JPH0628282B2 - Method for manufacturing semiconductor device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device,
It is optimal for forming an element isolation region in VLSI.

2. Description of the Related Art Conventionally, a selective oxidation method (LOCOS method) is generally used as a method for forming an element isolation region in VLSI. According to this LOCOS method, as shown in FIG. 2A, first, for example, a film thickness of 50 is formed on the p-type silicon substrate 1.
Forming a SiO ₂ film 2 of about 0 Å, then on the SiO ₂ film 2
After selectively forming the Si ₃ N ₄ film 3 (antioxidation film),
Using the Si ₃ N ₄ film 3 as a mask, impurities (for example, boron B) for forming a channel stopper 5 described later are ion-implanted into the silicon substrate 1 through the SiO ₂ film 2 (silicon substrate 1).
Injected impurities are represented by. Next, thermal oxidation is performed using the Si ₃ N ₄ film 3 as a mask, and as shown in FIG. 2B, the thick SiO ₂ film 4 (field SiO ₂ film) is formed on the silicon substrate 1.
Film) is formed. During the thermal oxidation, the impurities injected into the silicon substrate 1 are electrically activated and diffused in the depth direction. As a result, p is formed below the SiO ₂ film 4.
^{A +} type channel stopper 5 is formed. After this, Si
After removing the ₃ N ₄ film 3 by etching, the SiO ₂ films 2 and 4 are etched into the shape shown in FIG. 2C.

However, during the thermal oxidation, the oxidation progresses not only in the direction perpendicular to the surface of the silicon substrate 1 but also in the direction parallel to this surface, so that the so-called bird's beak 4a (second B2B) is formed at the end of the SiO ₂ film 4. (See the figure) is formed. This bird's beak 4a not only becomes larger in proportion to the film thickness of the SiO ₂ film 4 but also has a gentle slope on its surface, so that the channel of an element such as a transistor formed in the element forming region 1a of the silicon substrate 1 is formed. The width is the actual mask size (in the paper
The width of the Si ₃ N ₄ film 3 is smaller than the width of the Si ₃ N ₄ film 3), and as a result, the performance of the LSI is deteriorated. In particular, in the case of manufacturing VLSI, if the width of the Si ₃ N ₄ film 3 is reduced to, for example, 1.0 μm or less,
As is clear from FIGS. A to 3C, bird's beak 4a
Due to the occurrence of, the density of the device is prevented from increasing.

Although the object is different from that of the present invention, the method disclosed in JP-A-56-70644 is cited as a prior art related to the present invention. According to this method, as shown in FIG. 4, first, a polycrystalline silicon film 8 is formed on the SiO ₂ film 2 formed on the silicon substrate 1, and then Si ₃ N is formed on the polycrystalline silicon film 8. ₄ After partially forming the film 3, the S
Boron is ion-implanted through the polycrystalline silicon film 8 using the i ₃ N ₄ film 3 as a mask, and then thermal oxidation is performed.
According to this method, the stress generated at the time of the thermal oxidation is relaxed by the polycrystalline silicon film 8, and as a result, it is possible to prevent the generation of crystal defects in the silicon substrate 1.

However, in the above-mentioned prior art, the polycrystalline silicon film 8
Among these, the film thickness of the portion located below the Si ₃ N ₄ film 3 and the other portion are substantially the same. Therefore, the thickness of the polycrystalline silicon film 8 should be made sufficiently large so that the stress generated during the thermal oxidation can be sufficiently relaxed in the portion of the polycrystalline silicon film 8 located below the Si ₃ N ₄ film 3. In that case, since the silicon substrate 1 must be supplied with oxygen through the polycrystalline silicon film 8 having a large film thickness, the selective oxidation of the silicon substrate 1 cannot be performed easily and reliably.

Since ions have to pass through the polycrystalline silicon film 8 having a large film thickness during the boron ion implantation, the ions cannot be surely implanted unless the acceleration energy during the ion implantation is increased.

Causes the problem. Therefore, the film pressure of the multiple silicon film 8 cannot be sufficiently increased so that the stress generated during the thermal oxidation can be sufficiently relaxed.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In view of the above problems, the present invention provides a method of manufacturing a semiconductor device in which the above-mentioned drawbacks of a conventional method of manufacturing a semiconductor device for forming an element isolation region are corrected. The purpose is to do.

Means for Solving the Problems A method for manufacturing a semiconductor device according to the present invention includes a step of forming an insulating film (for example, a SiO ₂ film 2) on a semiconductor substrate (for example, a silicon substrate 1), and a predetermined process on the insulating film. Forming a semiconductor layer (for example, a polycrystalline silicon film 8) of the above, a step of forming an antioxidant film (for example, Si ₃ N ₄ film 3) on the predetermined semiconductor layer, In the step of selectively removing the predetermined semiconductor layer into a predetermined shape, the predetermined semiconductor layer is selectively removed in the plane direction and halfway in the thickness direction to obtain a predetermined film thickness. A step of distinguishing the semiconductor layer into a thick layer portion substantially corresponding to the predetermined shape and a thin layer portion formed of a portion other than the thick layer portion; and a step of performing thermal oxidation using the antioxidant film having the predetermined shape as a mask. It has each.

By doing so, the progress of oxidation in the direction parallel to the surface of the semiconductor substrate can be suppressed by the semiconductor layer, and the stress generated during thermal oxidation is absorbed by the thick layer portion of the semiconductor layer. Further, the semiconductor substrate can be ion-implanted through the thin layer portion of the semiconductor layer, and further, oxygen can be supplied to the semiconductor substrate through the thin layer portion of the semiconductor layer during thermal oxidation. .

EXAMPLE An example of a method of manufacturing a semiconductor device according to the present invention will be described below with reference to the drawings. Note that the following FIG. 1A to FIG.
In FIG. D, the same parts as those in FIGS. 2A to 2C are designated by the same reference numerals, and the description thereof will be omitted as necessary.

First, as shown in FIG. 1A, for example, the surface of a p-type silicon substrate 1 is thermally oxidized to form an extremely thin Si film having a film thickness of 25 Å, for example.
An O ₂ film 2 is formed, and then CV is formed on each SiO ₂ film 2.
A polycrystalline silicon film 8 having a film thickness of 500 Å and a Si ₃ N ₄ film 3 having a film thickness of 1000 Å, for example, are sequentially deposited by the D method. Next, a photoresist 9 is selectively formed on the Si ₃ N ₄ film 3.

Then, RIE is performed using the photoresist 9 as a mask to remove the Si ₃ N ₄ film 3 as shown in FIG. 1B.
By etching and selectively removing in the plane direction the Si ₃ N ₄ film 3a having a predetermined shape, and etching the polycrystalline silicon film 8 selectively in the plane direction and its thickness. By removing it halfway in the direction, a thin layer portion 8a having a predetermined film thickness is partially formed on the polycrystalline silicon film 8. Therefore, the polycrystalline silicon film 8 is divided into a thick layer portion 8b having a shape substantially corresponding to the Si ₃ N ₄ film 3a having a predetermined shape and a thin layer portion 8a composed of a portion other than this thick layer portion. Next, after removing the photoresist 9, a p-type impurity such as B is added to the polycrystalline silicon film 8 and Si using the Si ₃ N ₄ film 3a as a mask.
Ions are implanted into the silicon substrate 1 through the O ₂ film 2.

Next, for example, by using the Si ₃ N ₄ film 3a as a mask, the polycrystalline silicon film 8 and the silicon substrate 1 are thermally oxidized, and as shown in FIG. 1C, a thick SiO ₂ film 4 (field
SiO ₂ film) is formed.

Next, the Si ₃ N ₄ film 3a is removed by wet etching using phosphoric acid (H ₃ PO ₄ ), and then the polycrystalline silicon film 8 is removed by wet etching using, for example, an aqueous KOH solution, as shown in FIG. 1D. State. After that, steps are performed in accordance with a normal manufacturing process of a semiconductor device, for example, a MOS LSI to complete a target semiconductor device.

According to the above-described embodiment, the polycrystalline silicon film 8 is formed on the SiO ₂ film 2, and then Si ₃ N ₄ is formed on the polycrystalline silicon film 8.
Since the Si ₃ N ₄ film 3 is etched by RIE after forming the film 3 to form the Si ₃ N ₄ film 3a having a predetermined shape, the following advantages can be obtained. That is, the polycrystalline silicon film 8
Since the diffusion coefficient of O _{2 in} the inside is smaller than that in the SiO ₂ film, when the thermal oxidation is carried out using the Si ₃ N ₄ film 3a as a mask in the process shown in FIG. As a result, the bird's beak 4a can be made smaller than that of the conventional one. Therefore, the minimum distance between the elements can be made smaller than that of the conventional one, and thus the integration density of the elements can be increased.

Further, a SiO ₂ film 2 having a coefficient of thermal expansion smaller than that of silicon by about one digit is formed on the surface of the silicon substrate 1, a polycrystalline silicon film 8 is formed on the SiO ₂ film 2, and Below the Si ₃ N ₄ film 3a is a thick layer portion 8b.
Therefore, the stress generated during the thermal oxidation performed in the step shown in FIG. 1C can be sufficiently relieved by the thick layer portion 8b, so that the crystal defects in the silicon substrate 1 can be effectively prevented. You can

Further, since the polycrystalline silicon film 8 is formed on the SiO ₂ film 2 as described above, Si ₃ N ₄ is used in the step shown in FIG. 1B.
When the film 3 is etched by RIE, the selectivity is SiO ₂
The size of the Si ₃ N ₄ film 3 can be increased as compared with the case where the Si ₃ N ₄ film 3 is directly formed on the film 2, and therefore the processing is easier than in the conventional case.

Further, the ability to block the implanted ions at the time of the ion implantation performed in the step shown in FIG. 1B can be improved by the amount of the polycrystalline silicon film 8 formed. In addition, as shown in FIG. 1B, since the portion of the polycrystalline silicon film 8 which is not covered with the Si ₃ N ₄ film 3a is etched and removed by RIE to a predetermined thickness, Impurities for forming the channel stopper 5 can be easily ion-implanted into the silicon substrate 1 through the thin polycrystalline silicon film 8 and the SiO ₂ film 2 even with low acceleration energy.

Furthermore, since the silicon substrate 1 is supplied with oxygen via the thin layer portion 8a of the polycrystalline silicon film 8 during thermal oxidation,
Oxidation of the portion of the silicon substrate 1 corresponding to the thin layer portion 8a, that is, selective oxidation can be performed easily and reliably.

The present invention is not limited to the above-mentioned embodiments, but various modifications can be made based on the technical idea of the present invention. For example, the film thickness of the polycrystalline silicon film 8 is not limited to the numerical values used in the above-mentioned embodiments and can be changed as necessary, but the film thickness of 300 to 1000 Å is preferable. Similarly, the film thickness of the SiO ₂ film 2 can be different from that in the above-mentioned embodiment, but the film thickness is preferably 20 to 100Å. It can also be thermally oxidized and
If the diffusion coefficient of O ₂ is smaller than that of SiO ₂ , it is possible to use another type of semiconductor layer instead of the polycrystalline silicon film 8 if necessary. Furthermore, although the polycrystalline silicon film 8 is removed by wet etching using a KOH aqueous solution in the above-described embodiment, it is also possible to remove the polycrystalline silicon film 8 by RIE, for example. Further, the etching depth of the polycrystalline silicon film 8 by RIE performed in the step shown in FIG. 1B can be selected as needed.

EFFECTS OF THE INVENTION According to the method for manufacturing a semiconductor device of the present invention, the progress of oxidation in the direction parallel to the surface of the semiconductor substrate can be sufficiently suppressed by the semiconductor layer. Therefore, it is possible to increase the integration density of devices.

Further, since the stress generated during the thermal oxidation can be absorbed by the thick layer portion of the semiconductor layer, this stress can be sufficiently relaxed, and therefore, the crystal defects on the semiconductor substrate can be effectively prevented. You can

Further, since the semiconductor substrate can be ion-implanted through the thin layer portion of the semiconductor layer, it is possible to reliably ion-implant the semiconductor substrate even if the acceleration energy at the time of ion implantation is low.

Further, since oxygen is supplied to the semiconductor substrate through the thin layer portion of the semiconductor layer during the thermal oxidation, the portion of the semiconductor substrate corresponding to the thin layer portion, that is, the selective oxidation is performed easily and reliably. be able to.

[Brief description of drawings]

1A to 1D are sectional views showing an embodiment of a method for manufacturing a semiconductor device according to the present invention in the order of steps, and FIGS. 2A to 2C.
The figure is a sectional view showing a conventional LOCOS method in the order of steps, 3A.
Figures 3 to 3C show the conventional LOCOS method as VLSI.
2A to 2C when applied to
FIG. 4 is a sectional view for explaining a method for forming a field SiO ₂ film disclosed in Japanese Patent Laid-Open No. 56-70644. In the reference numerals used in the drawings, 1 ... silicon substrate 2 ... SiO ₂ film (insulating film) 3 ... Si ₃ N ₄ film (antioxidation film) 4 ... SiO ₂ film 4a ... bird's beak 8 ... many Crystal silicon film (predetermined semiconductor layer) 8a ... Thin layer portion 8b ... Thick layer portion.

Claims (1)

[Claims] 1. A step of forming an insulating film on a semiconductor substrate, a step of forming a predetermined semiconductor layer on the insulating film, a step of forming an antioxidant film on the predetermined semiconductor layer, and the oxidation. A step of selectively removing the prevention film in the plane direction to form a predetermined shape, and a step of removing the predetermined semiconductor layer selectively in the plane direction and halfway in the thickness direction to a predetermined film thickness Thus, a step of distinguishing the predetermined semiconductor layer into a thick layer portion corresponding to the predetermined shape and a thin layer portion formed of a portion other than the thick layer portion, and using the antioxidant film of the predetermined shape as a mask And a step of performing thermal oxidation, respectively.