JPS62133732A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To prevent the reduction of an active region as well as to form the active region in accordance with the designed value by a method wherein a patterning is performed on a second oxidation-resisting film utilizing the eave generated on a silicon oxide film, and an interelement isolation region is formed by oxidation using said oxide film as a mask. CONSTITUTION:A first oxidation-resistant film 3 is formed on the surface of a semiconductor substrate 1, and a polycrystalline silicon film 4 of active region form is formed thereon by patterning. The whole body of the above-mentioned films is converted into a silicon oxide film 5 by oxidizing the silicon film 4. An oxide film 3 is removed by etching using the oxide film 5 as a mask. The second oxidation-resistant film 8 is formed on the whole surface of the substrate 1, and an oxide film 8 is left on the lower side only of the oxide film 5 by performing an anisotropic etching on the film 8. The oxide film 5 is removed by etching. A selective oxidation is performed on the surface of the substrate 1 using the left oxide films 3 and 8 as masks, and a thick silicon oxide film 9 is formed. As a result, the contraction of an active region is prevented, and the active region in accordance with the designed value can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a semiconductor device in which a method for forming an isolation region between elements is improved.

[Conventional technology]

Conventionally, LOGOS (Local Oxidation) has been used as a method for forming element isolation regions in semiconductor devices.
A technique called the nofSilicon method is used.

This I,ocos method forms an interelement isolation region made of a thick oxide film by selectively oxidizing the surface of a silicon substrate.

Briefly, a silicon substrate is thermally oxidized to grow a thin silicon oxide film on the surface of the substrate, and a silicon nitride film is grown on top of it. After selectively removing the silicon nitride film in areas other than the active region and diffusing impurities as a guard ring onto the substrate surface, the substrate surface is further thermally oxidized using this silicon nitride film as a mask to form a thick silicon oxide film. is selectively formed and configured as an element isolation region. This state is shown in FIG. 2, where 11 is the silicon substrate, 12 is the previously formed silicon oxide film, 1
3 is a silicon nitride film used as a mask for selective oxidation, 14
is the element amount Nt consisting of the thick silicon oxide film on which the guard ring and 15 are formed? It'f area.

Thereafter, the silicon nitride film and the thin silicon oxide film are removed to expose the base surface of the active region 4, on which various elements will be formed.

(Problems to be Solved by the Invention) The conventional adhesive and OCOS methods described above are effective in that they can form guard rings and element isolation regions in a self-aligned manner using a silicon nitride film as a mask; Until now, it has been used in various semiconductor devices.

However, during thermal oxidation of the substrate surface using a silicon nitride film as a mask, it is difficult to effectively prevent oxidation from proceeding from both ends of the mask toward the inside of the mask. The %N region 15 intrudes inward by a dimension 7!2 from the edge of the mask 13, resulting in "ζ".As a result, the active region is reduced by twice this dimension 12, which is disadvantageous for high integration of devices. This intrusion portion is usually called a birth beak, but it has been found that this dimension 12 is approximately half the thickness of the inter-element isolation region, that is, the thick silicon oxide film 15. Therefore, this oxide film If the film thickness of is 1 μm, the birth beak will be 0.5 μm, and the active 14 regions having these on both sides will be reduced by 1 μm.

In recent semiconductor circuits called VLSIs, 1
Fine patterns on the order of μm have come to be used, and in the design of word patterns, such fine patterns can be reduced by as much as lpm from the designed active region pattern during manufacturing. This is a big restriction.

[Means for solving problems]

The method of manufacturing a semiconductor device according to the present invention does not cause the active region to be reduced from the design pattern, eliminates restrictions on the design, and makes it possible to form #region with an element amount suitable for a minute semiconductor device.

The method for manufacturing a semiconductor device of the present invention includes the steps of forming at least a first oxidation-resistant film on the surface of a semiconductor substrate, patterning a polycrystalline silicon film in the shape of an active region thereon, and oxidizing the polycrystalline silicon film. a step of converting the entire semiconductor substrate into a silicon oxide film; a step of etching and removing the first oxidation-resistant film using the silicon oxide film as a mask; forming a second oxidation-resistant film on the entire surface of the semiconductor substrate; A step of anisotropic etching to leave a second oxidation resistant film only under the silicon oxide film, a step of etching and removing the silicon oxide film, and a step of etching the remaining first and second oxidation resistant films. The method includes a step of selectively oxidizing the surface of the semiconductor substrate as a mask to form a thick silicon oxide film.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIGS. 1(a) to 1(h) are cross-sectional views showing, in order of steps, an embodiment in which the present invention is applied to an MO5 type semiconductor device.

First, as shown in Figure (a), about 300 silicon oxide films 2 are grown by thermal oxidation on a single crystal silicon substrate I of, for example, P-type conductivity and a specific resistance of 10 Ωcm.
Next, a silicon nitride film 3 and a polycrystalline silicon film 4 are sequentially grown to a thickness of 100 OA and a polycrystalline silicon film 4 to a thickness of 3000 Å, respectively, as a first oxidation-resistant film by a normal vapor growth method. Then, the polycrystalline silicon film 4 is selectively etched using a photolithography technique, leaving the polycrystalline silicon film 4 only in the area corresponding to the active region, as shown in FIG. 2(b). For the selective etching, for example, a plasma etching method using carbon tetrachloride gas is used.

Next, the polycrystalline silicon II! 4 is oxidized for about 3 hours in a steam atmosphere at 1000° C., and all of the polycrystalline silicon 1194 is oxidized as shown in FIG. Through this oxidation, the polycrystalline silicon film 4 is converted into a silicon oxide film 5 having a thickness of about 6,000 wafers, and due to the volume expansion at this time, the upper part of the silicon oxide film 5 protrudes to both sides to form an eaves 6. It has been confirmed that the protruding dimension of this eaves 6 is approximately equal to the thickness of the original polycrystalline silicon film 4, which is approximately 0.3 μm.

Next, using the silicon oxide film 5 as a mask, as shown in FIG.
The silicon nitride film 3 is etched with hot phosphoric acid, and the silicon oxide film 2 is etched with hydrofluoric acid, respectively. At this time, the silicon oxide film 5 is also etched by the hydrofluoric acid to an extent approximately equal to the thickness of the silicon oxide film 2 by 300 mm, but this can be almost ignored. Thereafter, using the silicon oxide I layer 5 as a mask again, boron, which is a P-type impurity, is ion-implanted at a concentration of 5.times.10@12 cm@-2 to form a guard ring layer 7 on the substrate (1).

Next, as shown in FIG. 4(e), a silicon nitride film 8 as a second oxidation-resistant film is grown over the entire surface to a thickness of 200 nm using a normal low pressure vapor phase growth method. Note that this silicon nitride film 8
is integrated with the silicon nitride film 3 below the silicon oxide film 5. If this silicon nitride film 8 is etched away by a highly anisotropic plasma etching method using a CF4 gas, the lower surface of the eaves 6 of the silicon oxide film 5 and this shadow are etched as shown in FIG. The silicon nitride film 8 is left only in the area where the
The upper surface of the silicon substrate 1 and the surface of the silicon substrate 1 are exposed.

Thereafter, when the silicon oxide film 5 is removed by etching with hydrofluoric acid, the silicon nitride film 8 is left as an eaves projecting obliquely in three directions at both ends of the silicon nitride film 3, as shown in FIG.

Then, by oxidizing the silicon substrate 1 by thermal oxidation using the silicon nitride film 3 and the silicon nitride film 8 as masks, a thick silicon layer of about 1 μm is formed on the surface of the silicon substrate 1 as shown in FIG. Oxide film 9 can be formed as an element isolation region.

Note that after the silicon nitride film 3.8 and the silicon oxide film 2 are removed by etching in sequence, MO3I- is etched in the active region.
Forming the transistor is the same as before.

According to this embodiment, by converting the polycrystalline silicon film 4 patterned into the shape of the active region into the silicon oxide film 5, the oxide film canopy 6 can be formed in a self-aligned manner around the active region. It can be advanced toward the non-active region by an amount corresponding to the size. Therefore, in this example, the silicon nitride film 8, which functions as a mask during oxidation of the thick silicon oxide film 9, is formed so as to protrude outward from the silicon nitride film 3 in the original active region by the dimension of the eaves 6. Therefore, when oxidizing the thick silicon oxide film 9 using this silicon nitride film 8 as a mask, the generation of bird's beaks that try to invade the active region is suppressed.
Substantial shrinkage of the active area can be avoided.

In this case, the thicker the silicon nitride film 8, the greater the effect of suppressing bird's beak, but if the silicon nitride film 8 becomes thicker, the stress concentration during thermal oxidation increases, causing junction leakage. In the case of this embodiment, the thickness of the silicon nitride film 8 is set to about 200, so the surface of the silicon substrate l is thermally oxidized to
As a result of forming the silicon oxide film 9 with a thickness of μm, the bird's beak dimension 11 from the pattern edge of the silicon nitride film 8 can be suppressed to approximately C), 3 μm, which is the same size as the silicon nitride film 3 formed first. It was possible to obtain active 6NM. Furthermore, with the silicon nitride film 8 having such a thickness, junction leakage does not occur.

Note that poron, which is an impurity constituting the guard ring, is also diffused outside the silicon nitride film 8 in a self-aligned manner.
It does not invade the active region during subsequent steps such as heat treatment and oxidation.

Note that the dimensions of the dimples 6 can be changed depending on the thickness of the polycrystalline silicon film 4, and the dimensions of the bird's beak can be changed depending on the thickness of the silicon nitride film 8, so these film thicknesses can be selected depending on the purpose.

Here, it goes without saying that the present invention can be applied not only to MO3 type semiconductor devices but also to bipolar type semiconductor devices.

〔Effect of the invention〕

As explained above, the present invention oxidizes polycrystalline silicon patterned in the shape of an active region to convert it into a silicon oxide film, and uses the eaves formed in this silicon oxide film to form a second oxidation-resistant film. Since the element isolation region is formed by patterning and oxidized using this oxidation-resistant film, the oxidized end position of the element isolation region can be set back toward the non-active region by the eaves dimension, thereby making it possible to isolate the element isolation region. It is possible to eliminate the shrinkage of the active region defined by the regions and form an active region that is larger than the design value, and it is possible to manufacture a semiconductor device with a fine pattern.

[Brief explanation of drawings]

FIGS. 1(a) to 1(h) are cross-sectional views showing an embodiment of the present invention in the order of steps, and FIG. 2 is a cross-sectional view showing problems in the conventional method. 1... Silicon base, 2... Silicon oxide 111.
3... Silicon nitride film (first oxidation resistant film), 4...
Polycrystalline silicon film, 5... silicon oxide film, 6...
Eaves, 7... Guard ring, 8... Silicon nitride film (second oxidation resistant film), 9... Thick silicon oxide film (
(inter-element isolation region), 11... silicon substrate, 12...
・Silicon oxide film, 13...Silicon nitride film, 14.
... Guard ring, 15... Inter-element isolation region. Figure 1 Figure 1 Figure 1 Figure 2

Claims (1)

[Claims] 1. Forming at least a first oxidation-resistant film on the surface of the semiconductor substrate, patterning a polycrystalline silicon film in the shape of an active region thereon, and oxidizing this polycrystalline silicon film to convert the entire film into a silicon oxide film. a step of etching away the first oxidation-resistant film using this silicon oxide film as a mask; and a step of forming a second oxidation-resistant film on the entire surface of the semiconductor substrate and anisotropically etching it to remove the silicon oxide film. A step of leaving a second oxidation resistant film only on the underside of the oxide film, a step of etching away the silicon oxide film, and selectively oxidizing the surface of the semiconductor substrate using the remaining first and second oxidation resistant films as a mask. and forming a thick silicon oxide film.