JP2556128B2 - Method for manufacturing semiconductor device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device using a groove type isolation structure for element isolation, and more specifically, a deep groove for groove type isolation is formed. It relates to an improvement in the surface flattening method after embedding.

[Conventional technology]

2 (a) to 2 (e), an outline of the main manufacturing steps of the groove type isolation structure in the semiconductor device using the groove type isolation structure with deep grooves for element isolation in the conventional example is shown in FIGS. Show.

That is, in the conventional method shown in FIGS. 2 (a) to 2 (e), the semiconductor device using the groove-shaped isolation structure by the deep groove is formed by first forming the first oxide film 2a on the main surface of the semiconductor substrate 1. Then, the oxide film 2a in the portion corresponding to the trench-shaped isolation region is selectively patterned and removed to make an opening, and the patterned first oxide film 2a is used as a mask to make the semiconductor substrate 1 different. Isotropic etching is performed to form a deep groove ZG ₁ having a predetermined depth (FIG. 2 (a)).

Then, after removing the first oxide film 2a used for the mask, the semiconductor substrate 1 including the inner wall surface and the inner bottom surface of the deep groove G ₁ is removed.
A second oxide film 2b and a nitride film 3 are sequentially formed on the surface of
Further, a polycrystalline silicon film 4 is deposited on these to sufficiently fill the deep groove G ₁ covered with the films 2b and 3,
At this time, the depression G ₂ remains at the surface portion of the polycrystalline silicon film 4 corresponding to the center of the deep groove G ₁ (FIG. 7B). Next, the portion of the depression G ₂ A film such as a photoresist is formed on the polycrystalline silicon film 4 including the recess G _{2 in} order to planarize the recess G _2. However, as long as the width of the recess G ₂ is sufficiently narrow, _The photoresist film 5 on ₂ is applied evenly ((c) in the figure). In order to narrow the lateral width of the depression G ₂ , the deposited film thickness of the polycrystalline silicon film 4 is It can be said that the thicker it is, the better.

Then, the photoresist film 5 and the polycrystal silicon film 4 are each made to have a height position of the polycrystal silicon film 4 below the surface of the semiconductor substrate 1 by using a gas having an etching rate substantially equal to each other. Etch back to a certain depth, but this etching back operation sufficiently reflects the surface shape of the photoresist film 5 on the upper layer side and maintains the flatness as much as possible. The lower polycrystalline silicon film 4 together with the film 5 can be removed by etching to a predetermined depth. As a result, the inside of the deep groove G ₁ covered with the second oxide film 2b and the nitride film 3 is removed. , The surface 7 is filled with the flat polycrystalline silicon film 4 while leaving the space 6 having a predetermined depth in the upper portion (FIG. 7 (d)).

Finally, by selectively oxidizing the surface portion 7 of the polycrystalline silicon film 4 filled in the deep groove G1 while leaving the upper space portion 6 left, the space portion 6 left in the upper portion of the polycrystalline silicon film 4 is first oxidized. 3 is capped by the oxide film 2c, and at this time, the nitride film 3 plays a role of relieving the stress at the time of forming the third oxide film 2c (see FIG. (E)) Through the above steps, it is possible to manufacture a groove-shaped separation structure with deep grooves as expected.

[Problems to be Solved by the Invention]

Here, in the conventional example method for obtaining the groove-shaped separation structure by the deep groove, as described above, the depressions remaining on the surface of the polycrystalline silicon film filling the deep groove are flattened as much as possible. For this reason, the etch back method is used. In this etch back method, in order to make the etching rates of the photoresist film and the polycrystalline silicon film almost equal, the mixing ratio of oxygen and fluorine-based gas as etching gas is used. However, there is a disadvantage that it takes a lot of time to set each etching condition such as, and on the other hand, there is a problem that it is necessary to sufficiently increase the deposited film thickness of the polycrystalline silicon film.

The present invention has been made in order to solve such a conventional problem, and an object of the present invention is to provide a polycrystalline silicon film filling a deep groove covered with an oxide film and a nitride film with A method for manufacturing a semiconductor device of this kind, which is capable of obtaining an effect equal to or higher than the etching back method as in the conventional method as an etching means for surface flattening The purpose of the present invention is to provide a manufacturing method for obtaining a groove-shaped isolation structure in a semiconductor device.

[Means for solving the problem]

In order to achieve the above-mentioned object, a method of manufacturing a semiconductor device according to the present invention provides a method for flattening a polycrystalline silicon film filling a deep groove covered with an oxide film and a nitride film, By applying a selective oxidation method instead of the etchback method as in the conventional method, a groove-shaped isolation structure can be obtained in the same manner.

That is, the present invention is a method of manufacturing a semiconductor device using a groove-shaped isolation structure for element isolation, which is the first method except for the portion corresponding to the groove-shaped isolation region on the main surface of the semiconductor substrate. Forming an oxide film and using the first oxide film as a mask to form a deep groove of a predetermined depth in the semiconductor substrate;
After removing the first oxide film, a second oxide film and a nitride film are sequentially formed on the inner wall surface, the inner bottom surface of the deep groove and the surface of the semiconductor substrate, and the second oxide film and the nitride film are covered with the oxide film and the nitride film. In the deep groove, the step of depositing and embedding a polycrystalline silicon film in a thickness such that the lower end of the recess remaining on the surface of the central portion is located above the surface of the nitride film; A step of selectively oxidizing the semiconductor substrate to a depth below the surface to form a third oxide film having a flat interface with an unoxidized polycrystalline silicon film, and removing the third oxide film, Exposing a flattened surface of the polycrystalline silicon film, leaving a space of a predetermined depth in an upper part inside the deep groove covered with the second oxide film and the nitride film. A method for manufacturing a characteristic semiconductor device.

[Action]

Therefore, in the method of the present invention, the deposited thickness of the polycrystalline silicon film filling the deep groove covered with the oxide film and the nitride film is determined by the lower end portion of the recess remaining on the surface of the central portion of the deep groove.
Since the polycrystalline silicon film is set so as to be positioned above the surface of the nitride film and the polycrystalline silicon film is selectively oxidized to a depth below the surface of the semiconductor substrate in this state, the polycrystalline silicon film is not oxidized with the unoxidized polycrystalline silicon film. The interface can be flattened, and by removing the oxidized portion here, the flattened surface can be exposed leaving a space of a predetermined depth in the upper part of the deep groove, In this way, the surface of the polycrystalline silicon film filling the deep trench can be made flat.

〔Example〕

An embodiment of a method of manufacturing a semiconductor device according to the present invention will be described in detail below with reference to FIG.

FIGS. 1 (a) to 1 (e) are cross-sectional views each schematically showing the outline of main manufacturing steps of a semiconductor device using a groove-shaped isolation structure with deep grooves to which the method of this embodiment is applied.

That is, in the method of the embodiment shown in FIGS. 1A to 1E, the semiconductor device using the groove-shaped isolation structure by the deep groove is firstly processed by the semiconductor substrate 11 as in the case of the conventional method. Forming a first oxide film 12a on the main surface of the first oxide film 12a, forming a first oxide film 12a on the trench isolation region, and selectively removing a portion of the oxide film 12a corresponding to the trench isolation region. The semiconductor substrate 1 is removed by patterning to make openings and using the patterned first oxide film 12a as a mask.
1 is anisotropically etched to form a deep groove G ₁ having a predetermined depth (FIG. 1 (a)).

Then, after removing the first oxide film 12a used for the mask, the semiconductor substrate including the inner wall surface and the inner bottom surface of the deep groove G ₁ is removed.
Similarly, on the surface of 11, the second oxide film 12b and the nitride film 13 are formed.
Are sequentially formed, and a polycrystalline silicon film 14 is further deposited thereon to sufficiently fill the deep groove G ₁ covered with each of the films 12b and 13. In the example method, the thicker the deposited thickness of the polycrystalline silicon film is, that is, the dent remaining on the surface of the central portion of the deep groove G _1.
The smaller G ₂ is, the more preferable it is. However, in the method of this embodiment, it is sufficient if the deposition thickness is such that the lower end portion of the depression G ₂ is located above the surface of the nitride film 13 (FIG. b)).

Next, the third oxide film 12c is formed by selectively oxidizing the polycrystalline silicon film 14 to a depth below the surface of the semiconductor substrate 11 (FIG. 7C). Here, in the selective oxidation treatment, the nitride film 13 covering the surface of the semiconductor substrate 11 first acts as a mask, and at this time, the third oxide film A depression G ₃ reflecting the shape of the depression G ₂ is formed on the surface of 12c. The third oxide film 12
The interface 15a between c and the unoxidized polycrystalline silicon film 14 becomes flat.

Then, the third oxide film 12c is appropriately removed by etching, so that the inside of the deep groove G ₁ covered with the second oxide film 12b and the nitride film 13 has a space 16 at a predetermined depth above. The exposed polycrystalline silicon film 14 has a flat exposed surface 15b.
Then, it is in a state of being filled (Fig. 4 (d)). Also, during this etching, the second oxide film is also formed.
The nitride film 13 that covers 12b acts as a mask.

Finally, similarly to the above, by selectively oxidizing the surface 15b portion of the polycrystalline silicon film 14 filled in the deep groove G ₁ while leaving the upper space portion 16 left, the surface 15b portion is left in the upper portion. The formed space 16 is capped by the fourth oxide film 12d, and at this time, the nitride film 13 is also formed by the fourth oxide film 12d.
It plays a role of relieving the stress at the time of forming the oxide film 12d (FIG. 6 (e)), and the groove-shaped separation structure with the deep groove can be manufactured as desired through the above steps. is there.

Therefore, in the case of the method of this embodiment, the second oxide film 12
The deposition thickness of the polycrystalline silicon film 14 filling the inside of the deep groove G ₁ covered with b and the nitride film 13 is set so that the lower end of the depression G ₂ remaining on the surface of the central portion of the deep groove G ₁ is In a state where the polycrystalline silicon film 14 is set to the above position, the polycrystalline silicon film 14 is selectively oxidized to a depth below the surface of the semiconductor substrate 11,
Since the third oxide film 12c is formed, the interface 1 between the third oxide film 12c and the unoxidized polycrystalline silicon film 14 is formed.
5a can be made extremely easy to be flat, and by removing the third oxide film 12c, the flattened surface 15b of the polycrystalline silicon film 14 can be moved to the upper part in the deep groove G ₁ . It can be exposed leaving a space 16 of a predetermined depth,
Unlike the conventional method, it does not use a laborious etchback method for setting etching conditions, etc., but instead, it uses an existing selective oxidation method that is simpler and requires less labor, and can be used in many cases. In addition to flattening the crystalline silicon film 14 easily and quickly, the thickness of the polycrystalline silicon film 14 itself can be made relatively thin.

〔The invention's effect〕

As described above in detail, according to the present invention, in the method of manufacturing a semiconductor device using the trench isolation structure for element isolation, the patterned first oxide film is used as a mask,
A deep groove is selectively formed in a portion corresponding to the groove-shaped isolation region of the semiconductor substrate, the substrate surface including the deep groove is covered with a second oxide film and a nitride film, and the deep groove covered with each of these films is formed. The thickness of the deposited polycrystalline silicon film is set so that the lower end of the recess remaining on the surface of the central portion of the deep groove is located above the surface of the nitride film. Is selectively oxidized to a depth below the surface of the semiconductor substrate to form a third oxide film, so that the interface between the third oxide film and the unoxidized polycrystalline silicon film can be made flat, Further, by removing the third oxide film portion here, the flattened surface can be exposed in the upper part of the deep groove leaving a space portion of a predetermined depth. As in the case of the conventional method, the poly-silicon Instead of using a complicated etching back method for setting etching conditions etc. as a flattening means for the film, instead of this, the existing selective oxidation method, which is a simpler means, is used to replace this polycrystal. The silicon film can be flattened easily and quickly, and the deposition thickness of the polycrystalline silicon film in the deep groove can be thinned to simplify the manufacturing process. It has the following features.

[Brief description of drawings]

FIGS. 1 (a) to 1 (e) are schematic cross-sectional views showing the outline of main manufacturing steps of a semiconductor device using a groove-shaped isolation structure with deep grooves to which the method of an embodiment of the present invention is applied. 2 (a) to 2 (e) are schematic sectional views showing the outline of main manufacturing steps of a semiconductor device using a groove-shaped separation structure with deep grooves in the conventional method. It is a figure. 11 ... Semiconductor substrate, 12a to 12d ... First to fourth oxide film, 13 ... Nitride film, 14 ... Polycrystalline silicon film, 15a
... flattened unoxidized interface, 15b ... flattened polycrystalline silicon film surface, 16 ... space. G ₁ ...... Deep groove for groove shape separation, G ₂ …… Dimple on the surface of polycrystalline silicon film, G ₃ …… Dimple on the surface of third oxide film.

Claims (1)

(57) [Claims] 1. A method of manufacturing a semiconductor device using a trench isolation structure for element isolation, comprising: a first oxide on a main surface of a semiconductor substrate except a portion corresponding to the trench isolation region; A step of forming a film and using the first oxide film as a mask to form a deep groove of a predetermined depth in the semiconductor substrate; and after removing the first oxide film, an inner wall surface, an inner bottom surface, and A second oxide film and a nitride film are sequentially formed on the surface of the semiconductor substrate, and the lower end portion of the recess remaining on the surface of the center portion in the deep groove covered with the oxide film and the nitride film is
A step of depositing and embedding a polycrystalline silicon film to a thickness located above the surface of the nitride film, and performing a selective oxidation treatment of the polycrystalline silicon film to a depth below the surface of the semiconductor substrate to obtain an unoxidized polycrystalline film Forming a third oxide film having a flat interface with the silicon film, removing the third oxide film, and providing a predetermined upper portion in the deep groove covered with the second oxide film and the nitride film. And a step of exposing the flattened surface of the polycrystalline silicon film while leaving a space of a depth, at least.