KR101687595B1 - Film forming method of nitride semiconductor layer and manufacturing method of semiconductor device - Google Patents

Abstract

A step of epitaxially growing a buffer layer made of AlN or AlGaN on a substrate; and a step of epitaxially growing a buffer layer made of AlN or AlGaN on a substrate by using a nitride target containing Ga and GaN on a buffer layer and setting a flow rate of the reactive gas containing nitrogen to less than 20% , There is a step of epitaxially growing at least a nitride semiconductor layer containing GaN by a sputtering method.

Description

TECHNICAL FIELD [0001] The present invention relates to a method of forming a nitride semiconductor layer, and a method of manufacturing the same. BACKGROUND OF THE INVENTION 1. Field of the Invention [0002]

The present invention relates to a film formation method of a nitride semiconductor layer for epitaxially growing a nitride semiconductor layer and a manufacturing method of the semiconductor device.

The nitride semiconductor is a compound semiconductor material composed of a group IIIb element such as aluminum (Al), gallium (Ga), indium (In) and nitrogen as a group V element, and is made of aluminum nitride (AlN), gallium nitride (GaN) , Indium nitride (InN), and mixed crystal thereof (AlGaN, InGaN, InAlN, AlGaInN). Among them, light emitting devices such as light emitting diodes (LEDs) and laser diodes (LDs) based on GaN have already been widely popularized. Thereafter, a high electron mobility transistor (HEMT) Transistors) are expected to become popular as well.

Generally, nitride semiconductors are formed by metal organic chemical vapor deposition (MOCVD). The MOCVD method has an advantage of controlling the film thickness and composition precisely and has a high film forming speed. However, it has demerits such as high running cost, easy generation of particles, and poor reproducibility of film quality.

On the other hand, a technique for forming a film of a nitride semiconductor by a sputtering method is also being developed. The sputtering method is advantageous in that it is easy to suppress the running cost to a low level, the particles are hardly generated, and the reproducibility of the film quality is good. Therefore, it is expected that at least one layer of the device made of the nitride semiconductor is formed by the sputtering method. In particular, since a device based on a GaN layer has a wide application field, it is required to establish a technique for obtaining a high-quality GaN layer with high reproducibility by a sputtering method.

As a sputtering target capable of obtaining a GaN layer by a sputtering method, a metal Ga target containing no N atom, a nitride GaN target bonded with a Ga atom and a N atom in a ratio of 1: 1, a mixture of a metal Ga and a nitride GaN And a nitride GaNx target made of GaN. Such a technique for forming a GaN layer by using a target is disclosed in, for example, Patent Documents 1 to 5.

Patent Document 1 discloses a technique of forming a GaN layer by sputtering a metal Ga target having a melting point of 29.8 DEG C as a low melting point metal in a state in which at least the surface layer is liquefied. In Patent Document 1, a buffer layer made of AlN is used as a base of a GaN layer.

Patent Document 2 discloses a technique of forming a GaN layer by a sputtering method without melting a metal Ga target having a melting point of 29.8 ° C as a low melting point metal. In Patent Document 2, a buffer layer made of AlN is used as the base of the GaN layer.

Patent Document 3 discloses a technique of forming a GaN layer by a sputtering method using a nitride GaN target. In Patent Document 3, a buffer layer made of GaN (hereinafter referred to as a low-temperature GaN buffer layer) formed at a low temperature by using a nitride GaN target is used as a buffer layer formed as a base of a GaN layer. Temperature GaN buffer layer is crystallized by heating the substrate in a temperature range of 1000 deg. C to 1100 deg. C after forming the low-temperature GaN buffer layer.

Patent Document 4 discloses a technique of forming a GaN layer by a sputtering method using a nitride GaNx target having a molar ratio of Ga / (Ga + N) of 55% or more and 80% or less. In Patent Document 4, N ₂ gas is used as a process gas for forming a GaN layer.

Patent Document 5 discloses a technique of forming a GaN layer by sputtering using either or both of a metal Ga and a nitride GaN as a target. Patent Document 5 discloses a method in which Ar is used as a sputtering gas, sputtering of the target is performed by using the Ar gas, and a step of supplying sputter particles onto the substrate and a step of supplying radicals containing N from the radical gun to the substrate are alternately repeated Thereby forming a GaN layer.

Japanese Patent Application Laid-Open No. 2008-153603 Japanese Patent No. 4974635 Japanese Patent Application Laid-Open No. 2012-222243 Japanese Patent Application Laid-Open No. 2012-144424 Japanese Patent Application Laid-Open No. 2013-125851

According to the conventional techniques (Patent Documents 1 to 5) already disclosed, it is possible to form a GaN layer by a sputtering method. However, the prior art does not disclose a technique for obtaining a flat GaN layer with high reproducibility. As will be described later, according to the independent experiments of the inventors of the present invention, it was difficult to obtain a flat GaN layer with high reproducibility only by the techniques described in Patent Documents 1 to 5. If a flat GaN layer can not be obtained, it becomes difficult to realize high-performance optical devices and high-frequency / power devices.

An object of the present invention is to provide a method of forming a nitride semiconductor layer capable of epitaxially growing a flat nitride semiconductor layer with high reproducibility.

According to one aspect of the present invention, there is provided a nitride semiconductor light emitting device including: a step of epitaxially growing a buffer layer made of AlN or AlGaN on a substrate; and a step of epitaxially growing a buffer layer on the substrate using a nitride target containing Ga and GaN, And a step of epitaxially growing at least a nitride semiconductor layer containing GaN by sputtering at a flow rate lower than 20% of the entire flow rate of the process gas.

According to the present invention, a flat nitride semiconductor layer can be obtained with high reproducibility by a sputtering method.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic structural view showing an example of a film forming apparatus used in a method of forming a nitride semiconductor layer according to a first embodiment of the present invention; Fig.
2 is a schematic structural view showing an example of a first sputtering chamber used for forming a buffer layer in a method of forming a nitride semiconductor layer according to a first embodiment of the present invention.
3 is a schematic structural view showing an example of a second sputtering chamber used for forming a nitride semiconductor layer in a method of forming a nitride semiconductor layer according to a first embodiment of the present invention.
4 is a schematic diagram showing + c and -c polarities in a nitride semiconductor.
5 is a graph showing an example of the film thickness dependence of the lattice constant of the a-axis at the interface with the GaN layer of the buffer layer made of AlN formed by the film formation method of the nitride semiconductor layer according to the first embodiment of the present invention.
6 is a cross-sectional TEM image (image) showing the cross-sectional structure of a GaN layer formed by the method of forming a nitride semiconductor layer according to the first embodiment of the present invention.
7 is a cross-sectional TEM image showing a cross-sectional structure of a GaN layer formed by a method of forming a nitride semiconductor layer according to Comparative Example 1 of the present invention.
8 is a cross-sectional TEM image showing a cross-sectional structure of a GaN layer formed by a method of forming a nitride semiconductor layer according to Comparative Example 2 of the present invention.
9 is a schematic sectional view showing a semiconductor device and a manufacturing method thereof according to a second embodiment of the present invention.

[First Embodiment]

A method of forming a nitride semiconductor layer according to a first embodiment of the present invention will be described with reference to Figs. 1 to 5. Fig.

In the present specification, the process gas means a mixed gas of a reactive gas containing nitrogen and a rare gas. The nitrogen-containing reactive gas means N ₂ gas or NH ₃ gas or a mixed gas thereof.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a schematic structural view showing an example of a film formation apparatus for a nitride semiconductor layer according to the present embodiment. FIG. Fig. 2 is a schematic structural view showing an example of a first sputtering chamber in the film forming apparatus of Fig. 1; 3 is a schematic structural view showing an example of a second sputtering chamber in the film forming apparatus of Fig. 4 is a schematic diagram for explaining + c polarity and -c polarity in the nitride semiconductor. 5 is a graph showing an example of the film thickness dependence of the lattice constant of the a-axis at the interface with the GaN layer of the buffer layer made of AlN formed by the film formation method of the nitride semiconductor layer according to the present embodiment.

First, an example of a film formation apparatus used in a method of forming a nitride semiconductor layer according to the present embodiment will be described with reference to Figs. 1 to 3. Fig.

As shown in Fig. 1, the film forming apparatus 100 used in the method of forming a nitride semiconductor layer according to the present embodiment includes a load lock chamber 101, a transport chamber 102, a pre-treatment chamber 103, a first sputtering chamber A first sputtering chamber 104, and a second sputtering chamber 105. A gate valve 107 for opening and closing the processing chamber is provided between the transfer chamber 102 and the load lock chamber 101, the preprocessing chamber 103, the first sputtering chamber 104 and the second sputtering chamber 105. , 108, 109, and 110, respectively. In the transport chamber 102, a transport robot 106 for transporting a substrate to be processed to each processing chamber is provided.

Fig. 2 is a schematic view showing a configuration example of a sputtering apparatus constituting the first sputtering chamber 104. Fig. The first sputtering chamber 104 is a processing chamber for forming a buffer layer made of AlN or AlGaN as a base of the nitride semiconductor layer.

The sputtering apparatus as the first sputtering chamber 104 has a vacuum vessel 201 as a processing chamber. An evacuation mechanism 214 for evacuating the inside of the vacuum vessel 201 and a gas introduction mechanism 213 for introducing a process gas into the vacuum vessel 201 are provided in the vacuum vessel 201. The vacuum container 201 is provided with a substrate mounting mechanism 211 for holding a substrate 212 to be processed, a heater 209 for heating the substrate 212, And a reflector 210 for increasing the heating efficiency. A chamber shield 202 is disposed around the substrate mounting mechanism 211. A sputtering cathode 203 holding a target 204 is disposed in the vacuum container 201 so as to face the substrate 212. The sputtering cathode 203 is a magnetron cathode including a magnet 206. A target shield 205 is disposed around the target 204. A sputtering power supply 207 is connected to the sputtering cathode 203. The sputtering power source 207 is a high frequency power source in the present embodiment, and is connected to the sputtering cathode 203 through a matching box (not shown). The sputtering power source 207 may be a high-frequency power source and a DC power source connected in parallel (not shown). In this case, the high frequency power source is connected to the sputtering cathode 203 via a matching box (not shown), and the DC power source is connected to the sputtering cathode 203 through a low pass filter.

The sputtering apparatus shown in Fig. 2 is a stationary counter-current sputtering apparatus, but an offset-type sputtering apparatus may be used instead of the stationary counter-current sputtering apparatus. Even when an offset type sputtering apparatus is used, the buffer layer described in this embodiment mode can be similarly formed. The offset type sputtering apparatus may be such that the normal direction of the substrate 212 and the normal direction of the target 204 are parallel to each other and the normal direction of the substrate 212 and the normal direction of the target 204 are a predetermined angle A sputtering apparatus of an oblique offset type may be used.

Fig. 3 is a schematic view showing a configuration example of a sputtering apparatus constituting the second sputtering chamber 105. Fig. The second sputtering chamber 105 is a processing chamber for forming a nitride semiconductor layer on the buffer layer.

The sputtering apparatus as the second sputtering chamber 105 has a vacuum chamber 301 as a processing chamber. The vacuum container 301 is provided with an exhaust mechanism 312 for evacuating the inside of the vacuum chamber 301 and a gas introducing mechanism 311 for introducing the process gas into the vacuum chamber 301. In the vacuum chamber 301, a heating stage 305 for holding and heating the substrate 313 to be processed is provided. The heating stage 305 is provided with a heating stage rotating mechanism 306 for rotating the heating stage 305. A chamber shield 302 is disposed around the heating stage 305. A plurality of sputtering cathodes 308 for holding a target 307 facing the substrate 313 are disposed in the vacuum container 301. [ The sputtering cathode 308 is a magnetron cathode including a magnet 309. A rotary shutter 303 rotatable by a shutter rotating mechanism 304 is disposed on a front portion of the target 307. [ A sputtering power supply 310 is connected to the sputtering cathode 308. The sputtering power source 310 is a high frequency power source in the present embodiment, and is connected to the sputtering cathode 308 through a matching box (not shown). The sputtering power source 310 may be a high frequency power source and a direct current power source connected in parallel (not shown). In this case, the high frequency power source is connected to the sputtering cathode 308 through a matching box (not shown), and the DC power source is connected to the sputtering cathode 308 through a low pass filter (not shown). When a high conductivity material is used as the target 307, a DC power source or a pulsed DC power source may be used as the sputtering power source 310.

The sputtering apparatus shown in Fig. 3 is an offset type sputtering apparatus, but a stationary counter sputtering apparatus may be used instead of the offset type sputtering apparatus. The nitride semiconductor layer described in this embodiment mode can be similarly formed even when a stationary counter-current sputtering apparatus is used. 3, the normal direction of the target 307 and the normal direction of the substrate 313 are parallel to each other, but the normal direction of the target 307 and the normal direction of the substrate 313 are always parallel to each other And may be an inclined offset type sputtering apparatus in which the normal direction of the target 307 and the normal direction of the substrate 313 intersect at a predetermined angle.

Next, a method for forming a nitride semiconductor layer according to the present embodiment will be described with reference to Figs. 1 to 5. Fig.

A method of forming a nitride semiconductor layer according to the present embodiment includes a step of epitaxially growing a buffer layer on a substrate and a step of forming a nitride semiconductor layer on the buffer layer. Here, the case where the nitride semiconductor to be formed is GaN is mainly described, but the nitride semiconductor need not necessarily be GaN as long as it contains Ga, and it may be InGaN, AlGaN, or AlGaInN as described later. The case of AlN for the buffer layer as the base of the nitride semiconductor layer is mainly described, but the buffer layer may be AlGaN.

First, a substrate (for example, a c-plane sapphire substrate) having an epitaxial relationship with the nitride semiconductor layer to be formed, here a GaN layer, is introduced into the load lock chamber 101 and a load And the lock chamber 101 is evacuated to a vacuum. The c-plane sapphire substrate is also applicable as a substrate for forming InGaN, AlGaN, and AlGaInN films.

Next, the gate valves 107 and 108 are appropriately operated and the substrate in the load lock chamber 101 is transported to the pretreatment chamber 103 by the transport robot 106 of the transport chamber 102.

Next, the substrate transferred to the preprocessing chamber 103 is subjected to predetermined preprocessing. As the pretreatment performed in the pretreatment chamber 103, a plasma treatment or a preheating can be appropriately selected. This pretreatment is not essential to the present invention. However, by performing the preheating in the pretreatment chamber, the temperature rise time of the substrate in the next step is shortened, or the water adsorbed on the substrate or the tray for transporting the substrate is removed, thereby improving the quality of the buffer layer formed in the next step Or reproducibility of the process becomes easy to be improved.

After the preprocessing in the preprocessing chamber 103 is completed, the gate valves 108 and 109 are appropriately operated and the transfer robot 106 in the transfer chamber 102 transfers the substrate (Hereinafter referred to as " substrate 212 ") is transferred to first sputtering chamber 104.

The substrate 212 introduced into the first sputtering chamber 104 is kept separated from the surface P of the heater 209 by the substrate placement mechanism 211. [ By holding the substrate in this way, a buffer layer of + c polarity is easily formed. Further, since a buffer layer of + c polarity is formed, a flat GaN layer is easily formed thereon. Therefore, it is preferable that the substrate 212 be kept apart from the surface P of the heater 209. On the other hand, if the substrate 212 is directly contacted with the surface P of the heater 209, a buffer layer in which -c polarity or -c polarity is mixed can be easily formed. The buffer layer in which -c polarity or -c polarity is mixed is not preferable because the GaN layer formed thereon is not easily flattened.

The growth mode of the nitride semiconductor thin film such as AlN has a growth of + c polarity as shown in Fig. 4 (a) and a growth of -c polarity as shown in Fig. 4 (b). a flat epitaxial film is likely to be obtained as compared with a nitride semiconductor in which the + c polarity or the -c polarity is mixed with the + c polarity nitride semiconductor. In addition, the buffer layer of + c polarity is more likely to be flat than that of the buffer layer in which -c polarity or -c polarity is mixed. Therefore, it is preferable to adopt a film formation condition in which an epitaxial film of + c polarity is obtained in the film formation process of the nitride semiconductor thin film. In the present specification, " + c polarity " refers to AlN, GaN, and InN and refers to Al polarity, Ga polarity, and In polarity, respectively. The term " -c polarity " refers to the N polarity.

The substrate 212 introduced into the first sputtering chamber 104 is preferably heated to a substrate temperature of 300 ° C or higher by the radiant heat from the heater 209. By doing so, the buffer layer is easily formed with + c polarity, and a flat GaN layer is easily formed thereon, which is preferable. On the other hand, when the substrate temperature is lower than 300 캜, the crystallinity of the buffer layer deteriorates, and a buffer layer in which -c polarity or -c polarity is mixed is likely to be formed. As described above, when a buffer layer in which -c polarity or -c polarity is mixed is used, the GaN layer formed thereon is not preferable because it is difficult to be flat. The upper limit of the substrate temperature at the time of forming the buffer layer is not particularly limited. However, when the temperature is higher than 1200 ° C, film formation of the buffer layer made of AlN can not be performed, .

In the present embodiment, the relationship between the temperature of the heater and the temperature of the thermocouple attachment substrate is checked in advance. When the nitride semiconductor is actually deposited, the temperature of the heater is set to a predetermined temperature, Substrate temperature.

After the substrate 212 is introduced into the first sputtering chamber 104, a mixed gas of a rare gas and a reactive gas is introduced from the gas introduction mechanism 213. Ar gas is preferably used as the rare gas, and N ₂ gas is preferably used as the reactive gas. The reactive gas flow rate and the rare gas flow rate are controlled by a mass flow controller (not shown) provided in the gas introduction mechanism 213. The reactive gas flow rate / (reactive gas flow rate + rare gas flow rate) is preferably less than 50%, more preferably less than 30%. By doing so, the buffer layer is easily formed with + c polarity, and a flat GaN layer is easily formed thereon, which is preferable. On the other hand, when the reactive gas flow rate / (reactive gas flow rate + rare gas flow rate) is 50% or more, a buffer layer in which -c polarity or -c polarity is mixed can be easily obtained. As described above, when a buffer layer in which -c polarity or -c polarity is mixed is used, the GaN layer formed thereon is not preferable because it is difficult to be flat.

Thereafter, electric power is applied to the sputtering cathode 203 from the sputtering power source 207 to generate plasma on the surface of the target 204, and the sputtering process is performed. A + c-polarized epitaxial film made of AlN is directly grown on the surface of the substrate 212 by sputtering using a plasma containing a reactive gas by using, for example, a metal Al target as the target 204 .

The buffer layer made of AlN according to the present invention is controlled so that the polarity is + c polarity and the lattice constant of the a-axis at the interface with the GaN layer is controlled to be not less than the bulk lattice constant (about 0.311 nm) . By doing so, since the lattice mismatch rate at the interface between the GaN layer and the AlN layer formed on the buffer layer thereafter is reduced, the probability of occurrence of a three-dimensional island made of GaN can be reduced. As a result, Direction. When the GaN layer grows in the lateral direction in this way, the GaN layer tends to be a flat GaN layer, which is preferable. On the other hand, when the lattice constant of the a-axis at the interface with the GaN layer is less than the lattice constant of the bulk, the lattice mismatch ratio at the GaN / AlN interface becomes large, so that a three-dimensional island made of GaN tends to occur. In this case, lateral growth of the GaN layer is suppressed and it is difficult to obtain a flat GaN layer, which is not preferable.

Although the upper limit of the lattice constant of the a-axis at the interface with the GaN layer of the AlN buffer layer is not particularly limited, if it is extremely larger than the lattice constant of the bulk, a tensile stress is generated in the buffer layer, . Therefore, the upper limit of the lattice constant of the a-axis at the interface with the GaN layer of the buffer layer made of AlN is preferably set to a lattice constant, for example, 0.314 nm or less, in which such a crack is unlikely to occur.

The mechanisms by which the three-dimensional islands are generated by increasing the lattice mismatch rate can be explained qualitatively by well-known VW (Volmer-Weber) or SK (Stranski-Krastanov) have. The mechanism by which the GaN layer is likely to grow laterally by reducing the lattice mismatch rate can be qualitatively explained by a well-known FM (Frank-van der Merwe) type growth model.

In this embodiment, the AlN layer is taken as an example of the buffer layer. However, it is also possible to use an AlN layer as an example of the buffer layer. However, a small amount of less than 5 at% of C, Si, Ge, Mg, Cr, Or an AlN layer in which Mn is added in a small amount less than 5 at%. The amount of C, Si, Ge, Mg, Cr, Mn, and the like may be added to the buffer layer made of AlN in a small amount of less than 5 at%, so that a gas containing these elements is contained in the mixed gas of the reactive gas and the rare gas A buffer layer made of AlN may be formed in an atmosphere. Alternatively, the AlGaN layer may be epitaxially grown directly on the Al target by using an Al-Ga target containing Ga in the Al target to be used as a buffer layer. In this case, if the content of Ga in the target becomes excessively high, a low melting point Al-Ga alloy is formed. Therefore, the composition ratio of Al and Ga is adjusted so that the Al-Ga target does not melt in the first sputtering chamber 104 .

A technique for obtaining an AlN layer in which the lattice constant of the a-axis at the interface with the GaN layer is not less than the lattice constant of the bulk is not disclosed in the prior arts of Patent Documents 1 to 5. Generally, if a buffer layer made of AlN is formed on a c-plane sapphire substrate, compressive deformation is likely to occur in the surface of the buffer layer even if it is intended to achieve lattice matching with the substrate. Further, in order to effectively make the buffer layer made of AlN + c polarity, the substrate temperature is set to 300 DEG C or more in the present invention, but the + c surface is also subjected to compressive deformation in the buffer layer surface due to the difference in thermal expansion coefficient between the sapphire substrate and the AlN buffer layer. . The means for obtaining such an AlN layer at the interface with the GaN layer by relaxing such compressive strain to have a bulk lattice constant or more is not particularly limited. For example, the buffer layer may have a thickness of 10 to 500 nm Is made larger than the film thickness of the film. For example, by making the film thickness of the buffer layer larger than 1 mu m, the lattice strain generated at the substrate interface can be relaxed at the surface side of the buffer layer.

5 is a graph showing an example of the film thickness dependence of the lattice constant of the a-axis at the interface with the GaN layer of the AlN film formed by the film formation method of the nitride semiconductor layer according to the present embodiment. In the figure, the dotted line is the lattice constant (0.311 nm) of the a-axis of bulk AlN. As shown in Fig. 5, the lattice constant of the a-axis of the AlN film increases with the relaxation of compressive strain due to the increase of the film thickness of the AlN film. For example, by increasing the film thickness of AlN to 1 占 퐉, the lattice constant of the a-axis can be increased to about 0.312 nm.

A method of forming a fine defect structure in the inside of the buffer layer to alleviate the lattice strain on the surface side of the buffer layer by making AlN having a small amount of C, Si, Ge, Mg, Cr, Mn or the like added in a small amount less than 5 at% . This method is preferable because the AlN layer in which the lattice constant a at the interface with the GaN layer is larger than the bulk lattice constant can be obtained with a film thickness thinner than that of the buffer layer made of AlN not containing the above element. Further, since the lattice constant of the a-axis at the interface of the buffer layer made of AlN with the GaN layer greatly varies depending on the ratio of the reactive gas flow rate and the rare gas flow rate, the pressure at the time of film formation, etc., .

Although the method of forming the buffer layer by the sputtering method is described in the present embodiment, it is also possible to control the polarity to be the + c polarity, and the lattice constant of the a-axis at the interface with the GaN layer is controlled by the bulk lattice constant The present invention is not limited to this. For example, instead of the first sputtering chamber 104, a buffer layer made of AlN can be formed using an MOCVD chamber, a molecular beam epitaxy chamber, or the like.

In the technique disclosed in Patent Documents 1 and 2, although a buffer layer made of AlN is used, a technique of obtaining an AlN layer of + c polarity and a technique of forming a lattice constant of the a-axis at the interface with the GaN layer, There is no description about a technique for controlling the voltage to be equal to or greater than a constant. According to the independent experiments of the present inventors, it is difficult to obtain an AlN layer with a + c polarity even when a buffer layer made of AlN is formed by the method disclosed in Patent Document 1 and Patent Document 2, It is difficult to control the lattice constant to be larger than the lattice constant of the bulk. For this reason, it is also difficult to planarize the GaN layer on the GaN layer.

The technique disclosed in Patent Document 3 is a low temperature GaN buffer layer formed by using a nitride GaN target as a buffer layer to be formed as a base of a GaN layer. After forming the buffer layer, the substrate is crystallized by heating in a temperature range of 1000 deg. C to 1100 deg. have.

However, when the low-temperature GaN buffer layer is crystallized by heat treatment, as shown in Patent Document 3, a part of the low-temperature buffer layer is sublimated, or an aggregation phenomenon accompanying crystallization occurs, and the flatness of the buffer layer is liable to be damaged. Since such a buffer layer itself acts as a three-dimensional island, lateral growth of the GaN layer is difficult to occur. For this reason, it is difficult to obtain a flat GaN layer, which is not preferable.

Patent Document 4 and Patent Document 5 do not disclose forming a buffer layer before forming a GaN layer. When a buffer layer is not formed before forming the GaN layer, a flat GaN layer can not be obtained, which is not preferable.

As an evaluation method of the lattice constant of the a-axis of the buffer layer made of AlN, the X-ray diffraction method is used as a simple method. When the GaN layer is formed on the buffer layer to a thickness of several micrometers, the lattice constant of the a-axis can be calculated from the angle formed by the lattice plane spacing of the symmetry plane, the lattice plane spacing of the asymmetric plane, and the symmetry plane and the asymmetric plane have. It is also possible to obtain the lattice constant of the a-axis of the buffer layer at the interface between the GaN layer and the buffer layer by electron diffraction or the like. After forming the buffer layer made of AlN, the GaN layer may be removed from the device without being laminated, and the lattice constant of the a-axis may be obtained by the X-ray diffraction method in the In-plane arrangement. With this method, the lattice constant of the a-axis at the outermost surface of the buffer layer made of AlN can be obtained. Since the lattice constant of the a-axis of the buffer layer at the interface with the GaN layer when the GaN layer is stacked and the lattice constant of the a-axis of the buffer layer without the GaN layer are not greatly changed, this method can be most conveniently used have.

Next, a substrate on which a buffer layer made of AlN is formed (hereinafter, a substrate on which a buffer layer is formed is referred to as a substrate 313) in the first sputtering chamber 104 is transferred to the transfer robot 106 of the transfer chamber 102 To the second sputtering chamber (105). It is preferable that the substrate 313 is transported from the first sputtering chamber 104 to the second sputtering chamber 105 without being exposed to atmosphere. Since the transport chamber 102 is always kept at a high vacuum, oxidation of the surface of the buffer layer can be reduced. If the substrate is exposed to the atmosphere after the formation of the buffer layer, an oxide layer is formed on the surface of the buffer layer and the epitaxial growth of the subsequent GaN layer is inhibited.

The substrate 313 conveyed to the second sputtering chamber 105 is directly placed on the heating stage 305 and set at a substrate temperature of 500 ° C or higher. The substrate temperature at the time of epitaxial growth of the GaN film in the second sputtering chamber 105 is preferably 500 DEG C or more, and more preferably 700 DEG C or more. By setting such a high substrate temperature, the sputtering particles physically adsorbed on the substrate (particularly the metal phase Ga described below) are easily migrated on the substrate, and the growth of the GaN layer in the lateral direction is promoted. That is, setting the substrate temperature at 500 ° C or higher is a preferable mode for obtaining a flat GaN layer by promoting lateral growth. When the substrate temperature is lower than 500 占 폚, the sputtering particles physically adsorbed on the substrate (especially the metal phase Ga described below) are difficult to migrate on the substrate. In such a case, growth in the lateral direction of the GaN layer is difficult to be promoted, which makes it difficult to obtain a flat GaN layer, which is not preferable. The upper limit of the substrate temperature at the time of epitaxial growth of the GaN layer is not particularly limited. However, when the temperature is higher than 1000 deg. C, the film formation of the GaN layer itself may be impossible, Do.

The substrate 313 conveyed to the second sputtering chamber 105 can be placed apart from the heating stage 305 in the same manner as the first sputtering chamber 104. However, from the viewpoint of facilitating realization of a higher substrate temperature, it is more preferable to directly mount the substrate 313 on the heating stage 305. [ It is more preferable that an electrostatic attraction (ESC) mechanism is provided on the heating stage 305 and the substrates are attracted to the heating stage 305 after the substrate is conveyed, since a higher substrate temperature is easily realized. The reason why the substrate 313 in the second sputtering chamber 105 does not necessarily need to be placed apart from the heating stage 305 is that the base buffer layer is directly epitaxially grown with the + c polarity. In other words, since the GaN layer formed on the buffer layer is easy to take over the polarity of the buffer layer, the + c polarity of the buffer layer is reflected, and therefore, the GaN layer tends to become the + c polarity. As a result, a flat GaN layer can be obtained It will be easy.

After the substrate 313 is transported to the second sputtering chamber 105, a mixed gas of a rare gas and a reactive gas is introduced into the second sputtering chamber 105 from the gas introduction mechanism 311. Ar gas is preferably used as the rare gas, and N ₂ gas is preferably used as the reactive gas. It is preferable that the reactive gas flow rate and the rare gas flow rate are controlled by a mass flow controller (not shown) provided in the gas introduction mechanism 311, and the reactive gas flow rate / (reactive gas flow rate + rare gas flow rate) , And preferably less than 10%.

When the reactive gas flow rate becomes 20% or more of the flow rate of the entire process gas, the sputter particles migrating on the substrate (in particular, the metal phase Ga described below) are liable to react with the active nitrogen in the plasma and can not sufficiently migrate. If the migration can not be sufficiently performed in this way, growth in the lateral direction of the GaN layer is suppressed, and a flat GaN layer is difficult to obtain, which is not preferable. On the other hand, when the reactive gas flow rate is less than 20%, the probability that the sputter particles migrating on the substrate (in particular, the metal phase Ga described below) reacts with the active nitrogen in the plasma is reduced and the growth of the GaN layer in the lateral direction is promoted do. As a result, a flat GaN layer is easily obtained. Therefore, it is a preferable form to set the reactive gas flow rate to less than 20%.

In this embodiment, sputtering using only a rare gas is not preferable. The nitride nitride target used in the present invention is likely to cause nitrogen deficiency in the course of sputtering, so that the composition of the target tends to change with time. If the target composition is changed over time, the reproducibility of the process is lowered, and it becomes difficult to obtain a flat GaN layer with high reproducibility.

In the present embodiment, the lower limit thereof is not limited as long as the reactive gas flow rate / (reactive gas flow rate + rare gas flow rate) is 0 (that is, only Ar gas) The nitride GaNx target used in the sputtering process tends to cause nitrogen deficiency in the course of sputtering. Therefore, it is necessary to increase the reactive gas flow rate to such an extent that the nitrogen deficiency can be compensated. For example, the reactive gas flow rate / (reactive gas flow rate + rare gas flow rate) is preferably 0.1% or more.

Thereafter, electric power is applied to the sputtering cathode 308 from the sputtering power source 310 to generate plasma on the surface of the target 307 to perform the sputtering process. As the target 307, a nitride GaNx target to be described later is used, and a sputtering process is performed using a plasma containing a reactive gas, whereby an epitaxial film made of GaN can be grown on the surface of the substrate 313.

The target 307 used for forming the GaN layer in the second sputtering chamber 105 is preferably a nitride GaN x target in which the mole ratio of Ga / (Ga + N) is in the range of 53.0 to 59.5%. By setting the composition of the target within this range, it is possible to supply GaNx on the nitride phase and Ga on the metal phase as balanced sputter particles on the substrate. It is believed that on nitride GaNx does not contribute much to migration on the substrate, but forms a dense initial nucleus. On the other hand, it is considered that metal-phase Ga migrates on the substrate and is received in the initial nucleus formed by GaNx on the nitride, so that it is likely to grow in the lateral direction. In this way, since the growth in the transverse direction continues with the initial nucleus formed at a high density as a starting point, a flat GaN layer is easily obtained. In addition, by setting the molar ratio of Ga / (Ga + N) to the above range, the metal Ga melted on the target surface is hardly precipitated, and a stable process can easily be reproduced.

When the molar ratio of Ga / (Ga + N) is less than 53.0%, the amount of metal Ga migrating on the substrate is small and growth of the GaN layer in the lateral direction is difficult to promote. As a result, it is difficult to obtain a flat GaN layer, which is not preferable. In addition, when the molar ratio of Ga / (Ga + N) is larger than 59.5%, molten metal Ga tends to precipitate on the target surface. If precipitation of such metal Ga is caused, an abnormal discharge tends to occur, and the reproducibility tends to be lowered. Further, the target composition changes in the target thickness direction due to the precipitation of the metal Ga, and the flat GaN layer can not be obtained with high reproducibility, which is not preferable.

Next, the substrate 313 on which the nitride semiconductor layer made of GaN is formed in the second sputtering chamber 105 is transported to the load lock chamber (not shown) through the transport chamber 102 by the transport robot 106 of the transport chamber 102 101). Thereafter, the substrate 313 is taken out from the load lock chamber 101 to complete a series of film forming processes.

Patent Document 1 and Patent Document 2 disclose that a GaN layer of relatively high quality can be formed by sputtering by using a metal Ga target.

However, in the technique described in Patent Document 1, since the surface of the metal Ga target is sputtered in the molten state, the nitride layer formed on the target surface intrudes into the target, and the composition of the target is liable to change over time. As a result, the stability of the process is lowered, and it becomes difficult to obtain a flat GaN layer with high reproducibility.

Further, in the techniques described in Patent Documents 1 and 2, since metal Ga is used as a target, it is considered that the sputter particles are likely to be released in the form of metal Ga as compared with a nitride GaNx target or a nitride GaN target. In the growth dominated by metal Ga, it is considered that the initial nucleus density of the GaN layer is likely to be low because the metal phase Ga migrates sufficiently on the substrate while the formation frequency of the initial nucleus tends to decrease. The GaN layer grows laterally from this low-density initial nucleus, but since the initial nucleus density is low, the two-dimensional island grown in the lateral direction is difficult to fuse. New nuclei are generated on the two-dimensional islands until the two-dimensional islands are fused, resulting in promotion of growth in the direction of stacking. This makes it difficult to planarize the GaN layer.

Further, in the present invention, the lattice constant of the a-axis at the interface with the GaN layer of the buffer layer made of AlN is set to a bulk lattice constant or more and the polarity is set to + c polarity. However, even when the lattice constant of the a-axis is set to be larger than the lattice constant of the bulk and the polarity is set to the + c polarity, in the case of using the metal Ga target described in Patent Document 1 and Patent Document 2, It is difficult to planarize the GaN layer.

In this way, it is difficult to obtain a flat GaN layer with high reproducibility even by using the technique described in Patent Document 1 and Patent Document 2 (a method of forming a GaN film using a metal Ga target).

In addition, when using a nitride GaN target as described in Patent Document 3, most of the sputter particles emitted from the target become GaNx on the nitride, and the metal Ga is not emitted much. Therefore, the migration of the sputter particles adhered to the substrate is not promoted, and growth in the lateral direction is difficult to occur. Therefore, it is difficult to obtain a flat GaN layer, which is not preferable.

In the present invention, the lattice constant of the a-axis at the interface with the GaN layer of the buffer layer made of AlN is set to be not less than the bulk lattice constant, and the polarity is + c polarity. However, even when the lattice constant of the a-axis is set to be larger than the lattice constant of the bulk and the polarity of the polarity is set to + c polarity, in the case of using the nitride GaN target described in Patent Document 3, migration in the nitride GaNx as the sputter particles can be promoted It is difficult to planarize the GaN layer.

In this way, it is difficult to obtain a flat GaN layer with high reproducibility even by using the technique described in Patent Document 3 (a method of forming a GaN film using a nitride GaN target).

In the technique described in Patent Document 4, a nitride GaNx target having a molar ratio of Ga / (Ga + N) of 55% or more and 80% or less is used. Especially when the mole ratio of Ga / (Ga + N) is larger than 59.5% The molten metal Ga tends to precipitate on the surface. When such metal Ga is precipitated, the target composition changes in the target thickness direction and the flat GaN layer can not be obtained with high reproducibility, which is not preferable.

In the technique described in Patent Document 5, a rare gas such as Ar is used as a target by using either or both of metal Ga and nitride GaN as sputtering gas. When the target containing nitride GaN is sputtered only with a rare gas such as Ar, the nitride GaN is selectively sputtered, and the composition of the target surface changes over time. For this reason, the reproducibility of the process is deteriorated, and consequently, it becomes difficult to obtain a flat GaN layer with high reproducibility, which is not preferable. In the case where only the metal Ga is used as a target, growth in the lamination direction tends to occur until the two-dimensional island is fused, similarly to the techniques of Patent Documents 1 and 2, and it becomes difficult to planarize the GaN layer.

In the present invention, in order to obtain a flat GaN layer with high reproducibility, a buffer layer made of AlN is directly epitaxially grown on the substrate as a first constitution, and thereafter the nitride GaNx target is reacted with a reactive gas flow rate / (reactive gas flow rate + rare gas Flow rate) is set to be less than 20%, it is preferable that the GaN layer is epitaxially grown on the buffer layer.

In addition to the first configuration, it is preferable that, as the second configuration, the lattice constant of the a-axis at the interface with the GaN layer of the buffer layer is controlled to be equal to or larger than the bulk lattice constant. By doing so, as described above, the lattice mismatch rate at the interface between the GaN layer and the AlN layer is reduced, and the planarization of the GaN layer is further promoted.

As a third configuration, it is more preferable that the buffer layer is controlled to have a + c polarity in addition to the first and second configurations. By doing this, as described above, the planarization of the GaN layer to be formed thereon is further promoted as compared with the buffer layer in which -c polarity or -c polarity is mixed.

As a fourth configuration, in addition to the first to third configurations, it is preferable that the substrate is placed apart from the heater, and the substrate is heated to a temperature of 300 ° C or higher and 1200 ° C or lower to form the buffer layer . By doing this, as described above, the buffer layer is easily formed with the + c polarity, thereby effectively functioning in planarization of the GaN layer.

In addition to the first to fourth structures, as the fifth structure, it is more preferable that the buffer layer is 1 mu m or more. By doing so, as described above, the lattice constant of the a-axis at the interface with the GaN layer tends to be equal to or larger than the bulk lattice constant, which effectively acts to planarize the GaN layer.

As a sixth configuration, it is preferable to use a nitride GaNx target having a mole ratio of Ga / (Ga + N) of 53.0% to 59.5% in addition to the first to fifth configurations. By doing so, as described above, the nitride-based GaNx and the metal-phase Ga can be supplied as balanced sputter particles onto the substrate, thereby promoting the planarization of the GaN layer. In addition, metal Ga is not easily precipitated on the surface of the target, and a stable process can be easily reproduced.

As a seventh configuration, in addition to the first to sixth configurations, the GaN layer is preferably formed at a temperature of 500 ° C or more and 1000 ° C or less. By doing so, the sputtering particles physically adsorbed on the substrate (particularly the metal phase Ga) are easily migrated on the substrate, and the planarization of the GaN layer is promoted.

In the present embodiment, a nitride GaNx target having a mole ratio of Ga / (Ga + N) of 53.0% to 59.5% is used as a target used for forming a GaN layer. However, AlGaInN, InGaN, or the like may be formed by further containing Al or In.

In view of the above, in order to obtain a flat GaN layer with high reproducibility, it is necessary to control the lattice constant of the a-axis at the interface with the GaN layer to be equal to or larger than the bulk lattice constant and to control the polarity to + c polarity, And a nitride GaNx target having a mole ratio of Ga / (Ga + N) set in a range of 53.0% to 59.5% was grown at a reactive gas flow rate / (reactive gas flow rate + The rare gas flow rate) is set to be less than 20%, it is preferable that the GaN layer is epitaxially grown on the buffer layer.

By using the above-described method and apparatus for forming a nitride semiconductor layer, it becomes possible to obtain a flat GaN layer with high reproducibility by a sputtering method.

[Second Embodiment]

A semiconductor device and a manufacturing method thereof according to a second embodiment of the present invention will be described with reference to FIG.

Fig. 9 is a schematic cross-sectional view showing an example of a semiconductor device manufactured by the method for forming a nitride semiconductor layer according to the first embodiment.

First, the structure of the semiconductor device according to the present embodiment will be described with reference to FIG. The semiconductor device shown in Fig. 9 is an example of a light emitting diode (LED) using a nitride semiconductor material.

On the substrate 400, a buffer layer 402 is formed. On the buffer layer 402, a nitride semiconductor intermediate layer 404 is formed. An n-type nitride semiconductor layer 406 is formed on the nitride semiconductor intermediate layer 404. On the n-type nitride semiconductor layer 406, a nitride semiconductor active layer 408 is formed. On the nitride semiconductor active layer 408, a p-type nitride semiconductor layer 410 is formed. A transparent electrode layer 412 is formed on the p-type nitride semiconductor layer 410. A part of the regions of the transparent electrode layer 412, the p-type nitride semiconductor layer 410, the nitride semiconductor active layer 408 and the n-type nitride semiconductor layer 406 is removed to the middle of the n-type nitride semiconductor layer 406 And an n-type electrode 414 is formed on the top surface of the n-type nitride semiconductor layer 406 exposed thereby. On the transparent electrode layer 412, a p-type electrode 416 is formed. A protective film 418 is formed on the side surfaces and the upper surface of the semiconductor laminated structure thus configured except for at least a part of the regions of the n-type electrode 414 and the p-type electrode 416.

Substrate 400 as for example may be applied to α-Al ₂ O ₃ substrate. AlN or AlGaN can be applied as a material for forming the buffer layer 402. [ GaN, AlGaN, AlGaInN, and InGaN may be used as a material for constituting the nitride semiconductor intermediate layer 404, the n-type nitride semiconductor layer 406, the nitride semiconductor active layer 408 and the p-type nitride semiconductor active layer 410. The n-type nitride semiconductor layer 406 is formed by adding a donor impurity such as silicon (Si) or germanium (Ge) to the nitride semiconductor material. The p-type nitride semiconductor layer 410 is formed by adding an acceptor impurity such as magnesium (Mg) or zinc (Zn) to the nitride semiconductor material. Although the nitride semiconductor active layer 408 is not particularly limited, for example, an active layer of a multiple quantum well (MQW) structure formed of such a nitride semiconductor material can be applied.

Next, an example of a manufacturing method of the semiconductor device according to the present embodiment will be described with reference to FIG.

First, a buffer layer 402, a nitride semiconductor intermediate layer 404, an n-type nitride semiconductor layer 406, a nitride semiconductor active layer 408, and a p-type nitride semiconductor layer (not shown) are formed on a substrate 400 by sputtering, 410, and a transparent electrode layer 412 are sequentially deposited. Here, the method of forming the nitride semiconductor layer according to the first embodiment can be applied to the steps from the buffer layer 402 to the formation of the p-type nitride semiconductor layer 410. The buffer layer formed in the sputtering chamber 104 corresponds to the buffer layer 402. The nitride semiconductor layer to be formed in the sputtering chamber 105 corresponds to at least a part of the nitride semiconductor intermediate layer 404, the n-type nitride semiconductor layer 406, the nitride semiconductor active layer 408 and the p-type nitride semiconductor layer 410 . By using the film formation method of the nitride semiconductor layer according to the first embodiment, the aforementioned nitride semiconductor laminated structure can be formed while maintaining the flatness of these nitride semiconductor layers. After the formation of the buffer layer 402 to the p-type nitride semiconductor layer 410, an annealing process for activating acceptor impurities in the p-type nitride semiconductor layer 410 before forming the transparent electrode layer 412 May be provided.

Next, a portion of the transparent electrode layer 412, the p-type nitride semiconductor layer 410, the nitride semiconductor active layer 408, and the n-type nitride semiconductor layer 406 is partially removed by photolithography and dry etching to form an n- Layer 406 is removed.

Next, a protective film 418 is formed on the side surfaces and the upper surface of the thus-formed nitride semiconductor laminated structure.

Next, an opening reaching the n-type nitride semiconductor layer 406 is formed in the protective film 418 by photolithography and dry etching, and then an n-type nitride semiconductor layer 406 connected to the n-type nitride semiconductor layer 406 by a lift- Type electrode 414 is formed. Similarly, an opening reaching the transparent electrode layer 412 is formed in the protective film 418, and a p-type electrode 416 connected to the transparent electrode layer 412 is formed by a lift-off method or the like.

Thus, by fabricating the semiconductor device using the film forming method of the nitride semiconductor layer according to the first embodiment, it is possible to form a laminated structure of the nitride semiconductor layers excellent in flatness and crystallinity, and a high-performance light emitting diode Can be realized.

[Modified embodiment]

The present invention is not limited to the above-described embodiment, and various modifications are possible.

For example, the film forming apparatuses shown in Figs. 1 to 3 are merely examples, and modifications and variations are possible without departing from the gist of the present invention. For example, in the film forming apparatus of Fig. 1, three or more sputtering chambers may be provided, and at least one of them may be changed to another film forming apparatus (for example, a CVD apparatus).

The process conditions shown in the first embodiment were obtained in a typical experimental apparatus used by the present inventors. The specific process conditions are preferably optimized appropriately in accordance with the film forming apparatus to be used so as to realize characteristics inherent to the buffer layer and the nitride semiconductor layer described in the above embodiment.

In the second embodiment, a light emitting diode is shown as an example of a semiconductor device to which the method for forming a nitride semiconductor layer according to the first embodiment is applied. However, a device capable of applying the method for forming a nitride semiconductor layer according to the first embodiment Is not limited to this. For example, the present invention can be applied to various semiconductor devices using a nitride semiconductor, such as a light emitting diode, a semiconductor laser, an optical semiconductor amplifier, a semiconductor light receiving element, a HEMT, and a MESFET.

It is to be understood that the above-described embodiments are merely illustrative of some aspects to which the present invention can be applied, and modifications and modifications may be appropriately made without departing from the spirit of the present invention.

[Example]

Hereinafter, examples of the present invention based on the above embodiments will be described together with a comparative example.

(Example)

First, a c-plane sapphire substrate was introduced into the load lock chamber 101 of the sputtering apparatus shown in Fig. 1, and the load lock chamber 101 was evacuated to a vacuum using an exhaust mechanism not shown.

Next, the substrate was transferred to the pretreatment chamber 103 by using the transfer robot 106 of the transfer chamber 102, and preheating was performed so that the substrate temperature became 800 DEG C or higher. In this way, the temperature rise time of the substrate in the next step is shortened, or the water adsorbed on the substrate or the tray for transporting the substrate is desorbed, thereby improving the quality of the buffer layer formed in the next step or improving the reproducibility of the process It gets easier.

Thereafter, the substrate was transported to the first sputtering chamber 104 by using the transport robot 106 of the transport chamber 102, and a buffer layer made of AlN was directly epitaxially grown on the substrate by a sputtering method. As a first sputtering chamber 104 for epitaxially growing a buffer layer made of AlN, a stationary-facing sputtering chamber as shown in Fig. 2 was used. Conditions for forming the buffer layer were as follows.

(Conditions for forming the buffer layer)

· Substrate: c-plane sapphire substrate

· Film formation method:

The final pressure before film formation: 1.0 × 10 ^-4 Pa

· Target: Al

Substrate temperature during film formation: 700 ° C

Pressure at the time of film formation: 1.3 Pa

Sputtering gas at the time of film formation: Ar + N ₂ (N ₂ flow rate / (N ₂ flow rate + Ar flow rate): 20%)

· High-frequency power at the time of film formation: 2500 W

Film thickness of the buffer layer: 1.1 mu m

Distance from the substrate facing surface of the substrate and the heater: 2 mm

The AlN film is epitaxially grown on the substrate under the above conditions to form a buffer layer made of AlN having a + c polarity and a lattice constant of the a-axis at the interface with the GaN layer (the surface of the AlN layer) . In this embodiment, when the N ₂ flow rate / (N ₂ flow rate + Ar flow rate) is 50% or more, an AlN film in which -c polarity is mixed is obtained. When the thickness of the buffer layer is less than 500 nm, a buffer layer made of AlN having a lattice constant of the a-axis less than the lattice constant of the bulk at the interface (the surface of the AlN layer) with the GaN layer is obtained.

Next, the substrate was transported to the second sputtering chamber 105 using the transport robot 106 of the transport chamber 102, and the GaN layer was epitaxially grown on the buffer layer made of AlN by the sputtering method. As the second sputtering chamber 105 for epitaxially growing the GaN layer, an offset type sputtering chamber as shown in Fig. 3 was used, and the deposition conditions of the GaN layer were as follows.

(Conditions for forming the GaN layer)

· Substrate: c-plane sapphire substrate

· Film formation method: offset film formation

The final pressure before film formation: 1.0 × 10 ^-4 Pa

Target: Nitride GaNx (Ga / (Ga + N) mole ratio: 53.0 to 59.5%)

Substrate temperature during film formation: 850 ° C

Pressure at the time of film formation: 0.13 Pa

Process gas at the time of film formation: Ar + N ₂ (N ₂ flow rate / (N ₂ flow rate + Ar flow rate): 5%)

· High-frequency power at the time of film formation: 1000 W

6 is a cross-sectional TEM (transmission electron microscope) image showing a sectional structure of the GaN layer formed under the above conditions. As shown in Fig. 6, a flat GaN layer could be obtained by epitaxially growing a GaN layer under the above conditions. When such a GaN layer is formed, it can be observed as a mirror image by visual observation. 6 shows a GaN layer having a film thickness of 400 nm and a convex structure is partially observed. However, by making the film thicker or optimizing film forming conditions, the convex structure can be reduced .

When the lattice constant of the a-axis of the buffer layer made of AlN is less than the lattice constant of the bulk, the flatness of the GaN layer is impaired and the surface becomes cloudy. Also, when the AlN layer in which the -c polarity is mixed is used, the flatness of the GaN layer is also impaired and the surface becomes cloudy. Also, in this embodiment, when the N ₂ flow rate / (N ₂ flow rate + Ar flow rate) was set to 20% or more, the flatness of the GaN layer was impaired and the surface became cloudy.

In addition, even when the same film-forming process as in the present example was carried out a plurality of times, the GaN film equivalent to the above was obtained with high reproducibility.

That is, according to this embodiment, a flat GaN film can be obtained with high reproducibility.

[Comparative Example 1]

As Comparative Example 1 of the present invention, the flatness and reproducibility of the GaN layer in the case of using the techniques described in Patent Document 1 and Patent Document 2 will be described.

In this comparative example, a liquid metal Ga target or a solid metal Ga target was used for forming the GaN layer. In order to prevent the metal Ga from being received in the GaN layer, an Ar flow rate of 80 sccm and an N ₂ flow rate of 20 sccm were used as a process gas for forming the GaN layer. In this comparative example, the sputtering apparatus of FIGS. 2 and 3 having inverted upper and lower structures was used as the first sputtering chamber 104 and the second sputtering chamber 105, respectively, in order to use the metal Ga target. Other conditions were the same as those in the above embodiment.

7 is a cross-sectional TEM image showing the cross-sectional structure of the GaN layer formed under the above conditions. The lattice constant of the a-axis at the interface with the GaN layer of the buffer layer made of AlN film formed under the above conditions was the same as in the above example. However, the morphology of the GaN layer formed on this buffer layer is as shown in Fig. 7, and it is found that the flatness is worse than in the above embodiment. In Fig. 7, a GaN layer having a film thickness of about 450 nm is shown, but even if the film thickness is increased, the flatness is not improved. Also, even if the polarity or lattice constant of the buffer layer made of AlN is changed, the morphology shown in Fig. 7 is not greatly improved.

Fig. 7 shows a cross-sectional TEM image of a GaN layer formed using a solid metal Ga target, but the case was also the same when a liquid Ga target was used. When the same evaluation is repeatedly performed, when the liquid Ga target is used, good reproducibility can not be obtained because the target changes with time.

From the results of this comparative example, it was found that the object of the present invention to obtain a flat GaN film with high reproducibility can not be attained by the techniques described in Patent Document 1 and Patent Document 2.

[Comparative Example 2]

As Comparative Example 2 of the present invention, the flatness and reproducibility of the GaN layer when the technique described in Patent Document 3 is used will be described. That is, after a low-temperature GaN buffer layer is formed using a nitride GaN target, the substrate is heated to a temperature range of 1000 ° C to 1100 ° C to crystallize the buffer layer. Thereafter, a GaN layer is formed by a sputtering method using a nitride GaN target The flatness and reproducibility of the GaN layer in the case of film formation will be described.

In this comparative example, a low-temperature GaN buffer layer is formed at room temperature using a nitride GaN target in the first sputtering chamber 104, and then the substrate is subjected to heat treatment at 1000 占 폚 in the pretreatment chamber 103 to crystallize the low- did. Thereafter, in the second sputtering chamber 105, a GaN layer was formed on the crystallized buffer layer using a nitride GaN target. Other conditions were the same as those in the above embodiment.

8 is a cross-sectional TEM image showing the cross-sectional structure of the GaN layer formed under the above conditions. As shown in Fig. 8, it can be seen that the GaN layer formed under the above conditions is inferior in planarity to the GaN layer formed under the conditions of the above embodiment. In Fig. 8, the GaN layer has a film thickness of about 180 nm. However, even if the film thickness is increased, the flatness is not improved. When the reproducibility was evaluated, only a GaN layer having poor flatness as in Fig. 8 was obtained. In this comparative example, even if the buffer layer according to the present invention, that is, the buffer layer made of AlN having the + c polarity and having the lattice constant of the a-axis at the interface with the GaN layer is larger than the bulk lattice constant, The same result was obtained.

From the results of this comparative example, it was found that the object of the present invention to obtain a flat GaN layer with high reproducibility can not be achieved by the technique described in Patent Document 3.

[Comparative Example 3]

As Comparative Example 3 of the present invention, the flatness and reproducibility of the GaN layer when the technique described in Patent Document 4 is used will be described. In particular, the flatness and reproducibility of the GaN film when the GaN film is formed by the sputtering method using the nitride GaNx target having a mole ratio of Ga / (Ga + N) of more than 59.5% and not more than 80% will be described. In this comparative example, the nitride-based GaNx target having a Ga / (Ga + N) molar ratio of 80% was used, and the apparatus for forming the buffer layer and the GaN layer and the film forming conditions were the same as those in the above embodiment.

In this comparative example, at the time of forming the GaN layer, the metal Ga was precipitated from the target surface, and an anomalous discharge occurred a plurality of times. As a result, stable film formation was difficult. In addition, even when an abnormal discharge did not occur, the composition of the target varied with time, and as a result, the flatness of the GaN layer changed over time.

From the results of this comparative example, it was found that the object of the present invention to obtain a flat GaN film with high reproducibility can not be attained only by the technique described in Patent Document 4.

[Comparative Example 4]

As Comparative Example 4 of the present invention, the flatness and reproducibility of the GaN layer when the technique described in Patent Document 5 is used will be described. That is, there is provided a method of manufacturing a sputtering target, comprising the steps of: sputtering the target by using a sputtering gas as a target of either or both of a metal Ga and a nitride GaN to supply sputter particles onto the substrate; The step of feeding the radical to the substrate is alternately repeated to explain the flatness of the GaN layer when the GaN layer is formed. In this comparative example, a nitride GaN target is used as a target used for forming a GaN layer, and the nitride GaN target is sputtered using Ar gas. In this comparative example, a sputtering apparatus in which a nitride GaN target was disposed on one sputtering cathode 308 of the sputtering apparatus shown in Fig. 3, and the other sputtering cathode 308 was replaced with a radical gun, . In Patent Document 5, a separation vessel for separating the space from the front surface of the radical gun is provided in the space on the front surface of the target to suppress the reaction between the reactive gas and the target.

In this comparative example, the separation vessel is provided to suppress the reaction between the reactive gas and the target, and the step of feeding the sputter particles to the substrate and the step of supplying the radical containing N from the radical gun to the substrate are alternately repeated I will. The conditions for forming the buffer layer and the GaN layer were the same as those of the above embodiment.

When the GaN layer was formed as described above, a GaN layer having a morphology similar to that shown in Fig. 8 and having a reduced flatness was obtained. Further, when the reproducibility was evaluated, good reproducibility was not obtained because the target varied with time.

From the results of this comparative example, it was found that the object of the present invention to obtain a flat GaN layer with high reproducibility can not be achieved by the technique described in Patent Document 5. [

100: Deposition device
101: Road lock room
102: Carrier
103: Pretreatment room
104: first sputtering chamber
105: second sputtering chamber
106: Transfer robot
201, 301: Vacuum container
203, 308: sputtering cathode
204, 307: target
207, 310: Sputtering power source
209: Heater
211: Substrate placement mechanism
212, 313: substrate
305: Heating stage

Claims (12)

A step of epitaxially growing a buffer layer made of AlN or AlGaN on a substrate,
A metal nitride target containing Ga and GaN is used on the buffer layer and the flow rate of the reactive gas containing nitrogen is set to be less than 10% of the flow rate of the entire process gas, and the nitride semiconductor containing at least GaN A step of epitaxially growing a layer
And forming a nitride semiconductor layer on the nitride semiconductor layer. The method according to claim 1,
Wherein the buffer layer has a lattice constant of the a-axis at the interface with the nitride semiconductor layer is not less than a bulk lattice constant
Wherein the nitride semiconductor layer is formed on the substrate. 3. The method according to claim 1 or 2,
The buffer layer has a + c polarity
Wherein the nitride semiconductor layer is formed on the substrate. 3. The method according to claim 1 or 2,
In the step of epitaxially growing the buffer layer, the substrate is heated to a temperature of 300 ° C or higher and 1200 ° C or lower by radiation heat from a heater disposed apart from the substrate
Wherein the nitride semiconductor layer is formed on the substrate. 3. The method according to claim 1 or 2,
The buffer layer has a thickness of 1 mu m or more
Wherein the nitride semiconductor layer is formed on the substrate. 3. The method according to claim 1 or 2,
The buffer layer is formed by a sputtering method
Wherein the nitride semiconductor layer is formed on the substrate. delete 3. The method according to claim 1 or 2,
The metal nitride target preferably has a molar ratio of Ga / (Ga + N) of 53.0% to 59.5%
Wherein the nitride semiconductor layer is formed on the substrate. 3. The method according to claim 1 or 2,
The nitride semiconductor layer is formed at a temperature of 500 ° C or higher and 1000 ° C or lower
Wherein the nitride semiconductor layer is formed on the substrate. 3. The method according to claim 1 or 2,
The nitride semiconductor layer may be made of GaN, AlGaN, InGaN or AlGaInN
Wherein the nitride semiconductor layer is formed on the substrate. 3. The method according to claim 1 or 2,
The substrate is a c-plane sapphire substrate
Wherein the nitride semiconductor layer is formed on the substrate. A method of manufacturing a nitride semiconductor light emitting device, comprising the steps of epitaxially growing the buffer layer and the nitride semiconductor layer on a substrate by the method of forming a nitride semiconductor layer according to any one of claims 1 to 5
Wherein the semiconductor device is a semiconductor device.

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