JPS6147642A - Plasma generating apparatus - Google Patents

Abstract

PURPOSE:To control voltage drop due to ion sheathing at the electrode surface by comparing a voltage difference between electrodes with a preset value and superposing a positive or negative voltage to a high frequency voltage in accordance with a result of comparison. CONSTITUTION:When a DC voltage of B electrode 3 is VB, a DC voltage of A electrode 2 is VA, a voltae drop due to ion in the side of A electrode becomes as follow, VB-VA=Vdc. A voltage difference detection circuit 13 is connected to the A electrode 2 and a voltage difference between both electrodes detected is applied to the one input of a differential amplifier 14. An output of a voltage difference setting circuit 10 is applied to the other input of amplifier 14, difference from an input from a detecting circuit 13 and a setting circuit 10 is detected and amplified and an output is then input to a positive/negative voltage generating circuit 11. Thereby, a positive or negative voltage is generated and is applied to the A electrode 2 through a filter 12. Accordingly the ion sheathing can be controlled at the A electrode 2 in accordance with Vdc set in the setting circuit 10 and the ion sheathing can be controlled by changing a setting value Vdc of the setting circuit 10.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a plasma generation device, and more particularly to a plasma generation device in which potential drop due to an ion sheath on an electrode surface can be controlled.

(Prior art) For example, when etching a wafer, conventionally liquid etching was mainly used, but recently electron beam etching and plasma etching have been used, and these are the mainstream methods for precision etching. It is becoming.

It is known that isotropic etching and anisotropic etching are performed in etching processing.Isotropic etching means that etching is performed without directionality, and anisotropic etching is Etching is performed in a directional manner. Either isotropic etching or anisotropic etching can be used depending on the purpose of etching, or a more precise etching effect can be obtained by alternately performing isotropic etching and anisotropic etching. I'm starting to be able to do that.

(Problems to be Solved by the Invention) When etching is performed using a plasma generator, there is a problem of potential drop on the electrode surface due to the ion sheath. Ion sheath refers to the formation of a sheath of ions on the electrode surface during plasma treatment. Since the etching becomes isotropic or anisotropic depending on the size of the ion sheath, that is, the magnitude of the potential drop at the electrode surface, it is a problem to control the degree of the ion sheath. Various attempts have been made to control the size of this ion sheath, but no particularly favorable results have been obtained.

Therefore, the problem to be solved by the present invention is how to control the size of the ion sheath on the electrode surface in the above-described plasma generator.

(Means for Solving the Problems) In order to solve the above problems, according to the present invention, in a plasma generation device equipped with a pair of parallel plate electrodes, a high frequency generation source that supplies a high frequency voltage between these electrodes is provided. , a potential difference detection circuit that detects a DC potential difference between the two electrodes; a potential difference setting circuit that sets a desired value of the DC potential difference between the two electrodes;
a differential amplifier into which the detected value by the potential difference detection circuit and the set value by the potential difference setting circuit are input; and a positive or negative voltage is generated in response to the output of the differential amplifier and is applied between the two electrodes. A positive/negative voltage generation circuit is provided to superimpose the supplied high frequency voltage.

(Function) In the plasma generator configured as described above, the size of the ion sheath can be changed by changing the set value by the potential difference setting circuit, so that anisotropic and isotropic etching can be selectively performed. can be done. In addition, the potential difference detection circuit detects the actual value of the potential difference between the electrodes, compares it with the set value by the potential difference setting circuit, and superimposes the voltage generated by the positive/negative voltage generation circuit on the high-frequency voltage accordingly. It is possible to maintain a constant potential difference between the ion sheaths and, therefore, to maintain a constant size of the ion sheath.

(Embodiment) A preferred embodiment of the present invention will be described in detail with reference to FIG. In the figure, l is a plasma generator. A plasma generator 1 includes an A electrode 2 and a B electrode 3, and a wafer 4 to be plasma-treated is placed in the plasma generator 1. The plasma generator l has high frequency generation @t
A high frequency voltage is applied from A to the A electrode 2 via a matching circuit 6.

Reference numeral 7 denotes an optical fiber that guides the plasma light within the plasma generator 1 and detects its emission intensity with a detector 8.

Next, the DC potential distribution between the A and B electrodes will be explained with reference to FIG. In the case of a normal parallel plate type plasma generator, the areas of both electrodes are significantly different. That is,
The area of the B electrode 3 is made sufficiently larger than the area of the A electrode 2. Under such conditions, the DC potential distribution between the A and B electrodes has characteristics as shown in FIG. Now, as shown in Figure 2, if the potential of the B electrode 3 is VB, the potential of the A electrode 2 is ■^, and the plasma potential is vP, the potential drop due to the ion sheath on the A electrode side is vP - v^ = ■α. Therefore, the DC potential difference of electrode B as seen from electrode A is V, -V^. As mentioned above, under the condition that the area of the B electrode 3 is sufficiently larger than the area of the A electrode 2, Vp V B <<
V p V A, and the potential drop due to the ion sheath on the A electrode side is approximately equal to Ve-V=vdc. Voltage drop vdc due to this ion sheath on the A electrode side
It is a feature of the plasma generating device according to the present invention that it attempts to control.

Returning to FIG. 1 again, the output of the potential difference setting circuit 10 is input to the positive/negative voltage generating circuit 11, and then passed through the filter 12 to the A
applied to electrode 2. In this way, the potential difference setting circuit 1
The positive/negative voltage generating circuit 11 generates a positive or negative voltage according to the value of the potential difference v, c set at 0, and sets the size of the ion sheath by applying it to the A electrode 2 via the filter 12. The potential difference is controlled so that it becomes the value of dC. Next, in order to control the value of the potential difference between the two electrodes to be constant, a potential difference detection circuit 13 is connected to the A electrode 2, and the value of the potential difference between the two electrodes detected by this circuit 13 is input to one side of the differential amplifier 4. is applied to The output from the potential difference setting circuit 10 is applied to the other input of the differential amplifier 14, and the difference between the input from the potential difference detection circuit 13 and the input from the potential difference setting circuit IO is detected and amplified to make the output positive/positive. The voltage is input to the negative voltage generation circuit 11, and a positive or negative voltage is generated accordingly and applied to the A electrode 2 via the filter 12.

With this configuration, the potential difference setting circuit lO
The size of the ion sheath at the A electrode 2 can be controlled according to the value of V7 set in , and the size of the ion sheath can be controlled by changing the set value V of this potential difference setting circuit 10. be able to. Further, as described above, by detecting the actual potential difference value between the two electrodes during the plasma discharge operation by the potential difference detection circuit 13, the potential difference can be kept constant at a value similar to the desired potential difference V set in the potential difference setting circuit 10. can be controlled.

Next, a practical example of double-layer etching using such a plasma generator will be described. FIGS. 3 and 4 are examples of the case where a gate electrode of a MOS transistor is formed by double-layer etching. Figure 3 shows
Both layers are anisotropically etched, and the fourth
The figure shows the state when the second layer is isotropically etched and the second layer is anisotropically etched. In the case of FIG. 3, Poly Si remains in the step portion, but in the case of FIG. 4, Poly Si does not remain in the step portion.

When actually carrying out such an etching process using the plasma generator according to the present invention as described above, MoSi
During the etching step 2, the potential difference 4c is set in the potential difference setting circuit 10 so as to be isotropic, and when a signal indicating the end point of plasma processing is output from the computer 9, the process shifts to the etching process of PolySi.

At that time, the potential difference V4c is set in the potential difference setting circuit 10 so that the potential difference becomes anisotropic, and the etching process is performed until a signal indicating the end point of this etching process is output from the computer 9. As shown in FIG. A gate electrode such as that shown in FIG. 1 can be formed in the same plasma processing and etching apparatus.

At the end point of the etching process, the etching gas is e.g.
In the case of 4, the emission of chlorine radicals at 385 nm is detected by the detector 8 via the optical fiber 7, and the calculation is performed by the computer 9 to determine the emission.

(Effects) According to the present invention, with the above-described configuration, the following effects can be produced.

(1) The potential drop value of the ion sheath in the parallel plate electrode plasma generator can be made constant, and the reproducibility of plasma processing such as etching, ashing, and deposition can be improved.

(2) Anisotropic and isotropic etching can be selectively performed by changing the potential drop of the ion sheath using a potential difference setting circuit without changing the high frequency power, pressure, electrode spacing, etc.

(3) Switching between anisotropy and isotropy can be easily performed during wafer processing.

[Brief explanation of drawings]

Figure 1 is a block diagram of a plasma generator according to an embodiment of the present invention, Figure 2 is a DC potential distribution diagram between electrodes to explain the potential drop due to the ion sheath, and Figures 3 and 4 are anisotropic diagrams. FIG. 3 is a cross-sectional view illustrating an etching process using etching and isotropic etching. 16. Plasma generator, 2.39. Electrode, 40. Wafer, 50. High frequency source, 62. Matching circuit, 70. Optical fiber, 890 emission intensity detector, 91. calculator, l
Oo, potential difference setting circuit, 110. Positive/negative voltage generation circuit,
120. filter, 139. Potential difference detection circuit, 140.
Differential amplifier. 2nd design

Claims (1)

[Claims] 1. In a plasma generation device equipped with a pair of parallel plate electrodes, a high frequency generation source that supplies a high frequency voltage between these electrodes, a potential difference detection circuit that detects a DC potential difference between both electrodes, and both a potential difference setting circuit that sets a desired value of the DC potential difference between the electrodes; a differential amplifier that receives the detected value by the potential difference detection circuit and the set value by the potential difference setting circuit; A positive/negative voltage generation circuit is provided to generate a positive or negative voltage and superimpose it on the high frequency voltage supplied between the two electrodes, thereby controlling the potential drop due to the ion sheath on the electrode surface. Characteristic plasma generator. 2. The plasma device as set forth in claim 1, wherein the area of one of the pair of electrodes is made sufficiently larger than the area of the other electrode. 3. Claims 1 or 2 are characterized in that the potential drop due to the ion sheath is controlled by selectively changing the magnitude of the set value by the potential difference setting circuit. Plasma generator.