JP3375064B2 - Method for growing nitride semiconductor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a nitride semiconductor (In _X Al _Y Ga) having a small number of crystal defects that can be used as a substrate.
_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 and an optical sensor, a light receiving element, or an electronic device such as a transistor and 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, since nitride-matched substrates do not currently exist in the world, nitride semiconductors are generally sapphire,
It is grown on heterogeneous substrates that are not lattice matched to nitride semiconductors such as spinel and silicon carbide.

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.

This selective growth means, for example, a protective film made of SiO ₂ is partially formed on a GaN layer grown on sapphire, and GaN is again grown on the protective film by metalorganic vapor phase epitaxy (MOVPE). ) Or the like, the growth starts from a portion where the protective film is not formed (hereinafter referred to as a window portion), and the Ga film is gradually formed on the upper portion of the protective film.
Lateral growth of N occurs, and GaN grown laterally from adjacent windows are joined to each other on the protective film to continue growth, so that a nitride semiconductor with extremely few crystal defects can be obtained.

A method of growing a nitride semiconductor by utilizing the lateral growth of the nitride semiconductor after forming such a protective film is called an epitaxial lateral over growth (ELOG). There is.

[0006]

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

However, such selective growth also has a problem. This is because the selective growth layer is formed by laterally growing on the upper part of the protective film and combining the selective growth layers as described above, so that the selective growth layers on the upper part of the protective film and the window part have different growth mechanisms. Therefore, a difference in crystallinity occurs. This is because, on the surface of the selective growth layer, the crystallinity is different between above the protective film and above the window portion between the protective films,
Areas of different crystallinity are distributed on the substrate surface.
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 occurs when the area of the protective film is increased in order to increase the proportion of the good region for forming such an element. That is, a void is formed between the protective film and the above-mentioned selective growth layer joint, and the number of voids generated on this protective film increases and increases as the width of the protective film increases. Tend. Since such voids may adversely affect the substrate, it is necessary to control them in order to form a good substrate.

[0009]

The present invention has been made in view of the above circumstances and provides a favorable nitride semiconductor substrate by controlling selective growth to a preferable state.

That is, the method for growing a nitride semiconductor of the present invention is made of sapphire or spinel, and has a first main surface and a second crystal plane perpendicular to the first main surface of a different type substrate. In the first step of growing the first nitride semiconductor, the stripe direction is in the range of 0.1 to 0.4 ° from the direction perpendicular to the plane of the second crystal of the foreign substrate. A second step of partially forming a stripe-shaped protective film on the surface of the first nitride semiconductor; and 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, wherein the first main surface of the heterogeneous substrate is sapphire A.
Plane, C plane, M plane, R plane, and the second crystal plane is one plane selected from sapphire A plane, C plane, M plane, R plane, or The first of different substrates
Is a spinel (111) plane, and the second crystal plane is a spinel (110) plane. In this way, by setting the stripe direction of the protective film within the above range, a uniform selective growth layer in which the bonding position is substantially constant in the stripe direction is formed, and thus a nitride semiconductor having good crystallinity and surface morphology. Is obtained.

Further preferably, the combination of the first main surface of the different type of substrate and the surface of the second crystal is sapphire C surface and A surface, sapphire A surface and R surface, and spinel (11).
It is one set selected from the 1) plane and the (110) plane. With this combination, remarkably favorable selective growth is achieved, 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 difficult in the past, can be favorably performed. Therefore, the region above the protective film, which can be preferably used for device formation, has a large area. Is obtained. Therefore, the degree of freedom in designing the device is high.

In addition, the stripe width W of the protective film
_s and, by 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, the protective film top of the area to be the frequently used (area), the other window It can be made larger than the area (area) of the part. This is in the above range where the ratio of the width of the protective film is high in the ratio of the width of the protective film and the width of the window portion,
A nitride semiconductor that enables favorable selective growth and is advantageous for device formation can be obtained.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.

According to the present invention, a substrate advantageous for device formation is formed by preferably controlling the growth of a nitride semiconductor selectively grown on a heterogeneous substrate. Specifically, the present invention controls the growth of a nitride semiconductor when a sapphire or spinel substrate is used as a heterogeneous substrate.

When a nitride semiconductor is selectively grown on a heterogeneous substrate, the selective growth layer is 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 not covered with the protective film ( 1 (b), (c)). In the ELOG growth which is focused on as the above-mentioned nitride semiconductor substrate, generally, a stripe-shaped protective film is formed on the substrate, and the nitride semiconductor is grown from the window portion where the protective film is not provided, and adjacent to each other. The selective growth layers are formed by bonding with each other on the protective film (FIG. 1). However, when the selective growth layers are bonded to each other, voids are formed as seen in FIGS. The present invention can control such voids, which 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 main surface of the heterogeneous substrate and the crystal plane used for determining the stripe direction of the protective film of the selective growth layer are plane orientations with respect to the crystal structure. Specifically, if it is a sapphire substrate, A surface, C surface, M surface, R surface
In the case of the plane, the spinel is the (111) or (110) plane, the plane on which the nitride semiconductor is formed (main plane), and the stripe direction of the protective film is determined (the 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 form an angle in the 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. Further, the plane orientation of the crystal is, 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), the R plane is (11-02),
(1-102), (01-12), (011-2), (101-
2), (1-012), C-plane is (0001), and spinel is (111) (110). Here, the notation of this surface index follows the notation in the specification corresponding to the actual surface index shown in FIG.

More specifically, the combination of the principal surface of the heterogeneous substrate forming the nitride semiconductor and the crystal plane (hereinafter referred to as an orientation flat surface) which determines the stripe direction is the C plane in the sapphire substrate. As 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 (A surface). Further, when the main surface of the salia 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 the (110) surface, a favorable selective growth layer is formed. That is, good selective growth is achieved, which generally differs in the growth mode such as the growth rate in the wafer, but even under such circumstances, if the above combination, in the plane of the wafer At any position, the stability of the bonding position and the uniformity at the time of ELOG (lateral direction) growth of the adjacent growth layers are excellent, as will be described later.

Here, the orientation flat surface does not have to be provided in particular corresponding to the surface of the substrate crystal, and may be formed deviating from the surface of the crystal in consideration of the stripe direction of the protective film in advance. good. When actually providing a protective film, either of different types of substrates 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 orientation flat surface. If the orientation flat surface is formed deviating from the surface of the substrate crystal so that the direction of is perpendicular to the orientation flat surface, the stripe direction may be taken perpendicular to it, 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 surface (nitride semiconductor surface) on which the crystal is grown, and from the region (window portion) where the protective film is not provided. The semiconductor layer is selectively grown. At this time, the protective film may be formed in a stripe shape and partially provided. In the present invention, a preferred selective growth layer is formed by providing the stripe direction within the range described later. . The stripe direction formed on the surface of the nitride semiconductor grown on the substrate is
From the direction perpendicular to the crystal plane of the single crystal substrate, 0.1 to
That is, the deviation is in the 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 was formed (θ = 0 °) perpendicularly to the orientation flat surface 3 (AA direction) corresponding to that surface. However, then, when the nitride semiconductor 14 in FIG. 1B grows laterally (ELO
G), as shown in FIG. 1C, the nitride semiconductors grown from the adjacent windows do not bond, the lateral growth stops midway, and a flat surface is not formed. Further, when the angle θ formed by the direction perpendicular to the crystal plane (AA direction) in FIG. 4 and the stripe direction of the protective film 1 is less than 0.1 °, the above-mentioned vertical case (θ = 0 ° Similarly, 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, as shown schematically in FIG. 3, the void 5 has a zigzag pattern. Be observed as. That is, as shown in FIG. 3, the voids formed are not stable, and the formation of such voids indicates that favorable selective growth is not performed.

The bending of the voids (see FIG. 3) observed in the conventional selective growth layer occurs because the selective growth is not uniformly performed. In such a state, the surface thereof is a mirror surface. However, since the non-uniform crystallinity on the surface is inherited in the semiconductor layer grown thereon, a good growth layer cannot be obtained. Normally, the selective growth layer formed by ELOG grows vertically from a window portion not provided with a protective film and then grows horizontally from the adjacent window portion as shown in FIG. 1B. The grown layer is formed by connecting the upper part of the protective film (FIG. 1B). Therefore, the zigzag pattern due to the voids indicates that the positions of the layers grown from the adjacent window portions are different from each other, and that the uniform growth is not achieved. That is, in the conventional selective growth layer, as shown in FIG. 5 in the stripe direction of the protective film, the voids 6 are bent and the widths thereof are greatly different, and the bonding positions at the selective growth are different. Has a large amount of strain and does not become a good crystalline nitride semiconductor. Alternatively, as described above, if the stripe direction of the protective film is substantially perpendicular to the crystal plane, there is a portion where the lateral growth is insufficient, and this also does not provide a good crystalline nitride semiconductor.

The present inventor was able to find a good method for forming a selective growth layer by paying attention to the shape of the void. That is, after forming the selective growth layer,
It was found that the growth morphology of the selective growth layer can be judged by observing the wafer. Specifically, in FIG. 4, the protective film 1 is partially striped on the surface of the nitride semiconductor 4.
From the direction perpendicular to the crystal plane of the substrate 2 (AA direction) to θ
It is formed by inclining by (0.1 ° <θ <0.4 °) to form the selective growth layer 5 in FIG. 5 and observing from the direction of the arrow in the figure. As seen in FIGS. 2 and 3, various forms of the voids formed by selective growth are observed depending on the growth form. The background behind this difference is
As shown in FIG. 1B, in the lateral growth during the selective growth, if the adjacent selective growth layers have substantially the same growth rate and growth form, as shown in FIG. 2, in the stripe direction of the protective film. Since the void has no bending, the bonding position is almost constant, and the selective growth layer is formed with a good growth morphology, the crystallinity of the obtained nitride semiconductor is also good. However, in the lateral growth during the selective growth seen in FIG. 1A, when the growth is not substantially equal, as shown in FIG. 3, the shape of the void 5 is bent,
The widths of the voids 5 are also different, and the selective growth layer is formed at nonuniform bonding positions in the stripe direction of the protective film 1. Therefore, the crystallinity of the obtained nitride semiconductor has the same tendency. , Has a distribution of variations in crystallinity in the stripe direction, which is the θ
It corresponds to the state of> 0.4. Furthermore, if the lateral growth is insufficient, the growth layers do not bond to each other and grow in the vertical direction (thickness direction) as they are, and as a result, the nitride semiconductor of the wafer has cracks on the surface. Become a thing,
This corresponds to the above 0 ° <θ <0.1 °, and the element cannot be formed 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.
Within the range of up to 0.4 °, the above-described favorable selective growth, particularly stable lateral growth and uniform growth in the stripe direction are possible, and a nitride semiconductor with good crystallinity can be obtained. is there.

In the above, the method of observing and determining the voids has been shown in order to explain the mode of selective growth, but the present invention is not particularly limited to the one in which the voids are necessarily formed. This is because the above-mentioned voids are formed in the lateral growth during selective growth because the selective growth layer is not bonded above the surface of the protective film, which is relatively close to the surface of the protective film. This indicates that voids may not be formed depending on the growth conditions of. That is, even when no void is observed in this way,
The occurrence of the disorder of the bonding position due to the non-uniform selective growth as described above has a similar tendency.
The effect of solving the problem by limiting the stripe direction of the protective film is very effective. Therefore, for example, as in the conventional case, a protective film is provided perpendicularly to the crystal plane,
Even if the voids do not occur, the uneven selective growth itself found by observing 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. Within the above range, uniform selective growth, particularly lateral growth in a form covering the protective film, becomes good, and the resulting selective growth layer also becomes good.

In the present invention, the width of the protective film and the interval between the protective film stripes (width of the window portion) are preferably set as follows. The width of the protective film is preferably 10μ
When it is at least m, 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 voids can be controlled to have a good shape in the present invention. That is, the selective growth layer grows laterally on the protective film, and the adjacent selective growth layers bond to each other to form a flat surface. This is because the distance becomes longer and the lateral growth rate greatly affects the selective growth layer. This is because, since the width of the protective film is wide, the bonding positions are different in the stripe direction of the protective film as in the above-described conventional example unless the adjacent selective growth layers grow uniformly in the lateral direction. Becomes a zigzag pattern. Therefore, in the present invention, by determining the stripe direction in the above range, the lateral growth covering the upper portion of the protective film during the selective growth is uniformly formed, and the bonding position and the void are formed, as compared with the conventional one. When present, the morphology also shows almost the same morphology in the stripe direction (FIG. 2), and the stripe width is 1
When the width is increased to 0 μm or more, a remarkable difference from the conventional one is created. In the present invention, the stripe width is 10 μm.
Even when it is less than or equal to m, it works favorably for forming the selective growth layer. Specifically, when the thickness is 10 μm or less, in the stripe of the protective film formed perpendicular to the crystal plane as in the conventional example, the uneven growth pattern of the selective growth as shown in FIG. 3 appears in all. In fact, a zigzag pattern due to such uneven growth is only partially observed in the entire wafer. However, when the stripe of the protective film exceeds 10 μm, such nonuniformity of selective growth is observed in almost all regions, and in the present invention, such a change is not observed with 10 μm as the boundary.
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, it becomes more remarkable, and in the conventional case, the above-mentioned 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, the effect becomes remarkable when the width of the protective film is as wide as more than 10 μm.
When it exceeds μm, it becomes more remarkable.

Increasing the width of the protective film described above has a very important effect on the device structure formed thereon. This is because the obtained selective growth layer is
Since the upper part of the protective film and the upper part of the window have different growth forms as described above, the crystallinity is also different. In general, the upper part of the protective film is more susceptible to crystal defects such as dislocations or the propagation of the crystal defects. Since the number is small, a region important for the device such as a waveguide is formed above the protective film. Alternatively, the element can be manufactured by using only the upper portion of the protective film as the element formation region. Therefore, widening the protective film increases the degree of freedom in designing and manufacturing the device structure, and the present invention forms a good selective growth layer even with the wide protective film, It is very useful.

In addition, in the present invention, the stripe width of the protective film is set to be wider than the width of the window portion, so that it is possible to form a nitride semiconductor which is very advantageous for forming an element. This is because the favorable selective growth described above becomes possible.
When the preferable selective growth is not achieved, it is possible to obtain a good nitride semiconductor especially in a region where the ratio of the width of the protective film is high due to the ratio of the width of the protective film and the width of the window 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 window width W _w.
Is in the range of 0.2 to 0.5, good selective growth is achieved, and the nitride semiconductor has a high area ratio of the protective film. 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 the region having good crystallinity is small at the time of device formation, so that variations in device characteristics within the wafer are reduced. Yield increases and yield decreases. This is because if W _w / W _s is 0.2 or less, the window portion that is the starting surface of the selective growth becomes narrow, and good selective growth tends to be not 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, and 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 withstand the growth temperature of the nitride semiconductor of 600 ° C. to 1100 ° C., and have the property that the nitride semiconductor does not grow on the surface or hardly grows. To form the protective film material on the surface of the nitride semiconductor, for example, vapor deposition, sputtering,
A vapor deposition technique such as CVD can be used. Also,
In order to form the film partially (selectively), a photomask having a predetermined shape is formed by using a photolithography technique, and the material is vapor-phase-deposited through the photomask to obtain a predetermined film. A protective film having the shape of can be formed.

Further, the shape of the protective film is that it has a stripe shape as described above.
A protective film is formed so that a selective growth layer by LOG is formed, specifically, the lateral growth is performed at the time of selective growth, and adjacent growth layers are bonded to each other to form a film. . As a specific example, stripe-shaped protective films are repeatedly formed at regular intervals. The present invention is not particularly limited to this, and the intervals between the protective films may be different, but the stripe direction of the protective film can be applied to all the protective films. The selective growth layer is uniformly formed, 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 on the entire wafer.

In the present invention, the nitride semiconductor and the selective growth layer grown on the heterogeneous substrate are made of In _X Al _Y Ga _{1 -XY.}
N (0 ≦ X, 0 ≦ Y, X + Y ≦ 1) nitride semiconductor. Preferably, undoped GaN provides a selective growth layer with the best crystallinity, and a nitride semiconductor doped with an n-type impurity, more preferably GaN,
A nitride semiconductor layer having good n-type conductivity is formed. Further, the film thickness of the selective growth layer is not particularly limited, but in order to combine the nitride semiconductor layers grown from the adjacent window portions at the upper portion of the protective film to form a flat surface, it is at least 1 μm or more. A film thickness is necessary. The upper limit of the film thickness is not particularly limited, but about 10 μm is sufficient, and as described above, if a flat surface is obtained by bonding at the upper part 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]

EXAMPLES Example 1 This example shows an example of growing a nitride semiconductor using MOVPE (metal organic chemical vapor deposition), but the method of the present invention is not limited to the MOVPE method. Instead, all known methods for growing a nitride semiconductor, 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 step shown below. A sapphire substrate having the C surface as the main surface and the orientation flat surface as the A surface is set in the reaction vessel and the temperature is set to 51.
At 0 ° C., hydrogen is used as a carrier gas, ammonia and TMG (trimethylgallium) are used as source gases, and a buffer layer made of GaN is grown to a thickness of 200 Å on the sapphire substrate 11. After growing the buffer layer,
Stop only TMG, raise the temperature to 1050 ° C, 1
When it 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 stacking 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 of 0.1 μm is formed by a CVD apparatus. It is formed with a film thickness (Fig. 1
(A)). The stripe direction of the protective film 13 is as shown in FIG.
As shown in, the direction is θ = 0.2 ° with respect to the direction AA perpendicular to the sapphire A surface (orientation flat surface 3).

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

The obtained nitride semiconductor had a good surface. At this time, when observed from the direction of the arrow in FIG. 5, the voids 15 of FIG. 1C formed in the selective growth layer are observed as shown in FIG. 2, and the voids are observed in the stripe direction of the protective film. No. 15 was formed almost equally. That is, this indicates that the bonding position of the selective growth layer is substantially constant with respect to the stripe direction of the protective film, and the selective growth layer is stably and uniformly formed, and the nitride semiconductor of good crystallinity is obtained. It suggests that it will be a substrate.

Example 2 In Example 1, the stripe direction of the protective film was θ = 0.4 ° (FIG. 4) with respect to the direction perpendicular to the plane A, and the stripe width of the protective film was 10 μm.
m, and a nitride semiconductor was formed in the same manner except that the width of the window portion was 4 μm.

In the obtained nitride semiconductor, although a slightly bent portion of the void is observed as compared with Example 1, most of the entire wafer is almost as good and the shape of the void is also shown in FIG. As seen in No. 2, the protective film had a substantially uniform shape in the stripe direction, and its surface was also uniformly good.

Example 3 A 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, the void shape has some cracks due to insufficient lateral growth in the stripe direction of the protective film as compared with Example 1, but In the whole wafer, that part is only slightly seen at the edge, and most of them are the same as in Example 1.
Similarly, the formation of uniform voids as observed in FIG. 2 was observed. Further, the surface thereof 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-plane as the main surface and the orientation flat surface as the R-plane.

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 plane and an orientation flat plane as a (110) plane A selective growth layer was formed in the same manner as in Example 1 except that At this time, the stripe direction of the protective film was a direction deviated from the direction perpendicular to the (110) plane by 0.2 °.

The obtained nitride semiconductor had a good crystallinity as in Example 1, and the voids were also formed in a substantially uniform manner in the stripe direction of the protective film, which was good. That is, selective growth is being made.
Therefore, the surface of the obtained nitride semiconductor has good uniformity, and it becomes a good substrate for forming a nitride semiconductor element.

[Sixth Embodiment] In the first embodiment, after the selective growth layer is grown, a protective film 16 is newly formed on the surface thereof to form a selective growth layer 17 as shown in FIG. . As shown in FIG. 8A, a protective film was provided on the surface of the selective growth layer 14 so as to cover the window portion 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 portion was 6 μm.

The obtained nitride semiconductor has a good crystallinity as in Example 1, and also has a good growth morphology during the selective growth thereof, so that 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 embodiments, the protective film is formed so as to cover the window portion in the already formed selective growth layer. By forming, it is possible to prevent the propagation of crystal defects from the window having relatively poor crystallinity, which is preferable. Further, 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 after the second time is formed to an extent sufficient to cover the window portion thereunder, The width of the protective film can be narrower than that of the first time.

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

The selective growth layer formed on the heterogeneous substrate 101 in Example 1 is used as the nitride semiconductor substrate 102 of each layer formed below. First, undoped GaN 104 is grown to a thickness of 15 μm on this, and this is also used as a nitride semiconductor substrate.

(N-side contact layer 105) Next, using ammonia and TMG, and silane gas as an impurity gas, Si is 3 × at 1050 ° C. on the nitride semiconductor substrate 104.
An n-side contact layer 105 made of GaN doped with 10 ¹⁸ / cm ³ is grown to a film thickness of 4 μm.

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

(N-side clad layer 107) Subsequently, 105
A layer of undoped Al _0.16 Ga _0.84 N was grown to a thickness of 25 Å using TMA (trimethylaluminum), TMG, and ammonia at 0 ° C., then TMA was stopped, and silane gas was flown to Si at 1 × 10 ¹⁹ / Cm ³ -doped layer of n-type GaN is grown to a film thickness of 25Å. An n-side clad layer 107 made of a superlattice having a total film thickness of 1.2 μm is formed by alternately stacking these layers.
Grow.

(N-side light guide layer 108) Subsequently, the silane gas is stopped, and n made of undoped GaN is formed at 1050 ° C.
The side light guide layer 108 is grown to a film 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 film thickness of 100 Å, and subsequently, at the same temperature, undoped In _0.2 Ga _0.8 N. The well layer is made to have a thickness of 40 Å. The barrier layer and the well layer are alternately laminated twice, and finally, the barrier layer is finished, and an active layer of a multiple quantum well structure (MQW) having a total film thickness of 380 Å is grown. The active layer may be undoped as in this embodiment, or may have n-type impurities and / or
Alternatively, p-type impurities may be doped. Impurities are well layers,
Both the barrier layers may be doped, or either one may be doped. It should be noted that if the barrier layer is doped with n-type impurities, the threshold value tends to decrease.

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

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

(P-side clad layer 112) Then, 105
A layer of undoped Al _0.16 Ga _0.84 N was deposited at 0 ° C.
Then, Cp ₂ Mg and TMA are stopped, and a layer of undoped GaN is grown to a film thickness of 25Å to form a p-side clad layer 112 made of a superlattice layer having a total film thickness of 0.6 μm. Grow. When the p-side clad layer includes a nitride semiconductor layer containing at least one of Al and is formed by a superlattice in which nitride semiconductor layers having different bandgap energies are stacked, one of the layers is heavily doped with impurities. The so-called modulation doping tends to improve the crystallinity, but both may be similarly doped. The cladding layer 112 is a nitride semiconductor layer containing Al,
A superlattice structure containing Al _x Ga ₁ -xN (0 <x <1) is preferable, and a superlattice structure in which GaN and AlGaN are stacked is more preferable. By forming the p-side cladding layer 112 with 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 becomes small and the bandgap energy becomes large. It is very effective in lowering it. Furthermore, since the superlattice is used, the number of pits generated in the cladding layer itself is smaller than that in the case where the superlattice is not formed.

(P-side contact layer 113) Finally, 10
Mg at 1 × 1 on the p-side cladding layer 109 at 50 ° C.
0²⁰/cm ³P-side contact made of doped p-type GaN
The growth layer 113 is grown to a film thickness of 150Å. p side contour
Layer is p-type In_XAl_YGa_1-XYN (0 ≦ X, 0 ≦
Y, X + Y ≦ 1), preferably Mg
If GaN is doped, it is most preferable as the p-electrode 120.
A good ohmic contact is obtained. The contact layer 113 is
Since it is a layer that forms an electrode, 1 × 10¹⁷/cm³More than
A high carrier concentration is desirable. 1 x 10¹⁷/cm
³If it is lower than that, it is difficult to obtain a preferable ohmic contact with the electrode.
It tends to be difficult. Further, the composition of the contact layer is Ga
When N is set, a preferable ohmic contact with the electrode material can be obtained.
I'm getting better.

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 p-side contact layer which is the uppermost layer.
Etching is performed with SiCl ₄ gas using RIE (reactive ion etching) to expose the surface of the n-side contact layer 105 on which the n-electrode is to be formed. Thus, SiO ₂ is optimal as a protective film for deeply etching a nitride semiconductor.

Next, the stripe-shaped waveguide region is etched to form a ridge stripe having a width of 2 μm and a depth such that the p-side cladding layer has a film thickness of 0.01 μm.
At this time, as described above, the selective growth layer has a crystallinity distribution 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 so doing, good element durability can be obtained. Further, when the selective growth layer has a void at the time of bonding, it is preferable to form the waveguide region so as to avoid the upper portion of the void, and by doing so, crystal defects extending from the void can be prevented.

After forming the ridge stripe, a protective film made of ZrO ₂ is formed on the side surface of the ridge and 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 the protective film. 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.

As described above, the sapphire substrate of the wafer on which the n electrode and the p electrode were formed was polished to 70 μm, and then cleaved in a bar shape from the substrate side in the direction perpendicular to the stripe electrodes, A resonator is formed on the cleavage plane ((11-00) plane, plane corresponding to side surface of hexagonal system = 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, and there were few variations in the device characteristics on the wafer, and the yield was greatly improved.

[Comparative Example 1] A selective growth layer was formed in the same manner as in Example 1, except that the stripe direction of the protective film was perpendicular to the plane A (orientation plane). Since the width of the protective film of the obtained nitride semiconductor is as wide as 14 μm, it is not sufficiently formed in the lateral growth stage shown in FIG. 1A, and the growth layers are not bonded to each other. When the obtained wafer was observed, cracks due to it were observed in most of the area. In such a nitride semiconductor, even if more nitride semiconductors are formed, only vertical growth (in the film thickness direction) occurs, and lateral growth does not occur. Therefore, it is naturally impossible to form an element. is there.

Comparative Example 2 In Example 1, θ = 0.
A nitride semiconductor was formed in the same manner except that the angle was 5 °. In the obtained nitride semiconductor, the formation of stable voids was broken as compared with Example 1, and the void shape as shown in FIG. 3 was observed, and the crystallinity was significantly deteriorated as compared with Example 1. This is because the void bends, as seen in Figure 3.
The width is also non-uniform, which means that the bonding position during 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, a large amount of strain was confirmed at the bent portion of the void seen in FIG. 3, and even if a device was formed using such a nitride semiconductor, good characteristics were obtained. Will not be shown and will be less reliable.

[0064]

The method of growing a nitride semiconductor according to the present invention is E
In the LOG growth, good growth is achieved, the bonding position on the upper part of the protective film is constant, and the growth forms of the adjacent selective growth are almost the same. Therefore, uniform selective growth is performed in the stripe direction of the protective film. A good crystalline nitride semiconductor is obtained over the entire wafer.

Further, even if the stripe width of the protective film is wide, the stable selective growth pattern is maintained, so that the growth using the protective film having a large area is possible, and the device formed on it can be grown. It will be extremely useful.

[Brief description of drawings]

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

FIG. 2 is a schematic diagram illustrating a growth mode in 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 diagram showing the notation of surface index in the present specification.

FIG. 8 is a schematic sectional view illustrating an embodiment of the present invention.

FIG. 9 is a schematic sectional view illustrating an 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 ...

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 33/00 H01L 21/205 H01S 5/00-5/50 H01L 31/04

Claims (4)

(57) [Claims] 1. A first nitride semiconductor is grown on a first major surface of a heterogeneous substrate made of sapphire or spinel and having a first major surface and a second crystal plane perpendicular thereto. The first step is partially performed on the surface of the first nitride semiconductor so that the stripe direction is in the range of 0.1 to 0.4 ° from the direction perpendicular to the plane of the second crystal of the heterogeneous substrate. And a second step of forming a stripe-shaped protective film on the first nitride semiconductor layer, 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. And the first main surface of the heterogeneous substrate is one surface selected from sapphire A surface, C surface, M surface and R surface,
The faces of the second crystal are sapphire A face, C face, M face, and R face.
One of the planes, or the first major surface of the heterogeneous substrate is a spinel (111) plane and the second crystal plane is a spinel (110) plane. Method for growing nitride semiconductor. 2. The combination of the first major 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, spinel (111) plane and (110) plane.
2. The method for growing a nitride semiconductor according to claim 1, wherein the number is one set selected from the planes. 3. The method for growing a nitride semiconductor according to claim 1, wherein the protective film has a stripe width of 10 μm or more. 4. The ratio W _w / W _s of 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. 4. The method for growing a nitride semiconductor according to 3.