OPTICAL HEATING METHOD, OPTICAL HEATING DEVICE FOR N-TYPE SiC SEMICONDUCTOR

Abstract

To provide an optical heating method that can efficiently heat a to-be-processed body containing n-type SiC semiconductors.SOLUTION: An optical heating method has a step (a) for heating the object to be processed by radiating the heating light with a color temperature in the range of 2,200 K to 2,600 K emitted from a light source equipped with an infrared light lamp onto the object containing the n-type SiC semiconductor through a window member.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an optical heating method, and more particularly to an optical heating method for a workpiece including an n-type SiC semiconductor.The present invention also relates to an optical heating device for an n-type SiC semiconductor. [Background technology]

[0002] In the semiconductor manufacturing process, various heat treatments such as film formation, oxidation and diffusion, modification, and annealing are performed on objects to be treated, including semiconductor wafers. Light is often used in carrying out these heat treatments. Heating an object to be treated using light in this manner is called "light heating." Furthermore, light used for heating is called "heating light."

[0003] A known example of a semiconductor heating device that utilizes optical heating is the technology described in the following Patent Document 1. The device in Patent Document 1 uses an LED lamp that emits heating light with a wavelength of 810 nm to 980 nm as a light source. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-009927 A [Non-patent literature]

[0005] [Non-Patent Document 1] "Polymer Materials Technology for Photoresist Materials" Akimasa Seiyano Journal of the Society of Rubber Science and Technology of Japan Vol. 85 No. 2 (2012) p.33~p.39 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, the development of power semiconductor devices that can handle higher voltages and currents than conventional devices has progressed. For this reason, while conventional devices generally use Si, the use of SiC is being considered for recent devices in order to realize small devices that exhibit high voltage resistance. SiC is classified into n-type SiC, which has a relatively low resistivity, and semi-insulating SiC (sometimes called "semi-insulating SiC"), which has a relatively high resistivity. N-type SiC in particular has attracted attention due to its wide range of uses.

[0007] Generally known examples of n-type SiC include SiC doped with nitrogen (N) as a dopant, and generally known semi-insulating SiC include SiC doped with vanadium (V) as a dopant or SiC with lattice defects intentionally formed therein.

[0008] SiC has a larger band gap than conventional Si, and has a high dielectric breakdown field strength, and is expected to reduce environmental impact through low loss, small size, and weight. However, SiC transmits most of the light emitted from an LED lamp as described in Patent Document 1, and there is a problem that it cannot be heated efficiently. Note that Patent Document 1 does not particularly consider the case where a SiC wafer is used as the heating object. For this reason, Patent Document 1 does not mention at all that there is a wavelength range of light suitable for heat-treating a SiC wafer.

[0009] In view of the above problems, the present invention aims to provide an optical heating method capable of efficiently heating a workpiece containing an n-type SiC semiconductor, and also aims to provide an optical heating device suitable for heating a workpiece containing an n-type SiC semiconductor. [Means for solving the problem]

[0010] The light heating method according to the present invention comprises the steps of: The method is characterized by comprising a step (a) of heating a workpiece including an n-type SiC semiconductor by irradiating the workpiece through a window member with heating light having a color temperature in the range of 2,200 K to 2,600 K emitted from a light source unit equipped with an infrared lamp.

[0011] In the above light heating method, The heating light preferably has a color temperature within a range of 2,400K to 2,600K.

[0012] The present inventors have been thoroughly investigating methods for heating objects containing SiC and have discovered the following. SiC comes in a variety of types, including 4H-SiC (band gap 3.3 eV), 6H-SiC (band gap 3 eV), and 3C-SiC (band gap 2.2 eV), depending on the crystal structure. In the case of 6H-SiC, which has a band gap of 3 eV, the transmittance of light gradually increases in the wavelength range longer than about 420 nm, and almost all light in the wavelength range longer than 500 nm is transmitted.

[0013] As mentioned above, SiC is classified into n-type, semi-insulating type, etc. according to the dopant used. The absorption rate of SiC can change even when doped with a dopant. For this reason, there is no wavelength range that is recognized as suitable for photothermal treatment of SiC.

[0014] In light of the above background, the present inventors have investigated how to derive the absorptance for each wavelength of n-type SiC, which is particularly expected to be put to practical use, and how to find a wavelength band of light suitable for optically heating n-type SiC. At the time of filing this application, it was difficult to directly measure the absorption spectrum of n-type SiC, so the present inventors adopted a method of measuring the reflectance R and transmittance S of n-type SiC and deriving the absorptance A (=1-RS), thereby deriving the absorptance for each wavelength of n-type SiC.

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

[0016] FIG. 1 is a graph showing the relationship between wavelength and absorptance in n-type SiC. The graph shown in FIG. 1 is a graph calculated based on reflectance characteristic data and transmittance characteristic data of n-type SiC measured by the above-mentioned method. According to FIG. 1, it is understood that the absorptance is 45% or more for light having a wavelength longer than 800 nm, and the absorptance increases beyond the maximum point present near 600 nm. In other words, it is understood that even when the workpiece includes n-type SiC, high heating efficiency is realized by irradiating the workpiece with light having a main emission wavelength longer than 800 nm from the light source unit for heating.

[0017] Figure 2 is a graph showing the radiant intensity spectrum of light for each color temperature when the power is constant. In the graph shown in Figure 2, the vertical axis shows the relative radiant intensity to the peak intensity of the spectrum when the color temperature is 2,600K, and the horizontal axis shows the wavelength. The relationship between color temperature T, wavelength λ, and radiant intensity E(λ) is derived from Planck's radiation formula, which is expressed as the following equation (1).

[0018]

number

[0019] As shown in Figure 2, light with a color temperature of 2,600 K or less has a radiant intensity spectrum with a peak wavelength in the wavelength band of 1,100 nm or more. If light showing such a radiant intensity spectrum is used as heating light, it corresponds to light in a wavelength band where the absorption rate of n-type SiC is relatively high, as can be seen from Figure 1, so that n-type SiC can be heated efficiently.

[0020] Furthermore, as shown in Figure 2, the lower the color temperature, the more the wavelength showing the intensity peak shifts to the longer wavelength side and the light radiation intensity (spectral radiance) tends to decrease. For this reason, light with a color temperature even lower than 2,200K experiences a rapid drop in radiation intensity, making it difficult to supply the energy required to heat an n-type SiC substrate.

[0021] Therefore, according to the graphs shown in FIGS. 1 and 2 and the circumstances described above, the color temperature of the light used to heat n-type SiC is preferably 2,200K to 2,600K, and more preferably 2,400K to 2,600K.

[0022] In the light heating method, by using heating light having a color temperature in the range of 2,200 K to 2,600 K, even if the object to be treated contains an n-type SiC semiconductor, the heating light can be absorbed by the object to be treated to an extent that the heating effect can be exerted. This makes it possible to heat the object to be treated efficiently without contact.

[0023] The light heating method includes: During the execution of the step (a), a step (b) may be included in which a radiation thermometer having a wavelength sensitivity range of a predetermined wavelength range of 2.5 μm to 14 μm receives light emitted from the object to be treated, thereby measuring the temperature of the object to be treated.

[0024] A radiation thermometer with a sensitivity wavelength range of 2.5 μm to 14 μm can detect light in a wavelength range with a relatively low radiation intensity in the heating light to measure the temperature of the object to be treated. In other words, according to the light heating method, the temperature of the object to be treated can be measured by a radiation thermometer that is not easily affected by the heating light, so that the temperature of the object to be treated during heating can be monitored with high accuracy.

[0025] The upper limit of the sensitivity wavelength range of the radiation thermometer may be appropriately set according to the melting point of SiC contained in the workpiece, but this does not exclude the use of a radiation thermometer capable of measuring a temperature range higher than the melting point to measure the temperature of the workpiece.

[0026] The light heating device of the present invention is An optical heating device for n-type SiC semiconductors, A chamber that accommodates a workpiece including an n-type SiC semiconductor; a support member for supporting the workpiece in the chamber; A light source unit having an infrared lamp that emits heating light with a color temperature in the range of 2,200K to 2,600K; a window member through which the heating light emitted from the light source passes and which guides the light to the object to be treated.

[0027] The light heating device is The infrared lamp may be a halogen lamp.

[0028] The optical heating device described above can efficiently perform heating in a non-contact manner when processing n-type SiC semiconductors used in power semiconductor devices, which are expected to have a particularly wide range of uses.

[0029] In the above-mentioned light heating device, A reflecting member may be provided for reflecting, toward the object, the light emitted from the infrared lamp and traveling in a direction opposite to the object.

[0030] The optical heating device of the above configuration can utilize the heating light emitted from the infrared lamp and traveling in the direction opposite to the workpiece to heat the workpiece, thereby making it possible to heat the workpiece more efficiently. Effect of the Invention

[0031] According to the present invention, an optical heating method capable of efficiently heating a workpiece including an n-type SiC semiconductor is realized. Also, according to the present invention, an optical heating device suitable for heating a workpiece including an n-type SiC semiconductor is realized. [Brief description of the drawings]

[0032] [Figure 1] 1 is a graph showing the relationship between wavelength and absorptance in n-type SiC. [Diagram 2] 1 is a graph showing a radiation intensity spectrum of light for each color temperature. [Diagram 3] FIG. 1 is a cross-sectional view showing a schematic configuration of an embodiment of a light heating device. [Figure 4] 1 is a graph showing the tendency of the light absorbance characteristics of a resin used in a semiconductor photoresist. [Diagram 5] FIG. 2 is a schematic plan view of the light source unit as viewed from the -Z side. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] The optical heating method according to the present invention includes a step (a) of irradiating an object to be treated, including an n-type SiC semiconductor, through a window member with heating light having a color temperature in the range of 2,200 K to 2,600 K emitted from a light source unit, thereby heating the object to be treated. Hereinafter, this optical heating method will be described with reference to drawings of an optical heating device that is one embodiment of the method.

[0034] In addition, the following drawings are all schematic illustrations, and the dimensional ratios and numbers in the drawings do not necessarily correspond to the actual dimensional ratios and numbers. In the following description, the object to be processed is assumed to be an object to be processed that includes an n-type 4H-SiC semiconductor doped with nitrogen (N) as a dopant. However, as described above, the object to be processed that is the subject of the present invention is assumed to be not only an object to be processed that includes an n-type 4H-SiC semiconductor doped with nitrogen (N), but also an object to be processed that includes a material that can be generally recognized as "n-type SiC" or classified as n-type SiC in the semiconductor industry. This idea is inferred based on the fact that, although it is assumed that the light absorption rate changes somewhat depending on the type of dopant and the crystal structure, it is unlikely that extreme differences in spectrum will appear in materials that are treated as similar products classified in the same category based on SiC.

[0035] Fig. 3 is a cross-sectional view showing a schematic configuration of one embodiment of the optical heating device 1. The optical heating device 1 shown in Fig. 3 includes a chamber 10 for accommodating a workpiece W1 including an n-type SiC semiconductor, a light source unit 2, and a radiation thermometer 14. The light source unit 2 includes a plurality of infrared lamps 11 and a reflecting member 12.

[0036] In the following description, an XYZ coordinate system will be referred to as appropriate, in which a plane parallel to the main surfaces (W1a, W1b) of the workpiece W1 is defined as an XY plane, and the normal direction of this XY plane is defined as a Z direction, as shown in Fig. 3. As shown in Fig. 3, the light source unit 2 and the workpiece W1 face each other in the Z direction.

[0037] In the following, when expressing a direction and distinguishing between positive and negative directions, the direction will be written with a positive or negative sign, such as "+Z direction" and "-Z direction." When expressing a direction without distinguishing between positive and negative directions, the direction will simply be written as "Z direction."

[0038] The light source unit 2 emits heating light L1 having a color temperature in the range of 2,200 K to 2,600 K. Several examples of the radiation intensity spectrum of heating light L1 having a color temperature in the range of 2,200 K to 2,600 K are shown in Fig. 2. Note that the radiation intensity spectrum shown in Fig. 2 is merely a waveform theoretically derived based on the above (1), and the actual heating light L1 only needs to have a measured color temperature within the above range, and the radiation intensity spectrum does not need to be the same as the radiation intensity spectrum shown in Fig. 2.

[0039] The color temperature of the heating light L1 emitted by the light source unit 2 is measured using a color temperature meter arranged at a position where the light emitted from the light source unit 2 can be directly observed.

[0040] As shown in FIG. 3, the chamber 10 includes a support member 13 on the inside. The support member 13 supports the object W1 to be processed so that the main surface W1a and the main surface W1b of the object W1 are arranged on the XY plane. In FIG. 3, the main surface W1b of the object W1 to be processed is arranged to face the light source unit 2. That is, circuit elements, wiring, etc. are formed on the main surface W1a or the main surface W1b, and the main surface W1b is a surface to which the heating light L1 emitted from the light source unit 2 is irradiated. However, the present invention does not exclude a case where the object W1 to be processed is a bare substrate on which wiring, etc. is not formed, and the main surface W1a of the object W1 to be processed is arranged to face the light source unit 2.

[0041] The support member 13 may support the workpiece W1 in any manner as long as the main surface W1a of the workpiece W1 is disposed on the XY plane. For example, the support member 13 may have a plurality of pin-shaped protrusions, and the workpiece W1 may be supported at points by the protrusions.

[0042] As shown in FIG. 3, the chamber 10 includes a first window 10a facing a main surface W1a of the object to be processed W1 supported by the support member 13, and a second window 10b facing a main surface W1b.

[0043] The first window 10a is a window that is used by the radiation thermometer 14 to measure the temperature of the main surface W1a of the workpiece W1. The radiation thermometer 14 is a thermometer that measures the surface temperature of an object to be measured 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 that falls within a range of 2.5 μm to 14 μm. In other words, the first window 10a is made of a material that transmits light that falls within the sensitivity wavelength range of the radiation thermometer 14. As an example, the first window 10a is made of general quartz glass, calcium fluoride, or the like.

[0044] 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 color temperature of the heating light L1 is within a range of 2,200 K to 2,600 K. The second window 10b is made of a material having a transmittance of 50% or more for at least a wavelength band in which the radiation intensity of the heating light L1 is 50% or more relative to the peak. As an example, the second window 10b is made of synthetic quartz. However, the material of the second window 10b may be appropriately selected depending on the color temperature of the heating light L1.

[0045] Fig. 4 is a graph showing the tendency of the light absorbance characteristics of resins used in semiconductor photoresists, as shown in the above-mentioned Non-Patent Document 1. Resins used in semiconductor photoresists include novolac resin, methacrylic resin, and PHS resin. As shown in Fig. 2, these resins are characterized by showing relatively high absorbance for light with a wavelength of 300 nm or less, and in particular, novolac resin and PHS resin suddenly show high absorbance for light with a wavelength of 300 nm or less.

[0046] For example, when the object to be processed is a SiC substrate, the semiconductor photoresist is used as a photoresist mask when ion implantation is performed on the SiC substrate. For this reason, important indices for the resin used in the semiconductor photoresist include light transmittance, chemical resistance, and solubility in a developer, and the light transmittance is adjusted according to the spectrum of the light emitted from the light source.

[0047] However, as described above, many of the resins used in semiconductor photoresists exhibit high absorbance for light with a wavelength of 300 nm or less. In contrast, the heating light L1 emitted from the light source unit 2 has extremely low radiation intensity at wavelengths of around 300 nm, as shown in Fig. 2. In other words, using light with a color temperature in the range of 2,200 K to 2,600 K as the heating light L1 has the advantage that there is little risk of it being absorbed by the semiconductor photoresist.

[0048] Fig. 5 is a schematic plan view of the light source unit 2 as viewed from the -Z side. As shown in Fig. 3 and Fig. 5, the light source unit 2 is composed of a plurality of infrared lamps 11 and a reflecting member 12 that reflects the heating light L1 emitted from the infrared lamps 11 and traveling toward the +Z side, toward the -Z side.

[0049] Each of the infrared lamps 11 emits heating light L1 with a color temperature in the range of 2,200 K to 2,600 K. It is preferable that the color temperatures of the heating light L1 emitted from the infrared lamps 11 are substantially the same. Here, "substantially the same" means that deviations in wavelength due to element variations during the manufacturing process are allowed. Typically, deviations in color temperature may be within ±50 K.

[0050] Specifically, the infrared lamp 11 in this embodiment is a halogen lamp, but for example, a sheath heater or a carbon heater may also be used. From the viewpoint of achieving higher light output, it is preferable that the infrared lamp 11 is a halogen lamp. It is also known that the color temperature emitted from the infrared lamp 11 depends on the input power, and for example, in the case of a halogen lamp, it can be controlled by adjusting the applied voltage.

[0051] 3, the reflecting member 12 is made of a frame arranged to cover the infrared lamp 11, and a reflecting surface 12a that reflects the heating light L1 emitted from the infrared lamp 11 is formed on the inner wall surface. The reflecting member 12 is made of, for example, an aluminum plate.

[0052] According to the optical heating device 1, since the color temperature of the heating light L1 emitted from the light source unit 2 is within a range of 2,200 K to 2,600 K, the heating light L1 is absorbed by the workpiece W1 even if the workpiece W1 includes an n-type SiC semiconductor. This allows non-contact heating of the workpiece W1.

[0053] Furthermore, during the 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. That is, the detection result by the radiation thermometer 14 is fed back to a controller (not shown) that controls the light output of the light source unit 2, thereby enabling highly accurate heating of the workpiece W1 including an n-type SiC semiconductor. Note that, as shown in Figs. 1 and 2, the main emission wavelength range including the peak wavelength of the heating light L1 is clearly outside the sensitivity wavelength range of the radiation thermometer 14.

[0054] For reference, a verification experiment was conducted to compare the heating efficiency of an LED element and a halogen lamp, and the details of the experiment are described below.

[0055] Example 1 A halogen lamp was used that emits light with a color temperature of 2,600 K. The peak wavelength of light emitted from a halogen lamp with a color temperature of 2,600 K is 1,115 nm.

[0056] Example 2 A halogen lamp was used that emits light with a color temperature of 2,400 K. The peak wavelength of light emitted from the halogen lamp with a color temperature of 2,400 K is 1,207 nm.

[0057] Example 3 A halogen lamp was used that emits light with a color temperature of 2,200 K. The peak wavelength of light emitted from a halogen lamp with a color temperature of 2,200 K is 1,317 nm.

[0058] Comparative Example 1 The LED element emitted light with a peak wavelength of 395 nm.

[0059] An n-type 4H-SiC substrate doped with nitrogen (N) as a dopant was irradiated with light from each light source to achieve the same illuminance, and the reflectance R and transmittance S of the n-type SiC were measured as described above, and the absorptance A (=1-RS) was calculated. The heating efficiency was then compared based on the value derived from the wavelength integral value of the product of the absorptance A and the radiant intensity (hereinafter referred to as "light absorption efficiency"). The method of comparison was such that, assuming that the light absorption efficiency when an LED element with a peak wavelength of 395 nm was used as the light source was 1, if the light absorption efficiency when another light source was used was greater than 1, it was determined that the heating efficiency was substantially high.

[0060] The results are shown in Table 1 below.

[0061] [Table 1]

[0062] As can be seen from the results in Table 1 above, it can be confirmed that all of Examples 1 to 3 have significantly higher heating efficiency than Comparative Example 1.

[0063] From the above, it is found that heating light L1 having a color temperature in the range of 2,200 K to 2,600 K can heat the n-type SiC semiconductor more efficiently.

[0064] From the viewpoint of increasing the heating efficiency, it is more preferable that the color temperature of the heating light L1 is within the range of 2,400K to 2,600K.

[0065] According to Table 1 above, the heating efficiency of the halogen lamp can be improved if the color temperature is further reduced from 2,200 K. However, if the color temperature is further reduced below 2,200 K, it becomes difficult to irradiate heating light L1 with sufficient radiant intensity to heat n-type SiC.

[0066] In the above-described embodiment, a configuration in which a reflective member 12 is mounted on the light source unit 2 has been described. However, for example, in cases in which the workpiece W1 can be sufficiently heated only by the heating light L1 emitted from the infrared lamp 11 to the -Z side, the light source unit 2 does not need to be equipped with a reflective member 12.

[0067] The reflective member 12 may be a reflective film provided on the wall surface of the infrared lamp 11. The reflective film provided on the wall surface of the infrared lamp 11 is, for example, a metal film made of aluminum (Al) or a reflective film formed by agglomerating particles whose main component is a metal oxide such as silica (SiO2) or alumina (Al2O3).

[0068] Furthermore, in the above-described embodiment, the infrared lamp 11 included in the light source unit 2 has a straight tube shape as shown in Fig. 5, but is not limited to this shape. The infrared lamp 11 may have, for example, a light bulb shape or a circle heater having a circular ring shape. [Explanation of symbols]

[0069] 1:Light heating device 2:Light source section 10: Chamber 10a: First window 10b: Second window 11: Infrared lamp 12: Reflective material 12a: Reflective surface 13: Support member 14: Radiation thermometer L1:Heating light W1: Object to be treated W1a, W1b: Main surfaces of the object to be treated

Claims

1. A light heating method comprising: a step (a) of irradiating a workpiece including an n-type SiC semiconductor with heating light having a color temperature in the range of 2,200 K to 2,600 K emitted from a light source unit equipped with an infrared lamp through a window member to heat the workpiece.

2. 2. The light heating method according to claim 1, wherein the heating light has a color temperature within a range of 2,400K to 2,600K.

3. 3. The optical heating method according to claim 1, further comprising a step (b) of measuring the temperature of the object to be treated by a radiation thermometer having a sensitivity wavelength range of a predetermined wavelength range ranging from 2.5 μm to 14 μm during the execution of the step (a) by receiving light radiated from the object to be treated.

4. An optical heating device for an n-type SiC semiconductor, A chamber that accommodates a workpiece including an n-type SiC semiconductor; a support member for supporting the workpiece in the chamber; a light source unit having an infrared lamp that emits heating light having a color temperature in the range of 2,200 K to 2,600 K; a window member that passes the heating light emitted from the light source unit and guides it to the object to be treated.

5. 5. The optical heating device for an n-type SiC semiconductor according to claim 4, wherein the infrared lamp is a halogen lamp.

6. 6. The optical heating device for n-type SiC semiconductor according to claim 4 or 5, further comprising a reflecting member that reflects light emitted from the infrared lamp and traveling toward the opposite side of the workpiece toward the workpiece.

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