Processing method and processing apparatus by high-density radical reaction

Abstract

The aim is to provide a technology that can further improve the processing speed of distortion-free etching for difficult-to-process materials such as wide-bandgap semiconductor materials like silicon carbide (SiC) and gallium nitride (GaN), as well as gallium oxide (Ga2O3), aluminum nitride (AlN), and diamond, without increasing the power of the high-frequency power used for plasma generation. [Solution] A bias power supply 5 is provided separately from the power supply 4 that generates high-pressure plasma. The bias voltage draws slow ions in the plasma, which have been accelerated, to the surface of the workpiece 9. The kinetic energy of these ions exceeds the activation energy of the radical reaction on the surface of the workpiece 9, thereby promoting the reaction. More specifically, a processing electrode 2 and a workpiece 9 are placed in a gas atmosphere. A high-frequency voltage is applied to the processing electrode 2 to generate the plasma, and a DC or AC bias voltage is applied between the processing electrode 2 and the workpiece 9 using the bias power supply 5.

Description

Technical Field

[0001] The present invention relates to a processing method and a processing apparatus by a high-density radical reaction, which generate plasma in a gas atmosphere of 0.1 kPa or more containing a reaction gas, generate neutral radicals based on the reaction gas, and vaporize and remove volatile substances generated by a radical reaction between the neutral radicals and atoms or molecules on the surface of the workpiece.

Background Art

[0002] The basic principle of this kind of distortion-free etching technology using high-pressure plasma of 0.1 kPa or more to near atmospheric pressure is disclosed in Patent Document No. 1, and various proposals have also been made regarding the form of the electrode, such as a wire electrode, a rotating electrode, a nozzle electrode for ejecting a process gas, or a narrow blade electrode (see Patent Documents 1 to 3). Further, a method of applying a pulse-modulated high-frequency voltage for controlling the plasma has also been proposed (see Patent Document 4).

[0003] However, silicon carbide (SiC), gallium nitride (GaN), diamond, etc., which are wide-gap semiconductor materials that will become increasingly important in the future, especially in the semiconductor field, are not only difficult to process in mechanical processing due to their high hardness, but also difficult to process in etching because they are chemically stable. In the conventional distortion-free etching method using high-pressure plasma, there is a problem that the processing speed can only be obtained at about one-fourth to one-fortieth of that of silicon (Si). Although attempts have been made to generate neutral radicals at a higher density or increase the temperature by increasing the power of the high-frequency power for plasma generation, the input of large power not only increases the risk of yield reduction due to abnormal discharge, but also consumes a large amount of power and is costly.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

[0005] Therefore, in view of the above situation, the present invention aims to provide a technology that can further improve the processing speed of distortion-free etching for difficult-to-process materials such as silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), aluminum nitride (AlN), aluminum oxide (Al2O3), and diamond, without increasing the power of high-frequency electricity. [Means for solving the problem]

[0006] Under these circumstances, the inventors considered that in strain-free etching technology using high-pressure plasma, by applying a small amount of energy to each of the numerous ions present in the plasma that exceeds the activation energy of the radical reaction between neutral radicals and atoms or molecules on the surface of the workpiece, this reaction could be promoted, and the processing speed could be increased even for difficult-to-process materials.

[0007] Unlike so-called low-pressure dry etching, which uses the principle of ion sputtering to physically remove atoms or molecules from the workpiece surface by applying an external electric field to ions in a plasma under a low-pressure gas atmosphere of tens of Pa or less and accelerating them to over several hundred electron volts, the mean free path (the average distance until gas particles collide) of each ion present in the plasma is short (submicron to at most about 1 μm), and even if an external electric field is applied, most of the accelerated ions are quickly scattered by colliding with each other, so it was thought that ions hardly contribute to the processing of the workpiece surface.

[0008] Therefore, in distortion-free etching technology using high-pressure plasma, no external electric field is applied, and research has continued to promote processing even for difficult-to-process materials by increasing the power of the high-frequency power used for plasma generation to generate neutral radicals at a higher density.

[0009] However, the inventors hypothesized that even a small amount of energy, accelerating even with a short mean free path, could significantly contribute to exceeding the activation energy of the radical reaction if it could be supplied to the workpiece surface via ions. Experiments with varying workpiece temperatures showed that the activation energy for the radical reaction between neutral radicals and atoms or molecules on the workpiece surface is a few tenths of an eV, and that supplying even a small amount of energy, around 1 eV, to atoms or molecules on the workpiece surface to which neutral radicals are attached would be sufficient to exceed the activation energy of the radical reaction. Furthermore, it was estimated that an average energy of a few tenths of an eV could be supplied by an external electric field even with a short mean free path in a gas atmosphere of 0.1 kPa or higher.

[0010] Further research revealed that energy of a few tenths of an eV can be imparted to ions by applying an external electric field, that sputtering does not occur with such small energies of a few tenths of an eV, thus maintaining distortion-free processing, and that the processing speed is improved by promoting radical reactions on the workpiece surface. This allows for improved processing speed even for difficult-to-process materials such as silicon carbide (SiC) without increasing the power of the high-frequency current, thus completing the present invention.

[0011] In other words, the present invention encompasses the following inventions. (1) A processing method by high-density radical reaction, comprising generating plasma in a gas atmosphere of 0.1 kPa or higher containing a reaction gas, generating neutral radicals based on the reaction gas, and vaporizing and removing volatile substances generated by radical reactions between the neutral radicals and atoms or molecules on the surface of a workpiece, characterized in that a bias power supply is provided separately from the power supply for generating the plasma, and the bias voltage is used to draw ions in the plasma to the surface of the workpiece, thereby promoting the radical reaction on the surface of the workpiece.

[0012] (2) The machining method according to (1), wherein a machining electrode and a workpiece are placed in the gas atmosphere, a high-frequency voltage is applied to the machining electrode to generate the plasma, and a DC or AC bias voltage is applied between the machining electrode and the workpiece using the bias power supply.

[0013] (3) The processing method according to (1), wherein the average energy of the ions (charged particles) accelerated and drawn in by the bias voltage is less than 10 eV.

[0014] (4) The processing method according to any one of (1) to (3), wherein the amount of processing due to the radical reaction is controlled by numerically controlling the bias voltage.

[0015] (5) A processing apparatus for high-density radical reaction, which generates plasma in a gas atmosphere of 0.1 kPa or higher containing a reaction gas, generates neutral radicals based on the reaction gas, and vaporizes and removes volatile substances generated by radical reactions between the neutral radicals and atoms or molecules on the surface of a workpiece, wherein the apparatus is equipped with a bias power supply separate from the power supply for generating the plasma, and the bias voltage attracts ions in the plasma to the surface of the workpiece, thereby promoting the radical reaction on the surface of the workpiece.

[0016] (6) The processing apparatus according to (5), wherein a processing electrode and a workpiece are placed in the gas atmosphere, a high-frequency voltage is applied to the processing electrode to generate the plasma, and a DC or AC bias voltage is applied between the processing electrode and the workpiece using the bias power supply.

[0017] (7) The processing apparatus according to (6), comprising a holding base that holds a workpiece and also serves as a counter electrode, wherein the high-frequency voltage is applied between the holding base and the processing electrode to generate the plasma, and the bias power supply applies the bias voltage between the holding base and the processing electrode. [Effects of the Invention]

[0018] According to the present invention as described above, when slow ions accelerated by a bias voltage are irradiated onto the workpiece surface, radical reactions between neutral radicals and atoms or molecules on the workpiece surface are promoted, enabling distortion-free etching using high-pressure plasma for difficult-to-process materials such as silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), aluminum nitride (AlN), aluminum oxide (Al2O3), and diamond, or significantly improving the processing speed. Furthermore, since there is no need to increase the power of the high-frequency power used for plasma generation, yield reductions due to abnormal discharge and increased power consumption can be avoided, and costs can be reduced.

[0019] Even with conventional low-pressure dry etching, the processing rate of silicon carbide (SiC) was at most about several μm / min. However, according to the present invention, as can be seen from the test results of the examples described later, a processing rate of 10 μm / min or more can be obtained by distortion-free etching using high-pressure plasma. Also, conventional distortion-free etching using high-pressure plasma was based on the chemical etching principle by neutral radicals in the plasma and was basically isotropic processing. In the present invention, since reaction energy is imparted by accelerating ions in the plasma and applying them to the workpiece, depending on how the bias voltage is applied, directional (anisotropic) processing, that is, it is possible to proceed with processing by setting a site that promotes radical reaction. For example, when processing with the surface of the workpiece masked, in conventional distortion-free etching using high-pressure plasma, it was isotropic processing where etching proceeded not only to the opening but also under the mask. However, according to the present invention, it becomes possible to proceed with anisotropic removal processing only in the depth direction directly under the opening without penetrating under the mask.

[0020] In particular, in a gas atmosphere, a processing electrode and a workpiece are arranged, a high-frequency voltage is applied to the processing electrode to generate the plasma, and a DC or AC bias voltage is applied between the processing electrode and the workpiece by the bias power supply. By selecting the form and arrangement of the processing electrode, the workpiece can be easily processed into a desired form.

[0021] Also, since the average energy of ions (charged particles) accelerated and drawn in by the bias voltage is less than 10 eV, the radical reaction on the surface of the workpiece can be sufficiently promoted, and it can be easily realized with a bias voltage that does not adversely affect the state of the plasma. If an attempt is made to give a large energy of 10 eV or more, the plasma tends to shift to arc discharge and become unstable due to the bias voltage, and there is also a risk that sputtering will occur due to high-energy ions accelerated to several 100 eV or more probabilistically, damaging (distorting) the surface of the workpiece.

[0022] Also, by numerically controlling the bias voltage to control the processing amount by the radical reaction, it becomes easy to automatically process the workpiece into a desired form. Especially when processing difficult-to-machine materials, the processing amount can be controlled to almost zero by setting the bias voltage to plus dozens of volts. In numerical control machining by general feed rate control (residence time control), it was impossible to achieve zero processing amount (the feed rate would become infinite), so the range of forms that can be machined by numerical control has been greatly expanded.

[0023] When a workpiece is held and a holding table that also serves as a counter electrode is provided, and the high-frequency voltage is applied between the holding table and the processing electrode to generate the plasma, and a bias power supply applies the bias voltage between the holding table and the processing electrode, ions in the plasma accelerated by the bias voltage can be more efficiently irradiated toward the workpiece, and the radical reaction can be more efficiently promoted by the bias voltage.

Brief Description of the Drawings

[0024] [Figure 1] Schematic diagram showing a representative embodiment of a processing apparatus by high-density radical reaction according to the present invention. [Figure 2] (a) is an explanatory diagram for explaining the principle by which processing is promoted according to the present invention, and (b) is an explanatory diagram showing the processing principle of conventional low-pressure dry etching (reactive ion etching (RIE)). [Figure 3] Graph (cross-sectional profile of the workpiece surface) showing the results of an evaluation test (1) of processing characteristics by bias voltage (workpiece: silicon (Si)). [Figure 4] Graph (cross-sectional profile of the workpiece surface) showing the results of an evaluation test (1) of processing characteristics by bias voltage (workpiece: silicon carbide (SiC)). [Figure 5] (a) and (b) are graphs (arbitrary three cross-sectional profiles of the groove shape formed on the workpiece surface) showing the respective results of an evaluation test (2) of processing characteristics by bias voltage (bias voltages: -50V, -100V). [Figure 6](a) and (b) are graphs showing the results of the bias voltage-based machining characteristics evaluation test (2) (bias voltage: -150V, -255V) (cross-sectional profiles of any three locations of groove shape formed on the workpiece surface). [Figure 7] A graph summarizing the results of the evaluation test (2) on processing characteristics using bias voltage. [Figure 8] A schematic diagram showing another embodiment of the processing apparatus. [Figure 9] (a) and (b) are graphs showing the results of evaluation tests of processing characteristics under atmospheric gas pressure (atmospheric gas pressure: 5kPa, 2.5kPa) (cross-sectional profiles of groove shapes formed on the workpiece surface). [Figure 10] (a) and (b) are graphs showing the results of evaluation tests of processing characteristics under atmospheric gas pressure (atmospheric gas pressure: 1 kPa, 0.5 kPa) (cross-sectional profiles of groove shapes formed on the workpiece surface). [Figure 11] (a) and (b) are graphs summarizing the results of the evaluation test of processing characteristics under atmospheric gas pressure, in terms of cross-sectional area and cross-sectional area ratio, respectively. [Figure 12] (a) and (b) are graphs summarizing the results of the machining characteristics evaluation test using atmospheric gas pressure, for machining depth and machining depth ratio, respectively. [Modes for carrying out the invention]

[0025] Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0026] Figure 1 shows a typical embodiment of the processing apparatus 1 for high-density radical reaction according to the present invention. The processing apparatus 1 has a processing electrode 2, a workpiece 9, and a holding base 3 that holds the workpiece 9 and also serves as a counter electrode arranged inside a chamber (not shown). An atmospheric gas containing a reaction gas determined according to the material of the workpiece 9 and, if necessary, an inert gas, is sealed or circulated inside. The pressure of the atmospheric gas is 0.1 kPa or higher, more preferably 0.4 kPa or higher. A pressure lower than 0.1 kPa is undesirable because it reduces the processing speed due to a decrease in neutral radical density. From the viewpoint of processing efficiency, 1 kPa or higher is even more preferable.

[0027] When the pressure is close to atmospheric pressure, the equipment configuration can be simplified, and costs can be reduced. It is also possible to operate in an environment pressurized above atmospheric pressure. However, if the pressure is increased too much, the processing gap for generating plasma becomes smaller than 100 μm, making it difficult to handle. Furthermore, even if ions are accelerated by the bias voltage, they quickly collide with other particles and scatter before reaching the workpiece surface, so radical reactions are not promoted and improvements in processing efficiency cannot be expected. Therefore, it is practical to limit the upper pressure to 10 atmospheres or less.

[0028] A processing gap G is formed between the processing electrode 2 and the workpiece 9 (the part being processed), and high-frequency power is supplied to the processing electrode 2 from a high-frequency power supply 4 via a matching device (not shown) that matches the impedance of the high-frequency power supply 4 with that of the load. By applying high-frequency power to the processing electrode 2, a high electric field is formed in the processing gap G, a plasma is generated from the atmospheric gas present in that region, the reaction gas present in the plasma region is excited and activated to generate neutral radicals, and processing is performed by generating, vaporizing, and removing volatile substances through radical reactions between these neutral radicals and atoms or molecules on the surface of the workpiece 9.

[0029] Furthermore, in this invention, a bias power supply 5 is provided that applies a DC or AC bias voltage between the processing electrode 2 and the workpiece 9. The system is configured such that slow ions accelerated by the bias voltage are irradiated onto the surface of the workpiece 9, thereby promoting the radical reaction on the surface of the workpiece 9. Specifically, the bias power supply 5 applies a bias voltage between the holder 3 and the processing electrode 2, causing the ions of the reaction gas, which are abundant in the plasma region, to be slightly accelerated, albeit only by a few eV due to the high pressure, as shown in Figure 2(a). These slow ions collide with atoms or molecules on the surface of the workpiece 9 on which the neutral radicals are adsorbed, imparting energy. This energy is then used as activation energy of a few eV or less, which is necessary for the radical reaction, thereby promoting the radical reaction, i.e., processing.

[0030] The idea of ​​using the slight acceleration of ions to generate activation energy for radical reactions is unthinkable in conventional low-pressure plasma etching. This is because, in low-pressure plasma etching, the ion acceleration energy is large, several hundred eV, and as shown in Figure 2(b), it physically removes atoms or molecules themselves from the surface of the workpiece. Furthermore, even in the conventional high-pressure processing method using the above-mentioned radical reaction, the ion acceleration energy is significantly smaller, only a few eV, compared to the low-pressure case. Therefore, for processing difficult-to-machine materials, it was usually more effective to increase the energy of the high-frequency power supply that generates the plasma to produce more neutral radicals rather than considering accelerating the ions. The idea of ​​applying a bias voltage to slightly accelerate ions and utilizing that small amount of acceleration energy as activation energy for radical reactions is a concept that the inventors have conceived for the first time.

[0031] In the apparatus of this embodiment, a feed mechanism (not shown) is used to maintain the machining gap G and induce a radical reaction, while the machining process is advanced by relatively displacing the machining electrode 2 and the workpiece 9. In this invention, the amount of machining can be controlled by controlling the bias voltage. Therefore, if the amount of machining for each position on the surface of the workpiece 9 is predetermined and set, the amount of machining can be numerically controlled by controlling the bias voltage without changing the feed rate of the machining electrode 2 or the holder 3.

[0032] In other words, since the processing amount can be controlled by changing only the bias voltage while keeping the plasma state constant, it is possible to set the processing amount to zero by, for example, adding a bias voltage of several tens of volts, allowing for more efficient processing compared to conventional processing methods using high-density radical reactions.

[0033] The reaction gas is not particularly limited and can be selected according to the workpiece, as is the case with conventional high-density radical reaction processing methods. For example, if the workpiece 9 is silicon (Si) or silicon carbide (SiC), SF6 can be suitably used. If the workpiece 9 is gallium nitride (GaN), chlorine gas can be suitably used.

[0034] The processing electrode 2 can also be of various forms and configurations, similar to conventional processing methods using high-density radical reactions. For example, known electrodes of various forms such as wire electrodes, rotating electrodes, nozzle electrodes that eject reaction gas, and narrow blade electrodes can be used. In the processing apparatus 1 shown in Figure 1, the reaction gas supplied to the processing gap between the processing electrode 2 and the workpiece 9 is supplied from the atmosphere inside the chamber. However, in the processing apparatus 1A shown in Figure 8, a nozzle electrode having a flow path 20 that guides the reaction gas into the interior is used as the processing electrode 2.

[0035] The processing gap (gap) is adjusted as appropriate according to the type of gas and ambient pressure, similar to conventional processing methods using high-density radical reactions, to a gap where the plasma is stable, for example, set to about 1-2 mm. In the case of low-pressure dry etching, a gap of several tens of millimeters or more is required to maintain the plasma, but it can be maintained with 1-2 mm. At most, it is 5 mm or less.

[0036] Suitable workpieces 9 include silicon (Si), silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), aluminum nitride (AlN), aluminum oxide (Al2O3), diamond, quartz glass, and crystal. In particular, the processing method of the present invention is effective for wide-bandgap semiconductor materials with high temperature dependence, such as silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), aluminum nitride (AlN), and diamond.

[0037] These wide-bandgap semiconductor materials have high binding energies and are chemically stable, making them difficult to process using conventional high-density radical reaction methods. However, according to the present invention, the processing speed can be dramatically improved simply by accelerating ions by a few eV using a bias voltage, without increasing the power of the high-frequency power, and a distortion-free processed surface can be efficiently achieved. Therefore, these materials are particularly suitable for application of the present invention.

[0038] In this embodiment, the holder 3, which serves as the counter electrode for holding the workpiece 9, has an insulating protective layer 7, such as an yttria thermal spray coating, formed on its surface and is placed on a grounded conductive base 6. The presence of this grounded base 6 ensures that a high electric field is stably formed in the processing gap G between the processing electrode 2 and the workpiece 9, thereby forming and stably maintaining plasma. Note that if the shape of the processing electrode 2 is such that it is a wire electrode or other shape that causes electric field concentration, such a base 6 can be omitted.

[0039] Furthermore, in this embodiment, a high-frequency discharge plasma is formed in the machining gap G through the machining electrode 2 using a high-frequency power supply 4, but a microwave discharge plasma may also be formed by supplying microwave power. The high-frequency discharge in the machining apparatus 1 in this example is a capacitively coupled type (electric field type) that forms a high electric field between the machining electrode 2 and the base 6, but an inductively coupled type (magnetic field type) using a coil (a method in which a magnetic field is induced by supplying a high-frequency current to a coil, thereby forming an electric field) can also be adopted.

[0040] The bias voltage is preferably DC or AC, and the power supply is configured accordingly. The diagram shows an example where a DC bias voltage is applied by a DC power supply. In this example, the bias voltage is applied to the holder 3 (counter electrode) and the processing electrode 2, but it is also possible to omit the counter electrode and apply a high-frequency or DC bias to the processing electrode 2.

[0041] If the workpiece 9 is a conductor or semiconductor, both direct current (DC) and alternating current (AC) are possible. In the case of insulators such as diamond or quartz, with DC, the accelerated ions become charged after reaching the surface, canceling out the bias voltage and making it difficult to achieve the desired effect. In this case, AC is preferable. When applying a high-frequency voltage as the bias voltage, it is set to a frequency that does not interfere with the high-frequency voltage from the high-frequency power supply 4 that generates the plasma.

[0042] The magnitude of the bias voltage is set so that the average energy of the ions (charged particles) accelerated by the bias voltage and drawn into the surface of the workpiece 9 is less than 10 eV. If an energy of 10 eV or more is applied, the plasma is likely to transition to abnormal discharge due to the bias voltage, becoming unstable. Furthermore, there is a risk that sputtering will occur due to high-energy ions accelerated to several hundred eV or more, potentially damaging (distorting) the surface of the workpiece.

[0043] The average energy of the ions mentioned above is the value obtained by multiplying the bias voltage applied over the mean free path distance (which is considerably smaller than the actually applied bias voltage because the mean free path is at most a few μm) by the charge of the ions. Once the ambient gas and reaction gas are determined, the required bias voltage can be calculated in reverse. Specifically, for example, in SiC, it is preferable to adjust the DC bias voltage within the range of -50V to -1000V. If the absolute value is greater than -1000V, as mentioned above, the risk of adversely affecting the plasma state increases, and the risk of sputtering also increases. If the absolute value is less than -50V, there is a risk that energy exceeding the activation energy of the radical reaction cannot be supplied.

[0044] Although embodiments of the present invention have been described above, the present invention is not limited in any way to these embodiments, and can be implemented in various forms without departing from the spirit of the invention. [Examples]

[0045] The following describes the results of processing various materials using the processing apparatus 1 / 1A according to the embodiment of the present invention shown in Figures 1 and 8.

[0046] (Evaluation test of processing characteristics using bias voltage (1)) Silicon (Si) and silicon carbide (SiC (000-1 plane)) were prepared as workpieces 9, and processing was performed on each material using the processing apparatus 1 shown in Figure 1. The results of processing were performed in three patterns: no bias voltage (floating), +255V DC bias voltage applied (processing electrode 2 side is positive), and -255V DC bias voltage applied (processing electrode 2 side is negative), and are shown in Figures 3 and 4, respectively. Figures 3 and 4 show the profile of the processed groove cross-section viewed from the scanning direction, with the vertical axis representing the position in the depth direction and the horizontal axis representing the horizontal position perpendicular to the scanning direction of the workpiece surface. Other processing conditions are as shown in Table 1.

[0047] [Table 1]

[0048] As can be seen from Figures 3 and 4, the processing efficiency of all materials improved when a DC bias voltage of -255V was applied during processing. In particular, when processing silicon carbide (SiC), a difficult-to-process material, as can be seen from Figure 4, processing to a depth of 10 μm or less was almost impossible without applying a DC bias voltage of -255V, but by applying this bias voltage, processing to a depth of nearly 80 μm (approximately 50 μm / min) became possible, showing a significant improvement in processing efficiency.

[0049] The applied bias voltage (-255V) corresponds to approximately 0.2 eV in terms of the average energy of ions in the plasma during this process, which is far from sufficient to cause sputtering. Nevertheless, significant processing progress was observed, indicating that the ions accelerated by the bias voltage provided enough energy to exceed the activation energy, thereby greatly promoting the high-density radical reaction on the workpiece surface.

[0050] (Evaluation test of processing characteristics using bias voltage (2)) Next, silicon carbide (SiC(000-1 plane)) was prepared as the workpiece 9, and processing was performed using the processing apparatus 1 shown in Figure 1. The DC bias voltage was adjusted to -50V / -100V / -150V / -255V (the processing electrode 2 side was negative), and processing was performed three times for each of these four patterns. The results are shown in Figures 5(a) and (b), and Figures 6(a) and (b), respectively. The vertical and horizontal axes are the same as in Figures 3 and 4. This shows the bias voltage dependence characteristics of the processing depth and demonstrates the possibility of numerically controlled processing by bias voltage control.

[0051] Figure 7 is a graph summarizing these results (the value for 0V (approximately 10 μm) is the result for floating in the "Evaluation Test of Processing Characteristics by Bias Voltage (1)" described above). The processing conditions are the same as those in Table 1 of the above-mentioned test (processing time is 100 seconds). As can be seen from the graph in Figure 7, the processing efficiency of silicon carbide (SiC) improves as the bias voltage (absolute value) increases.

[0052] (Evaluation test of processing characteristics under atmospheric gas pressure) Next, silicon carbide (SiC(000-1 plane)) was prepared as the workpiece 9, and processing was performed using the processing apparatus 1A shown in Figure 8. The atmospheric gas pressure was adjusted to 5kPa / 2.5kPa / 1kPa / 0.5kPa, and processing was performed for each of these four patterns with a DC bias voltage of -100V applied (processing electrode 2 side negative), no bias voltage (floating), and a DC bias voltage of +100V applied (processing electrode 2 side positive). The results are shown in Figures 9(a), (b) and 10(a), (b), respectively. This shows the pressure dependence of the processing characteristics under each bias voltage. Other processing conditions are as shown in Table 2. The processing gap was adjusted according to the gas pressure because the gap at which the plasma stabilizes differs depending on the gas pressure. Specifically, the dimensions were set as follows: 2.5 mm at a gas pressure of 0.5 kPa, 1.25 mm at 1 kPa, 0.5 mm at 2.5 kPa, and 0.25 mm at 5 kPa.

[0053] [Table 2]

[0054] Figures 9 and 10 show the cross-sectional profiles of the machined grooves. The vertical axis represents the position in the depth direction, and the horizontal axis represents the horizontal position perpendicular to the transverse direction of the paper on the workpiece surface in Figure 8. "Area" is the cross-sectional area of ​​the portion that disappeared due to machining on the upper part of the machined groove profile in each figure (shown as a negative value because it disappeared). This allows us to determine the amount of machining. "Minimum value" is the deepest machining depth position.

[0055] Figures 11 and 12 are graphs summarizing the results from Figures 9 and 10 (Figures 11(b) "Cross-sectional area ratio" and 12(b) "Processing depth ratio" both show the ratio to the result during floating, i.e., how many times greater the value is during floating).

[0056] The graphs in Figures 11(a) and 12(a) show that when the pressure of the ambient gas (reaction gas) is low, the absolute number of reaction species is small, which reduces the processing speed. Similarly, the graphs in Figures 11(b) and 12(b) show that when the pressure of the ambient gas (reaction gas) is low, the mean free path is large, and the radical reaction acceleration effect of the bias voltage, that is, the effect of improving processing efficiency by applying a bias voltage, becomes more pronounced. [Explanation of symbols]

[0057] 1 Processing equipment 1A processing equipment 2 Processing electrode 3 Holding stand 4 High frequency power supply 5. Bias power supply 6 Base 7. Insulating protective layer 9 Workpiece 20 flow channels G processed gap

Claims

1. A processing method by high-density radical reaction, comprising generating plasma in a gas atmosphere of 0.1 kPa or higher containing a reaction gas, generating neutral radicals based on the reaction gas, and vaporizing and removing volatile substances generated by radical reactions between the neutral radicals and atoms or molecules on the surface of the workpiece, A processing method characterized by providing a bias power supply separate from the power supply for generating the plasma, and using the bias voltage to draw ions in the plasma to the surface of the workpiece, thereby promoting radical reactions on the surface of the workpiece.

2. The processing electrode and the workpiece are placed in the aforementioned gas atmosphere, and the plasma is generated by applying a high-frequency voltage to the processing electrode. The bias power supply applies a DC or AC bias voltage between the machining electrode and the workpiece. The processing method according to claim 1.

3. The average energy of the ions accelerated and drawn in by the bias voltage is less than 10 eV. The processing method according to claim 1.

4. By numerically controlling the bias voltage, the amount of processing due to the radical reaction is controlled. The processing method according to claim 1.

5. A processing apparatus for high-density radical reaction, which generates plasma in a gas atmosphere of 0.1 kPa or higher containing a reaction gas, generates neutral radicals based on the reaction gas, and vaporizes and removes volatile substances generated by radical reactions between the neutral radicals and atoms or molecules on the surface of the workpiece, A processing apparatus characterized by comprising a bias power supply separate from the power supply for generating the plasma, wherein the bias voltage attracts ions in the plasma to the surface of the workpiece, thereby promoting radical reactions on the surface of the workpiece.

6. The processing electrode and the workpiece are placed in the aforementioned gas atmosphere, and the plasma is generated by applying a high-frequency voltage to the processing electrode. The bias power supply applies a DC or AC bias voltage between the machining electrode and the workpiece. The processing apparatus according to claim 5.

7. It is equipped with a holder that holds the workpiece and also serves as the opposing electrode, The high-frequency voltage is applied between the holding base and the processing electrode to generate the plasma, The bias power supply applies the bias voltage between the holder and the machining electrode. The processing apparatus according to claim 6.

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