JP2002184598A - High-frequency power source unit for icp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower the failure rate of elements in a high-frequency power source unit for an ICP and stand the reflected power in plasma lighting at a small rated value. SOLUTION: For the high-frequency power source unit for the ICP, which supplies high-frequency power to an induction coil, the unit comprises a high-frequency power amplifier and a control means for controlling the high-frequency power amplifier. In the first embodiment, supply voltage is changed over, thereby preventing build up of voltage before plasma lighting, in the second embodiment, bias voltage is changed over, thereby preventing power loss before plasma lighting, and in the third embodiment, an input power control is made an open loop in a state that the supply voltage is kept constant, thereby enhancing power efficiency before plasma lighting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency power supply, and more particularly to a high-frequency power supply for an ICP (Inductively Coupled Plasma) which supplies power to the ICP.

[0002]

2. Description of the Related Art ICP such as a high frequency plasma emission analyzer
(RF Inductively Coupled Plasma)
The plasma is turned on by supplying high-frequency power from the high-frequency power supply device for use, and the plasma is maintained. Generally, a high-frequency power supply device for ICP includes a high-frequency power amplifier, and supplies high-frequency power amplified by the high-frequency power amplifier to an induction coil via an impedance matching circuit. The magnitude of the output power of the ICP high-frequency power supply is determined by the power supply voltage applied to the high-frequency power amplifier, and the power amplification characteristic is determined by the bias voltage applied to the power amplification element provided in the high-frequency power amplifier. It is set so as to satisfy a predetermined rated value (for example, rated power or the like).

When using a high-frequency power supply device for ICP, an ICP having a rated value higher than the required high-frequency power is required.
By selecting a high-frequency power supply for the ICP, fixing the power supply voltage and the bias voltage of the high-frequency power supply for the ICP and always supplying the output power of the rated value, and providing an impedance matching circuit between the induction coil and the induction coil, High-frequency power is efficiently supplied to the coil to stably maintain the generated plasma. Before the plasma is turned on, the induction coil can be regarded as a transformer having a simple coil and a secondary side opened, whereas after the plasma is turned on, it can be regarded as a transformer having a load connected to the secondary side. Therefore, I
The inductance when the induction coil side is viewed from the CP high-frequency power supply side largely differs before and after plasma lighting.

Therefore, in order to maintain stable plasma, the impedance matching circuit usually sets circuit constants so that matching can be easily performed after plasma lighting, and reduces reflected power in the lighting state.

[0005]

As described above, as described above, IC
In the supply of high-frequency power by the high-frequency power supply for P, the output power of the high-frequency power supply for ICP is set and the circuit constant of the impedance matching circuit is set so that the plasma state is stably maintained after the plasma is turned on. Therefore, sufficient impedance matching cannot be achieved during plasma lighting, and most of the high-frequency input power is reflected to the power supply side. The reflected power reflected from the induction coil side to the power supply side increases the voltage applied to the elements constituting the high-frequency power supply device for ICP or is consumed as heat, so that the load on the elements increases, and in the worst case, There is a problem of destruction.

Therefore, conventionally, by using a high-frequency ICP high-frequency power supply having a higher withstand voltage and a higher withstand voltage by the amount of the reflected power returned to the power supply during plasma lighting, the reflected power during plasma lighting is increased. To avoid the effects of voltage rise and power increase. However, the high-frequency power supply device for ICP having a large rated value has a problem that the price is high in addition to a problem that the size is large.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances and has an object to reduce the failure rate of elements of a high-frequency power supply device for ICP. It is an object of the present invention to provide a high frequency power supply for ICP that can be obtained.

[0008]

SUMMARY OF THE INVENTION According to the present invention, a rated voltage (withstand voltage) of an ICP high-frequency power supply device is required for an element of the ICP high-frequency power supply device to withstand an increase in voltage or an increase in power loss due to reflected power. The condition that the value is larger than the sum of the applied voltage of the high-frequency power supply itself and the voltage rise due to the reflected power, and the rated power loss (withstand voltage) of the high-frequency power supply for ICP is the power due to the power loss and the reflected power of the high-frequency power supply for ICP itself The point that it is necessary to satisfy the condition of being larger than the sum of the losses and the reflected power returning from the induction coil to the high-frequency power supply device for ICP have a difference in the magnitude before and after the plasma lighting. Focusing on the fact that the reflected power before is larger than the reflected power after lighting the plasma, the voltage rise and the power loss before the lighting of the plasma with large reflected power are considered. By control, reduce the failure rate of the device, also those which lower the rated value.

Therefore, the present invention provides an ICP high-frequency power supply for supplying high-frequency power to an induction coil, comprising a high-frequency power amplifier and control means for controlling the high-frequency power amplifier. By switching the voltage, a voltage rise before plasma lighting is suppressed, in the second mode, the power loss before plasma lighting is suppressed by switching the bias voltage, and in the third mode, the power supply voltage is kept constant. Thus, the power efficiency before the plasma is turned on is enhanced by making the input power control an open loop.

In the first aspect of the present invention, the control means switches the power supply voltage to be applied to the high-frequency power amplifier between before and after the plasma generation, so that the power supply voltage before the plasma generation is higher than the power supply voltage after the plasma generation. Low voltage.
As a result, the rated voltage before plasma generation can be reduced. Therefore, the voltage rise due to the reflected power is greater before the plasma is generated than after the plasma is generated, so that the rated voltage of the high frequency power supply for ICP can be reduced.

In the second aspect of the present invention, the control means switches the bias voltage of the power amplifying element included in the high-frequency power amplifier between before and after plasma generation, and changes the bias voltage before plasma generation after plasma generation. The voltage is lower than the bias voltage. As a result, power supply efficiency before plasma generation can be increased and power loss can be reduced. Therefore, the power loss due to the reflected power is larger before plasma generation than after plasma generation.
Rated power of the high-frequency power supply device can be reduced.

In a third aspect of the present invention, the control means controls the maximum input in a state where the power supply voltage applied to the high-frequency power amplifier is fixed to the minimum voltage for supplying the high-frequency power required for plasma generation before the plasma generation. Supply power. Normally, since the maximum output power of the high frequency power supply for ICP is determined by the power supply voltage applied to the high frequency power amplifier, the voltage value of the power supply voltage is reduced to the minimum voltage capable of supplying the high frequency power required for plasma lighting. Fix to a value. At this time, the high-frequency power output from the high-frequency power supply device for ICP is substantially determined by the applied power supply voltage, and high power efficiency can be maintained.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic diagram for explaining a high frequency power supply for plasma of the present invention. ICP
The high frequency power supply device 1 includes a high frequency power amplifier 2 and a control unit 3 for controlling the high frequency power amplifier 2. Control means 3, the power supply voltage V _DD applied to the high frequency power amplifier 2 through a voltage source _4, a power amplifying element (e.g., a transistor or FET) controls the bias voltage V _B of, also, the high frequency power amplifier 5 The input power (input current I _D ) supplied to the high-frequency power amplifier 2 via the power supply is controlled.

An induction coil 6 is connected to the high-frequency power amplifier 2 via a matching circuit 7, and the plasma is lit by supplying high-frequency power to the induction coil 6. Output power Pout is supplied from the high frequency power amplifier 2 toward the induction coil 6 side. At this time, if the impedance matching when the matching circuit 7 is viewed from the high-frequency power amplifier 2 is insufficient, the reflected power Pref is returned from the matching circuit 7 toward the high-frequency power amplifier 2. The magnitude of the reflected power Pref differs between before plasma lighting and after plasma lighting. Normally, since the matching circuit 7 determines the circuit constant of impedance matching so that the plasma state after lighting is maintained, the reflected power Pre before plasma lighting is set.
f becomes larger than the reflected power Pref after plasma lighting.

Due to the reflected power Pref, the load voltage of the ICP high frequency power supply 1 increases, and the power loss Ploss also increases. The returned reflected power Pref finally becomes IC
Heat is generated in the high-frequency power supply device for P. So, IC
The high-frequency power supply device 1 for P uses the reflected power Pref to increase the power supply voltage Vref and the power loss Plos.
It is necessary to provide a rated voltage V ₀ and a rated power loss Ploss ₀ sufficient to withstand sref.

It is necessary that the rated voltage V ₀ substantially satisfies the following relational expression (1), and the rated power loss Ploss ₀ must satisfy the following relational expression (2). V _DD + Vref> V ₀ (1) Ploss + Plossref> Ploss ₀ (2) where V _DD is an applied power supply voltage, Vref is a voltage rise due to reflected power, V ₀ is a rated voltage, and P loss is a rated voltage.
Is the power loss in the RF power supply for ICP itself, Ploss
ref is the power loss due to the reflected power, and Ploss ₀ is the rated power loss.

The above-mentioned relational expressions (1) and (2) need to be satisfied both before and after plasma lighting, but the reflected power Pref before plasma lighting is the reflected power Pref after plasma lighting. Therefore, it is sufficient to satisfy the above relational expressions (1) and (2) before plasma lighting. Therefore, the reduction of the rated voltage V ₀ will be described below with reference to FIGS.
The reduction of ₀ will be described with reference to FIGS. 4 and 5, and the high power efficiency will be described with reference to FIGS. FIGS. 2, 4, and 6 show the case of the present invention, and FIGS.
Reference numerals 5 and 8 denote conventional cases for comparison with the present invention.

First, the rated voltage V ₀ will be described with reference to FIGS.
The reduction will be described. 2 and 3, (a)
FIG. 3 is a diagram showing a correlation between an applied power supply voltage _VDD and an output power Pout, and FIG. 4B is a diagram showing an input power Pin and an output power Pout.
FIG. 7C is a diagram showing a correlation with the rated voltage V _0.
FIG. 4 is a diagram comparing the relationship between the applied power supply voltage V _DD and the voltage increase Vref due to the reflected power before and after plasma lighting.

In a high frequency power amplifier, the input power P
When in is constant, the maximum output power Pout (max) is as shown in FIG.
As shown in (a), the applied power supply voltage V _{DD is} almost 2
It has a characteristic that is proportional to the power. In addition, the applied power supply voltage V _DD
And the output power Pout is the applied power supply voltage V
_{With the} maximum output power Pout (max) determined by the _DD as an upper limit, a characteristic proportional to the input power Pin is provided as shown in FIG. Normally, there is a difference between the power required for plasma lighting and the power required after plasma lighting, and the power required for plasma lighting is smaller than the power required after plasma lighting. Therefore, in the present invention, the maximum output power Pout (max1) is determined before and after plasma lighting based on the power required for plasma lighting (FIG. 2).
(In (a)), the maximum output power Pout (max2) is determined based on the power required to maintain the plasma (in (a) in FIG. 2).

From the correlation diagram between the applied power supply voltage _VDD and the output power Pout shown in FIG. 2A, the applied power supply voltage Vout corresponding to the maximum output power Pout (max1) required for plasma lighting is obtained.
_DD1 (in FIG. 2A) is the applied power supply voltage Vout corresponding to the maximum output power Pout (max2) required for maintaining the plasma.
_The voltage becomes smaller than _DD2 (in FIG. 2A). Therefore, when the applied power supply voltage V _DD before plasma lighting is set to V _DD1 (in FIG. 2A), the maximum output power Pout (max) output at this time is Pout (Pout (max) determined by the applied power supply voltage V _DD1. max1) (in FIGS. 2A and 2B). The high-frequency power output from the high-frequency power supply for ICP includes an input power Pin and an output power Pout shown in FIG.
The maximum output power Pout (max1) is maximized and changes according to the output characteristic A which is almost proportional to the input power Pin. Output power Pout1 is output for input power Pin1 before lighting (in FIG. 2B).

After the plasma is turned on, the plasma
Power supply voltage V after lighting_DDTo V _DD2If set to
(In FIG. 2A), the maximum output output at this time
Power Pout (max) is applied power supply voltage V_DD2Pout determined by
(max2) (in FIGS. 2A and 2B). For ICP
The high frequency power output from the high frequency power supply is shown in FIG.
(B) is a correlation diagram between the input power Pin and the output power Pout
From this, the maximum output power Pout (max2) is maximized and the input power
It changes according to the output characteristic B which is almost proportional to the force Pin.
You. Output power Pout2 for input power Pin2 after lighting
Output (in FIG. 2B).

Rated voltage V _{0 of} high frequency power supply for ICP
Is represented by the sum of the applied power supply voltage V _DD and the voltage rise Vref due to the reflected power from the relationship of the above equation (1). _Therefore, before lighting, (V _DD1 + V _ref1 ) (a in FIG. 2C) And after lighting, ( _VDD2
+ Vref2) (b in FIG. 2C). Normally, since the reflected power before lighting is larger than the reflected power after lighting, Vref1 becomes larger than Vref2,
The rated voltage V ₀ of the CP high-frequency power supply is (V _DD + V
ref1) (FIG. 2 (c)).

On the other hand, in the conventional high frequency power supply for ICP, one maximum output power Pout (max) is determined before and after lighting based on the power required to maintain the plasma.
(In FIG. 3A), and corresponds to the maximum output power Pout (max) required to turn on and maintain the plasma from the correlation diagram between the applied power supply voltage V _DD and the output power Pout shown in FIG. The applied power supply voltage V _DD to be applied is obtained (in FIG. 3A).

When the applied power supply voltage V _DD is set (FIG. 3
(In (a) and (b)), the maximum output power Pout (max) output at this time is Pout determined by the applied power supply voltage _VDD.
(max) (in FIG. 3B). The high-frequency power output from the high-frequency power supply device for ICP has the maximum output power Pout (max) as the maximum from the correlation diagram between the input power Pin and the output power Pout shown in FIG. It changes according to the output characteristic C which is approximately proportional. Output power Pout1 is output (in FIG. 3 (b)) for input power Pin1 (in FIG. 3 (b)) before lighting, and input power Pin2 (in FIG. 3 (b)) after lighting. Output power Pout
2 is output (in FIG. 3B).

At this time, the rated voltage V ₀ of the ICP high-frequency power supply is expressed by the sum of the applied power supply voltage V _DD and the voltage rise Vref due to the reflected power from the relationship of the equation (1) as described above. In this case, since the applied power supply voltage V _DD is constant, regardless of before and after lighting, (V _DD + Vre
f1) or (V _DD + Vref2). Usually, the reflected power before lighting is larger than the reflected power after lighting, so that Vref1 is larger than Vref2. Therefore, the rated voltage _{V 0} which ICP high-frequency power supply _{(V DD}
+ Vref1) (FIG. 3 (c)).

In FIG. 2C, the rated voltage V ₀ according to the present invention (a in FIG. 2C) and the conventional rated voltage V _{0 are shown.}
Comparing (c to be displayed in broken lines in FIG. 2 (c)), provided with a voltage rise Vref by the reflected power as a common component, the rated voltage V ₀ according to the present invention comprises an applied supply voltage V _DD1 of the previously lighted rated voltage V ₀ by conventionally comprises applying power source voltage V _DD which is common to the front and rear lights. Since the applied power supply voltage V _DD1 before lighting can be smaller than the applied power supply voltage V _DD common before and after lighting, ICP
Rated voltage of the high-frequency power supply device can be reduced.

Next, the reduction of the power loss Ploss will be described with reference to FIGS. 4A and 5A are diagrams showing the correlation between the output power Pout and the power efficiency η.
(B) is a diagram showing a correlation between the input power Pin and the output power Pout, and (c) is a diagram illustrating a power loss Ploss of the ICP high-frequency power supply itself and a power loss Pref due to the reflected power with respect to the rated loss power Ploss0. FIG. 4 is a diagram comparing the relationship before and after plasma lighting. In a high-frequency power amplifier, when the applied power supply voltage V _DD is constant,
Power efficiency η is almost proportional to the output power Pout as shown in FIG. 4 (a), provided with a characteristic that varies with the bias voltage V _B.

Here, the power supply efficiency η and the power loss Plo
ss is represented by the following equation. η = Pout / (V _DD × I _DD ) (3) Ploss = Pout ((1 / η) −1) (4) Therefore, when the applied power supply voltage V _DD is constant, FIG. As shown, the power loss Ploss changes with the bias voltage V _B (power efficiency η) and has a characteristic proportional to the output power Pout. Incidentally, FIG. 4 (a), the (b), the time that the bias voltage _{V B} is related to _V B1 _{<V B2,} the power efficiency eta for the same output power Pout becomes a relationship of η ₂ <η _1, the power loss for the same output power Pout Ploss is Ploss ₁ <Ploss
₂ is obtained. From the above relationship, the bias voltage V _B
And the power loss Ploss can be controlled by controlling the power efficiency η.

Therefore, if a low bias voltage _VB1 is set for the output power Pout1 (in FIG. 4A) before the plasma is turned on, the power supply efficiency η becomes higher than the power supply efficiency η1.
(In FIG. 4A). Power loss Plo at this time
As shown in FIG. 4B, ss becomes a power loss Ploss1 determined by a characteristic (in FIG. 4B) indicated by the power supply efficiency η1 with respect to a change in the output power Pout1 (FIG. 4B). In).

After the plasma is turned on, if a high bias voltage V _B2 (V _B1 <V _B2 ) is set with respect to the output power Pout 2 (in FIG. 4A), the power efficiency η becomes low and the power efficiency η 2 becomes low. (In FIG. 4A). The power loss Ploss at this time is, as shown in FIG. 4B, the power loss Ploss determined by the characteristic (in FIG. 4B) indicated by the power supply efficiency η2 with respect to the change in the output power Pout2.
loss2 (in FIG. 4B).

Rated power loss P of high frequency power supply for ICP
Since the loss ₀ is represented by the sum of the loss power Ploss of the ICP high-frequency power supply itself and the loss power Plossref due to the reflected power from the relationship of the equation (2), (Pl
oss1 + Plossref1) (a in FIG. 4 (c)). After lighting, (Ploss2 + Plossref2)
(B in FIG. 4 (c)).
(C)). Normally, the reflected power before lighting is larger than the reflected power after lighting, so the power loss due to the reflected power is Ploss
ref1 becomes larger than Plossref2. Further, the power loss Ploss of the ICP high-frequency power supply device itself can be suppressed to be smaller than the power loss Ploss2 after lighting by switching the bias voltage between before and after lighting. As a result, the rated power loss Ploss ₀ of the high frequency power supply device for ICP becomes (Ploss1 + Plossr
ef1) (a in FIG. 4 (c)) or (Ploss2 + Ploss
ref2) (b in FIG. 4C).

On the other hand, in the conventional high frequency power supply for ICP, the bias voltage is fixed in accordance with the output characteristics after lighting. Therefore, the output power Pout1 before lighting (in FIG. 5A) has a low power supply efficiency η1 (in FIG. 5A), and the output power after lighting Pout2 (in FIG. 5A).
(In (a)) has high power efficiency η2 (FIG. 5).
(In (a)). Therefore, before lighting,
Since the power efficiency η1 is low, the power loss Ploss1 increases (in FIG. 5A). At this time, the rated power loss Ploss ₀ of the ICP high-frequency power supply device is represented by the sum of the loss power Ploss of the ICP high-frequency power supply device itself and the loss power component Plossref due to the reflected power from the relationship of Expression (2) as described above. You.

Normally, the reflected power before lighting is greater than the reflected power after lighting, so the power loss Plossref1 before lighting due to this reflected power is greater than the power loss Plossref2 after lighting. Also, regarding the power loss of the high frequency power supply device for ICP itself, since the power efficiency before lighting is low, the power loss Ploss1 before lighting becomes large, and the ICP
Power loss Ploss ₀ of the high frequency power supply for
1 + Plossref1) (a in FIG. 5 (c)) or (Plos
s2 + Plossref2) (b in FIG. 5C).

In FIG. 4C, the rated power loss Ploss ₀ according to the present invention (a in FIG. 4C) and the conventional rated voltage rated power loss Ploss ₀ (shown by broken lines in FIG. 4C). c), the power loss Plo due to the reflected power
In addition to having the common ssref1, the present invention provides a bias voltage V
It has a rated power loss Ploss1 determined by _B1 , while a conventional power loss Plo determined by the bias voltage _VB2.
ss2. In the present invention, the rated power loss Ploss1 can be made smaller than the rated power loss Ploss2 by switching the bias voltage to _VB1 before lighting, so that the rated power loss of the high frequency power supply device for ICP can be reduced. it can.

Next, the high power supply efficiency according to the present invention will be described with reference to FIGS. Since the output power Pout does not need to be controlled very accurately in the high-frequency power supply before plasma lighting, the following method is possible. FIG. 6 (a)
In the diagram showing the correlation between the applied power supply voltage V _DD and the output power Pout shown in FIG. 6, the power supply voltage V _D is obtained until the output power Poutmax (in FIG. 6C) necessary for lighting the plasma is reached (step S2). _{Lower D} (Step S
1) The power supply voltage V _DD1 is determined and fixed (FIG. 6 (c)).
(Step S3).

The input power Pin and the output power Pou in FIG.
In the graph showing the correlation between the t, the output power Pout is the maximum output power Poutmax determined by the supply voltage V _DD1 to the upper limit, the output power characteristic to increase or decrease approximately in proportion to the input power Pin. Therefore, the present invention utilizes the characteristic that the maximum value of the output power is determined by the power supply voltage _VDD1 without _depending on the input power Pin, and controls the output power Pout without performing feedback control from the induction coil side. The power Pin is set to the maximum output of the preceding power amplifier (see FIG. 6 (c)).
) (Steps S4, 5, 6).

On the other hand, FIG. 8 shows an example of conventional output power stabilization control before lighting. In the output power stabilization control, in the output power characteristic having the maximum output power (in FIG. 8C) determined by the power supply voltage _VDD1 , the input power Pin is controlled by feedback from the induction coil side (see FIG. 8). (In (c)), the output power Pou
It controls t (in FIG. 8C). According to this, the power supply efficiency of the power amplifier can be improved.

[0038]

As described above, according to the high-frequency power supply for plasma of the present invention, the failure rate of the elements of the high-frequency power supply for ICP can be reduced, and the reflection at the time of plasma lighting can be reduced with a small rated value. Can withstand power.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a high-frequency power supply for plasma according to the present invention.

FIG. 2 is a diagram for explaining a reduction in the rated voltage of the high-frequency power supply device for ICP of the present invention.

FIG. 3 is a diagram for explaining a rated voltage of a conventional high frequency power supply for ICP.

FIG. 4 is a diagram for explaining a reduction in rated power loss of the high-frequency power supply device for ICP of the present invention.

FIG. 5 is a diagram for explaining a rated power loss of a conventional high frequency power supply device for ICP.

FIG. 6 is a diagram for explaining high power efficiency of the high frequency power supply device for ICP of the present invention.

FIG. 7 is a flowchart for explaining high power efficiency of the high frequency power supply device for ICP of the present invention.

FIG. 8 is a flowchart for explaining the operation of the conventional ICP high-frequency power supply device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... High frequency power supply device for ICP, 2 ... High frequency power amplifier, 3 ... Control means, 4 ... Voltage source, 5 ... High frequency power amplifier, 6 ... Induction coil, 7 ... Matching circuit.

Claims (3)

[Claims] An IC for supplying high frequency power to an induction coil
A high-frequency power supply for P, comprising a high-frequency power amplifier and control means for controlling the high-frequency power amplifier, wherein the control means switches a power supply voltage applied to the high-frequency power amplifier between before and after plasma generation, A high frequency power supply for ICP, wherein a power supply voltage before plasma generation is lower than a power supply voltage after plasma generation. 2. An IC for supplying high frequency power to an induction coil.
A high-frequency power supply device for P, comprising: a high-frequency power amplifier and control means for controlling the high-frequency power amplifier, wherein the control means adjusts a bias voltage of a power amplifying element included in the high-frequency power amplifier before and after plasma generation. Wherein the bias voltage before plasma generation is lower than the bias voltage after plasma generation. 3. An IC for supplying high frequency power to an induction coil
A high-frequency power supply device for P, comprising a high-frequency power amplifier and control means for controlling the high-frequency power amplifier, wherein the control means maximizes input power to the high-frequency power amplifier before plasma generation, and applies a power supply voltage to be applied. A high frequency power supply for ICP, wherein the power supply efficiency of the high frequency power amplifier is increased by fixing the voltage to a minimum voltage for supplying high frequency power required for plasma generation.