A method for optimizing characteristics of a power conversion system considering variation of plasma impedance

Abstract

The application belongs to the technical field of remote plasma source, and provides a power conversion system characteristic optimization method considering plasma impedance change, comprising: establishing an equivalent model of dissociation chamber plasma impedance, and obtaining equivalent inductance of the plasma; selecting an optimal resonance topology of the power conversion system according to the relationship between the equivalent inductance of the plasma and resonance inductance, so as to optimize system characteristics; the system characteristics are obtained through resonance current gain G Characterization is carried out. The application provides a power conversion system characteristic optimization method considering plasma impedance change, which proposes selection of a topology structure of the power conversion system under different equivalent inductance conditions, and according to different load conditions, a suitable resonance converter topology can be selected to solve the problems of low PCS power factor and increased switch tube current stress of the RPS when the flow change range of the input gas is large.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of remote plasma source, and particularly relates to a power conversion system characteristic optimization method considering plasma impedance change. BACKGROUND

[0002] Remote plasma source (RPS) is a core component of core equipment such as etching equipment and thin film deposition equipment in the field of integrated circuit manufacturing, can realize efficient and stable dissociation of process gases such as NF3, NH3, H2 and O2, is used to generate plasma required in photoresist ashing, wafer pre-cleaning and carbon chamber cleaning processes, has characteristics of high stability, high dissociation rate, corrosion resistance and wide gas flow range, and is beneficial to improving etching stability and process uniformity. At the same time, RPS is also widely used in various industrial fields such as display panels and solar panels. With the growth of the semiconductor, display and photovoltaic power generation markets, RPS has become more and more important in the industrial field.

[0003] RPS is usually composed of a power conversion system (PCS) and a corrosion-resistant plasma reaction chamber. The PCS provides a high-frequency electric field to the gas dissociation chamber through a transformer coupling. The high-frequency electric field ionizes the gas (N2, NF3, Ar, H2, etc.) entering the chamber. The electric field for gas ionization is generated according to the frequency and power of the current supplied by the PCS. Therefore, the PCS should provide a high switching frequency and low total harmonic distortion (THD) current or stable power, so that the gas is efficiently and stably dissociated.

[0004] The PCS of the existing industrial field widely used plasma generator such as ozone generator and dielectric barrier discharge (DBD) pulse generator can be divided into pulse voltage source, sinusoidal voltage source and current source according to its output mode. The topology has flyback converter, full-bridge converter, half-bridge converter and other structures. However, its general output power is small, the load gas state is switched between excitation and non-excitation, and it cannot maintain the high power required by RPS when a large flow of gas is input and is stable. At the same time, the characteristics of the gas dissociation chamber of the plasma generator, system efficiency and output power quality are not considered. Therefore, it is difficult to be directly applied to the plasma generator which needs to be stable and efficient.

[0005] Meanwhile, in the process of plasma generation using currently used resonant converters, the output current decreases due to the increase in plasma load impedance during the transition from electrostatic (E) to electromagnetic (H) modes. These dynamic changes severely reduce the conversion efficiency of the PCS and the power coupling efficiency of the transformer primary, while also affecting efficient and stable plasma generation. Currently used resonant converters do not consider the dynamic characteristics of plasma impedance and the changes in reactance circuits caused by nonlinearity. During RPS operation, changes in process chamber pressure and process gas flow rate lead to changes in plasma impedance. These changes in plasma impedance result in a low PCS power factor and hard switching of the switching transistors, significantly increasing the current stress on the switching transistors. Therefore, it is necessary to select an appropriate resonant converter topology based on different load conditions. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for optimizing the characteristics of a power conversion system that considers changes in plasma impedance, thereby solving the problems of low PCS power factor and increased switching current stress in current RPS systems when the gas flow rate varies over a large range.

[0007] This invention provides a method for optimizing the characteristics of a power conversion system considering changes in plasma impedance, comprising:

[0008] An equivalent model of the plasma impedance in the dissociation chamber is established to obtain the equivalent inductance of the plasma. ;

[0009] According to the plasma equivalent inductance With resonant inductor Based on the relationship, the optimal resonant topology of the power conversion system is selected to optimize system characteristics; these system characteristics are determined by the resonant current gain. G Characterize it.

[0010] As can be seen from the above technical solution, the present invention provides a method for optimizing the characteristics of a power conversion system considering changes in plasma impedance, and proposes different equivalent inductances. This paper proposes a topology selection method for power conversion systems under different plasma load conditions, providing a theoretical design basis and evaluation criteria for RPS topology selection. Furthermore, it proposes a method based on the resonant current gain of the power conversion system. G As a basis for evaluating the characteristics of power conversion systems, it solves the problem of focusing solely on reducing inverter current. When the design target is met, output current occurs. Reduce and power factor The problem of reduction.

[0011] Optionally, an equivalent model of the plasma impedance in the dissociation chamber is established based on an equivalent electrical model of the dissociation chamber; the equivalent electrical model of the dissociation chamber comprises:

[0012] a transformer connected to the power conversion system, the transformer comprising a primary leakage inductance, an excitation inductance and a secondary leakage inductance;

[0013] a plasma impedance R , and the secondary coil of the transformer.

[0014] Optionally, the equivalent model of the plasma impedance R is an equivalent L-R model, and the equivalent inductance and the equivalent resistance of the plasma are respectively

[0015] ,

[0016] wherein, the primary leakage inductance of the transformer, the secondary leakage inductance of the transformer, the excitation inductance, the frequency of the alternating signal, N the number of turns of the transformer, R the plasma impedance;

[0017] When the plasma impedance R increases, the equivalent inductance and the equivalent resistance increase synchronously.

[0018] According to the above technical solution, by equivalent the annular plasma impedance to and in series connection, the analysis of the annular plasma impedance characteristics is simplified.

[0019] Optionally, the optimal resonant topology of the power conversion system is selected according to the relationship between the equivalent inductance of the plasma and the resonant inductance , comprising:

[0020] when <0.6 , the power conversion system selects an LCL topology;

[0021] when 0.6 ≤ ≤ , the power conversion system selects an LC topology;

[0022] when > At this time, the power conversion system selects the LCC topology.

[0023] From the above technical solution, by selecting the power conversion system topology under different conditions, a theoretical design basis and evaluation standard are provided for the topology selection of the RPS under different plasma load conditions; based on this, the output current of the power conversion system can be reduced under the condition that the output current of the power conversion system is the same, the current stress of the switching tube is reduced, and the power factor of the system is improved .

[0024] Alternatively, the resonant current gain under the LCL topology, the LC topology and the LCC topology is calculated respectively according to the following formula,

[0025] The resonant current gain under the LC topology and the LCL topology is and :

[0026] ;

[0027] The corresponding frequency is the maximum resonant current gain point , :

[0028] ;

[0029] The resonant current gain under the LCC topology is :

[0030] ;

[0031] The corresponding frequency is the maximum resonant current gain point :

[0032] ;

[0033] Wherein, is the output current of the power conversion system, is the inverter current, is the quality factor, the inductance ratio , is the ratio of the equivalent inductance to the resonant inductance, is the ratio of the series inductance to the resonant inductance, is the ratio of the series capacitance to the resonant capacitance, is the normalized value of the switching frequency ; in the LC topology and the LCC topology, the ratio of the series inductance to the resonant inductance .

[0034] By adopting the above technical solution, the present application has the following beneficial effects:

[0035] This invention provides a method for optimizing the characteristics of a power conversion system considering changes in plasma impedance, and proposes different methods for optimizing the characteristics of power conversion systems with varying equivalent inductance. This paper proposes a topology selection method for power conversion systems under different plasma load conditions, providing a theoretical design basis and evaluation criteria for RPS topology selection. Furthermore, it proposes a method based on the resonant current gain of the power conversion system. G As a basis for evaluating the characteristics of power conversion systems, it solves the problem of focusing solely on reducing inverter current. When the design target is met, an output current occurs. Reduce and power factor The problem of reduction;

[0036] This invention utilizes ring plasma impedance Equivalent to and The series structure simplifies the analysis of the impedance characteristics of toroidal plasmas. Attached Figure Description

[0037] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0038] Figure 1 A schematic diagram of a transformer-coupled plasma structure is shown.

[0039] Figure 2 The flowchart illustrates a method for optimizing the characteristics of a power conversion system that takes into account changes in plasma impedance, according to an embodiment of the present invention.

[0040] Figure 3 A schematic diagram of a transformer-coupled plasma model provided in an embodiment of the present invention is shown;

[0041] Figure 4 A schematic diagram of the equivalent LR impedance model provided in an embodiment of the present invention is shown;

[0042] Figure 5 A schematic diagram illustrating the simulated changes in equivalent inductance and equivalent resistance as gas increases within the chamber, as provided in an embodiment of the present invention, is shown. Figure 5 (a) shows the simulated change trend of the equivalent inductance as the gas in the chamber increases. Figure 5 (b) The simulated trend of the equivalent resistance when the gas in the chamber increases;

[0043] Figure 6A schematic diagram of a fundamental wave equivalent circuit of a resonance topology provided by the embodiment of the present application is shown.

[0044] Figure 7 A schematic diagram of a fundamental wave equivalent circuit of a resonance topology provided by the embodiment of the present application is shown. At 0.6 K A curve diagram is shown.

[0045] Figure 8 A schematic diagram of a fundamental wave equivalent circuit of a resonance topology provided by the embodiment of the present application is shown. At 0.6 K A curve diagram is shown.

[0046] Figure 9 A waveform diagram of an LC topology provided by the embodiment of the present application is shown. At 0.6 A waveform diagram of an LC topology provided by the embodiment of the present application is shown.

[0047] Figure 10 A waveform diagram of an LCL topology provided by the embodiment of the present application is shown. At 0.6 A waveform diagram of an LCL topology provided by the embodiment of the present application is shown.

[0048] Figure 11 A waveform diagram of an LCC topology provided by the embodiment of the present application is shown. At 0.6 A waveform diagram of an LCC topology provided by the embodiment of the present application is shown.

[0049] Figure 12 A waveform diagram of an LCCL topology provided by the embodiment of the present application is shown. At 0.6 A waveform diagram of an LCCL topology provided by the embodiment of the present application is shown.

[0050] Figure 13 A waveform diagram of an LC topology provided by the embodiment of the present application is shown. At 0.6 A waveform diagram of an LC topology provided by the embodiment of the present application is shown.

[0051] Figure 14 A waveform diagram of an LCL topology provided by the embodiment of the present application is shown. At 0.6 A waveform diagram of an LCL topology provided by the embodiment of the present application is shown.

[0052] Figure 15 A waveform diagram of an LCC topology provided by the embodiment of the present application is shown. At 0.6 A waveform diagram of an LCC topology provided by the embodiment of the present application is shown.

[0053] Figure 16 A waveform diagram of an LCCL topology provided by the embodiment of the present application is shown. At 0.6 A waveform diagram of an LCCL topology provided by the embodiment of the present application is shown. DETAILED DESCRIPTION

[0054] The embodiments of the technical solutions of the present application will be described in detail below with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, and cannot limit the protection scope of the present application.

[0055] It should be noted that, unless otherwise specified, the technical terms or scientific terms used in the present application should be understood as the usual meanings understood by the skilled person in the field to which the present application belongs.

[0056] Currently, the plasma discharge structure is mainly flat plate structure, while the plasma of RPS is ring structure as shown in Figure 1 , and its load characteristics are more complex; it is necessary to simplify the impedance model of ring plasma to solve the problem of too many plasma load parameters in RPS and difficult analysis. Therefore, in one embodiment, as shown in Figure 2 , a power conversion system characteristic optimization method considering the change of plasma impedance is provided, comprising:

[0057] S1. Establishing an equivalent model of the plasma impedance of the dissociation chamber to obtain the equivalent inductance of the plasma.

[0058] Specifically, the equivalent model of the plasma impedance of the dissociation chamber is established based on the equivalent electrical model of the dissociation chamber; the equivalent electrical model of the dissociation chamber, as shown in Figure 3 , includes a transformer and a plasma impedance R , the transformer and the power conversion system are connected, the transformer includes a primary leakage inductance, an excitation inductance and a secondary leakage inductance; the plasma impedance R and the secondary coil of the transformer are connected.

[0059] In order to facilitate the study of the change of the working condition of the remote plasma source when the gas quantity in the gas dissociation chamber changes, the transformer coupled plasma model in Figure 3 is simplified to an equivalent L-R model, as shown in Figure 4 . The equivalent inductance and the equivalent resistance can be calculated by the following formula:

[0060] (1)

[0061] In formula (1), is the primary leakage inductance of the transformer, is the secondary leakage inductance of the transformer, is the excitation inductance, is the frequency of the alternating signal, N is the number of turns of the transformer, R is the plasma impedance.

[0062] Combined with Figure 4 and formula (1), the changeR While keeping other parameters constant, simulate the equivalent inductance as the gas in the chamber increases. and equivalent resistance The changing trend, such as Figure 5 As shown. By Figure 5 It can be concluded that when the plasma impedance R increases, i.e., the gas in the chamber increases, the equivalent inductance... and equivalent resistance Increased synchronously.

[0063] Figure 6 Four topological fundamental equivalent circuits are provided. This is the output voltage of the full-bridge inverter. For inverter current, For primary current, The primary voltage is used. Due to the resonant effect of the converter, the resonant frequency is defined. and switching frequency normalized value They are respectively:

[0064] ; (2)

[0065] Characteristic impedance of equivalent circuit and quality factors for:

[0066] (3)

[0067] (4)

[0068] Let the inductance ratio be:

[0069] (5)

[0070] The ratio of equivalent inductance to resonant inductance. The ratio of series inductance to resonant inductance. This is the ratio of the series capacitance to the resonant capacitance.

[0071] The current gain H of the four topologies is shown below:

[0072] (6)

[0073] (7)

[0074] (8)

[0075] (9)

[0076] Will =1 into (6), (7), (8), (9), we get 、 、 、 are all equal, that is 、 、 、 The values do not affect the constant current characteristics of the resonance topology. Since the transformer coupled plasma load has inductance , it is considered in the topology structure, that is , so the analysis of LC, LCC, LCL and LCCL can be simplified to the comparative analysis of LCL and LCCL topologies, that is, LC is equivalent to the analysis of LCL, and LCC is equivalent to the analysis of LCCL.

[0077] To improve the power factor of the system, the inverter current is as small as possible under the condition that the output load impedance is the same, but if only the inverter current is reduced as the design goal, and the output current is ignored, the phenomenon that the inverter current is reduced, but the output current is reduced more greatly, reduces the power factor of the system. Therefore, the resonance current gain G is introduced as a system performance index for analysis.

[0078] The LCL resonance current gain is:

[0079] (10)

[0080] The LCL topology has a maximum resonance current gain , and the corresponding frequency is the maximum resonance current gain point , as follows:

[0081] (11)

[0082] The LCCL resonance current gain ratio is:

[0083] (12)

[0084] The LCCL has a maximum resonance current gain , and the corresponding frequency is the maximum resonance current gain point , as follows:

[0085] (13)

[0086] The resonance current gain of the LC topology and maximum resonant current gain Resonant current gain of LCC topology and maximum resonant current gain same as formula (12) and formula (13), but LC topology and LCC topology, .

[0087] For more intuitive comparison of LCCL and LCL characteristics, let:

[0088] (14)

[0089] From formula (14) can be inferred that:

[0090] (15)

[0091] Set range is 0.8≤ ≤1.3, when much greater than 1 and take the maximum value 1.3, can get the minimum value of about 0.6, so when <0.6, regardless of the value of the size, in the range of 0.8≤ ≤1.3, K are less than 1, so with 0.6 as the critical value, as follows LCCL and LCL resonant current gain G comparison analysis.

[0092] When <0.6, get K curve as Figure 7 shown. It is known that in the range of 0.8≤ ≤1.3, K are less than 1, and in the range of 0.8≤ ≤1.3 every corresponding K value curve of the maximum increases with the increase of . Therefore, as long as <0.6, in the range of 0.8≤ ≤1.3 is always greater than 0, regardless of and the value of are less than .

[0093] Derivation of formula (14) K derivative of , deduce There exists a maximum point, which corresponds to the value in formula (12). G The maximum value points are the same, which are:

[0094] (16)

[0095] And at that point K The value is:

[0096] (17)

[0097] Combining formula (17), we can conclude that regardless of and What value should be taken? >1 is always true. and Proportional to, with It is inversely proportional, so LCCL has a greater advantage over LCL in highly inductive loads.

[0098] when When ≥0.6, we get K Value curve graph as follows Figure 8 As shown, Figure 8 From this, we can conclude that when 0.8 ≤ Each within the range of ≤1.3 Corresponding K The maximum value of the value curve as It increases with the increase of , consistent with formula (17). Combining formula (17) and Figure 8 It can be seen that when When ≥0.6, make K The operating frequency range ≥1 is simultaneously affected and The limitations lead to the derivation K Operating frequency ≥1 The intervals are shown below:

[0099] (18)

[0100] In conclusion, when When <0.6, LCCL is 0.8≤ LCCL resonant current gain in the range of ≤1.3 G All are lower than LCL; when When ≥0.6, there is a certain Value, making the operating frequency exist Within range K ≥1 holds true, meaning the LCCL resonant current gain is within this frequency range. G LCCL resonant current gain is greater than or equal to LCL, and remains constant across the remaining frequency range. GBelow LCL.

[0101] S2. Based on plasma equivalent inductance With resonant inductor Based on the relationship, the optimal resonant topology of the power conversion system is selected to optimize system characteristics; system characteristics are determined through the resonant current gain. G Characterize it.

[0102] Based on the above conclusions, as the amount of gas in the gas dissociation chamber increases, the plasma equivalent inductance... Increase the resonant current gain of the four topologies. G The comparison yielded the following results:

[0103] (1) When <0.6 At that time, in the LC topology If it is consistently greater than 1.3, then in order to increase the current operating frequency... Down G Value, needs To operating frequency If the location is close, then it needs to be reduced. .exist <0.6 If a compensation capacitor Cs is present, it will actually increase. Inverter current Increase the current operating frequency. Down G When the value decreases, an inductor should be connected in series. To increase The value of makes Reduce operating frequency Close to. Therefore, in <0.6 When using the resonant current gain of the LCL topology G Maximum, simulation results are as follows Figures 9-12 As shown, the output current of the four topologies All are equal, LCL topology inverter current Minimum, power factor angle θ Minimum, power factor Highest.

[0104] (2) When 0.6 ≤ ≤ At that time, none of the four topologies LC, LCL, LCC, and LCCL could be used in all cases. While maintaining optimal performance within the range, from the perspective of volume and cost, the LC topology, which has the simplest resonant topology, is the best choice.

[0105] (3) When > When β is always less than 1, at this time in order to increase the current operating frequency down G The value, need To the operating frequency Close, at this time need to series capacitor To reduce the value of beta. Therefore, in > When using LCC topology resonant current gain G Maximum. Simulation results as Figures 13-16 Shown, the output current of four kinds of topology Are equal, LCC topology inverter current Minimum, power factor angle Minimum, power factor The highest.

[0106] It should be noted that the resonant current gain is high, which means that the ratio of output current To inverter current High, the system can output greater current under the same switch tube current rating, and the same output current, the current stress of the switch tube is lower. The resonant current gain is low, which is the opposite.

[0107] Therefore, step S2 is specifically:

[0108] When <0.6 , the power conversion system selects LCL resonant topology;

[0109] When 0.6 ≤ ≤ , the power conversion system selects LC resonant topology;

[0110] When > , the power conversion system selects LCC resonant topology.

[0111] Based on this, under the condition of different equivalent inductance , the appropriate power conversion system topology is selected to ensure that the output current Is the same, the inverter current Is reduced, the current stress of the switch tube is reduced, and the power factor of the system is improved .

[0112] The above-described embodiments are merely illustrative of several embodiments of the present application, which are described in more detail and in a specific and detailed manner, but should not be construed as limiting the scope of the patent. It should be noted that for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present application, and these are all within the scope of the present application. Therefore, the scope of protection of the patent of the present application should be subject to the appended claims.

Claims

1. A method for optimizing the characteristics of a power conversion system taking into account variations in plasma impedance, characterized in that, Comprise: An equivalent model of plasma impedance of a dissociation chamber is established to obtain an equivalent inductance of the plasma ; According to the relationship between the plasma equivalent inductance and the resonant inductance , the optimal resonant topology of the power conversion system is selected to optimize the system characteristics, which are characterized by the resonant current gain G ; An equivalent model of the dissociation chamber plasma impedance is established based on an equivalent electrical model of the dissociation chamber; The equivalent electrical model of the dissociation chamber comprises: A transformer connected with the power conversion system, the transformer comprising a primary leakage inductance, an excitation inductance and a secondary leakage inductance; Plasma impedance R and a secondary winding of the transformer are connected; Plasma impedance R The equivalent model of the plasma impedance is an equivalent L-R model, in which the equivalent inductance and the equivalent resistance of the plasma are ， wherein, is a primary leakage inductance of the transformer, is a secondary leakage inductance of the transformer, is an excitation inductance, is an alternating signal frequency, N is a number of turns of the transformer, R is a plasma impedance; When the plasma impedance R increases, the equivalent inductance and the equivalent resistance increase synchronously.

2. The method of claim 1, wherein, The optimal resonant topology of the power conversion system is selected according to the relationship between the plasma equivalent inductance and the resonant inductance ​ When <0.6 The power conversion system selects LCL topology; When 0.6 ≤ ≤ , the power conversion system selects an LC topology; When > the power conversion system selects the LCC topology.

3. The method of claim 2, wherein, The resonance current gain under the LCL topology, LC topology and LCC topology is calculated respectively according to the following formula, Resonant current gain under LC topology and LCL topology and is: ； corresponding frequency is the maximum resonant current gain point , is: ； Resonant current gain under LCC topology is: ； corresponding frequency is the maximum resonant current gain point is: ； wherein, is the output current of the power conversion system, is the inverter current, is the quality factor, the inductance ratio , is the ratio of the equivalent inductance to the resonant inductance, is the ratio of the series inductance to the resonant inductance, is the ratio of the series capacitance to the resonant capacitance, is the normalized value of the switching frequency . In the LC topology and the LCC topology, the ratio of the series inductance to the resonant inductance .

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