JP2009004656A - Control method of self-bias voltage of board, and plasma processor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control a self-bias voltage with a simple structure. <P>SOLUTION: In a plasma processing, plasma is formed by an electric field and a magnetic field of microwaves and positive ions are entered onto a board by a plasma potential of the plasma. Further, a leakage current is flown from the board toward the ground through a board support mechanism for supporting the board in the plasma in a state that it is electrically floated, and the self-bias voltage of the board generated by the plasma potential is suppressed by a voltage drop by this leakage current. The control of the self-bias voltage by the voltage drop is carried out by setting a resistance between the board support mechanism and the ground. In setting the resistance, the self-bias voltage of the board is detected and the obtained voltage value is fed back to increase or decrease a magnitude of the resistance so that the self-bias voltage comes to a given value. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a plasma processing apparatus that oxidizes or nitrides a substrate surface with plasma generated by applying a high frequency, and more particularly to self-bias.

  The plasma processing apparatus generates plasma by electron cyclotron resonance (ECR) excitation using the interaction between a microwave electric field and a magnetic field. By irradiating the plasma on the substrate, plasma processing such as thin film formation is performed on the substrate. Since this plasma processing apparatus is excellent in ion directivity and uniformity, it is applied to a thin film forming apparatus and a semiconductor element manufacturing apparatus.

  FIG. 4 is a schematic view showing a configuration example of a conventional plasma processing apparatus. In FIG. 4, the plasma processing apparatus 101 includes a plasma generation chamber 102 and a reaction chamber 103. A microwave introduction hole 104 is provided in the wall of the plasma generation chamber 102. The microwave generated by the high-frequency power source 108 is impedance-matched by the transmitter and the EH tuner 109, guided through the microwave waveguide 110, and through a microwave introduction window (not shown) of the microwave introduction hole 104. It is introduced into the plasma generation chamber 102. A magnetic field coil 105 is provided on the outer periphery of the plasma generation chamber 102.

  The reaction chamber 103 communicates with the plasma generation chamber 102 through an opening for extracting plasma. An exhaust port 106 and a gas introduction port 107 are formed in the reaction chamber 103. The exhaust port 106 is connected to the vacuum exhaust device 113 and evacuates the inside of the reaction chamber 103. The gas inlet 107 has the other end connected to a gas supply source, and introduces a film forming gas or the like into the reaction chamber 103.

  In the plasma processing, the inside of the reaction chamber 103 and the plasma generation chamber 102 is depressurized to a predetermined pressure by the vacuum exhaust device 113, a direct current is supplied to the magnetic field coil 105, and the reaction chamber 103 and the plasma generation chamber 102 are supplied from the gas inlet 107. A deposition gas is introduced, and a 2.45 GHz microwave that is oscillated by a high-frequency power source 108 and impedance-matched by a transmitter and an EH tuner 109 is introduced into the plasma generation chamber 102. The film-forming gas generates a high-density plasma by electron cyclotron resonance by setting the microwave electric field and the magnetic field of the magnetic field coil 105 to 875 gauss, and separates it into positive ions and electrons.

  In the plasma, since the electrons are light, they move at a high speed, get out of the plasma in a short time, collide with the walls, and disappear. On the other hand, positive ions have a large mass and a low speed compared to electrons, and therefore exist in plasma for a long time. Thereby, the plasma becomes a positive charge as a whole and forms an ion sheath. The substrate support mechanism 111 that supports the substrate 112 is attracted by the positive charges of the ion sheath, accumulates negative charges, and generates a negative self-bias voltage. The positive ions in the plasma are transported to the reaction chamber by the divergent magnetic field of the magnetic field coil 105, are accelerated by the negative self-bias voltage, collide with the substrate 112, and accumulate on the substrate 112 to form a film.

  In addition to the above-described configuration for generating plasma by introducing microwaves, a configuration for generating plasma by connecting a high-frequency power source to an electrode (high-frequency input electrode) that supports a substrate is known (Patent Document 1). In the plasma processing apparatus having this configuration, it is shown that by increasing the plasma density, the decomposition of the film forming gas is promoted and the film forming characteristics are improved. At this time, the negative self-bias voltage increases as the plasma density increases. This increase in self-bias increases the incident energy of positive ions on the substrate, which increases the substrate temperature and increases the film stress in the film formation on the substrate, causing the substrate to warp and delaminate. Has been pointed out.

  In Patent Document 1 described above, a high frequency power source is connected to a high frequency input electrode via a coupling capacitor, and a self-bias is reduced by connecting a low pass filter between the high frequency input electrode and the coupling capacitor and the ground. It is also shown that the self-bias is controlled by connecting a variable resistance element in series with this low-pass filter.

  In order to control the self-bias generated on the substrate, a configuration in which the support mechanism of the substrate is set to the ground potential, a configuration in which an RF power source is connected to the substrate and a bias potential is applied by a DC voltage, and a pulse-modulated DC power source is connected to the substrate. A method of applying a bias potential has been proposed.

  For example, in Patent Document 2, a ground electrode is provided, and the negative self-bias voltage induced in the sample electrode is controlled by changing the area of the ground electrode, or installed close to the inner wall surface of the reaction chamber. A configuration for grounding the inner bell jar is shown.

  In Patent Document 3, self-bias is generated by applying a high-frequency RF bias voltage or a pulsed RF bias voltage, and the RF bias voltage, the pulsed RF bias voltage, and the pulse period can be varied. It is disclosed.

JP 2007-96051 A JP-A-10-177996 JP 2001-192825 A

  In the above-described method for reducing the self-bias, the configuration described in Patent Document 1 that controls the self-bias by adjusting the impedance of the power source connected to the high-frequency input electrode of the substrate, Since it does not have a high frequency input electrode or a power source connected to the electrode, there is a problem that it cannot be applied to the configuration to be generated because of the configuration.

  Further, in the configuration in which the self-bias is reduced by setting the portion supporting the substrate to the ground potential, the self-bias becomes “0” and the bias potential of the substrate becomes “0”, and the incident effect of positive ions on the substrate is reduced. There is a problem that the film formation efficiency is reduced.

  Also, in the configuration in which the self-bias is reduced by connecting the RF power source to the substrate and setting the bias potential to the DC voltage Vdc or connecting the pulse-modulated DC power source and applying the bias potential, the self-bias generated by the plasma potential is reduced. Furthermore, since a self-bias is added, there is a problem that it is difficult to suppress the self-bias voltage.

  In recent years, with the advancement of electronic devices, the surface properties of semiconductor substrates and the like tend to greatly affect performance. Under such circumstances, there is an increasing demand for suppressing damage to the substrate surface in processes such as film formation and etching.

  Therefore, in plasma processing, it is required to give energy to ions so as not to damage the substrate and to promote ion incidence on the substrate. It is required to easily control the self-bias voltage so as to give the ions energy satisfying such requirements.

  SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to solve the above-described conventional problems and to control the self-bias voltage with a simple configuration.

  The present invention realizes both the acceleration of ion incidence to the substrate and the reduction of damage to the substrate by setting the substrate support mechanism for supporting the substrate to a predetermined potential. Therefore, a voltage drop caused by a leak current flowing from the substrate to the ground is used. Thereby, the self-bias can be easily controlled.

  The present invention can be configured as an aspect of a control method and an aspect of a plasma processing apparatus to which the control method is applied.

  An embodiment of the control method of the present invention is a substrate self-bias voltage control method, in which plasma is generated by an electric field and a magnetic field of a microwave and positive ions are incident on the substrate by the plasma potential of the plasma. In FIG. 2, a leakage current is caused to flow from the substrate toward the ground through a substrate support mechanism that supports the substrate in an electrically floating state, and a self-bias voltage of the substrate caused by the plasma potential is suppressed by a voltage drop due to the leakage current.

  When no leakage current is passed, a voltage drop due to the leakage current does not occur. Therefore, the self-bias voltage of the substrate remains the self-bias voltage generated by the plasma potential, and the self-bias voltage is not suppressed. On the other hand, when a leak current is passed, a voltage drop occurs due to the leak current, and the voltage corresponding to this voltage drop is set as the self-bias voltage of the substrate and is suppressed to a voltage lower than the self-bias voltage generated by the plasma potential. The

  By controlling the voltage drop due to this leakage current, the degree of suppression of the self-bias voltage can be controlled. For example, when the voltage drop is set large, the suppression amount of the self-bias voltage is small, so that the decrease from the self-bias voltage caused by the plasma potential is set small. In addition, when the voltage drop is set small, the suppression of the self-bias voltage increases, so that the decrease from the self-bias voltage generated by the plasma potential can be set large.

  Control of the self-bias voltage by voltage drop can be performed by setting a resistance between the substrate support mechanism and the ground. When a leak current flows from the substrate toward the ground, a voltage drop occurs in this resistor, and a self-bias voltage corresponding to this voltage drop is set in the substrate support mechanism. Since this voltage drop is represented by the product of the leakage current and the resistance value, the self-bias voltage can be controlled by determining the size of the resistance.

  This resistance can be realized by connecting a resistance element. As the resistance element, a fixed resistance element having a predetermined resistance value or a variable resistance element having a variable resistance value can be used. When a fixed resistance element is used, the voltage value of the self-bias voltage is set according to the resistance value. On the other hand, when a variable resistance element is used, the voltage value of the self-bias voltage can be changed according to the change of the resistance value.

  When this variable resistance element is used, the resistance value is set by detecting the self-bias voltage of the substrate and feeding back the voltage value obtained by this detection so that the self-bias voltage becomes a predetermined value. By increasing or decreasing, the self-bias voltage can be automatically set to a predetermined voltage value.

  The substrate self-bias voltage control method described above can be applied to plasma processing performed in the reactive sputtering film forming process of the ECR sputtering apparatus.

  In the plasma processing apparatus of the present invention, a high-frequency power source that oscillates microwaves, a plasma chamber that introduces the microwaves and generates plasma by the electric field and magnetic field of the microwaves, and plasma generated on the substrate by the generated plasmas A reaction chamber in which processing is performed, a substrate support mechanism for supporting the substrate in an electrically floating state in the reaction chamber, and a self-bias controller for controlling the self-bias voltage of the substrate are provided.

  The self-bias control unit according to the present invention suppresses the self-bias voltage of the substrate due to the plasma potential by a voltage drop caused by a leak current in which charges accumulated on the substrate due to the plasma potential flow toward the ground through the substrate support mechanism.

  The self-bias control unit controls a voltage drop due to a leakage current. Since the voltage drop is determined by the product of the current value flowing through the resistance element and the resistance value of the resistance element, the leakage current circuit is connected by connecting the substrate support mechanism and the ground (ground point) via the resistance element. The voltage drop is controlled by forming and determining the resistance value of the resistance element, thereby controlling the self-bias voltage.

  In one form of the plasma processing apparatus, the self-bias control unit connects a fixed resistance element between the substrate support mechanism and the ground, determines a voltage drop based on a resistance value of the fixed resistance element, and determines a self-bias voltage of the substrate. .

  In another form of the plasma processing apparatus, the self-bias control unit connects the variable resistance element between the substrate support mechanism and the ground, and also detects the self-bias voltage detection unit and the resistance of the variable resistance element. A variable resistance setting unit for setting a value. The variable resistance setting unit sets the resistance value of the variable resistance element using the self-bias voltage detected by the self-bias voltage detection unit, and thereby controls the self-bias voltage value to a predetermined voltage value.

  According to the aspect of the substrate self-bias voltage control method of the present invention and the aspect of the plasma processing apparatus to which the substrate self-bias voltage control method is applied, the self-bias voltage of the substrate is controlled by the charge accumulated in the substrate. The voltage drop due to this leakage current can be realized simply by providing a resistor between the substrate support mechanism and the ground, and the voltage drop can be achieved. The size of can be easily controlled by determining the size of the resistance.

  Furthermore, the resistance element is a variable resistance element, and the resistance value of the variable resistance element can be automatically set by feeding back the self-bias voltage value detected by the variable resistance setting unit.

  Further, according to the aspect of the present invention, it is possible to suppress damage to the substrate by suppressing the self-bias voltage.

  Further, according to the aspect of the present invention, the self-bias control unit that suppresses the self-bias voltage is provided on the atmosphere side, and the self-bias of the substrate in the vacuum can be controlled on the atmosphere side.

  According to the aspect of the present invention, the self-bias voltage can be suppressed with a simple configuration, and the cost can be reduced.

  Moreover, according to the aspect of this invention, it can apply not only to ECR sputtering but to various plasma processes.

  According to the present invention, the self-bias voltage can be controlled with a simple configuration.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  1 and 2 are schematic views for explaining a configuration example of a plasma processing apparatus of the present invention.

  1 and 2, the plasma processing apparatus 1 is substantially the same as the configuration shown in FIG. 4 except for the configuration of the self-bias control unit 20 (20A shown in FIG. 1 and 20B shown in FIG. 2). FIG. 1 shows a configuration example using a fixed resistance element as the resistance element, and FIG. 2 shows a configuration example using a variable resistance element as the resistance element.

  1 and 2, the plasma processing apparatus 1 of the present invention includes a plasma generation chamber 2 and a reaction chamber 3. A microwave introduction hole 4 is provided in the wall of the plasma generation chamber 2. The microwave generated by the high-frequency power supply 8 is impedance-matched by an oscillator and an EH tuner 9, guided through the microwave waveguide 10, and plasma through a microwave introduction window (not shown) of the microwave introduction hole 4. It is introduced into the generation chamber 2. A magnetic field coil 5 is provided on the outer periphery of the plasma generation chamber 2.

  The reaction chamber 3 communicates with the plasma generation chamber 2 through an opening for extracting plasma. An exhaust port 6 and a gas introduction port 7 are formed in the reaction chamber 3. The exhaust port 6 is connected to the vacuum exhaust device 13 and evacuates the inside of the reaction chamber 3. The other end of the gas inlet 7 is connected to a gas supply source, and a film forming gas or the like is introduced into the reaction chamber 3.

  In the plasma processing, the inside of the reaction chamber 3 and the plasma generation chamber 2 is depressurized to a predetermined pressure by the vacuum exhaust device 13, a direct current is supplied to the magnetic field coil 5, and the reaction chamber 3 and the plasma generation chamber 2 are supplied from the gas inlet 7. A film forming gas is introduced, and a 2.45 GHz microwave oscillated by a high-frequency power source 8 and impedance-matched by an oscillator and an EH tuner 9 is introduced into the plasma generation chamber 2. The film-forming gas generates high-density plasma by electron cyclotron resonance by setting the microwave electric field and the magnetic field of the magnetic field coil 5 to 875 gauss, and separates them into positive ions and electrons.

  In the plasma, since the electrons are light, they move at a high speed, get out of the plasma in a short time, collide with the walls, and disappear. On the other hand, positive ions have a large mass and a low speed compared to electrons, and therefore exist in plasma for a long time. Thereby, the plasma becomes a positive charge as a whole and forms an ion sheath. The substrate support mechanism 11 that supports the substrate 12 is attracted by the positive charges of the ion sheath, accumulates negative charges, and generates a negative self-bias voltage. The positive ions in the plasma are transported to the reaction chamber by the divergent magnetic field of the magnetic field coil 5 and then accelerated by this negative self-bias voltage to collide with the substrate 12 and accumulate on the substrate 12 to form a film.

  The plasma processing apparatus 1 of the present invention includes a self-bias control unit 20 between the substrate support mechanism 11 and ground (ground). The self-bias control unit 20 forms a circuit that allows a leak current to flow between the substrate support mechanism 11 and ground (ground), and controls the self-bias voltage of the substrate 12 by a voltage drop caused by the leak current. .

  The self-bias control unit 20A shown in FIG. 1 is configured to connect a fixed resistance element 21 between the substrate support mechanism 11 and ground (ground). Here, when the leakage current is represented by Ileak and the resistance value of the fixed resistance element 21 is represented by Rfix, the voltage drop generated in the fixed resistance element 21 can be represented by “Rfix · Ileak”. Due to this voltage drop, the potential of the substrate support mechanism 11 becomes “Rfix · Ileak” with respect to the ground. The self-bias voltage of the substrate 12 can be expressed by the potential “Rfix · Ileak” with respect to the ground of the substrate support mechanism 11. Therefore, the self-bias voltage of the substrate 12 can be set by determining the resistance value Rfix of the fixed resistance element 21.

  When the resistance element of the self-bias control unit 20 is configured by a fixed resistance element, the self-bias voltage of the substrate 12 depends on the leak current Ileak in addition to the resistance value Rfix of the fixed resistance element 21, so that the leak current When Ileak fluctuates, the self-bias voltage also fluctuates.

  Thus, by making the resistance value of the resistance element of the self-bias control unit 20 variable, fluctuations in the self-bias voltage can be suppressed. The self-bias control unit 20B shown in FIG. 2 is configured to connect the variable resistance element 22 between the substrate support mechanism 11 and ground (ground). The self-bias control unit 20B includes a variable resistance element 22 that connects between the substrate support mechanism 11 and ground (earth), and a self-bias voltage detection unit 23 that detects the voltage of the substrate support mechanism 11 and detects the self-bias voltage. And a variable resistance setting unit 24 that sets the resistance value of the variable resistance element 22 based on the self-bias voltage value detected by the self-bias voltage detection unit 23. The self-bias control unit 20B maintains the self-bias voltage of the substrate 12 at a predetermined voltage by feeding back the self-bias voltage value detected by the self-bias voltage detection unit 23 to the variable resistance element 22 via the variable resistance setting unit 24. To do.

  Here, when the leakage current is represented by Ileak, the resistance value of the variable resistance element 22 is represented by Rvariable, the self-bias voltage detected by the self-bias voltage detection unit 23 is represented by Vbias, and the target self-bias voltage is represented by Vpreset. The voltage drop caused by the above can be expressed by “Rvariable · Ileak”, and the voltage detection unit 23 detects this voltage as the self-bias voltage Vbias.

  The variable resistance setting unit 24 compares the self-bias voltage Vbias (= voltage drop “Rvariable · Ileak”) obtained by detecting the target self-bias voltage with Vpreset, and the variable resistance element so that the difference decreases. The resistance value Rvariable of 22 is changed.

  By this feedback control, the self-bias voltage Vbias is set to the target self-bias voltage. Therefore, the self-bias voltage of the substrate 12 can be set by determining the resistance value Rvariable of the variable resistance element 22.

  FIG. 3 is a diagram for explaining the effect of suppressing the self-bias during ECR (electron cyclotron resonance) plasma processing, and shows the relationship between the resistance value (kΩ) and the self-bias voltage (−V). In FIG. 3, the microwave power is 500 W, the flow rate of N 2 (nitrogen) gas used for sputtering is 20 sccm, and the pressure is 0.2 Pa (diamond symbol in FIG. 3) and 0.3 Pa (rectangular symbol in FIG. 3), respectively. , 0.4 Pa (triangular symbols in FIG. 3).

  When the substrate is not grounded by the self-bias control unit 20 and is in a floating state, the self-bias voltages are −9.5 V (pressure 0.2 Pa), −5.5 V (pressure 0.3 Pa) −4 .4V (pressure 0.4 Pa).

  When the effect of suppressing the self-bias voltage by the self-bias control unit 20 is examined from the result of FIG. 3, for example, when the pressure is 0.2 Pa, the substrate is −9.5 V when the substrate is in a floating state. When the resistance value of the resistance element is 10 kΩ, it is about −7.5 V, and the effect of suppressing the self-bias voltage by about 2 V is confirmed. Further, when the pressure is 0.3 Pa and 0.4 Pa, the effect of suppressing the self-bias voltage to about −4.4V and −3.3V, respectively, is confirmed.

  The present invention is not limited to the ECR sputtering of the present invention and can be applied to various plasma processes.

It is the schematic for demonstrating the structural example of the plasma processing apparatus of this invention. It is the schematic for demonstrating the structural example of the plasma processing apparatus of this invention. It is a figure for demonstrating the suppression effect of the self-bias at the time of ECR plasma processing. It is the schematic which shows one structural example of the conventional plasma processing apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Plasma processing apparatus, 2 ... Plasma chamber, 3 ... Reaction chamber, 4 ... Microwave introduction hole, 5 ... Magnetic field coil, 6 ... Exhaust port, 7 ... Gas introduction port, 8 ... High frequency power supply, 9 ... Transmitter and EH Tuner, 10 ... Waveguide, 11 ... Substrate support mechanism, 12 ... Substrate, 13 ... Vacuum exhaust device, 20, 20A, 20B ... Self-bias control unit, 21 ... Fixed resistor, 22 ... Variable resistor, 23 ... Voltage detector 24 ... Variable resistance setting unit, 101 ... Plasma processing apparatus, 102 ... Plasma generation chamber, 103 ... Reaction chamber, 104 ... Microwave introduction hole, 105 ... Magnetic field coil, 106 ... Exhaust port, 107 ... Gas introduction port, 108 ... High-frequency power source, 109... Transmitter and EH tuner, 110... Waveguide, 111 .. substrate support mechanism, 112.

Claims (7)

In plasma processing, in which plasma is generated by an electric field and a magnetic field of microwaves, and positive ions are incident on the substrate by the plasma potential of the plasma,
A leakage current flows from the substrate to the ground through a substrate support mechanism that supports the substrate in an electrically floating state in the plasma, and a self-bias voltage of the substrate generated by the plasma potential is suppressed by a voltage drop due to the leakage current. A method for controlling a substrate self-bias voltage.   2. The method of controlling a substrate self-bias voltage according to claim 1, wherein the self-bias voltage is controlled by setting a resistance between the substrate support mechanism and ground. The resistance setting is
3. The self-bias voltage of the substrate is detected, the voltage value obtained by the detection is fed back, and the magnitude of the resistor is increased or decreased so that the self-bias voltage becomes a predetermined value. 4. A method for controlling a substrate self-bias voltage according to 1.   4. The substrate self-bias voltage control method according to claim 1, wherein the plasma treatment is performed in a reactive sputtering film forming step of an ECR sputtering apparatus. 5. Control method. A high-frequency power source that oscillates microwaves;
A plasma chamber that introduces the microwave and generates plasma by an electric field and a magnetic field of the microwave;
A reaction chamber in which a plasma treatment is performed on the substrate by the generated plasma;
A substrate support mechanism for supporting the substrate in an electrically floating state in the reaction chamber;
A self-bias controller for controlling the self-bias voltage of the substrate,
The self-bias control unit suppresses the self-bias voltage of the substrate due to the plasma potential due to a voltage drop caused by a leakage current in which charge accumulated on the substrate due to the plasma potential flows toward the ground through the substrate support mechanism. A plasma processing apparatus. The self-bias controller is
The fixed resistance element connected between the said board | substrate support mechanism and earth | ground is provided, The said voltage drop is defined by the resistance value of the said fixed resistance element, The self-bias voltage of a board | substrate is defined. Plasma processing equipment. The self-bias controller is
A variable resistance element connected between the substrate support mechanism and ground;
A self-bias voltage detector for detecting the self-bias voltage;
A variable resistance setting unit that sets a resistance value of the variable resistance element;
The variable resistance setting unit sets a resistance value of the variable resistance element using a self-bias voltage detected by a self-bias voltage detection unit, and controls the self-bias voltage value to a predetermined voltage value. Item 6. The plasma processing apparatus according to Item 5.

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