JPH09145675A - Method and device for measuring neutral radical - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress noise signals due to thermal dissociation of gas molecule and enable highly accurate plasma treatment by cooling an electron beam generator by using a liquid nitrogen cooling shroud. SOLUTION: Neutral radicals generated in a plasma generating chamber are fed into an ionizing chamber 34 within a mass analyzer 32 which is exhausted differentially, through an extractor 33, and they are ionized by electron beams generate by an electron beam generator 35, when they are led to a secondary electronic amplifying tube 39 through an ion lens 36, a Q pole 37, and an energy deflecting plate 38, and are outputted after they are amplified. In this case, a liquid nitrogen of 77 deg.K in temperature is supplied to a liquid nitrogen cooling shroud 41 from a liquid nitrogen cylinder, and the measurement is performed while the periphery of the generator 35 within the analyzer 32 is cooled. At this time, while the voltage of a bias power source 45 of the generator 35 is adjusted so as to change the energy of electron beam, the output of the analyzer 35 is measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a neutral radical measuring method and a neutral radical measuring apparatus, and particularly to measuring the amount of neutral radicals when plasma etching an oxide film or the like using neutral radicals. The present invention relates to a neutral radical measuring method and a neutral radical measuring device.

[0002]

2. Description of the Related Art Conventionally, when measuring neutral radicals in plasma, appearance mass spectrometry (Appearance Mass Spectrometer) using a mass spectrometer is used.
entry: For example, Japanese Journal
of Applied Physics, Vol. 3
3, 1993, pp. L353 to L356) are known.

In this appearance mass spectrometry method, neutral radicals are accurately detected by utilizing the ionization threshold energy of neutral radicals, that is, the difference between the appearance voltage and the dissociative ionization threshold energy of gas molecules. It is a measuring method.

That is, the energy of the electron beam introduced into the ionization chamber of the mass spectrometer is set to such a low energy that neutralized radicals can be ionized but gas molecules cannot be dissociated and ionized. By introducing an electron beam of energy into the ionization chamber and measuring the signal when the discharge is turned on and measuring the signal when the discharge is turned off in this state, and obtaining the difference between these signals, the net It detects neutral radicals.

See FIG. 8. FIG. 8 shows CF ₄ by using such a conventional appearance mass spectrometry method.
The measurement results of CF radicals in plasma are shown. The horizontal axis shows the energy of the electron beam introduced into the ionization chamber, and the vertical axis shows the mass spectrometer (QMS: Quad).
shows the output signal when the discharge is turned on, and the mark shows the output signal when the discharge is turned off.

Here, focusing on the discharge OFF signal, although it is difficult to understand from the semi-logarithmic graph, the signal increases from near the electron beam energy of 25 eV.
Dissociation ionization threshold energy of F ₄ molecule of 26.5
It corresponds to eV (for example, Japanese
Journal of Applied Physi
cs, Vol. 31, 1992, pp. 2919-29
24), and the dissociative ionization signal of the CF ₄ molecule is shown.

Next, looking at the signal when the discharge is turned on,
The signal tends to increase from the low energy side of the discharge OFF signal. This corresponds to the ionization threshold energy of CF radicals of 14.0 eV, and indicates the ionization signal of CF radicals.

Here, in the vicinity of 14.0 eV which is the ionization threshold energy of the CF radical, and 14.0 eV.
Discharge OF from discharge ON signal at 15 eV above eV
The net amount of CF radicals can be measured by subtracting the F signal. In addition, when the voltage greatly exceeds 14.0 eV, dissociative ionization of various radicals also occurs, and accurate measurement of CF radicals becomes impossible.

[0009]

However, in the measurement of neutral radicals having a large discharge OFF signal such as the CF radical described above, the measurement must be performed in a state where the S / N ratio is low, for example, 15 eV. Since the S / N ratio in 3 was as low as about 3, it was not possible to perform highly accurate measurement. The discharge OFF signal on the low energy side near 15 eV is a signal generated because CF ₄ gas molecules are thermally dissociated by the hot filament in the electron beam generator.

Therefore, according to the present invention, when the neutral radicals in the plasma are measured by the appearance mass spectrometry, S /
The purpose is to increase the N ratio and perform highly accurate measurement.

[0011]

Means for solving the problems in the present invention will be described with reference to FIG. 1. FIG. 1 is an explanatory view of the principle structure of the present invention. It is a figure which shows the principal part of the neutral radical measuring apparatus used for implementation of. See FIG. 1. (1) In the neutral radical measuring method of the present invention, a cooling shroud 11 is arranged around the electron beam generator 5 in the mass spectrometer 2 to prevent thermal dissociation of gas molecules in the electron beam generator 5. It is characterized in that the neutral radicals are measured while cooling to prevent them.

In this way, when measuring the neutral radical,
By providing the cooling shroud 11 around the electron beam generator 5 to cool the electron beam generator 5, thermal dissociation of gas molecules can be prevented, and thus a noise signal due to thermal dissociation of gas molecules can be reduced. Therefore, measurement with a high S / N ratio becomes possible.

(2) Further, the present invention is characterized in that in the above (1), the cooling shroud 11 is provided so as to surround only the electron beam generator 5.

As shown in FIG. 1, the electron beam generator 5
When the cooling shroud 11 is provided so as to surround the whole, a part of neutral radicals introduced into the ionization chamber 4 from the plasma processing chamber 1 through the extractor 3 is adsorbed on the shroud front wall 12 of the cooling shroud 11. Therefore, although the neutral radicals are reduced and the signal component S is also reduced, since S is not reduced by providing the cooling shroud 11 so as to surround only the electron beam generator 5,
The S / N ratio can be dramatically increased.

(3) Further, the present invention is characterized in that, in the above (1) or (2), the neutral radical is a CF radical.

The neutral radical measuring method of the present invention is most useful for measuring CF radicals having a large noise signal.

(4) Further, the present invention is characterized in that in the neutral radical measuring apparatus, the cooling shroud 11 is arranged around the electron beam generator 5 in the mass spectrometer 2.

(5) Further, the present invention is characterized in that, in the above (4), the cooling shroud 11 is provided so as to surround only the electron beam generator 5.

(6) Further, according to the present invention, in the plasma processing apparatus equipped with the neutral radical measuring apparatus according to the above (4) or (5), the density of the active ingredient is determined based on the emission of the active ingredient generated in the plasma. Is provided, a means for comparing the density of the active component and the density of the neutral radicals, and a means for changing the discharge condition according to the output of the comparing means.

The neutral radical measuring apparatus (4) or (5) above is typically provided in association with a plasma processing apparatus. In that case, active components generated in plasma, for example, In plasmaization of CF ₄ molecules, F
A means for measuring the density of F atoms based on the emission of atoms is provided, the CF / F ratio is measured, and the discharge conditions such as the inflow rate of raw material gas, pressure, or discharge power are changed based on the result. This enables etching under stable conditions.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Here, a neutral radical measuring method and a neutral radical measuring apparatus according to a first embodiment of the present invention will be described with reference to FIGS. 2 is an explanatory view of a schematic configuration of the neutral radical measuring apparatus used in the first embodiment of the present invention, and FIG. 3 is a detailed explanatory view of the neutral radical measuring apparatus, Further, FIG. 4 is a diagram showing a measurement result in the first embodiment.

Referring to FIG. 2, the neutral radical measuring apparatus of the present invention comprises a mass spectrometer 32. This mass spectrometer 32 is
It is attached to the plasma etching apparatus 21.

The plasma etching apparatus 21 comprises a plasma generating chamber 22 made of quartz and a plasma processing chamber 23, and the plasma generating chamber 22 has a source power supply 3
An RF antenna (RF coil) 24 that receives high-frequency electric power from 1 to generate plasma is provided.

The plasma processing chamber 23 is provided with a reaction gas flow rate control device 25 for supplying a reaction gas such as CF ₄ and an exhaust port 26 provided with a gate valve 27 for exhausting the reaction gas and the reaction product gas. Further, in the plasma processing chamber 23, there is provided a holder 28 on which a substrate 29 to be processed such as a silicon wafer is detachably mounted, and a bias voltage is applied from a bias power supply 30 to the holder 28.

FIG. 3 (a) is an enlarged view of the mass spectrometer 32 shown in FIG. 2, in which an ionization chamber 34 for ionizing neutral radicals and an extra for taking the neutral radicals into the ionization chamber 34 are shown. An electron beam generator 35 that supplies an electron beam for ionization to the ionization chamber 34, an ion lens 36 that converges ionized neutral radicals, and a Q-pole (Quadrupol) that selects the mass of the neutral radicals.
e) 37, energy deflection plate 3 for deflecting neutral radicals
8, a secondary electron multiplier 39 for amplifying and detecting neutral radicals, and a liquid nitrogen cooling shroud 41 for cooling at least the electron beam generator 35 are provided.

The extractor 33 is composed of a conical quartz tube and has an inner diameter of 0.15 m at its tip.
It has an mφ orifice hole, and the inside of the mass spectrometer 32 is evacuated from the exhaust port 40 provided in the mass spectrometer 32 to make it a vacuum higher than the vacuum degree of the plasma processing chamber 23 to realize differential exhaust. Then, the neutral radicals of the plasma processing chamber 23 are sucked from the orifice hole at the tip of the extractor 33 based on the pressure difference.

FIG. 3B is a diagram showing a conceptual configuration of the electron beam generator 35. The filament 43, the current source 44 for heating the filament 43, and the filament 43 are generated. The ionization chamber 34 that accelerates thermionic electrons into an electron beam
It is composed of a bias power supply 45 for supplying to.

Referring again to FIG. 2, the neutral radical measuring method according to the first embodiment of the present invention will be described below.
The F ₄ gas is supplied to the plasma processing chamber 23 at a flow rate of 80 sccm, and the gate valve 27 is adjusted to set the pressure inside the plasma processing chamber 23 to 10 mTorr.

The plasma processing chamber 23 in this case has a cylindrical shape with an inner diameter of 311 mm and a height of 235 mm, and the plasma generating chamber 22 has a height of 133 mm.
In addition, the inner diameter of the connection portion with the plasma processing chamber 23 is 250 mm and is dome-shaped.

Next, by applying high-frequency power of 500 w at 13.56 MHz from the source power source 31 to the RF antenna 24, an inductively coupled plasma (ICP) is generated in the plasma generation chamber 22.
ed Plasma) to generate CF from CF ₄ gas.
_It produces neutral radicals such as ₃ , CF ₂ , CF, and F.

The neutral radicals generated in this plasma are taken into the ionization chamber 34 in the mass spectrometer 32, which is differentially evacuated through the extractor 33, and ionized by the electron beam generated in the electron beam generator 35. The neutralized radicals thus ionized reach the secondary electron multiplier 39 through the ion lens 36, the Q pole 37, and the energy deflector 38, and the secondary electron multiplier 3
It is amplified in 9 and output.

In this case, the liquid nitrogen cooling shroud 41 is supplied with 77 ° K liquid nitrogen from a liquid nitrogen cylinder (not shown) to cool the periphery of the electron beam generator 35 inside the mass spectrometer 32. Measure with.

See FIG. 4. In this state, the QMS output was measured while changing the energy of the electron beam by adjusting the voltage of the bias power supply 45 of the electron beam generator 35. FIG. 4 shows the measurement at 15 eV. The result shows that the noise signal is reduced to about 1/200 and the S / N ratio is about 37, which is an improvement of about 10 times as compared with the conventional example in which the liquid nitrogen cooling shroud 41 is not used. Highly accurate measurement with a high / N ratio becomes possible.

That is, by using the liquid nitrogen cooling shroud 41, the vicinity of the electron beam generator 35 is cooled and the noise component due to the thermal dissociation of CF ₄ gas can be reduced in the vicinity of the filament 43, so that the S / N ratio is reduced. Greatly improved.

The electron beam energy is 15 eV.
At higher places, neutral radicals other than CF,
For example, CF ₃ , CF ₂ or the like collides with an electron beam and CF
Ions are generated and CF ions due to this collision dissociation are detected as a signal at the time of discharge ON, so that the amount of CF radicals in the original plasma is measured inaccurately.

Next, a second embodiment of the present invention will be described with reference to FIGS. 5 is a detailed explanatory diagram of the neutral radical measuring apparatus used in the second embodiment of the present invention, the configuration of the plasma etching apparatus 21 in the second embodiment of the present invention is the same as that of the present invention. Since it is exactly the same as the plasma etching apparatus 21 in the first embodiment, description thereof will be omitted. Further, FIG. 6 is a diagram showing a measurement result in the second embodiment of the present invention.

Referring to FIG. 5, the configuration of the mass spectrometer 32, which is the neutral radical measuring device according to the second embodiment of the present invention, is different from that of the first embodiment in the configuration of the liquid nitrogen cooling shroud 46. , And other configurations are exactly the same. That is, the liquid nitrogen cooling shroud 46 in the second embodiment is provided so as to surround only the electron beam generator 35.

This is taken in by the extractor 33 because the liquid nitrogen cooling shroud 41 is provided so as to surround the ionization chamber 34, the ion lens 36, and the Q pole 37 in the first embodiment. Some of the neutral radicals are adsorbed on the shroud front wall 42,
The amount of ionization is reduced. Therefore, as is clear from the comparison between FIG. 8 and FIG. 4, the signal at the time of discharge ON is reduced to about 1/20 as compared with the case without cooling, so the noise signal is reduced to 1/200. Despite this, the S / N ratio was 10
This is to remedy the drawback that the improvement is only about twice.

See FIG. 6. In this state, the QMS output was measured while changing the energy of the electron beam by adjusting the voltage of the bias power supply 45 of the electron beam generator 35. FIG. 6 shows the measurement at 15 eV. As a result, the noise signal is reduced to about 1/200, and the signal at the time of discharge ON is hardly reduced as compared with the case without cooling, so that the S / N ratio is about 590, which is higher than that of the first embodiment. And an S / N ratio of about 16 times can be obtained.

That is, in the second embodiment, most of the neutral radicals taken in by the extractor 33 are introduced into the ionization chamber 34 without being adsorbed by the liquid nitrogen cooling shroud 46, and the signal at the time of discharge ON is given. Does not decrease, so the S / N ratio is dramatically improved.

Next, with reference to FIG. 7, description will be given of a plasma etching apparatus having a neutral radical measuring apparatus according to a third embodiment of the present invention. The essential parts of the technical field and structure in the industry are the same as those of the first or second embodiment. See FIG. 7. The plasma etching apparatus equipped with this neutral radical measuring apparatus has almost the same structure as the plasma etching apparatus equipped with the neutral radical measuring apparatus shown in FIG. The difference is that the emission analyzer 47 is arranged so as to correspond to the provided viewport 48.

This optical emission analyzer 47 includes an optical fiber 4
9, a spectroscope 50, and a photomultiplier tube 51. The computer 52 compares the output of the photomultiplier tube 51 with the output of the secondary electron multiplier tube 39, and based on the comparison result, The discharge conditions such as reaction gas flow rate, pressure, or discharge power are changed.

[0043] For example, C ₄ F ₈ when selectively etching the SiO ₂ film formed on a silicon substrate by using a gas, the reaction gas flow rate control device 40sccm the C ₄ F ₈ gas through the 25, H ₂ gas Is supplied to the plasma processing chamber 23 at a flow rate of 40 sccm and a monitor gas of 4 sccm, and the gate valve 27 is adjusted to set the pressure inside the plasma processing chamber 23 to 10 mTorr.

Next, the frequency is changed to 4 from the bias power source 30.
A bias voltage of −500 V at 00 kHz is applied to the holder 28, and the RF power from the source power source 31 is applied to the RF antenna 24.
By applying high-frequency power of 500 w at 13.56 MHz, inductively coupled plasma is generated in the plasma generation chamber 22 and neutral radicals such as CF ₃ , CF ₂ , CF, and F are generated.

Then, as in the first embodiment, the neutral radicals generated in the plasma are extracted by the extractor 33.
The neutral radicals, which are differentially evacuated through the ionization chamber 34 in the mass spectrometer 32 and ionized by the electron beam generated in the electron beam generator 35, are ionized. ,
And the secondary electron multiplier 3 via the energy deflection plate 38.
9 and is amplified and output in the secondary electron multiplier tube 39.

On the other hand, the F atoms generated in the plasma, that is, the F neutral radicals, emit light at a predetermined wavelength. Therefore, this light emission is wavelength-resolved by the spectroscope 50 via the optical fiber 49 constituting the emission analyzer 47. Then, it is amplified by the photomultiplier tube 51 to obtain an output.

In this case, in order to accurately measure the density of F atoms, a small amount of monitor gas, in this case A
The measurement is performed using an actinometry method in which the relative density of F atoms is obtained by adding r gas and taking the emission intensity ratio of F and Ar.

When the number of processed substrates was the first, the etching property was normal, but when 100 substrates to be processed were etched, an abnormality occurred that the etching was stopped in the contact holes. Luminescence analyzer 47
When the F atom density in the plasma is accurately measured using the computer and the measurement result is compared with the CF radical density measured by the mass spectrometer 32 in the computer 52, the CF radical is compared to the case where the number of processed sheets is one. It was found that the density ratio of F atoms, that is, the CF / F ratio increased about twice.

This is because by stacking the number of processed sheets,
This is because reaction products adhere to the inner walls of the plasma generation chamber 22 and the plasma processing chamber 23, the probability of surface loss of CF radicals is reduced, and the CF / F ratio in plasma is consequently increased.

Therefore, under discharge conditions, specifically, 84 sccm under the condition that the flow rate of the reaction gas is the same as the flow rate ratio of each gas.
To 72 sccm, the number of processed sheets is 1
The etching characteristics at the time of one sheet can be reproduced, and stable and highly accurate etching can be performed again.

Incidentally, in the third embodiment,
Although the flow rate of the reaction gas is changed as the discharge condition, the etching characteristics when the number of processed wafers is 1 can be reproduced by changing other discharge conditions such as the pressure in the plasma processing chamber 23 and the discharge power. it can.

Further, although CF ₄ or C ₄ F ₈ is used as the reaction gas in the above embodiment, the reaction gas is not limited to such a gas and other F and C are used.
A gas containing: CHF ₃ , C ₂ F ₆ , or C ₃
F ₈ or the like may be used, and further, a gas containing a halogen element such as Cl or a gas containing oxygen (O) may be used.

Further, in the above embodiment, since CF ₄ or C ₄ F ₈ is used as the reaction gas, the CF radical is measured as the neutral radical. However, when another gas is used, Other radicals in which thermal dissociation is a problem, such as Cl atom or O atom, may be measured.

Further, in the embodiment of the present invention, the neutral radicals in the plasma generated by using the high frequency power are measured, but the technical idea of the present invention is that the plasma is generated by using the microwave. It is also applied when doing.

Further, in the embodiment of the present invention, liquid nitrogen is used for cooling, but the present invention is not limited to liquid nitrogen, and another refrigerant may be used.

[0056]

According to the present invention, when measuring the neutral radicals in the plasma, the electron beam generator is cooled by using the liquid nitrogen cooling shroud. Therefore, the hot filament in the electron beam generator is used. A noise signal generated as a result of thermal dissociation of gas molecules can be suppressed, so that measurement can be performed with a high S / N ratio, and highly accurate plasma processing can be performed based on the measurement result.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a principle configuration of the present invention.

FIG. 2 is an explanatory diagram of a schematic configuration of the neutral radical measuring apparatus according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram of details of the neutral radical measuring apparatus according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram of a measurement result according to the first embodiment of this invention.

FIG. 5 is an explanatory diagram of details of the neutral radical measuring apparatus according to the second embodiment of the present invention.

FIG. 6 is an explanatory diagram of measurement results according to the second embodiment of this invention.

FIG. 7 is an explanatory diagram of a schematic configuration of a plasma etching apparatus including a neutral radical measuring apparatus according to a third embodiment of the present invention.

FIG. 8 is an explanatory diagram of a conventional measurement result of neutral radicals.

[Explanation of symbols]

 1 Plasma Processing Chamber 2 Mass Spectrometer 3 Extractor 4 Ionization Chamber 5 Electron Beam Generator 6 Ion Lens 7 Q Pole 8 Energy Deflection Plate 9 Secondary Electron Multiplier Tube 10 Exhaust Port 11 Cooling Shroud 12 Shroud Front Wall 21 Plasma Etching Device 22 Plasma Generation Chamber 23 Plasma Processing Chamber 24 RF Antenna 25 Reactive Gas Flow Control Device 26 Exhaust Port 27 Gate Valve 28 Holder 29 Processed Substrate 30 Bias Power Supply 31 Source Power Supply 32 Mass Spectrometer 33 Extractor 34 Ionization Chamber 35 Electron Beam Generator 36 Ion lens 37 Q pole 38 Energy deflection plate 39 Secondary electron multiplier 40 Exhaust port 41 Liquid nitrogen cooling shroud 42 Shroud front wall 43 Filament 44 Current source 45 Bias power supply 46 Liquid nitrogen cooling Shroud 47 emission spectrometer 48 viewport 49 optical fiber 50 Spectrometer 51 photomultiplier 52 computer

Claims (6)

[Claims] 1. A method for arranging a cooling shroud around an electron beam generator in a mass spectrometer to measure neutral radicals while cooling so as to prevent thermal dissociation of gas molecules in the electron beam generator. Characteristic method for measuring neutral radicals. 2. The neutral radical measuring method according to claim 1, wherein the cooling shroud is provided so as to surround only the electron beam generator. 3. The neutral radical measuring method according to claim 1, wherein the neutral radical is a CF radical. 4. A neutral radical measuring device in which a cooling shroud is arranged around an electron beam generator in a mass spectrometer. 5. The neutral radical measuring apparatus according to claim 4, wherein the cooling shroud is provided so as to surround only the electron beam generator. 6. A plasma processing apparatus equipped with the neutral radical measuring apparatus according to claim 4, wherein the density of the active ingredient is measured based on the emission of the active ingredient generated in plasma, A plasma processing apparatus comprising: a means for comparing a density with the density of the neutral radicals; and a means for changing a discharge condition according to an output of the comparing means.