JP2003051554A - Method for manufacturing 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 trench type M
The present invention relates to a method for manufacturing a semiconductor device having an OS gate and a trench type MOS capacitor formed in an integrated circuit device.

[0002]

2. Description of the Related Art A trench type MOS gate structure is an MO
It is used to realize low on-resistance of the S transistor. Further, in the integrated circuit device, MOS transistors, capacitors and resistors are formed on the semiconductor substrate. In particular, DRAM (Dyn) that is often used as a semiconductor memory
Amic Random Access Memor
In y), etc., a capacitor having a large occupied area is formed by a trench type MOS capacitor in order to achieve high integration.

FIG. 4 shows a conventional method of manufacturing a trench type MOS capacitor, and FIGS. 4A to 4E are process sectional views showing the main part in the order of processes. A trench 52 is formed in the surface layer of the silicon substrate 51 by a trench etching apparatus using the photoresist and the insulating film as a mask. Next, the mask material not shown is removed ((a) in the same figure).

Next, a sacrificial oxide film 54 is formed on the inner wall of the trench 52 by thermal oxidation (FIG. 2 (b)). Next, by removing the first sacrificial oxide film 54 with hydrofluoric acid or the like,
The damage layer 53 formed on the surface layer in the trench 51 during the trench etching is removed (FIG. 7C).

Next, thermal oxidation is performed again to form trench 5
An oxide film 55 for capacitors is formed on the inner wall of 2 ((d) of the same figure). Next, CVD (Chemical Vap)
or Deposition) method, etc.
6 is deposited inside the trench 52 ((e) in the same figure).
A trench type MOS capacitor is formed by the polysilicon 56, the capacitor oxide film 55 and the silicon substrate 51.

An enlarged view of the vicinity of the bottom of the trench 52 when the trench 52 is formed by the above method is shown below. Figure 5
4B is an enlarged view of a portion B of FIG. 4C, where FIG. 4A shows a case where the side wall surface and the bottom surface intersect at a right angle, and FIG. 4B shows a case where the side wall surface and the bottom surface intersect at an obtuse angle. . In FIG. 5, side wall surface 57 and bottom surface 4 of trench 52 after trench etching
The bottom end portions 59 (FIG. (A)) and 60 (FIG. (B)) of the trench near the intersection of 8 are usually
It has a right angle or an angular shape (obtuse angle),
The shape remains even when the oxide film 55 for capacitors is formed through sacrificial oxidation.

[0007]

As described above, the oxide film for a capacitor formed on the bottom end of the trench having a right angle or an acute angle is generally compared to the oxide film for a capacitor formed on the side wall or the bottom of the trench. It is weak against electric field stress and easily causes dielectric breakdown. The main cause is that the electric field is apt to concentrate on the bottom end part structurally, and the bottom end part is a joint part of different orientation planes of the silicon substrate, which is formed when silicon is thermally oxidized. Since the thickness of the oxide film differs depending on the orientation plane, strain and stress are applied to the oxide film at the bottom edge, and as a result, the oxide film cannot grow sufficiently and the oxide film becomes thin at the bottom edge. Can be considered.

An object of the present invention is to solve the above problems and provide a method of manufacturing a semiconductor device in which concentration of an electric field at the bottom end of a trench and thinning of an insulating film are less likely to occur.

[0009]

In order to achieve the above object, a step of forming a trench in a surface layer of a semiconductor substrate, a step of forming a first sacrificial oxide film on an inner wall of the trench, and a step of forming the first sacrificial oxide film. A step of forming polysilicon on the oxide film, a step of leaving the polysilicon in the vicinity including the intersection of the bottom surface of the trench and the side wall surface, and removing the other polysilicon, and the exposed first Removing the sacrificial oxide film; oxidizing the bottom and sidewall surfaces of the trench and the residual polysilicon to form a second sacrificial oxide film; removing the second sacrificial oxide film; The manufacturing method includes a step of forming a concave roundness at the intersection, and a step of forming an insulating film on the inner wall of the trench.

Further, a step of forming a trench in the surface layer of the semiconductor substrate, a step of forming a first sacrificial oxide film on the inner wall of the trench, a step of forming polysilicon on the first sacrificial oxide film, A step of leaving the polysilicon in the vicinity thereof including the intersection of the bottom surface and the side wall surface of the trench and removing the other polysilicon, and a bottom surface and a side wall surface of the trench in which the first sacrificial oxide film is formed; Oxidizing the residual polysilicon to form a second sacrificial oxide film, removing the second sacrificial oxide film, and forming a concave roundness at the intersection, and insulating the inner wall of the trench. And a step of forming a film.

Further, the insulating film may be either a gate insulating film of a MOS type device or an insulating film of a capacitor formed in an integrated circuit device.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a method of manufacturing a semiconductor device according to a first embodiment of the present invention. FIGS. 1A to 1H are sectional views showing the main process steps in the order of steps. . This process drawing is a process cross-sectional view of the main part of the trench type MOS capacitor, and is an enlarged view corresponding to the portion A in FIG.

Using the photoresist and the insulating film as a mask,
The trench 2 is formed in the surface layer of the silicon substrate 1 by the trench etching apparatus. The surface of the trench is composed of a side wall surface 3 and a bottom surface 4, and a bottom end portion near the intersection 5 of the side wall surface and the bottom surface. After forming the trench 2,
The mask material not shown is removed ((a) in the same figure). Next, the first sacrificial oxide film 7 having a film thickness of about several tens to 100 nm is formed on the inner wall of the trench 2 by thermal oxidation at about 800 ° C. to 1000 ° C. This first sacrificial oxide film 7 is
Damage (polycrystalline part) formed in the surface layer of the trench is taken in (FIG. 2B).

Next, by a low pressure CVD method or the like, polysilicon 8 is deposited on the entire surface of the wafer (not shown) and inside the trench 2 by, for example, about 100 to 300 nm (FIG. 2C). Next, for example, the polysilicon 8 deposited by the isotropic polysilicon etching apparatus is removed. At this time, by setting the etching time to about 30 seconds to 90 seconds, the bottom end portion 6 of the trench and the polysilicon 8 in the vicinity thereof can be left as the residual polysilicon 9. In addition, the first sacrificial oxide film 7 is used as a protective film for the silicon substrate 1 (inner surface of the trench) during polysilicon etching ((d) in the figure).

Next, the first sacrificial oxide film 7 is removed with hydrofluoric acid to remove the damage formed on the surface layer of the trench 2 (FIG. 7E). Next, the second thermal oxidation is performed at a low temperature of about 800 ° C. to 1000 ° C. to oxidize the residual polysilicon 9 at the bottom end portion 6 of the trench, the bottom surface 4 and the side wall surface 3 of the trench, thereby performing the second sacrificial oxidation. The film 10 is formed. Since the residual polysilicon 9 is oxidized several times faster than the silicon substrate 1, the residual polysilicon 9 is entirely oxidized in a short time and taken into the second sacrificial oxide film 10.
While the residual polysilicon 9 is being oxidized, the silicon substrate 1 on the side wall surface 3 and the bottom surface 4 is deeply oxidized, while the silicon substrate 1 at the bottom end 6 having the residual polysilicon 9 is shallowly oxidized. In this way, the interface shape between the second sacrificial oxide film 10 at the bottom end 6 of the trench and the silicon substrate 1 is
The silicon substrate 1 has a shape rounded in a concave shape toward the inside (FIG. 6 (f)).

Next, the second sacrificial oxide film 10 is removed with hydrofluoric acid or the like (FIG. 9 (g)). Next, the oxide film 11 for a capacitor is provided inside the trench 2 whose bottom end 6 is rounded in a concave shape.
Are formed ((h) in the figure). Next, the trench is filled with polysilicon (not shown) to complete the MOS capacitor.

A trench type MOS capacitor is formed by the polysilicon, the capacitor oxide film and the silicon substrate. By thus rounding the bottom end portion 6 of the trench, it is possible to prevent electric field concentration due to the shape and to prevent thinning of the capacitor oxide film 11 at this portion.
As a result, dielectric breakdown of the capacitor oxide film 11 is prevented.

FIG. 2 shows a method of manufacturing a semiconductor device according to a second embodiment of the present invention, and FIGS. 2A to 2H are sectional views showing the essential steps in the order of steps. This process drawing is a cross-sectional view of a main part of a trench type MOS capacitor. The difference from FIG. 1 is that in the step of FIG. 2E, the first sacrificial oxide film is not removed and the process proceeds to the next step. This second
In the embodiment, the same effect as that of the first embodiment can be expected.

Of course, this method can also be applied to the gate portion of a trench type MOS transistor.
In that case, as shown in FIG. 3, the well region 12,
The trench 2 is formed in the silicon substrate 1 on which the source region 13 is formed. Subsequent steps are shown in FIG.
This is the same as the step (h), and the capacitor oxide film 11 becomes the gate oxide film 14. Also in this case, the same effect as that of FIG. 1 can be obtained.

Further, the capacitor oxide film 11 and the gate oxide film 14 may be an insulating film such as a nitride film.

[0021]

According to the present invention, the bottom end of the trench is rounded by using the residual polysilicon, so that the electric field concentration due to the shape is prevented and the oxide film for the capacitor and the gate oxide film at this position are thinned. Can be easily prevented. As a result, dielectric breakdown of the capacitor oxide film and the gate oxide film is prevented.

[Brief description of drawings]

FIG. 1 is a method for manufacturing a semiconductor device according to a first embodiment of the present invention, in which (a) to (h) are process cross-sectional views of essential parts shown in the order of processes.

FIG. 2 is a sectional view showing the essential part of a method for manufacturing a semiconductor device according to a second embodiment of the present invention, in which (a) to (h) are shown in the order of steps.

FIG. 3 is a diagram showing an example in which the present invention is applied to a gate portion of a trench type MOS transistor.

FIG. 4 is a cross-sectional view of a main part of a method of manufacturing a conventional trench type MOS capacitor, in which (a) to (e) are shown in the order of steps.

5A is an enlarged view of a portion B in FIG. 4C, where FIG. 5A is a view when the side wall surface and the bottom surface intersect at a right angle, and FIG. 5B is a view when the side wall surface and the bottom surface intersect at an obtuse angle.

[Explanation of symbols]

1 Silicon substrate 2 trench 3 Side wall surface 4 bottom 5 intersections 6 bottom edge 7 First sacrificial oxide film 8 Polysilicon 9 Residual polysilicon 10 Second sacrificial oxide film 11 Insulating film for capacitors 12 well area 13 Source region (emitter region) 14 Gate oxide film

Claims (3)

[Claims] 1. A step of forming a trench in a surface layer of a semiconductor substrate, a step of forming a first sacrificial oxide film on an inner wall of the trench, a step of forming polysilicon on the first sacrificial oxide film, A step of leaving the polysilicon in the vicinity including the intersection of the bottom surface of the trench and the side wall surface and removing the polysilicon other than the intersection, a step of removing the exposed first sacrificial oxide film, and a bottom surface of the trench And the side wall surface,
Oxidizing the residual polysilicon to form a second sacrificial oxide film, removing the second sacrificial oxide film, and forming a concave roundness at the intersection, and insulating the inner wall of the trench. A method of manufacturing a semiconductor device, comprising the step of forming a film. 2. A step of forming a trench in a surface layer of a semiconductor substrate, a step of forming a first sacrificial oxide film on an inner wall of the trench, a step of forming polysilicon on the first sacrificial oxide film, A step of leaving the polysilicon in the vicinity including the intersection of the bottom surface of the trench and the side wall surface, and removing the polysilicon other than that; a bottom surface and a side wall surface of the trench in which the first sacrificial oxide film is formed; Oxidizing the residual polysilicon to form a second sacrificial oxide film, removing the second sacrificial oxide film, and forming a concave roundness at the intersection, and insulating the inner wall of the trench. A method of manufacturing a semiconductor device, comprising the step of forming a film. 3. The semiconductor device according to claim 1, wherein the insulating film is either a gate insulating film of a MOS device or an insulating film of a capacitor formed in an integrated circuit device. Production method.