JP3386287B2 - Plasma etching equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma etching apparatus, and more particularly to a plasma etching apparatus capable of selectively etching silicon oxide.

[0002]

2. Description of the Related Art With the high integration of semiconductor devices, it has become essential to perform fine processing by dry etching. In particular, the step of etching the silicon oxide film, which is an insulating film, tends to increase with the high integration of semiconductors.
When etching a silicon oxide film, the base is often single crystal silicon or polycrystalline silicon,
At this time, it is necessary to etch only the oxide film without removing the underlying silicon. That is, selective etching is required.

The mechanism that enables selective etching will be described by taking the selective etching of SiO ₂ with respect to the underlying Si as an example. The gas used for etching is C
It is a highly reactive gas such as F ₄ , plasma is formed by this gas, and etching is performed by reacting radicals and ions generated in the plasma with SiO ₂ . In this case, the deposition of the polymerized film by CF ₄ is actually
Simultaneously occurring as a competition phenomenon for etching.

Since oxygen is present in the SiO ₂ layer, the oxygen dissociates during etching and combines with the polymer film to form volatile CO, CO ₂ , COF ₂ molecules. Therefore, in the case of etching the SiO ₂ layer, the deposition of the polymer film does not occur. However, when the etching reaches the Si layer, since oxygen does not exist in the Si layer, the above-described suppression of the polymer film deposition is not suppressed, and the polymer film is deposited. At this time, if the concentration of fluorine in the deposited polymer film is reduced and the high carbon film is deposited, fluorine is prevented from diffusing in the polymer film and etching Si,
A highly selective etching of SiO ₂ / Si is achieved.

[0005]

However, in the above-described selective etching of silicon oxide, it is generally difficult to set the optimum conditions for obtaining high selectivity. For example, simply setting general conditions such as the density of input energy such as high frequency for plasma formation, the flow rate of gas forming plasma, and the atmospheric pressure of the plasma space achieves high selective etching of silicon oxide. It was difficult to do. In particular, recently, it has become necessary to selectively etch a pattern such as a contact hole having a high aspect ratio, and it is necessary to etch silicon oxide at the bottom of a deep groove without removing the underlying material such as silicon. . Even if the optimum etching conditions are set, the conditions in the reaction vessel may change during the etching process or when the etching process is repeated, and as a result, the required selectivity may not be obtained. .

The invention of the present application has been made in view of the above problems, and provides an apparatus in which the optimum conditions for selective etching of silicon oxide are set so that high selectivity can always be obtained. Is intended.

[0007]

In order to achieve the above object, the plasma etching apparatus according to claim 1 of the present application is
A reaction vessel having an exhaust system, a gas introducing means for introducing a fluorocarbon-based gas into the reaction vessel, and a plasma generating means for generating plasma in the reaction vessel by the introduced gas, In a plasma etching apparatus for etching a silicon oxide film by plasma of a carbon-based gas, a measuring means for measuring the ratio of the number density of carbon monofluoride radicals and carbon difluoride radicals generated in the plasma, and this measurement. And a control unit that controls the etching conditions based on the measurement result of the means. Similarly, to achieve the above object, in the plasma etching apparatus according to claim 2, in the structure of claim 1, the reaction vessel is provided with a pressure adjuster for adjusting the pressure in the reaction vessel, and the control unit includes: It is configured to send a signal to the pressure regulator so as to maximize the ratio of the number density of carbon monofluoride radicals to the carbon difluoride radicals.
Similarly, in order to achieve the above object, in the plasma etching apparatus according to claim 3, in the structure according to claim 1 or 2, the gas introducing means includes a flow rate adjuster for adjusting the flow rate of the gas to be introduced, and the control unit. Has a configuration in which a signal is sent to the flow rate controller so that the ratio of the number density of carbon monofluoride radicals to the carbon difluoride radicals is maximized. Similarly, in order to achieve the above object, the plasma etching apparatus according to claim 4 is the structure of claim 1, 2, or 3, wherein hydrogen gas or a fluorocarbon compound gas containing hydrogen element is added to the fluorocarbon gas. Are mixed. Similarly, in order to achieve the above-mentioned object, the plasma etching apparatus according to claim 5 is the structure of claim 1, 2, 3 or 4, wherein the gas introducing means adjusts the mixing ratio of the gases to be introduced. The control unit has means for controlling the mixing ratio adjusting means so that the ratio of the number density of carbon monofluoride radicals to the carbon difluoride radicals is maximized. Similarly, in order to achieve the above-mentioned object, claim 6
The plasma etching apparatus according to claim 1, 2, 3,
In the configuration 4 or 5, the measuring means is a mass spectrometer that measures the type and amount of the gas existing in the reaction container by mass spectrometry. Further, similarly, in order to achieve the above-mentioned object, the plasma etching apparatus according to the seventh aspect has the configuration according to the sixth aspect, in which the mass spectrometer is a quadrupole mass spectrometer. Further, similarly, in order to achieve the above object, the plasma etching apparatus according to the eighth aspect has the configuration according to the seventh aspect, in which the quadrupole mass spectrometer includes an ionization energy adjusting mechanism.

[0008]

In the plasma etching apparatus of the above claims, plasma is formed by the fluorocarbon gas.
The silicon oxide is etched by the radicals generated by this plasma. At this time, the ratio of the number density of carbon monofluoride radicals and carbon difluoride radicals generated in plasma is measured, and the etching conditions are controlled based on the measurement result. Further, in particular, in the plasma etching apparatus according to claim 4 or 5, in addition to the above-mentioned action,
Fluorine is trapped by hydrogen radicals, which aids in selective etching of silicon oxide.

[0009]

EXAMPLES Examples of the present invention will be described below. Figure 1
2 is a schematic side view illustrating the configuration of a plasma etching apparatus according to an embodiment of the present invention, and FIG. 2 is a schematic cross-sectional view of a reaction vessel portion of the plasma etching apparatus of FIG.

The plasma etching apparatus shown in FIG. 1 has a reaction vessel 1 equipped with an exhaust system 13, gas introduction means 2 for introducing a fluorocarbon type gas into the reaction vessel 1, and plasma introduced by the introduced gas. A plasma generating means 3 generated in the reaction container 1, a stage 4 for arranging the substrate 10 at a position to be etched by the plasma of the fluorocarbon-based gas generated by the plasma generating means 3, and a stage 4 generated in the plasma A measuring unit 5 for measuring the ratio of the number density (hereinafter simply referred to as density) of the fluorocarbon radical and the carbon difluoride radical, and a control unit 6 for controlling the etching conditions based on the measurement result of the measuring unit 5. It is mainly composed of.

The embodiment shown in FIG. 1 is an embodiment in which the present invention is applied to a helicon wave plasma etching apparatus. The reaction container 1 is composed of a source chamber 11 and a diffusion chamber 12, and the source chamber 11 is placed on the diffusion chamber 12 and arranged.

The source chamber 11 is a cylindrical member having a hemispherical tip, and is made of a material capable of efficiently transmitting high frequencies, specifically, quartz glass. The size and shape of the source chamber 11 differ depending on the configuration of the plasma generating means 3, the size of the substrate 10, batch processing or single-wafer processing. For example, when processing a wafer having a diameter of 6 inches, the inside diameter is 160 mm and the height is 100 m.
A source chamber 11 having a dimension and shape in which a hemispherical portion having a radius of about 50 mm is provided at the tip of a cylindrical portion of about m is adopted. Further, the thickness of the quartz glass is, for example, about 3 mm. As a material other than quartz glass, for example, alumina or the like can be used.

The diffusion chamber 12 has a cylindrical box shape with its upper and lower sides closed and is made of aluminum. The diffusion chamber 12 has a circular opening 121 on the upper surface, and the diffusion chamber 12 is fitted into the opening 121 and has the circular shape.
Are arranged. Similar to the source chamber 11, the size of the diffusion chamber 12 varies depending on the size of the substrate 10 and the like. Similarly, when processing a wafer having a diameter of 6 inches, the height is 200 mm and the inner diameter of the cross section is about 350 mm. Is.

On the outer surface of the diffusion chamber 12 as described above, a rod-shaped permanent magnet 14 elongated in the height direction of the diffusion chamber 12 is provided. As shown in FIG. 2, the permanent magnets 14 are diagonally arranged along the outer surface of the diffusion chamber 12. And each permanent magnet 1 facing each other
The inner surface of 4 has the same polarity, and the inner surface of each adjacent permanent magnet 14 has a different polarity. By arranging the permanent magnets 14 in this way, a cusp magnetic field as shown in FIG. 2 is formed along the inner surface of the side wall of the diffusion chamber 12. This cusp magnetic field suppresses the electrons flying from the central plasma region from reaching the inner surface of the side wall, and as a result, acts to prevent the diffusion of the plasma to the side wall portion and obtains a uniform plasma over a wide region. Contribute to.

As shown in FIG. 1, the diffusion chamber 12
On the side wall of the exhaust system 12, an exhaust opening 12 for connecting an exhaust pipe 130 of an exhaust system 13 and a main pipe 20 for introducing gas of a gas introducing means 2 are provided.
A gas introduction opening 123 for connecting the substrate 10, a measurement opening 124 for connecting the measuring means 5 and the like are formed, and the gate valve 15 is provided in the opening for taking in and out the substrate 10.
Is provided.

Exhaust system 13 provided in the reaction vessel 1
Is provided on the exhaust path by the exhaust pump 131 such as an oil rotary pump for rough evacuation or a turbo molecular pump for main exhaust, an exhaust pipe 130 connecting the exhaust pump 131 and the reaction vessel 1, and the exhaust pipe 130. It is composed of a variable orifice 132 or the like as a pressure regulator. With such an exhaust system 13, the inside of the reaction vessel 1 is, for example, 1 × 10 5.
It is possible to exhaust up to the ultimate pressure of about ^-5 Torr. A vacuum gauge (not shown) for measuring the pressure inside the reaction vessel 1 is provided, and the measurement signal thereof is sent to the control unit 6 described later. The variable orifice 132 as a pressure adjuster adjusts the exhaust speed by changing the size of the opening.

The gas introduction means 2 comprises a plurality of gas introduction systems 21, 2 so that at least two kinds of gases can be mixed and introduced.
It consists of two. Each gas introduction system 21,22
Is a gas cylinder 21 (not shown) containing the gas to be introduced.
1, 221, gas introduction pipes 212, 222 for connecting the gas cylinders 211, 221 to the inside of the reaction vessel 1, and mass flow controllers 213, 223 as flow rate adjusters provided on the gas introduction pipes 212, 222. It is composed of a filter and the like not shown. Specifically, one of these gas introduction systems 21 and 22 is a gas introduction system 21 of carbon tetrafluoride gas, and the other is a gas introduction system 22 of hydrogen gas. In addition, each gas introduction system 2
Mass flow controllers 213 provided in
223 is configured to be independently controlled by a signal from the control unit 6 described later. Therefore, the mixing ratio of the mixed gas introduced by the gas introducing means 2 can be adjusted. That is, the mass flow controllers 213, 2
Reference numeral 23 corresponds to the mixing ratio adjusting means in claim 5.

As described above, the apparatus of this embodiment uses the helicon wave plasma, and the plasma generating means 3
As the above, a device that introduces a predetermined helicon wave is adopted. That is, the plasma generating means 3 includes a coil-shaped antenna 31 wound around the source chamber 11, a source plasma generating high frequency power source 32 for generating high frequency power supplied to the antenna 31, and a source plasma generating high frequency power source 32. A matching box 33 provided on a high frequency supply path from the antenna, and a solenoid coil 34 wound around the antenna 31 to generate a source magnetic field.
It is mainly composed of and.

The helicon wave plasma utilizes the fact that an electromagnetic wave having a frequency lower than the plasma frequency propagates in the plasma without being attenuated when a strong magnetic field is applied, and has recently been developed as a technique capable of forming a high density plasma at a low pressure. It has been receiving attention. When the propagation direction of the electromagnetic wave in the plasma and the direction of the magnetic field are parallel, the electromagnetic wave becomes circularly polarized light in a certain fixed direction and travels in a spiral shape. For this reason, it is called helicon wave plasma. However, the actual propagation shape of the electromagnetic wave depends on the conditions of the plasma space, and in the gas discharge plasma in the source chamber 11 as shown in FIG. 1, an electric field of only a certain mode determined by the shape dimension of the source chamber 11 and the like is generated. It is formed. In the configuration shown in FIG. 1, the high frequency power sources 32 to 100 for generating source plasma are used.
A high frequency of about 0 W is applied through the antenna 31, and a direct current magnetic field is applied by the solenoid coil 34 in parallel with the propagation direction of the high frequency. The strength of the magnetic field is about 100 gauss near the center of the source chamber 11. With such a configuration, 10 mTorr
A high-density plasma of about 1 × 10 ¹² cm ⁻³ is formed at a pressure of about 1 × 10 ¹² cm ⁻³ .

The stage 4 is arranged in the diffusion chamber 12, and is arranged from the lower end of the source chamber 11 to the stage 4.
Is about 150 mm, for example. The stage 4 is made of a metal such as aluminum, and a high frequency bias power source 41 is connected thereto via a matching box 42. The high frequency applied to the stage 4 by the bias high frequency power supply 41 is 50 at 13.56 MHz, for example.
It is about 0W. The substrate 10 placed on the stage 4 receives the high frequency and the plasma generating means 3 thus applied.
A self-bias voltage of about 100 V is applied due to the interaction with the plasma formed by. This self-bias voltage forms an electric field with the plasma (≈0 V) and enables anisotropic etching by extracting the ions in the plasma by the electric field. This self-bias voltage also enables the substrate 10 to be electrostatically attracted to the stage 4 by covering the surface of the stage 4 with a predetermined dielectric. In this embodiment, since the single-wafer type device is taken up, only one substrate is placed on the stage 4. However, in the batch type device, a plurality of substrates are arranged on a predetermined susceptor. The stage 4
Try to place it above. A water cooling mechanism or the like is attached to the stage 4 as needed.

As shown in FIG. 1, the measuring means 5 is provided on the side of the reaction vessel 1. The measuring opening 124 provided on the side wall of the diffusion chamber 12 is provided with a short tubular flange 125 extending outward, and the measuring means 5 is attached to the flange 125.

As the measuring means 5, in this embodiment, a quadrupole mass spectrometer (Quadrupole Mass Sp) is used.
50, which is abbreviated as "electrometer" (hereinafter abbreviated as QMS). QMS was developed to analyze the residual gas in the measurement space, and it was ionized between four cylindrical electrodes (hereinafter, quadrupole electrodes) 51 arranged in parallel on the diagonal. The measurement is performed by passing only the particles of In front of the quadrupole electrode 51, an ionization unit 500 described later for ionizing particles to be measured is arranged. The particles incident on the QMS 50 are ionized by the ionization section 500, and then enter the passage surrounded by the quadrupole electrode 51. Then, only predetermined ionized particles can pass between the quadrupole electrodes 51 . A detection element 501 such as a secondary electron multiplier is arranged at a position where the ionization particles have passed through the quadrupole electrode 51. The ionized particles that have passed through are detected by the detection element and the amount of the ionized particles is measured. Ionized particles that can pass through the portion of the quadrupole electrode 51 have a predetermined M / e (M is a mass,
Only e has an electric charge amount, and the ionized particles to be passed can be selected by controlling the magnitude of the hyperbolic electric field. As such a QMS 50, for example, model 360 of quadrupole mass spectrometer manufactured by Nichiden Anelva Co., Ltd. can be adopted.

Such a QMS 50 is equipped with an ionization energy adjusting mechanism. FIG. 3 shows the QMS50 of FIG.
It is an explanatory view of the ionization energy adjustment mechanism in,
3 shows an outline of the configuration of an ionization section 500 in QMS. The ionization unit 500 shown in FIG. 1 is arranged in front of the incident position on the quadrupole electrode 51, and has a filament 52 that emits electrons for ionizing the measurement particles and an electron that is emitted from the filament 52. It is mainly composed of an electron acceleration electrode 53 for accelerating the laser beam and an ion acceleration electrode 54 for accelerating and entering the ionized particles into the space surrounded by the quadrupole electrode 51 .

The filament 52 emits thermoelectrons, is made of a material such as tungsten, and is connected to a power supply 521 for energizing the filament. Electron acceleration electrode 53
Is a cylindrical cage-shaped electrode body 531 arranged coaxially with the central axis of the space surrounded by the quadrupole electrode 51 (hereinafter, simply referred to as the central axis), and a circular tubular electrode support holding the electrode body 531. And a plate 532. Electrode support plate 532
An ionization energy adjusting power source 533 is connected to the. The ion acceleration electrode 54 is an annular member similar to the electrode support plate 532 of the electron acceleration electrode 53, and is arranged coaxially with the central axis. An ion acceleration power source 541 is connected to the ion acceleration electrode 54. The ion accelerating power supply 541 supplies a negative DC potential to the ion accelerating power supply, and an electric field is formed between the ion accelerating power supply 541 and the electrode support plate 531 of the electron accelerating electrode 53 to which a positive DC potential is applied.
Ions are accelerated by this electric field. A slit electrode 55 is also coaxially arranged between the ion acceleration electrode 54 and the quadrupole electrode 51. The slit electrode 55 is grounded.

In the ionization section 500 having the above structure, the electrons emitted from the filament 52 are electron accelerating electrodes 53.
Is accelerated by and flies toward the central axis. When the measurement particles incident on the QMS reach the inside of the cylindrical cage-shaped electrode body 531 of the electron acceleration electrode 53, they are ionized by the electrons. The ionized measurement particles are accelerated by the electric field generated by the ion accelerating electrode 54 to generate the quadrupole electrode 51.
Reaches the space surrounded by. Then, as described above, only predetermined ionized particles pass through the quadrupole electrode 51 and are detected. In the above configuration, when adjusting the ionization energy, the output voltage of the ionization energy adjusting power supply 533 connected to the electron acceleration electrode 53 is adjusted. As a result, the acceleration energy of the electrons is adjusted, and it becomes possible to perform measurement by selecting only predetermined radicals as described later.

The QMS 5 which constitutes such measuring means 5
0 is provided with the sampling orifice 56, the unnecessary charged particle removing mechanism, the QMS exhaust system 57, and the like.
The sampling orifice 56 and the QMS exhaust system 57 are
It is provided to keep the pressure in the QMS 50 low. The pressure in the QMS 50 needs to be maintained at about 10 ⁻⁶ Torr or less, and when the pressure in the diffusion chamber 12 is higher than this, it is necessary to differentially exhaust the inside of the QMS 50. The sampling orifice 56 is arranged on the end face of the flange 125 described above, and the size of the orifice opening is about 0.5 mm. The measurement particles are adapted to enter the QMS 50 through this orifice opening. The distance from the side wall of the diffusion chamber 12 to the sampling orifice 56 is about 6 cm. The QMS exhaust system 57 provided in the QMS 50 is equipped with an oil rotary pump for rough evacuation, a turbo molecular pump for main exhaust, and the like, and is configured to exhaust up to an ultimate pressure of about 4 × 10 ⁻⁸ Torr. .

Sampling orifice 5 using FIG.
6 and the unnecessary charged particle removing mechanism 58 will be described in more detail. FIG. 4 is a schematic cross-sectional view illustrating details of the sampling orifice and the unnecessary charged particle removing mechanism adopted in the apparatus of FIG. The sampling orifice 56 is
As shown in FIG. 3, it is composed of an orifice 561 plate attached to the end surface of the flange 125, and an auxiliary orifice sheet 562 provided on the outer surface of the orifice plate 561 in order to further reduce the opening of the orifice plate 561. . The orifice hole of the auxiliary orifice sheet 562 has a diameter of about 0.5 mm as described above.

On the other hand, the unnecessary charged particle removing mechanism 58 is provided outside the sampling orifice 56.
The unnecessary charged particle removing mechanism 58 includes a pair of metal meshes 581 and 582 arranged in front and back so as to be perpendicular to the extraction direction of the measurement particles, and a positive direct current that gives a predetermined positive potential to the one metal mesh 581. It is composed of a power source 583 and a negative DC power source 584 that applies a predetermined negative potential to the other metal mesh 582. Positive DC power supply 58
The potentials given by the 3 and the negative DC power source 584 are, for example, + 30V and -30V, respectively. The distance between the pair of metal meshes 581 and 582 is set to about 1 mm, and the distance from the sampling orifice 56 to the front side metal mesh 581 is set to about 2 mm. Each metal mesh 581, 582 has an opening of about 200 μm, and stainless steel is used as the material. Electrons and ions formed in the plasma are prevented from being pushed back by the portions of the pair of metal meshes 581 and 582 to which the positive and negative potentials are applied as described above and unnecessarily entering the QMS.

The apparatus of this embodiment is characterized in that the measuring means 5 measures the density ratio of carbon monofluoride radicals and carbon difluoride radicals (hereinafter, CF ₁ / CF ₂ radical density ratio). It is one. Such a configuration is closely related to the object of the present invention of "setting optimum conditions for selective etching of silicon oxide". In a recently published paper, by optimizing the total gas flow to be able to maximize etch selectivity of SiO ₂ / Si is reported (Jpn. J. Appl. Phys. Vo
l.33 (1994) pp.2139-2144). However, in this experiment, under the condition of the total gas flow rate that maximizes the selectivity, S
During the etching of the iO ₂ layer, a polymer film is deposited, and S
It has been reported that the etching of iO ₂ has stopped.

The inventor has considered that the reason for stopping the etching may be that the balance of radicals in the plasma has an influence. In other words, there are several types of radicals generated from carbon fluoride gas in the plasma, but the effects of these radicals on the high carbon polymer film deposition are not uniform, and specific radicals cause high carbon polymer film deposition. I thought that it might play a major role in. It is considered that radicals having a low fluorine content, that is, CF ₁ , CF ₂ , CF _3, etc. are supposed to play a major role in the deposition of the carbon polymer film. Therefore, using the above device, CF in plasma
An experiment was conducted to measure in what balance ₁ , CF ₂ and CF ₃ were produced. As a result of this experiment, CF
It has been found that it is best to measure the density ratio of each of the ₁ , CF ₂ radicals and try to maximize it.

The results of experiments conducted by the inventor will be described below in order to show the effectiveness of this embodiment. The output of the QMS 50 employed in the measuring means 5 is the current due to the ions that have passed through the quadrupole electrode 51. Even if the ratio of the current values is taken as it is, the output of CF ₁ , CF ₂ , CF ₃ I don't know the density. This is because the ionization cross sections of these molecules are different. Ionization cross section means that molecules with number density N exist in a certain space, and a certain particle is 1c in a certain space.
Of the number of collisions with molecules during flight, it is Q / T when the number of ionizations due to collisions is T,
It represents the probability that ionization will occur. The ionization cross section depends on the number density N of molecules, but usually indicates a value at 0 ° C. and 1 Torr.

The output current I of the QMS is a function of the ionization energy (E) and can be expressed as I (E). The ionization cross section σ is also a function of the ionization energy (E) and is σ (E). It is known that there is the following relationship between I (E) and σ (E), and the ion density n. I (E) = α β σ (E) n In the above formula, α and β are proportional constants derived from the structure of the measuring instrument. Of these, α is the sampling orifice 5
It comes from the exhaust conductance of 6, M ^1/2
It is proportional to (M: mass of radical). β is QMS
It depends on the mass-dependent sensitivity factor of and the applied electrotechnical factors. The ionization cross section σ (E) is
Σ reported by Wentzel for CF ₃
A value of _i = 4.93x10 ^-18 cm ² can be used (RCWetzel, FA
Baiocchi and RSFreund: Abstr.37th Gaseous Electr
onics Conf., Boulder Co., (1984)). However, CF ₂
Since the for ionization cross section of CF ₁ not yet known, these values, CF ₃ of CF ₄ reported by value and Ce Ma et al of the CF ₃ is a known value ionization cross section sigma _i Value of dissociation ionization cross section σ _di (σ
_di = 8.84 × 10 ^{-1 / 2} cm ² (25 eV), Ce Ma, M.
R. Bruce and RABonham: Phys. Rev. A44 (1991) 2921)
Estimated from. This means that when E1 ′, E2 ′, and E3 ′ are the ionization critical energies of CF ₁ , CF ₂ , and CF ₃ , respectively, from CF ₂ radicals (or CF ₁ radicals) to CF ₂ ⁺ ions (or CF ₁ ⁺ ions). It is based on the assumption that the ionization cross-section of γ is almost equal to the value obtained by shifting from the ionization critical energy E3 ′ having the same cross-section size to the ionization critical energy E2 ′ (or E1 ′).

Then, according to the following equation, QM
The density of each radical is calculated from the S output. ^{_{[CF 3] = 5.24x10 23 ·}} (Ion (13.0eV) -6.00x10 -11) [cm -3] [CF 2] = 2.34x10 23 · (Ion (13.0eV) -6.80x10 -12) [cm - ³ ] [CF ₁ ] = 3.01x10 ²⁴ · (Ion (13.0eV) -1.40x10 ^-11 ) [cm ^-3 ] In the above formulas, from the QMS output Ion, 6.00x10 ^-11 、
6.80x10 ^-12, 1.40x10 ^{- 11} is the pulling each value of, in order to remove errors caused by ions generated by the electron beam irradiated in the QMS. That is, QMS
There is a current value of the detection for example CF ₃ ions, other current by the CF ₃ radicals of interest generated by the plasma ions, ionized directly from C ₄ F ₈ is the parent molecule by irradiation of the electron beam in the QMS The amount of CF ₃ ions generated is also included. Therefore, if the QMS output is used as it is, CF ₃ that does not actually exist in such a plasma space will be counted. The current value due to CF ₃ ions generated in such a QMS is equal to the QMS output when the discharge is turned off and the plasma is eliminated. Therefore, the value of the QMS output when the discharge is off is subtracted from the QMS output (Ion) when the discharge is on and plasma is formed.

Special attention must be paid to the ionization energy EE of electrons used for measurement. This is because, among the CF ₁ , CF ₂ , and CF ₃ molecules existing in the measurement space, only the radicals of these molecules must be ionized, and the molecules in the ground state can be ionized or the ground state can be ionized. It must be ensured that the molecule in is not excited into radicals. From the rising of the output current of the QMS when the ionization energy is increased, the thresholds of the ionization energy of the radicals of CF ₁ , CF ₂ and CF ₃ are 10.8 eV, 12.5 eV and 11.2 eV, respectively. Is judged. On the other hand, due to the energy of 13.8 eV, C
_A CF ₁ radical is generated from a ₂ F ₄ biradical. Therefore, the usable ionization energy is 1
The energy is larger than 2.5 eV and smaller than 13.8 eV, and the energy of about 13.0 eV is preferably adopted.

5, FIG. 6, FIG. 7, FIG. 9 and FIG. 10 are graphs of the radical densities calculated according to the above calculation from the obtained output current value of the QMS. First, FIG. 5 is a diagram showing the measurement results of the density of each radical with the hydrogen gas concentration in C ₄ F ₈ as a parameter. As can be seen from FIG. 5, the total amount of CF ₁ , CF ₂ , and CF ₃ radicals decreases as the hydrogen concentration increases, that is, as C ₄ F ₈ becomes more diluted. However,
The degree of reduction of CF ₁ appears to be greater than that of CF ₂ . CF ₁ radicals appear to be used in part in the deposition of polymeric films on the inner wall of the container. The CF ₃ radical density is kept at a small value and does not show a remarkable change.

FIG. 6 is a diagram showing the measurement results of the density of each radical of CF ₁ , CF ₂ and CF ₃ when the total pressure is used as a parameter. As can be seen from FIG. 6, CF
_{Both the 1} radical density and the CF ₂ radical density increase as the total pressure increases, that is, the total amount of gas molecules increases. It should be noted in FIG. 6 that the CF ₁ / CF ₂ radical density ratio shows the maximum value in the vicinity of 10 mTorr. Further, FIG. 7 is a diagram showing changes in the density of each radical of CF ₁ , CF ₂ , and CF ₃ when the high frequency power is used as a parameter. As can be seen from FIG. 7, when the high frequency power is increased, only C ₄ F ₈ or 3
In all cases with 0% hydrogen addition, CF ₁ rises sharply, in contrast to the decrease in CF ₂ radicals. It is considered that this increase in CF ₁ resulted from the dissociation of CF ₂ . The CF ₃ radical densities in FIGS. 6 and 7 were low and did not change similarly.

FIG. 8 is an explanatory diagram of an experiment for simulating etching of a deep groove such as a contact hole, and particularly for confirming the effect of hydrogen addition in such etching. Specifically, an experiment was conducted by arranging a thin tube 563 simulating a groove inside the sampling orifice 56 as shown in FIG. As the thin tubes 563, different ones having different lengths of 10 mm to 30 mm were prepared, which corresponded to the change of the aspect ratio of the contact holes and the like, and the experiments were conducted by exchanging these via the load lock system. These thin tubes 5
63 is made of quartz and has an inner diameter of about 1.5 mm.
As shown in FIG. 8, the tip of the thin tube 563 is located in the opening of the orifice plate 561 facing the orifice hole,
A seal material 564 made of silicon rubber is interposed between the tip of the thin tube 563 and the opening of the orifice plate 561.

FIG. 9 shows a thin tube 563 using the apparatus of FIG.
CF ₁ when the aspect ratio of
It is a view showing a measurement result of the density of each radical CF _2, CF _3. In the case of C ₄ F ₈ only, when the length of the narrow tube 563, that is, the aspect ratio, is increased, the CF ₂ radical density hardly shows a sharp drop. On the other hand, the CF ₁ radical density dropped sharply. This means that the activity of CF ₂ radicals is low and does not contribute to the deposition of polymer films, and that CF ₁ radicals are the major precursors for polymer film deposition. However, when 30% of hydrogen is added, the degree of decrease of CF ₁ radicals with respect to the increase of the aspect ratio is slower than that of C ₄ F ₈ alone. At the same time C
The F ₂ radical density has not changed. From this result, it seems that the probability of CF ₁ adhering to the inner surface of the thin tube 563 (corresponding to the inner wall surface of the contact hole) decreases in the presence of hydrogen.

Next, in order to investigate the mechanism of deposition of the polymer film on the Si surface in more detail, an experiment of exposing the silicon substrate to plasma was conducted. The substrate was given a floating potential of -20 eV or a self-bias voltage (Vdc) of -300V. This self-bias voltage is for confirming the effect of the so-called ion bombardment method. This is an effect that positive ions in the plasma collide with the substrate due to the self-bias voltage, and the energy of the collision promotes film deposition. The self-bias voltage is given by the interaction between the high-frequency power provided by the bias high-frequency power source 41 and the plasma. On the other hand, the gas introduced was C ₄ F ₈ only or C ₄ F ₈ + 30% H ₂ .

FIG. 10 shows the result of this experiment. FIG. 10 shows that the surface of the silicon substrate exposed to the plasma formed as described above for 3 minutes was analyzed by X-ray electron spectroscopy (XP).
The result measured by S) is shown. As shown in FIG. 10, in the plasma containing only C ₄ F ₈ , the peaks of CF ₁ , CF ₂ and CF ₃ were observed next to the peak of C—C, and a polymer film formed of these fluorocarbons was formed. I know that In the case of C ₄ F ₈ , the floating potential (-
The peak state does not show a large change between 20 eV) and the self-bias voltage (-300 V). On the other hand, C ₄
According to the plasma of F ₈ + 30% H ₂ , a high peak of C—C is observed, which shows that a high carbon polymer film is formed. In particular, it has been shown that a high carbon polymer film is formed not only when a self-bias voltage is applied but also when it is held at a floating potential. These results indicate that ion bombardment has no particular influence on the formation of the high carbon polymer film, and the gas composition is an important factor.

Next, the high carbon polymer film as described above is
An experiment conducted to confirm whether or not the silicon is also deposited on the bottom surface of a deep groove such as a contact hole will be described. The analysis of the film deposited on the surface is
Similar to the experimental example of FIG. 10, it was performed by XPS. However, it is difficult to detect the bottom surface nondestructively, so a certain simulation experiment was conducted.

In this experiment, a plate-shaped member (hereinafter referred to as a pore plate) provided with pores having a high aspect ratio was placed on a silicon substrate, and then the surface of the silicon substrate masked by this pore plate. Is exposed to plasma for etching, the plate is finally removed, and the surface of the silicon substrate is XPS.
I measured it with. As the pore plate used, a commercially available HAMAMATSU: J5022-11 was used. Similar to the experiment of FIG. 10, the self-bias voltage Vdc was applied to the pore plate on the substrate by the bias high frequency power source 41. However, in high-density plasma such as helicon wave plasma, it is difficult to apply Vdc due to the high sheath capacity due to the short Debye length. 1
High Vdc is applied to the stage 4 to which a high frequency of 00 kHz is applied.
To cover the surface of the stage with a thick polymer film excluding the area where the pore plate is located, thereby reducing the surface area of the stage, thereby reducing the -300
Vdc of V was applied to the pore plate.

FIG. 11 shows the result of the experiment conducted in this way. In FIG. 11, the horizontal axis represents the binding energy of the polymer and the vertical axis represents the photocurrent intensity of XPS. Figure 11
The results of the case where (a) in the middle and the lower side are the gas of only C ₄ F _{8 and} the case where (b) is the gas of C ₄ F ₈ + 30% H ₂ are shown. As can be seen from FIG. 11, in the case of 30% hydrogenation, the high carbon polymer film covered the silicon surface thickly with a slight mixing of fluorine. In the case of C ₄ F ₈ alone, a peak of CFx (x = 1-3) was observed from the polymerized film on the silicon surface, indicating that fluorine was mixed in at a high concentration.

FIG. 12 is a view showing a result of observing a surface state of a silicon substrate, which was tried to be etched by using the pore plate as a mask in the experiment of FIG. 11, by a scanning electron microscope (SEM). Of these, (a) shows the results when a gas containing only C ₄ F ₈ was used, and (b) shows the results when using a gas containing C ₄ F ₈ + 30% H ₂ . 12
(A) and (b) respectively show the deposition of the polymer film on the silicon surface. In the case of (a), it was confirmed that the silicon surface was etched and scraped when the polymer film was removed. It was On the other hand, in the case of (b), when the polymer film was removed, a flat silicon surface appeared, and it was confirmed that etching by the material in the polymer film was not performed. The etching of silicon in the case of (a) is caused because the polymerized film deposited on the silicon surface contains a large amount of fluorine. The formation of a high carbon thin film under the condition of C ₄ F ₈ + 30% H ₂ indicates that hydrogen radicals pass through deep holes and reach the bottom surface.

Finally, an experiment for investigating the degree of influence of the condition of the total gas flow rate on the selective etching of SiO ₂ / Si will be described. FIG. 13 is a diagram showing the results of examining etching conditions using the total gas flow rate as a parameter. Figure 1
3 (a) is S when the total gas flow rate is used as a parameter.
The changes in the etching rate and selectivity of iO ₂ , Si are shown in (b).
Is C when the total gas flow rate is also used as a parameter
Changes in the radical densities of F ₁ , CF ₂ and CF ₃ are represented by (c)
Is C-C when the total gas flow rate is used as a parameter
The XPS photocurrent intensity ratio of / F is shown.
Incidentally, these experiments were carried out by the same method as the method using the pore plate described above.

First, in FIG. 13A, the increase in the etching rate of silicon when the total gas flow rate is decreased is because the retention time of HF in the high density plasma is increased and the re-dissociation of HF is promoted. To be understood. Further, the etching rate of SiO ₂ has the maximum value at the total gas flow rate of 40 sccm, and if the total gas flow rate is further increased, the etching rate decreases conversely. It is considered that this is because the amount of gas becomes so large that deposition of a thick polymer film cannot be avoided even on the SiO ₂ surface. In addition, in FIG. 13B, although the radical densities of both CF ₁ and CF ₂ increased as the total gas flow rate was increased, the CF ₁ / CF ₂ radical density ratio was around 40 sccm as shown by the dotted line. Had the maximum value. Further, in FIG. 13C, the XPS photocurrent intensity ratio of C-C / F shows the maximum value under the condition of the total gas flow rate of about 40 sccm. This indicates that a polymer film having the highest carbon content, that is, the lowest fluorine content can be obtained under this flow rate condition.

What should be noted from the comparison of (a), (b) and (c) in FIG. 13 is that CF ₁ / CF ₂ in (b) is remarkable.
At the total gas flow rate value almost the same as the total gas flow rate value (near 40 sccm) at which the radical density ratio was obtained, C-C / of (c)
The XPS photocurrent intensity ratio of F also shows the maximum value. Further, the etching rate of SiO ₂ in (a) also reaches the maximum value near this total gas flow rate value. These facts, if as CF ₁ / CF ₂ radical density ratio flowing gas becomes largest flow rate, the highest carbon content in the polymerized film deposited on the silicon surface, SiO ₂
It means that the etching rate of can be the fastest.

From the SiO ₂ / Si selectivity data shown in FIG. 13A, the selectivity takes the maximum value in the vicinity of 70 sccm, so this flow rate condition seems to be more advantageous. However, the etching rate of SiO ₂ becomes zero (etching is stopped) near 80 sccm where the flow rate slightly increases, and this condition is very dangerous. On the other hand, the above-mentioned total gas flow rate of 40 sccm
Under these conditions, the highest SiO ₂ etching rate is obtained, and the SiO ₂ / Si selectivity is about 20, which is a sufficient value.

In this embodiment, the selective etching of the silicon oxide is performed by focusing on the "CF ₁ / CF ₂ radical density ratio" as in the invention of claim 1, and the evaluation of the above experimental results is performed. It is based on. That is, as described above, by measuring the “CF ₁ / CF ₂ radical density ratio” and controlling the etching conditions so that it takes the maximum value, sufficient selection can be made without impairing the etching rate of silicon oxide. Is possible.

Next, returning to FIG. 1, a specific configuration of the control system will be described. Control unit 6 for controlling etching conditions
Is an input unit 61 to which the signal from the measuring means 5 is input.
An arithmetic processing unit 62 that processes a signal from the input unit 61 to perform a predetermined arithmetic operation; and a storage unit 63 that stores an arithmetic result and the like.
And an output unit 64 that outputs a control signal based on the calculation result of the calculation processing unit 62. Further, the control unit 6 is configured to receive a measurement signal of a vacuum gauge (not shown) provided in the reaction vessel 1 and a measurement signal of a flow meter (not shown) provided in the gas introduction unit 2.

First, since the signal from the QMS 50 is an analog signal, the input section 61 includes a predetermined A / D conversion circuit. Processing unit 62, and arithmetic processing of the signal from the input unit 61 sequentially calculates the CF ₁ / CF ₂ radical density ratio, CF ₁ / CF ₂ radical density ratio becomes the maximum pressure value and the gas flow rate value or the like Data of etching conditions of the storage unit 6
3 is configured to store. The output unit 64 is configured to send a control signal to the variable orifice 132 as a pressure adjuster, the mass flow controllers 213 and 223 as a flow rate adjuster, etc., based on the etching conditions stored in the storage unit 63.

The control section 6 also serves as a control means for controlling the operation of each part of the apparatus, in addition to controlling the etching conditions by measuring the CF ₁ / CF ₂ radical density ratio.
In addition, the apparatus of FIG. 1 is provided with a substrate transfer system 7 for loading and unloading a substrate through the gate valve 15, an etching end point detection mechanism (not shown) for detecting the timing at which etching should be finished, and the like.

Next, the operation of the plasma etching apparatus of the present embodiment having the above structure will be described. Substrate transfer system 7
First, the substrate 10 on the surface of which silicon oxide is formed is carried into the diffusion chamber 12 through the gate valve 15 and placed on the stage 4. The gate valve 15 is closed and the exhaust system 13 is activated, and the inside of the diffusion chamber 12 is 1 × 10 ⁻⁵ To
Exhaust to about rr. Next, the gas introducing means 2 operates to introduce the mixed gas of CF ₄ / H _{2 into} the diffusion chamber 12 at a flow rate of about 50 sccm. The introduced mixed gas diffuses into the source chamber 11 and
Fill the inside. The pressure in the reaction vessel 1 is adjusted to 10 mT by adjusting the variable orifice 132 provided in the exhaust system 13.
It is about orr. In parallel, the QMS exhaust system 57 is also operating and exhausts the inside of the QMS 50 to about 1 × 10 ⁻⁵ Torr.

In this state, the plasma generating means 3 operates,
Source plasma generation high-frequency power source 32 to antenna 3
A high frequency wave is sent to the antenna 1 and is introduced into the source chamber 11 from the antenna 31. The introduced high frequency ionizes the mixed gas existing in the source chamber 11 to form plasma, and CF ₁ , CF ₂ , CF are generated in the plasma.
Radicals such as ₃ are generated. The generated radicals are
The substrate 1 diffuses into the diffusion chamber 12 and reaches the substrate 10.
Etch the silicon oxide on the 0 surface. And
When the etching end point detection mechanism (not shown) detects the timing of the end of etching, the operations of the plasma generation means 3 and the gas introduction means 2 are stopped, and the exhaust system 13 is restarted.
After evacuating the inside, the substrate transfer system 7 moves the substrate 10 to the reaction container 1
Take out from.

Next, the "control for maximizing the CF ₁ / CF ₂ radical density ratio" performed in the above etching operation will be described. There are several possible "controls for maximizing the CF ₁ / CF ₂ radical density ratio", but basically, the CF ₁ / CF ₂ radical density ratio is measured and the optimum etching conditions are found and stored. The etching process is performed by reproducing the conditions. Specifically, CF ₁ / C is added before the etching treatment and between the etching treatments.
The F ₂ radical density ratio is measured. That is, if necessary, a dummy substrate is placed on the stage 4, gas is introduced in the same manner as described above to form plasma, and radicals of CF ₁ and CF ₂ generated in the plasma are generated as described above. taking measurement. Then, the measurement result is sent to the control unit 6 and CF ₁ / CF
₂ Calculate the pressure value and flow rate value that maximize the radical density ratio.

For example, when calculating the pressure value at which the CF ₁ / CF ₂ radical density ratio becomes maximum, a signal is sent from the control section 6 to the variable orifice 132 as a pressure regulator to control the pressure in the reaction vessel 1 to, for example, 5 to 5. The density of each radical of CF ₁ and CF ₂ at that time is sequentially calculated by changing the density within a range of about 20 mTorr. Then, the pressure value determined to have the maximum CF ₁ / CF ₂ radical density ratio is stored in the storage unit 63 provided in the control unit 6. If the pressure does not have the maximum value within the pressure range, the pressure range to be changed is widened or shifted to perform the measurement and calculation again.

The same applies when calculating the flow rate value.
A signal is sent from the control unit 6 to the mass flow controllers 213 and 223 as flow rate adjusters, and for example, 10 to 100 seconds
The flow rate is changed within the range of about ccm, and CF ₁ /
The CF ₂ radical density ratio is sequentially calculated to obtain a flow rate value that maximizes the CF ₁ / CF ₂ radical density ratio, and this is stored in the storage unit 63. Further, the mixing ratio is the same, and a signal is sent to the mass flow controllers 213 and 223 to change the mixing ratio, and the mixing ratio that maximizes the CF ₁ / CF ₂ radical density ratio is obtained and stored in the storage unit 63. .

Based on the data of the pressure value, the flow rate value, the mixing ratio, etc. stored in this way, the etching condition that maximizes the CF ₁ / CF ₂ radical density ratio in the actual etching process is reproduced. That is, as described above, the substrate is placed on the stage 4 and the exhaust system 13 and the gas introducing means 2 are operated. At that time, the control unit 6 reads the data such as the pressure value, the flow rate value, and the mixing ratio stored in the storage unit 63, and operates as a pressure adjusting unit so that the pressure value, the flow rate value, the mixing ratio, and the like can be obtained. The variable orifice 132 and the mass flow controllers 213 and 223 as the flow rate adjusters and the mixing ratio adjusters are controlled by sending signals. As a result, the optimum etching condition that maximizes the CF ₁ / CF ₂ radical density ratio is reproduced, and as described above, high selective etching of silicon oxide becomes possible.

Further, during etching while reproducing the above optimum etching conditions, it is preferable that the pressure inside the reaction vessel 1 is feedback controlled by a vacuum gauge (not shown) provided in the reaction vessel 1. That is, the measurement value of the vacuum gauge is sent to the control unit 6, and the control unit 6 feedback-controls the variable orifice 132 so that the pressure value achieves the optimum etching condition. This prevents the optimum etching conditions from not being satisfied due to disturbance or the like. Similarly, it is preferable to send a measurement value of a flow meter (not shown) provided in the gas introduction unit 2 to the control unit 6 and feedback control the mass flow controllers 213 and 223 so that the stored gas flow rate is achieved. Furthermore, the CF ₁ / CF ₂ radical density ratio is calculated during the etching process, and the calculated value is compared with the value measured before or during the above etching process to estimate the CF ₁ / CF ₂ radical density ratio. It may be possible to monitor whether the maximum value has been reached.

For reference, the above CF ₁ / CF
_{2 The} etching conditions that maximize the radical density ratio may change over time. For example, in the apparatus shown in FIG. 1, the high frequency is set to 13.56 MHz 1000 W and the gas is CF ₄ +.
Under the etching condition of introducing 50% H ₂ gas at a flow rate of 50 sccm, the CF is initially at 10 mTorr.
The radical density ratio of ₁ / CF ₂ was maximized, but 180
After the similar etching treatment for about 2 seconds was repeated about 5 times, the maximum value of the CF ₁ / CF ₂ radical density ratio shifted to the low pressure side, and became the maximum at around 7 mTorr. Although the cause is not always clear, a polymer film is formed on the inner wall surface of the reaction vessel 1 by repeating the etching, and molecules having a high fluorination number such as CF ₂ and CF ₃ are released from the polymer film, or It is expected that this is due to the fact that the polymer film reduced the loss on the inner wall surface of such gas molecules having a high fluorination number. In any case, since the CF ₁ / CF ₂ radical density ratio may change with time in this way, as described above, the radical densities of CF ₁ and CF ₂ should be adjusted before or during the etching process. It is very important to measure and frequently find etching conditions that maximize the CF ₁ / CF ₂ radical density ratio.

Although the quadrupole mass spectrometer (QMS) is adopted as the measuring means 5 in the above-mentioned embodiment, the present invention is not limited to this, and a tandem type mass spectrometer, a flight mass spectrometer (TOF), etc. The mass spectrometer of can also be adopted. However, it can be said that the QMS is the most suitable for carrying out the present invention because it is small and the measurement operation is simple. The plasma generating means 3 is not limited to the one for forming the helicon wave plasma described above, but may be an ECR (Electron Cycle).
(tron resonance, electron cyclotron resonance) plasma generation means using discharge, capacitively coupled plasma generation means in which a high-frequency circuit is coupled by the capacity of the discharge space, high-frequency coil arranged around the reaction vessel or high-frequency wave inserted in the reaction vessel A plasma generating means using an antenna, a plasma generating means utilizing a DC bipolar discharge, or the like can be adopted.

Further, as the introduced gas, CF ₄
A gas with H ₂ added was used, but CF ₄ with CHF
May be added to gas fluorinated hydrocarbon compound having ₃ or the like, may be used only fluorinated hydrocarbon compounds such as CHF _3. In addition, as the "fluorocarbon gas",
In addition to such a fluorohydrocarbon compound gas, C ₂ F ₆ ,
C ₃ F ₈ , C ₄ F ₁₀ , CH ₂ F ₂ , CH ₃ F, C ₂ HF ₅ , C
₂ H ₂ F _{4 and the} like can be mentioned. Further, as the substrate 10 to be subjected to the etching treatment, a semiconductor wafer used in manufacturing an LSI, a liquid crystal substrate used in manufacturing a liquid crystal display, or the like is assumed.

[0063]

As described above, the claims 1 and 2 of the present application
According to the invention of 4 or 6, since the etching conditions are controlled based on the measurement result of the CF ₁ / CF ₂ radical density ratio, high selective etching of silicon oxide is always possible. According to the invention of claim 2, the above-mentioned claims 1, 4
In addition to the effect of 6 or 6, since the pressure in the reaction vessel is feedback-controlled under the condition that the selective etching is optimized, it is possible to maintain high selective etching even when the pressure in the reaction vessel changes due to disturbance. The effect of becoming According to the invention of claim 3, in addition to the effect of claim 1, 2, 4 or 6, the gas flow rate is feedback-controlled under the condition that the selective etching is optimized, so that the gas flow rate changes due to disturbance. Even in such a case, it is possible to obtain the effect that the high selective etching can be maintained. According to the invention of claim 5, in addition to the effect of claim 1, 2, 3, 4 or 6, the mixture ratio of the gas is feedback controlled under the condition that the selective etching is optimized. It is possible to maintain the high selective etching even when is changed by disturbance. According to the invention of claim 7, in addition to the effect of claim 6, a QMS which is small and has a simple measurement operation is used, which contributes to downsizing of the entire apparatus and simplification of the configuration of the measurement system. The effect is obtained. Furthermore, according to the invention of claim 8, in addition to the effect of claim 7, since it has an ionization energy adjusting mechanism, it is possible to extract and measure only the necessary radicals with high accuracy.
The effect of contributing to the improvement of the accuracy of control using the measurement result is obtained.

[Brief description of drawings]

FIG. 1 is a schematic side view illustrating a configuration of a plasma etching apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of a reaction vessel portion of the plasma etching apparatus shown in FIG.

FIG. 3 is an explanatory diagram of an ionization energy adjusting mechanism in the QMS of FIG. 1, and shows an outline of a configuration of an ionization section in the QMS.

FIG. 4 is a schematic cross-sectional view illustrating details of a sampling orifice and an unnecessary charged particle removing mechanism adopted in the apparatus of FIG.

FIG. 5 is a diagram showing the results of measuring the densities of CF ₁ , CF ₂ , and CF ₃ radicals by a measuring means including a quadrupole mass spectrometer, wherein the hydrogen gas concentration in C ₄ F ₈ is used as a parameter. It is a figure showing the measurement result of the density of each radical which was done.

FIG. 6 shows CF ₁ , C when total pressure is used as a parameter.
It is a view showing a measurement result of the density of each radical of F _2, CF _3.

FIG. 7 C when high frequency power is used as a parameter
F _1, is a view showing a measurement result of the density of each radical CF _2, CF _3.

FIG. 8 is an explanatory diagram of an experiment for simulating etching of a deep groove such as a contact hole, particularly for confirming the effect of hydrogen addition in such etching.

FIG. 9 is a diagram showing changes in the density of each radical of CF ₁ , CF ₂ , and CF ₃ when the aspect ratio of the narrow tube is set to a parameter.

FIG. 10 shows the results of measuring the surface of a silicon substrate exposed to plasma for 3 minutes by X-ray electron spectroscopy (XPS).

FIG. 11 is a diagram showing a result of an experiment conducted by disposing a pore plate on a silicon substrate.

FIG. 12 is a diagram showing a result of observing a surface state of a silicon substrate on which etching is attempted by using a pore plate as a mask in the experiment of FIG. 11 with a scanning electron microscope (SEM).

FIG. 13 is a diagram showing a result of examining etching conditions with a gas flow rate as a parameter.

[Explanation of symbols]

1 reaction vessel 10 substrates 13 Exhaust system 132 variable orifice 2 Gas introduction means 213 Mass Flow Controller 223 Mass Flow Controller 3 Plasma generation means 4 stages 5 Measuring means 50 quadrupole mass spectrometer 533 Ionization energy adjustment power supply 6 control unit

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-36642 (JP, A) JP-A-6-267900 (JP, A) JP-A-7-297173 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H01L 21/3065 C23F 4/00 C30B 33/12 C30B 35/00 JISST file (JOIS)

Claims (8)

(57) [Claims] 1. A reaction vessel provided with an exhaust system, a gas introducing means for introducing a fluorocarbon-based gas into the reaction vessel, and a plasma generating means for generating plasma in the reaction vessel by the introduced gas. In a plasma etching apparatus having a fluorocarbon-based gas plasma for etching a silicon oxide film, measurement for measuring the number density ratio of carbon monofluoride radicals and carbon difluoride radicals generated in plasma A plasma etching apparatus comprising: a measuring unit and a control unit that controls etching conditions based on a measurement result of the measuring unit. 2. The reaction vessel includes a pressure adjuster for adjusting the pressure in the reaction vessel, and the controller sends a signal to the pressure adjuster to send a carbon monofluoride radical to a carbon difluoride radical. 2. The plasma etching apparatus according to claim 1, wherein the plasma etching apparatus is controlled so that the ratio of the number densities of the above is maximized. 3. The gas introducing unit includes a flow rate adjuster that adjusts the flow rate of the gas to be introduced, and the control unit sends a signal to the flow rate adjuster to send a carbon monofluoride radical to a carbon difluoride radical. 3. The plasma etching apparatus according to claim 1 or 2, wherein the plasma etching apparatus is controlled so that the ratio of the number densities of the above is maximized. 4. The plasma etching apparatus according to claim 1, 2 or 3, wherein hydrogen gas or a fluorocarbon compound gas containing a hydrogen element is mixed with the fluorocarbon gas. 5. The gas introducing unit includes a mixing ratio adjusting unit that adjusts a mixing ratio of the gases to be introduced, and the control unit includes:
5. The plasma etching apparatus according to claim 4, wherein the mixing ratio adjusting means is controlled so as to maximize the ratio of the number density of carbon monofluoride radicals to the carbon difluoride radicals. 6. The mass spectrometer according to claim 1, 2, 3, 4 or 5, wherein the measuring means is a mass spectrometer for measuring the kind and amount of gas existing in the reaction vessel by mass spectrometry. Plasma etching equipment. 7. The plasma etching apparatus according to claim 6, wherein the mass spectrometer is a quadrupole mass spectrometer. 8. The quadrupole mass spectrometer is provided with an ionization energy adjusting mechanism.
The plasma etching apparatus described.