JP4214714B2 - Method for producing group III nitride compound semiconductor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a group III nitride compound semiconductor. The group III nitride compound semiconductor is, for example, a binary system such as AlN, GaN, InN, Al _x Ga _1-x N, Al _x In _1-x N, Ga _x In _1-x N (whichever Also includes ternary systems such as 0 <x <1) and quaternary systems of Al _x Ga _y In _1-xy N (0 <x <1, 0 <y <1, 0 <x + y <1) general formula is _{Al x Ga y in 1-xy} N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) with those represented. In this specification, unless otherwise specified, the group III nitride compound semiconductor is simply referred to as a group III nitride compound semiconductor doped with an impurity for making the conductivity type p-type or n-type. An expression that also includes
[0002]
[Prior art]
Group III nitride compound semiconductors, for example, when used as light-emitting elements, are direct transition semiconductors whose emission spectrum covers a wide range from ultraviolet to red, and are used in light-emitting elements such as light-emitting diodes (LEDs) and laser diodes (LDs). Applied. In addition, since the band gap is wide, stable operation can be expected at a higher temperature than elements using other semiconductors. Therefore, applications to transistors such as FETs have been actively developed. In addition, since it does not contain arsenic (As) as the main component, it is expected to develop various semiconductor devices in general from an environmental point of view. Some of these Group III nitride compound semiconductors use sapphire as a substrate and a silicon carbide (SiC) substrate or silicon (Si) substrate in addition to the element formed thereon.
[0003]
[Problems to be solved by the invention]
When epitaxially growing a III-nitride compound semiconductor on a substrate, the substrate may be contaminated even if it passes through the buffer layer, such as when the substrate is not completely cleaned, has fine flaws, or the growth conditions are not optimal. A single crystal group III nitride compound semiconductor may not be formed on the top of the scratch. Even in a region where such contamination and scratches on the substrate are extremely small, the region where the single crystal group III nitride compound semiconductor is not formed becomes wide enough to epitaxially grow the group III nitride compound semiconductor into a thick film. . This is called a pit and generally appears as an inverted hexagonal pyramid having a side surface of {1-101} in a group III nitride compound semiconductor. In this aspect, when the growth surface of a group III nitride compound semiconductor is a c-plane {0001} plane, the angle formed by them is about 62 degrees, and in some cases, a film obtained by epitaxially growing a group III nitride compound semiconductor In some cases, the pits may be as thick as the pits.
[0004]
Also, there is no substrate that can be obtained at low cost with a substrate having a lattice constant or thermal expansion coefficient close to that of the group III nitride compound semiconductor. Therefore, it is common to use different substrates such as sapphire, silicon, SiC and spinel (MgAl ₂ O ₄ ). However, when a group III nitride compound semiconductor is epitaxially grown on a dissimilar substrate such as sapphire, silicon, SiC, or spinel (MgAl ₂ O ₄ ), a group III nitride compound semiconductor having a very large amount of threading dislocations is formed. End up. This threading dislocation may also be the starting point of the pit formation.
[0005]
This is shown in FIG. FIG. 4 shows a state in which the group III nitride compound semiconductor layer 3 is formed on the substrate 1 via the buffer layer 2. If the area of a small area indicated by S on the substrate 1 is soiled or scratched, the buffer layer 2 may not cover the portion as shown in FIG. . By epitaxially growing the group III nitride compound semiconductor layer 3 as it is, the pits P ₁ having the {1-101} plane M ′ forming an angle of about 62 degrees with the epitaxial growth plane C are formed. That is, the group III nitride compound semiconductor is supposed to be stacked on the epitaxial growth surface C originally, but there is no epitaxial growth or very slow in the portion where there is no epitaxial growth surface in the lower layer. Further, threading dislocations D ₁ , D ₂ , D ₃ , and D ₄ are formed from the difference in lattice constant from the substrate 1. Those that disappear in the range of the buffer layer 2 such as threading dislocations D ₁ , those that disappear during the growth of the group III nitride compound semiconductor layer 3 such as threading dislocations D ₂ , and groups III such as threading dislocations D ₃ In addition to those that do not disappear during the growth of the nitride-based compound semiconductor layer 3 and follow the growth surface C, there are threading dislocations D ₄ that generate pits P ₂ from a certain point in time.
[0006]
Thus, once pits are formed, the pits never disappeared during normal epitaxial growth. Further, when the pit is formed, the characteristics of the group III nitride compound semiconductor element formed in the region including the portion are remarkably deteriorated. Further, even when the group III nitride compound semiconductor multilayer film is formed, the group III nitride compound semiconductor has a portion that is not flat, so that the device life is shortened. In addition, the device does not have the characteristics as designed. Thus, conventionally, when pits are formed, the group III nitride compound semiconductor element formed on the upper layer becomes a defective product, resulting in a decrease in yield.
[0007]
The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a group III nitride compound semiconductor with reduced pits by epitaxial growth.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, according to the means of claim 1, in the method for producing a group III nitride compound semiconductor using epitaxial growth, the first group III nitride compound semiconductor is fixed in a planar shape. A first step of epitaxial growth to a thickness and a second group III nitride compound semiconductor having a composition different from that of the first group III nitride compound semiconductor are formed under predetermined conditions such that the lateral growth is faster than the lengthwise direction. A second step of epitaxial growth and a third step of epitaxially growing the first group III nitride compound semiconductor are formed, and the second group III nitride compound semiconductor epitaxially grown in the second step is formed in the first step. all SANYO fill the pits have been the first group III nitride compound semiconductor surface, a second group III nitride compound semiconductor grown in the second step is aluminum Including, or are acceptor become magnesium other Group II element is doped, the growth temperature in the second step is a at 900 ° C. or higher, and wherein a lower than the growth temperature in and the first step and third step To do. Here, the term “planar” does not mean a complete plane. In addition, the predetermined condition that the lateral growth is faster than the vertical direction means a condition that the lateral growth is faster than the vertical direction when the vertical growth and the lateral growth are performed simultaneously. Further, filling the pit is not limited to smoothing by completely filling the pit, and it is sufficient that the state changes “in the direction in which the pit is filled”.
[0009]
Also, according to the means described in claim 2, the aluminum composition in the Group III of the second group III nitride compound semiconductor grown in the second step, the first Group III nitride compound semiconductor It is characterized by having a molar ratio of 5 percent or more than the aluminum composition in Group III. Here, when the molar ratio of the aluminum composition is 5 percent or more, the difference in aluminum composition among all the III groups is 5 such as GaN and Al _0.05 Ga _0.95 N, Al _0.1 Ga _0.9 N and Al _0.15 Ga _0.85 N. It means that it is more than a percentage , and it does not indicate what is called 1.05 times or more.
[0010]
Further, according to according to the means described in claim 3, the first group III aluminum composition of the nitride-based compound semiconductor of a group III in the molar ratio 5% or less, second group III nitride compound semiconductor of Group III The aluminum composition is characterized by having a molar ratio of 10 percent or more. According to the means of claim 4 , the aluminum composition in group III of the first group III nitride compound semiconductor has a molar ratio of 0 percent or more and 2 percent or less, and the second group III nitride compound semiconductor. The aluminum composition in group III is characterized by having a molar ratio of 7 percent or more.
[0011]
[0012]
According to the means of claim 5 , following the third step, after forming at least the first group III nitride compound semiconductor into an island state such as a dot shape, a stripe shape, or a lattice shape by etching, And a step of epitaxially growing a fourth group III nitride compound semiconductor in the vertical and horizontal directions using the upper surface and side surfaces of the upper step in the island state as nuclei. Here, to etch at least the first group III nitride compound semiconductor means to at least etch the first group III nitride compound semiconductor grown in the third step. The second group III nitride compound semiconductor grown in this manner may be etched, or the first group III nitride compound semiconductor grown in the first step may be etched.
[0013]
[Operation and effect of the invention]
The outline of the present invention will be described with reference to FIG. Now, it is assumed that the first group III nitride compound semiconductor layer 31 having the pits P is formed due to some small region S ((a) of FIG. 1). Here, the second group III nitride compound semiconductor layer 4 having a different composition is formed by switching the supply source amount under predetermined conditions. At this time, since the second group III nitride compound semiconductor layer 4 has growth conditions such that the lateral growth is faster than the vertical direction, the first III group nitride compound semiconductor layer 31 cannot cover the small region. The second group III nitride compound semiconductor layer 4 can cover S ((b) of FIG. 1). In this way, after the second group III nitride compound semiconductor 4 covers the bottom of the pit (vertical hexagonal pyramid apex) S in a laterally growing manner, the first group III nitride compound semiconductor layer 32 is again formed. If epitaxial growth is performed (FIG. 1 (c)), even if a recess remains, a group III nitride compound semiconductor 32 is rapidly formed in the recess, and an extremely flat c-plane is eventually formed. ((D) in FIG. 1, claim 1).
If the growth condition in the second step is a growth temperature of 900 ° C. or higher, lateral growth is facilitated.
[0014]
A second Group III nitride compound semiconductor layer containing aluminum, or by magnesium serving as an acceptor other Group II element is doped, can be provided fast such growth conditions of readily lateral growth . First, the difference in the aluminum composition of the second Group III nitride compound semiconductor layer is 5% or more, more desirably 10% or more (claim 2). For example, if the first group III nitride compound semiconductor is GaN, the composition of the second group III nitride compound semiconductor is Al _0.1 Ga _0.9 N or Al _0.15 Ga _0.85 N to reliably fill the pits. The present inventors have found that this is possible. Here, the aluminum composition in Group III of the first Group III nitride compound semiconductor is 5 percent or less, and the aluminum composition in Group III of the second Group III nitride compound semiconductor is 10 percent or more. ( Claim 3 ), or the aluminum composition in group III of the first group III nitride compound semiconductor is a molar ratio of 0 to 2 percent, and group III of the second group III nitride compound semiconductor If the aluminum composition is 7% or more by mole ratio ( Claim 4 ), the present invention can be applied.
[0015]
Also, following the third step, at least the first Group III nitride compound semiconductor punctate by etching, after forming the island state of stripe-shaped or lattice-like shape, the upper top surface and side surface of the step of the island state The fourth group III nitride compound semiconductor was grown epitaxially in the vertical and lateral directions with the nucleus as the nucleus, and through the epitaxial growth in the lateral direction with the fewer defects as the nucleus, the portion where the step was buried was suppressed from threading dislocations. It can be a region ( Claim 5 ).
[0016]
DETAILED DESCRIPTION OF THE INVENTION
The embodiment of the above invention can be selected from the following.
[0017]
In the case of sequentially forming a group III nitride compound semiconductor on a substrate, the substrate is sapphire, silicon (Si), silicon carbide (SiC), spinel (MgAl ₂ O ₄ ), LiGaO ₂ , NdGaO ₃ , ZnO MgO and other inorganic crystal substrates, III-V group compound semiconductors such as gallium phosphide or gallium arsenide, gallium nitride (GaN) and other group III nitride compound semiconductors can be used.
[0018]
As a method for forming the group III nitride compound semiconductor layer, metal organic vapor phase epitaxy (MOCVD or MOVPE) is preferable, but molecular beam vapor phase epitaxy (MBE), halide vapor phase epitaxy (Halide VPE), etc. Each layer may be formed by a different growth method.
[0019]
Group III nitride-based compound semiconductors can replace part or all of the composition of group III elements with boron (B) and thallium (Tl), and part of the composition of nitrogen (N) can be phosphorus (P ), Arsenic (As), antimony (Sb), and bismuth (Bi), the present invention can be substantially applied. Moreover, what doped such an extent that these elements cannot be displayed on a composition may be used. For example, Al _x Ga _1-x N (0 ≦ x ≦ 1), which is a group III nitride compound semiconductor that does not contain indium (In) and arsenic (As), is composed of aluminum (Al) and gallium (Ga). Indium (In), which has a large atomic radius, or arsenic (As), which has a larger atomic radius than nitrogen (N), can compensate for the expansion strain of the crystal due to the loss of nitrogen atoms by compressive strain and improve crystallinity. You may do it. By improving the crystallinity in this manner, the threading dislocation can be further reduced to about 100 to 1/1000 in combination with the present invention. In the case of constituting the light emitting element, it is desirable to use a binary or ternary group III-nitride compound semiconductor.
[0020]
When an n-type group III nitride compound semiconductor layer is formed, a group IV element such as Si, Ge, Se, Te, C, or a group VI element can be added as an n-type impurity. Further, as a p-type impurity, a group II element or group IV element such as Zn, Mg, Be, Ca, Sr, or Ba can be added. A plurality of these or n-type impurities and p-type impurities may be doped in the same layer.
[0021]
It is good also as a structure which performs what is called lateral epitaxial growth combining with this application. That is, a configuration in which threading dislocations are reduced by various lateral epitaxial growths may be combined. As the lateral epitaxial growth, it is desirable that the growth surface is perpendicular to the substrate, but growth may be performed with the facet surface oblique to the substrate. At this time, the bottom of the step may be V-shaped with no bottom surface.
[0022]
That is, the group III nitride compound semiconductor layer 300 with reduced pits formed on the substrate 1 via the buffer layer as shown in FIG. 2A is etched as shown in FIG. It is formed in an island state such as a shape, stripe shape or lattice shape. The group III nitride compound semiconductor layer 300 includes the first group III nitride compound semiconductor 31, the second group III nitride compound semiconductor 4, and the third group III nitride compound semiconductor of FIG. 32 is also shown. In this way, the fourth group III nitride compound semiconductor 33 is epitaxially grown in the vertical and horizontal directions with the top and side surfaces of the step of the group III nitride compound semiconductor layer 300 as nuclei (FIG. 2 (c)). In addition to filling, a region where threading dislocations are suppressed can be formed above the lower part of the step ((d) in FIG. 2).
[0023]
As a method for forming a group III nitride compound semiconductor layer 300 with reduced pits formed on the substrate 1 through a buffer layer into an island state such as a dot shape, a stripe shape, or a lattice shape by etching, FIG. 3 (a), until the substrate 1 is exposed, a method of covering the upper step of the step with a mask 5 as shown in FIG. 3 (b), or an upper step of the step as shown in FIG. 3 (c). Alternatively, a method of covering the lower stage with the mask 5 may be used.
[0024]
A semiconductor element such as an FET or a light emitting element can be formed on the wafer on which the group III nitride compound semiconductor with reduced pits is formed. In the case of a light emitting device, a multi-quantum well structure (MQW), a single quantum well structure (SQW), a homo structure, a hetero structure, or a double hetero structure can be considered, but it is formed by a pin junction or a pn junction. May be.
[0025]
The growth temperature of the second group III nitride compound semiconductor is preferably a growth temperature of 900 ° C. or higher from the viewpoint of lateral growth. This is because an amorphous layer is formed at a growth temperature lower than 900 ° C., which is inconvenient.
[0026]
The aluminum composition of the second group III nitride compound semiconductor is desirably 5 percent or more, preferably 10 percent or more, higher than the aluminum composition of the first group III nitride compound semiconductor. That is, for example, if the first group III nitride compound semiconductor is GaN, the second group III nitride compound semiconductor is preferably Al _0.05 Ga _0.95 N, preferably Al _0.1 Ga _0.9 N. By introducing the second group III nitride compound semiconductor having a higher aluminum composition, the bottom of the pit that cannot be covered by the first group III nitride compound semiconductor having a lower aluminum composition can be covered. The lateral growth can be accelerated by the dopant. By supplying a group II element that replaces the group III and serving as an acceptor, even when there is no aluminum, and when a second group III nitride compound semiconductor with a higher aluminum composition is formed, further lateral growth is performed. It is also possible to make it faster.
[0027]
[First embodiment]
The a-plane cleaned by organic cleaning and heat treatment is the main surface, and the temperature is lowered to 400 ° C on a single crystal sapphire substrate 1, H ₂ is 10 L / min, NH ₃ is 5 L / min, and TMA is 20 μmol / The AlN buffer layer 2 was formed to a thickness of about 20 nm by supplying about 3 minutes at a min. Next, the temperature of the sapphire substrate 1 was maintained at 1100 ° C., H ₂ was introduced at 20 L / min, NH ₃ was introduced at 10 L / min, and TMG was introduced at 300 μmol / min to form a GaN layer 31 having a thickness of about 1 μm. Next, the temperature of the sapphire substrate 1 is lowered to 1000 ° C., H ₂ is supplied at 10 L / min, NH ₃ is supplied at 10 L / min, TMG is supplied at 100 μmol / min, and TMA is supplied at 10 μmol / min. _A layer 4 composed of _0.15 Ga _0.85 N was formed. Next, the temperature of the sapphire substrate 1 is raised to 1100 ° C., H ₂ is introduced at 20 L / min, NH ₃ is introduced at 10 L / min, and TMG is introduced at 300 μmol / min to form a GaN layer 32 having a thickness of about 5 μm. . No pits were found on the wafer in the GaN layer 32 thus formed.
[0028]
[Comparative example]
The GaN layer 31 and the GaN layer 32 are continuously formed without forming the layer 4 made of Al _0.15 Ga _0.85 N without lowering and raising the temperature, and the film thickness is 6 μm as in the first embodiment. The GaN layer was formed on the a surface of the sapphire substrate via the AlN buffer layer. In the GaN layer thus formed, several tens of pits were formed on the wafer.
[0029]
[Second Embodiment]
In the first embodiment, the layer 4 formed after the GaN layer 31 having a thickness of about 1 μm was formed in the same manner except that Al _0.15 Ga _0.85 N: Mg having a thickness of about 100 nm was formed. The doping amount of magnesium (Mg) was about 10 ¹⁹ cm ⁻³ . No pits were found on the wafer in the GaN layer 32 having a thickness of about 5 μm on the layer 4. The formation of Al _0.15 Ga _0.85 N: Mg was confirmed to be faster in lateral growth than Al _0.15 Ga _0.85 N.
[0030]
[Third embodiment]
In the first embodiment, the layer 4 formed after the GaN layer 31 having a thickness of about 1 μm was formed in the same manner except that the GaN: Mg having a thickness of about 100 nm was used. The doping amount of magnesium (Mg) was about 10 ¹⁹ cm ⁻³ . No pits were found on the wafer in the GaN layer 32 having a thickness of about 5 μm on the layer 4. The formation of GaN: Mg was confirmed to be lateral growth unlike GaN.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing steps of a method for producing a group III nitride compound semiconductor according to a specific example of the present invention.
FIG. 2 is a cross-sectional view showing a process of a method for producing a group III nitride compound semiconductor according to another embodiment of the present invention.
FIG. 3 is a cross-sectional view showing a part of a process of a method for producing a group III nitride compound semiconductor according to another embodiment of the present invention.
FIG. 4 is a cross-sectional view showing a conventional group III nitride compound semiconductor having pits.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Substrate 2 Buffer layer 3, 31, 32 Group III nitride compound semiconductor 4 Group III nitride compound semiconductor with higher aluminum composition than P, P ₁ , P ₂ pits D ₁ , D ₂ , D ₃ , D ₄ penetration Dislocation S Dirt or bottom of pit C Epitaxial growth surface M 'Side of pit

Claims (5)

In a method for producing a group III nitride compound semiconductor using epitaxial growth,
A first step of epitaxially growing the first group III nitride-based compound semiconductor in a planar shape with a certain thickness;
A second step of epitaxially growing a second group III nitride compound semiconductor having a composition different from that of the first group III nitride compound semiconductor under predetermined conditions such that the lateral growth is faster than the vertical direction;
A third step of epitaxially growing the first group III nitride compound semiconductor,
Wherein said second group III nitride compound semiconductor is epitaxially grown in the second step all SANYO fill the pits of the first said formed in step a first group III nitride compound semiconductor surface,
The second group III nitride compound semiconductor grown in the second step contains aluminum, or is doped with magnesium or other group II element that serves as an acceptor ,
A method for producing a group III nitride compound semiconductor, wherein the growth temperature in the second step is 900 ° C. or higher and lower than the growth temperatures in the first step and the third step . The second group III nitride compound semiconductor grown in the second step contains aluminum, and the aluminum composition in group III is the group III of the first group III nitride compound semiconductor. 2. The method for producing a group III nitride compound semiconductor according to claim 1 , wherein the molar ratio is 5 percent or more than the aluminum composition therein.   The aluminum composition in group III of the first group III nitride compound semiconductor is 5 percent or less, and the aluminum composition in group III of the second group III nitride compound semiconductor is 10 percent or more. The method for producing a group III nitride compound semiconductor according to claim 2, wherein:   The aluminum composition in group III of the first group III nitride compound semiconductor has a molar ratio of 0 to 2 percent, and the aluminum composition in group III of the second group III nitride compound semiconductor has a molar ratio of 7 The method for producing a group III nitride compound semiconductor according to claim 2, wherein the method is a percentage or more. Following the third step, at least the first group III nitride compound semiconductor is formed into an island state such as a dot shape, a stripe shape, or a lattice shape by etching, and then the upper surface and side surfaces of the upper step of the island state are formed. 5. The group III nitride compound semiconductor according to claim 1, further comprising a step of epitaxially growing a fourth group III nitride compound semiconductor in the longitudinal and lateral directions as a nucleus. Manufacturing method.

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