JPS5982749A - Selective oxidation of semiconductor - Google Patents

Abstract

PURPOSE:To shorten length of the slant part of an oxide film, and to contrive to enhance the degree of integration of an element by a method wherein an insulating film not to be etched by an oxide film etching agent is formed by selfalignment with the oxide film on the surface of the oxide film thereof. CONSTITUTION:Underlay oxide films 2, nitride films 3 and oxide films 7 of thick film thickness to be used as space films for lifting off are formed selectively in order on the parts other than the part to be formed with an oxide film of the main surface part of a silicon substrate 1. Then a heat treatment is performed using the nitride films 3 as masks to form a thick oxide film 4 on the exposing main surface part of the substrate 1. Then nitride films 8 are formed on the whole upper surfaces of the oxide film 4 and the oxide films 7, and moreover polycrystalline silicon films 9 are formed on the surfaces of the nitride films 8. Then by lifting off the oxide films 7, the parts other than the part on the surface of the oxide film 4 of the nitride films 8 and the polycrystalline silicon films 9 are removed together with the oxide films 7. The nitride films 3 are removed protecting the nitride film 8 with the polycrystalline silicon film 9, then the polycrystalline silicon film 9 is removed, and the underlay oxide films 2 are removed finally to leave the nitride film 8 on the surface of the oxide film 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an improvement in a selective oxidation method in a manufacturing method for semiconductor integrated circuit devices (:tC) and the like.

[Prior art]

Hereinafter, a method for selectively forming a silicon oxide film on the main surface of a silicon substrate will be described as an example.

FIGS. 1(A) to 1(0) are cross-sectional views showing the main stages of an example of a conventional selective oxidation method.

First, as shown in FIG. 1(A), a silicon substrate fi+
An underlying oxide film (2) and a silicon nitride film (hereinafter referred to as "nitride film") (3) are formed on the main surface of the silicon oxide film (hereinafter referred to as "oxide film") on the parts other than those where the silicon oxide film (hereinafter referred to as "oxide film") is to be formed. They are selectively formed so as to sequentially overlap each other. Next, as shown in FIG. 1(B), heat treatment is performed in a high temperature oxidizing atmosphere using the nitride film (3) as a mask, and the silicon substrate f
A thick oxide film (4) is formed by oxidizing the exposed main surface portion of tl to a required thickness. At this time, a thin oxide film (5) is formed on the surface of the nitride film (3). Thereafter, as shown in FIG. 1(C), an oxide film (5) and a nitride film (
3) and the underlying oxide film (2) are sequentially removed by etching, and the work of this conventional example is completed. Note that the oxide film (51
When the underlying oxide film (2) is removed by etching, the thick oxide film (4) is also etched.

In such a conventional method, in the oxidation stage shown in FIG. 1(B), the thickness gradually decreases from the end surface of the nitride film (3) to the bottom of the oxide film (4). A sloped portion (6) is formed which becomes thinner. The length of this inclined portion (6) poses a problem when miniaturizing elements. In other words, if the oxide film (4) perfectly follows the scaling law when miniaturizing elements, the ratio of the size of the element after miniaturization to the size of the element before miniaturization is the same. If the thickness of the oxide film (4) is reduced by a certain proportion, the length of the slope part (6) will also be shortened by this proportion.

However, due to the etching during the removal of the oxide film (5) and the underlying oxide film (2) in the etching step shown in FIG. At the same time, the oxide film (4) is etched. At this time, since it is necessary to make the etching time extra long in order to eliminate any etching residue such as the underlying oxide film (2), an extra amount of the oxide film (4) is also etched. Moreover, since the extra etching amount of this oxide film (4) does not decrease as expected from scaling, the thickness of the oxide film (4) is scaled by an extra thickness corresponding to this extra etching amount. Do I need to make it thicker than the thickness that follows? Along with this, the length of the inclined portion (6) also increases by a portion corresponding to the portion where the oxide film (4) is made extra thick. As a result, when miniaturizing the device, the proportion of unnecessary portions occupied by the inclined portion (6) increases, making it difficult to improve the degree of integration of the device.

[Summary of the invention]

This invention was made to improve the above-mentioned drawbacks, and when an oxide film is selectively formed on the surface of the oxide film, it is not etched by the oxide film etching agent in self-alignment with the oxide film. so that an insulating film is formed,
By using this insulating film to prevent the oxide film from being excessively etched when removing unnecessary oxide films other than the oxide film, the thickness of the oxide film can be kept within the thickness that conforms to scaling. Accordingly, the present invention provides a method for selectively oxidizing a semiconductor in which the length of the sloped portion of the oxide film is not shortened, and the degree of integration of the device can be improved.

[Embodiments of the invention]

FIGS. 2A to 2E are cross-sectional views showing the state of the main stage of the selective oxidation method according to an embodiment of the present invention.

In the figure, the same reference numerals as those in the conventional example shown in FIG. 1 indicate equivalent parts.

First, as shown in FIG. 2(A), a silicon substrate fi+
An underlying oxide film (2), a nitride film (3), and a thick oxide film (7) serving as a lift-off space film are sequentially selectively formed on the main surface of the main surface other than the part where the oxide film is to be formed. Form. Next, as shown in FIG. 2(B), a nitride film (3
) is used as a mask to perform heat treatment in a high-temperature oxidizing atmosphere to oxidize the exposed main surface of the silicon substrate (11) to a required thickness to form a thick oxide film (4).

Next, as shown in FIG. 2(0), a nitride film (8) is formed on the entire upper surface of the oxide film (4) and the oxide film (7), and a polycrystalline film is further formed on the surface of the nitride film (8). A silicon film (9) is formed. Next, as shown in FIG. 2(D), an oxide film (7) is formed.
By lifting-on, the portions of the nitride film (8) and the polycrystalline silicon film (9) other than those on the surface of the oxide film (4) are removed together with the oxide film (7). Next, the second
As shown in Figure (E), first, the polycrystalline silicon film (9)
to protect the nitride film (8) and remove the nitride film (3), then remove the polycrystalline silicon film (9), and finally remove the underlying oxide film (2) to remove the surface of the oxide film (4). Nitride film on top (8)
, the work of this embodiment is completed.

In the method of this embodiment, in the oxidation stage shown in FIG. 2(B), the nitride film (3) is pressed against the thick oxide film (7), so that The oxidation of the part under the nitride film (3) is suppressed, and the oxide film (4)
The length of the inclined portion (6) is shortened. Moreover, Fig. 2 (
In the step shown in step 0), a nitride film (8) is formed on the surface of the oxide film (4), so this nitride film (8) prevents the oxide film (4) from being removed during the removal of the unnecessary oxide film in the subsequent step.
) can be protected from being etched.

Therefore, as in the conventional example shown in FIG.
Since there is no need to allow for a reduction in the thickness of the oxide film (4) due to extra etching, the thickness of the oxide film (4) can be kept within the thickness that follows the scaling law.
The length of the inclined portion (6) is also shorter than that of the conventional example, and the degree of integration of the device can be improved.

In this example, the nitride film (8) is used to protect the oxide film (4) from etching, but it does not necessarily have to be a nitride film, and may be an aluminum oxide film, for example, which is not etched by the oxide film etching agent. Other insulating films such as tantalum oxide films may also be used. In addition, in this example, an oxide film (7) was used as the lift-off space film, but this does not necessarily have to be an oxide film, but is made of a material that can withstand the oxidation temperature of silicon and is different from the etching agent for nitride films. Other lift-off spacing films may be used, such as aluminum oxide films that are etched with an etchant. 1. In this example, a silicon substrate ftl was used, but this does not necessarily have to be a silicon substrate, and an epitaxially grown silicon layer,
It may be a p-type silicon well, an n-type silicon well, an SOS silicon island, a laser recrystallized silicon layer, a polycrystalline silicon layer, or the like. These will be referred to as silicon substrates in the claims. Further, in this embodiment, the underlying oxide film (2) is used, but this is not necessarily essential and may be omitted.

〔Effect of the invention〕

As described above, according to the present invention, when forming a silicon oxide film on a required portion of the main surface of a silicon substrate, the oxide film is formed on the surface of the silicon oxide film in a self-aligned manner with the silicon oxide film. An insulating film that is not etched by a silicon film etching agent is formed, and this insulating film can protect the silicon oxide film from being etched during removal of the unnecessary silicon oxide film outside the disposed silicon substrate. Therefore, since there is no need to allow for a reduction in the thickness of the silicon oxide film due to extra etching, the thickness of the silicon oxide film can be kept within the thickness that follows the scaling law, and along with this, the silicon oxide film The length of the sloped portion of the film is also shortened, and the degree of integration of the device can be improved as shown in FIG.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the main stages of an example of a conventional selective oxidation method, and FIG. 2 is a sectional view showing the main stages of an embodiment of the present invention. In the figure, (1) is a silicon substrate (silicon base)
, (:ll is a silicon nitride film, (4) is a silicon oxide film, (6) is a sloped part, (7) is a silicon oxide film which is a space film for lift-off, (8) is a silicon nitride film (insulating film), (9) is a polycrystalline silicon film. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] il) A silicon nitride film on the main surface of the silicon substrate other than the part where the silicon oxide film is to be formed and is etched with an etching agent different from the etching agent for the silicon nitride film, which is made of a material that can withstand the oxidation temperature of silicon. A first step of sequentially and selectively forming lift-off space films, a heat treatment is performed in an oxidizing atmosphere using the silicon nitride film as a mask to oxidize the exposed main surface of the silicon substrate to a desired thickness to form a silicon oxide film. a third step of sequentially forming an insulating film and a polycrystalline silicon film that are not etched by the etching agent for the silicon oxide film on the entire upper surface of the silicon oxide film and the space film for lift-off; a fourth step of removing portions of the insulating film and the polycrystalline silicon film other than the portions on the surface of the silicon oxide film together with the lift-off space film by lifting off the silicon nitride film; A method for selectively oxidizing a semiconductor, comprising a fifth step of sequentially removing a polycrystalline silicon film.