JP2002124658A - Method for manufacturing solid-state imaging device - Google Patents

Abstract

(57) Abstract: A solid-state imaging device capable of easily manufacturing without reducing the resistance of the electrode and deteriorating characteristics such as withstand voltage and S / N ratio of the electrode of the solid-state imaging device. And a method for producing the same. SOLUTION: In manufacturing a solid-state imaging device formed by forming multilayer gate electrodes 5, 9, a step of forming gate electrodes 5, 9 comprising polycrystalline silicon films 3, 7 and metal silicide films 4, 8 is provided. A step of thermally oxidizing the surfaces of the gate electrodes 5 and 9, wherein a sufficient amount of hydrogen is added to the atmosphere to reduce an oxide of a metal constituting the metal silicide in the atmosphere in the step of thermal oxidation. Do.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a solid-state image sensor using metal silicide as a material for a gate electrode.

[0002]

2. Description of the Related Art In a solid-state imaging device, it has been considered to use a WSi (tungsten silicide) film as an electrode material in order to reduce the resistance of a gate electrode. WS
When the i film is used for the gate electrode, a polycrystalline silicon film is formed on the gate insulating film, and a WSi film is formed on the polycrystalline silicon film. Form.

In a solid-state imaging device having a gate electrode made of a normal polycrystalline silicon film, a gate electrode made of a polycrystalline silicon film is thermally oxidized to form an interlayer insulating film as a silicon oxide film. Have been done.

[0004]

However, when a WSi film is used as a material for a gate electrode, the W
When the interlayer insulating film is formed by directly thermally oxidizing the Si film, the following problems occur.

When the WSi film is directly thermally oxidized (for example, dry oxidation of oxygen only or pyro oxidation of hydrogen / oxygen <1.8), silicon is oxidized to silicon oxide (Si).
O ₂₎ also occurs oxidation of tungsten with formed. At this time, since the vapor pressure of the tungsten oxide is high, the tungsten oxide diffuses during thermal oxidation.

For this reason, the oxide of tungsten is taken into the interlayer insulating film between the gate electrodes, causing a problem that the dielectric strength voltage is deteriorated, or the oxide of tungsten is used in the sensor section of the solid-state imaging device. When the charge is transferred to the substrate of the charge transfer section, it becomes a source of noise such as formation of a level, and a problem of forming a solid-state imaging device with much noise occurs.

Accordingly, when a WSi film is used for a gate electrode, it is necessary to form an interlayer insulating film by a method other than direct thermal oxidation of the electrode.

As one of the methods, for example, a method in which a WSi film is covered with a polycrystalline silicon film and the WSi film is not exposed to an oxidizing agent as much as possible and indirectly thermally oxidized is considered.

However, this method complicates the electrode forming process, increases the number of steps, and increases the manufacturing cost. Further, since complicated processing is required to cover the WSi film with the polycrystalline silicon film, the difficulty of the processing is considerably increased. Furthermore, with such a structure, the W
The Si film needs to be formed in a pattern finer than the pattern of the gate electrode to be formed. That is, the line width of the WSi wiring used for lowering the electrode resistance becomes thin, and the advantage of lowering the resistance by WSi cannot be used.

As another method, a manufacturing method in which a thermal oxide film is not formed when an interlayer insulating film is formed in a multilayer electrode structure can be considered. In this case, instead of forming a thermal oxide film, an interlayer insulating film is formed by a film forming method such as a CVD method.

However, in this case, the thickness of the gate insulating film below the different layer electrode is different. For example, when forming the first layer transfer electrode and the second layer transfer electrode, the thickness of the gate insulating film under the first layer transfer electrode and the thickness of the gate insulating film under the second layer transfer electrode are different. Would. For this reason, for example, a process of thinning the gate insulating film under the upper electrode once formed is required, and this method also complicates the manufacturing process and leads to an increase in manufacturing cost.

In order to solve the above-mentioned problems, the present invention aims at reducing the resistance of the electrodes and without deteriorating the characteristics of the electrodes of the solid-state imaging device, such as the withstand voltage and the S / N ratio.
An object of the present invention is to provide a method for manufacturing a solid-state imaging device that can be easily manufactured.

[0013]

According to a method of manufacturing a solid-state imaging device of the present invention, a gate electrode made of a polycrystalline silicon film and a metal silicide film is used for manufacturing a solid-state imaging device having a multi-layered gate electrode. Forming, and thermally oxidizing the surface of the gate electrode, wherein in the thermal oxidizing step, a sufficient amount of hydrogen is added to the atmosphere to reduce the oxide of the metal constituting the metal silicide. is there.

According to the above-described method of the present invention, in the step of thermally oxidizing the surface of the gate electrode composed of the polycrystalline silicon film and the metal silicide film, it is sufficient to reduce the oxide of the metal constituting the metal silicide in the atmosphere. By adding an appropriate amount of hydrogen, only silicon can be oxidized without oxidizing the metal of the metal silicide film.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a method for manufacturing a solid-state image pickup device by forming a multi-layer gate electrode, comprising the steps of forming a gate electrode comprising a polycrystalline silicon film and a metal silicide film; Thermally oxidizing the surface of the electrode, and adding a sufficient amount of hydrogen to the atmosphere to reduce an oxide of the metal constituting the metal silicide in the thermal oxidation step. .

FIG. 1 shows a CC as an embodiment of the present invention.
The process drawing (sectional view) of the manufacturing process of D solid-state image sensor is shown.
FIG. 1 shows each step of forming a multilayer gate electrode (transfer electrode) constituting a transfer channel of a CCD solid-state imaging device.

In order to obtain a desired impurity profile,
After performing a patterning process such as a mask and an implantation process of impurities such as a well region of a transfer channel, the semiconductor substrate 1
A gate insulating film 2 on the surface of the substrate. Thereafter, a polycrystalline silicon film 3 serving as an initial gate electrode and a WSi film 4 are sequentially formed as a silicide film, and these films 3 and 4 are processed by patterning, dry etching, or the like. Thus, as shown in FIG. 1A, the first layer gate electrode 5 made of the polycrystalline silicon film 3 and the WSi film 4, that is, polycide is formed.

Next, as shown in FIG. 1B, the surface of the first-layer gate electrode 5 is thermally oxidized to form an interlayer insulating film 6 between different-layer gate electrodes.

Here, the interlayer insulating film may be formed to be thick in order to ensure the withstand voltage between the electrodes. However, when the interlayer insulating film is formed to be thick, the gap between the electrodes of different layers adjacent in the direction along the substrate surface becomes large. A region where the electric field is weak occurs in the transfer channel in the substrate. This causes a decrease in transfer efficiency in transferring signal charges. Therefore, the interlayer insulating film must be formed as a thin film using a material having good withstand voltage as much as possible.

As described above, when the WSi film is directly thermally oxidized, the tungsten is also oxidized, and the oxide of the tungsten is diffused, thereby causing a problem that the withstand voltage is degraded or a noise source is caused. . Therefore, a device for suppressing the oxidation of tungsten is required.

Therefore, in the present invention, when the WSi film is subjected to the thermal oxidation treatment, it is exposed to a large amount of hydrogen which is a reducing agent simultaneously with the oxidizing agent. By using the oxidizing agent and hydrogen in this way, the following oxidation reactions (1) and (2) and reduction reactions (3) and (4) occur.

Oxidation reaction: Si + O ₂ → SiO ₂ (1) 2W + 3O ₂ → 2WO ₃ (2) Reduction reaction: SiO ₂ + 2H ₂ → Si + 2H ₂ O (3) WO ₃ + 3H ₂ → W + 3H ₂ O (4)

At this time, the tungsten oxide WO_ThreeReturn of
The reaction rate of the original reaction (4) is SiO _TwoReduction reaction (3)
Faster than the reaction rate of Satisfy this condition
By doing so, SiO_TwoIs also reduced, but tungsten
Oxide WO_ThreeAs the reduction reaction (4) is faster,
Is not oxidized, and the oxide is SiO_Two
Only obtained.

Then, the concentrations of the oxidizing agent and hydrogen are adjusted so as to satisfy this condition.

Next, a polycrystalline silicon film 7 and a WSi film 8 serving as a gate electrode of a second layer are sequentially formed and processed into a predetermined pattern in the same manner as in the first layer, as shown in FIG. 1C. The second layer gate electrode 9 is formed. Subsequently, the gate electrode 9 of the second layer is subjected to a thermal oxidation treatment in which a large amount of hydrogen is added, and an interlayer insulating film 10 is formed on the surface of the gate electrode 9 as shown in FIG. 1D.

When three or more gate electrodes are formed, the third and subsequent gate electrodes are formed in the same manner.

In this manner, a CCD solid-state image pickup device having a multi-layered gate electrode 5, 9 can be formed by forming an interlayer insulating film by thermal oxidation without diffusing tungsten. .

Here, the thermal oxidation treatment in which a large amount of hydrogen was added to the gate electrode made of polycide was actually performed. Reacting hydrogen and oxygen in advance to obtain water vapor,
Thermal oxidation was performed in an atmosphere in which the steam and hydrogen were mixed. And the volume ratio of steam / hydrogen is 0.095-0.
In the range of 43, it was confirmed that diffusion of W can be prevented and an interlayer insulating film having good withstand voltage can be formed.

According to the present embodiment, in the step of thermally oxidizing the surfaces of gate electrodes 5 and 9 made of polycide,
By adding a large amount of hydrogen (reducing agent) sufficient to reduce the W oxide constituting the WSi films 4 and 8 to the atmosphere, thereby reducing the W oxide and preventing the diffusion of W. Can be. At this time, silicon in the WSi films 4 and 8 is thermally oxidized to form SiO ₂ . Then, the WSi film 4,
Since W in 8 does not diffuse outside, it is taken into the gate electrodes 5 and 9.

As a result, the interlayer insulating films 6, 10 formed of thermal oxide films on the surfaces of the gate electrodes 5, 9 are made of SiO ₂
It becomes a film and does not contain W in the interlayer insulating films 6 and 10,
Insufficient dielectric strength can be prevented. That is, the interlayer insulating films 6 and 10 formed by thermal oxidation can be formed as films having a sufficient withstand voltage as interlayer insulating films. Further, since W does not spread to the sensor unit and the transfer channel, W
Does not become a noise source, and the occurrence of noise in the solid-state imaging device can be suppressed.

Therefore, the characteristics of the solid-state imaging device can be improved according to the present embodiment. Therefore, a gate electrode made of polycide can be used in a solid-state imaging device having a multilayer electrode without deteriorating the characteristics of the solid-state imaging device. Thus, the resistance of the electrode can be reduced.

In addition, the step of thermally oxidizing the gate electrodes 5 and 9 made of polycide can be performed in the same manner as the step of thermally oxidizing the gate electrode made of an ordinary polycrystalline silicon film, and thus the manufacturing process is complicated. Never be.

In the above embodiment, the case where a WSi film is used as the silicide film has been described. However, in the present invention, a metal silicide film made of a metal other than tungsten may be used.

The gate electrode made of polycide using the silicide film according to the present invention is, for example, a transfer electrode of a transfer register having a CCD structure of a CCD solid-state image sensor, that is, a vertical transfer register and a horizontal transfer register of an area sensor, and a CCD of a line sensor. The present invention can be applied to a gate electrode constituting a transfer electrode of each transfer register having a structure. Also, C
A gate electrode made of polycide using a silicide film according to the present invention can also be applied to a transfer section of a delay element using a charge transfer element having a CD structure.

The present invention is not limited to the above-described embodiment, but may take various other configurations without departing from the gist of the present invention.

[0036]

According to the present invention described above, the surface of the gate electrode made of a polycrystalline silicon film and a metal silicide film can be heated without complicating the manufacturing process and without deteriorating the characteristics of the solid-state imaging device. Oxidation can form an interlayer insulating film. Therefore, according to the present invention, the resistance of the electrode can be reduced by using the polycide electrode in the solid-state imaging device having the multilayer electrode.

[Brief description of the drawings]

1A to 1D are process diagrams (cross-sectional views) of a manufacturing process of a CCD solid-state imaging device according to an embodiment of the present invention;

[Explanation of symbols]

REFERENCE SIGNS LIST 1 semiconductor substrate, 2 gate insulating film, 3,7 polycrystalline silicon film, 4,8 WSi film, 5 first layer gate electrode, 6,10 interlayer insulating film, 9 second layer gate electrode

Claims (1)

[Claims] 1. A method for manufacturing a solid-state imaging device comprising a multi-layer gate electrode, comprising the steps of: forming a gate electrode comprising a polycrystalline silicon film and a metal silicide film; Oxidizing, wherein in the thermal oxidizing step, hydrogen is added in an atmosphere in an amount sufficient to reduce an oxide of a metal constituting the metal silicide. Method.