JPH0743310A - Particle inspection method - Google Patents

Abstract

PURPOSE:To make particle inspection possible during actual processes such as film forming, etc., by forming only one arbitrary transparent layer on a semiconductor substrate, irradiating it with laser, and calculating a reflection intensity curve of the transparent film, so that scattering light of laser light is measured. CONSTITUTION:An arbitrary film 1 is film-formed on a bare wafer 2, and the wafer 2 is irradiated with laser. Here, refractivity of the film 1 is calculated, and energy reflectivity and transmission are calculated with an equation. Based on that, reflection intensity curve of the generated film 1 is calculated, and while referencing to the curve, measuring the scattering light of laser, particle 3 sticking to the film 1 is detected and measured. In short, reflectivity against respective film thickness of a nitride film is known from a reflectivity curve, further from the reflection intensity curve, a scattering cross section area, when film thickness changes, is calculated, thus particle size is calculated. Then from the particle scattering cross section area, the size of the particle 3 is calculated, and the particle 3 on the nitride film is detected, so that the size of particle 3 is identified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a particle inspection method.

[0002]

2. Description of the Related Art In recent years, along with the ultra-miniaturization of ULSI devices, there is an increasing need for clean processes. Above all, the particle inspection is an important technique from the viewpoint of yield control of semiconductor devices and device management.

Conventional particle inspection uses an inspection method as shown in the flow chart of FIG. That is, a bare silicon (hereinafter referred to as Si) wafer is used to carry several times in a semiconductor device, and the bare Si wafer is irradiated with a laser. Particle measurement is performed by measuring the laser scattered light. In this way, the particle inspection inside the semiconductor device and the device management are performed.

[0004]

However, in the conventional particle inspection technique, only bare Si wafers can be inspected, and wafers on which a film is formed cannot be inspected. Therefore, only the inspection at the time of transportation in the apparatus can be performed, and the particle inspection during the process such as film formation cannot be performed. Therefore, there is a problem that the particle inspection cannot be reflected in the actual device yield.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a method capable of performing particle inspection during an actual process such as film formation.

[0006]

In order to achieve this object, a method for inspecting particles according to the present invention comprises forming a single transparent film on a semiconductor substrate, irradiating the transparent film with a laser, The energy reflectance is calculated from the refractive index of the film, the reflection intensity curve of the transparent film is calculated from the energy reflectance, the scattered light of the laser light is measured, and the particles on the transparent film are measured.

Further, two or more arbitrary transparent films are formed on a semiconductor substrate, the uppermost transparent film is irradiated with a laser, the energy reflectance is calculated from the refractive index of the transparent film, and the energy reflectance is calculated from the energy reflectance. A reflection intensity curve of the transparent film is calculated, scattered light of the laser light is measured, and particles on the uppermost transparent film are measured.

Further, the size of a true sphere that gives the reflection intensity is calculated from the reflection intensity curve, and particles are measured.

Further, at least one arbitrary reflective film is formed on the semiconductor substrate, the transparent film is irradiated with a laser, the energy reflectivity is calculated from the refractive index and the reflectivity of the reflective film, and the energy reflectivity is calculated. Then, the reflection intensity curve of the transparent film is calculated from, the scattered light of the laser light is measured, and the particles on the reflective film are measured.

Further, an arbitrary transparent film is formed on a semiconductor substrate, and the transparent film is irradiated with a laser, and the energy reflectance is calculated from the refractive index of the transparent film as a function of the film thickness of the transparent film. , The reflection intensity curve of the transparent film from the energy reflectance is calculated as a function of the film thickness, and the scattered light of the laser light is measured by using the film thickness that gives the highest energy reflectance. Particle measurement.

In addition, when only one layer of an arbitrary transparent film is formed on a semiconductor substrate, the transparent film is irradiated with a laser, the scattered light of the laser light is measured, and the particles on the transparent film are measured, Calculate the energy reflectance of the transparent film from the refractive index of the transparent film as a function of the wavelength of the laser, and measure the particles on the transparent film by using a laser having a wavelength that gives the highest energy reflectance. .

Further, when forming only one layer of an arbitrary transparent film on a semiconductor substrate, irradiating the transparent film with a laser, measuring scattered light of the laser light, and measuring particles on the transparent film, The energy reflectance of the transparent film is calculated from the refractive index of the transparent film as a function of the wavelength of the laser, and a laser having a wavelength that gives the smallest change in reflectance is used.

[0013]

With the above construction, the reflection intensity curve of the transparent film can be calculated, and by referring to it, the particles on the formed wafer can be measured. In addition, the same particle measurement can be performed on a wafer on which two or more layers of transparent films are formed or a single-layer or multi-layer wafer including a reflective film.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a flowchart of the inspection method of the present invention. An arbitrary film is formed on a bare wafer, and this wafer is irradiated with a laser. Here, the refractive index of the film is calculated, and the energy reflectance is calculated therefrom. Generally, the energy reflectance R and the transmittance T are given by the following equations.

R = (r0 ² + r1 ² + 2r0 r1 cos2δ1) / (1 + r0 ² r1 ² + 2r0 r1 cos2δ1) T = (n2 cos φ2 / n0 cos φ0) × (t0 ² t
1 ² / (1 + r0 ² r1 ² + 2r0 r1 cos2δ1)) where n0, n1 and n2 are the refractive indices of the mediums 0, 1 and 2,
φ0, φ1, and φ2 are incident angles of light rays. Further, the amplitude reflection coefficient of Fresnel at the boundary surface when the light travels from medium 0 to medium 1 is r0, and the transmission coefficient is t0. Similarly, the coefficient when light travels from medium 1 to medium 2 is r1, and the transmission coefficient is t1. However, δ is a function of the wavelength λ of the laser light source used for the measurement and the film thickness d1 of the medium 1, and is represented by δ = 2π × n1 × d1 / λ. Energy reflectance and transmittance are calculated using the above equations. From these, the generated reflection intensity curve of the film is obtained, and the scattered light of the laser is measured with reference to the curve, whereby the particles adhering to the film can be detected and measured.

First, as the simplest example, a case where particles are present on a wafer in which a transparent film 1 which is a single-layer non-absorption medium is formed on a Si substrate 2 as shown in FIG. 2 will be described. In the above equation, when the medium is non-absorbing, the Fresnel coefficient for normal incidence is expressed by the following equation using the refractive index.

R0 = (n0-n1) / (n0 + n1) r1 = (n1-n2) / (n1 + n2) where n0 is the refractive index of the atmosphere and n1 is the refractive index of the transparent film.
n2 is the refractive index of the Si substrate. Accordingly, the energy reflectance R with respect to the vertical incidence of the ^{laser, R = [(n0 2 +} n1 2) (n1 2 + n2 2) -4n0n1 2 n2 + (n0 2 -n1 2) (n1 2 -n2 2) cos2δ] / ^{[(n0 2 + n1 2)} (n1 2 + n2 2) + 4n0n1 2 n2 + (n0 2 -n1 2) (n1 2 -n2 2) cos2δ] represented by the formula. However, δ is a function of the wavelength λ of the laser light source used for the measurement and the film thickness d1 of the transparent film 1, and is given by δ = 2π × n1 × d1 / λ. Here, the sum Is of the backscattered component Ib due to the particles of the incident light and the component RIf of the forward scattered light If that has passed through the particles and the transmission film and is reflected by the substrate Is.
It is assumed that um is reflected light. That is, Isum = Ib + RIf. Here, as an example, a case where particles on the nitride film are measured will be described. First, bare Si
A nitride film having a thickness of about 40 nm is formed thereon by the low pressure CVD method. Then, using Ar (wavelength 488 nm) as a laser light source, this laser is vertically incident on the wafer with the nitride film.

FIG. 3 is a schematic view of the detection optical system. The Ar laser 10 emitted from the light source passes through the polarizer 11, is S-polarized, is reflected by the galvanometer mirror 12, and becomes a parallel light beam via the telecentric lens 13. This light beam hits the wafer 14 with the nitride film, and the scattered light passes through the Fresnel lens 15 and is condensed by the photomultiplier tube 16.

FIG. 4 is a block diagram of a signal processing system.
A signal that has entered a photomultiplier tube (denoted as PMT in the drawing) is separated into a particle signal and a background signal by computer processing and displayed. Here, the dependency of the energy reflectance R of the nitride film on the film thickness d1 is calculated by computer processing. In this case, in the above equation, λ = 488 nm, atmospheric refractive index n0 = 1, nitride film refractive index n1 = 2.00, Si substrate refractive index n2 = 3.
It becomes 85. According to the measurement method of the present invention, when particles on a nitride film are measured, Ar laser is vertically applied to the nitride film, and the refractive index of the nitride film is used to calculate the film thickness dependence of the energy reflectance by using the above formula. Is calculated to obtain the energy reflectance at a given film thickness. Then, the reflection intensity curve of this nitride film can be calculated.

The + mark in FIG. 5 is a value calculated from the above calculation formula. The horizontal axis represents the film thickness d1 [nm] of the nitride film on the Si substrate.
Here, the vertical axis represents the normalized energy reflectance R when the case where the film thickness d1 of the nitride film is 0 is 1. Since the energy reflectance R is strengthened or weakened by the effect of interference of the reflected light of the laser light depending on the change of the film thickness d1,
It becomes a function with a certain periodicity, and has a maximum value that is the maximum value and a minimum value that is the minimum value. In the case of the nitride film shown in FIG. 5, the energy reflectance R is about 0 at a film thickness of about 60 nm, and R is about 1 at a film thickness of 120 nm.
It is a curve with a cycle of.

The mark ● in FIG. 5 is a value obtained by an experiment. As an experimental method, first, a depressurized CV was formed on bare Si.
A nitride film is formed to a thickness of about 40 nm by the D method, and standard particles are applied onto this wafer. The standard particles have a defined particle size and are assumed to be particles. The standard particles are made of polystyrene, for example, and their size is 0.1μ.
The one having a thickness of about m to about 4 μm is used. Here, for example, about 2000 standard particles having a particle diameter of 0.3 μm are dissolved in pure water, and the aqueous solution is sprayed on the wafer for about 10 seconds with dry air having high purity. Thereby, the standard particles are coated on the wafer.

FIG. 6 shows an example in which standard particles are applied to a wafer with a nitride film. In FIG. 6, about 1/3 of the wafer is coated on the right side. Ar laser (488 nm) is vertically incident on the wafer coated with the standard particles, and the scattered light intensity is measured. The value of the scattered light intensity thus obtained by the experiment is the point indicated by the ● mark at the horizontal axis of 40 nm in FIG. Similarly, a standard particle of 0.3 μm is applied to a wafer having a nitride film of 95 nm, and the scattered light intensity is measured. The value of the scattered light intensity obtained in this manner is shown by a ● mark at the horizontal axis of 95 nm in FIG. Then, similarly, a nitride film is formed at 120 nm and 16
A standard particle of 0.3 μm is applied to the wafer having a thickness of 0 nm and the scattered light intensity is measured. The graph thus obtained is shown in FIG. It can be seen that the  mark of the experimental value in FIG. 5 agrees well with the calculated curve.

Although a nitride film is used as the transparent film here as an example, the same applies when another oxide film or the like is used. Although the standard particles having a size of 0.3 μm were used, the same applies to the case of using standard particles having another particle size such as 0.1 μm.

For example, when the scattered light intensity is measured using standard particles of each particle size of 0.1 μm to 3 μm, FIG.
It becomes like.

In FIG. 7, the horizontal axis represents the size of the standard particle size [μm], and the vertical axis represents the scattering cross section [μm ² ] of the reflected light when the particle is irradiated with an Ar laser having a wavelength of 488 nm. is there. The standard particles having a particle diameter of 0.1 μm are coated on the wafer having the nitride film of 40 nm formed by the method as described above. Ar laser is vertically incident on the wafer and the scattering cross section of the reflected light is measured. Next, standard particles having a particle size of 0.15 μm are coated on the wafer on which the nitride film 40 nm is formed in the same manner, and A
Irradiate with r laser and measure the scattering cross section. further,
The scattering cross section is measured in the same manner for 0.2 μm standard particles. In this way, the particle size from 0.1 μm to 3
A reflection intensity curve is obtained by measuring the scattering cross section for standard particles up to μm. Further, in this manner, a nitride film having a thickness of about 95 nm is formed on the Si substrate, and the standard particles are made to have a thickness of 0.1 nm.
Apply from 1 μm to 3 μm. Ar these wafers
Irradiate the laser and measure their scattering cross sections. Also, the scattering cross section is measured by the same method with the film thickness of the nitride film set to 120 nm and 160 nm. The graph thus obtained is the reflection intensity curve of FIG. 7. In FIG. 7, bear S
The scattering cross section of the i-wafer was also measured, and the film thickness of the nitride film was 4
It can be compared with the scattering cross-sections of wafers formed in four ways of 0 nm, 95 nm, 120 nm and 160 nm. As can be seen from FIG. 7, the film thickness of the nitride film is 120
The curve of the scattering cross section of reflected light at nm is almost overlapped with the reflection intensity curve of bare Si.
The nm reflection intensity curve is located at the bottom. This agrees with the calculation result of FIG. That is, when the film thickness of the nitride film is 120 nm, the reflectance becomes highest,
It gives the same reflectance as when the nitride film thickness is 0 nm (that is, bare Si). In addition, the film thickness of the nitride film is 40 nm, 95
In the case of the wafers formed in four ways of nm, 120 nm, and 160 nm, the reflectance is the lowest at 40 nm.

In the present invention, the reflectance for each film thickness of the nitride film can be known from the reflectance curve of FIG. 5, and the scattering cross section when the film thickness changes can be calculated from FIG. Further, it is possible to calculate the particle size of the particles that gives the scattering cross section of the scattered light at that time. As a result, the size of the particle (size when the particle is considered to be a true sphere) can be calculated from the measured scattering cross section of the particle. In this way
According to this embodiment, it is possible to detect particles on the nitride film, and it is possible to identify the size of the particles.

In the above embodiment, Ar (wavelength 488 nm) was used as the laser light source, but He was used instead.
-Ne (wavelength 632.8 nm) may be used. FIG. 8 shows a He-N film on a wafer in which a nitride film is formed on a Si substrate.
It is a sensitivity calibration curve obtained using an e-laser (wavelength 632.8 nm). In this way, the same particle inspection as in the case where the laser light source is Ar can be performed.

FIG. 9 is a graph of the scattering cross section of scattered light obtained by experiments. In FIG. 9, similar to the previous example, the film thickness of the nitride film is 40 nm, 95 nm, 120 nm,
Wafers formed in four ways of 160 nm and bare Si wafers are coated with standard particles having a particle size of 0.3 μm to 2 μm, and the scattering cross section is measured. In the case of using a He-Ne laser, the curve of the scattering cross section of a wafer having a nitride film formed to have a thickness of 160 nm is located at the uppermost position and almost coincides with the bare Si curve. In addition, the scattering cross section of a wafer having a nitride film formed to a thickness of 95 nm could not be measured. These are in agreement with the calculation results of FIG. That is, when the nitride film thickness is 160 nm, the highest reflectance is obtained, and bare Si
Is almost the same as the reflectance of. Further, when the nitride film thickness is 95 nm, the reflectance becomes 0.1 or less, which suggests that sufficient scattered light cannot be obtained and measurement cannot be performed.

Further, in the above-mentioned embodiment, an example in which a single-layer transparent film is formed is shown, but a wafer having two or more layers is also obtained by obtaining the energy reflectivity from the refractive index thereof to obtain the same result. Particle inspection can be performed. Further, the same particle inspection can be performed on the wafer having the reflective film formed thereon by obtaining the energy reflectance from the refractive index and the reflectance.

Further, in FIG. 5, the film thickness of the nitride film 120
The energy reflectance has a maximum value at nm, and the energy reflectance has a minimum value at a film thickness of 60 nm. The higher the energy reflectance is, the higher the reflection intensity curve is located and the highly sensitive particle measurement can be performed. Therefore, when performing particle measurement, it is desirable to use a nitride film having a film thickness of 120 nm. It is useful to calibrate the sensitivity and inspect the particles using the film thickness that gives the highest reflectance.

FIG. 10 is a graph of energy reflectance with respect to a change in the film thickness of TEOS on a Si substrate when an Ar laser having a wavelength of 488 nm is used. Here, in calculation, the refractive index of the TEOS film is 1.64, and
The energy reflectance is calculated by changing the film thickness of the OS film from 0 nm to 350 nm. Energy reflectance is T
It is a function having periodicity with respect to the thickness of the EOS film. In the case of this TEOS film, the period is about 160 nm, and the reflectance takes a maximum value and a minimum value for each film thickness of about 80 nm. For example, when the TEOS film is about 320 nm, the reflectance has the maximum value. Therefore, if a wafer on which TEOS having a film thickness of about 320 nm is formed is subjected to particle measurement, a high energy reflectance close to 1.0 can be obtained, and highly sensitive measurement can be performed. When this is measured with a wafer on which TEOS having a film thickness of about 250 nm is formed, the energy reflectance is as low as about 0.2, so that sufficient reflected light cannot be obtained, resulting in detection light with low sensitivity. Will end up.
Therefore, the particle measurement becomes insufficient. That is, it can be said that it is useful to perform particle measurement using a film thickness that can obtain the highest energy reflectance.

In the above example, the TEOS film thickness dependence of the reflectance when the TEOS film was irradiated with Ar laser was shown. However, for other films, the AOS of wavelength 488 nm was also used.
The same measurement can be performed for other lasers having wavelengths other than the r laser. Therefore, it can be said that it is useful to perform particle measurement using a film thickness that can obtain the highest energy reflectance.

FIG. 11 is a graph showing the measured reflectance of a wafer having a P-SiO film formed on a Si substrate to a thickness of 100 nm and 200 nm. The vertical axis represents the reflectance and the horizontal axis represents the wavelength [unit: nm] of the light with which the wafer is irradiated. Thus P-
The wavelength dependence of the reflectance greatly differs depending on the thickness of the SiO film. A large reflectance is advantageous for highly sensitive particle measurement. Therefore, for example, when measuring particles on a P-SiO film having a film thickness of 100 nm, it is effective to use a laser having a laser wavelength of about 400 nm because a high reflectance can be obtained. Further, it can be seen from the graph of FIG. 11 that it is more effective to use a laser having a laser wavelength of around 550 nm when measuring particles on a P-SiO film having a thickness of 200 nm. Thus, by using a laser having a wavelength capable of obtaining a high energy reflectance according to the film thickness of P-SiO, particle measurement can be made advantageous.

In the above, the film thicknesses of 100 nm and 20
Although an example of a 0 nm P-SiO film is shown, the same can be said for other transparent films. That is, depending on the film thickness,
By using a laser capable of obtaining a high reflectance, highly sensitive particle measurement can be performed.

FIG. 12 shows a thermal oxide film 500 nm on a Si substrate.
FIG. 3 is a diagram showing the measured reflectance of a wafer on which a 100-nm-thick titanium nitride (hereinafter referred to as TiN) film is formed by sputtering at room temperature and 450 ° C. The vertical axis represents the reflectance and the horizontal axis represents the wavelength of the light used for the measurement. Thus, even if the TiN film has the same film thickness, the surface condition changes depending on the film forming conditions, and the reflectance varies. Here, in the reflectance measurement of the wafer on which the TiN film sputtered at 450 ° C. is formed, it is found that the change in the reflectance of the wafer is small when the wavelength of the light used for the measurement is 470 nm. Further, in the reflectance measurement on the wafer on which the TiN film sputtered at room temperature was formed, the wavelength of the light used for the measurement was 460 n.
It can be seen that the change in the reflectance of the wafer at m and 540 nm is gradual. Such a small change in reflectance means that the value of the reflectance obtained by measurement is stable even with a slight change in film thickness. Therefore, when the particles of the TiN film sputtered at 450 ° C. are measured, if the measurement is performed using a laser having a wavelength of 470 nm, stable detection sensitivity can always be obtained, and therefore stable measurement can be performed. I understand that it is a target. Similarly, T sputtered at room temperature
When measuring particles of the iN film, it is found that the measurement is effective if particle measurement is performed using lasers having laser wavelengths of 460 nm and 540 nm. As described above, it is very useful to manage particles by using a laser having a wavelength where the reflectance curve has the most gentle curve.

In the above example, a 100 nm TiN film is formed on the thermal oxide film 500 nm on the Si substrate at room temperature and 45 nm.
The reflectance of the wafer formed at 0 ° C. is shown. As in this example, the surface state of the film may change depending on the film forming method and process conditions, and the reflectance of the wafer may change. Therefore, this particle measuring method is also effective for films other than the TiN film. That is, it can be said that it is very useful to manage particles by using a laser having a wavelength at which the curve of the reflectance of the film-coated wafer is the most gentle.

[0037]

According to the present invention, the energy reflectance is calculated from the refractive index of the transparent film on the Si substrate, the reflection intensity curve of the transparent film is calculated from the energy reflectance, and the particles on the formed wafer are measured. Therefore, it is possible to realize an excellent inspection method capable of performing particle measurement during an actual process.

[Brief description of drawings]

FIG. 1 is a flowchart showing an inspection method according to an embodiment of the present invention.

FIG. 2 is a diagram showing a wafer to be inspected in one embodiment of the present invention.

FIG. 3 is a diagram showing a detection optical system according to an embodiment of the present invention.

FIG. 4 is a diagram showing a signal processing system according to an embodiment of the present invention.

FIG. 5 is a diagram showing film thickness dependence of energy reflectance in one example of the present invention.

FIG. 6 is a diagram showing a state where standard particles in one embodiment of the present invention are applied onto a wafer with a nitride film.

FIG. 7 is a diagram showing a result of measuring a scattering cross section of scattered light in an example of the present invention.

FIG. 8 is a diagram showing the film thickness dependence of energy reflectance when a He—Ne laser is used.

FIG. 9 is a diagram showing measurement of a scattering cross section of a wafer with a nitride film when using a He—Ne laser.

FIG. 10 is a diagram showing reflectance with respect to a change in TEOS film thickness.

FIG. 11 is a diagram showing wavelength dependence of reflectance of a P-SiO film.

FIG. 12 is a diagram showing the reflectance of a TiN film formed at room temperature and 450 ° C.

FIG. 13 is a flowchart showing a conventional particle inspection method.

[Explanation of symbols]

 1 transparent film 2 silicon substrate 3 particles 4,5 reflected light

Claims (7)

[Claims] 1. An arbitrary transparent film is formed on a semiconductor substrate by one layer, the transparent film is irradiated with a laser, the energy reflectance is calculated from the refractive index of the transparent film, and the transparent film is calculated from the energy reflectance. The particle inspection method, comprising: calculating a reflection intensity curve of the above, measuring scattered light of the laser light, and measuring particles on the transparent film. 2. An arbitrary transparent film is formed in two or more layers on a semiconductor substrate, the uppermost transparent film is irradiated with a laser, the energy reflectance is calculated from the refractive index of the transparent film, and the energy reflectance is calculated from the energy reflectance. A particle inspection method comprising: calculating a reflection intensity curve of the transparent film, measuring scattered light of the laser light, and measuring particles on the uppermost transparent film. 3. The particle inspection method according to claim 1, wherein the size of a true sphere that gives the reflection intensity is calculated from the reflection intensity curve and particles are measured. 4. An energy reflection coefficient is calculated by forming at least one arbitrary reflection film on a semiconductor substrate, irradiating the transparent film with a laser, and calculating an energy reflection coefficient from a refractive index and a reflection coefficient of the reflection film. A particle inspection method comprising: calculating a reflection intensity curve of the transparent film, measuring scattered light of the laser light, and measuring particles on the reflective film. 5. An arbitrary transparent film is formed on a semiconductor substrate by one layer, the transparent film is irradiated with a laser, and the energy reflectance is calculated from the refractive index of the transparent film as a function of the film thickness of the transparent film. , The reflection intensity curve of the transparent film from the energy reflectance is calculated as a function of the film thickness, and the scattered light of the laser light is measured by using the film thickness that gives the highest energy reflectance. A particle inspection method, which comprises measuring the particles of. 6. An arbitrary transparent film is formed on a semiconductor substrate in a single layer, the transparent film is irradiated with a laser, the scattered light of the laser light is measured, and the particles on the transparent film are measured. Calculate the energy reflectance of the transparent film from the refractive index of the transparent film as a function of the wavelength of the laser, using a laser having a wavelength that gives the highest energy reflectance of the particles on the transparent film Particle inspection method to measure. 7. An arbitrary transparent film is formed on a semiconductor substrate in a single layer, the transparent film is irradiated with a laser, the scattered light of the laser light is measured, and the particles on the transparent film are measured, Particles on the transparent film, wherein the energy reflectance of the transparent film is calculated from the refractive index of the transparent film as a function of the wavelength of the laser, and a laser having a wavelength giving the smallest change in reflectance is used. Particle inspection method to measure the.