Silicon carbide substrate or substrate processing method

Abstract

To provide a silicon carbide substrate processing method capable of achieving the thining of a substrate.SOLUTION: A silicon carbide substrate processing method comprises: providing a substrate having front and bottom surfaces facing each other, wherein the substrate defines a predetermined area and the predetermined area is defined to have a preset reaction part extending in a bottom surface direction from the front surface of the substrate; chemically reacting the preset reaction part by an electrochemical method to convert the preset reaction part into a weakened layer having a thickness; and removing the weakened layer to have an exposure surface in the substrate having the predetermined area.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for processing substrates, and in particular to a method for processing silicon carbide substrates. [Background technology]

[0002] With the rise of technologies such as 5G communications and autonomous driving, silicon carbide materials offer advantages such as high energy efficiency, high voltage, and high power output as semiconductor device substrates. However, semiconductor device substrates require a thickness of 100–200 μm. Silicon carbide substrates are highly hard, with a Knoop hardness (HK) of approximately 2150–2900 MPa. Conventional abrasive particles used to polish silicon substrates are typically SiO2, with a hardness ranging from approximately 200–500 MPa. Even with the use of high-hardness Al2O3 (hardness ~2000–2050 MPa) abrasive particles for general polishing applications, thinning silicon carbide substrates is difficult. Therefore, a commonly known technique is to use the most expensive diamond (hardness = 7000 MPa) to polish the silicon carbide substrate. In addition, the texture of silicon carbide is brittle and prone to cracking, and the hard cutting process easily introduces high stresses into the silicon carbide substrate, causing microcracks and material splitting, which in turn leads to high residual stresses and causes the sheet to warp. Summary of the Invention

[0003] The substrate processing method provided by the present invention includes providing a substrate having an opposing front surface and a bottom surface, the substrate defining a predetermined region, the predetermined region being defined as having a predetermined reaction portion extending from the front surface toward the bottom surface of the substrate, chemically reacting the predetermined reaction portion using an electrochemical method to convert the predetermined reaction portion into a weakened layer having a thickness, and removing the weakened layer to provide an exposed surface on the substrate in the predetermined region.

[0004] In an embodiment of the present invention, the material of the substrate is silicon carbide.

[0005] In an embodiment of the present invention, the electrochemical method is anodic oxidation.

[0006] In an embodiment of the present invention, the thickness of the weakened layer is controlled by the amount of input charge as the anodization proceeds.

[0007] In an embodiment of the present invention, when the anodic oxidation is performed, the preset reaction portion is brought into contact with an electrolyte containing fluoride ions.

[0008] In an embodiment of the present invention, the electrolyte is a hydrofluoric acid solution.

[0009] In an embodiment of the present invention, the weakened layer is removed by means of ultrasonic vibration.

[0010] In an embodiment of the present invention, the weakened layer is removed by means of polishing.

[0011] In an embodiment of the present invention, the polishing method includes removing the weakened layer with an abrasive slurry having a plurality of abrasive particles.

[0012] In an embodiment of the present invention, the abrasive particles include at least one of silica, cesium oxide, alumina, silicon carbide, boron nitride, and diamond, or a combination thereof.

[0013] In an embodiment of the present invention, the weakened layer is removed by a high temperature quenching method.

[0014] In an embodiment of the present invention, the weakened layer is removed by means of laser ablation.

[0015] In an embodiment of the present invention, the weakened layer is removed by a method of jet stream cutting.

[0016] In an embodiment of the present invention, the substrate processing method further includes surface processing of the exposed surface.

[0017] In an embodiment of the present invention, the surface treatment is chemical mechanical polishing.

[0018] In an embodiment of the present invention, the weakened layer is porous.

[0019] In an embodiment of the present invention, the weakened layer is layered.

[0020] The method for treating a silicon carbide substrate provided by the present invention includes providing a silicon carbide substrate having an opposing front surface and a bottom surface, defining a predetermined region on the silicon carbide substrate, the predetermined region being defined as having a predetermined reaction portion extending from the front surface toward the bottom surface of the silicon carbide substrate, bringing the predetermined reaction portion into contact with a hydrofluoric acid solution by anodization to cause a chemical reaction, thereby converting the predetermined reaction portion into a porous layer having a thickness, and removing the porous layer to leave an exposed surface on the silicon carbide substrate in the predetermined region.

[0021] The present invention uses an electrochemical method to convert the pre-determined reactive regions on a substrate into weakened layers. The weakened layers are porous or layer-like, with a hollow sponge-like or void layer-like structure, significantly reducing the material strength, while the solid regions on the substrate where no chemical reaction occurs still maintain their original high material strength. Therefore, in subsequent processes, the weakened layers with lower material strength can be removed by methods such as polishing, high-temperature quenching, laser ablation, jet stream cutting, or ultrasonic vibration, leaving the solid regions, thereby achieving thinning of the substrate.

[0022] Furthermore, since the electrochemical method of the present invention is anodization, the thickness of the weakened layer can be controlled by the amount of input charge during the anodization process, and therefore, the desired thickness of the weakened layer can be obtained by controlling the current, voltage, and time during the anodization process.

[0023] In order to make the above and other objects, features and advantages of the present invention more clearly understandable, the following detailed description, particularly with reference to the embodiments, is provided in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0024] [Figure 1]FIG. 1 is a flowchart of a substrate processing method according to an embodiment of the present invention. [Figure 2A] FIG. 2A is a schematic cross-sectional view of a substrate in each step of a substrate processing method according to an embodiment of the present invention. [Figure 2B] 2A to 2B are schematic cross-sectional views of the substrate in each step of the substrate processing method according to one embodiment of the present invention. [Figure 2C] 2A to 2C are schematic cross-sectional views of a substrate in each step of a substrate processing method according to an embodiment of the present invention. [Figure 3] FIG. 3 is a schematic three-dimensional view of the substrate shown in FIG. 2A. [Figure 4] FIG. 4 is a cross-sectional view of an electrochemical device for carrying out a chemical reaction according to one embodiment of the present invention. [Figure 5A] FIG. 5A is a photograph of a weakened layer formed in a substrate processing method according to an embodiment of the present invention, taken using a scanning electron microscope (SEM). [Figure 5B] FIG. 5B is a schematic view showing a direction in which the electrolyte enters the preset reaction section during the chemical reaction in the substrate processing method according to the embodiment of the present invention. [Figure 6] FIG. 6 is a photograph of a weakened layer formed by a substrate processing method according to an embodiment of the present invention, taken using a scanning electron microscope (SEM). [Figure 7A] FIG. 7A is an enlarged schematic view of the portion enclosed by the dashed line in FIG. 2C. [Figure 7B] FIG. 7B is a diagram showing the surface treatment of the substrate having the recess shown in FIG. 7A. [Figure 8] FIG. 8 is a cross-sectional schematic view of an electrochemical device for carrying out chemical reactions according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] FIG. 1 is a flowchart of a substrate processing method according to an embodiment of the present invention, and FIGS. 2A to 2C are schematic cross-sectional views of a substrate at each step of the substrate processing method according to an embodiment of the present invention. As shown in FIG. 1, the substrate processing method according to an embodiment of the present invention includes step S1: providing a substrate 10. FIG. 3 is a three-dimensional schematic diagram of the substrate shown in FIG. 2A. As shown in FIGS. 2A and 3, the substrate 10 has an opposing front surface 11 and a bottom surface 12. The substrate 10 defines a predetermined region 13, and the predetermined region 13 is defined as having a pre-set reaction portion 14 extending from the front surface 11 toward the bottom surface 12 of the substrate 10. In one embodiment, the material of the substrate 10 is, for example, silicon carbide, but the present invention is not limited thereto. The material of the substrate 10 may be, for example, a material commonly used for semiconductor substrates, such as silicon, germanium, gallium arsenide, indium phosphide, gallium nitride, or boron nitride. The substrate 10 has a thickness D0. In one embodiment, the predetermined region 13 is a portion of the substrate 10 to be processed, for example, the predetermined region 13 is a region of the substrate 10 to be thinned. The predetermined reaction portion 14 is a portion to be removed when thinning the predetermined region 13, for example, the predetermined reaction portion 14 has a thickness D1.

[0026] Next, in step S2, the preset reaction portion 14 is subjected to a chemical reaction by an electrochemical method, thereby converting the preset reaction portion 14 into a weakened layer 15 having a thickness D2. Referring to FIGS. 2B and 4, FIG. 4 is a cross-sectional schematic diagram of an electrochemical device for carrying out a chemical reaction according to one embodiment of the present invention. This electrochemical device is merely for illustrating the implementation of the present invention and does not limit the conceptual scope of the present invention. In one embodiment, the electrochemical device 20 is an anodization apparatus. As shown in FIG. 4, the electrochemical device 20 includes a base 21 and a tank 22, which are fixed to each other with bolts. A positive electrode 23 is provided on the base 21, and the positive electrode 23 is made of copper. A through-hole 221 is provided at the bottom of the tank 22, and an endless sealing gasket 25 is provided between the tank 22 and the base 21 and at a portion corresponding to the outer periphery of the through-hole 221.

[0027] When a chemical reaction is to occur on the substrate 10, the substrate 10 is placed on the positive electrode 23 and electrically connected to the positive electrode 23, and an endless seal gasket 25 abuts against the substrate 10. In one embodiment, an electrolyte 26 is filled in the tank 22, and the electrolyte 26 flows out through the through-holes 221 and onto the substrate 10 within the restricted area of ​​the endless seal gasket 25. In one embodiment, the shape and position of the endless seal gasket 25 correspond to the predetermined reaction site 14 in the predetermined area 13 of the substrate 10, thereby restricting the electrolyte 26 in the upper tank 22 to the location corresponding to the predetermined reaction site 14 through the endless seal gasket 25. The substrate 10 outside the restricted area of ​​the endless seal gasket 25 does not come into contact with the electrolyte 26, so that the predetermined reaction site 14 can chemically react with the electrolyte 26 after subsequent energization. A negative electrode 24 is provided on the electrolyte 26 in the tank 22, and the negative electrode 24 is a platinum electrode. When positive electrode 23 is energized to negative electrode 24, a voltage is applied to substrate 10, and electrolyte 26 initiates a chemical reaction from pre-determined reaction site 14 adjacent to surface 11 of substrate 10. In one embodiment, electrolyte 26 contains fluoride ions, such as hydrofluoric acid (HF) or ammonium fluoride (NHF).

[0028] Following the above explanation, if the electrolyte 26 is a hydrofluoric acid solution and the substrate 10 is made of silicon carbide, the silicon in the silicon carbide reacts with the fluorine in the hydrofluoric acid solution, dissolving fluorosilicic acid in water or forming silicon tetrafluoride, which disperses into the air as a gas. The remaining element in the pre-defined reaction region 14 becomes carbon through a chemical reaction. Furthermore, since silicon carbide is formed by assembling silicon in a specific lattice pattern, when silicon at a specific position within the lattice is removed from the silicon carbide substrate 10, the remaining carbon forms a weakened layer 15 with a hollow sponge-like or void layer-like structure. The weakened layer 15 has a thickness D2. The thickness D2 of the weakened layer 15 is essentially the same as the thickness D1 of the pre-defined reaction region 14, but is smaller than the thickness D0 of the substrate 10. The thickness D2 of the weakened layer 15 can be precisely controlled by adjusting the amount of input charge according to Faraday's law of electrolysis to change the number of atoms removed in the chemical reaction. The amount of input charge can be controlled by adjusting the current or voltage applied to the substrate 10 or the time for which the chemical reaction is carried out.

[0029] 5A, 5B, and 6, FIGS. 5A and 6 are photographs of a weakened layer in a substrate processing method according to an embodiment of the present invention, taken using a scanning electron microscope (SEM). FIG. 5B is a schematic diagram showing the direction in which an electrolyte infiltrates a predetermined reaction zone during a chemical reaction in a substrate processing method according to an embodiment of the present invention. FIG. 5A is a 3000x magnification image of a weakened layer 15 in an embodiment of the present invention, taken using a scanning electron microscope (SEM). When a chemical reaction occurs in the region indicated by the dashed line in FIG. 5A, an endless seal gasket 25 is pressed against a position on the substrate 10, concentrating stress there. As a result, the electrolyte 26 not only initiates a chemical reaction from the predetermined reaction zone 14 to a position adjacent to the surface 11 of the substrate 10, but also erodes downward at the stress concentration point and infiltrates toward the center of the predetermined reaction zone 14, where it continues chemical reaction (see FIG. 5B). The area indicated by the arrow in FIG. 5A is where the electrolyte 26 has penetrated laterally into the center of the preset reaction zone 14. As a result, the weakened layer 15 exhibits a layered structure as shown in FIG. 5A. Referring to FIGS. 2A-2C and 6, FIG. 6 is a scanning electron microscope (SEM) image of the weakened layer 15 according to one embodiment of the present invention, magnified 150,000 times. At this magnification, multiple pores are clearly visible in the layered weakened layer 15. The pores are formed by the remaining carbon structure when silicon is removed from the silicon carbide substrate 10 at specific positions within the silicon carbide crystal lattice. The weakened layer 15, having this hollow sponge-like structure, has significantly reduced material strength compared to that of a solid silicon carbide substrate 10 and can be easily removed in subsequent manufacturing processes. In one embodiment, the weakened layer 15 is a porous layer.

[0030] As shown in FIG. 1 , after the predetermined reaction area 14 of the substrate 10 is converted into a weakened layer 15, step S3 is subsequently performed: the weakened layer 15 is removed, leaving the substrate 10 in the predetermined area 13 with an exposed surface 17. As shown in FIGS. 2B and 2C , in removing the weakened layer 15 in step S3, due to the large difference in material strength between the weakened layer 15 and the solid substrate 10, conventional polishing or ultrasonic vibration techniques can be used to break down the weakened layer 15, while leaving the solid portion of the substrate 10 (i.e., the portion where no chemical reaction is occurring) unaffected, allowing the weakened layer 15 to be removed from the substrate 10. In this embodiment, the effect of breaking down the weakened layer 15 can be achieved by selecting either the polishing or ultrasonic vibration techniques. However, the present invention is not limited thereto; both the polishing and ultrasonic vibration techniques can be used in step S3, and the order in which they are used is not limited. In the above embodiment, the polishing method includes removing the weakened layer 15 with a polishing slurry having a plurality of abrasive particles, and the abrasive particles include, for example, at least one of silica, cesium oxide, alumina, silicon carbide, boron nitride, and diamond, or a combination thereof. In other embodiments, the weakened layer 15 can be removed by high-temperature quenching, laser cutting, or jet stream cutting.

[0031] Following the above description, after removing the weakened layer 15, a recess 16 (FIG. 2C) having a shape corresponding to the preset reaction section 14 is formed in the predetermined region 13 of the substrate 10, and the recess 16 has an exposed surface 17. The thickness from the bottom of the recess 16 to the bottom surface 12 of the substrate 10 is D3, which is smaller than the thickness D0 of the substrate 10. In one embodiment of the present invention, the weakened layer 15 is crushed by abrasive or ultrasonic methods, and the crushed fragments are removed to maintain a solid portion in the predetermined region 13 of the substrate 10, thereby quickly achieving thinning of the substrate 10 in the predetermined region 13.

[0032] FIG. 7A is an enlarged schematic diagram of the dashed-line frame portion in FIG. 2C, and FIG. 7B is a diagram illustrating a surface treatment of a substrate having a recess shown in FIG. 7A. In one embodiment, the substrate processing method of the present invention further includes a surface treatment of the exposed surface 17 of the recess 16. As shown in FIG. 7A, the recess 16 is formed by grinding the weakened layer 15 and then removing the crushed fragments. Therefore, the exposed surface 17 of the recess 16 may contain particles and protrusions remaining after grinding, resulting in an uneven surface 17. As shown in FIG. 7B, the exposed surface 17 can be planarized by a surface treatment, such as a planarization process such as chemical mechanical polishing. In one embodiment, the surface treatment is performed using a polishing slurry containing abrasive particles, where the particle size of the abrasive particles used for planarization is smaller than the particle size of the abrasive particles used for removing the weakened layer 15. The particle size of the abrasive particles used for planarization is, for example, nanometers or angstroms, while the particle size of the abrasive particles used for removing the weakened layer 15 is, for example, on the order of microns. In one embodiment, the surface treatment further includes a polishing process after planarization of the exposed surface, but the invention is not limited thereto, such as chemical mechanical polishing, and the polishing process after planarization can be a process such as microetching, plasma treatment, or ion beam surface treatment.

[0033] In an embodiment not shown, when the predetermined region 13 to be thinned is the entire surface 11 of the substrate 10, in step S2, the endless seal gasket 25 of the electrochemical device 20 is pressed against the periphery of the surface 11 of the substrate 10, or the endless seal gasket 25 is pressed against the side of the substrate 10, so that the entire surface 11 of the substrate 10 is brought into contact with the electrolyte 26 to cause a chemical reaction and form a weakened layer 15 throughout the entire layer. In step S3 of this embodiment, after removing the weakened layer 15, no recesses 16 are formed, but the exposed surface 17 remains rough even after removing the weakened layer 15.

[0034] Referring to FIG. 8, FIG. 8 is a cross-sectional schematic diagram of an electrochemical device for carrying out a chemical reaction according to another embodiment of the present invention. In one embodiment, when the predetermined region 13 to be thinned covers the entire surface 11 of a substrate 10, a chemical reaction can be carried out using the electrochemical device shown in FIG. 8. As shown in FIG. 8, an electrochemical device 20a includes a tank 22a filled with an electrolyte 26 and two brackets 27 provided at the bottom of the tank 22a for fixing a substrate 10 on which an electrochemical reaction is to be carried out. When the substrate 10 is fixed between the two brackets 27, the tank 22a can be divided into two tanks, one of which has a positive electrode 23a and the other has a negative electrode 24a. The positive electrode 23a and the negative electrode 24a do not contact the bottom surface 12 and the surface 11 of the substrate 10, respectively. The materials of the positive electrode 23a and the negative electrode 24a are the same as those of the positive electrode 23 and the negative electrode 24, respectively, of the previous embodiment. When the positive electrode 23a is connected to the negative electrode 24a and a power source is connected to perform an electrochemical process, the entire substrate 10 is immersed in the electrolyte 26, and a weakened layer 15 is formed on the entire surface 11 facing the negative electrode 24a. Step S3 in this embodiment: After removing the weakened layer 15, no recesses 16 are formed, but the exposed surface 17 is still rough after removing the weakened layer 15.

[0035] The present invention converts a predetermined reactive region on a substrate into a weakened layer using an electrochemical method. Based on the difference in material strength between the weakened layer and the solid region on the substrate where no chemical reaction occurs, the weakened layer, which has lower material strength, can be easily broken down by methods such as polishing or ultrasonic vibration, while retaining the solid region in the predetermined region of the substrate, thereby achieving rapid thinning of the predetermined region of the substrate. This avoids cracking and warping of the substrate material due to high stress, which occurs in conventional hard cutting methods, and overcomes the problem of the substrate material's low strength making it difficult to thin the substrate using conventional polishing methods.

[0036] Furthermore, the electrochemical method of the present invention can control the amount of input charge by varying the current, voltage, and time during the chemical reaction based on Faraday's law of electrolysis, thereby achieving a desired thickness of the weakened layer, and therefore the depth of the recess formed in a predetermined region of the substrate (i.e., the thickness of the weakened layer removed) can be accurately controlled.

[0037] Although the present invention discloses the above-mentioned examples, they are not intended to limit the present invention, and a person having ordinary knowledge in the technical field to which the present invention pertains may make some changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention is considered to be limited by the claims. [Explanation of symbols]

[0038] 10: Circuit board 11: Surface 12: Bottom 13: Prescribed area 14: Pre-set reaction section 15: Weak layer 16: Recess 17: Exposed surface 20, 20a: Electrochemical devices 21: Bass 22: Tank 221: Through hole 23, 23a: Positive electrode 24, 24a: Negative electrode 25: Endless seal gasket 26: Electrolyte 27: Bracket D0, D1, D2, D3: Thickness S1, S2, S3: Steps

Claims

1. providing a substrate having a top surface and a bottom surface opposite to each other, the substrate defining a predetermined region, the predetermined region having a predetermined reaction site extending from the top surface of the substrate toward the bottom surface; causing a chemical reaction of the predetermined reaction portion by anodization using an electrochemical device to convert the predetermined reaction portion into a weakened layer having a thickness; removing the weakened layer outside the electrochemical device to provide an exposed surface on the substrate in the predetermined area; The weakened layer is removed by ultrasonic vibration, laser cutting, or jet stream cutting. A substrate processing method comprising:

2. 2. The substrate processing method according to claim 1, wherein the material of the substrate is silicon carbide.

3. 2. The substrate processing method according to claim 1, wherein the thickness of the weakened layer is controlled by the amount of input charge when the anodic oxidation progresses.

4. 2. The substrate processing method according to claim 1, wherein the predetermined reaction section comes into contact with an electrolyte containing fluoride ions as the anodic oxidation progresses.

5. 5. The substrate processing method according to claim 4, wherein the electrolytic solution is a hydrofluoric acid solution.

6. The substrate processing method according to claim 1 , further comprising surface treatment of the exposed surface.

7. 7. The substrate processing method according to claim 6, wherein the surface processing is chemical mechanical polishing.

8. 2. The method of claim 1, wherein the weakened layer is porous.

9. providing a silicon carbide substrate having a top surface and a bottom surface opposite to each other, the silicon carbide substrate defining a predetermined region, the predetermined region being defined as having a predetermined reaction portion extending from the top surface of the silicon carbide substrate toward the bottom surface; a chemical reaction is carried out by bringing the predetermined reaction portion into contact with a hydrofluoric acid solution through anodization using an electrochemical device, thereby converting the predetermined reaction portion into a porous layer having a thickness; Outside the electrochemical device, the porous layer is removed to leave an exposed surface on the silicon carbide substrate in the predetermined region; The porous layer is removed by ultrasonic vibration, laser cutting, or jet stream cutting. A method for treating a silicon carbide substrate, comprising:

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