JPS58142541A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To obtain a fine MOS device by eliminating the generation of bird heads at the time of selective oxidation by a method wherein an Si3N4 film is stably left only on the side surface of the aperture of an Si substrate. CONSTITUTION:An SiO2 film 22 and an Si3N4 film 23 are superposed on the P type Si substrate 21, then the films 23 and 22 are opened by applying a resist mask 24, and when the substrate 21 is slightly etching-removed, the side surface is also etching-removed. Next, an aperture 21c is vertically provided by reactive ion etching, then B ions are implanted, and accordingly a channel stopper 25 is formed. An Si3N4 film 27' is provided over the entire surface by removing the mask and covering the aperture part with a thermal oxide film 26. An Si3N4 film 27' is left on the side surface of the aperture in self-alignment by reactive ion etching. Next, an SiO2 28 is formed by selective oxidation. Since bird heads are hardly generated, and a very deep field oxide film and a channel stopper are formed by this method, a fine MOSFET which has very high density and high accuracy and does not have the effect of narrow channel can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a MO8 semiconductor device that achieves higher density, higher precision, and stabilized threshold voltage vth.

In recent years, demands for higher density MO8 semiconductor devices have been increasing, and rapid progress has been made with advances in lithography technology. However, as density increases, new phenomena that have not occurred in conventional devices, such as short channel effect and narrow channel effect, have become major problems.As the gate length becomes shorter, vth becomes smaller. Regarding the narrow channel effect, which is a phenomenon in which vth increases as the gate width becomes shorter, extensive research has been conducted, and it has been found that the best method is to increase the impurity concentration of the substrate. Various measures have been taken to prevent the short channel effect. However, analysis of the narrow channel effect has only recently begun, and the current situation is that sufficient countermeasures have not yet been taken.

The structure of a conventional MO8 semiconductor device is shown in FIG.

Reference numeral 1 designates, for example, a p-type semiconductor substrate, and 2 designates a channel stopper, which has the effect of canceling out an inversion layer generated when forming a field oxide film. 3 is a field oxide film, and 4 is a gate oxide film.

5 is a pozyst gate, 6 is a source, and 6' is a drain. 7 is CV D (Chemical) for wiring.
This is an oxide film formed by the at Vapor Deposition method, and 8 is an At wiring.

Regarding the narrow channel effect, the p-type diffusion region 2 formed as a channel stopper is also diffused in the lateral direction by heat treatment, passes through the field oxide film 3, and spreads into the channel region, so that the channel region 4! It is thought that the impurity concentration is high near the boundary with the field oxide film. When the channel width is wide, even if the impurity concentration in the channel part increases near the boundary with the field oxide film, it has almost no effect on the center of the channel, but as the channel width becomes shorter, the p-type expansion of the channel stopper increases. It is thought that the lateral intrusion of the region increases the impurity concentration not only at the end of the channel section but also at the entire channel section, thereby causing a narrow channel effect. In order to prevent the narrow channel effect, even if the channel stopper is diffused in the lateral direction, the distance between the channel stopper and the channel stopper may be set to such an extent that it does not affect the impurity concentration in the channel portion. However, normal MOS
In the process, the channel stopper and heart field oxide film are formed in a self-aligned manner using a single mask, so in order to increase the distance between the channel stopper and the field oxide film, it is necessary to align the mask once again, which reduces the process time. It will increase. Furthermore, if the field oxide film is formed deeply to separate the channel stopper and the channel part, lateral oxidation that occurs during selective oxidation, so-called bird&
The peak becomes large, which also hinders high density.

In consideration of such problems, the present invention has been developed to suppress the narrow channel effect, which cannot be avoided in conventional MO8 semiconductor devices, even though the device is made to have high density and high precision. The present invention provides a method for manufacturing a semiconductor device with a small change in .

FIG. 2 shows the method for forming an insulating separation film that we previously proposed. In the figure A, 11 is, for example, a p-type semiconductor substrate,
12 is a base oxide film, 13 is a silicon nitride film through which oxygen does not pass, and 14 is an oxide film, which are formed on the side and bottom surfaces of an opening 11' formed by etching the p-type semiconductor substrate 11. 16 is a silicon nitride film that does not allow oxygen to pass through, like 13, and is formed only on the side surfaces of the opening of the p-type semiconductor substrate from the end of the silicon nitride film 13, and is not formed on the bottom surface. When etching the p-type semiconductor substrate 11, the first step is chemical etching or isotropic dry etching to create an opening (the area indicated by 16 in the figure), and the second step is anisotropic etching. The purpose is to form an oxide film 14 and a silicon nitride film 16 after forming a predetermined amount of openings perpendicularly and faithfully to the mask pattern by a strong dry etching process. The oxide film 14 is formed by opening the p-type semiconductor substrate 116 to form the opening 11' and then thermally oxidizing the entire surface, so that no oxide film is formed on the silicon nitride film 13 and the p-type semiconductor substrate 11 can be formed only in the open portion.

In FIG. 2, the oxide film 14 is formed only in the opening of the p-type semiconductor substrate by thermal oxidation, but CV D (C
hemicat Vapor Deposition )
An oxide film may also be formed on the silicon nitride film 13 by a method. After the silicon nitride film 16 is formed on the entire surface by CVD, it is etched by highly anisotropic dry etching.
If the entire surface is etched, only the silicon nitride film 15 formed on the open bottom part of the p-type semiconductor substrate 11 and the silicon nitride film 13 will be etched, and only the silicon nitride film 16 formed on the sides of the opened part will be etched. will remain in a self-consistent manner. Like the oxide film 12, the oxide film 14 has the effect of relieving stress applied to the p-type semiconductor substrate 11.

Here, the effect of leaving the silicon nitride film 16 only on the side surface of the open portion of the p-type semiconductor substrate 11 is to prevent the lateral supply of water or oxygen, and to prevent lateral oxidation, that is, bird
's+beak should not be generated. Since water or oxygen is supplied only to the bottom of the open section, oxidation is promoted only in the longitudinal direction.

Figure 2B shows the state of selective oxidation after Figure 2A.
7 is an oxide film formed by selective oxidation. At this time, bird's beak, bird's+ he
We have experimentally confirmed that ad hardly occurs. This means that when opening the p-type semiconductor substrate 11,
This is achieved by isotropically etching as a first step and anisotropically etching as a second step, and then forming the oxide film 14 and silicon nitride film 16.

Here, the reason for the two-step etching is that when the silicon nitride film 15 is left only on the side surfaces of the open portion by dry etching the entire surface, by leaving a thick silicon nitride film near the base oxide film 12, the bird's beak
It has the effect of preventing

To explain in detail, the first step of isotropically etching the p-type semiconductor substrate 11 is to etch the silicon nitride film 1.
This is to overhang the etching layer 3.The second step of anisotropic etching is to realize microfabrication with high dimensional accuracy.After isotropic and anisotropic etching, When forming the film 14 and the silicon nitride film 16, the oxide film 14
The silicon nitride film 16 is formed under the overhanging silicon nitride film 13, that is, on the side-etched portion 16 of the p-type semiconductor substrate 11. In other words,
The silicon nitride film 16 is formed inside the overhanging end of the nitride film 13. Therefore, the base oxide film 12 is completely covered by the silicon nitride films 13 and 16. After that, when the entire surface is subjected to highly anisotropic dry etching, the silicon nitride film formed on the silicon nitride film 13 and the silicon nitride film on the bottom surface where the p-type semiconductor substrate is opened are completely etched, and the opened holes are completely etched. The upper end of the silicon nitride film formed on the side surface is also etched to some extent, but the silicon nitride film formed 9 bases inward from the overhanging end of the silicon nitride film 13 is not etched. Therefore, the base oxide film 12 remains completely covered by the silicon nitride films 13 and 16, and the base oxide film 12 remains completely covered by the silicon nitride films 13 and 16.
Since no oxygen or water is supplied through 2, the bird
's peak rarely occurs.

Through experiments, we have found that when a p-type semiconductor substrate is opened anisotropically by dry etching alone, when opened isotropically and anisotropically, which is a feature of the present invention, and when compared with the conventional method, bird's beak The difference was compared. When a 2.0 μm oxide film is formed by selective oxidation, the bird's beak is 1 when the opening is made only by dry etching.
．． 2pm, bird's head is 0.5μm
but if it opens isotropically and anisotropically, b
ird's beak /do, 3 prn, bir
d'5head has not occurred. In the conventional method, bird
'5beak is 1.6 pm, bird's he
ad is 1.0 μm. Compared to the conventional method, using the method we proposed earlier, the bird's beak
can be as small as 19q6, bird
's head has no effect at all. If the opening is formed only by anisotropic dry etching, the silicon nitride film remaining near the underlying oxide film is thin, so biτd'
sbeak is occurring.

In view of the fact that the previously proposed method is process-stable and can produce a deep insulating isolation oxide film with good yield, the present inventors formed a channel stopper directly under this deep insulating isolation oxide film. The channel portion and the channel stopper are substantially separated from each other to reduce the narrow channel effect.

Hereinafter, an embodiment of a specific manufacturing method according to the present invention will be shown in conjunction with FIGS. 3A to 3E. In FIG. 3A, 21 is, for example, a p-type semiconductor substrate, 22 is a base oxide film formed with a thickness of 100 OA, and 23 is a 10 OA formed by CVD method.
00A silicon nitride film. 24 is a resist film which has been butter-printed by the 7-otolithography method.

Using this resist film 24 as a mask, the silicon nitride film 23 is dry etched, and then the base oxide 11' and film 24 are etched to form an opening 21a.

In this state, the resist film 24 remains sufficiently. Then, using the resist film 24 as a mask, the p-type semiconductor substrate 21 is
The opening 21b is formed by chemical etching of 0.1 μm. At this time, the side etch is the same as the depth direction <0.
1 μm is generated. The etching at this time is not chemical etching, but may be dry etching or plasma etching which etches in the same direction.

Next, using the resist film 24 as a mask, the opening 21a is formed by etching vertically by reactive sputter etching or ion etching, which is highly anisotropic even when dry etching is used. The total etching amount of the p-type semiconductor substrate 21 is 0.76 μm. In this way, the opening 21c
Further, using the resist film 24 as a mask, S+ is ion-implanted through the opening of the p-type semiconductor substrate.
Forming the channel stopper 25 After that, the resist film 24 is removed, and by thermal oxidation, the channel stopper 25 is formed only in the open portion of the p-type semiconductor substrate 21, and is not formed on the silicon nitride film 23.

However, this oxide film formation method may be performed by CVD method to form the entire surface. After that, a silicon nitride film 2 is applied to the entire surface.
7 to form 1000A (FIG. 3B).

In FIG. 3C, the entire surface is etched by reactive etching or ion etching, which is highly anisotropic dry etching.

During this etching, because the anisotropy is strong, it is etched in the vertical direction, but not in the horizontal direction, so
Only the silicon nitride film 27' formed on the side surface of the opening remains in a self-aligned manner. Thereafter, selective oxidation is performed to reduce the oxide film 28 to 1.6
μm is formed. This oxidation can be reduced to 1ooo using high pressure oxidation.
Oxidation can be carried out in a short time of about 90 minutes under the conditions of ℃ and 6.5 kg/c-.

According to such a method, bird's beak
field oxidation1 with high density and high precision.
The 3-layer membrane can be formed approximately twice as deep as conventional methods (
FIG. 3D)0 FIG. 3E shows a state in which a transistor is formed by a normal MOS process after field oxidation.

29 is a gate oxide film, 30 is a potySi gate,
31 is a source, and 31' is a drain. 32 is an oxide film for wiring formed by CVD method, and 33 is At wiring.

As described above, the present invention minimizes the bird's 5beak that occurs during selective oxidation by leaving a silicon nitride film stably only on the side surfaces of the open portion of the silicon substrate, and no bird's head occurs at all. It has this effect. By preventing bird's beak to the maximum extent possible, collapse of the active region of the transistor is extremely reduced, resulting in higher density.

Contributes to high precision (bird's head
Since At does not occur at all, the silicon substrate surface is flat and At
There are no disconnections at stepped portions during wiring or short circuits due to etch residue, and the process is stable, leading to improved yields.

14"- Moreover, there is almost no bird's beak and a very deep field oxide film can be formed, so the channel
The stopper is also formed deeply. Therefore, even if the channel stopper widens due to diffusion, it does not have any effect on the channel portion, so the narrow channel effect can be prevented, and even if the channel width becomes short, the variation in vth becomes extremely small. Therefore, it becomes possible to realize a fine MoS semiconductor device with extremely high density and high precision, and without narrow channel effects. In the present invention, the isodirectional etching of the silicon substrate is 0.
．． It has also been confirmed that the same effect can be obtained even if the thickness is not limited to 1 μm, but is slightly larger or smaller.

As described above, the present invention greatly contributes to a method for manufacturing a MoS semiconductor device with high density, high precision, and no narrow channel effect, and is also of great industrial value.

[Brief explanation of drawings]

FIG. 1 is a structural cross-sectional view of a conventional MoS semiconductor device, FIG. 2 is a process cross-sectional view showing the previously proposed method for manufacturing a semiconductor device, and FIGS. 3 (8) to (6) are an embodiment of the present invention. FIG. 3 is a manufacturing process diagram of main parts of the semiconductor device according to the present invention. 2.26...Channel stopper, 16...
・・・・・・Part side-etched by isotropic etching, 14.26・・・・Oxide film, 15°27
'...Silicon nitride film remaining only on the side surface of the opening in the silicon substrate, 17.28...Field oxide film formed by selective oxidation, 11'
21 a 21 b 2 I C"": Opening by r-etching. Name of agent: Patent attorney Toshio Nakao and one other person? ? Sword 3 Figure 230

Claims (1)

[Claims] (1) A first insulating film and a second insulating film are formed on one conductivity type semiconductor region.
forming an insulating film; opening the second and first insulating films; opening the one conductivity type semiconductor region isotropically from an end of the first insulating film; opening the one-conductivity type semiconductor region deeper inside than the isotropically opened region through the region where the first insulating film is opened; and the region where the first insulating film is opened. a step of forming a one conductivity type semiconductor layer in the one conductivity type semiconductor region via the first conductivity type semiconductor region; a step of forming a third insulating film in a region opening at least the one conductivity type semiconductor region; forming a fourth insulating film only on the side surface of the second insulating film, the first and second insulating films, and a region where the one conductivity type semiconductor region is opened; and a fourth insulating film in contact with the one conductivity type semiconductor layer. A method for manufacturing a semiconductor device 0, characterized in that it comprises step 2 of oxidizing the one lightning-induced semiconductor region.