Etching apparatus and etching method

Abstract

To provide an etching device and an etching method each using an etchant in which a phase transition occurs between solid and liquid.SOLUTION: An etching device includes a crucible in which an etchant is put in, a heater provided around the crucible, a movable holder holding an object to be etched, a first thermocouple provided outside the crucible, a movable second thermocouple provided inside the crucible, and a controller controlling the temperature of the heater on the basis of an electrical signal from the first thermocouple or the second thermocouple, and when the etchant is a solid, the temperature of the etchant is controlled on the basis of an electrical signal from the first thermocouple, and when the etchant is a liquid, the temperature of the etchant is controlled on the basis of an electrical signal from the second thermocouple immersed into the etchant, and the object to be etched is immersed in the etchant and etched.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an etching apparatus and an etching method, and more particularly to an etching apparatus and an etching method using an etchant that undergoes a phase transition between solid and liquid. [Background technology]

[0002] To evaluate the quality of SiC substrates, for example, the substrate is immersed in a potassium hydroxide melt and etched, which preferentially etches away crystal defects and forms etch pits. The quality of the SiC substrate can then be evaluated by observing these etch pits.

[0003] Conventional etching equipment used for etching SiC substrates includes a crucible containing potassium hydroxide, a heater installed around the crucible, and a heat insulating material surrounding the heater. The temperature of the crucible is measured and controlled by a thermocouple installed outside the crucible. Summary of the Invention [Problem to be solved by the invention]

[0004] However, in conventional etching equipment, the thermocouple is placed outside the crucible, making it difficult to accurately measure and control the temperature of the potassium hydroxide inside the crucible. In particular, when a SiC substrate is immersed in the molten potassium hydroxide, the temperature change is not well controlled, and it takes time for the temperature to stabilize. In particular, the etching rate of the molten potassium hydroxide is sensitive to temperature, making stable etching difficult.

[0005] To address this issue, we considered placing a thermocouple inside the crucible to measure and control the temperature of the molten potassium hydroxide, but when the temperature of potassium hydroxide is in a solid state below its melting point (360°C), the thermocouple had to be placed in the hollow inside the crucible above the potassium hydroxide, making it difficult to accurately measure and control the temperature of the potassium hydroxide.In particular, because the radiant heat from the heater is reflected by the outer surface of the crucible, the thermocouple placed in the hollow inside the crucible could not accurately measure the temperature.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an etching apparatus and an etching method that are capable of accurately measuring and controlling temperature in an etching apparatus that uses an etchant that undergoes a phase transition between solid and liquid. [Means for solving the problem]

[0007] One aspect of the present invention is An etching apparatus using an etchant that undergoes a phase transition between solid and liquid, A crucible for holding the etchant, a heater provided around the crucible; a movable holder for holding an object to be etched; a first thermocouple provided outside the crucible; a movable second thermocouple disposed inside the crucible; a controller that controls the temperature of the heater based on an electrical signal from the first thermocouple or the second thermocouple; When the etchant is a solid, a temperature of the etchant is controlled based on the electrical signal from the first thermocouple; When the etchant is a liquid, the temperature of the etchant is controlled based on an electrical signal from a second thermocouple immersed in the etchant, and the object to be etched is immersed in the etchant and etched in this etching apparatus.

[0008] Another aspect of the present invention is 1. An etching method using an etchant that undergoes a phase transition between solid and liquid, comprising: placing a solid etchant in a crucible; a step of heating the crucible with a heater provided around the crucible based on an electrical signal from a first thermocouple provided outside the crucible, thereby causing a phase transition of the etchant from a solid to a liquid; a switching step of immersing a second thermocouple in the liquid etchant and controlling the temperature of the etchant based on the electrical signal from the second thermocouple instead of the electrical signal from the first thermocouple; an etching step of immersing an object to be etched in an etchant and etching the object; removing the object to be etched from the etchant; controlling the temperature of the etchant based on the electrical signal from the first thermocouple instead of the electrical signal from the second thermocouple; withdrawing the second thermocouple from the etchant; and cooling the etchant to cause a phase transition from liquid to solid. [Effects of the Invention]

[0009] By using such an etching apparatus and etching method, it becomes possible to accurately measure and control the temperature of the etchant even when the etchant undergoes a phase transition between solid and liquid, making it possible to perform etching with high precision. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram of an etching apparatus according to an embodiment of the present invention; [Figure 2] 1 is a diagram showing the relationship between the temperature change of an etchant and each etching step. [Figure 3] 1 is a schematic diagram illustrating one step of an etching method according to an embodiment of the present invention. [Figure 4] 1 is a schematic diagram illustrating one step of an etching method according to an embodiment of the present invention. [Figure 5] 1 is a schematic diagram illustrating one step of an etching method according to an embodiment of the present invention. [Figure 6]1 is a schematic diagram illustrating one step of an etching method according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] 1 is a schematic diagram of an etching apparatus according to an embodiment of the present invention, generally designated 100. The etching apparatus 100 includes a crucible 20 for containing an etchant 60, and a heater 30 provided around the crucible 20. A heat insulating material 10 is provided around the crucible 20 and the heater 30 so as to surround them.

[0012] As the etchant, for example, potassium hydroxide (KOH) or a mixture of potassium hydroxide and sodium hydroxide (KOH+NaOH) that is solid at room temperature and liquid during etching is used, but these etchants are merely examples.

[0013] The crucible 20 is a cylindrical container made of, for example, nickel. The heater 30 is made of, for example, nichrome. The heat insulating material 10 is made of, for example, ceramic fiber.

[0014] A thermocouple (TC1) 40a is provided below the crucible 20 so as to contact the bottom of the crucible 20 from the outside. A thermocouple (TC2) 40b that can move up and down is held in the air inside the crucible 20. Thermocouples 40a and 40b are made of, for example, chromel and alumel. Thermocouple 40a is covered with, for example, a nickel alloy sheath, and thermocouple 40b is covered with, for example, a nickel sheath.

[0015] Electrical signals from the thermocouples 40a, 40b are input to a controller 80, and the measurement results of the thermocouples 40a, 40b are used to control the temperature of the heater 30. Although a common controller 80 is provided for the two thermocouples 40a, 40b in Fig. 1, separate controllers connected to the respective thermocouples 40a, 40b may also be provided.

[0016] A holder 50 that can move up and down is provided above the crucible 20. For example, a mesh-like nickel wire or a punched nickel plate is used for the holder 50. A substrate 70, which is the object to be etched, is placed on the holder 50. For example, a semiconductor substrate such as SiC, GaN, or GaAs is used as the substrate 70, but it is not limited to these.

[0017] The holder 50 is moved up and down by the movable means 90. When the etchant 60 is solid, the holder 50 is held above the etchant 60, and after the etchant 60 melts and becomes liquid, the holder 50 is moved downward and immersed in the etchant 60. After etching the substrate 70 for a predetermined time, the holder 50 is moved upward by the movable means 90, and the etching is completed. The holder 50 may be rotated by rotating the movable means 90 about its longitudinal axis.

[0018] Fig. 2 is a diagram showing the relationship between the temperature change of the etchant and each etching step. Figs. 3 to 6 are schematic diagrams of the etching apparatus in each etching step. In Figs. 3 to 6, the same reference numerals as in Fig. 1 indicate the same or corresponding parts.

[0019] A method for etching a SiC substrate using potassium hydroxide will be described with reference to Figures 1 to 6. The etching method includes the following steps 1 to 6.

[0020] Step 1 (preparation step in FIG. 2(1)): As shown in FIG. 1, an etchant 60 made of potassium hydroxide (solid) is placed in a crucible 20. A substrate 70 made of SiC is placed on a holder 50 with its surface facing up. In this preparation step, the heater 30 is not heated, and the thermocouple 40b and the holder 50 are held at positions away from the etchant 60.

[0021] Step 2 (Heating Step 1 in Figure 2(2)): Once preparations are complete, the etchant 60 contained in the crucible 20 is heated while the temperature of the heater 30 is controlled by the controller 80 using an electrical signal from the thermocouple 40a. The melting point of potassium hydroxide is 360°C, and at this temperature it melts and undergoes a phase transition from solid to liquid, becoming a potassium hydroxide melt.

[0022] Step 3 (Heating Step 2 in FIG. 2(3)): As shown in FIG. 3, when the etchant 60 becomes liquid, the thermocouple 40b is lowered in a direction perpendicular to the liquid surface and immersed in the etchant 60 to measure the temperature of the etchant 60. Subsequently, the electrical signal input to the controller 80 is switched from the thermocouple 40a to the thermocouple 40b, and the temperature of the heater 30 is controlled by the controller 80 using the electrical signal from the thermocouple 40b. This allows the temperature of the potassium hydroxide melt to be accurately measured and controlled.

[0023] Step 4 (etching step in FIG. 2(4)): As shown in FIG. 4, when the temperature of the potassium hydroxide melt reaches 500°C, the holder 50 is moved downward using the moving means 90 and immersed in the etchant 60. At this point, the temperature of the etchant 60 changes, but it can be stabilized in a short time by controlling the temperature of the heater 30 using the thermocouple 40b. In this state, the substrate 70 is etched. In particular, since the etching rate of the substrate (SiC) 70 is sensitive to the temperature of the etchant (potassium hydroxide) 60, accurate etching can be achieved by stabilizing the temperature of the etchant 60 in a short time. The etching conditions are, for example, 500°C for 5 minutes. The holder 50 may be rotated around its longitudinal axis at, for example, 10 to 20 rpm.

[0024] Step 5 (FIG. 2(5) etching completion step): As shown in FIG. 5, the holder 50 is moved upward using the movable means 90 and removed from the etchant 60, thereby completing the etching of the substrate 70.

[0025] Step 6 (cooling step in FIG. 2(6)): The temperature measurement is switched from thermocouple 40b to thermocouple 40a, and the controller 80 uses the electrical signal from thermocouple 40a to lower the temperature of crucible 20 and cool it. As shown in FIG. 6, thermocouple 40b is pulled out of etchant 60 before the temperature of the potassium hydroxide melt reaches its melting point (360°C) and it becomes solid.

[0026] The above steps 1 to 6 complete the etching of the substrate (SiC) 70 with the etchant (potassium hydroxide) 60. The substrate 70 is evaluated, for example, by observing etch pits formed on the surface of the substrate 70 by etching.

[0027] Thus, by using the etching apparatus 100 according to the embodiment of the present invention, even when the etchant undergoes a phase transition from a solid to a liquid, such as potassium hydroxide, accurate temperature measurement and control of the etchant can be achieved by measuring the temperature using the two thermocouples 40a and 40b. As a result, the etching temperature can be stabilized and the amount of etching can be accurately controlled. In particular, by switching the measuring thermocouple to thermocouple 40a and removing thermocouple 40b from the etchant before the etchant 60 becomes solid, the thermocouple 40b does not become stuck in the solid etchant 60. [Industrial Applicability]

[0028] The etching apparatus and method of the present invention can be widely applied to etching of semiconductor substrates using an etchant that undergoes a phase transition from solid to liquid, such as potassium hydroxide. [Explanation of symbols]

[0029] 10. Insulation 20 Crucible 30 Heater 40, 40a, 40b thermocouples 50 Holder 60 Etchant 70 boards 80 Controller 90 Movable means 100 Etching equipment

Claims

1. An etching apparatus using an etchant that undergoes a phase transition between solid and liquid, A crucible for holding the etchant, a heater provided around the crucible; a movable holder for holding an object to be etched; a first thermocouple provided outside the crucible; a movable second thermocouple disposed inside the crucible; a controller that controls the temperature of the heater based on an electrical signal from the first thermocouple or the second thermocouple; When the etchant is a solid, a temperature of the etchant is controlled based on the electrical signal from the first thermocouple; When the etchant is a liquid, the temperature of the etchant is controlled based on an electrical signal from a second thermocouple immersed in the etchant, and the object to be etched is immersed in the etchant and etched.

2. 2. The etching apparatus according to claim 1, wherein the control signal of the controller is switched between the electric signal of the first thermocouple and the electric signal of the second thermocouple while the etchant is in a liquid state.

3. 2. The etching apparatus according to claim 1, wherein the first thermocouple is disposed so as to be in contact with the crucible.

4. 2. The etching apparatus according to claim 1, wherein the second thermocouple is a thermocouple that is movable in a direction perpendicular to the surface of the liquid etchant.

5. 2. The etching apparatus according to claim 1, further comprising a heat insulating material disposed around the crucible and the heater.

6. 6. The etching apparatus according to claim 1, wherein the etchant is potassium hydroxide or a mixture of potassium hydroxide and sodium hydroxide.

7. 6. The etching apparatus according to claim 1, wherein the object to be etched is a semiconductor substrate.

8. 1. An etching method using an etchant that undergoes a phase transition between solid and liquid, comprising: placing a solid etchant in a crucible; a step of heating the crucible with a heater provided around the crucible based on an electrical signal from a first thermocouple provided outside the crucible, thereby causing a phase transition of the etchant from a solid to a liquid; a switching step of immersing a second thermocouple in the liquid etchant and controlling the temperature of the etchant based on the electrical signal from the second thermocouple instead of the electrical signal from the first thermocouple; an etching step of immersing an object to be etched in an etchant and etching the object; removing the object to be etched from the etchant; controlling the temperature of the etchant based on the electrical signal from the first thermocouple instead of the electrical signal from the second thermocouple; withdrawing the second thermocouple from the etchant; and cooling the etchant to cause a phase transition from liquid to solid.

9. 9. The etching method according to claim 8, wherein the switching step includes a step of moving a second thermocouple held on the surface of the etchant toward the etchant and immersing it therein.

10. 9. The etching method according to claim 8, wherein the etching step is a step of rotating the object to be etched in the etchant.

11. 11. The etching method according to claim 8, wherein the etchant is potassium hydroxide or a mixture of potassium hydroxide and sodium hydroxide.

12. The etching method according to any one of claims 8 to 10, wherein the object to be etched is a semiconductor substrate.

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