Remote plasma source transformer coupling model and power factor optimization method

Abstract

The invention belongs to the technical field of semiconductor manufacturing, and provides a remote plasma source transformer coupling model and a power factor optimization method, and the model comprises a full-bridge inverter circuit, an LC resonant topology and a transformer coupling plasma load model. The transformer coupling plasma load is connected with the output of the LC resonant topology; the transformer coupling plasma load model comprises a transformer, a primary side leakage inductor, an excitation inductor, a secondary side leakage inductor and a plasma impedance, and the primary side leakage inductor and a primary coil of the transformer are connected in series and connected to the two sides of the resonant capacitor in parallel; the excitation inductor is connected in parallel to two sides of a primary coil of the transformer; the secondary side leakage inductor and the plasma impedance are connected in series and connected with a secondary coil of the transformer. According to the method, the excitation inductance and the leakage inductance are designed into the remote plasma source transformer coupling model, the influence on the plasma power when the excitation inductance and the leakage inductance are changed is considered, and the influence of parameter variation on the transformer coupling plasma load can be intuitively shown.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor manufacturing, in particular to a transformer coupled model of a remote plasma source and a power factor optimization method. BACKGROUND

[0002] Plasma, as the fourth state of matter, has rich physical and chemical properties. Remote plasma source is a key plasma generation technology, which has a wide range of applications in material surface treatment, thin film deposition, gas purification and other fields. In order to improve the output power and working efficiency of the remote plasma source, more efficient plasma excitation methods are needed. Among them, transformer coupled plasma technology as a new plasma excitation method, compared with traditional inductively coupled plasma and capacitively coupled plasma, transformer coupled plasma can produce higher and more uniform plasma through the coupling effect of transformer magnetic core, especially suitable for high-power and high-density industrial application scenarios, and meets the strict requirements of various processes on plasma parameters.

[0003] However, in the remote plasma source, the parameters of the transformer have a crucial influence on the operation effect of the whole system. On the one hand, due to the particularity of the transformer coupled plasma load, the actual state of the plasma cannot be measured, and only the secondary plasma load state can be inferred from the primary transformer information; on the other hand, in the remote plasma source, the transformer primary side needs a constant current to provide a stable magnetic field strength for the plasma load, which usually requires full-bridge inverter and LC resonance topology to achieve together. Therefore, it is necessary to model and analyze the whole remote plasma source, and analyze the influence of transformer parameters on plasma and the front-stage inverter and resonance link according to the model results.

[0004] The traditional transformer coupled model of the remote plasma source only relies on the information of the transformer primary side current to determine the current and power of the plasma load , without designing the excitation inductance and leakage inductance in the transformer to the model, even if the excitation inductance and leakage inductance of the transformer change, the change of the plasma power cannot be confirmed through the traditional model, so the expression of the inverter current cannot be accurately derived under the traditional model, and therefore an effective strategy to reduce the inverter current cannot be proposed. SUMMARY

[0005] In view of the defects in the prior art, the present application provides a transformer coupled model of a remote plasma source and a power factor optimization method to solve the problem that the current remote plasma source model cannot confirm the change of plasma power, resulting in the inability to effectively reduce the inverter current.

[0006] In a first aspect, the present application provides a remote plasma transformer coupling model, comprising: a full-bridge inverter circuit for inverting an input DC voltage signal into an AC voltage signal; LC resonance topology, the input and the output of the full-bridge inverter circuit are connected; a transformer coupling plasma load model, and the output of the LC resonance topology is connected; the transformer coupling plasma load model comprises a transformer, a primary side leakage inductance, an excitation inductance, a secondary side leakage inductance and a plasma impedance, the primary side leakage inductance and the primary coil of the transformer are connected in series, and are connected in parallel to both sides of the resonance capacitor of the LC resonance topology; the excitation inductance is connected in parallel to both sides of the primary coil of the transformer; the secondary side leakage inductance and the plasma impedance are connected in series and are connected to the secondary coil of the transformer.

[0007] According to the above technical solution, the remote plasma transformer coupling model provided by the present application designs the excitation inductance and the leakage inductance of the transformer into the remote plasma transformer coupling model, considers the influence of the change of the excitation inductance and the leakage inductance of the transformer on the plasma power, and can intuitively show that the transformer coupling plasma load is affected by the change of all parameters of the transformer.

[0008] Optionally, the inverter current of the full-bridge inverter circuit is solved according to the following expression, specifically: , is the output voltage of the full-bridge inverter circuit, Z0 and Q are the characteristic impedance and the quality factor of the remote plasma transformer coupling model respectively, is the normalized value of the switching frequency , , is the ratio of the primary side leakage inductance to the resonance inductance, is the ratio of the primary side leakage inductance to the resonance inductance, is the ratio of the excitation inductance to the resonance inductance, is the resonance inductance, is the primary side leakage inductance of the transformer, is the excitation inductance.

[0009] According to the above technical solution, based on the remote plasma transformer coupling model, the inverter current expression can be calculated, which facilitates subsequent implementation of the strategy of reducing the inverter current and improving the power factor; and solves the problem that the traditional model cannot accurately deduce the inverter current.

[0010] Optionally, when the switching tube works at the resonance frequency , that is, inverter current I i The expression of the inverter current is: ; inverter current I i The expression of the inverter current is simplified and also expressed as: .

[0011] In a second aspect, the present application provides a remote plasma source power factor optimization method, based on any possible form of the remote plasma source transformer coupling model of the first aspect, comprising: A switchable capacitor-inductor module is connected in series on the primary side of the transformer, and the switchable capacitor-inductor module comprises a series capacitor and a series inductor respectively connected through a switch control. ; ; When the plasma is ignited, the series capacitor is controlled to be connected in the circuit. ; When the plasma is stable after ignition, the series inductor is controlled to be connected in the circuit. ;

[0012] According to the above technical solution, the remote plasma source power factor optimization method provided by the present application reduces the inverter current and improves the power factor by connecting a switchable capacitor-inductor module in series on the primary side of the transformer, controlling the series capacitor to be connected in the circuit when the plasma is ignited, and controlling the series inductor to be connected in the circuit when the plasma is stable after ignition.

[0013] Optionally, the inverter current is the smallest, and the corresponding series capacitor and series inductor are determined by the following formulas, specifically: The series capacitor ; The series inductor .

[0014] The above technical solution has the following beneficial effects: The magnetizing inductance and leakage inductance of the transformer are designed into the remote plasma source transformer coupling model, the influence of changes in the magnetizing inductance and leakage inductance of the transformer on the primary side current of the transformer, the secondary side current of the transformer, and the inverter current is considered, and the influence of parameter changes on the transformer coupling plasma load can be intuitively shown. The application provides a power factor optimization method of a remote plasma source. BRIEF DESCRIPTION OF DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the present application or the prior art, the drawings required in the specific embodiments or the prior art description 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 according to the actual scale.

[0016] Figure 1 A schematic diagram of a transformer coupled plasma production chamber provided by an embodiment of the application is shown; Figure 2 A sectional view of a transformer coupled plasma production chamber provided by an embodiment of the application is shown; Figure 3 A schematic diagram of a transformer coupled model of a remote plasma source provided by an embodiment of the application is shown; Figure 4 A schematic diagram of another transformer coupled model of a remote plasma source provided by an embodiment of the application is shown; Figure 5 A schematic diagram of a transformer coupled model of a remote plasma source provided by an embodiment of the application is shown; Figure 4 A schematic diagram of a transformer coupled model of a remote plasma source provided by an embodiment of the application is shown; Figure 6 A flow chart of a power factor optimization method of a remote plasma source provided by an embodiment of the application is shown; Figure 7 A waveform schematic diagram when the power factor optimization method is not implemented during ignition is shown; Figure 8 A waveform schematic diagram when the power factor optimization method is implemented during ignition is shown; Figure 9 A waveform schematic diagram when the power factor optimization method is not implemented after successful ignition is shown; Figure 10 A waveform schematic diagram when the power factor optimization method is implemented after successful ignition is shown. DETAILED DESCRIPTION

[0017] 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. It should be noted that the technical terms or scientific terms used in the present application should be understood as the general meaning understood by the skilled person in the field of the present application, unless otherwise stated.

[0018] Figure 1 Schematic diagram of transformer coupled plasma production chamber, Figure 2 Cross-sectional view of transformer coupled plasma production chamber, transformer primary side is N turns of coil, secondary side plasma impedance It can be regarded as a single-turn purely resistive load.

[0019] As Figure 3 shown, in the transformer coupled excitation mode of the plasma, a remote plasma source equivalent circuit is provided, including full-bridge inverter, LC resonance topology, plasma load; The full-bridge inverter circuit includes four switching tubes T1, T2, T3 and T4. The full-bridge inverter input is connected to a DC voltage source , and the output is connected to the input of the LC resonance topology. The full-bridge inverter inverts the input DC voltage signal into an AC voltage signal, which is the inverter current.

[0020] The LC resonance topology includes a resonance inductor L r and a resonance capacitor C r . The input of the LC resonance topology is connected to the output of the full-bridge inverter, and the output of the LC resonance topology is connected to the transformer coupled plasma load.

[0021] The plasma load part, is the transformer primary side current, is the transformer primary side leakage inductance, N is the number of turns of the transformer primary side coil, is the plasma impedance, is the equivalent load of the secondary side plasma load converted to the primary side.

[0022] Due to the particularity of the plasma load, the actual state of the plasma cannot be measured, and only the state of the secondary plasma load can be inferred from the primary information of the transformer. However Figure 3 The remote plasma source equivalent circuit shown in directly converts the secondary side plasma load to the primary side, and directly considers the plasma load current , and the plasma power .

[0023] Completely rely on the transformer primary side current determine the current and power of the plasma load, and in order to generate a stable plasma density, the plasma load front stage usually needs to access an LC resonance topology capable of providing a constant current, which will cause the primary side current to remain unchanged.

[0024] In order to determine the influence of the transformer coupled plasma load generated by the change of the transformer excitation inductance and leakage inductance, in an embodiment, as shown in Figure 4 , a remote plasma source transformer coupling model is provided, comprising: a full-bridge inverter circuit for inverting an input DC voltage signal into an AC voltage signal; an LC resonance topology, the input and the output of the full-bridge inverter circuit are connected; the LC resonance topology includes a resonance inductance L r and a resonance capacitance C r ; a transformer coupled plasma load model, connected with the output of the LC resonance topology; the transformer coupled plasma load model includes a transformer, a primary side leakage inductance, an excitation inductance, a secondary side leakage inductance and a plasma impedance, the primary side leakage inductance and the primary coil of the transformer are connected in series, and the excitation inductance is connected in parallel to both sides of the resonance capacitance of the LC resonance topology; the secondary side leakage inductance and the plasma impedance are connected in series and connected with the secondary coil of the transformer.

[0025] By designing the excitation inductance and leakage inductance of the transformer into the remote plasma source transformer coupling model, the influence of the change of the transformer excitation inductance and leakage inductance on the transformer primary side current, the transformer secondary side current and the inverter current is considered, and the influence of the parameter variation on the transformer coupled plasma load can be intuitively shown.

[0026] By comparing and analyzing Figure 3 and Figure 4 , the ratio of the primary side leakage inductance to the resonance inductance , the ratio of the primary side leakage inductance to the resonance inductance , the ratio of the excitation inductance to the resonance inductance , the voltage between the two points a and b , the normalized values of the resonance frequency and the switching frequency are defined as: (1) The characteristic impedance Z0 and the quality factor Q of the equivalent circuit are: (2)​ 1) In Figure 3 , the primary current is calculated as (3) In formula (3), when the switch tube works at the resonant frequency , i.e. , has a constant current characteristic, and the value is: .

[0027] 2) In Figure 3 , the plasma load current I o = NI p , and the plasma power P o is .

[0028] 3) In Figure 4 , the expression of the primary current is calculated as (4) In formula (4), when the switch tube works at the resonant frequency , i.e. , has a constant current characteristic, and the value is: .

[0029] 4) In Figure 4 , the plasma load current is calculated. The expression is derived as (5), and the plasma power expression is (6).

[0030] 5) Comparing 1) and 3), it can be concluded that the calculated primary current of the traditional model and the model proposed in this paper remains consistent at the resonant frequency .

[0031] 6) Compared with the load current calculated by the traditional model in 2) and the plasma rate , the formula (5) and formula (6) derived in 4) more detailedly represent the influence of the transformer coupling plasma model parameters on the load current and the plasma power . The traditional transformer coupling model of the remote plasma source completely relies on the primary side current Information is needed to determine the current and power of the plasma load. Even if the transformer's magnetizing inductance and leakage inductance change, it is impossible to confirm whether the plasma power has changed using traditional models. Therefore, Figure 3 The inverter current cannot be accurately derived under the equivalent model. Therefore, it is impossible to propose an effective expression to reduce inverter current. The strategy. Figure 4 The remote plasma source transformer coupling model shown can intuitively demonstrate the impact of changes in all transformer parameters, and the inverter current expression can be accurately derived based on this.

[0032] exist Figure 4 In the process, the inverter current is calculated. The expression is: (7) In formula (7), when the switching transistor operates at the resonant frequency... Place At that time, inverter current The expression is: (8) In the derivation of formula (5), the plasma load current along with It increases with the increase of [something]. along with The decrease increases the value; in the derived formula (6), the plasma load power along with It increases with the increase of [something]. along with The decrease leads to an increase. To improve the working efficiency of a remote plasma source, it is necessary to improve... Lambda And reduce Increasing the power requires maximizing the magnetizing inductance and minimizing the secondary leakage inductance. Much larger , >> Under the above conditions, formula (8) is simplified, and the simplified inverter current is obtained. The expression is: (9) What needs to be understood is the power factor. The expression is: ,in Inverter voltage and inverter current The phase angle is P, the active power is P, and the apparent power is S. When the active power and the inverter voltage are constant, the inverter current reduction strategy is implemented, the power factor is increased, the phase angle is reduced, and the effect of improving the power factor is achieved.

[0033] In order to improve the output power of the remote plasma source, the input voltage is increased, the excitation inductance is increased, and the like are usually used. However, these methods will cause the full-bridge inverter switch tube to bear a large current stress, and only a switch tube with a larger rated current value can be used, thereby increasing the manufacturing cost of the remote plasma source. How to effectively reduce the inverter current of the remote plasma source and optimize the power factor is disclosed in an embodiment. Figure 6 As shown in , a remote plasma source power factor optimization method is provided, which comprises the following steps: Figure 5 S1. As shown in , a switchable capacitor-inductor module is connected in series on the primary side of the transformer. The switchable capacitor-inductor module comprises a series capacitor and a series inductor controlled to be connected to the circuit by switches.

[0034] S2. When the plasma is ignited, the series capacitor is controlled to be connected to the circuit.

[0035] When the plasma is ignited, the plasma impedance is large, that is, Q is close to 0. At this time , in order to reduce the inverter current , the switchable capacitor-inductor module is adjusted in this step to control the series capacitor to be connected to the primary side of the transformer, so that the ratio of the series capacitor to the resonant capacitor is , and the inverter current is expressed as: (10) In formula (10), when , the inverter current is the smallest, and at this time the series capacitor on the primary side is .

[0036] S3. When the plasma is stable after ignition, the series inductor is controlled to be connected to the circuit.

[0037] When the plasma is stable after ignition, the plasma impedance is small, Q>1, and because the transformer coupling plasma needs to be uniformly distributed, the transformer magnetic core is in a symmetrical structure, so the leakage inductance on the primary side of the transformer and the leakage inductance on the secondary side of the transformer are kept close to each other, , and are both much smaller than 1, at this time In order to reduce inverter current In this step, the series inductor is controlled by adjusting the switchable capacitor-inductor module. Connect to the primary side of the transformer, and make The primary side current is obtained. The expression is: (11) In formula (11), when the switching transistor operates at the resonant frequency, It has constant current characteristics, and its value is: An inductor is then connected in series on the primary side of the transformer. This method does not change the primary-side current. And it will not change the current of the plasma load. and power To obtain inverter current The switching transistor is operating at the resonant frequency. Place The expression for time is: (12) when At that time, inverter current At its minimum, the primary side series inductance is at its lowest. Value .

[0038] In summary, the proposed method for optimizing the power factor of a remote plasma source in this embodiment is illustrated in the schematic diagram below. Figure 5 As shown, a switchable capacitor-inductor module is connected in series on the primary side of the transformer. When the plasma is ignited... Figure 5 In the process, switch S1 is closed and S2 is open; after successful ignition, when the plasma stabilizes, switch S1 is open and S2 is closed. The flowchart is as follows: Figure 6 As shown.

[0039] The following sections verify the effectiveness of this embodiment under two conditions: during ignition and when the plasma is stable after successful ignition.

[0040] Figure 7 The oscilloscope waveform is shown when no power factor optimization method was applied during ignition. Figure 8 The oscilloscope waveforms for implementing power factor optimization during ignition. Figure 7 and Figure 8 The input voltage of the resonant topology was recorded in both cases. Inverter current Waveform, comparison Figure 7 and Figure 8 The input voltage of the resonant topology of the two same, Figure 7 Inverter current The peak value is much greater than 150A.Figure 8 Inverter current The peak value is less than 150A, Figure 8 Compared with Figure 7 Inverter current The drop is obvious and the phase angle The reduction is obvious, so the experiment verifies that the power factor optimization method proposed in this embodiment has a significant effect when the remote plasma source is ignited.

[0041] Figure 9 The oscilloscope waveform after the ignition is successful without implementing the power factor optimization method, Figure 10 The oscilloscope waveform after the ignition is successful with implementing the power factor optimization method. Figure 9 And Figure 10 The resonant topology input voltage , inverter current , transformer primary current waveforms are recorded, Figure 9 And Figure 10 The resonant topology input voltage , transformer primary current of the two are the same, Figure 9 Inverter current The peak value is 80A, Figure 10 Inverter current The peak value is 70A, Figure 10 Compared with Figure 9 Inverter current The drop is obvious and the phase angle The reduction is obvious, so the experiment verifies that the power factor optimization method proposed in this embodiment has a significant effect when the remote plasma source is ignited successfully.

[0042] The above embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it cannot be understood as limiting the scope of the patent. It should be noted that for ordinary skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are within the scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A remote plasma source transformer coupling model, characterized in that, include: A full-bridge inverter circuit is used to invert an input DC voltage signal into an AC voltage signal. LC resonant topology, with input and output connections of the full-bridge inverter circuit; A transformer-coupled plasma load model is described, along with its output connection to an LC resonant topology. This model includes a transformer, primary-side leakage inductance, magnetizing inductance, secondary-side leakage inductance, and plasma impedance. The primary leakage inductance is connected in series with the primary coil of the transformer and in parallel across the resonant capacitor of the LC resonant topology; the magnetizing inductance is connected in parallel across the primary coil of the transformer. The secondary side leakage inductance and plasma impedance are connected in series and parallel to the secondary coil of the transformer.

2. The remote plasma source transformer coupling model according to claim 1, characterized in that, The inverter current of the full-bridge inverter circuit The solution is based on the following expression: ， Z0 and Q represent the output voltage of the full-bridge inverter circuit, respectively, and Z0 and Q represent the characteristic impedance and quality factor of the remote plasma source transformer coupling model. Switching frequency The normalized value, , It is the ratio of primary side leakage inductance to resonant inductance. It is the ratio of primary side leakage inductance to resonant inductance. It is the ratio of magnetizing inductance to resonant inductance. It is a resonant inductor. For leakage inductance on the primary side of the transformer, Here, N represents the magnetizing inductance, N represents the number of turns in the primary winding of the transformer, and j represents the imaginary unit.

3. The remote plasma source transformer coupling model according to claim 2, characterized in that, When the switching transistor is operating at the resonant frequency Place At that time, inverter current The expression is: ； Inverter current I i The simplified expression is also represented as: 。 4. A method for optimizing the power factor of a remote plasma source, characterized in that, Based on the remote plasma source transformer coupling model according to any one of claims 1-3, it includes: A switchable capacitor-inductor module is connected in series on the primary side of the transformer. The switchable capacitor-inductor module includes series capacitors that are connected via switches. and series inductors ; During plasma ignition, the series capacitor is controlled. Connected to the loop; After successful ignition and when the plasma stabilizes, control the series inductor. It is connected to the circuit.

5. The method according to claim 4, characterized in that, Inverter current When the series capacitance and series inductance are at their minimum values, they are determined by the following formulas: The series capacitor ; The series inductor .

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