KR20070076829A - Method for crystal growth of nitride semiconductor - Google Patents

Abstract

A method for growing a nitride-based compound semiconductor is provided to reduce the number of growing cores, threading dislocation, and residual stress by using only a first GaN epi formed on upper portions of protrusions as the growing core. Plural separated protrusions(105) are formed on a substrate. A dielectric and a metal thin film are sequentially formed on an upper portion of the substrate. A thermal process is performed on the metal thin film to form plural separated metal aggregations. The dielectric is etched by using the metal aggregations as etch masks to form plural separated rods on an upper portion of the substrate. The substrate is etched by using the rods as etch masks. First GaN epis are formed between the protrusion and the upper portion thereof. The first GaN epis formed on the upper portion of the protrusion are laterally grown to form a second GaN epi.

Description

Method for crystal growth of nitride semiconductor

1 is a view showing a penetration potential in a nitride compound semiconductor.

2A to 2H are cross-sectional views showing examples of the growth method of the nitride compound semiconductor of the present invention.

Explanation of symbols on the main parts of the drawings

100 sapphire substrate 110 insulating film

120: metal thin film 130: first GaN epi

140: second GaN epi 150: n-type nitride semiconductor layer

160: active layer 170: p-type nitride semiconductor layer

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of growing a nitride-based compound semiconductor, and more particularly, wherein a first GaN epitaxial layer is grown at a high temperature on a substrate having a plurality of spaced apart protrusions, and the second GaN epitaxial layer is formed on the first GaN epitaxial layer. The present invention relates to a growth method of a nitride compound semiconductor in which GaN epitaxial growth is performed to improve crystallinity.

Nitride-based compound semiconductors are direct-transition semiconductors that have a broad emission spectrum ranging from ultraviolet to infrared, and are widely used in light emitting devices such as light emitting diodes (LEDs) and laser diodes (LDs). .

Further, since the energy band gap is wide and stable operation can be expected at a higher temperature than devices using other semiconductors, applications to transistors such as field effect transistors (FETs) are also being developed.

In addition, since the nitride compound semiconductor does not use arsenic (As) as a main component, it has a high response in terms of environmental friendliness.

However, when growing a single crystal of a nitride compound semiconductor, it is difficult to grow the nitride compound semiconductor into a single crystal because the dissociation pressure of nitrogen is reached as high as 2000 atm at the growth temperature of the single crystal.

Therefore, single crystals of nitride compound semiconductors are currently used on heterogeneous substrates such as sapphire, such as metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), hybrid vapor phase epitaxy (HVPE), sublimation vapor phase epitaxy (SVPE), and the like. It is made by the vapor phase growth method.

However, sapphire (Al ₂ O ₃₎ When growing a single crystal of a nitride compound semiconductor on the substrate, sapphire (Al ₂ O ₃₎ on the substrate and the sapphire substrate between the epitaxially grown nitride semiconductor crystal to appear a large lattice mismatch do.

In the case of sapphire (Al ₂ O ₃ ) and gallium nitride (GaN), sapphire (α-Al ₂ O ₃ ) has a lattice constant of a: 4.758, c: 12.991 (Å), while gallium nitride (GaN) The lattice constants are a: 3.189 and c: 5.185 (kPa), resulting in about 16% lattice mismatch between the sapphire and gallium nitride.

This lattice mismatch causes dislocations on the interface between the sapphire substrate and the nitride-based compound semiconductor, which causes deterioration of the electrical characteristics of the device.

The dislocation due to lattice mismatch is a threading dislocation that penetrates the semiconductor layer in the longitudinal direction, that is, the direction perpendicular to the surface of the substrate. The nitride compound semiconductor grown on the sapphire substrate is 10 ⁹ to 10 ^{10 10} / cm ^It has a dislocation density of ³ .

The penetrating potential propagates along the respective layers of the nitride compound compound semiconductors having different compositions to the uppermost layer. As a result, for example, in the case of a light emitting device, a threshold current value of a laser diode (LD), LD, and a light emitting diode (LED) are transmitted. Device characteristics, such as device lifetime, are worsened.

This will be described with reference to FIG. 1. As shown in the drawing, a buffer layer 20 made of aluminum nitride (AlN) is formed on the sapphire substrate 10, and a nitride compound semiconductor layer 30 is formed on the buffer layer 20.

At the interface where the sapphire substrate 10 and the buffer layer 20 meet, a potential 40 due to lattice mismatch is generated.

The buffer layer 20 formed on the sapphire substrate 10 is formed to mitigate lattice mismatch between the sapphire substrate 10 and the nitride compound semiconductor layer 30, but the occurrence of dislocations can still be zero. There is no.

Penetration dislocations 41 propagate from the interface where the dislocations 40 occur in the longitudinal direction, that is, the direction perpendicular to the sapphire substrate 10. The penetration dislocations 41 are formed in the buffer layer 20 and the nitride compound semiconductor. Passes through layer 30.

Accordingly, when a plurality of semiconductor layers are stacked on the nitride compound semiconductor layer 30 to form a semiconductor device, the potential 43 that reaches the nitride compound semiconductor layer 30 is the nitride compound semiconductor layer. 30 continues to propagate to the plurality of semiconductor layers stacked thereon.

Due to this problem, there have been attempts to use heterogeneous substrates other than sapphire, for example, silicon carbide (SiC) as a substrate for growing single crystals of nitride compound semiconductors.

The silicon carbide (SiC) has a lattice mismatch of 6% smaller than the lattice mismatch between sapphire and gallium nitride in lattice mismatch with gallium nitride (GaN), and unlike natural sapphire substrates, dicing It has the advantage of easy dicing.

However, since silicon carbide (SiC) has a processing temperature for fabrication of 1500 ° C. or more, it is difficult to manufacture silicon carbide (SiC) substrate itself, and thus it is not expensive.

On the other hand, there is an attempt to grow a single crystal of a nitride compound semiconductor using a GaN substrate. In the case of a GaN substrate, since the material of the nitride compound semiconductor is the same, there is no lattice mismatch, and thus a good crystal may be grown.

In the case of using an n-type GaN substrate, the substrate can be used as an n-electrode because of its conductivity. Can be.

However, it is difficult to form GaN single crystals and cannot form liquid phase growth because no melt can be formed. That is, in order to be used in the semiconductor manufacturing process as a wafer, a crystal having a diameter of 2 inches or more is required. The growth of such large crystals includes the Czochralski method and the Bridgeman method. Solidify the solid.

However, the GaN does not become a melt only by heating, but sublimates into a gas. Therefore, a method of forming a GaN self-supporting film crystal by forming a GaN film thickly on the substrate using a vapor phase growth method of growing a thin film and removing the substrate is used.

However, even after a GaN freestanding substrate is made, even if a nitride semiconductor is grown on the GaN freestanding substrate, there is a high density potential in the GaN freestanding substrate itself, and since the nitride semiconductor grown on the GaN freestanding substrate inherits the potential, There is also a problem of having a high density of dislocations.

Currently, when manufacturing a light emitting device using a nitride compound semiconductor, it uses a technology of growing a GaN thin film in two stages at low and high temperatures, a high quality thin film capable of manufacturing a light emitting diode using the two-step growth method Could get

The two-stage growth method has been used to fabricate almost all GaN-based devices, and it is known that it is difficult to obtain a GaN thin film having a level of crystallinity obtained by the two-stage growth method through other methods. have.

In more detail about the two-stage growth method, first, the sapphire substrate is heat-treated at a high temperature of 1100 ° C. or higher, and then the lattice mismatch between the sapphire substrate and the nitride compound semiconductor layer is relaxed on the sapphire substrate, and the difference in thermal expansion coefficient is alleviated. The low temperature buffer layer is grown.

At this time, the low temperature buffer layer is grown at a temperature of 400 ~ 700 ℃, it will have a very large amount of crystalline defects.

Therefore, through the annealing (Annealing) process to secure the crystallinity necessary for the secondary growth. For example, there is a method of partially removing the surface of the low temperature buffer layer through mechanical polishing or reactive ion etching (RIE), followed by heat treatment.

Thereafter, a GaN thin film is grown on the low temperature buffer layer at a high temperature of 1000 ° C. or higher.

In the two-stage growth method, after the low temperature buffer layer is grown on the sapphire substrate, even if the annealing process is performed, the low temperature buffer layer has a low crystallinity, and the second high temperature GaN thin film formed on the low temperature buffer layer is also the low temperature buffer layer. This branch has a problem of inheriting the crystal defect as it is.

Accordingly, an object of the present invention is to grow a first GaN epi on a substrate having a plurality of spaced apart protrusions at a high temperature, and to form a second GaN epi by using a first GaN epi formed on the protrusion as a seed layer. By lateral growth, it is to provide a method for growing a nitride compound semiconductor having improved crystallinity.

Embodiments of the growth method of the nitride compound semiconductor of the present invention, forming a plurality of mutually spaced apart protrusions on the substrate;

Forming a first GaN epi in the region between the protrusion and the protrusion so as not to merge with each other; And

Side growth of the first GaN epi formed on the protrusions to form a second GaN epi.

The forming of the plurality of mutually spaced apart protrusions on the substrate may include sequentially forming an insulating film and a metal thin film on the substrate, and heat treating the metal thin film to form a plurality of mutually spaced metal aggregates. Forming a plurality of mutually spaced rods on the substrate by etching the insulating layer using the plurality of mutually spaced metal aggregates as an etch mask; and forming the plurality of spaced rods on the substrate. And etching the substrate using the rods as an etching mask.

Hereinafter, the growth method of the nitride compound semiconductor of the present invention will be described in detail with reference to FIGS. 2 to 3. 2A to 2H are cross-sectional views showing examples of the growth method of the nitride compound semiconductor of the present invention.

As shown in FIG. 2, first, an insulating film 110 is formed on the sapphire substrate 100 (FIG. 2A).

A silicon oxide film (SiO ₂ ), a silicon nitride film (SiN), or the like is used as the insulating film 110, and the insulating film 110 is preferably formed to a thickness of 100 to 1000 nm.

Next, the metal thin film 120 is formed on the insulating film 110 (FIG. 2B).

Here, the metal thin film 120 is made of any one material selected from Ag, Ni, Au, and particularly preferably made of Ag.

In addition, the metal thin film 120 may use various metals capable of forming metal agglomeration through heat treatment in addition to the metals.

The metal thin film 120 is deposited by electron beam evaporation (E-beam Evaporation) or sputtering (Sputtering), etc., is formed to a thickness of 10 ~ 100nm.

Subsequently, the metal thin film 120 is heat-treated to form a plurality of mutually spaced metal agglomerations 125 on the insulating layer 110 (FIG. 2C).

Here, the heat treatment of the metal thin film 120 uses a heat treatment equipment such as Rapid Thermal Process System (RTP) or Furnace.

The temperature during the heat treatment of the metal thin film 120 is heat treated at a temperature suitable for the type of the metal thin film 120, in particular, the temperature of the heat treatment when using Ag as the metal thin film 120 is 400 ~ 650 ℃ It is preferable to set it as.

When the metal thin film 120 is heat-treated, a plurality of mutually spaced metal aggregates 125 are formed on the insulating layer 110, wherein the size of the metal aggregates 125 is equal to the thickness of the metal thin film 120. It depends on the heat treatment temperature.

That is, the thinner the thickness of the metal thin film 120 and the higher the heat treatment temperature of the metal thin film 120, the smaller the size of the metal aggregates 125. Usually, the metal aggregate 125 is formed to a size of 50 to 500 nm.

Subsequently, the insulating film 110 is etched using the plurality of spaced apart metal aggregates 125 as an etching mask, and then the metal aggregates 125 are removed (FIG. 2D).

Here, when the insulating layer 110 is etched using the plurality of mutually spaced metal aggregates 125 as an etching mask, a plurality of mutually spaced rods 115 are formed on the sapphire substrate 100. .

Next, the sapphire substrate 100 is etched using the plurality of spaced apart rods 115 as an etch mask (FIG. 2E).

When the sapphire substrate 110 is etched using the plurality of spaced apart rods 115 as an etch mask, a plurality of spaced apart protrusions 105 are formed on the surface of the sapphire substrate 100.

As such, by using the metal aggregate 125 formed by heat-treating the metal thin film 120, a protrusion 105 having a nanoscale size may be formed on the surface of the sapphire substrate 100, in which case the protrusion ( Width between the 105 may also be formed in a size similar to the size of the protrusion 105.

Subsequently, a first GaN epi 130 is grown on the sapphire substrate 100 (FIG. 2F).

Here, since the plurality of mutually spaced apart protrusions 105 are formed on the surface of the sapphire substrate 100, the first GaN epi 130 may be formed between the tops of the protrusions 105 and the protrusions 105. Each area is grown.

The first GaN epi 130 formed on the sapphire substrate 100 is grown by MOCVD (Metal Organic Chemical Vapor Deposition) at a high temperature of 900 ~ 1100 ℃.

In the present invention, the first GaN epitaxial growth is performed immediately at a high temperature without forming a low temperature buffer layer. However, when the GaN epi is grown at a high temperature, too many growth nuclei are formed, and thus a high quality GaN thin film cannot be obtained.

In other words, when too many growth nuclei are formed, the growth nuclei are grown, respectively, so that the crystal planes are formed differently. Thus, when the growth nuclei with different crystal planes are coalesced, defects are merged. Since a lot of high quality GaN thin film is not obtained.

Accordingly, in the present invention, the first GaN layer 130 is not grown on the sapphire substrate having a flat surface, but the sapphire substrate 100 on which the plurality of mutually spaced protrusions 105 are formed. It grows at high temperature to suppress excessive growth nucleus formation.

That is, the first GaN epi 130 is grown on the sapphire substrate 100 having a plurality of mutually spaced protrusions 105 formed on the surface at a high temperature, and thus the first GaN epi 130 is formed on the protrusions 105. Bay is used as the seed layer of the second GaN epi to be described later to reduce the number of growth nuclei.

In this case, the first GaN epi 130 is also grown in the region between the protrusions 105, wherein the first GaN epi 131 and the protrusion 105 are formed in the region between the protrusions 105. The growth conditions must be adjusted so that the first GaN epi 133 formed on the top of the field is not merged with each other.

At this time, the first GaN epi 131 formed in the region between the protrusions 105 and the first GaN epi 133 formed on the protrusions 105 are controlled as growth variables that are not merged with each other. NH ₃ flow rate, temperature, H ₂ partial pressure and the like.

Here, if the flow rate of NH ₃ is increased and the temperature is increased, the horizontal growth is increased in the growth direction of the first GaN epi 130, and if the flow rate of NH ₃ is decreased, the temperature is decreased in the growth direction of the first GaN epi 130. Vertical growth will increase.

Therefore, the first GaN epi 131 formed in the region between the protrusions 105 and the first GaN epi 133 formed on the protrusions 105 may be adjusted so as not to merge with each other.

In addition, H ₂ serves as an etchant. Even if the first GaN epi 133 formed on the protrusions 105 is removed, too small growth nuclei are removed to reduce the density of the growth nuclei.

Thereafter, the second GaN epi 140 is grown using the first GaN epi 133 formed on the protrusions 105 as a seed layer (FIG. 2G).

The second GaN epi 140 is grown through a lateral growth method using the first GaN epi 133 formed on the protrusions 105 as a seed layer. That is, by controlling the growth conditions, the rate of horizontal growth is about 2-4 times faster than the rate of vertical growth.

As such, the second GaN epi 140 grown in both directions through the lateral growth method merges with each other in the region between the protrusions 105, resulting in a flat surface.

In this case, since the width of the region between the protrusions 105 does not exceed 1 μm, the distance that is laterally grown of the second GaN epi 140 also corresponds to a short distance of 1 μm or less, and thus, the second GaN. The epi 140 can be flattened at a thickness of 5 μm or less.

When the second GaN epi 140 is planarized at a thickness of 5 μm or less, residual stress in the second GaN epi 140 may be reduced, thereby reducing a warpage phenomenon due to the residual stress.

That is, in the case of lateral growth using a conventional dielectric mask, a thickness of 5 μm or more must be grown at a high temperature until complete planarization, so that residual stresses occur in the GaN thin film, causing warpage. Since it is short and can be flattened at a thickness of 5 μm or less, the warpage phenomenon due to the residual stress can be reduced.

In addition, by growing the second GaN epi 140 through a lateral growth method, a penetration potential may be reduced, thereby obtaining a GaN thin film having excellent crystallinity.

Let's take a closer look at this. In the first GaN epi 133 formed on the protrusions 105, the penetration potential generated at the interface between the sapphire substrate 100 and the first GaN epi 133 is initially applied to the sapphire substrate 100. As it propagates in a vertical direction, it meets a side wall of the first GaN epi 133.

Subsequently, when the second GaN epi 140 is laterally grown based on the first GaN epi 133, the penetrating potential existing on the side wall of the first GaN epi 133 changes the direction of propagation. The sapphire substrate 100 propagates in a horizontal direction.

In addition, since the dislocations propagated from both directions collide with each other when the second GaN epi 140 merges in an area between the protrusions 105, the number of through dislocations decreases.

Next, an n-type nitride semiconductor layer 150, an active layer 160, and a p-type nitride semiconductor layer 170 are sequentially stacked on the second GaN epi 140 to form a light emitting structure (FIG. 2H).

3A and 3B are SEM (Scanning Electron Microscope) photographs showing the sapphire substrate used in the growth method of the nitride compound semiconductor of the present invention. As shown in the drawing, the present invention grows a nitride compound semiconductor using a sapphire substrate having a plurality of mutually spaced protrusions on its surface.

On the other hand, while the present invention has been shown and described with respect to specific preferred embodiments, various modifications and variations of the present invention without departing from the spirit or field of the invention provided by the claims below It will be readily apparent to one of ordinary skill in the art that it can be used.

As described above, according to the present invention, by growing the first GaN epi on the substrate formed with a plurality of spaced apart protrusions by using only the first GaN epi formed on the protrusions as a growth nucleus, the number of growth nuclei In short, a high quality GaN thin film can be obtained.

In addition, by growing the second GaN epi by using the first GaN epi formed on the protrusions as a seed layer, the penetration potential may be reduced, thereby improving the crystallinity of the GaN thin film.

In addition, since the side growth distance of the second GaN epi corresponds to a short distance of 1 μm or less, the second GaN epi may be planarized at a thickness of 5 μm or less, thereby reducing residual stress and It is possible to reduce the warpage phenomenon.

Claims (7)

Forming a plurality of mutually spaced apart protrusions on the substrate; Forming a first GaN epi in the region between the protrusion and the protrusion so as not to merge with each other; And Forming a second GaN epitaxially by growing the first GaN epitaxially formed on the protrusion. The method of claim 1, Forming a plurality of mutually spaced apart protrusions on the substrate, Sequentially forming an insulating film and a metal thin film on the substrate; Heat treating the metal thin film to form a plurality of mutually spaced metal aggregates; Forming a plurality of mutually spaced rods on the substrate by etching the insulating layer using the plurality of spaced metal aggregates as an etching mask; And And etching the substrate using the plurality of spaced apart rods as an etch mask. The method of claim 2, And the insulating film is a silicon oxide film (SiO ₂ ) or a silicon nitride film (SiN). The method of claim 2, The metal thin film is a growth method of the nitride compound semiconductor, characterized in that made of any one material selected from Ag, Ni, Au. The method of claim 2, And the metal aggregate is controlled by the thickness of the metal thin film and the temperature during heat treatment. The method of claim 1, The first GaN epitaxial growth method of the nitride compound semiconductor, characterized in that for growing at a temperature of 900 ~ 1100 ℃. The method of claim 1, The forming of the first GaN epi in the region between the protrusion and the protrusion may not merge with each other. Method of growing a nitride-based compound semiconductor characterized in that the first GaN epi formed in the region between the protrusion and the protrusion so as not to merge with each other by adjusting the NH ₃ flow rate and temperature among the growth variables of the first GaN epi. .

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