Semiconductor substrate

Abstract

To provide a semiconductor substrate which is made of a gallium oxide semiconductor having marks on the surface and in which the generation of cracks and debris due to marking is suppressed and the marks are highly visible.SOLUTION: One embodiment is a semiconductor substrate 1 comprising a gallium oxide semiconductor, the semiconductor substrate having a mark 11 comprising a plurality of dots 12 on a surface 10, each of the plurality of dots 12 comprising a plurality of laser irradiation marks 120, a maximum depth of each of the plurality of dots 12 being between 5.7 μm and 14.5 μm.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a semiconductor substrate.

Background Art

[0002] Conventionally, in order to facilitate the identification and management of substrates, a technique of forming marks such as identifiers on the surface of a substrate has been known (see Patent Document 1). In Patent Document 1, a highly visible mark composed of a plurality of dots is formed by irradiating the surface of a glass substrate with laser light.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the conditions for forming a highly visible mark on a substrate vary depending on the characteristics of the substrate such as transparency, melting point, thermal conductivity, and cleavage property. Therefore, even if the technique described in Patent Document 1 is applied to a substrate other than a glass substrate, it is not always possible to form a highly visible mark.

[0005] An object of the present invention is to provide a semiconductor substrate made of a gallium oxide-based semiconductor having a mark on its surface, in which the occurrence of cracks and debris due to marking is suppressed and the visibility of the mark is excellent.

Means for Solving the Problems

[0006] One aspect of the present invention provides a semiconductor substrate according to the following [1] to [5] in order to achieve the above object.

[0007] [1] A semiconductor substrate made of a gallium oxide semiconductor, having a mark on its surface composed of a plurality of dots, each of the plurality of dots being composed of a plurality of laser irradiation marks, and the maximum depth of each of the plurality of dots being in the range of 5.7 μm or more and 14.5 μm or less. [2] The semiconductor substrate according to [1] above, wherein the maximum depth of each of the plurality of dots is within the range of 9.5 μm or more and 14.5 μm or less. [3] The semiconductor substrate according to [1] above, wherein the average line roughness (Ra) of each of the plurality of dots is in the range of 0.5 μm or more and 4.6 μm or less. [4] The semiconductor substrate according to [3] above, wherein the average line roughness (Ra) of the inner surface of each of the plurality of dots is within the range of 1.6 μm or more and 4.6 μm or less. [5] A semiconductor substrate according to any one of the above items [1] to [4], wherein the (001) plane is the main surface. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a semiconductor substrate made of a gallium oxide-based semiconductor having a mark on its surface, wherein the generation of cracks and debris due to the marking is suppressed, and the visibility of the mark is excellent. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1(a) is a perspective view of a semiconductor substrate according to an embodiment of the present invention. Figure 1(b) is a digital microscope observation image showing an example of marks formed on the surface of the semiconductor substrate. [Figure 2] Figure 2 is a schematic diagram illustrating the method of forming dots. [Figure 3] Figures 3(a) and 3(b) show digital microscope images of an example of a dot. [Figure 4] Figures 4(a), (b), and (c) show waveform data of the surface characteristics of dots formed at different laser scanning speeds. [Figure 5]Figure 5(a) is a graph showing the relationship between laser scanning speed and the maximum depth of the dot. Figure 5(b) is a graph showing the relationship between laser scanning speed and the average line roughness (Ra) of the inner surface of the dot. [Figure 6] Figure 6(a) is an image of an example of a dot observed with a digital microscope. Figure 6(b) is a graph showing the relationship between the laser scanning speed and the average line roughness (Ra) at five points on the inner surface of the dot. [Figure 7] Figure 7(a) is an optical photograph of marks formed at different laser scanning speeds. Figure 7(b) is a digital microscope image of marks formed at different laser scanning speeds. [Figure 8] Figures 8(a), (b), and (c) are magnified digital microscope images of the number "0," which is part of a mark formed at laser scanning speeds of 200 mm / s, 30 mm / s, and 10 mm / s, respectively. [Figure 9] Figures 9(a), (b), and (c) are digital microscope images of dots in different states. [Figure 10] Figure 10 is a graph showing the relationship between the laser scanning speed and the dot non-formation rate and defect rate mentioned above. [Figure 11] Figures 11(a), (b), and (c) are digital microscope images showing examples of three types of cracks that occur around a dot. [Figure 12] Figure 12 is a graph plotting the relationship between the average depth of the dots and the average line roughness (Ra) of the inner surface, with added information on the visibility of the marks and the occurrence of cracks and debris. [Modes for carrying out the invention]

[0010] (Semiconductor substrate structure) FIG. 1(a) is a perspective view of a semiconductor substrate 1 according to an embodiment of the present invention. The semiconductor substrate 1 is a semiconductor substrate made of a single crystal of a gallium oxide-based semiconductor having a mark 11 on a surface 10. Here, the gallium oxide-based semiconductor refers to β-Ga2O3 or β-Ga2O3 containing substitutional impurities such as Al and In or dopants such as Sn and Si.

[0011] FIG. 1(b) is an observation image of a digital microscope showing an example of the mark 11 formed on the surface 10. The mark 11 is an identifier or an alignment mark of the semiconductor substrate 1 and is composed of numbers, letters, figures, etc. Further, as shown in FIG. 1(b), the mark 11 is composed of a plurality of dots 12. The dot 12 is a dot-like depression formed on the surface 10.

[0012] FIG. 2 is a schematic diagram showing a method of forming the dot 12. The dot 12 is formed by irradiating the surface 10 of the semiconductor substrate 1 with pulsed laser light and scanning it in a direction corresponding to the shape of the dot 12. In the example shown in FIG. 2, a circular dot 12 is formed by scanning the pulsed laser light in a double circle.

[0013] When the pulsed laser light is irradiated on the surface 10 of the semiconductor substrate 1, lattice vibration occurs and the temperature rises, and the lattice bond is broken by heat, forming an irradiation mark (hereinafter referred to as a laser irradiation mark) 120 of the pulsed laser light, which is a depression. Since the pulsed laser light is output at a predetermined frequency, laser irradiation marks 120 are formed on the surface 10 at intervals corresponding to the scanning speed of the pulsed laser light, and the aggregate of the laser irradiation marks 120 becomes the dot 12. That is, each of the plurality of dots 12 constituting the mark 11 is composed of a plurality of laser irradiation marks 120.

[0014] The mark 11 is visually recognized by light scattering on the inner surface of the dot 12. Therefore, it is important for the visibility that the dot 12 has a certain depth. Also, it is preferable that the inner surface of the dot 12 has a certain roughness.

[0015] (Mark formation conditions) Gallium oxide-based semiconductors represented by Ga2O3 have characteristics that make it difficult to form the following mark 11. (1) Since the melting point is high and the thermal conductivity is low, it is difficult to form the laser irradiation mark 120. (2) Since it has cleavage properties, cracks due to cleavage are likely to occur when forming mark 11. In particular, when the semiconductor substrate 1 has the (001) plane as the main plane, two cleavage planes, the (100) plane and the (001) plane, are likely to become apparent, and cracks due to cleavage are more likely to occur. (3) Since heat conduction and thermal expansion have anisotropy, distortion is likely to occur due to the heat generated when forming mark 11, which may cause cracks. (4) Since it is transparent, it is difficult to form a mark 11 with good visibility.

[0016] In order to form a mark 11 with good visibility on the semiconductor substrate 1 made of a gallium oxide-based semiconductor without causing cracks, it is necessary to set the wavelength of the pulsed laser light (hereinafter referred to as the laser wavelength), the output of the pulsed laser light (hereinafter referred to as the laser output), the frequency of the pulsed laser light (hereinafter referred to as the pulse frequency), and the scanning speed of the pulsed laser light (hereinafter referred to as the laser scanning speed) to appropriate values respectively.

[0017] The shorter the laser wavelength, the higher the absorption rate, so it becomes easier to form mark 11 on the highly transparent semiconductor substrate 1. If the laser output is too large, cracks are likely to occur. On the other hand, if it is too small, it becomes difficult to form the laser irradiation mark 120 because the irradiation energy of the pulsed laser light does not exceed the reaction threshold value. Here, the reaction threshold value refers to the threshold value of the irradiation energy of the pulsed laser light for forming the laser irradiation mark 120. If the pulse frequency is too high, the energy per pulse becomes small, so it becomes difficult to form the laser irradiation mark 120 without exceeding the reaction threshold value.

[0018] Regarding laser wavelength, laser power output, and pulse frequency, as an example, it has been confirmed that using a UV-YAG laser (third harmonic) with a laser wavelength of 355 nm, a laser power output of 0.8 W, and a pulse frequency of 40 kHz is suitable for forming marks 11 on semiconductor substrate 1.

[0019] Unless otherwise specified, the dots 12 in all the experiments described later were formed using a UV-YAG laser (third harmonic) with a laser wavelength of 355 nm, under conditions of laser output of 0.8 W and pulse frequency of 40 kHz, and were formed by an aggregate of laser irradiation marks 120 with a diameter of approximately 25 μm, resulting in a diameter of approximately 100 μm. Furthermore, all the experiments described later were conducted using a Ga2O3 substrate with the (001) plane as the main surface, which is particularly prone to cracking, as the semiconductor substrate 1.

[0020] The diameter of dot 12, approximately 100 μm, is designed to comply with SEMI standards. While the diameter of dot 12 is not particularly limited, it is set to approximately 100 μm to comply with SEMI standards. In this case, increasing the overlap between the laser irradiation marks 120 that make up the inner circle of dot 12 and the laser irradiation marks 120 that make up the outer circle will reduce the diameter of dot 12. However, to prevent this overlap from becoming too large, the diameter of dot 12 is usually never less than 90 μm.

[0021] If the laser scanning speed is too high, the irradiation time of the pulsed laser light to one spot becomes short, making it difficult to form laser irradiation marks 120 without exceeding the reaction threshold. On the other hand, if the laser scanning speed is too low, the irradiation time of the pulsed laser light to one spot becomes long, causing the laser irradiation marks 120 to become blackened as if burned. This is thought to be because the heat generated when the irradiation energy does not exceed the reaction threshold, and which is not used to form the laser irradiation marks 120, damages the surface 10 of the semiconductor substrate 1.

[0022] Figures 3(a) and 3(b) are digital microscope images of an example of dot 12. Figures 4(a), 4(b), and 4(c) are waveform data of the surface characteristics of dots 12 formed at different laser scanning speeds, measured along a straight line passing near the center as shown in Figure 3(a). The waveform data in Figures 4(a), 4(b), and 4(c) were obtained by measurement using a laser microscope, with the horizontal axis representing the position in the planar direction and the vertical axis representing the height relative to the height of the flat area of ​​surface 10 where dot 12 is not formed.

[0023] The dots 12 shown in Figures 4(a), (b), and (c) were formed under laser scanning speeds of 200 mm / s, 30 mm / s, and 10 mm / s, respectively. Figures 4(a), (b), and (c) show that the maximum depth and inner surface roughness of the dots 12 tend to increase as the laser scanning speed decreases.

[0024] Furthermore, in the waveform of Figure 4(c), the presence of protrusions called debris formed on the edges of dot 12 can be confirmed. Debris is formed by evaporated material from the semiconductor substrate 1 generated during the formation of dot 12. Normally, the surface 10 on which the mark 11 is formed is the surface opposite to the surface on which the element is formed (the back surface of the substrate), and the presence of debris can cause cracks to occur when the surface 10 is vacuum-adsorbed by the measuring instrument.

[0025] Figure 5(a) is a graph showing the relationship between the laser scanning speed and the maximum depth of the dot 12. The maximum depth of the dot 12 in Figure 5(a) is obtained from waveform data of the surface characteristics measured along a straight line passing near the center of the dot 12, as shown in Figure 3(a).

[0026] Figure 5(b) is a graph showing the relationship between the laser scanning speed and the average line roughness (Ra) of the inner surface of the dot 12. The average line roughness (Ra) of the inner surface of the dot 12 in Figure 5(b) is obtained by measuring waveform data of the surface characteristics along five parallel lines passing through different positions on the dot 12, as shown in Figure 3(b), and taking the average of the average line roughness (Ra) obtained from these waveform data.

[0027] Figures 5(a) and (b) show that as the laser scanning speed decreases, the maximum depth of the dot 12 and the average line roughness (Ra) of the inner surface increase.

[0028] Figure 6(a) is a digital microscope image of an example of dot 12. Figure 6(b) is a graph showing the relationship between the laser scanning speed and the average line roughness (Ra) at five locations on the inner surface of dot 12. The five average line roughness (Ra) values ​​in Figure 6(b) were obtained from waveform data of the surface texture measured along five parallel lines (let's call them L1 to L5) passing through different positions on dot 12 as shown in Figure 6(a), and are denoted as Ra1 to Ra5. Ra1 to Ra5 ​​are the average values ​​obtained from two measurements. Figure 6(b) shows that the roughness decreases closer to the outer edge of dot 12.

[0029] Table 1 shows the numerical values ​​of the plotted points in Figure 6(b), as well as the maximum and minimum values ​​of the average line roughness (Ra) for each laser scanning speed. The maximum and minimum values ​​of the average line roughness (Ra) for each laser scanning speed were determined using two measurement data sets for each of the Ra1 to Ra5 ​​values.

[0030] [Table 1]

[0031] Figure 7(a) is an optical photograph of Mark 11 formed at different laser scanning speeds. Figure 7(b) is a digital microscope image of Mark 11 formed at different laser scanning speeds. Mark 11 shown in Figures 7(a) and (b) consists of numbers arranged from "0" to "9". The numbers on the left side of the images in Figures 7(a) and (b) all indicate the laser scanning speed (mm / s).

[0032] According to Figures 7(a) and (b), when the laser scanning speed is 100 mm / s or less, the visibility of Mark 11 is good. When the laser scanning speed is 150 to 200 mm / s, although the visibility is not particularly good, the printed numbers can be read, so a minimum level of visibility is ensured. This result indicates that a laser scanning speed of less than 150 mm / s is required to form a highly visible Mark 11.

[0033] Figures 8(a), (b), and (c) are magnified digital microscope images of the number "0", which is part of Mark 11, formed at laser scanning speeds of 200 mm / s, 30 mm / s, and 10 mm / s, respectively.

[0034] To quantify the visibility of mark 11, dots 12 that did not have any laser irradiation marks 120 formed were considered not to have been formed (dots 12 that had even a partial laser irradiation mark 120 formed were considered to have been formed), and the non-formation rate of the 23 dots 12 that make up the number "0" was determined. As a result, the non-formation rates of the number "0" shown in Figures 8(a), (b), and (c) were 39%, 0%, and 0%, respectively. Similarly, the non-formation rate of dots 12 was also determined for the number "0" included in mark 11 formed at laser scanning speeds of 150 mm / s, 100 mm / s, 90 mm / s, 80 mm / s, 50 mm / s, 40 mm / s, and 20 mm / s.

[0035] As a result, when a laser scanning speed of less than 150 mm / s was used to form a highly visible mark 11, the non-formation rate of the digit "0" dot 12 in the mark 11 was approximately less than 16%. When a laser scanning speed of 150-200 mm / s was used to ensure minimum visibility, the non-formation rate of the digit "0" dot 12 in the mark 11 was approximately 16% to 44%.

[0036] From this, a criterion for determining the visibility of Mark 11 based on the non-formation rate of Dot 12 was derived: when the non-formation rate of Dot 12 is less than 16%, the visibility of Mark 11 is good; when the non-formation rate of Dot 12 is 16% or more and 44% or less, the visibility of Mark 11 is possible; and when the non-formation rate of Dot 12 exceeds 44%, the visibility of Mark 11 is poor.

[0037] Furthermore, the blackening around the dot 12 of the number "0" shown in Figure 8(c) is thought to be due to the laser scanning speed being too low, resulting in a longer irradiation time of pulsed laser light to a single location. This caused damage to the surface 10 of the semiconductor substrate 1 due to heat that was not used to form the laser irradiation mark 120 when the irradiation energy did not reach the reaction threshold.

[0038] Furthermore, as another method to quantify the visibility of Mark 11, dots 12 that were not properly formed were considered defective, and the defect rate of the 186 dots 12 that make up the numbers "0" to "9" was calculated.

[0039] Figures 9(a), (b), and (c) are digital microscope images of dots 12 in different states. The dot 12 shown in Figure 9(a) is formed normally because both of the double circles are formed without interruption by a series of connected laser irradiation marks 120. The dot 12 shown in Figure 9(b) is judged to be defective because the inner circle is interrupted. The dot 12 shown in Figure 9(c) is judged to be defective because the outer circle is interrupted and the inner circle is not formed at all. Dots 12 in which no laser irradiation marks 120 are formed at all are also judged to be defective.

[0040] The defect rates of dots 12 on marks 11 formed at laser scanning speeds of 200 mm / s, 50 mm / s, 40 mm / s, 30 mm / s, 20 mm / s, and 10 mm / s were determined. The results showed that the defect rate of dots 12 was particularly high at over 84% when the laser scanning speed was 100 mm / s or higher, and particularly low at less than 8% when the laser scanning speed was less than 40 mm / s.

[0041] Furthermore, it has been confirmed that the defect rate of dot 12 correlates with the occurrence of cracks around dot 12. Specifically, at laser scanning speeds where cracks almost always occur around dot 12, the defect rate of dot 12 is particularly high, while at laser scanning speeds where cracks hardly occur, the defect rate of dot 12 is particularly low. The cracks that occur around dot 12 will be discussed later.

[0042] Figure 10 is a graph showing the relationship between the laser scanning speed and the non-formation rate and defect rate of the dots 12 described above. Figure 10 shows that the lower the laser scanning speed, the lower the non-formation rate and defect rate of the dots 12 tend to be. Table 2 below shows the numerical values ​​of the plotted points in Figure 10.

[0043] [Table 2]

[0044] Next, we will describe the results of our investigation into the conditions under which cracks occur around dot 12. First, it was confirmed that there are three main types of cracks that occur around dot 12: those caused by cleavage of the (100) plane of the gallium oxide semiconductor, those caused by cleavage of the (001) plane, and those caused by cleavage of both the (100) plane and the (001) plane.

[0045] Figures 11(a), (b), and (c) are digital microscope images showing examples of three types of cracks that occur around the dot 12 described above.

[0046] The crack shown in Figure 11(a) is due to cleavage of the (100) plane and occurred when the laser scanning speed was 200 mm / s. The low thermal conductivity of the gallium oxide semiconductor is considered to be one of the causes of crack formation due to cleavage of the (100) plane.

[0047] The crack shown in Figure 11(b) is a fine crack called a microcrack, caused by cleavage of the (001) plane, and occurred when the laser scanning speed was 200 mm / s. The low thermal conductivity of the gallium oxide semiconductor is thought to be one of the causes of crack formation due to cleavage of the (001) plane.

[0048] The crack shown in Figure 11(c) is due to both (100) plane cleavage and (001) plane cleavage, and occurred when the laser scanning speed was 80 mm / s and the laser power was 1.3 W. This type of crack, due to both (100) plane cleavage and (001) plane cleavage, tends to occur at higher laser power levels.

[0049] When the laser output is 0.8W, cracks due to cleavage of the (100) plane and cracks due to cleavage of the (001) plane are more likely to occur when the laser scanning speed is high, they hardly occur when the laser scanning speed is 10-30 mm / s, they may occur when it is 40-50 mm / s, and they almost always occur when it is 80 mm / s or higher.

[0050] Although cracks are more difficult to detect than dot 12 defects, they frequently occur around dot 12 defects. Therefore, inspecting for dot 12 defects during quality control also serves as a crack inspection, improving inspection efficiency.

[0051] Table 3 below summarizes the experimental results described above. In Table 3, "Mark Visibility" refers to the visibility of Mark 11 as determined from the optical photograph in Figure 7(a) and the digital microscope observation image in Figure 7(b). "Dot Defect Rate" is defined as "○" for less than 8%, "△" for 8% or more but less than 84%, and "×" for 84% or more. "Dot Non-Formation Rate" is defined as "○" for less than 16%, and "△" for 16% or more but 44% or less. "Debris Generation" is defined as "○" for no debris generation and "×" for debris generation. "Crack Generation" is defined as "○" for no crack generation, "△" for cracks that may occur, and "×" for cracks that always occur. "Average Ra" and "Ra Range" are the average value of R1 to R5 and the range from the minimum to the maximum value, respectively. The “average depth” and “depth range” are the average value of two measurements of the maximum depth of dot 12 and the range from the minimum to the maximum value, obtained from waveform data of the surface texture measured on a straight line passing near the center of dot 12 as shown in Figure 3(a).

[0052] [Table 3]

[0053] As can be seen from Table 3, in order to suppress the generation of debris and cracks and improve the visibility of Mark 11, the average maximum depth of the dots 12 constituting Mark 11 is preferably in the range of 5.9 μm or more and 14.4 μm or less, the maximum depth of the dots 12 constituting Mark 11 is preferably in the range of 5.7 μm or more and 14.5 μm or less, the average value of the average line roughness (Ra) of each dot 12 constituting Mark 11 is preferably in the range of 1.3 μm or more and 3.7 μm or less, and the average line roughness (Ra) of each dot 12 is preferably in the range of 0.5 μm or more and 4.6 μm or less. Furthermore, in order to more effectively suppress the occurrence of cracks, it is preferable that the average maximum depth of the dots 12 constituting the mark 11 is within the range of 10.0 μm or more and 14.4 μm or less, the range of the maximum depth of the dots 12 is within the range of 9.5 μm or more and 14.5 μm or less, the average value of the average line roughness (Ra) of each dot 12 constituting the mark 11 is within the range of 2.4 μm or more and 3.7 μm or less, and the range of the average line roughness (Ra) of each dot 12 constituting the mark 11 is within the range of 1.6 μm or more and 4.6 μm or less. Note that these conditions for the average value and range of the average line roughness (Ra) of the dots 12, and the average value and range of the maximum depth of the dots 12, do not apply to dots 12 constituting the mark 11 that do not have any laser irradiation marks 120 formed on them (non-formed dots 12).

[0054] Figure 12 is a graph plotting the relationship between the average depth of dot 12 and the average line roughness (Ra) of the inner surface, with added information on the visibility of the marks and the occurrence of cracks and debris.

[0055] (Effects of the embodiment) According to the above embodiment, in a semiconductor substrate made of a gallium oxide-based semiconductor having marks on its surface, by forming the marks under appropriate conditions, the occurrence of cracks and debris due to marking can be suppressed, and a semiconductor substrate with excellent visibility of the marks can be provided.

[0056] Furthermore, according to the above embodiment, even with a semiconductor substrate made of a gallium oxide-based semiconductor whose main surface is the (001) surface which is prone to cracking due to cleavage, it is possible to suppress the generation of cracks and debris due to marking and to form a mark that is easily visible.

[0057] Although embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the invention. Furthermore, the components of the above embodiments can be arbitrarily combined without departing from the spirit of the invention. Moreover, the embodiments described above do not limit the invention as claimed. It should also be noted that not all combinations of features described in the embodiments are necessarily essential for solving the problem of the invention. [Explanation of Symbols]

[0058] 1...Semiconductor substrate, 10...Surface, 11...Mark, 12...Dot, 120...Laser irradiation mark

Claims

1. A semiconductor substrate made of a gallium oxide-based semiconductor, It has a mark on its surface that is composed of multiple dots, Each of the aforementioned multiple dots is composed of multiple laser irradiation marks, The maximum depth of each of the aforementioned multiple dots is within the range of 5.7 μm or more and 14.5 μm or less. Semiconductor substrate.

2. The maximum depth of each of the aforementioned multiple dots is within the range of 9.5 μm or more and 14.5 μm or less. The semiconductor substrate according to claim 1.

3. The average line roughness (Ra) of each of the aforementioned multiple dots is within the range of 0.5 μm or more and 4.6 μm or less. The semiconductor substrate according to claim 1.

4. The average line roughness (Ra) of the inner surface of each of the aforementioned multiple dots is within the range of 1.6 μm or more and 4.6 μm or less. The semiconductor substrate according to claim 3.

5. (001) The main surface is the (001) surface, A semiconductor substrate according to any one of claims 1 to 4.

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