JP5938592B2 - Measuring method, measuring apparatus, and film forming apparatus for impurities in plasma - Google Patents

Description

  The present invention relates to an impurity measuring method, a measuring apparatus, and a film forming apparatus for measuring the density of impurities present in plasma.

  Currently, for example, so-called plasma treatment is actively used in film formation on semiconductors and glass substrates. In order to obtain desired film characteristics in such plasma processing, it is important that no impurities are mixed into the plasma itself. For example, during a process such as plasma ALD (Atomic Layer Deposition), oxygen or the like is taken into the film and the film characteristics are deteriorated. In particular, in a film forming apparatus using a dielectric such as quartz on the wall of a film forming container using an inductively coupled plasma method, the wall surface of the dielectric such as quartz is sputtered by the plasma, and oxygen is taken into the film as an impurity. It is easy.

In such film formation, for example, when a silicon nitride film is formed on a substrate, it is not preferable that oxygen (oxygen atoms) be taken into the film as an impurity. It is effective to obtain the density of oxygen (oxygen atoms) in the plasma in order to investigate the source of oxygen (oxygen atoms) that are impurities in the film formation container.
In emission spectroscopy, which measures the emission intensity of impurity atoms such as oxygen atoms in the plasma and the emission intensity of the trace gas added to the plasma, and calculates the density of the ground state of oxygen atoms from the ratio of the emission intensity, In high-density plasma, it can be measured with relatively high sensitivity. However, the density of excited atoms in the plasma caused by light emission is strongly dependent on the electron energy, so the calculated density of atoms in the ground state is high. Reliability is difficult to obtain.
On the other hand, there is known a laser light induced fluorescence method (LIF method) for receiving the fluorescence generated by oxygen atoms when the plasma being generated is irradiated with laser light to obtain the density of oxygen atoms (the following patent document). 1).

“Detection of atomic oxygen: Improvement of actinometry and comparison with laser spectroscopy”, H. M. Katsch et al., Journal Of Applied Physics, 88, Number 11 (2000), pp6232.

However, in the above LIF method, since the luminescent species (types of light emitting atoms) are limited to particles excited by a laser, when the density of the type of excited atoms is low, the induced fluorescence becomes weak and sufficient As a result, a problem of detection sensitivity occurs such that a high S / N ratio cannot be obtained.
Thus, even if the density of impurity atoms such as oxygen atoms is low at present. A method that can obtain a reliable calculation result of the density of oxygen atoms is not known.

  Accordingly, the present invention provides an impurity measurement method, a measurement apparatus, and the measurement apparatus that can reliably calculate the density of impurity atoms (hereinafter also referred to as impurity atoms) present in the generated plasma. An object of the present invention is to provide a film forming apparatus using the above.

One embodiment of the present invention is a measurement method for measuring impurities in plasma. The method is
A plasma generation step for generating plasma;
A first measurement step of measuring emission intensity caused by a downward transition from an excited state of a gas in the plasma to a metastable state and emission intensity caused by a downward transition of an impurity in the plasma from the excited state to a metastable state. When,
A second measuring step of irradiating the plasma with laser light and measuring the intensity of transmitted light that has passed through the plasma without being absorbed by the gas, and the fluorescence intensity of the gas induced by laser; ,
Using the light absorption coefficient of the gas calculated from the intensity of the transmitted light obtained in the second measurement step and the fluorescence intensity of the gas, the density of the metastable state of the gas is obtained, and the excitation of the gas The density of the impurity is calculated by using the emission intensity ratio between the emission intensity caused by the downward transition from the state and the emission intensity caused by the downward transition from the excited state of the impurity in the plasma, and the density. A calculation step.

In the first measurement step, the emission intensity ratio is measured as a distribution in the plasma,
In the second measurement step, the fluorescence intensity of the gas is measured as a distribution along the optical path of the laser beam,
In the calculating step, the density of the impurities is preferably calculated as a distribution in the plasma.

  In the calculation step, the density of the metastable state of the gas is obtained from the light absorption coefficient of the gas obtained in the second measurement step and the fluorescence intensity of the gas, and the density of the metastable state of the gas is calculated from the density of the gas. It is preferred that the electron temperature in the plasma is calculated.

  The density of the impurity is, for example, the following formula (4) that relates the emission intensity ratio, the density of the gas, the density of the metastable state of the gas, the electron temperature, and the density of the impurity atoms. Can be calculated using

The gas is, for example, argon gas, and the impurity is, for example, oxygen.
At this time, the emission intensity generated by the downward transition from the excited state of argon is a light intensity of 777.2 nm, the emission intensity generated by the downward transition from the excited state of oxygen is a light intensity of 777 nm, and the plasma The wavelength of the laser beam applied to the gas is 696.54 nm, and the wavelength of the fluorescence intensity of the gas is 772.4 nm.

Another aspect of the present invention is a measuring device that measures impurities in plasma. The measuring device is
A plasma generation vessel for generating plasma;
A plasma generation unit for generating plasma in the plasma generation vessel;
The light emission intensity generated by the downward transition from the excited state of the gas in the plasma to the metastable state and the light emission intensity generated by the downward transition of the impurity in the plasma from the excited state to the metastable state are measured. A first measurement unit for measuring the fluorescence intensity of the fluorescence of the gas emitted by the induction of
A second measuring unit that irradiates the plasma with laser light, and measures the intensity of the transmitted light that has passed through the plasma without being absorbed by the gas, and the fluorescence intensity of the gas induced by the laser; ,
Using the light absorption coefficient of the gas obtained by the second measurement unit and the fluorescence intensity of the gas obtained by the first measurement unit, the density of the metastable state of the gas is obtained, and from the excited state of the gas The calculation of calculating the density of the impurity using the emission intensity ratio between the emission intensity caused by the lower transition of the light emission and the emission intensity caused by the lower transition from the excited state of the impurity in the plasma and the obtained density And a unit.

At that time, the first measurement unit measures the emission intensity ratio as a distribution in the plasma,
The second measurement unit measures the fluorescence intensity of the gas as a distribution along the optical path of the laser light,
It is preferable that the calculation unit calculates the density of the impurity as a distribution in the plasma.

  The calculation unit obtains the metastable density of the gas from the measured light absorption coefficient of the gas and the fluorescence intensity of the gas, and uses the metastable density of the gas to calculate the electrons in the plasma. It is preferable to calculate the temperature.

  The calculation unit uses the following equation (4) that relates the emission intensity ratio, the gas density, the gas metastable state density, the electron temperature, and the impurity density: The density of the impurities can be calculated.

Another aspect of the present invention is a film forming apparatus that includes the measurement device and generates a thin film on a substrate. In the film forming apparatus,
A source gas for film formation is introduced into the plasma generation container together with the gas for plasma generation, and a substrate disposed in the plasma generation container is formed into a film,
Furthermore, a control device is provided that changes the conditions for generating the plasma so that the impurity density is reduced in accordance with the calculated impurity density.

  In the impurity measurement method and the measurement apparatus described above, the relationship between the excited state and the ground state density can be determined more precisely when the density of the ground state of the impurity atoms is determined by emission spectroscopy. It is possible to calculate the density of impurity atoms present in the substrate with reliability. Therefore, it is possible to provide a film forming apparatus that can control the density of impurities in the generated plasma and perform film formation in which impurities are hardly mixed.

It is a schematic block diagram of the film-forming apparatus which implements the measuring method of this embodiment. It is a schematic block diagram of the measuring system used for the film-forming apparatus of this embodiment. It is a flowchart of the calculation method of the density of impurity atoms which is this embodiment. (A) is a figure which shows the example of transition of an argon atom, (b) is a figure which shows the example of transition of an oxygen atom. It is a figure which shows the example of the density distribution of the oxygen atom mixed in the plasma calculated | required by the method of this embodiment. It is a figure which shows the calculation result of the average density of the oxygen atom which is an impurity obtained by this embodiment and the conventional method. It is a figure which shows the other example of transition of an argon atom.

Hereinafter, an embodiment of a method for measuring impurities in plasma, a measuring apparatus, and a film forming apparatus according to the present invention will be described in detail.
The impurity measuring method and the impurity measuring apparatus in plasma measure the density of atoms of impurities when the wall of the film forming container is sputtered by the plasma and when the atoms of impurities are contained in the plasma. Is the method. In the present embodiment, plasma emission spectroscopy for obtaining a light emission intensity ratio between the light emission intensity of plasma generating gas in plasma and the light emission intensity of impurity atoms, and plasma generation in plasma when laser light is irradiated to the plasma. The density of impurity atoms is calculated using a laser light induced fluorescence method (LIF method) that measures the fluorescence intensity of the fluorescence emitted by the gas for use.
In the following description, argon gas is taken as an example of the plasma generation gas, but the plasma generation gas is not limited to argon gas. Any gas that does not affect the film formation process with a small amount of addition may be used. For example, a rare gas such as helium gas may be used. As an example of an impurity atom, an oxygen atom will be described. However, the present invention is not limited to an oxygen atom. Any device capable of performing plasma emission spectroscopy may be used. For example, fluorine atoms and nitrogen atoms can be targeted.

(Overview of measurement method)
In the impurity measurement method of this embodiment,
(A) Plasma is generated using a plasma generation gas, for example, a tracer gas (hereinafter sometimes simply referred to as a gas) added for light emission observation.
(B) Next, a downward transition from an excited state of a gas in the generated plasma to a metastable state (for example, 4p ′ [1/2] ₁ → 4s ′ [1/2] ^O _{0 in the} case of argon gas). ) And the emission intensity caused by the downward transition from the excited state of the impurities (impurity atoms) in the plasma to the metastable state (for example, 3p ⁵ P → 3s ⁵ S ^O ₂ if oxygen atoms). Measure (first measurement).
(C) Furthermore, the plasma being generated is irradiated with laser light, and the intensity of transmitted light that has passed through the plasma without being absorbed by the plasma generation gas in the laser light, and the fluorescence of the gas induced by the laser. The intensity is measured (second measurement). At this time, the wavelength of the laser beam is selected such that the above-described plasma generation gas is excited to an excited state.
(D) The metastable density of the gas in the plasma is obtained using the light absorption coefficient of the gas obtained from the intensity of transmitted light obtained in the second measurement and the fluorescence intensity of the gas. Furthermore, the emission intensity ratio between the emission intensity caused by the downward transition from the excited state of the gas to the metastable state and the emission intensity caused by the downward transition of the impurity in the plasma from the excited state to the metastable state was determined. The density of impurities (impurity atoms) is calculated using the density and the electron temperature.

FIG. 1 is a schematic configuration diagram of a film forming apparatus 10 that implements the measurement method. FIG. 2 is a schematic configuration diagram of the measurement system 30 of the film forming apparatus 10.
The film forming apparatus 10 includes a film forming container 12, which is a plasma generating container, a susceptor 14, a substrate 16 for film forming, an exhaust unit 18, a gas supply valve 20, a source gas source 22, and a carrier gas source. 24, a plasma generation unit 26, a measurement system 30, and a control device 40.

The film forming container 12 is a vacuum chamber capable of exhausting the inside of the film forming container 12 to a vacuum, and is held at, for example, about 1 to 100 Pa.
The susceptor 14 mounts a substrate 16 for film formation, and moves up and down in a vertical direction on the paper surface in FIG. 1 by an elevator mechanism (not shown).
The exhaust unit 18 can be adjusted to a desired pressure in addition to maintaining the reduced pressure atmosphere of the film forming container 12 including a rotary pump or a turbo molecular pump at a constant pressure.
The gas supply valve 20 is a valve capable of adjusting the source gas and the argon gas that is the carrier gas to a predetermined flow rate, and introduces the argon gas that is the source gas and the carrier gas into the film forming container 12. For example, when forming a SiN film as the source gas, silane gas-nitrogen gas, silane gas-ammonia, or silane gas-nitrogen gas-ammonia is used. When there are a plurality of types of source gases, the source gas source 22 is used for each of the plurality of types of source gases. The carrier gas source 24 is a gas source that introduces a source gas into the film formation container 12 and stores a gas for generating plasma, such as argon gas.
The source gas and the carrier gas are simultaneously introduced into the film formation container 12, and plasma is generated in the film formation container 12 by the operation of the plasma generation unit 26. That is, the film formation of this embodiment is a film formation using plasma (PECVD: Plasma Enhanced Chemical Vapor Deposition). However, the film forming apparatus, the measuring method, and the measuring apparatus of the present embodiment flow a predetermined source gas to the substrate 16 to adsorb the components of the source gas on the substrate in units of atomic layers, and then convert the reaction gas into plasma. Applied to atomic layer deposition (PAALD) using plasma that forms a film by reacting with the adsorption layer of the component gas component of the atomic layer activated by the substrate and adsorbed on the substrate You can also.

The plasma generation unit 26 includes a high frequency power supply 26A, a matching box 26B, and an electrode plate 26C.
The high frequency power supply 26A outputs high frequency power of 13.56 MHz, for example. The matching box 26B performs impedance matching between the high frequency power supply 26A and the electrode plate 26C. The electrode plate 26C is a wide thin plate-shaped conductor plate, and power is supplied from one end of the electrode plate 26C, that is, the right end in FIG. 1 in the example of FIG. When a high frequency current flows through the electrode plate 26 </ b> C, a high frequency magnetic field is formed in the film forming container 12, and plasma is generated in the film forming container 12 by the formation of this magnetic field. A dielectric plate 26D made of quartz is used on the wall surface in the film forming container 12 so that the electrode plate 26C is not directly exposed to plasma and does not affect the magnetic field. The other end of the electrode plate 26C, the left end in FIG. 1 in the example of FIG. 1, is grounded.
The plasma generation unit 26 used in FIG. 1 is an ICP (Inductively-coupled Plasmas) system using an electrode plate 26C, but is not limited to this in the present invention. For the plasma generation unit 26, for example, a low-pressure high-density plasma source such as a CCP (Capacitively-Coupled Plasma) method or a SWAP (Surface Wave-excited Plasma) method can be used.

As shown in FIG. 2, the measurement system 30 includes a first measurement unit 32, a second measurement unit light source 34, a second measurement unit light receiving unit 36, a calculation unit 38, a display 41, and a printer 42. And having. The second measurement unit light source 34 and the second measurement unit light receiver 36 form a second measurement unit. FIG. 2 is a cross-sectional view of the film forming container 12 taken along the line XX ′ in FIG.
The first measurement unit 32 is an ICCD (Intensified Charged Coupled Device) camera that captures the emission intensity and fluorescence intensity of plasma generated in the film formation container 12 as an image. The first measuring unit 32 is based on the emission intensity generated by the downward transition from the excited state of the plasma generating gas such as argon gas in the plasma and the downward transition from the excited state of the atoms of impurities such as oxygen atoms in the plasma. In addition to imaging the generated emission intensity, an image of the fluorescence intensity of the fluorescence of a gas for plasma generation such as argon gas emitted by the induction of laser light described later is captured. The captured emission image and fluorescence image are sent to the calculation unit 38.
That is, the film forming container 12 is provided with a measurement window 32A, and the emission and fluorescence of plasma transmitted through the window 32A can be measured by imaging. The first measurement unit 32 uses a filter 32B so as to transmit light of different wavelength bands determined in advance. By switching the filter 32B, the ICCD camera is configured to receive light emission and fluorescence images in different wavelength bands. For example, an interference filter is used as the filter 32B.

The second measuring unit light source 34 is configured to irradiate the plasma with laser light. The film forming container 12 is provided with a transparent window 34E made of quartz or the like, and laser light is incident on the film forming container 12 through the window 34E.
The second measurement unit light source 34 includes a laser light source unit 34A, a reflection mirror 34B, a lens system 34C, and an incident window 34D.
The laser light source unit 34A emits laser light having a predetermined wavelength, for example, laser light having a wavelength of 696.54 nm, using a YAG laser or a die laser. The laser light is reflected by the reflection mirror 34B, and generates parallel light L having a certain width through a lens system 34C in which cylindrical lenses are combined. The parallel light L enters the film forming container 12 through an incident window 34D provided at one end of the film forming container 12, and irradiates the plasma in the film forming container 12. An exit window 36A is provided at the end of the film formation container 12 opposite to the entrance window 34D, and the parallel light L transmitted without being absorbed by the plasma passes through the exit window 36A and is received by the second measurement unit light receiving unit. 36 receives light.

The second measurement unit light receiving unit 36 uses a photoelectric converter, for example, a photoelectric converter such as a PIN photodiode or a phototransistor, and the photoelectric converter is not absorbed by argon gas, which is a plasma generating gas. A filter is provided on the front surface of the light receiving surface of the photoelectric converter so as to receive transmitted light having a specific wavelength transmitted through the light, for example, 696.54 nm. Of course, since the second measurement unit light receiving unit 36 receives laser light, an ND (Neutral Density) filter or polarizing plate is used to reduce the intensity of transmitted light, and the second measurement unit light receiving unit 36 receives light. The light reception signal generated by the light reception of the second measurement unit light receiver 36 is sent to the calculation unit 38.
In addition, when the laser beam is irradiated to the plasma, the first measurement unit 32 displays a fluorescence image of a predetermined wavelength, for example, a fluorescence image of 772.4 nm, emitted from the atoms of the plasma generating gas when the laser beam is irradiated to the plasma. Receive light. The fluorescence image obtained by light reception by the first measurement unit 32 is sent to the calculation unit 38.

The calculation unit 38 is a plasma emission gas emission image obtained by the first measurement unit 32, an impurity atom emission image, a plasma generation gas fluorescence image obtained by the first measurement unit 32, and The density of the impurity atoms is calculated based on the light reception signal obtained by the second measurement unit light receiving unit 36.
The calculation unit 38 is a software module that is configured by, for example, a computer including a CPU and a memory, and is formed by starting software that exhibits the above-described functions.
Specifically, the calculation unit 38 uses the ratio of the light intensity of the transmitted light received by the light receiving unit 36 for the second measurement unit to the light intensity of the laser light irradiated to the plasma. A light absorption coefficient is calculated, and from this light absorption coefficient and a fluorescence image, a metastable state density distribution of the plasma generation gas is calculated. That is, the calculation unit 38 obtains the light absorption coefficient by dividing the value of the light reception signal obtained by the light receiving unit 36 for the second measurement unit by the value corresponding to the light intensity of the laser light. The light absorption coefficient of the laser light is a value of light absorption along the optical path of the laser light. The calculation unit 38 uses this light absorption coefficient to calculate the average density n of metastable states of atoms of plasma generating gas in the optical path (hereinafter referred to as gas atoms) based on the following formula (1). To do.

  Here, the value of l is stored in advance in a memory (not shown) of the calculation unit 38, and the calculation unit 38 reads and uses the value of l stored in the memory.

Further, the absorption cross section σ (ν) from the metastable state of the gas atoms for plasma generation is the center wavelength of the irradiated laser beam (more specifically, the light absorbed by the gas atoms for metastable state plasma generation) In the case of ν = ν ₀ , the following equation (2) is established.

In relation to Δν _{d in the} above formula (2) and the temperature T of the gas atom for plasma generation in the metastable state, the following relational expression (3) is established. M in the formula (3) is the mass of the gas atoms for plasma generation, and k is the Boltzmann constant.

Thus, the calculation unit 38 obtains the average density n of the metastable state of the gas atoms for plasma generation using the equation (1).
Since the obtained average density n is an absolute value and is a value along the optical path length l, the calculation unit 38 calculates the average density n at each position corresponding to the optical path of the fluorescence image. A density distribution of metastable states of gas atoms for plasma generation is generated by giving a high or low density value in proportion to the value of the fluorescence image. Hereinafter, this density n is described as density n ₁ ^M. At this time, when the distribution of density n ₁ ^M is averaged along the optical path, the averaged value is normalized so as to be the averaged density value obtained. Thereby, the distribution of the metastable density n ₁ ^M of gas atoms for plasma generation is obtained.

Further, the calculation unit 38 obtains the density of gas atoms in the ground state by using the amount of plasma generation gas introduced into the film formation container 12.
The calculation unit 38 uses the value at each position of the density of gas atoms for generating plasma in the ground state and the density n ₁ ^M of gas atoms for generating plasma in the metastable state obtained by measurement, in the plasma. Calculate the distribution of electron temperature. Details will be described later.
The calculation unit 38 uses the obtained electron temperature to calculate n ₂ that is the density of impurity atoms using the following formula (4).

The above equation (4) includes a rate equation shown in the following equation (5) including a light emission process performed between a gas atom for generating plasma in an excited state and a metastable state, and an impurity atom in an excited state being in a metastable state. In the stable state during plasma generation, the density of gas atoms for generating plasma in the excited state and the density of atoms of the impurity in the excited state are used. In consideration of the fact that is constant, an equation relating to the density of gas atoms for generating excited state plasma and an equation relating to the density of impurity atoms in excited state are derived, respectively. The above formula (4) can be obtained by obtaining the formulas (the following formulas (7) and (8)) of the emission intensity I ₁ of the gas atoms and the emission intensity I ₂ of the impurity atoms, respectively, and taking this ratio. . In equations (5) and (6), t is time, n ₁ ^* is the density of excited states of gas atoms for plasma generation, and n ₂ ^* is the density of excited states of impurity atoms. _ne is the electron density in the plasma.

Here, the emission intensity ratio I ₂ / I ₁ is a value that can be obtained from the measurement result of the first measurement unit 32 described above, and is a value obtained by dividing the emission intensity of the impurity by the emission intensity of the plasma generating gas. is there. Further, k _ex ^(s) (s = 1 or 2) and k _ex ^{(1) M} can be uniquely calculated from the calculated electron temperature. Here, k _ex ^(s) and k _ex ^{(1) M} are both represented by the following formulas (9) and (10).

In the above formulas (9) and (10), σ _ex ^(s) (ν) and σ _ex ^{(1) M} (ν) are known. f (ν) is a Maxwell distribution function, and since the electron temperature is calculated as described above, the Maxwell distribution function is also known. Therefore, k _ex ^(s) (s = 1 or 2) and k _ex ^{(1) M} are both known values. On the other hand, g _s , A _ij ^(s) , A _i ^(s) and n ₁ in the formula (4) are known values. Since n ₁ ^M has already been obtained by the calculation unit 38 as described above, except for the density n ₂ of impurity atoms in the equation (4), it is already known. Therefore, based on the equation (4), the calculation unit 38 can calculate n ₂ that is the density of impurity atoms.
Since the emission intensity ratio I ₂ / I ₁ obtained by measurement is obtained from the values of the two emission images, it has a value at each position. Further, the metastable density n ₁ ^M of the gas atoms for plasma generation also has a value at each position. The calculated electron temperature also has a value at each position. For this reason, n ₂ which is the calculated density of impurity atoms is also obtained as a distribution having values at each position. That is, the calculation unit 38 obtains a distribution in which n ₂ that is the density of impurity atoms also has a value at each position in the emission intensity ratio I ₂ / I ₁ and the fluorescence image acquisition range. The calculation unit 38 outputs the density of such impurity atoms to the display 41 or the printer 42 as a distribution.
Thus, the calculation unit 38 can calculate the density of impurity atoms. The calculated density of impurity atoms is sent to the control device 40.

  The control device 40 controls the plasma such as the high-frequency power of the high-frequency power supply 26A or the supply amount of the plasma generating gas in the gas supply valve 20 so that the density of the impurity atoms is lowered according to the density of the impurity atoms sent. Change the conditions for generating Specifically, the relationship between the density of impurity atoms and the supply amount of high-frequency power or gas is acquired in advance by experiments or the like, and the high-frequency power is determined according to the density distribution of impurity atoms sent from the calculation unit 38. Alternatively, the gas supply amount is controlled. Thereby, the amount of impurities contained in the plasma can be reduced.

(Calculation of electron temperature in plasma)
The calculation unit 38 obtains the electron temperature in the plasma described above by the following method.
From the rate equation of metastable state of gas atoms for plasma generation in plasma, in the stable state during plasma generation, considering that the density of gas atoms for metastable plasma generation is constant, metastable The following equation (11) can be obtained by deriving an equation relating to the density of gas atoms for plasma generation in the state.
Here, k _dex ^e is a rate coefficient of the reaction in which the metastable state of the gas atom for plasma generation disappears due to collision between the gas atom for plasma generation in the metastable state and the electron, for example, 2 × 10 ^{− It is known as 7} cm ³ / sec, 3.5 × 10 ⁻⁷ cm ³ / sec (the above two values indicate values in different metastable states). Therefore, n ₁ ^M , n ₁ and k _dex ^e in formula (11) are known. Since k _ex ⁽¹⁾ is expressed by Equation (9) and σ _ex ⁽¹⁾ (ν) is known, the electron temperature included in the Maxwell distribution function f (ν) can be calculated. Thus, the calculation unit 38 uses the density n ₁ of the gas atom for generating plasma in the ground state and the density n ₁ ^M of the gas atom for generating plasma in the metastable state obtained by the above-described measurement, The electron temperature in the plasma can be calculated.
Such a calculation method of the electron temperature is a known method, and is described in detail in, for example, Japanese Patent No. 4933860.

(Calculation method of impurity atom density)
FIG. 3 is a flowchart of a method for calculating the density of impurity atoms. In the example shown in FIG. 3, argon gas is used as plasma generation gas, and oxygen atoms are used as impurity atoms.

  First, argon gas is introduced into the film formation container 12 to generate plasma. At that time, the dielectric plate 26D made of quartz is sputtered in the plasma, and oxygen as a component of the dielectric plate 26D is mixed as oxygen atoms in the plasma. These oxygen atoms collide with electrons in plasma and are excited to emit light, like argon atoms.

The first measurement unit 32 measures the emission of excited argon atoms Ar ^* and excited oxygen atoms O ^{* in} the plasma.
FIG. 4A is a diagram illustrating an example of the transition of argon atoms. The argon atom is excited from the ground state ¹ S ₀ of the argon atom to 4p ′ [1/2] ₁ , and then transitions downward to the metastable state 4S ′ [1/2] ^O ₀ . At this time, the argon atoms emit light of 772.4 nm]. In addition, the argon atom is excited from the ground state ¹ S ₀ of the argon atom to 4p [3/2] ₁ and then transitions downward to fall into the metastable state 4S [3/2] ^O ₂ . At this time, the argon atoms emit light of 772.4 nm].
FIG. 4B is a diagram illustrating an example of transition of oxygen atoms. The oxygen atom is excited from the ground state 3p ₂ to 3p ⁵ P of the oxygen atom, and then transitions downward to fall into the metastable state 3s ⁵ S ⁰ ₂ . At this time, the oxygen atoms emit light of 777 nm.

As described above, the first measurement unit 32 uses the filter 32B in order to measure light emission of different wavelengths.
Since the first measurement unit 32 captures an image of the emission intensity of argon atoms Ar ^* and oxygen atoms O ^* , the image data is sent to the calculation unit 38. The calculation unit 38 calculates the ratio of the image values at the same position, thereby calculating the emission intensity ratio of the argon atom Ar ^* and the oxygen atom O ^* (step S10).

Next, the laser light source 34A emits laser light. At this time, argon atoms in the plasma generate laser-induced fluorescence. Specifically, a laser beam of 696.54 nm is emitted so that argon atoms are excited from the metastable state 4S [3/2] ^O ₂ to the state 4p ′ [1/2] ₁ . The excited state 4p ′ [1/2] ₁ is an example. Thus, in order to excite the argon atoms in the plasma to a desired state, it is preferable to use a die laser that can emit laser light having a desired wavelength.
Of the irradiated laser light, the transmitted light that has passed through the plasma is received by the second measurement unit light receiving unit 36, and the light reception signal generated by this light reception is sent to the calculation unit 38. The first measurement unit 32 captures a fluorescence image of laser-induced fluorescence of argon atoms along the laser beam path. The image data of the captured fluorescent image is sent to the calculation unit 38.

The calculation unit 38 uses the received light signal to send the light of the laser light, which is the ratio of the light intensity of the transmitted light received by the light receiving unit 36 for the second measurement unit to the light intensity of the laser light irradiated to the plasma. Calculate the absorption coefficient. Since the light intensity of the laser light applied to the plasma is controlled to a predetermined intensity in advance and is known, the calculation unit 38 calculates the laser light from the light reception signal of the transmitted light obtained by the light receiving unit 36 for the second measurement unit. The light absorption coefficient of the laser light can be calculated by dividing by a value corresponding to the light intensity of.
Further, the calculation unit 38 obtains an averaged density along the optical path of the laser light of the metastable argon gas from the calculated light absorption coefficient of the laser light. Since the obtained averaged density is an absolute value and is an integrated value along the optical path length l, the calculation unit 38 uses the averaged density for the fluorescence image at each position corresponding to the optical path of the fluorescence image. A density distribution along the optical path is generated by giving a high or low density value in proportion to the value of. In this way, the calculation unit 38 acquires the distribution of atomic density in the metastable state of argon (step S20).

Subsequently, the computing unit 38 uses the distribution of the density n ₁ ^M between the density n ₁ of the gas atoms in the ground state argon metastable argon gas atoms, further, using Equation (11), in the plasma An electron temperature distribution is acquired (step S30). The density n ₁ of argon gas atoms in the ground state is obtained from the amount of argon gas introduced into the film formation container 12.

Further, as described above, the calculation unit 38 calculates the equation (4), the emission intensity ratio of the argon atom Ar ^* and the oxygen atom O ^* , the calculated electron temperature, and the density n ₁ of the argon gas atoms in the ground state. Then, using the metastable argon gas atom density n ₁ ^M , the density n ₂ of oxygen atoms O is calculated as a distribution (step S40).

FIGS. 5A and 5B are diagrams showing examples of the density distribution of oxygen atoms mixed in the plasma using argon obtained by the method of the present embodiment. FIG. 5A shows the density distribution when plasma is generated by applying low power to the electrode plate 26C, and FIG. 5B is when plasma is generated by applying high power to the electrode plate 26C. Density distribution. In general, the density of oxygen atoms increases and the density distribution of oxygen atoms changes as compared to the case of low voltage. Specifically, when the power is low as shown in FIG. 5A, the distribution in which the density is high in the region A on the power feeding side is high, and when the power is high as shown in FIG. 5B, the density is in the region B on the ground end side. It is high. Thus, it can be seen that the density distribution of oxygen atoms changes according to the power applied to the electrode plate 26C. Further, as shown in FIGS. 5A and 5B, a stable distribution can be calculated even at a density of 10 ¹² pieces / cm ³ .

  FIG. 6A shows the calculation result of the average density of oxygen atoms as impurities obtained by this embodiment and the conventional method (“Detection of atomic oxygen: Improvement of actinometry and comparison with laser spectroscopy”). FIG. The horizontal axis of the graph shown in FIG. 6A is the power applied to the electrode plate 26C. As shown in FIG. 6A, in the present embodiment, since the density distribution of oxygen atoms as impurities is calculated in consideration of excitation from metastable argon atoms, it can be obtained more accurately. In FIG. 6A, an average density of oxygen atoms is obtained that is about 20% higher than the conventional method.

  FIG. 6B shows the calculation of the density distribution of oxygen atoms as impurities when plasma is generated by applying power 1200 W to an aluminum electrode plate 26C having a length of 15 cm, a width of 7.5 cm, and a thickness of 2 cm. It is a result. According to FIG. 6B, it can be seen that, in addition to the density itself being calculated to be about 20% higher, in the region C, the method of this embodiment shows a distribution in which the density rises. On the other hand, in the conventional method, the rise of density is small. This is considered to be due to the fact that the method of this embodiment takes into account the density distribution of metastable argon atoms that has not been obtained by the conventional method. From this, it can be said that the method of the present embodiment can calculate the density of the impurity atoms present in the generated plasma with reliability.

In this embodiment, 772 is generated when the ground state ¹ S ₀ of the argon atom is excited to 4p ′ [1/2] ₁ and then transitions downward to fall into the metastable state 4S ′ [1/2] ^O _0. .4 nm] light or when excited from the ground state ¹ S ₀ of argon atoms to 4p [3/2] ₁ and then transitions down to the metastable state 4S [3/2] ^O ₂ 772.4 nm] is used, but in addition to this, 826 nm light as shown in FIG. 7 can also be used. FIG. 7 is a diagram showing another example of the transition of argon atoms. Specifically, it is emitted from the ground state ¹ S ₀ of the argon atom to 4p ′ [1/2] ₁ , and then emits when it transitions downward and falls to the metastable state 4S ′ [1/2] ^O _1. It is also possible to use the light. In this case, also in the laser-induced fluorescence, it is preferable to use a laser beam having such a wavelength as to be excited from the metastable state 4S ′ [1/2] ^O ₁ to 4p ′ [1/2] ₁ by the induction of the laser beam.

As described above, in this embodiment, since the density of impurities is calculated as a distribution in plasma, it is possible to identify a source of impurity by specifying a high density region.
In the present embodiment, the electron temperature in the plasma is calculated from the absorption coefficient of the plasma generating gas and the fluorescence intensity of the gas, and the density of the state in which the plasma generating gas has transitioned downward is calculated using this electron temperature. Therefore, a highly accurate calculation result can be obtained.

  Since the contamination of impurities in the plasma changes depending on the device configuration of the film formation container and the contamination of the inner wall surface of the film formation container, the present distribution of the density of impurity atoms in the plasma generated in the current film formation container 12 is implemented. The form can be calculated with high accuracy. For this reason, in the present film formation container 12, the conditions at the time of plasma generation, for example, the power applied to the electrode plate 26C, or the amount of argon gas introduced into the film formation container 12 so that the density of impurity atoms is minimized. Can be operated.

  As described above, the impurity measurement method, measurement apparatus, and film formation apparatus of plasma of the present invention have been described in detail. However, the impurity measurement method, measurement apparatus, and film formation apparatus of the present invention are the same as those in the above embodiment. Of course, various improvements and modifications may be made without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Film-forming apparatus 12 Film-forming container 14 Susceptor 16 Substrate 18 Exhaust unit 20 Gas supply valve 22 Raw material gas source 24 Carrier gas source 26 Plasma generation unit 26A High frequency power supply 26B Matching box 26C Electrode plate 26D Dielectric plate 30 Measurement system 32 1st Measurement unit 34 Light source for second measurement unit 36 Light receiver for second measurement unit 38 Calculation unit 40 Control device 41 Display 42 Printer 40 Control device

Claims (11)

A measurement method for measuring impurities in plasma,
A plasma generation step of generating plasma using a plasma generation gas;
A first measurement step of measuring emission intensity caused by a downward transition from an excited state of the gas in the plasma and emission intensity caused by a downward transition from an excited state of impurities in the plasma;
A second measuring step of irradiating the plasma with laser light and measuring the intensity of transmitted light that has passed through the plasma without being absorbed by the gas, and the fluorescence intensity of the gas induced by laser; ,
Using the light absorption coefficient of the gas calculated from the intensity of the transmitted light obtained in the second measurement step and the fluorescence intensity of the gas, the density of the gas that has transitioned downward is obtained, The density of the impurity is calculated using the emission intensity ratio between the emission intensity caused by the downward transition from the excited state and the emission intensity caused by the downward transition of the impurity in the plasma from the excited state, and the density. And a calculating step. In the first measurement step, the emission intensity ratio is measured as a distribution in the plasma,
In the second measurement step, the fluorescence intensity of the gas is measured as a distribution along the optical path of the laser beam,
The measurement method according to claim 1, wherein in the calculating step, the density of the impurities is calculated as a distribution in the plasma.   In the calculation step, the electron temperature in the plasma is calculated from the light absorption coefficient of the gas obtained in the second measurement step and the fluorescence intensity of the gas, and the downward transition of the gas is performed using the electron temperature. The measurement method according to claim 1, wherein the density of the processed state is obtained. The density of the impurities is calculated using the following equation (4) that relates the emission intensity ratio, the density of the gas, the density of the gas in the state of lower transition, and the density of the impurity atoms. The measurement method according to any one of claims 1 to 3.

  The measurement method according to claim 1, wherein the gas is an argon gas, and the impurity is oxygen. The emission intensity generated by the downward transition from the excited state of argon is a light intensity of 777.2 nm, the emission intensity generated by the downward transition from the excited state of oxygen is a light intensity of 777 nm,
The measurement method according to claim 5, wherein a wavelength of laser light applied to the plasma is 696.54 nm and a wavelength of fluorescence intensity of the gas is 772.4 nm. A measuring device for measuring impurities in plasma,
A plasma generation container for generating plasma using a plasma generation gas;
A plasma generation unit for generating plasma in the plasma generation vessel;
The emission intensity caused by the downward transition from the excited state of the gas in the plasma and the emission intensity caused by the downward transition from the excited state of the impurity in the plasma are measured, and the fluorescence of the gas emitted by the induction of laser light A first measurement unit for measuring the fluorescence intensity of
A second measuring unit that irradiates the plasma with laser light, and measures the intensity of the transmitted light that has passed through the plasma without being absorbed by the gas, and the fluorescence intensity of the gas induced by the laser; ,
Using the light absorption coefficient of the gas obtained by the second measurement unit and the fluorescence intensity of the gas obtained by the first measurement unit, the density of the gas that has transitioned downward is obtained, and the excited state of the gas The density of the impurity is calculated using the emission intensity ratio between the emission intensity caused by the downward transition from the emission intensity and the emission intensity caused by the downward transition from the excited state of the impurity in the plasma, and the obtained density. And a calculation unit. The first measurement unit measures the emission intensity ratio as a distribution in the plasma,
The second measurement unit measures the fluorescence intensity of the gas as a distribution along the optical path of the laser light,
The measurement apparatus according to claim 7, wherein the calculation unit calculates the density of the impurity as a distribution in the plasma.   The calculation unit calculates an electron temperature in the plasma from the measured light absorption coefficient of the gas and the fluorescence intensity of the gas, and uses the electron temperature to obtain a density of a state in which the gas has transitioned downward. The measuring device according to claim 7 or 8. The calculation unit uses the following formula (4) that relates the emission intensity ratio, the density of the gas, the density of the gas that has been transitioned downward, and the density of the impurity, and The measuring apparatus according to claim 7, wherein the density is calculated.

A film forming apparatus for generating a thin film on a substrate, comprising the measuring apparatus according to claim 7.
A source gas for film formation is introduced into the plasma generation container together with the gas for plasma generation, and a substrate disposed in the plasma generation container is formed into a film,
The film forming apparatus further includes a control device that changes a condition for generating the plasma so that the impurity density decreases in accordance with the calculated impurity density.

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