JPH02132830A - Selective oxidation - Google Patents

Abstract

PURPOSE:To remove a semiconductor film without locally etching away a semiconductor substrate by a method wherein, after thermally oxidizing the semiconductor film into an oxide film, the semiconductor film is removed by removing the oxide film. CONSTITUTION:An oxide mask laminated with an SiO2 film 2, a polycrystalline Si film 3 and an Si3N4 film 5 is formed on an Si substrate 1. Next, the film 3 thermal oxidized after etching away the film 5 is perfectly oxidized and then the surface of the substrate 1 is sacrifice-oxidized to form SiO2 films 7, 8. Furthermore, the SiO2 films 7, 8 are etched away using a fluorine base etchant to expose the surface of the substrate 1. Then, a gate SiO2 film 9 is formed on the surface of the exposed substrate 1 by thermal oxidation. Through these procedures, the semiconductor film 3 can be removed without locally etching away the substrate 1 by thermal oxidizing the film 3 to be changed into the film 7 which is to be etched away later.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a selective oxidation method, and in particular, to isolation between elements in a semiconductor integrated circuit device with high integration density. , a step of forming an oxide mask on a semiconductor substrate in which at least a semiconductor oxide film, a semiconductor film, and an oxidation-resistant film are sequentially laminated; a step of selectively oxidizing the semiconductor substrate using the oxide mask; and a step of selectively oxidizing the semiconductor substrate using the oxide mask; oxidizing the surfaces of the semiconductor layer and the semiconductor substrate; and removing the oxide film formed by oxidizing the surfaces of the semiconductor layer and the semiconductor substrate and the semiconductor oxide film. It is equipped with a process.

Thereby, the semiconductor film constituting the oxidation mask can be removed without causing local etching of the semiconductor substrate.

[Conventional technology]

2. Description of the Related Art Interelement isolation regions in semiconductor integrated circuit devices are usually formed by a selective oxidation method (LOCOS method). However, as is well known, follow? In the LOCOS method, the length of the bird's beak formed at the end of the field oxide film is large, which is a factor that prevents high integration density.

Therefore, a technique for forming a field oxide film with a smaller bird's beak length has been proposed (for example, JP-A-61
-74350 and Japanese Patent Application No. 63-220209)
.

FIGS. 2A to 2F show one method, in which St. N. The lower layer of the film is polycrystalline silicon (Si).
) selective oxidation is performed using an oxidation mask with a multi-N structure including a film. According to this method, as shown in FIG. 2A, the surface of the St substrate 101 is first coated with a film of, for example, a Sin. Membrane (Pad Sift membrane) 10
2, a polycrystalline Si film 103 having a thickness of, for example, about 500 wafers is formed on the entire surface of the StO2 film 102 by, for example, the CVD method. Next, a Sing film 1 having a thickness of about 80 mm is formed on the surface of the polycrystalline St film 103 by thermal oxidation.
After forming the SiO2 film 104, a SiO2 film 104 with a thickness of about 1,000 layers is formed on the entire surface of the SiO2 film 104 by, for example, the CVD method.
4 films 105 are formed. After this, these Si3N4 films 105, Sin. The film 104 and the polycrystalline St film 103 are patterned into a predetermined shape by etching as shown in FIG.
Shape as shown in .

Next, thermal oxidation is performed in this state. As a result, as shown in FIG. 2B, a field S is formed on the surface of the Si-based temporary 101.
in. A film 106 is selectively formed to provide isolation between devices. During this thermal oxidation, the polycrystalline Si film 103 below both ends of the Si3N4 film 105 is also oxidized, so that the field Sin. The length of the bird's beak formed at the end of the membrane 106 can be reduced.

Next, Si. N. The film 105 and the Si02 film 104 are removed by etching to obtain the state shown in FIG. 2C.

Next, the polycrystalline Si film 1o3 is removed by dry etching to obtain the state shown in FIG. 2D.

Next, the SiO2 film 102 is removed by etching to expose the surface of the Si substrate 101 as shown in FIG. 2E.

? Next, a SiO2 film 107 is formed on the exposed surface of the Si substrate 101 by performing pre-oxidation (sacrificial oxidation) for the purpose of improving gate breakdown voltage. Next, this S i O
After removing the T film 107 by etching, thermal oxidation (gate oxidation) is performed again to form the gate Sin. A film (not shown) is formed. After this, the process proceeds according to the manufacturing process of the target semiconductor integrated circuit device. [Problems to be Solved by the Invention] According to the findings of the present inventors, in the methods shown in FIGS. 2A to 2F, distortion occurs in the polycrystalline Si film 104 due to stress during thermal oxidation. A minute hole is formed in this polycrystalline St film lO4. Therefore, when removing this polycrystalline Si film 104 by dry etching, this polycrystalline Si film 104
There was a problem in that the St substrate 101 was locally etched through the minute hole No. 4, causing inconvenience in the subsequent process. Therefore, an object of the present invention is to provide a selective oxidation method that can remove a semiconductor film forming an oxidation mask without causing local etching of a semiconductor substrate.

[Means to solve the problem]

In order to solve the above problems, the selective oxidation method according to the present invention provides an oxidation mask in which at least a semiconductor oxide film (2), a semiconductor # (3), and an oxidation-resistant film (5) are sequentially laminated on a semiconductor substrate (1). ), a step of selectively oxidizing the semiconductor substrate (1) using an oxidation mask, and a step of selectively oxidizing the semiconductor substrate (1) using an oxidation mask;
), a step of oxidizing the surfaces of the semiconductor ff (3) and the semiconductor substrate (1), and an oxide film ( 7.8) and a step of removing the semiconductor oxide film (2).

[Effect]

According to the above-mentioned means, the semiconductor film (3) is removed by converting the semiconductor film (3) into oxidized 1fi (7) by oxidation and then removing this oxide film (7).
This eliminates the problem of the semiconductor substrate (1) being locally etched, which occurs when the semiconductor film (3) is removed by dry etching. That is, the semiconductor film (3) can be etched without causing local etching of the semiconductor substrate (1).
can be removed. ? Embodiment] An embodiment of the present invention will be described below with reference to the drawings. 1A to 1E show an embodiment of the present invention. In this embodiment, the selective oxidation is completed by proceeding with the same steps as shown in FIGS. 2A and 2B. Figure 1A shows this situation. In FIG. 1A, numeral 1 is an Sl substrate, numeral 2 is an SiO2 film, numeral 3 is a polycrystalline St film, and numeral 4 is a Si substrate.
Oz film, code 5 is Si3N4 film, code 6 is field S
An iOz film is shown.

Next, Si3N. The film 5 is etched away using, for example, hot phosphoric acid to obtain the state shown in FIG. 1B. ．． Next, by performing thermal oxidation in this state, polycrystalline Si
The film 3 is completely oxidized, and then the surface of the Si substrate 1 is oxidized to perform sacrificial oxidation. Reference numeral 7 indicates a Sift film formed by oxidizing the polycrystalline St film 3. This Sin! Membrane 7
The film thickness is approximately 1.5 times the thickness of the polycrystalline Si film 3. Further, reference numeral 8 indicates a SiO2 film formed by oxidizing the surface of the Si substrate 1. The thickness of this Sing film 8 is, for example, about several hundred.

Next, these SiOt films 7, 2.8 are removed by etching using, for example, a hydrofluoric acid-based etching solution to expose the surface of the Si substrate 1 as shown in FIG. 1D. Note that during this etching, the field Sin. Although the film 6 is also etched and its thickness is reduced, this is not a problem in practice.

Next, a gate Sing film 9 is formed on the exposed surface of the St substrate 1 by thermal oxidation.

After this, the steps are performed according to, for example, a MOSLSI manufacturing process.

As described above, according to this embodiment, after the polycrystalline Si film 3 is thermally oxidized to change into the Si02 film 7, this SiO2 film 7 is removed by etching, so the polycrystalline Si film 3 is dry etched. As in the case of the prior art, Si
This completely solves the problem of local etching of the base l. Moreover, since the polycrystalline St film 3 can be oxidized simultaneously with the sacrificial oxidation, there is no increase in the number of steps.

Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments, and various modifications can be made based on the technical idea of the present invention.

For example, the present invention is applicable not only to the manufacture of MOSLSI, but also to
It can also be applied to the manufacture of bibolar CMOS LSIs and bibolar LSIs.

[Brief explanation of the drawing]

1A to 1E are sectional views for explaining an embodiment of the present invention in the order of steps, and FIGS. 2A to 2F are sectional views for explaining the conventional selective oxidation method in the order of steps. It is. Explanation of main symbols in the drawings 1: Si substrate, 2, 4, 7.8: SiOz film, 3:
Polycrystalline St film, 6: Field Sin2 film, 9: Gate Sing film.

Claims (1)

[Claims] A step of forming on a semiconductor substrate an oxidation mask in which at least a semiconductor oxide film, a semiconductor film, and an oxidation-resistant film are sequentially laminated, and selectively oxidizing the semiconductor substrate using the oxidation mask. a step of removing the oxidation-resistant film; a step of oxidizing the surfaces of the semiconductor layer and the semiconductor substrate; and an oxide film formed by oxidizing the surfaces of the semiconductor layer and the semiconductor substrate and the semiconductor. A selective oxidation method comprising the step of removing an oxide film.