfaces is formed. When the insulating film 23 is formed of an oxide film, the surfaces of the polycrystalline silicon films 4 and 5 may be thermally oxidized to form an oxide film. Alternatively, the polycrystalline silicon films 4 and 5 may be nitrided to form the insulating film 23 with a nitride film.
[0038]
Subsequently, in the insulating film 23 covering the polycrystalline silicon films 4 and 5, a part covering the upper surfaces of the polycrystalline silicon films 4 and 5 is partially etched off, so that a plan view is shown in FIG. As shown in FIG. 4B, an opening 31 is formed in the insulating film 23 to expose a part of the polycrystalline silicon films 4 and 5.
The region exposed by the opening 31 is laid out on the conductive portions of the polycrystalline silicon films 4 and 5 in the direction (horizontal direction) H in which the transfer clock propagates.
[0039]
Next, a cobalt film is deposited as a high melting point metal film by, for example, a sputtering method.
Subsequently, the cobalt film is reacted with the underlying polycrystalline silicon films 4 and 5 by performing a short-time heat treatment in a nitrogen atmosphere at about 500 ° C., for example. As a result, the upper portions of the polycrystalline silicon films 4 and 5 react with the cobalt film to be silicided.
Next, unreacted cobalt films in regions other than on the surfaces of the polycrystalline silicon films 4 and 5 are removed by wet etching.
Thereafter, annealing at 800 ° C. to 900 ° C. is performed to stabilize the silicide film 6, and a plan view is shown on FIG. 5A and a sectional view is formed on the polycrystalline silicon films 4 and 5 as shown in FIG. 5B. Transfer electrodes 11 and 12 having a salicide structure formed by laminating silicide films 6 are formed.
[0040]
Next, an interlayer insulating film 24 is formed to cover the polysilicon films 4 and 5 and the silicide film 6 of the transfer electrodes 11 and 12.
Further, a metal film serving as a light-shielding film 8 is entirely formed so as to cover the surface, and the metal film is patterned, and an opening 8A is opened on the light receiving section 2 to form the light-shielding film 8.
The light-shielding film 8 may be Cu-based, tungsten-based, or aluminum-based.
Thereafter, a step of forming a metal wiring, a step of forming an insulating layer 25 (see FIG. 2) such as a passivation film and a flattening film, and the like are performed.
Further, a color filter and an on-chip lens are formed as necessary.
[0041]
Thus, the solid-state imaging device 1 of the present embodiment shown in FIGS. 1 and 2 can be manufactured.
[0042]
Although the impurity regions of the light receiving section 2 are formed in advance in the above-described manufacturing process before the polycrystalline silicon films 4 and 5 are formed, for example, the polycrystalline silicon films 4 and 5 of the transfer electrodes 11 and 12 are formed. After the formation, it is also possible to use the polycrystalline silicon films 4 and 5 as a mask so as to be self-aligned with the openings of the polycrystalline silicon films 4 and 5.
However, when this manufacturing method is adopted, it is necessary to take measures to prevent the silicide film 6 from being damaged and the refractory metal from being mixed into the light receiving portion 2 during the ion implantation for forming the impurity region of the light receiving portion 2. Become. For example, it is preferable not to form a silicide film very close to the edge of the polycrystalline silicon film. For example, after forming the polycrystalline silicon films 4 and 5 and before forming the cobalt film, the light receiving section 2 is formed. It is conceivable to perform ion implantation.
[0043]
According to the above-described manufacturing process, it is possible to manufacture the solid-state imaging device 1 in which the transfer electrodes 11 and 12 are formed in a salicide structure, the transfer electrodes 11 and 12 have low sheet resistance, and can suppress propagation delay.
In addition, since all the transfer electrodes 11 and 12 can have a salicide structure in a series of steps, a configuration in which the resistance of the transfer electrodes 11 and 12 is reduced by a relatively short process can be manufactured.
[0044]
In the above-described embodiment, the silicide film 6 is formed as a stripe pattern only on the conductive portions of the polycrystalline silicon films 4 and 5, but the silicide film slightly extends over the electrode portion of the polycrystalline silicon film. It may be formed by.
However, if the silicide film is formed very close to the edge of the polycrystalline silicon film, the refractory metal of the silicide film is scattered in subsequent steps (for example, the step of forming and patterning the interlayer insulating layer 24). And may enter the silicon substrate of the light receiving section. For this reason, the silicide film is formed by being receded to some extent from the edge of the polycrystalline silicon film. The same can be said for the portion between pixels (conductor portion).
[0045]
Further, in the above-described embodiment, the present invention is applied to the CCD solid-state imaging device. However, the present invention can be applied to solid-state imaging devices having other configurations.
For example, the present invention can be similarly applied to a solid-state imaging device having a configuration in which a charge transfer unit other than a CCD structure is provided on one side of a row of light receiving units.
[0046]
The configuration of the solid-state imaging device of the present invention can be applied to any of the CCD solid-state imaging devices of the FT (frame transfer) system, the IT (interline transfer) system, and the FIT (frame interline transfer) system. It is possible.
[0047]
The present invention is not limited to the above-described embodiment, and may take various other configurations without departing from the gist of the present invention.
[0048]
【The invention's effect】
According to the above-described present invention, since the transfer electrodes are formed of the same electrode layer, a step due to the transfer electrodes can be reduced, thereby reducing the vignetting of incident light and improving the sensitivity. become.
Further, since the sheet resistance of the transfer electrode can be reduced, propagation delay in the transfer electrode can be suppressed.
Therefore, according to the present invention, it is possible to increase the number of pixels and the screen size of the solid-state imaging device, and to perform high-speed reading in the solid-state imaging device.
[0049]
Further, according to the present invention, since the refractory metal can be suppressed from entering the silicon substrate of the light receiving portion, the occurrence of white flaws and dark current is reduced, and the solid-state imaging device capable of suppressing propagation delay is provided. An element can be realized.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram (plan view) of a solid-state imaging device according to an embodiment of the present invention.
FIG. 2 is a sectional view taken along line AA of FIG.
FIGS. 3A and 3B are process diagrams showing a manufacturing process of the solid-state imaging device of FIG. 1;
FIGS. 4A and 4B are process diagrams showing a manufacturing process of the solid-state imaging device of FIG. 1;
FIGS. 5A and 5B are process diagrams showing a manufacturing process of the solid-state imaging device of FIG. 1;
FIGS. 6A and 6B are process diagrams showing a manufacturing process of the solid-state imaging device of FIG. 1;
[Explanation of symbols]
REFERENCE SIGNS LIST 1 solid-state imaging device, 2 light receiving section, 3 vertical transfer register, 4, 5 polycrystalline silicon film, 6 silicide film, 8 light shielding film, 11 and 12 transfer electrode

Claims (4)

A charge transfer unit is provided on at least one side of at least one row of the light receiving units arranged in a line or a matrix,
The transfer electrode of the charge transfer section is made of the same layer of polycrystalline silicon,
A solid-state imaging device, wherein a high melting point metal silicide is formed on at least a portion of the polycrystalline silicon between the light receiving portions in a direction parallel to the charge transfer portion. The solid-state imaging device according to claim 1, wherein the refractory metal silicide is cobalt silicide. A method for manufacturing a solid-state imaging device in which a charge transfer unit is provided on at least one side of at least one row of light-receiving units arranged in a line or a matrix,
Forming a polycrystalline silicon film on a silicon substrate via an insulating film, and patterning the polycrystalline silicon film;
After forming an insulating film covering the surface of the polycrystalline silicon film, an opening is formed in at least a portion between the light receiving units in a direction parallel to the charge transfer unit in the insulating film on the polycrystalline silicon film. Forming,
Forming a high-melting-point metal film, reacting the high-melting-point metal film with the polycrystalline silicon film below the opening by heat treatment, and forming a high-melting-point metal silicide;
Removing the unreacted refractory metal film,
Forming a dielectric layer covering the polycrystalline silicon film and the refractory metal silicide. 4. The method according to claim 3, wherein a cobalt film is formed as the refractory metal film.

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