JP3027871B2 - Etching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching technique, and more particularly to a dry etching technique used for fine processing in a semiconductor process.

[0002]

2. Description of the Related Art In recent years, the degree of integration of semiconductors has been remarkably improved.
Along with that, the design rules are becoming finer. At present, DRAM (Dynamic Random Access Memory) is approaching the era of 16 Mbits integration and 0.5 μm design rule. With the progress of miniaturization, the semiconductor etching technology has changed from wet etching using a chemical solution to dry etching using charged particles such as plasma. Recently, as shown in FIG. 3, mainly C (carbon) such as CH ₄ (carbon tetrafluoride)
Plate-type RIE (reactive ion ion) in which a plasma 3 is generated between two parallel plate electrodes 22 by high frequency discharge to etch the substrate 19 using a gas containing
(Etching: reactive ion etching) Dry etching using a device is mainly used. In microfabrication by etching, low damage, high selectivity, and high anisotropy must be simultaneously satisfied. In addition, for mass production, it is necessary to uniformly process a large area and ensure a practical etching rate. However, RI
In E, since the controllability of the plasma is poor, it is becoming difficult to satisfy the requirements of high selectivity and high anisotropy at the stage of miniaturization, especially in a gas containing C such as CH ₄ gas. Anisotropy is becoming difficult to achieve. Therefore, the etching by the RIE apparatus reaches its limit sooner or later.

In order to solve this problem, an etching apparatus using ECR (Electron Cyclotron Resonance: Electron Cyclotron Resonance) discharge using Cl ₂ (chlorine) gas has been proposed. High-speed and uniform processing without a side wall protective film, and high selectivity and high anisotropy are being achieved (see Nikkei Microdevices, August 1990, p. 85). However, regardless of the RIE device or the ECR device, in any case, when etching is performed using ions in plasma, there is a physical spatter that occurs when the ions are accelerated by a sheath electric field and collide with a substrate. Therefore, it is very difficult to eliminate the damage to the substrate.

[0004] On the other hand, it is known that damage to a substrate is considerably smaller than etching by ions because electrons have a smaller mass than ions. Therefore, an etching technique utilizing this low damage property of electrons has begun to be studied. This is achieved by using, for example, XeF ₂ (xenon fluoride), F ₂ (fluorine), Cl _2, etc.
(Silicon), GaAs (gallium arsenide), etc.
Irradiation of the etching gas activates the etching gas to perform etching. At this time, in order to protect the cathode of the electron gun from the etching gas, as shown in FIG. 4, differential exhaust is performed between the container 35a for introducing the etching gas and the container 35b in which the electron gun 32 is installed. It is necessary to maintain a high vacuum around the electron gun 32 (Mototane Taneya et
al., Japanese Journal of Applied Physics, Volume2
8, Number 3, March, 1989, pp. L515-L517: Mototan
Taneya et al., Japanes Journal of Applied Physics, Vol. 28, No. 3, March, 1989
Year, see pages L515-L517). Also, as shown in FIG. 5, from the viewpoint of mass productivity, an electron beam emitted from an electron gun is used.
A method of collectively irradiating a large area with a so-called broad beam, which does not stop the beam 34 with a lens, has also been studied (Matsui et al., "Electron Beam Excited Dry Etching", 1990).
Proceedings of the 51st Annual Meeting of the Japan Society of Applied Physics Fall 27pZ
F6 / II).

[0005]

However, in the etching by electron beam irradiation, if the differential evacuation is performed to protect the cathode, as shown in FIG.
Due to the presence of a and 33b, it is difficult to collectively irradiate a large area electron beam to the sample. Further, in order to allow the electron beam 34 to pass through the orifices 33a and 33b, it is necessary to provide directivity to the beam, so that the acceleration voltage is unavoidably relatively high (for example, 10 kV). Therefore, although the damage is smaller than that of the ions, there is a strong possibility that the damage is not negligible, and the advantage of the etching by the electron beam is impaired. In addition, in the case where broad beam irradiation is performed as shown in FIG. 5 with emphasis on mass productivity, since the differential evacuation is difficult, the electron gun 32 cannot be maintained at a high vacuum, and the cathode is etched. There is a drawback that it is difficult to protect from gas and the life of the cathode is significantly shortened.

It is conceivable to use a plasma electron gun to make up for these drawbacks. However, in the plasma electron gun, a low vacuum (normally several mTorr to several tens Torr) in which radicals causing isotropic etching rapidly increase is considered. is necessary. In addition, since electrons are extracted from plasma using a cylindrical or mesh-shaped electrode, it is difficult to secure the directionality of the electron beam over a large area. Acceleration voltage (for example, 10
kV) (edited by the 132nd Committee of the Japan Society for the Promotion of Science, “Electron / Ion Beam Handbook 2nd Edition”, 1
P. 59, see Nikkan Kogyo Shimbun). Accordingly, from the viewpoint of etching by electron beams, large-area irradiation can be performed at a time, electron beams with low energy of about several tens eV to several hundreds eV can be obtained, and the apparatus is not damaged by the etching gas. An electron beam excited etching method has been desired.

On the other hand, in the etching by ions, as described above, uniform processing over a large area, a practical etching rate, high anisotropy and high selectivity are being obtained.
There was a disadvantage that some damage could not be avoided in principle. Therefore, from the viewpoint of broad etching, an etching method that simultaneously satisfies low damage, high selectivity, and high anisotropy has been desired. The present invention has been made in view of the above-described conventional circumstances, has a practical etching rate and an etching range suitable for mass production, and has high selectivity while hardly damaging the etching. It is another object of the present invention to provide a simple etching method that realizes high anisotropy.

[0008]

The present invention provides a fluorine gas,
A plasma having a gas pressure of 1 × 10 ⁻³ Torr or less is generated using an etching gas containing chlorine gas or bromine gas as a main component, a workpiece is placed in the plasma, and the workpiece is electrically connected to the plasma. Insulation or etching in the plasma by setting the workpiece to a negative potential with respect to the plasma potential
A first step of etching the workpiece by irradiating ions of a gas, and after the first step, irradiating the workpiece with electrons in plasma by setting the workpiece to a positive potential with respect to a plasma potential. The same plasm as the one that pulled out the electron
Supply neutral etching gas to the surface of the workpiece
The neutral gas by the electrons to excite the neutral gas.
And a second step of etching a workpiece .

[0009]

When the workpiece placed in the plasma is electrically insulated or made negative with respect to the plasma potential, the ions in the plasma pass through the ion sheath formed between the plasma and the workpiece. Is irradiated on the workpiece surface. The irradiated ions convert kinetic energy into reaction energy, and the etching proceeds. As mentioned above, this is already being established, for example, as an ECR etching technique, but physical damage is unavoidable due to the ion assisted etching. On the other hand, electrons can be extracted from the plasma by setting the workpiece placed in the plasma at a potential higher than the plasma potential. The introduced etching gas is adsorbed on the workpiece surface. Unless the adsorbed gas is activated by heating the substrate or the like, etching by the adsorbed gas is usually very small. The electrons emitted from the plasma to the workpiece excite and activate the gas adsorbed on the surface, thereby etching the workpiece. This reaction is a pure chemical reaction between the atoms adsorbed on the surface and the workpiece, and the kinetic energy of the neutral etching gas introduced at room temperature is very small (about 0.03 eV). No physical reaction occurs between the etching gas and the workpiece. Irradiated electrons hardly distort the lattice of the workpiece if the incident energy is low. It is clear that the lower the incident energy of the electron beam is, the better the activation energy of the etching gas is. Therefore,
In etching by low energy electron beam irradiation,
There is little physical damage to the workpiece.

In etching by irradiation of electrons in plasma, plasma is generated by an etching gas, so that the plasma serves as an electron emission source and an etching gas supply source. There is one feature. Further, by using plasma as an electron emission source, uniform electron irradiation over a large area is possible, and since a workpiece is inserted into the plasma, it is possible to irradiate electrons at a relatively low voltage.
Further, by setting the gas pressure of the plasma to 1 × 10 ⁻³ Torr or less, radicals that cause isotropic etching are extremely reduced in the plasma, so that anisotropic processing can be realized. . As described above, the etching mechanism using electrons and the etching mechanism using ions are different, and each has its own characteristics. Therefore, at the initial stage of etching, the workpiece in the plasma is electrically insulated or a negative bias voltage is applied to the plasma potential to perform high-speed, high-anisotropic processing by ion-assisted etching. Ideal etching can be performed by etching the workpiece by positively biasing the plasma potential with electrons and removing the physically damaged layer that has entered by ion etching. Further, since this only requires changing the bias voltage of the workpiece, etching can be achieved with the same apparatus.

[0011]

Next, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory view for explaining an etching method of the present invention. FIG. 1A shows a state before etching, and FIG. 1B shows a state where silicon is etched by ions in plasma. FIG. 1C is a diagram illustrating a state where silicon is etched by electrons. FIG. 2 is a schematic sectional view of an example of an apparatus for carrying out the present invention. In this embodiment, an ECR device is used for plasma generation. In FIG. 2, 2.45 GHz generated by the microwave generator 11
Microwave 20 is transmitted through waveguide 12 and quartz transmission window 1.
3 into the cavity 14. Chlorine is introduced into the same cavity 14 as an etching gas, and the interaction between the magnetic field and the microwave 20 by the main coil 15 provided around the cavity 14 causes an ECR discharge to generate the chlorine plasma 3. The introduction amount of chlorine is about 20 sccm, and the degree of vacuum is set to 5 × 10 ⁻⁴ Torr. A bias voltage of −100 to 100 V can be freely applied to the silicon wafer 19 installed on the holder 17 by using the bias power supply 4, and this can be electrically insulated from the outside. I can do it.

Next, an etching method using this apparatus will be described with reference to FIG. In FIG. 1, first, a chlorine plasma 3 is generated by ECR discharge while the silicon wafer 2 is insulated. At this time, the potential of the silicon wafer 2 becomes a floating potential, and an ion sheath is formed between the silicon wafer 2 and the plasma 3. The chlorine ions 6 in the plasma are accelerated by the difference between the space potential of the plasma 3 and the floating potential of the silicon wafer 2, and are irradiated on the silicon wafer 2 through the ion sheath. The plasma space potential and the floating potential vary depending on the plasma generation conditions, the position of the silicon wafer, and the like, but are typically about 15 to 20 V and -5 to -15 V. Therefore, the chlorine ions 6 enter the silicon wafer 2 with an energy of about 20 to 30 eV. FIG.
As shown in FIG.
The chlorine ions 6 irradiated to the silicon through the holes of the mask react with the silicon 2 to form silicon chloride 7 and separate from the silicon as shown in FIG. 1B. Then, etching is performed. At this time,
Since the degree of vacuum is as high as 5 × 10 ⁻⁴ Torr, there is almost no influence of radicals that cause isotropic etching.
High anisotropic etching has been achieved. The current density of chlorine ions is typically about 10 to 15 mA / cm ² , and the etching rate is about 0.2 μm / min, which is practically sufficient. However, the energy held by chlorine ions is 20 to 30 eV, which is larger than the displacement energy of silicon, 12.9 eV, so that physical damage 5 occurs during etching.

In the case of digging a 1 μm trench, after etching by about 0.9 to 0.95 μm by ion etching,
The bias power supply 4 is set to about 50 to 100 V, and a voltage is applied to the silicon wafer. As a result, the chlorine atoms 8 adsorbed on the surface of the silicon are activated by the electrons 9 to become excited chlorine atoms 10 as shown in FIG. 1C, and the workpiece is etched. An electron current can be obtained at about the same level as an ion current, and an etching rate of about 1 μm / min can be obtained. Then, only the damage entered into the silicon by the ion etching is etched. In the etching by the electrons in the plasma, since the directionality of the electrons is not as good as that of the ions, the side surfaces are also slightly etched. According to experiments, the ratio of the side etching to the depth direction is about 0.5.
2. However, since most of the etching is performed by ions capable of achieving high anisotropy, and the purpose of the electron is to etch only the damaged portion, there is no practical problem at all. In this embodiment, silicon is used as the workpiece and chlorine is used as the etching gas. However, it is apparent that similar effects can be obtained by using gallium arsenide as the workpiece and fluorine and bromine as the etching gas.

[0014]

As described above, according to the etching method of the present invention, high speed, high anisotropy and high selectivity can be achieved over a wide range only by controlling the potential of the workpiece in the plasma.
Since a low damage etching is achieved, and it is not necessary to use a separate apparatus when performing the ion etching and the electron etching, and this can be performed by one process, a semiconductor manufacturing process expected to be further miniaturized in the future. The impact on the environment is significant.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an etching method according to the present invention.

FIG. 2 is a schematic cross-sectional view of an example of an apparatus for performing the method of the present invention.

FIG. 3 is a schematic sectional view of the RIE apparatus.

FIG. 4 is a schematic sectional view of an electron beam excited etching apparatus using differential evacuation.

FIG. 5 is a schematic cross-sectional view of an electron beam excited etching apparatus using a broad beam.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Resist 2 Silicon wafer 3 Plasma 4 Bias power supply 5 Irradiation damage layer 6 Chloride ion 7 Silicon chloride 8 Adsorption chlorine atom 9 Electron 10 Electron excited chlorine atom 11 Microwave generator 12 Waveguide 13 Quartz window 14 Cavity 15 Main Coil 16 Sub coil 17 Holder 18 Exhaust port 19 Substrate 20 Microwave 21 High frequency power supply 22 Parallel plate type electrode 31 Stage 32 Electron gun 33a, 33b Orifice 34 Electron beam 35a, 35b Container

Claims (1)

(57) [Claims] A gas pressure of 1.times.10 using an etching gas mainly containing fluorine gas, chlorine gas or bromine gas.
^-3 Torr or lower plasma is generated, a workpiece is placed in the plasma, and the workpiece is electrically insulated, or the workpiece is set at a negative potential with respect to the plasma potential. A first step of etching the workpiece by irradiating ions of an etching gas of
After the first step, the workpiece is irradiated with electrons in the plasma while setting the workpiece at a positive potential with respect to the plasma potential.
Neutral etching gas from the same plasma as
To the surface of the workpiece and adsorb it,
The etching the workpiece to excite more neutral gas
2. An etching method, comprising: