JP2003101157A - Semiconductor device and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor device using a nitride semiconductor which comprises a thin and flat buffer layer while providing an active layer with less dislocation density. SOLUTION: A first Mg-doped GaN buffer layer 11 is formed as a highly dense layer of growth nucleus of truncated six-sided pyramid crystals having a density of about 10<6> /cm<2> , on a sapphire substrate 10. On the GaN buffer layer 11, a second single crystal GaN buffer layer 12 of Mg-doped is formed by an MOCVD method.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a nitrogen-containing compound III.
The present invention relates to a semiconductor device including a group V compound semiconductor and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, a light emitting device and a semiconductor laser using a III-V group compound semiconductor containing nitrogen (hereinafter, simply referred to as a nitride semiconductor) have been actively developed. The nitride semiconductor laser can theoretically oscillate in a wide wavelength range from ultraviolet to visible region. Especially in the 400 nm band, the reliability of several thousand hours or more has been confirmed, and it is considered to be promising for optical disk system applications and the like. In addition, nitride semiconductors are excellent materials that do not contain harmful substances such as arsenic,
It is an essential semiconductor material for the near future such as optical information systems and solid-state lighting.

In order to form a light emitting device or a semiconductor laser having a laminated structure of nitride semiconductors, it was necessary to epitaxially grow a semiconductor layer (buffer layer) as an underlying layer in two steps. For example, a low-temperature grown GaN buffer layer with a film thickness of 0.02 μm is formed on a single crystal sapphire substrate at about 500 ° C., then the temperature is raised to 1020 ° C., and a high-temperature grown GaN layer buffer layer is grown about 4 μm (special feature). See the specification of Kaihei 4-297023).

The growth mechanism of the GaN buffer layer by such a two-step growth is explained as follows. The low-temperature grown GaN buffer layer is not a single crystal, but the surface of the low-temperature grown GaN buffer layer is 10 ¹⁰ cm ⁻³ during the process of raising the temperature to 1020 ° C.
Some degree of c-axis oriented growth nuclei are formed. Then, in the process of thickening the high-temperature grown GaN buffer layer, the growth nuclei coalesce into three-dimensional crystal growth, resulting in the formation of a single-crystal, substantially flat GaN layer.

However, since the sapphire substrate and the GaN crystal have different lattice constants of about 14%, dislocations of about 10 ¹⁰ / cm ² exist in the low temperature grown GaN buffer layer formed at 500 ° C. Growth Ga formed in
Dislocations of 10 ⁸ / cm ² or more also exist in the N layer buffer layer. Therefore, when a semiconductor laser is formed on the buffer layer, dislocations of about 10 ⁴ / cm ² also penetrate into the active layer, which causes a problem of current deterioration.

On the other hand, as a method of improving the crystallinity of the GaN semiconductor layer by the epitaxial method, ELO (Epitaxia
L lateral overgrowth) selective growth method has been developed. This is a method of forming a SiO ₂ stripe mask on a substrate and growing a GaN crystal. In this method, the GaN layer grows selectively only in the opening of the stripe mask, but when the film thickness increases, it grows laterally on the stripe mask in a lateral direction, and merges with the growth layer from the adjacent opening to grow thicker. To make Ga almost flat
An N layer can be obtained. Thus, by utilizing the lateral crystal growth on the stripe mask, it is possible to suppress threading dislocations to the upper part of the buffer layer.

However, this method has a problem in that vacancy is formed between the GaN layers that are united on the SiO ₂ mask, which makes the fragile. Further, in order to flatten the upper surface of the GaN layer, a thick film of 10 μm or more is required. As a result, there is a problem that the wafer warps in the order of several tens of μm due to thermal stress with the sapphire substrate when returning to room temperature after crystal growth.

[0008]

As described above, in the conventional nitride semiconductor device, the dislocation density is high, which causes deterioration in current flow, and is thus unreliable. Further, a thickness of at least 2 μm or more is required to obtain a flat nitride semiconductor layer. When the selective growth method is used to reduce the dislocation density, it is necessary to obtain a flat nitride semiconductor layer by 10
Since the thickness of μm or more is required, the wafer warp becomes remarkable. This hinders the lithographic process and the like and causes the yield to deteriorate.

The present invention provides a semiconductor device using a nitride semiconductor, which has a thin buffer layer capable of achieving flatness and can obtain an active layer having a low dislocation density, and a manufacturing method thereof. Has an aim.

[0010]

A semiconductor device according to the present invention comprises a substrate and a Mg-containing polycrystalline or amorphous state of nitrogen formed on the substrate.
A first buffer layer made of a group V compound semiconductor, and a second buffer layer formed on the first buffer layer and made of a III-V group compound semiconductor containing Mg-added single crystal nitrogen. , And an active layer formed on the second buffer layer.

A method of manufacturing a semiconductor device according to the present invention is
A first III-V group compound semiconductor containing nitrogen in a polycrystalline or amorphous state to which Mg is added on a substrate.
And a step of forming a buffer layer of Mg-added single crystal nitrogen III-V on the first buffer layer by metalorganic vapor phase epitaxy or molecular beam epitaxy.
The method is characterized by including a step of forming a second buffer layer made of a group compound semiconductor, and a step of forming an active layer on the second buffer layer.

When the substrate is a single crystal substrate, the first buffer layer is preferably formed by metalorganic vapor phase epitaxy, and when the substrate is an amorphous substrate, the first buffer layer is formed. The layer may be formed by either a plasma chemical deposition method or a sputtering method. Further, a step of forming an insulating film mask having a fine window can be provided on the first buffer layer.

In the present invention, the "active layer" refers to a layer forming an active element such as a light emitting diode, a semiconductor laser and a field effect transistor, and includes a case where a passive element such as a capacitor is partially formed.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. [First Embodiment] FIG. 1 is a sectional view of a nitride semiconductor device according to a first embodiment of the present invention. On the single crystal sapphire substrate 10, Mg-doped polycrystalline first Ga
An N buffer layer 11 (film thickness 0.04 μm) is formed, and Mg-doped single crystal second GaN is formed on the N buffer layer 11.
A buffer layer 12 (film thickness 1 μm) is formed. Ga
On the N buffer layer 12, an undoped GaN layer 13 (film thickness 1 μm) is formed as a pseudo active layer.

The detailed manufacturing process of this embodiment will be described below. First, a metal-organic vapor phase epitaxy apparatus (hereinafter, MOC
A clean 2 ″ φ sapphire substrate 10 having a (0001) plane is installed in a reaction furnace of a VD apparatus). Then, the inside of the reaction furnace is replaced with hydrogen, and the temperature of the sapphire substrate 10 is raised to 1200 ° C. for 10 minutes. Heat treatment of 50. After this, 50
The temperature was lowered to 0 ° C., a mixed gas of hydrogen and nitrogen serving as a carrier gas was supplied together with 5 l / min of ammonia gas serving as an N raw material, and then TMGa was formed for forming a buffer layer.
40 μmol / min of (trimethylgallium) and 0.45 μmol / min of Cp2Mg (biscyclopentadienylmagnesium), which is a Mg raw material, were supplied for 2 minutes to supply the polycrystalline Mg-doped GaN buffer layer 11 (film thickness 0.04 μm).
m) grow.

Then, only the supply of TMGa and CP2Mg is stopped, and the temperature is raised to 1080 ° C. over 10 to 15 minutes. Then, TMGa (trimethylgallium) is added to 120 μmo
l / min, Cp2Mg (biscyclopentadienylmagnesium) is supplied at 0.45 μmol / min for 20 minutes to grow the single crystal Mg-doped GaN buffer layer 12 to 1 μm. After that, the supply of Cp2Mg is stopped and the crystal growth is continued to grow the undoped GaN layer 13 to 1 μm.

The undoped GaN layer 13 obtained according to this embodiment had a surface dislocation density of 2 × 10 ⁴ / cm ² . Further, from room temperature photoluminescence evaluation, band edge emission was sharp and emission from a deep level was suppressed to 1/100 or less. Further, according to an atomic force microscope observation, the surface roughness was 10 nm or less, and the half width of the X-ray rocking curve was 190 seconds.

The reason why excellent crystallinity with a small dislocation density is obtained by this embodiment is as follows. First, the polycrystalline GaN buffer layer 11 grown at a low temperature of 500 ° C. is formed as a layer in which c-axis oriented growth nuclei having hexagonal pyramid-shaped facets with a flat surface are uniformly arranged on the substrate surface. At this time, the areal density of the growth nuclei affects the dislocation density and the growth rate of the next buffer layer. If the density is too high, dislocations will enter the next buffer layer. On the contrary, if the density is low, dislocations will be less generated but the growth rate will not be obtained. Taking these into consideration, the areal density of the growth nuclei is preferably set to about 10 ⁴ to 10 ⁸ / cm ² .

The layer of growth nuclei formed with such a density determines the dislocation density of the crystal layer which is subsequently grown at a high temperature,
It is possible to realize a dislocation density lower than that of the conventional one. That is, the GaN buffer layer 12 grown at a high temperature of 1080 ° C.
In the growth, the crystal grows in the horizontal direction rather than the vertical direction with respect to the substrate with the low-temperature grown GaN buffer layer 11 as a nucleus. That is, dislocation penetration to the upper part is suppressed by the same mechanism as in the conventional selective growth method. But S
Unlike the selective growth method using an iO ₂ stripe mask,
Since the denser layer of smaller growth nuclei serves as the growth nuclei of the second buffer layer, a flat single crystal GaN buffer layer can be obtained without requiring the second buffer layer to have a conventional thickness. . However, in order to obtain a single crystal buffer layer with fewer dislocations even if the growth rate of the second buffer layer is sacrificed, the areal density of growth nuclei may be 10 ⁴ / cm ² or less.

In this embodiment, addition of a large amount of Mg to the first and second GaN buffer layers 11 has an important meaning for the formation of growth nuclei having hexagonal truncated pyramid facets. The Mg concentration taken into these GaN buffer layers 11 is preferably 10 ¹⁸ / cm ³ or more, more preferably 10 ¹⁹ / cm ³ or more, and further preferably 1 × 10 ²⁰ / cm ³ or more. . M
When the g concentration is less than 10 ¹⁸ / cm ³ , a hexagonal truncated pyramid facet cannot be obtained. As described above, by adding a large amount of Mg, even at low temperature growth of 500 ° C.,
A regular growth nucleus structure called a hexagonal pyramid trapezoid having {1-101} facets is obtained. That is, compared with the irregular-shaped growth nuclei observed in the conventional low-temperature-grown GaN buffer layer and the smoothing due to the island-like crystals and the lateral growth that are subsequently grown, dislocations are generated by single-crystal growth of about half the thickness. A flat single-crystal GaN layer with less amount of impurities can be obtained. Therefore, without using a method of intentionally forming a pattern and performing selective growth,
Dislocation density can be suppressed with a thin film. As a result, a nitride semiconductor device in which wafer warpage, cracks, and residual strain are suppressed can be obtained.

The thickness of the first GaN buffer layer 11 is preferably 0.1 in order to reduce the total buffer layer thickness.
μm or less. As described above, in the first GaN buffer layer 11, hexagonal pyramidal trapezoidal growth nuclei may be arranged with an areal density of about 10 ⁶ / cm ² , and with a minimum film thickness that satisfies such a condition, The second GaN buffer layer 12 can be formed to a flatness of 1 μm or less and a sufficiently low dislocation density.

Further, in this embodiment, it is desirable that the Mg-doped GaN buffer layer 11 made of polycrystal has a hydrogen bond. By including hydrogen, hydrogen and nitrogen are bonded even when an irregular surface other than the {1-101} facets is exposed, and as a result, Ga of the irregular surface is formed.
For N, thermal etching occurs during the temperature rising process for single crystal growth, and as a result, stable {1-101}
Only facets are the growth nucleus.

Instead of the single crystal sapphire substrate,
Other single crystal substrates, such as SiC, Si, and GaN substrates, can also be used. Further, although the MOCVD method is used for the film growth, the same result can be obtained by using the molecular beam epitaxy (MBE) method.

[Second Embodiment] FIG. 2 is a sectional view of a nitride semiconductor device according to a second embodiment of the present invention. In this embodiment, an amorphous quartz glass substrate 20 is used as the substrate. An amorphous or polycrystalline Mg-doped first GaN layer buffer layer 21 (film thickness 0.04 μm) is formed on the substrate 20, and further Mg-doped single crystal second layer is formed thereon. A GaN buffer layer 22 (film thickness 1 μm) is formed. An undoped Ga layer is formed on the GaN buffer layer 22 as a pseudo active layer.
An N layer 23 (film thickness 1 μm) is formed.

In this embodiment, the first Mg-doped GaN layer buffer layer 21 is formed by the plasma CVD method or the sputtering method. Thereby, Mg-doped GaN
The layer 21 is deposited in an amorphous state, but due to the effect of the addition of Mg, thermal etching occurs during the temperature rising process for single crystal growth and becomes a dense layer of growth nuclei in which {1-101} facets appear.

After that, Mg is formed in the same manner as in the first embodiment.
-Doped second single crystal GaN layer buffer layer 22
And further grow undoped Ga as a pseudo active layer.
The N layer 23 is grown. The undoped GaN layer 23 had a dislocation density higher than that of the first embodiment by about one digit, but a flat crystal film was obtained, which was sufficient for forming a light emitting device.

[Third Embodiment] FIG. 3 is a sectional view of a nitride semiconductor device according to a third embodiment. This is based on the second embodiment of FIG. 2 and is based on the first GaN buffer layer 2
1 is formed on the first GaN buffer layer 21, SiO 2 is formed.
_{2 The} difference is that the mask 24 is formed. Other than that,
This is the same as the second embodiment.

The mask 24 is patterned so that fine stripe-shaped windows or dot-shaped windows are formed. As a result, the GaN buffer layer 21 exposed in the window of the mask 24 may have a thickness of {1-10 in the temperature rising process for the next crystal growth.
1} Growth nuclei in which facets appear are formed. As a result, similarly to the second embodiment, the second GaN buffer layer 22 becomes a flat single crystal layer having a small dislocation density even if it is as thin as about 1 μm. Dislocations in the undoped GaN layer 23 are formed in a state of being concentrated in a region not covered with the mask 24, but the crystal film has excellent flatness.

[Embodiment 4] FIG. 4 illustrates the present invention.
This is an embodiment applied to a semiconductor laser. here
Is the sapphire substrate 11 according to the process of the first embodiment.
And the first and second Mg-doped GaN buffer layers 11 and
And 12 are formed. Single crystal GaN buffer layer 12
An n-type GaN contact layer (5 × 10¹⁸/ Cm³of
Si-doped, 2 μm), n-type Al_0.14Ga_0.86N crack
Layer (5 × 10¹⁸/ Cm³Si doped, 1.4 μm)
44, n-type GaN optical waveguide layer (5 × 10¹⁸/ Cm³Si
Doped, 0.1 μm) 45a, InGaN multiple quantum well
Layers (3 nm, 3 layers of In_0.11Ga _0.89N well layer, 6n
In of m_0.02Ga_0.98N barrier layer) 46, p-type GaN optical
Wave layer (2 x 10¹⁷/ Cm³Mg-doped, 0.1 μm)
45a, p-type Al_0.14Ga_{0 .86}N / GaN clad layer
(2 x 10¹⁷/ Cm³Mg-doped, 0.7 μm) 47
And p-type GaN contact layer (2 × 10¹⁸/ Cm³M
g-doped, 0.1 μm) 48 is sequentially grown to form S
CH-MQW (Separate Confinement Heterostructure)
-Multi Quantum Well) Active area is configured.

The SCH-MQW active region has a width of 0.2 μm.
Patterned to a degree of ridge waveguide structure. The element surface and side surfaces are covered with the SiO ₂ film 51. A p-side electrode 49 made of Pt / Ti / Pt / Au is formed on the p-type contact layer 48, and Ti /
An n-side electrode 50 made of Pt / Au is formed. Although not shown in the figure, ZrO ₂ (4
A reflection film is formed by laminating multiple layers of (1/4 wavelength thickness) / SiO ₂ (1/4 wavelength thickness).

It has been confirmed that the semiconductor laser according to this embodiment continuously oscillates at room temperature at a threshold current of 10 mA and an operating voltage of 4.4 V, and continuously up to 100 ° C. Further, it was confirmed that the operation was performed for 8,000 hours under the conditions of 50 ° C. and 30 mW. In the semiconductor laser according to this embodiment, since the buffer layer can be made thin, the total film thickness becomes thin, and the thermal stress applied to the element can be reduced. This reduction in stress also leads to an improvement in chip yield. Moreover, high reliability was confirmed by the reduction of the transition density.

[0032] In the above respective embodiments, as the first and second buffer layer, GaN is used layer, more generally, as the first and second buffer layer, an In _x Al _y G
It is possible to use a nitride semiconductor a _{1- xy} N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, x + y ≦ 1). That is, any material system may be used as long as a hexagonal pyramid trapezoidal crystal composed of {1-101} facets is formed as a buffer by adding a large amount of Mg.

[0033]

As described above, according to the present invention, the buffer layer of a semiconductor device using a nitride semiconductor can be formed in a thin state with a low dislocation density.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of a semiconductor device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a structure of a semiconductor device according to another embodiment.

FIG. 3 is a diagram showing a structure of a semiconductor device according to another embodiment.

FIG. 4 is a diagram showing a structure of a semiconductor device according to another embodiment.

[Explanation of symbols]

10 ... Single crystal sapphire substrate, 11 ... 1st GaN buffer layer, 12 ... 2nd GaN buffer layer, 13 ... Undoped GaN layer, 20 ... Quartz glass substrate, 21 ... 1st G
aN buffer layer, 22 ... Second GaN buffer layer, 23
... undoped GaN buffer layer, 24 ... SiO ₂ mask, 43 ... n-type GaN contact layer, 44 ... n-type AlG
aN clad layer, 45a, 45b ... InGaN optical waveguide layer, 46 ... InGaN multiple quantum well layer, 47 ... P-type Al
GaN clad layer, 48 ... P-type GaN contact layer, 4
9 ... p-side electrode, 50 ... n-side electrode, 51 ... SiO ₂ film.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoshiyuki Harada             1st Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa             Inside the Toshiba Research and Development Center F-term (reference) 5F041 CA40 CA65                 5F073 AA13 AA45 AA74 CA07 CB07                       CB22

Claims (8)

[Claims] 1. A substrate, a first buffer layer formed on the substrate and made of a III-V group compound semiconductor containing Mg-doped polycrystalline or amorphous nitrogen, and the first buffer layer. A second buffer layer formed of a III-V group compound semiconductor containing single crystal nitrogen to which Mg is added, and an active layer formed on the second buffer layer. A semiconductor device characterized by the above. 2. The semiconductor device according to claim 1, wherein the first buffer layer is a dense layer of hexagonal pyramidal trapezoidal growth nuclei formed containing hydrogen. 3. The semiconductor according to claim 2, wherein the first buffer layer is a layer in which growth nuclei of hexagonal pyramidal crystals are arranged at an areal density of 10 ⁴ to 10 ⁸ / cm ^2. apparatus. 4. The Mg concentration of the first and second buffer layers
10 degrees¹⁸/ Cm ³Claims characterized by the above
Item 4. The semiconductor device according to any one of Items 1 to 3. 5. A step of forming a first buffer layer made of a III-V compound semiconductor containing nitrogen in a polycrystalline or amorphous state, to which Mg is added, on the substrate, and on the first buffer layer. Forming a second buffer layer composed of a Mg-added single crystal nitrogen-containing III-V group compound semiconductor by metalorganic vapor phase epitaxy or molecular beam epitaxy, and the second buffer layer And a step of forming an active layer thereon, the method of manufacturing a semiconductor device. 6. The method for manufacturing a semiconductor device according to claim 5, wherein the first buffer layer is formed as a dense layer of hexagonal pyramid trapezoidal crystal growth nuclei containing hydrogen. 7. The semiconductor according to claim 6, wherein the first buffer layer is formed as a layer in which hexagonal pyramidal trapezoidal crystal growth nuclei are densely packed at an areal density of 10 ⁴ to 10 ⁸ / cm ^2. Device manufacturing method. 8. The first and second buffer layers are 10
8. The method of manufacturing a semiconductor device according to claim 5, wherein the Mg concentration is ¹⁸ / cm ³ or more.