Ion current measurement system and method during plasma processing

Abstract

A system and method for ion current measurement during plasma processing is disclosed. The system includes a control circuit with a thermal feedback loop and pulse width modulation to enable dynamic power regulation. The ion current is determined by measuring the drop in heating power required to maintain a target temperature before and after plasma ignition and based on previously executed test program data.

Description

[0001] Cross-reference to related applications

[0002] This invention claims priority to U.S. Patent Application No. 18 / 974,819, filed on December 10, 2024. Technical Field

[0003] This invention relates to a system and method for determining ion current during plasma processing in semiconductor manufacturing. Specifically, it utilizes the precise temperature control of an electrostatic chuck (ESC) and various testing procedures to infer the ion current based on the decrease in heating power before and after plasma ignition within a vacuum chamber, achieving high-precision, fast-response real-time measurement. Background Technology

[0004] Ion current is a critical parameter in plasma-based semiconductor manufacturing processes such as etching and deposition, directly impacting process outcomes. Accurate, real-time ion current measurement is essential for monitoring plasma characteristics and optimizing process conditions. However, traditional ion current measurement techniques, such as the Langmuir probe or Faraday cup, are typically invasive, difficult to implement in situ, or have limited adaptability to varying operating conditions.

[0005] Electrostatic chucks are indispensable components in plasma processing, providing stable substrate positioning and precise temperature control. In many cases, the heating power required to maintain the target temperature on the electrostatic chuck surface indirectly but accurately reflects ion current information. However, existing electrostatic chuck temperature control systems typically rely on simple feedback loops or basic calibration methods, making it difficult to effectively adapt to variations in plasma operating conditions, target electrostatic chuck surface temperature, and cold plate temperature. These limitations hinder their applicability for ion current measurement in dynamic processing environments.

[0006] This invention proposes a novel system and method for determining ion current by utilizing the advanced temperature control capabilities of an electrostatic chuck. The invention introduces a control circuit with a thermal feedback loop and a pulse-width modulation (PWM) mechanism to achieve precise heating power regulation. During the testing process, the ion current is measured under various operating conditions using established techniques, and the reduction in heating power required to maintain the temperature of the electrostatic chuck region is recorded. This data is used to generate a lookup table or train a neural network to achieve real-time inference of the ion current based on the reduction in heating power before and after plasma ignition.

[0007] This real-time measurement capability enhances process monitoring and control, ensuring the uniformity and reliability of semiconductor manufacturing. Summary of the Invention

[0008] This invention provides a novel system and method for determining ion current during plasma processing in a semiconductor manufacturing system. By utilizing a precise temperature control mechanism of an electrostatic chuck, and based on the decrease in heating power required to maintain the target temperature before and after plasma ignition within the vacuum chamber, this invention enables real-time determination of the ion current.

[0009] In some embodiments, the system includes a control circuit with a thermal feedback loop and a PWM power delivery mechanism. A temperature sensor located in the electrostatic chuck provides real-time data, which the control circuit uses to dynamically adjust the PWM duty cycle to achieve precise regional temperature regulation. The system has a fast response speed.

[0010] This invention introduces a testing procedure to establish the relationship between ion current and heating power reduction under specific process conditions. In some embodiments, one such testing procedure includes operating the electrostatic chuck at a target temperature and measuring the ion current using techniques such as a Langmuir probe, Faraday cup, or electrode current monitoring. The testing procedure also includes recording the heating power reduction for each electrostatic chuck region during plasma processing and correlating these reductions with the ion current under different cold plate temperatures, zone temperatures, and plasma conditions.

[0011] In one embodiment, a lookup table is generated using data from a testing procedure to map the heating power reduction under specific operating conditions to ion currents. In other embodiments, this data is used to train a neural network to dynamically infer ion currents during processing. These methods are flexible enough to handle complex thermal interactions and variations in plasma operating conditions.

[0012] During operation, the system controller uses lookup tables or neural networks to infer the ion current in real time. By monitoring the heating power reduction in each zone, the system can accurately and reliably determine the ion current, achieving enhanced process control.

[0013] This invention provides a robust solution for ion current measurement, ensuring accurate measurements. The system is applicable to a variety of plasma processing operations and helps improve the uniformity and performance of semiconductor manufacturing processes. Attached Figure Description

[0014] The clarity of the various embodiments can be enhanced by referring to the following description in conjunction with the accompanying drawings:

[0015] Figure 1A An exemplary process system is shown, which includes a temperature control system equipped with an ESC.

[0016] Figure 1B Provides a schematic functional block diagram of a heating unit for adjusting the temperature of a specific area of ​​an electrostatic chuck.

[0017] Figure 2A This demonstrates a first implementation of an electrostatic chuck, which is divided into three concentric zones, each of which is independently controlled to achieve different temperature adjustments.

[0018] Figure 2B This demonstrates a second embodiment of an electrostatic chuck, which is configured with independently controlled grid-like areas to achieve precise temperature control of the surface.

[0019] Figure 3 Highlighting the schematic diagram of the control circuit for the electrostatic chuck temperature control system, which includes a thermal feedback loop for dynamically adjusting zone temperatures.

[0020] Figure 4A The flowchart presents a detailed explanation of the first test procedure, used to calibrate the electrostatic chuck and determine the reference voltage for the control circuit under different conditions.

[0021] Figure 4B The flowchart illustrates the electrostatic chuck partition temperature control method, explaining how the data generated by the first test program is used to maintain a precise temperature during operation.

[0022] Figure 5A The process flow diagram, which details how the second and third test procedures correlate ion current with plasma conditions, is presented.

[0023] Figure 5B This document presents a flowchart illustrating a method for determining ion current in real time during plasma processing using a lookup table or neural network. Detailed Implementation

[0024] To facilitate a full understanding of the invention, specific embodiments thereof will be described in detail below. While specific details are provided for ease of explanation, any modifications and variations consistent with the technical principles of the invention are considered appropriate. Certain well-known procedures and components are described selectively only to highlight the unique features of the invention.

[0025] Terminology definition:

[0026] ESC: A device used in semiconductor manufacturing that uses electrostatic force to firmly adhere a substrate (such as a semiconductor wafer) during processing, while simultaneously achieving precise temperature control of the substrate.

[0027] Processing chamber: A vacuum chamber used for plasma-based semiconductor processes such as etching or deposition, typically containing components such as electrostatic chucks and plasma sources.

[0028] Zoned temperature control: A method for independently controlling the temperature of different areas (or zones) on the surface of an electrostatic chuck to ensure uniform thermal conditions on the substrate or to meet customized requirements, which is crucial for maintaining process consistency.

[0029] Thermal feedback loop: a control mechanism that dynamically adjusts heating power in real time based on temperature sensor data and reference voltage to maintain the target temperature.

[0030] PWM: A technique that adjusts the power applied to a heater by modulating the duty cycle of electrical pulses, allowing for precise control of the heater's energy input.

[0031] Calibration procedure: A pretreatment step for determining the reference voltage or other parameters required for temperature control and ion current measurement, including testing the surface temperature and heating power of the electrostatic chuck under various operating conditions.

[0032] Lookup table: A data structure generated during the testing process that links parameters such as target electrostatic chuck temperature, cold plate temperature, heating power reduction, and ion current to enable real-time system control.

[0033] Neural network: A machine learning model trained using data generated during the testing process to dynamically infer ion current or reference voltage based on real-time measurements.

[0034] Cold plate: A cooling mechanism integrated with the electrostatic chuck, which uses internal coolant channels to regulate the reference temperature of the electrostatic chuck, ensuring stable thermal conditions during operation.

[0035] Heating unit: A local heating mechanism set in an electrostatic chuck for zoned temperature control, typically including a heater, temperature sensor and control circuit.

[0036] Temperature sensor: A device (such as a diode, transistor, or resistor) placed in an electrostatic chuck or cold plate to measure temperature in real time and provide feedback control data.

[0037] Control circuit: An electronic system that uses data generated by a temperature sensor to adjust the PWM duty cycle, ensuring precise and stable temperature control of the electrostatic chuck partition.

[0038] Reference voltage: The target voltage value used in the thermal feedback loop of the control circuit to maintain the electrostatic chuck at a specified temperature.

[0039] Ion current measurement: The process of quantifying the ion flux in the chamber can be indirectly determined by correlating the reduction in heating power before and after plasma ignition with calibrated ion current data.

[0040] Plasma ion flux: The ion flow rate generated in the plasma processing chamber can transfer energy to the substrate surface adsorbed by the electrostatic chuck, affecting its thermal balance and heating power requirements.

[0041] Heating power reduction: The reduction in power delivered to the electrostatic chuck heater to maintain the target temperature when the plasma ion flux provides additional heat.

[0042] Plasma source: A component in a process system that generates and sustains plasma; its operating conditions affect the ion current and the thermal effect on the electrostatic chuck.

[0043] Bias unit: A component that applies an electrical bias voltage to an electrostatic chuck or substrate, affecting the ion energy and flux in the processing chamber, and is crucial for processes such as etching.

[0044] Figure 1A A schematic diagram of a semiconductor manufacturing process system 100 is shown. The process system 100 includes a chamber 102 configured to create a vacuum processing environment. The process system 100 also includes a plasma source 103, powered by a radio frequency (RF) power generator 105, for generating plasma 104 within the chamber 102. An ESC 106 is used to adsorb substrates (such as semiconductor wafers) during processing.

[0045] For many processes, precise control of the substrate temperature during processing is crucial. Temperature control is achieved by balancing the heating and cooling of ESC106. The cooling mechanism of the cold plate 108 involves coolant circulation in one or more coolant channels 112. The cold plate 108 is typically made of a metal such as aluminum. The cold plate 108 also includes a temperature sensor 117 for measuring the temperature near the coolant channels 112. The placement of the temperature sensor 117 needs to be carefully designed to avoid interference from coolant flow while ensuring measurement accuracy. Multiple sensors can be used to measure the temperature distribution of the cold plate 108.

[0046] Above the cold plate 108 is a dielectric layer 110, typically made of materials such as aluminum nitride. Suction cup electrodes 114 are disposed within the dielectric layer 110, providing electrostatic force to attract the substrate. On the surface of ESC 106, grooves ( Figure 1A (Not shown) is used to provide a high-pressure inert gas flow. Helium is typically used to achieve this function. Substrate stability is achieved by balancing electrostatic forces with the pressure difference (the pressure difference between the inert gas layer and the vacuum environment inside chamber 102).

[0047] In some implementations, ESC 106 receives RF power from bias unit 111 via RF electrode 107 to generate a substrate bias. This bias is used to accelerate ions in plasma 104, which is crucial for high aspect ratio (HAR) etching.

[0048] The dielectric layer 110 also includes one or more heating units 116 for heating the surface of the ESC 106. A schematic diagram of the heating unit 116 is shown below. Figure 1B As shown. Heating unit 116 includes heater 118. Heater 118 may be a resistor or an active device, such as a metal-oxide-semiconductor field-effect transistor (MOSFET) or a bipolar transistor. Heating unit 116 includes an ion flux 138 from plasma 104 as an additional heat source. Heating unit 116 also includes a temperature sensor 120 disposed within dielectric layer 110 for measuring the temperature of the ESC 106 surface. Depending on the embodiment, temperature sensor 120 may include a diode, transistor, or resistor. Heating unit 116 also includes control circuitry 122 for controlling the temperature of a defined surface region or zone of ESC 106.

[0049] The process system 100 operates under the monitoring of the system controller 109. During plasma processing, the ion flux (also known as ion current) 138 impacting the surface of the electrostatic chuck can provide additional power to heat the various sections of the ESC 106. The bias unit 111 provides a bias voltage to accelerate the ions from the plasma 104. Therefore, the heating power required to maintain the temperature of the target region is reduced. The reduction in heating power before and after ignition of the plasma 104 is measured by the ion current.

[0050] ESC 106 may include multiple zones for providing different temperatures. (Reference) Figure 2A The top view of Embodiment 200 shows three regions of the electrostatic chuck: a central region 204, a middle region 206, and an edge region 208. Each region is designed to provide independently controlled temperature. Each region includes an independent heating unit 116. Each region may also include one or more temperature sensors 120.

[0051] When multiple zones are used, the cold plate 108 may also include one or more temperature sensors 117.

[0052] Figure 2BAnother embodiment 202 is shown, in which the ESC 106 is divided into grid-like regions. These regions are labeled as region 1, region 2, region 3, region 4, ..., region i, ... and region n. Each region is provided with an independently controlled temperature via an independent heating unit 116. Similarly, additional sensors 117 can be placed within the cold plate 108.

[0053] In one implementation, these areas may be thermally isolated. In another implementation, these areas may not be thermally isolated.

[0054] Figure 3 An exemplary control circuit 122 based on a thermal feedback loop is shown for controlling the surface temperature of the ESC 106. Figure 3 In the illustrated embodiment, the control circuit 122 includes a DC power supply 124 derived from a conventional power source, which can be an AC power source. If the power source is AC, an AC / DC converter is required to convert the power from AC to DC.

[0055] In one aspect of this embodiment, DC power modulator 126 modulates DC power supply 124 using PWM signal 134. In one embodiment, the PWM signal comprises a square wave waveform. The ratio of the signal's on-time to its period is defined as the duty cycle. The PWM output power of module 126 is supplied to heater 118. The power received by heater 118 is a function of the amplitude and duty cycle of the PWM signal. In one embodiment, the modulated DC power supply may also be converted back to DC power supply before being supplied to heater 118.

[0056] It should be noted that in the chamber 102 with plasma 104, especially when a high bias voltage is applied to the substrate to accelerate ions, the surface of ESC 106 is also affected by the ion flux 138.

[0057] Temperature sensor 120 measures the temperature near the surface of dielectric layer 110. Temperature sensor 120 outputs a voltage signal. Comparator 128 converts the output from temperature sensor 120 (labeled as...) into a voltage signal. 130) is used as an input and the generated reference voltage (labeled as) from controller 136 is used as an input. 132) As another input, the PWM output of comparator 128 is coupled to one input of DC power modulator 126 to modulate DC power supply 124, thus completing the thermal feedback loop. The temperature will fluctuate around a small value set by the reference voltage. Reference voltage The reference voltage is determined by controller 136 or system controller 109 and can be inferred using a lookup table or neural network. The lookup table and neural network are created during the calibration phase with a first test procedure, which will be described below.

[0058] It should be noted that the power required to maintain the temperature within its fluctuation range also depends on other factors, such as the temperature of the cold plate 108. Therefore, the controller 136 or system controller 109 generates... These factors must be taken into account, and precise temperature control must be achieved through calibration procedures.

[0059] Figure 4A A flowchart illustrating the calibration process for determining the reference voltage of control circuit 122 is shown. Process 400 begins at step 404, where the process system is in calibration mode under the control of system controller 109. In step 406, an electrostatic chuck surface temperature measurement device is set up. In one case, a specialized device resembling a wafer is placed on top of the electrostatic chuck. This device includes a high-precision temperature sensor array for measuring the temperature distribution on the electrostatic chuck surface. In step 408, system controller 109 runs a test program for each heating unit 116 at a selected cold plate temperature. After the test program is completed, the reference voltage for each heating unit in each region at different cold plate temperatures is determined. In step 410, the generated data is stored in the memory of controller 136 or system controller 109. In one embodiment, a lookup table is created for real-time derivation of the reference voltage based on the process recipe. In another embodiment, a neural network is trained based on this data. By running the neural network in inference mode, the reference voltage can be determined in real time.

[0060] Figure 4B A flowchart illustrating the zoned temperature control of the electrostatic chuck is shown. Process 402 begins at step 412, where the process is initiated according to the process recipe. In step 414, lookup table or neural network data stored in controller 136 or system controller 109 is retrieved. Then, controller 136 or system controller 109 generates a reference voltage for each electrostatic chuck region in each process recipe step. The appropriate reference voltage is inferred based on the cold plate temperature using the lookup table or neural network.

[0061] In step 416, plasma 104 is ignited, and the control circuit dynamically adjusts the PWM signal to achieve the desired zone temperature.

[0062] This invention provides an effective solution for controlling the temperature of electrostatic chucks. The system and method mitigate noise or interference by dynamically adjusting the duty cycle of the PWM signal, thereby robustly maintaining the desired temperature. For example, if the PWM signal changes due to the electromagnetic field of the RF power generator, the duty cycle is rapidly adjusted to maintain the required temperature.

[0063] Furthermore, with an ion flux of 138 serving as an additional heat source, the control circuit automatically reduces the power required to maintain the target temperature. This adaptive capability ensures precise and efficient temperature regulation of each area of ​​the electrostatic chuck under varying process conditions.

[0064] Figure 5A A flowchart of process 500 is shown for calibrating the ion current to suit the different operating conditions of the plasma source 103 and bias unit 111 of ESC 106. Process 500 begins at step 504, where system controller 109 causes process system 100 to operate in ion current calibration mode. In step 506, the ion current measurement device used for calibration is initialized.

[0065] Several commonly used methods for measuring ion current in plasma processing chambers include:

[0066] Langmuir probe: A small electrode inserted into the plasma. By applying varying voltages to the probe, current-voltage characteristics are measured to obtain information on ion current, electron temperature, and plasma density.

[0067] Ion energy analyzer: A device used to measure the energy distribution of ions reaching the chamber wall or substrate. It employs a grid electrode system to filter ions by energy before measuring the ion current.

[0068] Faraday cup: A metal cup designed to collect charged particles. Ion current is measured by detecting the charge collected when ions strike the surface of the cup; it is commonly used in beam diagnostics.

[0069] Electrode current measurement: Ion current is indirectly measured by monitoring the current flowing through the top electrode of the electrostatic chuck during plasma operation. A current sensor or ammeter integrated into the electrode or ground return path is used.

[0070] Deceleration field energy analyzer: This instrument uses a series of grids to filter ions according to their energy. Ions passing through the grids are collected by electrodes, and the ion current is measured as a function of the deceleration voltage.

[0071] In step 508, the system controller 109 executes a second test procedure using one of the methods described above to measure the ion current as a function of the operating conditions of the plasma source 103 and the bias unit 111. These operating conditions are derived from the process formulation. The measured ion current associated with the operating conditions is recorded in the storage unit of the system controller 109.

[0072] In step 510, system controller 109 operates each region of ESC 106 at the target temperature and records the heating power of each heater. Subsequently, plasma 104 in the chamber is ignited under specified operating conditions, while ion current is measured, executing the third test procedure. System controller 109 records the decrease in heating power for each region before and after plasma 104 ignition, establishing a relationship between power decrease and ion current under specified conditions (including target electrostatic chuck surface temperature and cold plate temperature).

[0073] In step 512, the system controller 109 generates a lookup table or trains a neural network based on the data collected in step 510. Using the lookup table or the trained neural network, the ion current is inferred in real time based on the decrease in heating power.

[0074] Figure 5B A flowchart illustrating a method for determining ion current during plasma treatment based on data acquired during previous test procedures is presented. Process 502 begins at step 514, where system controller 109 initiates the process according to the process recipe. In step 516, system controller 109 operates each region of the electrostatic chuck at the target temperature in each process recipe step. System controller 109 measures and records the heating power.

[0075] In step 518, the process recipe is executed step by step, and the system controller 109 measures the duty cycle of the PWM signal and determines the heating power. In step 520, the system controller 109 calculates the heating power reduction for each region in each process recipe step. Then, the ion current is inferred using a lookup table or neural network to achieve real-time determination of the ion current during plasma treatment.

[0076] The measured decrease in heating power in each region can be directly used to assess the uniformity of the ion current within the plasma processing chamber, simplifying real-time control. In some cases, a control mechanism can be employed, using a plasma source or bias unit configuration with adjustable knobs, to adjust the ion current to achieve the desired uniformity.

Claims

1. An electrostatic chuck for a process system, characterized in that, include: Multiple regions, each containing: A heating unit, used to regulate the temperature of the area; and A temperature sensor, used to measure the temperature of the area; Cold plate, which includes one or more temperature sensors and coolant channels; The control circuit for the heating unit includes: A thermal feedback loop, used to dynamically adjust the power applied to the heater of the heating unit based on the measured zone temperature; and The PWM mechanism is used to regulate the power applied to the heater in order to achieve the target temperature of the region specified in the process recipe; The system controller is configured to execute a first test program, a second test program, and a third test program, wherein... The first test procedure is used to determine the reference voltage of the control circuit in order to achieve the target temperature of the area; The second test procedure is used to determine the ion current as a function of the operating conditions of the plasma source and bias unit of the process system; The third test procedure is used to determine the ion current as a function of the decrease in heating power required to maintain the target temperature after plasma ignition.

2. The electrostatic chuck according to claim 1, wherein, The first test program, the second test program, and the third test program are all executed for each region.

3. The electrostatic chuck according to claim 2, wherein, The data generated by the test program is stored in the storage unit of the system controller and organized into one or more lookup tables.

4. The electrostatic chuck according to claim 3, wherein, One of the lookup tables is used to derive the ion current in real time based on the heating power measured before and after plasma ignition.

5. The electrostatic chuck according to claim 2, wherein, The data generated by the testing program is used to train one or more neural networks.

6. The electrostatic chuck according to claim 5, wherein, One of the neural networks is used to infer the ion current in real time during processing, based on the heating power measured before and after plasma ignition.

7. The electrostatic chuck according to claim 1, wherein, The control circuit includes a PWM generator configured to adjust the power duty cycle delivered to each heater based on feedback signals from temperature sensors.

8. The electrostatic chuck according to claim 7, wherein, The control circuit also includes a comparator that compares a reference voltage with a measured temperature signal from a temperature sensor to generate a feedback signal for controlling the power supplied to the heater, wherein the power is modulated according to the ion current.

9. The electrostatic chuck according to claim 1, wherein, The system controller measures the ion current using an ion current measuring device and, at the target region temperature, correlates the measured ion current with the decrease in heating power before and after plasma ignition to execute the third test procedure.

10. The electrostatic chuck according to claim 1, wherein, The control circuit includes a controller.

11. The electrostatic chuck according to claim 10, wherein, The controller operates under the monitoring of the system controller.

12. A method for determining the ion current during plasma treatment in a processing chamber, characterized in that, include: An electrostatic chuck with multiple zones is provided, wherein each zone includes a heating unit configured with control circuitry; Using the thermal feedback loop of the control circuit, each region is brought to the target temperature based on the process formula, and the required heating power is recorded. Ignite the plasma according to the process formula described above; as well as Measure and record the decrease in heating power required to maintain the target temperature.

13. The method according to claim 12, wherein, The uniformity of ion current within the chamber was assessed using the measured decrease in heating power.

14. The method according to claim 12, wherein, The method further includes performing a first test procedure to determine the reference voltage required for the control circuit to achieve the target temperature of the region.

15. The method according to claim 14, wherein, The method further includes performing a second test procedure to determine the ion current as a function of the operating conditions of the plasma source and bias unit of the process system.

16. The method according to claim 15, wherein, The second test procedure uses one or more of the following to measure ion current: a Langmuir probe, a Faraday cup, or an electrode current monitor.

17. The method according to claim 15, wherein, The method further includes performing a third test procedure to determine the ion current as a function of the decrease in heating power required to maintain the target temperature before and after plasma ignition.

18. The method according to claim 17, wherein, The method also includes determining the ion current value based on the measured decrease in heating power by means of a lookup table or neural network.

19. The method according to claim 18, wherein, The lookup table is generated using data collected during the testing process.

20. The method according to claim 18, wherein, The neural network is trained using data collected during the testing process.

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