Optical heating method, and optical heating device for n-type 4h-sic semiconductor

Abstract

Provided is an optical heating method with which a to-be-treated object constituted by an n-type 4H-SiC semiconductor can be heated efficiently.　The present invention involves a step (a) for radiating, via a window member onto a to-be-treated object constituted by an n-type 4H-SiC semiconductor, heating light which is emitted from a light source unit and has a peak wavelength within a range of 415-500 nm, and thereby heating the to-be-treated object.

Description

Optical heating method, optical heating device for n-type 4H-SiC semiconductor

[0001] The present invention relates to an optical heating method, and particularly to an optical heating method for a workpiece that is an n-type 4H-SiC semiconductor. The present invention also relates to an optical heating device for an n-type 4H-SiC semiconductor.

[0002] In the semiconductor manufacturing process, various heat treatments such as film formation treatment, oxidation diffusion treatment, modification treatment, or annealing treatment are performed on workpieces including semiconductor wafers. When these heat treatments are carried out, light is often used. Thus, heating a workpiece using light is referred to as "optical heating". Also, the light used for heating is called "heating light".

[0003] As a semiconductor heating device using optical heating, for example, the technology of Patent Document 1 below is known. In the device of Patent Document 1, an LED lamp that emits heating light with a wavelength of 810 nm to 980 nm is used as a light source.

[0004] Japanese Patent Application Laid-Open No. 2020-009927

[0005] "Polymer Material Technology in Photoresist Materials" by Koya Masano, Journal of the Rubber Society of Japan, Vol. 85, No. 2 (2012), pp. 33 - pp. 39

[0006] In recent years, the development of power semiconductor devices that can handle higher voltages and larger currents than conventional devices has been underway. For this reason, Si has generally been used in conventional devices, but recently, for realizing devices with small size and high breakdown voltage characteristics, the use of SiC has been under consideration. Note that SiC has classifications such as n-type SiC semiconductors with relatively low resistivity and semi-insulating SiC (sometimes also referred to as "semi-insulating SiC") with relatively high resistivity. Due to the wide range of applications, particularly, n-type SiC semiconductors have attracted attention.

[0007] Note that as an n-type SiC semiconductor, SiC doped with nitrogen (N) as a dopant, and as a semi-insulating SiC semiconductor, SiC doped with vanadium (V) as a dopant or intentionally formed with lattice defects are generally known.

[0008] SiC has a larger band gap and higher dielectric breakdown field strength compared to conventional Si, and is expected to reduce environmental impact through lower losses, miniaturization, and weight reduction. However, SiC has the problem of not being able to heat efficiently because it transmits most of the light emitted from LED lamps, such as those described in Patent Document 1. Furthermore, Patent Document 1 does not specifically consider the case where SiC wafers are used as the object to be heated. For this reason, Patent Document 1 does not mention at all that there is a suitable wavelength range of light for heating SiC wafers.

[0009] Furthermore, SiC is classified into several types based on differences in its crystal structure, including 4H-SiC (bandgap 3.3 eV), 6H-SiC (bandgap 3 eV), and 3C-SiC (bandgap 2.2 eV). Among these materials, 4H-SiC, in particular, is the most advanced in research and development toward practical application in terms of material properties, crystal quality, maturity of the manufacturing process, and progress of device development. For this reason, in recent years, there has been a growing demand for more efficient optical heating methods and devices applicable to the manufacturing process of n-type 4H-SiC semiconductors.

[0010] In view of the above problems, the present invention aims to provide a photothermal heating method that can efficiently heat a workpiece that is an n-type 4H-SiC semiconductor. The present invention also aims to provide a photothermal heating apparatus suitable for heating a workpiece that is an n-type 4H-SiC semiconductor.

[0011] The photoheating method according to the present invention is characterized by comprising the step (a) of heating a workpiece, which is an n-type 4H-SiC semiconductor, by irradiating it with heating light having a peak wavelength in the range of 415 nm to 500 nm emitted from a light source through a window member.

[0012] In the above-described optical heating method, it is preferable that the heating light has a peak wavelength in the range of 420 nm to 490 nm.

[0013] As mentioned above, SiC is classified into n-type and semi-insulating types depending on the dopant used for doping. Even just the doping of SiC can change its absorption rate. For this reason, there is no wavelength range that is recognized as suitable for photothermal treatment of SiC.

[0014] Given the above background, the inventors investigated how to derive the absorption rates for each wavelength of n-type SiC semiconductors, which have particularly high potential for practical application, and how to find a suitable wavelength range for optical heating of n-type SiC semiconductors. At the time of filing this application, it was difficult to directly measure the absorption spectrum of n-type SiC semiconductors. Therefore, the inventors adopted a method of measuring the reflectance R and transmittance T of n-type SiC semiconductors and deriving the absorption rate A (= 1 - R - T) to determine the absorption rates for each wavelength of n-type SiC semiconductors.

[0015] Specifically, the reflectance R is measured and derived using an n-type SiC wafer, a light source whose emitted light intensity spectrum is known, and a spectrophotometer positioned on the same side as the light source relative to the n-type SiC wafer. The transmittance T is measured and derived using an n-type SiC wafer, a light source whose emitted light intensity spectrum is known, and a spectrophotometer positioned on the opposite side of the light source relative to the n-type SiC wafer.

[0016] Figure 1A is a graph showing the relationship between wavelength and absorptivity in an n-type 4H-SiC semiconductor, and Figure 1B is an enlarged graph of Figure 1A covering the wavelength range of 200 nm to 600 nm. The graph shown in Figure 1A was calculated based on the reflectivity characteristic data and transmittance characteristic data of the n-type 4H-SiC semiconductor measured by the method described above. According to Figures 1A and 1B, the absorptivity for light in the wavelength range of 415 nm to 500 nm is 45% or higher, which is higher than the absorptivity for light with wavelengths longer than 500 nm. In other words, even when the material to be treated is an n-type 4H-SiC semiconductor, high heating efficiency can be achieved by irradiating it with heating light from a light source with a peak wavelength in the range of 415 nm to 500 nm.

[0017] Furthermore, Figure 1B shows that the n-type 4H-SiC semiconductor exhibits an absorption rate of 50% or more in the wavelength range of 420 nm to 490 nm. In other words, even when the material to be treated is an n-type 4H-SiC semiconductor, higher heating efficiency can be achieved by irradiating it with heating light from the light source with a peak wavelength in the range of 420 nm to 490 nm.

[0018] The window member is made of a material with high transmittance to heating light as described above. This transmittance is preferably 50% or more, more preferably 70% or more, and particularly preferably 80% or more. Suitable materials for the window member include synthetic quartz, fused quartz, sapphire, magnesium fluoride (MgF2), calcium fluoride (CaF2), or barium fluoride (BaF2). By constructing the window member with such a material, heating light is not significantly absorbed by the window member, and the heating light from the light source can be efficiently used to heat the workpiece.

[0019] Here, the inventors confirmed that the temperature at which SiC crystal growth occurs for each crystal structure during subsequent high-temperature annealing differs depending on the wafer temperature during ion implantation. Specifically, after annealing at 200°C or below, mainly 3C-SiC crystal growth was observed, while after annealing at 300°C or above, mainly 4H-SiC crystal growth was observed.

[0020] Given these characteristics, it is considered important to raise the temperature of the material to be treated to 300°C or higher as quickly as possible during the annealing process in order to more precisely control the crystal growth of 4H-SiC. Therefore, the inventors conducted verification experiments to confirm the difference in heating rates when n-type 4H-SiC is heated by irradiating it with light emitted from light sources with different peak wavelengths of emitted light, using the same power value.

[0021] Figure 1C is a graph plotting the time change in temperature of the n-type 4H-SiC semiconductor from the start of heating for each light source. Details of this verification experiment will be described later in the "Modes for Carrying Out the Invention" section, but as shown in Figure 1C, the final temperature reached is higher with heating light of wavelength 395 nm, but the heating rate is faster with heating light of wavelength 450 nm. Figure 1C also shows the temperature change of SiC with heating light of wavelength 850 nm, and it can be seen that the heating rate with heating light of wavelength 850 nm is significantly slower than that with heating light of 395 nm, which has a relatively similar absorption rate.

[0022] In other words, considering the relatively high absorptivity and relatively fast heating rate, it can be said that for heating n-type 4H-SiC, a peak wavelength of heating light of 415 nm to 500 nm is preferable. In this determination, the absorptivity of SiC was assumed to be 45% or higher, as described above. Furthermore, in this determination, the heating rate was based on the range in which, assuming a continuous change between heating light wavelengths as shown in the graph of Figure 1C, the time from the start of heating light irradiation to reaching 300°C is estimated to be less than or equal to twice the result obtained with heating light of 450 nm.

[0023] Figure 2 is a graph showing the trend of the absorbance characteristics of resins used in semiconductor photoresists, as presented in Non-Patent Document 1. Resins used in semiconductor photoresists include novolac resin, methacrylate resin, and PHS resin. As shown in Figure 2, these resins exhibit relatively high absorbance to light with wavelengths of 300 nm or less, and in particular, novolac resin and PHS resin show a sudden increase in absorbance to light with wavelengths of 300 nm or less.

[0024] Semiconductor photoresists are used, for example, as photoresist masks when ion implantation is performed on a SiC substrate. Therefore, important indicators for resins used in semiconductor photoresists include light transmittance, chemical resistance, and solubility in developing solutions. Regarding light transmittance, it is adjusted according to the spectrum of light emitted from the light source.

[0025] However, as mentioned above, many resins used in semiconductor photoresists exhibit high absorbance to light with wavelengths of 300 nm or less. For these reasons, it is preferable that the light emitted from the LED element has a certain bandwidth and that the peak wavelength of the emitted heating light is at least 370 nm or higher, in order to further reduce absorption by the resin. In other words, in the waveform shown in Figure 1, there is a wavelength band below 390 nm that shows a relatively high absorption rate, but since absorption by the resin is a concern with light in this wavelength band, it is preferable to use light in the wavelength band of 400 nm or higher.

[0026] The above optical heating method utilizes heating light with a peak wavelength in the range of 420 nm to 490 nm, which is considerably shorter than conventional methods. By using heating light in this wavelength range, the heating light can be absorbed by the workpiece to an extent that allows for heating, even when the workpiece is a SiC semiconductor. As a result, the workpiece is heated without contact.

[0027] Furthermore, since the above photoheating method utilizes heating light with a peak wavelength in the range of 420 nm to 490 nm, the effect of absorption by semiconductor photoresists is reduced compared to the case where heating light with a peak wavelength in a shorter wavelength band is used.

[0028] The above-described photothermal heating method may also include a step (b) during the execution of step (a) in which a radiation thermometer, whose sensitivity wavelength range is a predetermined wavelength range belonging to the range of 0.7 μm to 5 μm, receives light emitted from the object to be treated to measure the temperature of the object to be treated.

[0029] It is known that semiconductor light-emitting elements, such as LEDs, emit not only light in the wavelength range including the peak wavelength and with relatively high emission intensity (main emission wavelength range), but also light in the wavelength range longer than the main emission wavelength range, with relatively low emission intensity. Although the emission intensity of this longer wavelength light is very low compared to the intensity of the main emission wavelength range, it shows an intensity slightly higher than the intensity of the tail when approximated by a Gaussian distribution. This longer wavelength light is light that originates from defects or impurity levels in the active layer that inevitably occur during the manufacturing of semiconductor light-emitting elements, and is called "deep light".

[0030] For example, if a light source with a peak wavelength in the range of 400 nm to 1000 nm is used as a heating light source, the wavelength range with relatively high intensity among the deep light emitted from this light source will overlap with the sensitive wavelength range of the radiation thermometer. As a result, there is a risk that some of the light from the heating light source will be received by the radiation thermometer, leading to a false detection of the temperature of the object being treated.

[0031] A radiation thermometer with a sensitivity wavelength range of 0.7 μm to 5 μm can measure the temperature of the object being treated from a relatively low temperature range of 200°C to 500°C, thus enabling more precise temperature control. From the viewpoint of accurately detecting the temperature from the initial stage after heating of the object being treated has begun, the sensitivity wavelength range of the radiation thermometer is more preferably 0.8 μm to 4 μm, and particularly preferably 1 μm to 3 μm.

[0032] The upper limit of the sensitivity wavelength range of the radiation thermometer may be appropriately set according to the melting point of the SiC contained in the material being treated. However, this does not preclude measuring the temperature of the material being treated using a radiation thermometer capable of measuring a temperature range higher than the melting point.

[0033] The present invention relates to a photothermal heating apparatus for n-type 4H-SiC semiconductors, characterized by comprising: a chamber for housing a workpiece which is an n-type 4H-SiC semiconductor; a support member for supporting the workpiece within the chamber; a light source unit that emits heating light having a peak wavelength in the range of 415 nm to 500 nm; and a window member that allows the heating light emitted from the light source unit to pass through and guide it to the workpiece.

[0034] According to the above optical heating device, when processing n-type 4H-SiC semiconductors, which are used in power semiconductor devices and are expected to have a wide range of applications, heating can be performed efficiently without contact.

[0035] In the above-described optical heating device, the light source unit comprises a plurality of substrates on which a plurality of semiconductor light-emitting elements are mounted, and the plurality of substrates may be arranged symmetrically along a line, point, or rotation when viewed in the direction normal to the main surface of the substrate.

[0036] According to the above configuration, the light intensity distribution on the object to be treated is homogenized, thus enabling uniform heating of the object to be treated.

[0037] According to the present invention, a photothermal heating method is realized that can efficiently heat a workpiece that is an n-type 4H-SiC semiconductor. Furthermore, according to the present invention, a photothermal heating device suitable for heating a workpiece that is an n-type 4H-SiC semiconductor is realized.

[0038] This graph shows the relationship between wavelength and absorptivity in n-type 4H-SiC semiconductors. This is an enlarged version of Figure 1A, showing the wavelength range from 200 nm to 600 nm. This graph plots the time change in temperature of the n-type 4H-SiC semiconductor from the start of heating for each light source. This graph shows the trend of the light absorbance characteristics of resins used in semiconductor photoresists. This is a schematic cross-sectional view showing the configuration of one embodiment of a light heating device. This is an example of the spectrum of heating light with a peak wavelength of 460 nm emitted from the light source. This is a schematic plan view of the light source as seen from the -Z side. This is a schematic plan view showing the configuration of the substrate.

[0039] The photoheating method according to the present invention includes a step (a) of heating a workpiece, which is an n-type 4H-SiC semiconductor, by irradiating it with heating light having a peak wavelength in the range of 420 nm to 490 nm emitted from a light source through a window member. The photoheating method will be described below with reference to a drawing of a photoheating apparatus that is one embodiment of the method.

[0040] It should be noted that the following drawings are all schematic illustrations, and the dimensional ratios and numbers shown in the drawings do not necessarily correspond to the actual dimensional ratios and numbers. Furthermore, in the following explanation, the workpiece is assumed to be an n-type 4H-SiC semiconductor doped with nitrogen (N) as a dopant. However, as mentioned above, the workpiece targeted by this invention is not limited to n-type 4H-SiC semiconductors doped with nitrogen (N), but is also assumed to be a workpiece that can be generally recognized as being classified as an "n-type 4H-SiC semiconductor" in the semiconductor industry. This way of thinking is based on the assumption that the absorption rate to light will change somewhat depending on the type of dopant and crystal structure, but it is unlikely that extreme spectral differences will appear in materials that are classified as 4H-SiC and treated as similar products.

[0041] Figure 3 is a schematic cross-sectional view showing the configuration of one embodiment of the optical heating device 1. The optical heating device 1 shown in Figure 3 comprises a chamber 10 in which a workpiece W1, which is an n-type 4H-SiC semiconductor, a light source unit 2, and a radiation thermometer 14. The light source unit 2 comprises an LED element 11, which is a type of semiconductor light-emitting element, and a support substrate 12 on which the LED element 11 is mounted. More specifically, the light source unit 2 in this embodiment comprises a plurality of substrates 20 on which the plurality of LED elements 11 are mounted, and these plurality of substrates 20 are mounted on the support substrate 12.

[0042] In the following description, as shown in FIG. 3, a plane parallel to the main surfaces (W1a, W1b) of the workpiece W1 is defined as the X-Y plane, and the normal direction of this X-Y plane is defined as the Z direction, and an X-Y-Z coordinate system is appropriately referred to. As shown in FIG. 3, the light source unit 2 and the workpiece W1 face each other in the Z direction. When described using this notation, FIG. 5 to be described later corresponds to a schematic cross-sectional view when the optical heating device 1 is cut in the X-Z plane.

[0043] Incidentally, hereinafter, when distinguishing between positive and negative directions when expressing a direction, it is described with positive and negative signs such as “+Z direction” and “−Z direction”, and when expressing a direction without distinguishing between positive and negative directions, it is simply described as “Z direction”.

[0044] The light source unit 2 emits heating light L1 having a peak wavelength in the range of 415 nm to 500 nm. In this specification, the peak wavelength of the heating light L1 emitted by the light source unit 2 refers to the wavelength indicating the highest light intensity (light output) on the emission spectrum. [[ID=VII]] [[ID=VIII]]

[0045] Further, it is more desirable that the main emission wavelength of the light source unit 2 is in the range of 415 nm to 500 nm. Specifically, it is desirable to employ a light source unit 2 in which the wavelength band showing a light intensity of 50% or more with respect to the peak intensity of the heating light L1 falls within the range of 415 nm to 5OO nm. Furthermore, it is more desirable to employ a light source in which the wavelength band showing a light intensity of 50% or more with respect to the peak intensity of the heating light L1 falls within the range of 420 nm to 490 nm. Thereby, the light source unit 2 becomes a light source more suitable for the heat treatment of the workpiece which is an n-type 4H-SiC semiconductor.

[0046] Further, it is more desirable that most of the emission wavelengths of the emitted heating light L1 of the light source unit 2 are in the range of 415 nm to 500 nm. Specifically, it is desirable to employ a light source unit 2 in which the wavelength band showing 90% or more with respect to the peak intensity of the heating light L1 falls within the range of 415 nm to 500 nm. Furthermore, it is more desirable to employ a light source in which the wavelength band showing a light intensity of 90% or more with respect to the peak intensity of the heating light L1 falls within the range of 420 nm to 490 nm. Thereby, the light source unit 2 becomes a light source more suitable for the heat treatment of the workpiece which is an n-type 4H-SiC semiconductor.

[0047] FIG. 4 is an example of the spectrum of the heating light L1 having a peak wavelength of 460 nm emitted from the light source unit 2. In FIG. 4, the vertical axis is in logarithmic notation.

[0048] According to the spectrum shown in FIG. 4, in the vicinity of 610 nm to 690 nm on the longer wavelength side than the peak wavelength, the light intensity of about 0.1% to 0.3% with respect to the light intensity of the peak wavelength is shown (region A1 in FIG. 4). This is the light derived from the impurity level or defect level that inevitably occurs when the light source is an LED, and corresponds to the above-described "deep light".

[0049] The light source unit 2 included in the optical heating apparatus 1 has a shorter emission wavelength range than the LED lamp included in the apparatus of Patent Document 1 described above.

[0050] As shown in FIG. 3, the chamber 10 includes a support member 13 inside. The support member 13 supports the workpiece W1 such that the main surfaces W1a and W1b of the workpiece W1 are arranged on the X-Y plane. In FIG. 3, the main surface W1b of the workpiece W1 is arranged to face the light source unit 2. That is, circuit elements, wirings, etc. are formed on the main surface W1a or W1b, and the main surface W1b is the surface irradiated with the heating light L1 emitted from the light source unit 2. However, the present invention does not exclude the case where the main surface W1a of the workpiece W1 is arranged to face the light source unit 2 when the workpiece W1 is a bare substrate on which no wirings or the like are formed.

[0051] The support mode of the workpiece W1 by the support member 13 is arbitrary as long as its main surface W1a is arranged on the X-Y plane. For example, the support member 13 may include a plurality of pin-shaped protrusions and support the workpiece W1 at points by the protrusions.

[0052] As shown in FIG. 3, the chamber 10 includes a first window 10a facing the main surface W1a of the workpiece W1 supported by the support member 13 and a second window 10b facing the main surface W1b.

[0053] The first window 10a is a window used by the radiation thermometer 14 to measure the temperature of the main surface W1a of the object to be treated W1. The radiation thermometer 14 is a thermometer that measures the surface temperature of an object by receiving light emitted from the object to be measured. In this embodiment, the sensitivity wavelength range of the radiation thermometer 14 is a predetermined wavelength range belonging to the range of 0.7 μm to 5 μm. In other words, the first window 10a is made of a material that transmits light belonging to this sensitivity wavelength range of the radiation thermometer 14. As an example, the first window 10a is made of general quartz glass or calcium fluoride, etc.

[0054] The sensitive wavelength range of the radiation thermometer 14 in the optical heating device 1 is located at a longer wavelength than the main emission wavelength range of the heating light L1 emitted from the light source unit 2. More preferably, the lower limit of the sensitive wavelength range of the radiation thermometer 14 is at a longer wavelength than the wavelength that shows the maximum intensity of the deep light contained in the heating light L1. As mentioned above, although the intensity of the deep light is about 0.1% to 0.3% of the peak intensity of the heating light L1, if the wavelength of this deep light is included in the sensitive wavelength range of the radiation thermometer 14, there is a possibility of falsely detecting the temperature of the object to be treated W1.

[0055] Furthermore, the shorter the peak wavelength of the heating light L1 emitted from the light source unit 2, the shorter the wavelength at which the deep light shows maximum intensity. Therefore, in order to minimize the overlap between the wavelength range of the deep light and the sensitivity wavelength range of the radiation thermometer 14, one method is to make the emission wavelength of the light source unit 2 shorter, or to make the lower limit of the sensitivity wavelength range of the radiation thermometer 14 longer. However, if the sensitivity wavelength range of the radiation thermometer 14 is shifted to the longer wavelength side, the relative detection capability of the detection element included in the radiation thermometer 14 decreases, making high-precision temperature measurement difficult. For this reason, when heating the object to be treated W1 while measuring the temperature with high precision within the low-temperature range, it is preferable to make the emission wavelength of the light source unit 2 shorter.

[0056] The second window 10b is a window member for guiding the heating light L1 emitted from the light source unit 2 to the main surface W1b of the workpiece W1. As described above, the peak wavelength of the heating light L1 is in the range of 420 nm to 490 nm. The second window 10b is made of a material that has a transmittance of 50% or more to this heating light L1. As an example, the second window 10b is made of synthetic quartz. However, the material of the second window 10b may be appropriately selected according to the peak wavelength of the heating light L1.

[0057] Figure 5 is a schematic plan view of the light source unit 2 as seen from the -Z side. As shown in Figure 5, the light source unit 2 is constructed by arranging a plurality of light source regions 12a, each containing a plurality of LED elements 11, on the main surface of the support substrate 12. More specifically, the light source regions 12a are formed on the substrate 20. A plurality of substrates 20 are placed on the main surface of the support substrate 12.

[0058] In the light source unit 2 shown in Figure 5, multiple substrates 20 forming the light source region 12a are arranged regularly. In the present invention, the arrangement pattern of the substrates 20 is not limited, but it is preferable that each substrate 20 is arranged symmetrically when viewed in the Z direction. Typically, it is preferable that each substrate 20 is arranged symmetrically along a line, point, or rotation. This ensures that the heating light L1 is uniformly irradiated onto the main surface W1b of the workpiece W1.

[0059] Figure 6 is a schematic plan view showing the configuration of the substrate 20. As shown in Figure 6, the substrate 20 comprises a plurality of LED elements 11 and an anode electrode 30a and a cathode electrode 30b. The plurality of LED elements 11 are electrically connected to the anode electrode 30a and the cathode electrode 30b. In the example shown in Figure 6, a Zener diode 30c is mounted on the substrate 20. This Zener diode 30c is connected in parallel with the plurality of LED elements 11 between the anode electrode 30a and the cathode electrode 30b. The Zener diode 30c is placed to prevent the LED elements 11 from degrading due to static electricity or surge currents.

[0060] In the example shown in Figure 6, the multiple LED elements 11 mounted on the substrate 20 are connected in series and parallel. That is, some of the multiple LED elements 11 are connected in series to form an LED element group 11s, and these LED element groups 11s are connected in parallel to each other.

[0061] Each of the multiple LED elements 11 emits heating light L1 with a peak wavelength in the range of 415 nm to 500 nm. Preferably, the peak wavelengths of the heating light L1 emitted from these multiple LED elements 11 are substantially the same. "Substantially the same" here means to allow for wavelength deviations due to variations in the elements during the manufacturing process. Typically, a wavelength deviation of within ±5 nm is acceptable.

[0062] (Verification Experiment) Here, we conducted a verification experiment to confirm the difference in heating rates when the same power value is applied to light sources with different peak wavelengths of emitted light, and n-type 4H-SiC is heated by irradiating it with the light emitted from those light sources. The details of this experiment are described below.

[0063] <Verification Conditions> A light source unit equipped with multiple LED elements whose emitted light peak wavelength is 395 nm was designated as the first sample, a light source unit equipped with multiple LED elements whose emitted light peak wavelength is 450 nm was designated as the second sample, and a light source unit equipped with multiple LED elements whose emitted light peak wavelength is 850 nm was designated as the third sample.

[0064] The power input to each sample in the light source was kept the same.

[0065] The distance (WD) between the light source and the object being processed was set to 41 mm in all cases.

[0066] <Results> As shown in Figure 1C, the shortest time to reach 300°C from the start of irradiation with heating light was for the second sample. Comparing the first and third samples, as shown in Figure 1A, despite having relatively similar absorption rates, the third sample took more than twice as long to reach 300°C compared to the first sample.

[0067] Considering the results in Figure 1C, it can be inferred that the heating rate of 4H-SiC increases as the wavelength approaches 450 nm, regardless of whether the heating light has a wavelength shorter than 450 nm or a wavelength longer than 450 nm. Furthermore, assuming that the change in heating rate within these wavelength ranges is linear for wavelengths below 450 nm and wavelengths above 450 nm, it can be inferred that the heating rate is less than twice that of the second sample when the wavelength range of the heating light is approximately within the range of 300 nm to 650 nm.

[0068] However, considering heating efficiency, as mentioned above, the wavelength of the heating light is preferably 415 nm to 500 nm, as shown in Figure 1A, where the SiC absorption rate is 45% or higher. In other words, from the above considerations, it is confirmed that, considering the absorption rate of SiC and the heating rate of SiC, the wavelength of the heating light is preferably in the range of 415 nm to 500 nm when heat-treating a workpiece that is n-type 4H-SiC.

[0069] According to the optical heating device 1, since the peak wavelength of the heating light L1 emitted from the light source unit 2 is in the range of 415 nm to 500 nm, even if the object to be treated W1 is an n-type 4H-SiC semiconductor, this heating light L1 is absorbed by the object to be treated W1. As a result, non-contact heating of the object to be treated W1 can be performed.

[0070] Furthermore, the temperature of the workpiece W1 can be detected by receiving the light emitted from the workpiece W1 with the radiation thermometer 14 during the execution of this light irradiation process. As described above, false detection of the temperature of the workpiece W1 due to receiving light originating from deep light can be prevented by setting the sensitivity wavelength range of the radiation thermometer 14 to a wavelength longer than the wavelength showing the maximum intensity of deep light contained in the heating light L1. In other words, by feeding back the detection result from the radiation thermometer 14 to a controller (not shown) that controls the light output of the light source unit 2, highly accurate heating of the workpiece W1, which is an n-type 4H-SiC semiconductor, becomes possible. Note that the main emission wavelength range, which includes the peak wavelength of the heating light L1, is clearly outside the sensitivity wavelength range of the radiation thermometer 14.

[0071] Furthermore, it is more preferable that the peak wavelength of the heating light L1 be within the range of 420 nm to 490 nm. In this case, even when the light source unit 2 is placed in the atmosphere, the effect of suppressing ozone generation can be obtained.

[0072] [Alternative Embodiments] Alternative embodiments will be described below.

[0073] <1> Figure 5 shows an example where the light source area 12a is square-shaped, but this shape is merely one example. Similarly, Figure 6 shows an example where the substrate 20 is rectangular-shaped, but this shape is merely one example.

[0074] In Figure 5, multiple substrates 20 are arranged in a staggered pattern on the support substrate 12, but the arrangement pattern of the multiple substrates 20 is arbitrary. As another example, the multiple substrates 20 may be arranged in a ring around the center 12c of the support substrate 12.

[0075] In Figure 6, the multiple LED element groups 11s mounted on the substrate 20 are all composed of the same number of LED elements 11. However, the number of LED elements 11 included in the LED element group 11s may be different, taking into account the difference in voltage drop that occurs depending on the distance from the anode electrode 30a and the cathode electrode 30b.

[0076] <2> In the optical heating device 1 shown in Figure 3, the first window 10a for measuring the temperature by a radiation thermometer 14 was provided at a position opposite to the main surface W1b on which the heating light L1 is irradiated to the object to be treated W1, and facing the main surface W1a. However, in the present invention, the position of the first window 10a is arbitrary. For example, the first window 10a may be provided on the side wall of the chamber 10, or it may be provided on the main surface W1b side.

[0077] In the latter case, as described above, the sensitive wavelength range of the radiation thermometer 14 is adjusted so as to be far outside the main emission wavelength range of the heating light L1, and also so as not to overlap with the wavelength range in which deep light shows maximum intensity. As a result, even if the heating light L1 is reflected off the main surface W1b of the object to be treated W1, the wavelength range of this reflected light is outside the sensitive wavelength range of the radiation thermometer 14, so even if the radiation thermometer 14 receives the reflected light, there is little risk of misinterpreting the temperature of the object to be treated W1.

[0078] <3> In each of the embodiments described above, the semiconductor light-emitting elements mounted on the light source unit 2 are all described as LED elements 11. However, the light source unit 2 may be an LD element, which is a type of semiconductor light-emitting element, and furthermore, LED elements and LD elements may be mixed together.

[0079] <4> The above-described photothermal heating method and the configuration of the photothermal heating device 1 are merely examples, and the present invention is not limited to the illustrated configurations.

[0080] 1: Light heating device 2: Light source unit 10: Chamber 10a: First window 10b: Second window 11: LED element 11s: LED element group 12: Support substrate 12a: Light source area 12c: Center of support substrate 13: Support member 14: Radiation thermometer 20: Substrate 30a: Anode electrode 30b: Cathode electrode 30c: Zener diode L1: Heating light W1: Object to be treated W1a, W1b: Main surface of object to be treated

Claims

1. A phototherapeutic method characterized by comprising step (a) of heating a workpiece, which is an n-type 4H-SiC semiconductor, by irradiating the workpiece with heating light having a peak wavelength in the range of 415 nm to 500 nm emitted from a light source unit equipped with a semiconductor light-emitting element, through a window member.

2. The photoheating method according to claim 1, characterized in that the heating light has a peak wavelength in the range of 420 nm to 490 nm.

3. The optical heating method according to claim 1 or 2, characterized in that, during the execution of step (a), a radiation thermometer having a sensitivity wavelength range in a predetermined wavelength range belonging to the range of 0.7 μm to 5 μm receives light emitted from the object to be treated, thereby measuring the temperature of the object to be treated.

4. An optical heating apparatus for n-type 4H-SiC semiconductors, comprising: a chamber for housing a workpiece which is an n-type 4H-SiC semiconductor; a support member for supporting the workpiece within the chamber; a light source unit that emits heating light having a peak wavelength in the range of 415 nm to 500 nm; and a window member that allows the heating light emitted from the light source unit to pass through and guide it to the workpiece.

5. The light source unit comprises a plurality of substrates on which a plurality of semiconductor light-emitting elements are mounted, and the plurality of substrates are arranged in a line-symmetric, point-symmetric, or rotationally symmetric manner when viewed in the direction normal to the main surface of the substrate, as described in claim 4, an optical heating device for n-type 4H-SiC semiconductors.

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