JP3277957B2 - Method for manufacturing SOI semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an SOI semiconductor device, and more particularly to a method for selectively etching an element isolation region on a surface of a first semiconductor substrate and forming an insulating film on the surface of the first semiconductor substrate. Forming a first semiconductor substrate by bonding a second semiconductor substrate on the insulating film, and etching the back surface of the first semiconductor substrate with the insulating film filling the element isolation region as a stopper. Forming an SOI layer surrounded by the element isolation region, forming a sacrificial oxide film on the surface of the SOI layer, removing the sacrificial oxide film, forming a gate insulating film on the SOI layer, and then forming the SOI layer and The present invention relates to a method for manufacturing an SOI semiconductor device in which a layer serving as a gate electrode is formed over an element isolation region.

[0002]

2. Description of the Related Art There are first and second methods for manufacturing a semiconductor device.
There is a method of manufacturing an SOI semiconductor device in which semiconductor substrates are bonded together and elements are formed in an SOI layer formed of a first semiconductor substrate. FIGS. 2 and 3 show a conventional example of a method of manufacturing an SOI semiconductor device in the order of steps. 2A to 2E show the first half, and FIGS. 3A to 3D show the second half.
First, the first half will be described with reference to FIG.

(A) An element isolation region on the surface of the first semiconductor substrate 1 is selectively etched (etching depth, for example, 100 n)
m) Then, a silicon oxide film (thickness, for example, 20 to 60 nm) 10 is formed by thermal oxidation. FIG. 2A shows a state after the silicon oxide film 10 is formed. (B) Next, as shown in FIG. 2B, a silicon oxide film 2 having a thickness (for example, 300 to 400 nm) that completely fills the concave portion of the element isolation region is formed. (C) Next, as shown in FIG.
A polysilicon layer (thickness, for example, 5 microns) 3 is formed thereon by, for example, CVD, and its surface is polished to form a flat bonding surface.

(D) Next, the surface of the polysilicon layer 3 is bonded to the surface of a second semiconductor substrate 4 serving as a base, and as shown in FIG. The first semiconductor substrate 1 is turned upside down, that is, the back surface of the first semiconductor substrate 1 faces upward. (E) Next, the SOI layer 5 is formed by polishing the back surface of the first semiconductor substrate 1 using the silicon oxide film 10 on the element isolation region as a stopper. Since this polishing is performed by physical polishing using so-called chemical polishing in combination with a polishing liquid (solvent for silicon), as shown in FIG. (The polished rear surface of the semiconductor substrate 1 without any modification) is generally concave. The thickness of the SOI layer 5 is, for example, 80
-10 nm, and it is difficult to make it thinner at least with current technology.

Next, according to FIGS. 3A to 3D, the SO
The latter half of the conventional example of the method of manufacturing the I semiconductor device will be described. (A) By thermally oxidizing the surface of the SOI layer 5, FIG.
A sacrificial oxide film 11 is formed as shown in FIG. (B) Next, as shown in FIG. 3B, the sacrificial oxide film 11 is etched with hydrofluoric acid.

As described above, the sacrificial oxide film 11 is formed on the surface of the SOI layer 5 and the formed sacrificial oxide film 11 is removed by wet etching.
In order to reduce the irregularities on the surface of the gate insulating film (12) and increase the reliability of the gate insulating film (12) to be formed next.
Second, it is necessary to reduce the thickness of the SOI layer 5 in order to prevent punch-through. To explain this point in detail, the back surface of the first semiconductor substrate 1 for forming the SOI layer 5 is polished by a combination of mechanical polishing and chemical polishing. The irregularities are larger than the surface. Therefore, the SOI layer 5
If a transistor is formed on the surface, it is difficult to increase the reliability of the gate oxide film. Therefore, the surface portion of the SOI layer 5 is once oxidized (sacrificial oxidation), and then the sacrificial oxide film 11 formed by the oxidation is wet-etched.
Then, the SOI layer 5 with small surface irregularities appears, and the highly reliable gate insulating film 12 can be formed there.

Further, the SOI layer 5 can be made thinner by forming and removing the sacrificial oxide film 11. That is, if transistors are miniaturized to meet the demand for high integration of ICs, the necessity of reducing the thickness of the SOI layer 5 to prevent punch-through increases.
As described above, at least the current technology has a limit of 80 to 100 nm as described above, and it is very difficult to reduce the thickness further. However, the formation of the sacrificial oxide film 11,
Subsequent removal of the sacrificial oxide film 11 by wet etching can make the SOI layer 5 thinner than 80 to 100 nm. These are the reasons for forming the sacrificial oxide film 11 and removing it.

(C) Thereafter, as shown in FIG. 3C, a gate insulating film 12 is formed on the surface of the SOI layer 5 by thermal oxidation. (D) Thereafter, as shown in FIG. 3D, a gate electrode made of, for example, polysilicon is formed.

[0009]

FIGS. 2 and 3 show an embodiment of the present invention.
The method for manufacturing the conventional SOI semiconductor device shown in FIG.
There is a problem that the electric field concentration may occur at the boundary between the element isolation region and the SOI layer as shown in an enlarged manner at the lowermost portion of FIG. When the cause was investigated, the SOI layer 5
When the sacrificial oxide film 11 formed on the surface of the device is removed with hydrofluoric acid, the silicon oxide film 10 in the element isolation region is also etched, and if the silicon oxide film 10 is over-etched, the SOI layer 5 is removed from the element isolation region. The protrusion protrudes above the silicon oxide film 10, and a corner is formed in the gate insulating film 12. When a voltage is applied between the SOI layer 5 and the gate electrode 13, an electric field is concentrated on the corner. It has been found. This is, of course, the gate insulating film 12
Degradation and dielectric breakdown are undesirable.

The present invention has been made to solve such a problem. In a method of manufacturing an SOI semiconductor device, the surface of an element isolation region is etched by wet etching of a sacrificial oxide film to form an SOI layer. It is an object of the present invention to eliminate a possibility that an electric field concentration portion is generated in a gate insulating film at a boundary portion with an element isolation region.

[0011]

According to a first aspect of the present invention, there is provided a method for manufacturing an SOI semiconductor device, comprising: selectively etching an element isolation region on a surface of a first semiconductor substrate; Nitrogen ions are implanted into the silicon nitride to form silicon nitride, and the silicon nitride forms at least the surface of the element isolation region.

[0012]

According to the method for manufacturing an SOI semiconductor device of the first aspect, the surface of the element isolation region is made of silicon nitride,
Since the silicon nitride has a lower etching rate with a silicon oxide etchant such as hydrofluoric acid than the sacrificial oxide film, the element isolation region is etched more than the sacrificial oxide film by wet etching of the sacrificial oxide film, and the surface of the element isolation region is etched. Can be prevented from being lower than the surface of the SOI layer. Since the inner part of the element isolation region is not made of silicon nitride, the surface level can be reduced and the reliability can be increased.

The surface of the semiconductor substrate can be made into silicon nitride having a lower etching rate by hydrofluoric acid than the sacrificial oxide film by ion implantation of nitrogen. Therefore, the element isolation region is formed by wet etching of the sacrificial oxide film. It can be prevented that the surface of the element isolation region becomes lower than the surface of the SOI layer by being etched more than the sacrificial oxide film. And since the back part is not nitrided, the surface level of the lower part of the SOI layer can be reduced.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for manufacturing an SOI semiconductor device according to the present invention will be described in detail with reference to the illustrated embodiments. FIGS. 1A to 1E are cross-sectional views showing a main part of a first embodiment of a method of manufacturing an SOI semiconductor device according to the present invention in the order of steps. (A) The surface of the first semiconductor substrate 1 is etched by using the resist film 7 as a mask to etch the element isolation region.
After forming an island-shaped portion to be an OI layer, the resist film 7 used as the mask is left as it is, and FIG.
As shown in FIG. 6, in this state, nitrogen is ion-implanted to form silicon nitride 8 on the inner surface of the concave portion serving as element isolation region 15.

(B) Next, as shown in FIG. 1B, the resist film 7 is removed, and a silicon oxide film 9 is formed on the surface of the first semiconductor substrate 1 by thermal oxidation. (C) Next, as shown in FIG. 1C, a silicon oxide film 3 is formed on the surface of the first semiconductor substrate 1 by CVD. (D) Next, the surface of the polysilicon film 3 is bonded to the surface of the second semiconductor substrate 4, and then the semiconductor substrate is turned upside down as shown in FIG.

(E) Thereafter, the back surface of the first semiconductor substrate 1 is polished using the silicon nitride 8 in the element isolation region as a stopper to form the SOI layer 5. After that, sacrificial oxidation, removal of the sacrificial oxide film, formation of the gate insulating film, and formation of the gate are performed, but illustration and description thereof are omitted.

In the present embodiment, the fact that no electric field concentration portion occurs is apparent from the fact that the surface of the element isolation region 15 is made of silicon nitride 8 whose etching rate by hydrofluoric acid is smaller than that of the silicon oxide film. Further, since the inter-element isolation film is composed of the thin silicon nitride 8 and the silicon oxide film 2, the surface level generated below the SOI layer 5 is lower than that in the case where the inter-element isolation film is formed only of the silicon nitride 14. The amount can be reduced. Therefore, the SOI layer 5
The stability of the characteristics of the transistor formed on the substrate can be further improved.

[0018]

According to the method of manufacturing an SOI semiconductor device of the first aspect, after selectively etching an element isolation region on the surface of the first semiconductor substrate, nitrogen is applied to the surface of the first semiconductor substrate. Is performed to form a silicon nitride, and the silicon nitride forms at least a surface portion of the element isolation region.

Therefore, according to the method of manufacturing an SOI semiconductor device of the first aspect, the surface of the element isolation region is made of silicon nitride, and the silicon nitride is more suitable for silicon oxide such as hydrofluoric acid than the sacrificial oxide film. Since the etching rate by the etchant is low, it is possible to prevent the element isolation region from being etched more than the sacrificial oxide film by the wet etching of the sacrificial oxide film, so that the surface of the element isolation region becomes lower than the surface of the SOI layer. Since the inner part of the element isolation region is not made of silicon nitride, the surface level can be reduced and the reliability can be increased.

The surface portion of the semiconductor substrate can be made of silicon nitride having a lower etching rate by hydrofluoric acid than the sacrificial oxide film by ion implantation of nitrogen. It can be prevented that the surface of the element isolation region becomes lower than the surface of the SOI layer by being etched more than the sacrificial oxide film. Since the back portion is not nitrided, the surface level at the lower portion of the SOI layer can be reduced.

[Brief description of the drawings]

FIGS. 1A to 1E are cross-sectional views showing a main part of a first embodiment of a method for manufacturing an SOI semiconductor device of the present invention in the order of steps.

FIGS. 2A to 2E are sectional views showing the first half of a conventional example of a method of manufacturing an SOI semiconductor device in the order of steps.

FIGS. 3A to 3D are cross-sectional views showing the latter half of the conventional example in the order of steps.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st semiconductor substrate 2 Silicon oxide film which forms the lower part of an element isolation region 4 2nd semiconductor substrate 5 SOI layer 6 Silicon nitride which forms the surface of an element isolation region 10 Silicon nitride which forms the surface of an element isolation region

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 27/12 H01L 21/265 H01L 21/318 H01L 21/762

Claims (1)

(57) [Claims] An element isolation region on a surface portion of a first semiconductor substrate is selectively etched, an insulating film is formed on the surface of the first semiconductor substrate, and a second semiconductor substrate is formed on the insulating film. The SOI layer made of the first semiconductor substrate and surrounded by the element isolation region is formed by bonding and etching the back surface of the first semiconductor substrate using the insulating film filling the element isolation region as a stopper. Forming a sacrificial oxide film on the surface of the SOI layer, removing the sacrificial oxide film, forming a gate insulating film on the SOI layer, and then forming a gate electrode layer on the SOI layer and the element isolation region; In the method of manufacturing a semiconductor device, an element isolation region on a surface portion of the first semiconductor substrate is selectively formed.
After etching, the surface of the first semiconductor substrate is
Nitrogen ion implantation to form silicon nitride
And the silicon nitride is applied to at least the surface of the element isolation region.
A method for manufacturing an SOI semiconductor device, comprising forming a surface portion .