Patent Application
20240222125
The present disclosure relates to a SiC epitaxial wafer and a method for manufacturing a SiC epitaxial wafer.
Priority is claimed on Japanese Patent Application No. 2022-211232, filed Dec. 28, 2022, the content of which is incorporated herein by reference.
Silicon carbide (SiC) has a dielectric breakdown field one order of magnitude larger and a bandgap three times larger than silicon (Si). In addition, silicon carbide (SiC) has a thermal conductivity about three times higher than that of silicon (Si). For these reasons, SiC epitaxial wafers have come to be used for semiconductor devices such as power devices, high frequency devices, and high temperature operation devices.
A SiC epitaxial wafer is manufactured by stacking a SiC epitaxial layer on the surface of a SiC single crystal substrate. Hereinafter, a substrate before a SiC epitaxial layer is stacked thereon will be referred to as a SiC single crystal substrate. Further, a substrate after a SiC epitaxial layer is stacked on the surface of a SiC single crystal substrate is referred to as a SiC epitaxial wafer.
Currently, the mainstream SiC single crystal substrate in the market is 6 inches (150 mm) in diameter. Development for mass production of SiC single crystal substrates with a diameter of 8 inches (200 mm) is progressing, and full-scale mass production is about to begin. Increasing the diameter of SiC single crystal substrates from 6 inches to 8 inches is expected to be a key for improving production efficiency and reducing costs.
In the related art, as a method for evaluating a SiC single crystal substrate, there is a method using photoluminescence (PL) measurement.
For example, Patent Document 1 describes a SiC single crystal that exhibits a PL spectrum with a near-infrared PL emission peak in a wavelength of 650 to 750 nm upon electronic excitation, and describes that a dislocation density is evaluated by PL imaging.
Further, Patent Document 2 describes a method for evaluating a SiC substrate in which a first surface of the SiC substrate cut out from a SiC ingot is irradiated with excitation light before an epitaxial film is stacked thereon and photoluminescence is measured. Further, Patent document 2 describes a SiC epitaxial wafer in which on the first surface of the SiC substrate, a region where the intensity of photoluminescence caused by impurities is stronger than the intensity of photoluminescence caused by a SiC band edge is 50% or less of the total area of the first surface.
Further, Patent Document 3 describes a silicon carbide single crystal substrate in which a first main surface and a second main surface are provided, the maximum diameter of the first main surface is 100 mm or more, the first main surface includes a first central region excluding a region within 3 mm from the outer circumference, and in a case where the first central region is divided into first square regions of 250 μm on a side, an oxygen concentration in the first square region is 5 atomic % or more and less than 20 atomic %.
In addition, Patent Document 4 describes a silicon carbide single crystal substrate with a diameter of 100 mm or more, an oxygen concentration of 1×1017 cm−3 or less, a dislocation density of 2×104 cm−2 or less, and an area ratio of stacking faults of 2.0% or less.
However, it was found that in the SiC epitaxial wafer of the related art, there is a region where no defects are present even though the photoluminescence (PL) light emitted by irradiation with excitation light has a high emission intensity. In particular, it was found that the emission intensity in a portion near the outer circumference of the SiC epitaxial wafer is higher than in other portions. That is, it was found that even in a defect-free SiC epitaxial wafer, the emission intensity of the PL light is not uniform, and there is a region where the emission intensity of the PL light is high and a region where the emission intensity of the PL light is low.
As a result, in the technology of the related art, when evaluating a SiC epitaxial wafer using a difference in emission intensity of the PL light from the SiC epitaxial layer of the SiC epitaxial wafer, it was difficult to check for the presence or absence of defects due to PL light from a defect-free region, and thus it was not possible to obtain sufficient evaluation accuracy.
Further, in a region where the emission intensity of the PL light is high even though no defects are present, an energy level that should inherently not be present is present. Therefore, in a device using a SiC epitaxial wafer in which a SiC epitaxial layer is stacked in a region where the emission intensity of the PL light is high even though no defects are present, carriers are annihilated in a location that is not an inherently intended portion. For this reason, the influence on device operation due to a decrease in carrier lifetime has become a problem.
The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a SiC epitaxial wafer in which the emission intensity of photoluminescence (PL) light from a SiC epitaxial layer which is emitted by irradiation with excitation light is uniform, and a method for manufacturing the SiC epitaxial wafer.
In order to solve the above problems, the present inventors focused their attention on a manufacturing apparatus for a SiC epitaxial wafer and diligently investigated as shown below.
A member made of quartz is used in the manufacturing apparatus for a SiC epitaxial wafer. This is because quartz is a material with good gas barrier properties, heat insulation properties, and corrosion resistance, and does not contain elements that can become dopants for SiC, such as boron (B), nitrogen (N), and aluminum (Al). Moreover, quartz is not expensive and is highly versatile.
The member made of quartz is installed, for example, to cover the surface of a metal member. This is because if the metal member is exposed, power efficiency is reduced, or the metal member corrodes and metal powder is generated, which causes contamination of the SiC epitaxial wafer and defects originating from the contamination.
Further, in an apparatus for manufacturing a SiC epitaxial wafer having a diameter of 150 mm (6 inches) or more, it is desirable to use a member made of quartz. Particularly, in an apparatus for manufacturing a SiC epitaxial wafer having a diameter of 200 mm (8 inches) or more, a member made of quartz is often used. This is because when manufacturing a SiC epitaxial wafer with a large diameter, the same level of quality cannot be obtained even using a manufacturing apparatus optimized for manufacturing a SiC epitaxial wafer with a current diameter, and the larger the diameter of the SiC epitaxial wafer, the greater the influence of contamination.
The present inventors focused their attention on a member made of quartz used in the manufacturing apparatus and diligently investigated the cause of the formation of regions where defects are not present, even though these regions have high emission intensity of PL light due to the irradiation with excitation light. As a result, it was found that the above cause was due to the desorption of water molecules contained in quartz from a member made of quartz when growing a SiC epitaxial layer.
Then, the present inventors subjected a member made of quartz to vacuum heat treatment under predetermined conditions to remove water molecules contained in the quartz, and then installed the member in a manufacturing apparatus. Then, using this manufacturing apparatus, a SiC epitaxial layer was stacked on the surface of the SiC single crystal substrate to manufacture a SiC epitaxial wafer. As a result, it was confirmed that a SiC epitaxial wafer in which the emission intensity of the PL light having a wavelength of 660 nm or more from the SiC epitaxial layer emitted by irradiating the SiC epitaxial wafer with excitation light having a wavelength of 313 nm is uniform can be obtained, and the present disclosure was conceived.
That is, the present disclosure relates to the following matters.
{(IMAX−Imin)/Iaverage}×100≤40(%) (1)
(In formula (1), IMAX is a maximum value of the emission intensity in the entire measurement region, Imin is a minimum value of the emission intensity in the entire measurement region, and Iaverage is an average value of the emission intensity of the entire measurement region.)
{(IMAX−Imin)/Iaverage}×100≤20(%) (2)
(In formula (2), IMAX is a maximum value of the emission intensity in the entire measurement region, Imin is a minimum value of the emission intensity in the entire measurement region, and Iaverage is an average value of the emission intensity of the entire measurement region.)
{Io-average/Iaverage}×100≤200(%) (3)
(In formula (3), Io-average is an average value of the emission intensities of the measurement regions located at a portion closest to an outer circumference of the SiC epitaxial wafer among the measurement regions, and Iaverage is an average value of the emission intensity of the entire measurement region.)
In the SiC epitaxial wafer of the present disclosure, results of irradiating the SiC epitaxial wafer, which has the SiC epitaxial layer on the surface thereof, with the excitation light having a wavelength of 313 nm and measuring the emission intensity of the photoluminescence light having a wavelength of 660 nm or more for each square measurement region of 2 mm on a side, which is obtained by dividing the surface, satisfy formula (1). Therefore, in the SiC epitaxial wafer of the present disclosure, the emission intensity of photoluminescence (PL) light from a SiC epitaxial layer which is emitted by irradiation with excitation light is uniform. For this reason, in the SiC epitaxial wafer of the present disclosure, when evaluating the SiC epitaxial wafer using a difference in emission intensity of the PL light from the SiC epitaxial layer, it is possible to perform the evaluation with high accuracy. Further, in the SiC epitaxial wafer of the present disclosure, there is no region where the emission intensity of PL light is high even though there are no defects. Therefore, the device obtained by using the SiC epitaxial wafer of the present disclosure is preferable because a device operation is not affected by a decrease in carrier lifetime.
In the method for manufacturing a SiC epitaxial wafer of the present disclosure, the epitaxial layer growth step is performed using the epitaxial apparatus including the members made of quartz which have been subjected to the vacuum heat treatment before being installed in the epitaxial apparatus. Then, in the vacuum heat treatment, the members are held at a temperature of 600° C. or higher under a pressure of 1 kPa or lower for 1 hour or more. For this reason, according to the manufacturing method of the present disclosure, water molecules contained in quartz are not desorbed from a member made of quartz when growing a SiC epitaxial layer. As a result, the SiC epitaxial wafer of the present disclosure in which results of irradiating the SiC epitaxial wafer, which has the SiC epitaxial layer on the surface thereof, with the excitation light having a wavelength of 313 nm and measuring the emission intensity of the photoluminescence light having a wavelength of 660 nm or more for each square measurement region of 2 mm on a side, which is obtained by dividing the surface, satisfy formula (1) can be obtained.
Hereinafter, a SiC epitaxial wafer of the present disclosure will be explained in detail. The present disclosure is not limited only to embodiment which will be described below.
{(IMAX−Imin)/Iaverage}×100≤40(%) (1)
(In formula (1), IMAX is a maximum value of the emission intensity in the entire measurement region, Imin is a minimum value of the emission intensity in the entire measurement region, and Iaverage is an average value of the emission intensity of the entire measurement region.)
The above formula (1) indicates the uniformity of the emission intensity of the PL light obtained from the entire measurement region. In the SiC epitaxial wafer of the present embodiment, the value of {(IMAX−Imin)/Iaverage}×100 is 40(%) or less, and thus the unevenness of the emission intensity of the PL light from the SiC epitaxial layer is sufficiently small and the emission intensity is uniform. In the SiC epitaxial wafer of the present embodiment, the value of {(IMAX−Imin)/Iaverage}×100 is preferably 20(%) or less, more preferably 10(%) or less, and the smaller the better.
In the SiC epitaxial wafer of the present embodiment, it is preferable that the results of measuring the emission intensity of the PL light described above for each measurement region satisfy the following formula (3).
{Io-average/Iaverage}×100≤200(%) (3)
(In formula (3), Io-average is an average value of the emission intensities of the measurement regions located at a portion closest to an outer circumference of the SiC epitaxial wafer among the measurement regions, and Iaverage is an average value of the emission intensity of the entire measurement region.)
The above formula (3) indicates that the emission intensity of the measurement region disposed at a portion closest to the outer circumference OC of the SiC epitaxial wafer is suppressed. In the example shown in
In the present embodiment, as a method in which the SiC epitaxial wafer 10 having the SiC epitaxial layer 2 on the surface S10 is irradiated with the excitation light having a wavelength of 313 nm and the emission intensity of the PL light having a wavelength of 660 nm or more is measured for each of the measurement regions MA1 to MAn, the apparatus and method known in the related art can be used.
A nitrogen concentration on the surface of the SiC epitaxial wafer 10 of the present embodiment is appropriately determined according to the tolerance and resistance standards of a semiconductor device in which the SiC epitaxial wafer is used. In the SiC epitaxial wafer of the present embodiment, the nitrogen concentration on the surface is preferably 4×1018 atoms/cm3 or less, more preferably 4×1017 atoms/cm3 or less, and further more preferably 4×1016 atoms/cm3 or less. When the nitrogen concentration on the surface is 4×1018 atoms/cm3 or less, it is easy to measure and inspect the concentration of the surface, and the resulting SiC epitaxial wafer can prevent breakdown voltage defects and on-resistance defects of the device, and thus which is preferable.
An aluminum concentration on the surface of the SiC epitaxial wafer of the present embodiment is appropriately determined according to the tolerance and resistance standards of a semiconductor device in which the SiC epitaxial wafer is used. In the SiC epitaxial wafer of the present embodiment, the aluminum concentration on the surface is preferably 4×1018 atoms/cm3 or less, more preferably 4×1017 atoms/cm3 or less, and further more preferably 4×1016 atoms/cm3 or less. When the aluminum concentration on the surface is 4×1018 atoms/cm3 or less, it is preferable because the measuring and inspecting of the concentration of the surface are easy and the resulting SiC epitaxial wafer can prevent breakdown voltage defects and on-resistance defects of the device.
In the SiC epitaxial wafer of the present embodiment, an oxygen concentration on the surface is preferably less than 1×1014 atoms/cm3. When the oxygen concentration on the surface is less than 1×1014 atoms/cm3, the emission intensity of the PL light having a wavelength of 660 nm or more which is emitted by irradiating the SiC epitaxial layer with the excitation light having a wavelength of 313 nm is not increased by the additional light emission due to the oxygen concentration on the surface. The oxygen concentration on the surface of the SiC epitaxial wafer is more preferably 1×1013 atoms/cm3 or less, and the lower the better.
In the SiC epitaxial wafer of the present embodiment, a triangular defect density on the surface is preferably 1 cm−2 or less. A SiC epitaxial wafer having a triangular defect density on the surface of 1 cm−2 or less has sufficiently few defects and is preferable as a wafer for semiconductor devices. The triangular defect density on the surface is more preferably 0.1 cm−2 or less, and the smaller the better.
The size of the SiC epitaxial wafer of the present embodiment is not particularly limited, and may be 150 mm (6 inches) or more in diameter or may be 200 mm (8 inches) or more in diameter. In a case where the SiC epitaxial wafer of the present embodiment has a large diameter of 200 mm (8 inches) or more, it is preferable because semiconductor devices can be efficiently produced by using the SiC epitaxial wafer as a wafer for semiconductor devices.
The SiC epitaxial wafer of the present embodiment can be manufactured using, for example, a manufacturing method which will be described below.
First, the SiC single crystal substrate, which is a substrate before the SiC epitaxial layer is stacked thereon, is manufactured by a known method. Next, the SiC epitaxial layer is stacked on the surface of the SiC single crystal substrate to manufacture the SiC epitaxial wafer of the present embodiment.
In the present embodiment, as an apparatus (sometimes referred to as an “epitaxial apparatus”) for stacking the SiC epitaxial layer on the surface of the SiC single crystal substrate, an apparatus in which one or more members made of quartz are provided and some or all of the members made of quartz have been subjected to vacuum heat treatment before being installed is used. The vacuum heat treatment is preferably performed on all of the members made of quartz included in the epitaxial apparatus. The epitaxial apparatus may be any apparatus as long as it includes the members made of quartz, and may include a vertical furnace or may include a horizontal furnace.
An epitaxial apparatus 100 shown in
The chamber 20 has a main body 21 surrounding a film forming space S, a gas introduction part 22 for supplying a gas to the film forming space S, and a gas exhaust port 23 for exhausting a gas from the film forming space S.
The epitaxial apparatus 100 shown in
The main body 21 has a hollow, substantially cylindrical shape. As shown in
The gas introduction part 22 is provided at the center of the upper surface of the main body 21. The gas introduction part 22 has a hollow, substantially cylindrical shape that is concentric with the main body 21 and has a smaller diameter than the main body 21. As shown in
In the epitaxial apparatus 100 shown in
In the epitaxial apparatus 100 shown in
In a case where the SiC epitaxial wafer is manufactured using the manufacturing method of the present embodiment, the epitaxial apparatus 100 in which at least some of the members made of quartz provided in the epitaxial apparatus 100 have been subjected to the vacuum heat treatment which will be described below before being installed is used. When at least some of the members made of quartz are subjected to the vacuum heat treatment before being installed in the epitaxial apparatus 100, the emission intensity of the PL light of the SiC epitaxial wafer manufactured using the epitaxial apparatus 100 becomes uniform, and the contamination of the SiC epitaxial layer can be effectively suppressed. The effect of the members made of quartz installed in the epitaxial apparatus 100, which have been subjected to the vacuum heat treatment before being installed, can be obtained more remarkably, and thus all of the members made of quartz provided in the epitaxial apparatus 100, are preferably subjected to the vacuum heat treatment before being installed.
In the present embodiment, the vacuum heat treatment of the members made of quartz, which are installed in the epitaxial apparatus 100, is performed using a vacuum heat treatment apparatus in a state where the members are removed from the epitaxial apparatus 100. This is because if at least some of the members made of quartz installed in the epitaxial apparatus 100 are subjected to the vacuum heat treatment in the epitaxial apparatus 100, the effect of the vacuum heat treatment may not be sufficiently obtained, or members made of other materials disposed around the members made of quartz may be adversely affected.
In the vacuum heat treatment of the members made of quartz, the members made of quartz are held at a temperature of 600° C. or higher under a pressure of 1 kPa or lower for one hour or more. As a result, water molecules contained in the members made of quartz can be sufficiently desorbed from the quartz and removed.
More specifically, since the temperature in the vacuum heat treatment is 600° C. or higher, the effect of desorbing the water molecules contained in the members made of quartz from the quartz can be obtained. The temperature in the vacuum heat treatment is preferably 800° C. or higher, and more preferably 900° C. or higher. When the temperature in the vacuum heat treatment is 800° C. or higher, the diffusion of the water molecules in the members made of quartz is promoted, and the water molecules are easily desorbed from the quartz. For this reason, when the temperature in the vacuum heat treatment is 800° C. or higher, the holding time in the vacuum heat treatment can be shortened, and the vacuum heat treatment can be performed efficiently. The temperature in the vacuum heat treatment is preferably 1300° C. or lower, and more preferably 1000° C. or lower to avoid devitrification or melting of the members made of quartz.
Further, since the pressure in the vacuum heat treatment is 1 kPa or lower, the effect of desorbing the water molecules contained in the members made of quartz from the quartz can be obtained. The pressure in the vacuum heat treatment is preferably 1×10−2 Pa or lower, and more preferably 1×10−4 Pa or lower. This is because the effect of desorbing the water molecules contained in the members made of quartz from the quartz can be more effectively obtained through the vacuum heat treatment.
Further, since the holding time in the vacuum heat treatment is one hour or more, the effect of desorbing the water molecules contained in the members made of quartz from the quartz can be obtained. The holding time in the vacuum heat treatment is preferably two hours or more, and more preferably four hours or more. This is because the effect of desorbing the water molecules contained in the members made of quartz from the quartz can be more effectively obtained through the vacuum heat treatment. The holding time in the vacuum heat treatment is preferably 100 hours or less, and more preferably 50 hours or less. This is because the vacuum heat treatment can be performed in a short time and thus productivity is improved.
The vacuum heat treatment of the members made of quartz in the present embodiment only needs to be performed once before manufacturing the SiC epitaxial wafer using the epitaxial apparatus 100 including the members made of quartz. This is because even if moisture may adhere to the outermost surface of the members made of quartz after manufacturing the SiC epitaxial wafer and before manufacturing the SiC epitaxial wafer again, the moisture is extremely small compared to the amount of the water molecules incorporated into the members made of quartz in the process of manufacturing the members made of quartz. The vacuum heat treatment of the members made of quartz in the present embodiment may be performed every time or intermittently before manufacturing the SiC epitaxial wafer using the epitaxial apparatus 100 including the members made of quartz.
The members made of quartz which have been subjected to the vacuum heat treatment are installed at a predetermined location in the epitaxial apparatus 100 by a known method.
The support 30 provided in the epitaxial apparatus 100 shown in
The susceptor 40 is transported into the chamber 20 with the SiC single crystal substrate 1 placed thereon.
The lower heater 50 is installed within the support 30. The lower heater 50 heats the SiC single crystal substrate 1 via the support 30.
The upper heater 60 heats the upper portion of the chamber 20 from outside the chamber 20.
In the present embodiment, as a method for stacking the SiC epitaxial layer on the surface of the SiC single crystal substrate 1, a method known in the related art can be used except that the epitaxial apparatus 100 in which some or all of the members made of quartz have been subjected to the above-mentioned vacuum heat treatment is used.
Hereinafter, as an example of the method for manufacturing the SiC epitaxial wafer of the present embodiment, a method of stacking the SiC epitaxial layer on the surface of the SiC single crystal substrate 1 using the epitaxial apparatus 100 shown in
First, as shown in
As a method for forming the SiC epitaxial layer, for example, a method in which the SiC single crystal substrate 1 is heated to 1550° C. or higher by the lower heater 50 and the upper heater 60 and a gas at 1550° C. to 1700° C. is supplied to the film forming space S above the SiC single crystal substrate 1 from the gas introduction part 22 can be used.
Examples of gases used for forming the SiC epitaxial layer include a source gas, a dopant gas, and a purge gas. As the source gas, Si source gas and C source gas are used. The Si source gas, the C source gas, the dopant gas, and the purge gas may be supplied independently, or some or all of them may be mixed and supplied.
The Si source gas is a gas containing Si in its molecules. For example, monosilane (SiH4) can be used as the Si source gas. As the Si source gas, a chlorine-based Si material-containing gas (a chloride-based source gas) having an etching action, such as dichlorosilane (SiH2Cl2), trichlorosilane (SiHCl3), or tetrachlorosilane (SiCl4), may be used. Furthermore, hydrogen chloride gas may be added to the Si source gas.
As the C source gas, for example, propane (C3H8), ethylene (C2H4), or the like can be used.
The dopant gas is a gas containing an element that serves as a carrier in the SiC epitaxial layer, and controls the conductivity of the SiC epitaxial layer stacked on the SiC single crystal substrate 1. As the dopant gas, for example, nitrogen or the like can be used in a case where the conductivity type is n-type. As the dopant gas, TMA (trimethylaluminum) or the like can be used in a case where the conductivity type is p-type.
The purge gas is a gas for transporting the source gas and the dopant gas to the surface of the SiC single crystal substrate 1. As the purge gas, for example, hydrogen that is inert to SiC can be used. The flow rate of the purge gas is preferably 20 times or more the flow rate of the C source gas.
Through the above steps, the SiC epitaxial wafer of the present embodiment can be obtained.
In the SiC epitaxial wafer of the present embodiment, results of irradiating the SiC epitaxial wafer, which has the SiC epitaxial layer on the surface thereof, with the excitation light having a wavelength of 313 nm and measuring the emission intensity of the PL light having a wavelength of 660 nm or more for each square measurement region of 2 mm on a side, which is obtained by dividing the surface, satisfy formula (1). Therefore, the emission intensity of the PL light from the SiC epitaxial layer that emits light upon irradiation with the excitation light is uniform. For this reason, in the SiC epitaxial wafer of the present embodiment, when evaluating the SiC epitaxial wafer using a difference in emission intensity of the PL light from the SiC epitaxial layer, it is possible to perform the evaluation with high accuracy. Further, in the SiC epitaxial wafer of the present embodiment, there is no region where the emission intensity of PL light is high even though there are no defects. Therefore, the semiconductor device obtained by using the SiC epitaxial wafer of the present embodiment is preferable because a device operation is not affected by a decrease in carrier lifetime.
In the embodiment described above, the method for stacking the SiC epitaxial layer on the surface of the SiC single crystal substrate 1 using the epitaxial apparatus 100 shown in
The heat shield plate 70 reflects radiation from an upper heater 60 in a film forming space S, and thermally shields the inner wall member 22a and the rectifying plate 22c provided in the gas introduction part 22. The heat shield plate 70 includes, for example, a plate member made of carbon and a SiC layer or TaC layer covering the surface of the plate member.
As shown in
As a method for stacking the SiC epitaxial layer on the surface of the SiC single crystal substrate 1 using the epitaxial apparatus 101 shown in
In a case where the SiC epitaxial layer is stacked on the surface of the SiC single crystal substrate 1 using the epitaxial apparatus 101 shown in
In the embodiment described above, although the case in which the epitaxial apparatuses 100 and 101 shown in
As the epitaxial apparatus that includes the horizontal furnace, for example, the following can be used. Each of
In the epitaxial apparatuses 102, 103, 104, and 105 shown in
In the epitaxial apparatus 102 shown in
The epitaxial apparatus 103 shown in
The epitaxial apparatus 104 shown in
The epitaxial apparatus 105 shown in
The gas introduction part 25 in the epitaxial apparatus 105 shown in
The epitaxial apparatuses 100, 101, 102, 103, 104, and 105 shown in
Hereinafter, the present disclosure will be explained in more detail with reference to examples and a comparative example. The present disclosure is not limited only to the following examples.
A SiC single crystal substrate with a diameter of 6 inches was prepared. Next, using the epitaxial apparatus 100 shown in
In the epitaxial apparatus 100 shown in
As the vacuum heat treatment, heat treatment in which the quartz member removed from the epitaxial apparatus 100 was held at 1000° C. for 48 hours under a pressure of 1×10−3 Pa or less using a vacuum heat treatment apparatus was performed.
The member made of quartz which had been subjected to the vacuum heat treatment was cooled to room temperature in the vacuum heat treatment apparatus, and then installed in the epitaxial apparatus 100 shown in
Further, the SiC single crystal substrate 1 was placed on the susceptor 40 and transported to the film forming space S in the chamber 20 of the epitaxial apparatus 100 shown in
For forming the SiC epitaxial layer, a method in which the SiC single crystal substrate 1 is heated to 1600° C. by the lower heater 50 and the upper heater 60, the Si source gas, the C source gas, the dopant gas, and the purge gas are supplied from the gas supply pipe 22d of the gas introduction part 22, and the gas at 1600° C. which has been passed through the rectifying plate 22c is supplied to the film forming space S above the SiC single crystal substrate 1 was used.
Through the above steps, the SiC epitaxial wafer of Example 1 which has a SiC epitaxial layer with a thickness of 350 μm on the surface of the SiC single crystal substrate 1 was obtained.
A SiC epitaxial wafer of Example 2 was obtained by the same method as that for the SiC epitaxial wafer of Example 1, except that the epitaxial apparatus 101 shown in
A SiC epitaxial wafer of Comparative Example 1 was obtained by the same method as that for the SiC epitaxial wafer of Example 1, except that the inner wall member 22a and the rectifying plate 22c were installed in the epitaxial apparatus 100 without being subjected to the vacuum heat treatment.
The SiC epitaxial wafers of Example 1, Example 2, and Comparative Example 1 obtained in such a way were irradiated with the excitation light, and the emission intensity of the PL light (the PL intensity) was measured for each square measurement region of 2 mm on a side, which is obtained by dividing the surface. The measurement conditions for the PL light will be shown below.
In addition, using the results of measuring the emission intensity of PL light for each measurement region, a value of {(IMAX−Imin)/Iaverage}×100(%) (in the formula, IMAX is a maximum value of the emission intensity in the entire measurement region, Imin is a minimum value of the emission intensity in the entire measurement region, and Iaverage is an average value of the emission intensity of the entire measurement region.) was calculated. The results are shown in Table 1.
In addition, using the results of measuring the emission intensity of PL light for each measurement region, a value of {Io-average/Iaverage}×100(%) (in the formula, Io-average is an average value of the emission intensities of the measurement regions located at a portion closest to an outer circumference of the SiC epitaxial wafer among the measurement regions, and Iaverage is an average value of the emission intensity of the entire measurement region.) was calculated. The results are shown in Table 1.
In addition, for Example 1 and Comparative Example 1, from the measurement results of the emission intensity of the PL light for each measurement region along the diameter of the SiC epitaxial wafer, a relationship between the position (the X coordinate) from the center in the diametrical direction of the SiC epitaxial wafer and the emission intensity of the PL light (the PL intensity) was investigated. The results are shown in
As shown in Table 1, in Example 1 and Example 2, the value of {(IMAX−Imin)/Iaverage}×100, which indicates the uniformity of the emission intensity of the PL light obtained from the entire measurement region, was a very low compared to that in Comparative Example 1.
Further, in Example 1 and Example 2, the value of {Io-average/Iaverage}×100, which indicates that the emission intensity of the measurement region located at a portion closest to the outer circumference of the SiC epitaxial wafer is suppressed, was very low compared to that in Comparative Example 1. In particular, in Example 2, the value of {Io-average/Iaverage}×100 was low. This is presumed to be because in Example 2, the heat shield plate 70 suppressed the temperature rise of the inner wall member 22a and the rectifying plate 22c provided in the gas introduction part 22 when the SiC epitaxial layer is formed.
Further, as shown in
Furthermore, in Comparative Example 1, the emission intensity of the measurement region located at a portion close to the outer circumference of the SiC epitaxial wafer is very high. In contrast, in Example 1, the emission intensity of the measurement region located at a portion close to the outer circumference of the SiC epitaxial wafer is suppressed.
In addition, the SiC epitaxial wafers of Example 1, Example 2, and Comparative Example 1 were analyzed using a secondary ion mass spectrometry (SIMS) device (manufactured by Cameca; Dynamic SIMS), and the oxygen concentration, the nitrogen concentration, and the aluminum concentration were obtained. The results are shown in Table 2.
In addition, the SiC epitaxial wafers of Example 1, Example 2, and Comparative Example 1 were observed using an optical microscope (manufactured by Lasertec; trade name: SICA88), and the focal position was shifted from the surface of the SiC epitaxial wafer toward the interface between the SiC epitaxial layer and the SiC single crystal substrate (in a depth direction of the SiC epitaxial layer), and thus the presence or absence of triangular defects originating from particulate deposits was confirmed, and the density thereof was obtained. The results are shown in Table 2.
As shown in Table 2, in all of Example 1, Example 2, and Comparative Example 1, the oxygen concentration, the nitrogen concentration, and the aluminum concentration are sufficiently low.
The lower limit of detection of the oxygen concentration when analyzed using the secondary ion mass spectrometer (SIMS) device is 1×1015 atoms/cm3. For this reason, as shown in Table 2, it cannot be determined from the results of the above oxygen analysis whether or not the oxygen concentration on the surface of the SiC epitaxial wafer of each of Example 1, Example 2, and Comparative Example 1 is less than 1×1014 atoms/cm3.
However, as shown in Table 1, in the SiC epitaxial wafers of Example 1 and Example 2, the value of {(IMAX−Imin)/Iaverage}×100, which indicates the uniformity of the emission intensity of the PL light obtained from the entire measurement region, was a very low. From this, it can be presumed that the SiC epitaxial wafers of Example 1 and Example 2 have surface oxygen concentrations of less than 1×1014 atoms/cm3. This means that when the oxygen concentration on the surface of the SiC epitaxial wafer is more than 1×1014 atoms/cm3, the emission intensity of the PL light having a wavelength of 660 nm or more which is emitted by irradiating the SiC epitaxial wafer with the excitation light having a wavelength of 313 nm is increased by the additional light emission due to the oxygen concentration on the surface. As a result, the uniformity of the emission intensity of the PL light obtained from the entire measurement region becomes poor, and the value of {(IMAX−Imin)/Iaverage}×100 exceeds 40(%). Even if the emission intensity of the PL light is large over the entire in-plane region, if the in-plane distribution is uniform, by correcting the emission intensity by background removal processing, when evaluating the SiC epitaxial wafer using a difference in emission intensity of the PL light from the SiC epitaxial layer, it is possible to perform the evaluation with high accuracy.
Furthermore, in all of Example 1, Example 2, and Comparative Example 1, the triangular defect density is sufficiently low.
As described above, the preferable embodiments of the present disclosure have been described in detail, the present disclosure is not limited to specific embodiments, and various modifications and changes can be made within the scope of the gist of the present disclosure described in the claims.
While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit or scope of the present disclosure. Accordingly, the invention is not to be considered as being limited by the foregoing description, and is only limited by the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-211232 | Dec 2022 | JP | national |
