Patent Publication Number: US-2022231155-A1

Title: Semiconductor device and method for manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-006881, filed on Jan. 20, 2021, and Japanese Patent Application No. 2021-115503, filed on Jul. 13, 2021; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a semiconductor device and a method for manufacturing the same. 
     BACKGROUND 
     For example, characteristics are desired to be improved for a semiconductor device such as a transistor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view illustrating a semiconductor device according to a first embodiment; 
         FIG. 2  is a schematic cross-sectional view illustrating a semiconductor device according to the first embodiment; 
         FIGS. 3A and 3B  are graph views illustrating characteristics of the semiconductor device; 
         FIG. 4  is a graph view illustrating characteristics of the semiconductor device; 
         FIG. 5  is a schematic cross-sectional view illustrating a semiconductor device according to the first embodiment; 
         FIG. 6  is a schematic cross-sectional view illustrating a semiconductor device according to the first embodiment; 
         FIG. 7  is a schematic cross-sectional view illustrating a semiconductor device according to the first embodiment; 
         FIG. 8  is a schematic cross-sectional view illustrating a semiconductor device according to the first embodiment; 
         FIG. 9  is a schematic cross-sectional view illustrating a semiconductor device according to the first embodiment; 
         FIGS. 10A to 10D  are schematic cross-sectional views illustrating a method for manufacturing a semiconductor device according to a second embodiment; and 
         FIGS. 11A to 11D  are schematic cross-sectional views illustrating a method for manufacturing a semiconductor device according to a second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     According to one embodiment, a semiconductor device includes a first electrode, a second electrode, a third electrode, a first semiconductor region, a second semiconductor region, a first insulating member, and a second insulating member. A direction from the first electrode toward the second electrode is along a first direction. The third electrode includes a first electrode portion. A position of the first electrode portion in the first direction is between a position of the first electrode in the first direction and a position of the second electrode in the first direction. The first semiconductor region includes Al x1 Ga 1-x1 N (0≤x 1 &lt;1). The first semiconductor region includes a first partial region, a second partial region, a third partial region, a fourth partial region, and a fifth partial region. A direction from the first partial region toward the first electrode is along a second direction crossing the first direction. A direction from the second partial region toward the second electrode is along the second direction. A direction from the third partial region toward the first electrode portion is along the second direction. The fourth partial region is between the first partial region and the third partial region in the first direction. The fifth partial region is between the third partial region and the second partial region in the first direction. The second semiconductor region includes Al x2 Ga 1-x2 N (x 1 &lt;x 2 ≤1). The second semiconductor region includes a first semiconductor portion and a second semiconductor portion. A direction from the fourth partial region toward the first semiconductor portion is along the second direction. A direction from the fifth partial region toward the second semiconductor portion is along the second direction. The first insulating member includes at least one of silicon or aluminum, and oxygen. The first insulating member includes a first insulating portion. The first insulating portion is between the third partial region and the first electrode portion. The second insulating member includes silicon and nitrogen. The second insulating member includes a first insulating region and a second insulating region. A position of the first insulating region in the first direction is between the position of the first electrode in the first direction and the position of the first electrode portion in the first direction. A position of the second insulating region in the first direction is between the position of the first insulating region in the first direction and the position of the first electrode portion in the first direction. The first semiconductor portion is between the fourth partial region and the first insulating region, and between the fourth partial region and the second insulating region. The second insulating region has at least one of a second nitrogen concentration higher than a first nitrogen concentration in the first insulating region, a second hydrogen concentration lower than a first hydrogen concentration in the first insulating region, or a second density higher than a first density in the first insulating region. 
     According to one embodiment, a semiconductor device includes a first electrode, a second electrode, a third electrode, a first semiconductor region, a second semiconductor region, a first insulating member, and a second insulating member. A direction from the first electrode toward the second electrode is along a first direction. The third electrode includes a first electrode portion. A position of the first electrode portion in the first direction is between a position of the first electrode in the first direction and a position of the second electrode in the first direction. The first semiconductor region includes Al x1 Ga 1-x1 N (0≤x 1 &lt;1). The first semiconductor region includes a first partial region, a second partial region, a third partial region, a fourth partial region, and a fifth partial region. A direction from the first partial region toward the first electrode is along a second direction crossing the first direction. A direction from the second partial region toward the second electrode is along the second direction. A direction from the third partial region toward the first electrode portion is along the second direction. The fourth partial region is between the first partial region and the third partial region in the first direction. The fifth partial region is between the third partial region and the second partial region in the first direction. The second semiconductor region includes Al x2 Ga 1-x2 N (x 1 &lt;x 2 ≤1). The second semiconductor region includes a first semiconductor portion and a second semiconductor portion. A direction from the fourth partial region toward the first semiconductor portion is along the second direction. A direction from the fifth partial region toward the second semiconductor portion is along the second direction. The first insulating member includes at least one of silicon or aluminum, and oxygen. The first insulating member includes a first insulating portion. The first insulating portion is between the third partial region and the first electrode portion. The second insulating member includes silicon and nitrogen. The second insulating member includes a first insulating region and a second insulating region. A position of the first insulating region in the first direction is between the position of the first electrode in the first direction and the position of the first electrode portion in the first direction. A position of the second insulating region in the first direction is between the position of the first insulating region in the first direction and the position of the first electrode portion in the first direction. The first semiconductor portion is between the fourth partial region and the first insulating region, and between the fourth partial region and the second insulating region. A second thickness of the second insulating region along the second direction is thinner than a first thickness of the first insulating region along the second direction. 
     According to one embodiment, a method for manufacturing a semiconductor device is disclosed. The method can include forming a first insulating film including silicon and nitrogen on a portion of a second semiconductor region of a semiconductor member. The semiconductor member includes a first semiconductor region including Al x1 Ga 1-x1 N (0≤x 1 &lt;1) and a second semiconductor region including Al x2 Ga 1-x2 N (x 1 &lt;x 2 ≤1). The method can include forming a second insulating film including silicon and nitrogen on an other portion of the second semiconductor region. The method can include removing a portion of the second insulating film, and forming a hole in the semiconductor member exposed by the removing the portion of the second insulting film. The method can include forming a first insulating member including silicon and oxygen in the hole. The method can include forming a third electrode in a remaining space of the hole, and forming a first electrode and a second electrode. The first insulating film and the second insulating film are between the first electrode and the second electrode, and between the second electrode and the third electrode. The second insulating film has at least one of a second nitrogen concentration higher than a first nitrogen concentration in the first insulating film, a second hydrogen concentration lower than a first hydrogen concentration in the first insulating film, or a second density higher than a first density in the first insulating film. 
     Various embodiments are described below with reference to the accompanying drawings. 
     The drawings are schematic and conceptual; and the relationships between the thickness and width of portions, the proportions of sizes among portions, etc., are not necessarily the same as the actual values. The dimensions and proportions may be illustrated differently among drawings, even for identical portions. 
     In the specification and drawings, components similar to those described previously or illustrated in an antecedent drawing are marked with like reference numerals, and a detailed description is omitted as appropriate. 
       FIG. 1  is a schematic cross-sectional view illustrating a semiconductor device according to a first embodiment. 
     As shown in  FIG. 1 , a semiconductor device  110  according to the embodiment includes a first electrode  51 , a second electrode  52 , a third electrode  53 , a first semiconductor region  10 , a second semiconductor region  20 , a first insulating member  41 , and a second insulating member  42 . 
     The direction from the first electrode  51  toward the second electrode  52  is along a first direction. The first direction is taken as an X-axis direction. One direction perpendicular to the X-axis direction is taken as a Z-axis direction. The direction perpendicular to the X-axis direction and the Z-axis direction is taken as a Y-axis direction. 
     The third electrode  53  includes a first electrode portion  53   a . The position of the first electrode portion  53   a  in the first direction (X-axis direction) is between the position of the first electrode  51  in the first direction and the position of the second electrode  52  in the first direction. 
     The first semiconductor region  10  includes Al x1 Ga 1-x1 N (0≤x 1 &lt;1). The composition ratio x 1  is, for example, not less than 0 and less than 0.1. The first semiconductor region  10  includes, for example, GaN. 
     The first semiconductor region  10  includes a first partial region  11 , a second partial region  12 , a third partial region  13 , a fourth partial region  14 , and a fifth partial region  15 . The direction from the first partial region  11  toward the first electrode  51  is along a second direction crossing the first direction. The second direction is, for example, the Z-axis direction. The direction from the second partial region  12  toward the second electrode  52  is along the second direction. The direction from the third partial region  13  toward the first electrode portion  53   a  is along the second direction. The fourth partial region  14  is between the first partial region  11  and the third partial region  13  in the first direction (X-axis direction). The fifth partial region  15  is between the third partial region  13  and the second partial region  12  in the first direction. 
     The second semiconductor region  20  includes Al x2 Ga 1-x2 N (x 1 &lt;x 2 ≤1). The composition ratio x 2  is, for example, not less than 0.1 and 0.35 or less. The second semiconductor region  20  is, for example, AlGaN. A region including AlN may be provided between the first semiconductor region  10  and the second semiconductor region  20 . The thickness of the region containing AlN (length in the Z-axis direction) is, for example, not more than 1.5 nm. 
     The second semiconductor region  20  includes a first semiconductor portion  21  and a second semiconductor portion  22 . The direction from the fourth partial region  14  toward the first semiconductor portion  21  is along the second direction (for example, the Z-axis direction). The direction from the fifth partial region  15  toward the second semiconductor portion  22  is along the second direction. 
     In this example, the semiconductor device  110  includes a substrate body  18   s  and a nitride layer  18   b . The substrate body  18   s  may be, for example, a substrate. The substrate body  18   s  may be, for example, a silicon substrate. A nitride layer  18   b  is provided on the substrate body  18   s . The first semiconductor region  10  is provided on the nitride layer  18   b . The second semiconductor region  20  is provided on the first semiconductor region  10 . The nitride layer  18   b  is, for example, a buffer layer. The nitride layer  18   b  includes Al, Ga and nitrogen. The first semiconductor region  10  and the second semiconductor region  20  are included in, for example, a semiconductor member  10 M. 
     The first insulating member  41  includes at least one of silicon or aluminum, and oxygen. The first insulating member includes, for example, SiO 2 , Al 2 O 3 , or AlSiO. The first insulating member  41  may include nitrogen. The first insulating member  41  may include AlON or SiON. A thickness of the first insulating member  41  is, for example, not less than 20 nm and not more than 150 nm. By such thickness, a high breakdown voltage and low channel resistance can be obtained. 
     The first insulating member  41  includes a first insulating portion  41   a . The first insulating portion  41   a  is between the third partial region  13  and the first electrode portion  53   a.    
     The second insulating member  42  includes silicon and nitrogen. A concentration of nitrogen in the second insulating member  42  is higher than a concentration of nitrogen in the first insulating member  41 . A concentration of oxygen in the first insulating member  41  is higher than a concentration of oxygen in the second insulating member  42 . 
     The second insulating member  42  includes a first insulating region  42   a  and a second insulating region  42   b . The position of the first insulating region  42   a  in the first direction (X-axis direction) is between the position of the first electrode  51  in the first direction and the position of the first electrode portion  53   a  in the first direction. The position of the second insulating region  42   b  in the first direction is between the position of the first insulating region  42   a  in the first direction and the position of the first electrode portion  53   a  in the first direction. The first semiconductor portion  21  is between the fourth partial region  14  and the first insulating region  42   a , and between the fourth partial region  14  and the second insulating region  42   b.    
     For example, a distance between the first electrode  51  and the first electrode portion  53   a  is longer than a distance between the first electrode portion  53   a  and the second electrode  52 . 
     The first electrode  51  is electrically connected to, for example, at least one of the first partial region  11  or the first semiconductor portion  21 . The second electrode  52  is electrically connected to, for example, at least one of the second partial region  12  or the second semiconductor portion  22 . 
     A current flowing between the first electrode  51  and the second electrode  52  can be controlled by a potential of the third electrode  53 . The potential of the third electrode  53  is, for example, a potential based on a potential of the second electrode  52 . The first electrode  51  is, for example, a drain electrode. The second electrode  52  is, for example, a source electrode. The third electrode  53  is, for example, a gate electrode. The first insulating portion  41   a  functions as, for example, a gate insulating film. 
     For example, the semiconductor device  110  is a transistor. A carrier region (for example, a two-dimensional electron gas) is formed in a portion of the first semiconductor region  10  facing the second semiconductor region  20 . The semiconductor device  110  is, for example, HEMT (High Electron Mobility Transistor). 
     In the embodiment, for example, a material of the second insulating region  42   b  is different from a material of the first insulating region  42   a . In the embodiment, the second insulating region  42   b  has at least one of a second nitrogen concentration higher than a first nitrogen concentration in the first insulating region  42   a , a second hydrogen concentration lower than a first hydrogen concentration in the first insulating region  42   a , or a second density higher than a first density in the first insulating region  42   a . With such a second insulating member  42 , for example, fluctuations in the threshold voltage can be suppressed. The threshold voltage can be stabilized. For example, current collapse can be suppressed. For example, a high breakdown voltage can be obtained. 
     For example, the second nitrogen concentration in the second insulating region  42   b  near the third electrode  53  is higher than the first nitrogen concentration in the first insulating region  42   a . As a result, a high breakdown voltage can be easily obtained. For example, the second hydrogen concentration in the second insulating region  42   b  near the third electrode  53  is lower than the first hydrogen concentration in the first insulating region  42   a . As a result, a high breakdown voltage can be easily obtained. For example, the second density in the second insulating region  42   b  near the third electrode  53  is higher than the first density in the first insulating region  42   a . As a result, a high breakdown voltage can be easily obtained. According to the embodiment, it is possible to provide a semiconductor device whose characteristics can be improved. 
     For example, the first nitrogen concentration in the first insulating region  42   a  near the first electrode  51  is lower than the second nitrogen concentration in the second insulating region  42   b . As a result, the current collapse is easily suppressed. For example, the first hydrogen concentration in the first insulating region  42   a  near the first electrode  51  is higher than the second hydrogen concentration in the second insulating region  42   b . As a result, the current collapse is easily suppressed. For example, the first density in the first insulating region  42   a  near the first electrode  51  is lower than the second density in the second insulating region  42   b . As a result, the current collapse is easily suppressed. According to the embodiment, it is possible to provide a semiconductor device whose characteristics can be improved. 
     For example, a ratio of a silicon concentration to the nitrogen concentration in the second insulating region  42   b  is lower than 0.75. The second insulating region  42   b  is, for example, a nitrogen-rich silicon nitride. 
     For example, a ratio of a silicon concentration to the nitrogen concentration in the first insulating region  42   a  is higher than 0.75. The first insulating region  42   a  is, for example, a silicon-rich silicon nitride. 
     In one example, such a second insulating member  42  can be obtained by separately forming a film that becomes the first insulating region  42   a  and a film that becomes the second insulating region  42   b  when the second insulating member  42  is formed. 
     In the embodiment, the boundary between the first insulating region  42   a  and the second insulating region  42   b  may be clear or unclear. As will be described later, a region having intermediate characteristics may be provided between these insulating regions. 
     As shown in  FIG. 1 , the second insulating member  42  may include a third insulating region  42   c  and a fourth insulating region  42   d . The position of the third insulating region  42   c  in the first direction (X-axis direction) is between the position of the first electrode portion  53   a  in the first direction and the position of the second electrode  52  in the first direction. The position of the fourth insulating region  42   d  in the first direction is between the position of the third insulating region  42   c  in the first direction and the position of the second electrode  52  in the first direction. The second semiconductor portion  22  is between the fifth partial region  15  and the third insulating region  42   c , and between the fifth partial region  15  and the fourth insulating region  42   d.    
     The third insulating region  42   c  has at least one of a third nitrogen concentration higher than a fourth nitrogen concentration in the fourth insulating region  42   d , a third hydrogen concentration lower than a fourth hydrogen concentration in the fourth insulating region  42   d , or a third density higher than a fourth density in a fourth insulating region  42   d . With such a third insulating region  42   c , it is easy to obtain a high breakdown voltage. For example, a gate leak current can be reduced. 
     For example, a material of the third insulating region  42   c  may be substantially the same as the material of the second insulating region  42   b . A material of the fourth insulating region  42   d  may be substantially the same as the material of the first insulating region  42   a.    
     For example, a ratio of a silicon concentration to the nitrogen concentration in the third insulating region  42   c  is lower than 0.75. For example, a ratio of the silicon concentration to the nitrogen concentration in the fourth insulating region  42   d  is higher than 0.75. 
     As shown in  FIG. 1 , in this example, at least a portion of the first electrode portion  53   a  is between the first semiconductor portion  21  and the second semiconductor portion  22  in the first direction (X-axis direction). For example, at least a portion of the first electrode portion  53   a  is between the fourth partial region  14  and the fifth partial region  15  in the first direction. The third electrode  53  is, for example, a trench type gate electrode. For example, it is easy to obtain a high threshold voltage. For example, normal off characteristics can be obtained. 
     In this example, the third electrode  53  further includes a second electrode portion  53   b . A portion of the first semiconductor portion  21  is between the fourth partial region  14  and the second electrode portion  53   b . The second electrode portion  53   b  is, for example, an eaves portion. At least a portion of the second insulating region  42   b  is between a portion of the first semiconductor portion  21  and the second electrode portion  53   b.    
     In this example, the third electrode  53  further includes a third electrode portion  53   c . A portion of the second semiconductor portion  22  is between the fifth partial region  15  and the third electrode portion  53   c . The third electrode portion  53   c  is, for example, an eaves portion. At least a portion of the third insulating region  42   c  is between a portion of the second semiconductor portion  22  and the third electrode portion  53   c.    
     By providing the second electrode portion  53   b  and the third electrode portion  53   c , for example, a low electrical resistance can be obtained in the third electrode portion  53 . When such an eaves portion is provided, by providing the second insulating region  42   a  and the third insulating region  42   c  as described above, it is easy to obtain a high breakdown voltage and a stable threshold voltage. 
     As shown in  FIG. 1 , the first insulating member  41  includes a second insulating portion  41   b  and a third insulating portion  41   c . The second insulating portion  41   b  is between the first semiconductor portion  21  and the first electrode portion  53   a . The third insulating portion  41   c  is between the first electrode portion  53   a  and the second semiconductor portion  22 . 
     As shown in  FIG. 1 , the first insulating member  41  may include a fourth insulating portion  41   d  and a fifth insulating portion  41   e . For example, the first insulating region  42   a  is between the first semiconductor portion  21  and the fourth insulating portion  41   d . The fourth insulating region  42   d  is between the second semiconductor portion  22  and the fifth insulating portion  41   e.    
     As shown in  FIG. 1 , in this example, the semiconductor device  110  further includes a nitride member  30 . The nitride member  30  includes Al x3 Ga 1-x3 N (x 2 &lt;x 3 ≤1). The composition ratio x 3  is, for example, not less than 0.8 and not more than 1. The nitride member  30  is, for example, AIN. At least a portion of the nitride member  30  is between the third partial region  13  and the first insulating portion  41   a . By providing the nitride member  30 , a higher electron mobility can be obtained. For example, a lower on-resistance is obtained. A thickness of the nitride member  30  is, for example, not less than 1.5 nm and not more than 10 nm. High channel mobility can be obtained when the thickness of the nitride member  30  is not less than 1.5 nm. The nitride member  30  can be stable and a gate leak current can be suppressed when the thickness of the nitride member  30  is not more than 10 nm. 
     A portion of the nitride member  30  may be provided, for example, between the fourth partial region  14  and the first electrode portion  53   a . A portion of the nitride member  30  may be provided, for example, between the first electrode portion  53   a  and the fifth partial region  15 . A portion of the nitride member  30  may be provided, for example, between the first semiconductor portion  21  and the first electrode portion  53   a . A portion of the nitride member  30  may be provided, for example, between the second electrode portion  53   a  and the second semiconductor portion  22 . 
     For example, the first insulating region  42   a  may be provided between the first semiconductor portion  21  and a portion of the nitride member  30 . The second insulating region  42   b  may be provided between the first semiconductor portion  21  and a portion of the nitride member  30 . The third insulating region  42   c  may be provided between the second semiconductor portion  22  and a portion of the nitride member  30 . The fourth insulating region  42   d  may be provided between the second semiconductor portion  22  and a portion of the nitride member  30 . 
       FIG. 2  is a schematic cross-sectional view illustrating a semiconductor device according to the first embodiment. 
     As shown in  FIG. 2 , a semiconductor device  111  according to the embodiment also includes the first electrode  51 , the second electrode  52 , the third electrode  53 , the first semiconductor region  10 , the second semiconductor region  20 , the first insulating member  41 , and the second insulating member  42 . In the semiconductor device  111 , a thickness of the first insulating region  42   a  is different from a thickness of the second insulating region  42   b , and a thickness of the fourth insulating region  42   d  is different from a thickness of the third insulating region  42   c . Other configurations in the semiconductor device  111  may be the same as those in the semiconductor device  110 . 
     As shown in  FIG. 1 , the thickness of the first insulating region  42   a  along the second direction (Z-axis direction) is taken as a first thickness t 1 . The thickness of the second insulating region  42   b  along the second direction is taken as a second thickness t 2 . The thickness of the third insulating region  42   c  along the second direction is taken as a third thickness t 3 . The thickness of the fourth insulating region  42   d  along the second direction is taken as a fourth thickness t 4 . In this example, the second thickness t 2  is thinner than the first thickness t 1 . The third thickness t 3  is thinner than the fourth thickness t 4 . The third thickness t 3  may be substantially the same as the second thickness t 2 . The fourth thickness t 4  may be substantially the same as the first thickness t 1 . 
     Since the second thickness t 2  is thin, the fluctuation of the threshold voltage can be further suppressed. Since the third thickness t 3  is thin, the fluctuation of the threshold voltage can be further suppressed. 
     For example, the second thickness t 2  is not more than 5 nm. For example, a ratio of the second thickness t 2  to the first thickness t 1  is not more than 0.5. For example, the first thickness t 1  is more than 5 nm and not more than 150 nm. 
       FIGS. 3A and 3B  are graph views illustrating characteristics of the semiconductor device. 
     The horizontal axis of  FIG. 3A  is the second thickness t 2 . The horizontal axis of  FIG. 3B  is a thickness ratio Rt 1 . The thickness ratio Rt 1  is a ratio of the second thickness t 2  to the first thickness t 1  (that is, t 2 /t 1 ). The vertical axis of these figures is the fluctuation amount VC 1  of the threshold voltage when a voltage stress is applied to the third electrode  53 . In this example, as a voltage stress, a voltage of +15V is applied to the third electrode  53  for a period of 1000 seconds. The fluctuation amount VC 1  is the difference between the threshold voltage before the voltage stress is applied and the threshold voltage after the voltage stress is applied. The measurement temperature is 150° C. In these figures, the condition that the second thickness t 2  is 0 corresponds to the case where the second insulating region  42   b  is not provided. 
     As shown in  FIG. 3A , when the second thickness t 2  is larger than 0, the fluctuation amount VC 1  becomes larger when the second thickness t 2  is larger. The second thickness t 2  is preferably not more than 5 nm, for example. The second thickness t 2  may be, for example, not more than 3.5 nm. The fluctuation amount VC 1  can be reduced. 
     As shown in  FIG. 3B , the higher the thickness ratio Rt 1 , the larger the fluctuation amount VC 1 . The thickness ratio Rt 1  is preferably not more than 0.5, for example. The thickness ratio Rt 1  may be, for example, not more than 0.3. The fluctuation amount VC 1  can be reduced. 
       FIG. 4  is a graph view illustrating characteristics of the semiconductor device. 
       FIG. 4  illustrates the characteristics when a negative voltage is applied to the third electrode  53 . The horizontal axis of  FIG. 4  is a negative voltage −Vg applied to the third electrode  53 . The vertical axis is a leak current IL between the third electrode  53  and the second electrode  52 . In this measurement, the potential of the first electrode  51  is the same as the potential of the second electrode  52 .  FIG. 4  illustrates the characteristics when the second thickness t 2  is changed. The condition that the second thickness t 2  is 0 corresponds to the case where the second insulating region  42   b  is not provided. 
     As shown in  FIG. 4 , when the second thickness t 2  is 0 and the second insulating region  42   b  is not provided, the leak current IL increases rapidly when the absolute value of the negative voltage −Vg is about 145V. The rapid increase in leak current IL corresponds to the destruction of semiconductor devices. In the embodiment, the second thickness t 2  is preferably larger than 0 nm. For example, the second thickness t 2  is preferably not less than 0.5 nm. For example, the second thickness t 2  may be not less than 1 nm. 
       FIG. 5  is a schematic cross-sectional view illustrating a semiconductor device according to the first embodiment. 
     As shown in  FIG. 5 , a semiconductor device  112  according to the embodiment includes a first conductive member  61  and a third insulating member  43  in addition to the first electrode  51 , the second electrode  52 , the third electrode  53 , the first semiconductor region  10 , the second semiconductor region  20 , the first insulating member  41 , and the second insulating member  42 . Other configurations in the semiconductor device  112  may be the same as those in the semiconductor device  111 . 
     In the semiconductor device  112 , at least a portion of the first insulating region  42   a  is between the first semiconductor portion  21  and the first conductive member  61 . 
     The first conductive member  61  is electrically connected to either the second electrode  52  or the third electrode  53 . Alternatively, it is possible to be electrically connected to either the second electrode  52  or the third electrode  53 . For example, the first conductive member  61  is electrically connected to, for example, either the second electrode  52  or the third electrode  53  by the connecting member  61 C. In the example of  FIG. 5 , the first conductive member  61  is electrically connected to the second electrode  52  by the connecting member  61 C. The connecting member  61 C may be provided at a position different from the cross section shown in  FIG. 5 . For example, a terminal  61 T electrically connected to the first conductive member  61  may be provided. For example, a terminal  52 T electrically connected to the second electrode  52  may be provided. These terminals may be electrically connected by the connecting member  61 C. 
     For example, the first conductive member  61  can function as a field plate. For example, the concentration of the electric field can be suppressed. For example, a high breakdown voltage can be obtained. For example, current collapse can be suppressed. 
     For example, an electric capacity is formed between the first conductive member  61  and the carrier region. Since the first insulating region  42   a  is thick, the distance between the first conductive member  61  and the carrier region becomes long. Since the first insulating region  42   a  is thick, the electric capacity can be reduced. Parasitic capacitance can be reduced. For example, good switching characteristics can be easily obtained. For example, switching loss can be reduced. 
       FIG. 6  is a schematic cross-sectional view illustrating a semiconductor device according to the first embodiment. 
     As shown in  FIG. 6 , a semiconductor device  113  according to the embodiment also includes the first electrode  51 , the second electrode  52 , the third electrode  53 , the first semiconductor region  10 , the second semiconductor region  20 , the first insulating member  41 , and the second insulating member  42 . In the semiconductor device  113 , the second insulating member  42  includes a fifth insulating region  42   e  and a sixth insulating region  42   f . Other configurations in the semiconductor device  113  may be the same as those in the semiconductor device  111  (or the semiconductor device  110 ). 
     The first insulating region  42   a  is between the first semiconductor portion  21  and the fifth insulating region  42   e . The fifth insulating region  42   e  has at least one of a fifth nitrogen concentration higher than the first nitrogen concentration, a fifth hydrogen concentration lower than the first hydrogen concentration, or a fifth density higher than the first density. A material of the fifth insulating region  42   e  may be the same as the material of the second insulating region  42   b , for example. The fifth insulating region  42   e  may be continuous with the second insulating region  42   b .    
     The fourth insulating region  42   d  is between the second semiconductor portion  22  and the sixth insulating region  42   f . The sixth insulating region  42   f  has at least one of a sixth nitrogen concentration lower than the third nitrogen concentration, a sixth hydrogen concentration higher than the third hydrogen concentration, or a sixth density lower than the third density. A material of the sixth insulating region  42   f  may be the same as the material of the third insulating region  42   c , for example. The sixth insulating region  42   f  may be continuous with the third insulating region  42   c.    
     A high breakdown voltage can also be obtained in the semiconductor devices  111  to  113 . A stable threshold voltage can be obtained. Current collapse can be suppressed. The characteristics can be improved. 
       FIG. 7  is a schematic cross-sectional view illustrating a semiconductor device according to the first embodiment. 
     As shown in  FIG. 7 , a semiconductor device  114  according to the embodiment also includes the first electrode  51 , the second electrode  52 , the third electrode  53 , the first semiconductor region  10 , the second semiconductor region  20 , the first insulating member  41 , and the second insulating member  42 . In the semiconductor device  114 , a shape of the third electrode  53  is different from a shape of the third electrode  53  in the semiconductor device  112 . Other configurations in the semiconductor device  114  may be the same as those in the semiconductor device  113 . 
     As shown in  FIG. 7 , the third electrode  53  includes the second electrode portion  53   b . A portion of the first semiconductor portion  21  is between the fourth portion region  14  and the second electrode portion  53   b . At least a portion of the first insulating region  42   a  is between a portion of the first semiconductor portion  21  and the second electrode portion  53   b . At least a portion of the second insulating region  42   b  is between another portion of the first semiconductor portion  21  and the second electrode portion  53   b.    
     In the semiconductor device  114 , the first insulating region  42   a  overlaps the second electrode portion  53   b  in the Z-axis direction. For example, the gate-drain capacity can be reduced. For example, the second electrode portion  53   b  can function as a gate field plate. For example, it becomes easy to obtain a high breakdown voltage. 
       FIG. 8  is a schematic cross-sectional view illustrating a semiconductor device according to the first embodiment. 
     As shown in  FIG. 8 , in a semiconductor device  115  according to the embodiment, the first conductive member  61  is provided. Other configurations in the semiconductor device  115  may be the same as those in the semiconductor device  113  (or the semiconductor device  114 ). For example, concentration of the electric field can be suppressed. For example, a high breakdown voltage can be obtained. 
       FIG. 9  is a schematic cross-sectional view illustrating a semiconductor device according to the first embodiment. 
     As shown in  FIG. 9 , a semiconductor device  116  according to the embodiment also includes the first electrode  51 , the second electrode  52 , the third electrode  53 , the first semiconductor region  10 , the second semiconductor region  20 , the first insulating member  41 , and the second insulating member  42 . In the semiconductor device  116 , the configuration of the second insulating member  42  is different from the configuration of the second insulating member  42  in the semiconductor device  113 . Other configurations in the semiconductor device  116  may be the same as those in the semiconductor device  113 . 
     As shown in  FIG. 9 , the second insulating member  42  includes a seventh insulating region  42   g . At least a portion of the seventh insulating region  42   g  is between the first insulating region  42   a  and the second insulating region  42   b  in the first direction (X-axis direction). 
     The seventh insulating region  42   g  includes at least one of a seventh nitrogen concentration between the first nitrogen concentration and the second nitrogen concentration, a seventh hydrogen concentration between the first hydrogen concentration and the second hydrogen concentration, or a seventh density between the first density and the second density. 
     As shown in  FIG. 9 , the second insulating member  42  may include an eighth insulating region  42   h . At least a portion of the eighth insulating region  42   h  is between the third insulating region  42   c  and the fourth insulating region  42   d  in the first direction (X-axis direction). 
     The eighth insulating region  42   h  includes at least one of an eighth nitrogen concentration between the third nitrogen concentration and the fourth nitrogen concentration, an eighth hydrogen concentration between the third hydrogen concentration and the fourth hydrogen concentration, or an eighth density between the third density and the fourth density. 
     As described above, the second insulating member  42  may include an intermediate region (seventh insulating region  42   g  and eighth insulating region  42   h ). The number of intermediate regions is arbitrary. For example, the boundary between the multiple insulating regions in the second insulating member  42  may be clear or unclear. 
     A high breakdown voltage can also be obtained in the semiconductor devices  114  to  116 . A stable threshold voltage can be obtained. Current collapse can be suppressed. The characteristics can be improved. 
     When the second thickness t 2  is thinner than the first thickness t 1 , such as the semiconductor device  111  or the semiconductor device  112 , the characteristics (composition ratio, density, etc.) of the second insulating region  42   b  may be substantially the same as the characteristics (composition ratio or density, etc.) of the first insulating region  42   a . Due to the difference in thickness, it is easy to obtain a stable threshold voltage. 
     Second Embodiment 
     The second embodiment relates to a method for manufacturing a semiconductor device. 
       FIGS. 10A to 10D , and  FIGS. 11A to 11D  are schematic cross-sectional views illustrating a method for manufacturing a semiconductor device according to the second embodiment. 
     As shown in  FIG. 10A , the semiconductor member  10 M is prepared. The semiconductor member  10 M includes the first semiconductor region  10  including Al x1 Ga 1-x1 N (0≤x 1 &lt;1) and the second semiconductor region  20  including Al x2 Ga 1-x2 N (x 1 &lt;x 2 ≤1) provided on the first semiconductor region  10 . 
     As shown in  FIG. 10A , a first insulating film F 1  is formed on the second semiconductor region  20 . The first insulating film F 1  includes at least one of silicon or aluminum, and oxygen. 
     As shown in  FIG. 10B , a mask material M 1  is formed on the first insulating film F 1 , and a portion of the first insulating film F 1  is removed by using the mask material M 1  as a mask. The removal is performed, for example, by performing wet etching. 
     In this way, the first insulating film F 1  including silicon and nitrogen is formed on a portion of the second semiconductor region  20  of the semiconductor member  10 M. 
     As shown in  FIG. 10C , a second insulating film F 2  including silicon and nitrogen is formed on the other portion of the second semiconductor region  20 . The second insulating film F 2  including silicon and nitrogen may be formed on the other portion of the second semiconductor region  20 , and the first insulating film F 1 . 
     As shown in  FIG. 10D , a portion of the second insulating film F 2  is removed, and a hole  10 H is formed in the semiconductor member  10 M exposed by removing a portion of the second insulating film F 2 . The hole  10 H reaches the first semiconductor region  10 . 
     As shown in  FIG. 11A , a first insulating member  41  including at least one of silicon or aluminum, and oxygen is formed in the hole  10 H. If necessary, a film to be the nitride member  30  may be formed before the formation of the first insulating member  41 . 
     As shown in  FIG. 11B , the third electrode  53  is formed in the remaining space of the hole  10 H. 
     As shown in  FIG. 11C , a portion of the first insulating film F 1  and a portion of the second insulating film F 2  are removed. 
     As shown in  FIG. 11D , the first electrode  51  and the second electrode  52  are formed. There are the first insulating film F 1  and the second insulating film F 2  between the first electrode  51  and the third electrode  53 , and between the second electrode  52  and the third electrode  53 . 
     The second insulating film F 2  has at least one of the second nitrogen concentration higher than the first nitrogen concentration in the first insulating film F 1 , the second hydrogen concentration lower than the first hydrogen concentration in the first insulating film F 1 , or the second density higher than the first density in the first insulating film F 1 . For example, the first insulating film F 1  provides the first insulating region  42   a  and the fourth insulating region  42   d . For example, the second insulating film F 2  provides the second insulating region  42   b  and the third insulating region  42   c . 
     According to the manufacturing method according to the embodiment, a semiconductor device which is possible to improve characteristics can be obtained. 
     The first electrode  51  includes, for example, at least one selected from the group consisting of aluminum, titanium, nickel, and gold. The second electrode  52  includes, for example, at least one selected from the group consisting of aluminum, titanium, nickel, and gold. The third electrode  53  includes, for example, at least one selected from the group consisting of TiN, WN, Ni, Au, Pt and Ti. The first conductive member  61  includes, for example, a metal. The metal included in the first conductive member  61  includes, for example, at least one selected from the group consisting of aluminum, copper, and gold. The third electrode  53  and the first conductive member  61  may include, for example, conductive silicon or polysilicon or the like. 
     According to the embodiment, a semiconductor device and a method for manufacturing the same can be provided, in which characteristics are possible to be improved. 
     Hereinabove, exemplary embodiments of the invention are described with reference to specific examples. However, the embodiments of the invention are not limited to these specific examples. For example, one skilled in the art may similarly practice the invention by appropriately selecting specific configurations of components included in semiconductor devices such as semiconductor members, semiconductor regions, conductive members, electrodes, insulating members, etc., from known art. Such practice is included in the scope of the invention to the extent that similar effects thereto are obtained. 
     Further, any two or more components of the specific examples may be combined within the extent of technical feasibility and are included in the scope of the invention to the extent that the purport of the invention is included. 
     Moreover, all semiconductor devices practicable by an appropriate design modification by one skilled in the art based on the semiconductor devices described above as embodiments of the invention also are within the scope of the invention to the extent that the spirit of the invention is included. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.