JPH06342777A - Dry etching method of compound semiconductor - Google Patents

Abstract

PURPOSE:To solve troubles in an in-situ electron beam patterning method wherein a compound semiconductor of GaAs or the like is patterned with a semiconductor epitaxial layer as an etching mask, wherein the troubles are that patterns vary in pattern width when they are formed. CONSTITUTION:A double mask of GaAs/InGaAs 12 is formed on a GaAs 11 serving as a work material. Then, an upper GaAs mask 13 is irradiated with an EB 19 and chlorine gas 18 at the same time to be etched thicker than a InGaAs mask 12 to provide a recess. The recess is transferred to the InGaAs mask 12 by a reactive ion beam etching process wherein chlorine radicals and ions are used. Then, only a part of GaAs 11 serving as a work material where the InGaAs mask is removed is etched as irradiated with an electron beam in showers in an atmosphere of chlorine gas.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fine structure forming technique for a compound semiconductor by a low damage dry etching method.

[0002]

2. Description of the Related Art In order to form a nanometer-sized fine structure such as a quantum wire of a compound semiconductor by processing, in order to avoid surface contamination due to exposure to the atmosphere, a grown compound semiconductor sample is processed in vacuum as it is, so-called vacuum. It is important to have a consistent process. Further, in the processing at this time, it is effective to use a focused electron beam having both fineness and low damage.

Compound semiconductor gallium arsenide (GaA)
As a method for performing such fine processing on s),
There is a method of forming a fine structure using a focused electron beam and chlorine gas, using a GaAs oxide film as an etching mask.
For example, Semiconductor Science and Technology (Semicond.Sci.Techno)
l. ), Vol. 7, (1992) pp. 160-16
There is a dry etching method as described in 3.
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 epitaxy method is irradiated with light from a halogen lamp in an oxygen gas 22 atmosphere.
3 is performed to form a GaAs oxide film 24 (FIG. 2).
(A)). Next, the focused electron beam 25 is irradiated to the GaAs oxide film 24 to selectively modify the irradiated portion of the GaAs oxide film,
The chlorine gas etching resistance is deteriorated (FIG. 2 (b)).
Next, the GaAs growth layer 21 is etched by chlorine gas 26 using the modified patterned GaAs oxide film as a mask. As a result, the GaAs oxide film at the location where the focused electron beam 25 is irradiated is selectively etched, and thus the GaAs in this portion is also selectively etched (FIG. 2).
(C)).

However, in this method, since a substance different from the semiconductor material called oxide is used, there is a concern that the processed surface by chlorine gas etching is contaminated by this oxide film.

In order to solve this problem, a method of using a semiconductor epitaxial layer as an etching mask has recently been proposed (Autumn 1992 Autumn Proceedings of the 53rd Annual Meeting of the Society of Applied Physics, 3rd Volume, p. .1149).
This method will be described with reference to FIG. In this method, the following steps are continuously performed in vacuum. First, a GaAs layer 31 which is a material to be processed and an InGaAs layer 32 which serves as an etching mask are continuously grown by a molecular beam epitaxy method (FIG. 3A). Next, the focused electron beam 33 and the chlorine gas 34 are simultaneously irradiated to the surface of the InGaAs layer to expose the InGa layer.
The As layer 32 is removed by etching, and irradiation is further continued to etch the GaAs layer 31, which is the material to be processed (FIG. 3B). At this time, the portion of the InGaAs layer 32 which is not irradiated with the electron beam has a chlorine gas etching resistance and thus serves as a mask. In this method, since InGaAs, which is the same compound semiconductor as GaAs, which is the material to be processed, is used as the etching mask, there is no contamination by different substances as in the case of the oxide mask.

[0006]

[Problems to be Solved by the Invention] However, InG
In the conventional method using aAs as an etching mask,
Etching conditions that can remove InGaAs, that is,
Under the conditions of high sample temperature and high chlorine gas pressure, the GaAs layer, which is the material to be processed, is etched in the direction parallel to the surface and in the vertical direction at a very high speed even with only chlorine gas. Therefore, when forming a plurality of adjacent structures on the same sample, after the first structure is formed by simultaneous irradiation with an electron beam and chlorine gas, the irradiation position of the electron beam is moved to form the second structure. During formation, the GaAs portion of the first structure is exposed to chlorine gas, so etching proceeds at a high speed. Therefore, there is a problem in that the processing dimensions such as the depth and width of these plural structures greatly vary.

An object of the present invention is to achieve a very small variation in depth and width in a vacuum integrated processing process using a compound semiconductor of the same type as the material to be processed as a mask for etching with an electron beam and a reactive gas. It is to provide a new dry etching method.

[0008]

The present invention is a method of processing a compound semiconductor using an electron beam, a reactive gas and ions, wherein the surface of the compound semiconductor to be processed is irradiated with the reactive gas or the electron beam. Forming a first mask made of a compound semiconductor that is not etched by simultaneous irradiation with the above-mentioned reactive gas and is easily etched by irradiation with ions or simultaneous irradiation with the ions and the reactive gas. , Is easily etched on the first mask by simultaneous irradiation with the electron beam and the reactive gas,
Forming a second mask made of a compound semiconductor that is easily etched by simultaneous irradiation with the ions or the ions and the reactive gas; and reacting the electron beam with the electron beam on the surface of the second mask. Forming a recess having a depth equal to or greater than the thickness of the first mask by simultaneously irradiating gas, irradiating the surface of the second mask with the ions, or combining the ions with the reactive gas A step of removing only the portion of the first mask below the recess by simultaneous irradiation; and irradiating the entire surface of the compound semiconductor to be processed with the reactive gas, or the electron beam and the reactive gas. And a step of simultaneously irradiating the compound semiconductor.

[0009]

According to the present invention, first, a so-called maskless etching method is carried out by simultaneously irradiating a second mask on the first mask with a concave portion according to a desired structure with a focused electron beam and a reactive gas. Formed in. Next, the second mask is etched by irradiating the entire surface of the second mask with ions or simultaneously irradiating ions and a reactive gas. Then, the first mask is exposed earlier in the concave portion than in the other portions. If you continue etching,
If the depth of the recess is set in advance as follows, it is possible to remove the first mask below the recess before the second mask other than the recess is etched to expose the first mask. it can.

D ₂ > d ₁ × R ₂ / R ₁ where D ₂ is the depth of the concave portion formed in the second mask, which is necessary for transferring the pattern to the first mask, and d ₁ is the first mask. , R ₁ is the etching rate of the first mask,
R ₂ is the etching rate of the second mask.

Thereafter, when the entire surface of the compound semiconductor to be processed is irradiated with the reactive gas or the electron beam and the reactive gas are simultaneously irradiated, the compound semiconductor to be processed in the portion without the first mask is etched. The other portions are not etched by the second mask. As a result, the recess pattern initially formed in the second mask is transferred to the compound semiconductor to be processed.

Here, since the step of transferring / etching the concave portion to the first mask is performed by ion irradiation or simultaneous irradiation of ion and reactive gas, R _{1 to} R ₂ . Therefore, since D ₂ > d ₁ , the depth of the recess previously formed on the second mask may be about the thickness of the first mask.
Since the thickness of the first mask has only to be resistant to the irradiation of the reactive gas or the simultaneous irradiation of the electron beam and the reactive gas,
Since several nm is sufficient, the depth of the recess may be about several nm, and the time required for this etching is short. Therefore, the pattern width spread when forming a plurality of recesses is very small. On the other hand, regarding the depth, when forming a plurality of recesses by simultaneous irradiation etching of an electron beam and a reactive gas on the second mask, if the simultaneous irradiation time is the same, the etching depth is the order of the recesses to be formed. Since it is constant regardless of, there is no problem. Since there is no variation in depth and a pattern with little variation in width is transferred to the first mask by ions having good straightness, and the compound semiconductor to be processed is collectively etched using this as a mask, the variation in depth / width can be prevented. Fewer structures can be formed.

[0013]

EXAMPLES Next, a dry etching method according to the present invention will be described with reference to FIG. First, by a molecular beam epitaxy method, In _0.2 Ga _0.8 As (hereinafter referred to as InGaAs) 12 as a first mask has a thickness of 5 nm and GaAs 13 as a second mask has a thickness of 5 nm on GaAs 11 as a compound semiconductor to be processed. Thickness of 10 nm, and epitaxial growth is sequentially and continuously performed (FIG. 1A). Next, with the sample temperature kept at 65 ° C., a focused electron beam 15 with a kinetic energy of 5 keV and a beam diameter of 50 nm was applied in an atmosphere of 3 × 10 ⁻⁶ Torr of chlorine gas 14 with an electron dose of 1 × 10 ¹⁷ (electrons / c
m ^-2) to become so etched by being irradiated for 2 minutes, the depth 7.5n to GaAs13 a second mask
10 patterns of m and 50 nm in width are formed (FIG. 1).
(B), but one pattern in this figure). The depth is constant if the etching time is the same. At this time,
The width of the first etched pattern due to chlorine gas etching in the atmosphere is as small as 1.3 nm at most. Next, the sample temperature is kept at room temperature, and ten patterns formed on the second mask 13 are transferred to the first mask 12 by the reactive ion beam etching method using the chlorine radicals 16 and the acceleration voltage of the ions 17 of 30 V. (FIG. 1 (c)).
At this time, with the first and second masks, In _0.2 Ga _0.8 A
Although the material is different from that of s and GaAs, the reactive ion beam etching method using ions has almost the same etching rate, and InGaAs 12 is very thin at 5 nm, so that pattern transfer is easily performed. Next, with the sample temperature kept at room temperature, kinetic energy of 500 eV was applied to the entire surface of the sample in an atmosphere of chlorine gas of 5 × 10 ⁻⁵ Torr.
Of the shower-shaped electron beam 19 (FIG. 1)
(C)). At this time, the material GaAs11 to be processed is easily etched, but the first mask InGaAs
Since 12 is hardly etched, Ga of the material to be processed is
In As11, a structure having a constant etching depth and a very small width can be formed.

It should be noted that only chlorine gas may be used in the etching of GaAs as the material to be processed.

[0015]

According to the present invention, since the structure of the compound semiconductor in which the variation in the depth and width processing dimensions is very small can be formed using only the compound semiconductor of the same kind as a mask, there is no contamination by foreign matter. Can be processed. In addition, since this method can be continuously performed in a vacuum, the processed structure can be embedded and grown by the compound semiconductor after the structure is formed by etching and without exposing the sample to the atmosphere. By doing so, improvement in electrical and optical quality of the processed structure can be expected. Further, in the above-mentioned embodiment, for example, unlike the conventional method, the GaAs of the InGaAs mask and the material to be processed is not directly etched with the electron beam and the reactive gas, but GaAs which is easier to etch is reactive with the electron beam. The etching may be performed with a gas, and since this etching may be shallow, the time required for patterning can be significantly reduced.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a conventional etching method.

FIG. 3 is a diagram showing a conventional etching method.

[Explanation of symbols]

 11 GaAs 12 InGaAs (first mask) 13 GaAs (second mask) 14, 18, 26, 34 chlorine gas 15, 25, 33 Focused electron beam 16 Chlorine radical 17 Ion 19 Shower electron beam 21 GaAs layer 22 Oxygen Gas 23 Light irradiation 24 GaAs oxide film 31 GaAs 32 InGaAs layer (mask)

Claims (1)

[Claims] 1. The surface of a compound semiconductor to be processed is not etched by irradiation with a reactive gas or simultaneous irradiation with an electron beam and the reactive gas, and is irradiated with ions or with the ions and the reactive gas. A step of forming a first mask made of a compound semiconductor that is easily etched by simultaneous irradiation with, and being easily etched by simultaneous irradiation of the electron beam and the reactive gas on the first mask, Forming a second mask made of a compound semiconductor that is easily etched by simultaneous irradiation of ions or the ions and the reactive gas; and the electron beam and the reactive gas on the surface of the second mask. Simultaneously forming a recess having a depth equal to or greater than the thickness of the first mask, and irradiating the surface of the second mask with the ions. Or simultaneously irradiating the ions and the reactive gas to remove only the portion of the first mask below the recess, and irradiating the entire surface of the compound semiconductor to be processed with the reactive gas. Or a step of simultaneously irradiating the electron beam and the reactive gas, a dry etching method for a compound semiconductor.