JPH0917893A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE: To improve the quality of gate oxide films of a semiconductor MOS element wherein the oxide films differ in thickness. CONSTITUTION: On a interconnection substrate 11, for example, an oxide film is formed only a region intended to form a thin gate oxide film and again oxidized to form an oxide film on the entire surface of the substrate 11. After removing this oxide film, the thin gate oxide film 15 is formed on the surface of the substrate 11 and its part formed on a region intended to form a thick gate oxide film on the substrate 11 is removed. The thick gate oxide film 19 is newly formed this region. This suppresses the retrogression amount of the film 19 into the substrate to reduce the probability of involving oxygen precipitates.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device in which, for example, a gate oxide film having a different thickness is provided on a semiconductor substrate, and in particular, it has been previously heat-treated in a non-oxidizing gas atmosphere. It is used when a semiconductor MOS (Metal Oxide Semiconductor) element is manufactured using a semiconductor substrate.

[0002]

2. Description of the Related Art Conventionally, in a semiconductor MOS device having a gate oxide film having a different film thickness, the amount of consumed (oxidized) semiconductor substrate varies depending on the thickness of the gate oxide film. The position of the interface of the film with the semiconductor substrate recedes toward the inside of the substrate, that is, the thick gate oxide film is formed deeper inside the substrate than the thin gate oxide film.

A factor that promotes the deterioration of a gate oxide film in a semiconductor MOS device or the like is an oxygen precipitate due to excess oxygen mixed in a semiconductor substrate during crystal pulling.

It has been found that oxygen precipitates have a depth profile during the MOS manufacturing process, are low in the surface layer of the substrate, and have high density inside the substrate. Especially,
In the case of a substrate that has been preliminarily heat-treated in a non-oxidizing gas atmosphere, the feature of the depth profile of oxygen precipitates, which is low near the surface layer of the substrate and has a high density inside the substrate, becomes more prominent.

Therefore, when the position where the gate oxide film is formed recedes toward the inside of the substrate, the probability that oxygen precipitates existing inside the substrate will be taken into the gate oxide film increases, and the breakdown voltage of the gate oxide film deteriorates. Easier to do.

Further, focusing on the thickness of the gate oxide film,
The thicker the gate oxide film is, the more the substrate is oxidized, and the substrate at the more recessed position is used. Therefore, the thicker gate oxide film has a higher probability of capturing oxygen precipitates, and the defect rate tends to increase.

For these reasons, the E ² PROM (El
ectrically Erasable Programmable Read-Only Memory
In a semiconductor MOS device in which a high electric field stress is applied to a thick gate oxide film such as), there is a concern that the quality of the thick gate oxide film may deteriorate.

[0008]

As described above, conventionally, there has been a problem that the quality of the gate oxide film deteriorates as the position where the gate oxide film is formed recedes toward the inside of the substrate. Therefore, the present invention provides a method of manufacturing a semiconductor device capable of suppressing the amount of recession of the gate oxide film formation position toward the inside of the substrate during manufacturing, and improving the quality of the gate oxide film. Has an aim.

[0009]

In order to achieve the above object, in the method of manufacturing a semiconductor device according to the present invention, when a gate oxide film having a different film thickness is provided on a semiconductor substrate, A step of forming an oxide film on the surface of the semiconductor substrate, and selectively forming the oxide film in a region on the semiconductor substrate where a gate oxide film having a second film thickness smaller than a first film thickness is formed. A step of removing, an oxide film is formed again on the surface of the semiconductor substrate, a step of removing the oxide film on the semiconductor substrate to form a step on the surface of the semiconductor substrate, Forming a gate oxide film having a second film thickness on the surface of the formed semiconductor substrate; and forming the second film thickness on a region of the semiconductor substrate where the gate oxide film having a first film thickness is formed. Selectively removing the gate oxide film of Forming a gate oxide film of a first thickness on a region of the semiconductor substrate where a gate oxide film of a first thickness is formed, wherein the semiconductor of the gate oxide film of the first thickness is formed. It is characterized in that the interface with the substrate is formed at a position equal to or higher than the interface of the gate oxide film having the second film thickness with the semiconductor substrate.

Further, in the method for manufacturing a semiconductor device of the present invention, when the gate oxide films having different thicknesses are provided on the semiconductor substrate, the step of forming the oxide film on the surface of the semiconductor substrate. And on the semiconductor substrate,
A step of selectively removing the oxide film in a region where a gate oxide film having a first film thickness is formed;
Again, the step of forming an oxide film, and on the semiconductor substrate,
A step of selectively removing the oxide film in a region where a gate oxide film having a second film thickness smaller than the first film thickness is formed; and an oxide film is formed again on the surface of the semiconductor substrate, On the semiconductor substrate, a gate oxide film having a first film thickness is formed in a region where a gate oxide film having a first film thickness is formed, and a second film thickness is formed in a region where a gate oxide film having a second film thickness is formed. Gate oxide film of
And a step of forming the gate oxide film having the first thickness with the semiconductor substrate and the second step.
The interface of the gate oxide film having the above thickness with the semiconductor substrate is formed at substantially the same height position.

[0011]

According to the present invention, since the thick gate oxide film can be formed at a position closer to the surface layer of the substrate by the above means, the probability that oxygen precipitates are taken into the gate oxide film can be reduced. It will be.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 10 schematically show a main part of a manufacturing process of a semiconductor MOS device according to a first embodiment of the present invention, in which a gate oxide film having a different film thickness is provided on a semiconductor substrate. Is. In addition, here, a thick gate oxide film (gate oxide film of the first film thickness) is set to 25 n.
A case will be described in which a thin gate oxide film (second gate oxide film) having a thickness of m is formed with a thickness of 10 nm.

First, the semiconductor substrate 11 is subjected to an oxidation treatment.
An oxide film 12 having a thickness of 100 nm is formed on the surface of the (FIG. 1). As the semiconductor substrate 11, an H ₂ annealed wafer which has been previously heat-treated in a non-oxidizing gas atmosphere is used.

Then, after applying a resist on the oxide film 12, it is patterned by a lithographic process to leave the resist 13 only in a region on the semiconductor substrate 11 where a thick gate oxide film is to be formed (see FIG. 2).

Usually, in a semiconductor manufacturing process, it is necessary to form a mark (substrate step) serving as an alignment reference in the first lithography process in order to perform several types of patterning. In the present embodiment, for example, in order to form the substrate step between the region where the thick gate oxide film is formed and the region where the thin gate oxide film is formed, only the region where the thick gate oxide film is formed is covered with the resist 13. To

Then, using the resist 13 as a mask, NH
The oxide film 12 is selectively etched by ₄ F or the like to remove only the oxide film 12 existing on the region where the thin gate oxide film is formed on the semiconductor substrate 11 (FIG. 3).

Then, after removing the resist 13,
Oxidation is performed again, and 100 nm is formed in the region where the thin gate oxide film is formed on the semiconductor substrate 11 without the oxide film 12.
A thick oxide film 14 is formed (FIG. 4). At this time, in the region where the thin gate oxide film is formed on the semiconductor substrate 11, the oxide film 14 grows 50 nm upward and downward from the substrate surface, respectively. Further, the oxide film 12 remaining in the region where the thick gate oxide film is formed on the semiconductor substrate 11 grows by 35 nm in the vertical direction, and the thickness increases to 170 nm.

Then, the oxide films 12 and 14 are etched with NH ₄ F or the like to expose the surface of the semiconductor substrate 11 (FIG. 5). In this case, by setting the thickness of the oxide film 14 formed by the second oxidation to 100 nm, a step 11a of about 15 nm is formed on the surface of the semiconductor substrate 11.

After that, the semiconductor substrate 1 is oxidized by oxidation.
A thin gate oxide film 15 having a thickness of 10 nm is formed on the surface of No. 1, and poly silicon 16 is further deposited thereon (FIG. 6). The thin gate oxide film 15 having a thickness of 10 nm is
The semiconductor substrate 11 is formed at a position recessed from the surface of the semiconductor substrate 11 by about 5 nm.

Then, after applying a resist on the poly-silicon 16 and patterning it by a lithography process, the resist 17 is left only in the portion where the poly-silicon 16 is left (FIG. 7).

Then, using the resist 17 as a mask, the CD
By E (Chemical Dry Etching) etc.,
Selective etching of the silicon 16 is performed (FIG. 8). Then, after removing the resist 17, only the region on the semiconductor substrate 11 where the thin gate oxide film is to be formed is covered with the resist 18, and the resist 18 is used as a mask to perform selective etching. Thin gate oxide film 1 existing in the region where the thick gate oxide film is formed
5 is removed (FIG. 9).

After that, the semiconductor substrate 1 is oxidized by oxidation.
25n only in the region where a thick gate oxide film is formed on
A thick gate oxide film 19 having a thickness of m is formed (FIG. 10). At this time, the thick gate oxide film 19 with a thickness of 25 nm is retracted from the surface of the semiconductor substrate 11 by about 12.5 nm,
The interface with the semiconductor substrate 11 has a thin gate oxide film 15
Is formed at a position approximately 2.5 nm above the interface with the semiconductor substrate 11.

That is, a step of 15 nm is formed on the surface of the semiconductor substrate 11, that is, the interface between the thin gate oxide film 15 and the semiconductor substrate 11 forms a thick gate oxide film on the semiconductor substrate 11. 15n more than the area
It has retreated about m. As a result, the thick gate oxide film 1
If the film thickness of 9 is 30 nm or less, the thick gate oxide film 1
The interface between the semiconductor substrate 11 and the semiconductor substrate 11 can be formed to be equal to or above the interface between the thin gate oxide film 15 and the semiconductor substrate 11. Therefore, even when the H ₂ annealed wafer is used as the semiconductor substrate 11, it is possible to reduce the probability that the internal oxygen precipitates are taken into the thick gate oxide film 19, and the breakdown voltage of the thick gate oxide film 19 is reduced. It is possible to prevent deterioration.

Moreover, the thin gate oxide film 15 has a thick gate oxide film 19 at the interface with the semiconductor substrate 11.
Even if the gate oxide film 19 is located below the interface with the semiconductor substrate 11, it has a high probability of incorporating oxygen precipitates.
The quality is not significantly degraded, since it is lower than.

Next, another embodiment of the present invention will be described. 11 to 17 are schematic views showing a main part of a manufacturing process of a semiconductor MOS device according to a second embodiment of the present invention, in which a gate oxide film having a different film thickness is provided on a semiconductor substrate. Is. It should be noted that, here, the oxide film formed before the implantation step for forming the well is used to make a gate oxide film of 60 nm thickness (the gate oxide film of the first film thickness) and a gate oxide film of 25 nm thickness. A case of forming a film (gate oxide film having a second film thickness) will be described.

First, the semiconductor substrate 21 is subjected to oxidation treatment.
An oxide film 22 having a thickness of 100 nm is formed on the surface of the (FIG. 1
1). Then, after applying a resist on the oxide film 22, it is patterned by a lithography process so that only the region of the semiconductor substrate 21 where a thin gate oxide film is formed is covered with the resist 23 (FIG. 12). ).

Subsequently, NH 3 is used with the resist 23 as a mask.
The oxide film 22 is selectively etched by ₄ F or the like to remove only the oxide film 22 existing on the region where the thick gate oxide film is formed on the semiconductor substrate 21 (see FIG. 1).
3).

After removing the resist 23,
Oxidation is performed again to form a thick gate oxide film 24 having a thickness of 44 nm in the region where the thick gate oxide film is to be formed on the semiconductor substrate 21 without the oxide film 22 (FIG. 14). At this time, in the region where the thick gate oxide film is to be formed on the semiconductor substrate 21, the thick gate oxide film 24 grows 22 nm upward and downward from the surface of the semiconductor substrate 21, respectively. Further, the oxide film 22 remaining in the region where the thin gate oxide film is formed on the semiconductor substrate 21.
Grows in the vertical direction by 17.5 nm, and the thickness increases to 135 nm.

Subsequently, after a resist is applied on the oxide films 22 and 24, the resist is patterned by a lithography process to form a thick gate oxide film 24 on the semiconductor substrate 21.
Only the resist is covered with the resist 25 (FIG. 15).

Then, using the resist 25 as a mask, NH
The oxide film 22 is selectively etched by ₄ F or the like to remove the oxide film 22 existing on the region where the thin gate oxide film is formed on the semiconductor substrate 21 (see FIG. 1).
6). In this case, due to the difference in film thickness between the oxide film 22 existing on the region where the thin gate oxide film is formed and the thick gate oxide film 24, the surface of the semiconductor substrate 21 has a thickness of about 4.5 n.
A step 21a of m is formed.

After removing the resist 25, oxidation is performed to form a thin gate oxide film 26 having a thickness of 25 nm in the region on the semiconductor substrate 21 where the thin gate oxide film is to be formed (FIG. 17). This 25 nm thin gate oxide film 2
6 is formed at a position retracted from the surface of the semiconductor substrate 21 by about 12.5 nm. In addition, the semiconductor substrate 2
The thick gate oxide film 24 having a thickness of 44 nm on 1 is further retracted at the interface with the semiconductor substrate 21 by about 8 nm, and the thickness increases to 60 nm.

As a result, the interface of the 60 nm thick gate oxide film 24 with the semiconductor substrate 21 and the interface of the 25 nm thin gate oxide film 26 with the semiconductor substrate 21 are formed at substantially the same height position. .

As described above, the semiconductor substrate 21 having the thick gate oxide film 24 is formed with respect to the formation position of the thin gate oxide film 26.
The thick gate oxide film 24 can be formed without significantly retreating the position of the interface with the.

As described above, the thick gate oxide film can be formed at a position closer to the surface layer of the substrate. That is, the interface of the thick gate oxide film with the semiconductor substrate can be formed to be equal to or higher than the interface of the thin gate oxide film with the semiconductor substrate. As a result, a thick gate oxide film can be formed without significantly retreating the position of the interface with the semiconductor substrate, so that even if an H ₂ annealed wafer is used, the internal oxygen precipitates are thick. It is possible to reduce the probability of being taken into the gate oxide film. Moreover,
Since the probability of incorporating oxygen precipitates is originally lower in the thin gate oxide film than in the thick gate oxide film, the quality of the thin gate oxide film is not significantly deteriorated. Therefore, it is possible to realize the high quality of the gate oxide film in the semiconductor MOS device in which the gate oxide films having different thicknesses are provided.

In each of the above embodiments, a semiconductor MOS having two gate oxide films having different film thicknesses.
Although the element has been described as an example, the present invention is not limited to this and can be applied to various semiconductor MOS elements having two or more gate oxide films, for example. Of course, various modifications can be made without departing from the scope of the present invention.

[0036]

As described above in detail, according to the present invention, it is possible to suppress the amount of recession of the formation position of the gate oxide film toward the inside of the substrate during manufacturing, and to improve the quality of the gate oxide film. A possible method for manufacturing a semiconductor device can be provided.

[Brief description of the drawings]

FIG. 1 is a semiconductor MOS according to a first embodiment of the present invention.
FIG. 4 is a schematic cross-sectional view shown for explaining the manufacturing process of the element.

FIG. 2 is also a schematic cross-sectional view explaining the manufacturing process of the semiconductor MOS device.

FIG. 3 is also a schematic cross-sectional view illustrating the manufacturing process of the semiconductor MOS device.

FIG. 4 is a schematic sectional view illustrating a manufacturing process of a semiconductor MOS device.

FIG. 5 is a sectional view showing an enlarged main part of the same for explaining the manufacturing process of the semiconductor MOS device.

FIG. 6 is a sectional view showing a main part in an enlarged manner for explaining the manufacturing process of the semiconductor MOS device.

FIG. 7 is also a schematic cross-sectional view illustrating the manufacturing process of the semiconductor MOS device.

FIG. 8 is a schematic sectional view illustrating a manufacturing process of the semiconductor MOS device.

FIG. 9 is also a schematic cross-sectional view explaining the manufacturing process of the semiconductor MOS device.

FIG. 10 is a sectional view showing a main part in an enlarged manner for explaining the manufacturing process of the semiconductor MOS device.

FIG. 11 is a semiconductor MO according to the second embodiment of the present invention.
FIG. 6 is a schematic cross-sectional view shown for explaining the manufacturing process of the S element.

FIG. 12 is also a schematic cross-sectional view explaining the manufacturing process of the semiconductor MOS device.

FIG. 13 is also a schematic cross-sectional view explaining the manufacturing process of the semiconductor MOS device.

FIG. 14 is also a schematic cross-sectional view explaining the manufacturing process of the semiconductor MOS device.

FIG. 15 is also a schematic cross-sectional view illustrating the manufacturing process of the semiconductor MOS device.

FIG. 16 is also a schematic cross-sectional view explaining the manufacturing process of the semiconductor MOS device.

FIG. 17 is also a schematic cross-sectional view illustrating the manufacturing process of the semiconductor MOS device.

[Explanation of symbols]

11, 21 ... Semiconductor substrate, 11a, 21a ... Step, 1
2, 14, 22 ... Oxide film, 13, 17, 18, 23, 2
5 ... Resist, 15, 26 ... Thin gate oxide film, 16 ...
Poly silicon, 19, 24 ... Thick gate oxide film.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H01L 21/316 27/115

Claims (4)

[Claims] 1. A method of manufacturing a semiconductor device, wherein a gate oxide film having a different film thickness is provided on a semiconductor substrate, the method comprising: forming an oxide film on a surface of the semiconductor substrate; A step of selectively removing the oxide film in a region where a gate oxide film having a second film thickness smaller than the first film thickness is formed; and a step of forming an oxide film again on the surface of the semiconductor substrate, Removing an oxide film on the semiconductor substrate to form a step on the surface of the semiconductor substrate; and forming a gate oxide film having a second thickness on the surface of the semiconductor substrate on which the step is formed. And a step of selectively removing the gate oxide film having the second film thickness in a region on the semiconductor substrate where the gate oxide film having the first film thickness is to be formed, First in the region where the gate oxide film having a thickness is formed A step of forming a gate oxide film having a film thickness, wherein an interface between the gate oxide film having the first film thickness and the semiconductor substrate is an interface between the gate oxide film having the second film thickness and the semiconductor substrate. A method for manufacturing a semiconductor device, characterized in that it is formed at a position equal to or higher than the above. 2. The method of manufacturing a semiconductor device according to claim 1, wherein a semiconductor substrate that has been previously heat-treated in a non-oxidizing gas atmosphere is used. 3. A method of manufacturing a semiconductor device, wherein a gate oxide film having a different film thickness is provided on a semiconductor substrate, the method comprising: forming an oxide film on a surface of the semiconductor substrate; A step of selectively removing the oxide film in a region where a gate oxide film having a thickness of 1 is formed; a step of forming an oxide film again on the surface of the semiconductor substrate; Selectively removing the oxide film in a region for forming a gate oxide film having a second film thickness smaller than that of the semiconductor film, and forming an oxide film again on the surface of the semiconductor substrate to form the semiconductor film. A gate oxide film having a first film thickness is formed in a region where a gate oxide film having a first film thickness is formed on a substrate, and a gate film having a second film thickness is formed in a region where a gate oxide film having a second film thickness is formed. And a step of forming an oxide film on each of them. An interface of the gate oxide film having a film thickness with the semiconductor substrate and an interface of the gate oxide film having the second film thickness with the semiconductor substrate are formed at substantially the same height position. Manufacturing method of semiconductor device. 4. The method for manufacturing a semiconductor device according to claim 3, wherein a semiconductor substrate that has been previously heat-treated in a non-oxidizing gas atmosphere is used.