JPH05343373A - Dry etching method - Google Patents

Abstract

PURPOSE:To provide a dry etching method which can form fine patterns with low loss. CONSTITUTION:To an etching mask 14 which has resistance against reactive gas etching with a certain threshold electron application amount or less and loses the resistance against etching gas with more application, a focused electron beam 15 of this threshold electron application amount is applied. Then a sample is etched on the sample surface. Thus etching can easily proceed on a part with the focused electron beam 15 applied in advance, while a part without application serves as an etching mask until the threshold electron application amount is reached. Since sample etching is accelerated in a direction perpendicular to the surface by the electron application at this time, etching with very small width spreading in a direction parallel to the surface with respect to desired etching depth can be done on an entire sample.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for forming a fine structure of a solid, particularly a semiconductor.

[0002]

2. Description of the Related Art When processing a solid, especially a semiconductor, in a size of nanometer level, it is suitable to use a focused electron beam having both fineness and low damage. Here, as one method for performing such fine processing on gallium arsenide (GaAs), which is a compound semiconductor, conventionally, a fine structure is formed by using a focused electron beam and chlorine gas with a GaAs oxide film as an etching mask. A method of forming the same is known, and for example, Semiconductor Science and Technology (Semi)
cond. Sci. Technol. ), Vol7,
(1992) pp. There is a dry etching method as described in 160-163. This method will be described with reference to FIG. In this method, the following steps are continuously performed in vacuum. First, the surface of the GaAs growth layer 21 grown by the molecular beam crystal growth method is irradiated with light 23 by a halogen lamp in an atmosphere of oxygen gas 22 to perform GaAs oxide film 2 irradiation.
4 is formed (FIG. 2A). Next, the focused electron beam 25
The aAs oxide film 24 is irradiated to selectively modify the GaAs oxide film in the irradiated portion to deteriorate the chlorine gas etching resistance (FIG. 2B). Then modified patterned GaAs
Using the oxide film as an etching mask, chlorine gas 26
Etching of aAs21 is performed. As a result, the GaAs oxide film in the area irradiated with the focused electron beam 25 is selectively etched, and thus the GaAs in this area is also selectively etched (FIG. 2C).

[0003]

However, in the above-mentioned conventional method, since the substantial structure is formed by chlorine gas etching, the GaAs oxide film is easily formed in the lateral direction of the surface. The width of the structure becomes wider than the width of the electron beam used for the modification. Therefore, the dimensional controllability of the fine structure to be formed is poor, and the fine structure cannot be densely formed.

An object of the present invention is to collectively form a structure having a width equal to the electron beam width over a large surface area by making the etching rate in the surface vertical direction sufficiently higher than the etching rate in the surface horizontal direction. It is to provide a novel dry etching method that can be formed.

[0005]

SUMMARY OF THE INVENTION The present invention provides an etching mask on a solid surface, which has etching resistance to a reactive gas and whose reactive gas etching resistance is lowered by irradiation with electrons at a certain threshold electron dose or more. Then, the etching mask is partially irradiated with an electron beam in an amount not less than the threshold electron dose, and then a reactive gas for etching the solid and electrons are simultaneously included in the electron irradiation part. It is a dry etching method characterized by irradiating an area.

[0006]

In the present invention, the portion of the etching mask that has been previously irradiated with electrons in the amount equal to or more than the threshold electron dose is rapidly etched when the irradiation with the subsequent reactive gas is performed simultaneously. Solids are also etched. On the other hand, in this etching mask, the part which has not been subjected to electron irradiation in advance is exposed to the reactive gas until the electron dose reaches the above-mentioned threshold electron dose when the reactive gas and electrons are simultaneously irradiated. Acts as an etching mask. The structure is formed on the solid by the above two points.
At this time, since the etching of the solid is performed by both actions of electron irradiation and reactive gas, the etching rate in the vertical direction of the surface is sufficiently increased as compared with the etching rate in the horizontal direction of the surface. Therefore, it is possible to form a structure in which the width of the etching is very small with respect to the etching of the desired depth, that is, the width of the electron beam irradiated in advance is effectively reproduced.

[0007]

EXAMPLE Next, the dry etching method according to the present invention will be described with reference to FIG. 1 using GaAs as a sample and a GaAs oxide film as an etching mask. First, a GaAs sample 12 is placed in an atmosphere of oxygen gas 11 of 760 Torr, and light irradiation 13 with a halogen lamp is performed on this surface for 1 hour to obtain Ga.
An As surface oxide film 14 is formed (FIG. 1A). The GaAs oxide film thus formed has an irradiation electron dose of 2 × 10
It has a modified threshold value of 17 cm ^-2 . That is, the electron irradiation below this level has a sufficient chlorine gas etching resistance, but the chlorine gas etching resistance is lost by a large amount of electron irradiation. Then, a focused electron beam 15 with a motion energy of 10 keV is applied to this GaAs oxide film at an electron dose of 1 × 10 ¹⁸ c.
m ^- to form a radiation pattern in 2 (Figure 1 (b)). This electron dose is a value sufficient to modify the GaAs oxide film 14 to eliminate the chlorine gas etching resistance of the irradiated portion. After that, the sample is heated and kept at 60 ° C. and kept at 5 × 10 ⁻⁵ T
At the same time as being exposed to an atmosphere of chlorine gas 16 of orr, electrons 17 having a kinetic energy of 500 eV are vertically irradiated to the entire surface of the sample (FIG. 1C). Thereby, the focused electron beam 1
The portion of the GaAs oxide film which has been irradiated with 5 is selectively etched by the action of both electrons and chlorine gas, and the GaAs sample thereunder is also etched. On the other hand, the portion of the GaAs oxide film that has not been previously irradiated with the electron beam acts as an etching mask for chlorine gas up to the above-mentioned modified electron dose of 2 × 10 ¹⁷ cm ^-2 . On the other hand, when etching a GaAs sample, the etching rate in the vertical direction of the surface is sufficiently increased by the electron beam irradiation as compared with the horizontal direction of the surface. In addition, a sufficient etching depth can be secured. In addition, since the entire surface of the sample is irradiated with electrons and a large area is collectively etched, high processing productivity can be obtained.

[0008]

As described above, according to the present invention, the etching rate in the vertical direction of the surface can be made sufficiently larger than the etching rate in the horizontal direction of the surface, and a wide structure having a width equivalent to the electron beam width can be obtained. It can be formed collectively over the surface area.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an embodiment according to the method of the present invention.

FIG. 2 is a diagram illustrating a conventional method.

[Explanation of symbols]

 11 Oxygen Gas 12 GaAs Growth Layer 13 Light Irradiation 14 GaAs Oxide Film 15 Focused Electron Beam 16 Chlorine Gas 17 Electrons 21 GaAs Growth Layer 22 Oxygen Gas 23 Light Irradiation 24 GaAs Oxide Film 25 Focused Electron Beam 26 Chlorine Gas

Claims (1)

[Claims] 1. An etching mask is formed on a solid surface, which has an etching resistance to a reactive gas, and the etching resistance of which is reduced when the electron irradiation is performed at a threshold electron dose or more. , Partially irradiating the etching mask with an electron beam in an amount equal to or more than the threshold electron dose, and then simultaneously irradiating an area including the electron-irradiated portion with a reactive gas and an electron for etching the solid. Characteristic dry etching method.