JP2005156221A - Particle distribution measuring instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform measurement with high sensitivity, with a high dynamic range, and at a high speed, by enhancing the S/N ratio of a detection signal on light emitted from measuring object particles, in a measuring instrument for measuring the distribution of the object particles by measuring light emitted from the object particles such as plasma-state molecules owing to laser light irradiation. <P>SOLUTION: This particle distribution measuring instrument 10 comprises a laser light generation unit 12, a focus lens 18a for focusing laser light as irradiation light to the measuring object particles, a detection unit 20 for detecting light emitted from the object particles irradiated with the irradiation light, and a confocal optics system forming means for causing at least a part of laser light incoming from the generation unit 12 to exit from a point at an image surface position of the focus lens 18a as irradiation light and causing light focusing at a point of a focal position of the focus lens 18a out of light emitted by the object particles to progress to the detection unit 20. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention irradiates particles of active species such as generated radicals, excited species, and ions with laser light, detects light emitted from the excited particles, and detects the concentration distribution of particles in the flow field. The present invention relates to a particle distribution measuring apparatus for measuring a concentration distribution of generated particles.

Nowadays, in semiconductor processes, CVD (Chemical Vapor Deposition), PVD (Physical Vapor Deposition), and semiconductor manufacturing equipment used for sputtering use the plasma generated in the gas phase in the chamber to form and etch thin films. Used for.
In recent years, with the increase in size of Si substrates and the like, the chambers of semiconductor manufacturing apparatuses used for CVD, PVD and sputtering are also increased in size, and it is strongly required to form a thin film uniformly on the enlarged Si substrates in these apparatuses. It has been. For this reason, it is necessary to confirm whether or not plasma molecules or the like are uniformly generated in the chamber.

In general, when measuring molecules in a plasma state with laser light, the molecules to be measured are irradiated with the laser light, and the light emitted from the excited molecules in the plasma state is measured to determine the types of molecules in the plasma state. An LIF (Laser Induced Fluorescence) method for observation is known.
In the LIF method, as shown in Non-Patent Document 1, one point in the gas phase is measured by irradiating one point in the gas phase having molecules in the plasma state with laser light. For this reason, in order to measure the distribution of molecules in the plasma state, the laser light source and the associated optical unit must be moved together in order to change the focus position of the laser light. If the movement of the focusing position is not performed accurately, an accurate distribution cannot be obtained. To provide an accurate moving unit, the apparatus itself must be enlarged, and the apparatus itself becomes complicated. End up.

On the other hand, the distribution of light emitted in the plasma state is measured by using an imaging tube such as a CCD imaging device to measure the distribution in the gas phase, but the light emitted by the imaging tube or the like is imaged. When the distribution is obtained, the emitted light is extremely weak with respect to the irradiating laser light, and cannot be accurately detected in a short time in units of photons by the imaging tube. Further, the image pickup signal obtained by the image pickup tube is a detection signal obtained by accumulating light emitted in the depth direction with respect to the image pickup person, and a detection signal of light emitted at a predetermined pinpoint position cannot be obtained.
In addition, the light emitted from the excited plasma is extremely weak compared to the irradiated laser light, so it is caused by disturbance light such as the return light of the laser light reflected by the wall surface of the chamber and the light that spontaneously emits plasma molecules. Under the influence of the offset component, the S / N ratio in the detection signal of light emitted from excited molecules or the like is extremely low and is easily buried in noise.

“Latest Plasma Process Monitoring Technology and Analysis / Control”, Yasuaki Hayashi, Realize, Inc., pages 29-31, 280

  Therefore, the present invention is a measuring apparatus for measuring the distribution of particles to be measured by measuring the light emitted from the particles to be measured such as molecules in a plasma state by irradiating the laser beam. An object of the present invention is to provide a small particle distribution measuring apparatus capable of increasing the S / N ratio of a detection signal of light to be measured and measuring at high speed with high sensitivity and high dynamic range.

  In order to achieve the above object, the present invention provides a particle distribution measuring apparatus for detecting the light emitted from the measurement target particle by irradiating the measurement target particle with laser light and measuring the distribution of the measurement target particle. A laser light generation unit that emits laser light; and a lens unit that includes a focus lens that focuses the laser light as irradiation light on the measurement target particles at a predetermined position in a space in which the measurement target particles are distributed; A detection unit that detects the light emitted from the measurement target particle upon receiving the irradiation light, and at least a part of the laser light incident from the laser light generation unit as the irradiation light, the image plane position of the focus lens Of the light emitted from the particles to be measured and collected at the focal point of the focus lens. To provide a particle distribution measuring apparatus characterized by comprising: a confocal optical system forming means for advancing the unit.

  Here, the confocal optical system forming means has a reflecting surface for reflecting incident light, the image plane position is on the reflecting surface, and the laser beam incident on the focal point from the laser beam generating unit is received. It is preferable to have a reflecting mirror that reflects and emits the irradiation light, reflects the light collected at the focal point out of the light emitted from the measurement target particle, and advances the light to the detection unit.

The present invention also relates to a particle distribution measuring apparatus for detecting the light emitted from the measurement target particle by irradiating the measurement target particle with laser light and measuring the distribution of the measurement target particle, and emitting the laser light. A laser light generating unit, a lens unit including a focus lens that focuses the laser light as irradiation light on the measurement target particles at a predetermined position in a space where the measurement target particles are distributed, and irradiation of the irradiation light And detecting the light emitted from the measurement target particle, and controlling the irradiation light so as to scan the focused position of the irradiation light in at least one direction within the space in which the measurement target particle is distributed. Irradiation light control means,
Provided is a particle distribution measuring apparatus that measures the distribution of the measurement target particles in the space by scanning the focusing position of the irradiation light by the irradiation light control means.

Here, the irradiation light control means emits at least a part of the laser light incident from the laser light generation unit as the irradiation light from a point at the image plane position of the focus lens, and emits light from the measurement target particles. It is preferable to have confocal optical system forming means for causing the light collected at the focal point of the focus lens to travel to the detection unit.
The laser light generation unit includes a laser light source that emits laser light, and a beam expander that expands a light beam of the laser light emitted from the laser light source, and the confocal optical system forming unit includes incident light. The reflecting mirror has a reflecting surface that reflects the laser beam. The reflecting mirror has a plurality of micromirrors arranged on a plane that reflect the laser beam expanded by the beam expander and is incident on each of these micromirrors. The micromirror array element is movable so that the direction of the micromirrors can be controlled so as to change the reflection direction of the laser beam to be controlled, and the direction of each micromirror of the micromirror array element is controlled to increase the luminous flux of the laser light By generating irradiation light having a part of the light beam as a luminous flux, the space in which the particles to be measured are distributed is scanned in one direction or two directions, Preferably, irradiating the measurement target particles. Further, the lens unit includes a moving stage that moves the focus lens along the direction of the optical path of the laser light, and moving the moving stage allows the irradiation light to pass through the space in which the particles to be measured are distributed. It is preferable to change the focusing position.

  An optical element that transmits and reflects incident light at a predetermined transmittance and reflectance in an optical path between the laser light generation unit and the mirror array element, the laser light and the measurement target particle A beam splitter is provided on which the light emitted from the laser beam is incident, and the laser light emitted from the laser light generation unit travels toward the beam splitter, the mirror array element, and the lens unit, and emits light from the measurement target particles. Light travels in a direction opposite to the traveling direction of the laser light toward the lens unit, the mirror array element, and the beam splitter, and the detection unit emits light emitted from the measurement target particle emitted from the beam splitter. Is preferably arranged at a position different from that of the laser light generation unit.In this case, the beam splitter mainly reflects one polarization component of the first polarization component and the second polarization component of the incident light, and mainly transmits the other polarization component of the incident light. A polarizer that transmits one polarization component of the laser beam is provided in an optical path between the laser beam generation unit and the polarization beam splitter, and the polarization component of the laser beam is incident on the polarization beam splitter. Is preferred.

  The particles to be measured are, for example, activated particles in plasma in the gas phase, and more specifically, activated particles in plasma in the gas phase confined in the chamber. It is preferable that the irradiation light is irradiated into the gas phase in the vacuum chamber from a window provided on the wall surface of the chamber.

The laser beam emitted from the laser beam generation unit is a pulse laser beam having an emission time of 5 nanoseconds or less, and the detection unit performs sampling to count the detection signal of the light emitted from the measurement target particle. The focus lens of the lens unit preferably has an image plane distance on the measurement target particle side that is equal to or longer than a value obtained by dividing the product of the sampling period and the speed of light in the sampling by two.
The particles to be measured in the present invention are particles such as radicals, excited species, ions, and other active molecules and atoms generated in the gas phase, for example, in a chamber in a semiconductor manufacturing apparatus or a liquid crystal manufacturing apparatus. In addition to activated molecules and atoms in combustion flames, particles in liquid and solid phases are also included.

In the present invention, the confocal optical system forming means is used to irradiate the measurement target particle with laser light and detect the weak light emitted from the measurement target particle. Thus, the influence of disturbance light or the like can be suppressed, and detection with improved S / N ratio is realized.
In addition, since the irradiation of the laser beam is controlled so as to scan the space in which the measurement target particles are located using the micromirror array element, a small apparatus that can measure the distribution of the planar measurement target particles is configured. be able to. Further, by placing the focus lens on the moving stage, the irradiation position can be changed in the depth direction of the optical axis of the focus lens in the space where the measurement target particle is located, and the three-dimensional measurement target particle in the space can be changed. Distribution can be measured in a short time.
In addition, by using a polarizer and a polarizing beam splitter, the detection unit performs high-speed sampling with a sampling period of several nanoseconds or less, so that the irradiation light is surfaced on the wall surface that forms the space where the particles to be measured are located. Even in the case of reflection, the offset component due to disturbance light such as reflected light can be reduced, and the dynamic range of the detection signal of the light emitted from the particles to be measured can be widened.

  Hereinafter, the particle distribution measuring apparatus of the present invention will be described in detail based on a preferred embodiment shown in the accompanying drawings.

FIG. 1 is an explanatory view schematically showing a configuration of a plasma distribution measuring apparatus 10 which is an example of a particle distribution measuring apparatus of the present invention.
The plasma distribution measuring apparatus 10 generates a laser light generation unit 12 that generates laser light of a predetermined light flux, a beam splitter 14 that transmits and reflects laser light, and irradiation light that irradiates measurement target particles in a plasma state. An irradiation light generating unit 16 that functions as a confocal optical system forming unit, a lens unit 18 that focuses the irradiation light into a predetermined space where particles in a plasma state are located, and a detection unit 20 that detects the light emitted from the particles to be measured. And a control unit 22 that controls the driving of each of these units. The irradiation light generation unit 16 and the control unit 22 function as irradiation light control means for controlling the irradiation light so as to scan the convergence position of the irradiation light in at least one direction within the space in which the measurement target particles are distributed.
Note that the confocal optical system forming means emits at least a part of the laser light incident from the laser light generation unit 12 as irradiation light from a point on the image plane position of the focus lens included in the lens unit 18 and is a measurement target. Of the light emitted by the particles, the light having the function of advancing to the detection unit 20 the light collected at a point on the focal position of the focus lens.

The laser light generation unit 12 includes a semiconductor laser 12a, a beam expander 12b, and a polarizer 12c.
The semiconductor laser light source 12a is, for example, a known semiconductor laser light source in which an active layer and a cladding layer are stacked on a GaAs substrate or an InP substrate, and a short pulse laser beam is supplied from the control unit 22 with a time width of 5 nanoseconds or less. Injecting according to the control signal. The emitted laser light has, for example, a wavelength of 250 nm to 500 nm and a maximum light intensity of several kW.
In the present invention, various laser light sources such as a pulse dye laser light source, an excimer laser light source, and a YAG laser light source can be used in addition to the semiconductor laser light source. These may be appropriately selected according to the activated particles to be measured in consideration of the wavelength of the emitted laser beam, the light intensity, the emission time width, and the like.

The beam expander 12b expands a laser beam having a small luminous flux emitted from the semiconductor laser light source 12a into a thick luminous flux, and has two sets of lenses facing each other so that their focal positions overlap. The reason why the laser light beam is enlarged is that, as will be described later, a part of the light beam is used as irradiation light for irradiating particles in a plasma state to be measured.
The polarizer 12c extracts the S-polarized component of the laser light whose beam has been expanded.

The beam splitter 14 is an optical element that receives laser light and light emitted from particles in a plasma state to be measured, which will be described later, and transmits and reflects the incident light with a predetermined transmittance and reflectance. This beam splitter 14 is a polarization beam splitter that mainly reflects when incident light is an S-polarized wave and transmits mainly when incident light is a P-polarized wave. Mainly reflection means that the reflectance of the S-polarized wave is 99% or more, and mainly transmission means that the transmittance of the P-polarized wave is 99% or more.
Therefore, the S-polarized component of the laser light emitted from the polarizer 12 c is mainly reflected by the beam splitter 14 and proceeds to the irradiation light generation unit 16. On the other hand, light emitted from plasma particles to be measured, which will be described later, travels from the irradiation light generation unit 16 to the beam splitter 14, and only the P-wave polarization component travels mainly through the beam splitter 14.

The irradiation light generation unit 16 includes a prism 16a and a micromirror array element 16b, and functions as a confocal optical system forming unit and an irradiation light control unit as will be described later.
The prism 16 transmits the S-polarized component of the laser light from the beam splitter 14 and advances it to the micromirror array element 16b. At the same time, the light emitted from particles in the plasma state to be measured, which will be described later, is directed toward the micromirror array element 16b. Configured to reflect. Further, the light reflected by the micromirror array element 16 b is advanced toward the beam splitter 14.

The micromirror array element 16b is a spatial modulation element that is movable by a control signal supplied from the control unit 22 so that a plurality of micromirrors 17 are arranged on a plane and the direction of the micromirrors changes. In FIG. 1, it is provided vertically below the prism 15. As the micromirror array element 16b, for example, a digital micromirror device (DMD) (trademark) manufactured by TI, USA is suitably used. The DMD is configured to be movable at a predetermined angle around the rotation axis of each micromirror, and the rotation angle of the micromirror is + 12 ° or −12 ° according to a control signal supplied from the outside. Controlled.
Only one of the arranged micromirrors 17 (the micromirror 17a in FIG. 1) has the same incident direction of the laser beam and the reflected direction of the light emitted from the particle to be measured. The direction of the micromirror 17 is controlled so that the angle is deviated.
Accordingly, the S-polarized component of the laser light transmitted through the prism 16a is only totally reflected by the inclined surface of the prism 16a only in the light reflected by the micromirror 17a, and proceeds to the left in FIG. 1 (to the lens unit 18 side). The irradiation light is applied to the particles in the state.

The lens unit 18 includes a focus lens 18a, a moving stage 18b, and a drive motor 18c connected to the moving stage 18c.
The focus lens 18a is placed on the moving stage 18b and is configured to move freely in the optical axis direction of the focus lens 18a. Further, the drive motor 18c connected to the moving stage 18b rotates so that the moving stage 18b moves forward or backward toward the side of the chamber 24 where the measurement target particles are located, according to the control signal of the control unit 22.
The irradiation light that travels by being totally reflected by the slope of the prism 16 a passes through the focus lens 18 a, passes through the window 24 a of the chamber 24, and is configured such that the irradiation light is focused at a predetermined position in the chamber 24.

The chamber 24 is in a low pressure state, for example, 5 to 133 Pa in order to form a thin film by plasma CVD, and gas molecules in the chamber 24 are activated as particles in a plasma state by an applied voltage. Gas molecules activated in such a plasma state are particles to be measured.
Note that the micromirrors arranged in a planar shape of the micromirror array element 16b are provided at the image plane position of the focus lens 18a, and a part of the laser beam, which is a parallel beam with an expanded luminous flux, is generated as the irradiation light, and the focus The light is focused on the focal position in the chamber 24 by the lens 18a.
The particles in the plasma state are excited by irradiation with irradiation light, and emit light when transitioning from the excited state to the ground state. The emitted light travels to the beam splitter 14 via the focus lens 18a, the prism 16a, the minute mirror 17a, and the prism 16a. Only the P-polarized light component is transmitted through the beam splitter 14 and proceeds to the detection unit 20.

The detection unit 20 includes a lens 20a, a narrow band filter 20b, a photomultiplier tube 20c, an amplifier 20d, a counter board 20e, and a computer 20f.
The lens unit 20a is arranged so that the light (P-polarized component) emitted from the measurement target particles reaching the detection unit 20 is focused by the photocathode that is the light receiving surface of the photomultiplier tube 20c.
The narrow band filter 20b has a narrow band filter characteristic so that the light emitted from the measurement target particle is extracted separately from the light of the irradiation light, and filters the light in the wavelength band.
The photomultiplier tube 20c is an electron tube that changes incident light into a large current signal (detection signal). As is well known, the photomultiplier tube 20c includes several dynodes between a photocathode and an anode.

The counter board 20e is a circuit that counts light incident on the photomultiplier tube 20c as photons using a detection signal of light generated by the photomultiplier tube 20c and amplified by the amplifier 20.
A sampling period of 2 nanoseconds or less so that the detection signal amplified by the amplifier, that is, the weak light emitted from the measurement target particle is generated as a detection signal of photon (also called photon) and the number of photons detected is counted. The detection signal is sampled at high speed and configured to count one count for the detection of one photon. Specifically, a predetermined threshold value is set for the counter board 20e, and if the detection signal from the amplifier 20d crosses the threshold value, it is counted that one photon has been detected.
For example, a high-speed sampling of 2 nanoseconds or less is preferably an A / D conversion board CompuScope 85G manufactured by GaGe (Gage Applied Sciences Inc.) that samples 5G times per second. The reason why high-speed sampling is performed in this way is to efficiently detect only the weak light emitted from the particles to be measured together with the narrow band filter 20b. In particular, the effect on detection sensitivity by high-speed sampling is large.
The computer 20f is a device that controls driving of the entire apparatus via the control unit 22, accumulates photon data counted by the counter board 20e, processes the data, and displays a processing result.
The control unit 22 is a circuit that generates and supplies a control signal to each unit in accordance with an instruction from the computer 20f.

FIG. 2 is a diagram illustrating an example of the light intensity distribution in the wavelength band of the irradiation light irradiated to the measurement target particle and the light intensity distribution of the light emitted from the measurement target particle, together with the filter characteristics of the narrow band filter 20b.
The light emitted by the particles to be measured has an extremely weak light intensity compared to the irradiated light (the light intensity is 1/10 ⁹ or less of the irradiated light), and the Stokes shift is approximately 10 nm (the difference between the center wavelengths is approximately 10 nm). And is very close to the irradiation light in the wavelength band. For this reason, a part of the irradiation light may overlap with the side lobe part in the filter characteristics of the narrow band filter 20b, and a part of the irradiation light may be mixed into the light of the measurement target particle even after the filtering process. Part of this mixed irradiation light is very weak compared to the irradiation light, so even if most of the light is removed by filtering, the weak light emitted by the measurement target particles For this, the light intensity is sufficiently high, which is a very big obstacle to measurement. For this reason, the detection unit 20 performs high-speed sampling of 2 nanoseconds or less.

  FIG. 3 shows a light intensity distribution A that changes with the time of weak light emitted from the measurement target particle. In FIG. 3, the photomultiplier tube of the detection unit 20 passes through the focus lens 18 a, the prism 16 a, the micromirror array element 16 b, the prism 16 a, and the beam splitter 14 from the position irradiated with the irradiation light that irradiates the measurement target particles. A virtual time point at which light is received at 20 is used as a reference. A light intensity distribution B in FIG. 3 is the light intensity distribution of the return light reflected by the inner wall surface of the chamber 24. As shown in FIG. 3, the light emitted from the measurement target particle reaches the photomultiplier tube 20c before the return light arrives.

  Further, FIG. 3 shows a light intensity distribution C that is a disturbance, including an intensity distribution of light that the plasma in the chamber 24 spontaneously emits. The level of the light intensity distribution C is lower than the peak level of the light intensity distribution A. However, since the light intensity distribution C is always present as disturbance light, photons are accumulated and counted for a period of several tens of nanoseconds. The light intensity distribution A is buried in the light intensity distribution C in a light receiving sensor that generates an image pickup signal by setting an accumulation time like an image pickup tube. Further, the light intensity distribution A is already attenuated in the sampling period of several tens of nanoseconds, and becomes below the level of the light intensity distribution C caused by the disturbance light. For this reason, the light intensity distribution A is buried in the light intensity distribution C and cannot be detected by a light receiving sensor that receives and accumulates light for a predetermined time.

Further, the distance between the imaging position of the irradiation light focused by the focus lens 18a and the focus lens 18a, that is, the imaging distance (image surface distance) s, which is the time s / c of 2 during which light (the speed of light is c) passes. High-speed sampling is performed at a period equivalent to or shorter than twice the time. Specifically, when the imaging distance s is 15 cm, the light velocity c = 3.0 × 10 ¹⁰ (cm / sec) and the sampling period is 1 nanosecond (= 15 / (3.0 × 10 ¹⁰ × 2). It becomes as follows.
The upper limit value of the sampling period is defined in this case when the measurement target particle is immediately excited by irradiation light passing through the focus lens 18a, and the measurement target particle is immediately excited, and the excited particle emits light immediately. This is because the light emitted in the measurement time band can be distinguished from the reflected irradiation light component generated when the light enters the focus lens 18a.
Therefore, if the focus lens 18a is fixed, the upper limit value of the sampling period of the counter board 20e is determined using the above-described relationship between the imaging distance s and the light velocity c, so that the light received by the detection unit 20 can be received by the focus lens 18a. It can be distinguished from the reflected irradiation light component in FIG.
If the sampling period is fixed, the lower limit value of the imaging distance s can be determined using the relationship between the imaging distance s and the light velocity c, and the focus lens 18a can be selected accordingly.

  In such a plasma distribution measuring apparatus 10, in the micromirror array element 16b, as described above, a part of the laser light, which is parallel light with spread light flux, is reflected by the micromirror 17a to generate irradiation light. For this reason, the irradiation light which is parallel light can be regarded as laser light using the point of the micromirror 17a of the micromirror array element 16b as a point light source. In this case, the point light source is placed at a position at infinity to generate parallel light. Further, when the light emitted from the measurement target particle enters the micromirror array element 16b, the light focused on the point of the micromirror 17a is reflected toward the detection unit 20.

That is, only the laser beam reflected by the micromirror 17a whose direction is adjusted so as to be reflected in the same direction as the incident direction in the micromirror array element 16b is reflected toward the focus lens 18a as irradiation light, and this irradiation light The light emitted by the light advances to the micro mirror 17a by the focus lens 18a and further reaches the detection unit 20. Therefore, when viewed from the focus lens 18 a, the micromirror 17 a can be regarded as a point light source that generates irradiation light, and the micromirror 17 a measures the light of particles emitted at a predetermined position in the chamber 24. For this reason, it can be regarded as a single point. Therefore, the micromirror array element 16b and the focus lens 18a constitute a confocal system such as a confocal laser microscope having a high S / N ratio. That is, the position serving as the light source of the irradiation light and the position where the light emitted from the measurement target particles is collected for measurement are the positions of the same micromirror 17a, and these positions are optically beneficial to the focus lens. It becomes confocal in the positional relationship.
Therefore, the S / N ratio of the detection signal of the light that proceeds to the micromirror 17a and is received by the detection unit 20 is improved as in the confocal laser microscope. In addition, it is preferable to increase the aperture angle when the irradiation light is focused by the focus lens 18a in terms of improving the S / N ratio of the detection signal, and the F number (focal length / lens aperture) of the focus lens 18a is 2. .5 or less is preferable.
Further, since the inner wall surface of the chamber 24 has a mirror finish, the irradiation light irradiated into the chamber 24 is easily reflected and scattered. However, since the confocal system is configured, the influence of disturbance light that is reflected light and scattered light can be suppressed.

The micromirror array element 16b is controlled so as to move the position of the micromirror that matches the reflection direction of the incident illumination light (laser light) with the incident direction of the light emitted from the measurement target particle with time. That is, the control unit 22 controls the direction of each micromirror 17 of the micromirror array element 16b, and changes the micromirror in which the incident direction of the illumination light matches the reflection direction of the light emitted from the measurement target particle. Supply. Accordingly, for example, by controlling the micromirrors arranged in one direction of the micromirror array element 16b so that the light incident direction and the reflection direction coincide with each other in order, the position where the irradiation light converges in one direction in the chamber 24 Can be scanned. Therefore, by scanning the micromirrors arranged in the plane of the micromirror array element 16b in two directions, the position where the irradiation light in the chamber 24 is focused can be scanned in two directions on the plane. It is possible to know the distribution of particles to be measured. Of course, the position where the irradiation light in the chamber 24 is focused may be scanned in one direction by scanning the micromirror in one direction.
Further, the control unit 22 controls the rotation of the drive motor 18c connected to the moving stage 18b, so that the particles to be measured in the chamber 24 in the optical axis direction (left-right direction in FIG. 1) viewed from the focus lens 18a. The distribution can also be measured.

In the example shown in FIG. 1, the particles to be measured are particles in a plasma state generated in the chamber 24 of the plasma CVD apparatus. In the present invention, the particles to be measured are particles in a closed gas phase space such as a chamber. It is not limited to. For example, it may be plasma particles in a flame or particles in a solid or liquid, and at least measure the light emitted from the measurement target particles by irradiating the measurement target particles with laser light. It is only necessary to measure the distribution of the particles to be measured in the space.
The above is the configuration of the plasma distribution measuring apparatus 10.

Next, the operation of the plasma distribution measuring apparatus 10 will be described.
In the plasma distribution measuring apparatus 10, first, a short pulse laser beam of several nanoseconds is emitted from the semiconductor laser light source 12a by a control signal of the control unit 22, and a light beam is expanded by the beam expander 12b. The laser beam with the expanded luminous flux generates an S-polarized component of the laser beam by the polarizer 12c.
Thereafter, the laser light (S-polarized component) is reflected by the beam splitter 14, proceeds downward in FIG. 1, and enters the prism 16a.

In the prism 16a, the laser light (S-polarized component) is transmitted and is incident on the micromirror array element 16b positioned vertically below the prism 16a. At this time, according to the control signal from the control unit 22, for example, only one of the micromirrors (the micromirror 17a in FIG. 1) has the same incident direction of the laser light and the reflection direction of the light emitted from the measurement target particle. The direction of the micromirror is controlled vertically upward, and only the laser light incident on the micromirror is returned to the prism 16a, totally reflected by the slope of the prism 16a, and directed to the focus lens 18a. On the other hand, the direction of the other minor mirrors is controlled so that the incident direction and the reflection direction of the laser beam are different from each other, so that the laser beam reflected by the prism 16a does not travel to the focus lens 18a. Thereby, for example, only laser light reflected by one minute mirror is generated as irradiation light and transmitted through the focus lens 18a.
The irradiation light is focused at a position in the gas phase in the chamber 24 determined according to the image plane distance of the focus lens 18a, and the measurement target particles in the plasma state existing at this position are excited to emit light. Luminescence does not always occur frequently, but occurs three to five along a predetermined stochastic process.

The emitted light travels through the focus lens 18a and the prism 16a to the minute mirror 16b positioned vertically downward. At this time, since the minute mirror 16b is controlled to one minute mirror (the minute mirror 17a) whose reflection direction of the light emitted from the measurement target particle coincides with the incident direction of the laser light as described above, this minute mirror 16b is controlled. The light incident on the mirror is reflected by the micromirror toward the prism 16a and passes through the prism 16a. Other than this, the light is totally reflected on the slope of the prism 16a and does not travel toward the detection unit 20.
Only the P-polarized light component of the light transmitted through the prism 16 a is selected by the beam splitter 14 which is a polarization beam splitter, passes through the beam splitter 14, and proceeds to the detection unit 20.

  The reason why the beam splitter 14 is a polarization beam splitter is that the light emitted from the measurement target particle is extremely weak with respect to the irradiation light, and it is required to detect the light with high accuracy. That is, by making the polarization component of the laser light used as the irradiation light and the light emitted from the measurement target particle different, the light emitted from the measurement target particle in the detection unit 20 can be detected with high sensitivity, and the S / N ratio can be increased. This is because a high detection signal is obtained and sampling is performed with a high dynamic range.

  As described above, the micromirror array element 16b functions as a point light source in which one micromirror (micromirror 17a) generates irradiation light, and also functions as the point light source among the light emitted from the measurement target particles. Since the light incident on the mirror proceeds to the detection unit 20 as the light to be measured, it can be said that the light to be measured gathers at the position of the micromirror that functions as a point light source. That is, the micromirror array element 16b has a pinhole function in a confocal system.

The light emitted from the measurement target particles that has traveled to the detection unit 20 is collected by the lens 20a, and further filtered by the narrow band filter 20b so as to be roughly separated from the wavelength band of the irradiation light. In this way, light of a predetermined wavelength band is received by the photomultiplier tube 20c, and a detection signal is generated.
The detection signal generated by the photomultiplier tube 20c is amplified by the amplifier 20d and sampled by the counter board 20e. In the counter board 20e, it is assumed that one photon is received by the photomultiplier 20c when a threshold value set while checking the level of the sampled detection signal is exceeded. The time delay of the detected photon is obtained as data using the time measured in synchronization with the emission timing of the semiconductor laser light source 12a. This data is sent to and stored in the computer 20f.
Such detection of photons by light emission of the measurement target particles cannot always be reliably performed with one laser beam. Therefore, it is preferable to detect the photons by intermittently irradiating the irradiation light a plurality of times.

The sampling period by the counter board 20e is 2 nanoseconds or less. The reason why high-speed sampling is performed in this way is that there is a large difference in intensity between the light intensity of the irradiated light and the light emitted from the measurement target particle. This is to effectively separate the irradiation light. In addition, the offset component due to disturbance light can be suppressed to a small value by such high-speed sampling, and a detection signal with a high S / N ratio can be obtained and measured at high speed with a high dynamic range.
As described above, the use of the confocal system configuration, the polarization component, and the narrow band filter can detect the weak light emitted from the measurement target particle with high sensitivity.

Next, the direction of the micromirrors 17 of the micromirror array element 16 b is changed based on the control signal supplied from the controller 22, and the irradiation light is focused at different positions in the chamber 24. In this way, the particles to be measured are excited at different positions to detect and count photons.
In this manner, while controlling the direction of the micromirror 17 sequentially, the photons of the measurement target particles on one plane in the chamber 24 are detected, and the number of detected photons is counted. Further, the focus lens 18a on the moving stage 18 is moved in the optical axis direction, and photons of the measurement target particles on another plane in the chamber 24 are detected and counted.

Thus, by counting the photons generated in the chamber 24, the distribution of the measurement target particles can be measured in three dimensions. Since the measurement target particles excited by the irradiation light emit light when transitioning to the ground state with a predetermined probability, the distribution of the measurement target particles can be measured by counting the number of detected photons.
As described above, by using the moving stage 18 on which the micromirror array element 16b and the focus lens 18a are mounted, a small apparatus for measuring the three-dimensional distribution of the measurement target particles in the space can be configured.
The computer 20f accumulates the time delay data of the counted photons, for example, summarizes the number of photons within a predetermined time delay range, and uses this result to determine the distribution of the measurement target particles on the monitor of the computer 20f. Is displayed.

  The beam splitter 20 of the above apparatus is a polarizing beam splitter. However, in the present invention, a normal beam splitter whose reflectance and transmittance do not change depending on the polarization component may be used. In this case, the polarizer 12c is also unnecessary. The detection unit 20 counts photons using the narrow band filter 20b and the photomultiplier tube 20c. However, the detection unit 20 is not limited to this. For example, a spectroscope is provided to obtain an emission spectrum. May be.

FIG. 4A is a diagram illustrating measurement positions P, Q, and R in the flame, where the particles to be measured are activated molecules in the flame of the alcohol lamp.
4 (b) to 4 (d) are graphs showing time series of photon counts detected in a flame state, a return light state of irradiation light, and a state in which irradiation light is irradiated on the flame, respectively. Region R in FIG. 4D is a region where the number of photons detected by the activated particles emitting light is dominant. The graph of FIG. 4E shows the photon count number in the region R and is expressed as a distribution in space. As can be seen from FIG. 4 (e), the photon count varies depending on the measurement position, and the distribution of activated molecules in the flame can be known.

The particle distribution measuring apparatus of the present invention has been described in detail above. However, the present invention is not limited to the above-described embodiment, and various modifications and changes may be made without departing from the gist of the present invention. It is.
In the present invention, particles including activated molecules or atoms in plasma are measured, and particles activated by heating a gas such as NO _x may be measured. In addition to particles in a gas phase, particles in a liquid phase or a solid phase may be measured.

It is explanatory drawing which showed typically the structure of the plasma distribution measuring apparatus which is an example of the particle | grain distribution measuring apparatus of this invention. It is a figure which shows the example of the light intensity distribution of the irradiation light irradiated to the particle | grains of a plasma state, and the light intensity distribution of the light emitted from the measurement object particle. It is a figure which shows the light intensity distribution of the weak light which the measurement object particle | grains shown in FIG. (A) is a figure which shows the measurement position at the time of measuring the distribution of the particle | grains in a flame using the particle | grain distribution measuring apparatus of this invention, (b)-(d) is the photon to be detected to be measured. It is a time-sequential graph which shows a count number, (e) is a figure which shows the result of the count number of the measured photon.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Plasma distribution measuring device 12 Laser light generation unit 12a Semiconductor laser light source 12b Beam expander 12c Polarizer 14 Beam splitter 16 Irradiation light generation unit 16a Prism 16b Micro mirror arrangement element 17, 17a Micro mirror 18 Lens unit 18a Focus lens 18b Moving stage 18c Drive motor 20 Detection unit 20a Lens 20b Narrow band filter 20c Photomultiplier tube 20d Amplifier 20e Counter board 20f Computer 22 Controller

Claims (11)

A particle distribution measuring apparatus that detects light emitted from the measurement target particle by irradiating the measurement target particle with laser light and measures the distribution of the measurement target particle,
A laser light generation unit for emitting laser light;
A lens unit comprising a focus lens that focuses the laser light as irradiation light on the measurement target particles at a predetermined position in a space in which the measurement target particles are distributed;
A detection unit that receives the irradiation of the irradiation light and detects light emitted from the measurement target particles;
At least a part of the laser light incident from the laser light generation unit is emitted from the point of the image plane position of the focus lens as the irradiation light, and the focal position of the focus lens among the light emitted from the measurement target particle is emitted. A particle distribution measuring apparatus comprising: confocal optical system forming means for causing light collected at a point to travel to the detection unit.   The confocal optical system forming means has a reflection surface that reflects incident light, the image plane position is on the reflection surface, and reflects the laser light incident on the focus from the laser light generation unit. The particle distribution measuring apparatus according to claim 1, further comprising: a reflection mirror that is emitted as the irradiation light and reflects light collected at the focal point out of light emitted from the measurement target particle and travels to the detection unit. A particle distribution measuring apparatus that detects light emitted from the measurement target particle by irradiating the measurement target particle with laser light and measures the distribution of the measurement target particle,
A laser light generation unit for emitting laser light;
A lens unit comprising a focus lens that focuses the laser light as irradiation light on the measurement target particles at a predetermined position in a space in which the measurement target particles are distributed;
A detection unit that receives the irradiation of the irradiation light and detects light emitted from the measurement target particles;
Irradiation light control means for controlling the irradiation light so as to scan the focusing position of the irradiation light in at least one direction within the space in which the particles to be measured are distributed;
A particle distribution measuring apparatus that measures the distribution of the measurement target particles in the space by scanning the focusing position of the irradiation light by the irradiation light control means.   The irradiation light control unit emits at least a part of the laser light incident from the laser light generation unit as the irradiation light from a point of the image plane position of the focus lens, and among the light emitted from the measurement target particle The particle distribution measuring apparatus according to claim 3, further comprising confocal optical system forming means for advancing light collected at a focal point of the focus lens to the detection unit. The laser light generation unit includes a laser light source that emits laser light, and a beam expander that expands the luminous flux of the laser light emitted from the laser light source,
The confocal optical system forming means is a reflecting mirror having a reflecting surface that reflects incident light, and the reflecting mirror has a minute mirror that reflects the laser beam expanded by the beam expander on a plane. It is a micromirror array element in which a plurality of micromirrors are arranged so that the direction of the micromirrors can be controlled so as to change the reflection direction of laser light incident on each of these micromirrors.
By controlling the direction of each micromirror of this micromirror array element and generating irradiation light that uses a part of the light flux of the enlarged laser light as a light flux, the space in which the particles to be measured are distributed in one direction. Or the particle distribution measuring apparatus of Claim 4 which scans to two directions and irradiates the said measuring object particle | grain.   The lens unit includes a moving stage that moves the focus lens along the direction of the optical path of the laser light. By moving the moving stage, the irradiation light is focused in a space where the measurement target particles are distributed. The particle distribution measuring apparatus according to any one of claims 3 to 5, wherein the position is changed. An optical element that transmits and reflects incident light at a predetermined transmittance and reflectance in an optical path between the laser light generation unit and the mirror array element, and emitting the laser light and the particles to be measured. A beam splitter on which light to enter is provided,
The laser light emitted from the laser light generation unit travels toward the beam splitter, the mirror array element, and the lens unit, and the light emitted from the measurement target particles is the lens unit, the mirror array element, and the Advancing in the direction opposite to the traveling direction of the laser beam toward the beam splitter,
The particle distribution measurement apparatus according to claim 5, wherein the detection unit is arranged at a position different from the laser light generation unit so as to detect light emitted from the beam splitter and emitted from the measurement target particle. The beam splitter is a polarization beam splitter that mainly reflects one of the first polarization component and the second polarization component of incident light and mainly transmits the other polarization component of incident light. ,
The polarizer which permeate | transmits one polarization component of a laser beam is provided in the optical path between the said laser beam production | generation unit and the said polarization beam splitter, The polarization component of a laser beam injects into the said polarization beam splitter. The particle distribution measuring apparatus described.   The particle distribution measuring apparatus according to claim 1, wherein the measurement target particles are activated particles in plasma in a gas phase. The particles to be measured are activated particles in a gas phase plasma confined in a chamber;
The particle distribution measuring apparatus according to any one of claims 1 to 9, wherein the irradiation light is irradiated into a gas phase in the vacuum chamber from a window provided on a wall surface of the chamber. The laser beam emitted from the laser beam generation unit is a pulsed laser beam having an emission time of 5 nanoseconds or less,
The detection unit samples in order to count a detection signal of light emitted from the measurement target particle,
The focus lens of the lens unit has an image plane distance on the measurement target particle side that is equal to or longer than a value obtained by dividing the product of the sampling period and the speed of light in the sampling by two. 2. The particle distribution measuring apparatus according to item 1.

Images