JPH0720039B2 - High frequency impedance matching circuit - Google Patents

Description

Detailed Description of the Invention

 [Object of the Invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of a high frequency impedance matching circuit used in an etching apparatus or the like.

[0002]

2. Description of the Related Art In a conventional etching apparatus or the like, a high frequency voltage for plasma formation is connected in a vacuum chamber in order to effectively perform etching. That is, as shown in FIG. 5, a high frequency source 1 that outputs a high frequency of 13.5 MHz, for example, is supplied to a load 4 via a coaxial cable 2 and an impedance matching circuit 3. In the load 4, a high frequency is supplied between the container 41 that forms the vacuum chamber and the backing plate 42 that supports the target in the container 41.

Normally, the coaxial cable 2 has a characteristic impedance of 50Ω and matches with the high frequency source 1, while the load 4 has a predetermined resistance value such as 200Ω other than 50Ω depending on the shape and size thereof. Indicates. The matching circuit 3 is composed of an LC circuit including a coil 31 and series-parallel capacitors 32 and 33, but a high frequency transmission loss in the coil 31 is large, and a temperature rise due to heat generation cannot be avoided. Therefore, the coil 31 is formed by winding a tubular body in a coil shape, and is supplied with cooling water 6 by the pump 5 from the water supply / drainage pipes 31a and 31b connected to both ends and is cooled. In addition, the backing plate 42 is also provided with a water supply passage 42a for the cooling water 6 inside and is cooled via the water supply / drainage pipes 43a and 43b in order to prevent deformation due to temperature rise and the like.

By the way, when the output of the high-frequency source 1 is constant, the amount of high-frequency power actually supplied to the load 4 depends on the amount of transmission loss in the high-frequency impedance matching circuit 3 and the like on the way. In order for the high frequency from the high frequency source 1 to be efficiently supplied to the load 4, it is necessary to suppress the amount of power consumed by the coil 31 or the like to a minimum, but in reality, the transmission loss in the coil 31 is simply generated. It has been noticed that there is an amount of leakage power that exceeds the amount, and the amount of power actually supplied to the load 4 may be considerably lower than the design value. Looking into the cause, the fact that the transmission loss in the impedance matching circuit 3 actually includes high-frequency power that leaks through the cooling water 6, and the backing plate 42 similarly passes through the cooling water 6. It turns out that the leaking high-frequency power cannot be ignored. That is, the cooling water 6 flowing in the water supply / drainage pipes 31a and 31b is a kind of conductor having a dielectric constant, and although not shown, the ground potential level near the water source at the tip and the connection point between the coil end, that is, the water supply / drainage pipe. Due to the potential difference between A and B, the high frequency of the cooling water 6 disappears, and the stray capacitances 31a ′ and 31b ′ formed between the conductor path of the cooling water 6 and the container 41 of the vacuum chamber are used. For the first time, I also learned that a large amount of high frequency leaked. Since the amount of leakage (electric power) is proportional to the potential difference, that is, the square of the voltage, the higher the potential of the connection points A and B, the more the amount of leakage increases by the square. This phenomenon also applies to the cooling water 6 on the backing plate 41 side. However, in the conventional high frequency impedance matching circuit, it has not been predicted so far that the high frequency leaks through the cooling water 6 as described above, and a means for reducing the leakage has not been considered.

In the present invention, the leakage power is supplied to the water supply / drain pipe 31a,
It was made paying attention to the fact that it depends on the height of the potential difference between the connection points A and B between 31b and the coil 31 and the ground potential.
By arranging the connection points A and B to be located at low potential points, high frequency transmission loss can be reduced.

[0006]

The conventional high-frequency impedance matching circuit has a drawback in that the amount of power leaked in the water cooling system in the matching circuit is large and the high-frequency power cannot be efficiently supplied to the load.

An object of the present invention is to provide a high frequency impedance matching circuit which solves the above-mentioned conventional drawbacks and improves the power supply efficiency.

[Structure of Invention]

[0009]

A first invention is a coil formed of a tubular body to which a water supply / drainage pipe is connected and through which cooling water passes,
In a high frequency impedance matching circuit consisting of a combination connection with a variable capacitor, the coil is composed of a pair of coils connected in parallel so that tubular bodies communicate with each other, and the high frequency voltage level propagating through the pair of coils is high. It is characterized in that the water supply / drainage pipe is connected in the vicinity of the minimum position.

A second invention is characterized in that, in the high-frequency impedance matching circuit of the first invention, a pair of coils are connected so as to communicate with the water supply / drainage pipe for cooling the load.

[0011]

In the high frequency impedance matching circuit according to the present invention, attention is paid to the fact that the potential of the transmitted high frequency signal on the tubular cooling coil varies depending on the position on the coil.
A cooling water supply / drainage pipe is connected near the position where the electric potential is the smallest. As a result, the potential difference between the connection point and the ground potential becomes small, so that the amount of electric power leaking through the cooling water can be suppressed. In order to circulate the cooling water in the vicinity of the position where the high-frequency potential is minimized on the coil, in the present invention, the coils are connected to each other in a parallel configuration, and one of the connected water supply / drain pipes is connected to the water supply pipe. Since the other can be configured as a drain pipe, cooling water can be effectively circulated.

Further, the coil is connected to the water supply / drain pipe for cooling the load so that the power feeding line and the cooling water channel are shared, so that the power leakage on the load side can be reduced and the power can be efficiently supplied.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a high frequency impedance matching circuit according to the present invention will be described in detail below with reference to FIGS. The same components as those of the conventional configuration shown in FIG. 5 are designated by the same reference numerals, and detailed description thereof will be omitted.

That is, in FIG. 1, the high frequency source 1 has a load 4 via a coaxial cable 2 and an impedance matching circuit 3.
Are connected. The impedance matching circuit 3 is composed of a series variable capacitor 32, a parallel variable capacitor 33, and a parallel coil 34 connected in cascade to the series variable capacitor 32. The parallel coil 34 is formed of a tubular body as in the conventional case, one of which is directly connected in common and the other of which is a water supply / drainage pipe 43a, 43b for cooling the backing plate 42.
They are commonly connected to each other through a ring shape. Further, the water supply / drainage pipes 34a and 34b for cooling are connected to the parallel coil 34.
The cooling water 6 from the pump 5 can be circulated in the direction of the arrow by being connected to the connection points C and C'in the middle. 3
Reference numeral 4c is a valve for adjusting the amount of cooling water 6 flowing therethrough as necessary.

Therefore, the present invention is characterized in that the connection points C and C'between the parallel coil 34 and the water supply / drainage pipes 34a and 34b are mounted at or near the position where the high-frequency potential transmitted is minimized. And Since the transmission high frequency potential is low at the positions of the connection points C and C ′, it is assumed that the cooling water 6 (having conductivity) flowing in the water supply / drainage pipes 34a and 34b is connected to the ground potential at its tip. However, since the potentials at the connection points C and C'are sufficiently low, the leakage amount of high frequency power can be suppressed. This means that load 4
The same applies to the cooling water channel, and by using the cooling water channel also as the power feeding line, the leakage power can be significantly reduced. Further, as a result, it is assumed that the water supply / drainage pipes 34a, 34
Even if there is a stray capacitance 34a 'or the like between b and the ground potential, since the potential difference is small, the high frequency loss due to it is small, and the power supply efficiency to the load 4 is greatly improved.

Next, for the understanding of the present invention, the point at which the high-frequency potential is minimized at the position of the connection points C, C'of the parallel coil 34 and the water supply / drainage pipes 34a, 34b, or the position at which it is minimized. 2 to FIG.
Will be described with reference to. FIG. 2 shows an equivalent circuit of FIG. 1, in which the load 4 has a capacitance Cs between the resistance X and the container 41.
And a high-frequency current flowing through each of them, and a supply voltage to the load 4 is Vx.
If x is the high frequency current IL flowing in the parallel coil 34,
The vector relationship of these Ix, Vx, Ics and IL is expressed as shown in FIG.

Further, the current IL in the parallel coil 34 and the high-frequency voltage VL applied to the parallel coil 34 have a phase difference of 90 degrees (perpendicular to each other), and the high-frequency voltage Vcc applied to the series capacitor 32 has a phase opposite to that of the voltage VL. 180
Degree) correction and adjustment to match the output voltage Vi of the high frequency source 1, these IL, VL, Icc and Vi are adjusted.
The vector relation of is also expressed as shown in FIG.

Therefore, the impedance seen from the high-frequency source 1 toward the load side is regarded as a pure resistance of 50Ω in the impedance matching state, so that the output voltage Vi and the output current I are in phase, and as shown in FIG. Match. Moreover, the output current I is the sum of the high frequency current Ici flowing through the parallel variable capacitor 33 and the current IL flowing through the series variable capacitor 32 (parallel coil 34), and the current Ici in the impedance matching state is 9 with respect to the output current I.
The phase is advanced by 0 degree. In other words, when the capacitance values of the series-parallel variable capacitors 32 and 33 are adjusted and the values of Vcc and Ici are changed to achieve impedance matching, I and Vi are changed.
The vector directions of and coincide with each other, and Ici leads the phase by 90 degrees with respect to Vi.

As can be seen from the vector diagram of FIG. 3, when the voltage VL of the parallel coil 34 is considered, it is on the vector of the current IL starting from the ground potential O and orthogonal to each other. As an example of the potential difference up to some points on 34, as shown in FIG. 4, Vx, V1, V2, V3, and V4 are sequentially applied from the load 4 side, and the connection point C on the coil that coincides with the direction of the current IL, C'is the minimum potential difference V2
It turns out that

Therefore, according to the present invention, the parallel coil 3
4, a pair of pipe mounting ports for cooling water can be selected in the vicinity of positions C and C'where the potential difference from the ground potential O is at least minimum. Therefore, high-frequency power transmission by the cooling water to the mounting ports is possible. The loss can be minimized. Of course, even if the permittivity differs depending on the quality of the cooling water, the connection points C and C ′ are always at the minimum high-frequency potential, so that the transmission power loss can always be minimized.

[0021]

As described above, in the high frequency impedance matching circuit according to the present invention, since the cooling water outlet is provided in the vicinity of the position where the voltage level is the smallest on the matching coil, the high frequency loss in the cooling water channel system is reduced. It can be held down, and it can be used in an etching device or the like to obtain a remarkable effect.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a high frequency impedance matching circuit according to the present invention.

FIG. 2 is an equivalent circuit diagram of the high frequency impedance matching circuit shown in FIG.

FIG. 3 is a vector diagram for explaining the operation of the high frequency impedance matching circuit shown in FIG.

FIG. 4 is a vector diagram showing a part of the vector diagram shown in FIG.

FIG. 5 is a configuration diagram showing a conventional high frequency impedance matching circuit.

[Explanation of symbols]

 1 ... High frequency source 2 ... Coaxial cable 3 ... Matching circuit 31, 34 ... Coil 32, 33 ... Variable condenser 34a, 34b ... Water supply / drainage pipe 4 ... Load 43a, 43b ... Water supply / drainage pipe 6 ... Cooling water

Claims (2)

[Claims] 1. A high-frequency impedance matching circuit comprising a combination of a coil formed of a tubular body, to which a water supply / drainage pipe is connected, for passing cooling water, and a variable capacitor, wherein the coils are arranged so that the tubular bodies communicate with each other. A high frequency impedance matching circuit comprising a pair of coils connected in parallel, wherein the water supply / drainage pipe is connected near a position where a high frequency voltage level propagating through the pair of coils is minimized. 2. The high-frequency impedance matching circuit according to claim 1, wherein the pair of coils are connected so as to communicate with the water supply / drainage pipe for cooling the load.