JPH02301134A - Plasma controller for plasma generator - Google Patents

Abstract

PURPOSE:To accelerate etching speed while preventing damage of a mask and a layer to be etched by regulating high frequency power to control plasma density and controlling ion energy via DC discharge current. CONSTITUTION:Many slits, holes are opened oppositely to an anode electrode 16, or meshlike high frequency cathode electrode 17 is disposed, opposed to a high frequency cathode electrode, and a DC cathode electrode 18 is disposed to the opposite side of an anode electrode 16. High frequency power and DC power are supplied between the electrode 16 and the electrode 17, and between the electrode 17 and the electrode 18 to generate a high frequency plasma 22, a DC plasma 23. Auxiliary electrons are supplied via the holes of the electrode 17 from the plasma 23 side to a cathode sheath 10 generated at the high frequency plasma side of the electrode 17, and a sheath voltage is reduced by supplying the auxiliary electrons. The supplying amount of the electrons can be controlled by increasing or decreasing the DC power.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a control device for a plasma generator used in dry etching, CVD, etc., which are the main steps in the manufacturing process of semiconductor devices.

[Conventional Technique] A conventional plasma generator will be described with reference to FIG.

A flat plate electrode (cathode electrode) 2 connected to the high frequency @ source 1 via a capacitor 8 for DC interruption, and a facing type i<anode electrode f 3 at ground potential opposite to the flat plate electrode 2 are installed. 4 the cathode electrode 2, anode electrode 3
is housed in a vacuum container 4, and the cathode electrode 2 is insulated from the vacuum container 4 by an insulating material 5.

The vacuum vessel 4 is provided with an introduction system 6 for introducing a reactive gas and an exhaust system 7 for keeping the pressure inside the vacuum vessel 4 constant.

An object to be processed, for example a silicon wafer 9, is usually placed a on the cathode electrode 2.

High frequency power, for example 13.56M, is applied between the two electrodes 2.3.
When a plasma is generated between both electrodes by applying Hz, a large cathode drop voltage ( self-bias) occurs.

The reactive gas ions are accelerated by this cathode drop voltage and are perpendicularly incident on the object to be processed '$A9, so that vertical etching progresses.

[Problems to be Solved by the Invention] When performing etching processing using such an apparatus, the main factors that determine the etching rate are the cathode drop voltage (ion energy) and the number of ions incident on the object to be processed (ion density - plasma density).

In order to increase the etching rate, it is necessary to increase the ion energy and the plasma density in particular, and the plasma density can be increased by increasing the applied high frequency power.

However, when this high frequency power is increased, the cathode fall voltage (ion energy) is also inevitably increased.

Therefore, when the object to be processed is a wafer for manufacturing semiconductor devices, in the conventional etching method, increasing the etching rate also increases the ion energy, and if the ion energy increases more than necessary, a film may be formed on the surface of the wafer. There is a problem in that it damages the etched mask, the layer below the layer to be etched, or the base material.

In view of these circumstances, the present invention seeks to provide a plasma generating apparatus that can increase the etching speed while preventing damage to the mask and the layer to be etched.

[Means for Solving the Problems] The present invention provides an auxiliary device to the cathode sheath area as a means for controlling the sheath voltage generated in the cathode sheath in an apparatus that generates plasma by applying high frequency power to an anode electrode and a cathode sheath. An auxiliary electron supply means for supplying electrons is provided, a sheath voltage setting device is provided, and a sheath voltage detector is provided so that the sheath voltage detected by the sheath voltage detector matches the setting value of the sheath voltage setting device. The present invention is characterized in that it is configured to control the auxiliary electronic supply means.

[Function] Ions in the cathode fall region are neutralized by the supply of auxiliary electrons, and as a result, the cathode fall voltage is reduced.

In addition, the cathode drop voltage is detected by a sheath voltage detector,
The amount of auxiliary electrons supplied from the auxiliary electron supply means is controlled so that the detection result becomes the voltage value set by the sheath voltage setting device.

[Example〕 An embodiment of the present invention will be described below with reference to the drawings.

First, the principle of the present invention will be explained.

FIG. 1 shows a principle diagram of the present invention, in which the same parts as those shown in FIG. 5 are given the same reference numerals.

As mentioned above, when plasma is generated by applying high frequency power between the anode electrode and the cathode 1c electrode, due to the moving speed of electrons and ions in the plasma, the cathode Kff
A large #R pole voltage drop occurs on the cathode sheath of illll. In other words, the cathode sheath is a collection band of ions, and the cathode drop voltage is caused by an unbalanced state of ions and electrons.If electrons are separately supplied to the cathode sheath and the ions are neutralized, the cathode drop voltage can be reduced. reduced.

Therefore, even if the applied high-frequency power is increased, if sufficient electrons are supplied to the cathode sheath, the plasma density can be increased without increasing the cathode drop voltage.

In the figure, reference numeral 13 denotes an auxiliary electron supply means that is connected to the power supply line of the cathode electrode 2 and includes a filament 11 and a power source 12.

A cathode sheath 10 is formed between the cathode electrode 2 and the plasma 14, and the potential gradient of this cathode sheath voltage (self-bias) 8 is schematically represented by a curve 15. is superimposed on the high frequency voltage.

In such a system, the auxiliary electron current (emission current from the filament) ■1. Otherwise, the electron type II- flowing into the cathode sheath 10 and the ionic current IIm are balanced by the sheath voltage VII.

Therefore, the following formula holds true.

Lm=(A/4)en+vl'=It.

I *t= (A/4) e n@V* e xp[
−(e/kT,)x (V*+V*sin(J)t) 1=
1. . eXP [-(e/kT,)x(V, 10V,'
)] I 1m"' I @l), Lo=L, exp [-(e/kT,)X(V, 10V
, '> 1, solving for ■, we get V, = (kT, /e)in [(I, .exp<-
eV,'/kT-))/Ir. ], which is the sheath voltage when there is no external electron current.

Here, ■0. Electron current 1, flowing into the two cathode sheaths: Ionic current A flowing into the cathode sheath: Area e of the cathode electrode: ! Load nl : Ion density in plasma n, : Electron density in plasma ■, : Average velocity of ions ■, : Average velocity of electrons k : Boltzmann constant T, : Temperature ■, Two sheath voltage ■, : High frequency voltage Amplitude ω: Angular frequency t of high-frequency voltage: Time ■,. : (A/4) en, V.

V, ' : V, Sinω Next, when an electron current I am is supplied into the cathode sheath 10 by the electron supply means 13 described above, I −e
From = I +a +1-, 11°10■.

”I**eXp (eVa/kT*).

exp (-eV,' /kT*) From this, solving for V, we get V, = (kT, /e)In [(L*exp(eV
t'/kTa)/(Le+Lm)], which results in [(■,.exp (-eVt'/kT*)/(
II. +1. , )]=1 10. By increasing V, it is possible to make V=0.

Thus, the sheath voltage can be controlled by supplying auxiliary electrons into the cathode sheath from a circuit superimposed on the high-frequency voltage.

In the basic configuration example described above, the electron supply means uses an emission current from a filament, but it is also possible to supply electrons generated by direct current discharge.

FIG. 2 is a basic configuration diagram of a plasma generating apparatus in which the present invention is implemented, and the apparatus is equipped with auxiliary electron supply means by direct current discharge.

Anode electricity f! A high frequency cathode electrode 17 with many slits and holes or a mesh shape is arranged facing the high frequency cathode electrode 16, and the anode is placed opposite to the high frequency cathode electrode 17.
DC cathode t4i on the opposite side of 6! 18 will be installed.

The anode electrode 16 is a ground electrode, and the high frequency cathode pole 17 is connected to the high frequency power source 1 via a DC blocking capacitor 8. Further, the high frequency cathode electrode 11 also serves as an anode electrode of the auxiliary DC discharge circuit 19 and is connected to the + side of the DC power supply 20. Further, the DC cathode electrode 18 is connected to one side of a DC power source 20 via a resistor 21.

Thus, the anode is connected between the pole 16 and the high frequency cathode electrode 17, and between the high frequency cathode electrode 17 and the DC canned electrode @18.
By supplying high frequency power and direct current power between them, high frequency plasma 22 and direct current plasma 23 are generated.

This DC plasma 231 is applied to the cathode sheath 10 generated on the high frequency plasma side of the high frequency cathode electrode 17.
I! Auxiliary electrons are supplied from I through the hole in the high-frequency cathode electrode 17, and the sheath voltage V decreases due to the supply of the auxiliary electrons. Further, the supply amount of auxiliary electrons can be controlled by increasing or decreasing the DC power.

Therefore, the sheath voltage VII can be controlled by controlling the DC power, and the plasma density can be controlled by the high frequency power.

The present invention will be explained in detail below with reference to FIG.

In FIG. 3, components equivalent to those shown in FIG. 2 are given the same reference numerals as in FIG. 2.

A disk-shaped anode electrode 16 is provided on the ceiling side of the vacuum container 4, and a high frequency cathode electrode 17 is provided on the floor side opposite to the anode electrode 16 with an insulator 24 in between.

As shown in FIG. 4, the high frequency cathode electrode 17 has a main electrode part 17a facing the anode electrode 16, and a flange electrode part 17b that extends around the main electrode part 17a and also serves as an anode ti of a DC cathode electrode 18, which will be described later. The flange electrode portion 17b is provided with an arc-shaped slit hole 25.

The DC cathode electrode 18 described above has a ring shape in which a recess 26 that acts as a hollow cathode facing the slit hole 25 is formed, and is attached to the high frequency cathode electrode 17 with an insulator 24 interposed therebetween.

The high frequency cathode electrode 17 is provided with a high frequency output regulator 27.
The high frequency power source 1 equipped with the The electrodes are connected via a filter 29.

The control device 31 is of the DC type -! It is connected to the JA 20 and the high frequency cathode electrode 17 via a high frequency cutoff filter 30.

The control device 31 will be explained below.

A DC voltage divider 32 is connected to the high frequency cutoff filter 30, and the detected voltage signal -Vdc of the DC voltage divider 32 is connected to the high frequency cutoff filter 30.
is input to the adder 33. Further, the adder 33 includes a reference voltage generator V (from the reference voltage generator 34 provided separately).
, (enter.

The output of the adder 33 is amplified by an amplifier 35, processed into a digital signal by an A/D converter 36, and then sent to a transmitter 37.
The signal is processed and converted into an optical signal, and sent to a receiver 39 via an optical fiber cable 38.

The receiver 39 processes and converts the optical signal into an electrical digital signal and outputs it. The signal from the receiver 39 is sent to the D/A converter 40
The signal is processed and converted into an analog signal.

The operational amplifier 41 controls the output of the DC power supply 20 based on the analog signal.

The driving power for the DC power supply 20, receiver 39, D/A converter 40, operational amplifier 41, etc. is provided by a shield isolation transformer 42.
Supplied via.

The action will be explained below.

The high frequency power to be applied is set by the high frequency output regulator 27.

As described above, by supplying high frequency power to the high frequency cathode electrode 17 via the matching box 28, a sheath voltage is generated at the high frequency cathode electrode 17.

The sheath voltage is detected by the DC voltage divider 32, and the detected voltage signal -Vdc is input to the adder 33. A reference voltage signal +VDC from a reference voltage generator 34 is input to the adder 33, and the adder 33 outputs the difference between the two pressure signals to the amplifier 35. The signal from the amplifier 35 is processed in an A/D converter 36 and a transmitter 37, and sent as an optical digital signal to a receiver 39 via an optical fiber cable 38.

The optical digital signal is converted into an electrical analog signal in the receiving riI 39 and the D/A converter 40, and is input to the amplifier 41.

As explained in FIG. 2, by applying a DC voltage between the high frequency cathode electrode 17 and the DC cathode electrode 18 by the DC power supply 20, a DC discharge occurs between the high frequency cathode electrode 17 and the DC cathode electrode 18, The plasma generated by this DC discharge is transmitted to the slit hole 2 of the high-frequency canned electrode 17.
Auxiliary electrons are supplied through 5 into the high frequency cathode sheath.

The sheath voltage changes depending on the supply amount of the auxiliary electrons, and the supply amount of the auxiliary electrons changes depending on the applied voltage of the DC power supply 20.

Thus, the operational amplifier 41 is configured such that the output of the adder 33 is 0.
That is, the output of the current power source 20 is controlled so that the sheath voltage becomes the set voltage value vDc.

Note that the optical fiber cable 38 was used as a signal transmission means from the transmitter 37 to the receiver 39, and although the value of the sheath voltage Vdc is detected as a value with respect to the ground potential, it is not necessary to control the sheath voltage. This is because the DC power supply 20 that supplies the auxiliary electrons is superimposed on the high-frequency voltage, so it is preferable to perform signal processing by insulating the DC voltage divider 32 for sheath voltage detection and the operational amplifier 41. If a means is provided, it does not need to be an optical fiber cable.

Also, for the same reason, the DC power supply 20, operational amplifier 41, D
Since the /A converter 40 and receiver 39 are also superimposed on the high frequency voltage, their driving power is transferred to the shield isolation transformer 4.
2, it is supplied while being insulated from the AC line.

As described above, the sheath voltage can be controlled by setting the reference voltage signal by the reference voltage generator 34, and the applied high frequency power can be controlled by adjusting the high frequency output regulator 27, and the ion energy and plasma density can be controlled. can be controlled independently.

[Effects of the Invention] As described above, according to the present invention, plasma density can be controlled by adjusting high frequency power, and ion energy can be controlled by DC discharge current, and each can be controlled independently. The ion energy can be maintained at an appropriate value even when the high frequency power is increased, the plasma density is increased, and the etching speed is increased. Therefore, it is possible to perform various etching conditions at high speed and without damaging the base material. It has an excellent effect of satisfying the following.

[Brief explanation of the drawing]

Fig. 1 is a principle diagram showing the principle of the present invention, Fig. 2 is a basic configuration diagram of a plasma generator, Fig. 3 is an explanatory diagram showing an embodiment of the present invention, and Fig. 4 is a high-frequency cathode in the embodiment. FIG. 5, which is a perspective view showing the shape of the electrode, is a basic configuration diagram of a conventional example. 1 is a high frequency power supply, 13 is an auxiliary electron supply means, 16 is an anode electrode, 17 is a high frequency cathode electrode, 18 is a DC cathode electrode, 19 is an auxiliary DC discharge circuit, 20 is a DC power supply,
27 is a high frequency output regulator, 31 is a control device, 32 is a DC voltage divider, 34 is a reference voltage generator, and 41 is an operational amplifier. Patent application Hito Kokusai Electric Co., Ltd.

Claims (1)

[Claims] 1) In a device that generates plasma by applying high frequency power between an anode electrode and a cathode electrode, an auxiliary electron supply means for supplying auxiliary electrons to the cathode sheath region is provided as a means for controlling the sheath voltage generated at the cathode sheath. A sheath voltage setting device is also provided, and a sheath voltage detector is provided to control the auxiliary electronic supply means so that the sheath voltage detected by the sheath voltage detector matches the set value of the sheath voltage setting device. A plasma control device for a plasma generator characterized by the following.