JP2023135330A - Semiconductor device and method for manufacturing the same - Google Patents

Abstract

To provide semiconductor devices with lower hole density than conventional devices by suppressing crystal defects in polycrystalline Ge films.SOLUTION: A semiconductor device 100 of the present invention has a base material 101 and a semiconductor film (semiconductor thin film) 102 formed (synthesized) on one surface 101a of the base material, and the semiconductor film 102 is a non-doped polycrystalline Ge film comprising crystal particles having an average particle size of 1 μm or more, and the hole density of the semiconductor film 102 is 1×1017 cm-3 or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a semiconductor device used for a thin film transistor, a solar cell, a light receiving sensor, etc., and a method for manufacturing the same.

Semiconductor films synthesized on insulators (SiO ₂ , glass, plastic, etc.) are key to realizing three-dimensional integrated circuits (LSIs) and higher performance and lower prices for information terminals and solar cells. It is being actively researched as a component.

Ge and SiGe, which are group IV semiconductors, have high affinity with Si, which is an existing material, and also have higher carrier mobility and lower crystallization temperature than Si, and are therefore expected to be the next generation semiconductor materials. However, it is known that defect levels in the crystal of polycrystalline Ge or polycrystalline SiGe act as holes after crystallization, and exhibit p-type conductivity even in a non-doped state. In the case of polycrystalline SiGe, this tendency becomes more pronounced as the Ge content increases. Therefore, the lower limit of the range of p-type hole density that can be adjusted by doping depends on the amount of crystal defects in polycrystalline Ge or polycrystalline SiGe immediately after formation. The hole density of polycrystalline Ge is known to be at the lowest level of 3×10 ¹⁷ cm ⁻³ (see Patent Document 1).

In addition, polycrystalline Ge or polycrystalline SiGe that exhibits p-type without doping remains p-type and does not become n-type even if a small amount of group V element, which is an n-type dopant, is implanted. In order to exhibit conductivity, it is necessary to generate more electrons than holes. Therefore, the lower limit of the range of n-type electron density that can be adjusted by doping depends on the amount of polycrystalline Ge or crystal defects in polycrystalline Ge immediately after formation. The electron density of Sb-doped n-type polycrystalline Ge is known to be at the lowest level of 5×10 ¹⁷ cm ⁻³ (see Non-Patent Document 1).

Polycrystalline Si has grain boundaries and intragranular defects, and these form localized levels. Localized levels cause a decrease in carrier mobility and an increase in leakage current, and are a factor in deteriorating the characteristics of a semiconductor element. It is known that when hydrogen is added to polycrystalline Si, grain boundaries and intragranular defects become electrically inactive, improving the characteristics of semiconductor devices (see Patent Document 2).

Patent Document 3 discloses that by subjecting polycrystalline Ge or polycrystalline SiGe containing group V elements, which are n-type dopants, to hydrogen treatment, p-type defect levels are reduced and the effects of group V elements are enhanced. It is described that it manifests and exhibits n-type characteristics.

Japanese Patent Application Publication No. 2018-142672 Japanese Unexamined Patent Publication No. 62-84562 Japanese Patent Application Publication No. 2004-335494

D. Takahara, K. Moto, T. Imajo, T. Suemasu, and K. Toko, Appl. Phys. Lett. 114, 082105 (2019)

As mentioned above, although it is known that hydrogen treatment has the effect of reducing p-type defect levels (in other words, the effect of reducing hole density), research on Ge thin film devices has not been sufficiently conducted to date. It didn't move forward. The main reason for this is that the effect was not sufficient.

A method for producing large-grained polycrystalline Ge or polycrystalline SiGe consisting of crystal grains with an average grain size of 1 μm or more has been developed based on a solid-phase growth method (see Patent Document 1).

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a semiconductor device in which crystal defects are suppressed in a polycrystalline Ge film and a hole density lower than that of the conventional semiconductor device, and a method for manufacturing the same.

The present invention provides the following means to solve the above problems.

A semiconductor device according to a first aspect of the present invention includes a base material and a semiconductor film formed on one surface of the base material, and the semiconductor film is composed of crystal grains having an average grain size of 1 μm or more. The semiconductor film is a non-doped polycrystalline Ge film, and the hole density of the semiconductor film is 1×10 ¹⁷ cm ⁻³ or less.

In the semiconductor device according to the above aspect, the semiconductor film may include Ge crystal grains having a maximum grain size of 5 μm or more.

A semiconductor device according to a second aspect of the present invention includes a base material and a semiconductor film formed on one surface of the base material, and the semiconductor film is composed of crystal grains having an average grain size of 1 μm or more. The semiconductor film is a non-doped polycrystalline Ge film, and the hydrogen concentration of the semiconductor film is 1×10 ¹⁹ cm ⁻³ or more.

In the semiconductor device according to the above aspect, the semiconductor film may include Ge crystal grains having a maximum grain size of 5 μm or more.

The semiconductor device according to the above aspect may exhibit p-type conductivity by containing a group III element as an impurity in the semiconductor layer.

In the semiconductor device according to the above aspect, the semiconductor layer may have a hole density of 1×10 ¹⁵ cm ⁻³ or more and 1×10 ²³ cm ^{−3 or} less.

In the semiconductor device according to the above aspect, the semiconductor film may have a hole mobility of 25 cm ² /V·s or more.

The semiconductor device according to the above aspect may exhibit n-type conductivity by containing a Group V element as an impurity in the semiconductor layer.

In the semiconductor device according to the above aspect, the semiconductor layer may have an electron density of 1×10 ¹⁶ cm ⁻³ or more and 1×10 ²³ cm ^{−3 or} less.

In the semiconductor device according to the above aspect, the semiconductor layer may have an electron mobility of 50 cm ² /V·s or more.

A method for manufacturing a semiconductor device according to a third aspect of the present invention includes a base material and a semiconductor film formed on one surface of the base material, and the semiconductor film is made of crystal grains having an average grain size of 1 μm or more. A method for manufacturing a semiconductor device that is a polycrystalline film, the method comprising: forming an amorphous semiconductor film on one surface of the base material while heating the base material; heating the semiconductor film to form the semiconductor device; a second step of promoting solid-phase growth of the film; and a fourth step of introducing hydrogen into the semiconductor film, the semiconductor film is a Ge film, and the heating temperature in the first step is set to The heating temperature in the first step is adjusted to be 50% or more and less than 100% of the temperature at which a crystal angle occurs in the film, and the heating temperature in the first step is adjusted so that the density of the particles constituting the semiconductor film is higher than that of the particles in the crystal of the same material. Adjust so that the density is 98% or more and less than 102%.

The method for manufacturing a semiconductor device according to the above aspect includes a third step of adjusting conductivity by doping the semiconductor film with a group III element or a group V element between the second step and the fourth step. May have.

In the method for manufacturing a semiconductor device according to the above aspect, the third step may be performed simultaneously with the first step, and a group III element or a group V element may be vapor-deposited on the amorphous semiconductor film.

In the method for manufacturing a semiconductor device according to the above aspect, the fourth step includes hydrogen plasma treatment, hydrogen radical treatment, hydrogen ion implantation treatment, hydrogen ion beam operation treatment, halogen plasma treatment, halogen radical treatment, halogen ion implantation treatment, halogen It may be one or more of the ion beam scanning processes.

In the method for manufacturing a semiconductor device according to the above aspect, the fourth step may include turning an inert gas containing 5% hydrogen into plasma, and exposing the surface side of the semiconductor film to the plasma.

According to the present invention, the hole density depending on the p-type defect level in the non-doped state of polycrystalline Ge or polycrystalline SiGe after crystallization can be reduced. As a result, the range of p-type or n-type carrier concentration that can be controlled by doping can be expanded compared to conventional polycrystalline Ge or polycrystalline SiGe, and the performance of semiconductor devices containing Ge can be improved.

FIG. 1 is a schematic cross-sectional view of a semiconductor device according to a first embodiment of the present invention. FIG. 3 is a schematic cross-sectional view of a modification of the semiconductor device according to the first embodiment of the present invention. FIG. 3 is a schematic cross-sectional view of a semiconductor device according to a second embodiment of the present invention. FIG. 3 is a diagram illustrating a manufacturing process of a semiconductor device according to a first embodiment or a second embodiment. FIG. 3 is a schematic cross-sectional view of a semiconductor device according to a third embodiment of the present invention. FIG. 7 is a schematic cross-sectional view of a semiconductor device according to a fourth embodiment of the present invention. FIG. 7 is a diagram illustrating a manufacturing process of a semiconductor device according to a third embodiment or a fourth embodiment. 2 is a graph showing the results of analyzing the depthwise concentration of hydrogen contained in a polycrystalline Ge film obtained through hydrogen plasma treatment by secondary ion mass spectrometry. 2 is a graph showing changes in hole density of a polycrystalline Ge film obtained through hydrogen plasma treatment. It is a graph showing the relationship between the hole density of a polycrystalline Ge film obtained through hydrogen plasma treatment and the hydrogen plasma treatment time. 2 is a graph showing the relationship between the electron density of an Sb-doped n-type polycrystalline Ge film obtained through hydrogen plasma treatment and the hydrogen plasma treatment time. It is an EBSD image (grain map) of Example 3.

Hereinafter, the present invention will be described in detail with reference to the drawings as appropriate. In the figures used in the following explanation, characteristic parts of the present invention may be enlarged for convenience in order to make it easier to understand, and the dimensional ratios of each component may differ from the actual ones. . Further, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto, and can be implemented with appropriate changes within the scope of achieving the effects of the present invention. .

[Semiconductor device (first embodiment)]
FIG. 1 is a cross-sectional view of a semiconductor device 100 according to a first embodiment of the present invention.
The semiconductor device 100 according to the first embodiment includes a base material 101 and a semiconductor film (semiconductor thin film) 102 formed (synthesized) on one surface 101a of the base material, and the semiconductor film 102 has an average grain size of 1 μm. This is a non-doped polycrystalline Ge film composed of the above crystal grains, and the hole density of the semiconductor film 102 is 1×10 ¹⁷ cm ⁻³ or less.

In this specification, the "average grain size" of Ge crystal grains in a semiconductor film refers to the diameter (circle equivalent diameter) when each crystal grain is made into a circle with the same area in an electron microscope image or an EBSD image. It refers to the average of the grain size of the crystal grains. It may be automatically calculated by analysis software. Moreover, the average shall be the average of 10 or more crystal grains. Ge crystal particles targeted for average particle size calculation may be selected from one image or from a plurality of images. In the case of an image in which 10 crystal grains are visible, the average of all the visible crystal grains will be the "average grain size" of the Ge crystal grains in the semiconductor film. Since some Ge crystal particles are only partially visible in the image, the "average grain size" of the Ge crystal particles obtained using this definition is the It will be evaluated to be smaller than the average particle size. Therefore, the "average grain size" of the Ge crystal grains in the examples shown later is the "average grain size" of the lower limit of the Ge crystal grains for which the average grain size was calculated.
In addition, in this specification, the "maximum grain size" of Ge crystal particles in a semiconductor film refers to the diameter (circle equivalent diameter ) is the grain size of the crystal grain, the grain size refers to the grain size of the largest crystal grain. Further, the grain sizes of 10 or more crystal grains in the image are compared, and the largest one is defined as the "maximum grain size" of the Ge crystal grains in the semiconductor film. The Ge crystal particles visible in the image are part of the Ge crystal particles in the semiconductor film, and the semiconductor film may contain Ge crystal particles larger than the determined "maximum grain size." The "maximum grain size" determined can be said to be the lower limit "maximum grain size" of Ge crystal grains in the semiconductor film.

As the base material 101, a known base material for forming a semiconductor film can be used, and examples thereof include insulators such as SiO ₂ , glass, and plastic, substrates on which they are mounted, and LSI chips.

Further, the base material 101 may be an inorganic material substrate (for example, a silicon substrate) or a base material in which an insulating layer is formed on an organic material substrate. Such an insulating layer may be any known insulating layer capable of forming polycrystalline Ge; for example, an insulating layer made of SiO ₂ , Al ₂ O ₃ or a compound containing Ge (for example, GeO ₂ ) can be used. .

The semiconductor film 102 is a polycrystalline film composed of large crystal grains of germanium in an undoped (non-doped) state. This undoped polycrystalline film may contain elements unrelated to the function as impurities to the extent that the function is not affected.
The average grain size of the Ge crystal particles constituting the polycrystalline Ge film is 1 μm or more. The average particle diameter of the Ge crystal particles is preferably 3 μm or more, more preferably 5 μm, and even more preferably 10 μm or more.
Note that in this specification, "large grain size" means that the crystal grains constituting the polycrystalline film are 1 μm or more.

The grain size of the crystal grains constituting the polycrystalline film can be evaluated, for example, by electron microscopic observation of a cross section of the film or electron beam diffraction (for example, electron backscatter diffraction (EBSD) method).
Electron backscatter diffraction (EBSD) is an electron diffraction method that can measure crystal orientation texture. It is usually mounted on a scanning electron microscope, and can simultaneously scan and observe the surface of a sample using an electron microscope while simultaneously analyzing crystal orientation. This makes it possible to index the crystal at each measurement point, and considers a region surrounded by grain boundaries (random grain boundaries) where adjacent crystals have different orientations at unspecified angles as one crystal grain. A mapping image of the distribution of can be obtained. This mapping image is called a grain map, and in this specification, this mapping image is called an EBSD image.

The semiconductor film 102 may include Ge crystal grains having a maximum grain size of 5 μm or more.
Including Ge crystal grains with a large maximum grain size also leads to a reduction in the number of grain boundaries, which is preferable as a semiconductor film.
The semiconductor film 102 preferably contains Ge crystal particles with a maximum grain size of 10 μm or more, more preferably contains Ge crystal particles with a maximum grain size of 15 μm or more, and contains Ge crystal particles with a maximum grain size of 20 μm or more. It is even more preferable.

The hole density of the semiconductor film 102 is 1×10 ¹⁷ cm ⁻³ or less.
As mentioned above, it is known that a polycrystalline Ge film exhibits p-type conductivity even in a non-doped state because the defect levels in its crystal act as holes, and the present inventors have developed a technology to increase the grain size. Even a non-doped polycrystalline Ge film made of crystal grains with a small grain size has a hole density of about 1×10 ¹⁸ cm ^-3 , and a non-doped polycrystalline Ge film with a large grain size has a hole density of the lowest level. The pore density was 3×10 ¹⁷ cm ⁻³ .
On the other hand, by introducing hydrogen into a polycrystalline Ge film, it was possible to obtain a polycrystalline Ge film with a hole density significantly lower than that of the conventional hole density.
As will be shown later, in the non-doped polycrystalline Ge film with large grain size developed by the present inventor, a hole density of about 2×10 ¹⁵ cm ^-3 has been obtained, which is higher than the conventional small grain size. Compared to a non-doped polycrystalline Ge film made of crystal grains, a reduction of about three orders of magnitude has been achieved.
The hole density of the semiconductor film 102 is preferably 1×10 ¹⁶ cm ⁻³ or less and 2×10 ¹⁵ cm ^{−3 or} more, more preferably 2×10 ¹⁵ cm ^{−3 or} less.

The hole mobility of the semiconductor film 102 is preferably 25 cm ² /V·s or more, more preferably 50 cm ² /V·s or more and 125 cm ² /V·s or less, 125 cm ² /V·s. It is more preferable that it is above.

As shown in FIG. 2, the semiconductor film 102 may be composed of a plurality of polycrystalline Ge films having different hole densities. FIGS. 2A and 2B illustrate the case where the semiconductor film 102 is composed of three layers of polycrystalline Ge films (102-1, 102-2, 102-3).
A plurality of polycrystalline Ge films having different hole densities can be obtained by adjusting the hydrogen treatment conditions, such as changing the hydrogen treatment time and the microwave output of the hydrogen treatment, for each layer.
Other layers (103-1, 103-2) may be provided between adjacent polycrystalline Ge films, for example, a hydrogen diffusion prevention layer that prevents hydrogen movement between adjacent polycrystalline Ge films. Good too. FIG. 2(b) illustrates a case where there are two other layers. The hydrogen diffusion prevention layer can be made of known materials, such as SiO ₂ , GeO ₂ , and Al ₂ O ₃ . Note that in this case, the semiconductor film 102 is composed of a plurality of polycrystalline Ge films having different hole densities, and layers other than the polycrystalline Ge film, such as the hydrogen diffusion prevention layer, do not constitute the semiconductor film 102. .

[Semiconductor device (second embodiment)]
A semiconductor device according to a second embodiment will be described using FIG. 3. Descriptions of configurations common to the semiconductor device according to the first embodiment are omitted as appropriate.

The semiconductor device 200 according to the second embodiment includes a base material 201 and a semiconductor film (semiconductor thin film) 202 formed (synthesized) on one surface 201a of the base material, and the semiconductor film 202 includes: The semiconductor film 202 is a non-doped polycrystalline Ge film composed of crystal grains with an average grain size of 1 μm or more, and the hydrogen concentration of the semiconductor film 202 is 1×10 ¹⁹ cm ⁻³ or more.

In the semiconductor device 200, the average grain size of the Ge crystal particles constituting the polycrystalline Ge film is 1 μm or more. The average particle diameter of the Ge crystal particles is preferably 3 μm or more, more preferably 5 μm, even more preferably 7 μm or more, and even more preferably 10 μm or more.

In the semiconductor device 200, the semiconductor film 202 may include Ge crystal grains having a maximum grain size of 5 μm or more.
Including Ge crystal grains with a large maximum grain size also leads to a reduction in the number of grain boundaries, which is preferable as a semiconductor film.
The semiconductor film 202 preferably contains Ge crystal particles with a maximum grain size of 10 μm or more, more preferably contains Ge crystal particles with a maximum grain size of 15 μm or more, and contains Ge crystal particles with a maximum grain size of 20 μm or more. It is even more preferable.

The hydrogen concentration of the semiconductor film 202 is 1×10 ¹⁹ cm ⁻³ or more.
By containing hydrogen at an atomic concentration of 1×10 ¹⁹ cm ⁻³ or more, the polycrystalline Ge film 202 has a low hole density, which is significantly lower than the hole density of a conventional film.
The hydrogen concentration of the semiconductor film 202 is preferably 1×10 ²⁰ cm ⁻³ or more and 1×10 ²² cm ⁻³ or less, and more preferably 1×10 ²² cm ⁻³ or more.

The hole mobility of the semiconductor film 202 may be 25 cm ² /V·s or more, more preferably 50 cm ² /V·s or more and 125 cm ² /V·s or less, and 125 cm ² /V·s or more. It is even more preferable if it exists.

The semiconductor film 202 may be composed of a plurality of polycrystalline Ge films having different hydrogen concentrations (see FIG. 2). A plurality of polycrystalline Ge films having different hydrogen concentrations can be obtained by adjusting the hydrogen treatment conditions, such as changing the hydrogen treatment time and the microwave output of the hydrogen treatment, for each layer.
Another layer may be provided between adjacent polycrystalline Ge films (see FIG. 2(b)), for example, a hydrogen migration prevention layer that prevents migration of hydrogen introduced between adjacent polycrystalline Ge films. You may prepare. As the hydrogen migration prevention layer, known materials can be used, such as SiO ₂ , GeO ₂ , and Al ₂ O ₃ .

[Semiconductor device manufacturing method (first embodiment)]
Three main steps for manufacturing the semiconductor device 100 or the semiconductor device 200 will be described using FIG. 4. Note that although the semiconductor device 100 will be described in FIG. 4, the semiconductor device 200 can also be manufactured through similar steps.

(Amorphous film formation process)
While heating the base material 101, Ge particles 102A are deposited on one surface 101a of the base material to form an amorphous semiconductor film 102B (left side in FIG. 4).

The heating method and deposition method are not particularly limited, and general methods (such as molecular beam deposition, CVD, and sputtering) can be used. When using the molecular beam deposition method, particles 102A are deposited in a high vacuum to form an amorphous film 102B. Since this method allows the film formation temperature to be set low, it is a preferred method when forming a film on a base material with low heat resistance such as plastic, an LSI chip, or the like.

The heating temperature in the step of forming the amorphous film is such that the amorphous film 102B to be formed has a particle number density as close to that of a crystal as possible (98% or more and less than 102% of the particle density in a crystal of the same material). , and the conditions are adjusted so that no crystal nuclei are generated. In other words, the temperature is adjusted to be as high as possible without generating crystal nuclei in the amorphous film 102B.

In reality, the temperature may be adjusted to be 30% or more and less than 100% of the temperature at which crystal nuclei are generated in the amorphous film 102B, and more preferably adjusted to be 50% or more and less than 100%. Specifically, the temperature is approximately 100°C or higher and 700°C or lower. This temperature is adjusted depending on the material and thickness of the semiconductor film 102 to be formed. For example, when forming the semiconductor film 102 with a thickness of 100 nm, the temperature is 100 to 150°C.

(Solid phase growth process)
A heat treatment (in any atmosphere) is performed to promote solid phase growth of the amorphous semiconductor film 102B formed in the amorphous film formation step, and a polycrystalline semiconductor film (polycrystalline film) 102C is synthesized ( (center of Figure 4). In the solid phase growth step, the heating temperature is preferably 350°C or more and 800°C or less, and the heating time is preferably 0.1 hour or more and 300 hours or less.

By adjusting the heating temperature during amorphous film formation as described above, the formed semiconductor film 102C becomes a polycrystalline film made of particles with a large grain size of 1 μm or more.

(Hydrogen treatment process)
Hydrogen element 102D is introduced into the polycrystalline semiconductor film (polycrystalline film) 102C formed in the solid-phase growth step, and a polycrystalline semiconductor film 102E into which hydrogen is introduced is synthesized (see FIG. 4). right side).

The method for introducing hydrogen is not particularly limited, and general methods (hydrogen plasma treatment, hydrogen annealing treatment, thermal diffusion method, etc.) can be used. When hydrogen plasma treatment is used, hydrogen is introduced into the polycrystalline film 102C by turning hydrogen-containing Ar into plasma in a high vacuum and exposing it to one surface 102a of the base material to form the hydrogen-treated polycrystalline film 102E. will be formed. With this method, the amount of hydrogen element introduced can be controlled by adjusting the mixing ratio of hydrogen and argon and the time of exposure to hydrogen plasma.

In the semiconductor device 100 obtained through the steps of amorphous film formation and solid phase growth, an amorphous film 102B having a density close to that of a crystal is formed within a range where crystal nuclei are not generated during the manufacturing process, and this is solidified. It has a polycrystalline semiconductor film 102C obtained by phase growth. Since this semiconductor film 102C is a polycrystalline film made of crystal grains with a large grain size of 1 μm or more, the amount of hydrogen introduced in the hydrogen introduction process is lower than that of a conventional polycrystalline Ge film with a small grain size of 1 μm or less. You can do more.

If the grain size of the crystal grains constituting the semiconductor film 102 is smaller than 1 μm, the hole density cannot be reduced to the same extent as in the present invention.

As described above, the semiconductor device 100 according to the present embodiment includes a semiconductor 102E in which the hole density is reduced by forming a polycrystalline film 102C with a large grain size and introducing hydrogen into the polycrystalline film 102C during its manufacturing process. are doing. Since this semiconductor film 102E is a polycrystalline film made of large crystal grains of 1 μm or more, it is possible to realize a hole density lower than that of the conventional semiconductor film.
In addition to the steps described in Patent Document 1, (i) the deposition temperature was changed stepwise in the amorphous film formation (deposition) step, and (ii) a base layer containing Ge was formed on the surface. By using a base material, it is possible to further increase the particle size. As (i), for example, a high-density layer (deposited at 150° C., for example) is used as a nucleation layer, and a low-density layer (deposited at 75° C., for example) is formed thereon as a nucleation suppression layer.

When the semiconductor film 102 is composed of a plurality of polycrystalline Ge films with different hole densities or a plurality of polycrystalline Ge films with different hydrogen concentrations, the hydrogen treatment step is performed on each polycrystalline Ge film. It consists of sub-steps in which the hydrogen treatment conditions are adjusted for each step.

[Semiconductor device (third embodiment)]
FIG. 5 is a cross-sectional view of a semiconductor device 300 according to the third embodiment. Descriptions of configurations common to the semiconductor device according to the above embodiments will be omitted.

The semiconductor device 300 according to the third embodiment includes a base material 301 and a semiconductor film (semiconductor thin film) 302 formed (synthesized) on one surface 301a of the base material, and the semiconductor film 302 has an average grain size of 1 μm. It is a polycrystalline Ge film composed of the above crystal grains, the hydrogen concentration of the semiconductor film 302 is 1 × 10 ¹⁹ cm ^-3 or more, and the semiconductor film 302 contains a group III element as an impurity, so that it becomes p-type. Indicates conduction type.

The semiconductor film 302 is a polycrystalline germanium film made of crystal grains with increased grain size. The average grain size of the Ge crystal particles constituting the polycrystalline Ge film is 1 μm or more. The average particle diameter of the Ge crystal particles is preferably 3 μm or more, more preferably 5 μm, and even more preferably 10 μm or more.

In the semiconductor device 300, the semiconductor film 302 may include Ge crystal grains having a maximum grain size of 5 μm or more.
Including Ge crystal grains with a large maximum grain size also leads to a reduction in the number of grain boundaries, which is preferable as a semiconductor film.
The semiconductor film 302 preferably contains Ge crystal particles with a maximum grain size of 10 μm or more, more preferably contains Ge crystal particles with a maximum grain size of 15 μm or more, and contains Ge crystal particles with a maximum grain size of 20 μm or more. It is even more preferable.

The semiconductor film 302 is a polycrystalline Ge film containing a group III element and exhibiting p-type conductivity. Examples of group III elements include boron B and aluminum Al.
The hole density of the semiconductor film 302 is preferably 1×10 ¹⁵ cm ⁻³ or more and 1×10 ²³ cm ⁻³ or less.

It is preferable that the hole mobility of the semiconductor film 302 is 25 cm ² /V·s or more.

The semiconductor film 302 may be composed of a plurality of polycrystalline Ge films having different hole densities (see FIG. 2). A plurality of polycrystalline Ge films having different hole densities can be obtained by adjusting the hydrogen treatment conditions, such as changing the hydrogen treatment time and the microwave output of the hydrogen treatment, for each layer.
Another layer may be provided between adjacent polycrystalline Ge films (see FIG. 2(b)), for example, a hydrogen migration prevention layer may be provided between adjacent polycrystalline Ge films to prevent hydrogen migration. good. As the hydrogen migration prevention layer, known materials can be used, such as SiO ₂ , GeO ₂ , and Al ₂ O ₃ .

[Semiconductor device (4th embodiment)]
A semiconductor device according to a fourth embodiment will be described using FIG. 6. Description of the configuration common to the semiconductor device according to the third embodiment will be omitted.
The semiconductor device 400 according to the fourth embodiment includes a base material 401 and a semiconductor film (semiconductor thin film) 402 formed (synthesized) on one surface 401a of the base material, and the semiconductor film 402 has an average grain size of 1 μm. It is a polycrystalline Ge film composed of the above crystal grains, the hydrogen concentration of the semiconductor film 402 is 1 × 10 ¹⁹ cm ^-3 or more, and the semiconductor film 402 contains a group V element as an impurity to achieve n-type conduction. Show type.

The semiconductor film 402 is a polycrystalline germanium film made of crystal grains with increased grain size. The average grain size of the Ge crystal particles constituting the polycrystalline Ge film is 1 μm or more. The average particle diameter of the Ge crystal particles is preferably 3 μm or more, more preferably 5 μm, and even more preferably 10 μm or more.

In the semiconductor device 400, the semiconductor film 402 may include Ge crystal grains having a maximum grain size of 5 μm or more.
Including Ge crystal grains with a large maximum grain size also leads to a reduction in the number of grain boundaries, which is preferable as a semiconductor film.
The semiconductor film 402 preferably contains Ge crystal particles with a maximum grain size of 10 μm or more, more preferably contains Ge crystal particles with a maximum grain size of 15 μm or more, and contains Ge crystal particles with a maximum grain size of 20 μm or more. It is even more preferable.

The semiconductor film 402 is a polycrystalline Ge film containing a group V element and exhibiting n-type conductivity.
Examples of group V elements include phosphorus P, arsenic As, and antimony Sb.
The electron density of the semiconductor film 402 is preferably 1×10 ¹⁶ cm ⁻³ or more and 1×10 ²³ cm ⁻³ or less.

The electron mobility of the semiconductor film 402 may be 50 cm ² /V·s or more, more preferably 100 cm ² /V·s or more and 200 cm ² /V·s or less, and preferably 200 cm ² /V·s or more. It is even more preferable.

The semiconductor film 402 in the semiconductor device according to the fourth embodiment may be composed of a plurality of polycrystalline Ge films having different electron densities. A plurality of polycrystalline Ge films having different electron densities can be obtained by adjusting the hydrogen treatment conditions, such as changing the hydrogen treatment time and the microwave output of the hydrogen treatment, for each layer.
In this configuration, another layer may be provided between adjacent polycrystalline Ge films, for example, a hydrogen migration prevention layer may be provided between adjacent polycrystalline Ge films to prevent hydrogen migration. As the hydrogen migration prevention layer, known materials can be used, such as SiO ₂ , GeO ₂ , and Al ₂ O ₃ .

[Semiconductor device manufacturing method (second embodiment)]
Four main steps for manufacturing the semiconductor device 300 or 400 will be described using FIG. 7. Note that although the semiconductor device 300 will be described in FIG. 7, the semiconductor device 400 can also be manufactured using the same process. The method for manufacturing the semiconductor device of the first embodiment further includes a step of introducing impurities to make the semiconductor device p-type or n-type conductive. Descriptions of steps common to those of the method for manufacturing a semiconductor device of the first embodiment will be simplified or omitted as appropriate.

(Amorphous film formation and impurity introduction process)
The impurity introduction method is not particularly limited, and general methods (ion implantation method, thermal diffusion method, impurity vapor deposition method, etc.) can be used.

When using the impurity vapor deposition method, in the step of forming an amorphous film, while heating the base material 301, Ge particles 302A are deposited on one surface 301a of the base material, and at the same time, an impurity element 302B is simultaneously deposited. do. Thereafter, heat treatment is performed in the solid phase growth process to simultaneously perform polycrystalization and doping. When using the ion implantation method or the thermal diffusion method, the ion implantation method or the thermal diffusion method is performed as the impurity introduction step after polycrystallization in the solid phase growth step.

The impurity element is not particularly limited, and impurity elements for making the conduction type p-type can be, for example, B, Al, Ga, In, and Tl, and impurity elements for making the conduction type n-type can be, for example, B, Al, Ga, In, and Tl. The impurity element can be, for example, P, As, Sb, or Bi.

The heating temperature in the step of forming the amorphous film is such that the amorphous film 302C to be formed has a particle number density as close to that of a crystal as possible (98% or more and less than 102% of the particle density in a crystal of the same material). , and the conditions are adjusted so that no crystal nuclei are generated. In other words, the temperature is adjusted to be as high as possible without generating crystal nuclei in the amorphous film 302C.

In reality, the temperature may be adjusted to be 30% or more and less than 100% of the temperature at which crystal nuclei are generated in the amorphous film 302C, and more preferably adjusted to be 50% or more and less than 100%. Specifically, the temperature is approximately 100°C or higher and 700°C or lower. This temperature is adjusted depending on the material and thickness of the semiconductor film 302 to be formed. For example, when forming the semiconductor film 302 with a thickness of 100 nm, the temperature is 100 to 150°C.

(Solid phase growth process)
An amorphous semiconductor film formed in the amorphous film formation process by performing heat treatment (in any atmosphere) in the same manner as in the solid phase growth process in the method of manufacturing a semiconductor device of the first embodiment. Solid phase growth of 302C is promoted to synthesize a polycrystalline semiconductor film (polycrystalline film) 302D (center of FIG. 7). In the solid phase growth step, the heating temperature is preferably 350°C or more and 800°C or less, and the heating time is preferably 0.1 hour or more and 300 hours or less.

By adjusting the heating temperature in forming the amorphous film as described above, the semiconductor film 302D that is formed becomes a polycrystalline film made of particles with a large grain size of 1 μm or more.

(Hydrogen treatment process)
Similar to the hydrogen treatment step in the semiconductor device manufacturing method of the first embodiment, a process of introducing hydrogen element 302E into the impurity-introduced polycrystalline semiconductor film 302D formed in the solid phase growth step is performed. , an impurity-doped polycrystalline semiconductor film (hydrogen-treated polycrystalline film) 302F into which hydrogen is introduced is synthesized.

Similarly to the above process, when hydrogen plasma treatment is used, hydrogen is introduced into the polycrystalline film 302D by turning hydrogen-containing Ar into plasma in a high vacuum and exposing it to one surface 302a of the base material. A treated polycrystalline film 302F will be formed. With this method, the amount of hydrogen element introduced can be controlled by adjusting the mixing ratio of hydrogen and argon and the time of exposure to hydrogen plasma.

The semiconductor device 300 includes a polycrystalline semiconductor film 302D obtained by forming an amorphous film 302C with a density close to that of a crystal within a range in which crystal nuclei are not generated during the manufacturing process, and growing the amorphous film in a solid phase. ing. Since this semiconductor film 302D is a polycrystalline film made of crystal grains with a large grain size of 1 μm or more, the amount of hydrogen introduced in the hydrogen introduction process is lower than that of a conventional polycrystalline Ge film with a small grain size of 1 μm or less. You can do more.

The above method for manufacturing a semiconductor device can be applied by replacing the polycrystalline Ge film with a polycrystalline SiGe film.

Hereinafter, the effects of the present invention will be made clearer by way of Examples. It should be noted that the present invention is not limited to the following examples, and can be implemented with appropriate modifications within the scope of the gist thereof.

(Example 1)
Ge particles were deposited on a quartz glass substrate by a molecular beam deposition method with the substrate temperature Td set in the range of 125° C. to form an amorphous Ge film with a thickness of 100 nm. The film formation rate was 1 nm/min, and the film formation time was 100 minutes.

Thereafter, the amorphous Ge film was introduced into an electric furnace with a nitrogen atmosphere, and heat treated at 450° C. for 5 hours to promote solid phase growth and obtain a polycrystalline Ge thin film.

The obtained polycrystalline Ge thin film was subjected to electron beam backscatter diffraction measurement, and the average grain size of the Ge crystal particles was automatically calculated using analysis software based on the EBSD image (grain map), and was found to be 3.6 μm. . Moreover, the maximum particle size was 6.2 μm. Note that the average particle size obtained by automatic calculation is not the average particle size divided by the number of particles, but the average particle size weighted by area. The influence of microscopic particles, etc.) generated is small.

Defects in the polycrystalline Ge thin film act as acceptors (holes), and the hole density after forming the polycrystalline Ge film was 3×10 ¹⁷ cm ⁻³ .

Thereafter, the polycrystalline Ge film was introduced into a vacuum chamber in which plasma was generated by irradiating Ar gas containing 5% hydrogen with electromagnetic waves with an output of 150 W to 450 W under vacuum, and then left standing for 20 minutes to form a polycrystalline Ge film. Hydrogen plasma treatment was performed on the membrane surface to introduce hydrogen.

Figure 8 is a graph showing the results of secondary ion mass spectrometry (SIMS) analysis of the depthwise concentration of hydrogen contained in a polycrystalline Ge film obtained through hydrogen plasma treatment (output 300W, 20 minutes). be. The horizontal axis of the graph indicates the thickness [nm] in the depth direction of the sample when the surface of the polycrystalline Ge film is taken as 0, and the vertical axis indicates the hydrogen concentration [cm ⁻³ ].

When hydrogen plasma treatment was not performed, the hydrogen concentration contained in the polycrystalline Ge thin film was on the order of 10 ¹⁹ [cm ⁻³ ] (lower limit of detection sensitivity). On the other hand, in the case of this embodiment in which hydrogen plasma treatment was performed, the maximum value is 1×10 ²³ [cm ⁻³ ] at the surface of the polycrystalline Ge thin film, and decreases depending on the depth direction, and the value at the interface with the glass substrate is 1×10 23 [cm −3 ]. It shows a minimum value of 2×10 ¹⁹ [cm ⁻³ ] in the vicinity. Hydrogen is introduced into the polycrystalline Ge film by hydrogen plasma treatment.

The electrical characteristics of the polycrystalline Ge film according to Example 1 were calculated using the van der Pauw method. FIG. 9 is a graph showing changes in hole density in a polycrystalline Ge film obtained through hydrogen plasma treatment. The horizontal axis of the graph indicates the presence or absence of hydrogen treatment, and the vertical axis indicates the hole density [cm ⁻³ ]. Here, the polycrystalline Ge film of large grain size particles with an average grain size of 3.6 μm and the polycrystalline Ge film of small grain size particles with an average grain size of 0.5 μm according to Example 1 are plotted as circles, respectively. Shown as a triangular plot.

The hole density of the polycrystalline Ge film according to Example 1 was significantly reduced from 3×10 ¹⁷ [cm ⁻³ ] before hydrogen plasma treatment to 3×10 ¹⁵ [cm ⁻³ ] after hydrogen plasma treatment. . On the other hand, for conventional small-grain polycrystalline Ge films, the current density after hydrogen plasma treatment is 2×10 ¹⁷ [cm ^-3 ], although this decreases from 9× ^{10 17} [cm ^-3 ] before hydrogen plasma treatment. . In the polycrystalline Ge film according to Example 1, the effect of reducing the hole density by hydrogen treatment is greater than that of the conventional polycrystalline Ge film with small grain size.

FIG. 10 is a graph showing the relationship between the hole density of a polycrystalline Ge film obtained through hydrogen plasma treatment and the hydrogen plasma treatment time. The horizontal axis of the graph represents the hydrogen treatment time [minutes], and the vertical axis represents the hole mobility [cm ⁻³ ]. Here, the hole density when the microwave output in the hydrogen treatment step is 150 W, 300 W, and 450 W is shown as a square plot, a circle plot, and a triangular plot, respectively.

The hole density of the polycrystalline Ge film strongly depends on the hydrogen plasma treatment time, and reaches its minimum value (2×10 ¹⁵ [cm ⁻³ ]) when the hydrogen plasma treatment time is 20 minutes. This result shows that the amount of hydrogen introduced increases according to the length of the hydrogen plasma treatment time, and when the hydrogen plasma treatment time is the same, the amount of hydrogen introduced increases according to the magnitude of the plasma output. do.

The hole mobility of the polycrystalline Ge film according to Example 1 is 125 [cm ² /V·s].

(Example 2)
By molecular beam deposition method, Ge particles were deposited on a quartz glass substrate with the substrate temperature Td set at 125°C to form an amorphous Ge film with a thickness of 100 nm (amorphous film formation process ). The film formation rate was 1 nm/min, and the film formation time was 100 minutes.

At the same time as the Ge particles were deposited, Sb particles were deposited as an n-type dopant (step of impurity introduction). The temperature of the K cell for evaporating Sb was 290° C., the film formation rate was 1.0 nm/min, and the film formation time was 100 minutes. This amount of vapor deposition corresponds to the amount by which holes originating from crystal defects in the polycrystalline Ge film are inactivated and a p-type semiconductor is inverted to an n-type semiconductor.

After that, it was introduced into an electric furnace with a nitrogen atmosphere, and the amorphous Ge film was heat-treated at 450° C. for 5 hours to promote solid phase growth. Through this heat treatment, amorphous Ge is crystallized into polycrystalline Ge, and at the same time, Sb particles as an n-type dopant are diffused into the polycrystalline Ge film to form an Sb-doped n-type polycrystalline Ge film exhibiting n-type conductivity. It is formed.

Regarding the electrical characteristics of the Sb-doped n-type polycrystalline Ge film, the electron density calculated using the van der Pauw method was 3×10 ¹⁸ [cm ⁻³ ].

Thereafter, the Sb-doped n-type polycrystalline Ge thin film was introduced into a vacuum chamber in which plasma was generated by irradiating Ar gas containing 5% hydrogen with electromagnetic waves with an output of 300 W under vacuum, and then left standing for 20 minutes to form a Ge Hydrogen was added to the surface of the thin film by hydrogen plasma treatment.

FIG. 11 is a graph showing the relationship between the electron density of an Sb-doped n-type polycrystalline Ge film obtained through hydrogen plasma treatment and the hydrogen plasma treatment time. The hydrogen treatment time [minutes] is shown, and the vertical axis shows the electron density [cm ⁻³ ].

The electron density of the polycrystalline Ge film strongly depends on the hydrogen plasma treatment time, and reaches its minimum value (1×10 ¹⁶ [cm ⁻³ ]) when the hydrogen plasma treatment time is 20 minutes. This result shows that the amount of hydrogen introduced increases according to the length of the hydrogen plasma treatment time, and when the hydrogen plasma treatment time is the same, the amount of hydrogen introduced increases according to the magnitude of the plasma output. do. This shows that the hole density of the non-doped polycrystalline Ge film was reduced by the hydrogen plasma treatment, which resulted in the n-type electron density being reduced. This expanded the controllable range of n-type electron density.

The Sb-doped n-type polycrystalline Ge film according to this example has an electron mobility of 200 [cm ² /V·s].

(Example 3)
Example 3 was the same as Example 1 except that a substrate with a GeO ₂ film (thickness: 100 nm) formed on a quartz glass substrate was used, and the solid phase growth process was performed under heat treatment conditions of 375°C and 150 hours. A polycrystalline Ge film was obtained under these conditions.
When electron beam backscatter diffraction measurements were performed on the polycrystalline Ge film before hydrogen plasma treatment, the average grain size of the Ge crystal particles was 10.1 μm, and the maximum grain size was 17.5 μm.
FIG. 12 shows an example of the obtained EBSD image (grain map). Ten Ge crystal particles are visible in the EBSD image, and the maximum particle size in this image is 17.5 μm.

The present invention relates to the development of high-speed, low-power thin film transistors, high efficiency and low cost multi-junction thin film solar cells, three-dimensional and multifunctional integrated circuits, and near-infrared light for optical communications. It can be widely used in applications such as "light-receiving sensors."

100 semiconductor device,
101 base material,
102 semiconductor film,
200 semiconductor device,
201 base material,
202 semiconductor film,
300 semiconductor device,
301 base material,
302 semiconductor film 400 semiconductor device,
401 Base material,
402 Semiconductor film

Claims (15)

comprising a base material and a semiconductor film formed on one surface of the base material,
The semiconductor film is a non-doped polycrystalline Ge film composed of crystal grains with an average grain size of 1 μm or more,
A semiconductor device, wherein the semiconductor film has a hole density of 1×10 ¹⁷ cm ⁻³ or less. 2. The semiconductor device according to claim 1, wherein the semiconductor film includes Ge crystal grains having a maximum grain size of 5 μm or more. comprising a base material and a semiconductor film formed on one surface of the base material,
The semiconductor film is a non-doped polycrystalline Ge film composed of crystal grains with an average grain size of 1 μm or more,
A semiconductor device, wherein the semiconductor film has a hydrogen concentration of 1×10 ¹⁹ cm ⁻³ or more. 4. The semiconductor device according to claim 3, wherein the semiconductor film includes Ge crystal grains having a maximum grain size of 5 μm or more. 5. The semiconductor device according to claim 3, wherein the semiconductor layer exhibits p-type conductivity by containing a group III element as an impurity. 6. The semiconductor device according to claim 5, wherein the semiconductor layer has a hole density of 1×10 ¹⁵ cm ⁻³ or more and 1×10 ²³ cm ⁻³ or less. 5. The semiconductor device according to claim 1, wherein the semiconductor film has a hole mobility of 25 cm ² /V·s or more. 5. The semiconductor device according to claim 3, wherein the semiconductor layer exhibits n-type conductivity by containing a Group V element as an impurity. 9. The semiconductor device according to claim 8, wherein the semiconductor layer has an electron density of 1×10 ¹⁶ cm ⁻³ or more and 1×10 ²³ cm ^{−3 or} less. The semiconductor device according to claim 8 , wherein the semiconductor layer has an electron mobility of 50 cm ² /V·s or more. A method for manufacturing a semiconductor device comprising a base material and a semiconductor film formed on one surface of the base material, the semiconductor film being a polycrystalline film made of crystal grains with an average grain size of 1 μm or more,
a first step of forming an amorphous semiconductor film on one surface of the base material while heating the base material;
a second step of heating the semiconductor film to promote solid phase growth of the semiconductor film;
a fourth step of introducing hydrogen into the semiconductor film,
The semiconductor film is a Ge film,
Adjusting the heating temperature in the first step to be 50% or more and less than 100% of the temperature at which a crystal angle occurs in the semiconductor film,
A method for manufacturing a semiconductor device, wherein the heating temperature in the first step is adjusted so that the density of particles constituting the semiconductor film is 98% or more and less than 102% of the density of particles in a crystal of the same material. 12. The semiconductor device according to claim 11, further comprising a third step of adjusting conductivity by doping the semiconductor film with a group III element or a group V element between the second step and the fourth step. Production method. 13. The method for manufacturing a semiconductor device according to claim 12, wherein the third step is performed simultaneously with the first step, and a group III element or a group V element is deposited on the amorphous semiconductor film. The fourth step includes one or more of hydrogen plasma treatment, hydrogen radical treatment, hydrogen ion implantation treatment, hydrogen ion beam manipulation treatment, halogen plasma treatment, halogen radical treatment, halogen ion implantation treatment, and halogen ion beam scanning treatment. 14. The method for manufacturing a semiconductor device according to claim 13, which is a process. 15. The method for manufacturing a semiconductor device according to claim 11, wherein in the fourth step, an inert gas containing 5% hydrogen is turned into plasma, and a surface side of the semiconductor film is exposed to the plasma.

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