Etching device 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 particularly to an etching apparatus and an etching method using an etchant that undergoes a phase transition between a solid and a liquid.

Background Art

[0002] For the quality evaluation of a SiC substrate, for example, by immersing the SiC substrate in a potassium hydroxide melt and etching it, crystal defects are preferentially etched to form etch pits, and the quality of the SiC substrate can be evaluated by observing these etch pits.

[0003] A conventional etching apparatus used for etching a SiC substrate includes a crucible containing potassium hydroxide, a heater provided around the crucible, and a heat insulating material covering the periphery of the heater, and measures and controls the temperature of the crucible by a thermocouple provided outside the crucible.

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the conventional etching apparatus, since the thermocouple is disposed outside the crucible, it has been difficult to accurately measure and control the temperature of the potassium hydroxide inside the crucible. In particular, when the SiC substrate is immersed in the molten potassium hydroxide melt, the control for temperature changes is insufficient and it takes time for the temperature to stabilize. In particular, since the etching rate of the potassium hydroxide melt is sensitive to temperature, stable etching has been difficult.

[0005] In contrast, we considered placing a thermocouple in the crucible to measure and control the temperature of the potassium hydroxide melt. However, when the temperature of potassium hydroxide is in a solid state below its melting point (360 °C), the thermocouple has to be placed in the hollow above the potassium hydroxide inside the crucible. Therefore, it was difficult to accurately measure and control the temperature of potassium hydroxide. In particular, since the radiant heat from the heater is reflected on the outer surface of the crucible, the temperature could not be accurately measured by the thermocouple placed in the hollow inside the crucible.

[0006] Therefore, an object of the present invention is to provide an etching apparatus and an etching method capable of accurately measuring and controlling the temperature in an etching apparatus using an etchant that undergoes a phase transition between a solid and a liquid.

Means for Solving the Problems

[0007] One aspect of the present invention is an etching apparatus using an etchant that undergoes a phase transition between a solid and a liquid, comprising a crucible for containing 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 provided inside the crucible, a controller for controlling the temperature of the heater based on an electrical signal from the first thermocouple or the second thermocouple, and when the etchant is in a solid state, the temperature of the etchant is controlled based on the electrical signal from the first thermocouple, when the etchant is in a liquid state, the temperature of the etchant is controlled based on the electrical signal from the second thermocouple immersed in the etchant, and the object to be etched is immersed in the etchant for etching.

[0008] Another aspect of the present invention is an etching method using an etchant that undergoes a phase transition between a solid and a liquid, comprising The step of putting a solid etchant into a crucible, Based on the electrical signal from the first thermocouple provided outside the crucible, heating the crucible with a heater provided around the crucible to cause a phase transition of the etchant from solid to liquid, The switching step of immersing the 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, The etching step of immersing an object to be etched in the etchant for etching, The step of taking out the object to be etched from the etchant, The step of controlling the temperature of the etchant based on the electrical signal from the first thermocouple instead of the electrical signal from the second thermocouple, The step of pulling out the second thermocouple from the etchant, The step of cooling the etchant to cause a phase transition from liquid to solid, which is an etching method including these steps.

Advantages of the Invention

[0009] By using such an etching apparatus and etching method, even when the etchant undergoes a phase transition between solid and liquid, accurate measurement and control of the temperature of the etchant are possible, enabling high-precision etching.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

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

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

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

[0014] Below the crucible 20, a thermocouple (TC1) 40a is provided so as to contact the bottom of the crucible 20 from the outside. Inside the crucible 20, a vertically movable thermocouple (TC2) 40b is held in a hollow manner. As the thermocouples 40a and 40b, for example, a thermocouple made of chromel and alumel is used. The thermocouple 40a is covered with, for example, a nickel alloy sheath, and the thermocouple 40a is covered with, for example, a nickel sheath.

[0015] Electrical signals from the thermocouples 40a and 40b are input into a controller 80, and the temperature of the heater 30 is controlled using the measurement results of the thermocouples 40a and 40b. In FIG. 1, a common controller 80 is provided for the two thermocouples 40a and 40b, but controllers connected to the respective thermocouples 40a and 40b may be provided separately.

[0016] Above the crucible 20, a holder 50 that is movable in the vertical direction is provided. For the holder 50, for example, a mesh-like nickel wire or a nickel punching plate is used. On the holder 50, a substrate 70 to be etched is placed. As the substrate 70, for example, semiconductor substrates such as SiC, GaN, and GaAs are used, but it is not limited thereto.

[0017] The holder 50 moves in the vertical direction by a 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, it moves downward and is immersed in the etchant 60. After etching the substrate 70 for a predetermined time, it moves upward by the movable means 90, and the etching is completed. The holder 50 may be rotated by rotating the movable means 90 about the longitudinal axis.

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

[0019] With reference to FIGS. 1 to 6, an etching method of an SiC substrate using potassium hydroxide will be described. 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 the crucible 20. Also, a substrate 70 made of SiC is placed on the holder 50 with the 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] Process 2 (Heating Process 1 in Fig. 2(2)): Once the preparation is complete, using the electrical signal from the thermocouple 40a, while controlling the temperature of the heater 30 with the controller 80, the etchant 60 in the crucible 20 is heated. The melting point of potassium hydroxide is 360 °C. At this temperature, it melts and undergoes a phase transition from solid to liquid, becoming a potassium hydroxide melt.

[0022] Process 3 (Heating Process 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. Thereby, the temperature of the potassium hydroxide melt can be accurately measured and controlled.

[0023] Process 4 (Etching Process 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 movable means 90 and immersed in the etchant 60. At this point, the temperature of the etchant 60 changes, but by controlling the temperature of the heater 30 using the thermocouple 40b, it can be stabilized in a short time. 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 becomes possible 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, for example, at 10 - 20 rpm around the longitudinal axis.

[0024] Process 5 (Etching Completion Process in Fig. 2(5)): As shown in Fig. 5, the etching of the substrate 70 is completed by moving the holder 50 upward using the movable means 90 and taking it out of the etchant 60.

[0025] Step 6 (Figure 2(6) Cooling Step): Switch the temperature measurement from thermocouple 40b to thermocouple 40a, and use the electrical signal from thermocouple 40a to lower the temperature of the crucible 20 with the controller 80 for cooling. As shown in Figure 6, pull out the thermocouple 40b from the etchant 60 before the temperature of the potassium hydroxide melt reaches the melting point (360 °C) and becomes solid.

[0026] In the above Steps 1 to 6, the etching of the substrate (SiC) 70 by the etchant (potassium hydroxide) 60 is completed. The evaluation of the substrate 70 is performed, for example, by observing the etch pits on the surface of the substrate 70 formed by etching.

[0027] In this way, 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 etching can be achieved by performing temperature measurement using two thermocouples 40a and 40b. As a result, it becomes possible to stabilize the etching temperature and accurately control the etching amount. In particular, by switching the thermocouple for measurement to thermocouple 40a and pulling out the thermocouple 40b from the etchant before the etchant 60 becomes solid, the thermocouple 40b will not get stuck in the solid etchant 60.

Industrial Applicability

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

Explanation of Reference Numerals

[0029] 10 Heat insulation material 20 Crucible 30 Heater 40, 40a, 40b Thermocouples 50 Holder 60 Etchant 70 Substrate 80 Controller 90 Movable means 100 Etching apparatus

Claims

1. An etching apparatus using an etchant that undergoes a phase transition between a solid and a liquid, comprising: a crucible for containing 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 provided inside the crucible; a controller for controlling the temperature of the heater based on an electrical signal from the first thermocouple or the second thermocouple; when the etchant is in a solid state, the temperature of the etchant is controlled based on an electrical signal from the first thermocouple; when the etchant is in a liquid state, the temperature of the etchant is controlled based on an electrical signal from the second thermocouple immersed in the etchant, and the object to be etched is immersed in the etchant for etching.

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

3. The etching apparatus according to claim 1, wherein the first thermocouple is arranged to contact the crucible.

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

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

6. The etching apparatus according to any one of claims 1 to 5, wherein the etchant is potassium hydroxide or a mixture of potassium hydroxide and sodium hydroxide.

7. The etching apparatus according to any one of claims 1 to 5, wherein the object to be etched is a semiconductor substrate.

8. An etching method using an etchant that undergoes a phase transition between a solid and a liquid, comprising: a step of putting a solid etchant into 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 to cause the etchant to undergo a phase transition 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 an 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 the etchant for etching; a step of taking out the object to be etched from the etchant. A step of controlling the temperature of the etchant based on an electrical signal from the first thermocouple instead of the electrical signal from the second thermocouple; A step of withdrawing the second thermocouple from the etchant; An etching method comprising a step of cooling the etchant to cause a phase transition from a liquid to a solid.

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

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

11. The etching method according to any one of claims 8 to 10, 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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