TWI884103B - Plasma processor and heater - Google Patents

Abstract

The present invention provides a driving control circuit for a multi-zone heater of a plasma processor. A protection circuit is provided in each driving circuit, and a protection circuit including a high-frequency impedance element and a discharge capacitor is provided in the protection circuit to realize the output of a DC heating voltage, and at the same time prevent the leakage of a radio frequency signal, and can also lead the abnormally high voltage to the ground terminal through a voltage regulator diode and a discharge capacitor to avoid the destruction of the core optical coupler switch. The presence of the high-frequency impedance element makes the driving circuit have an area that is not interfered by the radio frequency signal. The present invention sets the state detection circuit in this area to realize stable temperature measurement, and further realizes the precise temperature control of each heating unit.

Description

Plasma processor and heater

The present invention relates to a plasma processor, and in particular to a temperature control driving device of a multi-zone temperature control base in a plasma reactor.

In the production process of semiconductor chips, a large amount of micro-processing is required. Common plasma etching reactors can form various micron or even nano-sized through holes or grooves on the wafer, and then combine with other processes such as chemical vapor deposition to finally form various semiconductor chip products. With the increasing requirements of etching processes, the control accuracy requirements for wafer or substrate temperature during plasma processing are also getting higher and higher. The original several independent temperature control areas can no longer meet the process requirements for the temperature difference within the same control area. In order to further improve the temperature control capability of the wafer, the previous technology proposed a matrix-arranged array of independently controlled heating units, which is integrated between the electrostatic chuck and the conductive base serving as the lower electrode.

Patent application CN 111211029 B filed by the same applicant describes a multi-zone temperature control structure. The plasma reactor in the patent application includes a cavity, the bottom of the cavity is a conductive base, and the conductive base is also connected to at least one high-frequency radio frequency power source as a lower electrode. After the plasma above the wafer is ignited, the radio frequency power source can adjust the plasma concentration or energy. Other radio frequency power sources can also be set in the plasma reactor, such as connecting the radio frequency power source to the gas nozzle at the top of the reaction chamber, or an inductor is set above the reaction chamber, so that the magnetic field generated by the inductor enters the reaction chamber to generate and maintain the plasma concentration. The conductive base is fixed to the bottom of the cavity through a supporting device, wherein the cavity and the supporting device are both made of a conductor and electrically grounded to prevent the radio frequency electric field from leaking outward. The conductive base includes an electrostatic chuck, which is made of an insulating material and has electrodes buried inside for achieving electrostatic adsorption. A multi-zone heating heater is also included under the electrostatic chuck, and the heater includes a large number of independently controllable heating units, wherein the number of heating units can be 10*10=100, or 15*15=225, or even more. The heating power enters the heater group controller through the power bus. At the same time, the heater controller is connected to the process controller through the control signal input line to receive the heating power distribution data required by the process. The controller can convert the received heating power distribution data into a driving signal for the opening time of the drive switch or the switch duty cycle.

In the technical solution described in the patent, each heating unit is driven by a driving circuit, and the driving circuit includes an optocoupler switch to achieve electrical isolation between the driving signal side and the control signal side. On the driving signal side, the optocoupler switch is directly connected in series with a driven heating unit. In the actual working environment, since the heating unit is in an RF radiation environment, when the RF power increases, resulting in an increase in RF voltage or arcing in the plasma processor, high voltage will be generated temporarily. Both of these high voltages will cause the optocoupler switch to collapse, causing the heater to fail. The existing drive circuit structure cannot avoid this problem, so the working stability is extremely poor and frequent maintenance and replacement of parts are required.

Therefore, it is necessary to propose a new multi-zone temperature-controlled plasma reactor that can prevent the optocoupler switch from collapsing and failing, and improve the reliability of the system.

The present invention provides a heater for a plasma processor, the heater comprising a plurality of heating units arranged in a horizontal direction, each heating unit being used for heating a different area above, and a plurality of driving circuits, each driving circuit being used for driving at least one heating unit for heating; the driving circuit comprising an optocoupler switch, two ports on one side of the optocoupler switch being used for receiving a control signal (S1) from a controller, and a first port and a second port on the other side being respectively connected to a direct current power source and one of the heating units; the driving circuit further comprising a protection circuit, the protection circuit comprising a high-frequency impedance unit connected in series between the second port of the optocoupler switch and the heating unit, and a discharge capacitor having one end connected to the direct current power source and the other end connected between the high-frequency impedance unit and the heating unit. The heater further includes a grounding capacitor group connected between the DC power source and the ground terminal, wherein the grounding capacitor group includes a plurality of capacitors with different capacitances connected in parallel to output abnormally high voltage currents of different frequencies to the ground terminal.

Optionally, the heater further includes a voltage regulator diode connected in parallel between two output ports of the optocoupler switch to further protect the optocoupler switch from being collapsed by high voltage.

The impedance of the high frequency impedance unit to DC is less than 1/100 of the impedance to RF signal, and preferably less than 1/1000, so that the RF power will not leak to the optocoupler switch.

Optionally, the heater further includes a detection circuit, which includes a sampling resistor connected between the second end of the optocoupler switch and the high-frequency impedance unit.

The present invention also provides a plasma processor, including a chamber and a base located in the chamber, the base is used to support a wafer to be processed, the base includes the above-mentioned heater and an electrostatic chuck located above the heater, and at least one radio frequency power source outputs radio frequency power to the base.

The multiple driving circuits in the heater further include a detection circuit, each detection circuit is used to detect a sampling signal on the driving circuit, the sampling signal is a voltage signal of a resistor connected in series with the heating unit, the detection circuit amplifies the sampling signal and transmits the processed signal to at least one input end of the controller through a second optical coupler switch. The controller receives the processed signal through at least one input end, calculates the processed signal, and adjusts the control signal output to the driving circuit where the detection circuit is located.

Optionally, the controller outputs an adjusted control signal to multiple driving circuits where and around the detection circuit to control the heating power of multiple heating units.

The technical solution of the present invention will be described in detail below in conjunction with the drawings. It should be emphasized that this is only an exemplary description and does not exclude other implementation methods that utilize the ideas of the present invention.

As shown in Figures 1a and 1b, the heating unit driving circuit of the present invention includes: a control signal S1 receiving end located at the first side (ends 1 and 2) of the photo-controlled relay OC1, a capacitor C10 is connected in parallel to the first side of the photo-controlled relay OC1 to form a stable control voltage, so that the second side (ends 3 and 4) of the photo-controlled relay OC1 is turned on. A voltage regulator diode D20 is also connected in parallel between the third and fourth ends of the optocoupler switch to protect the optocoupler switch from being damaged by excessive voltage. The fourth end of the optocoupler switch is connected to a DC drive power supply Vdc, which outputs a current for heating, and the output voltage can be 24V DC or other higher voltages. The DC drive power source Vdc is connected to the ground terminal GND through a ground capacitor group, wherein the ground capacitor group includes parallel ground capacitors C21 and C23. The DC drive power source Vdc is connected to the heating unit through a discharge capacitor C20. The present invention also includes a micro high-frequency impedance element M1 made of ferrite material, which has an impedance of less than 1 ohm to DC, but has an impedance greater than 1000 ohms corresponding to high-frequency signals such as 100Mhz signals, and the volume size of the micro high-frequency impedance element is only millimeter-level, so it can be installed in large quantities in the drive circuit of each heating unit. As long as the impedance to DC is less than 1/100 of the impedance to RF signal, it can be a single component or a functional circuit composed of multiple components, which can achieve the purpose of the present invention and is a high-frequency impedance element or RF impedance element required by the present invention. The micro high-frequency impedance element M1 is connected between the third terminal of the optical coupling switch and the heating unit, and one end of the voltage regulator diode D20 and the discharge capacitor C20 are connected to the two ends of the micro high-frequency impedance element M1.

During operation, the control signal S1 sends a high-level signal for heating, the optocoupler switch OC1 is turned on, and the current flows from the DC power supply Vdc through the current path i1 shown in Figure 1a to the heating unit. The heating unit and the entire driving circuit are both in an RF radiation environment, so the high-voltage RF signal will flow in the entire driving circuit. In the present invention, due to the blocking of the micro high-frequency impedance element M1, the RF signal will not flow to the optocoupler switch, but will flow as a weak current to C20 with a higher impedance to the RF signal and the grounding capacitor C21 and grounding capacitor C23 of the grounding capacitor group, wherein the capacitance value selection of the grounding capacitor C21 and the grounding capacitor C23 can adapt to RF signals of different frequencies, so that the fundamental wave and the additionally generated frequency harmonics in the plasma reaction chamber can reach the ground terminal through a suitable path. In addition, the discharge capacitor C20 needs to have a smaller capacitance value to reduce the large amount of RF power supplied to the plasma processor base leaking through the driving circuit, and only a small amount of RF power will reach the ground terminal through the discharge capacitor C20, the grounding capacitor C21, and the grounding capacitor C23. The present invention blocks the high-frequency signal from reaching the fragile optocoupler switch OC1 through the above-mentioned micro high-frequency impedance element M1, and blocks the leakage of RF power required for normal operation through the discharge capacitor C20. When an abnormal signal mutation (such as arcing) occurs, the pulse-shaped large current generated by the mutation signal can flow to the ground terminal through the discharge capacitor C20, the grounding capacitor C21, and the grounding capacitor C23, thereby achieving guided grounding of the destructive current. As shown in the dotted line in Figure 1b, it is the flow path of the destructive current i2. It can be seen that the destructive current flows to the ground terminal. Even if the voltage at both ends of the discharge capacitor C20 shows signs of temporarily exceeding the safety threshold, the voltage regulator diode D20 will be turned on, causing the current to pass through the high-frequency impedance M1, the voltage regulator diode D20, and the grounding capacitor C21/C23 in sequence to reach the ground terminal, ultimately maintaining both ends of the optocoupler switch OC1 in the safe voltage range.

Since the side of the high-frequency impedance element M1 close to OC1 (the left side in the figure) in the present invention basically blocks the passage of the radio frequency signal, while the DC signal can still pass through, a temperature measurement circuit can be further set in this area. As shown in FIG2, a heating unit driving circuit including a temperature measurement circuit is provided. Compared with FIG1a and FIG1b, a resistor R2 is provided between the first end of the high-frequency impedance element M1 and the voltage regulator diode D20, and two signal receiving ends (12, 13) of a comparator B1 are connected to the two ends of the resistor R2. The output end (14) of the comparator B1 is output to a transistor U1 for signal amplification, so as to amplify the comparison signal. The transistor includes a power supply terminal connected to the DC drive power source Vdc through a resistor R4. The output terminal of the transistor U1 is connected to the first terminal of the capacitor C31 and the first terminal (7) of the second optical coupling switch OC2, and the other terminal of the capacitor C31 is connected to the second terminal (8) of the second optical coupling switch OC2 and grounded. The two output terminals (9, 10) on the other side of the second optical coupling switch OC2 are respectively connected to the two ends of the voltage divider circuit composed of two series capacitors C31 and capacitor C32, and the output terminal 9 is grounded through a resistor R6, wherein the first terminal of the capacitor C31 is connected to the low-voltage DC power source, and the second terminal is connected to the capacitor C32 and outputs the feedback signal S2. During the heating process, since the heating unit is composed of a resistor wire, the temperature rise will simultaneously cause the overall resistance of the heating unit to rise. By measuring the resistance value of the heating unit, the current temperature of the heating unit can be calculated. Resistor R2 and the heating unit are connected in series, and resistor R2 is much smaller than the resistance of the heating unit, so the resistance of the heating unit dominates the impedance change of the entire series resistance. By detecting the voltage at both ends of R2, the current flowing through R2 and the heating unit can be calculated. Since the drive power supply voltage Vdc is fixed, the actual resistance of the heating unit can be calculated, and the actual temperature of the heating unit can also be calculated.

The above-mentioned temperature measurement circuit does not necessarily need to be configured on each drive circuit. Among the large number of temperature control areas on the base, the temperature of a large number of heating units in the first part of the area is relatively uniform, and only a few temperature measurement circuits need to be set in this area to monitor the temperature well. In addition, due to the presence of lifting pins or cooling gas holes in the second part of the area, or other hardware structures that seriously affect the temperature uniformity, this area requires a large number of temperature measurement circuits to accurately control the temperature of each heating unit and improve the overall temperature uniformity. The number of heating units corresponding to the first part of the area (70%) is much larger than the number of heating units corresponding to the second part of the area (30%). Taking 100 zones as an example, only 10 of the 70 heating units located in the first area can complete basic temperature monitoring, and the remaining 30 units need to be equipped with 15-20 temperature measurement circuits, so the total number of temperature measurement circuits required is 25-30. This can greatly reduce the number of temperature measurement circuits and save the number of input ports required for the controller 80.

The above-mentioned driving circuit composed of the optocoupler switch, the protection circuit and the status detection circuit, each of which needs to withstand a relatively high driving voltage and various abnormal high-voltage signals in the plasma processor. The other side of the two optocoupler switches is the controller 80 and the attached signal processing circuit, which are only used for signal processing and only require a relatively low voltage (such as 3-5V) to operate. The two areas are electrically isolated from each other by the optocoupler to avoid electrical signal interference between the two and to prevent the impact of high-voltage pulses from affecting the low-voltage control circuit area.

As shown in Figure 3, the overall heating unit drive control structure of the present invention, the heating voltage in the external RF radiation-free environment supplies heating power to a large number of heating units in the plasma processor through a filter. The upper computer (PC) is set by the staff to set the process function table of plasma processing, including the set process temperature, and transmits the control signal to the controller 80 located in the RF environment through the optical transceiver (optical fiber). The controller 80 outputs the control signal to the optocoupler switch in each drive circuit through multiple output ports S11-S1n. After being driven by the optocoupler switch, the heating voltage Vdc passes through the protection circuit to reach each heating unit for heating. A state detection circuit is connected between the optocoupler switch and the protection circuit. The state detection circuit transmits the electrical signals S21-S2n detected in the RF environment back to the controller 80 through the second optocoupler switch. Each optocoupler switch separates the circuit in the RF environment into a low-voltage control circuit including the controller 80 and its auxiliary circuits, and a high-voltage drive circuit including the state detection circuit and the protection circuit. Such a circuit structure design realizes the smooth bidirectional transmission of the control signal, the drive signal, and the feedback detection signal, while achieving electrical isolation, avoiding abnormal high voltage from propagating in the entire drive and control circuit to damage internal components. The low-voltage control circuit and high-voltage drive circuit of the present invention can be located below the base of the plasma processing device. The base has a temperature-controlled cooling liquid channel. The control circuit and drive circuit close to the base are in a low-temperature environment, which prevents the control and drive circuits from being affected by excessively high temperatures and damaging components, thereby further improving the long-term stability of the heater control circuit and drive circuit.

The detection circuit in the present invention may have other circuit structures besides the structure shown in FIG. 2 . For example, the comparator B1 and transistor U1 used for signal amplification may be replaced by other circuits capable of realizing signal amplification. As long as the circuit can detect the temperature of the heating unit in a radio frequency environment, it belongs to a variant embodiment of the present invention.

The present invention sets a protection circuit in the driving circuit, and sets a protection circuit including a high-frequency impedance element M1 and a discharge capacitor C20 in the protection circuit to realize the output of the DC heating voltage, and at the same time prevent the leakage of the radio frequency signal, and can also avoid the destruction of the core optical coupler switch by diverting the abnormal high voltage to the ground terminal through the diode D20 and the discharge capacitor C20. The existence of the high-frequency impedance element M1 makes the driving circuit have an area that is not interfered by the radio frequency signal. The present invention sets the state detection circuit in this area to realize stable temperature measurement, and further realizes the precise temperature control of each heating unit.

Although the content of the present invention has been described in detail through the above preferred embodiments, it should be recognized that the above description should not be considered as a limitation of the present invention. After reading the above content, various modifications and substitutions of the present invention will be obvious to those skilled in the art. Therefore, the protection scope of the present invention should be defined by the attached patent application scope.

OC1: photo-controlled relay S1: control signal C10: capacitor D20: voltage regulator diode Vdc: DC drive power supply GND: ground terminal C20: discharge capacitor C21: ground capacitor C23: ground capacitor M1: micro high-frequency impedance element R2: resistor B1: comparator U1: transistor C31: capacitor C32: capacitor OC2: second optocoupler switch S2: feedback signal R4: resistor R6: resistor i1: current path i2: destructive current path

Figures 1a and 1b are schematic diagrams of the heating unit drive circuit of the present invention; Figure 2 is a schematic diagram of the heating unit drive circuit of the present invention including a temperature measurement circuit; Figure 3 is a schematic diagram of the heater drive control circuit of the present invention.

S1: Control signal

C10: Capacitor

OC1: Light-controlled relay

D20: Voltage regulator diode

Vdc: DC drive power supply

C20: discharge capacitor

C21: Grounding capacitor

C23: Grounding capacitor

M1: Micro high frequency impedance element

i1: current path

Claims (12)

A heater for a plasma processor, the heater comprising a plurality of heating units arranged horizontally, each heating unit being used to heat a different area above, and a plurality of driving circuits, each driving circuit being used to drive at least one heating unit for heating; the driving circuit comprising an optocoupler switch, two ports on one side of the optocoupler switch being used to receive a control signal (S1) from a controller, and the first and second ports on the other side being respectively connected to a DC power source and the heating unit; the driving circuit further comprising a protection circuit, the protection circuit comprising a high-frequency impedance unit connected in series between the second port of the optocoupler switch and the heating unit, and a discharge capacitor having one end connected to the DC power source and the other end connected between the high-frequency impedance unit and the heating unit. A heater as described in claim 1, wherein the heater also includes a grounding capacitor group connected between a DC power source and a ground terminal. A heater as described in claim 1, wherein the heater further includes a voltage regulator diode connected in parallel between two output ports of the optocoupler switch. A heater as described in claim 1, wherein the impedance of the high-frequency impedance unit to direct current is less than 1/100 of the impedance to radio frequency signals. A heater as described in claim 1, wherein the heater further includes a detection circuit, wherein the detection circuit includes a sampling resistor connected between the second end of the optocoupler switch and the high-frequency impedance unit. The heater as described in claim 5 further includes a signal processing circuit connected to the sampling resistor, which compares and amplifies the signal on the sampling resistor and outputs it to a second optocoupler switch, and the second optocoupler switch outputs a feedback signal to the controller. A heater using the method as described in claim 1, wherein the heater comprises a grounding capacitor group, wherein the grounding capacitor group connects in parallel a plurality of capacitors having different capacitance values. A plasma processor includes a chamber and a base located in the chamber, wherein the base is used to support a wafer to be processed, and above the base includes a heater as described in claim 1 and an electrostatic chuck located above the heater, and at least one radio frequency power source outputs radio frequency power to the base. A plasma processor as described in claim 8, wherein the controller is located below the base, and the plasma processor further includes a host computer, which transmits a control signal to the controller via an optical fiber. In the plasma processor as described in claim 8, the multiple driving circuits in the heater also include a detection circuit, each detection circuit is used to detect a sampling signal on the driving circuit, the sampling signal is a voltage signal of a resistor connected in series with the heating unit, the detection circuit amplifies the sampling signal and transmits the processed signal to at least one input terminal of the controller through a second optocoupler switch. In the plasma processor as described in claim 10, the controller receives the processed signal through at least one input terminal, calculates the processed signal, and adjusts the control signal output to the drive circuit where the detection circuit is located. In the plasma processor as described in claim 10, the controller outputs an adjusted control signal to multiple driving circuits where and around the detection circuit to control the heating power of multiple heating units.