Process for producing a silicon carbide single crystal

Abstract

A process for producing a silicon carbide single crystal, comprising: Providing a substrate of a SiC single crystal on a {1-100} plane which is a growth plane of a seed crystal using a seed crystal having an exposed {1-100} plane, Producing a seed crystal with an exposed {11-20} plane from the SiC single crystal, Cutting out the SiC single crystal parallel to the {0001} plane or with a predetermined offset angle to the {0001} plane, Growing the SiC single crystal on the {11-20} plane, which is the growth plane of the seed crystal, such that the substrate has a surface that is parallel to a {0001} plane or has a predetermined offset angle with respect to the {0001} plane, wherein the predetermined offset angle is up to 10 degrees in a <11-20> direction with respect to a {0001} plane, Growing the silicon carbide single crystal on the surface of the substrate as a seed crystal and characterized by Selecting a silicon carbide single crystal with an L-dislocation density equal to or less than 300 dislocations / cm 2 , where the L-dislocation has a Burgers vector defined as b which satisfies the expression b > <0001> + 1 / 3 <11-20> fulfilled.

Description

Technical field

[0001] The present invention relates to a method for producing the SiC single crystal. State of the art

[0002] Until now, a high-quality SiC single-crystal wafer has been disclosed in JP 2008-515 748 A and its family member US 7,314,520 A. In the SiC single-crystal wafer disclosed in JP 2008-515 748 A, the dislocation density, which adversely affects device properties, is set to a specified value or lower, and in particular, for wafers with a diameter of 3 inches, the dislocation density is set to 2500 cm -2 or lower, so as to be suitable for device fabrication. In this specification, the term dislocation refers to linear crystal defects, and a targeted dislocation is a spiral dislocation having an orientation parallel to a c-axis.

[0003] DE 102 47 017 A1 teaches a method for producing a SiC single crystal with an epitaxial film for producing an electronic device from wafers made from this single crystal. US 2012 0 073 495 A1, which is considered closest, teaches a method according to the preamble of claims 1 and 2.

[0004] US 2012 0 294 790 A1 describes methods for producing SiC single crystal ingots on a SiC substrate having a tilt of 0.1° to 10° relative to the (0001) plane in the <11-20> or <1-100> direction.

[0005] The inventors of the present invention have conducted investigations based on extensive experiments, and as a result, it was found that even if the density of the spiral dislocation is set to only the specified value or less, a SiC single crystal suitable for manufacturing a device capable of suppressing a leakage current as shown in Patent Literature 1 is not obtained. Summary of the invention

[0006] It is an object of the present invention to provide a method for producing a high-quality SiC single crystal suitable for producing a device capable of suppressing leakage current. This object is achieved by a method according to claim 1 or 2.

[0007] According to one aspect of the present invention, the silicon carbide single crystal produced by the inventive methods comprises a spiral dislocation. The spiral dislocation comprises an L-dislocation with a Burgers vector defined as b, which satisfies the following equation: b > <0001> + 1 / 3 <11-20>. The L dislocation has a density equal to or less than 300 dislocations / cm 2 is.

[0008] In the SiC single crystal, the density of L-dislocations, which can cause the formation of a leakage current, in the spiral dislocations is equal to or less than 300 / cm 2 This makes it possible to provide a high-quality SiC single crystal suitable for fabricating a device that can suppress leakage current.

[0009] According to the present invention, a method for producing a silicon carbide single crystal comprises the features recited in claim 1 or 2. As described above, growth of a new SiC single crystal is enabled using a SiC single crystal, and as a result, a high-quality SiC single crystal inheriting the quality of the base seed crystal can be produced. Short description of the drawings

[0010] The above and other objects, features, and advantages of the present invention will become apparent from the following detailed description and with reference to the accompanying drawings. The drawings depict: Fig. 1 is a schematic cross-sectional view of a SiC single crystal produced by the methods of the invention. Fig. 2A is an enlarged schematic view showing a state of an L-dislocation and a spiral distortion occurring around the L-dislocation in a region R1 of Fig. 1 illustrates. Fig. 2B is a schematic view showing a direction of the Fig. 2A illustrates the spiral distortion. Fig. Figure 2C is a diagram illustrating the details of a Burgers vector, which represents a direction of the Fig. 2B is the spiral distortion. Fig. 3A is an enlarged schematic view showing a state of an nL dislocation and a spiral distortion occurring around the nL dislocation in a region R2 of Fig. 1 illustrates. Fig. 3B is a schematic view showing a direction of the Fig. 3A illustrates the spiral distortion. Fig. Figure 3C is a diagram illustrating the details of a Burgers vector, which represents a direction of the Fig. 3B illustrated spiral distortion. Fig. Figure 4 is a schematic view illustrating a crystal orientation of a SiC single crystal. Fig. Figure 5 is a graph illustrating the results of investigating a leakage current when a pn diode is made of a SiC single crystal. Embodiments for carrying out the inventionFirst embodiment

[0011] A first embodiment of the present invention will be described with reference to the drawings. A SiC single crystal 1 produced by the inventive method according to this embodiment, as shown in Fig. 1 is obtained by setting a SiC single crystal ingot (SiC single crystal ingot) formed by, for example, a sublimation recrystallization method or a gas supply method, parallel to a {0001} plane or at a predetermined offset angle to the {0001} plane, and cutting the SiC single crystal into the substrate shape. The SiC single crystal 1 cut into the substrate shape is illustrated. The SiC single crystal is not limited to the SiC single crystal cut into the substrate shape, but includes an ingot shape and also a structure in which an unnecessary part is removed from the ingot.

[0012] The SiC single crystal 1 includes a spiral dislocation 2. In the crystal, the density of spiral dislocation 2, that is, the number of spiral dislocations 2 per 1 cm 2are present when the SiC single crystal 1 is cut in a direction perpendicular to the spiral dislocation 2, a relationship described later.

[0013] The inventors of the present invention investigated a relationship between the density of the spiral dislocation 2 and a leakage current through various experiments. For example, the inventors of the present invention provided a structure commonly used to investigate whether a leakage current occurs, specifically, a pn diode, and investigated whether a leakage current occurs when a desired voltage is applied. The pn diode is configured, for example, by ion-implanting impurities into the SiC single crystal 1 and setting the impurity concentration to 1 × 10 21 cm -3As a result, it was confirmed that although the density of the spiral dislocation 2 and the leakage current have a correlation, the leakage current does not remain constant even if the density of the spiral dislocation 2 remains the same, and that spiral dislocations 2 that are intentional and unintentional in the manufacture of a device exist.

[0014] The inventors of the present invention have conducted intensive studies and, as a result, found that two types of spiral dislocations 2 occur, that is, spiral dislocations 2 having a larger and a smaller distortion, wherein the spiral dislocation 2 with a smaller distortion hardly causes the generation of the leakage current and the spiral dislocation 2 with a larger distortion causes the generation of the leakage current.

[0015] Until now, all spiral dislocations 2 have been considered equivalent regardless of the magnitude of the strain. A spiral dislocation density 1c is defined in patent literature 1. The general definition of the spiral dislocation is the Burgers vector b = 1c = <0001> However, no detailed description is given regarding the technique for measuring the Burgers vector. For this reason, all spiral dislocations 2 are considered equal, regardless of the distortion magnitude, and the spiral dislocation density 2 is defined accordingly. However, according to the results found by the present inventors, it was found that when defining whether the SiC single crystal is intended for device fabrication or not by the spiral dislocation density 2, it is necessary to define the spiral dislocation density 2 while also considering the distortion magnitude of the spiral dislocation 2.In other words, even if the density of the spiral dislocation 2 is set equal to or less than a specified value, a SiC single crystal suitable for manufacturing a device capable of suppressing the leakage current can be obtained if all the spiral dislocations 2 are uniformly regarded as the same spiral dislocation 2 without considering the magnitude of the distortion of the spiral dislocation 2.

[0016] The Fig. 2A to 2C and the Fig. 3A to 3C are diagrams illustrating spiral dislocations 2 different in terms of the magnitude of the distortion. The spiral dislocation 2 with a larger distortion is shown with reference to the Fig. 2A to 2C, and the spiral dislocation 2 with a lower distortion is described with reference to the Fig. 3A to 3C. In the following description, the dislocation with a larger distortion that causes the formation of the leakage current in the spiral dislocations 2 is referred to as "dislocation with leakage current 2a (L-dislocation 2a)", and the dislocation with a smaller distortion that hardly causes the formation of the leakage current is referred to as "dislocation with negligible leakage current 2b (nL-dislocation 2b)".

[0017] As in the Fig. 2A and Fig. 3A, a distortion is formed spirally around a dislocation core of the spiral dislocation 2. As a result of the confirmation obtained by the experiments, the spiral distortion in the Fig. 2A is larger and the spiral distortion in the one shown in Fig. 3A illustrated nL dislocation 2b is smaller than comparatively the L dislocation 2a.

[0018] In the Fig. 2B and Fig. 3B, in the L-dislocation 2a and the nL-dislocation 2b, the Burgers vectors corresponding to the direction of the spiral distortions are shown as directions b1 and b2, respectively. Such Burgers vectors b1 and b2 can be Fig. 2C and 3C respectively.

[0019] Basically, the spiral dislocation 2 becomes a dislocation with a C-axis component

[0001] , as shown by the Fig. 4 is a schematic view of a crystal orientation of the SiC single crystal 1 configured by a hexagonal crystal. As a result of conducting various investigations and analyses on the SiC single crystal 1, it was confirmed that there is a spiral dislocation 2 in which, in addition to a c-axis component

[0001] , a dislocation of [1-100] and a dislocation of 1 / 3 [11-20] are present.

[0020] In particular, for the L-dislocation 2a, it was experimentally confirmed that the Burgers vector b1 contains a vector c in the <0001> -direction and a vector m in the <1-100>-direction. In the nL dislocation 2b, the Burgers vector b2 includes a vector c in the <0001> -direction and a vector a in the 1 / 3 <11-20>-direction.

[0021] The spiral dislocation 2 with a smaller Burgers vector b than the confirmed nL dislocation 2b can therefore be regarded as the nL dislocation 2b that hardly causes leakage current generation. In other words, if the magnitude of the Burgers vector b is equal to or less than the magnitude of the combination of at least the vector c in the <0001> -direction and the vector a in the 1 / 3 <11-20>-direction, the spiral dislocation 2 can be regarded as the nL dislocation 2b. This means that b ≤ <0001> + 1 / 3 <11-20> is satisfied, that is, the relationship b 2 ≤ c 2 + 2a c + a 2(inner product of the vector a c = a × c × cos90 degrees = 0) is satisfied. Regarding the sizes of the corresponding vectors, in the case of 4H-SiC, vector c is equal to 1.008 nm, vector a is equal to 0.309 nm, and vector m is equal to 3 0,5 × a = 0.535 nm.

[0022] If, on the other hand, the size of the Burgers vector b is the size of the combination of the vector c in the <0001> -direction and the vector a in the 1 / 3 <11-20> direction, the spiral dislocation 2 is more likely to become the nL dislocation 2b. Therefore, the spiral dislocation 2 is regarded as the L dislocation 2a. That is, if the magnitude of the Burgers vector b exceeds the magnitude of the combination of the vector c in the <0001> -direction and the vector a in the 1 / 3 <11-20> direction, the spiral dislocation 2 is considered to be the L-dislocation 2a. If b > <0001> + 1 / 3 <11-20> is satisfied, that is, if the relationship b 2 > c 2 + 2a c + a 2(inner product of the vector a c = a × c × cos90 degrees = 0) is satisfied, the spiral dislocation 2 is considered to be the L-dislocation 2a.

[0023] In this way, the spiral dislocation 2 is divided into the L dislocation 2a and the nL dislocation 2b. Ions are implanted into the SiC single crystal 1 to form a pn diode. Experiments were conducted to measure the density of the L dislocation 2a and the density of the nL dislocation 2b, and to investigate whether a leakage current is generated. As a result, it is confirmed that the generation of a leakage current mainly depends on the density of the L dislocation 2a, and the occurrence of a large amount of nL dislocation 2b hardly causes the formation of a leakage current.

[0024] As in Fig. 5, it can be specifically confirmed that in the configuration of a diode, hardly any leakage current is generated when the density of the L-dislocation 2a is equal to or less than 100 dislocations / cm 2If the density of the L-dislocation 2a is equal to or less than 300 dislocations / cm 2 a small amount of leakage current is generated, but it hardly affects the device fabricated. Therefore, in this case, it can also be determined that the SiC single crystal 1 is intended for device fabrication. On the other hand, if the density of the L-dislocation 2a is approximately 1000 dislocations / cm 2 a leakage current is generated. Since the manufactured device is affected by the leakage current in this case, such a SiC single crystal 1 is not intended for device fabrication.

[0025] Whether the spiral dislocation 2 is the L-dislocation 2a or the nL-dislocation 2b can be confirmed by large-angle convergent beam electron diffraction (LACBED). Alternatively, other techniques such as transmission electron microscopy (TEM) observation or X-ray topography can be used to confirm whether the spiral dislocation 2 is the L-dislocation 2a or the nL-dislocation 2b.

[0026] Therefore, in the SiC single crystal 1, the density of the L-dislocation 2a in the spiral dislocation 2, in which the Burgers vector b satisfies the relationship b > <0001> + 1 / 3 <11-20>, equal to or less than 300 dislocations / cm 2 , preferably 100 dislocations / cm 2 As a result, a high-quality SiC single crystal 1 suitable for manufacturing a device capable of suppressing a leakage current can be provided.

[0027] The high-quality SiC single crystal 1 described above can be manufactured, for example, by the following methods. First, a SiC single crystal is grown on a {1-100} plane, which is a growth plane of a seed crystal, using a seed crystal with an exposed {1-100} plane. Next, a seed crystal with an exposed {11-20} plane is prepared from the SiC single crystal. The SiC single crystal is then grown on the {11-20} plane, which is the growth plane of the seed crystal. Subsequently, a substrate-like SiC single crystal can be manufactured by cutting the SiC single crystal parallel to the {0001} plane or at a predetermined offset angle from the {0001} plane. Since the SiC single crystal is manufactured from a so-called a-plane-grown crystal, the SiC single crystal originally contains almost no spiral dislocation 2.

[0028] When a new SiC single crystal ingot is grown using the high-quality SiC single crystal as a seed crystal by a sublimation-recrystallization method or a gas-supply method, a high-quality SiC single crystal ingot inheriting the quality of the parent seed crystal can be produced. Specifically, when the surface of the SiC single crystal has a predetermined offset angle to the {0001} plane, a high-quality SiC single crystal ingot can be produced while preventing heterogeneous polymorphism from forming due to step growth. The substrate-like SiC single crystal 1 can be produced by cutting from the SiC single crystal ingot parallel to the {0001} plane or at a predetermined offset angle to the {0001} plane.Furthermore, the SiC single crystal 1 in which the density of the L dislocation 2a corresponds to the above-specified range is selected from the produced SiC single crystals 1. This makes it possible to obtain the high-quality SiC single crystal 1 described in this embodiment, which is intended for device fabrication.

[0029] As a result, when the predetermined offset angle from the {0001} plane is up to 10 degrees in a <11-20> direction, the Burgers vector b of the L dislocation 2a of the spiral dislocation 2 present in the seed crystal is <0001> + <1-100> expected to <0001> + 1 / 3 <11-20>. Therefore, the L dislocation 2a can be transformed into the nL dislocation 2b and is more effective. This principle is based on the fact that the orientation of the spiral dislocation 2 tends to shift from the <1-100> direction to the <11-20> direction due to growth.

[0030] Since the growth, in which the predetermined offset angle from the {0001} plane is up to 10 degrees in the <11-20> direction, is repeated several times, the Burgers vector b tends to <0001> + 1 / 3 <11-20>, and the L dislocation 2a can be exponentially converted into the nL dislocation 2b, which is therefore even more effective. As noted above, this principle is based on the fact that the orientation of the spiral dislocation 2 tends to shift from the <1-100> direction to the <11-20> direction due to growth.

[0031] In the above growth, if the offset angle is greater than 10 degrees, the problem of stacking faults occurs. Therefore, a high-quality SiC single crystal suitable for use in device fabrication cannot be obtained.

[0032] As described above, in this embodiment, the spiral dislocation 2 is divided into the L dislocation 2a and the nL dislocation 2b, and the density of the L dislocation 2a is set to be equal to or less than 300 dislocations / cm 2 , preferably 100 dislocations / cm 2 As a result, a high-quality SiC single crystal 1 suitable for manufacturing a device capable of suppressing a leakage current can be provided. Further embodiments

[0033] The present invention is not limited to the above embodiments and can be suitably modified within the scope of the claims.

[0034] For example, the plane orientation and manufacturing method of the SiC single crystal 1 manufactured by the methods of the present invention described in the above embodiments can be arbitrarily selected, and at least the density of the L-dislocation 2a in the SiC single crystal 1 can be within the range described in the above embodiments. In the manufacture of the SiC single crystal ingot, a spiral dislocation-generating region in which the spiral dislocation 2 is positively formed may be partially provided, and a low spiral dislocation density region in which the density of the spiral dislocation 2 becomes lower may be provided in the other region. In this case, in the low spiral dislocation density region used for manufacturing the device, the density of the L-dislocation 2a can be within the range described in the above embodiments.

[0035] In the above embodiments, a pn diode is fabricated as an example of the device for forming the SiC single crystal 1, and whether or not a leakage current is generated is examined. Other elements such as a MOSFET have the same relationship as the pn diode in terms of whether or not a leakage current is generated. Therefore, when the density of the L dislocation 2a is within the range described in the above embodiments, the SiC single crystal 1 is intended for fabricating a device other than the diode.

[0036] When representing a vector, the selected letter should typically be bolded or a right-pointing arrow should be placed above the letter. However, due to limitations of electronic applications, the vector is displayed before the desired letter. When representing crystal alignment, a bar (-) should typically be placed above the desired number. However, in this description, due to limitations of electronic applications, the bar is placed before the desired number.

Claims

[1] A process for producing a silicon carbide single crystal, comprising: Providing a substrate of a SiC single crystal on a {1-100} plane which is a growth plane of a seed crystal using a seed crystal having an exposed {1-100} plane, Producing a seed crystal with an exposed {11-20} plane from the SiC single crystal, Cutting out the SiC single crystal parallel to the {0001} plane or with a predetermined offset angle to the {0001} plane, Growing the SiC single crystal on the {11-20} plane, which is the growth plane of the seed crystal, such that the substrate has a surface that is parallel to a {0001} plane or has a predetermined offset angle with respect to the {0001} plane, wherein the predetermined offset angle is up to 10 degrees in a <11-20> direction with respect to a {0001} plane, Growing the silicon carbide single crystal on the surface of the substrate as a seed crystal and characterized by Selecting a silicon carbide single crystal with an L-dislocation density equal to or less than 300 dislocations / cm 2 , where the L-dislocation has a Burgers vector defined as b which satisfies the expression b > <0001> + 1 / 3 <11-20> fulfilled. [2] A method according to claim 1 for producing a silicon carbide single crystal, further comprising the following steps: Defining the step of growing the SiC single crystal on the {11-20} plane, which is the growth plane of the seed crystal, such that the substrate has a surface having an offset angle of up to 10 degrees in a <11-20> direction with respect to a {0001} plane, and growing the silicon carbide single crystal on the surface of the substrate as a seed crystal as a first step, Defining a step of cutting a substrate with a surface, which has an offset angle of up to 10 degrees in the <11-20> direction with respect to the {0001} plane, from the silicon carbide single crystal grown in the first step and growing the silicon carbide single crystal on the surface of the substrate as the seed crystal as a second step, Repeating the first step and the second step several times and characterized by Selecting a silicon carbide single crystal with an L-dislocation density equal to or less than 300 dislocations / cm 2 , where the L-dislocation has a Burgers vector defined as b, which satisfies the expression b > <0001> + 1 / 3 <11-20> fulfilled.

Images