JP2763291B2 - Plasma processing method and processing apparatus - Google Patents

Description

The present invention relates to a plasma processing method and a plasma processing apparatus, and in particular, to a plasma processing method and a plasma processing apparatus.
The present invention relates to a plasma processing method and a processing apparatus suitable for processing various process technologies such as CVD, etching, sputtering, and ashing at a high speed. [Prior art] An apparatus using low-temperature plasma is roughly classified into an apparatus using a technique of generating a plasma by applying a high frequency voltage of about 10 KHz to 30 MHz to one of parallel plate electrodes in a vacuum (Semiconductor Research) 18; P121-P170, Semiconductor Research 19; P225-P267)
And a technique using a technique of introducing a 2.45 GHz microwave into a vacuum chamber to generate plasma. Conventionally, the technique using parallel plate electrodes has been mainly used among them. On the other hand, with the miniaturization of semiconductor elements, there has been a problem that element characteristics are affected by the impact of ions generated during plasma processing. Further, it is required to increase the processing speed in order to improve the plasma processing capability. When increasing the processing speed, simply increasing the density of plasma or the concentration of radicals (active particles immediately before ionization) is not sufficient. In dry etching by plasma treatment and plasma CVD, ion energy plays an important role. In the case of dry etching, if the energy of ions is too large, the underlying film is scraped or the crystal structure is adversely affected, and the device characteristics deteriorate. On the other hand, if it is too small, the polymer formed on the etched surface is not sufficiently removed, and the etching rate is reduced. Or conversely, a protective film made of a polymer is not formed, and the side surface of the pattern is etched, resulting in a problem that the dimensional accuracy of the pattern deteriorates. Even in plasma CVD, the ion composition affects the film formation such that the film composition becomes coarse when the energy of the ions is small, and the film composition becomes dense when the energy is large. Therefore, increasing the density of the plasma and appropriately controlling the ion energy are indispensable in future plasma processing. As a related technology of this kind, for example,
56-13480 and JP-A-56-96841 are known. When plasma is generated by microwaves, even if the microwaves generated by the magnetron are radiated to the plasma generation chamber at low pressure, sufficient energy is not supplied to the electrons due to insufficient microwave electrolysis strength, and plasma is generated. It is difficult to do that. Therefore, in order to generate plasma by microwaves, there is a method of supplying electron energy in a state of resonance by matching the frequency of the microwave with the frequency of the cyclotron where electrons rotate on a plane perpendicular to the magnetic field, and using cavity resonance There are two methods of supplying electron energy by irradiating a vessel with a microwave to increase the amplitude of the microwave and increase the electric field strength. The former is JP-A-56-
Magnetic field microwave or ECR as shown in 13480
(Elect-ron Cyclotron Resonance) method. The latter is disclosed in JP-A-56-96841. In plasma generated by microwaves, energy is supplied directly to electrons from the microwaves, so that the voltage between the sheaths formed between the plasma and the substrate hardly changes. Therefore, by applying a high-frequency voltage to the electrode on which the substrate is mounted and arbitrarily controlling the inter-sheath voltage, it is possible to control the plasma density and the appropriate ion energy necessary for high-speed operation. [Problems to be Solved by the Invention] As mentioned earlier, the energy of ions plays an important role in plasma processing. In the prior art, in the ECR method, when a high-frequency voltage is applied to the electrode on which the substrate is mounted, there is no ground electrode on the opposite side of this electrode, so the high-frequency current flows between the surrounding processing chamber and the substrate. The effect of the ion energy is strong around the substrate and weak at the center, and there is a problem that the entire substrate cannot be processed under uniform conditions. In the method using a cavity resonator, plasma is generated in the resonator, so when plasma is generated,
Since the wavelength of the microwave changes depending on the density of the plasma, there is a problem that the resonance condition is not satisfied and the plasma becomes unstable. That is, since the resonance condition is satisfied until the plasma is generated, the electric field strength of the microwave is increased and the plasma is generated. However, when plasma is generated and the plasma density is increased, the wavelength of the microwave changes and the resonance condition is no longer satisfied, and the electric field intensity decreases. Then, the supply of energy to the electrons decreases, and the plasma density decreases. When the plasma density decreases, the resonance condition is satisfied, and the plasma density increases again. Due to such a phenomenon, it has been difficult to generate plasma stably. In addition, if a high-frequency voltage application electrode is provided in the cavity resonator to control the energy of ions entering the substrate from these plasmas, microwave reflection occurs and the plasma becomes more unstable. was there. SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved plasma processing method and apparatus capable of generating stable and high-density plasma and making the energy of ions incident on the substrate uniform over the entire substrate. . [Means for Solving the Problems] A plasma processing method capable of achieving the above object of the present invention is a plasma processing method in which a plurality of types of gases having different excitation energies are supplied to a plasma generation chamber to perform a plasma processing on a substrate. A first gas supply step of pre-exciting a first gas having a high excitation energy and then supplying the first gas to a plasma generation chamber; and directly supplying a second gas having a low excitation energy to the plasma generation chamber without pre-excitation. A second gas supply step of supplying the first gas having a high excitation energy to the first gas having a high excitation energy, and exciting the first gas in the plasma generation chamber together with the second gas having a low excitation energy which is not pre-excited. A plasma is generated, and the substrate is plasma-treated with the first gas and the second gas. Then, a plasma processing apparatus capable of achieving the object of the present invention will be described in detail below. Generally, when a microwave travels in a waveguide or a cavity that is considered to be a kind of waveguide, a current corresponding to an electric field and a magnetic field flows on the surface of the waveguide. Therefore, if a slit is provided in a part of the waveguide so as to cross this current, charges accumulate at both ends of the slit, and this changes with the progress of microwaves. Is radiated to the outside of the device. The object of the present invention is to supply microwaves to the plasma generation chamber from a slit provided in the waveguide according to this principle, or connect the waveguide to a cavity resonator, and connect the cavity to the cavity resonator. This is achieved by providing a slit for emitting microwaves and supplying microwaves to the plasma generation chamber. More specifically, the plasma processing apparatus of the present invention is provided in a cavity in which microwaves are supplied from a magnetron through a waveguide, and is provided in an airtight state adjacent to the cavity. A plasma generating chamber provided through a slit plate capable of radiating microwaves from the cavity resonator into the chamber, wherein a first gas having high excitation energy is reserved in the cavity resonator. First gas supply means for supplying the gas after being excited to the plasma generation chamber is provided, and the second gas having a low excitation energy is directly supplied to the plasma generation chamber without preliminary excitation of the second gas having a low excitation energy. A second gas supply means and a gas exhaust means for supplying are provided, and the first gas pre-excited by the first gas supply means and the pre-excitation supplied by the second gas supply means are not excited. The second gas is excited in the plasma generation chamber by the microwave radiated from the cavity resonator into the plasma generation chamber to generate plasma, and the substrate is plasma-generated by the first gas and the second gas. It is characterized in that processing is performed. Preferably, an electrode whose one end is connected to a power source different from the microwave power source is provided facing the slit plate, and the power source connected to this electrode is a high-frequency power source. As a power supply connected to the electrodes, a high-frequency power supply is essential when the sample substrate is an insulator, but a current power supply may be used when the sample substrate is conductive such as a metal. The cavity resonator may be circular, coaxial, or rectangular. The slit plate may be a good conductive material having a small current loss, that is, aluminum, copper, or the like having a small resistance.
The slit may be formed so as to cross the current of the microwave so that the longitudinal direction of the slit is perpendicular to the flow of the current.Therefore, the pattern of the slit is selected according to the mode of the microwave. do it. The length of the slit is desirably at least half the wavelength of the microwave so that the microwave is easily radiated to the plasma generation chamber. Further, in order to hermetically seal the plasma generation chamber, a gas partition plate is provided facing a surface of the cavity resonator to which a part of the waveguide is coupled, but this gas partition plate does not allow gas to pass therethrough. An insulating material having air permeability and low absorption of microwaves, for example, quartz or ceramics is used. Furthermore, the slit plate has a high-frequency power source at one end (a DC power source is also possible when the substrate is conductive such as metal).
Are connected to the electrode on which the processing substrate is mounted, and it is desirable that these are installed so that the opposing surfaces are parallel to each other, and the slit plate itself is grounded and is connected to the processing substrate. It is desirable to operate as a ground electrode facing the electrode to be mounted. [Operation] In the conventional ECR method, microwaves are directly radiated from the opening of the waveguide to the plasma generation chamber. Therefore, if an earth electrode is provided between the plasma generation chamber and the opening of the waveguide, the microwave is reflected by the earth electrode and cannot be supplied to the plasma generation chamber. According to the present invention, the end face of the waveguide is closed, and a slit for radiating microwaves is provided on this end face. If necessary, the end face of the waveguide, that is, the slit plate was set to the ground potential. The total opening area of the slit can be set to about 1/3 to 1/10 of the entire end face of the waveguide for facilities, and preferably 1/5 to 1/7. When the total opening area of the slit is 1/3 or more, the performance of the resonator is reduced. When the total area is 1/10 or less, plasma discharge becomes unstable. Therefore, when a high-frequency voltage is applied to the electrode on which the substrate is mounted, the high-frequency current flows evenly between the end face of the waveguide and the electrode, and the effect of ions can be generated uniformly over the entire surface of the substrate. In addition, a sufficient amount of microwaves can be supplied to the plasma generation chamber through the slit, and high-density plasma can be generated. On the other hand, when a cavity resonator is connected to the waveguide, a microwave whose amplitude is increased by resonance in the cavity resonator is emitted to the plasma generation chamber through the slit. Therefore, high-density plasma can be generated without having a plasma generation chamber having a cavity resonator structure as in the related art. For this reason, the electrode structure according to the present invention is not restricted by the relationship with the cavity resonator as in the related art. Further, since no plasma is generated in the cavity resonator, there is no change in the resonance state, and the plasma can be generated stably. Further, by connecting the cavity resonator to the ground potential, it is possible to make the counter electrode parallel to the electrode, and the effect of ions can be uniformly generated on the entire substrate. Embodiment An embodiment of the present invention will be described below with reference to FIG. The cavity resonator 1 is a circular cavity resonator of _E01 mode.
Microwaves are supplied from the magnetron 3 through the waveguide 2. The waveguide 2 is mounted eccentrically with respect to the circular cavity resonator 1 in order to improve the coupling with the _E01 mode. A quartz plate 4 is provided on the other side of the circular cavity resonator 1.
And the slit plate 5 are fixed. A plasma generation chamber 6 is connected underneath. The plasma generation chamber 6 has a structure in which the quartz plate 4 serves as a partition wall serving as a partition plate and is sealed in a vacuum. The plane structure of the slit plate 5 is E ₀₁ as shown in FIG.
There is a ring-shaped slit opening 5c in a direction perpendicular to the mode electric field. When a microwave of 2.45 GHz is used, each slit 5c has a length of 60 mm or more, which corresponds to a half wavelength of the microwave, in order to improve the radiation of the microwave from the slit. The plasma generation chamber 6 (FIG. 1) has an electrode 7, a gas supply pipe 9,
A gas exhaust pipe 10 is provided. The electrode 7 is fixed to the plasma generation chamber 6 via an insulating material 8, and further includes a high-frequency power supply.
11 is connected. The gas supply pipe 9 can be supplied with a set amount of plasma processing gas from a gas source (not shown). A vacuum exhaust pump (not shown) is connected to the gas exhaust pipe 10 so that the inside of the plasma generation chamber 6 can be controlled to a pressure of 1 to 10 ^-3 Torr. The magnetron 3 is operated to oscillate a microwave, which is supplied to the cavity resonator 1 by the waveguide 2. The energy of the microwave whose amplitude is increased in the cavity resonator is radiated to the plasma generation chamber 6 from the slit 5c of the slit plate 5. Since the amplitude of the microwave radiated into the plasma generation chamber is large in the cavity 1, the plasma is turned on and maintained even if the plasma generation chamber 6 does not have a cavity structure. First, a case of performing an etching process using this apparatus will be described. An etching gas is supplied from a gas supply pipe 9, exhausted from a gas exhaust pipe 10, and a microwave is supplied at a constant pressure to generate plasma between the slit plate 5 and the electrode 7. Since the microwave acts directly on the electrons in the plasma, the potential difference between the plasma and the electrode 7 is at a level of 20 to 30V. The processing wafer 12 is placed on the electrode 7, and a high frequency voltage is applied to the electrode 7 from the high frequency power supply 11. The electrode 7 and the slit plate 5 are installed in parallel, and a high-frequency current flows evenly between the electrode 7 and the slit 5. Therefore, the electric field generated between the electrode and the plasma becomes uniform, and the ions of the etching gas having uniform energy on the entire surface are controlled and applied to the wafer 12 by applying a high-frequency voltage. The ions of the etching gas and the active species (radicals) of the etching gas excited in the plasma react with the film to be processed on the wafer 12, and the etching proceeds. At this time, since the energy of the incident ions is uniform, uniform etching can be performed on the entire surface of the wafer. As for the example of etching of the SiO ₂ film formed on the Si substrate, comparing the conventional device with the device of the present invention,
The etching characteristics of the SiO ₂ film are as follows:
The ratio of the etching rate to the underlying Si film was 10 times, and the uniformity was ± 5%. When the etching rate was increased to 500 nm / min or more in this conventional apparatus, the ratio of the etching rate to the underlying film was reduced by a factor of 5, and the uniformity was also reduced to ± 12%. In the apparatus of the present invention, even when the etching rate is 520 nm / min, the ratio of the etching rate to the underlying Si film is 10 times, and the uniformity is ± 10%.
5% can be obtained. An etching rate ratio of 10 times is a practically necessary condition. Next, application of the present apparatus to plasma CVD will be described. S
iH ₄ and a mixed gas of N ₂ and N ₂ O are supplied from a gas supply pipe 9, and N ₂ O and SiH ₄ are decomposed by plasma to generate SiO ₂ ,
A film is formed on the wafer 12. Further, the film quality is controlled by the incidence of ions from the plasma. At this time, since the incident energy of ions can be equalized, a uniform film can be formed on the entire surface of the wafer. In this embodiment, the microwave mode in the circular waveguide is E ₀₁
Although the case of the mode has been described, the present invention is not limited to this. However, since good efficiency is the microwave radiation in the direction perpendicular to the current slit flows on the surface of the cavity resonator, in the case of H ₀₁ mode becomes the structure shown in FIG. 3, in the case of H ₁₁ mode 4 The structure shown in FIG. As described above, according to the present invention, the effects of ions indispensable for plasma processing can be equalized, and there is an effect that stable plasma can be generated. When observing the stability of the plasma in the light emission state at the time of discharge, in the case of the conventional device, the light emission was blinking and unstable, but in the case of the present invention, there was no fluctuation and the stable light emission state Observation confirmed that the plasma was stable. Next, another embodiment in which the present invention is applied to plasma CVD will be described with reference to FIG. Plasma CVD is used to form silicon oxide films using SiH ₄ gas and N ₂ O or O ₂ gas, and nitride films using SiH ₄ and NH ₃ or N ₂ gas as described earlier. I have. In this case, since the excitation energies of the SiH ₄ gas and the N ₂ O, O ₂ , N ₂ , NH ₃ gas are different,
N ₂ O, O ₂ , N, which have higher gas excitation energy than SiH ₄ gas
_{2. It} is necessary to flow a large amount of NH ₃ . For this reason, the flow rate of the SiH ₄ gas is restricted in terms of the exhaust capacity, and the rate of film formation is limited. In the present embodiment, the N ₂ O, O ₂ , N ₂ , and NH ₃ gases are pre-excited and supplied to the plasma generation chamber to increase the excitation efficiency of these gases. Since the basic configuration of the device is the same as that of FIG. 1, an added portion will be described. A pre-excitation tube 17 made of quartz is provided in the cavity resonator 1 and is integrally joined to the quartz plate 4 to be vacuum-sealed so that there is no vacuum leakage. There is a hole 18 at the joint of the preliminary excitation tube 17 with the slit plate 5 so that the gas flowing through the preliminary excitation tube 17 blows out to the processing chamber. The slit plate 5 is provided with a slit 5c for emitting microwaves. A link-shaped gas blowing pipe 20 is provided between the electrode 7 and the slit plate 5. The gas is individually supplied to the gas blowing pipe 20 from the first gas supply pipe 9, and to the preliminary excitation pipe 17 from the gas supply pipe 15 through the branch pipe 16. A description will be given below by taking the formation of a silicon oxide film according to this embodiment as an example. N ₂ O gas is supplied from a gas flow controller (not shown) from the second gas supply pipe 15, and SiH ₄ gas is supplied from a gas flow controller (not shown) from the first gas supply pipe 9. The gas is exhausted from the gas exhaust pipe 10 to a constant pressure, a voltage is applied to the magnetron 3 from a magnetron power supply (not shown), and a microwave is supplied to generate plasma between the slit plate 5 and the electrode 7. Since the pre-excitation tube 17 is in the cavity 1,
The N ₂ O gas is turned into plasma. However, since the volume of the plasma is small, the influence on the resonance condition is small, and the resonance condition is not lost. The N ₂ O gas is excited in the tube to become oxygen radicals and is supplied to the plasma generation chamber 6. Thus merely the oxygen radical concentration is higher than in passing a mixture of SiH ₄ gas and N ₂ O gas into the plasma generation chamber 6, the gas blowout tube 20, oxygen is also channel more SiH ₄ gas Since there are enough radicals, the reaction proceeds, and a silicon oxide film can be formed at a high speed. In addition, since the incident energy of ions can be equalized as described above, a uniform film can be formed on the entire surface of the wafer serving as the substrate 12. Although the present embodiment has been described above in connection with the case where the present embodiment is applied to plasma CVD, the present embodiment is not limited to this, and when etching the substrate 12 by mixing two or more gases, the excitation of one of the gases is promoted and the etching rate It is also effective for improving the etching characteristics such as. As described above, according to the present invention, when plasma is generated using microwaves, the slit plate 5 provided on the surface facing the electrode for processing the wafer can be operated as the counter electrode. Therefore, uniform plasma processing can be performed. Further, since it is not necessary for the plasma generation chamber 6 to have the structure of the cavity resonator 1, there is no restriction on the structure of the electrodes and the plasma generation chamber. In addition, by passing the preliminary excitation tube through the cavity resonator, there is an effect that the excitation state of the supplied gas can be controlled. [Effects of the Invention] According to the present invention, there is an effect that generation of plasma using microwaves is stabilized. According to the present invention, there is an effect that the apparatus configuration is not restricted by the relation with the cavity resonator. Therefore, by connecting the cavity resonator to the ground potential, a counter electrode parallel to the electrode on which the object to be processed is placed can be formed. As a result, the energy of the microwave can be transmitted through the slit provided in the counter electrode, and the effect of ions and radicals generated by this energy can be uniformly applied to the object to be processed. In addition, the effects of ions and radicals can be generated uniformly. As a result, plasma processing can be performed at a high speed with an optimum ion energy. Furthermore, a fine pattern of a semiconductor wafer can be formed with high accuracy, at high speed, and with low damage. Furthermore, there is an effect that uniform film formation can be performed at high speed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of one embodiment showing the overall configuration of the apparatus of the present invention, FIG. 2 is a plan view of a slit used in the embodiment of FIG. 1, and FIG. FIG. 4 is a plan view of another embodiment having a different pattern from the slit of FIG. 2, FIG. 4 is a plan view of another embodiment having a further different pattern, and FIG. It is sectional drawing of an example. In the figure, 1 ... cavity resonator, 5 ... slit plate 6 ... plasma generation chamber, 7 ... electrode 11 ... high frequency power supply, 17 ... pre-excitation tube

──────────────────────────────────────────────────の Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 21/3065

Claims (1)

(57) [Claims] A plasma processing method for performing plasma processing on a substrate by supplying a plurality of gases having different excitation energies to a plasma generation chamber, wherein a first gas having a high excitation energy is pre-excited and then supplied to the plasma generation chamber. And a second gas supply step of directly supplying the second gas having low excitation energy to the plasma generation chamber without preliminary excitation without exciting the first gas having high excitation energy. In the state, the plasma is generated by exciting in the plasma generation chamber together with the second gas having low excitation energy which is not pre-excited, and the substrate is plasma-treated with the first gas and the second gas. Plasma processing method. 2. A cavity in which microwaves are supplied from a magnetron through a waveguide, and a cavity provided in an airtight state adjacent to the cavity and capable of radiating microwaves from the cavity into a room. A plasma generation chamber provided through a slit plate, wherein the cavity resonator is provided with first gas supply means for pre-exciting a first gas having high excitation energy and then supplying the first gas to the plasma generation chamber. A second gas supply unit and a gas exhaust unit that directly supply the second gas having a low excitation energy to the plasma generation chamber without performing preliminary excitation in the plasma generation chamber provided in the airtight state; The first gas pre-excited by the first gas supply means and the second gas not pre-excited supplied by the second gas supply means are emitted from the cavity resonator to the plasma generation chamber. Is excited by the plasma generation chamber by microwave to generate plasma, a plasma processing apparatus characterized by being configured so that the substrate is plasma processed by said first gas and a second gas. 3. An electrode having one end connected to a power source different from the microwave power source is provided facing the slit plate, and the power source connected to the electrode is a high-frequency power source. Item 6. The plasma processing apparatus according to item 1. 4. 4. The plasma processing apparatus according to claim 2, wherein a length of the slit provided in the slit plate is at least a half wavelength of a microwave. 5. 5. The plasma processing apparatus according to claim 2, wherein said cavity resonator is a circular cavity resonator. 6. 6. The plasma processing apparatus according to claim 2, wherein the cavity resonator, the slit plate, and the plasma generation chamber are electrically grounded, respectively. 7. A waveguide is eccentrically coupled to one surface of the circular cavity resonator, and a gas partition plate and a slit plate are fixed to the opposite surface, and the plasma generation chamber is vacuum-sealed by the gas partition plate. 7. The plasma processing apparatus according to claim 5, wherein the plasma processing apparatus has a stopped structure. 8. 8. The plasma processing apparatus according to claim 7, wherein said gas partition plate is made of a gas impermeable insulating material that absorbs less microwaves. 9. 9. The plasma processing apparatus according to claim 8, wherein said partition plate is made of one of quartz and ceramics. 10. 4. The method according to claim 2, wherein the total area of the opening of the slit is 1/10 to 1/3 of the total area of the slit plate forming the end face of the cavity resonator. Term,
10. The plasma processing apparatus according to any one of items 5, 6, 7, 8, and 9.