Structure and method for improving plasma stability

Abstract

The invention discloses a structure for improving plasma stability. The structure 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 in direct proportion to a 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 the plasma stability is improved. The invention further discloses a method for improving plasma stability. According to the invention, the discharge voltage of the plasma can be controlled, so that the plasma discharge is stable, the arc generation probability is reduced, and the product process and the productivity can be improved.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor integrated circuit manufacturing, and in particular to a structure for improving plasma stability. The present invention also relates to a method for improving plasma stability. Background Art

[0002] At present, dual-frequency RF glow discharge is mainly used in dry etching equipment. The main material on the surface of the electrostatic chuck is ceramic, which plays the role of dielectric barrier. As the RF discharge intensity increases, the stability of the discharge will deteriorate, especially when the discharge current is large. When the wafer surface is uneven or other accidental factors occur, it is easy to cause arcing, causing downtime or even chip breakage, which has a certain degree of damage to process stability and production capacity. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a structure for improving plasma stability, which can control the discharge voltage of plasma, thereby stabilizing plasma discharge and reducing the probability of arc occurrence, thereby improving product process and increasing production capacity. To this end, the present invention also provides a method for improving plasma stability.

[0004] In order to solve the above technical problems, the present invention provides a structure for improving plasma stability, which includes: a radio frequency generator, a matcher, a discharge adjustment 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 regulating resistor, and the second end of the discharge regulating resistor is connected to the plasma load structure.

[0006] 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, thereby improving plasma stability.

[0007] A further improvement is that the discharge regulating resistor is a fixed resistor or an adjustable resistor.

[0008] A further improvement is that when a discharge current is generated in the plasma load structure, the size of the discharge regulating resistor ensures that the size of the discharge voltage is reduced to below a critical value at which the discharge mode changes.

[0009] A further improvement is that the plasma loading structure includes a process chamber, and when the plasma is formed, the process chamber is filled with gas, and a sheath is formed around the plasma.

[0010] A further improvement is that the change in the discharge mode refers to a change from an alpha mode to a gamma mode.

[0011] A further improvement is that the discharge voltage includes a sheath voltage of the sheath, and the critical value at which the discharge mode changes corresponds to a minimum sheath voltage corresponding to a secondary breakdown of the gas in the sheath.

[0012] A further improvement is that the process chamber includes a dry etching chamber.

[0013] A further improvement is that the radio frequency generator provides a dual-frequency radio frequency source signal.

[0014] In order to solve the above technical problems, the method for improving plasma stability provided by the present invention comprises:

[0015] A discharge regulating resistor is provided, the output end of the matcher is connected to the first end of the discharge regulating resistor, the second end of the discharge regulating resistor is connected to the plasma load structure, and the output end of the radio frequency generator is connected to the input end of the matcher.

[0016] 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 proportional to the discharge current and thereby reduces the discharge voltage on the plasma load structure, thereby improving plasma stability.

[0017] A further improvement is that the discharge regulating resistor is a fixed resistor or an adjustable resistor.

[0018] A further improvement is that when a discharge current is generated in the plasma load structure, the size of the discharge regulating resistor ensures that the size of the discharge voltage is reduced to below a critical value at which the discharge mode changes.

[0019] A further improvement is that the plasma loading structure includes a process chamber, and when the plasma is formed, the process chamber is filled with gas, and a sheath is formed around the plasma.

[0020] A further improvement is that the change in the discharge mode refers to a change from an alpha mode to a gamma mode.

[0021] A further improvement is that the discharge voltage includes a sheath voltage of the sheath, and the critical value at which the discharge mode changes corresponds to a minimum sheath voltage corresponding to a secondary breakdown of the gas in the sheath.

[0022] A further improvement is that the process chamber includes a dry etching chamber.

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

[0024] The present invention is connected in series with a resistor, i.e., a discharge regulating resistor, before a load, i.e., a plasma load. After discharge occurs, a voltage drop is generated on the resistor, which plays a role of voltage division, so that the voltage applied to the dielectric layer and the gas of the plasma load is lower than the voltage output by the power supply, i.e., the radio frequency generator, so that the peak value of the discharge current is reduced. Therefore, the present invention can control the discharge voltage of the plasma, thereby stabilizing the plasma discharge and reducing the probability of arc occurrence. Since the probability of arc occurrence is reduced, the impact on the product and the downtime are reduced, thereby improving the product process and increasing the production capacity.

[0025] In addition, the series resistor added by the present invention will only generate a voltage drop when the plasma discharge occurs. If there is no discharge, there is 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 resistor, no voltage drop is generated. When the discharge occurs, there is a conduction current passing through the resistor, and a voltage drop will be generated on the resistor, which plays a role of voltage division. The conduction current is formed by the discharge current; and the ratio of the voltage drop generated by the series resistor to the circuit conduction current is the resistance value of the resistor; the resistance value of the resistor is a fixed value, so the voltage on the resistor and the conduction current have the same change trend, which 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, and the voltage division on the resistor increases. The increase in the voltage division on the resistor will reduce the discharge voltage. After the discharge voltage is reduced, the discharge current will also decrease, so the discharge is suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0027] Figure 1 Schematic diagram of a structure for improving plasma stability according to an embodiment of the present invention. DETAILED DESCRIPTION

[0028] like Figure 1 , which is a schematic diagram of a structure for improving plasma stability according to an embodiment of the present invention. The structure for improving plasma stability according to an embodiment of the present invention comprises: a radio frequency generator 101, a matcher 102, a discharge adjustment resistor 103 and a plasma load structure 104.

[0029] The output end of the RF generator 101 is connected to the input end of the matcher 102 , the output end of the matcher 102 is connected to the first end of the discharge regulating resistor 103 , and the second end of the discharge regulating resistor 103 is connected to the plasma load structure.

[0030] The discharge regulating resistor 103 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, thereby improving plasma stability.

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

[0032] When a discharge current is generated in the plasma load structure, the size of the discharge regulating resistor 103 ensures that the discharge voltage is reduced to below the critical value at which the discharge mode changes.

[0033] In the embodiment of the present invention, the plasma loading structure 104 includes a process chamber. When plasma is formed, the process chamber is filled with gas, and a sheath is formed around the plasma.

[0034] In an embodiment of the present invention, the process chamber includes a dry etching chamber.

[0035] The RF generator 101 provides dual-frequency RF source signals.

[0036] The matcher 102 is used to achieve impedance matching, and is usually composed of capacitors and inductors, but does not include resistors. The matcher 102 needs to set the impedance to maximize the effective power of the RF source signal propagating into the plasma load structure 104.

[0037] The change in discharge mode refers to the change from alpha mode to gamma mode. Alpha mode discharge is mainly maintained by positive ions, and the discharge is relatively stable. Gamma mode discharge is mainly maintained by secondary electrons. Secondary electrons are formed by bombarding gas after being accelerated by incident electrons, and have an avalanche effect, so gamma mode discharge is unstable. In the embodiment of the present invention, the discharge regulating resistor 103 can adjust the discharge voltage to prevent the discharge voltage from further increasing and thereby prevent the generation of gamma mode discharge.

[0038] 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 corresponding to the secondary breakdown of the gas in the sheath. The positive and negative charges in the plasma are balanced and maintained at a fixed potential; in the sheath, since the electron movement speed is greater than that of the positive ions, there will be fewer electrons than positive ions, so the sheath will be subjected to voltage in the lateral direction from the plasma to the sheath, that is, it has a sheath voltage. After the sheath voltage increases, the electrons are accelerated by the sheath voltage and are prone to secondary collisions, thereby forming secondary electrons. In the embodiment of the present invention, the discharge voltage can be reduced, and the sheath voltage is a component of the discharge voltage, so the sheath voltage will be reduced. 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, so the secondary breakdown can be prevented, so the gamma mode discharge can be prevented.

[0039] The embodiment of the present invention is connected in series with a resistor, i.e., a discharge regulating resistor 103, before a load, i.e., a plasma load. After discharge occurs, a voltage drop is generated on the resistor, which plays a role of voltage division, so that the voltage applied to the dielectric layer and the gas of the plasma load is lower than the voltage at the output of the power supply, i.e., the RF generator 101, so that the peak value of the discharge current is reduced. Therefore, the embodiment of the present invention can control the discharge voltage of the plasma, thereby stabilizing the plasma discharge and reducing the probability of arc occurrence. Since the probability of arc occurrence is reduced, the impact on the product and the downtime are reduced, thereby improving the product process and increasing production capacity.

[0040] In addition, the series resistor added by the embodiment of the present invention will only generate a voltage drop when the plasma discharge occurs. If there is no discharge, there is 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 resistor, no voltage drop is generated. When the discharge occurs, there is a conduction current passing through the resistor, and a voltage drop will be generated on the resistor, which plays a role of voltage division. The conduction current is formed by the discharge current; and the ratio of the voltage drop generated by the series resistor to the circuit conduction current is the resistance value of the resistor; the resistance value of the resistor is a fixed value, so the voltage on the resistor and the conduction current have the same change trend, which 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, and the voltage division on the resistor increases. The increase in the voltage division on the resistor will reduce the discharge voltage. After the discharge voltage is reduced, the discharge current will also decrease, so the discharge is suppressed.

[0041] In the embodiment of the present invention, after the output end of the RF generator is connected to the matcher, a resistor with a suitable resistance is connected in series, and then connected to the cavity load end, i.e., the plasma load structure, thereby improving the stability of the RF discharge, reducing the probability of arcing, and improving the process and the production capacity.

[0042] In radio frequency discharge and dielectric barrier discharge, as the discharge intensity increases, the sheath voltage in the discharge space rises accordingly. When the sheath voltage reaches the critical value and secondary breakdown occurs, the discharge will change from the uniform and stable alpha mode to the unstable gamma mode. In dry etching equipment, when the discharge intensity increases and the mode changes, downtime will occur, which will affect production capacity and product quality. In the embodiment of the present invention, when a resistor with a suitable resistance value is introduced, part of the voltage drop in the output power of the radio frequency generator will be loaded on the resistor, thereby reducing the voltage of the sheath in the discharge space, reducing the possibility of breakdown, and enhancing stability.

[0043] The method for improving plasma stability according to an embodiment of the present invention comprises:

[0044] A discharge regulating resistor 103 is provided, the output end of the matcher 102 is connected to a first end of the discharge regulating resistor 103 , the second end of the discharge regulating resistor 103 is connected to the plasma load structure, and the output end of the RF generator 101 is connected to an input end of the matcher 102 .

[0045] Plasma is generated in the plasma load structure 104. When a discharge current is generated in the plasma load structure, the discharge regulating resistor 103 provides a discharge regulating voltage proportional to the discharge current and thereby reduces the discharge voltage on the plasma load structure, thereby improving plasma stability.

[0046] In the method of the embodiment of the present invention, the discharge regulating resistor 103 is a fixed resistor or an adjustable resistor.

[0047] When a discharge current is generated in the plasma load structure, the size of the discharge regulating resistor 103 ensures that the discharge voltage is reduced to below the critical value of the plasma generation mode transition.

[0048] The plasma loading structure 104 includes a process chamber. When plasma is formed, the process chamber is filled with gas, and a sheath is formed around the plasma.

[0049] The process chamber includes a dry etching chamber.

[0050] The RF generator 101 provides dual-frequency RF source signals.

[0051] The plasma mode changes from alpha mode to gamma mode.

[0052] The discharge voltage includes a sheath voltage of the sheath, and the critical value at which the discharge mode changes corresponds to the minimum sheath voltage corresponding to the secondary breakdown of the gas in the sheath.

[0053] In the method of the embodiment of the present invention, by connecting in series with a resistor before the load, after the discharge occurs, a voltage drop will be generated on the resistor, which plays a role of voltage division, so that the voltage applied to the dielectric layer and the gas is lower than the voltage at the power supply output, so that the peak value of the discharge current is reduced. It should be pointed out here that if there is no discharge, there is 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 resistor, no voltage drop is generated. When the discharge occurs, a conduction current passes through the resistor, and a voltage drop will be generated on the resistor, which plays a role of voltage division. The ratio of the voltage drop generated by the series resistor to the circuit conduction current is the resistance value of the resistor. The resistance value of the resistor is a fixed value, so the voltage on the resistor and the conduction current have the same trend of change.

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

[0055] In the method of the embodiment of the present invention, in the radio frequency circuit of the dry etching equipment, the radio frequency generator output is connected to the radio frequency matcher, and the radio frequency matcher is first connected in series with a resistor with a suitable resistance value before being connected to the load of the cavity.

[0056] In RF discharge, when a resistor is introduced, a voltage drop will be generated when the current is conducted through the resistor, so that the voltage loaded on the plasma load in the circuit is suppressed, making it less likely for the plasma to undergo a mode transition and arcing phenomenon due to excessive discharge intensity.

[0057] In dielectric barrier discharge, after the introduction of the resistor, as the discharge occurs, the gas voltage that causes the discharge also rises with the increase of the applied voltage. When the gas voltage reaches the breakdown voltage, the discharge occurs, and the discharge current begins to generate pulses. With the occurrence of discharge, the charge formed by the discharge begins to move to the dielectric layer under the action of the electric field. Because it is opposite to the charge accumulated on the surface of the dielectric layer in the previous discharge, the charge generated by the discharge will quickly neutralize the charge accumulated in the previous discharge on the surface of the dielectric layer, thereby causing the gas voltage to drop, causing the discharge to extinguish and forming a discharge current peak. After the introduction of the series resistor, as the discharge occurs, a conduction current is formed in the discharge circuit, so a voltage drop will be formed on the series resistor, which plays a role of voltage division, further accelerating the drop of the gas voltage, thereby causing the discharge to extinguish more quickly. When the resistance value of the series resistor is large, the voltage division effect of the resistor will be more obvious. Therefore, after the series resistor is introduced and the discharge occurs, the voltage division effect of the resistor will accelerate the extinction of the discharge, thereby making the pulse of the discharge current shorter in time, that is, the half-height width of the discharge current pulse will become narrower. Therefore, the introduction of the series resistor will suppress the generation of multiple discharge current peaks during discharge and improve the stability of discharge.

[0058] The present invention has been described in detail above through specific embodiments, but these do not constitute limitations of the present invention. Without departing from the principle of the present invention, those skilled in the art may also make many variations and improvements, which should also be considered as the protection scope of the present invention.

Claims

1. A structure for improving plasma stability, characterized in that: include: RF generator, matcher, discharge regulating resistor and plasma load structure; The output end of the RF 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 regulating resistor, and the second end 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, thereby improving plasma stability.

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

3. The structure for improving plasma stability according to claim 2, wherein: When a discharge current is generated in the plasma load structure, the size of the discharge regulating resistor ensures that the size of the discharge voltage is reduced to below a critical value at which a discharge mode transition occurs.

4. The structure for improving plasma stability according to claim 3, characterized in that: The plasma loading structure comprises a process chamber. When the plasma is formed, the process chamber is filled with gas, and a sheath is formed around the plasma.

5. The structure for improving plasma stability according to claim 4, characterized in that: The change in discharge mode refers to a change from an alpha mode to a gamma mode.

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

7. The structure for improving plasma stability according to claim 4, wherein: The process chamber includes a dry etching chamber.

8. The structure for improving plasma stability according to claim 1, wherein: The radio frequency generator provides a dual-frequency radio frequency source signal.

9. A method for improving plasma stability, characterized in that: include: A discharge regulating resistor is provided, wherein the output end of the matcher is connected to the first end of the discharge regulating resistor, the second end of the discharge regulating resistor is connected to the plasma load structure, and the output end of the radio frequency generator is connected to the input end of the matcher; 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 proportional to the discharge current and thereby reduces the discharge voltage on the plasma load structure, thereby improving plasma stability.

10. The method for improving plasma stability according to claim 9, wherein: The discharge regulating resistor is a fixed resistor or an adjustable resistor.

11. The method for improving plasma stability according to claim 10, wherein: When a discharge current is generated in the plasma load structure, the size of the discharge regulating resistor ensures that the size of the discharge voltage is reduced to below a critical value at which a discharge mode transition occurs.

12. The method for improving plasma stability according to claim 11, wherein: The plasma loading structure comprises a process chamber. When the plasma is formed, the process chamber is filled with gas, and a sheath is formed around the plasma.

13. The method for improving plasma stability according to claim 12, wherein: The change in discharge mode refers to a change from an alpha mode to a gamma mode.

14. The method for improving plasma stability according to claim 13, wherein: The discharge voltage includes a sheath voltage of the sheath, and the critical value at which the discharge mode changes corresponds to a minimum sheath voltage corresponding to a secondary breakdown of the gas in the sheath.

15. The method for improving plasma stability according to claim 12, wherein: The process chamber includes a dry etching chamber.

16. The method for improving plasma stability according to claim 9, wherein: The radio frequency generator provides a dual-frequency radio frequency source signal.

Images