JP2714703B2 - Selective epitaxial growth method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a selective epitaxial growth method on a group III-V compound semiconductor region such as GaAs (gallium arsenide).

[Problems to be Solved by the Related Art and the Invention] When a semiconductor epitaxial layer is selectively grown on a compound semiconductor region using a mask, silicon oxide or silicon nitride is conventionally used as the mask.
The formation of these mask material layers involves the use of plasma to minimize the adverse effect on the compound semiconductor region (mainly that constituent elements are separated from the surface region and the surface region is altered).
Utilizes low-temperature growth technologies such as CVD and optical CVD. In addition, in order to form an opening at a location where epitaxial growth is performed,
A photolithography process using a photoresist (formation of a photoresist film, exposure, etching of a development mask material layer, removal of the photoresist film) is performed. In order to perform high-definition patterning, it is necessary to form a mask material as thin as possible and employ a high-precision photolithography process.

When it is necessary to remove the mask material layer after the epitaxial growth, it is necessary to selectively remove the mask material layer by etching so as not to adversely affect the compound semiconductor region (substrate) and the semiconductor epitaxial layer. The same applies to the etching of a mask material layer for forming an opening in a photolithography step.

One of the application fields of the selective epitaxial growth method is creation of a quantum wire structure. In recent years, research has been energetically made to realize a new functional device. In this case, the thickness of the epitaxial growth becomes extremely thin at the level of controlling the number of atomic layers, and the planar pattern of the epitaxial growth becomes an extremely fine pattern. In addition, it is necessary to realize an extremely fine structure with less processing damage. In many cases, a crystal different from the first crystal is grown in the second selective epitaxial growth in a region where no crystal is grown in the first selective epitaxial growth. Therefore, when the selective epitaxial growth using the mask is adopted, a step of removing the mask of the first selective epitaxial growth is required for the second selective epitaxial growth.

By the way, it is difficult at present to adopt the above-described selective epitaxial growth using a conventional mask for producing a quantum wire structure. That is, it is difficult to realize an extremely fine mask pattern (for example, a mask having a width of 200 mm) required for the quantum wire structure. There is also a problem that semiconductor crystals are likely to be damaged in the process of forming / removing the mask material layer and forming openings in the mask material layer. As described above, in order to epitaxially grow an extremely fine pattern by a method using a mask, there is a problem in selecting a mask material and limiting the minute region.

As a method of epitaxially growing an extremely fine pattern, a method of locally limiting a chemical reaction by locally applying excitation energy by light irradiation or the like is known. However, during epitaxial growth,
Excitation must be performed continuously and without misalignment, which is a very difficult problem.

Accordingly, an object of the present invention is to realize a selective epitaxial growth method that causes less processing damage to a semiconductor crystal and enables crystal growth of an extremely fine pattern.

[Means for Solving the Problems] The present invention for achieving the above object has been achieved by using Ga (gallium)
Forming a thin layer of S (sulfur) atoms bonded to the constituent elements on the surface of a semiconductor region made of a group III-V compound semiconductor having one of the constituent elements; Irradiating the semiconductor region with an oxygen atmosphere by exposing the semiconductor region to an oxygen atmosphere by exposing the semiconductor region to an oxygen atmosphere by irradiating the semiconductor region with an electromagnetic wave or a particle beam to separate the S atoms from the predetermined portion; Forming a thin layer of oxygen bonded to the constituent elements at the portion of the first opening on the surface of
By applying predetermined energy to the thin layer of S and the thin layer of oxygen, the S atoms are detached from the surface of the semiconductor region to remove the thin layer of S, and formed by removing the thin layer of S. Using the oxygen thin layer having the formed second opening as a mask for epitaxial growth,
And a selective epitaxial growth method for forming a semiconductor epitaxial layer on the semiconductor region exposed at the opening of (a).

As described in claim 2, a semiconductor can be epitaxially grown on the thin S layer without removing the thin S layer to form the second opening.

[Operation] The thin layer of S has a large bonding force to the semiconductor region and has a property of being sensitive to electromagnetic waves (light, X-rays, etc.) and particle beams (electron beams, ion beams, etc.) like a photoresist. Therefore, it is like having both a conventional photoresist and a mask material layer. In addition, since the S thin layer is composed of S atoms bonded to the constituent elements of the semiconductor region, it is an extremely thin film. Therefore, the first opening of the thin layer of S can be formed in an extremely high-definition pattern by irradiating a portion where the first opening is to be formed with electromagnetic waves or particle beams.

When the surface side of the semiconductor region in which the thin layer of S having the first opening is formed is exposed to an oxygen atmosphere, oxygen is not chemically adsorbed on the thin layer of S, and only the portion of the first opening has oxygen. A thin layer of oxygen is formed by chemisorption.

Since a thin layer of oxygen has a large bonding force between Ga, which is a constituent element of the semiconductor region, and oxygen, the bonding force to the semiconductor region is larger than that of a thin layer of S. Therefore, given a predetermined energy (energy of a value that releases S but does not release oxygen) to the thin layer of S and the thin layer of oxygen by heat treatment, electromagnetic wave irradiation, particle beam irradiation, or a combination thereof, etc. , S only a thin layer can be removed,
A thin layer of oxygen is formed having a second opening that is a reverse pattern of the first opening. Since the second opening inherits the pattern accuracy of the first opening as it is, it can be formed into an extremely high-definition pattern.

Since the thin layer of oxygen has a large bonding force with the semiconductor region as described above, it is stable even in a temperature region where epitaxial growth is possible. When epitaxial growth is performed, the thin layer of oxygen functions as a mask, and selective epitaxial growth is performed. That is, molecules involved in epitaxial growth are:
It is not chemisorbed on the oxygen thin layer, but is selectively chemisorbed only on the second opening. Therefore, epitaxial crystal growth proceeds only in the portion of the second opening.

In the steps of forming, processing, and removing the thin layer of S and the thin layer of oxygen, damage to the semiconductor crystal is small.

On the other hand, a thin layer of S has a large effect of stabilizing the surface.
May be grown on a thin layer of. In this case, after forming a thin layer of oxygen, epitaxial growth is performed with the thin layer of S remaining. Molecules involved in epitaxial growth are more likely to be chemically adsorbed to a thin layer of S than to a thin layer of oxygen, so that epitaxial crystal growth proceeds only on the thin layer of S.

Example 1 An example of a selective epitaxial growth method according to the present invention will be described with reference to FIGS. 1 (A) to 1 (G).

First, as shown in FIG. 1A, a semiconductor substrate 1 having a semiconductor region 2 made of GaAs having a (001) surface.
Prepare The semiconductor substrate 1 is cleaned by light etching with a mixed solution of H ₂ SO ₄ (sulfuric acid) -H ₂ O ₂ (hydrogen peroxide) -H ₂ O (water), and then 50% HF (hydrofluoric acid) Treat with solution. As a result, Ga (gallium) dissolves into the HF solution on the surface of the semiconductor region 2, and the semiconductor region 2 becomes As (arsenic).
An oxide layer (lower layer) and an As layer (upper layer) are covered. Next, the surface of the semiconductor region 2 is irradiated with ultraviolet rays while maintaining the temperature at 550 ° C. in a vacuum. Thereby, As oxide and
The As layer is removed, and the surface of the semiconductor region 2 becomes a Ga surface.

Next, as shown in FIG. 1B, S (sulfur) is vacuum-deposited extremely thinly on the surface of the semiconductor region 2. Further, heat treatment is performed at 480 ° C. for 30 minutes in a vacuum. As a result, most of the vacuum-deposited S is discrete and S
Is formed. The S thin layer 3 is composed of S atoms bonded (chemisorbed) to constituent elements (Ga in this case) on the surface of the semiconductor region 2 and has an extremely thin thickness of a monoatomic layer or a biatomic layer level. Is a thin layer. The thin S layer 3 is dissociated from the semiconductor region 2 when heat treatment is performed at an excessively high temperature, but is stable against heat treatment at 500 ° C. or lower.

Subsequently, the thin layer 3 of S is irradiated with an electron beam so as to draw a predetermined pattern. In the part irradiated with the electron beam,
When the S atoms are released, a thin layer 3a of S having the first opening 4 is formed as shown in FIG. 1 (C). Since the direct writing method in which the electron beam is scanned so as to irradiate only the portion of the first opening 4 is used, the pattern edge is sharply drawn because the thin layer of S is extremely thin. ,
Patterning can be performed with extremely high definition.

Next, when the semiconductor substrate 1 is left in an oxygen atmosphere, as shown in FIG. 1 (D), oxygen is chemically adsorbed to the semiconductor region 2 only in the portion of the first opening 4 and the oxygen thin layer 5 is formed.
Is formed. That is, the thin layer 3a of S functions as a mask for the chemical adsorption of oxygen. The oxygen thin layer 5 is, like the S thin layer 3, a thin layer having a minimum thickness of a monoatomic layer or a diatomic layer. The oxygen thin layer 5 has a larger bonding force to the semiconductor region 2 than the S thin layer 3a, and is stable against heat treatment at 600 ° C. or lower.

Next, heat treatment is performed at 550 ° C. for 30 minutes in a vacuum. First
As shown in FIG. 3E, the S atoms are separated from the semiconductor region 2 and the thin layer 3a of S is removed, and a second opening 6 is formed in a pattern opposite to the first opening 5. The second opening 6 inherits the high definition pattern of the first opening 4 as it is.

Thereafter, as shown in FIG. 1F, GaAs is vapor-phase epitaxially grown. Here, in order to prevent dissociation of the oxygen thin layer 5 and to form a good growth interface,
A known migration enhanced epitaxy method (MEE method) capable of low-temperature growth was employed. That is, while maintaining the semiconductor substrate 1 at 550 ° C. in a vacuum, molecules containing As and molecules containing Ga are alternately supplied onto the semiconductor substrate 1 to grow a monoatomic layer to several atomic layers of the GaAs epitaxial layer 7. Let it. The epitaxial layer 7 is not formed on the oxygen thin layer 5a, but is selectively epitaxially grown.

Finally, as shown in FIG. 1 (G), when the semiconductor substrate 1 is maintained at 550 ° C. in a vacuum and the entire surface of the semiconductor substrate 1 is irradiated with ultraviolet rays, oxygen atoms are separated from the semiconductor region 2 and oxygen is released. Is removed.

In the case of forming a quantum wire device, for example, AlAs (aluminum arsenide) is grown on the surface of the semiconductor region 2 covered with the thin layer 5 of oxygen. In this case, selective epitaxial growth of AlAs is performed by repeating the steps according to FIGS. 1 (B) to 1 (G).

Example 2 This is an example in which the formation of the thin layer 3 of S in FIG. 1 (B) is performed by a sulfide solution treatment, and the other points are exactly the same as those in Example 1. Therefore, the illustrations and reference numerals are common to the first embodiment.

First, the semiconductor substrate 1 shown in FIG. 1 (A) which has been subjected to the process of exposing the Ga surface is prepared.

Next, the semiconductor substrate 1 is immersed in a 1N ammonium sulfide solution maintained at room temperature. The immersion time may be several seconds or more. Ammonium sulfide contains S in excess of the standard compound represented by the chemical formula: (NH ₄ ) ₂ S, and is represented by the chemical formula: (NH ₄ ) ₂ Sx (x> 1). The semiconductor substrate 1 is removed from the ammonium sulfide solution, and N ₂ gas is blown onto the surface of the GaAs region 2 to remove most of the attached solution. As a result, the surface of the GaAs region 2 is approximately
An amorphous film having a thickness of 100 ° and containing S as a main component is formed. Subsequently, when the semiconductor substrate 1 is left in a vacuum for about 30 minutes, the film almost disappears, and as shown in FIG. 1 (B), a thin layer 3 of S at a monoatomic layer or a biatomic layer level is formed. Is done. If this solution is rapidly diluted with pure water after being immersed in the ammonium sulfide solution, a thin layer 3 of S is formed without performing vacuum standing.
Instead of immersion in ammonium sulfide solution, thin layer 3 of S can be obtained by immersion in an alkaline solution containing S or an organic solvent containing S.
Can be formed.

The formation of the first opening 4 in the S thin layer 3 and the subsequent steps are the same as the method described in the first embodiment based on FIGS. 1 (C) to 1 (G). I do.

[Modifications] The present invention is not limited to the above embodiment, and various modifications and applications can be made within the scope of the gist.

For example, the semiconductor material forming the semiconductor region 2 is GaAs
GaAlAs (gallium aluminum arsenide), Ga
Ga such as AsP (gallium arsenide phosphide) and GaP (gallium phosphide)
Any compound may be used as long as it is a group III-V compound semiconductor having as a constituent element. The semiconductor material constituting the epitaxial layer 7 is also GaAs
Not limited to this, any semiconductor may be used as long as the semiconductor can be epitaxially grown at a temperature that does not cause the oxygen thin layer 5 to dissociate. Usually, the semiconductor material constituting the epitaxial layer 7 is also III
-Selected from Group V compound semiconductors. For the formation of the thin layer 3 of S, a physical deposition method represented by a vacuum deposition may be selected, or a chemical deposition method represented by a treatment of contacting with a solution containing S may be selected. Since the bonding force between Ga and oxygen is large, a treatment for exposing a large amount of Ga atoms to the surface of the semiconductor region 2 prior to the formation of the thin layer 3 of S (HF in Examples 1 and 2)
Treatment and subsequent vacuum heat treatment), the high-temperature stability of the oxygen thin layer 5 is improved. However, if the temperature of the heat treatment is set to a low value while paying attention to the temperature, the process can be omitted. In forming the first opening 4, a direct drawing method without using an exposure mask such as an interference exposure method using an ultraviolet laser may be used, or a drawing method using an exposure mask may be used. However, in order to draw an ultra-high-definition pattern, a direct writing method using electron beam irradiation is currently selected. The method of applying energy to S atoms and oxygen atoms to remove the thin layer 3a of S is simple by heat treatment, but may be other methods such as a combination of ultraviolet irradiation and heat treatment. It is easy to remove the oxygen thin layer 5 by using both ultraviolet irradiation and heat treatment. However, irradiation of other electromagnetic waves or particle beams may be used, or depending on circumstances, S atoms may be released only by heat treatment. It is good also as a method.
The epitaxial growth method is a vapor phase growth method capable of growing at a relatively low temperature, for example, an MBE method (molecular beam epitaxial growth method:
The above-mentioned MEE method is one of MBE methods) and MOCVD method (organic metal decomposition method) as appropriate.

On the other hand, epitaxial growth may be performed from the state shown in FIG. Since the thin S layer 3a has excellent properties as a surface stabilizing film, there is no problem even if it remains, and S atoms are regularly arranged to the extent that it becomes a base for epitaxial growth. Since molecules involved in the epitaxial growth are unlikely to be chemically adsorbed on the oxygen thin layer 5, the epitaxial layer 7 grows only on the S thin layer 3a. However,
The temperature for epitaxial growth needs to be about 500 ° C. or less so as not to cause desorption of S atoms.

[Effects of the Invention] As described above, according to the present invention, a new method of selective epitaxial growth using a mask can be provided, and particularly, selective epitaxial growth of an ultra-high-definition pattern can be achieved. Therefore, it is possible to produce a compound semiconductor device having an extremely fine structure such as a quantum wire device.

[Brief description of the drawings]

1 (A) to 1 (G) are cross-sectional views showing a selective epitaxial growth method according to Embodiment 1 of the present invention in the order of steps. DESCRIPTION OF SYMBOLS 1 ... Semiconductor substrate, 2 ... Semiconductor region, 3 ... S thin layer, 4 ...
First opening, 5: thin layer of oxygen, 6: second opening, 7: epitaxial layer.

Claims (2)

(57) [Claims] 1. A method comprising Ga (gallium) as one of the constituent elements.
Forming a thin layer of S composed of S (sulfur) atoms bonded to the constituent elements on the surface of a semiconductor region composed of an IV group compound semiconductor, and irradiating a predetermined portion of the S layer with an electromagnetic wave or a particle beam; Forming a first opening in the thin layer of the S by detaching the S atoms from the predetermined portion; and exposing the semiconductor region to an oxygen atmosphere, thereby forming a first opening on the surface of the semiconductor region. Forming a thin layer of oxygen bonded to the constituent element at the opening; and applying a predetermined energy to the thin layer of S and the thin layer of oxygen to release the S atoms from the surface of the semiconductor region. The thin layer of S is removed, and the thin layer of oxygen having the second opening formed by the removal of the thin layer of S is used as a mask for epitaxial growth on the semiconductor region exposed to the second opening. Semiconduct Selective epitaxial growth method characterized by forming an epitaxial layer. 2. The method of claim 2, wherein Ga (gallium) is one of the constituent elements.
Forming a thin layer of S composed of S (sulfur) atoms bonded to the constituent elements on the surface of a semiconductor region composed of an IV group compound semiconductor, and irradiating a predetermined portion of the S layer with an electromagnetic wave or a particle beam; Forming a first opening in the thin layer of the S by detaching the S atoms from the predetermined portion; and exposing the semiconductor region to an oxygen atmosphere, thereby forming a first opening on the surface of the semiconductor region. A selective epitaxial growth method comprising: forming a thin layer of oxygen bonded to the constituent element at an opening; and forming a semiconductor epitaxial layer on the thin layer of S using the thin layer of oxygen as a mask for epitaxial growth. .