JP3599670B2 - Plasma processing method and apparatus - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a plasma processing method and apparatus, and more particularly to a plasma processing method and apparatus suitable for performing a surface treatment of a material to be processed such as a semiconductor using plasma.
[0002]
[Prior art]
In the case of a plasma processing apparatus that performs an etching process, the process gas is efficiently ionized and activated to increase the speed of the process, and a high-frequency bias power is supplied to the material to be processed so that ions in the plasma are applied to the material to be processed. By making the light incident perpendicularly, the anisotropy is improved and a highly accurate etching process is realized. As a plasma processing apparatus for performing such processing, for example, an etching apparatus in a magnetic field UHF band described in Japanese Patent Application Laid-Open No. 9-321031 is known.
[0003]
The magnetic field UHF band etching apparatus arranges a circular conductor plate at a position facing a sample to be processed in a vacuum vessel, supplies a UHF band electromagnetic wave to the circular conductor plate, and forms a magnetic field in the vacuum vessel to produce an ECR. Plasma is generated, an electric field having a frequency different from that of the UHF band is superimposed on the circular conductor plate, the bias applied to the circular conductor plate is increased, and the reactivity between the circular conductor plate and the reaction gas is increased, thereby contributing to the etching reaction. A large amount of active species is generated, and a bias voltage is applied to a sample stage on which the sample to be processed is placed, and the sample to be processed is plasma-processed. The apparatus includes a high-frequency power source applied to the sample stage, a UHF-band high-frequency power source applied to a circular conductor plate facing the sample stage, and a high-frequency power source different from the UHF-band high-frequency power source applied to the same circular conductor plate. Can be controlled independently.
[0004]
Further, in such a magnetic field plasma processing apparatus, “Charging Damage in Semiconductor Process” published by Realize Inc., 1996, edited by Moritaka Nakamura, P.S. 9 to 28, it has been known that the plasma impedance in the direction perpendicular to the magnetic field becomes larger than the plasma impedance in the direction parallel to the magnetic field, and that a potential distribution may be formed in the surface of the material to be processed. .
[0005]
[Problems to be solved by the invention]
As the degree of integration of a semiconductor integrated circuit is increasing, for example, a MOS (Metal Oxide Semiconductor) transistor, which is a typical example of a semiconductor element, is becoming thinner. The problem of dielectric breakdown (charging damage) of the gate oxide film is becoming more serious. In the above-described plasma processing apparatus in the related art, an electric field due to the high-frequency power applied to the material to be processed is formed between the sample stage and the side of the vacuum vessel at the ground potential, and the high-frequency power propagates in a direction crossing the magnetic field. For this reason, a potential distribution is formed in the surface of the material to be processed, and there is a possibility that charging damage that deteriorates the withstand voltage of the gate oxide film may occur.
[0006]
An object of the present invention is to provide a plasma processing method and apparatus capable of suppressing charging damage, increasing the yield of semiconductor devices, and performing highly accurate surface processing.
[0007]
[Means for Solving the Problems]
The object is to provide a processing chamber to which a vacuum exhaust device is connected and which can depressurize the inside, a gas supply device for supplying gas into the processing chamber, a substrate electrode provided in the processing chamber and capable of mounting a material to be processed, and a processing chamber. A first high-frequency power supply for radiating an electromagnetic wave for converting a gas supplied to the substrate into plasma into the processing chamber, and a second high-frequency power supply connected to the substrate electrode and applying a substrate bias voltage to the material to be processed, An auxiliary electrode that generates a positive peak voltage higher than the positive peak voltage of the high frequency voltage applied to the workpiece is provided on the outer peripheral portion of the material to be processed, and the processing gas is supplied and the inside is reduced to a predetermined pressure. Plasma is generated in the evacuated processing chamber, and a bias voltage is applied to the substrate electrode provided in the processing chamber to control the incident energy of ions in the plasma to the material to be processed independently of plasma generation. , When processing the processed material, the plasma potential of the substrate electrode peripheral portion by a method of processing to be higher than the plasma potential on the workpiece is achieved.
[0008]
That is, by increasing the plasma potential at the outer peripheral portion of the electrode, the plasma potential is formed on the inner wall surface of the vacuum chamber forming the processing chamber from the inner surface of the processing chamber having a lower potential (ground potential) from the surface of the material to be processed having a higher potential. Since the formation of the circuit to be performed is hindered, the potential difference generated in the surface of the material to be processed can be reduced. Thereby, the potential distribution in the surface of the material to be processed due to the in-plane distribution of the plasma characteristics can be made uniform. Further, in the case where an antenna electrode facing the substrate electrode is provided in the processing chamber, even if a high-frequency voltage is applied to the substrate electrode, the plasma potential at the outer peripheral portion of the substrate electrode is high, so that the substrate electrode is transferred to the processing chamber wall functioning as an earth. , The current flow between the antenna electrode and the antenna electrode functioning as the opposite ground electrode increases. That is, since the high-frequency current flows more between the electrodes facing each other than the inner wall of the processing chamber, the current in the direction crossing the magnetic field decreases, and the magnetic field is not affected by the plasma impedance in the direction perpendicular to the magnetic field. Since the plasma impedance in the horizontal direction with respect to the magnetic field is uniform in the plane, the potential distribution in the surface of the material to be processed due to the in-plane distribution of plasma characteristics is further reduced, and the occurrence of charging damage can be suppressed. Accurate plasma processing becomes possible.
[0009]
Also, a third high-frequency power supply is connected to the antenna electrode, and the first high-frequency power supply connected to the substrate electrode and the third high-frequency power supply connected to the antenna electrode are set to have the same frequency. By setting the phase difference of the power supply to 180 ° ± 30 °, the positive high-frequency peak voltage of the substrate electrode can be reduced, and the plasma potential at the outer periphery of the substrate electrode as viewed from the plasma potential on the material to be processed is further increased. be able to. This further amplifies the effect that the opposing electrode efficiently functions as the ground, suppresses the occurrence of charging damage, and enables highly accurate plasma processing.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
[Example 1]
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a longitudinal sectional view of an etching apparatus which is one embodiment of a plasma processing apparatus to which the present invention is applied. A processing chamber 104, a dielectric window 102 (for example, made of quartz), and an antenna electrode 103 (for example, made of Si) are provided on the upper portion of a vacuum vessel 101 having an open top, and a processing chamber 105 is formed by sealing with an antenna cover 121. . A magnetic field generating coil 114 is provided on the outer peripheral portion of the processing chamber 104 and on the antenna cover 121. The antenna electrode 103 has a porous structure for flowing an etching gas, and is connected to a gas supply device 107. Further, a vacuum exhaust device (not shown) is connected to the vacuum vessel 101 via a vacuum exhaust port 106.
[0011]
A high frequency power supply 108 (for example, a frequency of 450 MHz) is connected to the upper part of the antenna electrode 103 via a coaxial line 111, a matching unit 110, and a filter 109 as a power supply for plasma generation. Further, an antenna bias power supply 112 (for example, a frequency of 13.56 MHz) is connected to the upper portion of the antenna electrode 103 via a coaxial line 111, a matching unit 119, and a filter 113. The substrate electrode 115 on which the material to be processed 116 can be placed is installed below the vacuum vessel 101 and connected to the substrate bias power supply 117 (for example, frequency 800 KHz) via the coaxial line 122 and the matching unit 118. Plasma is generated by the high frequency power supply 108, the plasma composition or plasma distribution is controlled by the antenna bias power supply 112, and the amount of ions incident on the substrate is controlled by the substrate bias power supply 117. With such a configuration, there is an advantage that the plasma generation, the plasma composition / distribution, and the amount of ions incident on the target material 116 can be independently controlled. In addition, an electrostatic chuck power supply 120 is connected to the substrate electrode 115 in order to electrostatically attract the workpiece 116.
[0012]
An auxiliary electrode 127 is provided on the outer periphery of the substrate electrode 115, and the auxiliary electrode 127 is connected to the matching unit 118 via a potential control circuit 126 and a coaxial line 122.
[0013]
FIG. 2 shows a circuit configuration example of the potential control circuit 126. The potential control circuit 126 is a circuit that controls the waveform of the high-frequency voltage from the substrate bias power supply 117 to an arbitrary voltage waveform. A capacitor (C1) and a diode (D1) are connected in parallel between the auxiliary electrode 127 and the coaxial line 122. The diode (D1) is connected so that the direction from the auxiliary electrode to the coaxial line 122 is forward. When a high-frequency voltage is applied to the auxiliary electrode 127 by the substrate bias power supply 117, the circuit configuration suppresses the flow of electrons from the plasma to the auxiliary electrode 127, and reduces the high-frequency self-bias voltage (Vdc) of the auxiliary electrode 127. Act to reduce the absolute value.
[0014]
In the apparatus configured as described above, after the inside of the processing chamber 105 is depressurized by the vacuum exhaust device, the etching gas is introduced into the processing chamber 105 by the gas supply device 107 and adjusted to a desired pressure. The high-frequency power of, for example, 450 MHz, oscillated from the high-frequency power supply 108, propagates through the coaxial line 111, is introduced into the processing chamber 105 via the antenna electrode 103 and the dielectric window 102, and is supplied with a magnetic field generating coil 114 (for example, A high-density plasma is generated in the processing chamber 105 by interaction with a magnetic field formed by the solenoid coil). In particular, when a magnetic field intensity (for example, 160 G) that causes electron cyclotron resonance is formed in the processing chamber, high-density plasma can be efficiently generated. Further, high frequency power (for example, a frequency of 13.56 MHz) is supplied from the antenna bias power supply 112 to the antenna electrode 103 via the coaxial line 111. The workpiece 116 placed on the substrate electrode 115 is supplied with high-frequency power (for example, a frequency of 800 KHz) from the substrate bias power supply 117 and subjected to a surface treatment (for example, an etching process).
[0015]
The substrate electrode 115 is supplied with, for example, a high-frequency power of 800 V peak-to-peak voltage (Vpp) to generate a self-bias voltage (Vdc), and the positive high-frequency peak voltage of the substrate electrode 115 becomes about 100 V to 200 V. Fixed. At this time, a high frequency is also applied to the auxiliary electrode 127. However, since the diode (D1) is connected in the forward direction and the capacitor (C1) having a smaller capacity than the capacitor in the matching unit 118 is provided in parallel, When a positive voltage of a high-frequency voltage is applied to the auxiliary electrode, electrons attracted from the plasma by the diode (D1) cannot flow toward the matching unit 118, and the capacity of the capacitor (C1) is small, so that the auxiliary electrode is small. The amount of electrons stored in the auxiliary electrode 127 also decreases, and the absolute value of the self-bias voltage (Vdc) at the auxiliary electrode 127 becomes a small value. Since the electron current is suppressed and the absolute value of the self-bias voltage (Vdc) decreases, the positive high-frequency peak voltage of the auxiliary electrode 127 becomes higher than that of the substrate electrode 115, and the plasma potential on the auxiliary electrode 127 becomes higher than the plasma potential on the substrate electrode 115. The plasma potential increases. FIG. 3 shows a plasma potential state when a high-frequency voltage is applied to the auxiliary electrode 127. By increasing the plasma potential on the auxiliary electrode 127, the potential distribution in the surface of the processing target material 116 is reduced, and the in-plane distribution of plasma characteristics can be made uniform. Further, in a circuit formed through plasma between the substrate electrode 115 and the processing chamber 104 which is a side wall of the processing chamber 105, a high plasma potential exists on the way, so that a current flowing through the circuit is reduced, and a high-frequency current is reduced. Flow more between the opposing electrodes than the side walls. As a result, there is an effect that the current in the direction crossing the magnetic field is reduced, the occurrence of charging damage is suppressed, and more accurate etching can be performed.
[Example 2]
A second embodiment of the present invention will be described with reference to FIG. In this figure, the same reference numerals as those in FIG. 1 denote the same members, and a description thereof will be omitted. The difference between this figure and FIG. 1 will be described below. An antenna bias power supply 112 (for example, a frequency of 800 kHz) is connected to the upper part of the antenna electrode 103 via a coaxial line 111, a matching unit 119, and a filter 113. The substrate electrode 115 on which the workpiece 116 can be placed is installed below the vacuum vessel 101, and is connected to a substrate bias power supply 117 (for example, at a frequency of 800 KHz) via a coaxial line 122 and a matching unit 118. The antenna bias power supply 112 and the substrate bias power supply 117 are connected to a phase controller 125, and can control the phase of a high frequency output from the antenna bias power supply 112 and the substrate bias power supply 117. Here, the frequencies of the antenna bias power supply 112 and the substrate bias power supply 117 are the same.
[0016]
When the phase difference between the high-frequency voltages applied to the antenna electrode 103 and the substrate electrode 115 is 180 ° ± 30 °, for example, when a positive voltage is applied to the substrate electrode 115, a negative voltage is applied to the antenna electrode 103. Since the voltage is applied, ions are incident on the antenna electrode 103 but no electrons are incident thereon, and a lot of electrons exist in the vicinity of the antenna electrode 103, and the opposing electrode has a function as a ground efficiently. When the phase difference is applied at 180 ° ± 30 °, the impedance from the substrate electrode 115 to the opposing grounding antenna electrode 103 is reduced. For example, a high-frequency power of 800V peak-to-peak voltage (Vpp) is applied. Then, the positive high frequency peak voltage of the substrate electrode 115 is fixed at 20 to 30V. The positive high-frequency peak voltage of the substrate electrode 115 of this embodiment is smaller than the positive high-frequency peak voltage of the substrate electrode 115 shown in the first embodiment, and the effect that the opposing electrode efficiently functions as ground is further amplified and realized. It is possible to do. By further increasing the plasma potential on the auxiliary electrode 127 from the viewpoint of the plasma potential on the substrate electrode 115, more high-frequency current flows between the opposing electrodes than the side walls, so that the current in the direction crossing the magnetic field decreases and the charge increases. This has the effect that generation of etching damage can be suppressed and high-precision etching processing can be performed.
[Example 3]
A third embodiment of the present invention will be described with reference to FIG. 2, the same reference numerals as those in FIG. 2 denote the same members, and a description thereof will be omitted. The difference between this figure and FIG. 2 will be described below. 2 in that the diode (D1) of the potential control circuit 126 is connected in the opposite direction to that of FIG. 2 and a variable resistor R1 is additionally connected in series. The capacitor (C1) of the potential control circuit 126 is a variable capacitance capacitor. The point is that a control device 128 for adjusting the resistance value of the device R1 and the capacitance of the variable capacitor C1 is connected.
[0017]
With such a configuration, when a high-frequency voltage is applied to the auxiliary electrode 127 by the substrate bias power supply 117, for example, the resistance value of the resistor R1 is increased to suppress the flow of current, so that the auxiliary electrode 127 The flow of electrons into the auxiliary electrode 127 from the plasma can be increased by reducing the resistance value of the resistor R1 and making the current easier to flow. Thus, the absolute value of the high-frequency self-bias voltage (Vdc) of the auxiliary electrode 127 can be controlled, so that the self-bias voltage (Vdc) is reduced, and the plasma on the auxiliary electrode 127 is actuated as in the first embodiment. The potential in the plasma is increased or the self-bias voltage (Vdc) is slightly increased so that ions in the plasma are incident on the auxiliary electrode 127 so that the incident amount of ions can be controlled. It is also possible to control the reaction with the active species in the plasma on the surface of the auxiliary electrode 127 by the incidence of ions on the auxiliary electrode 127. For example, in oxide film etching using a CF-based gas, if the material of the auxiliary electrode 127 is made of high-purity silicon, the reaction of F radicals and CF radicals at the auxiliary electrode 127 is controlled by the scavenging action of silicon. In particular, it is possible to improve the etching uniformity in the outer peripheral portion of the wafer.
[0018]
Further, when a high-frequency voltage is applied to the auxiliary electrode 127 by the substrate bias power supply 117, for example, by reducing the capacity of the capacitor C1 and suppressing the applied high-frequency power, ions from the plasma to the auxiliary electrode 127 are reduced. The inflow can be suppressed, and the inflow of ions from the plasma to the auxiliary electrode 127 can be increased by increasing the capacity of the capacitor C1 and increasing the applied high frequency power. Thus, the absolute value of the high-frequency self-bias voltage (Vdc) of the auxiliary electrode 127 can be controlled, so that the self-bias voltage (Vdc) is reduced, and the plasma on the auxiliary electrode 127 is actuated as in the first embodiment. The potential in the plasma is increased or the self-bias voltage (Vdc) is slightly increased so that ions in the plasma are incident on the auxiliary electrode 127 so that the incident amount of ions can be controlled. By controlling the incidence of ions on the auxiliary electrode 127, it is also possible to control the reaction with active species in the plasma on the surface of the auxiliary electrode 127. Thereby, the same effect as when the above-described variable resistor (R1) is controlled can be obtained.
[0019]
As described above, the variable resistor (R1) and the variable capacitance capacitor (C1) may be individually controlled, or it is effective to control them in combination for more optimal control.
[0020]
According to the third embodiment, there is an effect that the plasma potential on the auxiliary electrode 127 can be controlled to suppress the occurrence of charging damage and improve the uniformity of etching by the scavenging action.
[0021]
Although the etching apparatus has been described in these embodiments, the present invention can be similarly applied to other plasma processing apparatuses that supply high-frequency power to the substrate electrode, such as an ashing apparatus and a plasma CVD apparatus.
[0022]
【The invention's effect】
According to the present invention, by making the plasma potential of the outer peripheral portion of the substrate electrode higher than the plasma potential on the material to be processed, the potential distribution in the plane of the material to be processed can be reduced, and the grounding of both opposing electrodes can be reduced. As the high-frequency current flows more to the opposing electrode than the inner wall of the processing chamber in the processing chamber, the current in the direction crossing the magnetic field decreases, and charging damage can be suppressed. It is possible to provide a plasma processing method and apparatus capable of increasing the yield and performing high-precision surface treatment.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a plasma processing apparatus according to a first embodiment of the present invention.
FIG. 2 is a diagram showing a potential control circuit of the device of FIG.
FIG. 3 is a diagram showing a plasma potential when the potential control circuit of FIG. 2 is used.
FIG. 4 is a longitudinal sectional view showing a plasma processing apparatus according to a second embodiment of the present invention.
FIG. 5 is a diagram showing a potential control circuit of a plasma processing apparatus according to a third embodiment of the present invention.
[Explanation of symbols]
Reference Signs List 101: vacuum container, 102: dielectric window, 103: antenna electrode, 104: processing container, 105: processing chamber, 106: vacuum exhaust port, 107: gas supply device, 108: high frequency power supply, 109, 113: filter, 110 ... matching device, 111 ... coaxial line, 112 ... antenna bias power supply, 114 ... magnetic field generating coil, 115 ... substrate electrode, 116 ... material to be processed, 117 ... substrate bias power supply, 118, 119 ... matching device, 120 ... electrostatic Chuck power supply, 121 antenna cover, 122 coaxial line, 125 phase controller, 126 potential control circuit, 127 auxiliary electrode, 128 control device.

Claims (3)

With internal processing gas is supplied to generate a plasma in the processing chamber that is evacuated to a predetermined pressure, the treatment of the substrate bias voltage indicia is applied from bias power source to the substrate electrode provided on the chamber, and generation of the plasma Independently control the incident energy of the ions in the plasma to the material to be processed, and in the plasma processing method for processing the material to be processed,
A bias voltage is applied to an auxiliary electrode provided on the outer peripheral portion of the material to be processed through a potential control circuit in which a diode and a capacitor connected in such a manner that the direction from the auxiliary electrode toward the substrate bias power supply is a forward direction are connected in parallel. ,
A plasma processing method, wherein a plasma potential at an outer peripheral portion of the substrate electrode is higher than a plasma potential on the material to be processed, and the material to be processed is processed. A processing chamber to which a vacuum evacuation device is connected and the inside of which can be decompressed; a gas supply device for supplying gas into the processing chamber; a substrate electrode provided in the processing chamber and capable of mounting a material to be processed; A plasma comprising: a first high-frequency power supply for radiating an electromagnetic wave for converting a supplied gas into plasma into the processing chamber; and a second high-frequency power supply connected to the substrate electrode and applying a substrate bias voltage to the material to be processed. In the processing device,
An auxiliary electrode in which a self-bias voltage having an absolute value smaller than the self-bias potential of the substrate electrode is provided on an outer peripheral portion of the workpiece,
A second high-frequency power source, and the substrate electrode, wherein the auxiliary electrode in a second direction toward the high-frequency power supply is connected such that the forward diode and auxiliary electrodes via a voltage control circuit connected in parallel and a capacitor A plasma processing apparatus , wherein the plasma potential at the outer periphery of the substrate electrode is higher than the plasma potential on the workpiece . 3. The plasma processing apparatus according to claim 2, wherein an antenna electrode facing the substrate electrode and generating an electromagnetic wave for plasma generation is provided in the processing chamber, a third high-frequency power supply is connected to the antenna electrode, and the antenna electrode is connected to the substrate electrode. The second high-frequency power supply and the third high-frequency power supply connected to the antenna electrode have the same frequency, and a means for controlling the phase of the second and third high-frequency power supplies within a range of 180 ° ± 30 ° is provided. Processing equipment.

Images