SiC epitaxial substrate

Abstract

To provide an SiC epitaxial substrate with excellent flatness.SOLUTION: An SiC epitaxial substrate 1 has an epitaxial film 3 formed by epitaxially growing silicon carbide on a surface of a silicon carbide substrate 2. The SiC epitaxial substrate 1 has a principal surface 1a made of the epitaxial film 3, and a principal surface 1b as an opposite surface thereof. On the principal surface 1b of the SiC epitaxial substrate 1, a maximum value of SBIR using a 10 mm square site as a reference satisfies a condition of 0.1 μm or more and 1.5 μm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] SiC epitaxial substrates, which have an epitaxial film made of silicon carbide (hereinafter sometimes referred to as "SiC") formed on the surface of a silicon carbide substrate, are generally produced by vapor phase growth. However, it is known that when SiC is grown in the vapor phase, it can adhere to the opposite side (back surface) from the surface where the epitaxial film is formed, causing the SiC to grow in the form of protrusions.

[0003] As described above, when SiC grows on the back surface of a substrate, the substrate surface changes, or irregularities are created due to three-dimensionally grown protrusions. In either case, the substrate shape changes from what was intended, resulting in a deterioration of the substrate's flatness. Therefore, fabricating semiconductor devices using such substrates can negatively affect the characteristics of the semiconductor devices.

[0004] In such cases, it was necessary to remove the SiC formed by unplanned epitaxial growth by polishing the back surface of the substrate. When such removal operations are performed, the manufacturing process of the SiC substrate becomes complicated, as a protective film must be formed on the surface of the substrate, and then the protective film must be removed after the removal operation.

[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, thereby making it easy to remove SiC protrusions and the like that are 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 Publication No. 2015-160750 [Overview of the project] [Problems that the invention aims to solve]

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

[0008] For example, in the case of epitaxial films on a SiC substrate, fluctuations in the source gas occur at the outer edges of the SiC substrate compared to the center, which can cause variations in the epitaxial growth rate and result in variations in the thickness of the formed epitaxial film.

[0009] Furthermore, if there is variation in the original flatness of the SiC substrate used, for example, if the thickness differs slightly between the center and the outer edge, and the entire surface is tapered, 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. Specifically, when the back surface of the SiC epitaxial substrate is fixed to a vacuum chuck and a mask pattern is formed on the surface with the epitaxial film, 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 diligently conducted 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 is a SiC epitaxial substrate having an epitaxial film of silicon carbide epitaxially grown on the surface of a silicon carbide substrate, wherein the SiC epitaxial substrate has a first main surface made of the epitaxial film and a second main surface opposite to it, 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] A method for manufacturing a SiC epitaxial substrate in one embodiment includes the steps of: (a) preparing a plate-shaped silicon carbide substrate; (b) epitaxially growing silicon carbide on the 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 opposite surface of the silicon carbide substrate to form a second main surface based on the shape of the first 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. Furthermore, this highly flat SiC epitaxial substrate can suppress the displacement of the mask pattern perpendicular to the main surface of the substrate during photolithography, which is one of the semiconductor chip manufacturing processes, thereby improving the manufacturing yield of semiconductor chips. [Brief explanation of the drawing]

[0015] [Figure 1] This is a side view of a SiC epitaxial substrate in one embodiment. [Figure 2] Figure 1 shows an example of how to divide the sites for evaluating flatness in a SiC epitaxial substrate. [Figure 3] This is a diagram illustrating the SBIR measurement method. [Figure 4] This is a diagram illustrating the measurement method for SFQR. [Figure 5]This is a diagram for explaining a method of manufacturing a SiC epitaxial substrate in one embodiment. [Figure 6] This is a diagram for explaining a method of manufacturing a SiC epitaxial substrate in one embodiment. [Figure 7] This is a diagram for explaining a method of manufacturing a SiC epitaxial substrate in one embodiment. [Figure 8] This is a diagram for explaining a method of manufacturing a SiC epitaxial substrate in one embodiment. [Figure 9] This is a diagram for explaining a method of manufacturing a SiC epitaxial substrate in one embodiment. [Figure 10] This is a diagram for explaining a method of manufacturing a SiC epitaxial substrate in one embodiment.

Embodiments for Carrying out the Invention

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

[0017] In all the drawings for explaining this embodiment, the same members are basically denoted by the same reference numerals, and repeated explanations thereof are omitted. For clarity of the drawings, there may be cases where hatching is added even in a plan view or where hatching is omitted even in a cross-sectional view.

[0018] <Background of the Study> First, in order to explain this embodiment, the problems of the prior art will be supplemented and explained. For example, in Patent Document 1 described in the above prior art, in addition to ensuring the flatness described above, there are also points that pose problems in practical use as follows.

[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 barriers 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 problem 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 was also studied. Hereinafter, including this point, the technical idea of the present embodiment will be described in detail.

[0023] <SiC Epitaxial Substrate> The SiC epitaxial substrate of the present embodiment includes, for example, as shown in FIG. 1, a SiC epitaxial substrate 1 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 good, satisfying a predetermined range as 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 considering efficiency and other factors in semiconductor chip manufacturing, 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 an epitaxial film 3 formed on the surface of the silicon carbide substrate 2, and is characterized by the fact that the substrate has excellent flatness.

[0028] Regarding the flatness of the SiC epitaxial substrate 1, we specifically focused on SBIR (Site Back Surface Referenced Ideal Ranges) and discovered a new manufacturing method that could improve this characteristic, thereby obtaining a SiC epitaxial substrate 1 with extremely good flatness.

[0029] In other words, the SBIR of the SiC epitaxial substrate 1 in this embodiment satisfies the condition that the maximum value on the main surface 1b of the SiC epitaxial substrate 1, based on a 10 mm square site, is 0.1 μm or more and 1.5 μm or less.

[0030] By setting the SBIR within a predetermined range, the SiC epitaxial substrate 1 of this embodiment exhibits good flatness as a substrate, enabling a good manufacturing yield for semiconductor chips. More specifically, when performing 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 the desired pattern, and deviations perpendicular to the main surface of the substrate can be suppressed. Therefore, when manufacturing semiconductor chips using this SiC epitaxial substrate 1, the deviation from the mask pattern can be made very small, thereby improving the manufacturing yield.

[0031] Furthermore, it is preferable that the SBIR has a site ratio of 65% or more where the thickness is 0.5 μm or less. When these site ratio conditions are met, the SiC epitaxial substrate 1 exhibits excellent flatness, further improving the manufacturing yield of semiconductor chips.

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

[0033] In measuring SBIR, first, as shown in Figure 2, on the SiC epitaxial substrate 1, for example, a 10 mm square area is defined as one site (evaluation area), and multiple sites 10 are partitioned and defined. Using this 10 mm square site as a reference, the SBIR can be determined as follows. In this embodiment, an example is shown in which a 10 mm square site is defined and the flatness is evaluated using that site as a reference, but the size of this site can be changed arbitrarily.

[0034] Next, as shown in Figure 3, the main surface 1a, which is the opposite side of the main surface 1b to be measured on the SiC epitaxial substrate 1, is flattened by adsorption and fixation to a flat surface. 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 and lowest points on the site surface with respect to the main surface 1b in a predetermined range (for example, a 10 mm square range) of the site (the height difference indicated by arrow tSBIR in Figure 3).

[0035] In this embodiment, it is preferable that the maximum value of the SBIR is 1.5 μm or less, as a smaller value is preferable because it improves focusing accuracy. According to this embodiment, when the SiC epitaxial substrate 1 is divided into multiple 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 ratio of sites with an SBIR of 0.5 μm or less is 65% or more. By satisfying these conditions, photolithography processing can be performed with high accuracy, and the manufacturing yield of the resulting semiconductor chips can be improved. Furthermore, it is preferable that the above site ratio is higher, as this makes it possible to realize finer wiring patterns when photolithography processing is applied. Improving flatness makes it possible to use an exposure apparatus with a shorter exposure wavelength and a smaller DOF (Depth of Focus) range, i.e., a narrower depth of focus, which is preferable because it allows for the realization of even finer wiring patterns.

[0036] Furthermore, regarding the flatness of the SiC epitaxial substrate 1, we have found that its SFQR (Site Front side least sQuares focal plane Range) can also be improved.

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

[0038] By setting the SFQR within a predetermined range, the SiC epitaxial substrate 1 of this embodiment exhibits better substrate flatness, resulting in a higher manufacturing yield for semiconductor chips. More specifically, when performing 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 the desired pattern, and deviations perpendicular to the main surface of the substrate can be suppressed. Therefore, when manufacturing semiconductor chips using this SiC epitaxial substrate 1, the deviation from the mask pattern can be made very small, thereby improving the manufacturing yield.

[0039] Furthermore, it is preferable that the site ratio of this SFQR to be 0.3 μm or less is 85% or more. When these site ratio conditions are met, 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 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 as shown in Figure 2 in the SiC epitaxial substrate 1 (number of sites with an SFQR of 0.3 μm or less / total number of sites).

[0041] In measuring this SFQR, first, as with the SBIR measurement described above, as shown in Figure 2, a 10 mm square area is defined as one site (evaluation area) on the SiC epitaxial substrate 1, and multiple sites 10 are partitioned accordingly. Using this 10 mm square site as a reference, the SFQR can be determined as follows. In this embodiment, a 10 mm square site is defined and the flatness is evaluated based on that site, but the size of this site can be arbitrarily changed.

[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 flattened. Here, the arrow 10a in FIG. 4 schematically represents the length of one side of 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 it can improve the focusing accuracy when exposing with a stepper (reduction projection exposure apparatus). 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 obtained semiconductor chip can be improved. Furthermore, the higher the above site ratio, the more preferable it is, and thereby, when applying photolithography processing, 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] (a) Substrate preparation step First, a plate-shaped silicon carbide substrate is prepared (step (a)). This step involves preparing the silicon carbide substrate 21, as shown in Figure 5. Figure 5 is a schematic diagram showing the side view of the silicon carbide substrate 21. This silicon carbide substrate 21 is the material for the silicon carbide substrate 2 that constitutes the SiC epitaxial substrate 1, and is a flat silicon carbide substrate.

[0046] The silicon carbide substrate 21 is flat as described above and has a main surface 21a and a main surface 21b. In this case, 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 that is processed by polishing or grinding).

[0047] The silicon carbide substrate 21 prepared here is preferably an off-surface substrate having an off-angle θ. Specifically, it is preferable that the main surface 21b, or the normal 21n of the main surface 21b, is 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.

[0048] To prepare the silicon carbide substrate 21 described above, first, a silicon carbide single crystal ingot is cut into a plate shape using a wire saw. Since the cut surface of the wire saw has undulations and irregularities, the irregular parts are selectively removed and flattened using a diamond grinding wheel or diamond slurry.

[0049] The main surface 21a of the planarized 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 is 1 nm or less. More preferably, the surface roughness Ra of the main surface 21a is 0.2 nm or less.

[0050] Surface roughness Ra can be measured, for example, by a white light interference microscope. For example, it is obtained by measuring the main surface 21a at three locations over a length of 100 μm and calculating the average. Ideally, surface roughness Ra can be 0 nm, but in reality, surface roughness Ra is never 0 nm. Therefore, the lower limit of the preferred range for surface roughness Ra is greater than 0. In this specification, surface roughness Ra is defined as surface roughness Ra in JIS B 0601-2001.

[0051] Furthermore, it is preferable that the silicon carbide substrate 21 prepared at this time has a main surface 21a with a surface roughness Ra of 0.2 nm or less in order to perform epitaxial growth. By making the surface so smooth, the epitaxial film formed by epitaxial growth, which will be described later, will also be a film with a desirable surface that inherits the smoothness of the substrate.

[0052] On the other hand, the main surface 21b may develop deposits or become rough during the process of forming the epitaxial film, which will be described later. Furthermore, in the subsequent polishing or grinding process, which will be described later, its surface layer is removed, and a new smooth surface is formed. Therefore, in the silicon carbide substrate 21 prepared in step (a) above, it is not necessary to perform any processing to improve the smoothness of this main surface 21b beforehand. That is, this main surface 21b can be made into a rough surface, for example, with a surface roughness Ra of 200 nm or more.

[0053] Thus, in the silicon carbide substrate 21, it is sufficient to prepare one side as a smooth surface and the other side as a rough, uneven surface, and it is not necessary to make both sides of the substrate smooth, which helps to reduce 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 in which an epitaxial film 3 is formed on the main surface 21a of the prepared silicon carbide substrate 21.

[0055] The following methods can be used to form this epitaxial film 3. For example, a silicon carbide substrate 21 is placed on a SiC-coated plate, and this is placed inside a SiC-coated susceptor. The plate and susceptor are then 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 epitaxially grow, for example, between 1500°C and 1700°C.

[0056] While maintaining this heating state, under reduced pressure, a mixed gas is flowed through the silicon carbide substrate 21, consisting of hydrogen as a carrier gas, monosilane, propane, etc. as a raw material gas, and nitrogen, etc. as a dopant gas, to epitaxially grow silicon carbide on the surface of the silicon carbide substrate 21.

[0057] This allows the epitaxial film 3 to be formed on the main surface 21a of the silicon carbide substrate 21, and as shown in Figure 6, a substrate is obtained in which the epitaxial film 3 is deposited over the entire main surface 21a of the silicon carbide substrate 21. The surface of the epitaxial film 3 formed in this way becomes the main surface 1a of the final SiC epitaxial substrate 1.

[0058] The thickness of the epitaxial film 3 obtained at this time can be arbitrarily set according to the performance required for the semiconductor device. For example, the thickness of the epitaxial film 3 can be between 1 μm and 100 μm.

[0059] In this process, deposits DP may form on surfaces other than the main surface 21a of the silicon carbide substrate 21 due to the epitaxial growth of SiC. Additionally, rough surfaces R may form on the silicon carbide substrate 21. In this embodiment, the formation of such deposits DP and rough surfaces R does not affect the final SiC epitaxial substrate, and the reason for this will be explained later in section (d) Grinding or Polishing Process.

[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). As shown in Figure 7, a protective film 22 is formed on the epitaxial film 3 in step (c).

[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, high-temperature resistance is not required, and known protective films can be used without particular limitation, allowing for the use of a wide range of protective films.

[0062] The protective film 22 formed here may be formed by applying a liquid material onto the epitaxial film 3 and drying it to create a protective film with a certain thickness, or a protective film with a certain thickness may be formed in advance and then bonded onto the epitaxial film 3.

[0063] When using a liquid material, known thin-film formation techniques can be applied, such as spin coating, dip coating, and spray coating. Among these, spin coating is preferred because it easily forms a protective film with a uniform thickness. The liquid material used in this case preferably has a viscosity of 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 protective film 22 materials include resists and liquid waxes. These materials are preferable because they allow for easy formation of the protective film 22 and can be removed with simple operations.

[0065] The resist that can be used here is not particularly limited as long as it can protect the epitaxial film 3, and any known resist can be used, for example, positive-type resists such as OFPR-800, 500, 8600, 8600 LB, TSMR-8900, and V90 (all manufactured by Tokyo Ohka Kogyo Co., Ltd., trade names). These positive-type 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 any known liquid wax can be used, for example, Sky Liquid LA-3011H, 4011H, 5011H, 5511H (all manufactured by Nichika Seiko Co., Ltd., product names). This liquid wax contains components such as rosin and isopropyl alcohol (IPA).

[0067] By using the resists and liquid waxes described above, the protective film can be removed with simple operations without 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 obtain flatness. If a film were to be applied as a protective layer, the film would be thick, which could lead to variations in flatness. By forming a protective layer from a liquid material, for example by spin coating, the desired flatness can be obtained by suppressing the in-plane film thickness distribution to, for example, 20% or less.

[0069] (d) Grinding or polishing process Furthermore, after forming the protective film, the opposite surface 21b of the silicon carbide substrate 21 to the main surface 21a 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 explained below using polishing as an example. In this polishing process, first, the side of the substrate having the silicon carbide substrate 21, epitaxial film 3, and protective film 22 is fixed to the protective film 22 side by suction or adhesive. As shown in Figure 8, 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.

[0071] As shown in Figure 9, the vacuum chuck 23, which holds the silicon carbide substrate 21 to be polished, can be positioned with its polishing surface facing the polishing platen 24 of the single-sided polishing machine, and by bringing it into contact with the polishing platen 24, it can be polished to the desired shape. Here, the polishing platen 24 rotates, for example, around a Z-axis provided along the vertical direction.

[0072] The polishing in this process can be carried out by any known method that is capable of polishing the silicon carbide substrate 21, and is not particularly limited. Furthermore, a single-sided polishing machine that can adjust the pressing force is preferable.

[0073] In this polishing process, diamond slurry is dropped onto the polishing platen 24, the main surface 1a is held in place, and the main surface 1b is pressed against the polishing platen 24. The polishing platen 24 can be a metal platen, a urethane pad, a nonwoven fabric pad, or the like.

[0074] In this case, the rotational speed of the polishing platen 24 is preferably 10 rpm to 30 rpm, the pressing force is preferably 5 kPa to 20 kPa, and the diamond slurry is used with a diamond particle size of 0.5 μm to 5 μm. Furthermore, 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.

[0075] Furthermore, for polishing substrates made of high-hardness materials such as silicon carbide, processing methods such as lapping using free abrasive grains, grinding using fixed abrasive grains, and processing using diamond wheels can be used.

[0076] Furthermore, although polishing was used 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 should be held and the main surface 1b should be ground. 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 the grinding wheel while applying a certain amount of cutting depth.

[0077] The grinding wheel contains diamond abrasive grains, preferably with a grit size of #2000 to #8000. Examples of grinding wheels used include vitrified bond wheels and resin bond wheels.

[0078] The grinding wheel rotation speed should preferably be between 2000 rpm and 5000 rpm, and the depth of cut should preferably be between 0.2 μm / min and 2 μm / min. For cooling the grinding wheel, pure water or water containing additives should be used, the grinding amount should be between 1 μm and 10 μm, and the surface roughness Ra of the polished surface should be between 0.3 nm and 1 nm.

[0079] Furthermore, after such grinding and polishing processes, CMP (polishing) can be performed as needed to remove polishing damage. CMP (polishing) may also be performed if an even smoother surface is required.

[0080] This polishing process is performed based on the shape of the main surface 1a. It is preferable to process the surface to match the shape of the main surface 1a to obtain the main surface 1b. By using such corresponding surfaces, the thickness of the SiC epitaxial substrate 1 becomes approximately the same, and the shapes have similar inclinations 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, not both sides. Double-sided processing makes it difficult to control the thickness of the epitaxial film because the film surface of the epitaxial film is also polished, but single-sided processing is superior in that it allows for control of the thickness of the epitaxial film.

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

[0083] Furthermore, in the SiC epitaxial substrate of the present invention, the epitaxial film has a basal plane dislocation density (BPD density) of 0.01 cm². -2 The following is preferable, with a basal dislocation density of 0.001 cm³. -2 It is even better if the following conditions are met, and it is particularly preferable that the basal plane dislocation density is zero. When the above SBIR and SFQR conditions are met and the site ratio is high, defects in the elements formed on the epitaxial film are suppressed, and the wasted effort required to manufacture the SiC epitaxial substrate with an epitaxial film having a low basal plane dislocation density for that element is suppressed. The epitaxial film may also include a buffer layer and a drift layer. The buffer layer can consist of two or more layers (for example, a low-concentration layer and a hole barrier layer), and the impurity concentration of the hole barrier layer is, for example, 5 × 10⁻⁶ 18 cm -3 The above 1 x 10 19 cm -3 The following conditions apply, and the basal plane dislocation density is 0 cm⁻¹ -2 Above 0.01cm -2 It is preferable to have the following layers:

[0084] Once the polishing process is complete, the SiC epitaxial substrate 1 with a protective film 22 and a main surface 1b is formed is removed from the vacuum chuck 23, as shown in Figure 10.

[0085] (e) Removal of protective film Then, after step (d), the protective film 22 is removed from the SiC epitaxial substrate 1 with the protective film 22, as shown in Figure 10 (step (e)). By performing this step (e), the SiC epitaxial substrate 1 is obtained. The removal of the protective film can be achieved by using a method suitable for the removal of the protective film, depending on the material of the protective film used.

[0086] When using a resist as the protective film, a solvent or stripping solution capable of removing the used resist can be used. For example, organic solvents such as acetone and N-methyl-2-pyrrolidone (NMP), stripping solutions - 104, 105, 106, 502A, SST-A47, Clean Strip HP, Clean Strip HP-2 (manufactured by Tokyo Ohka Kogyo Co., Ltd., trade names), etc. can be mentioned.

[0087] When using liquid wax as the protective film, removal by a scraper, removal by alkali cleaning, etc. can be mentioned. As cleaning agents, for example, Devale, Kira Clean (manufactured by Nippon Kasei Chemical Co., Ltd., trade names) can be mentioned.

[0088] The above-mentioned cleaning agents and stripping solutions are stored in a protective film removal tank, and the silicon carbide substrate on which the (d) process has been completed is placed therein. The temperature of the cleaning agent and stripping solution is not particularly specified, and a temperature from room temperature (around 20°C) to 60°C is preferably used.

[0089] The stripping time is set to be 2 minutes or more and 10 minutes or less, and the substrate after stripping is rinsed so that no residue of the stripping solution remains. The rinsed substrate is dried with a spin dryer or the like. In this way, the target SiC epitaxial substrate 1 is obtained. <000032,7> In this protective film removal process, in order to efficiently remove the protective film 22, ultrasonic vibration (for example, 45 kHz - 600 W) may be added to the protective film removal tank, or the silicon carbide substrate placed in the protective film removal tank may be rocked up and down in the removal tank.

[0091] After inspecting the SiC epitaxial substrate 1 from which the protective film has been removed for necessary inspection items, the substrate that satisfies the predetermined characteristics is used in the manufacturing process of semiconductor chips. In particular, among the above, when a resist or liquid wax is used as the protective film, its removal can be performed extremely well, and the number of residues on the substrate surface of the obtained SiC epitaxial substrate 1 is less than 0.1 pieces / cm 2 and can be made very good.

[0092] The SiC epitaxial substrate 1 obtained in this manner is a substrate with good flatness as described above, and can significantly improve the manufacturing yield of subsequent semiconductor chips. [Examples]

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

[0094] (Example 1) A silicon carbide substrate 21 with a diameter of 150 mm was prepared, with the main surface 21a being a (0001) Si plane and an off-angle θ of 4°. The main surface 21a was subjected to CMP 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] Subsequently, silicon carbide was epitaxially grown on the main surface 21a of the silicon carbide substrate to form an epitaxial film 3 with a thickness of 10 μm. The growth temperature was set to 1600°C, and the pressure inside the growth chamber during growth was set to 30 kPa. The C / Si ratio in the raw material gas was set to 1.25 or 1.4. Hydrogen was used as the carrier gas, and propane and silane were used as the raw material gases. Nitrogen was also 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-type resist (manufactured by Tokyo Ohka Co., Ltd., product name: OFPR-8600 LB) was used as the protective film. This resist contains ethyl lactate, butyl acetate, etc. as components.

[0097] The protective film was formed under the following conditions: substrate rotation speed: 1500 rpm, rotation time: 30 sec, coating amount: 3.6 mL, bake temperature: 140 degrees Celsius, bake time: 120 sec, and cooling time: 60 sec. A film with a uniform thickness of approximately 1 μm was formed.

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

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

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

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

[0102] [Evaluation of flatness] One hundred SiC epitaxial substrates were prepared from each of the above-described Examples 1 and Comparative Example 1, and SBIR and SFQR measurements were taken to evaluate the flatness of each substrate. The maximum and average values, as well as the site ratios for SBIR (0.5 μm or less and 0.8 μm or less) and SFQR (0.3 μm or less and 0.5 μm or less) were investigated for each of the 100 substrates measured. The results are summarized in Table 1.

[0103] [Table 1]

[0104] (Example 2) A SiC epitaxial substrate was manufactured using the same procedure as in Example 1, except that liquid wax was used as a protective film.

[0105] The liquid wax used here was a liquid wax containing rosin and isopropyl alcohol (IPA) (manufactured by Nichika Seikou Co., Ltd., product name: Sky Liquid LA-3011H), and the coating equipment (manufactured by Fujikoshi Machinery Co., Ltd., product name: SCMM-7) was used.

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

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

[0108] From the above results, it was found that, according to the SiC epitaxial substrate and its manufacturing method according to this embodiment, a SiC epitaxial substrate with excellent flatness can be reliably obtained with simple operations.

[0109] The present invention has been described in detail above based on its embodiments, but it goes without saying that the present invention is not limited to the above embodiments and can be modified in various ways without departing from its essence. [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. The SiC epitaxial substrate group consists of 100 SiC epitaxial substrates. The SiC epitaxial substrate comprises a silicon carbide substrate and a SiC epitaxial film formed on the surface of the silicon carbide substrate. The SiC epitaxial substrate has a first main surface made of the SiC epitaxial film and a second main surface which is the opposite surface of the first main surface. The first main surface and the second main surface each have multiple evaluation areas of 10 mm square, The maximum value of SBIR in the evaluation regions provided in the second main surface is 0.1 μm or more and 1.5 μm or less. The number of evaluation regions on the first main surface in which the SFQR is 0.3 μm or less is 85% or more of the total number of evaluation regions on the first main surface. SiC epitaxial substrates.

2. The SiC epitaxial substrate group consists of 100 SiC epitaxial substrates. The SiC epitaxial substrate comprises a silicon carbide substrate and a SiC epitaxial film formed on the surface of the silicon carbide substrate. The SiC epitaxial substrate has a first main surface made of the SiC epitaxial film and a second main surface which is the opposite surface of the first main surface. The aforementioned second main surface is provided with multiple evaluation areas, each measuring 10 mm on each side. The maximum value of SBIR in the evaluation regions provided in the second main surface is 0.1 μm or more and 1.5 μm or less. The number of evaluation regions on the second main surface in which the SBIR is 0.5 μm or less is 65% or more of the total number of evaluation regions on the second main surface. SiC epitaxial substrates.

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