JP6575224B2 - Semiconductor device - Google Patents

Description

  The present invention relates to a semiconductor device having a heterojunction structure of gallium nitride (hereinafter referred to as GaN) and aluminum gallium nitride (hereinafter referred to as AlGaN) which are nitride semiconductors.

  GaN, which is a nitride semiconductor, has a wide band gap, is excellent in withstand voltage, and has a high saturation electron velocity, so that it is a semiconductor material suitable for high speed operation. For example, conventionally, as a lateral switching device having a heterojunction structure in GaN, a semiconductor device including a HEMT (High Electron Mobility Transistor) that is a field effect transistor has been proposed.

  This semiconductor device is provided with a lateral HEMT having a heterojunction structure of GaN and AlGaN. Specifically, a GaN layer serving as an electron transit layer and an AlGaN layer serving as an electron supply layer are sequentially stacked on the substrate. A gate electrode is provided on the AlGaN layer, and a source electrode and a drain electrode are formed on the AlGaN layer on both sides of the gate electrode.

  In the HEMT configured as described above, a two-dimensional electron gas (hereinafter referred to as 2DEG) carrier is induced below the AlGaN layer located on both sides of the gate electrode due to the piezoelectric effect and the spontaneous polarization effect. Then, with the surface layer portion of the GaN layer at a position below the gate electrode as a channel portion, an operation is performed in which current flows between the source and drain through the 2DEG carrier and the channel portion. As described above, by using the 2DEG carrier, it is possible to reduce the loss of the switching device.

  On the other hand, when a reverse voltage is applied to the element, an electric field due to the 2DEG layer is applied in addition to the electric field due to the applied voltage, so that a site (for example, a gate structure) that strongly concentrates the electric field in the device is likely to occur. There is a problem that the reliability of the device is lowered. Therefore, measures are taken to improve the breakdown voltage by securing the distance between the gate and the drain, or to reduce the concentration of the 2DEG layer by reducing the Al mixed crystal ratio of the AlGaN layer.

  However, these methods lead to an increase in the resistance of the access region and increase the on-resistance. Ensuring high breakdown voltage and reducing on-resistance have a trade-off relationship, and it is difficult to achieve both.

  Also, in order to solve the above problem, as disclosed in Patent Document 1, a method is adopted in which the Al mixed crystal ratio in the AlGaN layer is lowered only at the lower part of the drain-side gate electrode where electric field concentration occurs when a reverse voltage is applied. You can also. In this way, the concentration of the 2DEG layer can be lowered below the gate structure where the electric field strength is particularly high, and the generation of crystal defects can be suppressed by reducing the Al mixed crystal ratio. It is possible to prevent the decrease.

JP 2014-41965 A

  However, as disclosed in Patent Document 1, it is difficult in the process to selectively vary the Al mixed crystal ratio in the AlGaN layer, and problems such as a decrease in crystallinity of the AlGaN layer and formation of interface states Will be generated.

  In view of the above points, an object of the present invention is to provide a semiconductor device having a structure capable of increasing 2DEG concentration and reducing on-resistance while suppressing a decrease in breakdown voltage and reliability.

  In order to achieve the above object, according to the first aspect of the present invention, a substrate (1) made of semi-insulating or semiconductor, a GaN layer (3) formed on the substrate and constituting an electron transit layer, and A channel forming layer having a heterojunction structure with an AlGaN layer (4) constituting an electron supply unit, a gate structure (5) including a gate electrode (7) formed on the AlGaN layer, and a channel forming layer; And a source electrode (8) and a drain electrode (9) disposed on both sides of the gate structure portion, and between the source electrode and the drain electrode based on a voltage applied to the gate electrode It is equipped with a lateral switching device that allows current to flow, and is formed on the AlGaN layer between the gate structure and the drain electrode, away from the gate structure. It is characterized in that the tensile stress formed film to apply a to tensile stress (10, 11) are formed.

  As described above, a tensile stress forming film is formed between the gate structure portion and the drain electrode in the surface of the AlGaN layer so as to generate a tensile stress on the AlGaN layer. Accordingly, a semiconductor device having a structure capable of increasing the 2DEG concentration and reducing the on-resistance while suppressing a decrease in breakdown voltage and reliability can be obtained.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows an example of a corresponding relationship with the specific means as described in embodiment mentioned later.

1 is a top surface layout of a semiconductor device according to a first embodiment of the present invention. It is II-II sectional drawing of FIG. FIG. 3 is a sectional view taken along line III-III in FIG. 1. It is a top surface layout of the semiconductor device concerning a 2nd embodiment of the present invention. It is VV sectional drawing of FIG. It is a top surface layout of the semiconductor device concerning a 3rd embodiment of the present invention. It is VII-VII sectional drawing of FIG. It is a top surface layout of the semiconductor device concerning a 4th embodiment of the present invention. It is IX-IX sectional drawing of FIG. It is a top surface layout of the semiconductor device concerning a 5th embodiment of the present invention. It is XI-XI sectional drawing of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other will be described with the same reference numerals.

(First embodiment)
A semiconductor device according to a first embodiment of the present invention will be described with reference to FIGS. As shown in FIGS. 1 to 3, the semiconductor device according to the present embodiment is configured to include a lateral HEMT as a switching device.

  As shown in FIG. 2, the horizontal HEMT of this embodiment is formed using a structure in which an i-type GaN layer 3 is laminated on the surface of a substrate 1 with a buffer layer 2 interposed therebetween as a compound semiconductor substrate. . An AlGaN layer 4 is formed on the surface of the GaN layer 3, and the GaN layer 3 and the AlGaN layer 4 constitute a heterojunction structure. The horizontal HEMT operates by using the GaN layer 3 and the AlGaN layer 4 as channel forming layers and inducing 2DEG carriers on the GaN layer 3 side of the AlGaN / GaN interface by a piezoelectric effect and a spontaneous polarization effect.

  The substrate 1 is made of a semi-insulating material such as Si (111), SiC, or sapphire, or a semiconductor material, and a buffer layer 2 serving as a base film for forming a GaN layer 3 with good crystallinity thereon. Is formed. The buffer layer 2 is composed of, for example, an AlGaN-GaN superlattice layer. If the GaN layer 3 can be formed on the substrate 1 with good crystallinity, the buffer layer 2 may be omitted. Here, the crystallinity means defects or dislocations in the GaN layer 3 and has an influence on electrical and optical characteristics.

  A GaN layer 3 and an AlGaN layer 4 are formed on the buffer layer 2 by, for example, heteroepitaxial growth.

  The GaN layer 3 constitutes an electron transit layer made of a first GaN-based semiconductor material that is a GaN-based semiconductor material. In the present embodiment, the GaN layer 3 is made of i-GaN, but may be made of n-GaN or p-GaN.

  The AlGaN layer 4 is made of a semiconductor material having a larger band gap energy than the first GaN-based semiconductor material, and constitutes an electron supply unit. Here, the AlGaN layer 4 is made of i-GaN.

  On the AlGaN layer 4, a gate electrode 7 is formed as a gate structure portion 5 via a gate insulating film 6.

The gate insulating film 6 is made of a silicon oxide film (SiO ₂ ), alumina (Al ₂ O ₃ ) or the like, and the gate electrode 7 is made of a metal such as aluminum or platinum or a poly-semiconductor doped with impurities. It is configured. The gate insulating film 6 and the gate electrode 7 are formed on the AlGaN layer 4 to constitute a MOS structure. Here, the MOS structure in which the gate electrode 7 is formed on the gate insulating film 6 is exemplified as the gate structure portion 5, but the gate electrode 7 may be formed on the AlGaN layer 4 as a Schottky electrode. good.

  On the other hand, a source electrode 8 and a drain electrode 9 are formed on both sides of the surface of the AlGaN layer 4 with the gate structure 5 interposed therebetween. The source electrode 8 and the drain electrode 9 are in ohmic contact with the AlGaN layer 4 respectively. These source electrode 8 and drain electrode 9 are made of, for example, a metal such as aluminum or titanium.

  Further, a strain forming film 10 and a stress film 11 are sequentially formed between the gate structure 5 and the source electrode 8 and between the gate structure 5 and the drain electrode 9 on the surface of the AlGaN layer 4. Yes.

The strain forming film 10 generates a strain by applying a stress to the AlGaN layer 4 as a base. The stress film 11 applies tensile stress to the strain forming film 10. The stress film 11 covers the strain forming film 10 and protrudes from the strain forming film 10 toward the gate structure 5 side, the source electrode 8 side, and the drain electrode 9 side. The strain forming film 10 is made of, for example, a silicon oxide film (SiO ₂ ), and the stress film 11 is made of, for example, a silicon nitride film (SiN).

  Specifically, the strain forming film 10 generates strain on the AlGaN layer 4 by applying tensile stress to the AlGaN layer 4. In the case of a single structure in which the stress film 11 is not provided, the strain forming film 10 may not be able to apply much tensile stress to the AlGaN layer 4. Any stress can be applied.

  That is, the strain forming film 10 and the stress film 11 are cooled and thermally contracted after these forming steps. At this time, if the thermal contraction rate of the strain forming film 10, in other words, the thermal expansion coefficient is smaller than that of the stress film 11, the stress film 11 causes The contraction of the strain forming film 10 is blocked, and a tensile stress is generated in the strain forming film 10. Therefore, the tensile stress can be applied to the underlying AlGaN layer 4 by the strain forming film 10 in which the tensile stress is generated.

  With such a configuration, the horizontal HEMT according to the present embodiment is configured. As shown in FIG. 2, the outer edge portion of the horizontal HEMT configured as described above has a mesa structure in which a recess 12 reaching the middle position in the thickness direction of the GaN layer 3 from the surface of the AlGaN layer 4 is formed. Yes. The dashed-dotted line shown in FIG. 1 describes the inner contour of the recess 12, and the recess 12 is formed so as to surround the current path connecting the source electrode 8 and the drain electrode 9. Although not shown, a gate wiring layer, a source wiring layer, and a drain wiring layer made of Al or the like are formed on the surfaces of the gate electrode 7, the source electrode 8, and the drain electrode 9, respectively. These are electrically separated through an interlayer insulating film, and an arbitrary voltage can be applied to each electrode.

  Thus, in the semiconductor device of the present embodiment, the strain forming film 10 and the stress between the gate structure 5 and the source electrode 8 and between the gate structure 5 and the drain electrode 9 in the surface of the AlGaN layer 4. The film 11 is formed.

The charge density of the 2DEG layer is expressed as Equation 1 with the Al mixed crystal ratio x in Al _x Ga _1-x N constituting the AlGaN layer 4 as a variable. According to this equation, it can be seen that the 2DEG concentration can be increased as the strain of AlGaN increases. Since AlGaN has a smaller lattice constant than GaN, the 2DEG concentration can be increased by applying tensile stress to the AlGaN layer 4 and increasing the strain. On the other hand, if the compressive stress is applied, the 2DEG concentration is lowered.

  In the present embodiment, a tensile stress is applied to the AlGaN layer 4 by forming the strain forming film 10 and the stress film 11. For this reason, it is possible to increase the 2DEG concentration at the site where the strain forming film 10 and the stress film 11 are formed. Therefore, even if the Al mixed crystal ratio of the AlGaN layer 4 is lowered, the concentration of the 2DEG layer can be increased and the on-resistance can be reduced.

  Further, a strain forming film 10 and a stress film 11 are formed between the gate structure portion 5 and the source electrode 8 and the drain electrode 9 at a position away from the gate structure portion 5. Therefore, the concentration of the 2DEG layer can be lowered particularly in the vicinity of the gate structure portion 5 where the electric field strength is high, and the electric field strength in the vicinity of the gate structure portion 5 can be suppressed to a desired value or less. It becomes possible. In addition, since the generation of crystal defects can be suppressed by reducing the Al mixed crystal ratio of the AlGaN layer 4, it is possible to prevent further reduction in reliability and improve the breakdown voltage.

  And since the concentration of the 2DEG layer can be changed depending on the location while making the Al mixed crystal ratio of the AlGaN layer 4 uniform instead of partially changing, the manufacturing process of the AlGaN layer 4 does not become difficult. . In addition, as in the case where the Al mixed crystal ratio of the AlGaN layer 4 is partially changed, the crystallinity of the AlGaN layer 4 and the formation of interface states can be suppressed.

  As described above, in the present embodiment, the strain forming film 10 and the stress film between the gate structure 5 and the source electrode 8 and between the gate structure 5 and the drain electrode 9 in the surface of the AlGaN layer 4. 11 to generate a tensile stress on the AlGaN layer 4. Accordingly, a semiconductor device having a structure capable of increasing the 2DEG concentration and reducing the on-resistance while suppressing a decrease in breakdown voltage and reliability can be obtained.

  The method of manufacturing the semiconductor device configured as described above is basically the same as that of the conventional method, but is obtained by adding the formation process of the strain forming film 10 and the stress film 11 to the conventional manufacturing method. . That is, an AlGaN layer 4 having a desired Al mixed crystal ratio is formed on the GaN layer 3. Subsequently, the gate structure 5 is formed by performing a step of forming the gate insulation 6, a film formation and patterning step of the gate electrode 7, and the like. Further, after the film formation and patterning process of the strain forming film 10 is performed, the film formation and patterning process of the stress film 11 is performed. Then, the semiconductor device of this embodiment can be manufactured by performing an interlayer insulating film forming process, a contact hole forming process, a source electrode 8 and a drain electrode 9 film forming process, and a patterning process.

(Second Embodiment)
A second embodiment of the present invention will be described. In this embodiment, the configuration of the strain forming film 10 is changed with respect to the first embodiment, and the other parts are the same as those in the first embodiment. Therefore, only the parts different from the first embodiment will be described.

  As shown in FIGS. 4 and 5, in this embodiment, a plurality of strain forming films 10 are arranged between the gate structure portion 5 and the source electrode 8 and between the gate structure portion 5 and the drain electrode 9. The structure is divided into two. Specifically, each strain forming film 10 has a line shape extending in a direction perpendicular to the arrangement direction of the source electrode 9, the gate structure 5 and the drain electrode 10, that is, in a direction perpendicular to the current flow direction. Therefore, a plurality of strain forming films 10 disposed between the gate structure portion 5 and the source electrode 8 and between the gate structure portion 5 and the drain electrode 9 are laid out in stripes. ing. Then, a plurality of strain forming films 10 formed between the gate structure portion 5 and the source electrode 8 are covered with one stress film 11, and a plurality of strains formed between the gate structure portion 5 and the drain electrode 9 are covered. The formation film 10 is also covered with one stress film 11.

  In this way, the strain forming film 10 may be divided into lines. Even with such a structure, the same effect as in the first embodiment can be obtained. Further, the tensile stress is generated particularly large at both ends of the strain forming film 10. For this reason, when the strain forming film 10 is divided and arranged, a plurality of places where a large tensile stress can be generated can be provided, and a place where a large tensile stress is applied to the underlying AlGaN layer 4. A wide range can be provided. As a result, it becomes possible to apply a large tensile stress to the surface of the AlGaN layer 4 over a wider range, and the effects shown in the first embodiment can be obtained.

(Third embodiment)
A third embodiment of the present invention will be described. In this embodiment, the configuration of the strain forming film 10 is changed with respect to the first embodiment, and the other parts are the same as those in the first embodiment. Therefore, only different portions from the first embodiment will be described.

  As shown in FIGS. 6 and 7, also in the present embodiment, a plurality of strain forming films 10 disposed between the gate structure portion 5 and the source electrode 8 and between the gate structure portion 5 and the drain electrode 9 are provided. The structure is divided into two. Specifically, the respective strain forming films 10 are arranged in a dot shape, and in the present embodiment, the respective strain forming films 10 are arranged in a staggered manner. Then, a plurality of strain forming films 10 formed between the gate structure portion 5 and the source electrode 8 are covered with one stress film 11, and a plurality of strains formed between the gate structure portion 5 and the drain electrode 9 are covered. The formation film 10 is also covered with one stress film 11.

  In this manner, the strain forming film 10 may be divided into dots. Even with such a structure, the same effect as in the second embodiment can be obtained.

(Fourth embodiment)
A fourth embodiment of the present invention will be described. In the present embodiment, tensile stress is not applied to the AlGaN layer 4 by the strain forming film 10 or the stress film 11 as compared with the first embodiment, but the concentration of the 2DEG layer is controlled by another method. Since the rest of the present embodiment is the same as that of the first embodiment, only the parts different from the first embodiment will be described.

As shown in FIGS. 8 and 9, in this embodiment, a stress film 20 that generates compressive stress is formed so as to cover the gate structure 5. Specifically, the stress film 20 is formed so as to protrude from the gate structure portion 5 toward the source electrode 8 and the drain electrode 9 side. For example, a silicon oxide film (SiO ₂ ) can be used as the stress film 20. Thus, when the stress film 20 is formed so as to cover the gate structure portion 5, it is possible to apply a compressive stress to the AlGaN layer 4 in the vicinity of the gate structure portion 5. As for the stress film 20, it is known that the direction and magnitude of the film stress can be controlled from compression to tension by changing the film density by changing the film formation conditions such as plasma CVD. In the case of this embodiment, the film forming conditions are set so that a compressive stress is generated in the stress film 20.

  As described above, when a compressive stress is applied to the AlGaN layer 4, the 2DEG concentration decreases. For this reason, by applying a compressive stress to the AlGaN layer 4 in the vicinity of the gate structure portion 5, it is possible to reduce the 2DEG concentration particularly in the vicinity of the gate structure portion 5 where the electric field strength is increased. If the Al mixed crystal ratio of the AlGaN layer 4 is set so that the 2DEG concentration can be increased to some extent except in the vicinity of the gate structure portion 5, the distribution of the 2DEG concentration becomes the same as that of the semiconductor device of the first embodiment. .

  Thus, by providing the stress film 20 that can apply a compressive stress to the AlGaN layer 4 in the vicinity of the gate structure portion 5, it is possible to obtain the same effect as in the first embodiment.

(Fifth embodiment)
A fifth embodiment of the present invention will be described. In this embodiment, the tensile stress is not applied to the AlGaN layer 4 by the strain forming film 10 or the stress film 11 as compared with the first embodiment, but the concentration of the 2DEG layer is controlled by another method. Since the rest of the present embodiment is the same as that of the first embodiment, only the parts different from the first embodiment will be described.

As shown in FIGS. 10 and 11, in this embodiment, a strain forming film 30 and a stress film 31 are formed in this order on the gate structure 5 side between the gate structure 5 and the drain electrode 9. . The strain forming film 30 applies strain to the underlying AlGaN layer 4 to generate strain. The stress film 31 applies compressive stress to the strain forming film 30. Here, although the strain forming film 30 and the stress film 31 are formed at a position away from the gate structure 5 by a predetermined distance, they may be formed so as to contact the gate structure 5. The strain forming film 30 is made of, for example, a silicon oxide film (SiO ₂ ), and the stress film 31 is made of, for example, a silicon nitride film (SiN).

  In this way, the strain forming film 30 and the stress film 31 are formed between the gate structure 5 and the drain electrode 9 on the side of the gate structure 5, that is, particularly at a position where the electric field strength is high, and compress the AlGaN layer 4 Stress can be applied. Even in the case of such a structure, if the Al mixed crystal ratio of the AlGaN layer 4 is set so that the 2DEG concentration can be increased to some extent except in the vicinity of the gate structure portion 5, the distribution of the 2DEG concentration is the same as that of the first embodiment. This is the same as a semiconductor device. Therefore, even with the structure of the present embodiment, it is possible to obtain the same effect as that of the first embodiment.

(Other embodiments)
The present invention is not limited to the embodiment described above, and can be appropriately changed within the scope described in the claims.

  For example, in the first to third embodiments, the multilayer structure including the strain forming film 10 and the stress film 11 is taken as an example of the tensile stress forming film that applies a tensile stress to the AlGaN layer 4. It may be of a structure. Further, the tensile stress forming film has a structure in which a tensile stress is applied from the strain forming film 10 to the AlGaN layer 4 by applying a tensile stress to the strain forming film 10 by the stress film 11. However, it is not limited to this. In other words, other forms may be used as long as a tensile stress can be formed on the AlGaN layer 4 by the tensile stress forming film. Of course, the material of the tensile stress forming film is not limited to the silicon oxide film or the silicon nitride film.

  Similarly, as the compressive stress forming film for applying compressive stress to the AlGaN layer 4, the stress film 20 is taken as an example in the fourth embodiment, and the strain forming film 30 and the stress film 31 are taken as examples in the fifth embodiment. It was. However, these are merely examples of the compressive stress forming film. For example, a compressive stress forming film having a multilayer structure may be applied to the fourth embodiment, or a single layer structure may be used for the fifth embodiment. Alternatively, a compressive stress forming film may be applied.

  In the first to third embodiments, the tensile stress forming film is provided not only between the gate structure 5 and the drain electrode 9 but also between the gate structure 5 and the source electrode 8. What is necessary is just to form between the gate structure part 5 and the drain electrode 9. FIG.

DESCRIPTION OF SYMBOLS 1 Substrate 3 GaN layer 4 AlGaN layer 5 Gate structure part 6 Gate insulating film 7 Gate electrode 8 Source electrode 9 Drain electrode 10, 30 Strain forming film 11, 20, 31 Stress film

Claims (5)

A semi-insulating or semiconductor substrate (1);
A channel forming layer having a heterojunction structure formed on the substrate and having a GaN layer (3) constituting an electron transit layer and an AlGaN layer (4) constituting an electron supply unit;
A gate structure (5) including a gate electrode (7) formed on the AlGaN layer;
A source electrode (8) and a drain electrode (9) disposed on both sides of the gate structure portion on the channel formation layer;
A lateral switching device for passing a current between the source electrode and the drain electrode based on a voltage applied to the gate electrode;
Tensile stress forming films (10, 11) that are formed on the AlGaN layer between the gate structure and the drain electrode and are separated from the gate structure and apply tensile stress to the AlGaN layer. Formed ,
The tensile stress forming film is
A strain forming film (10) for generating strain by applying stress to the AlGaN layer;
A stress film (11) formed on the strain forming film and applying tensile stress to the AlGaN layer in the strain forming film by applying tensile stress to the strain forming film; It is composed of a laminated structure,
2. The semiconductor device according to claim 1, wherein the stress film is formed so as to protrude from the strain formation film to the gate structure portion side and the drain electrode side while covering the strain formation film . The semiconductor device according to claim 1, wherein the strain forming film is divided into a plurality of parts. A semi-insulating or semiconductor substrate (1);
A channel forming layer having a heterojunction structure formed on the substrate and having a GaN layer (3) constituting an electron transit layer and an AlGaN layer (4) constituting an electron supply unit;
A gate structure (5) including a gate electrode (7) formed on the AlGaN layer;
A source electrode (8) and a drain electrode (9) disposed on both sides of the gate structure portion on the channel formation layer;
A lateral switching device for passing a current between the source electrode and the drain electrode based on a voltage applied to the gate electrode;
Tensile stress forming films (10, 11) that are formed on the AlGaN layer between the gate structure and the drain electrode and are separated from the gate structure and apply tensile stress to the AlGaN layer. Formed,
The tensile stress forming film is
A strain forming film (10) for generating strain by applying stress to the AlGaN layer;
A stress film (11) formed on the strain forming film and applying tensile stress to the AlGaN layer in the strain forming film by applying tensile stress to the strain forming film; It is composed of a laminated structure,
The strain formed film, semi-conductor device you characterized in that it is divided into a plurality. 4. The semiconductor device according to claim 2 , wherein the strain forming film has a line shape extending in a direction perpendicular to an arrangement direction of the gate structure portion and the drain electrode. The semiconductor device according to claim 2 , wherein the strain forming film has a dot shape.

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