JP2002343856A - Method of manufacturing insulated isolation semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To materialize the simplification of an etch back process for flattening the top of an insulated isolation trench, and secure the flatness of the top of the insulated isolation trench enough at the same time. SOLUTION: (b): A trench 16 is made on the single crystalline silicon layer 11C of an SOI substrate 11 by anisotropic dry etching using a silicon oxide film 14 as a mask. (c) and (d): The silicon oxide film 14 is removed by wet etching, and a relatively thin base oxide film 17 is made on the sidewall of the trench 16 by thermal oxidation. (e) and (f): A polysilicon film 18 is accumulated and then it is etched to form a polysilicon sidewall film 18a in the trench 16. (g): The sidewall film 18a is thermally oxidized to form a sidewall oxide film 19. (h) and (i): The trench 16 is stopped with a polysilicon film 21, and then it is etched back. (j): A field oxide film 22 is made by performing the LOCOS treatment using the silicon nitride film 13 patterned in specified form as a thermal oxidation mask.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing an isolation type semiconductor device having an isolation trench.

[0002]

2. Description of the Related Art FIG. 4 shows an SOI (Silicon On Insulat).
or) An example of a manufacturing process of a semiconductor device in which an insulating isolation trench for element isolation is formed on a substrate is shown in a schematic cross-sectional view (only the main part is shown: the dimensional ratio is not accurate).
Hereinafter, the contents of each step will be individually described.

(A) Mask forming step First, as shown in FIG.
An SOI substrate 1 on which a single-crystal silicon layer 1C is formed via an insulating isolation film 1B made of a silicon oxide film is prepared on A, and a silicon oxide film 2, a silicon nitride film 3, and a silicon nitride film 3 are formed on the single-crystal silicon layer 1C. An opening 5 is formed at a predetermined position by sequentially forming a silicon oxide film 4 and patterning the three-layer structure film using a photo-etching technique. Here, the silicon oxide film 4 functions as an etching mask when the single crystal silicon layer 1C is anisotropically etched to form a trench. The silicon nitride film 3 functions as a stopper when removing the silicon oxide film 4.
Serves to alleviate the stress when the silicon nitride film 3 is formed.

(B) Trench etching step After the above-described mask forming step, anisotropic dry etching is performed on the single crystal silicon layer 1C using the silicon oxide film 4 as a mask. As shown in b), a trench 6 reaching the insulating isolation film 1B is formed.

(C) Sidewall Oxidation Step After the trench etching step is performed, a sidewall oxide film 7 is formed by thermally oxidizing the sidewall of the trench 6 (see FIG. 4C).

(D) Trench-backfilling step By depositing polysilicon by CVD over the entire surface of the silicon oxide film 4, a polysilicon film 8 with the trench 6 backfilled is formed (FIG. 4D). )reference).

(E) First Etch-Back Step By performing a CMP (chemical mechanical polishing) process using the silicon oxide film 4 as a stopper, the polysilicon film 8 is etched back to the surface of the silicon oxide film 4 (FIG. 4). (E)).

(F) Mask Removal Step The silicon oxide film 4 used as a trench etching mask is removed by wet etching using the silicon nitride film 3 as a stopper (see FIG. 4F).

(G) Second etch-back step The polysilicon film 8 protruding above the trench 6
Is removed to the surface of the silicon oxide film 2 by dry etching using the silicon nitride film 3 as a mask (FIG. 4 (g)).
reference).

(H) Polysilicon Film Oxidation Step The polysilicon film 8 exposed above the trench 6 is oxidized by performing a thermal oxidation process, and the upper portion of the trench 6 is integrated with the silicon oxide film 2 and the side wall oxide film 7. (See FIG. 4 (h)).

(I) Step of Removing Silicon Nitride Film The silicon nitride film 3 is removed by wet etching with a processing liquid having an etching selectivity with the silicon oxide film 2 (see FIG. 4I).

[0012]

In the above-mentioned conventional manufacturing method, a process necessary for flattening the upper portion of the trench 6 is provided.
That is, the process of removing the polysilicon film 8 while leaving the buried portion in the trench 6 is performed in a first etch-back step (FIG. 4).
(E)) and the second etch-back step (FIG. 4 (g)), so that the number of steps required for flattening the upper part of the trench is increased and the productivity is deteriorated. In the first etch-back process, costly CM
Due to the P treatment, there was also a situation that the production cost increased. Under such circumstances, the reason why the polysilicon film 8 is etched back twice is as follows.

That is, FIG. 5 is a schematic sectional view showing an example of a manufacturing process in which the polysilicon film 8 is etched back to the surface of the silicon oxide film 2 by one process. In this case, the polysilicon film 8 formed in the trench backfilling step of FIG. 5A is etched back to the surface of the silicon oxide film 2 by, for example, dry etching in an etchback step shown in FIG. 5B. Will be. However, when such a manufacturing method is adopted, the mask removing step shown in FIG. 5C, that is, the silicon oxide film 4 used as the trench etching mask is thereafter used as a stopper, and the silicon nitride film 3 is used as a stopper. When the step of removing by wet etching is performed, the etchant erodes the silicon oxide film 2 and the side wall oxide film 7, so that a depression 9 is generated in the side wall oxide film 7 as shown in FIG. become.

Although the dents 9 described above are repaired to some extent in accordance with the subsequent thermal oxidation in the polysilicon film oxidation step (see FIG. 5D), the silicon nitride film removal step (see FIG. 5 (e)) is performed,
Large irregularities occur in the silicon oxide film 2 above the trench 6. Since the flatness of the upper portion of the trench 6 is impaired in this manner, deterioration of the wettability of the photoresist and poor resolution in a photolithography process performed in a later process are caused, and particles due to residual etching in the later process are accordingly caused. And the possibility of causing defects such as disconnection and short-circuit of the wiring film increases,
There is a problem that the quality of the finally obtained semiconductor device generally deteriorates.

As a countermeasure against such a problem, it is conceivable to adopt a process sequence as shown in a schematic sectional view in FIG. In this case, after performing a mask forming step (FIG. 6A) and a trench etching step (FIG. 6B) similar to those of FIGS. 4A and 4B, the sidewall of the trench 6 is thermally oxidized. In the previous stage, a mask removing step shown in FIG. 6C, that is, a step of removing the silicon oxide film 4 by wet etching using the silicon nitride film 3 as a stopper is performed. Thereafter, in a sidewall oxidation step as shown in FIG. 6D, a sidewall oxide film 7 is formed by thermally oxidizing the sidewall of the trench 6. In the case of such a process order, the occurrence of the depression 9 as shown in FIG. 5C can be prevented when the silicon oxide film 4 serving as the trench etching mask is removed.

However, according to this manufacturing method, the following problems occur. That is, in a semiconductor device in which a surge or an overvoltage from the outside may enter, it is necessary to set the thickness of the sidewall oxide film 7 to a somewhat large value (for example, 100 nm to 600 nm).
It is inevitable that the thermal oxidation processing time in the sidewall oxidation step (FIG. 6D) for forming such a sidewall oxide film 7 becomes relatively long. However, in the manufacturing method shown in FIG. 6, in the mask removing step (FIG. 6C), a side etch (undercut) occurs in the silicon oxide film 2 and the end of the silicon nitride film 3 projects like an eaves. If the thermal oxidation time in the subsequent sidewall oxidation step becomes relatively long as described above, the silicon oxide that grows (expands in volume) with the thermal oxidation of the single crystal silicon layer 1C As a result, the end of the silicon nitride film 3 is lifted and turned up. For this reason, in the subsequent trench backfilling step (see FIG. 6E), the polysilicon film 8 enters under the silicon nitride film 3 in a state of being rolled up like an eaves.

In this state, when an etch-back step of dry-etching the polysilicon film 8 is performed, as shown in FIG. 6F, the eaves-shaped silicon nitride film 3 serves as a mask. Then, an etching residue 8a of polysilicon is generated thereunder. Such an etching residue 8a is then removed by a silicon nitride film removing step (FIG. 6 (g)).
(See FIG. 6 (h)), and is thermally oxidized in the polysilicon film oxidation step (see FIG. 6 (h)) to form projections of the oxide film.
There is a problem that the flatness of the upper portion is significantly deteriorated.

In short, according to the conventional manufacturing method, the steps required to planarize the upper portion of the isolation trench are simplified (that is, the manufacturing cost is reduced), and the flatness of the upper portion of the isolation trench is ensured (that is, the upper portion is separated). (Quality improvement of semiconductor devices) is difficult to achieve, and this has been an unsolved problem.

The present invention has been made in view of the above circumstances, and an object of the present invention is to simplify an etch-back process performed for planarizing an upper portion of an isolation trench, and at the same time, to realize an upper portion of the isolation trench. It is an object of the present invention to provide a method of manufacturing an insulation-isolation type semiconductor device which can sufficiently secure the flatness of the semiconductor device.

[0020]

According to the method of manufacturing a semiconductor device according to the present invention, when forming a side wall oxide film required for an insulating isolation trench, a semiconductor layer (single crystal silicon layer) is formed in a conventional manner. Instead of directly oxidizing the semiconductor layer after forming a trench in), a polysilicon film is formed in the trench after removing a mask film made of an oxide semiconductor material used as an etching mask when forming the trench. Is formed, and the side wall film is thermally oxidized to form a side wall oxide film. Then, after forming the sidewall oxide film in this manner, the etching back process of the polysilicon film deposited in the trench backfilling process is completed by one etching.

Accordingly, it is not necessary to perform the above-described etch-back step for flattening the upper part of the isolation trench in two steps as in the conventional method, so that the number of steps required for the flattening can be reduced. In addition to this, the conventional CMP process can be eliminated, and the etch-back process can be simplified. As a result, the manufacturing cost can be reduced. Further, since the mask film used as the trench etching mask is removed by wet etching at a stage before forming the sidewall oxide film, the sidewall oxide film is removed by the mask film as in the conventional method. There is no danger of being eroded by an etching solution for removing the metal. As a result, the flatness of the upper portion of the isolation trench can be sufficiently ensured, so that the quality of the finally obtained isolation semiconductor device can be improved.

According to the second aspect of the present invention, prior to the side wall film forming step for forming the side wall film made of polysilicon by deposition, the side wall of the trench is subjected to a thermal oxidation treatment to be relatively thin. Since the method is to form a base oxide film made of silicon oxide having a thickness, the deposition rate of polysilicon in the side wall film forming step is stabilized, and as a result, the quality of the side wall oxide film can be expected to be improved. Become like

According to the third aspect of the present invention, after forming the polysilicon film covering the stopper film and the trench, the polysilicon film on the stopper film is etched back by dry etching and removed. Along with this, a sidewall film is formed from the polysilicon film remaining in the trench, and this sidewall film is thermally oxidized to form a sidewall oxide film. Therefore, the polysilicon film on the stopper film can be removed at a stage before the film thickness is increased by thermal oxidation, and an etch-back process for the removal can be easily performed.

According to a fourth aspect of the present invention, the polysilicon film is formed so as to cover the stopper film and the trench, and a part of the polysilicon film is used as the sidewall film. A silicon oxide film covering the stopper film and a sidewall oxide film of the trench are formed by thermally oxidizing the whole, and further, the silicon oxide film is
In this method, the polysilicon film deposited in the trench backfill process is used as a stopper when etching back and then removed. For this reason, the thickness of the stopper film does not decrease during the etch back of the polysilicon film. Therefore, it is useful when the stopper film is used in a subsequent process (for example, a process using the stopper film as a mask). Becomes

In the method of manufacturing a semiconductor device according to the fifth aspect of the present invention, when forming a sidewall oxide film required for an insulating isolation trench, a conventional method is performed after forming a trench in a semiconductor layer (single-crystal silicon layer). Instead of directly oxidizing the semiconductor layer, a mask film made of an oxide semiconductor material used as an etching mask when forming the trench is removed, and then a stopper film and an oxide semiconductor film covering the trench are deposited. In addition, a sidewall oxide film is formed by etching the oxide semiconductor film in a later step, and after the sidewall oxide film is formed in such a manner, the polysilicon film deposited in the trench backfilling step is etched back. This is a procedure in which the process is completed by one etching.

Therefore, it is not necessary to perform the etch-back step for planarizing the upper part of the isolation trench in two steps as in the conventional method, so that the number of steps required for the planarization can be reduced. In addition to this, the conventional CMP process can be eliminated, and the etch-back process can be simplified. As a result, the manufacturing cost can be reduced. Further, since the mask film used as the trench etching mask is removed by wet etching at a stage before forming the sidewall oxide film, the sidewall oxide film is removed by the mask film as in the conventional method. There is no danger of being eroded by an etching solution for removing the metal. As a result, the flatness of the upper portion of the isolation trench can be sufficiently ensured, so that the quality of the finally obtained isolation semiconductor device can be improved. Furthermore, since the oxide semiconductor film deposited so as to cover the stopper film is used as a stopper when etching back the polysilicon film deposited in the trench backfilling step, the oxide semiconductor film is removed at the time of etching back. The film is not reduced. Therefore,
This is useful when this stopper film is used for processing in a later step.

According to the manufacturing method of the sixth aspect, the stopper film can be used also as a thermal oxide film when a field oxide film is formed on a semiconductor layer by a selective oxidation method.
The manufacturing process can be simplified.

[0028]

(First Embodiment) A first embodiment of the present invention will be described below with reference to FIG.
FIG. 1 is a schematic cross-sectional view showing only steps for manufacturing a semiconductor device having an isolation trench and a field oxide film having a LOCOS structure on the isolation trench for isolation of elements (only essential parts are shown: (The dimensional ratio is not accurate), and the content of each step will be described individually below.

(A) Step of Forming Mask First, as shown in FIG.
An SOI substrate 11 having a single crystal silicon layer 11C (corresponding to a semiconductor layer) formed on 1A (corresponding to a supporting substrate in the present invention) via an insulating separation film 11B (corresponding to an insulating function portion) made of a silicon oxide film is provided. A silicon oxide film 12 (corresponding to an insulating film), a silicon nitride film 13 (corresponding to a stopper film), and a silicon oxide film 14 (corresponding to a mask film) are sequentially formed on the single crystal silicon layer 11C. The opening 15 is formed at a predetermined position by patterning the three-layer structure film using a photo-etching technique, thereby forming a trench etching mask having a layer structure.

Here, the silicon oxide film 14 functioning as an etching mask when forming a trench by anisotropically etching the single-crystal silicon layer 11C is particularly suitable for forming a trench having a large depth dimension. The thickness is set so as to ensure the masking property at the time of trench etching.
Also, the silicon nitride film 13 is
Function as a stopper when removing
As will be described later, the silicon oxide film 14 is patterned into a predetermined shape after removal, so that the silicon oxide film 14 is also used as a thermal oxidation mask when a field oxide film made of a thick silicon oxide film is formed by a selective oxidation method (LOCOS method). Is done. Further, the silicon oxide film 12 plays a role of suppressing the generation of crystal defects on the surface of the single crystal silicon layer 11C by relaxing the stress when the silicon nitride film 13 is formed.

The insulating isolation film 11 of the SOI substrate 11
B is made of silicon oxide. When the silicon oxide film 14 is removed by wet etching as described later, a portion exposed at the bottom of the trench is similarly etched. The film has a thickness such that the film thickness required for the guaranteed breakdown voltage of the structure remains (note that the dimensional ratio is not shown correctly in FIG. 1).

(B) Trench Etching Step After the above-described mask forming step is performed, anisotropic dry etching is performed on the single crystal silicon layer 11C using the silicon oxide film 14 as a mask, so that the trench is etched as shown in FIG.
As shown in (b), a trench 16 reaching the insulating isolation film 11B is formed.

(C) Mask Removal Step The silicon oxide film 14 used as the trench etching mask is removed by wet etching using the silicon nitride film 13 as a stopper (see FIG. 1C). At the time of this wet etching, a side etch (undercut) occurs in the silicon oxide film 12, and an end of the silicon nitride film 13 protrudes like an eaves.

(D) Base Oxide Film Forming Step After the mask removing step is performed, the side wall of the trench 16 (portion where the single-crystal silicon layer 11C is exposed) is subjected to a thermal oxidation treatment to thereby form a relatively thin film. A base oxide film 17 made of silicon oxide is formed (see FIG. 1D). The base oxide film 17 functions as a base for stabilizing the deposition of polysilicon when a polysilicon film 18 to be described later is formed by deposition, and is therefore required to exhibit its function. It is sufficient that the film has a thickness of the order. Specifically, the thickness of the base oxide film 17 is, for example, about 40 nm, which is sufficient, and is controlled so as to be less than this.

(E) Depositing Polysilicon Film Polysilicon is deposited on the entire surface of the silicon nitride film 13 by the CVD method, so that the polysilicon covering the silicon nitride film 13 and the silicon oxide film 17 in the trench 16 is covered. A silicon film 18 is formed. This polysilicon film 1
Reference numeral 8 denotes a film which is thermally oxidized in a step described later to become a sidewall oxide film of the trench 16, and its film thickness is set in consideration of an expansion amount due to the thermal oxidation. Specifically, for example, it is set to a value of about １ ／ of the silicon oxide film thickness (for example, 100 nm to 600 nm) necessary for securing the withstand voltage of the trench 16.

(F) Polysilicon film shaping step The above-mentioned polysilicon film deposition step constitutes a side wall film forming step according to the present invention. 13 is removed by dry etching using 13 as a stopper. Thereby, the sidewall film 18a is formed by the polysilicon film remaining in the trench 16 (see FIG. 1F).

(G) Thermal Oxidation Step By performing a thermal oxidation process, the side wall film 18 a made of polysilicon is completely thermally oxidized, and the silicon oxide film integrated with the base oxide film 17 in the trench 16 is formed. A side wall oxide film 19 is formed (see FIG. 1G). That is, the single-crystal silicon layer 1 is formed by the sidewall oxide film 19.
1C is completely insulated and isolated, thereby forming the original shape of the isolation trench 20 shown in FIG. 1 (j).

(H) Trench backfilling step By depositing polysilicon over the entire surface of the silicon nitride film 13 to have a thickness of about 1/2 or more of the opening width of the trench 16 by the CVD method, A polysilicon film 21 is formed with the backfilled (FIG. 1).
(H)).

(I) Etchback Step The polysilicon film 21 is etched back to the surface of the silicon oxide film 12 by performing dry etching using the silicon nitride film 13 as a stopper (see FIG. 1 (i)).

(J) Flattening Step The silicon nitride film 13 used as a stopper in each of the above steps is dry-etched using a photomask for forming a field oxide film by a selective oxidation method (LOCOS method). The silicon nitride film 13 after patterning is patterned into a predetermined shape, and a LOCOS process is performed using the patterned silicon nitride film 13 as a thermal oxidation mask.
A field oxide film 22 made of a thick silicon oxide film is formed at a position corresponding to the upper part of FIG. That is, simultaneously with the formation of the field oxide film 22, the polysilicon film 21 above the trench 16 is thermally oxidized to perform a planarization process.
At the same time, a buried polysilicon 21a buried in the trench 16 is formed. The field oxide film is formed at other positions as needed.

In short, the method of manufacturing a semiconductor device according to the present embodiment has the following features. That is, in the present embodiment, in forming the relatively large film thickness of the sidewall oxide film 19 necessary for the insulating isolation trench 20, the trench 16 is formed in the single crystal silicon layer 11A and the single crystal silicon Instead of directly oxidizing the layer 11A, after removing the silicon oxide film 14 used as an etching mask at the time of forming the trench 16 by wet etching, a sidewall film 18a made of a polysilicon film is formed in the trench 16.
Is formed and the side wall film 18a is thermally oxidized to form the side wall oxide film 1
9 is adopted. In this embodiment, after the sidewall oxide film 19 is formed in this manner,
This is a procedure in which the etch back process of the polysilicon film 21 deposited for the buried polysilicon 21a in the isolation trench 20 is completed by one dry etching.

Accordingly, the above-described etch-back step performed to planarize the upper portion of the isolation trench 20 is performed in accordance with FIG.
Since it is not necessary to perform the process in two steps as in the conventional method shown in (1), the number of steps required for the flattening can be reduced, and the CMP process as in the prior art can be abolished. Can be simplified,
As a result, the manufacturing cost can be reduced. Further, since the silicon oxide film 14 used as the trench etching mask is subjected to wet etching at a stage before the formation of the side wall oxide film 19, the side wall oxide film 19 is formed by the conventional method shown in FIG. Unlike the method, there is no risk of erosion by the etching solution for the silicon oxide film 14. As a result, the flatness of the upper portion of the isolation trench 20 can be sufficiently ensured, and the quality of the finally obtained isolation type semiconductor device can be improved.

In this embodiment, a mask removing step for removing the silicon oxide film 14 by wet etching (FIG. 1)
In (c)), a side etch occurs in the silicon oxide film 12 and the end of the silicon nitride film 13 is projected in an eaves shape. It does not cause deterioration of the flatness of the substrate. That is, in the present embodiment, the base oxide film 17 obtained by thermally oxidizing the single-crystal silicon layer 11A is formed as the base for stabilizing the deposit when the polysilicon film 18 is deposited. Although the quality of the finally obtained sidewall oxide film 19 is improved, the underlying oxide film 17 may have a relatively small thickness capable of functioning as an underlayer, and is required for its thermal oxidation. Time is short. For this reason, even if the end of the silicon nitride film 13 protrudes in an eaves shape according to the execution of the mask removing step, the silicon nitride film 1
The end of 3 is lifted up by the expansion of the base oxide film 17 due to the thermal oxidation in the base oxide film forming step (FIG. 1D), so that there is no fear of being turned up. Then, from the state where the end of the silicon nitride film 13 is not curled up as described above, a polysilicon film deposition step of forming the polysilicon film 18 so as to cover the end (FIG. 1E). By etching back the polysilicon film 18 by dry etching, a sidewall film forming step of forming a sidewall film 18a made of polysilicon remaining in the trench 16 (FIG. 1)
(F)) Since the side wall film 18a is completely thermally oxidized to form a side wall oxide film 19 made of a silicon oxide film (FIG. 1 (g)), insulation separation is performed. In forming the side wall oxide film 19 for ensuring the required withstand voltage in the trench 20, an etching residue due to the polysilicon penetrating below the end of the silicon nitride film 13 occurs as in the conventional manufacturing method. There is no danger (in the conventional manufacturing method, an etching residue 8a of polysilicon is generated as shown in FIG. 6F), and it is possible to prevent the flatness of the upper portion of the trench 16 from being deteriorated.

When forming the trench 16 in the single-crystal silicon layer 11C,
Although it is inevitable that a damaged layer in which the crystal is defective is formed on the surface of C, if a thermal oxidation treatment is performed from such a state, a new crystal defect (OSF: Ox:
It is known to induce idation induced Stacking Fault). For this reason, the technique of forming the sidewall oxide film by directly thermally oxidizing single-crystal silicon after the formation of the trench as in the conventional manufacturing method has a problem that crystal defects with the damage layer as a nucleus are generated. . On the contrary,
In the present embodiment, a method of thermally oxidizing the side wall film 18a made of the polysilicon film formed in the trench 16 to form the side wall oxide film 19 is employed.
There is an advantage that generation of crystal defects at 1C can be suppressed.

Further, in this embodiment, the silicon oxide film 1
Silicon nitride film 13 which functions as a stopper when removing silicon nitride film 4 and etching back polysilicon films 18 and 21.
Is also used as a thermal oxidation mask when the field oxide film is selectively oxidized, which can contribute to simplification of the manufacturing process.

(Second Embodiment) FIG. 2 is a schematic sectional view showing a method of manufacturing a semiconductor device according to a second embodiment of the present invention. Only different parts will be described. That is, in the second embodiment, the mask forming step, the trench etching step, the mask removing step, the base oxide film forming step, and the polysilicon film depositing step shown in FIGS. 1 (a) to 1 (e) are performed in the same manner as in FIG.
Thereafter, the following steps (f) to (j) are performed.
In this embodiment, the polysilicon film depositing step (FIG. 2E) constitutes the side wall film forming step of the present invention, and a portion of the polysilicon film 18 located in the trench 16 is formed. Functions as a side wall film.

(F) Thermal Oxidation Step The polysilicon film 18 formed in the polysilicon film deposition step (FIG. 2E) is completely thermally oxidized to form the silicon nitride film 1.
3 and a silicon oxide film 23 integrated with the underlying oxide film 17 in the trench 16 is formed (see FIG. 2F). Then, as described later, this silicon oxide film 2
2 is used to form the sidewall oxide film 23 shown in FIGS.
a is completely formed, and the sidewall oxide film 23a completely insulates and isolates from the single crystal silicon layer 11C, thereby forming the original shape of the isolation trench 24 shown in FIG. 2 (j). .

(G) Trench Backfilling Step By depositing polysilicon over the entire surface of the silicon oxide film 23 by CVD, a polysilicon film 25 with the trenches 16 backfilled is formed (FIG. 2 ( g)
reference).

(H) Etchback Step The polysilicon film 25 is etched back by performing dry etching using the silicon oxide film 23 as a stopper (see FIG. 2H).

(I) Oxide Film Removal Step The silicon oxide film 23 is removed by anisotropic dry etching using the silicon nitride film 13 as a stopper, and the side wall oxide film 23a is formed by the silicon oxide film 23 remaining in the trench 16. (See FIG. 2 (i)).

(J) Planarization Step The silicon nitride film 13 is patterned by dry etching using a photomask for forming a field oxide film by a selective oxidation method (LOCOS method). A LOCOS process using the film 13 as a thermal oxidation mask is performed to form a field oxide film 26 made of a thick silicon oxide film located above the insulating isolation trench 24, and at the same time, the upper portion of the trench 16 is planarized. At the same time, a buried polysilicon 25a buried in the trench 16 is formed (see FIG. 2 (j)).

In short, the procedure of the second embodiment is exactly the same as that of the first embodiment up to the step of forming the polysilicon film 18 in the trench 16 after removing the silicon oxide film 14 by wet etching. Thus, the polysilicon film 18 is thermally oxidized as it is to form a silicon oxide film 23, and the silicon oxide film 23 is dry-etched to form a sidewall oxide film 23a. Although there is a difference, the isolation trench 24 is basically formed in the same manner as in the first embodiment.
Therefore, the effect of the first embodiment as described above can be similarly obtained. In particular,
In the second embodiment, an etch-back process (FIG.
The stopper in (h) is not the silicon nitride film 13 as in the first embodiment, but the silicon oxide film 23 thereon.
Therefore, the silicon nitride film 13 does not decrease in film thickness due to the execution of the etch-back step. As a result,
When the silicon nitride film 13 is used also as a thermal oxidation mask at the time of LOCOS processing in a planarization step (FIG. 2 (j)) performed later, the formation of the field oxide film 26 using the thermal oxidation mask is adversely affected. There is an advantage that there is no danger of appearing.

(Third Embodiment) FIG. 3 is a schematic sectional view showing a method of manufacturing a semiconductor device according to a third embodiment of the present invention. Only different parts will be described. That is, in the third embodiment, the mask forming step, the trench etching step, and the mask removing step shown in FIGS.
The steps are performed in the same manner as the steps shown in FIGS. 1A to 1C of the embodiment, and thereafter the steps shown in the following (d) to (h) are performed.

(D) Oxide Film Deposition Step For example, a silicon nitride film is formed by a CVD method of supplying TEOS as a reaction source (plasma TEOS-CVD performed in a reduced pressure atmosphere or TEOS-O3-CVD performed in a normal pressure atmosphere). A silicon oxide film 27 covering the trench 13 and the trench 16 is deposited (see FIG. 3D). At this time, the silicon oxide film 27 is
Is deposited such that the film thickness deposited on the side wall of the trench 16 can secure the dielectric strength required for the trench 16. Then, as will be described later, the side wall oxide film 27a shown in FIGS. 3G and 3H is formed using the silicon oxide film 27, and the side wall oxide film 27a forms a single crystal silicon layer. 11C is completely insulated and isolated, thereby forming the original shape of the isolation trench 28 shown in FIG.

(E) Trench backfilling step By depositing polysilicon over the entire surface of the silicon oxide film 27 by the CVD method, a polysilicon film 29 with the trench 16 backfilled is formed (FIG. 3 ( e)
reference).

(F) Etchback Step The polysilicon film 29 is etched back by performing anisotropic dry etching using the silicon oxide film 27 as a stopper (see FIG. 3F).

(G) Oxide Film Removal Step The silicon oxide film 27 is removed by dry etching using the silicon nitride film 13 as a stopper, and the trench 16 is removed.
The side wall oxide film 27a is formed by the silicon oxide film 27 remaining inside.
Is formed (see FIG. 3G).

(H) Planarization Step The silicon nitride film 13 is patterned by dry etching using a photomask for forming a field oxide film by a selective oxidation method (LOCOS method). A LOCOS process using the film 13 as a thermal oxidation mask is performed to form an insulating isolation trench 28 and a field oxide film 30 made of a thick silicon oxide film located thereon, and at the same time, flatten the upper portion of the trench 16. And the buried polysilicon 2 buried in the trench 16.
9a is formed (see FIG. 3H).

In short, in the procedure of the third embodiment, after the silicon oxide film 14 is removed by wet etching, the silicon oxide film 27 is formed in the trench 16 by the TEOS-CVD method having a good step coverage.
And a method of forming a side wall oxide film 27a by dry-etching the silicon oxide film 27. Thereafter, the buried polysilicon 29a is embedded in the isolation trench 28. The second embodiment is similar to the first embodiment in that the etch-back process for the polysilicon film 29 deposited for this purpose is completed by a single dry etching. Therefore, the effect of the first embodiment as described above can be similarly obtained. Also in the third embodiment, the stopper in the etch-back step (FIG. 3F) is not the silicon nitride film 13 but the silicon oxide film 27 thereon, as in the second embodiment. There is an advantage that the silicon nitride film 13 does not decrease in film thickness due to the execution of the etch-back step, and there is no possibility that the formation of the field oxide film 26 using the silicon nitride film 13 as a thermal oxidation mask is adversely affected.

(Other Embodiments) The present invention is not limited to the above-described embodiment, but can be modified or expanded as follows. In the first and second embodiments, the base oxide film 17 serving as a base when depositing the polysilicon film 18 may be provided as needed. Therefore, the base oxide film forming step (FIG. 1D, FIG. 2 (d)) can be omitted. In short, the step of forming the base oxide film 17 is not a component of the present invention. Third
In this embodiment, in the oxide film deposition step (see FIG. 3D), a method of depositing the silicon oxide film 27 by the CVD method using TEOS is adopted, but sufficient step coverage can be obtained by other methods. In such a case, it is not necessary to adopt such a technique using TEOS.

Although the example using the SOI substrate 11 using the single crystal silicon substrate 11A as a support substrate has been described, the material of the support substrate is not limited to the single crystal silicon substrate, but may be another semiconductor substrate or an insulating ceramic material. A substrate, a glass substrate, or the like can be used. In particular, when a substrate having an insulating property is used, the insulating separation film (the insulating separation film 11B made of a silicon oxide film in each of the above-described embodiments) becomes unnecessary ( For example, a case where an SOS (Silicon On Sapphire) substrate is used corresponds to this.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a flow of a manufacturing process according to a first embodiment of the present invention.

FIG. 2 is a view corresponding to FIG. 1 showing a second embodiment of the present invention.

FIG. 3 is a view corresponding to FIG. 1, showing a third embodiment of the present invention;

FIG. 4 is a diagram corresponding to FIG. 1 showing a first conventional example.

FIG. 5 is a diagram corresponding to FIG. 1 showing a second conventional example.

FIG. 6 is a view showing a third conventional example and corresponding to FIG. 1;

[Explanation of symbols]

11 is an SOI substrate, 11A is a single crystal silicon substrate (support substrate), 11B is an insulating separation film (insulating function part), 11C
Is a single crystal silicon layer (semiconductor layer), 12 is a silicon oxide film (insulating film), 13 is a silicon nitride film (stopper film),
14 is a silicon oxide film (mask film), 15 is an opening, 1
6 is a trench, 17 is a base oxide film, 18 is a polysilicon film, 18a is a side wall film, 19 is a side wall oxide film, 20 is an isolation trench, 21 is a polysilicon film, 21a is buried polysilicon, and 22 is a field oxide. Film, 23 is a silicon oxide film, 23a is a sidewall oxide film, 24 is an isolation trench,
25 is a polysilicon film, 25a is buried polysilicon, 2
6 is a field oxide film, 27 is a silicon oxide film, 27a
Is a side wall oxide film, 28 is an isolation trench, 29 is a polysilicon film, 29a is buried polysilicon, and 30 is a field oxide film.

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 5F032 AA01 AA35 AA45 AA47 AA69 AA75 AA78 BB01 DA02 DA04 DA23 DA24 DA25 DA30 DA53 DA78

Claims (6)

[Claims] 1. A method of manufacturing an insulation-isolated semiconductor device, comprising: forming an insulation-isolation trench that reaches an insulating function portion in a semiconductor layer formed on a support substrate while being electrically insulated from the support substrate. In the above, an insulating film, a stopper film made of a material having etching selectivity to an oxide semiconductor material, and a mask film made of an oxide semiconductor material are sequentially formed on the semiconductor layer, and the insulating isolation trench is formed on those films. A mask forming step of forming a trench etching mask having a layer structure by forming an opening corresponding to a formation position; and performing anisotropic dry etching using the trench etching mask on the semiconductor layer, A trench etching step of forming a trench reaching the insulating function portion at a position corresponding to the opening; A mask removing step of removing a mask film by wet etching; a sidewall film forming step of forming a sidewall film made of polysilicon on a sidewall of the trench by deposition; and a thermal oxidation process of thermally oxidizing the sidewall film to form the trench. A thermal oxidation step of forming a sidewall oxide film therein, a trench backfill step of filling the trench by depositing polysilicon, and an etchback step of etching the polysilicon film deposited in the trench backfill step. Performing a planarization step of thermally oxidizing and planarizing the polysilicon film on the upper portion of the trench. 2. Prior to the side wall film forming step, a base oxide film forming step of forming a base oxide film made of silicon oxide having a relatively small thickness by performing a thermal oxidation process on the side wall of the trench is performed. The method for manufacturing an insulated semiconductor device according to claim 1, wherein: 3. The step of forming a side wall film, the step of forming a polysilicon film covering the stopper film and the trench, and the step of forming a polysilicon film on the stopper film by using the stopper film as a stopper. A polysilicon film shaping step of forming the sidewall film by the polysilicon film remaining in the trench by etching back and removing the etched back by the dry etching. 3. The method according to claim 1, wherein the etching of the deposited polysilicon film is performed using the stopper film as a stopper. 4. The step of forming a sidewall film includes a step of forming a polysilicon film covering the stopper film and the trench, and depositing a polysilicon film using a part of the polysilicon film as the sidewall film. In the thermal oxidation process, a silicon oxide film and a sidewall oxide film covering the stopper film are formed by thermally oxidizing the entire polysilicon film, and in the etch back process, the silicon oxide film and the sidewall oxide film are deposited in the backfilling process. 3. The method according to claim 1, wherein etching of the polysilicon film is performed using the silicon oxide film as a stopper, and thereafter, an oxide film removing step of removing the silicon oxide film is performed. . 5. A method of manufacturing an insulation-isolated semiconductor device, comprising: forming an insulation-isolation trench that reaches an insulating function portion in a semiconductor layer formed on a support substrate while being electrically insulated from the support substrate. In the above, an insulating film, a stopper film made of a material having etching selectivity to an oxide semiconductor material, and a mask film made of an oxide semiconductor material are sequentially formed on the semiconductor layer, and the insulating isolation trench is formed on those films. A mask forming step of forming a trench etching mask having a layer structure by forming an opening corresponding to a formation position; and performing anisotropic dry etching using the trench etching mask on the semiconductor layer, A trench etching step of forming a trench reaching the insulating function portion at a position corresponding to the opening; A mask removing step of removing the mask film by wet etching; an oxide film depositing step of depositing an oxide semiconductor film covering the stopper film and the trench; and a trench filling up the trench by depositing polysilicon. A backfilling step; an etchback step of etching the polysilicon film deposited in the trench backfilling step using the oxide semiconductor film as a stopper; and etching the trench using the oxide semiconductor film with the stopper film as a stopper. A method of removing an oxide film for forming a sidewall oxide film on the trench, and a planarization process of thermally oxidizing and planarizing the polysilicon film on the trench. 6. The method according to claim 1, wherein the stopper film is formed of a nitride semiconductor film, and is used as a thermal oxide film when a field oxide film is formed on the semiconductor layer by a selective oxidation method. 6. The method for manufacturing an insulation-separated semiconductor device according to any one of 5.