JPH09134916A - Formation of element isolation insulating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the crystal defects, which are developed in the ends of an element isolation region in a selective oxidation, to reduce a junction leakage current and to make long an element isolation length to form an element isolation insulating film increased the resistance against a punch through. SOLUTION: An oxide film 2 and a nitride film 3 are formed in order on the main surface of a semiconductor substrate 1 and an aperture is formed in the films 2 and 3 in such a way that one part of the main surface is exposed as a main surface exposed part. Moreover, a sidewall part 5, which covers the sidewalls, which form the side surface of the aperture, of the films 2 and 3 and the part other than the central part of the main surface exposed part in such a way that the central part of the main surface exposed part is kept in a state that the central part is exposed as a center exposed part, has the exposed surface consisting of a protuberant curved surface and consists of an oxide film, is formed. Then, the center exposed part is etched using the part 5 as a mask to form an isolation groove 6 in the substrate 1, the substrate 1 in the vicinity of the groove 6 is selectively oxidized using the film 3 and the part 5 as masks and an element isolation insulating film 7 is formed.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art As the element isolation conventionally used,
First, there is LOCOS (Local Oxidation of Silicon) separation. As shown in FIG. 4, the LOCOS isolation is formed by patterning a two-layer structure formed of an oxide film 2 and a nitride film 3 formed on a semiconductor substrate 1 and then selectively oxidizing the semiconductor substrate.

In contrast to the LOCOS isolation, a RECESSED LO shown in FIG. 5 was proposed for the purpose of increasing the element isolation length in order to prevent punch-through.
COS separation (for example, described in JP-A-02-119137). RECESSED LOCO
In the S separation, similar to the LOCOS separation, the two-layer structure formed of the oxide film 2 and the nitride film 3 formed on the semiconductor substrate 1 is patterned, and then the semiconductor substrate is etched to form the separation groove 6
Is formed by selectively oxidizing the semiconductor substrate after forming. RECESSED LOCOS separation
Compared with LOCOS isolation, the effective element isolation length becomes longer because the element isolation film thickness below the semiconductor substrate surface is thicker.

However, LOCOS separation and RECESS
In the ED LOCOS separation, in selective oxidation, an oxidizing species penetrates and diffuses from the side surface where the surface of the oxide film 2 is exposed, and oxidizes the surface of the semiconductor substrate 1 at the end of the element region, so that the oxide film is formed. It is difficult to miniaturize the cell because it bites into the element region (this oxide film is called bird's beak) and reduces the element width.

Therefore, OSELL was proposed for the purpose of keeping the bird's beak length short for miniaturization.
O II separation (for example, IEEE Trans. Elec
tron Devices, vol. 35, No. 7,
pp 893-898, JULY 1988. ). As shown in FIG. 6, the OSELLO II isolation is performed by using the second nitride film 8 and the second dioxide film 4 for the two-layer structure including the patterned first oxide film 2 and the first nitride film 3 on the semiconductor substrate 1. After the formation of the side wall portion made of, the side wall portion is used as a mask to etch the semiconductor substrate to form the separation groove 6 to remove the second dioxide film, and then the semiconductor substrate is selectively oxidized. In the OSELLO II isolation, the nitride film sidewall portions 9 formed on the semiconductor substrate at both ends of the element isolation region suppress the arrival of oxidizing species on the surface of the semiconductor substrate during selective oxidation, and suppress the growth of bird's beaks. It is effective for miniaturization of cells.

[0006]

LOCOS isolation, RECESSED L is used as element isolation that has been conventionally used.
There are OCOS separation and OSELLO II separation. LOCO
Compared with S separation, RECESSED LOCOS separation,
And OSELLO II isolation are effective in preventing punch-through because the element isolation film thickness below the surface of the semiconductor substrate is thick and the effective element isolation length becomes long.

However, in the OSELLO II isolation, the nitride film sidewall portions 9 formed on the semiconductor substrate at both ends of the element isolation region suppress the volume expansion of the edge of the element region due to the selective oxidation, so that Stress is generated on the semiconductor substrate at the edge. This stress causes a crystal defect in the semiconductor substrate, which causes a problem that a junction leak current flows with the crystal defect as a recombination center.

On the other hand, the RECESSED LOCOS isolation does not have a structure in which the semiconductor films at both ends of the element isolation region are directly suppressed by the nitride film.
The same stress as in II separation and the accompanying increase in junction leakage current do not occur. However, crystal defects occur in the semiconductor substrate on the side surface and the bottom surface of the separation groove due to the high-energy plasma used when the surface of the semiconductor substrate is etched to form the separation groove. Further, during the selective oxidation, the oxide film grows from the side surface and the bottom surface in the vicinity of the end portion of the element isolation region where the side surface and the bottom surface of the isolation groove intersect with each other.
Larger stress occurs as compared with OCOS separation, and more crystal defects occur in the semiconductor substrate. Therefore, REC
In the ESSED LOCOS isolation, there arises a problem that a junction leak current flows with a crystal defect occurring in the semiconductor substrate near the periphery of the isolation groove as a recombination center.

Also in the above-mentioned OSELLO II separation, since the surface of the semiconductor substrate is etched to form the separation groove, crystal defects are generated in the semiconductor substrate in the vicinity of the periphery of the separation groove, as in the RECESSED LOCOS separation. It is expected that the resulting junction leakage current will flow. However, in the OSELLO II isolation, since the semiconductor substrate between the side surface of the isolation trench and the end of the element region is selectively oxidized, the crystal defects generated in the semiconductor substrate in the vicinity of the isolation trench are separated by the element isolation oxide film. It is taken in. Therefore,
The junction leakage current generated by the OSELLO II separation is caused only by the crystal defects generated by suppressing the volume expansion due to the selective oxidation with the nitride film, and the RECESSEDLOCOS
In the separation, it is not caused by a crystal defect generated in the semiconductor substrate near the periphery of the separation groove.

Therefore, in the present invention, the crystal defects generated at the end of the element isolation region during the selective oxidation are reduced by the RECESSED L method.
It is an object of the present invention to form an element isolation that suppresses the junction leakage current by suppressing it than the OCOS isolation and the OSELLO II isolation, and makes the element isolation length longer than the LOCOS isolation to improve punch-through resistance.

[0011]

According to the present invention, in a method of forming an element isolation insulating film on a semiconductor substrate, a step of sequentially forming a first oxide film and a nitride film on the main surface of the semiconductor substrate, Forming an opening in the first oxide film and the nitride film so that a part of the main surface of the substrate is exposed as a main surface exposed portion; and exposing the central portion of the main surface exposed portion as a central exposed portion. A second oxide film covering the side walls of the first oxide film and the nitride film that define the side surface of the opening and the portion of the exposed main surface other than the central portion so as to be kept in the above state. Forming a sidewall portion, forming the isolation trench in the semiconductor substrate by etching the central exposed portion using the sidewall portion as a mask, and using the nitride film and the sidewall portion as a mask Serial selecting oxidizing said semiconductor substrate in the vicinity of the isolation trench, the isolation insulating film forming method characterized by including the steps of forming the device isolation insulating film is obtained.

Further, according to the present invention, in a method of forming an element isolation insulating film on a semiconductor substrate, a step of sequentially forming a first oxide film and a nitride film on the main surface of the semiconductor substrate, and a step of forming the main surface of the semiconductor substrate. Forming an opening in the first oxide film and the nitride film so that a part of the main surface exposed portion is exposed, and a central portion of the main surface exposed portion is kept exposed as a central exposed portion So as to cover the sidewalls of the first oxide film and the nitride film that define the side surface of the opening and a portion of the main surface exposed portion other than the central portion, the exposed surface has a protruding curved surface. Forming a sidewall portion formed of a dioxide film, etching the central exposed portion by using the sidewall portion as a mask to form an isolation groove in the semiconductor substrate, the nitride film and the sidewall portion The selected oxidizing said semiconductor substrate in the vicinity of the isolation trenches as a mask, the element isolation insulating film forming method characterized by including the steps of forming the device isolation insulating film is obtained.

Further, according to the present invention, in a method for forming an element isolation insulating film on a semiconductor substrate, a two-layer structure consisting of a patterned first oxide film and a patterned nitride film on the semiconductor substrate is used, and After the formation of the side wall portion, the side wall portion is used as a mask to etch the semiconductor substrate to form an isolation groove, and then the semiconductor substrate is selectively oxidized to form an element isolation insulating film. An insulating film forming method can be obtained.

[0014]

In the case of the RECESSED LOCOS isolation, a crystal defect occurs in the semiconductor substrate in the vicinity of the periphery of the isolation trench, and a junction leak current resulting from this occurs. On the other hand, in the case of the present invention, the isolation trench is formed using the oxide film sidewall portion as a mask, and the edge of the isolation trench is inside the edge of the element isolation region. Therefore, similar to the OSELLO II isolation, the isolation trench is formed. The crystal defects generated in the semiconductor substrate near the periphery of the are taken into the element isolation oxide film during the selective oxidation, and the junction leak current is suppressed.

Further, according to the present invention, the OSE is formed on the sidewall portion formed on the semiconductor substrate at both ends of the element isolation region.
Since an oxide film is used instead of a nitride film as in the case of LLO II isolation, the effect of suppressing the volume expansion due to the oxidation of the semiconductor substrate under the sidewall portion during the selective oxidation is small. Therefore, the junction leak current caused by the crystal defect caused by suppressing the volume expansion due to the selective oxidation can be suppressed.

Further, in the present invention, the presence of the oxide film side wall portions formed on the semiconductor substrate at both ends of the element isolation region suppresses the diffusion of the oxidizing species during the selective oxidation.
Compared with RECESSED LOCOS separation, bird's beak length can be shortened. However, since the silicon nitride film has a higher ability to suppress the diffusion of the oxidizing species than the silicon oxide film, in the present invention using the oxide film side wall portion, the bird's beak is similar to the OSELLO II isolation using the nitride film side wall portion. You cannot control the length.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings.

1 (a) to 1 (d) are sectional views showing a manufacturing process of an embodiment of the present invention. First, for a two-layer structure consisting of a patterned first oxide film 2 having a film thickness of, for example, about 100 A and a nitride film 3 having a film thickness of, for example, about 1200 A on the semiconductor substrate 1, the film thickness is, for example, 150.
A second oxide film 4 having a thickness of about 0 A is formed (FIG. 1 (a),
(B)). Here, as the second dioxide film, for example, an oxide film formed at a low temperature of about 400 ° C. by a chemical vapor deposition method (hereinafter referred to as a CVD method) is used. Next, the oxide film sidewall portion 5 made of the second dioxide film 4 is formed by anisotropic etching, and the semiconductor substrate 1 is etched using this as a mask to form the isolation groove 6 having a groove depth of, for example, about 600A. Formed (FIG. 1 (c)). Thereafter, the semiconductor substrate 1 is selectively oxidized to form an element isolation insulating film 7 having a film thickness of about 4000 A (FIG. 1D). Here, the oxide film side wall portion 5 remains as unevenness even after the nitride film 3 is removed, which causes a step difference on the surface of the semiconductor substrate. Since the step on the surface of the semiconductor substrate causes a reduction in the focus margin and a disconnection of the metal wiring in the subsequent aligning step, it is desired to reduce it as much as possible.

In summary, in this embodiment, the first oxide film 2 and the nitride film 3 are sequentially formed on the main surface of the semiconductor substrate 1, and a part of the main surface of the semiconductor substrate 1 is exposed as a main surface exposed portion. Thus, openings are formed in the first oxide film 2 and the nitride film 3 (FIG. 1A).

Next, the sidewalls of the first oxide film 2 and the nitride film 3 which define the side surfaces of the opening so that the central portion of the exposed portion of the main surface is kept exposed as the exposed portion of the central surface, An oxide film sidewall portion 5 made of the second dioxide film 4 is formed so that the exposed surface is a protruding curved surface and covers the surface exposed portion other than the central portion (FIGS. 1B and 1C).

Next, using the oxide film sidewall portion 5 as a mask, the central exposed portion is etched to form a separation groove 6 in the semiconductor substrate 1 (FIG. 1C).

Then, using the nitride film 3 and the oxide film sidewall portion 5 as a mask, the semiconductor substrate 1 in the vicinity of the isolation trench 6 is selectively oxidized to form an element isolation insulating film 7.

By the way, in a normal semiconductor device process, after the formation of the element isolation region, the first oxide film 2 on the surface of the element region is removed by using hydrofluoric acid or the like, and the surface of the element region is thermally oxidized called a sacrificial oxide film. By forming a film and then removing it with hydrofluoric acid or the like, defects and metal contamination existing on the substrate surface are removed. After that, a gate oxide film is formed on the surface of the element region by a thermal oxidation method or the like. If necessary, the sacrificial oxide film may be formed and removed a plurality of times. Therefore, the oxide film sidewall portion remaining by the manufacturing method of the present invention undergoes at least two oxide film removing steps prior to the formation of the gate oxide film, so that its shape becomes gentle and the influence of the step Can be almost ignored.

In the present invention, since the isolation trench is formed and the selective oxidation is performed, the element isolation film thickness below the semiconductor substrate surface is thicker than that in the LOCOS isolation. Therefore, the effective element isolation length becomes long, and the breakdown voltage against punch through is high. Where LOCOS separation, RECESSED LOCOS
Punch-through resistance for separation, OSELLO II separation, and the present invention is shown in FIG. The horizontal axis represents the element isolation width, and the vertical axis represents the punch-through breakdown voltage. From FIG. 2, LOCOS separation is possible up to 0.55 μm, while OSE
The LLO II separation and the present invention can be separated up to 0.4 μm, and the RECESSED LOCOS separation is 0.35.
It can be seen that separation is possible in μm. Therefore, the element isolation width required for element isolation of the present invention is 0.55 μm or less.

Next, in the present invention, the isolation groove is formed by using the sidewall portion as a mask, and the edge of the isolation groove is inside the edge of the element isolation region. Therefore, the semiconductor near the edge of the isolation groove is formed. Since the crystal defects generated in the substrate are taken into the element isolation oxide film, the RECESSED LOC
Junction leakage current is reduced as compared with OS isolation. Further, in the present invention, since the oxide film is used for the sidewall portion, the stress caused by suppressing the volume expansion due to the oxidation of the semiconductor substrate under the sidewall portion during the selective oxidation is smaller than that of the OSELLO II separation using the nitride film. Therefore, the junction leak current is reduced. Where LOCOS
Separation, RECESSED LOCOS separation, OSELL
The junction leakage current characteristics for O II separation and the present invention are shown in FIG. The horizontal axis represents the reverse bias voltage, and the vertical axis represents the junction leakage current. From FIG. 3, the junction leakage current of the present invention is
RECESSED LOCOS separation and OSELLO
It can be seen that the level is lower than that of II separation, and that the level is equivalent to LOCOS separation.

In the above-described embodiment, the height of the oxide film side wall portion 5 is set to be approximately the same as the thickness of the nitride film 3. However, the height of the oxide film sidewall portion 5 is not limited by the thickness of the nitride film 3.

If the height is lowered, the height of the oxide film side wall portion remaining after the oxide film removing process on the surface of the element region after forming the device isolation film also becomes lower. It is possible to obtain a fine element isolation structure with a small step. However, when the height of the oxide film side wall portion is reduced, the effect of suppressing the diffusion of the oxidizing species to the surface of the semiconductor substrate below the oxide film side wall portion is small in the selective oxidation, so that bird's beak is likely to occur. For this reason, if a CVD oxide film formed in a high-temperature atmosphere of, for example, about 800 ° C., which has a higher density than that of an oxide film formed at a low temperature of about 400 ° C., is used for forming the oxide film sidewall portion, selective oxidation is performed. At times, it is highly effective in suppressing the generation of bird's beak due to the diffusion of oxidizing species under the oxide film side wall portion, and since bird's beak can be suppressed, it is possible to form the oxide film side wall portion low.

[0028]

As described above, according to the present invention, by forming the isolation trench and performing the selective oxidation,
By increasing the effective element isolation length, the resistance to punch through is higher than that in LOCOS isolation. However, RECE
The resistance to punch-through is similar to that of SSED LOCOS separation and OSELLO II separation.

Further, according to the present invention, by forming the isolation groove using the sidewall portion as a mask and using the oxide film in the sidewall portion, crystal defects in the semiconductor substrate at the end portion of the element isolation region are eliminated. Suppress the occurrence, RE
CESSED LOCOS separation and OSELLO II
The junction leakage current could be reduced as compared with the separation.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view for explaining an embodiment of the present invention.

FIG. 2 is a diagram for explaining an effect of the embodiment of FIG.

FIG. 3 is a diagram for explaining an effect of the embodiment of FIG.

FIG. 4 is a cross-sectional view for explaining a conventional example.

FIG. 5 is a cross-sectional view for explaining another conventional example.

FIG. 6 is a cross-sectional view for explaining still another conventional example.

[Explanation of symbols]

 1 Semiconductor Substrate 2 First Oxide Film 3 Nitride Film 4 Second Dioxide Film 5 Oxide Film Sidewall 6 Isolation Groove 7 Element Isolation Insulation Film

Claims (3)

[Claims] 1. A method of forming an element isolation insulating film on a semiconductor substrate, the step of sequentially forming a first oxide film and a nitride film on the main surface of the semiconductor substrate, and a part of the main surface of the semiconductor substrate is the main surface. Forming an opening in the first oxide film and the nitride film so as to be exposed as an exposed portion; and so as to keep the central portion of the main surface exposed portion exposed as a central exposed portion, Forming a sidewall member made of a second dioxide film, which covers sidewalls of the first oxide film and the nitride film that define the side surface of the opening and a portion other than the central portion of the main surface exposed portion, Forming an isolation trench in the semiconductor substrate by etching the central exposed portion using the sidewall portion as a mask; and using the nitride film and the sidewall portion as a mask, the semiconductor near the isolation trench. Selectively oxidized substrate, the element isolation insulating film forming method characterized by including the steps of forming the element isolation insulating film. 2. A method of forming an element isolation insulating film on a semiconductor substrate, the step of sequentially forming a first oxide film and a nitride film on the main surface of the semiconductor substrate, and a part of the main surface of the semiconductor substrate being the main surface. Forming an opening in the first oxide film and the nitride film so as to be exposed as an exposed portion; and so as to keep the central portion of the main surface exposed portion exposed as a central exposed portion, A side formed of a second dioxide film, which covers the side walls of the first oxide film and the nitride film that define the side surface of the opening and a portion of the exposed portion of the main surface other than the central portion, the exposed surface being a protruding curved surface. Forming a wall portion; etching the central exposed portion using the sidewall portion as a mask to form an isolation trench in the semiconductor substrate; and using the nitride film and the sidewall portion as a mask, Said semiconductor substrate is selectively oxidized, the isolation insulating film forming method characterized by including the steps of forming the device isolation insulating film in the vicinity of the isolation trench. 3. A method of forming an element isolation insulating film on a semiconductor substrate, wherein a sidewall portion made of a second dioxide film is provided to a two-layer structure made of a patterned first oxide film and a nitride film on the semiconductor substrate. After the formation, the semiconductor substrate is etched by using the sidewall portion as a mask to form an isolation groove, and then the element isolation insulating film is formed by selectively oxidizing the semiconductor substrate.