JP2002100671A - Semiconductor device and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a high reliable semiconductor device by suppressing generation of foreign materials and electric field concentrations by preventing the excess removal of an oxide film. SOLUTION: A fixed portion of a pad oxide film 2 and a first silicon nitride film 3 or the like formed on the surface of a silicon substrate 1 are removed. A CVD oxide film 9 is only formed on side walls of the silicon nitride film 3 and the pad oxide film 2, and the inclined portion of the exposed portion of the silicon substrate 1 adjoining to the pad oxide 2 before a trench is formed. A thermal oxide film 4 and a secondary silicon nitride film 5 are formed under a condition that the angle θ2 of the side wall portion is smaller than that of θ1 of the trench upper end portion after the CVD oxide film 9 is removed. The silicon nitride film 5 in the trench upper end portion is removed by anisotropic dry etching method. By this, the silicon nitride film 5 on the side wall in the trench may not be removed when the silicon nitride film 3 is removed so that no silicon nitride film is present in the trench upper end portion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a semiconductor device having a highly reliable groove separation structure and a method of manufacturing the same.

[0002]

2. Description of the Related Art As a structure for electrically insulating and separating elements such as transistors adjacent to each other on a semiconductor substrate, SGI (S
hallow Groove Isolation) structure.

In this SGI structure, a shallow groove is formed in a silicon substrate, and an oxide film is buried in the groove. Since the processing dimensional accuracy is higher than that of the LOCOS structure which has been conventionally used, the SGI structure has a thickness of 0.1 mm. The structure is suitable for a device after the 25 μm process.

However, in this SGI structure, SG
In the oxidation step after the formation of I, the inside of the groove is oxidized, and at the time of oxidation, about twice the volume expansion is caused. When the stress increases, the leakage current of the transistor may increase.

As a method for preventing these stresses from occurring, as disclosed in Japanese Patent Application Laid-Open No. H11-260904, a silicon nitride film serving as an oxidation prevention mask is formed on the side wall of a groove so that the inside of the groove is not oxidized. There is a way to

Here, a method of manufacturing a semiconductor device according to the prior art will be described with reference to FIG. 7, a pad oxide film 2, a first silicon nitride film 3, and a photoresist 8 are deposited on a semiconductor substrate 1 (FIG. 7A). Next, the pad oxide film 2 at a desired position
Then, the first silicon nitride film 3 is removed, and a groove is formed in the semiconductor substrate 1 (FIG. 7B).

Thereafter, the groove surface is thermally oxidized to form a thermal oxide film 4 on the groove surface, and then a second silicon nitride film 5 serving as an oxidation prevention mask is deposited inside the groove (FIG. c)). Then, the trench is buried with the buried oxide film 6 and flattened by the CMP method (FIGS. 7D and 7E). Next, the first silicon nitride film 3 and the pad oxide film 2 are removed (FIG. 7F).

[0008]

However, in the above-described conventional method for manufacturing a semiconductor device, it is possible to deposit a silicon nitride film as a mask for preventing oxidation on the trench side wall. There are points that need improvement.

After planarization by the CMP method, the unnecessary first silicon nitride film 3 is removed. For removing the first silicon nitride film 3, phosphoric acid warmed to several tens degrees is used.

Since the first silicon nitride film 3 and the second silicon nitride film 5 are continuously connected as shown in FIG. 7C, the first silicon nitride film 3 Is removed, the second silicon nitride film 5 is also removed.

Further, the above-mentioned etching solution has poor controllability with respect to the silicon nitride film.
If the first silicon nitride film 3 is to be uniformly removed within the wafer surface, the second silicon nitride film 5
Is largely removed.

Further, the second silicon nitride film 5
Is removed to form a space 7 (shown in FIG. 8A). When such a space 7 is formed, when the pad oxide film 2 is removed, an etchant penetrates into the space 7 to remove the oxide films 4 on both sides of the second silicon nitride film 5. As a result, there is a case where something like "one ten" is formed (see FIG. 8B).

[0013] In the semiconductor manufacturing process, such "one one"
The formation of "0" is not preferable because this "one 10" breaks and causes the generation of foreign matter. Further, when there is the space 7, the buried oxide film 6 is largely removed at the upper end of the groove.

When a large amount of the buried oxide film 6 is removed, a gate electrode film is subsequently deposited so as to surround the upper end of the trench, so that electric field concentration occurs at the upper end of the trench during operation of the transistor, and the electrical characteristics are reduced. Causes a decline.

An object of the present invention is to realize a highly reliable semiconductor device and a method of manufacturing the same by preventing excessive removal of an oxide film, suppressing generation of foreign matter and concentration of an electric field.

[0016]

To achieve the above object, the present invention is configured as follows. (1) In a semiconductor device having an element isolation structure having an oxide film, the element isolation structure has a groove, in which a thermal oxide film, a silicon nitride film, and a buried oxide film are formed. The upper end of the silicon nitride film is located closer to the bottom surface of the groove than the upper ends of the thermal oxide film and the buried oxide film.

(2) Preferably, in the above (1),
Assuming that the thickness of the silicon nitride film formed on the side wall of the groove is d1 and the thickness of the silicon nitride film formed on the bottom of the groove is d2, d1 is greater than d2.

(3) In the method of manufacturing a semiconductor device,
(A) forming a pad oxide film on a circuit formation surface of a semiconductor substrate; (b) forming a first silicon nitride film on the pad oxide film; and (c) forming a first silicon nitride film on a desired position. Removing the first silicon nitride film and the pad oxide film to expose the surface of the semiconductor substrate; and (d)
The first silicon nitride film, a pad oxide film, a thin film serving as a mask is deposited on the exposed semiconductor substrate surface,
Thereafter, a step of leaving the thin film only on the side wall of the first silicon nitride film by an anisotropic etching method,
(E) forming a predetermined groove in the semiconductor substrate using the first silicon nitride film and the thin film as a mask; (f) removing the thin film; and (g) forming the semiconductor substrate. Oxidizing the surface of the groove thus formed to form a thermal oxide film on the surface of the groove; and (h) forming a second silicon nitride film on the surface of the first silicon nitride film and the surface of the thermal oxide film. (I) removing the second silicon nitride film formed near the upper end of the groove by anisotropic etching, (j) filling the groove with a buried oxide film, and (k). Removing the buried insulating film formed on the first silicon nitride film; and (l) removing the first silicon nitride film formed on a circuit forming surface of the semiconductor substrate. The process of m) and a step of removing the pad oxide film formed on the circuit formation surface of the semiconductor substrate.

After removing predetermined portions such as a pad oxide film and a first silicon nitride film formed on the surface of the semiconductor substrate, before forming a groove, a thin film serving as a mask is removed from the first silicon nitride film. End faces of the film and the pad oxide film;
It is formed only on the inclined portion of the exposed portion of the semiconductor substrate.

Then, the thin film is removed, and a thermal oxide film and a second silicon nitride film are formed in a state where the angle of the groove side wall is smaller than the angle of the groove upper end. The second silicon nitride film 5 at the upper end of the groove is removed by an etching method.

As a result, the second silicon nitride film does not exist at the upper end of the groove. Therefore, when the first silicon nitride film is removed, the second silicon nitride film on the side wall of the groove is removed. Not removed.

Therefore, it is possible to prevent the excessive removal of the oxide film, suppress the generation of foreign matter and the concentration of the electric field, and realize a highly reliable semiconductor device and a method of manufacturing the same.

[0023]

An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an explanatory diagram of steps in a method for manufacturing a trench isolation structure of a semiconductor device according to one embodiment of the present invention. In FIG. 1, the manufacturing process of the groove separation structure includes the following processes (1) to (10).

(1) The surface of a silicon substrate 1 is thermally oxidized to form a pad oxide film 2 having a thickness of about 10 nm and a thickness of about 200 n.
m of the first silicon nitride film 3 and a photoresist 8 is formed on the first silicon nitride film 3.
Is formed (FIG. 1A).

(2) Next, after removing the photoresist 8 at a desired position from the photoresist 8 formed in (1) by using a normal exposure method, the first silicon nitride at a desired position is removed. The ride film 3 and the pad oxide film 2 are removed. At this time, the silicon substrate 1 is slightly over-etched (FIG. 1B).

(3) Subsequently, the remaining photoresist 8
Is removed, a CVD oxide film 9 formed by a chemical vapor deposition (CVD) method is deposited, and thereafter, the CVD oxide film 9 is formed by an anisotropic dry etching method. Only the side wall of the pad oxide film 2 and the inclined portion of the exposed portion of the silicon substrate 1 adjacent to the over-etched portion of the pad oxide film 2 are left (FIG. 1C).

(4) Next, using the first silicon nitride film 3 and the CVD oxide film 9 as a mask, the side wall of the surface of the silicon substrate 1 is at a predetermined angle with respect to the silicon substrate 1 (for example, in FIG. 1). A shallow groove having an angle A of 90 to 110 degrees is formed (FIG. 1D).

(5) Thereafter, the CVD oxide film 9 is removed by HF or the like, and the surface of the silicon substrate 1 is thermally oxidized by about 10 nm to form a thermal oxide film 4 in the groove (FIG. 1 (e)).
In this case, when the oxide film 9 is removed by HF or the like, the pad oxide film 2 is removed from the end face of the first silicon nitride film 3 by one.
It is retracted by about 0 nm to 20 nm. That is, the end face of the first silicon nitride film 3 protrudes from the end face of the pad oxide film 2 by about 10 nm to 20 nm, and a space formed by the lower surface of the protruding portion, the silicon substrate 1 and the end face of the pad oxide film 2. Means that the thermal oxide film 4 is buried.

(6) Next, a second silicon nitride film 5 is deposited to a thickness of about 10 nm on the surfaces of the first silicon nitride film 3 and the thermal oxide film 4 by a CVD method or the like (FIG. 1 (f)). )).

(7) Subsequently, the second silicon nitride film 5 near the upper end of the groove is removed by anisotropic dry etching (FIG. 1 (g)). That is, the thermal oxide film 4
Of the second silicon nitride film 5 deposited on the surface, the second silicon nitride film 5 deposited near the upper end of the groove side wall is removed.

(8) Next, an insulating film such as a silicon oxide film is deposited by a CVD method, a sputtering method, or the like, and the trench is buried (hereinafter referred to as a buried insulating film 6). In addition, since silicon oxide films and the like manufactured by the chemical vapor deposition method, the sputtering method, and the like are generally rough films, after the buried insulating film 6 is deposited,
An annealing process at about 1100 ° C. is performed for the purpose of densification ((h) in FIG. 1).

(9) Subsequently, the embedded insulating film 6 is etched back by using a chemical mechanical polishing (CMP) method or a dry etching method. In this case, the first silicon nitride film 3 serves as an etching stopper and has a function of preventing the silicon substrate 1 from being etched (FIG. 1 (i)).

(10) Then, the trench filling step is completed by removing the first silicon nitride film 3 and the pad oxide film 2 (FIG. 1 (j)).

After that, a semiconductor device is formed through, for example, formation of a gate oxide film and a gate electrode, introduction of impurities, formation of a wiring and an interlayer insulating film, etc. necessary for the transistor structure, formation of a multilayer wiring structure, formation of a surface protection film and the like. Complete.

FIG. 2 shows the shape after the step shown in FIG. 1E in one embodiment of the present invention. The shape is such that the silicon substrate 1 protrudes from the end face of the first silicon nitride film 3. (The area indicated by L in FIG. 2).

The angle (θ1) between the upper end surface of the groove of the silicon substrate 1 and a line perpendicular to the upper and lower surfaces of the silicon substrate 1
(Θ2) between the groove sidewall and a line orthogonal to the upper and lower surfaces of the silicon substrate 1 are different from each other (θ1> θ).
2).

This is because the step shown in FIG.
This is because the trench is formed using the oxide film 9 as a mask.
In this state, that is, in a state where the angle θ2 is smaller than the angle θ1, the second silicon nitride film 5 is deposited, and an anisotropic dry etching method (etching proceeds in the depth direction).
When the film 5 is removed, the smaller the angle, the larger the thickness of the silicon nitride film 5 in the depth direction becomes. Therefore, the portion of θ1 having the larger angle is etched earlier.

Therefore, the second silicon nitride film 5 near the upper end of the groove, which is the portion at the angle θ1, is removed.

As a result, the first silicon nitride film 3 and the second silicon nitride film 5 have an angle θ1
Is divided at the part and does not exist continuously.
After removing the first silicon nitride film 3, the second silicon nitride film 5 on the side wall of the groove is not removed.

As a result, since the space 7 shown in FIG. 8 is not formed, the "one 10" generated by the conventional method does not occur, and the "one 10" does not break and become a foreign matter. Further, since the etchant does not enter, the buried oxide film 6 is not removed much at the upper end of the groove as shown in FIG.

As described above, according to one embodiment of the present invention, after the predetermined portions such as the pad oxide film 2 and the first silicon nitride film 3 formed on the surface of the silicon substrate 1 are removed, the groove is formed. Before the formation of the oxide film, the CVD oxide film 9 is formed by forming an end portion of the first silicon nitride film 3 and the pad oxide film 2 and an inclined portion of an exposed portion of the silicon substrate 1 in an over-etched portion adjacent to the pad oxide film 2. And formed only. Then, the CVD oxide film 9 is removed, and the thermal oxide film 4 and the second silicon nitride film 5 are formed with the angle θ2 of the groove side wall smaller than the angle θ1 of the groove upper end. The silicon nitride film 5 at the upper end of the groove is removed by an isotropic dry etching method.

Since the second silicon nitride film 5 does not exist at the upper end of the groove, the second silicon nitride film 5 on the side wall of the groove is removed when the first silicon nitride film 3 is removed. The film 5 is not removed.

Therefore, it is possible to prevent the excessive removal of the oxide film, suppress the generation of foreign matter and the concentration of the electric field, and realize a highly reliable semiconductor device and a method of manufacturing the same.

The second silicon nitride film 5
Since the protrusion from the surface of the silicon substrate 1 causes a step, it is preferable that the metal exists below the surface 12 of the silicon substrate 1 as shown in FIG.

Further, as shown in FIG. 4A, in the process of forming the transistor, when the drop B of the thermal oxide film 4 and the buried insulating film 6 with respect to the second silicon nitride film 5 is large, A part of the deposited second silicon nitride film 5 may protrude to form “one”.

In such a case, after the deposition of the second silicon nitride film 5. By changing the amount of dry etching, the amount of removal of the second silicon nitride film 5 can be adjusted as shown in FIG.
The occurrence of "one" can be prevented.

As shown in FIG. 5, there is an example in which an oxide film 11 exists between the thermal oxide film 4 and the buried oxide film 6. In this case, too, the buried oxide film 6 and the oxide film 1 are formed.
1, the second silicon nitride film 5 is deposited in the same manner as in the above-described embodiment of the present invention, thereby preventing the occurrence of “one” and the like. Antioxidation can be performed.

The second silicon nitride film 5 at the bottom of the groove is etched by the dry etching in the step (g) shown in FIG. The change in the thickness of the film 5 at the bottom of the groove is larger than that of the second silicon nitride film 5 on the side wall of the groove because the anisotropic etching is performed.

Therefore, as shown in FIG. 6A, the thickness d2 of the film 5 at the bottom of the groove is generally thinner than the thickness d1 of the film 5 at the side wall of the groove, and when the dry etching amount is large. As shown in FIG. 6B, the second silicon nitride film 5 at the bottom of the groove is completely removed.

The position of the thickness d1 is a position where the groove shape (the shape of the thermal oxide film 4) does not cross the tangent of the side wall near the center of the groove.

In the above-described example, the grooves are formed using the CVD oxide film 9 as a mask. However, the mask may be a thin film formed by another method instead of the CVD oxide film. The invention is applicable.

[0052]

According to the present invention, in the semiconductor device having the trench isolation structure, the second silicon nitride film is formed on the side wall of the groove but not on the upper end of the groove. Can be prevented from being excessively removed, generation of foreign matter and concentration of an electric field can be suppressed, and a highly reliable semiconductor device and a method for manufacturing the same can be realized.

Further, since no oxidation reaction occurs on the groove side wall even in an oxidizing atmosphere environment, no stress is generated, an increase in junction leakage current of the transistor can be prevented, and a high performance semiconductor device can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic view of a manufacturing process of a groove separation structure according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of one embodiment according to the present invention.

FIG. 3 is a supplementary explanatory diagram of one embodiment according to the present invention.

FIG. 4 is a supplementary explanatory diagram of one embodiment according to the present invention.

FIG. 5 is a supplementary explanatory diagram of one embodiment according to the present invention.

FIG. 6 is a supplementary explanatory diagram of one embodiment according to the present invention.

FIG. 7 is an explanatory view showing a manufacturing process of a conventional groove separation structure.

FIG. 8 is an explanatory view of a conventional groove separation structure.

[Explanation of symbols]

 Reference Signs List 1 silicon substrate 2 pad oxide film 3 first silicon nitride film 4 thermal oxide film 5 first silicon nitride film 6 buried insulating film 7 space 8 photoresist 9 CVD oxide film 10 11 oxide films 12 silicon substrate surface

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Norio Suzuki 5-2-1, Josuihonmachi, Kodaira-shi, Tokyo Within the Semiconductor Group, Hitachi, Ltd. No. 20-1, Hitachi Semiconductor Company, Ltd. (72) Inventor Hiroyuki Ota 502 Kandate-cho, Tsuchiura-shi, Ibaraki Pref. Machinery Research Laboratory, Hitachi, Ltd. CA24 DA23 DA25 DA28 DA74 DA78

Claims (3)

[Claims] 1. A semiconductor device having an element isolation structure having an oxide film, wherein the element isolation structure has a groove, and a thermal oxide film, a silicon nitride film, and a buried oxide film are formed inside the groove. The semiconductor device according to claim 1, wherein an upper end of the formed silicon nitride film is located closer to a bottom surface of the groove than upper ends of the thermal oxide film and the buried oxide film. 2. The semiconductor device according to claim 1, wherein the thickness of the silicon nitride film formed on the side wall of the groove is d.
1, where d1 is greater than d2, where d2 is the thickness of the silicon nitride film formed on the bottom surface of the groove. 3. A method of manufacturing a semiconductor device, comprising: (1) forming a pad oxide film on a circuit formation surface of a semiconductor substrate; and (2) forming a first silicon nitride film on the pad oxide film. (3) removing the first silicon nitride film and pad oxide film at desired positions to expose the surface of the semiconductor substrate; and (4) performing the first silicon nitride film and pad oxidation. Depositing a film and a thin film serving as a mask on the exposed surface of the semiconductor substrate, and thereafter leaving the thin film only on the side wall of the first silicon nitride film by an anisotropic etching method; Forming a predetermined groove in the semiconductor substrate using the first silicon nitride film and the thin film as a mask; (6) removing the thin film; and (7) forming a groove in the semiconductor substrate. (8) forming a thermal oxide film on the surface of the groove by oxidizing the surface; (8) forming a second silicon nitride film on the surface of the first silicon nitride film and the thermal oxide film; 9) removing the second silicon nitride film formed near the upper end of the groove by anisotropic etching; (10) filling the groove with a buried oxide film; Removing the buried insulating film formed on the silicon nitride film of (i), and (12) removing the first silicon nitride film formed on the circuit forming surface of the semiconductor substrate. (13) A method of manufacturing a semiconductor device, comprising: a step of removing the pad oxide film formed on a circuit formation surface of the semiconductor substrate.