JPH0766386A - Silicon quantum box and its manufacture - Google Patents

Abstract

PURPOSE:To realize uniform shape and excellent reproducibility and facilitate quantization without using lithography, by forming four faces equivalent to the (111) face constituting a quantum box, by anisotropic etching. CONSTITUTION:From a window 8 part, a silicon substrate 1 is etched about 0.01-2mum by SiRIE. The substrate 1 is dipped in anisotropic etching solution. The part under a triangular pyramid structure 20 is anisotropically etched. Thereby a (111) face is exposed on the lower surface of the triangular pyramid structure 20. By thermal oxidation, the exposed bottom surface part of the triangular pyramid structure 20 is oxidized, and an oxide film 9 is formed. By adjusting the size, a quantum box 10 formed by four faces equivalent to the (111) face is obtained. Thereby a quantum box having uniform shape and excellent reproducibility wherein quantization is easy can be formed without using lithography.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quantum box used in electronic devices, optical devices, etc., and more particularly to a quantum box made of silicon and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, semiconductor ultrafine processing technology has been remarkably developed, and a structure having a size of several nm has been formed. A quantum box is a structure formed by this ultra-fine processing technology, and along with a quantum wire, by making electrons into a single mode (or one-dimensionalization, zero-dimensionalization),
It has attracted attention due to the significant improvement in performance of electronic devices and optical devices, and the possibility of creating new devices with new concepts.

As a conventional quantum box structure and a method of manufacturing the quantum box, there are known ones using lithography by an electron beam drawing method, metalorganic vapor phase selective growth method (MOCVD), and the like. 61, No. 8 (1992), pp. 800-804, "Preparation of Quantum Wires by Induced Metal Vapor Phase Selective Growth and Their Optical Properties", along with preparation of quantum wires, selection on SIO ₂ pattern. Fabrication of GaAs dots (quantum boxes) by growth is disclosed.

In this method, first, as shown in FIG. 8a, a SiO ₂ film 40 is formed on the GaAs substrate 30 to a thickness of about 30 n.
m, and S by electron beam drawing and chemical etching
A window 41 of 650 × 650 nm ² is opened in the iO ₂ film to expose the silicon surface. As shown in FIG. 8B, an AlGaAs pyramid-shaped pedestal 31 is formed on the exposed silicon surface by a low pressure MOCVD method.

Continuing, as shown in FIG.
When GaAs is grown on the upper portion, GaAs is grown on the upper surface and the side surfaces of the quadrangular pyramid pedestal 31 and becomes as illustrated. The GaAs grown on the pedestal 31 is a quantum box 3.
It becomes 2.

Then, as shown in FIG. 8d, AlGaA
The s42 is further grown and completely embedded so as to cover the whole.

[0007]

However, in the conventional method of manufacturing a quantum box as described above, its size is defined by ultra-high definition lithography such as electron beam drawing method, which causes a problem in mass productivity. is there. In addition, the quantum box thus formed has an anisotropic quadrangular pyramid shape of 250 × 200 × 400 nm ^{3 due} to anisotropy of growth rate during GaAs growth.

Therefore, an object of the present invention is to provide a quantum box having a uniform shape and good reproducibility without using a special ultrahigh-definition lithography method, and easy to mass-produce, and a manufacturing method thereof.

[0009]

The present invention for solving the above-mentioned problems provides a quantum box formed on a silicon substrate via an insulating layer, the quantum box being made of a silicon material. It is a silicon quantum box characterized by having a tetrahedral structure composed of four planes equivalent to the planes.

Further, according to the present invention for solving the above object, there is provided a step of forming an oxidation resistant film on a plane-oriented (111) silicon substrate, and removing a part of the oxidation resistant film to obtain a silicon surface. The step of opening the exposed first window, the step of digging the silicon surface exposed from the first window portion, and the step of immersing the silicon substrate having the silicon surface dug in an anisotropic etching solution. 111) surface is exposed, a step of forming a silicon oxide film by thermal oxidation on the silicon surface exposed by the anisotropic etching solution immersion step, Removing a portion to open a second window that intersects with the first window, digging the silicon surface exposed in the second window portion, and the silicon surface of the second window portion. Anisotropic etching solution for silicon substrate A step of immersing to expose a surface equivalent to the (111) plane; a step of forming a silicon oxide film by thermal oxidation on the silicon surface exposed by the step of immersing the anisotropic etching solution; A step of removing the oxidizable film, a step of digging in the silicon portion exposed by the step of removing the oxidation resistant film, and a step of immersing the silicon substrate in which the exposed silicon portion is digged in an anisotropic etching solution, 111) surface is exposed, a step of removing the silicon oxide film, a step of forming an oxidation resistant film on the silicon surface exposed by the step of removing the silicon oxide film, the acid resistance The step of removing a part of the chemical conversion film to expose the silicon surface, the step of digging the exposed silicon surface, and the step of immersing the exposed silicon surface in the anisotropic silicon substrate. Te, (111)
A method of manufacturing a silicon quantum box, which comprises the step of exposing a surface equivalent to the surface.

[0011]

The quantum box of the present invention constructed as described above has a regular tetrahedron structure surrounded by the (111) plane of silicon and has a uniform quantum effect more easily than a quadrangular pyramid shape. It is predicted by calculation that the physical size for obtaining the quantum effect is roughly determined by the dimension of the sphere inscribed in the quantum box, and if the base size and height are the same, Since the radius of the inscribed circle is smaller in the regular pyramidal triangular pyramid shape than in the quadrangular pyramid shape, the quantum effect can be easily obtained.

Further, in the method for manufacturing a quantum box of the present invention, four planes equivalent to the (111) planes constituting the quantum box are formed by anisotropic etching.
The plane (and the plane equivalent thereto) is stable, and it is possible to easily manufacture a quantum box having a tetrahedral structure having a uniform shape with good reproducibility.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the accompanying drawings. First, an example of the method of manufacturing the quantum box of the present invention will be described.

First, as shown in the sectional view of FIG.
11) A SiN film 2 having a thickness of about 0.01 to 0.1 μm is formed on the silicon substrate 1 (SiN deposition step), and a resist 25 is applied thereto, and a rectangular window 3 is opened by photolithography and RIE (SiN patterning). Process), and RIE under Si etching conditions is continued to etch the silicon substrate by about 1 μm to dig down (SiRIE process).

At this time, the rectangular window 3 is formed as shown in the plan view of FIG.

[0016]

[Outer 1]

Next, the resist 25 is removed, and the resist 25 is dipped in an anisotropic etching solution. As the anisotropic etching liquid to be used, a KOH aqueous solution, a hydrazine aqueous solution, an ethylenediaminepyrocatechol solution or the like having an etching rate of the (111) plane which is much slower than other surfaces is used. In this example, the KOH aqueous solution (60 ° C., 30% by weight) is used because the KOH aqueous solution does not etch only the (111) plane but has excellent anisotropy selectivity for etching the planes of other orientations. I was there.

Thus, as shown in FIG. 1b, the SiR
The vertical part formed by IE

[0019]

[Outside 2]

Next, thermal oxidation is performed to form a SiO ₂ film 4 on the exposed silicon surface portion as shown in FIG. 1c (thermal oxidation step).

The steps up to this point, that is, the SiN deposition step, the SiN patterning step, the SiRIE step, the anisotropic etching step, and the thermal oxidation step are referred to as the first step for convenience of description. Note that FIG. 1 shows A- in FIG.
It is a cross section taken along line A.

Next, as in the plan view shown in FIG. 2b, as in the plan view shown in FIG.
A window 5 is opened in the SiN film 2 by the SiN patterning process, and the silicon surface exposed in the window 5 is dug down by the SiRIE process to perform anisotropic etching.

[0023]

[Outside 3]

Then, a SiO ₂ film 6 is formed on the exposed silicon surface by a thermal oxidation process. This is called the second step.

[0025]

[Outside 4]

In the SiRIE process in the second process, the SiO ₂ film 4 formed in the first process is

[0027]

[Outside 5]

Work as a ching mask material). S in Figure 3a
FIG. 3 shows a cross-sectional view taken along line BB of FIG. 2b after iRIE.
2C shows a cross section taken along line CC of FIG. 2B after anisotropic etching and thermal oxidation.

Next, the SiN film 2 is entirely removed by CDE or the like under SiN etching conditions. At this time, S
The iO ₂ films 4 and 6 remain. Then, similarly to the first step and the second step, the silicon surface exposed by the SiRIE step is dug down,

[0030]

[Outside 6]

By the above first to third steps, the triangular pyramid-shaped structure 20 is formed on the silicon substrate. A plan view after the completion of the third step is shown in FIG. 4a, and an enlarged cross section taken along line D-D in FIG. 4a is shown in FIG. 4b.

The height t of the triangular pyramidal structure 20 is one-third of the etching depth D in each of the first to third SiRIE steps (see FIG. 4b). In this example, the etching depth D of SiRIE in each of the first to third steps was substantially the same.

Next, the SiO ₂ films 4 and 6 formed in the first step and the second step are all removed, and the SiN film 7 is formed again to a film thickness of about 0.01 to 0.1 μm. And
As shown in the enlarged view of FIG. 5, the SiN film 7 is formed along the bottom portion of the triangular pyramid-shaped structure 20 formed up to the third step.
Is partially patterned by resist coating and etching to open a substantially V-shaped window 8.

The width L of the window 8 is not particularly limited as long as it is open, and is, for example, about 0.01 to 2 μm,
The distance x from the triangular pyramid-shaped structure 20 is as small as possible within the accuracy of photolithography, for example, about 1 μm. In addition, the triangular pyramid-shaped structure 20 and the tip of the window 7 (f in the figure)
The positional relationship with and may be 0 or more in order to separate the quantum boxes, and here it was set to 1 μm in view of the accuracy of photolithography.

Then, as shown in the enlarged cross-sectional view of FIG. 6A, the silicon substrate is exposed from the window 8 portion by SiRIE.
The substrate 1 is dipped in an anisotropic etching solution by etching about 01 to 2 μm, and the bottom of the triangular pyramidal structure 20 is anisotropically etched. As a result, the (111) plane is exposed on the lower surface of the triangular pyramidal structure 20 as shown in the figure. And
Thermal oxidation is performed to oxidize the exposed lower surface portion of the triangular pyramidal structure 20 to form the oxide film 9 and the size thereof is adjusted. A surface equivalent to the four (111) surfaces shown in FIG. The quantum box 10 formed by is completed. 6a and 6b are cross sections taken along the line D-D of FIG. 4a.

In the above-described embodiment, the etching depths D of SiRIE in the first to third steps are all the same, but next, as another example, the etching depths of SiRIE in the third step are the same as those in the first and second steps. The case where the depth is made shallower than in the second step will be described.

FIG. 7a is a line DD of FIG. 4a after etching under the triangular pyramidal structure 20 when the etching depth of SiRIE in the third step is shallower than that in the first and second steps. FIG. S in the third step
By making the etching depth of iRIE shallower than in the first and second steps, the triangular pyramidal structure 20 is partially connected to the silicon substrate 1.

Then, as a result of the subsequent thermal oxidation, as shown in FIG. 7b, the film is supported from below by SiO ₂ , and the upper SiN film can be removed as shown in FIG. 7c.

The quantum box of the present invention manufactured as described above has a tetrahedral structure formed by a plane equivalent to the (111) plane and has a uniform shape with a size of several nm to several tens of nm. It becomes a quantum box.

[0040]

As described above, in the quantum box of the present invention, the characteristic length that characterizes the quantum effect can be made smaller, so that the quantum effect increases the interval of energy levels. For this reason, what was normally available only at the liquid helium temperature can be used because the quantum effect is exhibited at a higher temperature.

Further, in the method of manufacturing a silicon quantum box of the present invention, a plane equivalent to four (111) planes is formed by anisotropic etching without using an ultrahigh precision lithography apparatus or MOCVD apparatus. Therefore, it is possible to easily mass-produce a silicon quantum box with a uniform shape, and the capital investment for mass-production can be relatively small.

[Brief description of drawings]

FIG. 1 is a cross-sectional view for explaining one embodiment of a method for manufacturing a quantum box according to the present invention in process order.

FIG. 2 is a plan view for explaining one embodiment using a method for manufacturing a quantum box according to the present invention in process order.

FIG. 3 is a cross-sectional view following FIG. 1 for explaining one embodiment of the method of manufacturing a quantum box according to the present invention in process order.

FIG. 4 is a plan view and a cross-sectional view subsequent to FIGS. 3 and 2 for explaining one embodiment using the method for manufacturing a quantum box according to the present invention in the order of steps.

FIG. 5 is a plan view following FIG. 4 for explaining one embodiment of the method of manufacturing a quantum box according to the present invention in process order.

FIG. 6 is a cross-sectional view following FIG. 5 for explaining one embodiment of the method of manufacturing a quantum box according to the present invention in process order.

FIG. 7 is a cross-sectional view for explaining another embodiment using the method of manufacturing a quantum box according to the present invention in process order.

FIG. 8 is a cross-sectional view for explaining a conventional method of manufacturing a quantum box in process order.

[Explanation of symbols]

1 ... Silicon substrate, 2, 7 ... S
iN film 3, 5, 8 ... Window,
4, 6, 9 ... SiO ₂ film, 10 ... Quantum box,
20 ... Triangular pyramid structure.

Claims (2)

[Claims] 1. A quantum box formed on a silicon substrate via an insulating layer, the quantum box being made of a silicon material and having a tetrahedral structure composed of four planes equivalent to a (111) plane. A silicon quantum box that is characterized. 2. A step of forming an oxidation resistant film on a surface-oriented (111) silicon substrate, and a step of removing a part of the oxidation resistant film and opening a first window having an exposed silicon surface. A step of digging the silicon surface exposed from the first window portion, and a step of immersing the silicon substrate having the silicon surface dug in an anisotropic etching solution to expose a surface equivalent to the (111) plane And a step of forming a silicon oxide film by thermal oxidation on the exposed silicon surface in the anisotropic etching solution dipping step, and removing a part of the oxidation resistant film to form the first window. A step of opening a second window that intersects with the step of: etching a silicon surface exposed in the second window portion; Surface equivalent to (111) plane A step of exposing, a step of forming a silicon oxide film by thermal oxidation on the silicon surface exposed by the step of immersing the anisotropic etching solution, a step of removing the oxidation resistant film, and a step of removing the oxidation resistance. A step of digging the silicon portion exposed by the step of removing the film, a step of immersing the silicon substrate in which the exposed silicon portion is digged in an anisotropic etching solution to expose a surface equivalent to the (111) plane, The step of removing the silicon oxide film, the step of forming an oxidation resistant film on the silicon surface exposed by the step of removing the silicon oxide film, and the step of removing part of the oxidation resistant film to remove the silicon surface. Exposing the exposed silicon surface, and immersing the exposed silicon surface in the anisotropic etching solution to form a surface equivalent to the (111) surface. A method of manufacturing a silicon quantum box, which comprises the step of exposing the silicon quantum box.