Sic epitaxial substrate

Abstract

To provide an SiC epitaxial substrate excellent in flatness.SOLUTION: The SiC epitaxial substrate 1 has a main surface 1a formed of the epitaxial film 3 and a main surface 1b opposite to the main surface 1b, and satisfies a condition that a maximum value of SBIR based on a site of a 10mm angle is 0.1 μm or more and 1.5 μm or less in the main surface center.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 vapor phase growth. However, it is known that when this SiC is grown by vapor phase growth, it also adheres to the surface opposite to the surface on which the epitaxial film is formed (back surface), and the SiC grows in protrusions.

[0003] In this way, when SiC grows on the backside of the substrate, the substrate surface changes, or unevenness occurs due to three-dimensionally grown protrusions. In either case, the substrate shape deviates from the intended shape, deteriorating the flatness of the substrate. Therefore, when semiconductor devices are fabricated using these substrates, this can adversely affect the characteristics of the semiconductor devices.

[0004] In such cases, it has been 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, as a protective film must be formed to protect the surface of the substrate, and then the removal operation is performed and 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 SiC protrusions and the like formed on the back surface of the substrate (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-160750 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, when growing an epitaxial film on a SiC substrate, fluctuations in the source gas occur at the periphery of the SiC substrate compared to the center, which can change the epitaxial growth rate and cause variations in the thickness of the formed epitaxial film.

[0009] Furthermore, if the original flatness of the SiC substrate used varies; for example, if the thickness differs slightly between the center and the 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 arise 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 poor, the position of the mask pattern will be shifted from the desired position, resulting in a decrease in the yield of the resulting semiconductor chips.

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

[0012] In one embodiment, the SiC epitaxial substrate has an epitaxial film formed by epitaxially growing silicon carbide on the surface of a silicon carbide substrate, and the SiC epitaxial substrate has a first main surface made of the epitaxial film and an opposite second main surface, and the second main surface satisfies the condition that the maximum SBIR value based on a 10 mm square site is 0.1 μm or more and 1.5 μm or less.

[0013] In one embodiment, a method for manufacturing a SiC epitaxial substrate includes the steps of: (a) preparing a plate-shaped silicon carbide substrate; (b) epitaxially growing silicon carbide on a surface of the silicon carbide substrate to form a first main surface consisting of an epitaxial film; (c) forming a protective film on the surface of the epitaxial film; (d) grinding or polishing the surface of the silicon carbide substrate opposite to the first main surface based on the shape of the first main surface to form a second main surface; and (e) removing the protective film. [Effects of the Invention]

[0014] According to one embodiment, a highly flat SiC epitaxial substrate can be provided, which can suppress misalignment of a mask pattern in the vertical direction relative to the main surface of the substrate during photolithography, which is one of the processes for manufacturing semiconductor chips, thereby improving the manufacturing yield of semiconductor chips. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a side view of a SiC epitaxial substrate according to an embodiment. [Figure 2] FIG. 2 is a diagram showing an example of division of sites for evaluating flatness in the SiC epitaxial substrate of FIG. [Figure 3] FIG. 1 is a diagram for explaining a method for measuring SBIR. [Figure 4] FIG. 10 is a diagram for explaining a method for measuring SFQR. [Figure 5]2A to 2C are diagrams illustrating a method for manufacturing a SiC epitaxial substrate according to an embodiment. [Figure 6] 2A to 2C are diagrams illustrating a method for manufacturing a SiC epitaxial substrate according to an embodiment. [Figure 7] 2A to 2C are diagrams illustrating a method for manufacturing a SiC epitaxial substrate according to an embodiment. [Figure 8] 2A to 2C are diagrams illustrating a method for manufacturing a SiC epitaxial substrate according to an embodiment. [Figure 9] 2A to 2C are diagrams illustrating a method for manufacturing a SiC epitaxial substrate according to an embodiment. [Figure 10] 2A to 2C are diagrams illustrating a method for manufacturing a SiC epitaxial substrate according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

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

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

[0018] <Background of the review> First, in order to explain this embodiment, we will provide a supplementary explanation of the problems of the prior art. For example, in Patent Document 1 described above in the prior art section, in addition to the above-described problem of ensuring flatness, there are the following practical problems.

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

[0020] Also, in this Patent Document 1, anisotropic etching and Wet etching are used to lift off the protective film after epitaxial growth. In this case, however, the adhering substances may act as a barrier and there is a risk that part of the protective film remains.

[0021] Also, it is conceivable to use tape peeling for removing the protective film. In this case, however, 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, and furthermore, there is a risk of contamination such as tape residues.

[0022] In the present invention, in addition to the flatness 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 simply forming and removing it and suppressing the occurrence of residues and the like has also been studied. Hereinafter, including this point, the technical idea of the present embodiment will be described in detail.

[0023] <SiC Epitaxial Substrate>[[ID=Z17]] The SiC epitaxial substrate of the present embodiment is, for example, as shown in FIG. 1, a SiC epitaxial substrate l in which an epitaxial film 3 is formed on the surface of a silicon carbide substrate 2. This SiC epitaxial substrate 1 is a flat substrate and has a main surface 1a (first main surface) made of the epitaxial film 3 and a main surface 1b (second main surface) which is the opposite surface thereof. In this specification, the surface made 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 made of single-crystal silicon carbide (SiC). In this embodiment, the flatness of the SiC epitaxial substrate 1 is excellent and satisfies a predetermined range, as will be described later.

[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, and more preferably 200 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, we focused on the SBIR (Site Back Surface Referenced Ideal Ranges) and discovered a new manufacturing method that can improve this characteristic, thereby enabling us 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 0.1 μm or more and 1.5 μm or less when based on a 10 mm square site.

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

[0031] Furthermore, it is preferable that the ratio of sites with SBIR of 0.5 μm or less is 65% or more. When 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 site ratio is calculated as the ratio of the number of sites with an SBIR of 0.5 μm or less to the total number of sites (number of sites with an SBIR of 0.5 μm or less / total number of sites) when the sites are divided in the SiC epitaxial substrate 1 as shown in FIG.

[0033] In measuring the SBIR, first, as shown in Fig. 2, a plurality of sites 10 are partitioned and defined in the SiC epitaxial substrate 1, each having a size of, for example, 10 mm square, as one site (evaluation area). Using this 10 mm square site as a reference, the SBIR can be determined 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 Figure 3, main surface 1a of SiC epitaxial substrate 1, which is the opposite surface to main surface 1b to be measured, is adsorbed and fixed to a flat surface to flatten main surface 1a. Here, arrow 10a in Figure 3 schematically represents 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 predetermined range (for example, a 10 mm square range) relative to main surface 1b (the height difference indicated by arrow tSBIR in Figure 3).

[0035] In this embodiment, the maximum SBIR value is preferably 1.5 μm or less, and a smaller value is more preferable because it improves focusing accuracy. 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 that the site ratio where the SBIR is 0.5 μm or less is 65% or more. By satisfying these conditions, photolithography processing can be performed with high accuracy, thereby improving the manufacturing yield of the resulting semiconductor chips. Furthermore, a higher site ratio is more preferable, which allows for the realization of finer wiring patterns when photolithography processing is applied. Improving flatness is more preferable because it allows the use of an exposure tool with a short exposure wavelength and a narrow DOF (Depth of Focus) range, i.e., a narrow depth of focus, and thus allows for the realization of finer wiring patterns.

[0036] Furthermore, it has been found that the flatness of the SiC epitaxial substrate 1 can also be improved in terms of SFQR (Site Front side least squares focal plane range).

[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 this embodiment has better flatness as a substrate, which can improve the chip manufacturing yield in the manufacture of semiconductor chips. More specifically, in the photolithography process, a mask pattern is formed on the epitaxial film 3 of the SiC epitaxial substrate 1. Because the SiC epitaxial substrate 1 has good flatness, the formed mask pattern is a desired pattern, and vertical deviation with respect to the main surface of the substrate can be suppressed. Therefore, when semiconductor chips are manufactured using this SiC epitaxial substrate 1, deviation from the mask pattern can be made very small, thereby improving the manufacturing yield.

[0039] Furthermore, it is preferable that the ratio of sites with SFQR of 0.3 μm or less is 85% or more. When 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.

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

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

[0042] Next, as shown in FIG. 4, by adsorbing and fixing the main surface 1b, which is the opposite surface of the main surface 1a to be measured on the SiC epitaxial substrate 1, to a flat surface, the main surface 1b is made flat. Here, the arrow 10a in FIG. 4 schematically represents the length of one side in a square site. In this state, SFQR calculates the reference plane 11 based on the surface shape of sites within a predetermined range (for example, a range of 10 mm square) using the least squares method, and it is the sum of the distance from the reference plane 11 to the highest point on the site surface and the distance to the lowest point on the site surface (the distance indicated by the arrow tSFQR in FIG. 4).

[0043] In the present embodiment, it is preferable that the maximum value of SFQR is 1.5 μm or less. The smaller this value is, the more preferable it is because the focusing accuracy during exposure with a stepper (reduction projection exposure apparatus) can be improved. According to the present embodiment, when the SiC epitaxial substrate 1 is divided into a plurality of sites with 10 mm square as a unit, it is preferable that the site ratio where the maximum value is within the above range (0.1 μm or more and 1.5 μm or less) and 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 resulting semiconductor chips can be improved. Furthermore, the higher the above site ratio, the more preferable it is, and thereby, when photolithography processing is applied, a finer wiring pattern can also be realized.

[0044] <Method for manufacturing SiC epitaxial substrate> Next, the method for manufacturing the SiC epitaxial substrate of the present embodiment will be described in detail using the SiC epitaxial substrate 1 described above as an example.

[0045] [[ID=…]] (a) Substrate preparation step First, a plate-shaped silicon carbide substrate is prepared (step (a)). In this step, as shown in FIG. 5, a silicon carbide substrate 21 is prepared. FIG. 5 is a diagram schematically showing a side surface of the silicon carbide substrate 21. The silicon carbide substrate 21 is a material for the silicon carbide substrate 2 that constitutes the SiC epitaxial substrate 1, and is a flat silicon carbide substrate.

[0046] As described above, silicon carbide substrate 21 has a flat plate shape and has main surfaces 21a and 21b. Main surface 21a is the surface on which silicon carbide is epitaxially grown, and main surface 21b is the opposite surface (the surface to be processed by polishing or grinding).

[0047] The silicon carbide substrate 21 prepared here is preferably an off-substrate having an off-angle θ. Specifically, it is preferable that main surface 21b or normal 21n to main surface 21b is tilted by an angle θ from the [000-1] direction toward 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.

[0048] To prepare the silicon carbide substrate 21, a silicon carbide single crystal ingot is first cut into a plate shape using 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.

[0049] The planarized main surface 21a of the silicon carbide substrate is preferably subjected to CMP (chemical mechanical polishing). Specifically, it is preferably 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.

[0050] The surface roughness Ra can be measured, for example, using a white light interference microscope. For example, it is a value obtained by measuring the main surface 21a at three locations over 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 reaches 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.

[0051] In order to perform epitaxial growth on silicon carbide substrate 21, it is preferable that main surface 21a have a surface roughness Ra of 0.2 nm or less. By providing such a smooth surface, the epitaxial film formed by epitaxial growth, which will be described later, can also have a preferable surface that inherits the smoothness.

[0052] On the other hand, main surface 21b may become rough or have deposits formed thereon in the step of forming an epitaxial film, which will be described later. Furthermore, in the subsequent polishing or grinding step, which will be described later, the surface layer is removed, and a new, smooth surface is formed. Therefore, in silicon carbide substrate 21 prepared in step (a) above, main surface 21b does not need to be processed in advance to improve its smoothness. That is, main surface 21b can be left as a rough surface, for example, with a surface roughness Ra of 200 nm or more.

[0053] In this way, silicon carbide substrate 21 only needs to be prepared with one smooth surface and the other rough, non-smooth surface, and there is no need for both surfaces to be smooth, which reduces manufacturing costs.

[0054] (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 prepared silicon carbide substrate 21.

[0055] 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 be epitaxially grown, for example, 1500°C or higher and 1700°C or lower.

[0056] 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.

[0057] As a result, epitaxial film 3 can be formed on main surface 21a of silicon carbide substrate 21, and as shown in Fig. 6, a substrate is obtained in which epitaxial film 3 is deposited over the entire main surface 21a of silicon carbide substrate 21. The surface of epitaxial film 3 formed in this manner becomes main surface 1a of SiC epitaxial substrate 1 to be finally obtained.

[0058] 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.

[0059] At this time, deposits DP may be formed on surfaces other than main surface 21a of silicon carbide substrate 21 due to epitaxial growth of SiC. Furthermore, roughness R may be formed on silicon carbide substrate 21. In the present embodiment, even if such deposits DP or roughness R are formed, the SiC epitaxial substrate finally obtained will not be affected, and the reason for this will be explained in the (d) Grinding or Polishing Process Step described later.

[0060] (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 step (b). In step (c), a protective film 22 is formed on the epitaxial film 3, as shown in FIG. 7 .

[0061] 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 need to be resistant to high temperatures. Therefore, any known protective film can be used without any particular restrictions, and a wide range of protective films can be used.

[0062] 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.

[0063] When a liquid material is used, known thin film formation techniques can be applied, such as spin coating, dip coating, and spray coating. Of these, 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, and more preferably 50 mPa s or less.

[0064] In this embodiment, it is particularly preferable to use a material that can reduce the load on the substrate and maintain good flatness. Examples of such materials for the protective film 22 include resist and liquid wax. These materials are preferable because they make it easy to form the protective film 22 and also allow for simple removal.

[0065] The resist that can be used here is not particularly limited as long as it can protect the epitaxial film 3, and known resists can be used, such as positive resists such as OFPR-800, 500, 8600, 8600 LB, and TSMR-8900, V90 (all of which are product names manufactured by Tokyo Ohka Kogyo Co., Ltd.). These positive resists contain components such as ethyl lactate and butyl acetate.

[0066] The liquid wax that can be used here is not particularly limited as long as it can protect the epitaxial film 3, and known liquid waxes can be used, such as Skyliquid LA-3011H, 4011H, 5011H, and 5511H (all of which are trade names manufactured by Nikka Seiko Co., Ltd.). This liquid wax contains components such as rosin and isopropyl alcohol (IPA).

[0067] By using the resist and liquid wax 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 the residue of the protective film can also be suppressed.

[0068] In this embodiment, a liquid material is used to achieve flatness. If a protective film were to be applied, the thickness of the film would be such that the flatness would vary. 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 achieving the desired flatness.

[0069] (d) Grinding or polishing process 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)).

[0070] This processing step will be described below using polishing as an example. For this polishing, first, the surface of the substrate having the silicon carbide substrate 21, epitaxial film 3, and protective film 22, facing the protective film 22, is fixed by suction, adhesive, or the like. As shown in FIG. 8, for example, a vacuum chuck 23 used for fixing comprises a base plate 23a and a suction plate 23b, and is connected to a vacuum device (not shown). The vacuum device allows the substrate to be fixed to the surface of the suction plate 23b by its suction action.

[0071] 9, vacuum chuck 23 to which silicon carbide substrate 21 to be polished is fixed is placed with its polishing surface facing polishing platen 24 of a single-side polisher, and can be polished into a desired shape by being brought into contact with polishing platen 24. Here, polishing platen 24 rotates, for example, about a Z-axis provided along the vertical direction.

[0072] The polishing in this step is not particularly limited and can be performed by any known method as long as it is a method that can polish the silicon carbide substrate 21. A single-side polisher is preferable because the pressing force can be adjusted.

[0073] In this polishing process, diamond slurry is dropped onto a polishing platen 24, and while the main surface 1a is held, 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.

[0074] At this time, the rotation speed of the polishing platen 24 is preferably 10 to 30 rpm, the pressing force is preferably 5 to 20 kPa, the diamond particle size of the diamond slurry is preferably 0.5 to 5 μm, the polishing amount is preferably 1 to 10 μm, and the surface roughness Ra of the polished surface is preferably 0.3 to 1 nm.

[0075] In addition, when polishing a substrate made of a high-hardness material such as silicon carbide, processing using free abrasive grains (lapping), processing using fixed abrasive grains (grinding), processing using a diamond wheel, etc. can be used.

[0076] Furthermore, although polishing has been described as an example above, processing can also be performed using a grinding machine. When using a grinding machine, similarly, the main surface 1a side on which the protective film 22 is formed can be held and main surface 1b can be ground. The holding method is the same as above, and main surface 1a can be held and ground by applying a certain amount of cut while main surface 1b is brought into contact with a grinding wheel.

[0077] The grinding wheel contains diamond abrasive grains, and the grain size is preferably between #2000 and #8000. For example, a vitrified bond grinding wheel or a resin bond grinding wheel is used as the grinding wheel.

[0078] The rotation speed of the grinding wheel is preferably 2000 rpm to 5000 rpm, and the cutting depth is preferably 0.2 μm / min to 2 μm / min. The grinding wheel is cooled with pure water or water containing additives, and the grinding 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] After such grinding and polishing, CMP (polishing) may be performed as needed to remove polishing damage. CMP (polishing) may also be performed when an even smoother surface is required.

[0080] This polishing is performed based on the shape of main surface 1a. Preferably, main surface 1b is processed to have a surface corresponding to the shape of main surface 1a. By achieving such a corresponding surface, the thickness of SiC epitaxial substrate 1 becomes approximately the same, and the shape has a similar slope at corresponding positions on the front and back surfaces, resulting in a substrate with excellent flatness.

[0081] In this embodiment, the SiC epitaxial substrate is processed on one side instead of both sides. In double-sided processing, the surface of the epitaxial film is also polished, making it difficult to control the thickness of the epitaxial film. However, single-sided processing is advantageous in that it allows the thickness of the epitaxial film to be controlled.

[0082] The SiC epitaxial substrate 1 obtained in this manner can satisfy the characteristics of the SiC epitaxial substrate described in the present embodiment above, such as SBIR and SFQR.

[0083] In addition, 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 0 or less, 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 device formed on the epitaxial film is prevented from becoming defective, and therefore the man-hours required to fabricate a SiC epitaxial substrate including an epitaxial film with a low basal plane dislocation density for that device are prevented from being wasted. The epitaxial film may also include a buffer layer and a drift layer. The buffer layer can be composed of two or more layers (for example, including a low-concentration layer and a hole barrier layer), and the hole barrier layer can 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:

[0084] 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.

[0085] (e) Protective film removal process After step (d), the protective film 22 is removed from the SiC epitaxial substrate 1 with the protective film 22 shown in FIG. 10 (step (e)). By performing step (e), the SiC epitaxial substrate 1 is obtained. The protective film can be removed by a method suitable for the removal depending on the material of the protective film used.

[0086] 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-pyrrolindone (NMP), Strippers-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.).

[0087] When a liquid wax is used as the protective film, it can be removed by using a scraper, by washing with an alkali, etc. Examples of cleaning agents include Deveil and Kirara Clean (both trade names, manufactured by Nikka Seiko Co., Ltd.).

[0088] The cleaning agent and stripping solution 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 (around 20°C) and 60°C is preferably used.

[0089] The stripping time is between 2 and 10 minutes, and the substrate is rinsed after stripping to remove any residue of the stripping solution. The rinsed substrate is then dried using a spin dryer or similar. In this way, the desired SiC epitaxial substrate 1 is obtained.

[0090] 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 silicon carbide substrate placed in the protective film removal tank may be swung up and down within the removal tank.

[0091] The SiC epitaxial substrate 1 from which the protective film has been removed is inspected for required inspection items, and the substrate that meets the predetermined characteristics is used in the semiconductor chip manufacturing process. In particular, when the protective film is made of resist or liquid wax, 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.

[0092] The SiC epitaxial substrate 1 thus obtained is a substrate with excellent flatness as described above, and can significantly improve the subsequent manufacturing yield of semiconductor chips. [Example]

[0093] The single crystal manufacturing apparatus and the single crystal manufacturing method of the present embodiment will be described in detail below with reference to examples. It goes without saying that the present invention is not limited to the description of these examples.

[0094] Example 1 A silicon carbide substrate 21 having a diameter of 150 mm and a main surface 21a that is a (0001) Si plane 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 was approximately 2 nm).

[0095] Silicon carbide was 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 was set to 1600°C, and the pressure in the growth chamber during growth was set to 30 kPa. The C / Si ratio in the source gas was set to 1.25 or 1.4. Hydrogen was used as the carrier gas, and propane and silane were used as the source gas. Nitrogen was used as the dopant source.

[0096] Next, a protective film 22 was 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) was used to form the protective film, and a positive resist (manufactured by Tokyo Ohka Kogyo Co., Ltd., product name: OFPR-8600 LB) was used as the protective film. This resist contains components such as ethyl lactate and butyl acetate.

[0097] The conditions for forming the protective film were: substrate rotation speed: 1500 rpm, rotation time: 30 sec, application amount: 3.6 mL, bake temperature: 140°C, bake time: 120 sec, cooling time: 60 sec, and a film with a uniform thickness of approximately 1 μm was formed.

[0098] Next, main surface 21b was polished while holding main surface 1a on which protective film 22 was formed. The substrate was held by vacuum suction to prevent the orientation from changing during polishing, and a single-side polisher (manufactured by Fujikoshi Machinery Co., Ltd., product name: SLM-35) was used to polish main surface 21b using main surface 1a as a reference until the surface roughness Ra became 0.5 nm, thereby forming main surface 1b.

[0099] After polishing of main surface 21b was completed, protective film 22 was removed. A protective film remover solution, NMP, was stored in a protective film removal tank, and the silicon carbide substrate whose back surface had been polished was immersed and placed in the protective film removal tank.

[0100] The temperature of the stripping solution was set to 60°C, and the substrate was immersed for 5 minutes to strip the protective film. After the stripping, the substrate was rinsed with a rinse solution to remove any residue from the stripping solution, and then dried with a spin dryer to obtain SiC epitaxial substrate 1.

[0101] (Comparative Example 1) In Example 1, an SiC epitaxial substrate was produced in the same manner as in Example 1, except that the main surface 21a was not polished (backside polishing).

[0102] [Flatness evaluation] One hundred SiC epitaxial substrates obtained in Example 1 and Comparative Example 1 were prepared, and SBIR and SFQR were measured to evaluate the flatness of each substrate. The maximum and average values ​​obtained by measuring 100 substrates each, as well as the site ratios of SBIR of 0.5 μm or less and 0.8 μm or less, and the site ratios of SFQR of 0.3 μm or less and 0.5 μm or less, were investigated. The results are summarized in Table 1.

[0103] [Table 1]

[0104] Example 2 An SiC epitaxial substrate was produced in the same manner as in Example 1, except that liquid wax was used as the protective film.

[0105] The liquid wax used here was 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) was used.

[0106] The conditions for forming the protective film were: substrate rotation speed: 2500 rpm, rotation time: 10 seconds, coating amount: 2 mL, bake temperature: 95 degrees, bake time: 20 seconds, cooling time: 60 seconds, and a film with a uniform thickness of approximately 2 μm was formed.

[0107] It was confirmed that the SiC epitaxial substrate obtained in Example 2 also had the same flatness as that of Example 1.

[0108] From the above results, it was found that, according to the SiC epitaxial substrate and the manufacturing method thereof of the present embodiment, a SiC epitaxial substrate with excellent flatness can be reliably obtained by a simple operation.

[0109] The invention made by the inventor has been specifically described above based on the embodiments thereof, but it goes without saying that the present invention is not limited to the above-described embodiments and can be modified in various ways without departing from the spirit of the invention. [Explanation of symbols]

[0110] 1. SiC epitaxial substrate 1a,1b Main surface 2,21 Silicon carbide substrate 3 Epitaxial film 10 sites 22 Protective film 23 Vacuum chuck 23a base plate 23b Adsorption plate 24 Polishing plate

Claims

1. A SiC epitaxial substrate having a SiC epitaxial film on a surface of a silicon carbide substrate, The SiC epitaxial substrate has a first main surface formed of the SiC epitaxial film; a second main surface opposite to the first main surface, the second main surface has a surface roughness Ra of 0.3 nm or more and 1 nm or less; The first principal surface and the second principal surface each include a plurality of evaluation regions each having a size of 10 mm square; a maximum value of SBIR in the plurality of evaluation regions provided on the second main surface is 0.1 μm or more and 1.5 μm or less; The maximum value of SFQR in the plurality of evaluation regions provided on the first main surface is 0.1 μm or more and 1.5 μm or less. SiC epitaxial substrate.

2. A SiC epitaxial substrate having a SiC epitaxial film on a surface of a silicon carbide substrate, The SiC epitaxial substrate has a first main surface formed of the SiC epitaxial film; a second main surface opposite to the first main surface, The first main surface is a reference for the shape and is not polished at all. the second main surface is polished as a surface corresponding to the first main surface serving as the reference; The first principal surface and the second principal surface each include a plurality of evaluation regions each having a size of 10 mm square; a maximum value of SBIR in the plurality of evaluation regions provided on the second main surface is 0.1 μm or more and 1.5 μm or less; The maximum value of SFQR in the plurality of evaluation regions provided on the first main surface is 0.1 μm or more and 1.5 μm or less. SiC epitaxial substrate.

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