JPS6366912B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to reactive ion etching, which uses ions in reactive gas plasma to form fine patterns with good controllability and high quality on electronic device substrates. It is about the method.

[Conventional technology]

BACKGROUND OF THE INVENTION As electronic devices such as semiconductor integrated circuits become faster and more highly integrated, there is a need for an etching method that can form fine patterns with high precision and quality.
In particular, when forming gate metal patterns for MOS devices, etc., the thin gate oxide film that serves as the base and the gate metal are processed with high selectivity and high precision, while minimizing damage to the underlying semiconductor. It is necessary to use high quality etching to avoid any residue such as.

Conventionally, plasma etching has been widely used as an etching method using gas plasma. In this case, the gas pressure is high at 10 to 100 Pa, so
Most etching reactions are non-directional and involve reactions with highly reactive neutral radicals. Therefore, etching can be performed with high selectivity to the oxide film, but since the etching is isotropic, undercuts occur and there is a limit to the miniaturization of patterns. On the other hand, there is a reactive sputter etching method in which etching is performed using ion bombardment reaction in a gas pressure range of 1 to 10 Pa. In this method, an etching reaction is caused by the bombardment effect of ions in plasma, so it is possible to form a pattern without undercuts. However, because the gas pressure is relatively high, a halogenated carbon gas that can suppress etching of reactive radicals is used, and an ion energy of 200 to 1000 eV is required. For this reason, it is difficult to achieve sufficiently high selectivity for the underlying oxide film or mask material, and the underlying semiconductor may be damaged, so its application as a gate metal etching method has been limited.

To compensate for these shortcomings, plasma is generated using electron cyclotron resonance (ECR) discharge in the gas pressure range of 0.001 to 1 Pa, giving the ions in the plasma less than 50 eV of energy and directionality, and eliminating undercuts. There is an ECR reactive ion etching method (see Japanese Patent Application No. 58-228645) which etches the gate metal with high precision and high selectivity. In this etching method, the concentration of neutral radicals is low because the gas pressure is low, and fluorine, which has relatively low reactivity with neutral radicals as a gas, and whose reactivity with metals is promoted at low energy of 50 eV or less. Since halogen gas such as chlorine gas is used as the main component, pattern processing without undercuts is possible. Furthermore, since the ion energy is low, it can be processed without damaging the underlying layer due to ion bombardment, making it an excellent etching method for gate metal films such as MOS devices.

However, in the above ECR reactive ion etching, the main component is a halogen gas other than fluorine, and the etching reaction product with the metal has a boiling point that is about the same as or lower than room temperature. On the other hand, since a resist made of a polymeric material with low heat resistance is used as a mask for etching a metal film, it is necessary to maintain the temperature at about room temperature. For this reason, the etching reaction product may not be removed and may remain as a residue on the etching surface, or the removal rate of the etching reaction product may vary greatly in the etching temperature range, causing the etching rate to become unstable. become. Furthermore, since halogen gases other than fluorine inherently have low reactivity, if the etching equipment is not sufficiently vented and water vapor remains and is adsorbed on the etching surface, or if the etching surface is extremely thin during the pre-etching process. However, if the quality has changed due to oxidation etc.
There were drawbacks such as etching not proceeding smoothly.

[Problem that the invention seeks to solve]

In the above ECR reactive ion etching,
The object of the present invention is to provide a highly reliable reactive ion etching method capable of forming fine patterns with low ion energy by preventing etching instability caused by etching reaction products and deterioration of the etching surface.

[Means for solving the problems] The reactive ion etching method according to the present invention includes:
Introducing a reactive gas into the plasma generation chamber to generate a reactive gas plasma, withdrawing the reactive gas plasma from the generation chamber and reducing the reactive gas plasma toward the sample into the reactive gas plasma flow toward the sample. In a reactive ion etching method in which a divergent magnetic field is applied to apply an electric field that decelerates electrons and accelerates ions, a gas containing fluorine gas or a fluorine compound gas is added to a halogen gas other than fluorine as the reactive gas. It is something.

[Effect]

In the above-mentioned reactive ion etching, the ion energy is as low as 10 to 50 eV, and the etching reaction proceeds chemically, so that the cleanliness of the etched surface is extremely susceptible. Etching is performed by adding fluorine or fluorine compound gas to a halogen gas other than fluorine whose reactivity is promoted in the above ion energy range, but fluorine is less affected by impurities in the atmosphere, and Since the fluorine compound which is the reaction product of etching has high volatility, the reaction product can be smoothly removed.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of an apparatus used in the reactive ion etching method according to the present invention;
FIG. 2 is a diagram showing the etching characteristics of polycrystalline silicon by a mixed gas of base and sulfur hexafluoride in this example, and FIG. 3 is another example of the present invention, where a is the etching rate of molybdenum and AZ resist. FIG. 1B is a diagram showing the etching rate when sulfur hexafluoride is added during the above etching. In FIG. 1, a plasma generation chamber 1 and a sample chamber 3 connected to each other via a plasma extraction window 2 are
A sample mounting table 6 on which a sample substrate 5 is mounted is provided on a sample table 4 attached to a sample table 4, and is provided with a second gas introduction system 7 and a connection part 8 to an exhaust system. The plasma generation chamber 1 is connected to a rectangular waveguide 1 via a microwave introduction window 9.
0, a magnetic coil 11 is provided around the outside, and a magnetic shield 12 is provided around the outer periphery of the magnetic coil 11. The plasma generation chamber 1 has a first gas introduction system 13 and a cooling water supply port 14.

When generating plasma, the connection part 8 of the exhaust system
The plasma generation chamber 1 and the sample chamber 3 are evacuated to a high vacuum, and gas is introduced from one or both of the first gas introduction system 13 and the second gas introduction system 7 to a temperature of 0.001~
At a pressure of 1 Pa, microwaves are introduced from a microwave source (not shown) into the plasma generation chamber 1 through the rectangular waveguide 10 and the microwave introduction window 9, and at the same time are introduced into the magnetic coil 11 installed around the plasma generation chamber 1. Therefore, a magnetic field that satisfies the electron cyclotron resonance conditions is applied to at least a portion of the plasma generation chamber 1. For example, a magnetron with a frequency of 2.45 GHz can be used as the microwave source, and the electron cyclotron resonance condition at this time is a magnetic flux density of 875 G.
In order to increase the electric field strength of the microwave and increase the discharge efficiency, it is preferable that the plasma generation chamber 1 be set to the condition of a microwave cavity resonator.
The circular cavity resonator mode was adopted, and the inner dimensions were cylindrical with a diameter of 15 cm and a height of 15 cm. The plasma extraction window 2 was a circular window with a diameter of 5 cm, and was used as a reflection surface for microwaves. The magnetic field generated by the magnetic coil 11 is directed from the electron cyclotron resonance region inside the plasma generation chamber 1 toward the sample stage 4 installed in the sample chamber 3, for example, when the surface of the sample stage is 100 to
It constitutes a diverging magnetic field that decreases with a predetermined slope of about 200 Gauss. In this configuration, a magnetic shield 12 is disposed around the outer periphery of the magnetic coil 11 in order to prevent the magnetic field from seeping out to the outside of the device and to efficiently configure a diverging magnetic field.

In the plasma generated by electron cyclotron resonance, the electrons are in a high-energy state and move in a circular motion, so the interaction between the magnetic moment of the electrons and the magnetic field gradient causes the magnetic field velocity to decrease, that is, in the plasma generation chamber. Electrons in the plasma are accelerated in the direction from 1 to the sample stage 4, resulting in a plasma flow 15
is formed. Furthermore, in this configuration, since the sample mounting table 6 is arranged on the sample table 4 in a state where it is electrically insulated from the plasma generation chamber 1, the plasma flow 1 is
An electric field that decelerates electrons and accelerates ions is generated inside the sample holder 5, and an equilibrium state is reached under the condition that the number of ions and electrons incident on the sample mounting table 6 match. Therefore, the ions in the plasma are effectively transported to the sample surface by the electric field in the plasma stream 15 in the present invention, unlike the conventional method in which they are moved by thermal diffusion. Further, a sample mounting table 6,
An electric field is generated on the surface of the sample substrate 5 due to the thermal movement of electrons, and a plasma sheath is formed. As a result, the ions in the plasma flow 15 are imparted with kinetic energy and directionality equal to the sum of the electric field in the plasma flow 15 and the electric field in the plasma sheath, and enter the sample mounting stage 6 and the sample substrate 5. The configuration of the apparatus as described above, the plasma flow forming method, and the principle of applying ion energy are the same as the reactive ion etching method of the previous application (Japanese Patent Application No. 58-228645). The present invention differs from the above method in that fluorine or a fluorine compound gas is mixed in order to eliminate etching instability that tends to occur when using a halogen gas other than fluorine, and to form a fine pattern with high reliability. It is.

FIG. 2 is a diagram showing the etching characteristics of polycrystalline silicon using a mixed gas of chlorine (Cl ₂ ) and sulfur hexafluoride (SF ₆ ) in this example. On the horizontal axis
The flow rate ratio (%) of SF ₆ is shown when the total flow rate of SF ₆ and Cl ₂ is 15 c.c./min. The vertical axis shows the polycrystalline silicon etching speed (X), polycrystalline silicon and silicon oxide. The etching rate ratio (Y) and the undercut amount (Z) of the polycrystalline silicon pattern are shown. When SF ₆ flow rate ratio is 0% (Cl flow rate ratio 100%),
Acicular etching residue is produced on the etched surface of polycrystalline silicon, and the etching rate is as low as 550 Å/min. However, in the region where the SF ₆ flow rate ratio is 10% or more, a clean etching surface without etching residue can be obtained, and an etching rate of 1000 Å/A or more can be obtained. On the other hand, a pattern without undercuts was obtained up to 20% SF ₆ flow rate;
When the SF ₆ flow rate ratio exceeds 30%, the undercut amount increases rapidly. Also, consistent with this tendency, the etching rate ratio (selectivity) between polycrystalline silicon and silicon oxide decreases rapidly when the SF ₆ flow rate ratio is 20% or more.

The needle-shaped etching residue observed when monocrystalline silicon is etched using chlorine gas by the conventional etching method has also been reported by HBPogge et al. (Reactive Ion
Etching of Silicon with Cl ₂ /Ar, J.
Electrochem.Soc., Vol.130, 1592 (1983). According to the above literature, it is estimated that the etching residue is caused by silicon oxide formed on the etching surface due to water vapor remaining in the apparatus. It is also said that the generation of etching residue can be prevented by sufficiently exhausting the residual gas inside the device. The inventors believe that the etching residue that occurs on the etched surface of polycrystalline silicon is due to the same cause, and the etching equipment is structured so that it does not come into direct contact with the atmosphere when exchanging samples. We devised ways to prevent impurities from remaining in the equipment. This reduced the number and size of residues, but the reproducibility was extremely poor and reliability was lacking. In conventional reactive ion etching, the ion energy is 200 to 1000 eV, so if the surface is only slightly contaminated, it is possible to remove the effects by semi-physical sputtering using high ion energy. is considered possible. However, in the reactive ion etching of the present invention, the ion energy is 10 to 50 eV, and etching proceeds chemically, making it extremely sensitive to surface cleanliness. In addition, the boiling point of silicon tetrachloride, which is a reaction product between chlorine and silicon, is as low as 57°C, so the removal of silicon tetrachloride does not proceed smoothly, and if conditions are bad, the silicon tetrachloride may be removed even more. It is thought that atmospheric impurities combine and cause etching residue.

In the present invention, in order to reduce the influence of impurities in the atmosphere and increase the smooth removal of etching reaction products, a fluorine compound gas is added to chlorine gas (Cl ₂ ).
In the example, sulfur hexafluoride (SF ₆ ) was added. In other words, the etching reaction is promoted by fluorine, which is less affected by impurities in the atmosphere, and a fluorochloride compound having a higher boiling point is formed as an etching reaction product, thereby facilitating the removal of the etching reaction product. . As shown in FIG. 2, in this example, etching could be performed at a high etching rate without producing an etching residue in the SF ₆ flow rate ratio range of 5 to 20%. Furthermore, within the above range, a high quality etching pattern was obtained with high precision and high selectivity to silicon oxide without causing any undercuts. In addition, in FIG. 2, when the SF ₆ flow rate was 30% or more, undercuts occurred and the selectivity with silicon oxide decreased, resulting in a decrease in etching characteristics. This is because highly reactive fluorine plays a leading role in the etching reaction. In other words, a halogen gas other than fluorine, which has low reactivity in the state of a neutral radical and ions endowed with energy and directionality play a major role in etching, is used as a main component in this example, chlorine gas. It is necessary.

FIG. 3 is a diagram showing another embodiment of the present invention, and FIG. 3A is a diagram showing the etching characteristics of a molybdenum Mo film and an AZ resist. The horizontal axis shows chlorine gas 10
The flow rate of mixed oxygen gas (O ₂ ) is shown in cc/min, and the etching rate is shown on the vertical axis. Molybdenum etching rate is lower than oxygen flow rate of 5c.c./min.
The etching rate was constant at 600 Å/min, and a clean etched surface without any etching residue was obtained in this region. However, in the above region, the etching speed of the AZ resist used as a mask is high and it is not suitable for forming fine patterns. Furthermore, if the oxygen flow rate is lower than 2 c.c./min, the etching rate of the resist is low and is suitable for forming fine patterns, but in this case, etching residue is generated, and if the oxygen flow rate is extremely low, the etching rate of molybdenum is reduced. also decreases significantly. On the other hand, Figure 3b shows the etching rate when sulfur hexafluoride is added to the conditions of chlorine 10c.c./min and oxygen 2c.c./min shown in Figure 3a above. be. In this example, when SF ₆ was added at a rate of 2 c.c./min or more, there was no residue from etching molybdenum, and etching could be performed at high speed and with high selectivity to the resist.

In each of the above examples, the case where chlorine gas was used as the main component was explained, but in addition, halogen gases such as bromine and iodine, and compound halogen gases composed of chlorine, bromine, iodine, etc., were used as the main component. The same applies when used as Further, as a method for adding fluorine, a gas of chlorinated fluoride or fluorinated iodide such as ClF or SO ₂ ClF can be used. By selecting these gases, metals such as tantalum and tungsten as well as metal compound films such as MoSi ₂ can be etched finely, with high precision, and with high quality.

〔Effect of the invention〕

As described above, in the reactive ion etching method according to the present invention, a reactive gas is introduced into a plasma generation chamber to generate a reactive gas plasma, the reactive gas plasma is extracted from the generation chamber, and the reactive gas plasma is directed toward a sample. In a reactive ion etching method that applies an electric field that decelerates electrons and accelerates ions inside a reactive gas plasma flow, the reactive gas is mainly composed of a halogen gas other than fluorine, and contains fluorine gas or fluorine compound gas. By adding gas, a plasma with a high ionization rate is generated by electron cyclotron resonance discharge using microwaves, and the plasma flow is guided onto the sample substrate by the effect of a diverging magnetic field, so that an ion energy of 10 to 50 eV can be obtained. Furthermore, since the main component is a halogen gas other than fluorine whose reactivity is promoted in the above ion energy range, and fluorine or fluorine compound gas is added for etching, there is no undercut and the selectivity is extremely high. High quality fine patterns with no residue can be formed.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the apparatus used in the reactive ion etching method according to the present invention, and Fig. 2 shows the etching characteristics of polycrystalline silicon using a mixed gas of chlorine and sulfur hexafluoride in this embodiment. Figure 3 shows another embodiment of the present invention; a is a diagram showing the etching speed of molybdenum and AZ resist;
b is a diagram showing the etching rate when sulfur hexafluoride is added during the above etching. 1... Plasma generation chamber, 5... Sample substrate, 15
...Reactive plasma flow.

Claims (1)

[Claims] 1 A reactive gas is introduced into a plasma generation chamber to generate a reactive gas plasma, the reactive gas plasma is extracted from the generation chamber, and the electrons are decelerated and ions are generated inside the reactive gas plasma flow toward the sample. In the reactive ion etching method that applies an electric field that accelerates the plasma, the reactive gas plasma is generated by electron cyclotron resonance discharge using microwaves in a plasma generation chamber, and is directed toward the sample from the plasma generation chamber at a predetermined gradient. The reactive ion is characterized in that an electric field is applied by interacting with a diverging magnetic field that decreases in , the reactive gas is mainly composed of a halogen gas other than fluorine, and a gas containing fluorine gas or a fluorine compound gas is added. Etching method.