JP2008230944A - Method for flattening surface of single crystal silicon carbide substrate, method for producing single crystal silicon carbide substrate, and single crystal silicon carbide substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for flattening the surface of a single crystal SiC substrate. <P>SOLUTION: A single crystal SiC substrate 15, in which unstable sites including crystal defects or a damaged layer 15a generated during polishing of its surface exist, is subjected to a heat treatment under a high vacuum environment so as to carbonize the surface and its vicinity of the single crystal SiC substrate 15 and to form a carbonized layer 15b (first process). Then, the resulting single crystal SiC substrate 15 is heat treated under saturated vapor pressure of silicon so as to form a sacrificial growth layer (amorphous SiC layer 15c) comprising amorphous SiC in the part of the carbonized layer 15b and at the same time, to perform thermal etching by sublimating the amorphous SiC layer 15c (second process). Thus, the unstable sites are self-restored and a flat surface of the single crystal SiC can be exposed (d). An extremely flattened (stabilized) single crystal SiC substrate 15 can be obtained by further applying slight thermal etching to the resulting single crystal SiC substrate 15 after that (e). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention mainly relates to a technique for performing surface planarization by improving the surface of a single crystal silicon carbide substrate.

  Silicon carbide (SiC) has excellent heat resistance and mechanical strength, is resistant to radiation, can easily control the valence electrons of electrons and holes by adding impurities, and has a wide band gap (6H-type single crystal SiC) About 3.0 eV, 4H type single crystal SiC having about 3.3 eV). Therefore, silicon carbide is said to be able to realize high temperature, high frequency, withstand voltage and environmental resistance that cannot be realized with existing semiconductor materials such as silicon (Si) and gallium arsenide (GaAs). Expectations are growing as a material for semiconductors for devices and high-frequency devices.

  In general, unstable sites including crystal defects and damage layers including polishing flaws and stress generated during polishing of the substrate surface exist on and near the surface of the single crystal SiC substrate. The unstable site and the damaged layer cause the quality of the crystal to deteriorate when the crystal is epitaxially grown on the surface of the single crystal SiC substrate. Therefore, from the viewpoint of improving throughput when manufacturing a semiconductor device or the like from a single crystal SiC substrate, it is strongly desired to overcome this problem of unstable sites and damaged layers.

In this regard, Non-Patent Document 1 describes that a single crystal SiC substrate can be etched with H ₂ gas before epitaxial growth using a CVD (chemical vapor deposition) apparatus for epitaxial growth, and thereby polishing damage to the substrate can be cleaned. Is disclosed.
A. Nakajima, H .; Yokoyama, Y. et al. Furukawa, and H.K. Yonezu: J.A. Appl. Phys. 97 (2005), 104919

  However, etching with hydrogen gas as described above is difficult to divert to a method or apparatus other than CVD, and the development of a surface planarization method that can easily cope with various epitaxial growth methods has been desired.

  The present invention has been made in view of the above circumstances, and its main purpose is easy to apply to epitaxial growth methods other than CVD, and removes unstable sites and damaged layers of a single crystal silicon carbide substrate. An object of the present invention is to provide a surface flattening method capable of obtaining a surface with extremely good flatness.

Means and effects for solving the problems

  The problems to be solved by the present invention are as described above. Next, means for solving the problems and the effects thereof will be described.

According to the first aspect of the present invention, the following method for planarizing a surface of a single crystal silicon carbide substrate is provided. That is, a first step of carbonizing the surface of the single crystal silicon carbide substrate and its vicinity to form a carbide layer by heat-treating the single crystal silicon carbide substrate in a high vacuum environment, and the single crystal silicon carbide substrate A heat treatment is performed under a saturated vapor pressure of silicon to form a sacrificial growth layer made of amorphous silicon carbide in the portion of the carbonized layer, and a second step of sublimating the sacrificial growth layer and performing thermal etching. In the present specification, “high vacuum environment” means a vacuum environment of 10 ⁻² Pa or less.

  As a result, in the first step, the surface of the single crystal silicon carbide substrate and the vicinity thereof, unstable sites including crystal defects, and damage layers including polishing scratches and stress on the surface are destroyed in the formation process of the carbonized layer. Or it can be broken down. Then, in the second step, a sacrificial growth layer made of amorphous silicon carbide is formed on the portion of the carbonized layer, whereby unstable sites on the surface of the single crystal silicon carbide are self-repaired, and then the sacrificial growth layer is By being removed, a self-repaired and extremely stable substrate surface can be obtained. As described above, a method for planarizing a surface of a single crystal silicon carbide substrate that can be easily applied to various epitaxial growth methods can be provided. The present invention is not limited to the pretreatment technology for epitaxial growth, but can be applied to a wide range of applications as a surface improvement and surface shape control technology of a single crystal silicon carbide substrate.

  In the method for planarizing the surface of the single crystal silicon carbide substrate, the exposed surface of the single crystal silicon carbide is preferably thermally etched after the sacrificial growth layer is thermally etched in the second step.

  Thereby, the thermal etching can be performed without leaving the sacrificial growth layer, and the substrate surface can be reliably planarized. In addition, since the single crystal silicon carbide substrate is etched from the stable exposed surface that is self-repaired as described above, the thermal etching rate is not uneven and a well-planarized surface can be obtained.

  In the method for planarizing the surface of the single crystal silicon carbide substrate, the following is preferable. That is, in the first step, the single crystal silicon carbide substrate is heat-treated at a temperature of 1500 ° C. or higher and 2300 ° C. or lower. In the second step, the single-crystal silicon carbide substrate is housed in a storage container that is made of tantalum metal and that has a tantalum carbide layer exposed to the internal space and that is fitted to the upper and lower sides. It heat-processes at the temperature of 1500 degreeC or more and 2300 degrees C or less in the state which maintained the vacuum environment in a container by the saturated vapor pressure of silicon | silicone so that it might become higher than an external pressure.

  Thereby, the formation of the carbonized layer in the first step can be performed satisfactorily and efficiently. In the second step, carbon molecules are selectively occluded in the tantalum carbide layer of the storage container, so that a high-purity Si atmosphere can be created in the internal space of the storage container, and other impurity storage containers Intrusion can be prevented. Therefore, formation of the sacrificial growth layer and removal by thermal etching can be performed satisfactorily and efficiently.

  In the method for planarizing the surface of the single crystal silicon carbide substrate, the following is preferable. That is, in at least one of the first step and the second step, the heat treatment is performed in a main heating chamber that is previously adjusted to a temperature of 1500 ° C. or higher and 2300 ° C. or lower under reduced pressure. Prior to the heat treatment, preheating is performed to heat the storage container containing the single crystal silicon carbide substrate at a temperature lower than the temperature during the heat treatment. The heat treatment is performed by moving the storage container from a preheating chamber that performs the preheating to the main heating chamber.

  As described above, the single crystal silicon carbide substrate is accommodated in the storage container and preheated in advance, and the temperature is rapidly increased by moving from the preheating chamber to the main heating chamber. The process or the second process can be efficiently performed in a short time, and the control thereof is facilitated.

  In the method for planarizing the surface of the single crystal silicon carbide substrate, the following is preferable. That is, in the first step, the single crystal silicon carbide substrate is heat-treated at a temperature of 1800 ° C. or higher and 2300 ° C. or lower. In the second step, the single crystal silicon carbide substrate is heat-treated at a temperature of 1800 ° C. or higher and 2300 ° C. or lower.

  Thereby, formation of the carbonized layer in the first step, formation of the sacrificial growth layer in the second step, and removal by thermal etching can be performed more satisfactorily and efficiently.

In the surface planarization method of the monocrystalline silicon carbide substrate, wherein in the second step, the internal pressure of the container is 10 ^-2 Pa or less of vacuum at the time of heat treatment, preferably 10 ^-4 Pa or less of vacuum It is preferred that

In the method for planarizing the surface of the single crystal silicon carbide substrate, the first step is preferably performed under a reduced pressure of 10 ⁻³ Pa or less, preferably 10 ⁻⁴ Pa or less.

  Thereby, it can prevent that another impurity penetrate | invades into a single crystal silicon carbide substrate (or storage container) in each process, and can obtain a single crystal silicon carbide substrate with good quality.

  In the method for planarizing the surface of the single crystal silicon carbide substrate, the surface flatness of the single crystal silicon carbide substrate after the planarization is preferably in the sub-nano order (that is, less than 1 nm).

  In the method for planarizing the surface of the single-crystal silicon carbide substrate, it is preferable to simultaneously remove impurities present on the surface of the single-crystal silicon carbide substrate at the atomic level.

  As described above, a single crystal silicon carbide substrate having a good surface quality can be provided.

  In the method for planarizing a surface of the single crystal silicon carbide substrate, the surface of the single crystal silicon carbide substrate after planarization has a planar shape whose step height is equal to or less than the unit cell length with respect to the stacking order direction of the polymorph of the crystal polymorph It is preferable that

  Thereby, the favorable morphology of the single crystal silicon carbide substrate surface is realizable.

  According to the 2nd viewpoint of this invention, the manufacturing method of the single crystal silicon carbide substrate including the process of planarizing the surface by the said surface planarization method is provided.

  Thereby, for example, a single crystal silicon carbide substrate suitable as a light emitting diode, various diodes, an electronic device, or the like can be provided.

  In the method for manufacturing a single crystal silicon carbide substrate, the chemical mechanical polishing step may or may not be performed before the step of planarizing the surface.

  That is, even when the chemical mechanical polishing step is omitted, a good substrate surface can be obtained by performing the planarization method of the present invention, and therefore the manufacturing cost and man-hour of the single crystal silicon carbide substrate can be reduced.

  According to the 3rd viewpoint of this invention, the single crystal silicon carbide substrate manufactured by the said manufacturing method is provided.

  As the polymorph, 3C—SiC, 4H—SiC or 6H—SiC can be employed.

  In the case where the crystal polymorph is 4H—SiC or 6H—SiC, the (0001) Si plane or the (000-1) C plane can be targeted for planarization.

  Further, when the crystal polymorph is 3H—SiC, the (111) Si surface or the (−1-1-1) C surface can be the target of planarization.

  Furthermore, the crystal orientation of the surface to be planarized can be a just plane or a plane having an off angle.

  Hereinafter, an embodiment of a method for planarizing a surface of a single crystal silicon carbide substrate according to the present invention will be described with reference to the drawings. First, an example of a heating furnace as a heat treatment apparatus suitable for performing the surface flattening method of the present embodiment will be described with reference to the schematic cross-sectional view of FIG.

  As shown in FIG. 1, the heating furnace 1 includes a main heating chamber 2, a preheating chamber 3, and a front chamber 4 in a portion following the preheating chamber 3 to the main heating chamber 2 as main portions. With this configuration, the container (heat treatment container) 16 in which the single crystal SiC substrate 15 or the like is stored sequentially moves from the preheating chamber 3 to the front chamber 4 and the main heating chamber 2, so that the single crystal SiC substrate 15 can be moved in a short time. The heating can be performed at a predetermined temperature (1500 ° C. to 2300 ° C., preferably 1800 ° C. to 2300 ° C., for example 1800 ° C.).

  In this heating furnace 1, as shown in FIG. 1, the connecting portion between the main heating chamber 2 and the front chamber 4 and the connecting portion between the front chamber 4 and the preheating chamber 3 are each partitioned with a communication portion. ing. For this reason, each of the chambers 2, 3, and 4 can be controlled under a predetermined pressure in advance. Further, if necessary, by providing a gate valve 7 for each chamber, the inside of the furnace under a predetermined pressure can be appropriately adjusted without touching the outside air when the container 16 containing the single crystal SiC substrate 15 or the like is moved. The moving means (not shown) can be moved, and contamination of impurities can be suppressed.

The preheating chamber 3 is provided with a halogen lamp 6 as preheating means. With this configuration, it is possible to rapidly heat to a predetermined range of temperature (for example, within a range of about 800 ° C. to 1000 ° C.) under a reduced pressure of about 10 ⁻² Pa or less. As described above, the gate valve 7 is provided at the connecting portion between the preheating chamber 3 and the front chamber 4 to facilitate the pressure control of the preheating chamber 3 and the front chamber 4.

  The container 16 in which the single crystal SiC substrate 15 or the like is stored is preheated to about 800 ° C. (a temperature lower than the temperature at the time of main heating described later) while being placed on the table 8 in the preheating chamber 3. The After that, pressure adjustment is performed between the preheating chamber 3 and the front chamber 4, and when the adjustment is completed, the container 16 is transported by a transport device (not shown) and is a liftable type provided in the front chamber 4. Placed on the susceptor 9.

The container 16 that has moved to the front chamber 4 is moved from the front chamber 4 to the main heating chamber 2 together with the susceptor 9 by the elevating type moving device 10. The main heating chamber 2 is preliminarily adjusted under a reduced pressure of about 10 ⁻⁴ Pa by a vacuum pump, and the temperature is adjusted by the heater 11 so as to reach a desired temperature (for example, 1800 ° C.).

The pressure environment of the main heating chamber 2 is preferably a vacuum of about 10 ⁻⁴ Pa or less as described above, but may be a vacuum of about 10 ⁻² Pa or less, for example. Further, for example, after a vacuum of about 10 ⁻² Pa or less, preferably about 10 ⁻⁴ Pa or less, a rare gas atmosphere into which some inert gas is introduced may be used.

  The state of the main heating chamber 2 is set in this way, and the container 16 is moved to the desired temperature by moving the container 16 from the front chamber 4 into the main heating chamber 2 at a high speed. It can be heated rapidly in a short time.

  In the main heating chamber 2, a reflecting mirror 12 is installed around the heater 11. The reflecting mirror 12 reflects the heat from the heater 11 so that the heat is concentrated on the single crystal SiC substrate 15 side located in the heater 11. The reflecting mirror 12 is preferably formed of gold-plated refractory metal such as W, Ta or Mo, or high heat resistant carbide such as WC, TaC or MoC.

  Further, a window 17 is provided in the main heating chamber 2, and the internal temperature of the main heating chamber 2 can be measured by an infrared radiation thermometer 18 installed outside the main heating chamber 2.

  The moving device 10 includes a convex stepped portion 21, while the heating chamber 2 includes a concave stepped portion 22. When the moving device 10 is driven and the container 16 is moved from the front chamber 4 to the main heating chamber 2, the convex stepped portion 21 is fitted to the concave stepped portion 22, and the fitting portion 25 is formed. An unillustrated seal member (for example, an O-ring) is provided at each step portion of the convex stepped portion 21, and the fitting portion 25 is sealed when the container 16 is moved to the main heating chamber 2. And it is comprised so that this heating chamber 2 can be sealed.

  A contaminant removal mechanism 29 is provided inside the heater 11 of the main heating chamber 2. The contaminant removal mechanism 29 removes impurities discharged out of the container 16 from the single crystal SiC substrate 15 or the like during the heat treatment so as not to come into contact with the heater 11. Thereby, it is possible to prevent the heater 11 from being deteriorated by reacting with the impurities. The contaminant removal mechanism 29 is not particularly limited as long as it can adsorb impurities discharged from the single crystal SiC substrate 15 or the like.

  The heater 11 is a resistance heater made of metal such as W or Ta, and includes a base heater 11a installed on the susceptor 9 side and an upper heater 11b provided on the main heating chamber 2 side. . When the container 16 rises and moves to the main heating chamber 2 side together with the base heater 11a by the moving device 10, the container 16 is surrounded by the heater 11 as shown by a chain line. With such a layout of the heater 11, it is possible to control the temperature distribution in the heating region to be uniform with high accuracy in combination with the reflector 12 described above. As a result, the container 16 can be heated uniformly, and variations and unevenness in the surface improvement of the single crystal SiC substrate 15 disposed inside can be reduced. Note that the heating method of the main heating chamber 2 is not limited to the resistance heater, and for example, a high frequency induction heating type can be adopted.

  Next, the container 16 used when the surface of the single crystal SiC substrate 15 of the present embodiment is planarized will be described with reference to FIG. FIG. 2 is a perspective view of the container with the upper and lower containers removed.

  The container 16 includes an upper container 16a and a lower container 16b as shown in FIG. Although the shape of the container 16 is substantially hexahedral as shown in the figure, this is an example, and may be configured in a cylindrical shape, for example. The upper container 16a and the lower container 16b are made of tantalum metal, and the entire surface thereof is covered with a tantalum carbide layer.

  Next, the step of planarizing the surface of the single crystal SiC substrate 15 will be described in order with reference to FIG.

  FIG. 3A shows the single crystal SiC substrate 15 before surface planarization. In the present embodiment, the crystal polymorph of the single crystal SiC substrate 15 is 4H—SiC, but is not limited thereto. In general, unstable sites including crystal defects and damage layers including polishing flaws and stress generated during polishing of the substrate surface exist on and near the surface of the single crystal SiC substrate 15. This unstable site and damaged layer are denoted by reference numeral 15a in FIG.

  In the surface planarization method of the present embodiment, first, the single crystal SiC substrate 15 shown in FIG. 3A is heated in a high vacuum environment (first step). Specifically, as shown in FIG. 4, single crystal SiC substrate 15 is arranged inside container 16. Single crystal SiC substrate 15 is placed on spacer (support) 13 installed on the inner bottom surface of lower container 16b. In addition, the code | symbol 31 of FIG. 4 is the said tantalum carbide layer which has covered the surface of the upper container 16a and the lower container 16b. And the container 16 is set to the heating furnace 1 in the state which fitted the lower container 16b and the upper container 16a, and is heat-processed.

An example of temperature control for this heat treatment is shown in FIG. As shown in FIG. 5, the temperature of the preheating chamber 3 of the heating furnace 1 is raised to about 800 ° C. in advance, and the temperature of the main heating chamber 2 is raised to about 1800 ° C. in advance. Then, the single crystal SiC substrate 15 is inserted into the preheating chamber 3 in a state of being arranged in the container 16 as shown in FIG. 4 and heated for several minutes to several tens of minutes (preheating). Thereafter, the container 16 is moved to the main heating chamber 2 together with the single crystal SiC substrate 15 as described above, and is heated for several tens of minutes at a temperature of about 1800 ° C. (main heating). At this time, the main heating chamber 2 is kept at a vacuum of about 10 ⁻³ Pa or less, preferably about 10 ⁻⁴ Pa or less. Thereafter, the container 16 and the single crystal SiC substrate 15 are returned to the preheating chamber 3 where the heating has been stopped, and are naturally cooled and taken out.

By the heat treatment described above, three basic reactions represented by the following formulas [1] to [3] occur in the SiC sublimation system.
[1] SiC (s) → Si (v) _I + C (s)
[2] 2SiC (s) → Si (v) _II + SiC ₂ (v)
[3] SiC (s) + Si (v) _{I + II} → Si ₂ C (v)

Here, the partial pressure on the surface of the single crystal SiC substrate in vacuum is such that when the temperature is 1600 ° C., Si is about 1 Pa, Si ₂ C is about 10 ⁻¹ Pa, and SiC ₂ is about 10 ⁻² Pa. In other words, the partial pressure of silicon is about one to two digits higher than that of silicon carbide. Comparing this from another viewpoint, the temperatures required for the partial pressure on the surface of the single crystal SiC substrate to be 1 Pa are about 1600 ° C. for Si, about 1800 ° C. for Si ₂ C, and about 2000 ° C. for SiC _2. It is. That is, silicon starts to evaporate at a low temperature, while silicon carbide starts to evaporate at a temperature 200 to 400 ° C. higher than silicon. Due to the time lag of evaporation, silicon preferentially sublimates on the surface of the single crystal SiC substrate 15 while carbon remains. As a result, the surface of the single crystal SiC substrate 15 and the vicinity thereof can be carbonized.

  By the above reaction, a carbonized layer 15b is formed on the surface of single crystal SiC substrate 15 as shown in FIG. During the carbonization process, the unstable site and the damaged layer 15a can be destroyed or decomposed. The thickness of the formed carbonized layer 15 b can be adjusted by the heat treatment time in the heating furnace 1. In the present embodiment, the thickness of the carbonized layer 15b is, for example, several μm, but may be less than 1 μm or several tens of μm.

  Next, the single crystal SiC substrate 15 is heated in a Si atmosphere (second step). Specifically, the single crystal SiC substrate 15 on which the carbonized layer 15b is formed as described above is arranged inside the container 16 as shown in FIG. Unlike the case of the first step (FIG. 4), this container 16 has silicon 14 as a Si supply source fixed to the inner surface of the side wall of the lower container 16b and the ceiling surface of the upper container 16a. With this configuration, the silicon 14 evaporates during the heat treatment, and a Si atmosphere can be formed inside the container 16. A spacer 13 is interposed between the single crystal SiC substrate 15 and the inner bottom surface of the lower container 16b. In the above storage state, the single crystal SiC substrate 15 is set in the same heating furnace 1 as in the first step and heated.

An example of temperature control of the heat treatment in the second step is shown in FIG. As shown in FIG. 7, the temperature of the preheating chamber 3 of the heating furnace 1 is raised to about 800 ° C. in advance, and the temperature of the main heating chamber 2 is raised to about 1800 ° C. in advance. Then, the single crystal SiC substrate 15 is inserted into the preheating chamber 3 in a state of being arranged in the container 16 as shown in FIG. 4 and heated for several minutes to several tens of minutes (preheating). Thereafter, the container 16 is moved to the main heating chamber 2 together with the single crystal SiC substrate 15 as described above, and heated at a temperature of about 1800 ° C. for several minutes to several tens of minutes (main heating). At this time, the main heating chamber 2 is maintained at a vacuum of about 10 ⁻² Pa or less, preferably about 10 ⁻⁴ Pa or less. Thereafter, the container 16 and the single crystal SiC substrate 15 are returned to the preheating chamber 3 where the heating has been stopped, and are naturally cooled and taken out.

  In addition, it is preferable that the play of a fitting part when the upper container 16a and the lower container 16b are fitted together as shown in FIG. 6 is about 2 mm or less. As a result, a substantially sealed state is realized, and in the heat treatment in the main heating chamber 2, the Si pressure in the container 16 is increased to a pressure higher than the external pressure (pressure in the main heating chamber 2), and impurities are removed. Intrusion into the container 16 through this fitting portion can be prevented.

  Further, as described above, the surface of the container 16 of the present embodiment is covered with the tantalum carbide layer 31, and the tantalum carbide layer 31 is exposed to the internal space of the container 16. Therefore, as long as the high-temperature treatment is continued under vacuum as described above, the container 16 has a function of continuously adsorbing and taking in carbon molecules from the surface of the tantalum carbide layer 31. In this sense, it can be said that the container 16 of the present embodiment has a carbon molecule adsorption ion pump function (ion getter function). Thereby, since only the carbon vapor is selectively occluded in the container 16 among the silicon vapor and the carbon vapor contained in the atmosphere in the container 16 during the heat treatment, the inside of the container 16 is maintained in a high purity Si atmosphere. be able to.

By the heat treatment in the Si atmosphere described above, supersaturated silicon is first recombined with carbon in the carbonized layer 15b, and a growth reaction by carbonization reduction as shown in the following formula [4] occurs. The reaction of this formula [4] is the reverse of the sublimation reaction shown in the above formula [1].
[4] C (s) + Si (v) → SiC (s)

  As a result of the above reaction, an amorphous SiC layer 15c is formed as shown in FIG. Simultaneously with the formation of the amorphous SiC, the above-described unstable sites are self-repaired on the surface of the single crystal SiC (the boundary between the amorphous SiC layer 15c and the single crystal SiC). In the present specification, the amorphous SiC layer 15c may be referred to as a “sacrificial growth layer” in the sense of a growth layer that will be removed in the future.

Since the amorphous SiC layer 15c as the SiC recrystallized layer (sacrificial growth layer) is thermally unstable, when the heat treatment is continued, the amorphous SiC layer 15c is decomposed and removed by thermal etching. This sublimation reaction is represented by the following formula [5].
[5] SiC (s) + Si (v) → Si ₂ C (v) ↑

  As a result, as shown in FIG. 3D, a flat single crystal SiC surface in which unstable sites are self-repaired can be exposed. Then, after the amorphous SiC layer 15c was completely removed, the surface of the single crystal SiC substrate 15 was further slightly etched by a certain amount so that it was very flattened (stabilized) as shown in FIG. A single crystal SiC substrate 15 can be obtained.

  The single crystal SiC substrate 15 thus obtained has no crystal defects, polishing scratches, etc., its surface flatness is on the sub-nano order (less than 1 nm), that is, at the atomic level, and the surface average roughness is 1.0 nm or less. Can do. Further, the surface of the single crystal SiC substrate 15 can realize a surface shape having a step height of 0.5 nm or less (that is, a unit cell length in the stacking order direction when the crystal polymorph is 4H—SiC) or less. it can. Further, by the above-described surface flattening, impurities existing on the surface of the single crystal SiC substrate 15 can be cleaned and removed at the atomic level.

  Therefore, the single crystal SiC substrate 15 after the planarization treatment can be used as a seed substrate for various epitaxial growth methods such as chemical vapor deposition (CVD) and liquid phase epitaxy (LPE). High quality epitaxially grown crystals can be obtained. Further, the surface planarization method of the present embodiment is not limited to the use for improving the substrate surface before epitaxial growth, but can be applied to a wide range of uses as a general surface improvement technique and surface shape control technique for a single crystal silicon carbide substrate. .

  Further, the single crystal SiC substrate 15 (FIG. 3A) before the planarization process may have been subjected to a chemical mechanical polishing process (CMP process), or this chemical mechanical polishing process may be omitted. Also good. That is, since the surface finish of the single crystal SiC substrate 15 can be satisfactorily performed by the planarization process of the present embodiment without performing chemical mechanical polishing, the manufacturing cost and the number of steps of the single crystal SiC substrate 15 can be reduced. However, the surface of the single crystal SiC substrate after chemical mechanical polishing can also be flattened by destroying unstable areas such as defects and strain inside the surface that are difficult to remove by the chemical mechanical polishing process. Therefore, it is effective to perform the planarization method of the present invention.

  Next, experimental results obtained by improving the (0001) Si plane and the (000-1) C plane of the 4H type single crystal SiC substrate by the surface planarization method of the present embodiment will be shown. FIG. 8 shows images obtained as a result of observing the substrate surface in the surface flattening process of the present embodiment with an atomic force microscope (AFM) on each of the Si plane and the C plane. The upper image in FIG. 8 is for the Si surface, and the lower image is for the C surface. Further, the parenthesized alphabetic characters (a) to (e) attached to the respective photographs in FIG. 8 correspond to the respective steps (a) to (e) described in FIG.

  Specifically, FIG. 8A is a photograph of the single crystal SiC substrate 15 (chemical mechanical polished) before the planarization treatment, and this single crystal SiC substrate 15 is heated at 1800 ° C. for 60 minutes in a high vacuum. The state after processing is shown in FIG. In addition, after the single crystal SiC substrate 15 is heat-treated at 1800 ° C. for 60 minutes in a high vacuum, photographs after heat treatment at 1800 ° C. for 1 minute, 3 minutes, and 15 minutes are shown in FIG. FIG. 8D and FIG. 8E.

  As shown in FIG. 8A, it can be seen that polishing scratches remain on the surface of the single crystal SiC substrate 15 before the planarization treatment. On the other hand, after heat treatment at 1800 ° C. for 60 minutes, a carbonized surface shape is observed as shown in FIG. Further, in the Si atmosphere at 1800 ° C. for 1 minute, as shown in FIG. 8C, the surface shape after the growth reaction by carbonization reduction is recognized, and it is considered that amorphous SiC is formed. . Similarly, in the state of heating for 3 minutes and 15 minutes, as shown in FIGS. 8D and 8E, the amorphous SiC disappears and the step on the surface of the single crystal SiC substrate is decomposed, resulting in a fine structure. Step is observed.

  Next, the photograph which observed the substrate surface of the surface planarization process of this embodiment with the optical microscope in each of Si surface and C surface is shown in FIG. The upper photograph in FIG. 9 is for the Si surface, and the lower photograph is for the C surface. Further, the parenthesized alphabetic characters (b) to (e) attached to the respective photographs in FIG. 9 correspond to (b) to (e) in FIG. 3 and (b) to (e) in FIG. Yes.

  As shown in FIG. 9B, uniform surface roughness due to carbonization is observed after heat treatment at 1800 ° C. for 60 minutes in a high vacuum. Further, in the Si atmosphere at 1800 ° C. for 1 minute, as shown in FIG. 9C, the surface shape after the growth reaction by carbonization reduction is recognized, and it is considered that amorphous SiC is formed. . Similarly, in the state heated for 3 minutes, it can be seen that amorphous SiC is etched and the surface is flattened as shown in FIG. However, in the photograph of FIG. 9 (d), a partially raised structure is observed, which is considered to be the remaining etching of amorphous SiC. In a Si atmosphere heated at 1800 ° C. for 15 minutes, the surface of the substrate is flattened very well as shown in FIG.

  Next, FIG. 10 shows a result of an experiment for measuring a change in thickness of the substrate accompanying the planarization process of the present embodiment. In this graph, the horizontal axis represents the heating time (cumulative), and the vertical axis represents the thickness change Δd with respect to the level before the flattening process.

  Note that 0 to 60 minutes on the horizontal axis represents heat treatment at 1800 ° C. in a high vacuum environment (first step), and 60 to 75 minutes represents heat treatment at 1800 ° C. in a Si atmosphere (second step). ). Moreover, the time points indicated by (a) to (e) on the upper side of the graph correspond to FIGS. 3 (a) to (e).

  As shown in the graph of FIG. 10, when the single crystal SiC substrate 15 is heated at 1800 ° C. for 60 minutes in a high vacuum environment, Si is mainly sublimated from the substrate to form a carbonized layer 15b. Thus, the single crystal SiC substrate 15 It can be seen that the thickness of is reduced. Thereafter, it was found that the thickness of the substrate increased at the stage of heating at 1800 ° C. for 1 minute in the Si atmosphere. This is considered because the amorphous SiC layer 15c (sacrificial growth layer) was formed. At the stage of heating for 3 minutes and 15 minutes in the Si atmosphere, the thickness of the substrate decreased again. This is presumably because the amorphous SiC layer 15c was thermally etched, and the exposed surface of the single crystal SiC substrate 15 was thermally etched.

  Next, as a comparative experiment, an experiment was performed in which the first step described above was omitted and heat treatment was performed. Specifically, the single crystal SiC substrate 15 in the state shown in FIG. 3A was stored in the container 16 as shown in FIG. 6, and was heated in the heating furnace 1 according to the temperature control shown in FIG. In the comparative experiment, 4H—SiC was used, and the processing target surface was a (0001) Si surface.

  In this comparative experiment, the unstable site and the damaged layer 15a of the single crystal SiC substrate 15 were thermally etched, but a bowl-shaped slope (mound structure) centered on the unstable site portion was formed on the surface of the substrate after the thermal etching. It was observed that macroscopic unevenness was formed. This is presumably because the rate of thermal etching is increased at the unstable sites and damaged parts such as polishing scratches, and the rate of thermal etching is uneven. The result of this comparative experiment is considered to prove the superiority of the surface planarization method of this embodiment in which the unstable site and the damaged layer 15a are decomposed or destroyed, and then the amorphous SiC layer 15c is grown and thermally etched. .

  As another comparative experiment, an experiment was conducted in which the single-crystal SiC substrate 15 after the formation of the carbonized layer 15b by performing the first step is heat-treated in an oxygen atmosphere instead of an Si atmosphere to remove the carbonized layer 15b. went. In this case, although the unstable site and the damaged layer 15a could be removed, it could not be said that the flatness of the substrate surface after the processing was better than that of the present embodiment. The result of this comparative experiment is also considered to prove the superiority of the surface flattening method of this embodiment.

  Although the preferred embodiment of the present invention has been described above, the above configuration can be modified as follows, for example.

  Any of 3C—SiC, 4H—SiC, and 6H—SiC can be used as the polymorph of the single crystal SiC substrate 15 to be planarized. When the crystal polymorph is 4H—SiC or 6H—SiC, for example, it is conceivable to flatten the (0001) Si plane or the (000-1) C plane. In the case where the crystal polymorph is 3C—SiC, for example, it is conceivable to flatten the (111) Si surface or the (−1-1-1) C surface. Further, it is conceivable to flatten a surface having a predetermined off angle instead of flattening a so-called just surface.

  As a method of forming the Si atmosphere in the container 16 in the second step, for example, silicon pellets may be arranged at appropriate positions of the container 16 instead of fixing the silicon 14 to the inner surface of the container 16.

  In the first step and the second step, the temperature of the preheating chamber 3 can be changed to be preheated at a temperature higher or lower than 800 ° C.

  The heat treatment in the first step and the second step is not limited to the heating furnace 1 having the configuration shown in FIG. 1, and can be performed by a heat treatment apparatus having another configuration. In particular, it is also possible in principle to use a heat treatment apparatus that does not have a configuration in which the single crystal SiC substrate 15 and the container 16 are moved rapidly from the preheating chamber 3 to the main heating chamber 2. However, from the viewpoint of easily controlling the formation process of the carbonized layer 15b and the amorphous SiC layer 15c and the control of the thermal etching process, it is preferable to adopt the device configuration capable of the rapid temperature increase described above.

The schematic cross section which shows an example of the heating furnace which performs the surface planarization method which concerns on one Embodiment of this invention. The perspective view which shows the structure of the container set to a heating furnace. Explanatory drawing which shows the process of the surface planarization method of this embodiment. Sectional drawing which shows the example of board | substrate arrangement | positioning in a container in the case of performing the 1st process of the surface planarization method. The graph which shows the temperature control example of the heating furnace in the case of performing a 1st process. Sectional drawing which shows the example of board | substrate arrangement | positioning in a container in the case of performing the 2nd process of the surface planarization method. The graph which shows the temperature control example of the heating furnace in the case of performing a 2nd process. The AFM photograph of the substrate surface corresponding to Drawing 3 (a)-Drawing 3 (e) in the process of flattening the Si surface and C surface of a single crystal SiC substrate. The optical microscope photograph of the substrate surface corresponding to FIG.3 (b)-FIG.3 (e) in the process in which the Si surface and C surface of a single crystal SiC substrate are planarized. The graph which shows the change of the thickness of a board | substrate in the process in which the Si surface and C surface of a single crystal SiC substrate are planarized.

Explanation of symbols

1 Heating furnace (heat treatment equipment)
2 Heating chamber 3 Preheating chamber 4 Front chamber 5 Single crystal SiC substrate 6 Halogen lamp 7 Gate valve 8 Table 9 Susceptor 10 Moving means 11 Heater 12 Reflector 13 Spacer 14 Silicon 15 Single crystal SiC substrate 15a Unstable site and damage Layer 15b Carbonized layer 15c Amorphous SiC layer (sacrificial growth layer)
16 Container 29 Pollutant removal mechanism 31 Tantalum carbide layer

Claims (20)

  A first step of carbonizing the surface of the single crystal silicon carbide substrate and its vicinity to form a carbide layer by heat-treating the single crystal silicon carbide substrate in a high vacuum environment; and A heat treatment under saturated vapor pressure to form a sacrificial growth layer made of amorphous silicon carbide in the portion of the carbonized layer, and a second step of sublimating the sacrificial growth layer and performing thermal etching. A method for planarizing a surface of a single crystal silicon carbide substrate.   2. The method for planarizing a surface of a single crystal silicon carbide substrate according to claim 1, wherein, in the second step, the surface of the exposed single crystal silicon carbide is thermally etched after the sacrificial growth layer is thermally etched. A method for planarizing a surface of a single crystal silicon carbide substrate, characterized in that: The method for planarizing a surface of a single crystal silicon carbide substrate according to claim 1 or 2, wherein in the first step, the single crystal silicon carbide substrate is heat-treated at a temperature of 1500 ° C or higher and 2300 ° C or lower,
In the second step, the single-crystal silicon carbide substrate is housed in a storage container that is made of tantalum metal and that has a tantalum carbide layer exposed to the internal space and that is fitted to the upper and lower sides. The surface of the single crystal silicon carbide substrate, which is heat-treated at a temperature of 1500 ° C. or higher and 2300 ° C. or lower in a state where the vacuum environment in the container is maintained at a saturated vapor pressure of silicon so as to be higher than the external pressure. Planarization method. A method for planarizing a surface of a single crystal silicon carbide substrate according to claim 3,
In at least one of the first step and the second step,
The heat treatment is performed in a main heating chamber adjusted to a temperature of 1500 ° C. or higher and 2300 ° C. or lower in advance under reduced pressure,
Before the heat treatment, preheating is performed to heat the storage container containing the single crystal silicon carbide substrate at a temperature lower than the temperature during the heat treatment,
The method for planarizing a surface of a single crystal silicon carbide substrate, wherein the heat treatment is performed by moving the storage container from a preheating chamber that performs the preheating to the main heating chamber. A method for planarizing a surface of a single crystal silicon carbide substrate according to claim 3 or 4,
In the first step, the single crystal silicon carbide substrate is heat-treated at a temperature of 1800 ° C. or higher and 2300 ° C. or lower,
In the second step, the single crystal silicon carbide substrate is heat-treated at a temperature of 1800 ° C. or higher and 2300 ° C. or lower. A method for planarizing a surface of a single crystal silicon carbide substrate according to any one of claims 3 to 5,
In the second step, the single-crystal silicon carbide substrate surface flattening method is characterized in that the internal pressure of the storage container is reduced to 10 ⁻² Pa or less during the heat treatment. A method for planarizing a surface of a single crystal silicon carbide substrate according to claim 6,
In the second step, the single-crystal silicon carbide substrate surface flattening method is characterized in that the internal pressure of the storage container is reduced to 10 ⁻⁴ Pa or less during the heat treatment. A method for producing a single crystal silicon carbide substrate according to any one of claims 1 to 7,
The method of planarizing a surface of a single crystal silicon carbide substrate, wherein the first step is performed under a reduced pressure of 10 ⁻³ Pa or less. A method for producing a single crystal silicon carbide substrate according to claim 8,
The method of planarizing a surface of a single crystal silicon carbide substrate, wherein the first step is performed under a reduced pressure of 10 ⁻⁵ Pa or less. A method for planarizing a surface of a single crystal silicon carbide substrate according to any one of claims 1 to 9,
A surface flattening method for a single crystal silicon carbide substrate, wherein the surface flatness of the single crystal silicon carbide substrate after flattening is in the sub-nano order. A method for planarizing a surface of a single crystal silicon carbide substrate according to any one of claims 1 to 9,
A surface flattening method for a single crystal silicon carbide substrate, wherein the single crystal silicon carbide substrate after flattening has an average surface roughness of 1.0 nm or less. A method for planarizing a surface of a single crystal silicon carbide substrate according to any one of claims 1 to 11,
A method for planarizing a surface of a single crystal silicon carbide substrate, wherein the surface planarization is used to simultaneously remove impurities present on the surface of the single crystal silicon carbide substrate at an atomic level. A method for planarizing a surface of a single crystal silicon carbide substrate according to any one of claims 1 to 12,
The surface of the single crystal silicon carbide substrate after planarization has a planar shape whose step height is not more than the unit cell length with respect to the stacking order direction of the polymorph of the crystal polymorph. Method.   A method for producing a single crystal silicon carbide substrate, comprising a step of planarizing a surface by the method for planarizing a surface of a single crystal silicon carbide substrate according to any one of claims 1 to 13.   15. The method for producing a single crystal silicon carbide substrate according to claim 14, wherein the chemical mechanical polishing step is not performed before the step of flattening the surface.   A single crystal silicon carbide substrate manufactured by the method for manufacturing a single crystal silicon carbide substrate according to claim 14.   The single crystal silicon carbide substrate according to claim 16, wherein the polymorph is 3C—SiC, 4H—SiC, or 6H—SiC. The single crystal silicon carbide substrate according to claim 16,
A single crystal silicon carbide substrate, wherein the polymorph is 4H—SiC or 6H—SiC, and the (0001) Si face or (000-1) C face is flattened. The single crystal silicon carbide substrate according to claim 16,
A single crystal silicon carbide substrate, wherein the polymorph is 3C-SiC, and the (111) Si face or (-1-1-1) C face is flattened.   The single crystal silicon carbide substrate according to any one of claims 16 to 19, wherein a crystal orientation of a surface to be flattened is a just plane or has an off angle. Single crystal silicon carbide substrate.