JPH06310593A - Manufacture of element isolation region - Google Patents

Abstract

PURPOSE:To make a manufacturing process easy by eliminating the need for the flattening treatment of the surface of a semiconductor base body at a time when a trench having a different area is buried with silicon oxide in a method, in which an element isolation region is formed by burying the trench with silicon oxide. CONSTITUTION:A trench 12 is formed to a semiconductor base body 11 in a first process, a silicon oxide film 13 is shaped onto the bottom of the trench 12 in a second process, silicon oxide 14 is grown selectively on the silicon oxide film 13 in a third process, and the trench 12 is buried with silicon oxide 14, thus forming an element isolation region 15.

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 an element isolation region in a semiconductor device manufacturing process.

[0002]

2. Description of the Related Art For example, a LOCOS method is widely used as a method of manufacturing an element isolation region which is a basic element of a semiconductor device. However, so-called bird's beak extends in the element formation region when the oxide film to be the element isolation region is grown.

To suppress the growth of this bird's beak, L
The OCOS oxide film may be thinly formed. But LOCO
When the S oxide film is formed thin, problems such as a reduction in breakdown voltage of the element isolation region and a reduction in the threshold voltage of the parasitic MOS occur. That is, suppressing the growth of the bird's beak and ensuring the breakdown voltage of the element isolation region are in a contradictory relationship. Therefore, there is a limit to miniaturization of the device.

Therefore, as a technique for forming an element isolation region as an alternative to the LOCOS method, a groove (hereinafter referred to as a trench) is formed in a silicon substrate, an oxide film is formed on the inner wall of the trench, and then polycrystal silicon is buried. A trench type element isolation method has been proposed.

This trench type element isolation method does not cause the problem of bird's beak unlike the LOCOS method described above. For this reason, it becomes possible to secure a sufficiently large element formation region and promote miniaturization.

[0006]

However, in the trench type element isolation method described above, the surface of the substrate must be flattened by burying an oxide film or a polycrystalline silicon film inside the trench. Moreover, the size of the trench is usually not constant, and some trenches are narrow and some trenches are wide.

In order to form the element isolation regions in the trenches having different sizes as described above, first, a film forming technique capable of being deposited and buried, such as a CVD method, is first formed on the substrate surface including the inside of the trench. For example, an oxide film is deposited. Then, in order to flatten the surface of the substrate, a flattening film is formed on the surface of the oxide film by, for example, a coating method. After that, the flattening film and the oxide film are removed by etch back until the surface of the substrate is exposed.

As described above, in the method of manufacturing the element isolation region in which the element isolation region is formed in the trench and the surface of the substrate is flattened, the manufacturing process becomes complicated.

Further, since the bottom of the trench is formed to be square, mechanical stress is likely to concentrate on that portion. For this reason, dislocations, crystal defects, etc. occur in the silicon substrate, and, for example, leaks are likely to occur. As a result, the electrical characteristics of, for example, a transistor formed in the element formation region deteriorates.

An object of the present invention is to provide a method for manufacturing an element isolation region which is excellent in easily forming an element isolation region having a trench structure.

[0011]

SUMMARY OF THE INVENTION The present invention is a method for manufacturing an element isolation region, which has been made to achieve the above object.
That is, a groove is formed in the semiconductor substrate in the first step, and a silicon oxide film is formed on the bottom of the groove in the second step. Then, in a third step, silicon oxide is selectively grown on the silicon oxide film and the inside of the trench is filled with the silicon oxide to form an element isolation region.

In the first step, after forming an oxidation preventing film on the surface of the semiconductor substrate, a groove is formed in the semiconductor substrate from this oxidation preventing film. And in the second step,
After forming a sidewall oxidation prevention film on the sidewall of the groove and further forming a silicon oxide film on the bottom of the groove by a thermal oxidation method, the sidewall oxidation prevention film is removed. Then, the third step is performed to form an element isolation region made of silicon oxide inside the groove.

[0013]

In the method of manufacturing the element isolation region described above, a silicon oxide film is formed at the bottom of the groove formed in the semiconductor substrate, and the silicon oxide film is selectively grown as a selective growth seed to selectively grow the silicon oxide film. Regardless of size, the inside of the trench is filled with grown silicon oxide.

By forming the anti-oxidation film on the surface of the semiconductor substrate and the side-wall anti-oxidation film on the side wall of the groove, the silicon oxide film is formed only on the bottom of the groove during the thermal oxidation. Then, by removing the antioxidant film and the sidewall antioxidant film, only the silicon oxide film is left at the bottom of the groove.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the manufacturing process chart of FIG.

As shown in (1) of FIG. 1, first, the first step is performed. In this step, the groove 12 is formed on the upper surface side of the semiconductor substrate 11 by the usual photolithography technique and etching.

Then, the second step shown in FIG. 1B is performed. In this step, the silicon oxide film 13 is formed only on the bottom of the groove 12.

After that, the third step shown in FIG. 1C is performed. In this step, the silicon oxide film 13 is used as a seed to selectively grow the silicon oxide 14 inside the trench 12 by the selective growth method. Then, by burying the inside of the groove 12 with silicon oxide 14, the element isolation region 1
5 is formed.

The above-mentioned selective growth method is used for the silicon oxide film 13
Under the condition that the growth of the silicon oxide 14 from other surfaces does not occur, the silicon oxide film 13 is used as a seed for the silicon oxide 14
Grow. Examples of such conditions include (1)
The silicon oxide 14 is selectively grown in the liquid phase by utilizing the chemical reaction represented by the formula and the formula (2).

[0020]

[Chemical 1]

[0021]

[Chemical 2]

As shown in the above formula (1), hexafluorosilicate (H ₂ SiF ₆ ) is reacted with water (H ₂ O) to produce hydrogen fluoride (HF) and silicon oxide (SiO ₂ ).
Produces and. The silicon oxide generated at this time grows only on the silicon oxide film 13 formed at the bottom of the groove 12. In this way, the silicon oxide 14 is grown to fill the inside of the groove 12.

The hydrogen fluoride generated by the reaction represented by the equation (1) is neutralized by the reaction represented by the equation (2). That is, orthoboric acid (H ₃ BO ₃ ) and hydrogen fluoride (H ₃
F) reacts and is converted into water (H ₂ O), boron fluoride ion (BF ₄ ⁻ ) and oxonium ion (H ₃ O ⁺ ).

In the method of manufacturing the element isolation region 15, the silicon oxide film 13 is formed on the bottom of the groove 12 formed in the semiconductor substrate 11, and the silicon oxide film 13 is selectively grown as a seed for selective growth of the silicon oxide 14. By doing so, the inside of the groove 12 is completely filled with the grown silicon oxide 14 regardless of the size of the groove 12. Moreover, the silicon oxide 14 embedded in the groove 12 is in a state of being slightly raised above the surface of the semiconductor substrate 11. However, there is no step difference that requires the surface of the semiconductor substrate 11 to be flattened. Further, since the silicon oxide 14 is grown from the silicon oxide film 13 formed on the bottom of the groove 12, no great stress is applied to the corners of the groove 12. Therefore, dislocations and crystal defects do not occur in the semiconductor substrate 11 around the element isolation region 15.

Next, in the method of manufacturing the element isolation region 15 described in the above embodiment, the method of forming the silicon oxide film 13 on the bottom of the groove 12 will be specifically described with reference to the process chart of forming the silicon oxide film of FIG. explain. In addition, in FIG.
The same reference numerals are given to the same components as those described in.

As shown in FIG. 2A, in the first step, a pad oxide film 21 made of silicon oxide is first formed on the surface of the semiconductor substrate 11 by, for example, a thermal oxidation method to a thickness of, for example, several nm. To form. Further, the antioxidant film 22 made of silicon nitride is formed to a thickness of 100 nm, for example, by the CVD method.

Then, by the photolithography technique,
An etching mask 23 is formed at a predetermined position on the upper surface of the antioxidant film 22. This etching mask 23 is
For example, it is made of resist.

After that, as shown in FIG. 2B, by a normal dry etching technique, the portion of the anti-oxidation film 22 indicated by the two-dot chain line, the portion of the pad oxide film 21 indicated by the two-dot chain line, and the semiconductor substrate 11 are formed. The part indicated by the two-dot chain line is removed by etching, and the semiconductor substrate 11 has a depth of 40
A 0 nm groove (trench) 12 is formed. After that, the etching mask 23 is removed by asher processing or wet etching.

Then, the second step shown in FIG. 2C is performed. In this step, the groove 1 is formed by, for example, a thermal oxidation method.
A silicon oxide film 24 is formed on the side wall of 2 with a thickness of several nm, for example. Further, the silicon nitride film 2 is formed on the antioxidant film 22 including the inner wall of the groove 12 by, for example, a CVD method.
5 is formed into a film.

After that, the silicon nitride film 25 in the portion indicated by the chain double-dashed line is removed by a normal etch back process, and the sidewall anti-oxidation film 26 made of the silicon nitride film (25) is formed on the sidewall of the groove 12. To do. The sidewall anti-oxidation film 26 is formed to have a film thickness of, for example, 50 nm to 100 nm. In the above etch-back process, a part (the part indicated by a chain double-dashed line) of the silicon oxide film 24 on the bottom side of the groove 12 is also removed. In this way, the portions other than the bottom of the groove 12 are covered with the antioxidant film 22 and the sidewall antioxidant film 26.

Subsequently, as shown in (4) of FIG. 2, the semiconductor substrate 1 exposed at the bottom of the groove 12 is formed by a thermal oxidation method.
1 is oxidized to form a silicon oxide film 13 on the bottom of the groove 12. The silicon oxide film 13 has
For example, it is formed to a thickness of 200 nm. At this time, like the oxide film formed by the normal LOCOS method, the silicon oxide film 13 also extends in the lower direction of the sidewall oxidation prevention film 26, so that the sidewall oxidation prevention film 26 is slightly lifted upward.

After that, the oxidation prevention film 22, the sidewall oxidation prevention film 26, the pad oxide film 21 and the silicon oxide film 24 are removed by an etching process. At this time, the surface layer of the silicon oxide film 13 is also removed. To remove the antioxidant film 22 and the sidewall antioxidant film 26, for example, wet etching using high-temperature phosphoric acid is performed. To remove the pad oxide film 21 and the silicon oxide film 24, for example, wet etching using a hydrofluoric acid solution is performed. At this time, the surface layer of the silicon oxide film 13 is also etched, but the film thickness of the silicon oxide film 13 is ensured to be a sufficient thickness to serve as a growth seed for the subsequent selective growth.

Thereafter, as shown in FIG. 2 (5), the silicon oxide film 14 is selectively grown from the silicon oxide film 13 in the same manner as in the third step described with reference to FIG. 1 (3). An element isolation region 15 is formed by filling the inside of the groove 12 with the silicon oxide 14.

In the above method of forming a silicon oxide film, the antioxidant film 22 is formed on the surface of the semiconductor substrate 11 and the sidewall of the groove 12.
By forming the sidewall oxidation prevention film 26 and
The semiconductor substrate 11 is exposed only at the bottom of the. Therefore, by performing the thermal oxidation method, the silicon oxide film 13 is formed only on the bottom of the groove 12. Then, the antioxidant film 22, the sidewall antioxidant film 26, and the pad oxide film 21.
By removing the silicon oxide film 24 and the silicon oxide film 24, only the silicon oxide film 13 is left at the bottom of the groove 12.

[0035]

As described above, according to the present invention,
Since the silicon oxide film formed at the bottom of the groove of the semiconductor substrate is used as a selective growth seed to selectively grow silicon oxide,
Silicon oxide grows only above. Therefore, the inside of the groove can be filled with silicon oxide regardless of the size of the groove. Further, since a complicated process of forming a flattening film and performing an etchback process for flattening the surface of the semiconductor substrate is not required, the manufacturing method is simple.

Further, since the antioxidant film is formed on the surface of the semiconductor substrate and the sidewall antioxidant film is formed on the sidewall of the groove, it is possible to form the silicon oxide film only on the bottom of the groove by the thermal oxidation method. After that, since the antioxidant film and the sidewall antioxidant film are removed, only the silicon oxide film can be left at the bottom of the groove. Therefore, it is possible to grow silicon oxide in the upper direction of the groove by using the silicon oxide left on the bottom of the groove as a selective growth seed.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram of an example.

FIG. 2 is a process drawing of forming a silicon oxide film.

[Explanation of symbols]

 11 Semiconductor Base 12 Groove 13 Silicon Oxide Film 14 Silicon Oxide 15 Element Isolation Region 22 Antioxidation Film 26 Sidewall Antioxidation Film

Claims (2)

[Claims] 1. A first step of forming a groove in a semiconductor substrate, a second step of forming a silicon oxide film on the bottom of the groove, and a step of selectively growing silicon oxide on the silicon oxide film. And a third step of forming an element isolation region by burying the groove with the grown silicon oxide. 2. The method for manufacturing an element isolation region according to claim 1, wherein in the first step, an antioxidant film is formed on the surface of the semiconductor substrate, and then a groove is formed in the semiconductor substrate from the antioxidant film. Then, in a second step, a sidewall oxidation prevention film is formed on the sidewall of the groove, and a silicon oxide film is further formed on the bottom of the groove by a thermal oxidation method, and then the sidewall oxidation prevention film is removed. In the third step, a device isolation region is formed by selectively growing silicon oxide on the silicon oxide film and filling the inside of the trench with the grown silicon oxide. Method of manufacturing isolation region.