JP7360180B2 - Semiconductor device and its manufacturing method - Google Patents

Description

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

Semiconductor films synthesized on insulators (SiO ₂ , glass, plastic) are the main components for realizing three-dimensional integrated circuits (LSIs) and higher performance and lower prices for information terminals and solar cells. This element is being actively researched.

Si is a typical semiconductor and is used in all kinds of electronic devices. In addition, Ge and SiGe, which are group IV semiconductors like Si, have a high affinity with the existing material Si, and also have higher carrier mobility and lower crystallization temperature than Si, so they are expected to be used as next-generation semiconductor materials. has been done.

When forming a semiconductor film, it is necessary to keep the process temperature low in consideration of the effect on the LSI chip, glass, and plastic that serve as the base material (substrate). As a method for forming the semiconductor film, a transfer method, chemical vapor deposition method (CVD method), flash lamp annealing (FLA), metal induced growth method (MIC), solid phase growth method, etc. can be used. The transfer method involves cutting a single crystal substrate into a thin film and bonding it onto an insulator, but the single crystal substrate used as the raw material is expensive, the process is complicated, and it is difficult to transfer uniformly and over a large area. Since it is difficult, it is considered that there is a high practical barrier (Non-Patent Document 1).

In addition, chemical vapor deposition is the most common method for synthesizing thin films on insulators, but it simultaneously performs film formation on a substrate and crystallization, and the constituent particles of the synthesized film are small. The particle size becomes (<1 μm). Therefore, the mobility of carriers in the formed semiconductor film is extremely low (Non-Patent Document 2).

In addition, flash lamp annealing is a method in which an amorphous semiconductor film is formed on an insulator and then heated with a lamp to promote crystallization. Although there is little thermal damage to the substrate, in this case as well, The mobility of carriers in the synthesized semiconductor film is low. In this method, it has been reported that when Ge is used as the material for the semiconductor film, the obtained hole mobility is about 200 cm ² /V·s (Non-Patent Document 3).

Further, the metal-induced growth method is a method of inducing crystallization in a planar direction using a catalyst metal deposited on an amorphous semiconductor film as a nucleus. In this method, it is possible to synthesize a semiconductor film at a low temperature, and the particle size of the constituent particles of the semiconductor film is increased to 50 μm or more. It has been reported so far that when Ge is used as a material for a semiconductor film, a maximum hole mobility of 210 cm ² /V·s can be obtained (Non-Patent Document 4).

Further, the solid phase growth method is a very simple method in which an amorphous film is crystallized by heating it in an electric furnace, and it is easy to obtain a film in which the constituent particles are relatively large in size. However, when Si and Ge are grown in solid phase using this method, heat treatment at 600° C. or higher and 400° C. or higher is usually required, respectively. In the case of using Ge, the highest hole mobility reported so far is 140 cm ² /V·s (Non-Patent Document 5). It has also been reported that a hole mobility of 320 cm ² /V・s can be obtained by adding Sn to Ge, which is the highest hole mobility ever obtained in a low-temperature synthetic thin film on an insulator. This is the highest value among those reported (Non-Patent Document 6).

G. Taraschi, A.J. Pitera, and E.A. Fitzgerald, Solid-State. Electronics. 48, 1297 (2004). T. Matsui, M. Kondo, K. Ogata, T. Ozawa, and M. Isomura, Appl. Phys. Lett. 89, 142115 (2006). K. Usuda, Y. Kamata, Y. Kamimuta, T. Mori, M. Koike, and T. Tezuka, Appl. Phys. Express 7, 56501 (2014). K. Kasahara, Y. Nagatomi, K. Yamamoto, H. Higashi, M. Nakano, S. Yamada, D. Wang, H. Nakashima, and K. Hamaya, Appl. Phys. Lett. 107, 142102 (2015). K. Toko, I. Nakao, T. Sadoh, T. Noguchi, and M. Miyao, Solid-State. Electronics. 53, 1159 (2009). T. Sadoh, Y. Kai, R. Matsumura, K. Moto, and M. Miyao, Appl. Phys. Lett. 109, 232106 (2016).

The present invention has been made in view of the above circumstances, and provides a semiconductor device and a semiconductor device that reduce the heat load that damages the base material and achieve higher carrier mobility and power generation efficiency than before when the device is operated. , the purpose is to provide a manufacturing method thereof.

The present invention provides the following means to solve the above problems.
(1) A semiconductor device according to one 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 polycrystalline grains having an average grain size of 1 μm or more. It is a crystalline film.
(2) In the semiconductor device according to (1), it is preferable that the semiconductor film has a thickness of 50 nm or more.
(3) In the semiconductor device according to either (1) or (2), it is preferable that the crystal particles are made of Ge.
(4) In the semiconductor device according to either (1) or (2), it is preferable that the crystal particles are made of SiGe.
(5) In the semiconductor device according to either (1) or (2), it is preferable that the crystal particles are made of Si.
(6) A method for manufacturing a semiconductor device according to one aspect of the present invention is the method for manufacturing a semiconductor device according to any one of (1) to (5), wherein while heating the base material, a first step of forming an amorphous semiconductor film on one surface of a base material; a second step of heating the semiconductor film to promote solid phase growth of the semiconductor film; The heating temperature is adjusted to be 50% or more and less than 100% of the temperature at which crystal nuclei are generated in the semiconductor film.
(7) In the method for manufacturing a semiconductor device according to (6), the heating temperature in the first step is such that the density of particles constituting the semiconductor film is 98% or more of the density of particles in a crystal of the same material. It is preferable to adjust it so that it is less than %.
(8) In the method for manufacturing a semiconductor device according to any one of (6) and (7), the heating temperature in the first step is preferably 100°C or more and 700°C or less.
(9) In the method for manufacturing a semiconductor device according to any one of (6) to (8), the heating temperature in the second step is preferably 350° C. or more and 800° C. or less.

The semiconductor device of the present invention has a semiconductor film obtained by forming an amorphous film 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. Since this semiconductor film is a polycrystalline film made of crystal grains having a large grain size, when the semiconductor device of the present invention is operated as a device, it is possible to realize higher carrier mobility than in the past.

In the semiconductor film of the present invention, since the heating temperature required for solid phase growth is reduced, it is possible to reduce the thermal load that would damage the base material.

FIG. 1 is a cross-sectional view of a semiconductor device of the present invention. FIG. 3 is a diagram illustrating a manufacturing process of a semiconductor device of the present invention. (a), (b) are graphs showing the relationship between the processing temperature in the first step and the particle density of the semiconductor film finally formed in the method for manufacturing a semiconductor device of the present invention. (a) to (c) are EBSD images of semiconductor films finally formed in accordance with the processing temperature in the first step in the method for manufacturing a semiconductor device of the present invention. 3 is a graph showing the relationship between the processing temperature in the first step and the particle size of the semiconductor film finally formed in the method for manufacturing a semiconductor device of the present invention. 3 is a graph showing the relationship between the processing temperature in the first step and the hole density and hole mobility of the finally formed semiconductor film in the method for manufacturing a semiconductor device of the present invention.

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. There is. 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 configuration]
FIG. 1 is a cross-sectional view of a semiconductor device 100 according to an embodiment of the present invention. The semiconductor device 100 includes a base material 101 and a semiconductor film (semiconductor thin film) 102 formed (synthesized) on one surface 101a of the base material.

The base material 101 is made of an insulator such as SiO ₂ , glass, or plastic, a substrate on which the insulator is mounted, an LSI chip, or the like.

The semiconductor film 102 is a polycrystalline film made of large crystal grains of any material that can be formed into a thin film, such as Ge, SiGe, Si, GeSn, SiC, GaAs, InP, GaN, ZnSe, CdS, and ZnO. be. The average particle size of the crystal particles may be 1 μm or more, preferably 5 μm or more and 30 μm or less, and more preferably about 30 μm.

The thickness of the semiconductor film 102 may be 50 nm or more, and preferably 50 nm or more and 5000 nm or less.

[Method for manufacturing semiconductor device]
Two main steps for manufacturing the semiconductor device 100 will be explained using FIG. 2.

(First step)
While heating the base material 101, particles 102A of Ge, SiGe, Si, GeSn, SiC, GaAs, InP, GaN, ZnSe, CdS, ZnO, etc. are deposited on one surface 101 of the base material to form an amorphous semiconductor. A film 102B is formed (left side in FIG. 2).

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, a molecular beam of the particles 102A is generated in a high vacuum and is irradiated onto one surface 101a of the substrate being heated, thereby depositing the particles 102A and forming an amorphous film. 102B will be formed. 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 first step is such that the amorphous film 102B to be formed has a particle number density as close as possible to that of a crystal (98% or more and less than 102% of the particle density in a crystal of the same material), and Adjust so that no nuclei are generated. In other words, the temperature is adjusted to be as high as possible without generating crystal nuclei in the semiconductor film 102B.

Actually, 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 semiconductor 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 made of Ge and having a thickness of 100 nm, the temperature is set at 100 to 150°C. Further, when forming a 100 nm thick semiconductor film 102 made of SiGe and Si, the temperature is 100 to 650° C. and 500 to 650° C., respectively.

(Second process)
Heat treatment (in any atmosphere) is performed to promote solid phase growth of the amorphous semiconductor film 102B formed in the first step, and to synthesize a polycrystalline semiconductor film (polycrystalline film) 102C (see right side of FIG. 2). ).
In the second 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 the first step 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.

In the manufacturing process of the semiconductor device 100 obtained through the first and second steps, an amorphous film 102B having a density close to that of a crystal is formed within a range where crystal nuclei are not generated, and this is grown in a solid phase. It has a polycrystalline semiconductor film 102C obtained by. Since this semiconductor film 102C is a polycrystalline film made of crystal grains with a large grain size of 1 μm or more, when the semiconductor device 100 is operated as a device, it is possible to achieve higher carrier mobility than in the past. For example, in a semiconductor film made of Ge and having a thickness of 100 nm, the hole mobility can be improved to 340 cm ² /V·s. Further, in a semiconductor film made of Ge and having a thickness of 300 nm, the hole mobility can be improved to 380 cm ² /V·s.

If the grain size of the crystals constituting the semiconductor film 102 is smaller than 1 μm, carrier scattering due to grain boundaries becomes significant, making it impossible to obtain a mobility equivalent to that of the present invention.

As described above, the semiconductor device 100 according to the present embodiment is obtained by forming an amorphous film 102B with a density close to that of a crystal within a range in which crystal nuclei are not generated during its manufacturing process, and performing solid phase growth on the amorphous film 102B. It has a semiconductor film 102C. Since this semiconductor film 102C is a polycrystalline film made of crystal grains with a large grain size of 1 μm or more, it is possible to achieve higher carrier mobility than in the past.

In the semiconductor film 102C in this embodiment, the heating temperature required for solid phase growth is reduced. For example, Ge can be formed without performing high-temperature treatment of 500° C. or higher that would damage the base material 101. Therefore, as the base material 101, a wide variety of materials such as LSI chips, glass with low heat resistance, plastic, etc. can be used.

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 changes without changing the gist thereof.

(Example 1)
By molecular beam deposition, germanium (Ge) particles are deposited on a quartz glass substrate with the substrate temperature T _d set in the range of 50°C to 200°C to form a 100 nm thick Ge thin film (evaporation). (first step). The film formation rate was 1 nm/min, and the film formation time was 100 minutes.

After that, the sample that underwent the first step was introduced into an electric furnace with a nitrogen atmosphere, and the Ge thin film formed in the first step was heated at 375°C for 140 hours, at 400°C for 60 hours, and at 450°C for 5 hours. Heat treatment was performed to promote solid phase growth (second step).

The graph of FIG. 3(a) shows the results of X-ray reflectance measurement (XRR) performed on the Ge thin film formed in the first step. The horizontal axis of the graph shows the tilt angle (2θ) [deg] of the sample, and the vertical axis shows the intensity of reflected light [a. u. ] is shown.

Based on this measurement result, the particle density of the Ge thin film corresponding to the substrate temperature T _d set in the first step was calculated. The calculation results are shown in the graph of FIG. 3(b). The horizontal axis of the graph represents the substrate temperature Td [° C.], and the vertical axis represents the particle density [g/cm ³ ]. The particle density when Ge is crystallized is estimated to be about 5.34 [g/cm ³ ], and this is shown by the dashed line.

Focusing on particle density, the constituent particles of the Ge thin film assume a low-density amorphous structure when formed at a low substrate temperature _Td , but become denser as the set temperature increases, and at 100°C In the above case, it can be seen that the particle density approaches asymptotically to the crystal.

When Raman spectroscopy was performed on the semiconductor device obtained through the second step, it was confirmed that nucleation occurred during deposition when T _d >175° C. in the first step.

Furthermore, the higher the substrate temperature Td set at the time of forming the Ge thin film, the higher the growth rate of nuclei in the second step. For example, when _Td is 100°C or higher, 375°C, It was confirmed that crystallization occurred after heat treatment for about 140 hours. This temperature (375° C.) is a temperature that also allows thin film synthesis on plastic.

The particle size of the constituent particles of the polycrystalline Ge film obtained through the second step was evaluated using an electron beam backscatter diffraction (EBSD) method.

FIGS. 4A to 4C are EBSD images when the substrate temperature Td is 50°C, 100°C, and 200°C. From these EBSD images, the crystal orientation of the polycrystalline Ge film is random when T _d is 50℃ and 200℃, but when T _d is 100℃, it has priority in a specific direction. It can be seen that it is oriented. Furthermore, it can be seen that when T _d is 100° C., crystal grains of 1 μm or more are obtained.

FIG. 5 is a graph showing the relationship between the grain size of the constituent particles of the polycrystalline Ge film and the substrate temperature Td set in the first step. The horizontal axis of the graph shows the substrate temperature T _d [°C], and the vertical axis shows the particle size [μm]. Here, the particle sizes when the heat treatment temperature T _g of the second step is 375° C., 400° C., and 450° C. are shown as square plots, triangular plots, and circular plots, respectively.

The grain size of the Ge thin film strongly depends on the substrate temperature _Td , and reaches its maximum value (approximately 5 μm) when the substrate temperature _Td is 125°C. This result suggests the following points [1] and [2].
[1] When the substrate temperature T _d is in the range of 100 to 150° C., the density of amorphous Ge is brought close to the crystal level, thereby promoting nucleus growth and increasing the grain size.
[2] In a range where the substrate temperature T _d is higher than 150° C., the initial nuclei generated during deposition are dense and promote reduction in grain size during solid phase growth.

The electrical properties of the polycrystalline Ge film obtained through the second step were evaluated using the van der Pauw method.

FIG. 6 is a graph showing the relationship between the substrate temperature Td set in the first step, the hole mobility of the polycrystalline Ge film, and the hole density. The horizontal axis of the graph indicates the substrate temperature T _d [° C.], and the vertical axis indicates hole mobility (left side) and hole density (right side). When the substrate temperature T _d is 125°C, it has the lowest hole density (3×10 ¹⁷ cm ^-3 ) and highest hole mobility (340 cm ² / V・s) is obtained.

(Example 2)
By molecular beam deposition, germanium (Ge) particles were deposited on a quartz glass substrate with the substrate temperature _Td set at 150°C to form (evaporate) a Ge thin film with a thickness of 300 nm (first step). ). The film formation rate was 1 nm/min, and the film formation time was 300 minutes.

Thereafter, the sample that had undergone the first step was introduced into an electric furnace with a nitrogen atmosphere, and the Ge thin film formed in the first step was heat-treated at 450°C for 5 hours to promote solid phase growth. 2 steps).

When the electrical properties of the polycrystalline Ge film obtained through the second step were evaluated in the same manner as in Example 1, a hole mobility of 380 cm ² /V·s, which was even higher than in Example 1, was obtained.

The present invention is applicable to "development of high-speed, lightweight and flexible portable information terminals", "3D and multifunctional LSI", "development of multi-junction solar cells that achieve both high efficiency and low cost", etc. It can be used widely.

100... Semiconductor device, 101... Base material, 101a... One side of base material,
102, 102A...Particles, 102B, 102C...Semiconductor film.

Claims (4)

base material and
a semiconductor film formed on one surface of a base material,
The semiconductor film is a polycrystalline Ge film made of crystal grains made of Ge with an average grain size of 1 μm or more and 5 μm or less obtained by electron beam backscatter diffraction method,
A semiconductor device having a hole mobility of 250 cm ² /V·s or more and 380 cm ² /V·s or less. It has a base material and a semiconductor film formed on one surface of the base material, and the semiconductor film is made of crystal grains made of Ge with an average grain size of 1 μm or more and 5 μm or less obtained by electron beam backscatter diffraction method. A method for manufacturing a semiconductor device that is a polycrystalline film, the method comprising:
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,
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 crystal nuclei are generated in the semiconductor film,
A semiconductor device characterized in that the heating temperature in the first step is adjusted so that the number 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. Production method. 3. The method of manufacturing a semiconductor device according to claim 2, wherein the heating temperature in the first step is 100° C. or more and 150° C. or less. 4. The method of manufacturing a semiconductor device according to claim 2, wherein the heating temperature in the second step is 350° C. or higher and 800° C. or lower.

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