JP3505357B2 - Gallium nitride based semiconductor device and method of manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gallium nitride based semiconductor device and a method for manufacturing the same. For more details,
The present invention relates to a semiconductor device in which a high-quality gallium nitride-based compound semiconductor layer is formed on various substrates such as a silicon substrate, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Since a gallium nitride based semiconductor has a direct transition type optical transition, it is possible to cause radiative recombination with high efficiency. Moreover, the range of the transition energy is as wide as 2 to 6.2 electron volts. Therefore, various short wavelength semiconductor lasers or high brightness visible LE
As a material for semiconductor elements such as D, its development is being advanced.

In the present specification, the term "gallium nitride-based semiconductor" means In _x Al _y Ga _{1- xy} N (0≤x≤
In the chemical formula of 1,0 ≦ y ≦ 1, x + y ≦ 1), semiconductors having all compositions in which the composition ratios x and y are changed within the respective ranges are included. For example, InGaN (x
= 0.4, y = 0) is also a "gallium nitride-based compound semiconductor"
Shall be included in.

A conventional gallium nitride-based compound semiconductor device has a sapphire (A) layer formed through a buffer layer grown at a low temperature.
L ₂ O ₃ ) formed on the substrate. As a reference disclosing this method, for example, Japanese Patent Laid-Open No. 2-229476.
And Japanese Patent Laid-Open No. 8-8217. However, since sapphire has an extremely high hardness of 9, it is difficult to etch or cleave the substrate. In addition, the substrate size that can be easily obtained at the present stage is a 2-inch diameter, and it is difficult to obtain a larger substrate.
There was also the problem that the price was high. As a solution to these problems, attempts have been made to grow a gallium nitride-based semiconductor on a substrate such as silicon that can be easily processed and a large-diameter wafer is available.

[0005]

FIG. 4 is a schematic view showing a cross-sectional structure of a gallium nitride-based semiconductor device using a conventional silicon substrate. This figure shows an example of growing the buffer layer disclosed in the above-mentioned reference on a silicon substrate. That is, the Ga _x Al _1-x N (0 ≦ x ≦ 1) buffer layer 1 is formed on the silicon substrate 110 at a relatively low growth temperature.
20 is grown, and a predetermined gallium nitride based semiconductor layer 130 is epitaxially grown thereon. However, FIG.
In the structure as shown in FIG.
When the layer thickness of 0 is 1 micron or more, there is a problem that the whole wafer is warped or the crystal layer is cracked, so that a good quality crystal layer cannot be grown. It is considered that this is due to the difference in thermal expansion coefficient between the gallium nitride based semiconductor and the silicon substrate. Looking at each coefficient of thermal expansion, sapphire is about 7.5 × 10 ^-6 , while
Gallium nitride is about 5.6 × 10 ^-6 , silicon is about 3.6.
It is × 10 ^-6 . That is, when gallium nitride is grown at a high temperature and then cooled to room temperature, gallium nitride on a sapphire substrate is loaded with compressive stress, whereas gallium nitride on a silicon substrate is loaded with tensile stress and cracks are generated. Cause.

That is, in view of the coefficient of thermal expansion, a gallium nitride layer grown on silicon is loaded with a tensile stress, and such a tensile stress becomes stronger as the gallium nitride film thickness becomes thicker, so that cracks also occur in the film. It becomes more remarkable as the thickness increases.

For semiconductor elements such as LEDs and semiconductor lasers, it is often necessary to stack semiconductor layers of 1 micron or more. Therefore, there is a problem that a semiconductor element cannot be produced unless a crystal of such a large thickness and good quality is obtained.

The present invention has been made in view of the above points. That is, it is an object of the present invention to provide a semiconductor device in which a high quality and thick film of a gallium nitride based semiconductor layer is laminated on various substrates such as a silicon substrate, and a method for manufacturing the same.

[0009]

That is, according to the present invention, a substrate, a gallium nitride based semiconductor buffer layer containing at least indium which is laminated on the substrate, and a nitride layer which is laminated on the buffer layer. A gallium-based semiconductor layer, and a stress caused by a difference in thermal expansion coefficient between the substrate and the gallium nitride-based semiconductor layer is configured to be relaxed by the buffer layer, so that the stress of silicon or the like can be reduced. A high quality gallium nitride based semiconductor layer can be stably grown on a substrate.

Further, by providing a gallium nitride based semiconductor buffer layer between the substrate and the buffer layer, the buffer layer can be stably formed.

Further, by using any one of silicon, spinel, 6H type SiC, GaP and GaAs as the substrate, the device forming process is facilitated and various semiconductor devices can be realized.

Further, if the buffer layer is made of GaN and the buffer layer is made of InGaN,
The present invention can be immediately practiced using conventional growth conditions.

Further, by providing the buffer layer with a role as a Bragg reflector, a highly efficient light emitting device can be realized.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is to deposit a gallium nitride based semiconductor buffer layer containing indium on a silicon substrate via a low temperature growth buffer layer, thereby forming a high quality gallium nitride based semiconductor layer thereon. It is intended to grow thickly.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic view showing a cross-sectional structure illustrating a gallium nitride based semiconductor device according to the present invention. That is, in the semiconductor device 10 shown in the figure, the first buffer layer 12, the second buffer layer 13, the buffer layer 14, and the gallium nitride based semiconductor layer 15 are deposited in this order on the silicon substrate 11.

Here, as the silicon substrate 11, (1
11) A substrate can be used. On a (111) silicon substrate, a gallium nitride-based semiconductor having a (0001) plane on its surface is usually epitaxially grown. The first buffer layer 12 has a role of alleviating a difference in lattice constant between the silicon substrate 11 and the gallium nitride based semiconductor. The material can be, for example, GaN and is required to grow at relatively low temperatures, as will be discussed in more detail below. The second buffer layer has a role of flattening the growth surface and is a buffer layer grown at a relatively high temperature. The material can be, for example, GaN, and the film thickness is 500 to 1000.
It is desirable to set to nm. If it is thinner than this, the growth surface is not sufficiently flattened, and if it is thicker than this, cracks may occur in the growth layer.

When a gallium nitride based semiconductor is epitaxially grown by MOCVD (Metal Organic Chemical Vapor Deposition) method, the first buffer layer and the second buffer layer described above are usually provided. This is because by providing these buffer layers, the quality of the gallium nitride based semiconductor layer formed thereon can be improved. However, in the present invention, these buffer layers may be provided if necessary, and may not be provided in some cases. That is, when the buffer layer 14 can be directly grown on the silicon substrate 11 depending on the growth conditions and the growth method, the first buffer layer 12 and the second buffer layer 12 are formed.
The buffer layer 13 can be omitted. Buffer layer 14
Has a role of relieving stress caused by the difference in coefficient of thermal expansion between the silicon substrate 11 and the gallium nitride based semiconductor layer 15. As the material, it is desirable to use a gallium nitride-based semiconductor containing indium, and the film thickness is desirably one atomic layer or more. The gallium nitride based semiconductor layer 15 is a layer corresponding to various element constituent parts such as an LED and a laser. That is, although shown as a single layer in FIG. 1, this layer 15 may have any laminated structure composed of a plurality of gallium nitride based semiconductor layers having different compositions.

According to the present invention, since the buffer layer 14 relaxes the stress caused by the difference in the coefficient of thermal expansion, the substrate warps even when the gallium nitride based semiconductor layer 15 is grown to a thickness of 1 micron or more. In addition, a high-quality gallium nitride based semiconductor layer 15 can be stably grown without cracks or cracks. As described above, the reason why the buffer layer 14 relieves the stress is considered to be that the buffer layer 14 contains indium, and as a result, the crystal becomes “soft”. That is, it is considered that the "soft" buffer layer absorbs the stress generated between the silicon substrate and the gallium nitride-based semiconductor layer to prevent the warp of the wafer and the crack of the growth layer.

According to the experiments conducted by the present inventor, it was observed that the higher the indium composition of the buffer layer 14, the more remarkable the stress relaxation effect. Generally, when growing by MOCVD (Metal Organic Chemical Vapor Deposition) method, for example, In _x G
As the indium composition x in the a _1-x N layer, x = 0 to
It can grow relatively easily up to a range of about 0.15. However, even when a crystal having a composition within this range is also used as the buffer layer 14, no crack is observed and a gallium nitride based semiconductor layer 15 having extremely high electrical and optical characteristics is obtained. I was able to. When the indium composition is higher than this, the effect of relieving stress is considered to be further improved.

According to the present invention, since a high-quality gallium nitride based semiconductor layer can be stably grown on a silicon substrate in this manner, the device fabrication process for processing the substrate is much easier than before. become. That is, compared to the sapphire substrate that has been conventionally used, the silicon substrate is
Processing such as etching and cleavage is extremely easy. Therefore, various semiconductor elements including a semiconductor laser can be easily realized.

Further, according to the present invention, the gallium nitride based semiconductor element formed on the silicon substrate can be formed monolithically with other electronic elements and light emitting elements formed on the same substrate. In this way, a small-sized and high-performance semiconductor device can be manufactured.

Further, according to the present invention, it becomes possible to form a gallium nitride based semiconductor element on a large-diameter substrate, and the manufacturing cost can be reduced. That is, the sapphire substrate that has been conventionally used has at most 2
Although it has an inch diameter, a silicon substrate having a large diameter of 8 inches or more can be easily obtained. Therefore, the manufacturing cost can be significantly reduced.

Furthermore, according to the present invention, an inexpensive silicon substrate can be used and the raw material cost can be reduced.

Next, a method of manufacturing the semiconductor device shown in FIG. 1 will be described.

First, for example, the silicon substrate 11 is introduced into a growth chamber of an MOCVD apparatus, and while flowing hydrogen gas, the substrate 11 is heated at about 1100 ° C. for about 10 minutes to remove oxides formed on the surface of the substrate. .

Next, the substrate temperature is cooled to 550 ° C., and trimethyl gallium (TMG), ammonia, and hydrogen gas which is a carrier gas are flowed to the first buffer layer 12.
As a GaN layer is grown. The GaN layer grown in this way is polycrystalline.

Next, the substrate temperature is heated to 1100 ° C.,
TMG, ammonia, and a hydrogen carrier gas are flown to form a second buffer layer 13 with a thickness of about 700 nm.
Grow an aN layer. Here, when the substrate temperature is raised to 1100 ° C., the polycrystal first buffer layer 12 is recrystallized to become a single crystal film, but its surface state is not sufficiently flat. However, by growing the second buffer layer at a high temperature, the growth surface can be flattened.

Next, the substrate temperature is cooled to 800 ° C., and T
MG, trimethyl indium (TMI), ammonia and a nitrogen carrier gas are passed to grow an InGaN layer having a thickness of about 100 nm as the buffer layer 14. Here, the substrate temperature is lowered to 800 ° C. because the equilibrium vapor pressure of the crystal containing indium is relatively high and the crystal is easily decomposed.

Next, the substrate temperature is raised to a predetermined temperature,
The gallium nitride based semiconductor layer 15 having a predetermined layer structure is grown. Here, as an example, the substrate temperature is set to about 1100.
C. and flowing TMG, ammonia and hydrogen carrier gas to grow a GaN layer about 4 microns thick.
Finally, the semiconductor device shown in FIG. 1 can be obtained by cooling to room temperature.

The inventor of the present invention made a prototype of a semiconductor device grown by the above-described method and a semiconductor device having no buffer layer 14 for comparison. As a result, in the semiconductor element having no buffer layer 14, the surface was clouded even by visual observation, and many cracks were observed. However, in the semiconductor device provided with the buffer layer 14 according to the present invention, no cracks are observed even under a microscope, and the gallium nitride based semiconductor layer 1 is not observed.
It was found that the various electrical and optical characteristics of No. 5 were comparable to those of those grown on the sapphire substrate.

Next, a specific example of the gallium nitride based semiconductor device according to the present invention will be described.

FIG. 2 is a schematic view showing a cross-sectional structure of a gallium nitride based semiconductor LED according to the present invention. That is, the LED 20 shown in the figure has the first buffer layer 22, the second buffer layer 23, the buffer layer 24, the
n-type contact layer 25, n-type cladding layer 26, light emitting layer 2
7, a p-type clad layer 28 and a p-type contact layer 29 are sequentially laminated.

The first buffer layer 22 can be, for example, the GaN layer grown at a relatively low temperature as described above. The second buffer layer 23 can be, for example, the GaN layer grown at a relatively high temperature as described above. The film thickness is 500 nm or more and 1000 n
It is desirable that it is m or less. Note that, as described above with reference to FIG. 1, in some cases, these first and second
The buffer layer can be omitted.

[0034] As the buffer layer 24, using an inclusive gallium nitride semiconductor indium, for example, an In _x described above
A Ga _1-x N layer can be used. The film thickness may be several atomic layers or more, and may be 100 nm, for example.

The n-type contact layer 25 is a layer for ensuring an n-side electrode contact, and can be, for example, an n-type GaN layer.

The n-type cladding layer 26 is a layer for confining light and injected carriers in the light emitting layer 27.
It can be an n-type GaAlN layer.

The light emitting layer 27 is a layer that recombines the injected carriers to generate light, and is, for example, undoped In.
It can be a GaN layer.

The p-type clad layer 28 is a layer for confining light and injected carriers in the light emitting layer 27.
It may be a p-type GaAlN layer.

The p-type contact layer 29 is a layer for ensuring a p-side electrode contact, and can be, for example, a p-type GaN layer.

A part of the laminated structure described above is etched from the surface to the n-type contact layer 25, and the n-side electrode 30 is provided. In addition, the p-type contact layer 29
A p-side electrode 31 having a light-transmitting property is provided on. Further, a bonding pad 32 is connected to each electrode, and the surface of the light emitting element is covered with protective films 36 and 38.

Conventionally, when such a laminated structure was formed on a silicon substrate, cracks were generated and it was impossible to produce an LED. However, according to the invention,
By providing the buffer layer 24, cracks do not occur at all, and an LED having good characteristics can be manufactured. That is, according to the result of the trial production by the present inventor, L of FIG.
The ED had an emission peak wavelength of 450 nm, and could obtain a brightness of 2 candela due to the lens shape having directivity of 8 °.

Next, another specific example of the gallium nitride based semiconductor device according to the present invention will be described.

FIG. 3 is a schematic view showing a cross-sectional structure of the second gallium nitride based semiconductor LED according to the present invention. That is, the LED 20A shown in the figure has a first buffer layer 22, a second buffer layer 23, a buffer layer 24A, an n-type contact layer 25, and an n-type cladding layer 2 on a silicon substrate 21.
6, the light emitting layer 27, the p-type cladding layer 28, and the p-type contact layer 29 are sequentially stacked. Regarding the respective layers in FIG. 3, the same layers as those described above in FIG. 2 are denoted by the same reference numerals in the figure and the description thereof will be omitted.

Here, the LED 20A is the above-mentioned LED 2
The difference from 0 is that the buffer layer 24A constitutes a Bragg reflector made of a multilayer film. That is, the buffer layer 2
4A can have a structure in which two types of thin film layers having different refractive indexes are alternately laminated. In this case, it is desirable that the two types of thin film layers be selected so that the difference between the respective refractive indices n is as large as possible. The thickness of each thin film layer is 1 / (4
n) is desirable.

As described above, when the structure of the Bragg reflector is adopted as the buffer layer 24A, the effect as the distributed feedback reflector can be obtained in addition to the above-mentioned effect as the buffer layer. That is, the light from the light emitting layer 26 is reflected upward with a high reflectance, and the light extraction efficiency can be significantly improved.

According to the results of trial production by the present inventor, MOCVD
As a result of forming an LED by forming a buffer layer 24A as a laminated structure of an InGaN layer and a GaN layer at a growth temperature of 800 ° C. by the method, 1.9 as compared with the LED 20 shown in FIG.
Double brightness was obtained.

Although the embodiments of the present invention have been described with reference to specific examples, the present invention is not limited to these. In addition to this, for example, according to the present invention, it becomes possible to grow a high-quality gallium nitride based semiconductor layer using various materials other than silicon as a substrate. For example, the conventionally used sapphire (Al ₂ O
By applying the present invention to ₃ ), it is possible to obtain a gallium nitride based semiconductor layer of higher quality than ever before. In addition, it becomes possible to epitaxially grow a high-quality gallium nitride based semiconductor layer using a substrate made of spinel (MgAl ₂ O ₄ ), 6H-type SiC, GaP, GaAs or the like.

The buffer layer in the present invention is InGa.
It is not limited to the N layer. Besides this, for example,
A compound containing In, such as InGaP, InBN, InAlAs, etc., in which any one of Al, Ga, and B as a group III element and any one of N, P, As, and Sb as a group V element is combined. , Can be used similarly.

Further, although the LED has been described as an example in FIGS. 2 and 3, the present invention can be similarly applied to a semiconductor laser using a gallium nitride based semiconductor. In addition, various modifications can be made without departing from the scope of the present invention.

[0050]

The present invention is carried out in the form as described above and has the following effects.

According to the present invention, since the buffer layer relaxes the stress caused by the difference in the coefficient of thermal expansion, the substrate warps even when the gallium nitride based semiconductor layer is grown to a thickness of 1 micron or more. It is possible to stably grow a high-quality gallium nitride based semiconductor layer without causing cracks or cracks.

Further, according to the present invention, since a high-quality gallium nitride based semiconductor layer can be stably grown on a silicon substrate as described above, the device fabrication process for processing the substrate is far more difficult than the conventional one. To be easier. That is, compared with the sapphire substrate used conventionally, the silicon substrate is extremely easy to process such as etching and cleavage. Therefore, various semiconductor elements including a semiconductor laser can be easily realized.

Further, according to the present invention, the gallium nitride based semiconductor element formed on the silicon substrate can be formed monolithically with other electronic elements and light emitting elements formed on the same substrate. In this way, a small-sized and high-performance semiconductor device can be manufactured.

Further, according to the present invention, it becomes possible to form a gallium nitride based semiconductor element on a large-diameter substrate, and the manufacturing cost can be reduced. That is, the sapphire substrate that has been conventionally used has at most 2
Although it has an inch diameter, a silicon substrate having a large diameter of 8 inches or more can be easily obtained. Therefore, the manufacturing cost can be significantly reduced.

Further, according to the present invention, an inexpensive silicon substrate can be used and the raw material cost can be reduced.

Further, according to the present invention, by adopting the structure of the Bragg reflector as the buffer layer, in addition to the above-mentioned effect as the buffer layer, the light from the light emitting layer is reflected with high reflectance, The light extraction efficiency of the light emitting element can be remarkably improved.

As described above, according to the present invention, it becomes possible to stably grow a high-quality gallium nitride based semiconductor layer on various substrates such as silicon, which is a great industrial advantage. .

[Brief description of drawings]

FIG. 1 is a schematic view showing a cross-sectional structure illustrating a gallium nitride based semiconductor device according to the present invention.

FIG. 2 is a schematic view showing a cross-sectional structure of a gallium nitride based semiconductor LED according to the present invention.

FIG. 3 is a second gallium nitride based semiconductor LE according to the present invention.
It is the schematic showing the cross-section of D.

FIG. 4 is a schematic diagram showing a cross-sectional structure of a gallium nitride based semiconductor device using a conventional silicon substrate.

[Explanation of symbols]

10,100 Gallium nitride semiconductor device 11,110 Silicon substrate 12 First buffer layer 13 Second buffer layer 14 Buffer layer 15 Gallium Nitride Semiconductor Layer 20, 20A LED 21 Silicon substrate 22 First buffer layer 23 Second buffer layer 24, 24A buffer layer 25 n-type contact layer 26 n-type clad layer 27 Light-emitting layer 28 p-type clad layer 29 p-type contact layer 30 n side electrode 31 p-side electrode 36, 38 Protective film

Continuation of the front page (56) Reference JP-A-10-303458 (JP, A) JP-A-10-214999 (JP, A) JP-A-10-150245 (JP, A) JP-A-9-148678 (JP , A) JP 9-36430 (JP, A) JP 8-228048 (JP, A) JP 8-116092 (JP, A) JP 8-97469 (JP, A) JP 8-70139 (JP, A) JP-A-8-56015 (JP, A) JP-A-8-18159 (JP, A) JP-A-7-249795 (JP, A) JP-A-6-164055 (JP, A) A) JP-A-5-206513 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 33/00 H01S 5/00-5/50 H01L 21/205

Claims (6)

(57) [Claims] 1. A silicon substrate, which is formed on the silicon substrate via a low temperature growth buffer layer and has a film thickness of 500 n.
a second buffer layer made of a single crystal gallium nitride-based semiconductor of m or more and 1000 nm or less, a buffer layer made of a gallium nitride-based semiconductor containing indium and formed on the second buffer layer, A gallium nitride-based semiconductor device, comprising: a gallium nitride-based semiconductor layer laminated on the above. 2. The buffer layer relieves stress caused by a difference in thermal expansion coefficient between the silicon substrate and the gallium nitride based semiconductor layer. 1. The semiconductor device according to 1. 3. The semiconductor device according to claim 1, wherein the silicon substrate is a (111) silicon substrate. 4. The semiconductor device according to claim 2, wherein the second buffer layer is made of GaN, and the buffer layer is made of InGaN. 5. The buffer layer comprises Ga _x Al _1-x N (0.
And ≦ x ≦ 1) _{layer, In y Ga z Al 1-} y-z N (0 <
y ≦ 1, 0 ≦ z ≦ 1, y + z ≦ 1) layers are alternately laminated to form a Bragg reflector, and the semiconductor according to any one of 1 to 3 is characterized in that element. 6. A step of forming a polycrystalline low temperature growth buffer layer on a silicon substrate, and a film thickness of 500 nm or more at a growth temperature higher than the growth temperature of the low temperature growth buffer layer on the low temperature growth buffer layer. Forming a second buffer layer made of a single crystal gallium nitride-based semiconductor of 1000 nm or less; growing a buffer layer made of a gallium nitride-based semiconductor containing indium on the second buffer layer; And a step of growing a gallium nitride-based semiconductor layer on the buffer layer.