Plasma regulation and control device based on quadrangular wire magnetic field unit

Abstract

The invention discloses a plasma regulation and control device and method based on a quadrangular wire magnetic field unit. The device comprises symmetrical discharge chambers, a radio frequency electrode, a grounding electrode, a single-frequency radio frequency power supply, a magnetic field generation unit composed of four parallel wires and a double-constant-current-source control unit. Parallel wires are arranged at four corners of a geometrically symmetrical single-frequency capacitive coupling plasma discharge chamber, and currents in the same direction but different in magnitude are introduced to generate a linear gradient static magnetic field parallel to a polar plate; the gradient of the magnetic field is changed by independently adjusting the current on the two sides of the electrode, and the generated magnetic asymmetry effect is utilized to enable the system to form direct-current self-bias voltage in a self-consistent manner, so that the ion bombardment energy is regulated and controlled independent of the ion flux. According to the invention, flexible and accurate regulation and control of ion energy can be realized without a dual-frequency power supply or changing a geometric structure, and the problems of high cost and poor flexibility of a traditional method are solved.

Description

Technical Field

[0001] This invention relates to the technical field of plasma material processing, and in particular to a plasma control device based on a four-corner wire magnetic field unit. Background Technology

[0002] Capacitively coupled plasma (CCP) sources are widely used in microelectronics processes such as thin film deposition, etching, and surface treatment due to their advantages of simple structure, low cost, and convenient control. Traditional CCP sources face the problem of low plasma density. To address this, the industry has developed magnetically enhanced CCP sources. By applying a uniform magnetic field parallel to the electrodes outside the discharge chamber, electron movement is constrained, reducing their loss at the electrodes and thus increasing the plasma density.

[0003] However, in fine processes such as etching, not only is high-density plasma required, but also independent and precise control of the ion energy bombarding the material surface. Currently, the main methods for achieving ion energy modulation include geometric asymmetry and electrical asymmetry. Geometric asymmetry generates a self-bias voltage by changing the area difference between the two electrodes, but the device structure is fixed and the control is inflexible. Electrical asymmetry (EAE) generates a self-bias voltage by driving a dual-frequency power supply and adjusting its phase difference. Although it can independently control ion energy, it places high demands on the power supply system, increasing the system's complexity and cost.

[0004] Furthermore, existing research on magnetically enhanced CCPs often suffers from problems such as complex structures, low integration with the plasma chamber, and difficulty in accurately matching the gradient field morphology to the CCP parallel electrode structure. Although some academic studies have verified through simulations that non-uniform magnetic fields can induce MAE, such research remains at the theoretical simulation level and has not provided a dedicated magnetic field generation device that can be practically integrated into industrial reactors. Therefore, there is an urgent need in this field for a novel dedicated device that is compact, easy to control, and can efficiently generate the required linear gradient magnetic field between parallel electrodes. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a plasma control device based on a quadrangular wire magnetic field unit. This device eliminates the need for a complex dual-frequency power supply or alterations to the device's geometry. By actively applying and adjusting a non-uniform static magnetic field (i.e., a magnetic field gradient) parallel to the electrodes, significant MAE can be generated in a symmetrical CCP discharge, thereby self-consistently generating a DC self-bias voltage and ultimately achieving independent and flexible control of ion bombardment energy. To achieve the above-mentioned objectives and other advantages of the present invention, a plasma control device based on a quadrangular wire magnetic field unit is provided, comprising: A method for controlling the asymmetry of capacitively coupled plasma using a magnetic field gradient includes the following steps: In a capacitively coupled plasma discharge device with a symmetrical geometric structure and driven by a single-frequency radio frequency power supply, a non-uniform static magnetic field parallel to the electrodes is applied in its discharge cavity. The non-uniform static magnetic field is generated by four parallel wires arranged at the four corners of the discharge cavity carrying currents in the same direction. The currents in the two wires on the radio frequency electrode side are equal in magnitude, and the currents in the two wires on the ground electrode side are equal in magnitude, but the currents on both sides are different, thereby forming a controllable magnetic field gradient between the two electrodes; The magnetic field gradient is adjusted by independently adjusting the current magnitudes on the radio frequency electrode side and the ground electrode side, thereby controlling the discharge to generate a DC self-bias voltage self-consistently; By changing the magnitude of the self-bias voltage, the ion bombardment energy reaching the electrode surface is controlled independently of the ion flux.

[0006] An apparatus for implementing the above method includes: a geometrically symmetrical plasma discharge chamber; a radio frequency electrode and a ground electrode disposed opposite each other within the chamber, the radio frequency electrode being connected to a single-frequency radio frequency power supply, and the ground electrode being grounded; a magnetic field generating unit consisting of four parallel straight wires perpendicular to the plane containing the radio frequency electrode and the ground electrode, respectively arranged at the four corners of the projection of the plane; the four wires are configured to carry currents in the same direction, and the magnetic field generating unit is configured such that the current magnitudes of the two wires located on the radio frequency electrode side are equal, and the current magnitudes of the two wires located on the ground electrode side are equal, thereby generating a linear gradient static magnetic field parallel to the electrode plate surface in the discharge region between the radio frequency electrode and the ground electrode; and a control unit connected to the magnetic field generating unit for changing the intensity of the gradient static magnetic field by independently adjusting the current magnitudes flowing to the wires on the radio frequency electrode side and the ground electrode side.

[0007] Compared with the prior art, the advantages and positive effects of the present invention are: Compact structure and easy integration: The four-corner conductor magnetic field unit has a simple structure that can tightly surround or embed in the discharge chamber. It is compatible with existing CCP devices and requires no complex mechanical modifications.

[0008] Precise and simplified control: By controlling only two current sources independently (corresponding to two wires on the same side), linear and precise control of the magnitude and direction of the magnetic field gradient can be achieved, greatly simplifying the control system.

[0009] Excellent performance: This specific structure can generate a highly linear gradient magnetic field between the two electrodes, which perfectly matches the geometry of the CCP, making the MAE control more efficient and the ion energy modulation range wider.

[0010] This invention achieves precise and linear control of the magnetic field gradient through a specific four-corner wire magnetic field unit. The device is compact, easy to integrate, and compatible with existing CCP production lines, overcoming the problems of complex structure and inaccurate control in traditional magnetic field generation methods. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the plasma control device based on a four-corner wire magnetic field unit according to the present invention; Figure 2 This is a schematic diagram of the three-dimensional spatial layout of the subtraction module of the plasma control device based on the four-corner wire magnetic field unit according to the present invention.

[0012] In the figure: 1. Plasma discharge chamber; 2. Radio frequency electrode; 3. Ground electrode; 4. Single-frequency radio frequency power supply; 5. Magnetic field generation unit; 6. Control unit; 7. Gas inlet; 8. Gas outlet; 9. Substrate. Detailed implementation method The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0013] In a symmetrical CCP discharge, a non-uniform static magnetic field, or magnetic field gradient, is actively created parallel to the electrode direction by a magnetic field generating unit (5) with specific four-corner wires. This gradient disrupts the symmetry of the system, causing the ion flux reaching the RF electrode 2 and the ground electrode 3 to be non-conserved within one RF cycle. To maintain charge balance, the system self-consistently generates a DC self-bias on one side of the RF electrode 2. This self-bias is directly superimposed on the sheath voltage, thereby determining the ion energy bombarding the substrate 9 placed on the ground electrode 3. By adjusting the magnetic field generating unit 5 through the control unit 6, the magnetic field gradient can be changed, thereby continuously controlling the self-bias and ion energy.

[0014] Reference Figure 1 A plasma control device based on a four-corner wire magnetic field unit, comprising: A plasma discharge chamber 1 is provided, in which a radio frequency electrode 2 and a ground electrode 3 are fixedly connected. The radio frequency electrode 2 and the ground electrode 3 are spaced apart and arranged in parallel. The radio frequency electrode 2 is connected to a single-frequency radio frequency power supply 4, and the ground electrode 3 is grounded. A magnetic field generating unit 5 includes a first wire, a second wire, a third wire, and a fourth wire, which are located at the four corners of the plasma discharge chamber 1. The first, second, third, and fourth wires are perpendicular to the plane containing the radio frequency electrode 2 and the ground electrode 3, and are respectively arranged at the four corners of the projection of this plane. The first, second, third, and fourth wires are spaced apart and arranged parallel to each other. The first, second, third, and fourth wires are carried by currents in the same direction. The control method is as follows: the two wires located on one side of the radio frequency electrode 2 are driven by a first controllable constant current source, ensuring that their current magnitudes are equal, both I2; the two wires located on one side of the ground electrode 3 are driven by a second controllable constant current source, ensuring that their current magnitudes are equal, both I1. By independently setting the magnitudes of I1 and I2 (I1 ≠ I2) through the control unit 6, a linear gradient static magnetic field with controllable intensity, parallel to the electrode plates and exhibiting linear variation between the two electrodes, can be generated in the plasma discharge region between the radio frequency electrode and the ground electrode. When the gradient direction needs to be changed, the current values ​​of I1 and I2 can be exchanged through the control unit 6. This embodiment has an extremely compact structure, and the wires can be directly embedded in the non-magnetic chamber wall or installed close to its outer wall, making it easy to integrate with existing CCP production lines. Precise and flexible ion energy regulation can be achieved through simple dual current source control, resulting in low cost and significant benefits. As an equivalent alternative to the above embodiment, each conductor in the magnetic field generating unit 5 can also be composed of multiple parallel-connected conductive wire bundles to obtain a stronger magnetic field strength when subjected to higher currents.

[0015] Example 1: Reference Figure 1 and Figure 2 The structure consists of a discharge chamber 1 containing two identical electrodes, RF electrode 2 and ground electrode 3, placed parallel to each other. The electrode spacing is adjustable, for example, 20-100mm. RF electrode 2 is connected to a single-frequency RF power supply 4 with a frequency of 13.56MHz. Ground electrode 3 is grounded, and a substrate 9 for supporting the silicon wafer sample is placed above it. The side wall of chamber 1 has an inlet 7 and an outlet 8 for introducing process gases, such as Ar. The magnetic field generating unit 5 is implemented using four parallel wires arranged at the four corners of the chamber, namely the first wire, the second wire, the third wire, and the fourth wire. The connection and control methods are described in [reference needed]. Figure 1As described above. During operation, Ar gas is introduced into chamber 1 through inlet 7, and the working pressure is maintained within the low-pressure discharge range, for example, in the tens of mTorr range. The RF power supply 4 is activated, with the voltage set to a typical RF discharge operating value, generating argon plasma. Subsequently, the output currents I1 and I2 of the first and second constant current sources are independently set via control unit 6, with I1 ≠ I2, forming a linear magnetic field gradient within the chamber. For example, the magnetic field strength on the RF electrode side is 10 G, and on the ground electrode side it is 100 G. Under the influence of this gradient magnetic field, MAE is generated, and the system self-bias itself on the RF electrode 2. This self-bias significantly increases the average energy of ions bombarding the silicon wafer on the ground electrode 3. If the current values ​​of I1 and I2 are exchanged via control unit 6, changing the direction of the magnetic field gradient, the polarity of the self-bias will also change accordingly.

[0016] Example 2: Refer to Figure 1 Based on Example 1, this study investigates the influence of the magnetic field gradient on the structure. By independently adjusting the output currents of the first and second constant current sources using a control unit, the magnetic field strength on one side is kept constant, while the magnetic field gradient on the other side changes with the current adjustment. For example, if the magnetic field strength BG at the fixed ground electrode 3 is kept constant at 100 G, the magnetic field strength BP at the radio frequency electrode 2 is increased from 0 G to 100 G. At this time, the magnetic field gradient between the two electrodes decreases from its maximum value to zero. The results show that the absolute value of the self-bias voltage decreases as BP increases, and when the magnetic field gradient is at its maximum (0-100 G), the self-bias voltage reaches its maximum value of approximately -50 V. Correspondingly, the ion energy bombarding the silicon wafer also changes.

[0017] Example 3: Reference Figure 1 Based on Example 1, the influence of gas pressure was studied. By fixing the output current of the constant current source (i.e., fixing I1 and I2), the magnetic field gradient was fixed at 10⁻⁵⁰ G, and the electrode gap was 30 mm. During operation, Ar gas was introduced into chamber 1 through inlet 7. The gas pressure in the discharge chamber was controlled by adjusting the inlet, ultimately maintaining a certain working pressure. The pressure was continuously adjusted to gradually increase from the low-pressure range to the medium-pressure range. The results showed that the absolute value of the self-bias voltage decreased with increasing gas pressure. This is because at high pressure, the collision frequency between electrons and neutral gas increases, weakening the effect of the magnetic field confining electrons, thus reducing the MAE (Magnetic Field Entrainment). When the gas pressure is high, the collision frequency between electrons and neutral particles increases, weakening the magnetic field's confinement effect on electrons, significantly reducing the MAE, and the self-bias voltage tends to zero. This indicates that the method described in this invention is particularly effective under low-pressure conditions.

[0018] This invention is also applicable to multi-frequency capacitively coupled plasma systems, radio frequency pulse source systems, or other parallel-plate plasma discharge systems. Any method that introduces a controllable gradient magnetic field between the plates to regulate the self-bias voltage falls within the scope of protection of this invention.

[0019] The number of devices and processing scale described herein are for simplification of the invention. Applications, modifications, and variations of this invention will be readily apparent to those skilled in the art. Although embodiments of the invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. It can be applied to various fields suitable for this invention, and further modifications can be readily implemented by those skilled in the art. Therefore, without departing from the general concept defined by the claims and their equivalents, this invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A plasma control device based on a four-corner wire magnetic field unit, characterized in that, include: A plasma discharge chamber (1) is provided with a radio frequency electrode (2) and a ground electrode (3) fixedly connected inside the plasma discharge chamber (1). The radio frequency electrode (2) and the ground electrode (3) are spaced apart and arranged in parallel. The radio frequency electrode (2) is connected to a single-frequency radio frequency power supply (4). The ground electrode (3) is grounded. The magnetic field generating unit (5) includes at least a first wire, a second wire, a third wire and a fourth wire, which are located at the four corners of the plasma discharge chamber (1). Control unit (6), which is signal connected to magnetic field generating unit (5), is used to independently adjust the current flowing to the wires on the radio frequency electrode (2) side and the ground electrode (3) side to change the intensity of gradient static magnetic field.

2. The plasma control device based on a four-corner wire magnetic field unit as described in claim 1, characterized in that, The first, second, third and fourth wires are all arranged parallel to the radio frequency electrode (2) and the ground electrode (3) on the horizontal plane.

3. The plasma control device based on a four-corner wire magnetic field unit as described in claim 1, characterized in that, The first, second, third, and fourth conductors are all carried by current in the same direction.

4. The plasma control device based on a four-corner wire magnetic field unit as described in claim 3, characterized in that, The current magnitudes of the first and second conductors near the radio frequency electrode (2) are equal; the current magnitudes of the third and fourth conductors near the ground electrode (3) are equal.

5. A plasma control device based on a four-corner wire magnetic field unit as described in claim 1, characterized in that, The magnetic field gradient can be adjusted by adjusting the current of the first and second wires on one side of the fixed radio frequency electrode (2) and the current of the third and fourth wires on one side of the grounding electrode (3), or by adjusting the current of the third and fourth wires on one side of the fixed grounding electrode (3) and the current of the first and second wires on one side of the radio frequency electrode (2).

6. A plasma control device based on a four-corner wire magnetic field unit as described in claim 5, characterized in that, By altering the magnitudes of the currents located on the radio frequency electrode (2) side and the ground electrode (3) side, the direction of the magnetic field gradient is changed, thereby changing the positive and negative polarities of the self-bias voltage.

7. A plasma control device based on a four-corner wire magnetic field unit as described in claim 1, characterized in that, The first, second, third, and fourth conductors are all made of a single conductor or are made of multiple insulated sub-conductors bundled together in parallel, so as to carry a larger current and generate a stronger magnetic field by increasing the total cross-sectional area.

8. A plasma control device based on a four-corner wire magnetic field unit as described in claim 1, characterized in that, The control unit (6) includes a first controllable constant current source and a second controllable constant current source. The first controllable constant current source simultaneously supplies power to the first wire and the second wire located on the side of the radio frequency electrode (2). The second controllable constant current source simultaneously supplies power to the third wire and the fourth wire located on the side of the ground electrode (3).

9. A plasma control device based on a four-corner wire magnetic field unit as described in claim 1, characterized in that, The plasma discharge chamber (1) is provided with an air inlet (7) and an air outlet (8). The air inlet (7) is connected to a gas source and a flow control device, and the air outlet (8) is connected to a vacuum pump system.

10. A plasma control device based on a four-corner wire magnetic field unit as described in claim 1, characterized in that, A substrate (9) for carrying the sample is placed on the ground electrode (3).

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