JPH047875A - Manufacture of semiconductor element - Google Patents

Abstract

PURPOSE:To prevent a semiconductor substrate from turning to a recessed shape, and prevent the fluctuation of impurity distribution, by selectively thermally oxidizing a polycrystalline semiconductor film on an active region by using a nitride film as a mask. CONSTITUTION:A first oxide film 2, a polycrystalline semiconductor film 3 and a nitride film 4 are grown and laminated on the surface of a substrate 1; the nitride film 4 is selectively eliminated; impurities for channel doping are implanted by using the nitride film 4 as a mask, and a channel region 5 is formed; the polycrystalline silicon film 3 in the active region 5 is thermally oxidized, and a second thick oxide film 6 is formed; the nitride film 4 and the polycrystalline semiconductor film 3 are eliminated; boron is implanted in the substrate 1 of a channel stopper forming region by using the second oxide film 6 as a mask, and a channel stopper 7 is formed; the oxide films 2, 6 on the surface are eliminated; a gate oxide film 8 of the active region is formed by thermal oxidation; an electrode 9 is formed. Thereby the semiconductor substrate is prevented from turning to a recessed shape, and the problem of impurity distribution fluctuation can be evaded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing a MOS type semiconductor device, and particularly to a method of manufacturing a MOS type semiconductor device for suppressing narrow channel effects.

rPrior Art] In realizing a high-density semiconductor integrated circuit, a problem called a narrow channel effect arises as elements become finer.

The narrow channel effect is a phenomenon in which the threshold voltage increases as the channel width of a transistor becomes narrower. For this reason, there are disadvantages such as having to apply a voltage higher than necessary to drive the element or not being able to flow a sufficient current.

Another disadvantage is that the charge transfer element cannot handle sufficient signal charges.

As a manufacturing method for suppressing the narrow channel effect, a technique called the reverse LOCO5 method is conventionally known (see Japanese Patent Application No. 58-2 No. 4545, or Technical Report ED942.1986 of the Television Society of Japan).

Figure 3 Ca) to (e) show the conventional manufacturing method of reverse LO.
1 shows a cross section of a MOS type semiconductor device in the main steps of the CO5 method. In this example, a P-type semiconductor substrate is used.

In the reverse LOCO5 method, first, a P-type semiconductor substrate l is thermally oxidized to form an oxide film 22, and then a nitride film 4 is grown (FIG. 3(a)). Next, the nitride film 4 in a region that will become an active region in the future is selectively removed, and impurities for channel doping are implanted using the nitride film as a mask if necessary. In this example, phosphorus is implanted to form an N-type channel region 5 (FIG. 3(b)). After that, thermal oxidation is performed to form the oxide film 2.
6 (Fig. 3(C)).

Next, the nitride film 4 is removed, and boron is implanted using the oxide film 26 as a mask to form a channel stopper 7 (see FIG. 3). Thereafter, the oxide film on the surface is removed, thermal oxidation is performed again to form a gate oxide film 8, and then an electrode 9 is formed to produce a device (FIG. 3(e)).

According to the reverse LOCO5 method explained above, as shown in FIG. 3(c), when performing selective thermal oxidation using the nitride film as a mask, oxidation progresses from the edge of the nitride film to the bottom of the nitride film. The bird's beak generated in the channel extends from the active region toward the channel stopper. For this reason, the actual width of the active region indicated by LA in Figure 3 is wider than the width originally defined by the photomask shown in Figure 3 (B), which reduces the channel width due to the bird's beak. This can be prevented and the narrow channel effect can be reduced even when the device is miniaturized.

[Problem to be solved by the invention]

However, in the reverse LOCOS method, as shown in FIG. 3(c), it is necessary to thermally oxidize a region that will become an active region in the future to form an oxide film 26 that is large enough to serve as a mask for boron implantation for a channel stopper. . Therefore, the N-type channel region 5 into which channel doping impurities have already been implanted is reduced, resulting in a concave shape. Further, there has been a problem in that the impurity distribution in the channel region 5 fluctuates due to the movement of impurities into the oxide film due to thermal oxidation.

Also, when implanting impurities for channel doping,
Although a nitride film is used as a mask, there is a limit to the thickness of the nitride film that can be grown in practical soil, so there is a drawback that impurities for channel doping cannot be implanted with high energy.

An object of the present invention is to provide a method for manufacturing a semiconductor device that eliminates such conventional drawbacks.

[Means for Solving the Problem] In order to achieve the above object, the method for manufacturing a semiconductor device according to the present invention includes a first oxide film forming step, a polycrystalline semiconductor film/nitride film forming step, and a second step. oxide film formation step,
A method for manufacturing a semiconductor device having an active region defined by a channel stopper in a semiconductor substrate of one conductivity type, including an impurity implantation step and an electrode formation step, wherein the first oxide film formation step includes the step of forming an electrode. This is a step of forming a first oxide film on the surface of a semiconductor substrate by thermally oxidizing the surface of the substrate, and the step of forming a polycrystalline semiconductor film/nitride film is a step of forming a first oxide film on the surface of the semiconductor substrate by thermally oxidizing the surface of the substrate. The second oxide film forming step is a step of laminating a crystalline semiconductor film and a nitride film, and the second oxide film forming step is to thermally oxidize the polycrystalline semiconductor film in the active region from which the nitride film has been removed to form a layer on the active region of the substrate. The impurity implantation step includes implanting impurities into a channel stopper formation region of the substrate from which the polycrystalline semiconductor film and the nitride film have been removed, using the second oxide film as a mask. and forming a channel stopper in the channel forming region, and in the electrode forming step, thermal oxidation is again performed on the surface of the substrate from which the first and second oxide films have been removed to remove the gate oxide film in the active region. This is the step of forming the electrode and forming the electrode.

Furthermore, in the method for manufacturing a semiconductor device according to the present invention,
A first oxide film formation step, a polycrystalline semiconductor film/nitride film/mask oxide film formation step, a first impurity implantation step, and a second impurity implantation step.
A method for manufacturing a semiconductor element having an active region defined by a channel stopper in a conductive type semiconductor substrate, the method comprising the steps of forming an oxide film, a second impurity implantation step, and an electrode formation step, the method comprising: The first oxide film forming step is a step of forming a first oxide film on the surface of the semiconductor substrate by thermally oxidizing the surface of the substrate.

The polycrystalline semiconductor film/nitride film/mask oxide film forming step is a step of forming a polycrystalline semiconductor film, a nitride film, and a mask oxide film on the first oxide film, and the first impurity implantation step is a step of forming a channel region by implanting impurities into the substrate in the active region from which the nitride film and mask oxide film have been removed, using the nitride film and mask oxide film as a mask, and the second oxide film forming step is a step of removing a mask oxide film in a channel stopper formation region and then thermally oxidizing the polycrystalline semiconductor film on an active region to form a second oxide film, and the second impurity implantation step is: a step of implanting impurities into a channel stopper formation region of the substrate from which the polycrystalline semiconductor film and the nitride film have been removed, using the second oxide film as a mask, to form a channel stopper in the channel formation region; forming the electrode; The step is to perform thermal oxidation again on the surface of the substrate from which the first and second oxide films have been removed to form a gate oxide film in the active region and to form an electrode.

[Operation] According to the first invention of the present application, the active region is not directly oxidized because the polycrystalline semiconductor film on the active region is selectively thermally oxidized using the nitride film as a mask. Therefore,
The semiconductor substrate does not have a concave shape, and the problem of fluctuations in impurity distribution can also be avoided. Furthermore, during this thermal oxidation treatment, the bird's beak extends from the active region toward the channel stopper, so it is possible to prevent the channel width from decreasing due to the bird's beak, and even when the device is miniaturized, the narrow channel effect can be reduced.

According to the second invention of the present application, since the nitride film and the mask oxide film serve as masks when implanting impurities for channel doping, the energy is higher than in the conventional method in which only the nitride film is used as a mask. Impurity for channel doping can be implanted 7 [Example] Next, an example of the present invention will be described with reference to the drawings.

(Embodiment 1) FIG. 1 is a diagram for explaining Embodiment 1 of the present invention.
A cross section of the device in main steps when applied to manufacturing an S-type semiconductor device is shown. In this example, a P-type semiconductor substrate is used.

In the figure, in this embodiment, the surface of a P-type semiconductor substrate 1 is first thermally oxidized, a first oxide film 2 is formed on the surface of the substrate 1, and a polycrystalline semiconductor film 3 is formed on the first oxide film 2. Then, the nitride film 4 in a region that will become an active region in the future is selectively removed, and if necessary, the active region from which the nitride film 4 is removed is A channel region (active region) 5 is formed on the substrate 1 in the region by implanting impurities for channel doping using the nitride film 4 existing outside the remaining active region as a mask. In this example, phosphorus is implanted to form an N-type channel region 5 (FIG. 1(g)). Thereafter, the polycrystalline semiconductor film 3 in the active region exposed by removing the nitride film 4 is thermally oxidized to form a thick second oxide film 6 (FIG. 1(C)). Next, future channel stopper 7
The nitride film 4 and the polycrystalline semiconductor film 3 in the region where the channel stopper is formed (the channel stopper formation region adjacent to the N-type channel region 5) are removed, and the substrate 1 in the channel stopper formation region is removed using the second oxide film 6 as a mask. Next, boron is implanted to form channel stoppers 7 on both sides of the N-type channel region 5 (FIG. 1(6)). After that, the oxide films 2 and 6 on the surface extending over the N-type channel region 5 and channel stopper 7 of the substrate 1 are removed, and the surface is thermally oxidized again to form a gate oxide film 8 in the active region. 9 to create an element (Fig. 1(e)).

Unlike the conventional reverse LOCO5 method, as shown in FIG. 1(c), the polycrystalline semiconductor film 3 is thermally oxidized to form a second oxide film 6.
When forming the channel region 5, which will become an active region in the future, since the polycrystalline semiconductor film 3 exists on that region, it is not directly oxidized, and the surface of the semiconductor substrate 1 is not directly oxidized as shown in FIG. 3(c). Unlike the conventional example, it does not have a concave shape, and the problem of fluctuations in impurity distribution can also be avoided. Furthermore, during this thermal oxidation, reduction in channel width due to bird's beak can be prevented, and narrow channel effects can be reduced even when devices are miniaturized.

(Example 2) Figures 2(a) to (→ are diagrams for explaining Example 2 of the present invention, showing device cross sections in main steps when applied to manufacturing a MOS type semiconductor device. In this example, a P-type semiconductor substrate is used.

In the figure, in this embodiment, first, the surface of a P-type semiconductor substrate 1 is thermally oxidized, a first oxide film 2 is formed on the surface of the substrate l, and a polycrystalline semiconductor film 3 is formed on the first oxide film 2. A nitride film 4 and a mask oxide film 11 are sequentially laminated (FIG. 20)).

Next, the nitride film 4 and mask oxide film 11 in a region that will become an active region in the future are selectively removed, and the nitride film 4 and mask oxide film 11 are placed on the substrate 1 in the active region from which the nitride film 4 and mask oxide film 11 have been removed. A channel region (active region) 5 is formed by implanting impurities for channel doping using the existing nitride film 4 and mask oxide film 11 as masks. In this example, phosphorus is implanted to form an N-type channel region 5 (second
Figure (b)). Thereafter, the mask oxide film 11 on the channel stopper formation region adjacent to both sides of the channel region 5 is removed, and the polycrystalline semiconductor film 3 on the active region is thermally oxidized to form a thick second oxide film 6. (Figure 2 (C)). Next, the nitride film 4 and polycrystalline semiconductor film 3 on the channel stopper formation region are removed, and boron is implanted using the second oxide film 6 as a mask to form the channel stopper 7 (FIG. 2(c)).
). After that, the oxide films 2 and 6 on the surface of the substrate 1 are removed, and the surface of the substrate 1 is thermally oxidized again to form the gate oxide film 8, and then the electrodes 9 are formed to create the device.
Figure (e)).

Unlike the conventional reverse LOCO5 method, as shown in FIG. 2(b), when implanting impurities for channel doping, the nitride film 4 and mask oxide film 1j serve as a mask.
Impurities for channel doping can be implanted at high energy. Furthermore, in this example, as in Example 1, when the polycrystalline semiconductor film 3 is thermally oxidized to form the second oxide film 6, as shown in FIG. Since the channel region 5 is not directly oxidized, the semiconductor substrate does not have a concave shape, and the problem of fluctuations in impurity distribution can also be avoided. Furthermore, during this thermal oxidation, the bird's beak extends from the active region to the channel stopper side, so it is possible to prevent the channel width from decreasing due to the bird's beak, and even when the device is miniaturized, the narrow channel effect can be reduced.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to prevent the channel width from decreasing due to bird's beak, and even when devices are miniaturized, the narrow channel effect can be reduced, and at the same time, the semiconductor substrate does not have a concave shape. , it is also possible to avoid the problem of fluctuations in impurity distribution. A further advantage is that impurities for channel doping can be implanted at high energy.

[Brief explanation of the drawing]

1(a)-(e) are diagrams for explaining Embodiment 1 of the present invention, and are sectional views of the device in main steps when applied to manufacturing an MO5 type semiconductor device, and FIG. 2(a)-(e). (e) is a diagram for explaining Embodiment 2 of the present invention, and is a cross-sectional view of the device in main steps when applied to manufacturing an MO5 type semiconductor device. 1 is a cross-sectional view of an MO3 type semiconductor device in the main steps of the reverse LOCOS method. 1... P-type semiconductor substrate 3... Polycrystalline semiconductor film 5... N-type channel region 7... Channel stopper 9... Electrode 22, 26... Oxide film 2... First Oxide film 4...Nitride film 6...Second oxide film 8...Gate oxide film 11...Mask oxide film

Claims (2)

[Claims] (1) A semiconductor substrate of one conductivity type, including a first oxide film formation step, a polycrystalline semiconductor film/nitride film formation step, a second oxide film formation step, an impurity implantation step, and an electrode formation step. A method for manufacturing a semiconductor device having an active region defined by a channel stopper in the first oxide film forming step, the step of forming a first oxide film on the surface of the semiconductor substrate by thermally oxidizing the surface of the semiconductor substrate. The polycrystalline semiconductor film/nitride film forming step is a step of forming a polycrystalline semiconductor film and a nitride film in layers on the first oxide film, and the second The oxide film forming step is a step of thermally oxidizing the polycrystalline semiconductor film in the active region from which the nitride film has been removed to form a second oxide film on the active region of the substrate, and the impurity implanting step is a step of forming a second oxide film on the active region of the substrate. , a step of implanting an impurity into a channel stopper formation region of the substrate from which the polycrystalline semiconductor film and the nitride film have been removed, using the second oxide film as a mask to form a channel stopper in the channel formation region; A semiconductor characterized in that the forming step is a step of again performing thermal oxidation on the surface of the substrate from which the first and second oxide films have been removed to form a gate oxide film in the active region and forming an electrode. Method of manufacturing elements. (2) First oxide film formation step, polycrystalline semiconductor film/nitride film/mask oxide film formation step, first impurity implantation step, second oxide film formation step, and second impurity implantation step and,
A method for manufacturing a semiconductor element having an active region defined by a channel stopper in a semiconductor substrate of one conductivity type, the method comprising: forming an electrode, the first oxide film forming step forming a surface of the semiconductor substrate; This is a step of forming a first oxide film on the surface of the substrate by thermal oxidation, and the step of forming a polycrystalline semiconductor film/nitride film/mask oxide film is a step of forming a first oxide film on the first oxide film. The first impurity implantation step is a step of forming a crystalline semiconductor film, a nitride film, and a mask oxide film, and the first impurity implantation step is performed by using the nitride film and the mask oxide film as a mask to implant the active region from which the nitride film and the mask oxide film have been removed. This is a step of forming a channel region by implanting impurities into the substrate, and in the second oxide film forming step, after removing the mask oxide film in the channel stopper formation region, the polycrystalline semiconductor film on the active region is heated. The step is to oxidize to form a second oxide film, and the second impurity implantation step is to apply the second oxide film to a channel stopper formation region of the substrate from which the polycrystalline semiconductor film and the nitride film have been removed. This step is a step of implanting impurities as a mask to form a channel stopper in the channel forming region, and the electrode forming step is to thermally oxidize the surface of the substrate from which the first and second oxide films have been removed again to activate it. 1. A method of manufacturing a semiconductor device, comprising a step of forming a gate oxide film in a region and forming an electrode.