JPH03277775A - Plasma treatment - Google Patents

Abstract

PURPOSE:To efficiently carry out plasma treatment with high anisotropy under low pressure by introducing gas into a vacuum vessel under low pressure, selectively introducing right-deflected microwaves into the vessel and using a microwave absorption mode in a high magnetic field. CONSTITUTION:Gas is introduced into a vacuum vessel under low pressure of <=5X10<-3>Torr, right-deflected microwaves in which the direction of an electric field is clockwise to the forward direction are selectively introduced into the vessel and a higher magnetic field than a magnetic field satisfying conditions in electron cyclotron resonance is formed in the vessel. The microwaves are absorbed in the introduced gas in the high magnetic field and CVD or sputtering is carried out with plasma generated in the vessel. Ionization efficiency and plasma density can be increased.

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a plasma processing method, and relates to a plasma processing method that irradiates a sample substrate with ions, excited active species, radicals, etc. in plasma, typified by, for example, dry vapor deposition. . [Prior Art] As plasma processing methods, methods such as dry etching, sputtering, and CVD are known. Dry etching is the process of removing particles such as ions in plasma with S.
Sputtering is a processing method that irradiates a sample substrate such as an i-wafer to erode the surface of the sample substrate. Sputtering is a process in which an inert gas such as argon is turned into plasma, and particles such as ions in the plasma are irradiated onto the target material. This is a processing method in which the components are ejected from the target material by the collision energy of the particles, and the ejected components are attached to a sample substrate placed in a vacuum container to form a thin film on the surface of the sample substrate. Converts deposition gases such as silane gas (Sins) and ammonia gas (NL) into plasma,
This is a processing method in which a thin film is formed on the surface of a sample substrate by irradiating the sample substrate with particles such as radicals and ions in the plasma. Conventionally, these plasma processing methods utilize electron cyclotron resonance (ECR) conditions to form high-density plasma, and perform plasma processing using ions, excited active species, and radicals present in the plasma. There is. The ECR conditions are conditions that allow gas to efficiently absorb microwaves, and are expressed by the following equation. B=2 x m f/e-3,57X 10-'f
(Gauss) B: Magnetic flux density m: 1 Mass of the child e: 1 Charge of the child f: Microwave frequency For example, 2.45 GHz, which is the frequency of magnetrons industrially mass-produced for home appliances. 875 when used
Gauss describes this condition. The principle of forming high-density plasma under ECR conditions will be explained using FIG. 2. FIG. 2a is a principle diagram showing the movement of electrons when ordinary linearly polarized microwaves are input under ECR conditions. In Figure 2a, when the Z-axis direction is from the front side to the back side of the page and a magnetic field B0 is applied between the Z-axis, the electrons will move along the broken line due to the Lorentz force due to the magnetic field B0 until the microwave is applied. It has the cyclotron motion shown in . Here, the polarization plane of the electric field is
- When a microwave with linear polarization in the Z plane is input (progressing direction is the Z-axis direction), the electric field is a vibration of the electric field in the X-axis direction, so the electrons are accelerated in the X-axis direction by this electric field. become. In the case of ECR conditions, the period T of the electric field and the period T6 of the cyclotron motion match, so the electron is always accelerated by the X component of the arrow, absorbs the energy of the electric field (microwave energy), and increases the velocity V. By increasing the kinetic energy, electrons can efficiently obtain microwave energy and form a high-density plasma. Plasma processing methods such as dry etching, sputtering, and CVD are essentially the same processing methods up to the point where gas is turned into plasma and particles such as ions in the plasma are irradiated onto the sample substrate. The case of the method will be explained in detail. Dry etching apparatuses using electron cyclotron resonance (ECR) conditions can be roughly divided into three types, and the apparatus configurations of each type are schematically shown in FIGS. 12 to 14. The device shown in FIG. 12 supplies a magnetic field with a coil and introduces microwaves with a waveguide into a vacuum container.
This is a type of device that creates electron cyclotron resonance (ECR) conditions directly above a sample substrate placed in a vacuum container and irradiates the sample with high-density plasma, and is the so-called microwave plasma etching device J. . (JP-A-53-96938, JP-A-60-134423
reference). In FIG. 12, 53 is a vacuum container whose interior can be evacuated by an evacuation boat 59, and a sample substrate 55 is placed in the vacuum container 53 on a sample stage 56. Further, the vacuum vessel 53 has a gas introduction port 58, and gas (for example, NF,
gas, etc.) is introduced to replace the gas atmosphere inside the vacuum container 53. One end of the sample stage 56 is drawn out to the outside of the vacuum container 53, and a high frequency power source 57 is connected to the portion outside the vacuum container 53. The frequency of this high frequency power supply 570 is normally 13.65 MHz. Further, the vacuum container 53 has a microwave irradiation window 54 made of quartz.
A waveguide 52 is connected to the microwave irradiation window 54, and microwaves from a microwave source (not shown) are transmitted to the vacuum vessel 53 through the waveguide 52 and the microwave irradiation window 54. to be introduced within. The frequency of this microwave is usually 2.45 GHz. Further, 51 is a magnetic field coil, and E is placed inside the vacuum container 53.
A magnetic field is supplied that produces a magnetic flux density near 875 Gauss, which is the CR condition. In this way, plasma is efficiently generated under ECR conditions, and the sample substrate 55 is irradiated with various particles of this plasma to perform the dry etching process. The apparatus shown in FIG. 13 is similar to the apparatus shown in FIG. 12 in terms of magnetic field supply and microwave introduction, but the vacuum chamber is replaced with a plasma generation chamber having electron cyclotron resonance (ECR) conditions. Separated into a sample chamber where the sample substrate is placed, high-density plasma is generated in the plasma generation chamber, and particles such as ions of this plasma are drawn into the sample chamber using the divergent magnetic field formed by the coil and applied to the sample. This type of device is called a so-called rECR etching device. (Japanese Patent Publication No. 56-155535, Japanese Patent Application Publication No. 5747797
(see 5). In FIG. 13, the same reference numerals as in FIG. 12 indicate substantially the same components as in FIG. 12, so the explanation will be omitted. In FIG. 13, reference numeral 63 denotes a sample chamber whose interior can be evacuated, and a sample substrate 55 is placed inside the sample chamber 63. The sample chamber 63 also communicates with a plasma generation chamber 61 whose interior can be evacuated, and the waveguide 5
2 and the quartz window 62, and a magnetic field is applied by the magnetic field coil 51 to generate ECR conditions, thereby generating high-density plasma in the plasma generation chamber 61. This plasma is drawn into the sample chamber 63 and irradiated onto the sample substrate 55 in a shower to perform a dry etching process. Finally, to explain the device shown in Fig. 14, the device shown in Fig. 14 supplies a magnetic field with a permanent magnet (multipole) and injects microwaves with antenna oscillation to form a flower-shaped ECR condition. This is a type in which high-density plasma generated under these ECR conditions is applied to the sample by diffusion. (*Reference 62-31999 WI). In FIG. 14, the same reference numerals as in FIG. 12 indicate substantially the same components as in FIG. 12, so the explanation will be omitted. In FIG. 14, reference numeral 53 denotes a vacuum container, and a multipolar permanent magnet 65 is disposed around the outer periphery of the vacuum container 53, and a microwave oscillation antenna 64 is inserted into the vacuum container 53. The microwave emitted from the microwave oscillation antenna 64 and the multipole permanent magnet 65
By forming the ECR conditions in a flower shape at many locations using the magnetic field applied by the magnetic field, a higher density plasma is generated, and by irradiating this plasma onto the sample substrate 55 placed in the vacuum container 53, a dry process is performed. It is an etching process. Here, the effect of the high frequency source will be explained. In the dry etching method using plasma, the fact that ion particles have a positive charge is used to add a negative charge to the sample stage, thereby attracting the ion particles to the sample substrate placed on the sample stage. Ion-assisted etching is effective, and a high-frequency power source is used to add a negative charge to the sample stage. A negative DC bias may be added instead of this high frequency power source. Next, an apparatus for performing CVD using ECR conditions will be described. FIG. 15 shows an apparatus for performing CVD with substantially the same apparatus configuration as that shown in FIG. 13. In FIG. 15, the same reference numerals as in FIG. 13 indicate substantially the same components as in FIG. 13, so the explanation will be omitted. In FIG. 15, 66 is a first gas introduction system that introduces ammonia gas, etc. for deposition reaction into the plasma generation chamber 61, and 67 is a first gas introduction system that introduces silane gas, etc., which is a deposition gas, into the sample chamber 63. It is a two-gas introduction system. This device is
ECR conditions are generated in the plasma generation chamber 61 to generate plasma such as ammonia gas, and various particles of the plasma are drawn into the sample chamber 63 and reacted with a deposition gas such as silane gas in the sample chamber 63. It is formed as a thin film on the surface of the sample substrate 55. (Refer to Japanese Patent Application Laid-Open No. 56-155535). [Problem to be solved by the invention] First, the problem to be solved by the invention according to claim 1 will be explained. In recent years, semiconductor design rules have entered the submicron era, and etching shapes are increasingly required to have high precision. The shape of the etching must faithfully reproduce the pattern, and vertical etching (improving anisotropy) is desirable.In plasma etching, the above-mentioned ion-assisted etching, which effectively utilizes ions incident on the sample, is anisotropic. This is effective for obtaining the same properties, thereby aligning the direction of ion incidence. FIG. 16 is a principle diagram depicting how ions are irradiated from plasma toward a sample substrate. The acceleration of ions (indicated by e in the figure) is achieved by applying an acceleration voltage vt due to a floating potential vf or a magnetic field gradient caused by a divergent magnetic field at the sheath part (from the part indicated by a broken line in the figure to the sample substrate 71), and by applying an acceleration voltage vt separately. RF bias or DC
Bias ■. If there is a collision with a neutral particle (indicated by ■ in the figure) in this acceleration region (sheath), the direction of the ions will be disturbed, making it impossible to align the direction of incidence on the sample substrate 71, and the side wall 72 will also be affected. Ion incidence occurs, making vertical etching impossible. That is, as shown on the right side of FIG. 16, the lower side wall 72 of the masking portion 73 becomes deviated. The condition under which the collision with such a neutral particle can be ignored is that the sheath width d is equal to the mean free path λ of the neutral particle. For d, 〈〈λ. and the mean free path λ of the neutral particle. For example, in the case of argon gas, the pressure is 1. It is on the order of Icm, which is inversely proportional to the pressure. On the other hand, the sheath width dj depends on the plasma density n D , the electron temperature T, and the floating potential ■, but as a guide,
In an ECR device, it is thought to be about 100 μ- (Semiconductor Plasma Process Technology, Sangyo Tosho, pages 138-144)
It is thought that the lower the pressure, the fewer collisions of ions with neutral particles. However, the above values mean average values and have a distribution, so the pressure 5xlO-'Torr
In reality, collisions with neutral particles also exist. Therefore, it is desirable to use electrical discharge at as low a pressure as possible to perform vertical etching. However, there was a problem in that the etching rate decreased as the pressure was lowered. This will be explained using FIG. 17. Figure 17 shows that using argon gas, the power of the microwave to be introduced is 120W, and the maximum magnetic field point is 87.
5 Gauss is a graph showing the pressure dependence of plasma density when discharge is performed under conditions where the conventional ECR condition is satisfied at the maximum magnetic field point. As can be seen from FIG. 17, since the gas density itself decreases under low pressure, the plasma density np also decreases. A decrease in the plasma density n2, that is, a decrease in ion density means a decrease in the ion assist effect and a decrease in reactive species, resulting in a decrease in the etching rate. The problems with dry etching have been described above, but in the case of sputtering and CVD, it is important to ensure that the thin film formed is of good quality and does not contain impurities in the gas (for example, Ol, H, O gas, etc.). It is desired to form a For example, when processing a metal sample substrate, there is a problem with oxidation, so it is necessary to prevent the 02 gas from entering. For this purpose, it is necessary to process at low pressure, and the reason for this is that when the pressure is increased, the reaction by-products generated after the radicals of the reaction gas react on the sample substrate surface are dissociated more efficiently. This is because reaction byproducts have a short mean free path and are more likely to exist near the surface of the sample substrate even after dissociation. The invention according to claim 1 provides a method for efficiently performing highly anisotropic plasma processing under low pressure by increasing plasma density by increasing the ionization rate, in order to solve the problems of the prior art described above. The purpose is to Next, the problem to be solved by the invention according to claim 2 will be explained. In recent years, in order to form films at low temperatures, CVD methods using plasma have been used instead of conventional thermal CVD methods. Among the CVD methods using plasma, a method of generating plasma using microwaves is effective and is in use. This is because radiation damage to the sample substrate is less likely to occur during the film formation process. As mentioned above, conventionally, E
The film formation rate is improved by using a plasma CVD apparatus using CR conditions. However, under high pressure,
Under normal ECR conditions, the Larvbor radius of the electron is not sufficiently short compared to the mean free path of the electron, so the electron
While the electron cyclotron was moving, it collided with neutrons before absorbing enough μ-wave energy, making it impossible to improve plasma density. Further, in sputtering, it has not been possible to further improve the film formation rate for the same reason. The invention as claimed in claim 2 aims to solve the above-mentioned problems of the prior art by providing a CVD method or a sputtering method that has an extremely high film formation rate under reduced pressure with a high particle density. . [Means for Solving the Problems] The present invention has been made in view of the problems of the prior art described above, and involves introducing gas and microwaves into a vacuum container to which a magnetic field is applied, and causing electrical discharge within the vacuum container. The introduced gas is turned into plasma by generation, and ions, excited active species, radicals, etc. in the plasma are irradiated onto the sample substrate to perform etching.
In plasma processing methods such as sputtering and CVD, right-polarized microwaves whose electric field direction is clockwise with respect to the direction of propagation are selectively introduced into a vacuum chamber, and the conditions are lower than electron cyclotron resonance conditions within the vacuum chamber. The purpose of the present invention is to generate high-density plasma in a high-field microwave absorption mode in which a high magnetic field is formed and microwaves are absorbed by the gas in the high-field region, Etching, sputtering, CVD, etc. are carried out at a pressure of 5 X 10-'' Torr or less.Furthermore, in the invention as claimed in claim 2, the gas pressure is set to 5 X 10-'' Torr or less.
CVD or swelling is performed under reduced pressure of X 10-'' Torr or more. (Operation) The inventors of the present invention have conducted intensive experiments to achieve the above object, and as a result, the gas introduced into the vacuum container While maintaining the pressure at a low pressure, right-polarized microwaves with an electric field clockwise relative to the direction of travel are selectively introduced into the vacuum chamber, and a magnetic field larger than the electron cyclotron resonance conditions is applied.
Etching speed, etc. when dry etching is performed by causing a discharge in a gas in a vacuum container to turn the gas into plasma, and irradiating ions, excited active species, radicals, etc. onto a sample substrate placed in a vacuum container. When I investigated, I found that
ECR for industrial microwave frequency 2.45GHz
A remarkable finding was obtained that the etching rate increases significantly when a magnetic field strength higher than the magnetic field strength of 875 Gauss, which is the condition, is applied to the entire space. The high magnetic field state formed within the vacuum container is similar to that in conventional ECR
Regardless of the conditions, this phenomenon is considered to be a unique phenomenon based on a completely different principle from microwave absorption under ECR conditions. The principle of this phenomenon has not yet been completely elucidated, but in comparison with ECR, the inventors present models 1 to 4 that are currently considered to be one model of the principle of this phenomenon.
This will be explained using figures. First, Figure 2 shows the movement of electrons when ordinary linearly polarized microwaves are input under ECR conditions. In Figure 2 a, the direction from the front side to the back side of the paper is the Z axis, and the 2
FIG. 3 is a conceptual diagram showing the trajectory of electrons when a magnetic field B0 is applied in the axial direction. Furthermore, FIG. 2 is a conceptual diagram showing changes in the electric field Ex with respect to time T at this time. In Figure 2a, the electrons are in the magnetic field B0 before the microwave is applied.
Due to the Lorentz force caused by this, the cyclotron motion is shown by the broken line. If a linearly polarized microwave with an electric field polarized in the x-z plane is input here (progressing direction is the z-axis direction), the electric field is an oscillation of the electric field in the x-axis direction, so
The electrons will be accelerated in the X-axis direction by this electric field. In the case of ECR conditions, the period T of the electric field and the period To of the cyclotron motion match, so the electrons are synchronously accelerated by the χ component of the arrow and absorb the energy of the electric field (microwave energy). The velocity V is increased (kinetic energy increases). At this time, there is no acceleration due to the electric field in the y direction. This means that a linearly polarized wave can be decomposed into a clockwise polarized wave (R wave) and a counterclockwise polarized wave (L wave), which have the same magnitude and phase, such that the sum of both electric fields in the y direction is always zero. This is because the electric field component of the microwave in the y direction is not absorbed by electrons. Next, Figure 3 shows the movement of electrons when right-handed circularly polarized microwaves are input under ECR conditions.
FIG. 3 is a conceptual diagram showing the trajectory of electrons when a magnetic field B is applied in the two axial directions. Further, FIG. 3 is a conceptual diagram showing changes in the period T of the electric field Ex due to the R wave and the electric field Ey due to the L wave at this time. The R wave is allowed to pass through as is, but the phase of the L wave of the microwave is delayed by π/2 rad from the phase of the R wave using a circular polarizer. As a result, the electric field direction rotates clockwise with a constant magnitude in accordance with the frequency of the microwave. This right-handed circularly polarized wave is E
When placed under CR conditions, the direction of the rotating electric field matches the direction of the cyclotron motion of the electrons, as shown in Figure 3, so the electrons are always accelerated in the rotational direction, and the χ component of the electric field,
Both y components can be absorbed, and more microwave absorption is achieved than when linearly polarized microwaves are input, and the electron velocity V' in this case is accelerated to more than the electron velocity V shown in Figure 2. . The velocity of the electrons, that is, the kinetic energy of the electrons, means the electron temperature T, and an increase in the electron velocity means an increase in the electron temperature T. Therefore, in ECR using right-handed circularly polarized microwaves, an electron temperature higher than ECR using linearly polarized microwaves is obtained. On the other hand, the mean free path λ of the electron is the pressure 5xlO−”T
About 5.8c+s at orr, pressure 5xlO-'Tor
It can be calculated to be about 588 cm at r. Therefore, the low pressure side, where the mean free path λ is larger and the collision frequency is smaller, is accelerated by the microwave electric field for a longer time, so
The energy (kinetic energy) of the electrons increases and the electron temperature rises. The relationship between this pressure and electron temperature is shown in the graph of FIG. 17 by the symbol. FIG. 4 is a graph showing the relationship between the electron energy, T, and the ionization cross section σ of the molecule. The ionization cross section σ corresponds to the probability that the gas will be ionized upon collision between electrons and molecules. In general, the ionization cross section σ8 has a value (ionization occurs) only when the electron energy T increases beyond FA [kmT], and -
It converges to zero after reaching a maximum value. Here, the dark value energy klT is the minimum energy required to ionize a molecule. In addition, the phenomenon that converges to zero after passing through the -degree maximum value is the collision time (interaction time) of electrons and molecules.
This can be understood by considering. That is, in order to ionize a molecule, the collision time between an electron and a molecule must be longer than the time for ionization of a molecule determined by the uncertainty principle. Therefore, as the energy of the electron increases, the collision time becomes shorter and the probability of ionization decreases. In this way, the probability that gas will be ionized during a collision is not proportional to the electron energy, T, so in order to improve the ionization rate, rather than simply increasing the electron energy, it is indicated by the maximum value. electron energy ktT
+may electron energy must be supplied. This appropriate electron energy is determined by the degree to which electrons absorb microwave energy, the strength of the microwave electric field (microwave power), and the collision frequency (microwave power), which is related to pressure.
(proportional to the reciprocal of the mean free path, 1/λ). Under low pressure, as mentioned above, the electron energy has T
, increases, and therefore has the electron energy at point A in FIG. 4 under ECR conditions. In order to improve the ionization rate, it is desirable to lower the electron energy T, either by increasing the pressure (collision frequency), decreasing the power of the microwave input, or by allowing the electrons to absorb the microwave energy. If the pressure is increased, highly anisotropic plasma processing as mentioned above will not be possible, and if the microwave power is lowered, the total energy absorbed by the gas will decrease, and the absolute Therefore, it is necessary to lower the electron energy while maintaining low pressure and microwave power, and in addition to using clockwise circularly polarized microwaves with high absorption efficiency, magnetic field It is necessary to set the magnetic field to a high magnetic field region higher than the ECR conditions. Next, we will explain what the inventors consider as another model for this phenomenon. Under ECR conditions, the E
Abnormal absorption of microwaves occurs at the CR point (a relatively narrow space near the ECR point), and due to the dispersion relationship regarding the propagation of microwaves (magnetic waves), microwaves cannot propagate to the space beyond that point. First, if the gas is absorbed only in a narrow space near the ECR point and cannot be absorbed in a wider space, that is, if it is absorbed only at the cough ECR point, the number of gas molecules existing in this limited space will be lower than the number of gas molecules under low pressure. Therefore, the number of accelerated electrons decreases for the above reasons, and the absolute amount of ionizing collisions decreases. is limited, making it impossible to improve plasma density. On the other hand, the dispersion relationship regarding the propagation of microwaves (IIIFF waves) in the high magnetic field region above the resonant magnetic field under ECR conditions has a real number solution for right-handed circularly polarized waves, and can sufficiently propagate into the plasma (Whistler mode). Therefore, the microwave can be propagated over a wide area from the window where the microwave is introduced to the sample position. In the cough high magnetic field region, the absorption of microwave energy is different from the absorption under the ECR conditions shown in Figures 2 and 3, and the direction of the cyclotron motion and the microwave electric field do not match, causing repeated acceleration and deceleration. It is thought that the increase in electron energy occurs as the sum of the effects of acceleration and deceleration. Although the energy absorbed by each electron is small, this absorption occurs throughout the space from the window that introduces the microwave to the sample position. In this wide space, there are a sufficient number of gas molecules even under low pressure, and the lifespan of electrons and ions is longer under low pressure, so there are many electrons and ions that absorb microwave energy. It is said that the electron temperature is lower than that obtained under ECR conditions, and a higher electron density than that obtained under ECR conditions is obtained, and the ion density is also improved, making it possible to increase plasma density under low pressure. A model can be considered. For example, if the applied magnetic field is twice the ECR condition, the electrons repeat equal acceleration and deceleration, and the electric field energy of the microwave is not absorbed by the electrons.The magnetic field in this vicinity is the window for introducing microwaves. If it exists widely in the space from the sample position to the sample position, the electron density and ion density decrease even in the high magnetic field region, the plasma density decreases, and the etching rate decreases. On the other hand, the applied magnetic field is EC
If it is three times the R condition, microwave absorption can be performed as a sum of acceleration and deceleration, and effective microwave absorption under a high magnetic field can be performed. Therefore, a condition for realizing the high magnetic field microwave absorption mode is to enable effective absorption of microwaves under a high magnetic field in the entire space from the microwave introduction window to the sample position. As described above, the "high magnetic field microwave absorption mode" of the present invention has the effect of lowering the electron temperature T, increasing the ionization cross section σ, and increasing the energy of right-handed circularly polarized microwaves under low pressure. In the discharge under low pressure, the absorption is spread over the entire space from the microwave introduction window to the sample position, and the absolute amount of electrons and ions is increased, or by improving the dominant effect. This mode can increase the ionization rate and improve the plasma density. In the invention set forth in claim 1, it is necessary to bring the inside of the vacuum container into a high vacuum state of 5 This is because it is necessary to realize a method for efficiently performing high-pressure plasma processing.In other words, when the pressure is higher than this, high anisotropy occurs as explained using Fig. 16 in the section on problems with the prior art. On the other hand, in the invention as claimed in claim 2, the inside of the vacuum container is
-''Torr or more. This is necessary in order to provide a CVD or sputtering method with extremely high film formation rate under reduced pressure with high particle density, which is the object of the invention as claimed in claim 2. This is because if the pressure is lower than this, the plasma density will decrease relatively, and the deposition rate will decrease (the anisotropy will increase). The degree of vacuum in the invention will be explained using Fig. 5. Fig. 5 shows the peak value of the flow density (the first The graph shows the ratio of the peak value of the ion IIT flow density (indicated by P2 in FIG. 1) in the high magnetic field microwave absorption mode according to the present invention for argon gas and nitrogen trifluoride. As can be seen from Figure 5, the ion current density in this mode is not only higher than the ion N'lJ = density when using ECR conditions at all vacuum degrees, but also on the high vacuum side. So, in this mode, the ECR is better.
It is larger than the ion current density when using the conditions, and is twice as high at lXl0-'Torr. The invention set forth in claim 1 is particularly intended to effectively utilize this portion. In addition, under pressure of 5X10-3 Torr or more,
Although the ratio between the peak value of the ion current density in this mode and the peak under ECR conditions changes rapidly, and the peak value under ECR conditions decreases, the 'ti1 degree in this mode is maintained high. This means that the plasma processing method using this mode can generate high-density plasma even at a higher pressure than the plasma processing method using ECR conditions. The invention recited in claim 2 is intended to effectively utilize this portion. The ion current density in this mode at lXl0-'Torr was 110 ^/cii. [Examples] Examples of the present invention will be described below. FIG. 6 is a diagram schematically showing a dry etching apparatus used in the invention according to claim 1, and the etching method according to the invention according to claim 1 was tested using this apparatus. 6th
In the figure, reference numeral 3 denotes a vacuum container whose interior can be evacuated through an evacuation port 9, and a sample substrate 5 is placed inside the vacuum container 3. Further, the vacuum vessel 3 has a gas introduction port 8, and gas to be turned into plasma is introduced from the boat 8. Further, a microwave irradiation window 12 made of quartz is fitted into the vacuum container 3, and a circular polarizer 21 and a circular waveguide 22 are connected in this order to the microwave irradiation window 12. It is connected. Further, a multipolar permanent magnet 13 and a magnetic field coil 1 are provided on the outer periphery of the vacuum container 3, and a mirror magnetic field coil 19 is provided on the outer periphery of the vacuum container 3 behind the sample substrate 5. . Microwaves generated by a 2.45 GHz microwave power source (not shown) are guided to the circular waveguide 22 through a rectangular waveguide and a rectangular circular tapered waveguide (also not shown), and are further guided to a circular polarizer 21 and a microwave. Wave irradiation window 12
high magnetic field microwave absorption mode by irradiating the gas introduced from the gas introduction port 8 into the vacuum container 3 through the 300° C., and adding a magnetic field formed by the magnetic field coil 1, multipolar permanent magnet 13, and mirror magnetic field coil 19. The gas is turned into plasma, and the sample substrate 5 is irradiated with various particles. Taking the dimensions of the apparatus shown in FIG. 6 as an example, the distance from the microwave irradiation window 12 to the sample substrate 5 is 330 mm.
1, which is about twice the wavelength of the microwave to be introduced, and the position of the sample substrate 5 is as close as possible to the lower end of the magnetic field coil 1 (!=45, in the figure), and the exhaust is exhausted from the lower end of the magnetic field coil 1. This reduces the effects of the magnetic field generated on the sides and the divergence of the ridges. By controlling the current values flowing through the magnetic field coil 1 and the mirror magnetic field coil 19 provided on the outer periphery of the vacuum container 3, the state of the magnetic field can be varied in various ways. The multipolar permanent magnets 13 with alternating magnetic poles assist in confining plasma, and may or may not be multipolar permanent magnets with the same magnetic poles. Also,
The mirror magnetic field coil 19 controls the state of the magnetic field, and the invention described in claim 1 can be carried out without it. Although not shown in FIG. 6, as explained in the prior art section, connecting a high frequency power source or a DC bias power source increases the anisotropy of etching.
Needless to say, processing speed can be improved. The effects of the invention according to claim 1 when the etching apparatus shown in FIG. 6 is used will be explained with reference to FIG. 7 and FIG. 1. Figure 7 shows the etching of a silicon (Si) substrate using nitrogen trifluoride (NFS) as the etching gas and a pressure of 5xl.
At low pressure of O-5 Torr, microwave power is 100-
3 is a graph showing the magnetic field strength vs. etching rate characteristics when . Multipolar permanent magnets with alternating magnetic poles are installed, and mirror magnetic field coils are not used. In addition, FIG. 1 is a graph showing the magnetic field strength-saturated ion current density characteristics obtained by probe measurement when a sufficiently large C bias of -100 V is applied as the probe voltage in the state shown in FIG. 7.
Field strength is the value of the maximum magnetic field strength that exists in the vacuum container. The shape of the magnetic field at this time was confirmed by actual measurement with a Gauss meter, and was found to be approximately at the center position P of the magnetic field coil 1, (specifically, at the center of the diameter φ (=96s+m) of the vacuum vessel 3, in the longitudinal direction. 7011I! from the microwave irradiation window 12 in the direction of the sample substrate 5, the distance from the sample substrate 5 is 2
601], and the magnetic field strength is approximately 1/2 of the maximum magnetic field strength at the sample position. FIG. 8 shows the magnetic field strength at each point of the apparatus at a maximum magnetic field strength of 2200 Gauss. As shown in Figure 8,
ECR point Q (875 Gauss) is sample substrate 5
It can be seen that the plasma processing method according to the present invention, which is located closer to the exhaust side, is caused by a completely different phenomenon from the plasma processing using conventional ECR. As shown in Figure 7, as the magnetic field strength increases, the etching rate first reaches a maximum magnetic field strength of 1400 Gauss.
When the magnetic field strength is further increased, the etching rate temporarily decreases, but then rises sharply and reaches the maximum value again at a maximum magnetic field strength of about 2200 Gauss.The characteristics of this etching rate are as follows: It corresponds well to the density, and is thought to be a change in etching rate due to an increase in ion density. Further, up to the first maximum point, the etching rate increases as the ECR point approaches the sample position, and can be regarded as etching due to ECR. On the other hand, at the second maximum point, as shown in FIG. 8, there is no ECR condition from the microwave irradiation window 12 to the sample position 5, and etching is performed in the high magnetic field microwave absorption mode according to the present invention. As shown in Figure 7, the etching rate due to this high magnetic field microwave absorption mode is 1000 people/win at the maximum point, which is twice as large as the value at the maximum point under ECR conditions (approximately 500 people/sin). , the effect of improving the processing efficiency of the plasma processing method of the present invention can be seen. Also, PI?, which indicates the plasma amount of fluorine? . 1. When the emission intensity was measured at the second maximum point, the value of the high-field microwave absorption mode at the second maximum point was equal to the ECR of the first maximum point.
It can be seen that the high-field microwave absorption mode generates fewer radicals than ECR and has a higher ion density, which makes it a highly anisotropic etching. Etched shape S E M (Sc
anning Electron Microscope
) Observations show that the shape in high magnetic field microwave absorption mode is
It was confirmed that the verticality was extremely good. Furthermore, when an enching experiment was conducted under the same conditions using a microwave power of 600-, it was confirmed that the same tendency as at 100- was observed, and that the same maximum point was found. In this case, etching using the high magnetic field microwave absorption mode showed an extremely high etching rate of 1500 people/tone 1n. The above etching rate is the accelerating voltage due to the divergent magnetic field■
The effect of L is also considered, but since it takes a maximum value, it is considered to be essentially due to the high magnetic field microwave absorption mode, and the magnetic field shape can be either a divergent type or a uniform magnetic field type using a mirror magnetic field coil. Furthermore, since the ion density has increased, the etching rate can be further increased by applying a bias voltage to the sample. In addition, the conditions for forming the high magnetic field microwave absorption mode are:
It varies depending on the type of process gas, the shape of the magnetic field, and
Gas pressure changes. In the case of nitrogen trifluoride (NFs), which is commonly used for dry etching, 1xlO-'Tor
It becomes noticeable from around r, and the results at 5xlO-'Torr are as already explained. Next, the improvement in etching anisotropy when the invention according to claim 1 is used will be explained using FIG. 11. 11th
Figure a is an SEM photograph of an etched cross section when etching is performed using the invention as claimed in claim 1, and Figure 11 is a photograph when etching is performed using the conventional method. This is a photograph of an etched cross section observed with an SEM. As can be seen by comparing FIGS. 11a and 11b, the etching anisotropy of the invention described in claim 1 is good, almost perfect vertical etching can be performed, and high anisotropy under low pressure is achieved. High-speed etching has been achieved. The etching method and apparatus described above can be applied to other plasma processing methods and apparatuses in which plasma irradiation under low pressure is effective. Needless to say, if a rare gas of 1 is used, it can be applied to a sputtering device. 9 and 10 are schematic configuration diagrams of a sputtering apparatus to which the invention according to claim 1 is applied. In FIG. 9 and FIG. 10, the parts numbered the same as 6r;jJ are substantially the same, so the explanation will be omitted. 9th
The figure shows an example in which a target 23 is placed in the drawer part of the vacuum container 3, an RF bias is applied to the target nod 23 by the high frequency power source 7, and discharge in the high magnetic field microwave absorption mode is utilized under low pressure. The figure shows an example in which a discharge section is covered with a ring-shaped target 23, an RF bias is applied to the target 23, and discharge in a high magnetic field microwave absorption mode under low pressure is utilized. In either device, particles such as ions are collided with the target material 23 from plasma generated at high density, and the components of the target material 23 are scattered into the vacuum container 3 by the collision energy, and these components are also transferred to the vacuum container 3. A thin film is formed on the surface of the sample substrate 5 by adhering it to the sample substrate 5 placed in the sample substrate 3 . In addition, under low pressure of 5X10-3 or less, as mentioned above, in the case of CVD, reaction by-products in the surface rate-controlled reaction are easily removed, and by-products, that is, impurities, are removed in the formed CVDP film. Contamination can be reduced. Furthermore, in the case of sputtering, it is possible to reduce the mixing of an inert gas such as Ar used in sputtering into a sputtered film that requires purity, and it is possible to form a film with a small amount of impurities. Although the apparatus used for CVD is not shown in the drawings, it goes without saying that the present invention can also be used for CVD. Next, the invention according to claim 2 will be explained in detail. 15th
Right-polarized microwaves are selectively introduced into a device separated into a sample chamber and a plasma generation chamber as shown in the figure, and a magnetic field higher than the electron cyclotron resonance conditions is created to generate silicon nitride (Si3N, ) film and silicon oxide (Si(h) film) were measured.The conditions and results of this experiment are shown below.N2 gas was supplied to the plasma generation chamber at a rate of 30cc/in. 5IHa gas was introduced into the sample chamber at a rate of 20cc/sin, and the inside of the container was heated to 8X10-'Tor.
CVD treatment was carried out by introducing microwaves at a pressure of R and a power of 200 W. At this time, the film formation rate was 1
The efficiency was approximately 2.5 times higher than that of 530 people/min when conventional ECR conditions were used. 1 ship ■1 Introduce 02 gas into the plasma generation chamber at a rate of 30cc/sin, introduce 5i) I4 gas into the sample chamber at a rate of 20cc/sin, and set the inside of the container to 8X10-3 Tor.
The CVD process was carried out by setting the pressure to r and introducing microwaves with a power of 200 W. At this time, the film formation rate was 2
000 people/gin, and considering that the film formation rate when using conventional ECR conditions is about 1000 people/win, the efficiency was about twice as high. On the other hand, under high pressures of 5X10-' or more, as mentioned above, in the case of CVD, the mean free path of electrons becomes short, and at the Larvor radius of electrons under ECR conditions, electrons can absorb enough μ-wave energy. Since the electrons collide with neutrons before performing the electron cyclotron movement necessary for absorption, sufficient dark energy cannot be obtained for filling and the plasma density cannot be increased. However, in the high magnetic field microwave absorption mode of this example, Since the Lars+or radius is smaller than under the ECR condition and the electron cyclotron motion is performed for a longer time than under the ECR condition, electrons can absorb sufficient energy for ionization from the μ-waves, and the plasma density can be improved. Therefore, the density of radicals and excited active species also increases, and the deposition rate improves. Furthermore, in the case of sputtering, the plasma density can be improved by a mechanism similar to that of CVD, and the ion density can be increased, thereby improving the sputtering film formation rate. The above has described the case of forming silicon nitride <5rsya> II and silicon oxide (Sing) films, but the type of gas is not limited to this, and the apparatus other than the one shown in FIG. It goes without saying that a CVD device may also be used. Moreover, it goes without saying that the invention described in claim 2 can also be applied to a spun ring.

【Effect of the invention】

As detailed above, the plasma processing method according to the present invention uses the "high magnetic field microwave absorption mode" to reduce the electron temperature T and increase the ionization cross section σ8 under low pressure, and the effect of increasing the ionization cross section σ8 and clockwise circular polarization. By expanding the absorption of microwave energy over the entire space from the microwave introduction window to the sample position and increasing the absolute amount of electrons and ions, or by improving the dominant effect. , it is possible to increase the ionization rate and plasma density under low pressure compared to the conventional method using ECR conditions. Furthermore, ionization can be maintained at a high level even in low vacuum conditions, and the plasma density can be improved in this area as well compared to the conventional method using ECR conditions.

[Brief explanation of the drawing]

Figure 1 is a graph showing the dependence of saturated ion current density on magnetic field strength, Figure 2 is a conceptual diagram explaining the principle of ECR using linearly polarized microwaves, and Figure 2a shows the movement of electrons. Conceptual diagram, Figure 2 is a graph showing changes in electric field over time, Figure 3 is ECR using clockwise circularly polarized microwaves.
Fig. 3a is a conceptual diagram showing the movement of electrons, Fig. 3 is a graph showing changes in electric field over time, and Fig. 4 is a graph showing the relationship between electron temperature and ionization cross section. A graph showing the relationship, FIG. 5 is a graph showing the ratio of ion current density when using ECR conditions with respect to pressure and ion current density when using the high magnetic field microwave absorption mode according to the present invention, and FIG. FIG. 7 is a graph showing the dependence of etching rate on magnetic field strength; FIG. 8 is a schematic diagram showing the shape of the magnetic field in the present invention. 9 and 10 are block diagrams schematically showing an embodiment in which the present invention is applied to a sputtering apparatus, and FIG. 11 is a metal structure photograph taken by SEM showing the effect of the invention according to claim 1, 11a is a photograph of the metal structure of the substrate surface when the invention according to claim 1 is applied, FIG. 11 is a photograph of the metal structure of the substrate surface when the conventional method is applied, and FIGS. 12 to 14 are photographs of the metal structure of the substrate surface when the conventional method is applied. Fig. 15 is a block diagram schematically showing a plasma processing apparatus using conventional ECR conditions, Fig. 15 is a block diagram schematically showing a CVD apparatus using conventional ECR conditions, and Fig. 16 explains the pressure dependence of etching shape. FIG. 17 is a graph showing the pressure dependence of plasma density and electron temperature, and the pressure dependence of electron temperature. 1-Magnetic field coil, 3-Vacuum vessel, 5-Sample substrate, 8-Gas introduction boat, 9-Evacuation boat, 2-Microwave irradiation core, 1-Circular polarizer, 2-Circular waveguide, 3- Target material.

Claims (2)

[Claims] (1) Gas and microwaves are introduced into a vacuum container to which a magnetic field is applied, and the introduced gas is turned into plasma by generating a discharge in the vacuum container, and ions, excited active species, radicals, etc. in the plasma are generated. etching by irradiating the sample substrate with
In plasma processing methods such as sputtering and CVD, the pressure of the gas is set to 5 x 10^-^3 Torr.
Right-polarized microwaves whose electric field direction is clockwise with respect to the traveling direction are selectively introduced into the vacuum container, and a magnetic field higher than the electron cyclotron resonance condition is formed in the vacuum container. A plasma processing method using plasma generated in the vacuum container using a high magnetic field microwave absorption mode in which the gas absorbs microwaves in a magnetic field region. (2) A plasma processing method in which a gas and microwave are introduced into a vacuum container to which a magnetic field is applied, and a discharge is generated in the vacuum container to turn the introduced gas into plasma, thereby performing CVD or sputtering. The gas pressure is reduced to 5 x 10^-^3 Torr or more, and right-polarized microwaves whose electric field direction is clockwise with respect to the traveling direction are selectively introduced into the vacuum vessel, and CVD or sputtering is performed using plasma generated in the vacuum container using a high magnetic field microwave absorption mode in which a magnetic field higher than electron cyclotron resonance conditions is formed and microwaves are absorbed by the gas in the high magnetic field region. The plasma treatment method used.