JP7718359B2 - Manufacturing method of silicon substrate for quantum computer, silicon substrate for quantum computer and semiconductor device - Google Patents

Description

The present invention relates to a method for manufacturing a silicon substrate for a quantum computer, a silicon substrate for a quantum computer, and a semiconductor device.

Expectations are high for quantum computers, which utilize quantum effects such as superposition and entanglement, as a computer capable of solving calculations that conventional computers cannot solve in a realistic amount of time. The elements used in quantum computers are also mounted on semiconductor substrates such as silicon substrates.

There are several methods for creating elements for quantum computing, but the main ones include those that use the Josephson effect using superconductors, and those that use electron spin resonance (ESR) to convert quantum effects into electrical signals.

In devices that use electron spins on a silicon substrate, the quantum effect is read out by irradiating electron spins placed in a magnetic field with microwaves and sweeping the frequency to cause resonance (Patent Document 1).

Japanese Patent Application Laid-Open No. 2022-025657 Japanese Patent Application Laid-Open No. 2021-111696

When using electron spin in this way, if unnecessary spin components exist in the vicinity, the electron spin energy is split by the Zeeman effect, making it impossible to use quantum effects in calculations. For this reason, it is necessary to form a Si layer that is mainly (rich in) ²⁸ Si, with ²⁹ Si, which has nuclear spin, minimized.

For this purpose, a silicon substrate with _a ^28Si epitaxial layer formed using isotopically enriched ^28SiH4 gas is used. Furthermore, to achieve a single-electron layer (the presence of multiple electrons makes calculations difficult due to spin interactions between electrons), electron confinement (single-electron transistors) is required.

To achieve this, a fin structure is often fabricated to confine electrons at the fin tip, or an SOI (Silicon On Insulator) structure is often adopted. The fin structure has the advantage of being formed entirely from silicon, but it is difficult to control the surface state of the silicon surface. On the other hand, with an SOI structure, the influence of the silicon-oxide film interface is small, but the method of forming the insulating layer is difficult. In other words, even if ²⁸ Si is oxidized, the diffusion of silicon during heat treatment causes the influence of ²⁹ Si, which has nuclear spin.

Furthermore, in the heat treatment during the process of forming SOI by conventional techniques such as bonding, diffusion of ²⁸ Si also occurs, and the isotope effect of ²⁸ Si cannot be fully utilized.

The present invention has been made to solve the above problems, and provides a silicon substrate for a quantum computer that can suppress the influence of ²⁹ Si and the influence of nuclear spin, and a method for manufacturing the same.

The present invention has been made to achieve the above-mentioned object, and provides a method for manufacturing a silicon substrate for a quantum computer, comprising the steps of: forming a Si epitaxial layer on a silicon substrate by epitaxial growth using a Si source gas as a silicon-based raw material gas, the Si source gas having a total content of ²⁸ Si and ³⁰ Si of 99.9% or more relative to the total silicon contained in the silicon-based raw material gas; oxidizing the surface of the Si epitaxial layer to form an oxygen (O) δ-doped layer; and forming a Si epitaxial layer on the δ-doped layer by epitaxial growth using a Si source gas having a total content of ²⁸ Si and ³⁰ Si of 99.9% or more relative to the total silicon contained in the silicon-based raw material gas.

This method of manufacturing a silicon substrate for quantum computers makes it possible to manufacture a silicon substrate for quantum computers that can suppress the effects of nuclear spin, fully exhibits the isotope effect suitable for quantum computers, and can easily form single-electron transistors on the silicon substrate.

In this case, the method for manufacturing a silicon substrate for a quantum computer can use monosilane gas as the Si source gas.

This makes it possible to manufacture silicon substrates suitable for quantum computers at lower temperatures.

In this case, the process of forming the oxygen (O) delta-doped layer and the process of forming the Si epitaxial layer on the delta-doped layer can be repeated to form multiple pairs of the delta-doped layer and the Si epitaxial layer on the delta-doped layer, resulting in a method for manufacturing a silicon substrate for a quantum computer.

This makes it possible to produce silicon substrates that are more suitable for quantum computers.

In this case, the method for manufacturing a silicon substrate for a quantum computer can be such that the thickness of the outermost Si epitaxial layer of the silicon substrate for a quantum computer is thicker than the thickness of Si epitaxial layers other than the outermost Si epitaxial layer.

This will enable the production of silicon substrates that are even more suitable for quantum computers.

In this case, by subjecting the silicon substrate for quantum computers to heat treatment, the multiple delta-doped layers can be integrated to form an SOI structure, thereby forming a method for manufacturing a silicon substrate for quantum computers.

This makes it possible to manufacture silicon substrates with an SOI structure suitable for quantum computers.

In this case, the method for manufacturing a silicon substrate for a quantum computer can use a silicon substrate having a resistivity of 1000 Ω·cm or more.

This makes it possible to manufacture silicon substrates for quantum computers that can stably extract signals obtained through spin resonance without distortion.

The present invention also provides a method for manufacturing a silicon substrate for a quantum computer, comprising the steps of: forming a ²⁸ Si epitaxial layer on a silicon substrate by epitaxial growth using a ²⁸ Si source gas as a silicon-based raw material gas; oxidizing the surface of the ²⁸ Si epitaxial layer to form an oxygen (O) δ-doped layer; and forming a ²⁸ Si epitaxial layer on the δ-doped layer by epitaxial growth using a ²⁸ Si source gas.

This method of manufacturing a silicon substrate for quantum computers makes it possible to manufacture a silicon substrate for quantum computers that can suppress the effects of nuclear spin, fully exhibits the isotope effect suitable for quantum computers, and can easily form single-electron transistors on the silicon substrate.

In this case, the method for manufacturing a silicon substrate for a quantum computer can be implemented by using ²⁸ Si monosilane gas as the ²⁸ Si source gas.

This makes it possible to manufacture silicon substrates suitable for quantum computers at lower temperatures.

In this case, the step of forming the oxygen (O) δ-doped layer and the step of forming the ²⁸ Si epitaxial layer on the δ-doped layer are repeatedly performed, thereby forming a plurality of pairs of the δ-doped layer and ^{the 28} Si epitaxial layer on the δ-doped layer, thereby forming a method for manufacturing a silicon substrate for a quantum computer.

This makes it possible to produce silicon substrates that are more suitable for quantum computers.

In this case, the method for manufacturing a silicon substrate for a quantum computer can be such that the thickness of ^{the 28} Si epitaxial layer at the outermost layer of the silicon substrate for a quantum computer is made thicker than the thickness of the ²⁸ Si epitaxial layers other than the outermost ²⁸ Si epitaxial layer.

This will enable the production of silicon substrates that are even more suitable for quantum computers.

In this case, by subjecting the silicon substrate for quantum computers to heat treatment, the multiple δ-doped layers can be integrated to form an SOI structure, thereby forming a method for manufacturing a silicon substrate for quantum computers.

This makes it possible to manufacture silicon substrates with an SOI structure suitable for quantum computers.

In this case, the method for manufacturing a silicon substrate for a quantum computer can use a silicon substrate having a resistivity of 1000 Ω·cm or more.

This makes it possible to manufacture silicon substrates for quantum computers that can stably extract signals obtained through spin resonance without distortion.

The present invention has also been made to achieve the above-mentioned object, and provides a silicon substrate for a quantum computer, comprising: a silicon substrate; an epitaxial layer on the silicon substrate, the Si epitaxial layer having a composition in which the total content of ²⁸ Si and ³⁰ Si relative to the total silicon in the epitaxial layer is 99.9% or more; a _SiO2 layer on the Si epitaxial layer, the _SiO2 layer having a composition in which the total content of ²⁸ Si and ³⁰ Si relative to the total silicon in the _SiO2 layer is 99.9% or more; and an epitaxial layer on the _SiO2 layer, the Si epitaxial layer having a composition in which the total content of ²⁸ Si and ³⁰ Si relative to the total silicon in the epitaxial layer is 99.9% or more.

This type of silicon substrate for quantum computers can be used to suppress the effects of nuclear spin, fully demonstrate the isotope effect suitable for quantum computers, and is a silicon substrate on which single-electron transistors can be easily formed.

In this case, the silicon substrate for quantum computers can be one in which the SiO ₂ layer is a δ-doped layer of oxygen (O).

This results in a silicon substrate with a delta-doped layer suitable for quantum computers.

In this case, the silicon substrate for quantum computers can be one in which the SiO ₂ layer is a buried oxide film (BOX) layer in an SOI structure.

This results in a silicon substrate with an SOI structure suitable for quantum computers.

In this case, the semiconductor device can be one that has elements on a silicon substrate for quantum computers.

This results in a semiconductor device in which the effects of nuclear spin are suppressed.

The present invention also provides a silicon substrate for a quantum computer, comprising: a silicon substrate; a ²⁸ Si epitaxial layer on the silicon substrate; ^{a 28} SiO ₂ layer on the ²⁸ Si epitaxial layer; and ^{a 28} Si epitaxial layer on the ²⁸ SiO ₂ layer.

This type of silicon substrate for quantum computers can be used to suppress the effects of nuclear spin, fully demonstrate the isotope effect suitable for quantum computers, and is a silicon substrate on which single-electron transistors can be easily formed.

In this case, the silicon substrate for quantum computers can be one in which the ²⁸ SiO ₂ layer is a δ-doped layer of oxygen (O).

This results in a silicon substrate with a delta-doped layer suitable for quantum computers.

In this case, the ²⁸ SiO ₂ layer can be a buried oxide film (BOX) layer in an SOI structure, forming a silicon substrate for a quantum computer.

This results in a silicon substrate with an SOI structure suitable for quantum computers.

In this case, the semiconductor device can be characterized as having elements on a silicon substrate for quantum computers.

This results in a semiconductor device in which the effects of nuclear spin are suppressed.

As described above, the method for manufacturing a silicon substrate for a quantum computer of the present invention makes it possible to manufacture a silicon substrate for a quantum computer that is capable of suppressing the effects of nuclear spin, and to manufacture a silicon substrate that fully exhibits the isotope effect suitable for a quantum computer and on which single-electron transistors can be easily formed. The silicon substrate for a quantum computer of the present invention makes it possible to manufacture a silicon substrate for a quantum computer that is capable of suppressing the effects of nuclear spin, and to manufacture a silicon substrate that fully exhibits the isotope effect suitable for a quantum computer and on which single-electron transistors can be easily formed.

1 is a schematic diagram illustrating an example of the structure of a silicon substrate for a quantum computer according to the present invention. 10A and 10B are schematic diagrams illustrating another example of the structure of a silicon substrate for a quantum computer according to the present invention. 1A and 1B are schematic diagrams illustrating the flow of a method for manufacturing a silicon substrate for a quantum computer according to the present invention.

The present invention is described in detail below, but is not limited to these.

As described above, there has been a demand for a silicon substrate for quantum computers that can suppress the influence of ²⁹ Si and the influence of nuclear spin, and a method for manufacturing the same.

As a result of intensive research into the above-mentioned problems, the present inventors have found that a method for manufacturing a silicon substrate for a quantum computer, comprising the steps of: forming a Si epitaxial layer on a silicon substrate by epitaxial growth using a Si source gas as a silicon-based raw material gas, the Si source gas having a total content of ^28Si and ^30Si of 99.9% or more relative to the total silicon contained in the silicon-based raw material gas; oxidizing the surface of the Si epitaxial layer to form an oxygen (O) δ-doped layer; and forming a Si epitaxial layer on the δ-doped layer by epitaxial growth using a Si source gas having a total content of ^28Si and ^30Si of 99.9% or more relative to the total silicon contained in the silicon-based raw material gas, can manufacture a silicon substrate for a quantum computer that can suppress the influence of nuclear spin; and can manufacture a silicon substrate that fully exhibits the isotope effect suitable for a quantum computer and on which single-electron transistors can be easily formed, thereby completing the present invention.

The present inventors have also discovered that a method for manufacturing a silicon substrate for a quantum computer that includes the steps of forming ^{a 28} Si epitaxial layer on a silicon substrate by epitaxial growth using a ²⁸ Si source gas as a silicon-based raw material gas, oxidizing the surface of the ²⁸ Si epitaxial layer to form an oxygen (O) δ-doped layer, and forming a ²⁸ Si epitaxial layer on the δ-doped layer by epitaxial growth using a ²⁸ Si source gas can manufacture a silicon substrate for a quantum computer that can suppress the influence of nuclear spin, and can manufacture a silicon substrate that fully exhibits the isotope effect suitable for a quantum computer and on which single-electron transistors can be easily formed, and have completed the present invention.

Furthermore, as a result of intensive research into the above-mentioned problems, the present inventors have found that a silicon substrate for a quantum computer comprising a silicon substrate, an epitaxial layer on the silicon substrate, a Si epitaxial layer having a composition in which the total content of ²⁸ Si and ³⁰ Si relative to the total silicon in the epitaxial layer is 99.9% or more, a SiO ₂ layer on the Si epitaxial layer, a SiO ₂ layer having a composition in which the total content of ²⁸ Si and ³⁰ Si relative to the total silicon in the SiO ₂ layer is 99.9% or more, and an epitaxial layer on the SiO ₂ layer, a Si epitaxial layer having a composition in which the total content of ²⁸ Si and ³⁰ Si relative to the total silicon in the epitaxial layer is 99.9% or more, can be used as a silicon substrate for a quantum computer that can suppress the influence of nuclear spin, and that can fully exhibit the isotope effect suitable for a quantum computer and can be a silicon substrate on which single-electron transistors can be easily formed, thereby completing the present invention.

The present inventors have also discovered that a silicon substrate for a quantum computer comprising a silicon substrate, ^{a 28} Si epitaxial layer on the silicon substrate, ^{a 28} SiO ₂ layer on the ²⁸ Si epitaxial layer, and a ²⁸ Si epitaxial layer on the ²⁸ SiO ₂ layer can be used to form a silicon substrate for a quantum computer that can suppress the influence of nuclear spin, that fully exhibits the isotope effect suitable for a quantum computer, and that is a silicon substrate on which single-electron transistors can be easily formed, and have completed the present invention.

The following explanation will be given with reference to the drawings.

Below, definitions of terms will be explained using " ²⁸ Si" as an example, but similar expressions may also be used for other isotopes ( ³⁰ Si, etc.).

In this specification, the term " ²⁸ Si source gas" as a silicon-based source gas refers to a gas containing silicon and having a composition in which the ²⁸ Si content of the total silicon is 99.9% or more. " ²⁸ Si monosilane gas" (sometimes written as " ²⁸ SiH ₄ ") refers to a monosilane (SiH ₄ ) gas having a composition in which the ²⁸ Si content of the total silicon is 99.9% or more. There are three stable silicon isotopes: ²⁸ Si, ²⁹ Si, and ³⁰ Si, and their natural abundances are 92.23%, 4.67%, and 3.1%. For example, ^{a 28} Si source gas can be produced by centrifuging a silicon-containing gas (silane-based gas) consisting of the natural Si isotope composition. ³⁰ Si source gas and "Si source gas in which the total content of ²⁸ Si and ³⁰ Si in the total silicon contained in the silicon-based raw material gas is 99.9% or more" can also be produced in the same manner.

In this specification, the term " ^28Si epitaxial layer" refers to an epitaxial layer having a composition in which the content of ^28Si relative to the total silicon content of the epitaxial layer is 99.9% or more. For example, the epitaxial layer can be obtained by epitaxial growth using a ^28Si source gas.

In this specification, " ²⁸ SiO ₂ " means SiO ₂ having a composition in which the content of ²⁸ Si relative to the total silicon content of the SiO ₂ is 99.9% or more. For example, it can be obtained by oxidizing ^{a 28} Si epitaxial layer.

In this specification, the term "δ-doped layer" refers to a layer in which an element different from the base material is introduced to a monoatomic layer. An oxygen (O) δ-doped layer includes, for example, a layer in which oxygen less than a monoatomic layer (1.36×10 ¹⁵ atoms/cm ² ) is introduced onto a silicon substrate. The δ-doping method is described, for example, in Patent Document 2.

[Silicon substrate for quantum computers]
(First embodiment)
As a result of extensive investigations into the above-mentioned problems, the present inventors have found that a silicon substrate for a quantum computer that includes a silicon substrate, an epitaxial layer on the silicon substrate, the Si epitaxial layer having a composition in which the total content of ²⁸ Si and ³⁰ Si relative to the total silicon of the epitaxial layer is 99.9% or more, a SiO ₂ layer on the Si epitaxial layer, the SiO ₂ layer having a composition in which the total content of ²⁸ Si and ³⁰ Si relative to the total silicon of the SiO ₂ layer is 99.9% or more, and an epitaxial layer on the SiO ₂ layer, the Si epitaxial layer having a composition in which the total content of ²⁸ Si and ³⁰ Si relative to the total silicon of the epitaxial layer is 99.9% or more, results in a silicon substrate for a quantum computer that is capable of suppressing the influence of ²⁹ Si and suppressing the influence of nuclear spin.

The Si epitaxial layer in the silicon substrate for a quantum computer according to the present invention need only have a composition in which the total content of ²⁸ Si and ³⁰ Si in the entire silicon of the epitaxial layer is 99.9% or more, and does not necessarily have to contain both ²⁸ Si and ³⁰ Si. The content of ²⁸ Si in the entire silicon of the epitaxial layer may be 99.9% or more, or the content of ³⁰ Si may be 99.9% or more.

In this case, the SiO ₂ layer is preferably a δ-doped layer of oxygen (O). Such a silicon substrate for a quantum computer is a silicon substrate having a δ-doped layer suitable for a quantum computer.

Furthermore, the SiO ₂ layer is preferably a buried oxide (BOX) layer in an SOI structure. Such a silicon substrate for a quantum computer has an SOI structure suitable for quantum computers.

Furthermore, it is preferable that the element is mounted on the silicon substrate for the quantum computer described above. Such a semiconductor device is one in which the influence of nuclear spin is suppressed.

A more detailed embodiment will be described in the second embodiment below, which corresponds to a silicon substrate for a quantum computer according to the first embodiment, in which the content of ²⁸ Si in the entire silicon of the epitaxial layer is 99.9% or more.

Second Embodiment
The inventors have also found that a silicon substrate for a quantum computer that can suppress the influence ^{of 29} Si and the influence of nuclear spin can be obtained by comprising a silicon substrate, a ²⁸ Si epitaxial layer on the silicon substrate, a ²⁸ SiO ₂ layer on the ²⁸ Si epitaxial layer, and a ²⁸ Si epitaxial layer on the 28 SiO ₂ layer. As described above, the silicon substrate for a quantum computer according to the second embodiment of the present invention corresponds to the silicon substrate for a quantum computer according to the above-mentioned first embodiment, in which the content of ²⁸ Si in the entire silicon of the epitaxial layer is 99.9% or more.

An example of the structure of a silicon substrate for a quantum computer according to the second embodiment is shown in Figure 1. The silicon substrate for a quantum computer according to the second embodiment includes a silicon substrate 1, ^{a 28} Si epitaxial layer 2 on the silicon substrate 1, ^{a 28} SiO ₂ layer 3 on the ²⁸ Si epitaxial layer 2, and a ²⁸ Si epitaxial layer 2 on the ²⁸ SiO ₂ layer 3.

_The ^28SiO2 layer 3 in the silicon substrate for quantum computers shown in Fig. 1 can be an oxygen (O) delta-doped layer. Fig. 2 shows an example in which a plurality of oxygen (O) delta-doped layers 3A are provided (plural pairs of oxygen (O) delta-doped layers 3A and adjacent ^28Si epitaxial layers 2), but the oxygen (O) delta-doped layer may be a single layer (one layer) like the ^28SiO2 layer ₃ in Fig. 1.

1 can be used as a buried oxide (BOX) layer in an SOI structure. In this case, ^{the buried oxide (BOX) layer ( 28 SiO} ₂ layer) can have a thickness of about 0.01 to ₁ μm.

The silicon substrate 1 used in the quantum computer silicon substrate according to the present invention will now be described. The silicon substrate 1 is not particularly limited, as long as it is capable of depositing a ²⁸ Si epitaxial layer on the substrate. There are no particular limitations on the diameter, thickness, dopants, etc. Quantum computers use microwaves and the like to read the spin state of electrons and other elements that exhibit quantized behavior. For this reason, it is preferable to use a high-resistivity substrate to reduce signal distortion in the electrical transmission path. In particular, a substrate with a resistivity of approximately 1000 Ω·cm or higher is preferable. This results in a silicon substrate for a quantum computer that can stably extract signals obtained by spin resonance without distortion.

A semiconductor device having elements mounted on the silicon substrate for quantum computers according to the present invention described above is a semiconductor device in which the effects of nuclear spin are suppressed.

[Method of manufacturing silicon substrate for quantum computer]
(Third embodiment)
Next, a method for manufacturing a silicon substrate for a quantum computer according to a third embodiment of the present invention will be described. The method for manufacturing a silicon substrate for a quantum computer according to the present invention includes the steps of forming a Si epitaxial layer on a silicon substrate by epitaxial growth using a silicon-based source gas, a Si source gas having a total content of ²⁸ Si and ³⁰ Si of 99.9% or more relative to the total silicon contained in the silicon-based source gas, oxidizing the surface of the Si epitaxial layer to form an oxygen (O) δ-doped layer, and forming a Si epitaxial layer on the δ-doped layer by epitaxial growth using a Si source gas having a total content of ²⁸ Si and ³⁰ Si of 99.9% or more relative to the total silicon contained in the silicon-based source gas.

The silicon-based source gas in the method for manufacturing a silicon substrate for a quantum computer according to the third embodiment of the present invention may be a Si source gas in which the total content of ²⁸ Si and ³⁰ Si relative to the total silicon contained in the silicon-based source gas is 99.9% or more, and does not necessarily need to contain both ²⁸ Si and ³⁰ Si. This also includes cases in which the content of ²⁸ Si relative to the total silicon contained in the silicon-based source gas is 99.9% or more, and cases in which the content of ³⁰ Si is 99.9% or more.

It is preferable to use monosilane gas as the Si source gas. This allows silicon substrates suitable for quantum computers to be produced at lower temperatures.

It is preferable to repeat the process of forming an oxygen (O) delta-doped layer and the process of forming a Si epitaxial layer on the delta-doped layer to form multiple pairs of delta-doped layers and Si epitaxial layers on the delta-doped layers. This makes it possible to manufacture silicon substrates that are more suitable for quantum computers.

It is also preferable to make the thickness of the outermost Si epitaxial layer of a silicon substrate for quantum computers thicker than the thickness of Si epitaxial layers other than the outermost Si epitaxial layer. This makes it possible to manufacture silicon substrates that are even more suitable for use in quantum computers.

In this case, it is preferable to use a silicon substrate with a resistivity of 1000 Ω·cm or more. This makes it possible to manufacture a silicon substrate for quantum computers that can stably extract signals obtained by spin resonance without distortion.

A more detailed embodiment will be described in the following fourth embodiment, which corresponds to a method for manufacturing a silicon substrate for a quantum computer according to the third embodiment, in which the content of ²⁸ Si in the total silicon contained in the silicon-based source gas is set to 99.9% or more.

(Fourth embodiment)
Furthermore, a method for manufacturing a silicon substrate for a quantum computer according to a fourth embodiment of the present invention includes the steps of forming ^{a 28} Si epitaxial layer on a silicon substrate by epitaxial growth using a ²⁸ Si source gas as a silicon-based raw material gas, oxidizing the surface of the ²⁸ Si epitaxial layer to form an oxygen (O) δ-doped layer, and forming a ²⁸ Si epitaxial layer on the δ-doped layer by epitaxial growth using a ²⁸ Si source gas. As described above, the method for manufacturing a silicon substrate for a quantum computer according to the fourth embodiment of the present invention corresponds to the method for manufacturing a silicon substrate for a quantum computer according to the third embodiment described above, except that the ²⁸ Si content of the total silicon contained in the silicon-based raw material gas is 99.9% or more. This will be described in detail below.

First, prepare a silicon substrate 1 as shown in Figure 3(A).

Next, as shown in Figure 3(B), epitaxial growth (deposition) is performed on the silicon substrate 1 to form a ^28Si epitaxial layer 2. In this case, the CVD method can form an epitaxial layer with good crystallinity. In the epitaxial growth, ^{a 28Si} source gas obtained by isotope enrichment, for example, is used as the silicon-based source gas. As the ^28Si source gas, it is particularly preferable to use ^28Si monosilane gas ( ^28SiH4 ). This allows epitaxial growth to be performed at _a lower temperature.

Although there are no particular limitations on the thickness of the ^28Si epitaxial layer 2, a thickness of approximately 0.01 to 1 μm is sufficient. This is reasonable considering that, as can be seen from the example of Si NMR, the influence of adjacent electron spin-nuclear spin interactions is strongest and the influence decreases when the distance is several atoms.

Next, as shown in Fig. 3C, a ²⁸ SiO ₂ layer is formed as an oxide film for electron confinement. In the example of Fig. 3, an oxygen (O) δ-doping method is used to form an oxygen (O) δ-doped layer 3A.

By using the delta-doping method to oxidize the surface of ^{the 28} Si epitaxial layer to form an oxygen (O) delta-doped layer 3A, it becomes possible to convert the silicon of the insulating film into silicon oxide ( ²⁸ SiO ₂ ), which is not affected by nuclear spins, and to avoid the effects of electron-nuclear spin interactions.

Next, as shown in FIG. 3D, a ²⁸ Si epitaxial layer 2 is deposited on this δ-doped layer. As with the first ²⁸ Si epitaxial layer 2 described above, CVD can form an epitaxial layer with good crystallinity. ^{A 28} Si source gas, such as isotopically enriched ²⁸ SiH ₄ , is used as the source gas. The thickness of the epitaxial layer at this time does not need to be as thick as the first ²⁸ Si epitaxial layer 2, and can be adjusted as needed to ensure electron confinement. For example, the thickness can be approximately 0.001 to 0.5 μm.

Although it is possible to fabricate a device using this structure as is, the insulating layer formed in the steps up to this point is called δ-doping, meaning that oxygen is merely inserted at the atomic level, and there is a possibility that the insulation may not be sufficient. Therefore, it is also preferable to repeat the process of forming the oxygen (O) δ-doped layer 3A shown in Figure 3(C) and the process of forming ^{the 28} Si epitaxial layer 2 on the δ-doped layer shown in Figure 3(D), thereby forming multiple pairs of oxygen (O) δ-doped layer 3A and ²⁸ Si epitaxial layer on the δ-doped layer, as shown in Figure 3(E). This results in a silicon substrate that is even more suitable for quantum computers.

As shown in Figure 3(F), a thick insulating layer can then be formed by further oxidizing and integrating the multiple delta-doped layers through heat treatment. The resulting thick insulating layer can form an SOI structure that functions as the buried oxide (BOX) layer 3B. This makes the silicon substrate even more suitable for quantum computers.

The number of times that the oxygen (O) delta-doped layer 3A and the ²⁸ Si epitaxial layer 2 are stacked on the delta-doped layer can be changed as needed to suit the device characteristics and design. Furthermore, when integrating multiple delta-doped layers by oxidation, it is preferable to make the outermost ²⁸ Si epitaxial layer ² thicker than the other ²⁸ Si epitaxial layers. For example, the thickness can be set to approximately 0.002 to 1 μm. In this way, the outermost ²⁸ Si epitaxial layer 2 will not be lost even when oxidation is performed.

By using a ²⁸ Si-rich silicon layer ( ²⁸ Si epitaxial layer) in this way, it becomes possible to form a ²⁸ Si-rich oxide film ( ²⁸ SiO ₂ layer) as an insulating layer as well.

The present invention will be explained in more detail below using examples, but these examples are not intended to limit the scope of the present invention.

(Example)
A boron- _{doped 300 mm diameter silicon substrate (resistivity: 1000 Ω·cm) was prepared and silicon epitaxial growth was performed using 28SiH4} ⁽ isotope 99.94%) as the source material. A 1 μm film was formed under reduced pressure conditions of 850° _C and 100 Torr (13,332 Pa). Next, the substrate was left in the atmosphere for 2 hours to form a native oxide film with _{a 28SiO2} ^composition (oxygen δ-doping). After that, a 3 nm silicon epitaxial layer was formed again using ^28SiH4 (isotope 99.94%) as the source material under reduced pressure conditions of 850°C and 100 Torr (13,332 Pa). The substrate was then left in the atmosphere for two hours to form a native oxide film with _{a 28SiO2} ^composition (oxygen delta-doping). This process was then repeated four times to form _a 3-nm silicon epitaxial layer using ^28SiH4 (isotope 99.94%) at a temperature of 850°C and a reduced pressure of 100 Torr (13,332 Pa). Finally, _{a 100-nm silicon epitaxial layer was formed using 28SiH4} ⁽ isotope 99.94%) at a temperature of 850°C and a reduced pressure of 100 Torr (13,332 Pa). Finally, a heat treatment was performed at 800°C for 10 minutes to oxidize the oxygen delta-doped layer and form a single oxide film (buried oxide (BOX) layer), resulting in an SOI substrate with a ^28Si epitaxial layer on top.

As described above, according to the embodiments of the present invention, it is possible to obtain a silicon substrate for quantum computers that can suppress the effects of nuclear spin, that fully exhibits the isotope effect suitable for quantum computers, and that can easily form single-electron transistors.

The present specification includes the following aspects.
[A]: A method for manufacturing a silicon substrate for a quantum computer,
forming a Si epitaxial layer on a silicon substrate by epitaxial growth using a silicon source gas containing 99.9% or more ^{of Si and 28 Si} in total, based on the total silicon content of the silicon source gas;
oxidizing the surface of the Si epitaxial layer to form an oxygen (O) δ-doped layer;
and forming a Si epitaxial layer on the δ-doped layer by epitaxial growth using a Si source gas in which the total content of ^28Si and ^30Si in the total silicon contained in a silicon-based source gas is 99.9% or more.
[B]: The method for manufacturing a silicon substrate for a quantum computer according to [A] above, in which monosilane gas is used as the Si source gas.
[C]: A method for manufacturing a silicon substrate for a quantum computer according to [A] or [B], in which the step of forming the oxygen (O) δ-doped layer and the step of forming the Si epitaxial layer on the δ-doped layer are repeated to form multiple pairs of the δ-doped layer and the Si epitaxial layer on the δ-doped layer.
[D]: A method for manufacturing a silicon substrate for a quantum computer according to [C] above, in which the thickness of the outermost Si epitaxial layer of the silicon substrate for a quantum computer is made thicker than the thickness of Si epitaxial layers other than the outermost Si epitaxial layer.
[E]: The method for manufacturing a silicon substrate for a quantum computer according to [D] above, wherein the silicon substrate for a quantum computer is heat-treated to integrate the plurality of δ-doped layers to form an SOI structure.
[1]: A method for manufacturing a silicon substrate for a quantum computer,
forming a ²⁸ Si epitaxial layer on a silicon substrate by epitaxial growth using ^{a 28} Si source gas as a silicon-based source gas;
oxidizing the surface of the Si epitaxial layer to form an oxygen (O) δ-doped layer ^;
forming a ²⁸ Si epitaxial layer on the δ-doped layer by epitaxial growth using a ²⁸ Si source gas.
[2]: The method for manufacturing a silicon substrate for a quantum computer according to [1] above, wherein ²⁸ Si monosilane gas is used as the ²⁸ Si source gas.
[3]: The method for manufacturing a silicon substrate for a quantum computer according to [1] or [2] above, in which the step of forming the oxygen (O) δ-doped layer and the step of forming the ²⁸ Si epitaxial layer on the δ-doped layer are repeated to form a plurality of pairs of the δ-doped layer and the ²⁸ Si epitaxial layer on the δ-doped layer.
[4]: The method for manufacturing a silicon substrate for a quantum computer according to [3] above, wherein the thickness of ^{the 28} Si epitaxial layer at the outermost layer of the silicon substrate for a quantum computer is made thicker than the thickness of the ²⁸ Si epitaxial layer other than the outermost layer.
[5]: A method for manufacturing a silicon substrate for a quantum computer according to the above [4], wherein the silicon substrate for a quantum computer is heat-treated to integrate the plurality of δ-doped layers to form an SOI structure.
[6]: A method for manufacturing a silicon substrate for a quantum computer according to [A], [B], [C], [D], [E], [1], [2], [3], [4] or [5], in which the silicon substrate has a resistivity of 1000 Ω cm or more. [F]: A silicon substrate for a quantum computer,
A silicon substrate;
an epitaxial layer on the silicon substrate, the epitaxial layer having a composition in which the total content of ^28Si and ^30Si in the entire silicon of the epitaxial layer is 99.9% or more;
a SiO ₂ layer on the Si epitaxial layer, the SiO ₂ layer having a composition in which the total content of ²⁸ Si and ³⁰ Si in the total silicon of the SiO ₂ layer is 99.9% or more;
and an epitaxial layer on the _SiO2 layer, the epitaxial layer having a composition in which the total content of ²⁸ Si and ³⁰ Si in the entire silicon of the epitaxial layer is 99.9% or more.
[G]: The silicon substrate for quantum computers according to [F] above, wherein the SiO ₂ layer is a δ-doped layer of oxygen (O).
[H]: The silicon substrate for quantum computers according to [F] above, wherein the SiO ₂ layer is a buried oxide film (BOX) layer in an SOI structure.
[7]: A silicon substrate for a quantum computer,
A silicon substrate;
^a Si epitaxial layer on the silicon substrate;
a ²⁸ _SiO2 layer on the ²⁸ Si epitaxial layer;
and ^{a 28} Si epitaxial layer on the ²⁸ SiO ₂ layer.
[8]: The silicon substrate for quantum computers according to [7] above, wherein _the ^28SiO2 layer is a δ-doped layer of oxygen (O).
[9]: The silicon substrate for quantum computers according to [7] above, wherein ^{the 28} SiO ₂ layer is a buried oxide film (BOX) layer in an SOI structure.
[10]: A semiconductor device characterized by comprising an element on a silicon substrate for a quantum computer according to [F], [G], [H], [7], [8] or [9].

The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical concept described in the claims of the present invention and that provides similar effects is within the technical scope of the present invention.

1... silicon substrate, 2... ²⁸ Si epitaxial layer,
3... ²⁸ SiO ₂ layer,
3A...Oxygen (O) δ-doped layer ( ²⁸ SiO ₂ layer),
3B: buried oxide (BOX) layer ( ²⁸ SiO ₂ layer),
10, 10A...Silicon substrate for quantum computers.

Claims (18)

A method for manufacturing a silicon substrate for a quantum computer, comprising:
forming a Si epitaxial layer on a silicon substrate by epitaxial growth using a silicon source gas containing 99.9% or more ^{of Si and 28 Si} in total, based on the total silicon content of the silicon source gas;
oxidizing the surface of the Si epitaxial layer to form an oxygen (O) δ-doped layer;
and forming a Si epitaxial layer on the δ-doped layer by epitaxial growth using a Si source gas in which the total content of ^28Si and ^30Si in the total silicon contained in the silicon-based source gas is 99.9% or more. The method for manufacturing a silicon substrate for a quantum computer according to claim 1, characterized in that monosilane gas is used as the Si source gas. The method for manufacturing a silicon substrate for a quantum computer described in claim 1, characterized in that the process of forming the oxygen (O) delta-doped layer and the process of forming the Si epitaxial layer on the delta-doped layer are repeated to form multiple pairs of the delta-doped layer and the Si epitaxial layer on the delta-doped layer. The method for manufacturing a silicon substrate for a quantum computer according to claim 3, characterized in that the thickness of the outermost Si epitaxial layer of the silicon substrate for a quantum computer is made thicker than the thicknesses of the Si epitaxial layers other than the outermost Si epitaxial layer. The method for manufacturing a silicon substrate for a quantum computer according to claim 4, characterized in that the silicon substrate for a quantum computer is heat-treated to integrate the multiple δ-doped layers to form an SOI structure. A method for manufacturing a silicon substrate for a quantum computer, comprising:
forming a ²⁸ Si epitaxial layer on a silicon substrate by epitaxial growth using a ²⁸ Si source gas as a silicon-based source gas;
oxidizing the surface of the Si epitaxial layer to form an oxygen (O) δ-doped layer ^;
forming a ²⁸ Si epitaxial layer on the δ-doped layer by epitaxial growth using a ²⁸ Si source gas. 7. The method for manufacturing a silicon substrate for a quantum computer according to claim 6, wherein ²⁸ Si monosilane gas is used as the ²⁸ Si source gas. 7. The method for manufacturing a silicon substrate for a quantum computer according to claim ⁶ , wherein the step of forming the oxygen (O) δ-doped layer and the step of forming the ²⁸ Si epitaxial layer on the δ-doped layer are repeated to form a plurality of pairs of the δ-doped layer and the 28 Si epitaxial layer on the δ-doped layer. 9. The method for manufacturing a silicon substrate for a quantum computer according to claim 8, wherein the thickness of ^{the 28} Si epitaxial layer in the outermost layer of the ^silicon substrate for a quantum computer is made thicker than the thickness of the ²⁸ Si epitaxial layer other than the outermost layer. The method for manufacturing a silicon substrate for a quantum computer according to claim 9, characterized in that the silicon substrate for a quantum computer is heat-treated to integrate the multiple δ-doped layers to form an SOI structure. A method for manufacturing a silicon substrate for a quantum computer according to any one of claims 1 to 10, characterized in that the silicon substrate has a resistivity of 1000 Ω-cm or more. A silicon substrate for a quantum computer,
A silicon substrate;
an epitaxial layer on the silicon substrate, the epitaxial layer having a composition in which the total content of ^28Si and ^30Si in the entire silicon of the epitaxial layer is 99.9% or more;
a SiO ₂ layer on the Si epitaxial layer, the SiO ₂ layer having a composition in which the total content of ²⁸ Si and ³⁰ Si in the total silicon of the SiO ₂ layer is 99.9% or more;
and an epitaxial layer on the _SiO2 layer, the epitaxial layer having a composition in which the total content of ^28Si and ^30Si in the entire silicon of the epitaxial layer is 99.9% or more. 13. The silicon substrate for quantum computers according to claim 12, wherein the SiO ₂ layer is a δ-doped layer of oxygen (O). 13. The silicon substrate for quantum computers according to claim 12, wherein the _SiO2 layer is a buried oxide (BOX) layer in an SOI structure. A silicon substrate for a quantum computer,
A silicon substrate;
^a Si epitaxial layer on the silicon substrate;
a ²⁸ _SiO2 layer on the ²⁸ Si epitaxial layer;
and ^{a 28} Si epitaxial layer on the ²⁸ SiO ₂ layer. 16. The silicon substrate for quantum computers according to claim 15, wherein _the ^28SiO2 layer is a δ-doped layer of oxygen (O). 16. The silicon substrate for quantum computers according to claim 15, wherein the ²⁸ SiO ₂ layer is a buried oxide (BOX) layer in an SOI structure. A semiconductor device comprising an element on a silicon substrate for a quantum computer according to any one of claims 12 to 17.