JPS5832417A - Method and apparatus for plasma etching - Google Patents

Abstract

PURPOSE:To carry out a highly accurate processing, by a method wherein a gas is introduced into a vacuum container, and a magnetic field is overlapped with the electric field between electrodes to induce plasma, and then a part of the plasma particles is employed to etch a substrate or thin film disposed in the gap between the electrodes. CONSTITUTION:A stainless steel container 1 is evacuated 19, and an etching gas is introduced 27 thereinto. An Al plate 20 (made to float, if necessary) as one of parallel electrodes, a cylindrical Al parallel plate electrode 21 supporting a mesh electrode 22, and another cylindrical anode electrode 23 are supported by a quartz cylinder 23'. A sample 25 is supported by a holder 24 which can be cooled. The holder 24 cna be set at a desired potential and has a variable distance (d) from the electrode 22 and moreover is supplied with a magnetic field by means of an electromagnet 26. In a high-vacuum region, e.g., 5X10<-3>Torr, the electrode 23 is taken as an anode, while the electrodes 20, 21 and the holder 24 are grounded, and the distance (d) and the gas flow rate are properly selected. Thereby, the total current from the anode and the substrate-ground current largely change in accordance with the magnetic field intensity. Accordingly, it is possible to select anisotropic and isotropic etchings with a small gas flow rate. In addtion, selection of the voltage applied between the electrodes permits the kinetic energy of ions to be set at will.

Description

DETAILED DESCRIPTION OF THE INVENTION An object of the present invention is to provide a novel dry etching apparatus and dry etching method for thin films on conductor, metal, semiconductor, or insulator substrates.

In recent years, especially with the increasing density of semiconductor integrated circuits,
, dimensions have become smaller. Along with this, dry etching has become mainstream in place of wet etching using chemicals for etching thin films of substrates such as silicon, metals, semiconductors, and insulators. Dry etching methods include 1) plasma etching method using high frequency, 2) active etching method using high frequency, 3.
) magnetic field microwave plasma etching method; and 4) ion etching method using an ion beam of argon or the like.

There are various types of equipment for plasma etching method l), and the material to be etched is polycrystalline S++S.
t02+Sl5N4+PSG or At. A wide variety of first class awards. However, the active species (neutral radicals) that contribute to the reactions within Zolazma are present in the vacuum region (~I Torr) where the discharge takes place.
), resulting in random motion, generally resulting in isotropic etching and so-called side etching, which limits the machining accuracy of minute turns. On the other hand, the etching method (3) uses the resonance phenomenon between the cyclotron motion of electrons in a magnetic field and microwaves to enable etching even at low discharge gas pressure without reducing plasma density and with low ion energy. It was announced that vertical etching became possible. However, this method requires a complicated device configuration and is expensive.

4) is a method in which argon ions or the like are accelerated and etched by the impact thereof to perform etching with little side etching, and the difference in etching rate depending on the material, that is, the selection ratio is not large. Furthermore, the etching rate is low and the element is seriously damaged by ion bombardment. 2) is a dry etching technique that is considered to be a promising method for processing microscopic patterns, and uses parallel plate electrodes and applies high frequency to them to induce plasma between the electrodes and process a sample placed on the parallel electrodes.

FIG. 1 is a schematic diagram of a dry etching apparatus having a parallel plate electrode structure. 1 is a lower electrode, and this electrode is water-cooled by water-cooled tubes shown at 5 and 6. 3 is a sample placed on this electrode 1. 4 is a high frequency power source of 13.56 MHz, which is applied between the upper electrode 2 and the lower electrode 1 to induce plasma between the electrodes. 9 is the etching speed introduction pipe 7,
8 is an exhaust pipe. This dry etching method uses a lower gas pressure than the conventional gas plasma etching method, and in addition to so-called isotropic etching using radicals, it also takes into account the element of suction etching due to ion bombardment.
Directional etching can be performed. For this reason, active research and development is being carried out as a powerful means for high-precision microfabrication of VLSIs. However, there are drawbacks such as damage to the sample due to ion bombardment accelerated within the ion sheath formed near the cathode, and the magnitude of this ion energy is difficult to identify and control. In order to obtain sufficient throughput for etching, it is necessary to increase the flow rate of the chlorine-based compound gas used for etching, which poses a major problem in terms of maintenace of the apparatus. In order to reduce damage caused by ion bombardment, a method has been proposed in which self-bias is reduced by using a dry etching device in which a third electrode is provided on the cathode electrode, as shown in FIG. In FIG. 2, IO is a container, and 11 is an exhaust port connected to a vacuum system for evacuating the container. 12 is a gas introduction pipe, 13, 1
4 are a cathode and an anode, respectively, of a conventional bipolar dry etching apparatus. The sample 17 is placed on a water-cooled cathode electrode, and a third electrode l5 is provided adjacent to it, which has a number of holes and is separated from the cathode by an alumina insulator separated by an interval l6. is maintained. The electrode 15 is at a floating potential and the high frequency power source is 135
6MT (z) is applied to the cathode. It has been shown that this method has better processing accuracy than the conventional bipolar type and reduces the amount of damage. However, it is difficult to use gases containing chlorine, such as CCI4. The flow rate is the same as in the conventional example, and the throughput does not increase.

Furthermore, the self-bias is determined secondarily depending on external inputs and other etching parameters, and there are major drawbacks such as the setting conditions being limited.

The present invention provides a completely new dry etching apparatus and dry etching method capable of high-precision machining that overcomes the above-mentioned drawbacks, and uses so-called PIG discharge as the discharge nolasma for etching. The principle of its construction will be described with reference to FIG. 3, 18 shows a stainless steel container, 19 an exhaust port for evacuating the interior of the stainless steel container, 27 an etching gas introduction pipe, and 20 one parallel electrode, which is, for example, a stainless steel disk or an aluminum disk. Moreover, this electrode can be made to float electrically if necessary. 21 is a parallel electrode made of cylindrical aluminum or stainless steel that supports a mesh-like electrode 22 serving as another electrode. Of course, this part may also be a disk with a number of holes. Reference numeral 23 is, for example, a cylindrical or hollow disk serving as another anode electrode, and the figure shows the case of a cylindrical electrode. 23' is an insulating material that supports the electrode, and is a cylinder made of quartz, for example. Reference numeral 24 denotes a holder for holding a coolable sample 25, which can be electrically set to an arbitrary potential. Further, the distance d between the mesh-shaped electrode 22 and the sample holder 24 is variable. 26 is an electromagnet placed outside the container 18. Third
In the figure, vacuum cylinders and the like are omitted to simplify the drawing.

FIG. 4 shows a configuration example of a large-sized discharge device, and its geometric dimensions and discharge embodiment will be described below. 28 is a glass belt gear with a diameter of 40011 m, and 29 is an exhaust port connected to a 6-inch diffusion ponder and an oil rotary pump. 30 is a gas introduction system, and in this example, parallel cathode electrodes 31
Gas is fed into the pipe-shaped metal 31' supporting the gas and is supplied to the discharge space. 31" is cathode electrode 3
This is the opening provided in 1. The cathode electrode 31 was made of aluminum and had a diameter of 220mm. A concave metal 32 holds a metal electrode 33 (for example, mesh-shaped metal in this embodiment) having an opening to serve as the other parallel cathode, and together constitutes the other parallel cathode. The lower circular part of the concave shape had a diameter of 220 mm and the opening had a diameter of 200 mm. The concave metal 32
``Secondly, there is a stainless steel menyu metal. Further, the distance between the cathodes was set to 5σ. 34 is a cylindrical anode electrode with an outer diameter of 240Ilφ, an inner diameter of 230φ, and a height of 10011M, and is made of aluminum. A holder 35 holds the substrate 36 and has a mechanism for cooling the substrate 36. In this example, water cooling was used. Reference numeral 37 denotes an electromagnet provided outside the belt wheel, and the direction of the magnetic flux generated thereby is perpendicular to the parallel cathode planes. N2ff gas is flowed into the discharge space through the introduction tube 30, and the pressure is adjusted to a range of 10 to 10 Torr by adjusting the opening of the gate valve 38. For example, an example will be described in which the distance between the substrate electrode and the mesh electrode is approximately 1 OII, and the pressure is set to 0.005 Torr. When the anode electrode 34 is placed at 450 V, the cathode electrode is placed at ground potential, and the magnetic field strength is approximately 100 G, there is a voltage of 0.06 W/crn2 only between the electrodes (corresponding to 0.06 W/crn2).
(When a metal plate is placed in contact with one mesh-like electrode). Next, with the metal plate removed, the current between the anode and cathode electrodes was set to 100 mA using the configuration shown in Figure 4, and when approximately 6.8 Ω was inserted between the substrate electrode and ground, the current between the substrate electrode and ground was approximately 10 mA. flowed. At this time, it was found that a voltage of about A, which is the anode voltage, was generated between the substrate and the ground.

Substrate-to-ground voltages and currents can be significantly controlled by varying the resistance values therebetween.

Therefore, it is possible to control the energy when charged particles in the plasma fly into the substrate. Generally, the etching rate can be arbitrarily changed by adjusting the anode voltage, the resistance value between the substrate and the ground, etc. Also, the total current flowing from the anode electrode and the substrate-to-ground current are particularly 0. O05Torr
It changes drastically depending on the magnetic field strength in high vacuum areas such as .

For example, 50 mA with a magnetic field of 50 Gauss is 100
Gauss gives 80mA. In this example, a positive voltage was applied to the anode electrode and the cathode electrode was set to ground potential. However, by applying a positive potential to the anode electrode and a negative potential to the cathode electrode, a discharge zolazma is induced between the electrodes, and the substrate is It goes without saying that it is also possible to deposit a thin film on the substrate by applying a ground or positive or negative potential. For example, with an anode voltage of +200 V, almost the same discharge as with a cathode voltage of 250 V can be obtained, and the potential difference between the plasma and the substrate is free depending on how this potential is applied, and by applying a direct current potential difference instead of the same potential to the parallel cathode electrodes, The kinetic energy of particles onto the substrate can be easily controlled. Place a metal plate in contact with a mesh-like metal, for example, for a mesonor-like metal
Apply a potential of 100V and ground the other end, and set + as the anode voltage.
450V, magnetic field 100G.

When the discharge was observed under a vacuum of 0.005 Torr, it was revealed that an asymmetrical discharge occurred and that the width of the ion sheath directly under the cathode was freely controlled by the cathode voltage value.

In the above example, an electrode having an opening, for example, a mesh-like metal, is used as one electrode, and a structure in which a substrate is placed opposite to it is described in connection with the embodiment and the discharge experiment example. FIG. 5 shows a case in which electrodes are used and a substrate holder is provided facing them. In FIG. 5, 39 is a vacuum container made of stainless steel, for example, and 40 is an exhaust port of the vacuum container 39 connected to the diffusion bomb 7D40' and the oil rotary pump 40. 41 and 42 are metal-shaped electrodes, 43 is, for example, a cylindrical anode electrode, and 44 is an external electromagnet. A required gas is introduced between the electrodes through the gas introduction pipe 51 to generate discharge plasma between the electrodes, and the substrate holders 45 and 46 facing the menyu-shaped electrodes 41 and 42 are
Plasma particles are introduced into the substrate 47 placed above to etch it. In this way, since the substrates can be placed on both sides facing both mesh-like electrodes, it is possible to have a deposition processing capacity that is approximately twice that of the conventional example. 50 is a window for observing the discharge plasma state generated between the electrodes. Also 48
and 49 is a date valve, and 51 is a bellows.
It forms a mechanism for taking out the substrate holder 45, 46 into the atmosphere and replacing the substrate without breaking the vacuum in the discharge space by integrating with the top valve.

The effects of the present invention when applied to microfabrication of a substrate or a thin film on a substrate will be described.

An experiment was conducted to investigate the etching rate of polycrystals using the apparatus shown in FIG. The gas used was C3F8 and the pressure was 5
For example, +50 to the anode electrode 23 at X 10-5 Torr.
0V% cathode electrodes 20 and 21 are at ground potential, substrate holder 24 is at ground potential, cathode electrode 21 and substrate holder 24
When the interval between electrodes is 20 mm, the gas flow rate is 308 CCM, and the anode current is 80 mA (power density is 0.1 W/cm2 per one electrode), it is approximately 5000 X/m.
An etching rate of in was obtained.

Based on this data, we conducted an experiment to form a 1 μm wide polycrystalline St (0.4 μm thick) using a resist as a mask, and found that it was possible to process the polycrystalline St into a width that was faithful to the width of the nof tan. . It was also revealed at this time that Lennost could withstand sufficiently as an etching mask. The present invention is a technique suitable not only for etching polycrystalline St but also for dry etching other thin films constituting semiconductor integrated circuits, such as 5i02 film, PSG film, and aluminum film. When etching aluminum, a chlorine compound such as CCl4 or BCl3 is used as the gas.

In this case, the amount of gas flow rate during etching is an extremely serious problem in terms of equipment maintenance. According to the present invention, the gas flow rate can be significantly reduced compared to conventional methods, so it is considered to be very effective from this point of view. Furthermore, since metal wiring, such as aluminum, is generally formed in areas with many irregularities, there is a possibility that step portions may remain unetched if a method that requires strong directional etching is used. However, with this method, in addition to energy lanocal control, it is possible to perform both directional and isotropic etching depending on the conditions, and the kinetic energy of the ions can be set arbitrarily by changing the voltage between the electrodes. The present invention, which enables dry etching in areas that could not be achieved previously, will provide an extremely large amount of investment and cost to the development and manufacture of semiconductor integrated circuits, semiconductor elements, and other devices in fields that require high-precision microfabrication. It is something.

[Brief explanation of the drawing]

Fig. 1 shows a conventional two-pole reactive etching device, Fig. 2 shows an improved active etching device, Fig. 3 shows a conceptual diagram of the basic configuration of the present invention, and Fig. 4 shows an example of the device configuration used in the discharge experiment. , FIG. 5 is a diagram showing an example in which substrates are placed on both parallel cathodes. 1... Lower electrode, 2... Upper electrode, 3... Sample to be etched, 4... High frequency power supply, 5, 6... Water cooling pipe, 7° 8... Exhaust pipe, 9...・Gas introduction pipe, 10...
・Vacuum container, 11...Exhaust port, 12...Gas introduction pipe, 13...Canode, 14...Anode, 15...
Electrode, 16... Insulating insulator (alumina), 17... Sample, 18... Vacuum container, 19... Exhaust port, 20...
One of the parallel electrodes, 21...another parallel electrode (for example, a holder for a mesh-like electrode), 22... a mesh-like electrode,
23... Cylindrical electrode, 23'... Quartz cylinder for holding the electrode 23, 24... Holder, 25... Sample, 26... Electromagnet, 27... Gas introduction tube, 28・・・
Glass Beltsya - 129...Exhaust port, 30...Gas inlet pipe, 31...Parallel cathode electrode, 31'...P iso-shaped metal, 311! - An opening provided in the parallel cathode electrode 31,
32...Other parallel cathode electrode, 33...Mesh-like electrode, 34...Positive electrode, 35...Substrate holder, 3
6... Board, 37... External electromagnet, 38... Valve,
39...Vacuum container, 40...Exhaust port, 40'...Diffusion ponder, 40...Oil rotary ponder, 41.42...
- Mesh-like electrode, 43... Anode electrode, 44... External electromagnet, 45.46... Substrate holder, 47. Sample to be etched, 48.49... Case plate, 50.
...Discharge peephole, 51...Bellows. Figure 3 Figure 4

Claims (6)

[Claims] (1) Exhaust means for reducing the pressure inside the container,
A device comprising a means for introducing gas into the container and a plurality of electrodes arranged in the container, and using an electric field applied between the electrodes and a magnetic field from a magnetic field generator installed outside or inside the container as an excitation source. A plasma etching apparatus characterized in that a discharge plasma is induced between the electrodes, and a part of the plasma particles generated between the electrodes etches a substrate on a substrate holder installed outside the electrode gap or a thin film on the substrate. . (2) The plurality of electrodes include parallel electrodes, another electrode (anode electrode) that provides electric field components perpendicular and parallel to the electrode surface, and a magnetic field generator that provides a magnetic field perpendicular to the parallel electrode surface. A plasma etching apparatus according to claim (1). (3) Claim characterized in that the same potential is applied to the parallel cathode electrodes and a positive potential is applied to the other electrodes = (
1) The plasma etching apparatus described in item 1). (4) The plasma etching apparatus according to claim (1), characterized in that a potential difference is applied to the parallel cathode electrodes, and a positive potential is applied to the other electrodes. (5) A parallel cathode electrode and another anode electrode that provide electric field components perpendicular and parallel to the cathode electrode surface are arranged in a container under reduced pressure, and while applying a voltage between these electrodes and supplying raw material gas, A plasma etching method characterized in that a magnetic field perpendicular to the parallel cathode surfaces is applied to induce discharge plasma between the electrodes, and the plasma particles are guided to a substrate placed outside between the electrodes for etching. (6) At least one of the parallel cathode electrodes is an electrode having an opening, and a ground potential or a negative DC potential is applied to the parallel cathode electrode, and a positive potential is applied to the other anode. The plasma etching method according to scope (5).