Lower electrode assembly and plasma processing equipment

Abstract

The invention provides a lower electrode assembly and plasma processing equipment. The lower electrode assembly is used for plasma process treatment and comprises an electrostatic chuck, the upper surface of which is used for bearing a substrate; the first electrode is positioned in the electrostatic chuck and is electrically connected with a pulse type direct current bias voltage source; the second electrode is positioned in the electrostatic chuck, is electrically connected with a direct-current voltage source through an isolating circuit, and is positioned above the first electrode; the isolation circuit comprises a diode, the negative electrode of the diode is electrically connected with the negative electrode of the direct-current voltage source, and the positive electrode of the diode is electrically connected with the second electrode. By eliminating the influence of the pulse type direct current bias voltage source on the clamping voltage, the problem of instability of the clamping voltage of the substrate in the technological process is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor equipment, and in particular to a lower electrode assembly and plasma processing equipment. Background Art

[0002] In plasma processing equipment, the electrostatic chuck is one of the core components of the equipment. The electrostatic chuck plays two main roles in plasma processing. One is to generate a bias on the surface of the substrate on the electrostatic chuck, thereby accelerating the movement of ions in the plasma sheath toward the substrate. The second is to fasten the substrate set on it so that the substrate remains stable during the plasma processing. In order to achieve higher aspect ratio etching or ALE etching, an effective method is to bias the substrate with a pulsed DC bias source, which can produce a single-peak ion energy distribution function.

[0003] An electrostatic chuck usually contains two electrodes. Among the existing schemes for biasing the substrate using a pulsed DC bias source, one scheme is to connect the pulsed DC bias source to one electrode in the electrostatic chuck and couple it to the substrate through capacitance; the substrate is fastened by applying a DC voltage to another electrode embedded in the electrostatic chuck to generate an electrostatic attraction force between the electrostatic chuck and the substrate. However, during the process, the pulsed DC bias will be adjusted as the process environment changes, resulting in mutual influence between the two electrodes, causing the electrostatic force between the substrates to change as the pulse voltage changes, resulting in insufficient or excessive clamping of the substrate during the etching process, resulting in substrate scrapping, etching failure and other losses. Summary of the invention

[0004] The object of the present invention is to provide a lower electrode assembly and a plasma processing device, which can solve the problem of instability of the substrate clamping voltage during the etching process by eliminating the influence of a pulsed DC bias source on the clamping voltage.

[0005] In order to achieve the above objectives, the present invention is implemented by the following technical solutions: A lower electrode assembly for plasma processing, comprising: an electrostatic chuck having an upper surface for supporting a substrate; a first electrode disposed in the electrostatic chuck and electrically connected to a pulsed DC bias source; a second electrode located in the electrostatic chuck, electrically connected to a DC voltage source via an isolation circuit, the second electrode being located above the first electrode; The isolation circuit includes a diode, a cathode of the diode is electrically connected to the cathode of the DC voltage source, and an anode of the diode is electrically connected to the second electrode.

[0006] Optionally, the pulsed DC bias source outputs a negative pulse voltage.

[0007] Optionally, the positive pole of the DC voltage source is grounded.

[0008] Optionally, the isolation circuit further includes a resistor connected in series with the diode, and the resistance of the resistor is 1 kΩ~1 GΩ.

[0009] Optionally, an RF filter is provided between the isolation circuit and the DC voltage source.

[0010] Optionally, the electrostatic chuck comprises a ceramic material layer and a metal base for supporting the ceramic material layer; The first electrode and the second electrode are both disk electrodes located on the ceramic material layer; Alternatively, the first electrode is the metal base, and the second electrode is a disk electrode located on the ceramic material layer.

[0011] Optionally, the isolation circuit is integrated with the DC voltage source.

[0012] Optionally, the voltage range of the DC voltage source is 0~-10kV.

[0013] Optionally, the duty cycle range of the pulsed DC bias source is 1%-95%, the frequency range is 10kHz~5MHz, and the output high and low level voltage difference is 100V~50kV.

[0014] Optionally, the isolation circuit is disposed on a circuit board, and the circuit board is disposed below the electrostatic chuck.

[0015] A plasma processing device, comprising: Reaction chamber; An air inlet mechanism, used for delivering process gas into the reaction chamber; A source radio frequency, used to ignite the process gas into plasma; The lower electrode assembly as described above is located at the bottom of the reaction chamber.

[0016] Compared with the prior art, the present invention has the following advantages: The present invention sets an isolation circuit between the DC voltage source and the second electrode. Since the diode has the characteristics of forward conduction and reverse cutoff, when the pulsed DC bias source outputs a pulse, the diode is reversely cutoff and cannot be charged and discharged through the loop of the DC voltage source, so that the two ends of the second capacitor will not bring about a potential difference due to the addition of the pulsed DC bias source. The potential difference between the two ends of the second capacitor depends only on the DC voltage source, so that the clamping voltage remains stable, eliminating the influence of the pulse voltage of the pulsed DC bias source on the clamping voltage, and solving the problem of instability of the substrate clamping voltage during the process. The diode in the isolation circuit is also connected in series with a resistor, which can block the AC component in the pulsed DC bias source and the radio frequency power for generating plasma, thereby stabilizing the current in the DC voltage source loop. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for the description. Obviously, the drawings described below are an embodiment of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work: Figure 1 is a structural diagram of a plasma processing device; Figure 2 It is a structural diagram of the lower electrode assembly in the prior art; Figure 3 for Figure 2 Equivalent circuit diagram of the structure shown; Figure 4 It is a curve diagram of the voltage across the capacitor C2 changing with time under different pulse output voltages in a simulation experiment using the prior art; Figure 5 A structural diagram of a lower electrode assembly in one embodiment of the present invention; Figure 6 for Figure 5 An equivalent circuit diagram of the structure shown; Figure 7 for Figure 5 Another equivalent circuit diagram of the structure shown; Figure 8 It is a curve diagram showing the voltage across the capacitor C2 changing with time under different pulse output voltages in a simulation experiment using the solution of the present invention; Fig. 9 is a structural diagram of a lower electrode assembly in another embodiment of the present invention; Fig.10 FIG. 4 is an equivalent circuit diagram of a lower electrode assembly in another embodiment of the present invention. DETAILED DESCRIPTION

[0018] The scheme proposed by the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. According to the following description, the advantages and features of the present invention will be clearer. It should be noted that the accompanying drawings are in a very simplified form and use non-precise proportions, which are only used to conveniently and clearly assist in explaining the purpose of the implementation method of the present invention. In order to make the purposes, features and advantages of the present invention more obvious and easy to understand, please refer to the accompanying drawings. It should be noted that the structures, proportions, sizes, etc. illustrated in the accompanying drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention, so they have no technical substantive significance. Any structural modification, change in proportional relationship or adjustment of size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope of the technical content disclosed by the present invention.

[0019] Figure 1 The schematic diagram of the structure of the plasma processing equipment is shown. The plasma processing equipment includes: a reaction chamber 10, a lower electrode assembly 20 located at the bottom of the reaction chamber 10, and the lower electrode assembly 20 includes an electrostatic chuck, and the electrostatic chuck is used to carry the substrate W. The reaction chamber 10 is also provided with an air intake mechanism 30 for conveying process gas into the reaction chamber 10. The air intake mechanism 20 can intake gas from the top or side wall of the reaction chamber 10. In the capacitively coupled plasma processing equipment, the air intake mechanism 20 can be a gas shower head, which also serves as an upper electrode for generating plasma. It also includes a radio frequency power supply 40 for igniting the process gas into plasma. One or more radio frequency power supplies 40 can be electrically connected to the lower electrode or the upper electrode individually, or to the upper electrode and the lower electrode simultaneously, so as to transmit radio frequency power to the lower electrode or to the upper electrode and the lower electrode simultaneously, thereby generating a large radio frequency electric field inside the reaction chamber 10. Some gas molecules in the reaction gas lose electrons when subjected to these strong electric fields, leaving positively charged ions. The positively charged ions are accelerated toward the lower electrode by the bias voltage, and combine with neutral substances in the processed substrate W to perform substrate processing, namely etching, deposition and other processes.

[0020] Figure 2 The schematic diagram of the structure of the lower electrode assembly in an existing plasma processing device is shown. The electrostatic chuck 21 is provided with a first electrode 22 and a second electrode 23, and the second electrode 23 is located above the first electrode 23. The areas of the two electrodes can be the same or different. The first electrode 22 is electrically connected to a pulsed DC bias source PDC, which is used to bias the substrate W on the electrostatic chuck 21 so that the charged particles in the sheath above it are accelerated to bombard the substrate W. The second electrode 23 is electrically connected to a DC voltage source DC, which is used to generate an electrostatic attraction between the electrostatic chuck 21 and the substrate W, thereby fixing the substrate W. The high-frequency RF power supply for generating plasma is not in Figure 2Although a resistor Re with a relatively large resistance is provided between the DC voltage source DC and the second electrode 23 to isolate the RF signal from the pulsed DC signal, the pulse voltage of the pulsed DC bias source PDC will still be coupled to the second electrode 23 through capacitance in the electrostatic chuck 21, thereby changing the clamping voltage and causing the substrate W to be insufficiently clamped or excessively clamped.

[0021] Figure 3 yes Figure 2 The equivalent circuit diagram of the structure shown in FIG. 1 shows the capacitance between the first electrode 22 and the second electrode 23, and C2 shows the capacitance between the second electrode 23 and the substrate W. The capacitance values ​​of C1 and C2 can be 1nF to 100nF. SH , C SH and R SH The parallel circuit of represents the equivalent circuit model of the surface plasma sheath of substrate W, D W , C W and R W The parallel circuit of represents the equivalent circuit model of the plasma sheath on the cavity wall surface, R pl represents the resistance inside the plasma, and Re represents the resistance between the direct current voltage source DC and the second electrode 23 .

[0022] Figure 4 This is a curve obtained by experimental simulation of the voltage across C2, i.e., the chucking voltage, changing with time under different pulse output voltages. The voltage of the DC voltage source DC is set to -12kV, and the pulse output voltages of the pulsed DC bias source PDC are -15kV, -10kV, and -5kV, respectively, with a duty cycle of 50% and a frequency of 400kHz. According to the simulation results, when the pulse output voltage switches between three values, the top curve corresponds to the clamping voltage value when the pulse output voltage is -15kV, the middle curve corresponds to the clamping voltage value when the pulse output voltage is -10kV, and the bottom curve corresponds to the clamping voltage value when the pulse output voltage is -5kV. It can be clearly seen that the clamping voltage value also fluctuates up and down. If the appropriate clamping voltage value is between the top and bottom two curves, the substrate has problems of over-clamping and under-clamping when the pulse output voltage changes.

[0023] It is understandable that in Figure 3In the figure, the potential signal at point B is the potential on the substrate W, which is affected by the pulsed DC bias source PDC, plasma and DC voltage source DC. The voltage output by the DC voltage source DC remains unchanged. The influence of the plasma on point B is related to the source RF and plasma equipment. When the source RF and equipment structure are fixed, the influence of the plasma at point B is also fixed, that is, the waveform at point B is approximately the output waveform of the pulsed DC bias source PDC -U~0 (-U is approximately the high and low level voltage difference of the pulsed DC bias source PDC). The potential at point A is the superposition of the output of the DC voltage source DC and the pulsed DC bias source PDC. The output voltage of the pulsed DC bias source PDC is shunted by the branch where the DC voltage source DC is located at point A. When the output voltage of the pulsed DC bias source PDC switches, in order to achieve dynamic balance at point A, a current will pass through the loop of the DC voltage source DC to charge and discharge point A. For the convenience of discussion, for example, if the high and low level duty cycle of PDC is 50% and the voltage difference is U, then the waveform at point A is approximately a voltage from ~ The changing pulse waveform is superimposed with a voltage output by a DC voltage source DC. It can be seen that the pulsed DC bias source PDC creates a potential difference between points BA, and the magnitude of this potential difference depends on the pulse output voltage of the pulsed DC bias source PDC.

[0024] During the plasma process, the pulse output voltage of the pulsed DC bias source PDC is usually different under different processing processes. When the pulse output voltage is adjusted, the clamping voltage will also change, causing process instability and even damage to the substrate W.

[0025] Based on this, the present invention provides a lower electrode assembly, in which an isolation circuit is arranged between the DC voltage source DC and the second electrode 23 to eliminate the influence of the pulse output voltage of the pulse DC bias source PDC on the clamping voltage.

[0026] Specifically, Figure 5 As shown, the lower electrode assembly 20 provided by an embodiment of the present invention includes: an electrostatic chuck 21, whose upper surface is used to carry a substrate W; a first electrode 22 located in the electrostatic chuck 21, which is electrically connected to a pulsed DC bias source PDC; a second electrode 23 located in the electrostatic chuck 21, which is electrically connected to a DC voltage source DC through an isolation circuit 24, and the second electrode 23 is located above the first electrode 22. The capacitor formed between the first electrode 22 and the second electrode 23 is called a capacitor C1, and the capacitor formed between the second electrode 23 and the substrate W is called a capacitor C2.

[0027] Figure 6 yes Figure 5 The equivalent circuit diagram of the structure shown, combined with Figure 6As shown, the isolation circuit 24 includes a diode D, a cathode of the diode D is electrically connected to the cathode of the DC voltage source DC, and a cathode of the diode D is electrically connected to the second electrode 23 .

[0028] In this embodiment, the positive electrode of the DC voltage source DC is grounded, the DC voltage source DC outputs a negative voltage, the positive electrode of the pulsed DC bias source PDC is grounded, and the pulsed DC bias source PDC outputs a negative pulse voltage. Figure 6 As shown, the cathode of the diode D is connected to the cathode of the DC voltage source DC. When the voltage output by the pulsed DC bias source PDC is 0, the diode D is turned on, and the voltage at point A is the DC output voltage -V chuck At this time, the potential at point B is 0, so the adsorption voltage is V chuck ; When the PDC output voltage is -V, since C1 is very large, point A jumps with the PDC output voltage and is (-V chuck -V), at this time the diode is cut off, and the corresponding potential of point B is -V, so the voltage difference between A and B is still V chuck Therefore, there will be no potential difference between the two points BA due to the addition of the pulsed DC bias source PDC, that is, the potential difference across C2 depends only on the DC voltage source DC, so that the clamping voltage remains stable.

[0029] In this embodiment, the voltage range of the DC voltage source is 0 to -10 kV, the duty cycle of the pulsed DC bias source is 1% to 95%, the frequency is 10 kHz to 5 MHz, and the output voltage range is -100 V to -50 kV.

[0030] like Figure 7 As shown, the isolation circuit 24 may further include a resistor R connected in series with the diode D, and the resistance of the resistor R is 1 kΩ to 1 GΩ. The resistor R is used to block the AC component and high-frequency RF power in the pulsed DC bias source PDC, thereby stabilizing the current in the DC voltage source DC loop.

[0031] Figure 8 The curve is obtained through experimental simulation, showing that the voltage across the capacitor C2, ie, the clamping voltage, changes with time under different pulse output voltages using the solution of the present invention. Figure 8 In the figure, the voltage of the DC voltage source DC is set to -5kV, the pulse output voltages of the pulsed DC bias source PDC are -15kV, -10kV, -5kV, respectively, the duty cycle is 50%, and the frequency is 400kHz. It can be seen that the isolation circuit 24 can well eliminate the influence of the output of the pulsed DC bias source PDC on the clamping voltage, and the clamping voltage does not change with the change of the output voltage of the DC bias source PDC.

[0032] In this embodiment, the two output voltages of the pulsed DC bias source may not be limited to 0V and a negative voltage, and the pulsed DC bias source is only limited to a high and low level voltage difference of the output voltage of 100V to 50kV. The isolation circuit 24 may be arranged on a circuit board, and the circuit board is arranged under the electrostatic suction cup. The isolation circuit 24 may be integrated with the DC voltage source DC to simplify the structure. Specifically, the various components of the isolation circuit 24 are integrated on a circuit board and fixed in a power box of the DC voltage source DC. Alternatively, the various components of the isolation circuit 24 may be separately assembled in the power box of the DC voltage source DC.

[0033] The electrostatic chuck 21 includes a ceramic material layer 211 and a metal base 212 for supporting the ceramic material layer 211. The metal base 212 is also used to assist in controlling the temperature of the ceramic material layer 211. Figure 5 In the illustrated embodiment, both the first electrode 22 and the second electrode 23 are disk electrodes buried in the ceramic material layer 211, and the second electrode 23 is located above the first electrode 22. Fig. 9 In the illustrated embodiment, the first electrode 22 is the metal base 212 , and the second electrode 23 is a disk electrode buried in the ceramic material layer 211 , thereby ensuring that the second electrode 23 is located above the first electrode 22 .

[0034] like Fig.10 As shown, an RF filter 25 may be further provided between the isolation circuit 24 and the DC voltage source DC to better block radio frequency signals from entering the DC voltage source DC.

[0035] In summary, the present invention sets an isolation circuit between the DC voltage source and the second electrode. Since the diode has the characteristics of forward conduction and reverse cutoff, the influence of the pulse voltage of the pulse DC bias source on the clamping voltage is eliminated, and the instability problem of the substrate clamping voltage during the process is solved. The diode in the isolation circuit is also connected in series with a resistor, which can block the AC component in the pulse DC bias source, thereby stabilizing the current in the DC voltage source loop.

[0036] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0037] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

Claims

1. A lower electrode assembly for plasma processing, characterized in that: include: an electrostatic chuck having an upper surface for supporting a substrate; a first electrode disposed in the electrostatic chuck and electrically connected to a pulsed DC bias source; a second electrode located in the electrostatic chuck, electrically connected to a DC voltage source via an isolation circuit, the second electrode being located above the first electrode; The isolation circuit includes a diode, a cathode of the diode is electrically connected to the cathode of the DC voltage source, and an anode of the diode is electrically connected to the second electrode.

2. The lower electrode assembly according to claim 1, characterized in that The pulsed DC bias source outputs a negative pulse voltage.

3. The lower electrode assembly according to claim 1, characterized in that The positive electrode of the DC voltage source is grounded.

4. The lower electrode assembly according to claim 1, characterized in that The isolation circuit further includes a resistor connected in series with the diode, and the resistance of the resistor is 1 kΩ to 1 GΩ.

5. The lower electrode assembly according to claim 1, characterized in that: An RF filter is provided between the isolation circuit and the DC voltage source.

6. The lower electrode assembly according to claim 1, characterized in that The electrostatic chuck comprises a ceramic material layer and a metal base for supporting the ceramic material layer; The first electrode and the second electrode are both disk electrodes located on the ceramic material layer; Alternatively, the first electrode is the metal base, and the second electrode is a disk electrode located on the ceramic material layer.

7. The lower electrode assembly according to claim 1, characterized in that: The isolation circuit is integrated with the DC voltage source.

8. The lower electrode assembly according to claim 1, characterized in that: The voltage range of the DC voltage source is 0~-10kV.

9. The lower electrode assembly according to claim 1, characterized in that: The duty cycle range of the pulsed DC bias source is 1%-95%, the frequency range is 10kHz-5MHz, and the output high and low level voltage difference is 100V-50kV.

10. The lower electrode assembly according to claim 1, wherein: The isolation circuit is arranged on a circuit board, and the circuit board is arranged below the electrostatic chuck.

11. A plasma processing device, characterized in that: include: Reaction chamber; An air inlet mechanism, used for delivering process gas into the reaction chamber; A source radio frequency, used to ignite the process gas into plasma; The lower electrode assembly according to any one of claims 1 to 10, located at the bottom of the reaction chamber.

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