Sic epitaxial substrate

Abstract

To provide an SiC epitaxial substrate with excellent flatness and restrained warpage.SOLUTION: An SiC epitaxial substrate has an epitaxial film formed by epitaxially growing silicon carbide on a surface of a silicon carbide substrate. The SiC epitaxial substrate has a first principal surface made of the epitaxial film, and a second principal surface as an opposite surface thereof. A diameter of the substrate is 150 mm or more. When the first principal surface is measured with vacuum suction on the second principal surface, a maximum value of SBIR using a 10 mm square site as a reference is 0.1 μm or more and 1.5 μm or less. When the first principal surface is measured with vacuum suction on the second principal surface, a warpage amount in an area within 5 mm from orientation flat is 2 μm or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a SiC epitaxial substrate having an epitaxial film on the surface of a silicon carbide substrate. [Background technology]

[0002] Silicon carbide (hereinafter sometimes referred to as "SiC") epitaxial substrates, in which an epitaxial film made of silicon carbide is formed on the surface of a substrate, are generally grown by a vapor phase growth method. However, it is known that when growing SiC in vapor phase, it also adheres to the opposite side (back side) from the surface on which the epitaxial film is formed, and the SiC grows in protrusions.

[0003] In this way, when SiC grows on the back surface of the substrate, the substrate surface changes, or unevenness occurs due to protrusions that grow three-dimensionally, and in either case, the substrate shape changes from the expected shape, deteriorating the flatness of the substrate. Therefore, when semiconductor elements are fabricated using such substrates, this can adversely affect the characteristics of the semiconductor elements.

[0004] In such a case, it was necessary to remove the SiC formed by the unexpected epitaxial growth by polishing the back surface of the substrate, etc. When performing such a removal operation, the manufacturing process of the SiC substrate becomes complicated, since a protective film for protecting the front surface of the substrate must be formed, the removal operation must be performed, and then the protective film must be removed.

[0005] Therefore, a method for manufacturing a SiC substrate has been proposed in which a protective film is formed on the back surface before epitaxial growth and protrusions are formed on the protective film, making it possible to easily remove the SiC protrusions formed on the back surface of the substrate (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2015-160750 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, when forming an epitaxial film by epitaxial growth, in addition to the above, flatness may be impaired.

[0008] For example, the epitaxial film on the SiC substrate may have a variation in thickness due to the change in the epitaxial growth rate caused by fluctuations in the source gas at the periphery compared to the center of the SiC substrate. When the thickness varies, a difference in stress occurs between the first and second main surfaces, which may cause warping near the orientation flat of the SiC substrate.

[0009] In addition, if the original flatness of the SiC substrate used varies; for example, if the thickness is slightly different between the center and the outer periphery and the substrate is tapered overall, the epitaxial film will inherit the flatness of the original substrate, and the flatness of the formed SiC epitaxial substrate may not be guaranteed.

[0010] Thus, if the flatness of the SiC epitaxial substrate is not sufficiently ensured, problems will occur in the subsequent photolithography process. That is, the back surface of the SiC epitaxial substrate is fixed to a vacuum chuck, and a mask pattern is formed on the surface having the epitaxial film. At this time, if the flatness of the SiC epitaxial substrate is deteriorated, the position of the mask pattern will be shifted from the desired position, and the yield of the obtained semiconductor chips will decrease.

[0011] Therefore, the present inventors have conducted extensive research in order to solve the above problems and provide a SiC epitaxial substrate that has excellent flatness and reduced warpage. [Means for solving the problem]

[0012] The SiC epitaxial substrate in one embodiment is a SiC epitaxial substrate having an epitaxial film formed by epitaxially growing silicon carbide on a surface of a silicon carbide substrate, The SiC epitaxial substrate has a first main surface formed of the epitaxial film and a second main surface that is the opposite surface, and has a diameter of 150 mm or more; When the second main surface is measured by vacuum adsorbing the first main surface, the maximum SBIR value based on a 10 mm square site is 0.1 μm or more and 1.5 μm or less, and when the second main surface is measured without vacuum adsorbing the first main surface, the amount of warping in a region within 5 mm from an orientation flat is 2 μm or less. In the SiC epitaxial substrate, the amount of warpage in the second main surface in a region within 5 mm from an orientation flat is preferably 1 μm or less. The SBIR is preferably such that a site ratio of 0.5 μm or less is 65% or more. The diameter is preferably 200 mm or more. The residues on the second main surface are preferably 0.1 particles / cm. 2 It is preferable that the amount of the ion exchange is less than 1000 nm.

[0013] The SiC epitaxial substrate in one embodiment is a SiC epitaxial substrate having an epitaxial film formed by epitaxially growing silicon carbide on a surface of a silicon carbide substrate, The SiC epitaxial substrate has a first main surface formed of the epitaxial film and a second main surface that is the opposite surface, and has a diameter of 150 mm or more; When the first main surface is measured by vacuum adsorbing the second main surface, the maximum SFQR value based on a 10 mm square site is 0.1 μm or more and 1.5 μm or less, and when the first main surface is measured without vacuum adsorbing the second main surface, the amount of warping in a region within 5 mm from an orientation flat is 2 μm or less. In the SiC epitaxial substrate, it is preferable that the amount of warpage in the first main surface in a region within 5 mm from an orientation flat is 1 μm or less. It is preferable that the SFQR has a site ratio of 0.3 μm or less of 85% or more. It is preferable that the diameter is 200 mm or more. It is preferable that the number of residues on the first main surface is 0.1 / cm. 2 It is preferable that the amount of the ion exchange is less than 1000 nm. Effect of the Invention

[0014] According to the SiC epitaxial substrate of the embodiment, it is possible to provide a SiC epitaxial substrate having excellent flatness and reduced warpage. [Brief description of the drawings]

[0015] [Figure 1] 1 is a side view of a SiC epitaxial substrate according to an embodiment; [Diagram 2] FIG. 2 is a diagram showing an example of division of sites for evaluating flatness in the SiC epitaxial substrate of FIG. [Diagram 3] FIG. 1 is a diagram for explaining a method for measuring SBIR. [Figure 4] FIG. 1 is a diagram for explaining a method for measuring SFQR. [Diagram 5] FIG. 13 is a diagram for explaining a method for measuring the amount of warpage in a region within 5 mm from the orientation flat. [Figure 6] 2A to 2C are diagrams for explaining a method for manufacturing a SiC epitaxial substrate according to one embodiment. [Figure 7] 2A to 2C are diagrams for explaining a method for manufacturing a SiC epitaxial substrate according to one embodiment. [Figure 8] 2A to 2C are diagrams for explaining a method for manufacturing a SiC epitaxial substrate according to one embodiment. [Figure 9] 2A to 2C are diagrams for explaining a method for manufacturing a SiC epitaxial substrate according to one embodiment. [Figure 10]2A to 2C are diagrams for explaining a method for manufacturing a SiC epitaxial substrate according to one embodiment. [Figure 11] 2A to 2C are diagrams for explaining a method for manufacturing a SiC epitaxial substrate according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, a SiC epitaxial substrate and a method for manufacturing the same according to one embodiment of the present invention will be described.

[0017] In addition, in all the drawings for explaining the present embodiment, the same members are generally given the same reference numerals, and the repeated explanations are omitted. In order to make the drawings easier to understand, hatching may be applied even in plan views, and hatching may be omitted even in cross-sectional views.

[0018] <Background to the review> First, in order to explain the present embodiment, the problems of the conventional technology will be described in more detail. For example, in Patent Document 1 described above in the conventional technology section, in addition to the above-described problem of ensuring flatness, there are practical problems as follows.

[0019] For example, in the method for manufacturing a SiC epitaxial substrate described in Patent Document 1, a protective film is formed on a silicon carbide substrate before forming an epitaxial film, and then epitaxial growth is performed. Then, substances attached to the back surface are removed by lifting off the protective film. However, in this method, since epitaxial growth is performed with the protective film attached, organic substances such as resist cannot be used as the protective film.

[0020] Furthermore, in Patent Document 1, anisotropic etching and wet etching are used to lift off the protective film after epitaxial growth, but in this case, there is a risk that the deposits will act as a barrier and cause part of the protective film to remain.

[0021] Also, it is conceivable to use tape peeling to remove the protective film. However, in this case, since the adhesive force of the tape is not uniform or the force acting during peeling is not uniform, there is still a risk that part of the protective film remains. Furthermore, there is also a risk of contamination such as tape residues.

[0022] In the present invention, in addition to the flatness and warpage suppression described in the problems to be solved above, regarding the protective film that can be a problem in Patent Document 1 as described above, a technique for more easily forming and removing it and suppressing the occurrence of residues and the like was also examined. Hereinafter, including this point, the technical idea of this embodiment will be described in detail.

[0023] <SiC Epitaxial Substrate> The SiC epitaxial substrate of this embodiment is, for example, as shown in FIG. 1, the SiC epitaxial substrate 1 in which the epitaxial film 3 is formed on the surface of the silicon carbide substrate 2. This SiC epitaxial substrate 1 is a flat substrate and has a main surface 1a (first main surface) composed of the epitaxial film 3 and a main surface 1b (second main surface) on the opposite side thereof. In this specification, the surface composed of this epitaxial film 3 (main surface 1a) or the surface of the silicon carbide substrate 2 on which the epitaxial film 3 is formed may be referred to as the "front surface", and the opposite surface of this surface may be referred to as the "back surface".

[0024] The silicon carbide substrate 2 is a substrate composed of single-crystalline silicon carbide (SiC). In this embodiment, the flatness when the SiC epitaxial substrate 1 is used satisfies a predetermined range as described later and is good.

[0025] The epitaxial film 3 is an epitaxial film formed by epitaxially growing silicon carbide on the surface of the silicon carbide substrate 2.

[0026] The size of this SiC epitaxial substrate 1 is not particularly limited, but in consideration of efficiency in manufacturing semiconductor chips, the diameter of the substrate is preferably 150 mm or more, more preferably 200 mm or more, and even more preferably 300 mm or more.

[0027] As described above, the SiC epitaxial substrate 1 has the epitaxial film 3 formed on the surface of the silicon carbide substrate 2, and is characterized in that the substrate has very good flatness.

[0028] Specifically, with regard to the flatness of the SiC epitaxial substrate 1, the researchers focused on SBIR (Site Back Surface Referenced Ideal Ranges) and discovered a new manufacturing method that can improve this characteristic, thereby enabling them to obtain a SiC epitaxial substrate 1 with extremely good flatness.

[0029] That is, the SBIR of SiC epitaxial substrate 1 in this embodiment satisfies the condition that the maximum value on main surface 1b of SiC epitaxial substrate 1 is not less than 0.1 μm and not more than 1.5 μm when based on a 10 mm square site.

[0030] By setting the SBIR within a predetermined range in this way, the SiC epitaxial substrate 1 of the present embodiment has good flatness as a substrate, and can improve the manufacturing yield of the chips in the manufacture of semiconductor chips. More specifically, when performing a photolithography process, a mask pattern is formed on the epitaxial film 3 of the SiC epitaxial substrate 1, and since the flatness of the SiC epitaxial substrate 1 is good, the formed mask pattern is a desired pattern, and it is possible to suppress the occurrence of a vertical deviation with respect to the main surface of the substrate. Therefore, when manufacturing a semiconductor chip using this SiC epitaxial substrate 1, the deviation with the mask pattern can be made very small, and the manufacturing yield can be improved.

[0031] Furthermore, it is preferable that the ratio of sites having an SBIR of 0.5 μm or less is 65% or more. If such a site ratio condition is satisfied, the flatness of the SiC epitaxial substrate 1 is very good, and the manufacturing yield of semiconductor chips can be further improved.

[0032] The above site ratio is a ratio calculated as the ratio of the number of sites with an SBIR of 0.5 μm or less to the total number of sites when the sites are divided in the SiC epitaxial substrate 1 as shown in FIG. 2 (number of sites with an SBIR of 0.5 μm or less / total number of sites).

[0033] In measuring the SBIR, first, as shown in Fig. 2, a plurality of sites 10 are partitioned in the SiC epitaxial substrate 1, with each site (evaluation area) being, for example, a 10 mm square. Using this 10 mm square site as a reference, the SBIR can be found as follows. Note that, although this embodiment shows an example in which a 10 mm square site is defined, and flatness is evaluated using this site as a reference, the size of this site can be changed as desired.

[0034] Next, as shown in Fig. 3, main surface 1a, which is the opposite surface of SiC epitaxial substrate 1 to main surface 1b to be measured, is adsorbed and fixed to a flat surface to flatten main surface 1a. Here, arrow 10a in Fig. 3 shows a schematic representation of the length of one side of a square site. SBIR is the difference in height between the highest point and the lowest point on the surface of a site within a given range (e.g., a 10 mm square range) with main surface 1b as the reference (height difference indicated by arrow tSBIR in Fig. 3).

[0035] In this embodiment, the maximum value of SBIR is preferably 1.5 μm or less, and the smaller the value, the more preferable it is because the focusing accuracy can be improved. According to this embodiment, when the SiC epitaxial substrate 1 is divided into a plurality of sites in units of 10 mm square, it is particularly preferable that the maximum value is within the above range (0.1 μm or more and 1.5 μm or less) and the site ratio where the SBIR is 0.5 μm or less is 65% or more. By satisfying such conditions, photolithography processing can be performed with high accuracy, and the manufacturing yield of the obtained semiconductor chip can be improved. Furthermore, the higher the site ratio, the more preferable it is, and therefore, when photolithography processing is applied, a finer wiring pattern can be realized. By improving the flatness, an exposure device with a short exposure wavelength and a small range of DOF (Depth of Focus) can be used, that is, a narrow depth of focus, and thus a finer wiring pattern can be realized, which is more preferable.

[0036] As for the flatness of the SiC epitaxial substrate 1, it has been found that the SFQR (Site Front Side Least Squares Focal Plane Range) characteristic can also be made favorable.

[0037] That is, the SFQR of SiC epitaxial substrate 1 in this embodiment satisfies the condition that the maximum value on main surface 1a of SiC epitaxial substrate 1 is 0.1 μm or more and 1.5 μm or less when based on a 10 mm square site.

[0038] By setting the SFQR within a predetermined range in this way, the SiC epitaxial substrate 1 of the present embodiment has good flatness as a substrate, and can improve the manufacturing yield of the chips in the manufacture of semiconductor chips. Specifically, when a photolithography process is performed, a mask pattern is formed on the epitaxial film 3 of the SiC epitaxial substrate 1, and since the flatness of the SiC epitaxial substrate 1 is good, the formed mask pattern is a desired pattern, and it is possible to suppress the occurrence of a vertical deviation with respect to the main surface of the substrate. Therefore, when manufacturing semiconductor chips using this SiC epitaxial substrate 1, the deviation with the mask pattern can be made very small, and the manufacturing yield can be improved.

[0039] Furthermore, it is preferable that the ratio of sites having a size of 0.3 μm or less in the SFQR is 85% or more. If such a condition for the ratio of sites is satisfied, the flatness of the SiC epitaxial substrate 1 is very good, and the manufacturing yield of semiconductor chips can be further improved.

[0040] The above site ratio is a ratio calculated as the ratio of the number of sites with an SFQR of 0.3 μm or less to the total number of sites when the sites are divided in the SiC epitaxial substrate 1 as shown in FIG. 2 (number of sites with an SFQR of 0.3 μm or less / total number of sites).

[0041] In measuring the SFQR, first, as in the above-mentioned SBIR measurement, in the SiC epitaxial substrate 1, for example, a 10 mm square size is defined as one site (evaluation area), and multiple sites 10 are partitioned and defined as shown in Fig. 2. Using this 10 mm square site as a reference, the SFQR can be obtained as follows. Note that in this embodiment, a 10 mm square site is defined, and flatness is evaluated based on this site, but the size of this site can be changed as desired.

[0042] Next, as shown in Fig. 4, main surface 1b, which is the opposite surface of main surface 1a to be measured in SiC epitaxial substrate 1, is adsorbed and fixed to a flat surface to flatten main surface 1b. Here, arrow 10a in Fig. 4 shows a schematic representation of the length of one side of a square site. In this state, SFQR is calculated by using the least squares method to calculate reference surface 11 based on the shape of the surface of a site within a predetermined range (for example, a range of 10 mm square), and is the sum of the distance from reference surface 11 to the highest point on the site surface and the distance to the lowest point on the site surface (the distance indicated by arrow tSFQR in Fig. 4).

[0043] In this embodiment, the maximum value of SFQR is preferably 1.5 μm or less, and the smaller the value, the better, since the focusing accuracy during exposure with a stepper (reduced projection exposure device) can be improved. According to this embodiment, when the SiC epitaxial substrate 1 is divided into a plurality of sites in units of 10 mm square, it is preferable that the maximum value is within the above range (0.1 μm or more and 1.5 μm or less) and the site ratio where SFQR is 0.3 μm or less is 85% or more. By satisfying such conditions, photolithography processing can be performed with high accuracy, and the manufacturing yield of the obtained semiconductor chips can be improved. Furthermore, the higher the site ratio, the better, and thus a finer wiring pattern can be realized when photolithography processing is applied.

[0044] An apparatus capable of measuring SBIR (or SFQR) (for example, a wafer flatness measuring device manufactured by Corning Tropel) is provided with a support base for placing and adsorbing a SiC epitaxial substrate.

[0045] For example, as shown in Fig. 5(a), to measure the amount of warpage in a region of SiC epitaxial substrate 1 within 5 mm from orientation flat 4, the SiC epitaxial substrate is held in its natural (free) state without being vacuum-adsorbed. Fig. 5(b) shows the state of the warpage of the surface when the SiC epitaxial substrate 1 in Fig. 5(a) is viewed on a virtual plane that is perpendicular to the X-axis and includes the Y-axis. In Figure 5(b), zero on the vertical axis corresponds to the three-point reference plane (defined in the following paragraph), and the 5 mm wide area at the right end of Figure 5(b) (the area between the two auxiliary lines parallel to the vertical axis) corresponds to the area within 5 mm of orientation flat 4 in Figure 5(a). Within the above region, the amount by which the first main surface (or the second main surface) changes relative to the three-point reference plane corresponds to the "amount of warping in a region of the first main surface (or the second main surface) within 5 mm from the orientation flat." When the change within the region is on both the positive and negative sides when the three-point reference plane is used as a reference, the "sum of the absolute value of the maximum positive change relative to the three-point reference plane and the absolute value of the maximum negative change relative to the three-point reference plane" within the region corresponds to the "amount of change." When the first main surface is placed on the support base, the amount of warping on the second main surface is measured in an area within 5 mm from the orientation flat.When the second main surface is placed on the support base, the amount of warping on the first main surface is measured in an area within 5 mm from the orientation flat.

[0046] The center of the surface of the SiC epitaxial substrate (hereinafter sometimes simply referred to as "center") corresponds to the center of a circle corresponding to the outer periphery of the SiC epitaxial substrate (excluding the orientation flat) when viewed from a direction perpendicular to the flat surface of the support base. The three-point reference plane is a plane that passes through the three inner points of the measurement area on the surface of the SiC epitaxial substrate, where "inside" is 3% of the diameter inside from the outer periphery of the SiC epitaxial substrate.

[0047] One of the three points is on a first virtual line that passes through the center and is orthogonal to the orientation flat, and is an inner point from the outer periphery on the side where the orientation flat is not provided when viewed from the direction orthogonal to the flat surface of the support base. Another one of the three points is on a "second virtual line" that passes through the center and is inclined by 120° with respect to the portion of the first virtual line that connects the center and the outer periphery, and is an inner point from the outer periphery when viewed from the direction orthogonal to the flat surface of the support base. Still another one of the three points is on a "third virtual line" that passes through the center and is inclined by -120° with respect to the portion of the first virtual line that connects the center and the outer periphery, and is an inner point from the outer periphery when viewed from the direction orthogonal to the flat surface of the support base.

[0048] <Method for manufacturing SiC epitaxial substrate> Next, the method for manufacturing the SiC epitaxial substrate according to the present embodiment will be described in detail by taking the SiC epitaxial substrate 1 described above as an example.

[0049] (a) Substrate preparation step First, a plate-shaped silicon carbide substrate is prepared (step (a)). In this step, as shown in FIG. 6, a silicon carbide substrate 21 is prepared. FIG. 6 is a diagram schematically showing the side surface of the silicon carbide substrate 21. This silicon carbide substrate 21 is the material of the silicon carbide substrate 2 that constitutes the SiC epitaxial substrate 1 and is a flat plate-shaped silicon carbide substrate.

[0050] This silicon carbide substrate 21 is flat plate-shaped as described above and has a main surface 21a and a main surface 21b. At this time, the main surface 21a is the surface on which silicon carbide is epitaxially grown, and the main surface 21b is the opposite surface (the surface processed by polishing or grinding).

[0051] The silicon carbide substrate 21 prepared here is preferably an off-substrate having an off-angle θ. Specifically, the main surface 21b or the normal 21n to the main surface 21b is preferably inclined at an angle θ from the [000-1] direction to the

[1120] direction. This off-angle θ is preferably 0.5° or more and 8° or less, and more preferably 0.5° or more and 5° or less.

[0052] In preparing the silicon carbide substrate 21, first, a silicon carbide single crystal ingot is cut into a plate shape by a wire saw. Since the cut surface of the wire saw has undulations and irregularities, the irregularities are selectively removed and flattened using a diamond grinding wheel, diamond slurry, or the like.

[0053] The planarized main surface 21a of the silicon carbide substrate is preferably subjected to CMP (chemical mechanical polishing). Specifically, it is preferable that the first main surface is polished by CMP until the surface roughness Ra of the first main surface becomes 1 nm or less. More preferably, the surface roughness Ra of the main surface 21a is 0.2 nm or less.

[0054] The surface roughness Ra can be measured, for example, by a white light interference microscope. For example, the surface roughness Ra is a value obtained by measuring three points on the main surface 21a with a length of 100 μm and calculating the average. Ideally, the surface roughness Ra can be 0 nm, but in reality, the surface roughness Ra never becomes 0 nm. For this reason, the lower limit of the preferable range of the surface roughness Ra is greater than 0. Note that the surface roughness Ra in this specification is the surface roughness Ra specified in JIS B 0601-2001.

[0055] In addition, in order to perform epitaxial growth, it is preferable that the main surface 21a of the silicon carbide substrate 21 prepared at this time has a surface roughness Ra of 0.2 nm or less. By making the surface smooth in this manner, the epitaxial film formed by epitaxial growth, which will be described later, can also have a preferable surface that inherits the smoothness.

[0056] On the other hand, in the step of forming an epitaxial film described below, the main surface 21b may have deposits formed thereon or may become rough, and in the subsequent polishing or grinding step described below, the surface layer is removed and a new smooth surface is formed. Therefore, in the silicon carbide substrate 21 prepared in the above step (a), the main surface 21b does not need to be processed in advance to improve its smoothness. That is, the main surface 21b may be made a rough surface having a surface roughness Ra of 200 nm or more, for example.

[0057] In this way, silicon carbide substrate 21 only needs to be prepared with one smooth surface and the other rough, non-smooth surface; there is no need to prepare a substrate with smooth surfaces on both sides, which helps reduce manufacturing costs.

[0058] (b) Epitaxial film growth process Next, silicon carbide is epitaxially grown on the surface of the silicon carbide substrate prepared in step (a) to form a first main surface on which an epitaxial film is formed (step (b)). This step is a step of forming an epitaxial film 3 on the main surface 21a of the silicon carbide substrate 21 prepared.

[0059] The epitaxial film 3 can be formed by the following method. For example, the silicon carbide substrate 21 is placed on a plate coated with SiC, which is then placed in a susceptor coated with SiC, and the plate and the susceptor are heated by induction heating or the like to raise the temperature of the silicon carbide substrate 21 to a temperature at which silicon carbide can grow epitaxially, for example, 1500° C. or higher and 1700° C. or lower.

[0060] While maintaining this heated state, a mixed gas of hydrogen as a carrier gas, monosilane, propane or the like as a source gas, and nitrogen or the like as a dopant gas is flowed under reduced pressure to epitaxially grow silicon carbide on the surface of silicon carbide substrate 21 .

[0061] As a result, the epitaxial film 3 can be formed on the main surface 21a of the silicon carbide substrate 21, and as shown in Fig. 7, a substrate is obtained in which the epitaxial film 3 is deposited all over the main surface 21a of the silicon carbide substrate 21. The surface of the epitaxial film 3 thus formed becomes the main surface 1a of the SiC epitaxial substrate 1 to be finally obtained.

[0062] The thickness of the epitaxial film 3 obtained at this time can be set arbitrarily depending on the performance required for the semiconductor device. The thickness of the epitaxial film 3 can be, for example, 1 μm or more and 100 μm or less.

[0063] At this time, epitaxial growth of SiC may cause deposits DP to be formed on surfaces other than main surface 21a of silicon carbide substrate 21. Furthermore, roughness R may be formed on silicon carbide substrate 21. In this embodiment, even if such deposits DP or roughness R are formed, the SiC epitaxial substrate finally obtained is not affected, and the reason for this will be explained in the (d) grinding or polishing process step described later.

[0064] (c) Protective film formation process Next, a protective film is formed on the surface of the epitaxial film formed in step (b) (step (c)). In this step, a protective film is formed on the surface of the epitaxial film 3 formed on the main surface 21a of the silicon carbide substrate 21 in the above step (b). In this step (c), a protective film 22 is formed on the epitaxial film 3, as shown in FIG. 8.

[0065] In this embodiment, the protective film 22 is formed after the epitaxial film 3 is formed. As described in Patent Document 1, the protective film is not exposed to high temperature conditions and does not require high temperature resistance.

[0066] The protective film 22 formed here may be formed by applying a liquid material onto the epitaxial film 3 and drying it to form a protective film with a constant thickness, or a protective film with a constant thickness may be formed in advance and then laminated onto the epitaxial film 3.

[0067] When a liquid material is used, methods such as spin coating, dip coating, spray coating, etc. can be used, among which spin coating is preferred because it is easy to form a protective film with a uniform thickness. The viscosity of the liquid material used in this case is preferably 100 mPa s or less, more preferably 50 mPa s or less.

[0068] In this embodiment, it is preferable to use a material that can reduce the load on the substrate and maintain the flatness of the substrate. Examples of materials for the protective film 22 include resist and liquid wax. These materials are preferable because the protective film 22 can be easily formed and can be easily removed.

[0069] Examples of resists that can be used here include positive resists such as OFPR-800, 500, 8600, 8600 LB, TSMR-8900, V90 (all of which are product names manufactured by Tokyo Ohka Kogyo Co., Ltd.) This positive resist contains, for example, components such as ethyl lactate and butyl acetate.

[0070] Examples of liquid waxes that can be used here include Skyliquid LA-3011H, 4011H, 5011H, and 5511H (all of which are product names manufactured by Nikka Seiko Co., Ltd.) This liquid wax contains, for example, components such as rosin and isopropyl alcohol (IPA).

[0071] By using the resist and liquid wax as described above, the protective film can be removed by a simple operation without the need for anisotropic etching or wet etching as described in Patent Document 1, and also the residue of the protective film can be suppressed.

[0072] In this embodiment, a liquid material is used to obtain flatness. If a film is applied to form a protective film, the film is thick and there is a risk of uneven flatness. By forming a protective film using a liquid material, for example, by spin coating, the in-plane film thickness distribution can be suppressed to, for example, 20% or less, thereby obtaining the desired flatness.

[0073] (d) Grinding or polishing processes Furthermore, after forming the protective film, the surface 21b opposite to the main surface 21a of the silicon carbide substrate 21 is ground or polished based on the shape of the surface (main surface 1a) of the epitaxial film 3 to form the main surface 1b (step (d)).

[0074] This processing step will be described below taking the case of polishing as an example. In this polishing, first, the surface of the substrate having the silicon carbide substrate 21, the epitaxial film 3, and the protective film 22 is fixed by suction, adhesion, or the like on the protective film 22 side. As shown in Fig. 9, for example, the vacuum chuck 23 used for fixing is composed of a base plate 23a and an adsorption plate 23b, and is connected to a vacuum device (not shown). This vacuum device allows the substrate to be fixed to the surface of the adsorption plate 23b by its suction action.

[0075] 10, the vacuum chuck 23 to which the silicon carbide substrate 21 to be polished is fixed is arranged with its polishing surface facing the polishing platen 24 of a single-sided polisher, and the substrate can be polished into a desired shape by contacting the polishing platen 24. Here, the polishing platen 24 rotates, for example, about a Z-axis provided along the vertical direction.

[0076] The polishing in this step is not particularly limited and may be performed by a known method as long as it is a method capable of polishing the silicon carbide substrate 21. In addition, a single-sided polisher is preferable because the pressing force can be adjusted.

[0077] In this polishing process, diamond slurry is dropped onto a polishing platen 24, and while holding the main surface 1a, the main surface 1b is pressed against the polishing platen 24. The polishing platen 24 may be a metal platen, a urethane pad, a nonwoven fabric pad, or the like.

[0078] At this time, the rotation speed of the polishing platen 24 is preferably 10 rpm to 30 rpm, the pressing force is preferably 5 kPa to 20 kPa, the diamond particle size of the diamond slurry is preferably 0.5 μm to 5 μm, the polishing amount is preferably 1 μm to 10 μm, and the surface roughness Ra of the polished surface is preferably 0.3 nm to 1 nm.

[0079] For polishing a substrate made of a high-hardness material such as silicon carbide, a process using free abrasive grains (lapping), a process using fixed abrasive grains (grinding), a process using a diamond wheel, or the like can be used.

[0080] Although the above description has been given taking polishing as an example, processing can also be performed using a grinding machine. When using a grinding machine, grinding of the main surface 1b can be performed by holding the main surface 1a side on which the protective film 22 is formed in the same manner. The holding method is the same as above, and grinding can be performed by holding the main surface 1a and bringing the main surface 1b into contact with a grinding wheel while applying a fixed amount of cut.

[0081] The grinding wheel contains diamond abrasive grains, and the grain size is preferably from #2000 to #8000. For example, a vitrified bonded grinding wheel or a resin bonded grinding wheel is used as the grinding wheel.

[0082] The rotation speed of the grindstone is preferably 2000 rpm to 5000 rpm, and the cutting depth is preferably 0.2 μm / min to 2 μm / min. Pure water or water containing additives is used to cool the grindstone, the grinding amount is 1 μm to 10 μm, and the surface roughness Ra of the polished surface is 0.3 nm to 1 nm.

[0083] After such grinding and polishing, CMP (chemical mechanical polishing) can be performed as necessary to remove polishing damage. In addition, CMP (chemical mechanical polishing) may be performed even when a smoother surface is required. CMP can be performed to reduce the difference between the stress on the main surface 1a side and the stress on the main surface 1b side. By reducing the difference in stress, warping is suppressed and the amount of warping in the region within 5 mm from the orientation flat is reduced. There are compressive stress and tensile stress, and there is no difference in stress at the point where the compressive stress and the tensile stress are balanced, but if there is a stress distribution on each of the main surface 1a and the main surface 1b, the stress will not be balanced between the main surface 1a and the main surface 1b, leading to warping. The diameter of the SiC epitaxial substrate having a smooth surface and suppressing warping is preferably 150 mm or more, more preferably 200 mm or more, and even more preferably 300 mm or more.

[0084] This polishing is performed based on the shape of the main surface 1a. At this time, it is preferable to obtain the main surface 1b by processing it as a surface corresponding to the shape of the main surface 1a. By forming the surfaces in this manner, the thickness of the SiC epitaxial substrate 1 becomes almost the same, and the shapes have the same inclination at corresponding positions on the front and back surfaces, so that a substrate with very good flatness is obtained.

[0085] In this embodiment, the SiC epitaxial substrate is processed on one side instead of both sides. In the case of double-sided processing, the surface of the epitaxial film is also polished, making it difficult to control the thickness of the epitaxial film, but the single-sided processing is advantageous in that it allows the thickness of the epitaxial film to be controlled.

[0086] The SiC epitaxial substrate 1 thus obtained can satisfy the characteristics of the SiC epitaxial substrate described in the above embodiment, such as at least one of SBIR and SFQR (it can also satisfy both SBIR and SFQR). Furthermore, the SiC epitaxial substrate 1 can satisfy at least one of the following (it can also satisfy both): the amount of warping of the second main surface in a region within 5 mm from an orientation flat is 2 μm or less when measured without vacuum-adhering the first main surface, and the amount of warping of the first main surface in a region within 5 mm from an orientation flat is 2 μm or less when measured without vacuum-adhering the second main surface.

[0087] In the SiC epitaxial substrate of the present invention, the epitaxial film has a basal plane dislocation density (BPD density) of 0.01 cm -2 The basal plane dislocation density is preferably 0.001 cm or less. -2 It is even better that the basal plane dislocation density is equal to or less than 100 nm, and it is particularly preferable that the basal plane dislocation density is zero. If the above SBIR and SFQR are satisfied and the site ratio is high, the element formed on the epitaxial film is prevented from becoming defective, and the man-hours required for fabricating a SiC epitaxial substrate having an epitaxial film with a low basal plane dislocation density for that element are prevented from being wasted. The epitaxial film may also include a buffer layer and a drift layer. The buffer layer may be composed of two or more layers (e.g., a low-concentration layer and a hole barrier layer), and the hole barrier layer may have an impurity concentration of, for example, 5×10 18 cm -3 More than 1×10 19 cm -3 or less and the basal plane dislocation density is 0 cm -2 More than 0.01cm -2 It may comprise the following layers:

[0088] After the polishing process is completed, the substrate is removed from the vacuum chuck 23, and the SiC epitaxial substrate 1 having the main surface 1b and the protective film 22 formed thereon is obtained as shown in FIG.

[0089] (e) Protective film removal process Then, after step (d), protective film 22 is removed from SiC epitaxial substrate 1 with protective film 22 shown in Fig. 11 (step (e)). By performing step (e), SiC epitaxial substrate 1 is obtained. Removal of the protective film can be achieved by a method suitable for the removal depending on the material of the protective film used.

[0090] When a resist is used as a protective film, a solvent or stripping solution capable of stripping the resist used may be used. Examples of such solvents include organic solvents such as acetone and N-methyl-2-pyrrolidone (NMP), Stripping Solution-104, 105, 106, 502A, SST-A47, Clean Strip HP, and Clean Strip HP-2 (all of which are product names manufactured by Tokyo Ohka Kogyo Co., Ltd.).

[0091] When liquid wax is used as the protective film, it can be removed by using a scraper, by washing with an alkali, etc. Examples of the cleaning agent include Deveil and Kirara Clean (both are product names of Nikka Seiko Co., Ltd.).

[0092] The cleaning agent and stripping solution as described above are placed in a protective film removal tank, and the silicon carbide substrate that has undergone step (d) is placed therein. The temperature of the cleaning agent and stripping solution is not particularly specified, and a temperature between room temperature (approximately 20°C) and 60°C is preferably used.

[0093] The peeling time is 2 to 10 minutes, and the substrate after peeling is rinsed to ensure that no residue of the peeling solution remains. The rinsed substrate is dried using a spin dryer or the like. In this manner, the desired SiC epitaxial substrate 1 is obtained.

[0094] In this protective film removal process, ultrasonic vibrations (e.g., 45 kHz-600 W) may be applied to the protective film removal tank in order to efficiently remove the protective film 22, and the SiC epitaxial substrate placed in the protective film removal tank may be swung up and down in the removal tank.

[0095] The SiC epitaxial substrate 1 from which the protective film has been removed is inspected for necessary inspection items, and the substrate that satisfies the prescribed characteristics is used in the manufacturing process of semiconductor chips. In particular, when the protective film is made of resist or liquid wax among the above, it can be removed extremely well, and the residue on the substrate surface of the obtained SiC epitaxial substrate 1 is 0.1 particles / cm. 2 It can be very good with less than 100%.

[0096] The SiC epitaxial substrate 1 thus obtained is a substrate with excellent flatness as described above, and can significantly improve the manufacturing yield of subsequent semiconductor chips.

[0097] Hereinafter, the single crystal manufacturing apparatus and the single crystal manufacturing method of the present embodiment will be described in detail with reference to the embodiment. It is needless to say that the present invention is not limited to the description of the embodiment.

[0098] (Embodiment 1) A silicon carbide substrate 21 having a diameter of 150 mm and a main surface 21a which is a (0001) Si surface and an off angle θ of 4° was prepared. CMP was applied to the main surface 21a until the surface roughness Ra was 0.5 nm or less (the surface roughness Ra of the main surface 1b is, for example, about 2 nm).

[0099] Silicon carbide is then epitaxially grown on the main surface 21a of the silicon carbide substrate to form an epitaxial film 3 having a thickness of 10 μm. The growth temperature can be set to 1600° C., and the pressure in the growth chamber during growth can be set to 30 kPa. The C / Si ratio in the source gas can be set to 1.25 or 1.4. Hydrogen is used as the carrier gas, and propane and silane are used as the source gas. Nitrogen is used as the dopant source.

[0100] Next, a protective film 22 is formed on the surface (main surface 1a) of the epitaxial film 3 formed on the surface of the silicon carbide substrate 21. A spin coater (manufactured by Tokyo Electron Limited, product name: CLEAN TRACK Mark) is used to form the protective film, and a positive resist (manufactured by Tokyo Ohka Co., Ltd., product name: OFPR-8600 LB) is used as the protective film. This resist contains ethyl lactate, butyl acetate, etc. as components.

[0101] The conditions for forming the protective film are, for example, substrate rotation speed: 1500 rpm, rotation time: 30 sec, coating amount: 3.6 mL, bake temperature: 140 degrees, bake time: 120 sec, and cooling time: 60 sec, forming a film with a uniform thickness of approximately 1 μm.

[0102] Next, the main surface 21b is polished while holding the main surface 1a on which the protective film 22 is formed. The main surface 21b is fixed by vacuum suction so that the posture does not change during polishing, and a single-sided polisher (manufactured by Fujikoshi Machinery Co., Ltd., product name: SLM-35) is used to polish the main surface 21b with respect to the main surface 1a until the surface roughness Ra becomes 0.5 nm, thereby forming the main surface 1b.

[0103] After polishing of main surface 21b is completed, protective film 22 is peeled off. A protective film remover liquid NMP is stored in a protective film removal tank, and the silicon carbide substrate whose back surface has been polished is immersed and placed in the protective film removal tank.

[0104] The temperature of the stripping solution is set to 60°C, and the substrate is immersed for 5 minutes to strip the protective film. After stripping, the substrate is rinsed with a rinse solution to remove residue from the stripping solution, and then the substrate is dried with a spin dryer to obtain the SiC epitaxial substrate 1. As a result, a SiC epitaxial substrate having a warpage of 2 μm or less in a region within 5 mm from the orientation flat can be obtained. Furthermore, by performing selection or re-polishing, a SiC epitaxial substrate having a warpage of 1 μm or less in a region within 5 mm from the orientation flat can also be obtained.

[0105] (Comparative form 1) An SiC epitaxial substrate is produced in the same manner as in the first embodiment, except that the main surface 21a is not polished (rear surface polishing).

[0106] [Flatness evaluation] 100 SiC epitaxial substrates were prepared in correspondence with the above-mentioned embodiment 1 and comparative embodiment 1, and SBIR and SFQR were measured to evaluate the flatness of each substrate. The maximum value, average value, and site ratios of SBIR of 0.5 μm or less and 0.8 μm or less, and site ratios of SFQR of 0.3 μm or less and 0.5 μm or less were investigated when measuring 100 substrates. The results are summarized in Table 1.

[0107] [Table 1]

[0108] (Embodiment 2) An SiC epitaxial substrate is manufactured by the same procedure as in the first embodiment, except that liquid wax is used as the protective film.

[0109] The liquid wax used here is a liquid wax containing rosin and isopropyl alcohol (IPA) (manufactured by Nikka Seiko Co., Ltd., product name: Skyliquid LA-3011H), and a coating device (manufactured by Fujikoshi Machinery Co., Ltd., product name: SCMM-7) is used.

[0110] The conditions for forming the protective film are, for example, substrate rotation speed: 2500 rpm, rotation time: 10 sec, coating amount: 2 mL, bake temperature: 95 degrees, bake time: 20 sec, and cooling time: 60 sec, and a film with a uniform thickness of approximately 2 μm is formed.

[0111] The SiC epitaxial substrate of the second embodiment has the same flatness as that of the first embodiment. In addition, it is possible to obtain a SiC epitaxial substrate having a warpage of 2 μm or less in a region within 5 mm from the orientation flat. Furthermore, by performing selection or re-polishing, it is also possible to obtain a SiC epitaxial substrate having a warpage of 1 μm or less in a region within 5 mm from the orientation flat.

[0112] As described above, according to the SiC epitaxial substrate and the manufacturing method thereof of the present embodiment, a SiC epitaxial substrate having excellent flatness and suppressed warping can be reliably obtained by a simple operation.

[0113] The invention made by the inventor has been described above based on an embodiment thereof. However, the present invention is not limited to the above embodiment, and it goes without saying that various modifications can be made without departing from the spirit of the invention. [Explanation of symbols]

[0114] 1. SiC epitaxial substrate 1a,1b Main surface 2,21 Silicon carbide substrate 3 Epitaxial film 4. Orientation Flat 10 Sites 22 Protective film 23 Vacuum Chuck 23a Base plate 23b Adsorption plate 24 Polishing plate

Claims

1. A SiC epitaxial substrate having an epitaxial film formed by epitaxially growing silicon carbide on a surface of a silicon carbide substrate, The SiC epitaxial substrate has a first main surface formed of the epitaxial film and a second main surface opposite thereto, and has a diameter of 150 mm or more; A SiC epitaxial substrate, wherein, on the second main surface, when measured with the first main surface vacuum-adsorbed, a maximum value of SBIR based on a 10 mm square site is 0.1 μm or more and 1.5 μm or less, and, on the second main surface, when measured without vacuum-adsorbing the first main surface, an amount of warpage is 2 μm or less in a region within 5 mm from an orientation flat.

2. 2. The SiC epitaxial substrate according to claim 1, wherein the amount of warping in a region within 5 mm from an orientation flat is 1 μm or less.

3. 3. The SiC epitaxial substrate according to claim 1, wherein the SBIR has a site ratio of 0.5 μm or less of 65% or more.

4. 3. The SiC epitaxial substrate according to claim 1, having a diameter of 200 mm or more.

5. 3. The SiC epitaxial substrate according to claim 1, wherein the number of residues on the second main surface is 0.1 / cm ２ A SiC epitaxial substrate having a thickness of less than 100 nm.

6. A SiC epitaxial substrate having an epitaxial film formed by epitaxially growing silicon carbide on a surface of a silicon carbide substrate, The SiC epitaxial substrate has a first main surface formed of the epitaxial film and a second main surface opposite thereto, and has a diameter of 150 mm or more; A SiC epitaxial substrate, wherein, on the first main surface, when measured with the second main surface vacuum-adsorbed, a maximum value of SFQR based on a 10 mm square site is 0.1 μm or more and 1.5 μm or less, and, on the first main surface, when measured without vacuum-adsorbing the second main surface, an amount of warping is 2 μm or less in a region within 5 mm from an orientation flat.

7. 7. The SiC epitaxial substrate according to claim 6, wherein the amount of warping in a region within 5 mm from the orientation flat is 1 μm or less.

8. 8. The SiC epitaxial substrate according to claim 6, wherein the SFQR has a site ratio of 0.3 μm or less of 85% or more.

9. 8. The SiC epitaxial substrate according to claim 6, having a diameter of 200 mm or more.

10. 8. The SiC epitaxial substrate according to claim 6, wherein the number of residues on the first main surface is 0.1 / cm ２ A SiC epitaxial substrate having a thickness of less than 100 nm.

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