JPH09219459A - Non-volatile semiconductor memory device and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain generation of a bird's beak in an interlayer insulating film between gate electrodes of a double-layer gate structure, enable fine processing, and improve insulating property of the interlayer insulating film. SOLUTION: A first gate electrode 4 formed on an insulating film 3 on a semiconductor substrate 1, an interlayer insulating film 10 on the first gate electrode 4, and a second gate electrode 5 formed on the interlayer insulating film 10 are provided. The interlayer insulating film 10 includes a plurality of insulating film layers 12-16 composed of alternately stacked oxide film layers and nitride film layers. Of these insulating film layers, the insulating film layers 12 and 16 in contact with the first gate electrode 4 and the second gate electrode 5 are made of nitride film layers.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonvolatile semiconductor memory device having a two-layer gate structure.

[0002]

2. Description of the Related Art Conventionally, a nonvolatile semiconductor memory device such as a flash memory has a two-layer gate structure composed of a floating gate electrode and a control gate electrode. These electrodes are formed of, for example, a polycrystalline silicon film, and as an interlayer insulating film between these electrodes, an oxide film, a nitride film,
An insulating film having a three-layer structure of an oxide film (hereinafter referred to as ONO structure) is used.

7 and 8 show a conventional method of manufacturing a nonvolatile semiconductor memory device. For example, a polycrystalline silicon film 4 is formed on a semiconductor substrate 1 such as a p-type Si substrate in which the element isolation region 2 is formed, with an insulating film 3 such as an oxide film interposed therebetween. After that, impurities such as arsenic or phosphorus are added to the polycrystalline silicon film 4 by ion implantation, for example. Next, an oxide film (SiO ₂ ) 11 is formed on the polycrystalline silicon film 4 by, for example, a thermal oxidation method, and further, for example, C
A nitride film (SiN) 12 is deposited on the oxide film 11 by the VD (chemical vapor deposition) method, and further, for example, high temperature CV
The HTO (High Temprature Oxide) film 13 is formed by the D method.
Is deposited to form an interlayer insulating film 10 having an ONO structure.
Then, for example, a polycrystalline silicon film 5 is deposited on the interlayer insulating film 10 ((a) of FIG. 7).

Next, for example, an ordinary lithography method and R
By using an anisotropic etching technique such as an IE (Reactive Ion Etching) method, the polycrystalline silicon film 5 and the interlayer insulating film 10 are
And the polycrystalline silicon film 4 are etched, and the floating gate electrode 4, the interlayer insulating film 10 having the ONO structure, and the control gate electrode 5 form a two-layer gate structure as shown in FIG. 7B.

Thereafter, for example, heat treatment is performed in an oxidizing atmosphere to form an oxide film (SiO ₂ ) 6 so as to cover the control gate electrode 5 and the floating gate electrode 4. This oxide film 6
Is for protecting the side walls of the gate electrodes 4 and 5 in particular. After that, an n-type impurity such as arsenic or phosphorus is added to the semiconductor substrate 1 using, for example, an ion implantation method, and an appropriate heat treatment is performed to form the n-type diffusion layer 7 ((a) in FIG. 8). Here, the formation of the n-type diffusion layer 7 and the formation of the thermal oxide film 6 can be performed in the reverse order.

After that, an interlayer insulating film is formed by a usual method, and after flattening by annealing or the like, a connection hole, a wiring and the like are formed to complete the nonvolatile semiconductor memory device.

As described above, in the conventional method for manufacturing a nonvolatile semiconductor memory device, in order to protect the control gate electrode 5 and the floating gate electrode 4, after etching these, the oxide film 6 is removed by thermal oxidation. Form. At this time, the thermal oxidation oxidizes the control gate electrode 5 and the floating gate electrode 4. In particular, as shown in FIG. 8B, which is an enlarged view of the portion surrounded by the broken line in FIG. 8A, the interface between the floating gate electrode 4 and the oxide film 11 and the control gate electrode 5 and the oxide film are shown. At the interface with 13, the oxidation progresses from the end, so that the film thicknesses of the oxide film 11 and the oxide film 13 increase at the end of the floating gate electrode 4, and the interlayer insulating film 10 has a so-called bird's beak shape.

Such bird's beak is heat-treated in an oxidizing atmosphere not only when the oxide film 6 is formed, but also in the subsequent step of forming the n-type diffusion layer 7 or the step of flattening the interlayer insulating film. May also occur if you do.

Generally, in a nonvolatile semiconductor memory device having a two-layer gate structure, a potential is applied to the control gate electrode 5 and the potential of the floating gate electrode 4 is controlled by coupling through the interlayer insulating film 10. Here, if bird's beaks occur in the interlayer insulating film 10, the thickness of the interlayer insulating film 10 becomes thicker in the bird's beak region, so that the coupling weakens and the control gate electrode 5 cannot sufficiently control the potential of the floating gate electrode. . In particular, if the gate length is shortened with the miniaturization of the device, this bird's beak region cannot be ignored with respect to the gate length. As described above, the conventional non-volatile semiconductor memory device has a problem that the miniaturization of elements is hindered by the occurrence of bird's beaks, and the non-volatile semiconductor memory device cannot be highly integrated.

Also, due to the occurrence of bird's beak, a region having a large film thickness and a region having a small film thickness are mixed in the interlayer insulating film 10, and the interlayer insulating film is caused by the voltage applied between the control gate electrode 5 and the floating gate electrode 4. The electric field generated in 10
There is a problem that the insulating property is deteriorated by concentrating on a thin film region.

[0011]

As described above, the conventional nonvolatile semiconductor memory device has a problem that it is difficult to miniaturize the gate electrode due to the occurrence of bird's beaks, and high integration cannot be achieved. In addition, there is a problem that the insulating property of the interlayer insulating film is deteriorated due to the occurrence of bird's beak.

The object of the present invention is to suppress the occurrence of bird's beaks in the interlayer insulating film between the gate electrodes of the two-layer gate structure, enable miniaturization, and improve the insulating property of the interlayer insulating film. Semiconductor memory device and a simple manufacturing method thereof.

[0013]

In order to solve the above problems and achieve the object, a nonvolatile semiconductor memory device according to the present invention includes a first gate electrode formed on an insulating film on a semiconductor substrate, and In a nonvolatile semiconductor memory device comprising an interlayer insulating film on a first gate electrode and a second gate electrode formed on this interlayer insulating film, the interlayer insulating film includes an oxide film layer and a nitride film layer. Of a plurality of insulating film layers that are alternately laminated, and an insulating film layer in contact with the first and second gate electrodes of the insulating film layers is a nitride film layer. To do.

Further, in the nonvolatile semiconductor memory device according to the present invention, the first gate electrode formed on the insulating film on the semiconductor substrate, the interlayer insulating film on the first gate electrode, and the interlayer insulating film. In a nonvolatile semiconductor memory device having a second gate electrode formed above, the interlayer insulating film is composed of a plurality of insulating film layers in which oxide film layers and nitride film layers are alternately laminated. Of the insulating film layers, the insulating film layer that is in contact with the first or second gate electrode is formed of an oxide film layer, and the oxide film layer has an allowable limit in the width of the edge region where the film thickness increases. It is characterized in that it has a film thickness equal to or less than the value.

Further, in the above-mentioned nonvolatile semiconductor memory device, the width of the oxide film layer along the edge of the region where the film thickness is increased is 1 with respect to the length of the first gate electrode. It is also possible to have a film thickness selected so as to be / 10 or less.

Further, in the nonvolatile semiconductor memory device according to the present invention, the first gate electrode formed on the insulating film on the semiconductor substrate, the interlayer insulating film on the first gate electrode, and the interlayer insulating film. In a nonvolatile semiconductor memory device having a second gate electrode formed above, the interlayer insulating film is composed of a plurality of insulating film layers in which oxide film layers and nitride film layers are alternately laminated. An insulating film layer of the insulating film layer, which is in contact with the first or second gate electrode, is formed of an oxide film layer, and the oxide film layer has a film thickness between a central portion and a peripheral portion of the interlayer insulating film. Is characterized by having a film thickness equal to or smaller than the film thickness at which the difference between the two becomes an allowable limit value.

Further, in the above-mentioned non-volatile semiconductor memory device, the oxide film layer may have a thickness of 2.5 nm or less. Further, in the above-mentioned nonvolatile semiconductor memory device, the interlayer insulating film may be composed of insulating film layers having five or more layers stacked.

In the nonvolatile semiconductor memory device described above, the oxide film layer is C at a temperature of 750 to 800 degrees.
It is also possible to use an HTO film formed by the VD method.

The method for manufacturing a non-volatile semiconductor memory device according to the present invention comprises the steps of forming a first gate electrode material film on a semiconductor substrate via an insulating film, and forming the first gate electrode material film on the first gate electrode material film. A step of forming a first nitride film layer, a step of alternately laminating an oxide film layer and a nitride film layer on the first nitride film layer to form an interlayer insulating film, and a step of forming an interlayer insulating film on the interlayer insulating film. A step of forming a second gate electrode material film, wherein the second gate electrode material film is formed so as to contact the nitride film layer of the interlayer insulating film after the formation of the nitride film layer. It is characterized in that it is formed on a film.

The method for manufacturing a non-volatile semiconductor memory device according to the present invention comprises the steps of forming a first gate electrode material film on a semiconductor substrate via an insulating film, and forming the first gate electrode material film on the first gate electrode material film. A step of alternately laminating an oxide film layer and a nitride film layer to form an interlayer insulating film; and a second step on the interlayer insulating film.
Forming a gate electrode material film, and forming the interlayer insulating film so that the oxide film layer is in contact with the first or second gate electrode material film. It is characterized in that the oxide film layer is formed so that the width of the edge region which is increasing has a film thickness equal to or less than a film thickness which is an allowable limit value.

Further, in the above-described method for manufacturing a nonvolatile semiconductor memory device, the width along the edge of the region where the film thickness of the oxide film layer is increased is relative to the length of the first gate electrode. It is also possible to form the oxide film layer so as to have a film thickness selected to be 1/10 or less.

Further, the method for manufacturing a nonvolatile semiconductor memory device according to the present invention comprises a step of forming a first gate electrode material film on a semiconductor substrate via an insulating film, and a step of forming the first gate electrode material film on the first gate electrode material film. A step of alternately laminating an oxide film layer and a nitride film layer to form an interlayer insulating film; and a second step on the interlayer insulating film.
Forming a gate electrode material film, and forming the interlayer insulating film so that an oxide film layer is in contact with the first or second gate electrode material film, and forming a central portion of the interlayer insulating film. It is characterized in that the oxide film layer is formed so that a difference in film thickness between the peripheral portion and the peripheral portion is equal to or smaller than an allowable limit value.

Further, in the above-mentioned method for manufacturing a nonvolatile semiconductor memory device, it is possible to form the oxide film layer so that the film thickness of the oxide film layer is 2.5 nm or less. Further, in the above-described method for manufacturing a nonvolatile semiconductor memory device, it is possible to form an interlayer insulating film by stacking five or more insulating film layers on the first gate electrode material film.

Further, in the above-mentioned method for manufacturing a non-volatile semiconductor memory device, the insulating film layer is formed by C using the same furnace.
It is also possible to continuously form by the VD method. Further, in the above-described method for manufacturing a nonvolatile semiconductor memory device, it is possible to form a nitride film layer on the first gate electrode material film by nitriding the first gate electrode with NH _3. is there.

Further, in the above-mentioned method for manufacturing a nonvolatile semiconductor memory device, a CV at a temperature of 750 to 800 degrees is used.
It is also possible to form the oxide film layer by the D method.
As described above, in the nonvolatile semiconductor memory device according to the present invention, the interlayer insulating film between the first gate electrode and the second gate electrode is formed of a plurality of insulating film layers in which a nitride film and an oxide film are alternately stacked. Since it is composed of, it is possible to improve the insulating property and reliability of the interlayer insulating film.

Here, in the case where the insulating film layer of the insulating film layer that is in contact with the first and second gate electrodes is composed of a nitride film layer, an oxidation step after these gate electrodes are formed. In, it is possible to prevent the first or second gate electrode from being oxidized. Therefore, it is possible to suppress the phenomenon that oxidation progresses from the edge of the gate electrode and the film thickness of the interlayer insulating film increases in this portion, that is, bird's beak is generated.

In addition, among the insulating film layers, the first or second
When the insulating film layer in contact with the gate electrode is made of an oxide film layer, the film thickness of the oxide film layer can be reduced to suppress the diffusion of oxygen in the oxide film layer. Therefore, the oxidizing agent is not supplied to the central portion of the gate electrode, and the thickness of the oxide film does not increase. In this way,
The width along the edge of the region where the film thickness of the oxide film is increased by the oxidation of the gate electrode, that is, the width of the bird's beak can be reduced.

As described above, the thickness of the oxide film layer in contact with the first or second gate electrode and the width of the bird's beak have a relationship that the width of the bird's beak increases as the thickness of the oxide film layer increases. is there. Therefore, by configuring the oxide film layer with a film thickness selected so that the width of the bird's beak falls within the allowable range, the width of the bird's beak can fall within the allowable range.

In particular, the width of the bird's beak is set to 1/10 of the length of the gate electrode by forming the oxide film layer with a film thickness selected so that the width of the bird's beak is 1/10 or less of the length of the gate electrode. It can be 10.

Further, since the oxide film thickness increases in the peripheral portion of the gate electrode due to the occurrence of bird's beak, a difference in film thickness occurs between the central portion and the peripheral portion of the interlayer insulating film. It is almost proportional to the width of the bird's beak. Further, similarly to the above, there is a relationship between the difference in the film thickness and the above-mentioned oxide film thickness that the difference in the film thickness increases as the film thickness of the oxide film layer increases. Therefore, the width of the bird's beak can be suppressed within the allowable range by forming the oxide film layer with a film thickness such that the difference in film thickness between the central portion and the peripheral portion is within the allowable range.

In particular, when the thickness of the oxide film layer is 2.5 nm or less, as described above, the supply of the oxidizing agent is suppressed, so that the width of the bird's beak can be reduced.
In this manner, in the nonvolatile semiconductor memory device according to the present invention, by suppressing the occurrence of bird's beak or the width thereof, it is possible to prevent the electric field from concentrating on the thin film portion in the interlayer insulating film, and to improve the insulating property. It becomes possible to improve. Further, by reducing the width of the bird's beak relative to the length of the gate electrode, the range in which the interlayer insulating film has a desired film thickness can be expanded. For this reason,
It is possible to increase the coupling between the second gate electrode and the first gate electrode and improve the controllability of the first gate electrode by the second gate electrode. In this way, it is possible to reduce the size of the gate electrode and improve the degree of integration of the nonvolatile semiconductor memory device.

Further, when the interlayer insulating film is composed of the insulating film layers in which five or more layers are laminated, the insulating property of the interlayer insulating film can be further improved. Further, in order to increase the number of laminated insulating film layers forming the interlayer insulating film without increasing the effective film thickness of the interlayer insulating film, it is necessary to reduce the film thickness of each insulating film layer. Therefore, the thickness of the insulating film layer in contact with the first or second gate electrode can be reduced, and as described above, the occurrence of bird's beaks can be suppressed.

When the oxide film layer is composed of the HTO film formed by the CVD method at the temperature of 750 to 800 ° C., the quality of the HTO film is excellent, so that the oxide film layer and the nitride film layer are excellent. It is possible to further improve the insulating property of the interlayer insulating film configured by alternately stacking and.

Since the method for manufacturing a nonvolatile semiconductor memory device according to the present invention includes the step of forming the first nitride film layer on the first gate electrode material film, the first oxide film is formed in the subsequent oxidation step. The nitride film layer serves as a protective film and can prevent the first gate electrode from being oxidized.

Since the interlayer insulating film is formed by alternately stacking the oxide film layer and the nitride film layer on the first nitride film layer, the insulating property of the interlayer insulating film can be improved. Further, a second gate electrode material film is formed on the interlayer insulating film, and the second gate electrode material film is formed on the interlayer insulating film so as to come into contact with the nitride film layer of the interlayer insulating film. Since this gate electrode material film is formed, the nitride film layer serves as a protective film in the subsequent oxidation step, and it is possible to prevent the second gate electrode from being oxidized.

As described above, in the method for manufacturing a nonvolatile semiconductor memory device according to the present invention, the insulating property of the interlayer insulating film is improved by alternately stacking the oxide film layer and the nitride film layer to form the interlayer insulating film. Further, by forming an interlayer insulating film so that the nitride film layer is in contact with the first and second gate electrodes, oxidation of the first and second gate electrodes is prevented and generation of bird's beaks is suppressed. can do.

In the method for manufacturing a non-volatile semiconductor memory device according to the present invention, an oxide film layer and a nitride film layer are alternately laminated to form an interlayer insulating film, and the first or second gate electrode material film is formed. The interlayer insulating film is formed so that the oxide film layers are in contact with each other. The thinner the oxide film layer in contact with the first or second gate electrode material film is, the more the supply of the oxidizing agent is reduced. The occurrence of bird's beaks is suppressed. By utilizing this, the width of the bird's beak can be suppressed within the allowable range by forming the oxide film layer with a film thickness selected so that the width of the bird's beak falls within the allowable range.

In particular, the width of the bird's beak is set to be equal to or less than the thickness of the bird's beak so that the width of the bird's beak becomes 1/10 of the length of the first gate electrode. It can be set to 1/10 of the length of the gate electrode.

Although the bird's beak causes a difference in film thickness between the central portion and the peripheral portion of the interlayer insulating film, as described above, the thinner the oxide film layer, the more suppressed the occurrence of bird's beak. . Therefore, the width of the bird's beak can be suppressed within the allowable range by forming an oxide film layer having a thickness such that the difference in film thickness between the central portion and the peripheral portion is within the allowable range.

In particular, when the thickness of the oxide film layer is 2.5 nm or less, as described above, the supply of the oxidizing agent is suppressed, so that the width of the bird's beak can be reduced.
In this manner, in the method for manufacturing a nonvolatile semiconductor memory device according to the present invention, it is possible to suppress the occurrence of bird's beaks or the width thereof. Therefore, as described above, the insulating property of the interlayer insulating film is improved and the gate electrode By miniaturizing the dimensions, it is possible to improve the integration degree of the nonvolatile semiconductor memory device.

When the interlayer insulating film is formed by stacking five or more insulating film layers on the first gate electrode material film, the insulating property of the interlayer insulating film can be further improved.

Further, in order to increase the number of laminated insulating film layers forming the interlayer insulating film so as not to increase the effective film thickness of the interlayer insulating film, it is necessary to reduce the film thickness of each insulating film layer. There is. Therefore, the thickness of the insulating film layer in contact with the first or second gate electrode can be reduced, and as described above, the occurrence of bird's beaks can be suppressed.

Further, in the method for manufacturing a nonvolatile semiconductor memory device according to the present invention, in which the stacked insulating film layers forming the interlayer insulating film are continuously formed by the CVD method using the same furnace, the individual interlayer insulating films are formed. Since it is possible to prevent contaminants, dust, etc. from adhering to the interlayer insulating film at the time of taking in and out of the furnace and at the time of sucking or releasing the vacuum, as compared with the case of separately forming each by using a different furnace. It is possible to improve the film quality. Further, as compared with the case where a plurality of laminated insulating film layers are separately formed by using different furnaces, work efficiency can be significantly improved by forming them by using the same furnace.

In the method of manufacturing a nonvolatile semiconductor memory device described above, when a nitride film layer is formed on the first gate electrode by nitriding the first gate electrode with NH ₃ , , NH ₃ has a reducing action,
The film thickness of the natural oxide film on the first gate electrode material film can be reduced. This prevents the oxidizing agent from being supplied through the natural oxide film formed on the first gate electrode to oxidize the first gate electrode and suppresses the occurrence of bird's beak. You can

Further, the interlayer insulating film is formed by stacking an oxide film layer and a nitride film layer, and is formed at 750 ° to 800 °.
In the method for manufacturing a non-volatile semiconductor memory device according to the present invention, in which the oxide film layer is formed by a CVD method at a temperature of 100 ° C.,
Since it becomes possible to form an oxide film layer having an excellent film quality by using the D method, it is possible to improve the insulating property of the interlayer insulating film.

Furthermore, since both the nitride film layer and the oxide film layer having excellent film quality can be formed by the CVD method,
It is possible to form these laminated films using the same furnace. Therefore, as described above, it is possible to prevent dust and the like from adhering, and improve the quality of the interlayer insulating film. In addition, work efficiency can be significantly improved.

[0047]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing the structure of a nonvolatile semiconductor memory device according to the first embodiment of the present invention. Similarly to the conventional method, on the semiconductor substrate 1 of, for example, p-type Si or the like in which the element isolation region 2 is formed by, for example, the selective oxidation method or the like, via the insulating film 3 of the oxide film or the like,
Floating gate electrode 4, interlayer insulating film 10 and control gate electrode 5
Are formed. The floating gate electrode 4 and the control gate electrode 5 are formed of, for example, a polycrystalline silicon film, and an insulating film 6 such as an oxide film is formed so as to cover the floating gate electrode 4 and the control gate electrode 5. There is.

Here, unlike the conventional case where the interlayer insulating film 10 has the ONO structure, in the present embodiment, the interlayer insulating film 10 is formed.
Has a NONON structure in which a nitride film 12, an HTO film 13, a nitride film 14, an HTO film 15, and a nitride film 16 are stacked. For example, the nitride film 12 has a thickness of 1 nm, the HTO film 13 has a thickness of 4 to 8 nm, and the nitride film 14 has a thickness of 5 nm.
12 nm, HTO film 15 is 4 to 8 nm, nitride film 16 is 1
nm.

As described above, in the present embodiment, among the insulating film layers forming the interlayer insulating film 10, the layer in contact with the floating gate electrode 4 is formed by the nitride film 12, and the control gate electrode 5 is formed.
The feature is that the layer in contact with is formed by the nitride film 16. Since the nitride film is generally hard to be oxidized, the nitride film 12 can prevent the floating gate electrode 4 from being oxidized from the interface with the interlayer insulating film 10. Similarly,
The nitride film 16 can prevent the control gate electrode 5 from being oxidized from the interface with the interlayer insulating film 10. In this way, it is possible to prevent the bird's beak from occurring in the nonvolatile semiconductor memory device of this embodiment.

Next, a method of manufacturing such a nonvolatile semiconductor memory device will be described with reference to FIG. 2A to 2D are process cross-sectional views showing the method for manufacturing the nonvolatile semiconductor memory device according to the first embodiment of the present invention.

In the same manner as in the prior art, the element isolation region 2 is formed on the semiconductor substrate 1 made of, for example, p-type Si by, for example, the selective oxidation method, and the insulating film 3 such as a thermal oxide film is further formed. Next, for example, a polycrystalline silicon film 4 to be a floating gate electrode is deposited, and if necessary, an n-type impurity such as arsenic or phosphorus is added by an ion implantation method or a phosphorus diffusion method. It is added to the crystalline silicon film 4 ((a) of FIG. 2).

Next, for example, by a CVD (chemical vapor deposition) method at a temperature of about 650 to 700 ° C., for example, the film thickness is 1 n.
m nitride film (SiN) 12 is deposited. Subsequently, in the same furnace, the temperature is raised to, for example, about 750 to 800 ° C., and the film thickness is, for example, 4 to 8 nm HTO (High Temprat).
ure Oxide) film 13 is deposited. Furthermore, successively, in the same furnace, a nitride film (Si
N) 14 is deposited, and further, an HTO film 15 having a film thickness of, for example, 4 to 8 nm is deposited in the same furnace. Then, in the same furnace, for example, a nitride film (Si
N) 16 is deposited. In this way, the interlayer insulating film 10 having the NONON structure is formed in the same furnace ((b) of FIG. 2).

At this time, after the semiconductor substrate is placed in the furnace, vacuum suction is performed, and thereafter, the temperature of the furnace and the source gas are changed, whereby the deposition by the CVD method can be continuously performed.

Thereafter, as in the conventional case, for example, a polycrystalline silicon film 5 to be a control gate electrode is deposited, and if necessary, for example, an ion implantation method or a phosphorus diffusion method is used,
For example, an n-type impurity such as arsenic or phosphorus is added to the polycrystalline silicon film 5 ((c) of FIG. 2).

Further, as in the conventional case, the polycrystalline silicon film 5 is formed by using an ordinary etching method and an anisotropic etching technique such as RIE (reactive ion etching).
The interlayer insulating film 10 and the polycrystalline silicon film 4 are etched to form a two-layer gate structure with the floating gate electrode 4, the interlayer insulating film 10 having the NONON structure and the control gate electrode 5 ((d) of FIG. 2). ).

After that, heat treatment is performed in, for example, an oxidizing atmosphere to form an oxide film (SiO ₂ ) 6 so as to cover the control gate electrode 5 and the floating gate electrode 4, and further, for example, using an ion implantation method, For example, an n-type impurity such as arsenic or phosphorus is added to the semiconductor substrate 1 and an appropriate heat treatment is performed.
The mold diffusion layer 7 is formed (FIG. 1). Here, similarly to the conventional case, the formation of the n-type diffusion layer 7 and the formation of the thermal oxide film 6 can be performed in the reverse order.

After that, an interlayer insulating film is formed by a usual method, flattening is performed by annealing or the like, and then connection holes and wirings are formed to complete the nonvolatile semiconductor memory device.

In this way, according to the method of manufacturing the nonvolatile semiconductor memory device in the first embodiment of the present invention,
Among the insulating film layers forming the interlayer insulating film 10, the insulating film layers in contact with the floating gate electrode 4 and the control gate electrode 5, which are formed of, for example, a polycrystalline silicon film, are nitride films 12 and 16. Occurrence can be suppressed. For example, in the past, the gate length was 0.3 μm
In the following cases, it was difficult to operate the device because the width of the bird's beak with respect to the gate length was large. However, the nonvolatile semiconductor memory having the two-layer gate structure with the gate length of 0.2 μm was formed by the above method. It becomes possible to manufacture the device.

Further, in the method of manufacturing the non-volatile semiconductor memory device according to the first embodiment of the present invention, the interlayer insulating film 10 having the NONON structure is formed by the CVD method using the same furnace for depositing the SiN film and the HTO film. The feature is that it is continuously performed in the inside.

Conventionally, when the interlayer insulating film 10 having a laminated structure such as the ONO structure is formed, it is general that these insulating film layers are not formed continuously in the same furnace but are formed independently of each other. It was target. This is a conventional CVD
According to the method, the oxide film was formed mainly at a temperature of about 500 ° C., and the quality of the film was more likely to deteriorate than the thermal oxide film. Therefore, in the conventional manufacturing method, the oxide film is formed mainly by thermal oxidation.

However, in this embodiment, 750 to 80
By forming an oxide film using the CVD method at a temperature of 0 ° C., an HTO film having an initial breakdown voltage equivalent to that of a thermal oxide film can be formed in a CVD furnace. In this way, since both the oxide film and the nitride film can be formed by using the CVD method, it becomes possible to continuously form a high-quality laminated insulating film in the same furnace.

Further, since the nitride film is generally difficult to oxidize,
When an oxide film is formed on the nitride film by thermal oxidation, it is necessary to perform heat treatment at a very high temperature for a long time such as about 1 hour in an oxygen atmosphere at 950 ° C. Therefore, for example, a diffusion layer formed before this thermal process may be further diffused, or a crystal defect may occur due to thermal stress between an insulating film and a semiconductor substrate such as element isolation. Invite. On the other hand, HTO film is 800 ℃
These problems do not occur because they can be formed by the following CVD method. Moreover, the working time can be significantly reduced.

Further, the HTO film generally has a property that the insulating property is easily deteriorated with time as compared with the thermal oxide film, but by forming a laminated structure with the nitride film, this defect can be compensated. it can.

As described above, in the method of manufacturing the non-volatile semiconductor memory device according to the present embodiment, the interlayer insulating film 10 is formed of the laminated film of the nitride film and the HTO film, so that the laminated film is formed in the same furnace. It becomes possible to form continuously.

The insulating film layers forming the interlayer insulating film 10 such as the SiN film or the oxide film are not continuously formed in the same furnace as in the prior art, but are independently formed in different furnaces. In this case, each time each insulating film layer is formed, the vacuum in the furnace is released, the semiconductor substrate is pulled out from the furnace, the semiconductor substrate is again inserted into another furnace, and the furnace is evacuated again. There is a need. Therefore, the work efficiency is very poor. In particular, as the number of insulating film layers forming the interlayer insulating film 10 increases as in the present embodiment, the time required for these operations becomes enormous.

During the formation of the interlayer insulating film 10,
When the semiconductor substrate is taken out of the furnace, the semiconductor substrate is exposed to the air, so that contaminants typified by organic substances such as carbon (C) tend to adhere to the surface of the insulating film layer forming the interlayer insulating film. . Further, since the insulating film layer is formed thereon, contaminants are taken into the inside of the interlayer insulating film 10. Therefore, there is a problem that the insulation property of the interlayer insulating film 10 is deteriorated.

Furthermore, in general, dust is easily generated inside the furnace when a vacuum is applied and when the vacuum is released.
Therefore, when vacuum suction and release are performed every time when each insulating film layer is formed, dust is more likely to adhere to the surface of the semiconductor substrate.

On the other hand, in the present embodiment, since the insulating film layers forming the interlayer insulating film 10 are continuously formed in the same furnace, the working time can be greatly shortened.
Further, since the semiconductor substrate is not taken out of the furnace during the formation of the interlayer insulating film 10, it is possible to prevent contamination by organic substances and the like. Further, since it is not necessary to perform vacuum suction and vacuum release each time each insulating film layer is formed, the possibility of dust contamination can be greatly reduced.

Although the nitride film 12 on the floating gate electrode 4 is formed by the CVD method in the above embodiment, the nitride film 12 is formed by nitriding the polycrystalline silicon film 4 using NH ₃ , for example. It is also possible to do so.

Generally, a natural oxide film is formed on the polycrystalline silicon film forming the floating gate electrode 4 to have a thickness of, for example, about 2 nm, and when the nitride film 12 is formed by the CVD method, the natural oxide film remains as it is. However, when the polycrystalline silicon film 4 is nitrided by using, for example, NH ₃ , NH ₃ has a reducing action, so that the natural oxide film can be reduced to, for example, about 1 nm. This makes it possible to further suppress the occurrence of bird's beaks. Moreover, since the oxide film equivalent thickness of the insulating film can be reduced, the controllability of the floating gate electrode 4 by the control gate electrode 5 is improved by increasing the coupling between the control gate electrode 5 and the floating gate electrode 4. Can be made.

A capacitor using the NONON film formed by the manufacturing method according to the present embodiment and a conventional O 2 film are used.
FIG. 3 shows the result of comparing the initial breakdown voltage characteristics of the capacitor using the NO film, and FIG. 4 shows the result of comparing the TDDB (dielectric breakdown with time) characteristics. (A) shows the characteristics of the capacitor according to the present invention, and (b) shows the characteristics of the conventional capacitor. Both effective oxide film thickness is 15 nm
It is.

From FIG. 3, the NONON according to the present embodiment is shown.
It can be seen that the initial breakdown voltage of the film is improved and the variation is reduced as compared with the conventional ONO film. Further, it can be seen from FIG. 4 that the NODB film according to the present embodiment has a TDDB (dielectric breakdown over time) characteristic improved by about one digit as compared with the conventional ONO film.

Further, in the above-mentioned embodiment, among the insulating film layers forming the interlayer insulating film 10, the layer in contact with the floating gate electrode 4 and the control gate electrode 5 is formed by the nitride film, but the insulating film layers are laminated. When the number is increased, it is not necessarily a nitride film, and an oxide film may be used instead of the nitride film. As a second embodiment, FIG. 5 shows a cross-sectional view of a nonvolatile semiconductor memory device in which the interlayer insulating film 10 has, for example, an ONONON structure.

In the present embodiment, the interlayer insulating film 10 having the NONON structure in the first embodiment is the HTO.
Film 13, SiN film 14, HTO film 15, SiN film 16,
It is composed of the HTO film 17 and the SiN film 18, and other than that, the structure is similar to that of the first embodiment.

The thickness of each insulating film layer constituting the interlayer insulating film 10 is appropriately selected so that the effective film thickness of the interlayer insulating film 10 becomes a desired film thickness of, for example, 15 nm when converted into an oxide film. adjust.

In the present embodiment, the insulating film layers forming the interlayer insulating film 10 are CV as in the first embodiment.
It is desirable that the layers are continuously formed in the same furnace by using the D method. Here, generally, the growth rate of the HTO film by the CVD method is, for example, 0.07 nm / min, and the growth rate of the SiN film is, for example, 0.3 nm / min, so that it is several nm.
The film thickness of can be sufficiently controlled.

As described above, the present embodiment is characterized in that the insulating film layers forming the interlayer insulating film 10 are multilayered so as not to increase the effective film thickness of the interlayer insulating film 10.
Generally, for example, the width of the bird's beak generated in the interlayer insulating film between the upper and lower electrodes formed of a polycrystalline silicon film is
It is almost proportional to the thickness of the oxide film in contact with this polycrystalline silicon film. FIG. 6 shows the relationship between the oxide film thickness y formed on the floating gate electrode 4 and the width x of the bird's beak. As shown in the figure, the width x of the bird's beak is defined as the width of the edge region where the film thickness of the interlayer insulating film is increased. Here, the side surface of the floating gate electrode 4 has a thickness of 30 nm due to post-oxidation.
Oxidation was performed under the condition that an oxide film of a certain degree was formed.
From this figure, for example, 1 formed on the floating gate electrode 4
It can be seen that the thinner the oxide film 13 of the layer is, the less likely bird's beak is to occur.

Therefore, as in the present embodiment, the thickness of each insulating film layer can be reduced by making the insulating film layers multilayer so as not to increase the effective film thickness of the interlayer insulating film 10. Therefore, it is possible to reduce the thickness of the oxide film 13 and reduce the occurrence of bird's beaks.

Generally, the width of the bird's beak is 1 of the gate length.
The presence of the bird's beak does not significantly affect the controllability of the floating gate electrode 4 by the control gate electrode 5 or the insulation property of the interlayer insulating film 10 up to about / 10. For example, 0.
In the case of manufacturing a nonvolatile semiconductor memory device having a gate length of 3 μm, if generation of a bird's beak with a width of 30 nm is allowed to be about 1/10 of that, the oxide film thickness on the floating gate electrode 4 is 2. It is necessary to keep it to 5 nm.

Further, FIG. 6 shows the relationship between the oxide film thickness y and the width x of the bird's beak. Generally, as the bird's beak becomes larger, the width x increases and the central portion of the interlayer insulating film 10 caused by the bird's beak becomes larger. The difference z in the film thickness between the peripheral part and the peripheral part also increases. Therefore, instead of FIG. 6, it is possible to show the relationship between the oxide film thickness y and the film thickness difference z of the interlayer insulating film due to the bird's beak. Use this to keep the bird's beak size within the acceptable range.
The oxide film thickness y can be selected.

As described above, when the film thickness of the oxide film is reduced, it becomes difficult to secure the insulating property with the single-layer interlayer insulating film 10. However, in the present embodiment, the insulating film layer is formed. By forming the multi-layered structure, it becomes possible to complement the defects of the respective insulating film layers with each other and improve the insulating property of the interlayer insulating film 10.

Further, similarly to the first embodiment, by forming the multi-layered insulating film layers in the same furnace, it is possible to suppress an increase in the number of steps due to the multi-layering, and to prevent contaminants, dust, etc. It is possible to prevent the insulating property from deteriorating due to the adhesion.

According to the present embodiment, the bird's beak can be more suppressed as the number of layers increases. However, if such a multi-layered insulating film layer is not continuously formed in the same furnace, problems such as an increase in the number of steps and deterioration of insulation due to contamination will occur. Therefore, in the present embodiment, a greater effect is produced by forming the insulating film layers to be laminated in the same furnace, as compared with the first embodiment.

As described above, when the interlayer insulating film 10 is composed of a plurality of insulating film layers, the insulating film layers contacting the floating gate electrode 4 and the control gate electrode 5 formed of, for example, a polycrystalline silicon film are not necessarily formed. It does not have to be a nitride film, and another insulating film such as an oxide film can be used.
Therefore, the number of insulating film layers is not limited to the five or six layers shown in the above-described embodiment, and can be increased without limitation.

[0085]

As described above, in the non-volatile semiconductor memory device according to the present invention, it is possible to suppress bird's beaks from occurring in the interlayer insulating film between the gate electrodes of the two-layer gate structure, and to miniaturize. The insulating property of the interlayer insulating film can be improved.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a nonvolatile semiconductor memory device according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing the method of manufacturing the nonvolatile semiconductor memory device according to the first embodiment of the invention.

FIG. 3 is a diagram showing initial withstand voltage characteristics of a capacitor insulating film manufactured according to the first embodiment of the present invention.

FIG. 4 is a diagram showing the breakdown characteristics over time of the capacitor insulating film manufactured according to the first embodiment of the present invention.

FIG. 5 is a sectional view showing a structure of a nonvolatile semiconductor memory device according to a second embodiment of the present invention.

FIG. 6 is a diagram showing a relationship between an oxide film thickness on a polycrystalline silicon film and a width of a bird's beak.

FIG. 7 is a cross-sectional view showing a method for manufacturing a conventional nonvolatile semiconductor memory device.

FIG. 8 is a sectional view showing the structure of a conventional nonvolatile semiconductor memory device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Semiconductor substrate, 2 ... Element isolation, 3 ... Insulating film, 4 ... Floating gate electrode, 5 ... Control gate electrode, 10 ... Interlayer insulating film, 11 ... Thermal oxide film, 12, 14, 16, 18 ... Nitride film, 13, 15, 17 ... HTO film

Claims (16)

[Claims] 1. A first gate electrode formed on an insulating film on a semiconductor substrate, an interlayer insulating film on the first gate electrode, and a second gate electrode formed on the interlayer insulating film. In the non-volatile semiconductor memory device including: a plurality of insulating film layers in which an oxide film layer and a nitride film layer are alternately laminated, and the interlayer insulating film includes: 2. A non-volatile semiconductor memory device, wherein each of the insulating film layers contacting the second gate electrode is composed of a nitride film layer. 2. A first gate electrode formed on an insulating film on a semiconductor substrate, an interlayer insulating film on the first gate electrode, and a second gate electrode formed on the interlayer insulating film. A non-volatile semiconductor memory device comprising: a plurality of insulating film layers in which an oxide film layer and a nitride film layer are alternately laminated, The insulating film layer that is in contact with the second gate electrode is composed of an oxide film layer, and the oxide film layer has a film thickness equal to or less than the film thickness at which the width of the edge region where the film thickness is increased becomes an allowable limit value. A non-volatile semiconductor memory device having. 3. The oxide film layer is selected such that the width along the edge of the region where the film thickness is increased is 1/10 or less of the length of the first gate electrode. The nonvolatile semiconductor memory device according to claim 2, having a different film thickness. 4. A first gate electrode formed on an insulating film on a semiconductor substrate, an interlayer insulating film on the first gate electrode, and a second gate electrode formed on the interlayer insulating film. A non-volatile semiconductor memory device comprising: a plurality of insulating film layers in which an oxide film layer and a nitride film layer are alternately laminated, The insulating film layer in contact with the second gate electrode is formed of an oxide film layer, and the oxide film layer has a film thickness such that the difference in film thickness between the central portion and the peripheral portion of the interlayer insulating film is an allowable limit value. A non-volatile semiconductor memory device having the following film thickness. 5. The nonvolatile semiconductor memory device according to claim 2, wherein the oxide film layer has a thickness of 2.5 nm or less. 6. The non-volatile semiconductor memory device according to claim 1, wherein the interlayer insulating film is composed of insulating film layers in which five or more layers are stacked. 7. The nonvolatile semiconductor memory device according to claim 1, wherein the oxide film layer is an HTO film formed by a CVD method at a temperature of 750 to 800 degrees. 8. A step of forming a first gate electrode material film on a semiconductor substrate via an insulating film, a step of forming a first nitride film layer on the first gate electrode material film, and A step of alternately stacking an oxide film layer and a nitride film layer on the first nitride film layer to form an interlayer insulating film; and a step of forming a second gate electrode material film on the interlayer insulating film. The second gate electrode material film is formed on the interlayer insulating film so as to be in contact with the nitride film layer of the interlayer insulating film after the nitride film layer is formed. Manufacturing method of semiconductor memory device. 9. A step of forming a first gate electrode material film on a semiconductor substrate with an insulating film interposed therebetween, and an oxide film layer and a nitride film layer are alternately laminated on the first gate electrode material film. Forming a second gate electrode material film on the interlayer insulating film, and forming a second gate electrode material film on the interlayer insulating film.
Alternatively, the interlayer insulating film is formed such that the oxide film layer is in contact with the second gate electrode material film, and the width of the edge region where the film thickness of the oxide film layer is increased becomes an allowable limit value. A method for manufacturing a nonvolatile semiconductor memory device, comprising forming the oxide film layer so as to have the following film thickness. 10. A film selected such that the width along the edge of the region where the film thickness of the oxide film layer is increased is 1/10 or less of the length of the first gate electrode. The method for manufacturing a nonvolatile semiconductor memory device according to claim 9, wherein the oxide film layer is formed to have a thickness. 11. A step of forming a first gate electrode material film on a semiconductor substrate with an insulating film interposed therebetween, and an oxide film layer and a nitride film layer are alternately laminated on the first gate electrode material film. A step of forming an interlayer insulating film by means of a second step on the interlayer insulating film.
Forming a gate electrode material film, and forming the interlayer insulating film so that an oxide film layer is in contact with the first or second gate electrode material film, and forming a central portion of the interlayer insulating film. A method of manufacturing a nonvolatile semiconductor memory device, comprising forming the oxide film layer so that a difference in film thickness between the peripheral portion and the peripheral portion is equal to or smaller than an allowable limit value. 12. The method for manufacturing a nonvolatile semiconductor memory device according to claim 8, wherein the oxide film layer is formed such that the film thickness of the oxide film layer is 2.5 nm or less. 13. The non-volatile semiconductor memory device according to claim 8, wherein an interlayer insulating film is formed by stacking five or more insulating film layers on the first gate electrode material film. Manufacturing method. 14. The CVD method using the same furnace for the insulating film layer.
14. The method for manufacturing a nonvolatile semiconductor memory device according to claim 8, wherein the nonvolatile semiconductor memory device is continuously formed by a method. 15. The nonvolatile semiconductor memory according to claim 8, 10 or 13, wherein a nitride film layer is formed on the first gate electrode by nitriding the first gate electrode material film with NH _3. Device manufacturing method. 16. The method for manufacturing a nonvolatile semiconductor memory device according to claim 8, wherein the oxide film layer is formed by a CVD method at a temperature of 750 to 800 degrees.