JP2000294827A - Growing method for nitride semiconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable formation of a substrate beneficial for element formation by controlling the growth of a nitride semiconductor, when a sapphire or spinel substrate is used as a substrate of a different kind. SOLUTION: This is for determining a surface for forming a nitride semiconductor 4 on and the direction of stripes of a protective film 1, as against surface A, surface C, surface M, and surface R if a sapphire substrate is used as a substrate of a different kind 2, and as against (111) surface and (110) surface if a spinel substrate is used. Selectively grown layers 5 are formed by forming protective films 1 in the shape of stripes partially on the surface of the nitride semiconductor 4 inclining them by θ (0.1 deg.<θ<0.4 deg.) from a direction AA vertical to the crystal surfaces of the substrate 2. Accordingly, excellent selective growth, especially stable transverse growth and uniform growth in the direction of the stripes become feasible, and a nitride semiconductor having excellent crystallinity is obtained, since the direction of the stripes of the protective films 1 is in a range of 0.1 deg.-0.4 deg. from a direction vertical to the crystal surfaces of the substrate 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is small nitride semiconductor crystal defects as may be the substrate (In _X Al _Y Ga
_1-XY N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1) growth method, light emitting diode (LED), laser diode (LD),
The present invention relates to a nitride semiconductor element used for a light emitting element such as a solar cell or an optical sensor, a light receiving element, or an electronic device such as a transistor or a power device.

[0002]

2. Description of the Related Art Generally, when a semiconductor is grown on a substrate,
It is known that when a substrate lattice-matched with a semiconductor to be grown is used, crystal defects of the semiconductor are reduced and crystallinity is improved. However, nitride semiconductors generally have sapphire,
Spinel is grown on a heterogeneous substrate that does not lattice match with a nitride semiconductor such as silicon carbide.

[0003] Therefore, in order to obtain a good nitride semiconductor device, various methods for growing a nitride semiconductor have been studied. Among them, a method of forming a protective film and selectively growing a nitride semiconductor has been actively studied.

[0004] This selective growth means that a protective film made of SiO ₂ is partially formed on a GaN layer grown on sapphire, for example, and GaN is again grown on the protective film by metal organic chemical vapor deposition (MOVPE). ), The growth starts from a portion where the protective film is not formed (hereinafter, referred to as a window portion), and gradually becomes Ga over the protective film.
Lateral growth of N occurs, and GaN grown in the lateral direction from the adjacent window portion is bonded on the protective film and continues to grow, so that a nitride semiconductor with extremely few crystal defects can be obtained.

A method of growing a nitride semiconductor by using the lateral growth of the nitride semiconductor after forming such a protective film is called an epitaxial lateral overgrowth (ELOG). I have.

[0006]

When a substrate having a selective growth layer as described above is used for, for example, a laser device, the state of the substrate greatly affects the characteristics of the device obtained thereby. That is, if the substrate has good crystallinity and surface morphology, the element characteristics can be improved. Therefore, it is important to improve the substrate.

However, such selective growth also has a problem. Since the selective growth layer is grown laterally above the protective film and formed by combining the selective growth layers as described above, the selective growth layer above the protective film and the selective growth layer above the window have different growth mechanisms. Therefore, there is a difference in crystallinity. This is because, on the surface of the selective growth layer, the crystallinity is different above the protective film and above the window portion between the protective films.
Regions having different crystallinity on the substrate surface are distributed.
At this time, a preferable region for forming the element structure is above the protective film, and it is necessary to effectively use this region.

However, another problem arises when the area of the protective film is increased in order to increase the ratio of a good region for forming such an element. That is, a void is formed between the selective growth layer and the protective film at the bonding portion of the selective growth layer described above. The generation of the void on the protective film increases as the width of the protective film increases and increases. Tend. Since such voids may have a bad influence on the substrate, it is necessary to control the voids to form a good substrate.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a good nitride semiconductor substrate by controlling selective growth to a preferable state.

In other words, the method of growing a nitride semiconductor according to the present invention provides a method for growing a nitride semiconductor on a heterogeneous substrate made of sapphire or spinel and having a first main surface and a second crystal surface perpendicular to the first main surface. A first step of growing a first nitride semiconductor and a stripe direction is in a range of 0.1 to 0.4 ° from a direction perpendicular to a second crystal plane of the heterogeneous substrate. A second step of forming a partially striped protective film on the surface of the first nitride semiconductor, and forming a selective growth layer made of a nitride semiconductor on the surface of the first nitride semiconductor via the protective film. And a third step of growing the sapphire substrate.
Plane, C plane, M plane, one plane selected from R planes, wherein the second crystal plane is one plane selected from sapphire A plane, C plane, M plane, R plane, or First of heterogeneous substrates
Is a spinel (111) plane, and the plane of the second crystal is a spinel (110) plane. As described above, by setting the stripe direction of the protective film within the above range, a uniform selective growth layer in which the coupling position is almost constant in the stripe direction is formed, and thus the nitride semiconductor having good crystallinity and surface morphology is formed. Is obtained.

More preferably, the combination of the first principal surface of the heterogeneous substrate and the surface of the second crystal is sapphire C-plane and A-plane, sapphire A-plane and R-plane, and spinel (11
1) A set selected from the plane and the (110) plane. In this combination, remarkably good selective growth is performed, and a more preferable nitride semiconductor is obtained.

The stripe width of the protective film is 10 μm.
When the thickness is at least m, the growth using a protective film having a wide width, which has been conventionally difficult, can be suitably performed. Therefore, the region above the protective film that can be preferably used for forming an element has a large area. Is obtained. For this reason, the degree of design freedom in element formation is high.

In addition, the stripe width W of the protective film
_When the ratio W _w / W _{s of s} to the width W _{w of the} window portion is in the range of 0.2 to 0.5, the area (area) above the frequently used protective film is limited to other windows. It can be made larger than the area (area) of the part. This is because, in the ratio between the width of the protective film and the width of the window, in the above range where the ratio of the width of the protective film is high,
Good selective growth is possible, and a nitride semiconductor advantageous for element formation is obtained.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

According to the present invention, a substrate advantageous for forming an element is formed by preferably controlling the growth of a nitride semiconductor selectively grown on a heterogeneous substrate. Specifically, in the present invention, the growth of a nitride semiconductor is controlled when a sapphire or spinel substrate is used as a heterogeneous substrate.

When a nitride semiconductor is selectively grown on a heterogeneous substrate, selective growth layers are formed in various forms depending on the conditions. FIG. 1 shows how a nitride semiconductor grows by selective growth. In the selective growth, a part of the substrate is covered with a protective film that does not react with the nitride semiconductor (FIG. 1A), and the nitride semiconductor is grown from a part of the substrate surface that is not covered with the protective film ( (FIG. 1 (b), (c)). ELOG growth, which has been noted as the nitride semiconductor substrate described above, generally forms a stripe-shaped protective film on the substrate, grows the nitride semiconductor from a window where the protective film is not provided, and grows adjacent ones. The selective growth layers are formed by bonding to each other above the protective film (FIG. 1). However, when the selective growth layers are bonded to each other, voids are formed as shown in FIGS. The present invention can control such a gap, and this will be described in detail below.

As the heterogeneous substrate in the present invention, a sapphire (Al ₂ O ₃ ) or spinel (MgAl ₂ O ₄ ) single crystal substrate is used. The principal plane and the crystal plane of the heterogeneous substrate used for determining the stripe direction of the protective film of the selective growth layer are plane directions with respect to the crystal structure. Specifically, if the substrate is a sapphire substrate, the A surface, the C surface, the M surface, and the R surface
In the case of a plane or spinel, the plane (main plane) on which a nitride semiconductor is formed is determined with respect to the (111) and (110) planes (crystal plane). Specifically, the direction perpendicular to the crystal plane and the stripe direction of the protective film provided on the surface of the nitride semiconductor formed on the main surface of the heterogeneous substrate make an angle in a range described later. At this time, the protective film is formed on the surface of the nitride semiconductor layer grown on the main surface of the heterogeneous substrate. The plane orientation of the crystal is, specifically, as shown in the unit cell diagram of sapphire in FIG.
(112-0), (1-1-20), (21-1-0), (2-11
0), (12-10), (121-0), M-plane is (11-0)
0), (01-10), (1-010), (1-100),
(011-0), (101-0), and the R plane are (11-02),
(1-102), (01-12), (011-2), (101-
2), (1-012), the C plane is (0001), and the spinel is (111) (110). Here, the notation of the surface index follows the notation in the specification corresponding to the actual surface index shown in FIG.

More specifically, the combination of the main surface of a heterogeneous substrate on which a nitride semiconductor is formed and a crystal surface for determining the stripe direction (hereinafter, simply referred to as an orientation flat surface) corresponds to a C-plane on a sapphire substrate. The main surface,
When the orientation flat surface (hereinafter, referred to as the orientation flat surface) is the A surface, the stripe direction of the protective film is determined with respect to the direction perpendicular to the orientation flat surface (the A surface). Further, a good selective growth layer is formed when the main surface of the Saraia is the A surface and the orientation flat surface is the R surface, or when the main surface of the spinel is the (111) surface and the orientation flat surface is (110). That is, good selective growth is achieved, which means that the growth form such as the growth rate is generally different in the wafer, but even in such a situation, if the above combination is used, the growth will be in the wafer plane. Regardless of the position, the stability of the bonding position and the uniformity during the ELOG (horizontal) growth of the adjacent growth layer are excellent, as described later.

Here, the orientation flat surface does not need to be provided particularly corresponding to the surface of the substrate crystal, and may be formed so as to be shifted from the surface of the crystal in consideration of the direction of the stripe of the protective film in advance. good. When actually providing a protective film, either type of substrate may be used, and if it corresponds to the surface of the substrate crystal, the stripe direction is determined by the angle from the direction perpendicular to the plane of the orientation flat, and the stripe is determined. If the orientation flat surface is formed so as to be perpendicular to the orientation flat surface and the orientation flat surface is formed, the stripe direction may be taken perpendicular to the orientation flat surface, and there is no particular difference in manufacturing.

In the present invention, the protective film used for forming the selective growth layer is partially formed on the crystal growth surface (nitride semiconductor surface), and starts from the region (window portion) where the protective film is not provided. This is for selectively growing a semiconductor layer. At this time, the protective film may be formed in a stripe shape and provided only partially, and in the present invention, a preferred selective growth layer is formed by providing this stripe direction in a range described later. . The direction of the stripe formed on the surface of the nitride semiconductor grown on the substrate is
0.1 to 0.1 from a direction perpendicular to the crystal plane of the single crystal substrate.
That is, it is shifted within a range of 0.4 °.

More specifically, conventionally, the plane of the substrate crystal,
For example, in FIG. 4, a stripe of the protective film 1 is formed perpendicularly to the orientation flat surface 3 (AA direction) (θ = 0 °). However, in this case, when the nitride semiconductor 14 of FIG.
G), as shown in FIG. 1 (c), the nitride semiconductors grown from the adjacent windows are not bonded, and the growth in the lateral direction stops on the way, and a flat surface is not formed. In FIG. 4, if the angle θ between the direction perpendicular to the crystal plane (AA direction) and the stripe direction of the protective film 1 is less than 0.1 °, the above-described perpendicular case (θ = 0 °) As in the case of (1), the lateral growth is insufficient, and a flat surface is not formed. When θ exceeds 0.4 °, the selective growth layer 5 is formed as shown in FIG. 5, but when observed from the direction of the arrow in the figure, the void 5 has a zigzag pattern as schematically shown in FIG. Is observed as That is, as shown in FIG. 3, the formed voids are not stable, and the formation of such voids indicates that good selective growth has not been achieved.

The bending of the voids (FIG. 3) observed in the conventional selective growth layer occurs because the selective growth is not uniform. In such a state, for example, the surface becomes a mirror surface. However, since a non-uniform crystallinity on the surface is inherited by the semiconductor layer grown thereon, a good growth layer cannot be obtained. Normally, as shown in FIG. 1B, the selective growth layer by ELOG grows vertically from a window where a protective film is not provided, and then grows from a neighboring window by growing horizontally. The grown layer is formed by being connected at the upper part of the protective film (FIG. 1B). For this reason, the zigzag pattern due to the voids indicates that the bonding positions of the layers grown from the adjacent windows are different, indicating that uniform growth has not been achieved. That is, in the conventional selective growth layer, as shown in FIG. 5, the gap 6 is bent in the stripe direction of the protective film, the width thereof is largely different, and the coupling position at the time of selective growth is different. Has many intrinsic strains and does not become a nitride semiconductor of good crystallinity. Alternatively, as described above, when the stripe direction of the protective film is substantially perpendicular to the crystal plane, there is a portion where growth in the lateral direction becomes insufficient, and this also does not become a good crystalline nitride semiconductor.

The present inventor has found a good method of forming a selective growth layer by paying attention to the shape of the void. That is, after forming the selective growth layer,
By observing the wafer, it has been found that the growth mode of the selective growth layer can be determined. More specifically, in FIG. 4, the protective film 1 in the form of a stripe is partially formed on the surface of the nitride semiconductor 4.
From the direction (AA direction) perpendicular to the crystal plane of the substrate 2
(0.1 ° <θ <0.4 °), the selective growth layer 5 in FIG. 5 is formed, and observation is performed from the direction of the arrow in the figure. As shown in FIGS. 2 and 3, various types of voids formed by selective growth are observed depending on the growth mode. Behind such a difference,
As shown in FIG. 1B, in the lateral growth at the time of the selective growth, if the growth speed and the growth form of the adjacent selective growth layers are almost the same, as shown in FIG. Since the void is not bent, the bonding position is almost constant, and the selective growth layer is formed in a good growth form, the crystallinity of the obtained nitride semiconductor is also good. However, in the lateral growth at the time of selective growth shown in FIG. 1A, if the growth is not substantially equal, the shape of the gap 5 is bent as shown in FIG.
Since the width of the void 5 varies, and the selective growth layer is formed at a non-uniform coupling position in the stripe direction of the protective film 1, the same tendency is observed in the crystallinity of the obtained nitride semiconductor. Have a distribution of variation in crystallinity in the stripe direction.
> 0.4. Furthermore, if the lateral growth is insufficient, the growth layers will grow in the vertical direction (thickness direction) as they are without bonding, and as a result, the nitride semiconductor of the wafer has cracks on the surface. And
This corresponds to the above-mentioned 0 ° <θ <0.1 °, and it is impossible to form an element in that portion.

Therefore, according to the present invention, the stripe direction of the protective film is 0.1% from the direction perpendicular to the crystal plane of the substrate.
By being in the range of ~ 0.4 °, the above-described good selective growth, particularly stable lateral growth and uniform growth in the stripe direction, are possible, and a good crystalline nitride semiconductor can be obtained. is there.

As described above, the method of observing and determining the voids has been described in order to explain the form of the selective growth, but the present invention is not particularly limited to the method in which the voids are always formed. This is because the voids are formed because the selective growth layer is not bonded above the surface of the protective film relatively close to the surface of the protective film in the lateral growth during the selective growth, and the crystal composition, the growth temperature, etc. It is shown that, depending on the growth conditions, the void may not be formed substantially. In other words, even when no void is observed,
As described above, since the occurrence of the disorder of the bonding position due to the non-uniform selective growth has the same tendency, as in the present invention,
The effect of solving the problem by limiting the stripe direction of the protective film is very effective. Therefore, as in the conventional case, a protective film is provided perpendicular to the crystal plane,
And even when the above-mentioned voids are not generated, the non-uniform selective growth itself found by the observation of the voids as described above is not solved at all, and the stripe direction of the protective film is changed as in the present invention. When the content is in the above range, uniform selective growth, particularly, lateral growth in the form of covering the protective film, is good, and the resulting selective growth layer is also good.

In the present invention, the width of the protective film and the interval between the protective film stripes (the width of the window) are preferably set as follows. The width of the protective film is preferably 10 μm.
By setting it to m or more, a good selective growth layer is formed.
This is because when the width of the protective film stripe exceeds 10 μm,
Although the voids formed during the ELOG growth become large,
This is because the gap can be controlled to have a good shape in the present invention. In other words, the selective growth layer grows laterally above the protective film, and the adjacent selective growth layers combine to form a flat surface. Therefore, when the width of the protective film is increased, the lateral growth naturally occurs. This is because the distance becomes longer and the growth rate in the lateral direction greatly affects the selective growth layer. This is because, since the width of the protective film is wide, if the adjacent selective growth layers do not grow evenly in the lateral direction, the coupling position is different in the stripe direction of the protective film as in the above-described conventional example. Has a zigzag pattern. Therefore, in the present invention, by determining the stripe direction in the above range, the lateral growth covering the upper part of the protective film at the time of selective growth is formed more uniformly than the conventional one, and the bonding position and the gap are reduced. When present, the form also shows substantially the same form in the stripe direction (FIG. 2), and the width of the stripe is 1
When the width is increased to 0 μm or more, a remarkable difference is generated from the conventional one. In the present invention, the stripe width is 10 μm.
Even in the case where m is equal to or less than m, it is advantageous for forming the selectively grown layer. Specifically, when the thickness is 10 μm or less, the non-uniform growth pattern of the selective growth as shown in FIG. 3 appears in the stripe of the protective film formed perpendicular to the crystal plane as in the conventional example. In fact, a zigzag pattern due to such non-uniform growth is only partially observed in the whole wafer. However, when the stripe of the protective film exceeds 10 μm, such non-uniformity of the selective growth is observed in most of the regions. In the present invention, such a change is not observed at the boundary of 10 μm.
Even if the thickness is not less than μm, a good and uniform selective growth layer is formed as shown in FIG. Further, when the width of the protective film exceeds 15 μm, the width becomes even more remarkable. In the conventional device, the above-described non-uniform selective growth is performed in almost all regions, but this is not the case in the present invention. as a result,
In the present invention, when the width of the protective film is as large as more than 10 μm, the effect is remarkable,
If it exceeds μm, it becomes more remarkable.

Increasing the width of the protective film described above has a very important effect on the element structure formed thereon. This means that the selective growth layer obtained is
As described above, the crystal growth is different between the upper portion of the protective film and the upper portion of the window portion, and thus the crystallinity is also different. In general, crystal defects such as dislocations or propagation of the crystal defects are higher in the upper portion of the protective film. Since the number is small, a region important for a device such as a waveguide is formed above the protective film. Alternatively, an element can be manufactured by using only the upper part of the protective film as an element formation region. For this reason, increasing the width of the protective film increases the degree of freedom in the design and manufacture of the device structure, and the present invention provides a good selective growth layer even with a wide protective film. Very useful.

In addition, in the present invention, by setting the stripe width of the protective film to be wider than the width of the window, it is possible to form a nitride semiconductor which is very advantageous for forming an element. This is because the above-mentioned good selective growth becomes possible,
If the preferred selective growth is not achieved, it is possible to obtain a good nitride semiconductor, particularly in a region where the ratio of the width of the protective film is high, by the ratio of the width of the protective film and the width of the window portion described later. Can not. More specifically, in the present invention, the ratio W _w / W _s between the stripe width W _s of the protective film and the width W _{w of the} window portion.
Is in the range of 0.2 to 0.5, good selective growth is performed, and a nitride semiconductor having a high area ratio of the protective film is obtained. That is, in the present invention, when W _w / W _s is 0.5 or more, the area ratio of the protective film is small, and a region having good crystallinity at the time of forming an element is reduced, so that the variation in element characteristics within a wafer is reduced. And the yield decreases. If W _w / W _s is 0.2 or less, the window portion, which is the starting surface for selective growth, becomes narrow, and good selective growth tends not to be achieved.

As the material of the protective film, a material having a property that the nitride semiconductor does not grow or hardly grows on the surface of the protective film is preferably selected. For example, silicon oxide (Si)
O _x ), silicon nitride (Si _x N _y ), titanium oxide (Ti
O _X), an oxide such as zirconium oxide (ZrO _X), nitrides, or other of these multilayer films, it is possible to use a metal or the like having a 1200 ° C. or more melting point. These protective film materials have the property of withstanding the growth temperature of the nitride semiconductor of 600 ° C. to 1100 ° C. and preventing the nitride semiconductor from growing or hardly growing on the surface thereof. To form a protective film material on a nitride semiconductor surface, for example, evaporation, sputtering,
A vapor deposition technique such as CVD can be used. Also,
In order to partially (selectively) form, a photomask having a predetermined shape is manufactured using a photolithography technique, and the material is vapor-phase-formed through the photomask, thereby forming a predetermined film. Can be formed.

The shape of the protective film is a stripe shape as described above.
A selective growth layer is formed by LOG, and more specifically, a protective film is formed so that the lateral growth is performed at the time of the selective growth and the adjacent growth layers are combined and formed. . As a specific example, a stripe-shaped protective film is repeatedly formed at regular intervals. The present invention is not particularly limited to this, and the interval between the protective films may be varied. However, the stripe direction of the protective film may be applied to all the protective films. The selective growth layer is formed uniformly, and more preferably, the protective film is repeatedly formed at the above-mentioned constant intervals, which also contributes to the formation of a uniform nitride semiconductor over the entire wafer.

In the present invention, the nitride semiconductor grown on the heterogeneous substrate and the selective growth layer are made of In _x Al _Y Ga _{1 -XY.}
N (0 ≦ X, 0 ≦ Y, X + Y ≦ 1) is a nitride semiconductor. Preferably, by using undoped GaN, it becomes a selective growth layer having the best crystallinity, and by using a nitride semiconductor doped with an n-type impurity, more preferably, GaN,
A good n-type conductive nitride semiconductor layer is formed. The thickness of the selective growth layer is not particularly limited, but is at least 1 μm or more in order for the nitride semiconductor layer grown from the above-described adjacent window to be bonded at the upper portion of the protective film and form a flat surface. A film thickness is required. Although the upper limit of the film thickness is not particularly limited, it is sufficient if it is about 10 μm. As described above, if a flat surface is obtained by bonding at the top of the protective film during selective growth, another layer is formed thereon. May be.

In the present invention, the first nitride semiconductor grown on the heterogeneous substrate is not particularly limited, but an undoped nitride semiconductor having good crystallinity, more preferably undoped GaN is used. That is.

[0033]

[Embodiment 1] This embodiment shows an example in which a nitride semiconductor is grown using MOVPE (metal organic chemical vapor deposition), but the method of the present invention is limited to the MOVPE method. Instead, all known methods for growing nitride semiconductors, such as HVPE (halide vapor phase epitaxy) and MBE (molecular beam vapor phase epitaxy), can be applied.

FIG. 1 is a schematic sectional view of a wafer in each of the following steps. A sapphire substrate having the C surface as the main surface and the orientation flat surface as the A surface was set in a reaction vessel, and the temperature was set at 51 ° C.
At 0 ° C., a buffer layer of GaN is grown to a thickness of 200 Å on the sapphire substrate 11 using hydrogen as the carrier gas and ammonia and TMG (trimethylgallium) as the source gas. After growing the buffer layer,
Stop TMG only, raise temperature to 1050 ° C,
When the temperature reaches 050 ° C., TMG, ammonia,
An undoped GaN layer 12 (first nitride semiconductor) is grown to a thickness of 5 μm using silane gas. After laminating the buffer layer and the GaN layer 12, a stripe-shaped photomask is formed on the GaN layer 12, and a protective film made of SiO _{2 having a} stripe width of 14 μm and a window portion of 6 μm is formed by a CVD apparatus to a thickness of 0.1 μm. It is formed with a film thickness (FIG. 1
(A)). Note that the stripe direction of the protective film 13 is
As shown in the figure, the direction is θ = 0.2 ° with respect to the direction AA perpendicular to the sapphire A plane (orifla plane 3).

After the protection film 13 is formed, the wafer is transferred to a reaction vessel, and a selective growth layer 14 made of undoped GaN is formed at 1050 ° C. using TMG and ammonia as source gases.
It is grown to a thickness of 5 μm (FIG. 1B). The selective growth layer 14 of undoped GaN grows in a vertical direction with respect to FIG. 1 to a certain thickness, and then grows in a horizontal direction (FIG. 1).
(B)), the selectively grown layers grown from the adjacent windows are combined to form a film (FIG. 1 (c)).

The obtained nitride semiconductor had a good surface. At this time, when observed from the direction of the arrow in FIG. 5, the void 15 in FIG. 1C formed in the selective growth layer is observed as shown in FIG. No. 15 was formed almost equally. In other words, this indicates that the bonding position of the selective growth layer is almost constant with respect to the stripe direction of the protective film, and the selective growth layer is formed stably and uniformly, and a good crystalline nitride semiconductor is formed. It suggests that it will be a substrate.

[Example 2] In Example 1, the angle θ of the stripe direction of the protective film with respect to the direction perpendicular to the A-plane was θ = 0.4 ° (FIG. 4), and the stripe width of the protective film was 10 μm.
m, except that the width of the window portion was 4 μm.

In the obtained nitride semiconductor, although the bent portion of the void is slightly observed as compared with Example 1, almost all of the entire wafer is almost as good as the wafer, and the shape of the void is also shown in FIG. As seen in FIG. 2, the shape was almost uniform in the stripe direction of the protective film, and the surface was uniformly good.

Example 3 A protective film was formed in the same manner as in Example 1, except that the stripe direction of the protective film was θ = 0.1 °.

In the obtained nitride semiconductor, although the shape of the voids in the stripe direction of the protective film has cracks due to slightly insufficient growth in the lateral direction as compared with Example 1, there are some places where cracks are observed. In the whole wafer, the portion is only slightly seen at the edge, and most of the portion is obtained in Example 1.
Similarly, the formation of uniform voids almost as shown in FIG. 2 was observed. In addition, the surface had good and uniform crystallinity.

Example 4 A selective growth layer was formed in the same manner as in Example 1 except that the heterogeneous substrate was a sapphire substrate having the A surface as the main surface and the orientation flat surface as the R surface.

The obtained nitride semiconductor has good crystallinity as in Example 1. [Example 5] As a heterogeneous substrate, a spinel substrate having a (111) plane as a main surface and an orientation flat surface as a (110) plane A selective growth layer was formed in the same manner as in Example 1 except for using. At this time, the stripe direction of the protective film was a direction shifted by 0.2 ° from the direction perpendicular to the (110) plane.

The obtained nitride semiconductor had good crystallinity in the same manner as in Example 1. Similarly, the shape of the void was formed almost uniformly in the stripe direction of the protective film. Selective growth.
Therefore, the surface of the obtained nitride semiconductor has good uniformity and serves as a good substrate for forming a nitride semiconductor element.

[Embodiment 6] In the embodiment 1, after the selective growth layer is grown, as shown in FIG. 8, a protective film 16 is newly formed on its surface, and the selective growth layer 17 is formed. . As shown in FIG. 8A, a protective film was formed on the surface of the selective growth layer 14 so as to cover the window of the underlayer 12, and the selective growth layer 17 was grown. At this time, the stripe direction of the protective film was formed in parallel with the protective film 13 formed first, and the stripe width was 14 μm and the width of the window was 6 μm.

Since the obtained nitride semiconductor has good crystallinity as in Example 1, and takes a good growth form even during selective growth, the bonding position is in the stripe direction of the protective film. It was almost uniform. Also, like this:
In the present invention, the selective growth layer may be formed twice or more times. At that time, as in the above embodiment, the protective film is formed so as to cover the window in the already formed selective growth layer. Is preferable because it is possible to prevent propagation of crystal defects from a window portion having relatively poor crystallinity. In addition, in the present invention, since the width of the protective film that can be formed can be widened, as shown in FIG. 8, the protective film formed in the second and subsequent times is formed to a sufficient degree to cover the window below the protective film. The width of the protective film can be formed narrower than the first time.

[Embodiment 7] Using the nitride semiconductor obtained in Embodiment 1 as a substrate, the respective layers described below are stacked to form a laser device shown in FIG.

The selective growth layer formed on the heterogeneous substrate 101 in the first embodiment is used as a nitride semiconductor substrate 102 of each layer formed below. On this, first, undoped GaN 104 is grown to a thickness of 15 μm, which is also used as a nitride semiconductor substrate.

(N-side contact layer 105) Next, using ammonia, TMG, and silane gas as an impurity gas, Si
An n-side contact layer 105 made of 10 ¹⁸ / cm ³ doped GaN is grown to a thickness of 4 μm.

(Crack prevention layer 106) Next, TMG,
Using TMI (trimethylindium) and ammonia,
At a temperature of 800 ° C., a crack prevention layer 106 of In _0.06 Ga _0.94 N is grown to a thickness of 0.15 μm.
The crack prevention layer can be omitted.

(N-side cladding layer 107)
At 0 ° C., a layer made of undoped Al _0.16 Ga _0.84 N is grown to a thickness of 25 ° using TMA (trimethylaluminum), TMG, and ammonia, and then TMA is stopped, silane gas is flown, and Si is added to 1 × 10 ^19. A layer made of n-type GaN doped with / cm ³ is grown to a thickness of 25 °. These layers are alternately stacked to form a superlattice layer, and an n-side cladding layer 107 made of a superlattice having a total film thickness of 1.2 μm.
Grow.

(N-side light guide layer 108) Subsequently, the silane gas is stopped, and n
The side light guide layer 108 is grown to a thickness of 0.1 μm.
The n-side light guide layer 108 may be doped with an n-type impurity.

(Active Layer 109) Next, at a temperature of 800 ° C., a barrier layer made of Si-doped In _0.05 Ga _0.95 N is grown to a thickness of 100 °, and then undoped In _0.2 Ga _0.8 N at the same temperature. A well layer made of 40 .ANG. Is grown. A barrier layer and a well layer are alternately stacked twice, and finally an active layer having a multiple quantum well structure (MQW) having a total thickness of 380 ° is grown, ending with the barrier layer. The active layer may be undoped as in this embodiment, or may be an n-type impurity and / or
Alternatively, a p-type impurity may be doped. The impurities are well layers,
Both the barrier layers may be doped, or one of them may be doped. Note that if only the barrier layer is doped with an n-type impurity, the threshold value tends to decrease.

(P-side cap layer 110)
Raise to 050 ° C, TMG, TMA, ammonia, Cp ₂
Using Mg (cyclopentadienyl magnesium), p
P-type Al _0.3 doped with Mg at 1 × 10 ²⁰ / cm ³ and having a larger band gap energy than the side light guide layer 111
A p-side cap layer 107 made of Ga _0.7 N is grown to a thickness of 300 °.

(P-side light guide layer 111) Subsequently, Cp ₂ M
g, TMA is stopped, and a p-side optical guide layer 111 made of undoped GaN having a band gap energy smaller than that of the p-side cap layer 110 is grown at 1050 ° C. to a thickness of 0.1 μm.

(P-side cladding layer 112)
At 0 ° C., 25 layers of undoped Al _0.16 Ga _0.84 N
成長, Cp ₂ Mg and TMA are stopped, a layer of undoped GaN is grown with a thickness of 25 °, and a p-side cladding layer 112 of a superlattice layer having a total thickness of 0.6 μm is formed. Let it grow. When the p-side cladding layer is made of a superlattice in which at least one includes a nitride semiconductor layer containing Al and has different band gap energies from each other, the impurity is doped into one of the layers in a large amount. When so-called modulation doping is performed, the crystallinity tends to be improved, but both may be doped in the same manner. The cladding layer 112 includes a nitride semiconductor layer containing Al,
Preferably, a superlattice structure including Al _X Ga ₁ -XN (0 <X <1) is desirable, and more preferably, a super lattice structure in which GaN and AlGaN are stacked. When the p-side cladding layer 112 has a superlattice structure, the Al mixed crystal ratio of the entire cladding layer can be increased, so that the refractive index of the cladding layer itself decreases and the band gap energy increases. It is very effective in lowering. Further, the use of the superlattice reduces the number of pits generated in the cladding layer itself as compared with the non-superlattice, thereby reducing the probability of short-circuit.

(P-side contact layer 113) Finally, 10
At 50 ° C., 1 × 1 Mg was added on the p-side cladding layer 109.
0²⁰/cm ^ThreeP-side contact made of doped p-type GaN
Layer 113 is grown to a thickness of 150 °. p-side contour
Is a p-type In layer._XAl_YGa_1-XYN (0 ≦ X, 0 ≦
Y, X + Y ≦ 1), preferably Mg
Doped GaN is most preferable to the p-electrode 120.
New ohmic contact is obtained. The contact layer 113
1 × 10¹⁷/cm^ThreeMore than
It is desirable to have a high carrier concentration. 1 × 10¹⁷/cm
^ThreeIf it is lower than this, it is difficult to obtain a favorable ohmic with the electrode.
It tends to be. Further, the composition of the contact layer is changed to Ga
When N is used, a preferable ohmic is obtained with the electrode material.
It will be cool.

The wafer on which the nitride semiconductor has been grown as described above is taken out of the reaction vessel, and a protective film made of SiO ₂ is formed on the surface of the uppermost p-side contact layer.
Etching is performed by SiCl ₄ gas using RIE (reactive ion etching) to expose the surface of the n-side contact layer 105 where the n-electrode is to be formed. In order to deeply etch the nitride semiconductor in this way, SiO ₂ is optimal as a protective film.

Next, a ridge stripe having a width of 2 μm is formed in the stripe-shaped waveguide region by etching so that the thickness of the p-side cladding layer becomes 0.01 μm.
At this time, as described above, the selective growth layer has a distribution of crystallinity in a direction perpendicular to the stripe of the protective film, and the waveguide region is formed on the protective film having relatively good crystallinity. By doing so, it is possible to have good element durability. Further, when the selective growth layer has a gap at the time of bonding, it is preferable to form a waveguide region so as to avoid an upper portion of the gap, thereby preventing crystal defects extending from the gap.

After the formation of the ridge stripe, a protective film made of ZrO ₂ is formed on the side surface of the ridge and on the exposed surface of the p-side cladding layer, and a p-electrode made of Ni / Au is formed on the surface of the p-side contact layer 113 so as to cover this. 120 is formed. n
On the surface of the side contact layer 105, n made of Ti / Al
The electrode 121 is formed in a direction parallel to the stripe.

After the sapphire substrate of the wafer on which the n-electrode and the p-electrode are formed is polished to 70 μm as described above, the wafer is cleaved in a bar shape from the substrate side in a direction perpendicular to the stripe-shaped electrodes. A resonator is formed on a cleavage plane ((11-00) plane, a plane corresponding to a hexagonal side surface = M plane). A dielectric multilayer film made of SiO ₂ and TiO ₂ is formed on this resonator surface, and finally, the bar is cut in a direction parallel to the p-electrode to obtain a laser device as shown in FIG. The resonator length at this time was 800 μm.

The obtained laser device had good device characteristics, had little variation in device characteristics on the wafer, and greatly improved the yield.

Comparative Example 1 A selective growth layer was formed in the same manner as in Example 1, except that the direction of the stripe of the protective film was perpendicular to the A-plane (orientation flat surface). In the obtained nitride semiconductor, since the width of the protective film is as large as 14 μm, it is not sufficiently formed in the lateral growth stage shown in FIG. When the obtained wafer was observed, cracks due to this were observed in most of the regions. In such a nitride semiconductor, even if the nitride semiconductor is further formed, only the growth in the vertical direction (the film thickness direction) occurs, and the growth in the horizontal direction is not performed. is there.

[Comparative Example 2] In Example 1, θ = 0.
Except for 5 °, a nitride semiconductor was formed in the same manner. In the obtained nitride semiconductor, the shape of the void was observed as shown in FIG. 3 in which the formation of a stable void was broken as compared with Example 1, and the crystallinity was greatly deteriorated as compared with Example 1. This is because the gap is bent, as seen in FIG.
The width is also non-uniform, which indicates that the coupling position at the time of selective growth varies in the stripe direction of the protective film, resulting in non-uniform formation. For this reason,
Even if the surface is flat as in Example 1, many distortions are observed in the bent portion of the void shown in FIG. 3, and even if an element is formed using such a nitride semiconductor, good characteristics can be obtained. , The reliability is inferior.

[0064]

According to the method for growing a nitride semiconductor of the present invention,
In the LOG growth, favorable growth is performed, the bonding position at the upper part of the protective film is constant, and the growth form of the adjacent selective growth is almost the same. Therefore, uniform selective growth is performed in the stripe direction of the protective film. Good crystalline nitride semiconductor can be obtained over the entire wafer.

Further, even if the stripe width of the protective film is widened, the stable growth pattern of the selective growth is maintained, so that the growth using the protective film having a large area becomes possible, and the element formed thereon can be formed. It will be very useful.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view illustrating selective growth.

FIG. 2 is a schematic diagram illustrating a growth mode according to the present invention.

FIG. 3 is a schematic diagram illustrating a growth mode in a conventional example.

FIG. 4 is a schematic perspective view illustrating selective growth in the present invention.

FIG. 5 is a schematic perspective view illustrating selective growth in the present invention.

FIG. 6 is a unit cell diagram for explaining a typical plane orientation of sapphire.

FIG. 7 is a control chart showing the notation of a plane index in the present specification.

FIG. 8 is a schematic cross-sectional view illustrating one embodiment of the present invention.

FIG. 9 is a schematic cross-sectional view illustrating one embodiment of the present invention.

[Explanation of symbols]

 1, 13, 16 · protective film 2, 11 · · · · heterogeneous substrate 4, 12 · · · first nitride semiconductor 5, 14, 17 · selective growth layer 6, 15 · · · · · voids

Continued on the front page F term (reference) 5F041 AA40 CA23 CA34 CA40 CA46 CA65 CA74 5F045 AA04 AB14 AB17 AB18 AC01 AC08 AC12 AD09 AD12 AD14 AF09 AF13 AF20 BB12 CA10 CA12 CA13 DA53 DA55 5F051 AA08 BA11 CB09 CB22 GA03 5F07A ACB A13 CB07 CB10 DA25 DA35 EA29

Claims (4)

[Claims] A first nitride semiconductor is grown on a first main surface of a heterogeneous substrate made of sapphire or spinel and having a first main surface and a second crystal plane perpendicular to the first main surface. A first step of partially covering the first nitride semiconductor surface such that a stripe direction is in a range of 0.1 to 0.4 ° from a direction perpendicular to a plane of the second crystal of the heterogeneous substrate. A second step of forming a stripe-shaped protective film on the substrate, and a third step of growing a selective growth layer made of a nitride semiconductor on the surface of the first nitride semiconductor via the protective film. Wherein the first main surface of the heterogeneous substrate is one surface selected from sapphire A surface, C surface, M surface, and R surface;
The plane of the second crystal is sapphire A plane, C plane, M plane, R plane.
Wherein the first main surface of the heterogeneous substrate is a spinel (111) plane and the second crystal plane is a spinel (110) plane. Of growing nitride semiconductor. 2. A combination of a first main surface of the heterogeneous substrate and a plane of the second crystal is a sapphire C plane and an A plane, a sapphire A plane and an R plane, a spinel (111) plane and a (110) plane.
2. The method for growing a nitride semiconductor according to claim 1, wherein the method is one set selected from surfaces. 3. The method for growing a nitride semiconductor according to claim 1, wherein a stripe width of said protective film is 10 μm or more. And the stripe width W _s of the claim 4, wherein the protective film, 1 to claim, characterized in that the ratio W _w / W _s of the width W _w of the window portion is in the range of 0.2 to 0.5 4. The method for growing a nitride semiconductor according to 3.