JP2015151291A - Nitride semiconductor free-standing substrate, method for manufacturing the same and semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a nitride semiconductor free-standing substrate capable of preventing cracks from occurring while achieving high resistivity by adding an impurity; a method for manufacturing the same; and a semiconductor device.SOLUTION: A nitride semiconductor free-standing substrate comprises: a first area 104 formed in the lower layer of a nitride semiconductor layer 102 close to a heterogeneous substrate 101; and a second area 105 formed in the upper layer of the nitride semiconductor layer 102 distant from the heterogeneous substrate 101. The diameter is 40 mm or more; the total thickness of the first area 104 and the second area 105 is 200 μm or more; an average dislocation density in the in-plane of the surface of the second area 105 is 1×10cmor more and 1×10cmor less; the electrical resistivity of the second area 105 is 0.02 Ωcm or more; and the electrical resistivity of the first area 104 is lower than that of the second area 105.

Description

  The present invention relates to a nitride semiconductor free-standing substrate, a manufacturing method thereof, and a semiconductor device.

  Nitride semiconductors typified by gallium nitride [GaN], indium gallium nitride [InGaN], and gallium aluminum nitride [GaAlN] have a large band gap and are direct transition type semiconductors. Research on shortening the wavelength of light-emitting elements using nitride semiconductors is underway.

  Furthermore, since the nitride semiconductor has a high electron saturation drift velocity and can use a high mobility two-dimensional electron gas due to a heterojunction, it is expected to be applied to an electronic device.

However, in the nitride semiconductor, the vapor pressure of nitrogen [N ₂ ] is very high, and thus the principle of suppressing the dissociation of group V elements by maintaining the pressure inside the growth furnace at a high pressure. It is extremely difficult to grow from a raw material melt into a bulk crystal using a boat method or a pulling method utilizing the above.

  Therefore, when a nitride semiconductor is manufactured, a vapor phase growth method is mainly used, and a nitride semiconductor such as a sapphire substrate, a silicon [Si] substrate, or a gallium arsenide [GaAs] substrate is used. An epitaxial wafer is manufactured by heteroepitaxially growing a nitride semiconductor layer on the surface of a heterogeneous substrate, and then the heterogeneous substrate is removed by subjecting the epitaxial wafer to a polishing process, an etching process, or a peeling process. By leaving only the layer, a so-called “self-standing substrate” (hereinafter referred to as a nitride semiconductor free-standing substrate) of a nitride semiconductor is obtained (see, for example, Patent Documents 1 to 4).

  In addition, after removing the heterogeneous substrate from the epitaxial wafer, when obtaining only one nitride semiconductor free-standing substrate from the remaining nitride semiconductor layer, or by thickly epitaxially growing the nitride semiconductor layer later, the nitride semiconductor A plurality of nitride semiconductor free-standing substrates may be obtained by slicing the layer (see, for example, Patent Document 5).

  In addition, the obtained nitride semiconductor free-standing substrate is used as a seed crystal, and a nitride semiconductor layer is thickly epitaxially grown on the surface thereof, and a plurality of nitride semiconductor free-standing substrates are formed by slicing the nitride semiconductor layer later. May get.

JP 2002-057119 A Japanese Patent No. 3631724 Japanese Patent No. 3744155 Japanese Patent No. 3788041 JP 2002-029897 A JP 2011-162407 A JP 2009-149483 A

  Unlike a silicon free-standing substrate or a gallium arsenide free-standing substrate, a nitride semiconductor free-standing substrate is generally manufactured using a heterogeneous substrate having a lattice constant different from that of an epitaxially grown layer, and nitrided in the process of heteroepitaxial growth. Since stress such as warpage of the physical semiconductor layer works and residual stress is generated in the crystal, it has a problem that it is very fragile.

  Furthermore, when impurities for increasing the resistance are added to the nitride semiconductor layer, different types of atoms from the atoms constituting the nitride semiconductor layer are added, resulting in mismatch of lattice constants. Then, a strain field is generated around the impurities, the crystal is cured, and cracks are likely to occur in the nitride semiconductor free-standing substrate. In particular, the higher the concentration of the impurity added to the nitride semiconductor layer and the thicker the portion with the higher impurity concentration, the higher the possibility of cracking.

  These characteristics are peculiar to a nitride semiconductor free-standing substrate in which a large residual stress is generated in a crystal by heteroepitaxially growing a nitride semiconductor layer on the surface of a different substrate.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a nitride semiconductor free-standing substrate, a method for manufacturing the same, and a semiconductor device that are less likely to generate cracks while achieving high resistance by addition of impurities.

The present invention created to achieve this object is a nitride semiconductor free-standing substrate manufactured by removing the heterogeneous substrate from an epitaxial wafer formed by heteroepitaxially growing a nitride semiconductor layer on the surface of the heterogeneous substrate. A first region formed in a lower layer of the nitride semiconductor layer close to the dissimilar substrate, and a second region formed in an upper layer of the nitride semiconductor layer far from the dissimilar substrate, and having a diameter of 40 mm or more The total thickness of the first region and the second region is 200 μm or more, and the average dislocation density in the plane of the surface of the second region is 1 × 10 ³ cm ⁻² or more and 1 × 10 ⁸ cm ^−2. Hereinafter, the nitride semiconductor self-supporting substrate has an electric resistivity of the second region of 0.02 Ωcm or more and an electric resistivity of the first region lower than an electric resistivity of the second region.

The second region may be formed of a nitride semiconductor layer to which an impurity including one or more transition metal atoms having a concentration of 1 × 10 ¹⁵ cm ⁻³ or more and 1 × 10 ²⁰ cm ⁻³ or less is added.

The first region may be formed of a nitride semiconductor layer to which the impurity containing one or more transition metal atoms having a concentration of less than 1 × 10 ¹⁵ cm ⁻³ is added.

  The second region may have a thickness of 50 μm or more.

The present invention also provides a nitride semiconductor free-standing substrate manufacturing method for manufacturing a nitride semiconductor free-standing substrate by removing the dissimilar substrate from an epitaxial wafer obtained by heteroepitaxially growing a nitride semiconductor layer on the surface of the dissimilar substrate. When the lower layer of the nitride semiconductor layer close to the dissimilar substrate is the first region and the upper layer of the nitride semiconductor layer far from the dissimilar substrate is the second region, the diameter is 40 mm or more, and the first region The total thickness of the second region is 200 μm or more, the average dislocation density in the plane of the surface of the second region is 1 × 10 ³ cm ⁻² or more and 1 × 10 ⁸ cm ⁻² or less, the second region The growth rate is 200 μm / h or more and the growth temperature is 900 so that the electrical resistivity of the first region is 0.02 Ωcm or more and the electrical resistivity of the first region is lower than the electrical resistivity of the second region. This is a method for manufacturing a nitride semiconductor free-standing substrate in which the second region is epitaxially grown at a temperature of from 1 ° C. to 1100 ° C. and a molar ratio of the Group V material to the Group III material being 6 or less.

  The nitride semiconductor layer may be heteroepitaxially grown using a hydride vapor phase growth method.

  In addition, the present invention is a semiconductor device manufactured using the nitride semiconductor free-standing substrate.

  ADVANTAGE OF THE INVENTION According to this invention, the nitride semiconductor self-supporting board | substrate which is hard to generate | occur | produce a crack, implement | achieving high resistance by addition of an impurity, its manufacturing method, and a semiconductor device can be provided.

It is a figure explaining the manufacturing method of the nitride semiconductor self-supporting substrate concerning an embodiment of the invention.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

  As shown in FIG. 1, the nitride semiconductor free-standing substrate 100 according to the present embodiment is manufactured by removing the heterogeneous substrate 101 from the epitaxial wafer 103 formed by heteroepitaxially growing the nitride semiconductor layer 102 on the surface of the heterogeneous substrate 101. The first region 104 formed in the lower layer of the nitride semiconductor layer 102 close to the dissimilar substrate 101 and the second region 105 formed in the upper layer of the nitride semiconductor layer 102 far from the dissimilar substrate 101. And.

  Here, since the purpose is to grow a nitride semiconductor larger than the boat method or the pulling method, the nitride semiconductor free-standing substrate 100 has a diameter of 40 mm or more, and the first region 104 and the second region 105. Although the case where the nitride semiconductor is gallium nitride will be described on the premise that the total thickness is 200 μm or more, the type of the nitride semiconductor is not particularly limited.

  As a method for obtaining the nitride semiconductor self-supporting substrate 100, a most typical method for manufacturing a nitride semiconductor self-supporting substrate by the void formation peeling method will be described. The void formation peeling method is a method for obtaining the nitride semiconductor free-standing substrate 100 by removing the heterogeneous substrate 101 from the epitaxial wafer 103 formed by heteroepitaxially growing the nitride semiconductor layer 102 on the surface of the heterogeneous substrate 101.

Specifically, first, a dissimilar substrate 101 made of a sapphire substrate is used, and the C surface of the sapphire substrate is used as the surface of the dissimilar substrate 101 and placed inside a metal organic vapor phase epitaxy (MOVPE) furnace. Then, the so-called “undoped” gallium nitride layer 106 to which impurities are not added using trimethylgallium [(CH ₃ ) ₃ Ga] and ammonia [NH ₃ ] as raw materials is grown epitaxially by metal organic vapor phase epitaxy ( FIG. 1 (a)).

Then, after depositing a titanium [Ti] thin film 107 on the surface of the gallium nitride layer 106, heat treatment is performed in an atmosphere of a mixed gas of ammonia gas and hydrogen [H ₂ ] gas by an electric furnace (see FIG. 1B). ).

  As a result, a part of the gallium nitride layer 106 is etched and voids 108 are formed at a high density, whereby the gallium nitride layer 106 is changed to the void-formed gallium nitride layer 109 and the titanium thin film 107 is nitrided to form a sub-layer. By forming the micron minute holes 110 at a high density, the titanium thin film 107 is changed to the hole-formed titanium nitride [TiN] layer 111 (see FIG. 1C).

  This is placed inside a hydride vapor phase epitaxy (HVPE) furnace as a base substrate 112, and heated by using a hydride vapor phase growth method using a mixed gas of hydrogen gas and nitrogen gas as a carrier gas. Hydrogen gas [HCl] gas is supplied to a [Ga] metal boat, and these are reacted to generate gallium chloride [GaCl] gas as a raw material gas. At the same time, ammonia gas is supplied, and the group V raw material of the group III raw material is supplied. The nitride semiconductor layer 102 made of gallium nitride is deposited while adjusting the molar ratio (V / III ratio).

  In this process, the crystal nuclei of gallium nitride grow in a three-dimensional island shape on the surface of the hole-formed titanium nitride layer 111, and then the island-like crystals grow laterally and bond to each other to form a flat surface. As a result, the first region 104 is formed in the lower layer of the nitride semiconductor layer 102 close to the dissimilar substrate 101, and the second region 105 is formed in the upper layer of the nitride semiconductor layer 102 far from the dissimilar substrate 101. Thus, the epitaxial wafer 103 is formed (see FIG. 1D).

  Here, the second region 105 is epitaxially grown at a growth rate of 200 μm / h or more, a growth temperature of 900 ° C. or more and 1100 ° C. or less, and a molar ratio of the group V material to the group III material of 6 or less. The reason for this will be described later.

  In the process of cooling the hydride vapor phase growth furnace, the nitride semiconductor layer 102 is naturally separated from the heterogeneous substrate 101 with the void-formed gallium nitride layer 109 as a boundary to become a gallium nitride free-standing substrate 113 (see FIG. 1E). ).

  Thereafter, the gallium nitride free-standing substrate 113 is taken out from the hydride vapor phase growth furnace and transferred to a polishing apparatus, and the front and back surfaces of the gallium nitride free-standing substrate 113 are polished using a diamond abrasive (see FIG. 1F).

In the nitride semiconductor free-standing substrate 100 obtained in this way, the average dislocation density in the plane of the surface of the second region 105 is 1 × 10 ³ cm ⁻² or more and 1 × 10 ⁸ cm ⁻² or less. .

The reason why the average dislocation density in the surface of the second region 105 is 1 × 10 ³ cm ⁻² or more and 1 × 10 ⁸ cm ⁻² or less is that the average dislocation density in the surface of the second region 105 is in the plane. Is less than 1 × 10 ³ cm ⁻² , the amount of dislocations on the surface of the second region 105 is small, and the residual stress generated in the crystal can be sufficiently relaxed by cross-slip of dislocations or the like. This is because brittle fracture progresses rapidly and cracks are likely to occur.

When the average dislocation density in the surface of the second region 105 exceeds 1 × 10 ⁸ cm ⁻² , the amount of dislocations on the surface of the second region 105 is large, and the nitride semiconductor free-standing substrate 100 This is because the lattice mismatch at the time of manufacturing a semiconductor device by forming another semiconductor layer on the surface increases, and the characteristics of the semiconductor device manufactured using the nitride semiconductor free-standing substrate 100 deteriorate.

  Further, in the nitride semiconductor free-standing substrate 100, the electric resistivity of the second region 105 is 0.02 Ωcm or more. The reason why the electric resistivity of the second region 105 is 0.02 Ωcm or more is that when the electric resistivity of the second region 105 is less than 0.02 Ωcm, the electric resistivity required for the high resistance substrate is Because we cannot be satisfied.

  The electrical resistivity of the second region 105 can be controlled by adjusting the concentration of impurities added to the second region 105, specifically, the concentration of transition metal atoms contained in the impurities.

Therefore, in the nitride semiconductor free-standing substrate 100, the second region 105 is doped with an impurity containing one or more transition metal atoms having a concentration of 1 × 10 ¹⁵ cm ⁻³ or more and 1 × 10 ²⁰ cm ⁻³ or less. It consists of a nitride semiconductor layer.

As described above, a hydride vapor phase growth furnace is known as a nitride semiconductor manufacturing apparatus. However, since quartz or the like is used as a material constituting the hydride vapor phase growth furnace, silicon [ Impurities such as Si] and oxygen [O ₂ ] are mixed and the nitride semiconductor is likely to be n-type.

  Although it is sufficient if a high-resistance substrate can be obtained by reducing only the impurity concentration, it has not been realized yet. Therefore, in the method for manufacturing a nitride semiconductor free-standing substrate according to the present embodiment, the nitride semiconductor layer is epitaxially grown under growth conditions that can suppress the entry of impurities such as silicon and oxygen into second region 105. This is the biggest feature.

  As a result of intensive studies by the present inventor, it is not sufficient to simply add no impurities. By increasing the growth rate, lowering the growth temperature, and lowering the molar ratio of the group V material to the group III material, It has been found that impurities mixed in the region 105 can be reduced.

  Therefore, in the method for manufacturing a nitride semiconductor free-standing substrate according to the present embodiment, the growth rate is 200 μm / h or more, the growth temperature is 900 ° C. or more and 1100 ° C. or less, and the molar ratio of the group V material to the group III material is 6 or less. The second region 105 is epitaxially grown, and an impurity containing a transition metal atom having a minimum concentration is added to the second region 105, thereby obtaining a high-resistance substrate.

  At this time, cracks are generated by thinning the second region 105 in a range that does not adversely affect other semiconductor layers formed on the surface thereof, that is, in a range that does not adversely affect the characteristics of the semiconductor device. Can be suppressed.

  In the nitride semiconductor free-standing substrate 100, the electrical resistivity of the first region 104 is lower than the electrical resistivity of the second region 105. In an electronic device manufactured using a high-resistance substrate, the second region 105 located on the front side only needs to have a high electrical resistivity, and the first region 104 located on the back side is finally back-wrapped ( This is because it is preferable that the first region 104 is not added with an impurity for increasing the resistance.

Therefore, the first region 104 is preferably formed of a nitride semiconductor layer to which an impurity including one or more transition metal atoms having a concentration of less than 1 × 10 ¹⁵ cm ⁻³ is added.

  In consideration of the characteristics of the electronic device, it is preferable that the second region 105 having a high electrical resistivity has a thickness of 50 μm or more.

  In addition, it is desirable that the first region 104 located on the rear surface side avoid intentional introduction of impurities in order to suppress the occurrence of cracks, but it is particularly necessary to increase the resistance of the first region 104. Therefore, the epitaxial growth may be performed while exposing the facet surface inclined with respect to the crystal growth direction.

  As a result, it is possible to obtain the nitride semiconductor free-standing substrate 100 in which the occurrence frequency of cracks is drastically reduced, so that the manufacturing yield is improved and the inexpensive nitride semiconductor free-standing substrate 100 is provided as a result. It becomes possible.

  For these reasons, a semiconductor device manufactured using the nitride semiconductor free-standing substrate 100 has very excellent characteristics.

  As described above, according to the present invention, it is possible to provide a nitride semiconductor free-standing substrate, a method for manufacturing the same, and a semiconductor device that are less likely to generate cracks while achieving high resistance by addition of impurities.

  Next, the grounds for limiting the numerical values of the present invention will be described.

(Experiment 1)
After the gallium nitride layer was epitaxially grown on the surface of the sapphire substrate by void formation peeling method, the sapphire substrate was removed to manufacture a gallium nitride free-standing substrate.

  Specifically, first, an undoped gallium nitride layer in which impurities are not added using trimethylgallium and ammonia as raw materials on the C-plane of a 2 inch sapphire substrate having a diameter of 50.8 mm by metalorganic vapor phase epitaxy. Was epitaxially grown.

  Then, after depositing a titanium thin film having a thickness of 20 nm on the surface of the gallium nitride layer, the temperature is set to 1050 ° C. for 20 minutes in a mixed gas atmosphere of 20% ammonia gas and 80% hydrogen gas by an electric furnace. The heat treatment was performed.

  As a result, a part of the gallium nitride layer is etched to form voids at a high density, so that the gallium nitride layer changes to a void-formed gallium nitride layer and the titanium thin film is nitrided to form submicron fine holes. As a result, the titanium thin film changed to a hole-formed titanium nitride layer.

  Using this as a base substrate, heating to 1000 ° C. and supplying a hydrogen chloride gas to a gallium metal boat heated to 900 ° C. using a mixed gas of hydrogen gas and nitrogen gas as a carrier gas by a hydride vapor phase growth method, These are reacted to generate gallium chloride gas as a source gas, and at the same time, ammonia gas is supplied to adjust the molar ratio of the group V source to the group III source, while the gallium nitride layer serving as the first region and the second region The gallium nitride layer, which becomes the region of, was continuously epitaxially grown.

  At this time, as shown in Table 1, the growth conditions of the gallium nitride layer serving as the second region were changed, and the epitaxial growth was performed while adding impurities for controlling the electrical resistivity.

In addition, impurities are added to the second region by using biscyclopentadienyl iron [Cp ₂ Fe], which is an organic metal for iron [Fe], and gallium metal for other transition metal atoms. A transition metal was floated on the boat, and hydrogen chloride gas was supplied and supplied at the same time as gallium.

  The gallium nitride layer was peeled off naturally from the sapphire substrate with the void-formed gallium nitride layer as a boundary during the cooling process, and a gallium nitride free-standing substrate could be obtained.

  Thereafter, the 19 self-supporting gallium nitride substrates manufactured in the same manner are polished and flattened until the thickness reaches 450 μm, and further polished to a mirror surface, so that the final thickness is 400 μm. A flat gallium nitride free-standing substrate was obtained.

  These 19 gallium nitride free-standing substrates were subjected to secondary ion mass spectrometry (SIMS) analysis, the impurity concentration in the second region located on the surface side was measured, and the appearance was further observed. The electrical resistivity of the second region was measured.

(Experiment 2)
The process up to the manufacture of the base substrate was carried out in the same manner as in Experiment 1. As shown in Table 2, the first region was changed and the second region was epitaxially grown under the tenth growth condition in Table 1. The polishing treatment after the epitaxial growth was performed in the same manner as in Experiment 1.

  The appearance of these gallium nitride free-standing substrates was observed, and the electrical resistivity of the second region and the average dislocation density in the plane of the surface of the second region were measured. Here, the number of dark spots was counted by cathodoluminescence measurement, and the average dislocation density was determined by dividing by the area of the measurement region.

Referring to Table 2, in the gallium nitride free-standing substrate having an in-plane average dislocation density of 1 × 10 ³ cm ⁻² or more in the surface of the second region, cracks are not generated and sufficient resistance is increased. It can be seen that it has been realized.

(result)
From Experiment 1 and Experiment 2, it was found that cracks are more likely to occur as the second region to which impurities are added becomes thicker and the concentration of impurities increases. However, as the undoped first region becomes thicker, cracks did not occur, and the average dislocation density in the surface of the second region could be reduced by the thicker epitaxial growth.

  In addition, cracks are less likely to occur as the concentration of impurities in the second region is lower. However, in order to obtain electrical characteristics necessary for a semiconductor device, a minimum amount of impurities corresponding to the thickness of the semiconductor device is added. I found it desirable.

  As described above, the basis for the numerical limitation of the present invention was derived.

  In this example, the sapphire substrate was used by the void formation exfoliation method. However, the generation of cracks is suppressed when the impurity concentration is as low as possible rather than the impurity being added to the entire nitride semiconductor layer. Therefore, a silicon substrate, a gallium arsenide substrate, a silicon carbide substrate, a gallium nitride substrate, or the like may be used, and the growth method is not limited to the hydride vapor phase growth method.

  In addition, when a semiconductor device is formed, it is sufficient that a high resistance layer having a certain thickness or more is formed from the surface side. However, in the embodiment, it is made thicker than necessary for ease of handling. . That is, it is not necessary to consider the electrical characteristics on the back side, and the impurity concentration may be adjusted so that it is difficult to break during epitaxial growth.

100 nitride semiconductor free-standing substrate 101 heterogeneous substrate 102 nitride semiconductor layer 103 epitaxial wafer 104 first region 105 second region 106 gallium nitride layer 107 titanium thin film 108 void 109 void formed gallium nitride layer 110 hole 111 hole formed titanium nitride layer 112 Base substrate 113 Gallium nitride free-standing substrate

Claims (7)

In a nitride semiconductor free-standing substrate manufactured by removing the heterogeneous substrate from an epitaxial wafer formed by heteroepitaxially growing a nitride semiconductor layer on the surface of the heterogeneous substrate,
A first region formed in a lower layer of the nitride semiconductor layer near the heterogeneous substrate;
A second region formed in an upper layer of the nitride semiconductor layer far from the dissimilar substrate;
With
The diameter is 40 mm or more, the total thickness of the first region and the second region is 200 μm or more, and the average dislocation density in the plane of the surface of the second region is 1 × 10 ³ cm ⁻² or more and 1 × 10 ⁸ cm ⁻² or less, the electrical resistivity of the second region is 0.02 Ωcm or more, and the electrical resistivity of the first region is lower than the electrical resistivity of the second region, Nitride semiconductor free-standing substrate. 2. The second region is formed of a nitride semiconductor layer to which an impurity including one or more transition metal atoms having a concentration of 1 × 10 ¹⁵ cm ⁻³ or more and 1 × 10 ²⁰ cm ⁻³ or less is added. The nitride semiconductor free-standing substrate as described. 3. The nitride semiconductor self-supporting according to claim 2, wherein the first region includes a nitride semiconductor layer to which the impurity containing one or more transition metal atoms having a concentration of less than 1 × 10 ¹⁵ cm ⁻³ is added. substrate.   4. The nitride semiconductor free-standing substrate according to claim 1, wherein the second region has a thickness of 50 μm or more. 5. In a method for manufacturing a nitride semiconductor free-standing substrate, a nitride semiconductor free-standing substrate is manufactured by removing the dissimilar substrate from an epitaxial wafer obtained by heteroepitaxially growing a nitride semiconductor layer on the surface of the different-type substrate.
When the lower layer of the nitride semiconductor layer close to the dissimilar substrate is a first region and the upper layer of the nitride semiconductor layer far from the dissimilar substrate is a second region, the diameter of the first region is 40 mm or more. And the total thickness of the second region is 200 μm or more, the average dislocation density in the plane of the surface of the second region is 1 × 10 ³ cm ⁻² or more and 1 × 10 ⁸ cm ⁻² or less, The growth rate is set to 200 μm / h or more, and the growth temperature is set so that the electric resistivity of the region is 0.02 Ωcm or more and the electric resistivity of the first region is lower than the electric resistivity of the second region. A method for producing a nitride semiconductor self-supporting substrate, wherein the second region is grown at 900 ° C. or higher and 1100 ° C. or lower and a molar ratio of a group V raw material to a group III raw material is 6 or less.   The method for manufacturing a nitride semiconductor free-standing substrate according to claim 5, wherein the nitride semiconductor layer is heteroepitaxially grown using a hydride vapor phase growth method.   A semiconductor device manufactured using the nitride semiconductor free-standing substrate according to any one of claims 1 to 4.