Optical heating method, optical heating device for wide-bandgap semiconductors

Abstract

To provide a method for optical heating that can efficiently heat a processed target body including a wide bandgap semiconductor.SOLUTION: The method for optical heating includes a step (a) of heating a processed target body including a wide bandgap semiconductor by irradiating the processed target body with an ultraviolet ray emitted from a UV-LED light source with a peak wavelength in the range of 175nm to 370nm through a window member.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a light heating method, and particularly to a light heating method for a workpiece including a semiconductor of a type called "wide bandgap semiconductor". Further, the present invention relates to a light heating device for a wide bandgap semiconductor.

Background Art

[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 performing these heat treatments, light is often used. Thus, heating a workpiece using light is called "light heating".

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

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Documents

[0005]

Non-Patent Document 1

[0006] In recent years, development has been progressing on power semiconductor devices that can handle higher voltages and currents than conventional devices. While silicon (Si) was commonly used in conventional devices, the development of semiconductor devices using materials with a higher Barriga gain coefficient than Si is expected in order to realize small devices with high breakdown voltage characteristics. Examples of such semiconductor materials include GaN, Ga2O3, and SiC. These semiconductors all have wide bandgaps and high dielectric breakdown field strength with thin depletion layers, enabling the realization of small, high-voltage devices.

[0007] Wide-bandgap semiconductors refer to semiconductors with a bandgap larger than that of silicon (Si), and more specifically, semiconductors with a band gap of 2 eV or more. Typical examples of this type of semiconductor include GaN, Ga2O3, and SiC, but other materials such as ZnO, ZnSe, and diamond are also included.

[0008] GaN, Ga2O3, and SiC, which have a higher Barriga gain index than Si, are classified as wide-bandgap semiconductors and therefore transmit light in the 810nm to 980nm wavelength range, as used by the apparatus described in Patent Document 1. In other words, wide-bandgap semiconductors cannot be heated using light in this wavelength range.

[0009] In view of the above problems, the present invention aims to provide a photothermal heating method that can efficiently heat a workpiece containing a wide-bandgap semiconductor. Furthermore, the present invention aims to provide a photothermal heating apparatus suitable for heating a workpiece containing a wide-bandgap semiconductor. [Means for solving the problem]

[0010] The photoheating method according to the present invention is characterized by comprising the step (a) of heating a workpiece including a wide bandgap semiconductor by irradiating it with ultraviolet light having a peak wavelength in the range of 175 nm to 370 nm emitted from a UV-LED light source through a window member.

[0011] The photoheating method according to the present invention utilizes ultraviolet light with a peak wavelength in the range of 175 nm to 370 nm, which is considerably shorter than conventional methods. By utilizing ultraviolet light in this wavelength range, the ultraviolet light can be absorbed by the workpiece to an extent that allows for heating, even when the workpiece contains a wide-bandgap semiconductor. This enables non-contact heating of the workpiece.

[0012] The window member is made of a material with high transmittance to ultraviolet light. This transmittance is preferably 50% or more, more preferably 70% or more, and particularly preferably 80% or more. When the peak wavelength of the ultraviolet light is 175 nm to 200 nm, synthetic quartz, magnesium fluoride (MgF2), calcium fluoride (CaF2), or barium fluoride (BaF2) are preferably used as the material for the window member. On the other hand, when the peak wavelength of the ultraviolet light is 200 nm to 370 nm, in addition to synthetic quartz, fused silica and sapphire are preferably used. By constructing the window member with such a material, ultraviolet light is not significantly absorbed in the window member, and ultraviolet light from the UV-LED light source can be efficiently used to heat the workpiece.

[0013] The method may also include step (b) during the execution of step (a) above, in which a radiation thermometer, whose sensitivity wavelength range is a predetermined wavelength range within the range of 0.5 μm to 5 μm, receives light emitted from the object to be treated to measure the temperature of the object to be treated.

[0014] 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".

[0015] 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 sensitivity wavelength range of the radiation thermometer. As a result, some of the light from the heating light source may be received by the radiation thermometer, potentially leading to a false detection of the temperature of the object being treated.

[0016] A radiation thermometer with a sensitivity wavelength range of 0.5 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 0.7 μm to 4 μm, and particularly preferably 1 μm to 3 μm.

[0017] Furthermore, the upper limit of the sensitivity wavelength range of the radiation thermometer may be appropriately set according to the melting point of the wide-bandgap semiconductor material contained in the object being treated. However, this does not preclude measuring the temperature of the object being treated using a radiation thermometer capable of measuring a temperature range higher than the melting point.

[0018] The aforementioned ultraviolet light may be defined as having a peak wavelength in the range of 190 nm to 370 nm.

[0019] When the wavelength of ultraviolet light is less than 190 nm, it is known that the absorption rate for oxygen (O2) increases (see Non-Patent Document 1 above). FIG. 1 is a graph showing the relationship between wavelength and absorption coefficient for several substances containing O2, which is disclosed in this Non-Patent Document 1.

[0020] According to FIG. 1, it is understood that from the region where the wavelength is less than 190 nm, the absorption coefficient of ultraviolet light for oxygen (O2) begins to show a tendency to increase rapidly. For example, when a wavelength component near 185 nm contained in the ultraviolet light emitted from a low-pressure mercury lamp is absorbed by oxygen, ground-state atomic oxygen O( 3 P) is generated according to the following formula (1). O2 + hν (185 nm) → O( 3 P) + O( 3 P) ··· (1)

[0021] This atomic oxygen O( 3 P) reacts with oxygen (O2) and generates ozone (O3) according to the following formula (2). O( 3 P) + O2 → O3 ··· (2)

[0022] When performing photo-heat treatment, the light source is generally installed in the atmosphere. In view of this point, when the UV-LED light source is installed in the atmosphere in the method according to the present invention, the ultraviolet light irradiated from the UV-LED light source is irradiated onto the object to be processed typically installed in a vacuum environment through a window for light transmission. Therefore, if the ultraviolet light contains a wavelength component less than 190 nm, as a result of this wavelength component of ultraviolet light being absorbed by oxygen in the atmosphere, it may cause the generation of ozone according to the above formulas (1) to (2).

[0023] As described above, by setting the peak wavelength of the ultraviolet light emitted from the UV-LED light source to 190 nm to 370 nm, even when the UV-LED light source is installed in the atmosphere, an effect of suppressing the amount of ozone generation can be obtained. From the viewpoint of further reducing the amount of ozone generation, it is more preferable to set the peak wavelength of the ultraviolet light emitted from the UV-LED light source to 200 nm or more.

[0024] The wide-bandgap semiconductor is Ga2O3, The ultraviolet ray may have a peak wavelength of 300 nm or less.

[0025] FIG. 2A is a graph showing the relationship between wavelength and absorption rate in Ga2O3. According to FIG. 2A, it is understood that in Ga2O3, the absorption rate shows an increasing trend within the range where the wavelength is 300 nm or less. That is, when the object to be processed contains Ga2O3, high heating efficiency can be achieved by irradiating the object to be processed with ultraviolet rays having a peak wavelength of 300 nm or less from a UV-LED light source. This peak wavelength is preferably 280 nm or less, and more preferably 260 nm or less.

[0026] In particular, according to FIG. 2A, within the range where the wavelength is 260 nm or less, the absorption rate of Ga2O3 is 50% or more. Therefore, when the object to be processed contains Ga2O3, higher heating efficiency can be achieved by setting the peak wavelength of the ultraviolet rays emitted from the UV-LED light source to 260 nm or less.

[0027] FIG. 2B is a graph showing the relationship between wavelength and penetration depth when light is irradiated on Ga2O3. The vertical axis is in logarithmic notation. According to FIG. 2B, when ultraviolet rays with a wavelength of 280 nm are irradiated, the penetration depth of the ultraviolet rays is about 290 nm. It is understood that the shorter the wavelength of the ultraviolet rays, the shallower the penetration depth. In FIG. 2B, although data on the penetration depth when ultraviolet rays in the wavelength range exceeding 280 nm are irradiated is not disclosed, it is clear from the trend of the graph that the longer the wavelength, the deeper the penetration depth.

[0028] In other words, the shorter the wavelength of the irradiated ultraviolet light, the more selectively the treatment can be applied to the vicinity of the surface of the workpiece containing Ga2O3 (for example, within a depth of 100 nm or less). This allows for heat treatment of the surface of the workpiece while suppressing the effects of thermal history and thermal damage to devices located in layers below the surface of the workpiece.

[0029] The wide-bandgap semiconductor is GaN or SiC. The aforementioned ultraviolet light may be defined as having a peak wavelength of 360 nm or less.

[0030] Figure 3A is a graph showing the relationship between wavelength and absorptivity in GaN. According to Figure 3A, in GaN, the absorptivity when irradiated with ultraviolet light at a wavelength of 360 nm is approximately 80%, and it can be seen that the absorptivity decreases sharply from wavelengths exceeding 360 nm, or more precisely, from wavelengths exceeding 369 nm, and that relatively high absorptivity is observed within the range of wavelengths below 360 nm. In other words, when the material to be treated contains GaN, high heating efficiency can be achieved by heating it by irradiating it with ultraviolet light with a peak wavelength of 360 nm or less from a UV-LED light source.

[0031] Figure 3B is a graph showing the relationship between wavelength and penetration depth when light is irradiated onto GaN, following the pattern of Figure 2B. According to Figure 3B, when ultraviolet light with a wavelength of 360 nm is irradiated, the penetration depth of ultraviolet light is approximately 100 nm. It can be seen that the penetration depth decreases as the wavelength of the ultraviolet light becomes shorter.

[0032] Therefore, the shorter the wavelength of the irradiated ultraviolet light, the more selectively the treatment can be applied to the vicinity of the surface of the GaN-containing workpiece (for example, within a depth of 100 nm or less). This allows for heat treatment of the surface of the workpiece while suppressing the effects of thermal history and thermal damage to devices located in layers below the surface of the workpiece. When aiming for even more selective treatment of the vicinity of the surface, the peak wavelength of the ultraviolet light is preferably 360 nm or less, and more preferably 300 nm or less.

[0033] Figure 4A is a graph showing the relationship between wavelength and absorptivity in SiC. According to Figure 4A, the absorptivity of SiC to ultraviolet light at a wavelength of 360 nm is approximately 50%. Furthermore, Figure 4A shows that the absorptivity is 40% or higher within the wavelength range of 360 nm and 50% or higher within the wavelength range of 300 nm. In other words, the material being treated... SiC Even when this is included, high heating efficiency can be achieved by irradiating the device with ultraviolet light having a peak wavelength of 360 nm or less from a UV-LED light source.

[0034] Figure 4B is a graph showing the relationship between wavelength and penetration depth when light is irradiated onto SiC, following the pattern of Figure 2B. According to Figure 4B, when ultraviolet light with a wavelength of 360 nm is irradiated, the penetration depth of ultraviolet light is less than 100 nm, approximately 30 nm. It can be seen that the penetration depth decreases as the wavelength of ultraviolet light becomes shorter.

[0035] Therefore, the shorter the wavelength of the irradiated ultraviolet light, the more selectively the treatment can be applied to the vicinity of the surface of the SiC-containing workpiece (for example, within a depth of 100 nm or less). This allows for heat treatment of the surface of the workpiece while suppressing the effects of thermal history and thermal damage to devices located in layers below the surface of the workpiece. When aiming for even more selective treatment of the vicinity of the surface, the peak wavelength of the ultraviolet light is preferably 360 nm or less, and more preferably 300 nm or less.

[0036] The optical heating device according to the present invention is an optical heating device for wide bandgap semiconductors, A chamber for housing an object to be processed, including a wide-bandgap semiconductor, A support member that supports the object to be processed within the chamber, A UV-LED light source that emits ultraviolet light with a peak wavelength in the range of 175nm to 370nm, The device is characterized by comprising a window member that allows the ultraviolet light emitted from the UV-LED light source to pass through and guide it to the object to be treated.

[0037] According to the above optical heating device, when processing wide-bandgap semiconductors used in power semiconductor devices, heating can be performed efficiently without contact.

[0038] In the above configuration, the UV-LED light source comprises multiple LED substrates on which multiple LED elements are mounted, The multiple LED substrates may be arranged in a manner that is symmetrical with respect to a line, point, or rotation when viewed in the direction normal to the surface of the LED substrate.

[0039] 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. [Effects of the Invention]

[0040] According to the present invention, it is possible to efficiently heat a workpiece containing a wide-bandgap semiconductor. [Brief explanation of the drawing]

[0041] [Figure 1] This graph shows the relationship between wavelength and absorption coefficient for several substances containing oxygen (O2). [Figure 2A] This graph shows the relationship between wavelength and absorption rate in Ga2O3. [Figure 2B] This graph shows the relationship between wavelength and penetration depth when light is irradiated onto Ga2O3. [Figure 3A] This graph shows the relationship between wavelength and absorption rate in GaN. [Figure 3B] This graph shows the relationship between wavelength and penetration depth when light is irradiated onto GaN. [Figure 4A] This graph shows the relationship between wavelength and absorption rate in SiC. [Figure 4B]This graph shows the relationship between wavelength and penetration depth when light is irradiated onto SiC. [Figure 5] This is a schematic cross-sectional view showing the configuration of one embodiment of a light heating device. [Figure 6] This is an example of the ultraviolet spectrum emitted from a UV-LED light source. [Figure 7] This is a schematic plan view of a UV-LED light source as seen from the +Z side. [Figure 8] This is a schematic plan view showing the configuration of an LED circuit board. [Modes for carrying out the invention]

[0042] The photoheating method according to the present invention includes a step (a) of heating a workpiece, which includes a wide-bandgap semiconductor, by irradiating it with ultraviolet light having a peak wavelength in the range of 175 nm to 370 nm emitted from a UV-LED light source through a window member. The following description will refer to the drawings of a photoheating apparatus that is one embodiment of the method.

[0043] Please note that the following drawings are schematic representations, and the dimensional ratios and quantities shown in the drawings do not necessarily correspond to the actual dimensional ratios and quantities.

[0044] Figure 5 is a schematic cross-sectional view showing the configuration of one embodiment of a photothermal heating device. The photothermal heating device 1 shown in Figure 5 comprises a chamber 10 in which a workpiece W1 containing a wide-bandgap semiconductor is housed, a UV-LED light source 2, and a radiation thermometer 14. The UV-LED light source 2 comprises a plurality of LED elements 11 and a support substrate 12 on which the LED elements 11 are mounted. More specifically, the UV-LED light source 2 in this embodiment comprises a plurality of LED substrates 20 on which the plurality of LED elements 11 are mounted, and these plurality of LED substrates 20 are mounted on the support substrate 12.

[0045] In the following explanation, as shown in Figure 5, an XYZ coordinate system will be referred to as appropriate, where the main surface of the object to be processed W1 is the XY plane and the normal direction of this XY plane is the Z direction. As shown in Figure 5, the UV-LED light source 2 and the object to be processed W1 are facing each other in the Z direction. Using this notation, Figure 5 corresponds to a schematic cross-sectional view when the light heating device 1 is cut along the XZ plane.

[0046] In the following, when expressing direction, positive and negative directions are distinguished, and these are indicated with a sign such as "+Z direction" or "-Z direction". When expressing direction without distinguishing between positive and negative directions, it is simply written as "Z direction".

[0047] The UV-LED light source 2 emits ultraviolet L1 with a peak wavelength in the range of 175 nm to 370 nm. In this specification, the peak wavelength of ultraviolet L1 emitted by the UV-LED light source 2 refers to the wavelength that shows the highest light intensity (light output) on the emission spectrum.

[0048] Figure 6 shows the spectrum of ultraviolet L1 when UV-LED light source 2 is a light source that emits ultraviolet L1 with a peak wavelength of 325 nm. Note that the vertical axis in Figure 6 is logarithmic.

[0049] According to the spectrum shown in Figure 6, near 500 nm, which is a longer wavelength than the peak wavelength, the light intensity is approximately 0.1% to 0.3% of that of the peak wavelength (region A1 in Figure 6). This is light originating from impurity levels or defect levels, which inevitably occurs when the light source is an LED, and corresponds to the "deep light" mentioned above.

[0050] The UV-LED light source 2 in the optical heating device 1 has a considerably shorter emission wavelength range compared to the LED lamp in the device described in Patent Document 1.

[0051] As shown in Figure 5, the chamber 10 is equipped with a support member 13 on its interior. The support member 13 supports the workpiece W1 such that its main surfaces W1a and W1b are positioned on the XY plane. In Figure 5, the main surface W1b of the workpiece W1 is positioned to face the UV-LED light source 2. That is, circuit elements, wiring, etc. are formed on either the main surface W1a or the main surface W1b, and the main surface W1b is the surface irradiated with ultraviolet light L1 emitted from the UV-LED light source 2. However, the present invention does not exclude the case where the workpiece W1 is a bare substrate without any wiring, etc. formed on it.

[0052] The manner in which the workpiece W1 is supported by the support member 13 is arbitrary, as long as its main surface W1a is positioned on the XY plane. For example, the support member 13 may have multiple pin-shaped protrusions, and the workpiece W1 may be supported at points by these protrusions.

[0053] As shown in Figure 5, 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.

[0054] 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 0.5 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.

[0055] The sensitive wavelength range of the radiation thermometer 14 in the optical heating device 1 is located at longer wavelengths than the main emission wavelength range of ultraviolet light L1 emitted from the UV-LED light source 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 deep light contained in ultraviolet light L1. As mentioned above, although the intensity of deep light is about 0.1% to 0.3% of the peak intensity of ultraviolet 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 W1 to be treated.

[0056] Furthermore, the shorter the peak wavelength of ultraviolet light L1 emitted from the UV-LED light source 2, the shorter the wavelength at which the maximum intensity of deep light is indicated. Therefore, in order to minimize the overlap between the wavelength range of deep light and the sensitivity wavelength range of the radiation thermometer 14, one method is to shorten the emission wavelength of the UV-LED light source 2 or to lengthen the lower limit of the sensitivity wavelength range of the radiation thermometer 14. 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 shorten the emission wavelength of the UV-LED light source 2.

[0057] The second window 10b is a window member for guiding ultraviolet light L1 emitted from the UV-LED light source 2 to the main surface W1b of the workpiece W1. As described above, the peak wavelength of ultraviolet light L1 is in the range of 175 nm to 370 nm. The second window 10b is made of a material that has a transmittance of 50% or more to ultraviolet light L1. As an example, the second window 10b is made of synthetic quartz. In this case, the second window 10b exhibits high transmittance to ultraviolet light L1 even when the peak wavelength of ultraviolet light L1 is less than 200 nm. However, the material of the second window 10b may be appropriately selected according to the peak wavelength of ultraviolet light L1.

[0058] Figure 7 is a schematic plan view of the UV-LED light source 2 as seen from the +Z side. As shown in Figure 7, the UV-LED light source 2 is constructed by arranging multiple light source regions 12a, each containing multiple LED elements 11, on the main surface of the support substrate 12. More specifically, the light source regions 12a are formed on LED substrates 20. Multiple LED substrates 20 are then mounted on the main surface of the support substrate 12.

[0059] In the UV-LED light source 2 shown in Figure 7, multiple LED substrates 20 forming the light source region 12a are arranged regularly. In the present invention, the arrangement pattern of the LED substrates 20 is not limited, but it is preferable that each LED substrate 20 is arranged symmetrically when viewed in the Z direction. Typically, it is preferable that each LED substrate 20 is arranged symmetrically along the line, at the point, or at the rotation. This ensures that ultraviolet light L1 is uniformly irradiated onto the main surface W1b of the workpiece W1.

[0060] Figure 8 is a schematic plan view showing the configuration of the LED substrate 20. As shown in Figure 8, the LED 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 8, a Zener diode 30c is mounted on the LED 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.

[0061] In the example shown in Figure 8, the multiple LED elements 11 mounted on the LED 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.

[0062] Each of the multiple LED elements 11 emits ultraviolet light L1 with a peak wavelength in the range of 175 nm to 370 nm. Preferably, the peak wavelengths of the ultraviolet light L1 emitted from these multiple LED elements 11 are substantially identical. "Substantially identical" here means that wavelength deviations due to variations in the elements during the manufacturing process are tolerable. Typically, a wavelength deviation of within ±5 nm is acceptable.

[0063] For example, the LED substrate 20 is equipped only with LED elements 11 that emit ultraviolet light L1 with a peak wavelength of 325 nm. As another example, the LED substrate 20 is equipped only with LED elements 11 that emit ultraviolet light L1 with a peak wavelength of 260 nm. Furthermore, as another example, the LED substrate 20 is equipped only with LED elements 11 that emit ultraviolet light L1 with a peak wavelength of 310 nm. Furthermore, as another example, the LED substrate 20 is equipped only with LED elements 11 that emit ultraviolet light L1 with a peak wavelength of 365 nm.

[0064] According to the optical heating device 1, since the peak wavelength of ultraviolet light L1 emitted from the UV-LED light source 2 is in the range of 175 nm to 370 nm, even if the object to be treated W1 contains a wide bandgap semiconductor, this ultraviolet light L1 is absorbed by the object to be treated W1. As a result, non-contact heating of the object to be treated W1 is possible.

[0065] Furthermore, during this light irradiation process, the temperature of the workpiece W1 can be detected by receiving the light emitted from the workpiece W1 with the radiation thermometer 14. As described above, 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 ultraviolet L1, false detection of the temperature of the workpiece W1 due to receiving light originating from deep light can be prevented. 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 UV-LED light source 2, highly accurate heating of the workpiece W1, which includes a wide-bandgap semiconductor, becomes possible. Note that the main emission wavelength range, which includes the peak wavelength of ultraviolet L1, is clearly outside the sensitivity wavelength range of the radiation thermometer 14.

[0066] Furthermore, as described above with reference to Figures 2B, 3B, and 4C, the short wavelength of the ultraviolet light L1 emitted from the UV-LED light source 2 limits the penetration depth of the ultraviolet light L1 into the workpiece W1 to near the surface. Therefore, heat treatment can be performed on the surface of the workpiece W1 while suppressing the effects of thermal history and thermal damage to devices located in layers below the surface of the workpiece W1.

[0067] Furthermore, it is more preferable that the peak wavelength of ultraviolet L1 be within the range of 190 nm to 370 nm. In this case, even when the UV-LED light source 2 is installed in the atmosphere, the effect of suppressing ozone generation can be obtained.

[0068] On the other hand, when the peak wavelength of ultraviolet light L1 is less than 190 nm, in order to reduce or suppress the amount of ozone generated, the UV-LED light source 2 itself may be housed in a vacuum or a closed space filled with nitrogen (N2) gas, and a light extraction window made of the same material as the second window 10b may be provided on a part of the wall surface of the closed space.

[0069] Furthermore, the peak wavelength of ultraviolet light L1 emitted from the UV-LED light source 2 may be appropriately selected depending on the type of wide-bandgap semiconductor contained in the workpiece W1. In other words, the type of UV-LED light source 2 (LED element 11) mounted on the photoheating device 1 may be selected depending on the type of wide-bandgap semiconductor contained in the workpiece W1 that is scheduled to be heat-treated by the photoheating device 1.

[0070] Typically, when the wide-bandgap semiconductor contained in the material to be treated W1 is Ga2O3, it is more preferable that the UV-LED light source 2 emits ultraviolet light L1 with a peak wavelength of 300 nm or less. Furthermore, when the wide-bandgap semiconductor contained in the material to be treated W1 is GaN or SiC, it is more preferable that the UV-LED light source 2 emits ultraviolet light L1 with a peak wavelength of 360 nm or less.

[0071] [Alternative Embodiment] Another embodiment will be described below.

[0072] <1> In Figure 7, the case where the light source area 12a is square is shown as an example, but this shape is merely one example. Similarly, in Figure 8, the case where the LED substrate 20 is rectangular is shown as an example, but this shape is merely one example.

[0073] In Figure 7, multiple LED substrates 20 are arranged in a staggered pattern on the support substrate 12, but the arrangement pattern of the multiple LED substrates 20 is arbitrary. As another example, the multiple LED substrates 20 may be arranged in a ring around the center 12c of the support substrate 12.

[0074] In Figure 8, the multiple LED element groups 11s mounted on the LED 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.

[0075] <2> In the optical heating device 1 shown in Figure 5, 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 ultraviolet light L1 is irradiated onto the workpiece W1. 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.

[0076] 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 ultraviolet L1 and not overlap with the wavelength range in which deep light shows maximum intensity. As a result, even if ultraviolet L1 is reflected from 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. [Explanation of Symbols]

[0077] 1:Light heating device 2:UV-LED light source 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 the support substrate 13: Support member 14: Radiation thermometer 20: LED board 30a: Anode electrode 30b: Cathode electrode 30c: Zener diode L1: Ultraviolet light W1: Object to be processed W1a, W1b: Main surface of the object to be processed

Claims

1. The process includes a step (a) of heating a workpiece containing a wide bandgap semiconductor by irradiating it with ultraviolet light having a peak wavelength in the range of 175 nm to 300 nm emitted from a UV-LED light source comprising a plurality of LED elements, through a window member. The wide bandgap semiconductor is Ga₂O₃, The object to be processed is housed in a chamber. The window member is positioned opposite the main surface of the workpiece, A light heating method characterized in that the UV-LED light source is arranged outside the chamber and facing the window member.

2. A process (a) comprising heating a workpiece including a wide bandgap semiconductor by irradiating it with ultraviolet light having a peak wavelength in the range of 175 nm to 360 nm emitted from a UV-LED light source comprising a plurality of LED elements, through a window member, The wide-bandgap semiconductor is SiC. The object to be processed is housed in a chamber. The window member is positioned opposite the main surface of the workpiece, A light heating method characterized in that the UV-LED light source is arranged outside the chamber and facing the window member.

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 of a predetermined wavelength range belonging to the range of 0.5 μm to 5 μm receives light emitted from the object to be treated, thereby measuring the temperature of the object to be treated.

4. The photoheating method according to claim 1 or 2, characterized in that the ultraviolet light has a peak wavelength of 190 nm or more.

5. A photoheating device for wide-bandgap semiconductors, A chamber containing a workpiece containing Ga₂O₃ as a wide-bandgap semiconductor, A support member that supports the object to be processed within the chamber, A UV-LED light source comprising multiple LED elements that emit ultraviolet light with a peak wavelength in the range of 175 nm to 300 nm, The system includes a window member that allows the ultraviolet light emitted from the UV-LED light source to pass through and guide it to the object to be treated, The window member is positioned opposite the main surface of the object to be processed when it is housed in the chamber. The photoheating device for wide-bandgap semiconductors is characterized in that the UV-LED light source is positioned outside the chamber and facing the window member.

6. A photoheating device for a wide bandgap semiconductor, A chamber for accommodating a workpiece containing SiC as a wide-bandgap semiconductor, A support member that supports the object to be processed within the chamber, A UV-LED light source comprising multiple LED elements that emit ultraviolet light with a peak wavelength in the range of 175 nm to 360 nm, The system includes a window member that allows the ultraviolet light emitted from the UV-LED light source to pass through and guide it to the object to be treated, The window member is positioned opposite the main surface of the object to be processed when it is housed in the chamber. The photoheating device for wide-bandgap semiconductors is characterized in that the UV-LED light source is positioned outside the chamber and facing the window member.

7. The UV-LED light source comprises multiple LED substrates on which the multiple LED elements are mounted, The optical heating apparatus for wide bandgap semiconductors according to claim 5 or 6, characterized in that the plurality of LED substrates are arranged in a line-symmetric, point-symmetric, or rotationally symmetric manner when viewed in the direction normal to the surface of the LED substrates.

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