JP4913674B2 - Nitride semiconductor structure and manufacturing method thereof - Google Patents

Description

  The present invention relates to a nitride semiconductor structure and a manufacturing method thereof, and more particularly to a nitride semiconductor structure formed by crystal growth of a nitride semiconductor film on a Si substrate and a manufacturing method thereof.

  In recent years, a nitride semiconductor has been used as a material for forming a light emitting device in a blue region such as a blue light emitting diode (blue LED) or a blue laser diode (blue LD).

  In order to obtain an arbitrary surface of a nitride semiconductor, for example, GaN, it is ideal to cut out from a bulk single crystal of GaN, but the bulk growth technique itself has not been established and is difficult at present. For this reason, crystal growth of nitride semiconductors on heterogeneous substrates such as sapphire substrates and SiC substrates using metalorganic vapor phase epitaxy (MOVPE), hydride vapor phase epitaxy (HVPE) and molecular beam epitaxy (MBE) Has been done. The semiconductor crystal is generally grown on the same type of substrate as the semiconductor to be grown, but it is difficult to produce a substrate of the same type as the nitride semiconductor at present. For this reason, heterogeneous substrates such as sapphire substrates and SiC substrates are generally used for crystal growth of nitride semiconductors.

  However, in a GaN heterostructure obtained, for example, by hetero-growth GaN on a heterogeneous substrate, a piezoelectric field is generated due to a large difference in lattice constant between the substrate and GaN. For this reason, in a light-emitting device having a GaN heterostructure, the piezoelectric electric field based on this lattice mismatch causes a problem that electrons and holes are largely spatially separated in the high composition In region, resulting in a decrease in luminous efficiency. is there.

  Here, the piezo electric field in a hexagonal crystal such as GaN is maximum in the C-axis [0001] direction. For this reason, if the hetero interface between GaN and the substrate is shifted from the C axis to produce GaN having a crystal plane different from the polar direction, the piezoelectric field can be reduced. Until now, crystal growth of GaN having nonpolar planes such as (1-100) plane and (11-20) plane parallel to the C axis, or (1-101) plane, (11-22) plane, etc. Attempts have been made to grow GaN crystals having a semipolar plane. If GaN has a nonpolar surface such as the (1-100) surface or the (11-20) surface, the generation of the piezoelectric field can be eliminated, and the (1-101) surface or the (11-22) surface can be eliminated. Even in the case of GaN having a semipolar surface such as the piezoelectric field, the piezoelectric field can be greatly reduced. Note that the (11-22) plane has a greater effect of reducing the piezoelectric field than the (1-101) plane.

  However, in GaN, the facet surface formed varies depending on growth conditions such as temperature and pressure, and nonpolar surfaces such as (1-100) surface and (11-20) surface that are not stable surfaces are formed as flat surfaces. Is difficult. On the other hand, semipolar surfaces such as the (1-101) plane and the (11-22) plane are relatively easy to form as a flat surface as a metastable surface next to the stable (0001) plane.

  Here, the GaN crystal grows with C-axis orientation on the Si (n11) plane. For this reason, if GaN is crystal-grown on a specific facet surface, the growth axis of GaN can be tilted. For example, in the Si substrate, the (311) plane is inclined about 58.5 ° with respect to the (111) plane. On the other hand, the angle difference between the (0001) plane and the (11-22) plane in GaN is 58.4 °. Therefore, if GaN is crystal-grown on the (111) plane of the (311) Si substrate, a GaN crystal having the (11-22) plane as the main surface can be obtained directly.

  Therefore, an attempt has been made to process a substrate so that a specific facet surface is formed, and selectively grow a GaN crystal having a specific semipolar surface on the facet surface of the processed substrate.

  For example, as a method for crystal growth of GaN having a (1-101) plane as a semipolar plane as a main plane, a (001) Si substrate of 7 ° off is processed to form a (111) plane, and this (111) A technique for selectively growing a GaN crystal on the surface) is known (for example, see Non-Patent Document 1).

In this technique, as shown in FIG. 5, after a SiO ₂ film 81 is deposited on a (001) Si substrate 80 off by 7 ° by sputtering, stripes along the <−110> direction of the Si substrate 80 are formed by photolithography. Form a pattern. Then, by anisotropically etching the substrate surface with a potassium hydroxide (KOH) solution, the substrate surface extends along the <−110> direction and has both sides of the (111) surface 82a and the (−1-11) surface 82b. A groove 82 is formed on the substrate surface. Next, the SiO ₂ film 83 is formed only on the (−1-11) surface 82b by sputtering. The processed substrate thus obtained is subjected to MOVPE, and GaN is crystal-grown on the (111) surface 82a to obtain the GaN film 84 having the (1-101) surface 84a as a main surface.

Here, the (−1-11) plane 82b is masked by the SiO ₂ film 83 because the (111) plane 82a and the (−1-11) plane 82b on both sides of the groove 82 are both hexagonal GaN. This is because the (n11) plane is easy for crystal growth. That is, the GaN film 84 obtained by crystal growth on the (111) plane 82a due to interference between the GaN crystal growing on the (-1-11) plane 82b and the GaN crystal growing on the (111) plane 82a. This is to prevent a GaN crystal from growing on the (−1-11) plane 82b in order to prevent the crystal quality from deteriorating. Note that the bottom surface 82c of the groove 82 is a (001) plane and is not masked by the SiO ₂ film 83 because the hexagonal GaN is not an (n11) plane where crystal growth is easy.

  Further, as a method for crystal growth of GaN having a (11-22) plane as a semipolar plane as a main surface, (311) a Si substrate is processed to form a (1-11) plane, and this (1-11) ) A technique for selectively growing GaN on the surface is known (see, for example, Non-Patent Document 2).

In this technique, as shown in FIG. 6, after a (311) SiO ₂ film 91 is deposited on a Si substrate 90 by sputtering, a stripe pattern along the <1-1-1> direction of the Si substrate 90 is formed by photolithography. Form. Non-Patent Document 2 describes (113) Si substrate, but the (113) Si substrate and the (311) Si substrate are the same except that they are expressed differently. Then, the substrate surface is anisotropically etched with a potassium hydroxide (KOH) solution to extend along the <1-1-1> direction, and the (1-11) plane 92a and the (-11-1) plane 92b. A groove 92 having both side surfaces and a bottom surface 92c is formed on the substrate surface. Next, a SiO ₂ film 93 is formed on the bottom surface 92c by sputtering. The processed substrate thus obtained is subjected to MOVPE, and GaN is crystal-grown on the (1-11) surface 92a, thereby obtaining a GaN film 94 having the (11-22) surface 94a as a main surface.

Here, the bottom surface 92c is masked with the SiO ₂ film 93 because the bottom surface 92c is a (311) plane which is the (n11) plane on which hexagonal GaN is likely to grow. That is, the crystal quality of the GaN film 94 obtained by crystal growth on the (1-11) surface 92a due to interference between the GaN crystal growing on the bottom surface 92c and the GaN crystal growing on the (1-11) surface 92a. This is to prevent a GaN crystal from growing on the bottom surface 92c in order to prevent the decrease of the GaN crystal.

On the other hand, the (-11-1) plane 92b is also an (n11) plane in which hexagonal GaN tends to grow. For this reason, from the viewpoint of preventing the deterioration of the crystal quality of the GaN film 94, it is desirable to mask the SiO ₂ film 93 also on the (-11-1) surface 92b. However, since the (-11-1) surface 92b is an obliquely downward side surface, it is extremely difficult to form the SiO ₂ film 93 on the (-11-1) surface 92b by sputtering. For this reason, the (-11-1) surface 92 _{b which} is the downward side surface is not masked by the SiO ₂ film 93.
JOURNAL OF CRYSTAL GROWTH 242 (2002) 82-86, “Growth of (1-101) GaN on a 7-degree off-oriented (001) Si substrate by selective MOVPE, Yoshio Honda, Norifumi Kameshiro, Masahito Yamaguchi, Nobuhiko Sawaki 53rd Joint Conference on Applied Physics Lecture Proceedings, pp. 347, “Processed (113) MOVPE Growth of (11-22) Planar GaN on Si Substrate”, Toshiyuki Hikosaka, Toshiyuki Kuroki, Yoshio Honda, Yamaguchi Masafumi, Nobuhiko Sawaki

  However, in the conventional techniques described in Non-Patent Documents 1 and 2 in which GaN is selectively grown using a processed substrate, a GaN film crystal formed on a facet surface by selectively growing a GaN crystal only on a specific facet surface. In order to prevent deterioration in quality, surfaces other than a specific facet surface must be masked by sputtering. For this reason, there existed a problem that the sputtering process for masking increased.

  In the prior art described in Non-Patent Document 2, in which a GaN crystal having a (11-22) plane is selectively grown on a (1-11) plane 92a formed by processing a (311) Si substrate 90, the groove The both groove side surfaces of (92) (1-11) surface 92a and (-11-1) surface 92b and the inner surface of all grooves of the bottom surface ((311) surface) 92c become (n11) surfaces on which hexagonal GaN is likely to grow crystals. . However, among these groove inner surfaces, the (-11-1) surface 92b is an obliquely downward side surface. For this reason, it is extremely difficult to mask the obliquely downward (-11-1) surface 92b by sputtering. Therefore, the GaN crystal 95 grows on the (-11-1) surface 92b, and the GaN crystal 95 interferes with the GaN film 94 formed on the (1-11) surface 92a, so that the GaN film There was a problem that the crystal quality of 94 deteriorated.

  The present invention has been made in view of the above circumstances, and when a semipolar nitride semiconductor advantageous for reducing the generation of a piezoelectric field is selectively grown on a processing substrate, a specific technique is not used without using a masking technique. It is a technical problem to be solved to selectively grow crystals on the facet surface and to improve the crystal quality of the semipolar nitride semiconductor formed by the selective growth.

  The present inventor has intensively studied semipolar GaN having a (11-22) plane, which has a large effect of reducing the piezoelectric field, in the technique of selectively growing a semipolar nitride semiconductor on a processed substrate. Then, if a (311) Si base material suitable for selective growth of a GaN crystal having a (11-22) plane is anisotropically etched with KOH, it is an obliquely upward and downward side surface extending in parallel and facing each other (1- 11) It was noted that a groove having a plane and a (-11-1) plane was formed. Then, by adjusting the width d and depth h of the groove, it was found that a nitride semiconductor could be preferentially grown on the obliquely upward (1-11) plane, and the present invention was completed.

  In the technique of selectively growing a GaN crystal having a (1-101) plane with respect to a 7 ° off (001) Si substrate, both side surfaces of the groove face obliquely upward and the width of the groove faces the opening. It is getting wider gradually. For this reason, the raw material is evenly supplied to both side surfaces during crystal growth, and the nitride semiconductor cannot be preferentially grown on one side surface.

  That is, the method for manufacturing a nitride semiconductor structure of the present invention that solves the above-described problems is (311) a side surface of diagonally upward and diagonally downward facing the (311) surface of the Si substrate and extending parallel to each other and facing each other (1- 11) a substrate processing step for forming a plurality of grooves having a surface and a (-11-1) surface and extending along the <1-1-2> direction of the (311) Si substrate; A crystal growth step of growing a nitride semiconductor on the (311) plane of the (311) base material formed with a nitride semiconductor film having a (11-22) plane as a main surface; The groove width d is set to 20 μm or less, the groove depth h is set to 0.2 μm or more, and the relationship between the groove width d and the depth h is adjusted to 1 ≦ h / d. The nitride semiconductor is preferentially grown on the (1-11) surface of the groove inner surface. It is characterized by that.

  In the method for manufacturing a nitride semiconductor structure according to the present invention, in the base material processing step, the (1-11) plane and the (-11-1) plane, which are diagonally upward and diagonally downward side surfaces that extend parallel to each other and face each other, are provided. And a groove having a specific width d and a specific depth h. In the crystal growth step, the nitride semiconductor is grown on such a groove, so that the nitride semiconductor can be preferentially grown on the (1-11) plane obliquely upward of the groove inner surface. it can. For this reason, by giving priority to crystal growth on the obliquely upward (1-11) plane to such an extent that it is not adversely affected by the crystal growth of the nitride semiconductor on the obliquely downward (-11-1) plane and bottom surface. Thus, it is possible to obtain a nitride semiconductor film with high crystal quality.

  Further, in the method for manufacturing a nitride semiconductor structure according to the present invention, the masking technique is not used for the selective growth of the nitride semiconductor on a specific facet surface, so that the number of steps can be reduced.

  Therefore, according to the method for manufacturing a nitride semiconductor structure of the present invention, a nitride semiconductor film having a (11-22) plane having a high crystal quality as a main surface can be obtained by a simple process.

  In the base material processing step, the relationship between the width d and the depth h of the groove is preferably adjusted to 3/2 ≦ h / d. Thus, by adjusting the relationship between the width d and the depth h of the groove to 3/2 ≦ h / d, it is possible to more reliably give priority to crystal growth on the obliquely upward (1-11) plane, A nitride semiconductor film with higher crystal quality can be obtained. At this time, the groove width d is preferably 5 μm or less. By making the groove width d 5 μm or less and adjusting the relationship between the groove width d and the depth h to 3/2 ≦ h / d, it is possible to reliably prevent crystal growth on the bottom surface and Crystals can be grown only on the (1-11) plane, and complete selectivity can be obtained.

  In the crystal growth step, it is preferable that the nitride semiconductor is grown only on the (1-11) plane of the inner surface of the groove. By growing a nitride semiconductor only on the (1-11) plane, a nitride semiconductor film having an extremely high crystal quality that is not adversely affected by crystal growth on the (-11-1) plane or the bottom is obtained. It becomes possible.

The nitride semiconductor structure of the present invention is a plurality of grooves extending along the <1-1-2> direction on the (311) plane, the width d of the grooves being 20 μm or less, and the depth h of the grooves being 0. (311) Si substrate having 2 μm or more and the groove having a ratio (h / d) of the depth h of the groove to the width d of the groove of 1 ≦ h / d, and the (311) Si A nitride semiconductor film having a (11-22) plane as a main surface formed on the (311) plane of the substrate, and the grooves extend in parallel with each other and face diagonally upward and diagonally downward The nitride semiconductor film has a (1-11) plane and a (-11-1) plane, and the nitride semiconductor film is formed by crystal growth of the nitride semiconductor only on the (1-11) plane of the groove inner surface. It is characterized by that.

  In the nitride semiconductor structure of the present invention, the nitride semiconductor crystal grows only on the obliquely upward (1-11) plane, so that a nitride semiconductor film having the (11-22) plane as the main surface is formed. . For this reason, this nitride semiconductor film has extremely high quality without any adverse effects caused by crystal growth of the nitride semiconductor on the obliquely downward (-11-1) plane and bottom surface.

  Therefore, when the nitride semiconductor structure of the present invention is applied to a light emitting device, it is possible to suppress the generation of a piezoelectric field and a decrease in light emission efficiency due to crystal defects.

  Hereinafter, embodiments of the present invention will be described.

  The method for manufacturing a nitride semiconductor structure according to this embodiment includes a base material processing step and a crystal growth step.

  In the substrate processing step, a plurality of grooves extending along the <1-1-2> direction of the (311) Si substrate are formed on the (311) plane of the (311) Si substrate.

  (311) The shape and size of the Si substrate are not particularly limited and can be set as appropriate.

(311) The method of forming the groove on the Si substrate is not particularly limited, and processing other than wet etching using a chemical reaction in a solution, dry etching using an ion beam such as reactive ion etching (RIE), and the like. Mechanical processing may be used if a predetermined flatness can be ensured on the surface. As wet etching, KOH, NaOH, CsOH, NH ₄ OH, hydrazine, KOH, TMAH, EDP and the like can be used, but KOH is preferably used from the viewpoint of cost and toxicity.

For example, when a groove is formed by wet etching, first, a mask made of a SiO ₂ film or the like is formed on the (311) surface of the (311) Si substrate by sputtering or the like. Note that the type and formation method of the mask are not particularly limited. Then, a periodic stripe pattern in which the opening extends along the <1-1-2> direction is formed by photolithography. Next, the (311) Si substrate on which the periodic stripe pattern is formed is immersed in a KOH solution or the like, and anisotropic etching is performed under predetermined conditions. As a result, a plurality of grooves having a predetermined width d and a predetermined depth h are formed.

  The groove formed in this way has a (1-11) plane and a (-11-1) plane, which are diagonally upward and diagonally downward side faces extending in parallel with each other, and a bottom surface.

  In such groove formation, the groove width d can be adjusted by changing the opening width of the periodic stripe pattern, and the etching conditions (concentration and temperature of the KOH solution and immersion time in the KOH solution) can be adjusted. By changing, the depth h of the groove can be adjusted.

  In the method for manufacturing a nitride semiconductor structure according to this embodiment, the groove width d is set to 20 μm or less, and the groove depth h is set to 0.2 μm or more.

  When the groove width d exceeds 20 μm, the nitride semiconductor is preferentially crystal-grown on the (1-11) surface of the groove inner surface, no matter how the relationship between the groove width d and the depth h is adjusted. Can not be. This is because the raw material can move only about 20 μm or less in the vapor phase in the crystal growth step, but when the groove width d exceeds 20 μm, the diagonally downward (-11-1) plane is also inclined upward (1 This is because the raw material is supplied in the same manner as in the -11) plane. Further, when the groove width d exceeds 20 μm, it becomes difficult to grow the crystal growing on the obliquely upward (1-11) plane in the entire width direction of the groove.

  Here, the lower limit of the width d of the groove can be set as appropriate within a formable range. In the substrate processing step, when a predetermined stripe pattern is formed by photolithography, it can be set to about several hundred nm from the technical viewpoint.

  When the groove depth h is less than 0.2 μm, the nitride semiconductor is preferentially crystallized on the (1-11) surface of the groove inner surface, no matter how the relationship between the groove width d and the depth h is adjusted. Can no longer grow. This is presumably because a large amount of raw material is supplied to the bottom surface in the crystal growth step, but the raw material supplied to the bottom surface diffuses in the plane and is evenly supplied to both side surfaces. Further, in the substrate processing step, when the groove is formed by anisotropic etching using wet etching, when the depth h of the groove is less than 0.2 μm, the (1-11) surface and the bottom surface which are obliquely upward side surfaces It becomes difficult to reliably form a diagonally upward side surface (1-11) inclined at a predetermined angle. Therefore, when the groove is formed by anisotropic etching using wet etching, the depth h of the groove is set to 0 from the viewpoint of reliably forming the obliquely upward side surface (1-11) inclined at a predetermined angle. It is preferably 3 μm or more, and more preferably 0.5 μm or more.

  Here, the relationship that the groove depth h is greater than or equal to a predetermined width with respect to the groove width d (the groove depth h with respect to the groove width d can reliably prevent crystal growth on the bottom surface of the groove. If it is such a relationship, it is meaningless to deepen the groove further. In addition, when forming a groove by anisotropic etching using wet etching in the substrate processing step, if the depth of the groove is excessively deep, the partition Si portion of the adjacent groove is scraped and becomes extremely thin. . Therefore, the upper limit of the depth h of the groove is appropriately set to such an extent that crystal growth on the bottom surface of the groove can be surely prevented and the thickness of the partition Si portion can be secured to a predetermined value or more. can do.

  Further, in the method for manufacturing a nitride semiconductor structure according to the present embodiment, the groove width d and the groove semiconductor so that the nitride semiconductor can be preferentially grown on the (1-11) plane of the groove inner surface in the crystal growth step. The relationship of depth h is adjusted to 1 ≦ h / d. When h / d is smaller than 1 (the value of depth h is smaller than the value of width d), the raw material is also supplied to the bottom surface, and a nitride semiconductor is formed on the (1-11) surface of the groove inner surface. It becomes impossible to grow crystals preferentially.

  From the viewpoint of preferentially growing a nitride semiconductor on the (1-11) plane of the groove inner surface, it is preferable to adjust the relationship between the width d and the depth h of the groove to 3/2 ≦ h / d. That is, by making the depth h relatively deeper than the groove width d, the nitride semiconductor can be preferentially grown on the (1-11) plane, which is preferable.

  Further, from the viewpoint of preferentially growing a nitride semiconductor on the (1-11) plane of the inner surface of the groove, the groove width d is preferably 5 μm or less, more preferably 3 μm or less, and 1 μm. The following is particularly preferable. From the same viewpoint, the depth h of the groove is preferably 1 μm or more, and more preferably 2 μm or more.

  Furthermore, in the method for manufacturing a nitride semiconductor structure according to the present embodiment, the relationship between the groove width d and the depth h is adjusted to 3/2 ≦ h / d, and the groove width d is set to 5 μm or less. Is preferred. By doing so, the nitride semiconductor can be crystal-grown only on the (1-11) plane of the groove inner surface in the crystal growth step.

  In the method for manufacturing a nitride semiconductor structure according to the present embodiment, from the viewpoint of further improving the selectivity of crystal growth with respect to the (1-11) plane, after performing the base material processing step, a thermal oxidation step is performed as necessary. Then, after performing the RIE treatment step, the crystal growth step may be performed.

In the thermal oxidation step, (311) a Si substrate is heated in an oxygen-containing atmosphere to form a thermally oxidized SiO ₂ film on the inner surface of the groove. The thermal oxidation conditions at this time include thermal oxidation SiO having a predetermined film thickness on the entire groove inner surface, that is, the (1-11) plane and (-11-1) plane, and the bottom surface, which are diagonally upward and diagonally downward side surfaces. There is no particular limitation as long as _two films can be formed. For example, a thermally oxidized SiO ₂ film having a film thickness of 10 to 200 nm is formed by thermal oxidation under conditions of gas used: O ₂ or H ₂ O, temperature: about 1000 ° C., oxidation time: 10 minutes to 3 hours. be able to.

In the RIE process, the thermally oxidized SiO ₂ film formed on the (1-11) plane is removed by reactive ion etching. Thus, the selectivity of crystal growth with respect to the (1-11) plane can be improved by performing the crystal growth step after removing the thermally oxidized SiO ₂ film formed on the (1-11) plane. . Further, if only the thermally oxidized SiO ₂ film formed on the (1-11) plane is removed and the thermally oxidized SiO ₂ film formed on the entire bottom surface and the (-11-1) plane is left, Since the crystal can be surely grown only on the (1-11) plane, it is possible to obtain complete selectivity of the crystal growth with respect to the (1-11) plane. However, in addition to the thermally oxidized SiO ₂ film formed on the (1-11) plane which is an obliquely upward side surface, the end portion on the side close to the (1-11) plane in the thermally oxidized SiO ₂ film formed on the bottom surface is partially May be removed.

As conditions for the RIE treatment, for example, gas used: CF ₄ , C ₄ H ₈ + O ₂ + Ar, C ₅ F ₈ + O ₂ + Ar, C ₃ F ₆ + O ₂ + Ar, C ₄ F ₈ + CO, CHF ₃ + O ₂ or CF ₄ + H ₂ , pressure: 0.1 to 10 Pa, incident power: 10 to 1000 W.

  In the crystal growth step, a nitride semiconductor crystal is grown on the (311) Si base material in which the groove is formed, thereby forming a nitride semiconductor film having the (11-22) plane as a main surface.

  The method of growing a nitride semiconductor crystal is not particularly limited. For example, the crystal can be grown as follows.

  First, an intermediate layer is formed as necessary. The intermediate layer is not necessarily required. For example, an intermediate layer made of a nitride semiconductor containing Al having a strong bonding force with Si, such as AlN, is formed as a base layer of the nitride semiconductor film. The bonding strength between the film and the Si substrate can be increased. The intermediate layer can be formed by metal organic vapor phase epitaxy (MOVPE), hydride vapor phase epitaxy (HVPE), molecular beam epitaxy (MBE), or the like.

  Next, the nitride semiconductor is crystal-grown. This method is also not particularly limited, and MOVPE, HVPE, MBE, or the like can be employed.

  When the intermediate layer is formed, it is preferable to continuously perform crystal growth of the intermediate layer and crystal growth of the nitride semiconductor film formed thereon.

As the nitride semiconductor film manufactured in this _{embodiment, In X Al Y Ga Z N} (X + Y + Z = 1,0 ≦ X <1,0 ≦ Y <1,0 <Z ≦ 1) may be a composition of preferably has a composition of _{in X Al Y Ga Z N (} X + Y + Z = 1,0 ≦ X ≦ 0.3,0 ≦ Y ≦ 0.3,0.4 <Z ≦ 1). The greater the Ga content in the nitride semiconductor film, the more advantageous the crystal growth selectivity with respect to the (1-11) plane. For this reason, in the initial stage of forming the nitride semiconductor film, GaN is crystal-grown, and then In and / or Al is appropriately added to the raw material, and a nitride semiconductor containing In and / or Al in addition to Ga is crystal-grown. It is preferable.

  In the crystal growth process according to the present embodiment, since a groove having a specific shape is formed in the base material processing process, a nitride semiconductor can be preferentially grown on the (1-11) plane of this groove. Therefore, the nitride semiconductor film formed by preferentially crystal growth on the (1-11) plane is not adversely affected by the crystal growth of the nitride semiconductor on the (-11-1) plane and the bottom surface. The crystal quality is high.

  In particular, according to the nitride semiconductor film structure according to the present embodiment in which a nitride semiconductor film is formed by crystal growth of a nitride semiconductor only on the (1-11) plane of the inner surface of the groove, the crystal quality is extremely high. can do.

  Embodiments of the present invention will be specifically described below with reference to the drawings.

Example 1
The nitride semiconductor structure according to this example shown in the schematic cross-sectional view of FIG. 1E includes a (311) Si substrate 10 and a (11-22) plane 20a formed on the (311) Si substrate 10. And a GaN film 20 having a main surface.

  The (311) Si substrate 10 has a plurality of grooves 30 extending along the <1-1-2> direction on the (311) plane.

  The groove 30 includes a (1-11) surface 31 and a (-11-1) surface 32 which are obliquely upward and obliquely downward side surfaces extending in parallel with each other and a bottom surface 33. The bottom surface 33 is a (110) surface because the groove 30 is deep. The (1-11) plane 31, the (-11-1) plane 32, and the bottom surface ((110) plane) 33 are all (n11) planes on which hexagonal GaN is likely to grow.

  The width (window width) d of the groove 30 is 1 μm, and the depth h of the groove 30 is 3 μm. Therefore, the relationship between the groove width d and the depth h is h / d = 3. The pitch of the grooves 30 (interval between the centers of adjacent grooves 30) p is 2 μm.

  In the nitride semiconductor structure according to this example, the GaN film 20 is formed by crystal growth of the nitride semiconductor only on the (1-11) surface 31 that is the obliquely upward side surface of the inner surface of the groove 30. Yes. In other words, the nitride semiconductor is not crystal-grown on the (−1-1-1) surface 32 and the bottom surface 33 which are the obliquely downward side surfaces of the groove 30.

  Hereinafter, a method for manufacturing the nitride semiconductor structure according to this example will be described.

<Base material processing step>
First, a (311) Si substrate 10 was prepared as a growth substrate (see FIG. 1A). Then, a mask 11 made of a SiO ₂ film having a thickness of about 70 μm was formed on the (311) surface 10a of the (311) Si substrate 10 by sputtering.

  Next, a periodic stripe pattern in which the openings 12 extend along the <1-1-2> direction was formed by photolithography (see FIG. 1B). In this periodic stripe pattern, the window width of the opening 12 is 1 μm, the mask width is 1 μm, and the pitch of the openings 12 (interval between the centers of the adjacent openings 12) p is 2 μm.

  Next, the (311) Si substrate 10 on which this periodic stripe pattern was formed was immersed in a 40 ° C. KOH solution (concentration: 25 mass%) for 10 minutes. By this anisotropic etching, a plurality of grooves 30 having a width d of 1 μm, a depth h of 3 μm, and h / d = 3 were formed on the (311) surface 10a of the (311) Si substrate 10 (FIG. 1C )reference).

<Crystal growth process>
MOVPE was applied to the (311) Si base material 10 with such grooves formed as described below to grow a nitride semiconductor crystal.

<< AlN growth >>
First, AlN was grown. Growth conditions are as follows: temperature: 1120 ° C., source gas: trimethylaluminum (TMA) and ammonia (NH ₃ ), TMA supply rate: 3.84 μmol / min, NH ₃ supply rate: 1 liter / min (0 ° C., 1 ° C. Pressure), carrier gas: hydrogen (H ₂ ), supply amount of H ₂ : 3 l / min (0 ° C., 1 atm), growth time: 8 minutes. As a result, an AlN intermediate layer having a thickness of several tens of nm was formed on the (1-11) surface 31 that is the obliquely upward side surface of the (311) Si substrate 10.

<< GaN primary growth >>
Subsequently, primary growth of GaN was performed. Growth conditions are as follows: temperature: 1100 ° C., source gas: trimethyl gallium (TMG) and ammonia (NH ₃ ), TMG supply rate: 14.4 μmol / min, NH ₃ supply rate: 2.5 liter / min (0 ° C. 1 atm), carrier gas: hydrogen (H ₂ ), H ₂ supply rate: 3 liters / min (0 ° C., 1 atm), and growth time: 10 minutes.

In the primary growth of GaN, the growth rate is 1100 ° C. and the supply amount of NH ₃ is 2.5 liter / min (0 ° C., 1 atm), so that the growth rate in the GaN stripe direction <1-100> To promote stripe bonding. Thereby, (311) GaN was crystal-grown on the (1-11) surface 31 that is the obliquely upward side surface of the Si base material 10 to form the GaN crystal portion 21 (see FIG. 1D).

<< GaN secondary growth >>
Subsequently, secondary growth of GaN was performed. Growth conditions are as follows: temperature: 1060 ° C., source gas: trimethylgallium (TMG) and ammonia (NH ₃ ), TMG supply rate: 14.4 μmol / min, NH ₃ supply rate: 0.25 liter / min (0 ° C. 1 atm), carrier gas: hydrogen (H ₂ ), supply amount of H ₂ : 3 l / min (0 ° C., 1 atm), and growth time: 20 minutes.

In the secondary growth of GaN, the growth rate is 1060 ° C. and the supply amount of NH ₃ is 0.25 liter / min (0 ° C., 1 atm), so that the growth rate of GaN in the <0001> direction. To promote the bonding between stripes. As a result, a GaN film 20 having a thickness of 2 μm and a flat (11-22) surface 20b was formed (see FIG. 1E).

  The crystal cross section of the GaN film 20 thus obtained was observed. As shown in FIG. 2, the hexagonal GaN is easy to grow from the (−1-1-1) plane 32 and the bottom plane ((110) plane) 33 which are obliquely downward side faces (n11). Despite the surface, no GaN crystal growth was observed. Further, no crystal defects such as stacking faults were observed in the obtained GaN film 20.

  Furthermore, as a result of evaluating the GaN film 20 with CL (cathode luminescence), it was found that a low dislocation region was formed. This is because (311) the contact area between the Si substrate 10 and GaN is small, and the dislocation is bent near the interface between the (311) Si substrate 10 and GaN, so that the dislocation propagates to the surface of the GaN film 20. It is thought that there was not.

  Therefore, it was confirmed that an extremely high quality GaN film 20 was obtained by this example.

(Example 2)
In the base material processing step, in the periodic stripe pattern, except that the window width of the openings 12 is changed to 2 μm, the pitch of the openings 12 (interval between the centers of the adjacent openings 12) p: 3 μm, A nitride semiconductor structure was manufactured by the same method as in Example 1.

  Therefore, in the nitride semiconductor structure of this example, the width d of the groove 30 is 2 μm, and the relationship between the width d and the depth h of the groove is h / d = 3/2. Further, the pitch p of the grooves 30 (interval between the centers of the adjacent grooves 30) p is 3 μm.

  The crystal cross section of the GaN film 20 in this nitride semiconductor structure was observed. As shown in FIG. 3, no GaN crystal growth was observed on the bottom surface ((110) plane) 33. On the other hand, on the (-11-1) surface 32 which is the downward side surface, a slight growth of GaN crystal was observed. However, the growth of the GaN crystal on the (-11-1) surface 32 that is the downward side surface is such that it hardly interferes with the GaN crystal grown on the (1-11) surface 31 that is the upward side surface. For this reason, crystal defects such as stacking faults were not observed in the GaN film 20.

(Comparative Example 1)
A nitride semiconductor structure was manufactured by the same method as in Example 1 except that the immersion time in anisotropic etching was changed to 2.5 minutes in the base material processing step.

  Therefore, in the nitride semiconductor structure of Comparative Example 1, the depth h of the groove 30 is 300 nm, and the relationship between the width d and the depth h of the groove is h / d = 3/10.

  The crystal cross section of the GaN film 20 in this nitride semiconductor structure was observed. As shown in FIG. 4, the electron micrograph shows that GaN has grown from all of the (1-11) plane 31, the (-11-1) plane 32, and the bottom surface 33, and the GaN film 20 The flat (11-22) surface 20a was not formed.

  The reason for this was that GaN was crystal-grown simultaneously from all the (1-11) plane 31, (-11-1) plane 32 and bottom plane 33 in the primary growth of GaN.

It is sectional drawing which shows typically the manufacturing process of the nitride semiconductor structure which concerns on Example 1 of this invention. It is an electron micrograph (15,000 times) which shows the crystal structure of the GaN film | membrane obtained in Example 1 of this invention. It is an electron micrograph (15,000 times) which shows the crystal structure of the GaN film | membrane obtained in Example 2 of this invention. It is an electron micrograph (15,000 times) which shows the crystal structure of the GaN film | membrane obtained by the comparative example. It is sectional drawing which shows the conventional nitride semiconductor structure typically. It is sectional drawing which shows the other conventional nitride semiconductor structure typically.

Explanation of symbols

10 ... (311) Si substrate 10a ... (311) plane 11 ... mask (SiO ₂ film) 12 ... opening 20 ... GaN film (nitride semiconductor film) 20a ... (11-22) plane 21 ... GaN crystal 30 ... Groove 31 ... (1-11) surface 32 ... (-11-1) surface 33 ... bottom surface

Claims (5)

(311) The (311) plane of the Si substrate has (1-11) plane and (-11-1) plane which are diagonally upward and diagonally downward side faces extending in parallel to each other, and (311) ) A substrate processing step for forming a plurality of grooves extending along the <1-1-2> direction of the Si substrate;
A crystal growth step of crystal-growing a nitride semiconductor on the (311) plane of the (311) base material in which the groove is formed to form a nitride semiconductor film having a (11-22) plane as a main surface; With
By setting the groove width d to 20 μm or less and the groove depth h to 0.2 μm or more, and adjusting the relationship between the groove width d and depth h to 1 ≦ h / d, A method of manufacturing a nitride semiconductor structure, wherein the nitride semiconductor is preferentially crystal-grown on the (1-11) surface of the inner surface.   2. The method of manufacturing a nitride semiconductor structure according to claim 1, wherein in the base material processing step, a relationship between the width d and the depth h of the groove is adjusted to 3/2 ≦ h / d.   3. The method for manufacturing a nitride semiconductor structure according to claim 2, wherein in the base material processing step, a width d of the groove is set to 5 μm or less. In the crystal growth process, the nitride semiconductor structure according to any one of claims 1 to 3, wherein the (1-11) the nitride semiconductor only surface that is grown out of the groove Production method. A plurality of grooves extending along the <1-1-2> direction on the (311) plane, wherein the width d of the groove is 20 μm or less, the depth h of the groove is 0.2 μm or more, and (311) Si substrate having the groove with a ratio (h / d) of the depth h of the groove to the width d of 1 ≦ h / d ;
A nitride semiconductor film having a (11-22) plane as a main surface formed on the (311) plane of the (311) Si base,
The groove has a (1-11) plane and a (-11-1) plane, which are diagonally upward and diagonally downward side surfaces extending in parallel with each other and facing each other.
The nitride semiconductor film is formed by crystal growth of a nitride semiconductor only on the (1-11) plane of the groove inner surface.

Images