Low frequency radiofrequency (RF) pulse shaping over a state

Abstract

A method is disclosed for plasma processing of a substrate. The method includes generating a low frequency radiofrequency (RF) signal. The low frequency RF signal has a frequency within a range extending from about 10 kilohertz to about 2 megahertz. The method also includes supplying the low frequency RF signal to a plasma processing chamber. The method also includes controlling a power level of the low frequency RF signal over a duration of a given state within a multi-state plasma processing operation, such that a plurality of different power levels of the low frequency RF signal are supplied to the plasma processing chamber during the given state. The duration of the given state is less than about 25 microseconds.

Description

Low Frequency Radiofrequency (RF) Pulse Shaping Over a State by inventorsJohn Holland, Ranadeep Bhowmick, Alexei Marakhtanov, Bradford J. Lyndaker, Chen Chen Background of the Invention

[0001] Plasma processing systems are used to manufacture semiconductor devices, e.g., chips / die, on semiconductor wafers. In the plasma processing system, the semiconductor wafer is exposed to various types of plasma to cause prescribed changes to a condition of the semiconductor wafer, such as through material deposition and / or material removal and / or material implantation and / or material modification, etc. During plasma processing of the semiconductor wafer, radiofrequency (RF) power is transmitted through a process gas within a chamber to transform the process gas into the plasma in exposure to the semiconductor wafer. Reactive constituents of the plasma, such as radicals and ions, interact with materials on the semiconductor wafer to achieve a prescribed effect on the semiconductor wafer. In some plasma processing systems, RF power is transmitted from an electrode structure to the processing region within the chamber in order to transform the process gas into the plasma in exposure to the semiconductor wafer. It is within this context that various embodiments described herein arise.Summary of the Invention

[0002] In an example embodiment, a method is disclosed for plasma processing of a substrate. The method includes generating a low frequency radiofrequency (RF) signal. The low frequency RF signal has a frequency within a range extending from about 10 kilohertz to about 2 megahertz. The method also includes supplying the low frequency RF signal to a plasma processing chamber. The method also includes controlling a power level of the low frequency RF signal over a duration of a given state within a multi-state plasma processing operation, such that a plurality of different power levels of the low frequency RF signal are supplied to the plasma processing chamber during the given state. The duration of the given state is less than about 25 microseconds.

[0003] Other aspects and advantages of the embodiments disclosed herein will become more apparent from the following detailed description and the accompanying drawings.Brief Description of the Drawings

[0004] Figure 1 shows a diagram of a system for performing an etch process, in accordance with some embodiments.

[0005] Figure 2 shows an example schematic of a multi-state plasma processing operation, in accordance with some embodiments.

[0006] Figure 3A shows a cross-section of an etched high-aspect-ratio (HAR) feature formedusing the system, in accordance with some embodiments.

[0007] Figure 3B shows a cross-section of an etched HAR feature showing twisting in a region of the HAR feature, in accordance with some embodiments.

[0008] Figure 4 shows plots of LF RF signal power modulation during a given plasma processing state within a multi- state plasma processing operation, in accordance with some embodiments.

[0009] Figure 5 shows plots of LF RF signal power modulation during a given plasma processing state within a multi- state plasma processing operation, with a burst of LF RF signal power provided at the end of the given plasma processing state, in accordance with some embodiments.

[0010] Figure 6 shows a flowchart of a method for plasma processing of a substrate, in accordance with some embodiments.Detailed Description of the Invention

[0011] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. It will be apparent, however, to one skilled in the art that embodiments of the present disclosure may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail so as to avoid unnecessarily obscuring the present disclosure.

[0012] Figure 1 shows a diagram of a system 100 for performing an etch process, in accordance with some embodiments. The system 100 includes a high-frequency (HF) radiofrequency (RF) generator 101, a low-frequency (LF) RF generator 103, an impedance matching network 105, a plasma chamber 107, and a computer 109. In some embodiments, the LF RF generator 103 is an RF generator having a low frequency of operation within a range extending from about 10 kilohertz (kHz) to about 2 megahertz (MHz). In some embodiments, the LF RF generator 103 is an RF generator having a selectable frequency of operation of one or more of 100 kHz, 400 kHz, 1 MHz, 2 MHz, and / or another frequency. In some embodiments, the HF RF generator 101 is an RF generator having a high frequency of operation within a range extending from about 2 MHz to about 200 MHz. In some embodiments, the HF RF generator 101 is an RF generator having a selectable frequency of operation of one or more of 2 MHz, 13.56 MHz, 27 MHz, 60 MHz, 120 MHz, and / or another frequency. The high frequency RF signals output by the HF RF generator 101 are of higher frequency than the low frequency RF signals output by the LF RF generator 103. In some embodiments, the LF RF generator 103 is an example of a primary generator with regard to a plasma generated within the plasma chamber 107, and the HF RF generator 101 is an example of a secondary RF generator with regard to the plasma generated within the plasmachamber 107.

[0013] An output 111 of the LF RF generator 103 is electrically connected to an input 133 of the impedance matching network 105 through an electrical connection 135, e.g., RF cable. Similarly, the output 113 of the HF RF generator 101 is electrically connected to an input 137 of the impedance matching network 105 through an electrical connection 139, e.g., RF cable. The impedance matching network 105 includes an arrangement of capacitors and / or inductors configured to ensure that an impedance seen at the output 111 of the LF RF generator 103 is sufficiently close to a load impedance for which the LF RF generator 103 is designed to operate, so that RF signals generated and transmitted by the LF RF generator 103 will be transmitted into the plasma present with the plasma chamber 107 in an efficient manner, i.e., without unacceptable reflection back toward the LF RF generator 103. Similarly, the impedance matching network 105 also includes an arrangement of capacitors and / or inductors configured to ensure that an impedance seen at the output 113 of the HF RF generator 101 is sufficiently close to a load impedance for which the HF RF generator 101 is designed to operate, so that RF signals generated and transmitted by the HF RF generator 101 will be transmitted into the plasma present with the plasma chamber 107 in an efficient manner, i.e., without unacceptable reflection back toward the HF RF generator 101.

[0014] The plasma chamber 107 includes a substrate support 119, such as an electrostatic chuck (ESC). The plasma chamber 107 also includes an upper electrode 121 that is located above the substrate support 119, so as to form a gap 123 between the upper electrode 121 and the substrate support 119. The upper electrode 121 is formed of an electrically conductive material, such as metal, e.g., aluminum, an alloy of aluminum, or other metal. The upper electrode 121 is electrically connected to a reference ground potential 127. The substrate support 119 includes a lower electrode 125. The lower electrode 125 is formed of an electrically conductive material, such as metal, e.g., aluminum, an alloy of aluminum, or other metal. In some embodiments, the substrate support 119 is formed of a ceramic, and the lower electrode 125 is embedded within the substrate support 119. In some embodiments, the substrate support 119 is formed of aluminum oxide (A12O3). An output 141 of the impedance matching network 105 is electrically connected to the lower electrode 125 through an electrical connection 143, e.g., RF power transmission line.

[0015] In some embodiments, the plasma chamber 107 includes a door 129 through which a substrate 131 can be moved into and out of the plasma chamber 107. In some embodiments, the plasma chamber 107 is a capacitively coupled plasma (CCP) chamber. The substrate 131 is disposed on a top surface of the substrate support 119 for processing. In some embodiments, thesubstrate 131 is a semiconductor wafer that includes integrated circuit devices in the form of multi-level structures defined on a silicon substrate. At a substrate level of the semiconductor wafer, transistor devices with diffusion regions are formed. In subsequent upper levels of the semiconductor wafer, interconnect metallization lines are patterned and electrically connected to the transistor devices to define a desired integrated circuit device. Electrically conductive vertical structures, such as vias and contacts, are formed to establish various vertical electrically connections with the semiconductor wafer. The interconnect metallization lines are insulated from other electrically conductive layers by intervening dielectric material.

[0016] Examples of the computer 109 include a desktop computer, a laptop computer, a tablet, a smart phone, and a controller. In some embodiments, the computer 109 includes a processor 115 and a memory device 117. In various embodiments, the processor 115 is one or more of a central processing unit (CPU), a graphical processing unit (GPU), a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), a programmable logic device (PLD), and a microcontroller, among others. In various embodiments, the memory device 117 includes one or more of a read-only memory (ROM) and a random access memory (RAM), among other types of computer memory. The processor 115 is connected in bi-directional data communication with the memory device 117. The processor 115 is connected in bi-directional data communication with LF RF generator 103, as indicated by connection 145. Similarly, the processor 115 is connected in bi-directional data communication with the HF RF generator 101, as indicated by connection 147.

[0017] In some embodiments, the processor 115 generates process recipe signals and sends the process recipe signals to each of the EF RF generator 103 and the HF RF generator 101. The process recipe signals include operational directions for the EF RF generator 103 and operational directions for the HF RF generator 101. In some embodiments, the process recipe signals define a multi-state plasma processing operation in which a set of multiple plasma processing states is performed successively in a repeating manner for a specified time period, where the set of multiple plasma processing states includes at least two different plasma processing states that are performed sequentially in a specified order.

[0018] Figure 2 shows an example schematic of a multi-state plasma processing operation, in accordance with some embodiments. The multi-state plasma processing operation is defined to include a set 201 of multiple plasma processing states S-l to S-3 that are repeatedly performed in a successive manner for a specified time period, where the multiple plasma processing states S-l to S-3 are performed sequentially in a specified order during performance of each set 201. While the example of Figure 2 shows three plasma processing states S-l to S-3 within the set201 of multiple plasma processing states S-l to S-3, it should be understood that in various embodiments the set 201 can include any number of plasma processing states greater than one. Each of the plasma processing states S-l to S-3 has a duty cycle DC-1 to DC-3, respectively, where the duty cycle DC-1 to DC-3 is the duration of the plasma processing state S-l to S-3, respectively.

[0019] Each plasma processing state S-l to S-3 is defined by a specified set of parameters for operating the plasma chamber 107 to affect plasma processing of the substrate 131 during performance of that particular one of the plasma processing states S-l to S-3. The example schematic of Figure 2 shows various parameters Pl, P2, and P3 to indicate that a given plasma processing state S-l to S-3 is defined by a corresponding set of plasma processing parameters. Essentially any parameter associated with operation of the plasma chamber 107 can be specified for each of the plasma processing states S-l to S-3 as needed. Various parameters associated with operation of the plasma chamber 107 includes one or more of process gas composition and flow rates into the plasma chamber 107, pressure within the plasma chamber 107, temperature of the substrate 131, exhaust flow rates from the plasma chamber 107, LF RF generator 103 operational parameters, and HF RF generator 101 operational parameters. The various embodiments disclosed herein are particularly concerned with the EF RF generator 103 operational parameters and the HF RF generator 101 operational parameters that are specified for a given plasma processing state, e.g., S-l to S-3. In some embodiments, the EF RF generator 103 operational parameters for a given plasma processing state, e.g., S-l to S-3, include specification of a frequency of RF signals generated by the EF RF generator 103. Also, in some embodiments, the EF RF generator 103 operational parameters for a given plasma processing state, e.g., S-l to S-3, include specification of a power level of the RF signals generated by the EF RF generator 103 as a function of time, and the duty cycle, e.g., DC-1 to DC-3, of the given plasma processing state. In some embodiments, the HF RF generator 101 operational parameters for a given plasma processing state, e.g., S-l to S-3, include specification of a frequency of RF signals generated by the HF RF generator 101. Also, in some embodiments, the HF RF generator 101 operational parameters for a given plasma processing state, e.g., S-l to S-3, include specification of a power level of the RF signals generated by the HF RF generator 101 as a function of time, and the duty cycle, e.g., DC-1 to DC-3, of the given plasma processing state.

[0020] The EF RF generator 103 operates to generate and output EF RF signals as specified by the process recipe signals received from the processor 115 for the multi-state plasma processing operation. The EF RF signals output by the EF RF generator 103 are conveyed through the impedance matching network 105 to the lower electrode 125. The HF RF generator 101 operatesto generate and output HF RF signals as specified by the process recipe signals received from the processor 115 for the multi-state plasma processing operation. The HF RF signals output by the HF RF generator 101 are conveyed through the impedance matching network 105 to the lower electrode 125.

[0021] When a recipe-prescribed plasma processing gas (or gas mixture) is supplied to the gap 123 within the plasma chamber 107 in conjunction with conveyance of the LF RF signals as output by the LF RF generator 103 to the lower electrode 125, and in conjunction with conveyance of the HF RF signals as output by the HF RF generator 101 to the lower electrode 125, a plasma is generated within the gap 123 from the plasma processing gas. The plasma is used to affect a change in a condition of the substrate 131 that is held on the substrate support 119 in exposure to the constituents of the plasma, such as radicals and ions. In various embodiments, the change in the condition of the substrate 131 that is affected by the plasma include one or more of etching material from the substrate 131, depositing material onto the substrate 131, and / or modifying a material already present on the substrate 131. In some embodiments, the plasma processing gas (or gas mixture) includes one or more of an oxygen containing gas, a fluorine containing gas, a carbon containing gas, a hydrogen containing gas, nitrogen containing gas, and / or essentially any other gas usable in plasma processing of semiconductor wafers. In some embodiments, the plasma processing gas (or gas mixture) includes CHF3, H2, CF4, NF3, CH2F2, SF6, NF3, CH3F, and / or essentially any other gas usable in plasma processing of semiconductor wafers.

[0022] Figure 3A shows a cross-section of an etched high-aspect-ratio (HAR) feature 300 formed using the system 100, in accordance with some embodiments. In some embodiments, the HAR feature 300 is a channel hole formed as part of a three-dimensional (3D) NAND memory semiconductor device fabrication process. However, it should be understood that in other embodiments the HAR feature 300 can be formed in any etching application as part of semiconductor device fabrication. In some embodiments, a combination of etchants and passivants are utilized in the plasma processing recipe to form the HAR feature 300. It is generally desirable for the completed HAR feature 300 to have substantially straight (vertical) sidewalls from the top of the HAR feature 300 to the bottom of the HAR feature 300. However, as etching proceeds to deeper and deeper depths in the HAR feature 300, there is a tendency to develop bowing of the sidewalls 302 within the HAR feature 300, because the sidewalls 302 get etched away at a faster rate due to more pronounced ion scattering as the etch front moves deeper in the HAR feature 300. More specifically, the increased ion scattering deeper within the HAR feature 300 negatively impacts the directionality (anisotropy) of the etching process, and causesetching of the sidewalls within the HAR feature 300, which causes bowing of the HAR feature 300 profile, which adversely increases the bow critical dimension (CD) of the HAR feature 300. Because the HAR feature 300 is typically ultimately filled with electrically conductive material to form an electrical connector, such as a via structure, it should be appreciated that when the bow CD of the HAR feature 300 becomes too great, device failures can occur due to electrical shorting.

[0023] During plasma-based etching processes, higher ion energies generally cause increased etching. There are various benefits associated with using higher ion energy to etch the HAR feature 300, such as increased directionality of the etch front so as to achieve a more vertical (straight) HAR feature 300. However, use of higher ion energy to etch the HAR feature 300 causes increased bowing at depth within the HAR feature 300. In general, a higher ion energy and a narrower ion energy distribution function (IEDF) are achieved by supplying higher RF signal power to drive / generate the plasma in the plasma chamber 107. However, a side-effect from using higher power to achieve higher ion energy within the plasma is that adverse bow is created at depth within the HAR feature 300. For this reason, the bow rate is a limiting condition for the maximum power level used to drive the plasma in HAR feature 300 formation.

[0024] Another issue of concern in fabricating a HAR feature is twisting of the HAR feature as the etch front moves deeper into the HAR feature. Figure 3B shows a cross-section of an etched HAR feature 320 showing twisting in a region 321 of the HAR feature 320, in accordance with some embodiments. Twisting of the HAR feature 320 occurs when the sidewalls of the etched hole are not formed in a straight manner as the hole is etched deeper through the material stack of the substrate 131, e.g., semiconductor wafer, such as shown by the region 321. Twisting is caused mostly by scattering of ions off of the sidewalls of the etched hole. Also, during some plasma etching processes that rely upon passivation of the sidewalls of the etched hole as the etch front moves deeper into the material stack of the substrate 131, twisting can be caused by insufficient passivation on the sidewalls of the etched hole as the etched front moves deeper through the material stack of the substrate 131. Twisting includes systematic twisting and random twisting. Systematic twisting is a global effect that is associated with the radial variation in the plasma conditions across the substrate 131, e.g., variation in the plasma sheath as a function of radial position across the substrate 131 and / or variation in the plasma density as a function of radial position across the substrate 131 and / or variation in the IEDF as a function of radial position across the substrate 131. Random twisting generally depends on how the etch front is shaped as the etch front moves deeper into the material stack of the substrate 131, e.g., pointy etch front shape, tapered etch front shape, flat etch front shape, among other etch frontshapes. Random twisting can also depend on etching byproducts that are generated within the etched hole as the etch front moves deeper into the material stack of the substrate 131. It should be understood that random twisting varies randomly for each hole that is etched to form the HAR features. Increasing the ion energy during HAR feature etching significantly decreases the random twisting. More specifically, because higher ion energy and narrower IEDF are achieved by supplying higher RF signal power to drive / generate the plasma in the plasma chamber 107, the adverse random twisting effect is reduced by driving / generating the plasma at higher RF signal power levels, which correspondingly results in formation of a more vertical (straight) HAR feature.

[0025] As the ion energy is increased during the plasma etching process, the random twisting decreases and the bowing increases. Therefore, increasing the RF signal power during plasma etching (which corresponds to increasing ion energy) has a trade-off between advantageously decreasing the random twisting effect and adversely increasing the bow effect. However, it is of interest to simultaneously achieve both decreased bowing and decreased random twisting.

[0026] With reference back to Figure 2, in a multi-state plasma processing operation, the minimum practical duration of a given plasma processing state S-x is about 25 microseconds, where x is an integer representing any given plasma processing state number. This minimum practical duration of the given plasma processing state S-x is generally too long to allow for increasing of the RF signal power for the entirety of the given state S-x in an attempt to decrease random twisting, because increasing of the RF signal power for the entirety of the given state S- x would cause an unacceptably large bow CD. Therefore, it is of interest to have methods for modulating the RF signal power with a temporal resolution that is less than the minimum practical duration of a given plasma processing state S-x, e.g., with a temporal resolution of less than 25 microseconds.

[0027] Figure 4 shows plots of LF RF signal power modulation during a given plasma processing state S-x within a multi-state plasma processing operation, in accordance with some embodiments. It should be understood that the given plasma processing state S-x represents any plasma processing state that may occur during any multi-state plasma processing operation that includes repeated sequential performance of a set of at least two different plasma processing states, such as generally described with regard to Figure 2. The example of Figure 4 shows delineation of the given plasma processing state S-x into two time frames, namely a first time frame T1 and a second time frame T2. The LF RF signal power is modulated during the given plasma processing state S-x by controlling the LF RF signal power in a different manner during each of the two time frames T1 and T2. Specifically, at the beginning of the first time frame Tl,which corresponds to the beginning of the given plasma processing state S-x, the LF RF signal power transitions to a first power level Pl from a power level PO at the end of the previous plasma processing state S-(x-l). The LF RF signal power is held substantially constant at the first power level Pl during the first time frame Tl. Then, at the temporal transition from the first time frame Tl to the second time frame T2, the LF RF signal power is transitioned from the first power level Pl to a second power level P2, where the second power level P2 is less than the first power level PL In some embodiments, the LF RF signal power transition from the first power level Pl to the second power level P2 is a step transition. In some embodiments, the LF RF signal power transition from the first power level Pl to the second power level P2 is a substantially linear transition. In some embodiments, the LF RF signal power transition from the first power level Pl to the second power level P2 is a non-linear transition, e.g., quadratic transition.

[0028] In some embodiments, the LF RF signal power is held substantially constant at the second power level P2 during the second time frame T2. In some other embodiments, the LF RF signal power is substantially linearly increased from the second power level P2 to a third power level P3 during the second time frame T2. The LF RF signal power ramping up from the second power level P2 to the third power level P3 provides for an increased LF RF signal power level at the end of the given plasma processing state S-x, without having an abrupt change in the LF RF signal power level during the middle of the given plasma processing state S-x, which could adversely affect overall frequency tuning during the multi-state plasma processing operation, especially when another RF generator is delivering RF signals at another frequency, such as at a high frequency, e.g., 60 MHz. In some other embodiments, the LF RF signal power is substantially linearly decreased from the second power level P2 to a fourth power level P4 during the second time frame T2. In the example of Figure 4, the end of the second time frame T2 is also the end of the given plasma processing state S-x. Therefore, at the end of the second time frame T2, the RF signal power transitions from the power level (P2 or P3 or P4) at the end of the second time frame T2 to a power level required at the beginning of the next plasma processing state S-(x+l).

[0029] The example of Figure 4 shows LF RF signal power level modulation within a given plasma processing state S-x of a multi-state plasma processing operation that provides a short burst of higher ion energy over a portion of the given plasma processing state S-x (over time frame Tl) in order to decrease the random twisting within HAR features without significantly increasing the bow within the HAR features. It should be appreciated that the LF RF signal power level is increased for less than the entire duration of the given plasma processing state S- x, i.e., Tl < (T1+T2). In some embodiments, the first time frame Tl over which the LF RF signalpower level is increased is less than or equal to about 30% of the entire duration of the given plasma processing state S-x, i.e., [T1 / (T1+T2)] <= 0.3. In some embodiments, the first time frame T1 over which the LF RF signal power level is increased is less than or equal to about 20% of the entire duration of the given plasma processing state S-x, i.e., [T1 / (T1+T2)] <= 0.2. In some embodiments, the first time frame T1 over which the LF RF signal power level is increased is less than or equal to about 10% of the entire duration of the given plasma processing state S-x, i.e., [T1 / (T1+T2)] <= 0.1.

[0030] While the duration of a given plasma processing state S-x is difficult to reduce below a certain amount, e.g., about 25 microseconds, a short burst of LF RF signal power (also known as overshoot) is achievable within the given plasma processing state S-x through control of the LF RF generator 103 in order to provide a burst of ion energy within the given plasma processing state S-x. In some embodiments, such as shown in Figure 4, LF RF signal power pulse shaping is used to decrease random twisting within etched features while simultaneously avoiding an adverse increase in bowing within the etched features. The ion energy burst serves to decrease the random twisting effect. However, because the ion energy burst is for a limited duration within the given plasma processing state S-x, the ion energy burst does not cause a substantial increase in bow. Also, by providing the ion energy burst at the beginning of the plasma processing state S-x, as opposed to in the middle of the given plasma processing state, it is possible to provide the ion energy burst without disrupting the overall RF signal frequency tuning for the given plasma processing state S-x. In some embodiments, the ion energy burst is provided through control of the LF RF generator 103. In some embodiments, the ion energy burst is provided by controlling of the LF RF generator 103 to give an overshoot of LF RF signal power as the multistate plasma processing operation transitions from one plasma processing state to the next plasma processing state.

[0031] In an example embodiment, the LF RF generator 103 is configured to generate and output LF RF signals having a frequency of about 400 kHz. Also, in some instances of this example embodiment, the LF RF generator 103 is configured to be controllable with regard to RF signal power level on a LF RF signal cycle-by-cycle basis, such that the LF RF signal power level can be changed as needed per cycle of the LF RF signal. Because there are a fixed number of RF signal cycles in a given plasma processing state S-x, there is a fixed number of control points for generating the LF RF signal during the given plasma processing state S-x. In the example in which the LF RF signal frequency is 400 kHz, each cycle of the LF RF signal has a duration (a full-cycle period) of 2.5 microseconds. Therefore, in this example, with the minimum plasma processing state duration set at 25 microseconds, there are ten control points (ten LF RFsignal cycles of 2.5 microseconds each) available during the given plasma processing state S-x at which the LF RF signal power level can be adjusted (by way of the LF RF generator 103) to attain the desired burst of ion energy within a portion of the given plasma processing state S-x in order to achieve the desired combination of reduced random twisting and sufficiently low bow in HAR feature etching. In this particular example, the LF RF generator 103 can be operated to adjust the LF RF signal power level every 2.5 microseconds within the given plasma processing state S-x, as needed. This LF RF signal cycle-by-cycle control resolution provides the LF RF signal power adjustment resolution for shaping the LF RF signal to have the burst of power at the beginning of the given plasma processing state S-x, such as shown in the example of Figure 4. For example, in some embodiments, the first time frame T1 of Figure 4 covers a number of LF RF signals cycles within a range extending from one cycle to about four cycles. In some embodiments, the first time frame T1 of Figure 4 covers a number of LF RF signals cycles within a range extending from one cycle to about three cycles. In some embodiments, the first time frame T1 of Figure 4 includes two LF RF signals cycles.

[0032] In some embodiments, the burst of LF RF signal power is provided at the end of the given plasma processing state S-x, rather than at the beginning of the plasma processing state S- x. Figure 5 shows plots of LF RF signal power modulation during a given plasma processing state S-x within a multi-state plasma processing operation, with a burst of LF RF signal power provided at the end of the given plasma processing state S-x, in accordance with some embodiments. In the example of Figure 5, it should be understood that the given plasma processing state S-x represents any plasma processing state that may occur during any multistate plasma processing operation that includes repeated sequential performance of a set of at least two different plasma processing states, such as generally described with regard to Figure 2. The example of Figure 5 shows delineation of the given plasma processing state S-x into two time frames, namely a first time frame T1 and a second time frame T2. The LF RF signal power is modulated during the given plasma processing state S-x by controlling the LF RF signal power in a different manner during each of the two time frames T1 and T2. Specifically, at the beginning of the first time frame Tl, which corresponds to the beginning of the given plasma processing state S-x, the LF RF signal power transitions to a first power level Pl from a power level P0 at the end of the previous plasma processing state S-(x-l). In some embodiments, the LF RF signal power is held substantially constant at the first power level Pl during the first time frame TL Then, at the temporal transition from the first time frame Tl to the second time frame T2, the LF RF signal power is transitioned from the first power level Pl to a second power level P2, where the second power level P2 is greater than the first power level PL In someembodiments, the LF RF signal power transition from the first power level Pl to the second power level P2 is a step transition. In some embodiments, the LF RF signal power transition from the first power level Pl to the second power level P2 is a substantially linear transition. In some embodiments, the LF RF signal power transition from the first power level Pl to the second power level P2 is a non-linear transition, e.g., quadratic transition. In some embodiments, the LF RF signal power is held substantially constant at the second power level P2 during the second time frame T2.

[0033] In the example of Figure 5, the end of the second time frame T2 is also the end of the given plasma processing state S-x. Therefore, at the end of the second time frame T2, the RF signal power transitions from the second power level P2 at the end of the second time frame T2 to a power level required at the beginning of the next plasma processing state S-(x+l). In this manner, the burst of LF RF signal power is provided at the end of the given plasma processing state S-x. Correspondingly, in these embodiments, the burst of ion energy is provided at the end of the given plasma processing state S-x.

[0034] In some embodiments, the LF RF signal power is substantially linearly increased from the first power level Pl to a third power level P3 during the first time frame Tl. Then, at the temporal transition from the first time frame Tl to the second time frame T2, the LF RF signal power is transitioned from the third power level P3 to the second power level P2, where the second power level P2 is greater than the third power level P3. In some embodiments, the LF RF signal power transition from the third power level P3 to the second power level P2 is a step transition. In some embodiments, the LF RF signal power transition from the third power level P3 to the second power level P2 is a substantially linear transition. In some embodiments, the LF RF signal power transition from the third power level P3 to the second power level P2 is a non-linear transition, e.g., quadratic transition. In the above-mentioned embodiments, the LF RF signal power is held substantially constant at the second power level P2 during the second time frame T2.

[0035] In some embodiments, the LF RF signal power is substantially linearly decreased from the first power level Pl to a fourth power level P4 during the first time frame TL Then, at the temporal transition from the first time frame Tl to the second time frame T2, the LF RF signal power is transitioned from the fourth power level P4 to the second power level P2, where the second power level P2 is greater than the fourth power level P4. In some embodiments, the LF RF signal power transition from the fourth power level P4 to the second power level P2 is a step transition. In some embodiments, the LF RF signal power transition from the fourth power level P4 to the second power level P2 is a substantially linear transition. In some embodiments, theLF RF signal power transition from the fourth power level P4 to the second power level P2 is a non-linear transition, e.g., quadratic transition. In the above-mentioned embodiments, the LF RF signal power is held substantially constant at the second power level P2 during the second time frame T2.

[0036] The various methods disclosed herein provide for control of the IEDF within / during a given plasma processing state of a multi-state plasma processing operation by controlling LF RF signal power delivery within / during the given plasma processing state. In particular, the various methods disclosed herein provide for manipulation of the LF RF signal power level profile as a function of time in a controlled manner at edges of the given plasma processing state. In various embodiments, such as described with regard to Figure 4, a short burst of high energy ions is provided by shaping the LF RF signal power level profile at the edges of the given plasma processing state over a duration that is substantially less than the total duration of the given plasma processing state. For example, if the minimum achievable total duration of the given plasma processing state is 25 microseconds, the methods herein provide for a short burst of high energy ions over a duration of up to about 8 microseconds at the beginning of the given plasma processing state. This approach provides for breaking of the trade-off between random twisting and high bow growth in HAR feature plasma etching processes.

[0037] Figure 6 shows a flowchart of a method for plasma processing of a substrate, in accordance with some embodiments. The method includes an operation 601 for generating an LF RF signal. The LF RF signal has a frequency within a range extending from about 10 kilohertz to about 2 megahertz. The method also includes an operation 603 for supplying the LF RF signal to a plasma processing chamber. The method also includes an operation 605 for controlling a power level of the LF RF signal over a duration of a given state within a multi- state plasma processing operation, such that a plurality of different power levels of the low frequency RF signal are supplied to the plasma processing chamber during the given state. The duration of the given state is less than about 25 microseconds. In some embodiments, a number of control points of the plurality of different power levels of the LF RF signal is equal to a number of cycle periods of the LF RF signal that occur during the given state. In some embodiments, the power level of the LF RF signal is controlled in accordance with a cycle period of the LF RF signal. In some embodiments, the multi-state plasma processing operation includes a set of multiple plasma processing states that is repeatedly performed in a successive manner for a specified time period, where the given state is included in the set of multiple plasma processing states, and where each plasma processing state in the set of multiple plasma processing states is defined by a statespecific set of plasma process parameter settings.

[0038] In some embodiments, the plurality of different power levels of the LF RF signal includes a first power level applied from a beginning of the given state for a first duration and a second power level applied within the given state after the first duration, where the first power level is greater than the second power level. In some embodiments, the first duration is a nonzero amount of time up to about 25 percent of a total duration of the given state. In some embodiments, the first duration is a non-zero amount of time up to about 10 percent of a total duration of the given state. In some embodiments, the first power level is at least two times the second power level. In some embodiments, the second power level is maintained substantially constant over a remaining amount of time within the given state after the first duration. In some embodiments, the second power level is linearly increased over a remaining amount of time within the given state after the first duration. In some embodiments, the second power level is linearly decreased over a remaining amount of time within the given state after the first duration.

[0039] In some embodiments, the plurality of different power levels of the LF RF signal includes a first power level applied from a beginning of the given state for a first duration, and a second power level applied within the given state for a second duration after the first duration, where the second power level is greater than the first power level. In some embodiments, the first duration and the second duration sum to a total duration of the given state. In some embodiments, the second duration is a non-zero amount of time up to about 25 percent of a total duration of the given state. In some embodiments, the second duration is a non-zero amount of time up to about 10 percent of a total duration of the given state. In some embodiments, the second power level is at least two times the first power level. In some embodiments, the first power level is maintained substantially constant over the first duration. In some embodiments, the first power level is linearly increased over the first duration. In some embodiments, the first power level is linearly decreased over the first duration.

[0040] In some embodiments, the plurality of different power levels of the low frequency RF signal includes a first power level applied at a beginning of the given state for a first duration, a second power level applied within the given state for a second duration after the first duration, and a third power level applied within the given state after the second duration In these embodiments, the first power level is greater than the second power level, and the third power level is greater than the second power level.

[0041] In various embodiments, the methods disclosed herein for within-state LF RF pulse power shaping are specified and controlled through a user interface provided through a computer or a controller, which may be the computer 109 of Figure 1. In some embodiments, such a user interface provides fields for entry of values of various plasma process parameters, and / orselectable icons enabling stepwise adjustment of the values, or other types of interface mechanisms for setting the various plasma process parameters. In some implementations, predefined values and / or pre-defined ranges for various plasma process parameters, particularly for the within-state LF RF pulse shaping, are provided through the user interface. In some embodiments, such pre-defined values or ranges are automatically generated in response to selection or input of other settings related to the plasma processing recipe. In some embodiments, a pre-defined value is provided as a default value which can be tuned or adjusted as desired by the user.

[0042] The various embodiments disclosed herein may be practiced with various computer system configurations including hand-held hardware units, microprocessor systems, microprocessor-based or programmable consumer electronics, minicomputers, mainframe computers and the like. The various embodiments disclosed herein can also be practiced in distributed computing environments where tasks are performed by remote processing hardware units that are linked through a network.

[0043] In some embodiments, a controller is part of the system 100. In various embodiments the system 100 includes semiconductor processing equipment, such as one or more processing tool(s), one or more processing chamber(s), one or more platform(s) for processing, and / or other processing-related components such a wafer pedestal, a gas flow system, etc. The various components / equipment in the system 100 are integrated with electronics for controlling their operation before, during, and after processing of the substrate 131. Depending on the processing requirements and / or the configuration of the system 100, the controller, e.g., computer 109, is programmed to control any of the processes disclosed herein, including the delivery of process gases, temperature settings (e.g., heating and / or cooling), pressure settings, vacuum settings, power settings, RF generator settings, RF impedance matching network settings, frequency settings, flow rate settings, fluid delivery settings, positional and operation settings, substrate 131 transfers into and out of the processing chamber 107 and / or transfer tools and / or load locks coupled to or interfaced with the system 100.

[0044] Broadly speaking, in various embodiments, the above-mentioned controller is defined as electronics having various integrated circuits, logic, memory, and / or software that receive instructions, issue instructions, control operations, enable cleaning operations, enable endpoint measurements, and the like. In some embodiments, the integrated circuits include computer chips in the form of firmware that store program instructions, digital signal processors (DSPs), chips defined as ASICs, PLDs, and / or one or more microprocessors, or microcontrollers that execute program instructions, e.g., software. The program instructions are instructionscommunicated to the controller in the form of various individual settings (or program files), defining the parameters, the factors, the variables, etc., for carrying out a particular plasma process on the substrate 131 within the plasma chamber 107 of the system 100. In some embodiments, the program instructions are part of a recipe defined by process engineers to accomplish one or more processing steps during the fabrication of one or more layers, materials, metals, oxides, silicon, silicon dioxide, surfaces, circuits, and / or dies of the substrate 131, e.g., semiconductor wafer.

[0045] In some embodiments, the controller is a part of or coupled to the computer 109 that is integrated with or coupled to the system 100, or otherwise networked to the system 100, or a combination thereof. For example, in some embodiments, the controller is in a computing cloud or at least partially in a fab host computer system, which allows for remote access of the substrate 131 processing controls. The computer 109 enables remote access to the system 100 to monitor current progress of substrate 131 plasma processing operations, examines a history of past substrate 131 fabrication operations, examines trends or performance metrics from a plurality of substrate 131 fabrication operations, to enable informed setting and / or adjustment of parameters associated with current plasma processing of the substrate 131, to set processing steps to follow in a recipe for a current plasma processing of the substrate 131, and / or to start a new plasma process on the substrate 131.

[0046] In some embodiments, a remote computer, e.g., a server, provides process recipes to the computer 109 of the system 100 over a network, which includes a local network or the Internet. The remote computer includes a user interface that enables entry or programming of parameters and / or settings, which are then communicated to the system 100 from the remote computer. In some examples, the computer 109 receives instructions in the form of data, which specify the parameters, factors, and / or variables for each of the plasma processing steps to be performed during one or more plasma processing operations on the substrate 131. In some embodiments, the controller is distributed, such as by including one or more discrete controllers that are networked together and working towards a common purpose, such as the processes and controls described herein. An example of a distributed controller for such purposes includes one or more integrated circuits within the system 100 in communication with one or more integrated circuits located remotely (such as at the platform level or as part of a remote computer) that combine to control a process performed by the system 100.

[0047] It is further noted that in some embodiments, the various methods disclosed herein are applicable to several types of plasma chambers, e.g., a capacitively coupled plasma (CCP) chamber, a plasma chamber including an inductively coupled plasma (ICP) reactor, atransformer coupled plasma chamber, conductor tools, dielectric tools, a plasma chamber including an electron cyclotron resonance (ECR) reactor, among others. As noted above, depending on the process step or steps to be performed by the system 100, the computer 109 communicates with one or more of other tool circuits or modules, other tool components, cluster tools, other tool interfaces, adjacent tools, neighboring tools, tools located throughout a factory, a main computer, another controller, or tools used in material transport that bring containers of substrates / wafers to and from tool locations and / or load ports in a semiconductor manufacturing factory.

[0048] Various embodiments described herein may also be practiced using various computer system configurations including hand-held hardware units, microprocessor systems, microprocessor-based or programmable consumer electronics, minicomputers, mainframe computers and the like. Embodiments described herein can also be practiced in distributed computing environments where tasks are performed by remote processing hardware units that are linked through a network. It should be understood that the embodiments described herein can employ various computer-implemented operations involving data stored in computer systems. These operations are those requiring physical manipulation of physical quantities. Any of the operations described herein that form part of the embodiments are useful machine operations. The embodiments also relate to a hardware unit or an apparatus for performing these operations. The apparatus may be specially constructed for a special purpose computer. When defined as a special purpose computer, the computer can also perform other processing, program execution or routines that are not part of the special purpose, while still being capable of operating for the special purpose. In some embodiments, the operations may be processed by a general purpose computer selectively activated or configured by one or more computer programs stored in the computer memory, cache, or obtained over a network. When data is obtained over a network, the data may be processed by other computers on the network, e.g., a cloud of computing resources.

[0049] Various embodiments described herein can be implemented through process control instructions instantiated as computer-readable code on a non-transitory computer-readable medium. The non-transitory computer-readable medium is any data storage hardware unit that can store data, which can thereafter be read by a computer system. Examples of the non- transitory computer-readable medium include hard drives, network attached storage (NAS), ROM, RAM, compact disc-ROMs (CD-ROMs), CD-recordables (CD-Rs), CD-rewritables (CD- RWs), magnetic tapes, and other optical and non-optical data storage hardware units. The non- transitory computer-readable medium can include computer-readable tangible mediumdistributed over a network-coupled computer system so that the computer-readable code is stored and executed in a distributed fashion.

[0050] The foregoing description of the embodiments has been provided for purposes of illustration and description, and is not intended to be exhaustive or limiting. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. In this manner, one or more features from one or more embodiments disclosed herein can be combined with one or more features from one or more other embodiments disclosed herein to form another embodiment that is not explicitly disclosed herein, but rather that is implicitly disclosed herein. This other embodiment may also be varied in many ways. Such embodiment variations are not to be regarded as a departure from the disclosure herein, and all such embodiment variations and modifications are intended to be included within the scope of the disclosure provided herein.

[0051] Although some method operations may be described in a specific order herein, it should be understood that other housekeeping operations may be performed in between method operations, and / or method operations may be adjusted so that they occur at slightly different times or simultaneously or may be distributed in a system which allows the occurrence of the processing operations at various intervals associated with the processing, as long as the processing of the method operations are performed in a manner that provides for successful implementation of the method.

[0052] Although the foregoing embodiments have been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications can be practiced within the scope of the appended claims. Accordingly, the embodiments disclosed herein are to be considered as illustrative and not restrictive, and are therefore not to be limited to just the details given herein, but may be modified within the scope and equivalents of the appended claims.

Claims

Claims1. A method for plasma processing of a substrate, comprising: generating a low frequency radiofrequency (RF) signal, the low frequency RF signal having a frequency within a range extending from about 10 kilohertz to about 2 megahertz; supplying the low frequency RF signal to a plasma processing chamber; and controlling a power level of the low frequency RF signal over a duration of a given state within a multi-state plasma processing operation, such that a plurality of different power levels of the low frequency RF signal are supplied to the plasma processing chamber during the given state, wherein the duration of the given state is less than about 25 microseconds.

2. The method as recited in claim 1, wherein the multi-state plasma processing operation includes a set of multiple plasma processing states that is repeatedly performed in a successive manner for a specified time period, wherein the given state is included in the set of multiple plasma processing states, and wherein each plasma processing state in the set of multiple plasma processing states is defined by a state- specific set of plasma process parameter settings.

3. The method as recited in claim 1, wherein a number of control points of the plurality of different power levels of the low frequency RF signal is equal to a number of cycle periods of the low frequency RF signal that occur during the given state.

4. The method as recited in claim 1, wherein the power level of the low frequency RF signal is controlled in accordance with a cycle period of the low frequency RF signal.

5. The method as recited in claim 1, wherein the plurality of different power levels of the low frequency RF signal includes a first power level applied from a beginning of the given state for a first duration and a second power level applied within the given state after the first duration, wherein the first power level is greater than the second power level.

6. The method as recited in claim 5, wherein the first duration is a non-zero amount of time up to about 25 percent of a total duration of the given state.

7. The method as recited in claim 5, wherein the first duration is a non-zero amount of time up to about 10 percent of a total duration of the given state.

8. The method as recited in claim 5, wherein the first power level is at least two times the second power level.

9. The method as recited in claim 5, wherein the second power level is maintained substantially constant over a remaining amount of time within the given state after the first duration.

10. The method as recited in claim 5, wherein the second power level is linearlyincreased over a remaining amount of time within the given state after the first duration.

11. The method as recited in claim 5, wherein the second power level is linearly decreased over a remaining amount of time within the given state after the first duration.

12. The method as recited in claim 1, wherein the plurality of different power levels of the low frequency RF signal includes a first power level applied from a beginning of the given state for a first duration, and a second power level applied within the given state for a second duration after the first duration, wherein the second power level is greater than the first power level.

13. The method as recited in claim 12, wherein the first duration and the second duration sum to a total duration of the given state.

14. The method as recited in claim 12, wherein the second duration is a non-zero amount of time up to about 25 percent of a total duration of the given state.

15. The method as recited in claim 12, wherein the second duration is a non-zero amount of time up to about 10 percent of a total duration of the given state.

16. The method as recited in claim 12, wherein the second power level is at least two times the first power level.

17. The method as recited in claim 12, wherein the first power level is maintained substantially constant over the first duration.

18. The method as recited in claim 12, wherein the first power level is linearly increased over the first duration.

19. The method as recited in claim 12, wherein the first power level is linearly decreased over the first duration.

20. The method as recited in claim 1, wherein the plurality of different power levels of the low frequency RF signal includes a first power level applied at a beginning of the given state for a first duration, a second power level applied within the given state for a second duration after the first duration, and a third power level applied within the given state after the second duration, wherein the first power level is greater than the second power level, and wherein the third power level is greater than the second power level.

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