Pulse voltage compensation for plasma processing applications.

Abstract

[0006] Embodiments provided herein generally include apparatus, e.g., plasma processing systems, and methods for plasma processing of substrates in a processing chamber. Some embodiments are directed to a method for waveform generation, generally including delivering a first waveform having an associated set point from an energy source, detecting at least one characteristic of the first waveform, evaluating a voltage decay during a portion of a pulse in the first waveform, calculating a compensation factor, and adjusting the at least one characteristic using the compensation factor to adjust the voltage decay.

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE Embodiments of the present disclosure relate generally to systems used in semiconductor device manufacturing, and more particularly to plasma processing systems used to process substrates. [Background technology]

[0002] Reliable formation of high-aspect ratio features is one of the key technological challenges for manufacturing next-generation semiconductor devices. High-aspect ratio openings used to form the features are typically formed using plasma-assisted etch processes, such as reactive ion etch (RIE) processes, which allow for directional, controlled (i.e., anisotropic) material removal to transfer a pattern from a mask layer to the exposed portion of the underlying substrate surface. As feature sizes continue to shrink and pattern densities continue to increase, the degree of anisotropy and within-substrate process uniformity of the RIE process become determining factors in the formation of closely spaced (fine-pitch) high-aspect ratio openings.

[0003] In etching processes in which plasma ions play a key role, ion energy control has always been a challenge for the semiconductor equipment industry. In a typical plasma-assisted etching process, a substrate is placed on an electrostatic chuck (ESC) located in a processing chamber, a plasma is formed above the substrate, and ions are accelerated from the plasma toward the substrate across a plasma sheath, i.e., an electron-depleted region formed between the plasma and the surface of the substrate. Traditionally, RF substrate biasing methods, which use sinusoidal radio frequency (RF) waveforms to excite the plasma and form the plasma sheath, have not been able to desirably form these smaller device feature sizes. Recently, it has been discovered that delivering high-voltage direct current (DC) pulses to one or more electrodes in the processing chamber can be useful for desirably controlling the plasma sheath formed above the surface of the substrate.

[0004] During plasma processing of a substrate, the voltage pulse is typically configured to include a sheath collapse phase, an ion current phase, and a sheath formation phase interposed between the sheath collapse phase and the ion current phase. The sheath collapse phase can be implemented by generating a positive voltage (e.g., 100 volts) that is used to collapse a sheath formed over the surface of a substrate disposed on a substrate support disposed within the processing chamber. During the ion current phase, ions within the processing chamber flow toward the surface of the substrate due to a generated negative voltage (e.g., −1600 volts) applied to an electrode disposed near the substrate. The ion current phase can be accompanied by an associated voltage decay in the voltage pulse established on the substrate during this phase, often referred to as “droop,” which can generally result in an undesirable ion energy distribution function (IEDF). The amount of voltage decay that occurs during plasma processing can vary due to several factors, including chamber pressure fluctuations, variations in process chemistry, and applied voltage and source power.

[0005] Therefore, there is a need in the art for an apparatus and method that provides improved control over the characteristics of the plasma sheath formed above a substrate during plasma-assisted processing of the substrate. Summary of the Invention

[0006] Embodiments herein provide a plasma processing chamber and method configured for fine tuning and controlling the plasma sheath formed during plasma-assisted processing of semiconductor substrates.

[0007] Some embodiments are directed to a method for waveform generation. The method generally includes delivering a first waveform from an energy source having an associated set point, detecting at least one characteristic of the first waveform using at least one sensor, determining a voltage attenuation value during a portion of a pulse in the first waveform by using the detected at least one characteristic and at least one stored voltage attenuation value function, determining a sheath coupling voltage value during a portion of the pulse of the first waveform by using the detected at least one characteristic and at least one stored sheath coupling voltage value function, calculating a compensation factor based on the determined voltage attenuation value and the determined sheath coupling voltage value, and adjusting the at least one characteristic using the compensation factor.

[0008] Some embodiments are directed to a method for waveform generation that includes delivering a first waveform from an energy source having an associated set point; detecting at least one characteristic of the first waveform using at least one sensor; determining a voltage attenuation value during a portion of a pulse provided in the first waveform by using the detected at least one characteristic and at least one stored voltage attenuation value function; determining a sheath coupling voltage value during the portion of the pulse of the first waveform by using the detected at least one characteristic and at least one stored sheath coupling voltage value function; calculating a compensation factor based on the determined voltage attenuation value and the determined sheath coupling voltage value; and adjusting the at least one characteristic of the first waveform by applying the calculated compensation factor to the at least one characteristic of the first waveform.

[0009] Some embodiments are directed to a waveform generator. The waveform generator generally includes a sensor assembly coupled to an output of a pulser, the sensor assembly including at least one sensor configured to detect at least one characteristic of a first waveform generated by the waveform generator, and a system controller coupled to the waveform generator. The system controller generally includes a processor and a memory, and the memory includes instructions, when executed by the processor, to: determine an amount of voltage attenuation in a portion of a pulse in the first waveform using at least one stored voltage attenuation value formula; determine an amount of sheath coupling voltage in the portion of the pulse of the first waveform using at least one stored sheath coupling voltage value formula; calculate a compensation factor based on the determined amount of voltage attenuation and the determined amount of sheath coupling voltage; and adjust the at least one characteristic using the compensation factor to adjust the voltage attenuation.

[0010] Some embodiments are directed to a waveform generator including: a sensor assembly coupled to an output of a pulser, the sensor assembly including at least one sensor configured to detect at least one characteristic of a first waveform generated by the waveform generator; and a system controller coupled to the waveform generator, the system controller including a processor and a memory, the memory including instructions, when executed by the processor, to: determine an amount of voltage attenuation in a portion of a pulse in the first waveform using at least one stored voltage attenuation value function; determine an amount of sheath coupling voltage in the portion of the pulse of the first waveform using at least one stored sheath coupling voltage value function; calculate a compensation factor based on the determined amount of voltage attenuation and the determined amount of sheath coupling voltage; and adjust at least one characteristic of the first waveform based on application of the calculated compensation factor.

[0011] To the accomplishment of the foregoing and related ends, the one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative features of the one or more aspects. These features are indicative, however, of but a few of the various ways in which the principles of the various aspects may be employed.

[0012] So that the above-mentioned features of the present disclosure may be understood in detail, a more particular description of the present disclosure briefly summarized above may be had with reference to embodiments, some of which are illustrated in the accompanying drawings. It should be noted, however, that the accompanying drawings depict only exemplary embodiments and are therefore not to be considered limiting of the scope thereof, which may admit of other equally effective embodiments. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a simplified cross-sectional schematic diagram of a processing system and signal detection module according to certain embodiments of the present disclosure. [Figure 2] FIG. 10 illustrates an example of an undercompensated voltage waveform established on a substrate in accordance with certain embodiments of the present disclosure. [Figure 3] FIG. 1 is a process flow diagram illustrating a method for waveform generation according to certain embodiments of the present disclosure. [Figure 4] FIG. 10 illustrates an example of a compensated voltage waveform established on a substrate in accordance with certain embodiments of the present disclosure. [Figure 5A] FIG. 10 shows a curve representing a detected voltage pulse formed in a burst of pulses of a voltage waveform, and a curve representing a plot of the portion of the voltage detected during the burst of pulses, in accordance with certain embodiments of the present disclosure. [Figure 5B] 5B shows a curve representing the current detected during delivery of a voltage pulse formed in a burst of pulses of the voltage waveform of FIG. 5A and a curve representing a plot of the current detected during a portion of the burst of pulses of FIG. 5A in accordance with certain embodiments of the present disclosure. [Figure 6A]FIG. 10 illustrates voltage decay value curves for waveforms in accordance with certain embodiments of the present disclosure. [Figure 6B] FIG. 1 illustrates a number of plasma sheath coupling curves in accordance with certain embodiments of the present disclosure. [Figure 7] FIG. 10 illustrates an example compensation factor as applied to a voltage waveform. DETAILED DESCRIPTION OF THE INVENTION

[0014] For ease of understanding, where possible, like reference numerals have been used to designate identical elements common among the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

[0015] Certain aspects of the present disclosure are generally directed to techniques for generating compensated voltage waveforms for plasma processing systems. During plasma processing of a substrate, a voltage waveform provided to an electrode disposed within a plasma processing chamber is typically configured to include a sheath collapse phase and an ion current phase. The sheath collapse phase can be implemented by generating a positive voltage (e.g., 100 volts) and is used to collapse a plasma sheath generated above the surface of a substrate disposed on a substrate support located within the processing chamber. During the ion current phase, ions within the plasma formed within the processing chamber begin to flow toward the surface of the substrate due to a negative voltage (e.g., >1000 volts) created by application of a pulsed voltage waveform to an electrode disposed near the substrate. The ion current phase can be accompanied by an associated voltage decay or "droop," which typically results in an undesirable energy distribution function (IEDF) at the surface of the substrate. The amount of voltage decay that occurs during plasma processing can vary due to several factors, including chamber pressure fluctuations, variations in process chemistry, and applied voltage and source power. Due to variations in plasma processing recipes and variations in voltage attenuation between the plasma processing chamber and the processing system, there is a need to account for voltage attenuation during plasma processing and compensate for the attenuation accordingly.

[0016] In aspects of the present disclosure, the waveform generator can use a ramp during the ion current phase of the pulse to perform voltage compensation to narrow the IEDF, as described in more detail herein. The compensated voltage waveform can be generated by applying a calculated compensation factor to the waveform generated by the pulsed voltage source to correct for voltage decay established on the substrate during plasma processing.

[0017] Plasma Processing System Example 1 is a simplified cross-sectional schematic diagram of a processing system and signal detection module according to certain embodiments of the present disclosure. In some embodiments, the processing system is configured for plasma-assisted etching processes, such as reactive ion etch (RIE) plasma processes. However, it should be noted that the embodiments described herein can also be used with processing systems configured for use in other plasma-assisted processes, such as plasma deposition processes, e.g., plasma-enhanced chemical vapor deposition (PECVD) processes, plasma-enhanced physical vapor deposition (PEPVD) processes, plasma-enhanced atomic layer deposition (PEALD) processes, plasma treatment processes, or plasma-based ion implantation processes, e.g., plasma doping (PLAD) processes.

[0018] As shown, the processing system includes a processing chamber 100 and a signal detection module 388 that can be used to monitor and control characteristics of the plasma sheath 101a during substrate processing. The processing chamber 100 includes the signal detection module 388, a support assembly 136, and a bias module 198. The bias module 198 can include one or more pulsed voltage (PV) waveform generators 150 and / or one or more RF generator assemblies 118. The support assembly 136 includes a support base 107 and a substrate support 105 disposed on and thermally coupled to the support base 107. As shown, the processing chamber 100 is configured to generate a capacitively coupled plasma by delivering a radio frequency (RF) signal from the RF power source 118 to the support base 107. However, it is contemplated that the signal detection module 388 can be used with any number of processing chambers, support assemblies, and bias modules to facilitate monitoring and control of the plasma sheath 101a during substrate processing.

[0019] Here, electrical signals that can be used to determine one or more characteristics of the plasma sheath 101a are received by the signal detection module 388, which then communicates information related to the electrical signals to the system controller 126 for use in controlling aspects of the plasma process. The system controller 126 can include a processor 190, a memory 192, and support circuits 194. The processor 190 can be a general-purpose computer processor configured for use in controlling processing chambers and associated sub-processors in an industrial environment. The memory 192, which is generally non-volatile memory, can include local or remote random access memory, read-only memory, floppy or hard disk drives, or other suitable forms of digital storage. The support circuits 194 are typically coupled to the processor 190 and include cache, clock circuits, input / output subsystems, power supplies, etc., and combinations thereof. Software instructions (programs) and data can be encoded and stored in the memory 192 for instructing the processor 190. Software programs (or computer instructions) readable by the processor 190 of the system controller 126 determine which tasks can be performed by components within the processing system.

[0020] Typically, a program readable by the processor 190 of the system controller 126 may be stored in memory 192 and includes code that, when executed by the processor 190, performs tasks associated with the plasma processing schemes described herein. The program may include computer-implemented instructions used to control various hardware and electrical components within the processing system to perform various processing tasks and sequences used to implement the methods described herein. In one embodiment, the program includes instructions used to perform one or more of the operations described below in connection with FIG. 3.

[0021] Typically, the system controller 126 determines one or more characteristics of the plasma sheath 101a based on information received from the signal detection module 388 and compares the determined sheath characteristics with desired sheath characteristics. Based on the difference between the determined sheath characteristics and the desired sheath characteristics, the system controller 126 can use the sheath compensation scheme described herein to adjust the one or more sheath characteristics, for example, by changing the configuration of one or more pulsed voltage (PV) waveforms established at the bias electrode 104. For example, the system controller 126 can cause the PV waveform generator 150 to change one or more characteristics of the pulsed voltage waveform delivered to the bias electrode 104. In some embodiments, a second PV waveform generator 150 (not shown) is coupled to the edge electrode 115 and is therefore configured to deliver one or more PV waveforms to the edge electrode 115. In this configuration, the system controller 126 can also cause the second PV waveform generator 150 to change one or more characteristics of the pulsed voltage waveform delivered to the edge electrode 115 during plasma processing.

[0022] In some embodiments, the RF generator assembly 118 delivers an RF signal to the support base 107 (e.g., a powered electrode or cathode) that can be used to generate (maintain and / or ignite) the plasma 101 in the processing region 129 disposed between the substrate support assembly 136 and the chamber lid 123. In some embodiments, the RF generator 118 is configured to deliver an RF signal to the support base 107 having a frequency of greater than 1 MHz or greater than about 2 MHz or greater, such as about 13.56 MHz or greater.

[0023] In some embodiments, the RF generator 118 and the RF generator assembly 160 are configured to deliver a desired amount of continuous wave (CW) or pulsed RF power, sometimes referred to herein as “source power,” at a desired, approximately fixed sinusoidal waveform frequency to the support base 107 of the substrate support assembly 136 based on control signals provided from the system controller 126. The RF generator 118 and the RF generator assembly 160 are configured to deliver RF power (e.g., an RF signal) to the support base 107 disposed near the substrate support 105 and within the substrate support assembly 136 during processing. The RF power delivered to the support base 107 is configured to ignite and maintain a plasma 101 containing a process gas disposed within the processing region 129. In some embodiments, the RF generator assembly 118 may alternatively be configured to deliver an RF signal to the chamber lid 123 to ignite and maintain a plasma 101 containing a process gas disposed within the processing region 129.

[0024] 1 illustrates the electrical connections between the signal detection module 388 and the node N, the connection point, and the bias electrode 104, the first PV module 196, and the electrostatic chuck clamping network 116. To reduce visual clutter, only one PV waveform generator 150 is illustrated in FIG. 1, but it should be noted that in embodiments herein, the signal detection module 388 is configured to receive electrical signals through the node N, the connection point, and electrical connections to elements within the bias module 198.

[0025] As shown, the signal detection module 388 is electrically coupled to individual electrical components within the processing chamber 100 through the use of multiple signal lines 387. The multiple signal lines 387 include multiple signal traces 392 coupled to various electrical components within the processing chamber 100 and are configured to deliver electrical signals to signal detection elements within the signal detection module 388. Generally, the signal detection module 388 includes one or more input channels 372 and a high-speed data acquisition module 320. The one or more input channels 372 are each configured to receive an electrical signal from the signal traces 392 and are electrically coupled to the high-speed data acquisition module 320. The received electrical signals may include one or more characteristics of a waveform established by the PV waveform generator 150 and / or the RF power supply 118.

[0026] The high-speed data acquisition module 320 includes one or more acquisition channels 322 that receive signal information from individual components of the processing chamber 100a via signal line 387 and one or more input lines 172. The high-speed data acquisition module 320 processes the received signal information to determine one or more characteristics of the waveform produced by the bias module and communicates the processed signal information to the system controller 126.

[0027] Generally, the signal detection module 388 includes multiple input channels 372, each electrically coupled to a corresponding acquisition channel 322 of the high-speed data acquisition module 320. As shown in FIG. 1 , the multiple input channels 372 are coupled to connection points located at various locations of the bias module 198 and clamping network 116 to measure and correct electrical data from those connection points or nodes N during processing. In some embodiments, the multiple input channels 372 may also be coupled to various electrical sensing elements, such as one or more current sensors configured to measure and correct electrical data at various points within the processing chamber 100.

[0028] Here, the high-speed data acquisition module 320 includes a plurality of acquisition channels 322, a data acquisition controller 323, and a memory 324 (e.g., non-volatile memory). The data acquisition controller 323 is electrically coupled to the output of each of the acquisition channels 322 and is configured to receive a digitized voltage waveform from each of the acquisition channels 322. Further, an algorithm stored in the memory 324 of the data acquisition controller 323 is adapted to analyze each of the digitized voltage waveforms to determine one or more waveform characteristics of each of the waveforms. The analysis may include a comparison of information received in the digitized voltage waveforms with information related to one or more stored waveform characteristics stored in the memory 324, as discussed further below.

[0029] The data acquisition controller 323 may include one or more of an analog-to-digital converter (ADC) (not shown), a processor 321, a communication interface (not shown), a clock (not shown), and optional drivers (not shown). The processor may be any general computing processor. Additionally, the processor may be a field programmable gate array (FPGA). The ADC converts signals in the output waveform from the analog domain to the digital domain, and the output digital signals of the ADC are provided to the processor 321 for processing. The processor 321 determines one or more waveform characteristics of the output waveform by analyzing the output digital signals provided by the ADC.

[0030] The memory 324 may be any non-volatile memory. The data acquisition controller 323 may be electrically coupled to the memory 324 and configured to store the waveform characteristics in the memory 324. In various embodiments, the memory 324 includes instructions executable by the data acquisition controller 323 to cause the data acquisition controller 323 to analyze the received output waveform and transmit information corresponding to the waveform characteristics determined based on the analysis of the received output waveform. A waveform analyzer stored in the memory 324 is executable by the data acquisition controller 323 and includes instructions that, when executed, cause the data acquisition controller 323 to analyze the output waveform and determine the waveform characteristics.

[0031] Information related to the analyzed waveform characteristics may then be transmitted to one or more of the feedback processor 325 and / or the system controller 126. The analysis performed by the data acquisition controller 323 may include comparing the waveform characteristics to one or more waveform characteristic thresholds stored in memory 324. In some embodiments, the analysis is based on one or more electrical characteristics of the process chamber 100 that are known and stored in memory.

[0032] In some embodiments of the processing chamber 100, a sensor assembly 170 is disposed between the PV waveform generator 150 and one or more of the bias electrodes 104. The sensor assembly 170 includes a current sensor that may be an in-line current sensor or may be disposed within the PV waveform generator 150.

[0033] In general, the PV waveform generated by the PV waveform generator 150 is configured to provide a nearly constant sheath voltage during a majority of the PV waveform cycle (e.g., the "ion current phase" in FIG. 2), which, in combination with the sheath thickness, enables the formation of a desired ion energy distribution function (IEDF) at the surface of the substrate 103. As described in the following manner, the ability to compensate the PV waveform to account for voltage decay at the bias electrode 104 enables fine tuning, control, and tailoring of process results across the surface of the substrate 103.

[0034] During processing, multiple PV waveforms are provided to the bias electrode 104 and ultimately to a complex load within the processing chamber 100 by the PV waveform generator 150 of the bias module 198. Overall control of the delivery of the PV waveforms from the PV waveform generator 150 is controlled through the use of signals provided from the signal detection module 388 and / or the system controller 126, as discussed below.

[0035] Example voltage waveform FIG. 2 illustrates an example of an undercompensated voltage waveform established on a substrate during plasma processing according to certain embodiments of the present disclosure. In some embodiments, the waveform may be applied in bursts rather than continuously during the performance of the plasma processing performed on the substrate. Burst of pulses 200A is an example of a single burst of pulses established on the substrate 103 by the delivery of a voltage waveform to the bias electrode 104 by the PV waveform generator 150. In some embodiments, the substrate 103 may be a wired version of the substrate 103, referred to herein as a “wired wafer.” The wired wafer may be used to detect one or more characteristics of the waveform and plasma characteristics established on the wafer during plasma processing. In some embodiments, the wired wafer may be coupled to the signal detection module 388 via wire 392A, as shown in FIG. 1, so that information related to one or more plasma processing characteristics (e.g., substrate voltage) can be determined in the plasma processing chamber. Waveform 200B illustrates an example of two pulses and portions of adjacent pulses on either side of the two pulses generated during a portion of burst of pulses 200A. In some embodiments, waveform 200B is a PV waveform that includes a first portion within each pulse (e.g., portion 204 between T1 and T2 and portion 206 between T3 and T4) that includes a positive slope (e.g., voltage per unit time) related to the voltage “droop” established on the substrate. The positive slope is formed on the substrate during the ion current phase of the PV waveform. Portions 204 and 206 of waveform 200B illustrate an example of an undercompensated voltage waveform established on a substrate, measured using a wired wafer. A voltage decay step count or staircase ramp includes several steps (e.g., ≥ 2 steps) and is applied at a fixed step voltage to the PV waveform to create a negative voltage ramp used to compensate for the positive voltage ramp created by the voltage decay or droop. A voltage decay step count may not be applied to waveform 200B, and waveform 200B may be uncompensated.

[0036] In some embodiments, portions 204, 206 of waveform 200B in FIG. 2 represent exemplary sampling windows used by signal detection module 388 to detect and / or determine characteristics of “droop” in the voltage waveform established on substrate 103 by the voltage waveform generated by PV waveform generator 150. In one example, the sampling window encompasses between about 50% and about 90% of the 400 kHz pulse waveform. Several parameters can affect the 400 kHz “droop,” including plasma density / species, baseline pulse voltage (PV) set point, temperature, and PV on-time. Several parameters can affect burst shape / spread, including burst on-time and source L2L pulsing.

[0037] The pulse in waveform 200B generally includes two main phases: an ion current phase and a sheath collapse phase. Both the ion current phase and sheath collapse phase portions of the waveform established at the substrate 103 are shown in FIG. 2. At the beginning of the ion current phase, delivery of the negative portion (e.g., ion current portion) of the PV waveform provided by the PV waveform generator 150 to the bias electrode 104 creates a voltage drop at the substrate 103, creating a high-voltage sheath above the substrate 103. The high-voltage sheath allows positive ions generated by the plasma to be accelerated toward the biased substrate. As more positive ions impinge on the surface of the substrate, over time, more positive charge accumulates on the surface of the substrate 103. This increase in positive charge on the surface of the substrate slowly increases the voltage or “substrate potential” at the substrate, creating a “droop.” As seen in FIG. 2, the voltage of waveform 200B slowly and undesirably increases from a more negative voltage at the beginning of the ion current phase to a less negative voltage during the latter portion of the ion current phase. If uncontrolled, the gradual buildup of positive charge on the surface of the substrate will result in a gradual discharge of the high-voltage sheath and chuck capacitance, slowly lowering the sheath voltage and causing the substrate potential to approach zero. The voltage difference between the beginning and end of the ion current phase determines the width of the ion energy distribution function (IEDF). A larger voltage difference results in a wider IEDF width, which is undesirable for several reasons and makes it more difficult to reliably form high aspect ratio features.

[0038] Process Monitoring and Control Examples 3 is a process flow diagram illustrating a method 300 of waveform generation according to certain embodiments of the present disclosure. The blocks of method 300 may be implemented through use of the system controller 126, as described above. Method 300 may enable the waveform generator 150 to compensate for voltage decay seen on the substrate 103, as illustrated in the example voltage waveform illustrated in FIG. 4. Method 300 includes delivering a first waveform having an associated set point to an electrode in a process chamber, detecting at least one characteristic of the delivered first waveform, evaluating voltage decay during a pulse portion during delivery of the first waveform to the electrode, calculating a compensation factor, and applying the compensation factor to correct for voltage decay in subsequent waveforms delivered to the electrode.

[0039] 4 illustrates an example of a compensated voltage waveform established on a substrate 103 by delivery of a voltage waveform to an electrode (e.g., bias electrode 104) disposed near the substrate, according to certain embodiments of the present disclosure. Burst of pulses 400A is an example of a burst of pulses of a compensated voltage waveform established at a substrate, which may be measured using a wired wafer. Waveform 400B illustrates an example of two pulses and portions of adjacent pulses on either side of the two pulses formed in burst of pulses 400A. In some embodiments, the compensated voltage waveform illustrated by waveform 400B has a region 402 or a region 404 within each pulse that is adjusted to compensate for voltage decay, similar to the voltage decay illustrated in waveform 200B.

[0040] To achieve monoenergetic ions and a narrower IEDF width during the ion current phase of the voltage waveform established at the substrate, operations are performed to compensate for the changing substrate potential during the ion current phase and create a region of approximately flat shape (e.g., approximately zero slope) in the established voltage waveform experienced by the substrate during plasma processing. An example of a voltage waveform experienced by a substrate during plasma processing is illustrated by the ion current phase portion of waveform 400B in FIG. 4. To establish a region of approximately flat shape in the voltage waveform established at the substrate, a waveform including a negative slope during the ion current phase (i.e., the ion current portion seen in FIG. 4) can be delivered to the bias electrode 104 by the PV waveform generator 150. Driving and / or implementing a negative voltage slope in the bias electrode 104 is also known as current compensation and can be created by the use of a current source coupled to the bias electrode 104. The negative voltage slope implemented during the ion current portion of waveform 400B is created by increasing the amount of electrons provided to bias electrode 104 by PV waveform generator 150 to counteract the otherwise increasing field caused by the positive charge that accumulates due to incoming ions striking the substrate during plasma processing. Thus, by determining the slope (dV / dt) of the voltage waveform established at substrate 103 using the methods described herein, system controller 126 can adjust the current provided by the current source and / or modify the characteristics of the PV waveform generated by the energy source (e.g., PV waveform generator 150) to maintain a constant sheath potential throughout the ion current phase of the waveform established at substrate 103. In some embodiments, a direct current (DC) supply current is used to implement a ramp with the desired slope during the ion current phase.

[0041] In block 302, a first waveform having associated set points is delivered to the electrode from an energy source (e.g., PV waveform generator 150). In some embodiments, the first waveform can be a high-voltage pulse waveform, and the first waveform can establish a plasma sheath 101a. The associated set points can be a baseline process including a waveform voltage set point, a process pressure set point, an RF power set point, and a substrate temperature set point during one or more phases of delivery of the waveform (e.g., waveform 400B) to the electrode, and can include a PV waveform on-time set point (e.g., the length of the ion current phase of the waveform).

[0042] In block 304, a sensor (e.g., a current sensor in sensor assembly 170) may detect at least one characteristic of the first waveform generated by PV waveform generator 150. The at least one characteristic may be a magnitude of the current detected by the current sensor (e.g., a current transformer reading taken from the sensor). In some embodiments, the sensor may be an in-line sensor positioned between the energy source (e.g., PV waveform generator 150) and the bias electrode 104.

[0043] In block 306, a voltage decay during a portion of a pulse formed during delivery of the first waveform may be evaluated. Evaluating the voltage decay may optionally include determining a voltage decay value during a portion of a pulse formed in the first waveform by using at least one detected characteristic and at least one stored voltage decay value function stored in memory 192 of the system controller 126, and determining a sheath coupling voltage value during the portion of the pulse of the first waveform by using at least one detected characteristic and at least one stored sheath coupling voltage value function. The sheath coupling voltage value is an empirically determined value representing capacitive coupling between a wired wafer and an electrode biased by delivery of a voltage waveform from an energy source (e.g., PV waveform generator 150) to the electrode. The sheath coupling voltage value is believed to vary as a function of one or more plasma processing parameters, including, but not limited to, the magnitude of the applied voltage delivered during the pulse, the process pressure, and characteristics of hardware within the processing chamber (e.g., the capacitance of a dielectric layer disposed between the substrate and the electrode). The sheath coupling voltage value may be determined for each processing chamber in a multi-chamber plasma processing system by a system controller through the use of an empirically derived function or through the use of a table of values ​​predetermined by measurements on previously processed substrates during plasma processing in the processing chamber. In some embodiments, the measurements are made through the use of a wired wafer that is at least capable of detecting the voltage established on the substrate during the plasma processing recipe performed in the processing chamber.

[0044] In some embodiments of method 300, both the stored voltage attenuation value function and the stored sheath coupling voltage value function may be previously determined and / or programmed, stored in memory 192, and retrieved from memory 192 for use in assessing and correcting voltage attenuation experienced by a substrate during a plasma processing recipe performed in the processing chamber. In some embodiments of method 300, the stored voltage attenuation value function and the stored sheath coupling voltage value function may be determined using a wired wafer, as discussed below. The stored voltage attenuation value function and the stored sheath coupling voltage value function may each include a single value, or may each include two or more values. The stored voltage attenuation value function and the stored sheath coupling voltage value function may each form a library or repository of data associated with multiple processing conditions and recipes for a given processing chamber.

[0045] 5A and 5B illustrate pulse characteristics of a voltage waveform established on substrate 103 through the use of sensing elements included in wired wafer and sensor assembly 170, according to certain embodiments of the present disclosure. Bursts of pulses 500A and 502A are examples of two different measurements used to characterize the electrical properties of a burst of pulses established on substrate 103. Burst of pulses 500A includes a detected fluctuating voltage established on the substrate due to delivery of a voltage waveform in a burst of pulses by PV waveform generator 150 to an electrode (e.g., bias electrode 104). Burst of pulses 502A includes a detected fluctuating current flowing between the electrode and PV waveform generator 150 due to delivery of a voltage waveform in a burst of voltage pulses by PV waveform generator 150 to the electrode. Waveform 500B (FIG. 5A) illustrates a time-varying voltage measured during a portion of a pulse formed within detected pulse burst 500A, and waveform 502B (FIG. 5B) illustrates a time-varying current measured during a portion of a pulse formed within detected pulse burst 502A. In some embodiments, waveform 500B is measured on substrate 103 through the use of a wired wafer. In some embodiments, it may be desirable to perform similar measurements in each processing chamber within a plasma processing system to characterize the actual electrical characteristics for each processing chamber. In other embodiments, it may be desirable to perform measurements in one processing chamber within a plasma processing system and then use the measured electrical characteristics for that processing chamber as representative electrical characteristics for other processing chambers within the plasma processing system.

[0046] Method 300 optionally includes generating a function with at least one voltage decay value, the function used to determine at least one sheath coupling voltage associated with a substrate during plasma processing. In some embodiments, method 300 can include detecting initial and final voltage values ​​established on substrate 103 during a pulse portion (e.g., waveform 500B of FIG. 5A ) of a burst of pulses (e.g., burst of pulses 500A of FIG. 5A ) generated during plasma processing to determine the at least one voltage decay value. The at least one voltage decay value can be detected through the use of one or more sensing elements coupled to one or more voltage sensing elements coupled to substrate 103. The pulse portion of the voltage waveform can be an interval of time within the pulse of waveform 500B (e.g., between T1 and T2) and can correspond to part or all of the ion current phase of waveform 500B. In some embodiments, the pulse portion of the waveform can be selected to avoid a pulse transition time, such as the transition between the sheath collapse phase and the ion current phase (e.g., the portion of the ion current phase immediately prior to time T1 of FIG. 5A ). 5A, the measured portion of the pulse is generally defined after the sheath formation phase of the voltage pulse occurs (i.e., the vertical drop just before the start of the ion current phase), beginning a short time after the start of the ion current phase. In some embodiments, the initial voltage value during the ion current phase is a function of the voltage waveform set point set by the PV waveform generator 150. The method 300 can also include determining a voltage delta value during the portion of the pulse (e.g., final voltage minus initial voltage) by use of the established initial and final voltage values ​​measured on the substrate 103.

[0047] Method 300 may optionally include detecting at least one measured current value (e.g., C1) during a pulse portion of waveform 502B ( FIG. 5B ) by use of a sensor (e.g., a current sensor in sensor assembly 170) configured to detect current flowing between PV waveform generator 150 and bias electrode 104. The pulse portion of the waveform may be measured at an initial time (e.g., T1) in waveform 502B and may correspond to the start of an ionic current phase of waveform 502B. In some embodiments, the current sensor may be an in-line sensor disposed between the energy source (e.g., PV waveform generator 150) and bias electrode 104 or a sensor disposed in a power delivery circuit within the energy source.

[0048] Method 300 can optionally include storing a plurality of voltage decay values ​​that are a function of the generated and measured current value (e.g., C1). As shown in FIG. 6A, the stored plurality of voltage decay values ​​can be used to form a curve 602 that represents the change in voltage (i.e., droop) on the substrate as a function of the detected and measured current value (e.g., C1) during the ion current phase portion of the voltage waveform. The voltage decay value can be predetermined by measuring the actual amount of voltage change (i.e., droop) of the voltage established on the substrate at a plurality of detected and measured current values ​​in the processing chamber at various plasma processing conditions, such as different pulsed voltage bias levels applied to the electrodes by the PV waveform generator, using a wired wafer.

[0049] In some embodiments, the method 300 can include storing multiple sheath coupling values ​​in memory. The sheath coupling value represents the capacitive coupling relationship between the substrate and the bias electrode (e.g., the bias electrode) when a voltage waveform is applied to the electrode by the PV waveform generator 150. The sheath coupling value is a measure of the difference between the voltage established on the substrate and the voltage applied to the electrode at the instant of a measured current value (e.g., C1 measured at time T1 in FIG. 5B). It has been found that the sheath coupling value varies as a function of the measured current value and the magnitude of the voltage applied to the electrode (e.g., the initial voltage measured at time T1). The generated initial voltage value is a function of the PV setpoint. For example, each curve (e.g., 604, 606, 608, 610, 612, 614) in FIG. 6B is associated with a different PV setpoint. The sheath coupling value can be determined by measuring the voltage on the wired wafer, comparing the measured voltage to the voltage delivered to the electrode, and noting the measured current value (e.g., C1) generated at the same instant. Note that the measured current value C1 is based on or affected by the response of the plasma processing chamber to the applied PV set point and the applied source power used to generate the plasma.

[0050] The voltage attenuation values ​​and sheath coupling values ​​may be stored, for example, in memory 192 of system controller 126. At least one voltage attenuation value and at least one sheath coupling value may be stored, for example, in the form of a table, graph, equation, or any other available means for recording a relationship. For example, Figures 6A and 6B illustrate examples representing voltage attenuation values ​​and sheath coupling values ​​(e.g., voltage delta, measured current value) associated with measurements of a waveform as measured on substrate 103, according to certain embodiments of the present disclosure.

[0051] In FIG. 6A , graph 600A illustrates the relationship (e.g., voltage droop) between voltage decay values ​​(i.e., the slope (dV / dt) of the voltage during the ion current phase) and measured current values ​​(e.g., C1). In some embodiments, determining the voltage decay value during the portion of the pulse in the first waveform (see block 306) includes finding a feature on graph 600A where a matching value of the first waveform is found, such as a measured current value or current C1, and then finding a corresponding voltage decay value (e.g., DV1) based on the relationship established by curve 602. As mentioned above, the voltage decay values ​​stored in memory 192 as a function of the measured current value may be stored in a table, graph, or equation such that when compared to the measured current value C1, the voltage decay value DV1 may be determined. Generally, the single voltage decay value is a measure of the rate of expected decay (i.e., droop) of the substrate voltage during the ion current phase of the voltage pulse based on the measured current value. In some embodiments, the determined voltage decay value DV1 may be used directly during the subsequent compensation factor determination (block 308). In some other embodiments, a voltage delta (ΔV) may be determined based on the determined voltage decay value DV1 by multiplying the determined voltage decay value DV1 by the known length of the ionic current phase during which the measured current value C1 was measured. The length of the ionic current phase is related to the PV on-time of the voltage pulse.

[0052] In FIG. 6B, graph 600B illustrates the relationship between initial voltage and measured current value (current_i) for various PV set points used to find the sheath coupling voltage value. Each of curves 604, 606, 608, 610, 612, and 614 represents a single PV set point, and therefore the sheath coupling voltage value (i.e., Y-axis) can be determined with knowledge of the measured current value (i.e., X-axis) at the known PV set point. Note that in the example illustrated in FIG. 6B, the magnitude of the PV set points (e.g., the magnitude of the ion current voltage during the ion current phase) used to generate curves 604, 606, 608, 610, 612, and 614 decrease in magnitude from curve 604 to curve 614. In one example, the sheath coupling voltage value (see block 306) during the pulse portion of the first waveform may be determined by detecting the measured current value C1 (amperes) and finding the corresponding sheath coupling value DV2 (volts) using the known PV set point indicated by curve 614 in sheath coupling graph 600B. As mentioned above, the sheath coupling values ​​stored in memory 192 as a function of the measured current value may be stored in a table, graph, or equation such that when compared to the measured current value C1, a single sheath coupling value may be determined. In some embodiments, multiple different sets of curves, such as two or more sets of curves 604, 606, 608, 610, 612, and 614, may be stored in memory and used and / or selected based on adjustment of one or more different plasma processing parameters, such as source power, percentage on-time of the PV pulse, pulse frequency, or other plasma processing parameters that will affect the sheath coupling value.

[0053] In some plasma process steps performed on a substrate, it is desirable to adjust the PV set point to achieve a desired voltage on the substrate during the ion current phase of the applied PV pulse. In some cases, the actual desired PV set point required to achieve the desired voltage and process result may not match one of the generated curves 604, 606, 608, 610, 612, and 614 stored in memory and utilized to determine the sheath coupling value DV2 (volts). In some embodiments, as illustrated in FIG. 6B, it is desirable to adjust the PV set point to a value that falls between two known curves, such as curves 612 and 614, to achieve a desired process result on the substrate during the plasma process performed on the substrate. In FIG. 6B, the measured current value C1 ’ In the figure, the new PV set point is shown as curve 613, which can be determined by interpolating points between 612 and 614 of the two known curves. Thus, the measured current value C1 at the new PV set point ’ (FIG. 6B) and by using the system controller 126 to find the interpolated PV set point, the new sheath coupling value DV2 ’ (FIG. 6B) can be determined. Using this technique, for any desired PV set point, a new sheath coupling value DV2 ’ can be determined.

[0054] At block 308, a compensation factor may be calculated based on the determined voltage delta (ΔV) determined from the voltage decay value DV1 and the determined sheath coupling value DV2. The compensation factor is calculated based on the voltage delta (ΔV) and the determined sheath coupling voltage value DV2, which is determined from information received by detecting the measured current value C1 during one or more pulses in the generated waveform. In some embodiments, the compensation factor is used to adjust the magnitude of the voltage applied during the ion current phase as a function of time based on the expected slope determined from the voltage decay value DV1 and the expected offset of the voltage determined from the sheath coupling value DV2. For example, as described above, FIG. 4 illustrates example optimally compensated voltage waveforms (e.g., 402, 404) established on the substrate 103 through the implementation of voltage decay steps.

[0055] 7 illustrates an example of the effect of applying the compensation factor determined in block 308 to a voltage waveform applied to an electrode, such as bias electrode 104 shown in FIG. 1, by use of system controller 126. The example waveform illustrated in FIG. 7 generally includes two main phases applied to the electrode: an ion current phase and a sheath collapse / ion neutralization phase. At the start of the ion current phase, a drop in the applied voltage causes positive ions formed in the plasma to flow to the surface of substrate 103, establishing a high-voltage sheath above the substrate. As discussed above, charging of the surface of the substrate due to the flow of positive ions to the substrate surface creates a voltage droop.

[0056] Thus, by applying the compensation factor determined in block 308, the slope of the waveform established on the substrate during the ion current phase can be adjusted to be zero or close to zero, improving the ion energy distribution function (IEDF) produced during plasma processing. An example of a compensated waveform is shown in FIG. 4B. The compensated portion of the voltage waveform delivered from the power supply (e.g., waveform generator 150) to the bias electrode 104 can include the portions of the waveform represented by lines 712, 714, 716 in FIG. 7.

[0057] In some embodiments, calculating the compensation factor involves using the voltage delta (ΔV) and the determined sheath coupling voltage value DV2, as well as the known PV on-time found within the pulse of the voltage waveform. In some embodiments, the PV setpoint on-time of the waveform may be stored in memory 192 and used along with the determined voltage decay value DV1 and sheath coupling voltage value DV2 to calculate the compensation factor. The determined sheath coupling voltage value DV2 sets an offset for the voltage established at the substrate 103 during plasma processing, and may include, for example, a larger voltage drop (e.g., more negative) from the initial voltage drop (V0) formed during the sheath formation phase used in the previous pulse to an amount equal to the magnitude of the sheath coupling voltage value DV2, as shown in FIG. 7. For example, the sheath coupling voltage value DV2 may be applied to the initial applied voltage V0 generated by the power supply to shift the voltage to a compensated voltage value (e.g., V0 + DV2) to allow a more optimized negative voltage to be applied at the beginning of the ion current phase. The voltage decay value DV1 is also multiplied by the PV setpoint on-time value (seconds) to determine the voltage delta (ΔV) compensation (e.g., the required slope of curves 712, 714, 716) needed over the length of PV on-time to allow for a more optimized IEDF that compensates for voltage decay (e.g., droop). Thus, in some cases, the compensation factor includes the amount of correction made by the determination of the sheath coupling voltage value DV2 and the determined voltage delta (ΔV) derived from the determined voltage decay value DV1.

[0058] While the voltage delta (ΔV) compensation applied during the ion current phase is illustrated in FIG. 7 as a straight line (e.g., a first-order curve), this configuration is not intended to be limiting with respect to the scope of the present disclosure provided herein, and thus the compensation provided during the ion current phase can include a nonlinear shape depending on the need to better tune the plasma process performed during this phase of the PV pulse. In some examples, the voltage delta (ΔV) compensation provided during the ion current phase can include second-order, third-order, fourth-order, or even higher-order corrections (e.g., Nth-order). In another example, the voltage delta (ΔV) compensation provided during the ion current phase may include dividing the compensation provided during the ion current phase into a series of interconnected substeps that form a staircase, spline, or other desired curve shape. In this example, each of the interconnected substeps can include a first-order, second-order, third-order, fourth-order, or Nth-order correction.

[0059] In block 310, a compensation factor is applied to correct for voltage decay in subsequent portions of the waveform, such as during one or more voltage pulses. Correcting the voltage decay in subsequent waveforms can include adjusting at least one characteristic (e.g., bias voltage, current C1) using the compensation factor. In some embodiments, the compensation factor can be applied as a continuous slope. In some embodiments, rather than forming a linear ramp during the ion current phase, the calculated compensation factor can be used to determine the number of voltage decay steps applied during each ion current phase of the pulse to correct for the voltage decay, as well as the length and / or size of each step. In other words, the compensation factor can be applied in steps as a continuous voltage ramp or a nonlinear voltage ramp. In some embodiments, the compensation factor can be applied to subsequent waveforms as a number of voltage decay steps (e.g., stepped ramp correction). An example of a compensated waveform established in a substrate including three steps is shown in FIG. 4B.

[0060] In some embodiments, the voltage decay may be evaluated during processing of a wafer (e.g., substrate 103), and a compensation factor may be applied to correct for the voltage decay in pulses of subsequent bursts to the wafer. In other embodiments, the voltage decay may be evaluated during processing of a wafer, and a compensation factor may be applied to correct for the voltage decay in pulses of subsequent bursts.

[0061] In some embodiments, the voltage attenuation may be evaluated during processing of a wafer (e.g., substrate 103), and a compensation factor may be applied to correct for the voltage attenuation in subsequent waveforms on subsequent wafers. However, with stored voltage attenuation and sheath coupling values, the subsequent wafer need not be an interconnected wafer, and the calculation of the compensation factor may rely on previously stored voltage attenuation and sheath coupling values.

[0062] In some examples, such as that illustrated in FIG. 7, the voltage waveform is oscillated at frequencies between about 50 kHz and 1000 kHz (1 / T p The voltage waveform established at the electrodes can be determined by the ion current time period (e.g., the length of the ion current step) and the waveform period T P The voltage waveform having a waveform cycle may have an on-time defined as a ratio of the on-time to the on-time of the voltage waveform, and may be greater than 50%, or greater than 70%, such as between 80% and 95%. P (e.g., about 2.5 μs) and may be continuously repeated in waveform bursts with burst periods that are between about 100 microseconds (μs) and about 10 milliseconds (ms). The PV waveform bursts may have a burst duty cycle between about 5% and 100%, such as between about 50% and about 95%, where the duty cycle is the ratio of the burst period divided by the burst period plus the non-burst periods (i.e., no PV waveform is generated) that separate the burst periods. As shown, the sheath collapse phase has a duration T that may be about 200 ns. SH (e.g., off time).

[0063] Addendum As used herein, the term "coupled" refers to a direct or indirect coupling between two objects. For example, if object A is in physical contact with object B, which is in contact with object C, then objects A and C may also be considered coupled to each other, even though they are not in direct physical contact with each other. For example, a first object may be coupled to a second object even though the first object is not in any direct physical contact with the second object.

[0064] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, the scope of which is determined by the appended claims.

Claims

1. delivering a first waveform having an associated set point from an energy source; Detecting at least one characteristic of the first waveform using at least one sensor; determining a voltage decay value during a portion of a pulse provided in the first waveform by using the at least one detected characteristic and at least one stored voltage decay value function; determining a sheath coupling voltage value during the portion of the pulse of the first waveform by use of the at least one detected characteristic and at least one stored sheath coupling voltage value function; calculating a compensation factor based on the determined voltage attenuation value and the determined sheath coupling voltage value; adjusting at least one characteristic of the first waveform by applying the calculated compensation factor to the at least one characteristic of the first waveform; 11. A method for waveform generation, comprising:

2. The method of claim 1 , wherein the first waveform is a high voltage pulse waveform and establishes a sheath.

3. The method of claim 1 , wherein the associated setpoint is a baseline process, voltage, and temperature (PVT) setpoint.

4. The method of claim 1 , wherein the at least one characteristic is a current sensor indicator.

5. The method of claim 1 , wherein the at least one sensor is an in-line sensor and is contained within a current transformer.

6. detecting at least one value associated with an initial voltage and at least one value associated with a final voltage during the portion of the pulse of the first waveform by using at least one second sensor coupled to the wired wafer; determining at least one voltage delta value by using the at least one value associated with an initial voltage and the at least one value associated with a final voltage; detecting at least one measured current value during the portion of the pulse of the first waveform using the at least one sensor; storing the at least one stored voltage decay value representing a relationship between the at least one voltage delta value and the at least one measured current value; The method of claim 1 further comprising:

7. 7. The method of claim 6, further comprising storing at least one stored sheath coupling voltage value representing a second relationship between the at least one value associated with an initial voltage and the at least one measured current value.

8. The method of claim 1 , wherein the process, voltage, and temperature (PVT) on-time of the first waveform is known.

9. The method of claim 1 , wherein the compensation factor is a number of voltage decay steps.

10. The method of claim 1 , wherein adjusting the at least one characteristic of the first waveform comprises applying a continuous voltage ramp to a portion of the pulse.

11. 1. A waveform generator comprising: a sensor assembly coupled to an output of the pulser, the sensor assembly including at least one sensor configured to detect at least one characteristic of a first waveform generated by the waveform generator; a system controller coupled to the waveform generator; Equipped with the system controller includes a processor and a memory; The memory, when executed by the processor, determining an amount of voltage decay during a portion of a pulse in said first waveform using at least one stored voltage decay value function; determining an amount of sheath coupling voltage during said portion of a pulse of said first waveform using at least one stored sheath coupling voltage value function; calculating a compensation factor based on the determined amount of voltage attenuation and the determined amount of sheath coupling voltage; adjusting the at least one characteristic of the first waveform based on application of the compensation factor. Including instructions, Waveform generator.

12. the first waveform is a high-voltage pulse waveform; the first waveform establishes a sheath; 12. The waveform generator of claim 11.

13. the first waveform has an associated set point; the associated setpoint is a baseline process, voltage, and temperature (PVT) setpoint; 12. The waveform generator of claim 11.

14. The waveform generator of claim 11 , wherein the at least one characteristic is a current sensor index.

15. The waveform generator of claim 11 , wherein the at least one sensor is an in-line sensor.

16. The memory, when executed by the processor, determining at least one value associated with an initial voltage and at least one value associated with a final voltage during said portion of said first waveform using at least one second sensor coupled to the wired wafer; determining at least one voltage delta value by using the at least one value associated with an initial voltage and the at least one value associated with a final voltage; using the at least one sensor to determine at least one measured current value during the portion of the first waveform; storing in the memory the at least one stored voltage decay value function representing a relationship between the at least one voltage delta value and the at least one measured current value; 12. The waveform generator of claim 11, further comprising instructions.

17. The memory, when executed by the processor, storing in said memory at least one stored sheath coupling voltage value formula representing a second relationship between said at least one value associated with an initial voltage and said at least one measured current value; 17. The waveform generator of claim 16, further comprising instructions.

18. 12. The waveform generator of claim 11, wherein the process, voltage, and temperature (PVT) on-time of the first waveform is known.

19. 12. The waveform generator of claim 11, wherein the compensation factor is a number of voltage decay steps.

20. 12. The waveform generator of claim 11, wherein the compensation factor is applied as a continuous voltage ramp or a non-linear voltage ramp.

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