Structure and method for improving plasma stability

Abstract

The application discloses a structure for improving plasma stability, which comprises a radio frequency generator, a matcher, a discharge adjusting resistor and a plasma load structure. The output end of the radio frequency generator is connected with the input end of the matcher, the output end of the matcher is connected with the first end of the discharge adjusting resistor, and the second end of the discharge adjusting resistor is connected with the plasma load structure. The discharge adjusting resistor is used for providing a discharge adjusting voltage which is proportional to the discharge current when the discharge current is generated in the plasma load structure, so that the discharge voltage on the plasma load structure is reduced, and thus the plasma stability is improved. The application also discloses a method for improving plasma stability. The application can control the discharge voltage of the plasma, so that the plasma discharge is stable, the probability of arc generation is reduced, and thus the product process can be improved and the production capacity can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of semiconductor integrated circuit manufacturing, and in particular to a structure for improving plasma stability. BACKGROUND

[0002] At present, the main method for dry etching equipment is to use double-frequency radio frequency glow discharge, and the main material on the surface of the electrostatic chuck is ceramic, which plays a role of dielectric barrier. With the increase of radio frequency discharge intensity, the stability of discharge will become poor, especially when the discharge current is large, the unevenness of the wafer surface or other accidental factors can easily lead to arcing phenomenon, causing the machine to down or even break, which has a certain degree of damage to process stability and production capacity. SUMMARY

[0003] The technical problem to be solved by the present application is to provide a structure for improving plasma stability, which can control the discharge voltage of the plasma, so as to stabilize the plasma discharge and reduce the probability of arcing, thereby improving the product process and increasing the production capacity. Therefore, the present application also provides a method for improving plasma stability.

[0004] To solve the above technical problems, the structure for improving plasma stability provided by the present application comprises: a radio frequency generator, a matcher, a discharge adjusting resistor and a plasma load structure.

[0005] The output end of the radio frequency generator is connected to the input end of the matcher, the output end of the matcher is connected to the first end of the discharge adjusting resistor, and the second end of the discharge adjusting resistor is connected to the plasma load structure.

[0006] The discharge adjusting resistor is used to provide a discharge adjusting voltage proportional to the discharge current in the plasma load structure, so as to reduce the discharge voltage on the plasma load structure, thereby improving the stability of the plasma.

[0007] Further improvement is that the discharge adjusting resistor is a fixed resistor or an adjustable resistor.

[0008] Further improvement is that the size of the discharge adjusting resistor is ensured to be reduced to below the critical value of the transition of the discharge mode when the discharge current is generated in the plasma load structure.

[0009] Further improvement is that the plasma load structure comprises a process cavity, and when the plasma is formed, the process cavity is filled with gas, and a sheath layer is formed on the periphery of the plasma.

[0010] Further improvement is that the discharge mode transition is from alpha mode to gamma mode.

[0011] Further improvement is that the discharge voltage includes a sheath voltage of a sheath layer of the plasma, and the critical value of the discharge mode transition corresponds to a minimum sheath voltage when secondary breakdown of gas in the sheath layer occurs.

[0012] Further improvement is that the process cavity includes a dry etching cavity.

[0013] Further improvement is that the radio frequency generator provides a double-frequency radio frequency source signal.

[0014] To solve the above technical problems, the method for improving plasma stability provided by the application includes:

[0015] A discharge adjusting resistor is arranged, an output end of a matching device is connected to a first end of the discharge adjusting resistor, a second end of the discharge adjusting resistor is connected to a plasma load structure, and an output end of a radio frequency generator is connected to an input end of the matching device.

[0016] Plasma is generated in the plasma load structure, and when a discharge current is generated in the plasma load structure, the discharge adjusting resistor provides a discharge adjusting voltage proportional to the discharge current and thus reduces the discharge voltage on the plasma load structure, thereby improving plasma stability.

[0017] Further improvement is that the discharge adjusting resistor is a fixed resistor or an adjustable resistor.

[0018] Further improvement is that when a discharge current is generated in the plasma load structure, the size of the discharge adjusting resistor ensures that the size of the discharge voltage is reduced to below the critical value of the discharge mode transition.

[0019] Further improvement is that the plasma load structure includes a process cavity, and when the plasma is formed, the process cavity is filled with gas, and a sheath layer is formed on the periphery of the plasma.

[0020] Further improvement is that the discharge mode transition is from alpha mode to gamma mode.

[0021] Further improvement is that the discharge voltage includes a sheath voltage of a sheath layer of the plasma, and the critical value of the discharge mode transition corresponds to a minimum sheath voltage when secondary breakdown of gas in the sheath layer occurs.

[0022] Further improvement is that the process cavity includes a dry etching cavity.

[0023] A further improvement is that the radio frequency generator provides a dual frequency radio frequency source signal.

[0024] The application can control the discharge voltage of the plasma, so that the plasma discharge is stable, and the probability of arc occurrence is reduced. As the probability of arc occurrence is reduced, the impact on the product and the downtime are reduced, so that the product process is improved and the production capacity is increased.

[0025] In addition, the series resistance added by the application only produces a voltage drop when the plasma discharges. If there is no discharge, only displacement current but no conduction current in the circuit, the load can be equivalent to a capacitor. At this time, the resistance does not produce a voltage drop because there is no conduction current passing through it. When the discharge occurs, the conduction current passes through the resistance, and the resistance produces a voltage drop, which acts as a voltage divider. The conduction current is formed by the discharge current. The ratio of the voltage drop produced by the series resistance to the conduction current in the circuit is the resistance value of the resistance. The resistance value of the resistance is a constant value, so the voltage across the resistance and the conduction current have the same trend. This will form a feedback control effect on the discharge, so that the discharge is suppressed. That is, when the discharge increases, the discharge current increases, the voltage drop across the resistance increases, and the voltage drop across the resistance increases, which reduces the discharge voltage. When the discharge voltage decreases, the discharge current also decreases, so the discharge is suppressed. BRIEF DESCRIPTION OF DRAWINGS

[0026] The application will be further described in detail below in combination with the drawings and specific embodiments:

[0027] Figure 1 is a schematic diagram of the structure for improving the stability of the plasma according to an embodiment of the application. DETAILED DESCRIPTION

[0028] As Figure 1 shown, is a schematic diagram of the structure for improving the stability of the plasma according to an embodiment of the application. The structure for improving the stability of the plasma according to an embodiment of the application includes: a radio frequency generator 101, a matching device 102, a discharge adjusting resistance 103, and a plasma load structure 104.

[0029] The output end of the radio frequency generator 101 is connected to the input end of the matching device 102. The output end of the matching device 102 is connected to the first end of the discharge adjusting resistance 103. The second end of the discharge adjusting resistance 103 is connected to the plasma load structure.

[0030] The discharge adjusting resistor 103 is used to provide a discharge adjusting voltage proportional to the discharge current when the discharge current is generated in the plasma load structure, and thus to reduce the discharge voltage on the plasma load structure, and to improve the stability of the plasma.

[0031] In the embodiment of the present application, the discharge adjusting resistor 103 is a fixed resistor or an adjustable resistor.

[0032] The size of the discharge adjusting resistor 103 ensures that the size of the discharge voltage is reduced below the critical value of the discharge mode transition when the discharge current is generated in the plasma load structure.

[0033] In the embodiment of the present application, the plasma load structure 104 includes a process cavity, and the process cavity is filled with gas when the plasma is formed, and a sheath layer is formed on the periphery of the plasma.

[0034] In the embodiment of the present application, the process cavity includes a dry etching cavity.

[0035] The radio frequency generator 101 provides a double-frequency radio frequency source signal.

[0036] The matching device 102 is used to achieve impedance matching, and is usually composed of a capacitor and an inductor, and does not include a resistor. The matching device 102 needs to set the impedance so that the effective power of the radio frequency source signal propagating into the plasma load structure 104 reaches the maximum.

[0037] The discharge mode transition refers to the transition from the alpha mode to the gamma mode. The alpha mode discharge is mainly maintained by positive ions, and the discharge is relatively stable. The gamma mode discharge is mainly maintained by secondary electrons. The secondary electrons are formed by the bombardment of the gas after the acceleration of the incident electrons, and have an avalanche effect, so the gamma mode discharge is unstable. In the embodiment of the present application, the discharge adjusting resistor 103 can adjust the discharge voltage, prevent the discharge voltage from further increasing, and thus prevent the generation of the gamma mode discharge.

[0038] The discharge voltage includes a sheath voltage of a sheath layer, and the critical value of the discharge mode transition corresponds to the minimum sheath voltage when the gas in the sheath layer has secondary breakdown. The positive and negative charges in the plasma are balanced and maintained at a fixed potential; in the sheath layer, because the electron moving speed is greater than that of the positive ion, the electron is less than the positive ion, so that the sheath layer bears voltage in the circumferential direction of the plasma to the sheath layer, that is, the sheath layer has a sheath voltage, and after the sheath voltage increases, the electron is easily subjected to secondary collision under the acceleration of the sheath voltage, thereby forming secondary electrons. In the embodiment of the present application, the discharge voltage can be reduced, the sheath voltage is a component of the discharge voltage, so the sheath voltage will be reduced, and when the discharge voltage is less than the critical value, the sheath voltage will also be less than the minimum sheath voltage corresponding to the secondary breakdown of the gas in the sheath layer, so that the secondary breakdown can be prevented, and the gamma mode discharge can be prevented.

[0039] In the embodiment of the present application, the resistance is connected in series with the load, that is, the plasma load, before the load, and the resistance is a discharge adjusting resistance 103, so that after the discharge occurs, a voltage drop will be generated on the resistance, which plays a voltage dividing role, so that the voltage applied to the dielectric layer of the plasma load and the gas is reduced compared with the voltage output by the power supply, that is, the radio frequency generator 101, so that the peak value of the discharge current is reduced. Therefore, the discharge voltage of the plasma can be controlled in the embodiment of the present application, so that the plasma discharge is stable, and the probability of arc occurrence is reduced. Since the probability of arc occurrence is reduced, the influence on the product and the downtime will be reduced, so that the product process can be improved and the production capacity can be improved.

[0040] In addition, the series resistance added in the embodiment of the present application will only generate a voltage drop when the plasma discharges. If there is no discharge, only displacement current but no conduction current in the circuit, and the load can be equivalent to a capacitor. At this time, because there is no conduction current passing through the resistance, no voltage drop is generated on the resistance. When the discharge occurs, the conduction current passes through the resistance, and the voltage drop is generated on the resistance, which plays a voltage dividing role. The conduction current is formed by the discharge current. The ratio of the voltage drop generated by the series resistance to the conduction current in the circuit is the resistance value of the resistance. The resistance value of the resistance is a fixed value, so the voltage on the resistance and the conduction current have the same change trend. This will form a feedback control effect on the discharge, so that the discharge is inhibited. That is, when the discharge increases, the discharge current increases, the voltage division on the resistance increases, and the voltage division on the resistance increases, which reduces the discharge voltage. After the discharge voltage is reduced, the discharge current is also reduced, so the discharge is inhibited.

[0041] In the embodiment of the present application, a resistance with a suitable resistance value is connected in series after the radio frequency generator output end is connected to the matching device, and then connected to the cavity load end, that is, the plasma load structure, so as to improve the stability of the radio frequency discharge and reduce the probability of arcing occurrence, thereby improving the process and production capacity.

[0042] In the radio frequency discharge and dielectric barrier discharge, with the increase of the discharge intensity, the sheath voltage in the discharge space rises, and when the sheath voltage reaches a critical value, the secondary breakdown occurs, and the discharge changes from the uniform and stable alpha mode to the unstable gamma mode. In the dry etching device, when the discharge intensity increases and the mode conversion occurs, the machine is shut down, thereby affecting the production capacity and product quality. In the embodiment of the present application, when the resistance with appropriate resistance is introduced, part of the voltage drop in the output power of the radio frequency generator is loaded on the resistance, thereby reducing the voltage drop of the sheath in the discharge space, reducing the possibility of breakdown, and enhancing the stability.

[0043] The method for improving the plasma stability in the embodiment of the present application comprises:

[0044] The discharge adjusting resistance 103 is arranged, the output end of the matching device 102 is connected to the first end of the discharge adjusting resistance 103, the second end of the discharge adjusting resistance 103 is connected to the plasma load structure, and the output end of the radio frequency generator 101 is connected to the input end of the matching device 102.

[0045] The plasma is generated in the plasma load structure 104, and when the discharge current is generated in the plasma load structure, the discharge adjusting resistance 103 provides a discharge adjusting voltage proportional to the discharge current and thereby reduces the discharge voltage on the plasma load structure, thereby improving the plasma stability.

[0046] In the method of the embodiment of the present application, the discharge adjusting resistance 103 is a fixed resistance or an adjustable resistance.

[0047] When the discharge current is generated in the plasma load structure, the size of the discharge adjusting resistance 103 ensures that the size of the discharge voltage is reduced to below the critical value of the mode conversion of the plasma.

[0048] The plasma load structure 104 comprises a process cavity, and when the plasma is formed, the process cavity is filled with gas, and the sheath is formed on the periphery of the plasma.

[0049] The process cavity comprises a dry etching cavity.

[0050] The radio frequency generator 101 provides a double-frequency radio frequency source signal.

[0051] The mode conversion of the plasma is the conversion from the alpha mode to the gamma mode.

[0052] The discharge voltage comprises the sheath voltage of the sheath, and the critical value of the mode conversion corresponds to the minimum sheath voltage when the secondary breakdown of the gas in the sheath occurs.

[0053] In the method of the embodiment of the present application, a voltage drop is generated on the resistor after the discharge is generated by connecting the resistor in series before the load, which plays a role of voltage division, so that the voltage applied on the dielectric layer and the gas is reduced compared with the voltage when the power supply is outputted, so that the peak of the discharge current is reduced. It is pointed out here that if there is no discharge, only displacement current but no conduction current in the circuit, the load can be equivalent to a capacitor. At this time, no voltage drop is generated on the resistor because no conduction current passes through the resistor, and a voltage drop is generated on the resistor only when the conduction current passes through the resistor after the discharge is generated, which plays a role of voltage division. The ratio of the voltage drop generated by the series resistor to the conduction current in the circuit is the resistance of the resistor. The resistance of the resistor is a constant, so the voltage on the resistor and the conduction current have the same variation trend.

[0054] Therefore, in the method of the embodiment of the present application, the stability of the discharge can be improved in the radio frequency circuit (or dielectric barrier discharge at kHz) by introducing the series resistor.

[0055] In the method of the embodiment of the present application, in the radio frequency circuit of the dry etching equipment, a radio frequency generator is connected with a radio frequency matcher, and the radio frequency matcher is connected with a load in series with a resistor with a proper resistance before the load is connected with a cavity.

[0056] In the radio frequency discharge, when the resistor is introduced, a voltage drop is generated on the resistor after the conduction current passes through the resistor, so that the voltage applied on the plasma load in the circuit is suppressed, so that the plasma is less likely to generate arcing phenomenon due to excessive discharge intensity.

[0057] In the dielectric barrier discharge, when the resistor is introduced, when the discharge is generated along with the rise of the applied voltage, the gas voltage causing the discharge also rises. When the gas voltage reaches the breakdown voltage, the discharge is generated, and the discharge current begins to generate pulses. Along with the generation of the discharge, the charges formed by the discharge begin to move to the dielectric layer under the action of the electric field, and the charges generated by the discharge are neutralized with the charges accumulated on the surface of the dielectric layer in the previous discharge, so that the gas voltage is reduced, leading to the extinction of the discharge, forming a discharge current peak. After the series resistor is introduced, the conduction current is formed in the discharge loop along with the generation of the discharge, so that a voltage drop is generated on the series resistor, which plays a role of voltage division, further accelerating the drop of the gas voltage, so that the discharge is extinguished more quickly. When the resistance of the series resistor is large, the voltage division effect of the resistor is more obvious. Therefore, after the series resistor is introduced and the discharge is generated, the voltage division effect of the resistor accelerates the extinction of the discharge, so that the pulse of the discharge current becomes shorter in time, that is, the half width of the discharge current pulse is narrowed. Therefore, after the series resistor is introduced, the generation of multiple discharge current peaks in the discharge is suppressed, and the stability of the discharge is improved.

[0058] The application is described in detail above with specific examples, but these do not constitute a limitation on the application. Those skilled in the art can make many modifications and improvements without departing from the principles of the application, and these should be considered as within the scope of the application.

Claims

1. A structure for improving plasma stability, characterized in that, include: Radio frequency generator, matching unit, discharge regulating resistor and plasma load structure; The output terminal of the radio frequency generator is connected to the input terminal of the matching unit, the output terminal of the matching unit is connected to the first terminal of the discharge regulating resistor, and the second terminal of the discharge regulating resistor is connected to the plasma load structure. The discharge regulating resistor is used to provide a discharge regulating voltage proportional to the discharge current when a discharge current is generated in the plasma load structure, thereby reducing the discharge voltage on the plasma load structure and improving plasma stability.

2. The structure for improving plasma stability as described in claim 1, characterized in that: The discharge regulating resistor is a fixed resistor or an adjustable resistor.

3. The structure for improving plasma stability as described in claim 2, characterized in that: When a discharge current is generated in the plasma load structure, the magnitude of the discharge regulating resistor ensures that the magnitude of the discharge voltage is reduced below the critical value at which the discharge mode transitions.

4. The structure for improving plasma stability as described in claim 3, characterized in that: The plasma load structure includes a process cavity. When the plasma is formed, the process cavity is filled with gas, and a sheath is formed around the plasma.

5. The structure for improving plasma stability as described in claim 4, characterized in that: The change in discharge mode refers to the transition from alpha mode to gamma mode.

6. The structure for improving plasma stability as described in claim 5, characterized in that: The discharge voltage includes the sheath voltage of the sheath, and the critical value at which the discharge mode changes corresponds to the minimum sheath voltage at which the gas in the sheath undergoes secondary breakdown.

7. The structure for improving plasma stability as described in claim 4, characterized in that: The process chamber includes a dry etching chamber.

8. The structure for improving plasma stability as described in claim 1, characterized in that: The radio frequency generator provides dual-frequency radio frequency source signals.

9. A method for improving plasma stability, characterized in that, include: A discharge regulating resistor is set up, the output terminal of the matching unit is connected to the first terminal of the discharge regulating resistor, the second terminal of the discharge regulating resistor is connected to the plasma load structure, and the output terminal of the radio frequency generator is connected to the input terminal of the matching unit. Plasma is generated in the plasma load structure. When a discharge current is generated in the plasma load structure, the discharge regulating resistor provides a discharge regulating voltage that is proportional to the discharge current, thereby reducing the discharge voltage on the plasma load structure and improving plasma stability.

10. The method for improving plasma stability as described in claim 9, characterized in that: The discharge regulating resistor is a fixed resistor or an adjustable resistor.

11. The method for improving plasma stability as described in claim 10, characterized in that: When a discharge current is generated in the plasma load structure, the magnitude of the discharge regulating resistor ensures that the magnitude of the discharge voltage is reduced below the critical value at which the discharge mode transitions.

12. The method for improving plasma stability as described in claim 11, characterized in that: The plasma load structure includes a process cavity. When the plasma is formed, the process cavity is filled with gas, and a sheath is formed around the plasma.

13. The method for improving plasma stability as described in claim 12, characterized in that: The change in discharge mode refers to the transition from alpha mode to gamma mode.

14. The method for improving plasma stability as described in claim 13, characterized in that: The discharge voltage includes the sheath voltage of the sheath, and the critical value at which the discharge mode changes corresponds to the minimum sheath voltage at which the gas in the sheath undergoes secondary breakdown.

15. The method for improving plasma stability as described in claim 12, characterized in that: The process chamber includes a dry etching chamber.

16. The method for improving plasma stability as described in claim 9, characterized in that: The radio frequency generator provides dual-frequency radio frequency source signals.

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