JPH07130725A - Semiconductor device and method of forming its element isolating film - Google Patents

Abstract

PURPOSE:To improve the reliability of a semiconductor device comprising an element having a thin gate oxide film and an element for driving at a high voltage, both formed on a semiconductor substrate. CONSTITUTION:A semiconductor device has a first element isolating thick film 11, a first element 13 isolated by this film, a second element isolating thin film 12 and a second element 14 isolated by this film on a semiconductor substrate 102. The element 13 is comprises a thick insulation film 102 formed on the upper side of the substrate 101 and a conductive layer 103 formed on the upper side of the film 102. The element 14 has a floating gate 106 and a thin insulation film 104 is formed on the substrate 101. A high driving voltage is applied to the element 103, thereby suppressing the edge part of the film 104 of the second element from being thinned.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device and a method for forming an element isolation film for the same.

[0002]

2. Description of the Related Art In a semiconductor device having a plurality of elements formed on a semiconductor substrate, an element isolation film is formed on the semiconductor substrate in order to separate the elements from each other. For example, in the semiconductor device 3 shown in FIG. 3, element isolation films 31 and 32 made of an oxide film are formed on a semiconductor substrate 301. Then, the elements 33, 34 are formed in the respective regions on the semiconductor substrate 301 which are electrically separated by the element isolation films 31, 32.
Are formed. 2. Description of the Related Art In recent years, the types of elements formed on a single semiconductor chip have been diversified as semiconductor devices have become highly integrated and highly functional. For example, the semiconductor device 3 is provided with an element 33 driven by a high voltage and an element 34 having a floating gate.

The element 33 includes a gate insulating film 302 formed on a semiconductor substrate 301 and the gate insulating film 30.
2 and the conductive layer 303 formed on the upper surface. Since this element 33 is driven by a high voltage, the gate insulating film 3
02 is formed with a relatively thick film thickness. Also, element 3
4 is a gate insulating film 3 formed on the semiconductor substrate 301.
04 and a conductive layer 305 formed on the gate insulating film 304. The conductive layer 305 has a two-layer structure of a floating gate 306 on the gate insulating film 304 and a control gate 308 formed on the floating gate 306 via an insulating film 307. Since the element 34 is a memory element having the floating gate 306, the gate insulating film 304 is formed to have a smaller film thickness than the gate insulating film 302 of the element 33.

In the semiconductor device 3 in which the plurality of types of elements 33 and 34 are formed on the semiconductor substrate 301 as described above, the thicknesses of the element isolation films 31 and 32 are set to match the elements used at higher voltage. Is set. For example, the voltage used by the element 33 is 15v and the voltage used by the element 34 is 10v.
In the case of V, the element isolation films 31 and 32 are set to a thickness such that element isolation is sufficiently performed for a voltage of 15V.

An example of a method of forming the element isolation films 31 and 32 will be described with reference to FIG. First, as shown in FIG. 4A, a pad oxide film 401 is formed on the surface of the semiconductor substrate 301 before forming an element. Then, on the upper surface of the pad oxide film 401, an antioxidant film 402 patterned so as to cover a region where an element is formed is formed. afterwards,
As shown in FIG. 4B, the pad oxide film 401 on the surface of the semiconductor substrate 301 exposed from the antioxidant film 402 is grown by the thermal oxidation process using the antioxidant film 402 as a mask. As a result, the element isolation film 31 made of an oxide film,
32 is formed.

When the semiconductor device shown in FIG. 3 is formed after the element isolation film is formed as described above, the antioxidant film and the pad oxide film on the lower surface thereof are removed. Then, gate insulating films 302 and 304 are formed on the semiconductor substrate 301 in respective regions separated by the element isolation films 31 and 32, and conductive layers 303 and 305 are formed on at least the upper surfaces of the gate insulating films 302 and 304. .

[0007]

However, the above-mentioned semiconductor device and the method for forming the same have the following problems. That is, in the above semiconductor device, when the gate insulating film is formed on the semiconductor substrate, the edge portion of the gate insulating film is formed thin due to the effect of the element isolation film formed in advance on the semiconductor substrate. . The thinning of the edge portion of the gate insulating film is particularly remarkable in the element isolation film having a large film thickness and the element isolation film formed by the improved LOCOS method for suppressing bird's beag.

Under such circumstances, the gate insulating film of each element tends to be thinned with the miniaturization of the element due to the high integration of the semiconductor device in recent years. On the other hand, the drive voltage of each element does not tend to decrease, and therefore the element isolation film cannot be thinned. Therefore, the local thinning of the edge portion of the gate insulating film expands the influence on the film thickness of the gate insulating film. When the thickness of the gate insulating film is 20 nm or less, the breakdown voltage of the gate insulating film deteriorates due to the above local thinning, and the reliability of the element and the semiconductor device decreases. In particular, an element having a floating gate has a gate insulating film formed thinner than other elements, and thus the above-mentioned problem is likely to occur.

Therefore, the present invention provides a semiconductor device and a method for forming an element isolation film for solving the above problems, so that an element having a thin gate oxide film and an element driven at a high voltage are the same semiconductor. It is an object of the present invention to improve the reliability of a semiconductor device formed on a substrate.

[0010]

A semiconductor device of the present invention for achieving the above object is formed on a semiconductor substrate in a first element isolation film having a large film thickness and in a region separated by the first element isolation film. It has a first element, a second element isolation film having a small film thickness, and a second element formed in a region separated by the second element isolation film. The first element is composed of a semiconductor substrate, a thick insulating film formed on the upper surface, and a conductive layer formed on the upper surface. The second element is composed of a semiconductor substrate, a thin insulating film formed on the upper surface of the semiconductor substrate, and a conductive layer formed on the upper surface. A floating gate is provided in the conductive layer of the second element.

Further, the element isolation film of the semiconductor device is
It is formed by the following procedure. First, in the first step, the first opening is patterned in the antioxidant film formed on the semiconductor substrate. Then, in the second step, an oxide film is grown on the surface of the semiconductor substrate exposed in the first opening by a thermal oxidation process using the antioxidant film as a mask.
Next, in a third step, a second opening is formed in the antioxidant film. Then, in a fourth step, a first element isolation film made of an oxide film is formed in the first opening by a thermal oxidation process using the antioxidant film as a mask, and
A second element isolation film made of an oxide film is formed in the second opening.

[0012]

In the above semiconductor device, the first element having the thick insulating film is separated by the thick first element isolation film, and the second element having the thin insulating film is formed as the film. They are separated by a thin second element isolation film. Therefore, a high drive voltage can be applied to the first element. Then, the second element having the thin insulating film is separated by the second element isolation film having the thin film thickness which suppresses the thinning of the edge portion of the insulating film, and therefore, the local edge portion of the insulating film is locally formed. It is possible to suppress thinning.
Further, by separating the first element having the floating gate by the first element isolation film, in the element having the floating gate, the dielectric strength failure due to the local thinning of the insulating film is prevented.

In the above method for forming the element isolation film, the oxide film grows on the semiconductor substrate exposed in the first opening by the two heat treatments, and the semiconductor substrate exposed in the second opening is exposed. On the other hand, the oxide film grows by one heat treatment. Therefore, the second opening formed in the second opening
The element isolation film of is formed to have a smaller film thickness than the first element isolation region formed in the first opening. Therefore, when a thick first element isolation film having a high element isolation capability and a MIS type semiconductor element are formed on the same semiconductor substrate, a film that suppresses local thinning of the insulating film is formed. A thin second element isolation film is formed.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a semiconductor device according to an embodiment. As shown in the figure, the semiconductor device 1 includes a semiconductor substrate 10
A first element isolation film 11 and a second element isolation film 12 are formed on the surface 1. Then, the first element isolation film 11
The first element 13 is formed on the semiconductor substrate 101 electrically isolated by the second element 14, and the second element 14 is formed on the semiconductor substrate 101 isolated by the second element isolation film.

The first and second element isolation films 11 and 12
Is an oxide film. The first element isolation film 11 has a film thickness of about 650 nm, and the second element isolation film 12 has a film thickness of about 250 nm. The film thicknesses of the first and second element isolation films 11 and 12 are the same as those of the first or second element 1 used at the respective driving voltages.
It is thick enough to separate 3,14. Then, with a film thickness of about 300 nm as a boundary, the first element isolation film 11 is formed of an oxide film having a larger film thickness and the second element isolation film 12 is formed of a thinner oxide film.

The first element 13 includes a semiconductor substrate 101,
The gate insulating film 102 formed on the upper surface, and the conductive layer 1 formed on at least the upper surface of the gate insulating film 102.
And 03. The first element 13 is driven by a high voltage, and the gate insulating film 102 is formed relatively thick, for example, a film thickness of about 30 nm.

Further, the second element 14 is the first element 13
The same semiconductor substrate 101, a gate insulating film 104 formed on the upper surface, and at least the gate insulating film 10
4 and the conductive layer 105 formed on the upper surface of the wiring 4. The conductive layer 105 is the floating gate 106.
And an insulating film 107 on the floating gate 106.
And the control gate 108 formed via the. Since the second element 14 is a memory element having the floating gate 106, the gate insulating film 104 is formed to be relatively thin, for example, about 15 nm in film thickness.

In the semiconductor device 1 formed as described above, the first element 13 having the thick gate insulating film 102 and having a high driving voltage and the first element isolation film 11 having the thick film thickness are formed. Separate with. Therefore, the isolation of the first element 13 is sufficiently performed. Then, the second element 14 having the thin insulating film 104 is replaced by the thin second element isolation film 1
Separate at 2. Therefore, in the second element 14,
Localized thinning of the thin gate insulating film 104 can be suppressed. Further, since the second element 14 has a lower drive voltage than the first element 13, the second element isolation film 12 allows sufficient isolation.

Next, a method of forming the element isolation film of the semiconductor device will be described with reference to FIG. First, in the first step,
As shown in FIG. 2A, an antioxidant film 201 is formed on the surface of the semiconductor substrate 101 on which the pad oxide film 110 is formed. Then, the first opening 202 is patterned on the antioxidant film 201. In this step, the pad oxide film 110 having a film thickness of about 50 nm is previously formed on the surface of the semiconductor substrate 101. And pad oxide film 1 on the surface
10 is formed on the upper surface of the semiconductor substrate 101.
An antioxidant film 201 made of a nitride film with a thickness of about 0 nm is formed. Then, this antioxidant film 2 is formed by lithography.
At 01, the first opening 202 is patterned. The first opening 202 is provided in a portion where the first element isolation film is formed.

Then, in the second step, as shown in FIG. 2B, the surface of the semiconductor substrate 101 exposed in the first opening 202 is subjected to a thermal oxidation process using the above-mentioned antioxidant film 201 as a mask. The pad oxide film 110 is grown. As a result, the oxide film 20 having a thickness of about 400 nm is formed on the surface of the semiconductor substrate 101 exposed in the first opening 202.
3 is formed.

Next, in the third step, as shown in FIG. 2C, a second opening 204 is formed in the antioxidant film 201. The second opening 204 is provided in a portion where the second element isolation film is formed.

Then, in the fourth step, as shown in FIG. 2 (4), the antioxidant film 201 in which the first opening 202 and the second opening 204 are patterned is used as a mask. Perform thermal oxidation treatment. In this step, the oxide film 203 in the first opening 202 is further grown to about 300 nm, and the semiconductor substrate 1 exposed in the second opening 204 is formed.
The pad oxide film 110 on the surface 01 is grown to a thickness of about 300 nm. Then, the first element isolation film 11 made of an oxide film having a thickness of about 700 nm is formed in the first opening 202, and the second element isolation made of an oxide film having a thickness of about 300 nm is formed in the second opening 204. The film 12 is formed. The film thickness of the first and second element isolation films 11 and 12 formed here is set to a thickness obtained by adding in advance the amount of reduction of the oxide film in the subsequent process. Finally, a first element isolation film 11 made of an oxide film thicker than this and a second element isolation film 12 made of a thin oxide film are formed with a film thickness of 300 nm as a boundary.

After the element isolation films having different thicknesses are formed on the semiconductor substrate as described above, the MIS including the gate insulating film and the conductive layer is formed on the semiconductor substrate in each region separated by the element isolation film. Form a semiconductor device.

In the method of forming the element isolation film, the first element isolation film 11 is formed by two thermal oxidation treatments, and the second element isolation film 12 is formed by one thermal oxidation treatment. Therefore, the film thickness of the first element isolation film 11 is formed to be thicker than the film thickness of the second element isolation film 12. Therefore, on the same semiconductor substrate 101, a thick first element isolation film 11 having high element isolation capability and M
A second element isolation film 12 having a small film thickness that suppresses local formation of an insulating film when an IS type semiconductor element is formed.
And are formed.

In the semiconductor device of the embodiment, the case where the element having the floating gate and the element for high voltage driving are formed on the same semiconductor substrate has been described as an example. However, when an element having a lower breakdown voltage is formed in the above semiconductor device, the gate insulating film formed in this element is relatively thin. Therefore, the low breakdown voltage element is separated by the thin second element isolation film. It should be noted that each element formed in the semiconductor device is classified into an element having a driving voltage of 10 V or more and an element having a driving voltage of about 3 to 5 V, and the thickness of an element isolation film separating each element is a boundary of 300 nm. You may use it properly.
However, this does not apply to the element having the floating gate.

In the method of forming an element isolation film of the embodiment, when the element isolation film is formed by applying a so-called normal LOCOS method in which a nitride film formed on a semiconductor substrate is patterned and used as an antioxidant film. Explained. However, the present invention is not limited to this. For example, pol
It is also possible to apply an improved LOCOS method such as the y-buffered-LOCOS method. Since the element isolation film formed by the improved LOCOS method has a short bird's beak, the edge portion rises more rapidly than the element isolation film formed by the normal LOCOS method. Therefore, the edge portion of the gate insulating film is likely to be thinned, and the effect of applying the present invention can be further expected.

[0027]

As described above, according to the semiconductor device of the present invention, a thick insulating film is formed on the semiconductor substrate by the first element isolation film having a large film thickness, and a conductive layer is formed on the insulating film. A second element in which the formed first element is separated, a thin insulating film is formed on a semiconductor substrate by a thin second element isolation film, and a conductive layer is formed on the insulating film. By separating the elements, it is possible to prevent the local thinning of the insulating film in the element having the thin insulating film while sufficiently achieving the separation of the element having a high driving voltage and the thick insulating film. Therefore, in a semiconductor device in which an element having a high driving voltage and a floating gate element having a thin gate insulating film are formed on the same semiconductor substrate, it is possible to prevent element isolation failure and gate insulating film insulation failure. it can. Therefore, the reliability of the semiconductor device can be improved. further,
According to the method for forming an element isolation film of the present invention, a thick element isolation layer having a high element isolation capability is formed on the same semiconductor substrate by two thermal oxidation processes using a single anti-oxidation film as a mask. It is possible to form a film and an element isolation film having a small film thickness that suppresses local thinning of the insulating film when a MIS type semiconductor device is formed. Therefore, an element having a high driving voltage and an MIS type element having a thin insulating film can be formed on the same semiconductor substrate.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a semiconductor device of an example.

FIG. 2 is a diagram illustrating a method of forming an element isolation film of an example.

FIG. 3 is a configuration diagram of a conventional semiconductor device.

FIG. 4 is a diagram illustrating a conventional method of forming an element isolation film.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor device 11 1st element isolation film 12 2nd element isolation film 13 1st element 14 2nd element 101 Semiconductor substrate 102,104 Gate insulating film 103,105 Conductive layer 106 Floating gate 201 Antioxidation film 202 1st opening 204 2nd opening

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H01L 29/788 29/792 H01L 29/78 371

Claims (3)

[Claims] 1. Compared to a semiconductor substrate, a first element isolation film formed on the semiconductor substrate and made of a thick oxide film, and a first element isolation film formed on the semiconductor substrate. A second element isolation film made of a thin oxide film, a first element formed in each region on the semiconductor substrate separated by the first element isolation film, and a second element isolation film In a semiconductor device including a second element formed in each region on the semiconductor substrate separated by, the first element has a semiconductor substrate and a thick film formed on the semiconductor substrate. An insulating film and a conductive layer formed on the insulating film, wherein the second element is a semiconductor substrate and an insulating film of the first element formed on the semiconductor substrate. A thin insulating film and a conductive layer formed on the insulating film Wherein a the at it. 2. The semiconductor device according to claim 1, wherein the second element is an element having a floating gate. 3. The method for forming an element isolation film of a semiconductor device according to claim 1, wherein an antioxidant film is formed on the semiconductor substrate, and a first opening is formed in the antioxidant film. A first step; a second step of growing an oxide film on the surface of the semiconductor substrate exposed in the first opening by a thermal oxidation process using the antioxidant film as a mask; A third step of forming the second opening and a thermal oxidation process using the antioxidant film as a mask further grow the oxide film grown in the first opening to form a thick oxide film. And forming a second element isolation film made of a thin oxide film while growing an oxide film on the surface of the semiconductor substrate exposed in the second opening. Of the element isolation film, characterized in that Forming method.