JPS597212B2 - Plasma etching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in plasma etching methods used in the manufacture of semiconductor devices.

FIG. 1 is a schematic diagram showing an example of the configuration of a parallel plate type plasma etching apparatus conventionally used for plasma etching processing.

Figure 1 shows a metal or glass reaction tube having a gas inlet 2 and a gas outlet 3. Reference numeral 4 denotes a ground side electrode which is located inside the reaction tube 1 and is grounded together with the reaction tube 1.

Reference numeral 5 denotes an electrode located inside the reaction tube 1 and opposed to the earth side electrode.

Reference numeral 6 is an insulating bushinder, 1 and 8 are impedance matching capacitors 9, and the same is an inductance.

10 is a high frequency power supply with a frequency of 13.56 [MH2],
The output is about 5 [kW].

Reference numeral 11 denotes a wafer (semiconductor substrate) to be processed that is set on the ground side electrode 4.

When performing plasma etching with such an apparatus, CF4, CHF, which becomes the etching agent, is supplied from the gas inlet 2.
3, CCl4, BC2, SF6, C3F8 or B
After introducing a halogen compound gas such as Br3 into the reaction tube 1 and setting the internal pressure to 10-3 to 1 Torr, a high frequency voltage is applied between the electrode 5 and the earth side electrode 4 to start the reaction. A gas discharge is caused between the electrode 5 in the tube 1 and the earth side electrode 4 to dissociate the etchant gas.

The active components generated by this dissociation react with the wafer and are vaporized to perform etching. By the way, in the conventional plasma etching as described above, the wafer 1
Since the earth side electrode 4 set to 1 is grounded together with the reaction tube 1, ions that contribute to etching (etch-and) are hardly accelerated, and even if they are accelerated, they are independent of the power of plasma generation. cannot be controlled.

Therefore, when etching silicon (Si), isotropic etching is performed and the lower part of the mask material is also etched, causing problems such as so-called undercuts. Furthermore, when etching aluminum (Al), it is difficult to remove oxides generated on the surface of the aluminum, which makes it extremely difficult to etch aluminum. The present invention is a new invention that improves the above-mentioned drawbacks of the conventional method, and its purpose is to provide a plasma etching method that can etch various materials in precise patterns without undercutting. . In order to achieve this purpose, the plasma etching method of the present invention involves disposing two electrodes facing each other in a reaction tube, and placing the object to be etched on the surface of one of the electrodes facing the other electrode. In the plasma etching method, the object to be etched is etched by introducing a halogen compound gas into the reaction tube and applying a high frequency voltage between the electrodes or between both electrodes and the reaction tube. is connected to the non-grounded terminal of the high frequency power source via a matching impedance, and when applying a high frequency voltage between both electrodes, connect one electrode to the grounded side terminal of the high frequency power source via a variable impedance, When applying a high frequency voltage between both electrodes and the reaction tube, one electrode is connected to the other electrode via a variable impedance, and the voltage of one electrode is changed with respect to the ground point. Examples will now be described in detail.

FIG. 2 is a schematic diagram showing an example of a processing apparatus for carrying out the present invention.

In the figure, 20 is a grounded reaction tube, and the reaction tube 20 is provided with a gas inlet 21 and a gas outlet 22. Moreover, 23 and 24 are electrodes provided oppositely in the reaction tube 20, and the reaction tube 20 is
isolated from 0. 27 is a high frequency power source, one output end 27A of which is grounded.

27B is the other terminal of the high frequency power supply.

28 and 29 are the electrode 23 and the output end 2 of the high frequency power source 27
7A, the value of which is adjustable, and the potential of the electrode 23 can be adjusted with the values of the impedances 28 and 29.

30, 31, and 32 are matching impedances.

33 is a wattmeter, 34 and 35 are DC voltmeters, 3
6 and 37 are low-pass filters for blocking alternating current.

38 is a wafer placed on the electrode 23.

Note that the voltmeter 34 and low-pass filter 36 are not necessarily required. Further, FIG. 3 is a schematic diagram showing another embodiment of a processing apparatus for carrying out the present invention, and parts common to those of the processing apparatus shown in FIG. 2 are given the same numbers.

In this embodiment, the potential of the electrode 23 can be determined by the value of the adjustable impedance 28'.

We will first give a theoretical explanation of these, and then explain the effects of actual etching.

As shown in FIG. 4a, when one electrode 41 of two parallel electrodes 41, 42 is grounded and a high frequency of 13.56 MHz is applied to the other electrode 42 from a high frequency power source 44 via a capacitor 43, a voltage of 13.56 MHz is created between the two. A plasma is generated, and ions and electrons in the plasma are moved by a high frequency electric field.

However, at high frequencies of 1 MHz and above, ions have a small charge compared to their mass, so only electrons are moved by the 13.56 MHz electric field and accumulate on the electrode surface, self-biasing the electrode 42 on the high frequency side to a value almost equal to the high frequency voltage. (V
sB). On the other hand, the ground side electrode 41 is at the ground potential, and the plasma becomes a positive voltage due to the outflow of electrons with respect to the ground basket level (
p). For example, electrode diameter 28CTL1 spacing 10 (7rL.
．． When around 0.02T0rr1200W, VSB=-6
00, Vp=+40. FIG. 2 or 5 of the present invention
When the ground side electrode 23 is grounded through adjustable impedances 28 and 29 as shown in Figure a (hereinafter referred to as the ground electrode), a self-bias is generated in the ground electrode 23 (VDc), and as shown in Figure 5B. The potential distribution will be as follows.

The DC value at this time can be varied from 0 to 600 V under the same conditions by changing the impedances 28 and 29. Further, FIG. 6 illustrates the embodiment shown in FIG. 3 using an equivalent circuit diagram a and a potential distribution b.

In FIG. 6a, Zt is the impedance of the sheath between the electrode 24 and the plasma, Zs is the impedance of the sheath between the electrode 23 and the plasma, and Zw is the impedance of the sheath between the plasma reaction tube 20 and the plasma. It is. The high frequency voltage between the electrode 23 and ground is controlled by the adjustable impedance 28' and the sheath impedance Zs,
The high frequency voltage at the connection point between impedance 28' and impedance Zs is applied between electrode 23 and ground. As a result, a self-bias voltage DC having a value approximately equal to the high-frequency voltage is generated in the electrode 23, and the sixth
The potential distribution is as shown in Figure b. In this case as well, electrode 2
The value of the self-bias voltage VDC of No. 3 can be changed by adjusting the impedance 28. Now, when etching is actually performed, if the sample is placed on the high frequency side with a normal etching device, the ions emitted by the person will be VSB + VP.
(to 640V).

The incident ion when placed on the ground side is Vp (″.40V)
It has the energy of The difference in the energy of these incident ions greatly changes the actual etching characteristics, directionality, selectivity, and damage to the underlying layer. The energy of this incident ion can be changed by changing the radio frequency power density, etching pressure, gas type, and device shape (area ratio of the two electrodes), but at the same time the state of the plasma changes, so etching It is unsuitable for controlling characteristics. According to the method of the present invention, it is possible to change the energy of injected ions without substantially changing the plasma state, which is useful.

[Example 1] Using C2ClF5 as an etching gas and a SiO2 film as a mask, an experiment was carried out on the dependence of the voltage applied to the ground electrode 23 when etching polysilicon, and the results shown in Table 1 were obtained.

This makes it possible to control the etching shape and selectivity.

[Example 2] When etching Al using CCl4 as an etching gas, an experiment was conducted to determine the dependence of the removal time on the voltage applied to the grounded electrode to remove the natural oxide film on the Al surface, and the results shown in Table 2 were obtained. Ta.

Note that the etching rate of Al after removing the natural oxide layer on the Al surface remains unchanged at 1000 A/Mm.

That is, as is clear from Table 2, this has the effect of stabilizing the removal of the Al surface oxide film, which was unstable with the parallel plate etching device. According to the present invention, as described above, the electrode 23, which serves as the etching table, is not directly grounded, but an appropriate impedance is inserted between it and the ground. A negative voltage is induced.

Therefore, when plasma etching is performed using a halogen compound, the ions contributing to the etching collide almost perpendicularly to the surface of the object to be etched, such as the top surface of the wafer, thereby reducing the undercuts mentioned above. When performing etching, it has many effects, such as being able to particularly reduce the influence of surface oxides and making uniform etching possible.
Note that the negative voltage induced between the earth side and the electrode 23 can be reduced to 1/7 to 1/7 of the negative voltage induced between the earth side and the electrode 24 by adjusting the impedances 28 and 29.
The value can be adjusted up to about 100, and the value can be adjusted depending on the type of object to be etched while reading it with a DC voltmeter, so that each object can be etched under optimal conditions.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a conventional plasma etching apparatus, FIGS. 2 and 3 are schematic diagrams of a plasma etching apparatus embodying the present invention, and FIG. 4 shows one electrode connected through a matching impedance. Fig. 5 shows a diagram of the device when one electrode is connected to a high-frequency power source via a matching impedance source, and the other electrode is grounded. Fig. 6 shows a diagram of the device when the electrodes are grounded through an adjustable impedance, and a diagram showing the potential distribution between the electrodes.
Equivalent circuit diagram (a) when the other electrode is connected to one electrode via an adjustable impedance (5) Diagram (b) showing the potential distribution between the electrodes (o) In the diagram, 20 is the reaction tube, 23 and 2
4 is an electrode, 25 and 26 are insulating bushes, 27 is a high frequency power source, 27A is one terminal of the high frequency power source, 28, 29
, 30, 31 and 32 are impedances.

Claims (1)

[Claims] 1. After arranging two electrodes facing each other in a reaction tube and placing an object to be etched on the surface of one electrode opposite to the other electrode, a halogen compound gas is introduced into the reaction tube, and In the plasma etching method in which the object to be etched is etched by applying a high frequency voltage between the electrodes or between both electrodes and the reaction tube, the other electrode is connected to an ungrounded terminal of the high frequency power source via a matching impedance. When applying a high frequency voltage between both electrodes, connect one of the electrodes to the ground terminal of the high frequency power supply via a variable impedance, and when applying a high frequency voltage between both electrodes and the reaction tube, connect one of the electrodes to the ground terminal of the high frequency power supply via a variable impedance. A plasma etching method characterized in that an electrode is connected to the other electrode via a variable impedance, and the voltage of one electrode relative to a ground point is varied.