Patent Application
20230282721
The present technology (the technology according to the present disclosure) relates to a semiconductor device and an electronic apparatus, and particularly to a technology which is effectively operative when applied to a semiconductor device and an electronic apparatus each including a field effect transistor.
A GaN HEMT (High Electron Mobility Transistor), which is a field effect transistor mounted on a compound semiconductor substrate, has been attracting attention. Gallium nitride (GaN), which is a wide gap semiconductor material, has such characteristics as high breakdown voltage, operability at high temperature, and high saturated drift velocity. Moreover, a two-dimensional electron gas (2DEG) layer formed at GaN-based hetero junction has characteristics of high mobility and high sheet electron density. The GaN HEMT as a GaN-based hetero FET having these characteristics is capable of performing low-resistance, high-speed, and high-breakdown-voltage operations, and therefore is expected to be applied to power devices, RF (Radio Frequency) devices such as switches, and others used in 5G high-speed communication systems.
The GaN HEMT has a barrier layer above a channel layer. In a case of an ordinary GaN HEMT, AlGaN or AlInN is formed as a barrier layer above GaN corresponding to the channel layer. For controlling current flowing between a drain and a source, an insulation film is formed in an upper part of the barrier layer, and a gate metal (gate electrode) is formed above the insulation film.
The GaN HEMT exhibits phenomena of fluctuation of characteristics, such as a drain-lag and a shift of a threshold voltage Vth, due to physical properties and crystalline of the GaN HEMT. When a negative bias is applied to a gate of a device to apply off stress (high electric field), electrons are captured in a film or inside a semiconductor. Accordingly, drain current (Id) at this time appears to be more deteriorated than that during ordinary DC measurement. In this case, traps release electrons with a certain time constant. Accordingly, responsiveness of current to voltage lowers. This phenomenon is called the drain-lag. Moreover, the Vth shift is a phenomenon of deviation from original Vth as a result of traps or de-traps of carriers similarly produced by a trigger of an electric field. Fluctuation of characteristics influences extraction or design of a model.
It is effective to relieve concentration of an electric field to reduce fluctuation of characteristics. In general, an electric field is most concentrated on a gate end when bias is applied to a gate. For avoiding this concentration, a field plate structure has conventionally been used, and the field plate structure has a gate metal projected from an opening toward the outside to promote depletion inside a semiconductor immediately below the gate metal, and thereby smoothen electric field distribution.
Note that the following PTL 1 to PTL 3 are presented in a citation list associated with the present technology.
Meanwhile, for conventional manufacture of a semiconductor device including the GaN HEMT described above, a gate insulation film and an insulation film are formed on a semiconductor (barrier layer) surface, and a gate opening for defining a gate length (Lg) is formed by dry-etching of this insulation film. Thereafter, a T-shaped gate electrode is formed with use of the gate opening. The T-shaped gate electrode has a body part penetrating the insulation film, and a head part having a larger width than a width of the body part and located on the insulation film.
However, when the semiconductor surface is damaged by dry-etching, many levels are produced in an interface with the gate insulation film. Specifically, exposure to plasma during etching and entrance of ions or the like contained in etching gas into the semiconductor have adverse effects. As a result, traps or de-traps of carriers are produced, and cause characteristic fluctuation. Further, the etching damage given to the surface increases sheet resistance, and deteriorates off-characteristics, i.e., causes an increase in leak current and lowering of breakdown voltage.
For preventing this surface damage, it is effective to form a second insulation film above the first insulation film, and form an opening by double steps, i.e., an initial step of performing dry etching reaching an intermediate position of the first insulation film from the second insulation film, and a subsequent step of performing wet-etching after the dry etching. In this case, it is important to form an opening only in the first insulation film without etching the second insulation film which defines the gate length. In this case, however, the first insulation film is withdrawn by wet-etching which is isotropic etching. Accordingly, a hollow portion is formed on the side of the body part of the gate electrode. This hollow portion is effective in view of reduction of gate capacitance.
However, an effect produced by a field plate including a projected portion of the head part of the gate electrode for the purpose of relief of an electric field generated in the semiconductor surface increases as combined capacitance from the projected portion of the head part of the gate electrode to the semiconductor surface in the longitudinal direction increases. This is because carriers induced in the semiconductor surface by the gate electrode are allowed to increase.
However, when the hollow portion (relative permittivity εr = 1) is formed on the side of the body part of the gate electrode, the capacitance lowers. As a consequence, the relief of the electric field becomes insufficient by the decrease in the field plate effect. As a result, reduction of fluctuation of characteristics caused by the trigger of the electric field becomes difficult.
Moreover, when the thickness of the first insulation film is reduced for the purpose of increasing the capacitance, the surface is still damaged by dry etching. Further, when the permittivity of the entire first insulation film is raised, the gate capacitance increases. As a result, a cutoff frequency ft, which is a characteristic necessary for a power amplifier, deteriorates. In addition, even when these countermeasures are applied, the electric field relieving effect is not considered to be sufficient since the hollow portion immediately below the projected portion of the head part of the gate electrode is dominant.
An object of the present technology is to provide a technology capable of reducing fluctuation of characteristics and deterioration of characteristics.
A semiconductor device according to an aspect of the present technology includes a field effect transistor mounted on a semiconductor base, in which the field effect transistor includes an insulation layer that includes a first insulation film provided on a main surface of the semiconductor base, and a second insulation film provided on the first insulation film and having etching selectivity higher than etching selectivity of the first insulation film, a gate electrode that has a head part located on the insulation layer, and a body part extending from the head part toward the semiconductor base, and that is configured such that the head part has a width larger than a width of the body part, and an embedded film provided between the first insulation film and the body part of the gate electrode in a gate length direction of the gate electrode, and having a relative permittivity equal to or higher than a relative permittivity of the second insulation film.
A semiconductor device according to another aspect of the present technology includes a field effect transistor mounted on a semiconductor base, in which the field effect transistor includes an insulation layer that includes a first insulation film provided on a main surface of the semiconductor base, and a second insulation film provided on the first insulation film and having etching selectivity higher than etching selectivity of the first insulation film, a gate electrode that has a head part located on the insulation layer, and a body part extending from the head part toward the main surface of the semiconductor base, and that is configured such that the head part has a width larger than a width of the body part, and a third insulation film provided between the first insulation film and the body part of the gate electrode and between the semiconductor base and the body part of the gate electrode in a gate length direction of the gate electrode, and having a relative permittivity equal to or higher than a relative permittivity of the second insulation film.
An electronic apparatus according to a further aspect of the present technology includes the semiconductor device.
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Embodiments of the present technology will hereinafter be described in detail with reference to the drawings.
Note that parts having identical functions are given identical reference signs in all the figures for explaining the embodiments of the present technology. Repetitive explanation of these parts will be omitted.
Moreover, the respective figures are only schematic figures and include illustrations different from reality in some cases. Further, the embodiments presented below are only examples of devices and methods for embodying the technical ideas of the present technology, and do not limit configurations to those described below. Accordingly, the technical ideas of the present technology can be modified in various manners within the technical scope described in the claims.
Described in a first embodiment will be an example of a semiconductor device to which the present technology is applied, on which device field effect transistors are mounted to relieve concentration of an electric field on a semiconductor surface.
As depicted in
As depicted in
The semiconductor base 10 includes a substrate 11, a buffer layer 12 formed on the substrate 11, a channel layer 13 formed on the buffer layer 12, and a barrier layer (obstruction layer) 14 formed on the channel layer 13. In addition, an active region 10a sectioned by a non-active region 16 is provided in the main surface of the semiconductor base 10. For example, the non-active region 16 includes an impurity diffusion region where boron (B+) ions are diffused as impurities. Besides, as depicted in
The substrate 11 includes a semiconductor material. For example, the substrate 11 thus configured includes a III-V group compound semiconductor material. For example, the substrate 11 includes a semi-insulating monocrystal GaN (gallium nitride) substrate. The substrate 11 may include a substrate material having a lattice constant different from a lattice constant of the channel layer 13. For example, the substrate 11 thus configured has a constituent material such as SiC (silicon carbide), sapphire, or Si (silicon). In this case, the lattice constant is adjusted by the buffer layer 12 between the substrate 11 and the channel layer 13.
The buffer layer 12 includes a compound semiconductor layer formed by epitaxial growth on the substrate 11, for example, and includes a compound semiconductor which achieves lattice matching with the substrate 11 in a preferable manner. For example, an epitaxial growth layer including u-GaN to which no impurities are added (“u-” represents no addition of impurities; the same is applicable hereinafter) is formed on the substrate 11 including a monocrystal GaN substrate. Even when the lattice constant of the substrate 11 is different from the lattice constant of the channel layer 13, the buffer layer 12 provided between the substrate 11 and the channel layer 13 improves a crystal state of the channel layer 13, and can reduce a warp of a wafer. For example, when the substrate 11 and the channel layer 13 include Si and GaN, respectively, the buffer layer 12 can include AlN (aluminum nitride), AlGaN (aluminum gallium nitride), GaN, or others, for example. The buffer layer 12 may include a single layer, or may have a layered structure. When the buffer layer 12 includes a ternary material, respective compositions may be gradually varied within the buffer layer 12.
The channel layer 13 between the buffer layer 12 and the barrier layer 14 is a current path between a pair of main electrodes 17 and 18 functioning as a source electrode and a drain electrode. Carriers are accumulated in the channel layer 13 by polarization from the barrier layer 14. The two-dimensional electron gas (2DEG: Two Dimensional Electron gas) layer 15 is provided in the vicinity of a junction surface (hetero junction interface) with the barrier layer 14. It is preferable that the channel layer 13 thus configured include a compound semiconductor material where carriers are easily accumulated by polarization from the barrier layer 14. For example, the channel layer 13 includes GaN formed by epitaxial growth on the buffer layer 12. The channel layer 13 may include u-GaN to which no impurities are added. The channel layer 13 including u-GaN can reduce impurity scattering of carriers within the channel layer 13. Accordingly, mobility of carriers can be increased.
As depicted in
The third insulation film 25 is so formed as to cover the first insulation film 21, the second insulation film 22, and the main surface of the semiconductor base 10 (barrier layer 14) within a chamber 26 described below. The third insulation film 25 includes a material which has a property of insulation from the barrier layer 14, the first insulation film 21, and the second insulation film 22 exposed to the chamber 26, which protects the barrier layer 14 from impurities such as ions, and which forms a preferable interface with the barrier layer 14 to reduce deterioration of characteristics of the device. For example, the third insulation film 25 includes laminated films of an Al2O3 film or a hafnium oxide (HfO2) film each having a film thickness of approximately 10 nm and laminated in this order from the main surface side of the semiconductor base 10. The third insulation film 25 may include a single film including Al2O3 or HfO2. Here, a portion of the third insulation film 25 interposed between the barrier layer 14 and the gate electrode 31 functions as a gate insulation film.
As depicted in
As depicted in
Moreover, the width of the body part 31b in the gate length direction is larger on the semiconductor base 10 side than on the head part 31a side. Further, the width of the body part 31b in the gate length direction on the semiconductor base 10 side is larger than the width of the gate opening 27.
As depicted in
As described below, the chamber 26 is formed by withdrawal of the first insulation film 21 as a result of side etching performed when the gate opening defining the gate length of the gate electrode 31 is formed in the insulation layer 20. As depicted in
The chamber 26 has a width larger than each width of the body part 31b of the gate electrode 31 and the gate opening 27 in the gate length direction of the gate electrode 31. Moreover, the chamber 26 has a width smaller than a width of the head part 31a of the gate electrode 31 in the gate length direction of the gate electrode 31. In other words, a contour of the chamber 26 as viewed in the plan view is located outside a contour of the gate opening 27, but inside a contour of the head part 31a of the gate electrode 31.
The embedded film 29 is an insulation film allowing wet-etching. Moreover, the embedded film 29 includes a material different from a material of the first insulation film 21. For example, in a case where the first insulation film 21 includes an aluminum oxide (Al3O2) film, for example, the embedded film 29 may include a single layer film which is any one of a zirconium oxide (ZrO2) film, a lanthanum oxide (La2O3) film, and an yttrium oxide (Y2O3) film, or a laminated film containing at least any two of these films, for example.
Moreover, the embedded film 29 has a relative permittivity equal to or higher than the relative permittivity of the first insulation film 21. For example, the relative permittivity of the embedded film 29 is 10 or higher.
As depicted in
Moreover, the chamber 26 filled with the embedded film 29 is formed by withdrawal of the first insulation film 21 as a result of side etching performed at the time of formation of the gate opening 27. Accordingly, the embedded film 29 is provided between the first insulation film 21 and the body part 31b of the gate electrode 31 in the gate length direction of the gate electrode 31. Each of the first portion 29-L and the second portion 29-R of the embedded film 29 is provided between the first insulation film 21 and the body part 31b of the gate electrode 31. Moreover, as depicted in
As depicted in
Moreover, as depicted in
Further, the head part 31a of the gate electrode 31 is located on the insulation layer 20. Accordingly, as depicted in
Here, the width of the body part 31b of the gate electrode 31 is defined by the width of the gate opening 27 in the gate length direction. In addition, the width of the gate opening 27 in the gate length direction is defined by the width of an opening 23 in the gate length direction depicted in
As depicted in
As depicted in
Assuming that a position of a projection start of the first projected portion 31c-L of the gate electrode 31 from the body part 31b is a reference position, the position of the end 29a-L of the embedded film 29 in the gate length direction corresponds to a position away from the gate electrode 31 by an amount of 80% of the projection amount La. Similarly, assuming that a position of a projection start of the second projected portion 31c-R of the gate electrode 31 from the body part 31b is a reference position, the position of the end 29a-R of the embedded film 29 in the gate length direction corresponds to a position away from the gate electrode 31 by an amount of 80% of the projection amount La. In other words, the contour of the embedded film 29 in the plan view is located at a position corresponding to 80% of the projection amount of the projected portion of the gate electrode 31.
Here, for reducing damage to the semiconductor base 10 by dry etching, the thickness of the first insulation film 21 is desired to be increased. In this case, however, the thickness of the chamber 26 produced by withdrawal of the first insulation film 21 also becomes large. Accordingly, the thickness of the embedded film 29 embedded in the chamber 26 similarly becomes large. As depicted in
The relative permittivity of the embedded film 29 will hereinafter be described with reference to
The capacitance here refers to combined capacitance in the longitudinal direction between the head part 31a of the gate electrode 31 and the main surface of the semiconductor base 10.
A first plot group from the left in
A second plot group from the left represents capacitance ratios in a case where the relative permittivity of the embedded film 29 is the same as the relative permittivity of the silicon oxide film, i.e., the second insulation film 22.
A third plot group from the left represents capacitance ratios in a case where the relative permittivity of the embedded film 29 is the same as the relative permittivity of the aluminum oxide film, i.e., the first insulation film 21.
Moreover, a fourth plot group from the left represents capacitance ratios in a case where the relative permittivity of the embedded film 29 is higher than the relative permittivity of the aluminum oxide film, i.e., the first insulation film 21.
The combined capacitance increases, i.e., the field plate effect increases, as the relative permittivity of the embedded film 29 is raised from 1 corresponding to the vacuum (the first plot group from the left). Moreover, as can be seen, in a case where the film thickness of the embedded film 29 is changed from 30 nm (triangle plot) to 70 nm (circle plot) to avoid dry etching damage to the main surface of the semiconductor base 10 or the gate insulation film, the combined capacitance considerably decreases when the relative permittivity of the embedded film 29 is lower than the relative permittivity of the silicon oxide film (the second plot group from the left) (the difference between the triangle plot and the circle plot is large). However, this capacitance decrease is reduced (the difference between the triangle plot and the circle plot becomes smaller) as the relative permittivity of the embedded film 29 becomes higher than the relative permittivity of the silicon oxide film. In this case, sensitivity of the thickness of the silicon oxide film to the combined capacitance increases. Moreover, when the difference between the triangle plot and the circle plot decreases, the capacitance ratio can be raised even by the embedded film 29 having a large thickness. In addition, the field plate effect increases as the capacitance ratio increases.
It is obvious from
In this manner, the field plate effect increases by setting the relative permittivity of the embedded film 29 to a value equal to or higher than the relative permittivity of the second insulation film 22. Moreover, the capacitance ratio can be raised by setting the relative permittivity of the embedded film 29 to a value higher than the relative permittivity of the second insulation film 22 even when the thickness of the first insulation film 21 is increased to avoid the surface damage of the semiconductor base 10. As a result, the field plate effect improves.
As depicted in
The pair of main electrodes 17 and 18 are joined to the barrier layer 14 by ohmic junction in the active region 10a. The pair of main electrodes 17 and 18 each include laminated films of a titanium (Ti) film, an Al film, an Ni film, and an Au film sequentially laminated from the semiconductor base 10 side, for example.
In a case where the field effect transistor QA is of a depression type which designates a negative voltage as a threshold voltage, for example, the number of carriers in a carrier depleted region included in a surface portion of the channel layer 13 immediately below the gate electrode 31 decreases when a gate voltage Vg is applied to the gate electrode 31. In this case, the number of electrons in the channel layer 13 decreases, and therefore substantially no drain current Id flows. In addition, when a positive gate voltage Vg is applied to the gate electrode 31, the carrier depleted region disappears. In this case, the number of electrons in the buffer layer 12 increases, and the drain current Id is modulated.
As apparent from above, according to the semiconductor device 1A of the first embodiment, fluctuation of characteristics and deterioration of characteristics of the field effect transistor QA, i.e., fluctuation of characteristics and deterioration of characteristics of the semiconductor device 1A, can be reduced while damage to the main surface of the semiconductor base 10 is lowered.
Moreover, according to the semiconductor device 1A of the first embodiment, the embedded film 29 as an insulation film is provided on the side of the gate electrode 31. Accordingly, capacitance between the head part 31a of the gate electrode 31 and the main surface of the semiconductor base 10 can improve. In addition, with improvement of the capacitance, the field plate effect also improves. Accordingly, concentration of the electric field on the main surface of the semiconductor base 10 can further be relieved. As a result, fluctuation of characteristics and deterioration of characteristics, such as a drain-lag and Vth fluctuation, can be reduced.
Further, according to the semiconductor device 1A of the first embodiment, each thickness of the embedded film 29 and the first insulation film 21 can be increased by raising the permittivity of the embedded film 29. Accordingly, not only relief of the electric field, but also avoidance of damage to the semiconductor surface and the gate insulation film by dry etching during gate opening is achievable. As a result, fluctuation of characteristics can be reduced by improvement of the interface condition.
In addition, according to the semiconductor device 1A of the first embodiment, the embedded film 29 is provided between the head part 31a of the gate electrode 31 and the semiconductor base 10. Accordingly, the capacitance between the head part 31a of the gate electrode 31 and the main surface of the semiconductor base 10 can be improved without increasing the permittivity of the entire first insulation film 21. Moreover, the portion having a high permittivity is only the portion below the head part 31a of the gate electrode 31. Accordingly, the increase in the capacitance is controllable by the width, the thickness, and the permittivity of the embedded film 29 corresponding to the high permittivity region.
Note that the projected portions 31c include both the first projected portion 31c-L located on one side surface side of the body part 31b (left side), and the second projected portion 31c-R located on the other side surface side of the body part 31b (right side). However, the projected portions 31c may include at least any one of the first and second projected portions 31c-L and 31c-R.
Note that a wiring layer and other insulation layers are provided as layers above the insulation layer 20. However, the wiring layer and the other insulation layers as layers above the insulation layer 20 are not depicted in
A manufacturing method of the semiconductor device 1A will subsequently be described with reference to
Initially, as depicted in
Subsequently, as depicted in
The non-active region 16 can be formed by selectively implanting boron (B+) ions or the like as impurity ions into the surface portion on the main surface side of the semiconductor base 10, and then conducting heat treatment for activating the implanted B+ ions.
The pair of main electrodes 17 and 18 can be formed by sequentially accumulating a Ti film, an Al film, an Ni film, and an Au film, for example, on the entire main surface of the semiconductor base 10 including the active region 10a from the semiconductor base 10 side by CVD or sputtering to form a conductive film having a multilayer structure, and then by patterning this conductive film with use of a known photolithography technology and a dry etching technology having high directivity. The pair of main electrodes 17 and 18 each have a long shape, and are disposed away from each other in a short direction (width direction) crossing a long direction at right angles.
Subsequently, as depicted in
By this step, the active region 10a of the main surface of the semiconductor base 10 is covered with the first insulation film 21 and the second insulation film 22.
Subsequently, as depicted in
The opening 23 is formed between the pair of main electrodes 17 and 18 in the plan view, and formed in a long-shaped planar pattern extending in the long direction of the pair of main electrodes 17 and 18. The width of the opening 23 formed herein in the gate length direction defines the width of the gate opening 27 in the gate length direction as an opening formed in a step described below (
Subsequently, as depicted in
Etching of the first insulation film 21 is achieved by isotropic wet etching which gives less damage to the main surface of the semiconductor base 10, i.e., the surface of the barrier layer 14. At this time, the chamber 24 is formed by side etching applied to the first insulation film 21. The wet etching of the first insulation film 21 is performed under such a condition that etching selectivity of the first insulation film 21 is securable for the second insulation film 22. Specifically, wet etching of the first insulation film 21 is performed under such a condition of a higher wet etching rate than that of the second insulation film 22. Higher selectivity is more preferable. For example, etching is performed under such a condition that the ratio of the etching selectivity of the first insulation film 21 to the etching selectivity of the second insulation film 22 is set to 10 or more to 1.
Subsequently, formed as depicted in
In this step, the insulation layer 20 including the first insulation film 21, the second insulation film 22, and the third insulation film 25 is formed on the active region 10a of the semiconductor base 10. In this case, the upper part of the active region 10a of the semiconductor base 10 including the pair of main electrodes 17 and 18 is covered with the insulation layer 20.
Moreover, the chamber 26 which has the inner surface covered with the third insulation film 25 is formed in this step.
Further, the respective side walls of the opening 23 in the second insulation film 22 are covered with the third insulation film 25 in this step. Accordingly, the gate opening 27 which has an opening width smaller than the width of the opening 23 is formed. The width of the gate opening 27 in the gate length direction defines the width of the gate electrode 31 in the gate length direction as a gate electrode formed in a step described below.
Subsequently, as depicted in
Subsequently, as depicted in
In the manner described above, the inside of the first portion 26-L and the second portion 26-R of the chamber 26 is selectively filled with the embedded material 28 to constitute the embedded film 29.
Note that the side surface of the embedded film 29 on the gate opening 27 side is flush with the inner wall surface of the gate opening 27 in
Subsequently, as depicted in
In this step, the inside of the gate opening 27 is filled with the gate material 30, and also the portion immediately below the gate opening 27 within the chamber 26 is selectively filled with the gate material 30. Thereafter, the gate material 30 is patterned with use of a known photolithography technology and a dry etching technology having high directivity to form the gate electrode 31 on the active region 10a of the semiconductor base 10. In this manner, the gate electrode 31 depicted in
Note that the gate electrode 31 may be formed by lift-off.
In this step, the gate electrode 31 is formed into such a gate electrode which has the head part 31a located on the insulation layer 20, and the body part 31b penetrating from the head part 31a through the insulation layer 20, protruding to the chamber 26, and further extending toward the main surface of the semiconductor base 10, and also is shaped such that the head part 31a has a larger width than the width of the body part 31b.
By this step, manufacture of the field effect transistor QA depicted in
Thereafter, the wiring layer and the other insulation layers are formed on the insulation layer 20. As a result, manufacture of the semiconductor device 1A depicted in
According to the manufacturing method of the semiconductor device 1A of the first embodiment, the first insulation film 21 is etched by wet etching. Accordingly, damage to the main surface of the semiconductor base 10 (barrier layer 14) can be reduced. Specifically, exposure of the main surface of the semiconductor base 10 to plasma during etching, and entrance of ions or the like contained in etching gas into the semiconductor base 10 are prevented. Accordingly, deterioration of on-resistance, i.e., an increase in sheet resistance, and deterioration of off-characteristics, i.e., an increase in leak current and lowering of breakdown voltage, are not caused.
In addition, according to the manufacturing method of the semiconductor device 1A of the first embodiment, the embedded film 29 is formed inside the chamber 26 produced by side etching of the first insulation film 21 with use of wet etching described above. Accordingly, capacitance between the head part 31a of the gate electrode 31 and the main surface of the semiconductor base 10 can be improved. According to the improvement of the capacitance, the field plate effect improves, and concentration of the electric field on the main surface of the semiconductor base 10 can further be relieved. As a result, fluctuation of characteristics and deterioration of characteristics, such as a drain-lag and Vth fluctuation, can be reduced.
Further, according to the manufacturing method of the semiconductor device 1A of the first embodiment, each thickness of the embedded film 29 and the first insulation film 21 can be increased by raising the permittivity of the embedded material 28 constituting the embedded film 29. Accordingly, not only relief of the electric field, but also avoidance of damage to the semiconductor surface and the gate insulation film by dry etching during gate opening is achievable. As a result, fluctuation of characteristics can be reduced by improvement of the interface condition.
In addition, according to the manufacturing method of the semiconductor device 1A of the first embodiment, the third insulation film 25 is formed after formation of the opening 23 is completed. Accordingly, damage to the third insulation film 25 during dry etching can be reduced.
Note that the side surface of the embedded film 29 on the gate opening 27 side (the body part 31b side of the gate electrode 31) is substantially flush with the inner wall surface of the gate opening 27 in
As depicted in
As depicted in
For example, in a case where the first insulation film 21 includes an aluminum oxide (Al3O2) film, the embedded film 29A1 includes an aluminum oxide film. The relative permittivity of the embedded film 29A1 is the relative permittivity of the aluminum oxide film.
As depicted in
In addition, as in the first embodiment, the embedded film 29A1 and the first insulation film 21 are separated from each other by the third insulation film 25.
The semiconductor device 1A1 according to the first modification of the first embodiment also offers advantageous effects similar to those of the semiconductor device 1A of the first embodiment described above.
Further, according to the semiconductor device 1A1 of the first embodiment, each thickness of the embedded film 29A1 and the first insulation film 21 can be increased by equalizing the relative permittivity of the embedded film 29A1 with the relative permittivity of the first insulation film 21. Accordingly, not only relief of the electric field, but also avoidance of damage to the semiconductor surface and the gate insulation film by dry etching during gate opening is achievable. As a result, fluctuation of characteristics can be reduced by improvement of the interface condition.
A manufacturing method of the semiconductor device 1A1 according to the first modification of the first embodiment will subsequently be described. The manufacturing method of the semiconductor device 1A1 according to the first modification of the first embodiment is the same as the manufacturing method of the semiconductor device 1A of the first embodiment depicted in
The manufacturing method of the semiconductor device 1A1 according to the first modification of the first embodiment also offers advantageous effects similar to those of the manufacturing method of the semiconductor device 1A of the first embodiment described above.
Further, according to the manufacturing method of the semiconductor device 1A1 of the first modification of the first embodiment, each thickness of the embedded film 29A1 and the first insulation film 21 can be increased by equalizing the material of the embedded material 28 constituting the embedded film 29A1 with the material of the first insulation film 21 and thereby raising the relative permittivity of the embedded film 29A1. Accordingly, not only relief of the electric field, but also avoidance of damage to the semiconductor surface and the gate insulation film by dry etching during gate opening is achievable. As a result, fluctuation of characteristics can be reduced by improvement of the interface condition.
Note that the side surface of the embedded film 29A1 on the gate opening 27 side (the body part 31b side of the gate electrode 31) is also substantially flush with the inner wall surface of the gate opening 27 in the first modification of the first embodiment as depicted in
As depicted in
As depicted in
As depicted in
As depicted in
Note that the first modification of the first embodiment described above may be applied to the semiconductor device 1A2 of the second modification of the first embodiment.
The semiconductor device 1A2 according to the second modification of the first embodiment also offers advantageous effects similar to those of the semiconductor device 1A of the first embodiment described above.
Moreover, the manufacturing method of the semiconductor device 1A2 according to the second modification of the first embodiment also offers advantageous effects similar to those of the manufacturing method of the semiconductor device 1A of the first embodiment described above.
Note that the side surface of the embedded film 29A2 on the gate opening 27 side (the body part 31b side of the gate electrode 31) is also substantially flush with the inner wall surface of the gate opening 27 in the second modification of the first embodiment as depicted in
As depicted in
As depicted in
As depicted in
Note that the first modification of the first embodiment described above may be applied to the semiconductor device 1A3 of the third modification of the first embodiment.
The semiconductor device 1A3 according to the third modification of the first embodiment also offers advantageous effects similar to those of the semiconductor device 1A of the first embodiment described above.
Moreover, the manufacturing method of the semiconductor device 1A3 according to the third modification of the first embodiment also offers advantageous effects similar to those of the manufacturing method of the semiconductor device 1A of the first embodiment described above.
Note that the side surface of the embedded film 29A3 on the gate opening 27 side (the body part 31b side of the gate electrode 31) is also substantially flush with the inner wall surface of the gate opening 27 in the third modification of the first embodiment as depicted in
As depicted in
As depicted in
As depicted in
As depicted in
The semiconductor device 1B according to the second embodiment also offers advantageous effects similar to those of the semiconductor device 1A of the first embodiment described above.
Note that at least any one of the first modification, the second modification, and the third modification of the first embodiment described above is applicable to the semiconductor device 1B of the second embodiment.
A manufacturing method of the semiconductor device 1B according to the second embodiment will subsequently be described with reference to
Initially, steps similar to the steps depicted in
Subsequently, steps similar to the steps depicted in
Subsequently, as depicted in
In this step, the insulation layer 20 including the first insulation film 21, the second insulation film 22, and the third insulation film 25B is formed on the active region 10a of the semiconductor base 10.
Further, the respective side walls of the opening 23 in the second insulation film 22 are covered with the third insulation film 25B in this step. Accordingly, the gate opening 27 which has an opening width smaller than that of the opening 23 is formed.
Thereafter, a step similar to the step depicted in
The manufacturing method of the semiconductor device 1B according to the second embodiment also offers advantageous effects similar to those of the manufacturing method of the semiconductor device 1A of the first embodiment described above.
As depicted in
As depicted in
As depicted in
As depicted in
The first portion 25C-L of the third insulation film 25C is provided between the main surface of the semiconductor base 10, and the first portion 29-L of the embedded film 29 and the first insulation film 21 adjacent to the first portion 29-L. Moreover, the second portion 25C-R of the third insulation film 25C is provided between the main surface of the semiconductor base 10, and the second portion 29-R of the embedded film 29 and the first insulation film 21 adjacent to the second portion 29-R. As described above, the third insulation film 25C is provided between the main surface of the semiconductor base 10, and the embedded film 29 and the first insulation film 21 adjacent to the embedded film 29.
Note that at least any one of the first modification, the second modification, and the third modification of the first embodiment described above may be applicable to the semiconductor device 1C of the third embodiment.
The semiconductor device 1C according to the third embodiment also offers advantageous effects similar to those of the semiconductor device 1A of the first embodiment described above.
A manufacturing method of the semiconductor device 1C according to the third embodiment will subsequently be described with reference to
First, as depicted in
Subsequently, steps similar to the steps depicted in
Subsequently, steps similar to the steps depicted in
Subsequently, steps similar to the steps depicted in
Thereafter, a step similar to the step depicted in
The manufacturing method of the semiconductor device 1C according to the third embodiment also offers advantageous effects similar to those of the manufacturing method of the semiconductor device 1A of the first embodiment described above.
Note that the side surface of the embedded film 29 on the opening 23 side (the body part 31b side of the gate electrode 31) is also substantially flush with the inner wall surface of the opening 23, in the third embodiment, as depicted in
As depicted in
As depicted in
As depicted in
The head part 31Da of the gate electrode 31D has a larger width than a width of the body part 31Db. The width of the body part 31Db of the gate electrode 31D in the gate length direction decreases from the head part 31Da toward the main surface of the semiconductor base 10. Specifically, the body part 31Db has an inverted tapered shape having two side surfaces which are located at positions opposite to each other in the gate length direction, and are inclined in such directions as to form an acute angle on the interior angle side by these two side surfaces and the main surface of the semiconductor base 10. Moreover, a distance between the gate electrode 31D including the head part 31Da and the body 31Db and the semiconductor base 10 decreases with nearness to the body part 31Db in the gate length direction of the gate electrode 31D. Further, capacitance between the gate electrode 31D and the semiconductor base 10 increases as the distance between the gate electrode 31D and the semiconductor base 10 decreases.
Note that the third insulation film 25B of the semiconductor device 1D according to the fourth embodiment basically has a configuration similar to the configuration of the third insulation film 25B of the second embodiment described above. However, the third insulation film 25B of the fourth embodiment may have a configuration similar to the configuration of the third insulation film 25 of the first embodiment described above, and of the third insulation film 25C of the third embodiment described above.
Moreover, at least any one of the first modification, the second modification, and the third modification of the first embodiment, and the third embodiment described above may be applicable to the semiconductor device 1D of the fourth embodiment.
The semiconductor device 1D according to the fourth embodiment also offers advantageous effects similar to those of the semiconductor device 1C of the first embodiment described above.
Further, according to the semiconductor device 1D of the fourth embodiment, the body part 31Db of the gate electrode 31D to be provided has an inverted tapered shape. In this case, the capacitance between the gate electrode 31D and the semiconductor base 10 increases with nearness to the body part 31Db of the gate electrode 31D in the gate length direction. Accordingly, relief of the electric field is promoted, and the field plate effect is enhanced.
As depicted in
As depicted in
Concerning the pair of main electrodes 17 and 18 functioning as a source electrode and a drain electrode here, the main electrode 17 functions as a source electrode, while the main electrode 18 functions as a drain electrode in
As depicted in
Note that at least any one of the first modification, the second modification, and the third modification of the first embodiment, the second embodiment, the third embodiment, and the fourth embodiment described above may be applicable to the semiconductor device 1E of the fifth embodiment.
The semiconductor device 1E according to the fifth embodiment also offers advantageous effects similar to those of the semiconductor device 1 of the first embodiment described above.
Moreover, according to the semiconductor device 1E of the fifth embodiment, the embedded film 29E is provided on the drain electrode side, while an ordinary structure is provided on the source electrode side without the embedded film 29E. Accordingly, relief of concentration of an electric field and prevention of a parasitic capacitance increase are simultaneously achievable on the drain electrode side.
Note that the side surface of the embedded film 29D on the gate opening 27 side (the body part 31b side of the gate electrode 31) is also substantially flush with the inner wall surface of the gate opening 27 in the fifth embodiment as depicted in
As depicted in
As depicted in
Concerning the pair of main electrodes 17 and 18 functioning as a source electrode and a drain electrode here, the main electrode 17 functions as a source electrode, while the main electrode 18 functions as a drain electrode in
As depicted in
Note that at least any one of the first modification, the second modification, and the third modification of the first embodiment, the second embodiment, the third embodiment, and the fourth embodiment described above may be applicable to the semiconductor device 1F of the sixth embodiment.
The semiconductor device 1F according to the sixth embodiment also offers advantageous effects similar to those of the semiconductor device 1A of the first embodiment described above.
Moreover, according to the semiconductor device 1F of the sixth embodiment, the embedded film 29F is provided on the drain electrode side, while the hollow portion 34 is provided on the source electrode side. Accordingly, relief of concentration of an electric field and prevention of a parasitic capacitance increase are simultaneously achievable on the drain electrode side.
Note that the side surface of the embedded film 29F on the gate opening 27 side (the body part 31b side of the gate electrode 31) is also substantially flush with the inner wall surface of the gate opening 27 in the sixth embodiment as depicted in
As depicted in
Specifically, as depicted in
On the other hand, as depicted in
According to the field effect transistor QG of the seventh embodiment, capacitance between the gate electrode 31G and the semiconductor base 10 similarly increases as the distance between the gate electrode 31G and the semiconductor base 10 decreases. Accordingly, the semiconductor device 1G of the seventh embodiment also offers advantageous effects similar to those of the fourth embodiment described above.
Described in an eighth embodiment will be a case where the third insulation film is adopted as an embedded film and a gate insulation film.
As depicted in
As depicted in
As depicted in
The insulation layer 20H has the chamber 26 similarly to the insulation layer 20 of the first embodiment described above. As described above, the chamber 26 is formed by withdrawal of the first insulation film 21H by side etching performed when the gate opening 27 defining the gate length of the gate electrode 31 is formed in the insulation layer 20H. Similarly to the chamber 26 of the first embodiment described above, a planar pattern of the chamber 26 of the eighth embodiment as viewed in the plan view and explained with reference to
As depicted in
As depicted in
The third insulation film 25H is provided between the first insulation film 21H and the body part 31b of the gate electrode 31, and between the main surface of the semiconductor base 10 (barrier layer 14) and the body part 31b of the gate electrode 31 in the gate length direction of the gate electrode 31. Moreover, the third insulation film 25H has a relative permittivity equal to or higher than a relative permittivity of the second insulation film 22H similarly to the embedded insulation film 29 of the first embodiment described above. In addition, it is preferable that the third insulation film 25H have a relative permittivity higher than the relative permittivity of the second insulation film 22H, and equal to or higher than a relative permittivity of the first insulation film 21H, similarly to the embedded film 29 of the first embodiment described above.
The third insulation film 25H fills the chamber 26. In other words, the third insulation film 25H is embedded in the chamber 26. A planar pattern of the third insulation film 25H filling the chamber 26 as viewed in the plan view is an annular planar pattern surrounding the body part 31b of the gate electrode 31. Accordingly, as depicted in
The third insulation film 25H provided between the main surface of the semiconductor base 10 (barrier layer 14) and the body part 31b of the gate electrode 31 functions as a gate insulation film. In other words, in the eighth embodiment, the third insulation film 25H is adopted as an embedded film and a gate insulation film.
As depicted in
As depicted in
Moreover, the third insulation film 25H between the first insulation film 21H and the body part 31b of the gate electrode 31 is preferably configured such that the width of the third insulation film 25H in the gate length direction of the gate electrode 31 is equal to or larger than the film thickness of the first insulation film 21H.
As depicted in
A manufacturing method of the semiconductor device according to the eighth embodiment will subsequently be described with reference to
Initially, steps similar to the steps depicted in
By this step, the active region 10a of the main surface of the semiconductor base 10 is covered with the first insulation film 21H and the second insulation film 22H.
Subsequently, as depicted in
The opening 23 is formed between the pair of main electrodes 17 and 18 in the plan view, and formed in a long-shaped planar pattern extending in the long direction of the pair of main electrodes 17 and 18. The width of the opening 23 formed herein in the gate length direction defines the width of the gate opening 27 in the gate length direction as an opening formed in a step described below (see
Note that the opening 23 having a depth larger than the film thickness of the second insulation film 22H may be formed by over-etching which selectively removes the second insulation film 22H side of the first insulation film 21H such that the first insulation film 21H remains on a bottom portion of the opening 23.
Subsequently, as depicted in
Etching of the first insulation film 21H is achieved by isotropic wet etching which gives less damage to the main surface of the semiconductor base 10, i.e., the surface of the barrier layer 14. At this time, the chamber 24 is formed by withdrawal of the first insulation film 21H caused by side etching applied to the first insulation film 21H. The wet etching of the first insulation film 21H is performed under such a condition that etching selectivity of the first insulation film 21H is securable for the second insulation film 22H. Specifically, wet etching of the first insulation film 21H is performed under such a condition of a higher wet etching rate than that rate of the second insulation film 22H. Higher selectivity is more preferable. For example, etching is performed under such a condition that the ratio of the etching selectivity of the first insulation film 21H to the etching selectivity of the second insulation film 22H is set to 10 or more to 1.
Subsequently, as depicted in
In this step, the first insulation film 21H, the second insulation film 22H, and the main surface of the semiconductor base 10 (the surface of the barrier layer 14) within the chamber 24 are covered with the third insulation film 25H. In addition, the surface of the second insulation film 22H and the side surface of the second insulation film 22H within the opening 23 are covered with the third insulation film 25H.
Moreover, in this step, the insulation layer 20H including the first insulation film 21H, the second insulation film 22H, and the third insulation film 25H is formed on the active region 10a of the semiconductor base 10. Accordingly, the upper part of the active region 10a of the semiconductor base 10 including the pair of main electrodes 17 and 18 is covered with the insulation layer 20H.
Moreover, the chamber 26 which has the inner surface covered with the third insulation film 25H is formed in this step.
Further, the respective side walls of the opening 23 in the second insulation film 22H are covered with the third insulation film 25H in this step. Accordingly, the gate opening 27 which has an opening width smaller than the width of the opening 23 is formed. The width of the gate opening 27 in the gate length direction defines the width of the gate electrode 31 in the gate length direction as a gate electrode formed in a step described below.
Thereafter, a step similar to the step depicted in
Main advantageous effects of the eighth embodiment will subsequently be described with reference to
Each of
Moreover,
As apparent from
Accordingly, the semiconductor device 1H according to the eighth embodiment also offers advantageous effects similar to those of the semiconductor device 1A of the first embodiment described above.
Further, manufacture of the semiconductor device 1H of the eighth embodiment is similar to the manufacture of the first embodiment described above in that the third insulation film 25H is formed after withdrawal of the first insulation film 21H caused by double-step etching including dry etching and wet etching. However, the chamber (hollow portion) 26 is isotropically filled with the third insulation film 25H due to a film thickness relation between the first insulation film 21H and the third insulation film 25H. In this manner, the necessity of forming a new insulation film (embedded insulation film 29) as in the first embodiment is eliminated, and therefore, the number of manufacturing steps can be made smaller than that number in the first embodiment described above. Accordingly, cost reduction of the semiconductor device 1H is achievable. Moreover, according to the first embodiment described above, a small hollow (space portion) is formed in some cases at the body part 31a side end of the gate electrode 31 during wet etching of the embedded insulation film 29. However, such a small hollow described above is not formed in the eighth embodiment. Accordingly, the field effect further increases at a position where electric field concentration is an important factor.
In addition, in the case of the third insulation film 25H formed through the ALD, the depth side of the chamber 24 (26) may not be filled (completely closed) if the entrance thereof is initially closed. However, sufficient effects can be obtained when the gate electrode 31 on the body part 31a side, which has a dominant influence on reduction of fluctuation of characteristics and improvement of breakdown voltage, is closed.
Further, while each of the first portion 26-L and the second portion 26-R of the chamber 26 is filled with the third insulation film 25H in the eighth embodiment, such a configuration that at least any one of the first portion 26-L and the second portion 26-R of the chamber 26 is filled with the third insulation film 25H is also adoptable. In a case where any one of the first portion 26-L and the second portion 26-R of the chamber 26 is filled with the third insulation film 25H, it is preferable that the chamber 26 located on the side of the main electrode, which is one of the pair of main electrodes 17 and 18 and functions as a drain electrode, be filled with the third insulation film 25H.
In addition, while the embedded insulation film filling the chamber 26 is expressed as the third insulation film 22H in the eighth embodiment, the third insulation film 22H may be expressed as the embedded insulation film 22H.
According to the eighth embodiment described above, a case in which the chamber 26 is filled with the third insulation film 25H has been described. However, the present technology is not limited to the eighth embodiment. For example, as depicted in
Moreover, as depicted in
Note that, in the first embodiment to the eighth embodiment described above, there has been described a case where the pair of main electrodes 17 and 18 are formed before the insulation layer 20 or 20H is formed. However, the present technology is not limited to this case. For example, the present technology is also applicable to a case where the pair of main electrodes 17 and 18 are formed after the insulation layer 20 or 20H is formed.
Moreover, in the first embodiment to the seventh embodiment described above, there has been described a case where the insulation layer 20 has the first insulation film 21, the second insulation film 22, and the third insulation film 25. However, the present technology is not limited to this case. For example, the present technology is also applicable to a case of an insulation layer including the first insulation film 21 and the second insulation film 22 other than the third insulation film 25.
Further, according to the first embodiment to the eighth embodiment described above, each layer in an upper part of the substrate 11 includes an AaN-based compound semiconductor. However, the present technology is not limited to this configuration. For example, a compound semiconductor such as GaAs, or a semiconductor layer such as silicon may be adopted.
In addition, according to the first embodiment to the eighth embodiment described above, there has been described the semiconductor device having the one semiconductor chip including the high-frequency power amplifier unit PA, the high-frequency low noise amplifier unit LNA, the high-frequency filter unit BRF, and the high-frequency switch units SW thereon. However, the present technology is not limited to this case. For example, the present technology is applicable to a semiconductor device having a single structure where one field effect transistor is mounted on one semiconductor chip.
According to the wireless communication device 4, during transmission, i.e., in a case of output of a transmission signal from a transmission system of the wireless communication device 4 to the antenna ANT, the transmission signal output from the baseband unit BB is output to the antenna ANT via the high-frequency integrated circuit RFIC, the high-power amplifier HPA, and the antenna switch circuit 5.
During reception, i.e., in a case of input of a signal received by the antenna ANT to a reception system of the wireless communication device, the reception signal is input to the baseband unit BB via the antenna switch circuit 5 and the high-frequency integrated circuit RFIC. The signal processed by the baseband unit BB is output from the output units such as the voice output unit MIC, the data output unit DT, and the interface unit I/F.
The wireless communication device 4 at least includes a semiconductor device which has any of the field effect transistors QA, QA1, QA2, QA3, and QB to QH described above.
Note that the present technology may also have following configurations.
A semiconductor device including:
The semiconductor device according to (1) described above,
in which the relative permittivity of the embedded film is higher than the relative permittivity of the second insulation film.
The semiconductor device according to (1) described above,
in which the relative permittivity of the embedded film is equal to or higher than a relative permittivity of the first insulation film.
The semiconductor device according to any one of (1) to (3) described above,
in which the embedded film is provided between the head part of the gate electrode and the semiconductor base.
The semiconductor device according to any one of (1) to
described above,
in which the embedded film includes a material different from a material of the first insulation film.
The semiconductor device according to any one of (1) to (5) described above,
The semiconductor device according to any one of (1) to (4) described above,
in which the embedded film includes a material identical to a material of the first insulation film.
The semiconductor device according to any one of (1) to (4) described above,
in which each of the first insulation film and the embedded film includes an aluminum oxide film.
The semiconductor device according to any one of (1) to (8) described above,
in which the field effect transistor includes a space portion formed at least any one of between the embedded film and the body part of the gate electrode and inside the embedded film.
The semiconductor device according to any one of (1) to (9) described above,
in which the field effect transistor includes the embedded film formed on at least any one of one side surface side and the other side surface side of the body part of the gate electrode in the gate length direction of the gate electrode.
The semiconductor device according to any one of (1) to (10) described above,
in which the field effect transistor includes the embedded film on the one side surface side of the body part of the gate electrode in the gate length direction of the gate electrode, and a hollow portion between the other side surface side of the body part of the gate electrode and the first insulation film.
The semiconductor device according to any one of (1) to (10) described above,
in which a width of the body part of the gate electrode in the gate length direction decreases from the head part toward the main surface of the semiconductor base.
The semiconductor device according to any one of (1) to (12) described above,
in which the field effect transistor includes a third insulation film between the first insulation film and the embedded film.
The semiconductor device according to any one of (1) to (12) described above,
in which the field effect transistor includes a third insulation film between the embedded film and the gate electrode.
The semiconductor device according to any one of (1) to (12) described above,
in which the field effect transistor includes a third insulation film between the main surface of the semiconductor base, and the embedded film and the first insulation film.
The semiconductor device according to any one of (1) to (12) described above,
in which the field effect transistor includes a third insulation film between the body part of the gate electrode and the main surface of the semiconductor base.
The semiconductor device according to (1) described above,
in which the embedded film is also provided between the semiconductor base and the body part of the gate electrode.
A manufacturing method of a semiconductor device, including:
An electronic apparatus including:
A semiconductor device including:
The semiconductor device according to (20) described above,
in which the third insulation film between the first insulation film and the body part of the gate electrode has a plurality of layers.
The semiconductor device according to (20) or (21) described above,
in which the third insulation film between the first insulation film and the body part of the gate electrode is folded.
The semiconductor device according to any one of (20) to (22) described above,
in which the third insulation film between the semiconductor base and the body part of the gate electrode has a film thickness equal to or larger than a half of a film thickness of the first insulation film.
The semiconductor device according to any one of (20) to (23) described above,
in which the third insulation film between the first insulation film and the body part of the gate electrode has a width that is a width in the gate length direction of the gate electrode and is equal to or larger than a film thickness of the first insulation film.
The semiconductor device according to any one of (20) to (24) described above,
in which the third insulation film includes at least any one of an aluminum oxide film and hafnium oxide.
The semiconductor device according to any one of (20) to (25) described above,
in which the third insulation film is also provided between the second insulation film and the body part and the head part of the gate electrode.
The semiconductor device according to any one of (20) to (26) described above,
in which the field effect transistor includes the third insulation film between the semiconductor base and the second insulation film.
The semiconductor device according to any one of (20) to (27) described above,
in which the field effect transistor includes a space portion between the first insulation film and the third insulation film.
The semiconductor device according to any one of (20) to (26) described above,
in which the field effect transistor includes a space portion in the third insulation film between the first insulation film and the body part of the gate electrode.
A manufacturing method of a semiconductor device, including:
An electronic apparatus including:
The scope of the present technology is not limited to the exemplary embodiments described and depicted in the drawings, and includes all embodiments offering effects similar to those intended to be offered by the present technology. Moreover, the scope of the present technology is not limited to combinations of characteristics of the invention defined by the claims, and may be defined by any specific desired combinations of characteristics included in all disclosed characteristics.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-133351 | Aug 2020 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/020076 | 5/26/2021 | WO |
