JPH0384900A - Plasma treatment device - Google Patents

Abstract

PURPOSE:To improve the reproducibility of dry-etching treatment by keeping the plasma impedance of a plasma generating means at a desired constant value. CONSTITUTION:A plasma treatment device is constituted in such a manner that the capacitance of each of impedance-matching variable capacitors C1, C2 in a matching box 2a is detected as the turning angle of this capacitor and the detected capacitance is then converted into the corresponding voltage to be taken into a CPU 11a whereby the impedance of a plasma load 3 can be computed. Besides, a change of reproducibility in a plasma treatment process is measured as a change of plasma impedance and accordingly the output magnetic-field of each of magnetic coils 14 arranged outside a plasma chamber 3a is controlled to make the impedance of the plasma chamber 3a constant. Thus, plasma treatment can be obtained with high precision in the reproducibility thereof.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention measures plasma impedance during plasma processing of a plasma processing apparatus that performs processing such as dry etching, particularly a plasma generator, and measures the plasma impedance so that it becomes constant. The present invention relates to a plasma processing apparatus that controls a magnetic field applied to a plasma generator.

[Conventional technology] FIG. 3 is a block diagram of a conventional plasma processing apparatus.

A plasma load (3), which is a plasma generator, and an RF power source (1) that supplies high frequency power (hereinafter referred to as RF power) to the plasma load (3).
), a matching box (2) is inserted between them to perform matching. Each of these is shown as an equivalent circuit. Further, between the RF power source (1) and the process load (3), there is a phase difference/impedance detector ( 4) are connected.Phase control servo unit (5>) and impedance control servo unit (6)
is the matching variable capacitor (C2>(C
The RF power source (1) and the plasma load (3) are matched by controlling the capacities of the RF power source (1) and the plasma load (3).

Setting of the output power of the RF power source (1) is performed from the CPU (11) via the D/A conversion unit (10), and this set power amount, incident power amount, and reflected power amount are determined by the A/D conversion unit (9). ) is taken into the CPU (11) and displayed on the CRT (12).

Next, the operation will be explained. 13 by RF power supply (1)
High frequency power of 56 MHz is supplied to the plasma load (3) via the matching box (2). RF power supply (
The matching box (2) has a phase difference and a According to the detection results of the impedance detector (4), the capacitances of the variable capacitors (C2) (C1) in the matching box (2) are controlled by the phase control servo unit (5) and the impedance control servo unit (6), respectively. The power source (1) and the load (3) are matched together. The output setting of the RF power supply (1) is CP
It is performed from U (11) via the D/A conversion unit (10). In addition, as a monitor, the amount of incident power and the amount of reflected power are sent to the CPU (11) via an A/D conversion unit (9).
The set power amount, incident power amount, and reflected power amount are displayed on the CRT (12).

[Problems to be Solved by the Invention] As described above, in the conventional plasma processing apparatus, it is necessary to match the power supply and the plasma load using the matching box, and to adjust the set power amount, incident power amount, and reflected power amount. There was a problem in that the method was limited to monitoring and no active means were provided to obtain a more stable matching state, such as controlling the impedance of the plasma load to a constant level.

This invention was made to solve the above-mentioned problems, and its purpose is to obtain a more stable matching state by controlling plasma impedance to a constant value. In other words, changes in the processing gas state, degree of vacuum, and supplied RF power in the plasma chamber that houses the plasma generator (plasma load) appear in changes in plasma impedance, so it can be used as an in-process monitor during wafer processing.
In order to improve the reproducibility of the dry etching process by automatically measuring changes in plasma impedance, we control the magnetic field strength generated by the magnet coil placed outside the plasma generator chamber to maintain a constant plasma impedance. The purpose of this study is to obtain a plasma processing apparatus that can maintain high temperatures.

[Means for Solving the Problems] In view of the above object, the present invention provides a plasma processing apparatus that includes a plasma generation means for generating plasma, an RF power supply means for supplying RF power to the plasma generation means, and a plasma generation means for supplying RF power to the plasma generation means. A matching means inserted between the means and the RF power supply means to match the means, a magnetic field generating means provided outside the plasma generating means for applying a magnetic field to the plasma generating means, and a matching means inserted between the means and the RF power supply means; means for detecting plasma impedance during discharge of the plasma generation means from a circuit factor; display means for displaying the detected plasma impedance; and magnetic field control means for controlling the magnetic field intensity generated by the magnetic field generation means in accordance with the detected plasma impedance. There is provided a plasma processing apparatus characterized in that the plasma impedance of the plasma generating means is maintained at a desired constant value.

[Operation] In this invention, the rotation angle θ of the variable capacitor for matching in the matching box is converted into a voltage, the voltage is digitally converted and input into the CPU, and the rotation angle θ is converted into a voltage.
is calculated as a function to calculate the plasma load, that is, the plasma impedance of the plasma generating means. Then, the magnetic field strength applied to the plasma generating means is controlled so as to keep the plasma impedance constant.

[Example 1] An example of the present invention will be described below with reference to the drawings. 1st
The figure is a block diagram of a plasma processing apparatus according to an embodiment of the present invention, and parts indicated by the same reference numerals are the same as those in the conventional apparatus described above. In the figure, the plasma chamber (also present in the conventional device 3aH, but omitted in Figure 3) is a container that houses the plasma load (3), and the outside of the plasma chamber (3a) is a container that houses the plasma load (3). A magnetic screw 1 to a coil (14) for applying a magnetic field are provided. 1st
The second capacitor capacity/voltage converters (7) and (8) are variable capacitors for matching (CI HO2
) is converted into a voltage. This voltage is converted into an analog/digital signal by the A/D conversion unit (9a).
It is digitally converted and taken into the CPU (lla). The CPU (lla) calculates the impedance of the plasma load from this value and displays the calculation result on the CRT (12). In addition, this calculation result is transmitted to the magnet coil (14) via the D/A conversion unit (10a).
Magnetic field controller I roller (13) that controls the output magnetic field strength of
This magnetic field controller (13) controls the magnet coil (13) to keep the plasma impedance constant.
14) Control the magnetic field strength. Further, FIG. 2 is a diagram showing the relationship between plasma impedance and the magnetic flux density of the output magnetic field of the magnet coil (14), and the magnetic field controller (13) is operated according to this diagram.
) controls the output magnetic field.

Next, the operation will be explained. RF power supply (1> by 13
．． RF power of 56 MHz is supplied to the plasma load (3>) via the matching box (2).The power supplied from the RF power source (1) has no reflection from the plasma load (3>) and has the maximum power. In order to be able to The unit (6) controls the capacitance of variable capacitors (C2) and (C1) in the matching box (2), respectively, to achieve matching between the source (1) and the load (3).RF The output setting for power supply 1> is C.
This is performed from the PU (11) via the D/A conversion unit (10).

Also, as a monitor, the amount of incident power and the amount of reflected power are taken into the cpU (11) via the A/D conversion unit (9),
The RT (12) displays the set amount of power, the amount of incident power, and the amount of reflected power. The impedance of the plasma load (3) is measured using the capacitor capacitance/voltage converter (7) (8) that converts the rotation angle θ of the matching variable capacitor (cB (C2)) of the matching box (2) into a voltage. The value is sent to the CPU via the A/D conversion unit (9a).
(lla) and matching capacitor (C
1) Calculate the capacity of (C2) as a function of rotation angle θ,
I am now looking for plasma impedance. This will be explained in detail later. As shown in Fig. 2, plasma impedance can be controlled by changing the magnetic flux density of the output magnetic field generated by the magnet coil (14). ) The plasma impedance can be kept constant by controlling the magnetic flux density applied to the plasma.

A method for measuring plasma impedance by measuring the rotation angle of a matching variable capacitor will be described in detail with reference to FIGS. 4 to 7.

The matching conditions for the matching box, or matching circuit, between the RF power source and the plasma load are that when looking left and right between the input terminals of the matching circuit, both image impedances are equal, and that the left and right image impedances are equal between the output terminals. Equal impedance is a condition for delivering maximum power to the load without reflection.

The image impedance can be determined from the open impedance (Z f) and the short circuit impedance (Z s) using equation (1).

Z. 1=puff 7] = Xl(XA・XB)/(XA+X−)
...(1) Z. 2 = 4T] 7 =F GY1 ... (2> In order to match here, Z01 = R0 (usually 50Ω), Z62 = RL
(resistance valve of plasma equivalent impedance) is a necessary condition, and equations (3) and (4) are derived.

R,=Z,,=xl(xA-X,)/(xA+xi
)--(3) RL=ZO2= (X-"Xs) million=...
・(4) From formula (3) and formula <4), X-=ROR=, /(R6-RL)”
' (5) XA-Puff F page bottom...(
6) is required.

As shown in the formula
CI) can be determined as a function of the rotation angle θ.

X, = 1/ωC + (θ) ... (7>
Therefore, the resistance component RL of the plasma equivalent impedance is (5
〉 can be obtained as shown in equation (8) by expanding the equation.

RL=(XB'/(R,'+XB2)l·R.

= (1/LAC, (θ)〉2÷ [(1/ωC+(θ))'/(50"(1/61C+
(θ))2) Ko・50・ (8) However, R9=50Ω.

The actual plasma equivalent impedance is as shown in FIG. 7 because a capacitive load is connected in series.

The actual plasma equivalent impedance Z is expressed by equation (9) % (9) If the value of XA is corrected as shown in equation (10) in order to cancel the JXL component, the imaginary part will be canceled and matching will be achieved.

Therefore, XA'=XA+XL...(10>
From equation (10), the imaginary part Xt of the plasma equivalent impedance can be determined as a function of the rotation angle θ of the variable capacitor (VC2) in FIG.

X, = XA - From the formula, Zp=Rt, JXL = [(1/ωC+(θ)) 2/(502+(1h
c+ (θ))2)]・50−j[(1/ωC2(θ)
> - to T ball 7i here...(12) becomes 1, which can be found as the number between the circuit angles of the variable capacitor (VCINVC2) of the matching circuit.

[Effects of the Invention] As described above, according to the present invention, the capacitance of the matching variable capacitor in the matching box is detected as its rotation angle, and this is converted into a voltage and inputted into the CPU.
The configuration is configured to calculate the plasma load impedance from this, measure changes in the process in the plasma as changes in plasma impedance, and control the output magnetic field of the magnet coil placed outside the plasma chamber to keep the impedance of the plasma chamber constant. This has the effect of providing plasma processing with high reproducibility and accuracy.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a plasma processing apparatus according to an embodiment of the present invention, and FIG. 2 is a diagram showing the relationship between plasma impedance and magnetic field density of the output magnetic field of the magnet coil.
FIG. 3 is a block diagram showing a conventional plasma processing apparatus, and FIGS. 4 to 7 are diagrams for explaining a method of measuring plasma impedance. In the figure, (1) is the RF power supply, (2a) is the matching box, (3) is the plasma load, (4) is the phase difference/impedance detector, (5) is the phase control servo unit, and (6) is the impedance. Control servo unit, (7)
(8> is the second capacitor capacity/voltage conversion unit, (9a) is the A/D conversion unit, (10a) is the D/A conversion unit, (1, 1a)
) is a CPU, (12) is a CRT, (13) is a magnetic field controller, and (14> is a magnet coil. In the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] A plasma generation means for generating plasma, an RF power supply means for supplying RF power to the plasma generation means, and a matching between the plasma generation means and the RF power supply means. A matching means inserted between the two, a magnetic field generating means provided outside the plasma generating means for applying a magnetic field to the plasma generating means, and detecting plasma impedance during discharge of the plasma generating means from a circuit factor of the matching means. a display means for displaying the detected plasma impedance; and a magnetic field control means for controlling the magnetic field intensity generated by the magnetic field generating means according to the detected plasma impedance, the plasma impedance of the plasma generating means 1. A plasma processing apparatus characterized in that: is maintained at a desired constant value.