JPH0435682B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Object of the Invention [Field of Industrial Application] The present invention relates to a film thickness measuring device for measuring the thickness of a thin film using interferometry.

Technology for measuring the thickness of thin films, polymer films, etc. on which optical components are attached to substrates such as LSIs has become increasingly important in recent years.

[Prior Art] When measuring a thin film such as a resist coated on the surface of a chromium (Cr) mask blank, conventional techniques have been used to measure the surface using a stylus as shown in Fig. 4. Using a roughness measuring device, bring the tips of the diamond stylus 201 and skid 202 as shown in FIG. 4a into contact with the chrome surface 203 as shown in FIG.
4 and detects the change by electrically amplifying it. For example, if the diameter of the film on the sample is l ₀ , the measurement result is obtained as shown in FIG. 4c.

However, such a mechanical and electrical method does not necessarily make it easy to measure with high precision, and in cases where a step cannot be taken between the chromium surface 203 and the film 204, in other words, the film 204 is formed on the entire surface of the chromium surface.
If a thin film is formed, it is impossible to measure the film thickness using the above-mentioned measuring means, and for this reason, it is desired to develop a technique for measuring the film thickness of a thin film.

Therefore, the inventor of the present invention previously proposed a film thickness measuring device that can easily measure the film thickness of a thin film with high precision and in a non-contact manner (see Patent Application No. 040467 of 1985). We also proposed a film refractive index measurement device that can easily measure the refractive index of thin films with high precision and without contact (see Patent Application No. 135756 of 1985).

The newly proposed interferometric film thickness measuring device and interferometric film refractive index measuring device are as shown in Figure 5.
After changing the optical path of the laser beam with mirrors 103 and 104, it passes through the pinhole 105 and then passes through the film to be measured 110.
reflected light I _A from the surface of the film to be measured 110
(See FIG. 2) and the reflected light I _B (See FIG. 2) on the back surface of the film to be measured 110 or the reflective surface 112 of the substrate 113 interfere with each other due to their optical path lengths, and the focal point of the lens 106 The interference light is detected by a light receiver 107 at the position, photoelectrically converted, and the intensity change of the interference light when the film to be measured 110 is rotated by a rotation device 114 is measured.

[Problems to be solved by the invention] The newly proposed interferometric film thickness measuring device and interferometric film refractive index measuring device can easily measure the film thickness and refractive index of thin films with high precision and without contact. However, during measurement, it is necessary to rotate the film to be measured, and it is necessary to rotate the lens 106 and the light receiver 107 in accordance with the rotation of the film to be measured. This causes the structure of the device to become complicated.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a film thickness measuring device with a simple structure that can easily measure the film thickness of a thin film with high precision and without contact. The purpose is to

(B) Structure of the Invention [Means for Solving the Problems] In order to achieve this purpose, the sample rotation type interferometry film thickness measuring device of the present invention illuminates a film body, which is an object to be measured, with a laser beam. A laser light source is used to obtain a laser light source, and among the incident light that is incident on the object to be measured at an incident point, the light reflected on the surface of the object to be measured and the light that is transmitted through the object to be measured and reflected at the back surface are passed through the incident point to the incident light. a reflection device that returns the light in the direction of the optical path of the object, and the light reflected by the surface of the object to be measured that is returned by the reflection device and the light that is transmitted through the object to be measured and reflected by the back surface to interfere with each other to form interference fringes. The present invention is characterized by comprising an interferometer that measures the intensity of the interference fringes, a light intensity measuring device that measures the intensity of the interference fringes, and a measurement rotation device that changes the angle of incidence of the laser beam on the object to be measured.

Hereinafter, the details of this invention will be explained with reference to one embodiment.

In FIG. 1, 1 is a film thickness measuring device. The film thickness measurement device 1 includes a laser light source 2, a reflection device 20, an interferometer 30, a light intensity measurement device 40, and a rotation device 50.
It is equipped with

As the laser light source 2, a helium neon laser,
Argon laser, krypton laser, helium cadmium laser, ruby laser, etc. can be used.

The interferometer 30 includes a lens 3, a beam splitter 4,
Beam splitter 5, pinhole 6, lens 7,
It has a screen 8.

The reflection device 20 includes a cylindrical lens 11 on the incident side of the film to be measured 10, and a cylindrical mirror 12 on the reflection side of the film to be measured 10. The cylindrical mirror 12 is located on the reflective side of the film to be measured 10 and has a mirror surface centered on the rotation axis of the film to be measured 10 facing toward the film to be measured 10 .

The film to be measured 10 is a reflective surface 1 such as a lens or a glass plate.
3, and is formed in close contact with the substrate 14 having the structure No. 3. The film to be measured 10 and the substrate 14 (FIG. 2) are rotated by a rotation device 50.

The rotation device 50 includes a pulse rotation stage 15 and a controller 16 that controls the rotation of the pulse rotation stage 15.

The light intensity measuring device 40 includes a photodetector 17 and an amplifier 1.
8, a data analysis device 21, a processing device 22, a printer 23, and a monitor TV 24.

[Function] In the film thickness measuring device configured as described above,
The operation when measuring the film thickness of the film to be measured 10 is as follows.

A beam from a laser light source 2 passes through a lens 3, a beam splitter 4, and a beam splitter 5, and then passes through a cylindrical lens 11 and irradiates the film to be measured 10 on a pulse rotation stage 15. Measuring film 1
The light reflected from the front surface and back surface 13 of 0 interferes, and this interference light is reflected by the cylindrical mirror 12 and returns to the original direction of incidence, passes through the same point on the film to be measured 10, is reflected, and follows the incident optical path. The light is reflected by the beam splitter 5, focused by the lens 7 onto the photodetector 17, and detected. The signal photoelectrically exchanged by the photodetector 17 is amplified through the amplifier 18 and then input to the data analysis device 21, where the data is processed and the waveform is observed.

Each time a pulse stage controller 16 sends one pulse to the rotating pulse stage 15, a light intensity signal is detected and data processing is performed.

Next, the principle of determining the film thickness of the film to be measured 10 will be explained.

[A] First, the incident light at the incident angle θ ₁ and the incident angle θ ₂
When both the wavelengths of the incident light and the wavelength of the incident light are λ, the following is true.

Film 1 to be measured with refractive index n and thickness h as shown in Fig. 2
Consider the case where a laser beam is incident at an angle θ.

If the light reflected from the front surface of the film to be measured 10 is I _A and the light reflected from the back surface is I _B , then the optical path difference d between I _A and I _B is -=d...(1) If d=2h√ ² - ² ...It is expressed as (2).

The intensity of the interference light in this case is expressed as I=A+Bcos(2πd/λ) I=A+Bcos{(4π/λ)h×(√ ² − ² )} (3).

The optical path difference when the incident angle is θ ₁ is d ₁ , the optical path difference when the angle is θ ₂ is d ₂ , and the position where the intensity of the interference fringe is max and min is d ₁ − d ₂ = (1/2) mλ (m is an integer) ……(4) Therefore, 2h(√ ² − ² ₁ −√ ² − ² ₂ ) = (1/2) mλB ……(5) The thickness h is h=mλ/{4(√ ² − ² ₁ −√ ² − ² ₂ )} ...(6)

Therefore, the refractive index n of the film to be measured and the wavelength λ of the incident light
is given, and the thickness h of the film to be measured 10 can be found by finding the incident angles θ ₁ and θ ₂ from the extreme value of the change in the intensity of the interference light given by equation (3). can.

[B] Next, the wavelength of the incident light at the incident angle θ ₁ is λ ₁ ,
When the wavelength of the incident light at the incident angle θ ₂ is λ ₂ , the equation is as follows.

The phase at wavelength λ ₁ , angle θ ₁ , wavelength λ ₂ , and angle θ ₂ is (4π/λ ⁺ h√ ² − ² ₁ = mπ ...(7) (4π/λ ₂ ) h√ ² − ² ₂ = ( m+1)π……(
8). As a result, the film thickness h is h=1/[4{(√ ² − ² ₂ /π ₂ ) −(√ ² − ² ₁ /λ ₁ )}] …(9) Therefore, the refractive index n of the film to be measured If the wavelengths λ ₁ and λ ₂ of the incident light are given, and the angles of incidence θ ₁ and θ ₂ are determined from the extreme value of the change in the intensity of the interference light given by equation (3), the measurement target film 10 can be determined. The thickness h can be determined.

[C] Also, in [A] and [B], even if the refractive index is unknown, the film thickness can be determined as follows. In this case, it is first necessary to find the refractive index of the film to be measured, so the principle of finding the refractive index will be explained.

(A) First, when the wavelengths of the incident light at the incident angle θ ₁ and the incident light at the incident angle θ ₂ are both incident, the following is true.

Angle θ ₁ , θ ₂ , θ ₃ at adjacent extreme values of interference fringes
Then, the phase is (4π/λB) h√ ² − ² ₁ = mπ……(10) (4π/λ) h√ ² − ² ₂ = (m+1)π …(11) (4π/λ) h√ ² − ² ₃ = (m+2)π ...(12) It is expressed as above. Taking the ratio of each difference from these three equations and expanding and solving, the refractive index n is n=√(− ⁴ ₁ −16 ⁴ ₂ − ⁴ ₃ +8 ² ₁・² ₂ +8 ² ₂・² ₃ +2 ² ₃・² ₁ ) {8( ² ₁ −2 ² ₂ + ² ₃ )} ...(13) It is expressed as above.

Therefore, if the incident angles θ ₁ , θ ₂ and θ ₃ are known from the extreme value of the change in the intensity of the interference light, the refractive index n of the film to be measured can be determined, and this n can be calculated using equation (6) or (9). The film thickness can be determined by substituting it into the formula.

(B) Next, if the wavelength of the incident light at the incident angle θ ₁ is λ ₁ , the wavelength of the incident light at the incident angle θ ₂ is λ ₂ , and the wavelength of the incident light at the incident angle θ ₃ is λ ₃ , then the following is true. be.

The wavelength λ ₁ , angle θ ₁ , wavelength λ ₂ , angle θ ₂ , wavelength λ ₃ , and phase at angle θ ₃ at the extreme values of the interference fringe are (4π/λ ₁ A) h√ ² − ² ₁ = mπ ……( 14) (4π/λ ₂ )h√ ² − ² ₂ = (m+1)π (15) (4π/λ ₃ )h√ ² − ² ₃ = (m+2)π (16) From these three equations, taking the ratio of each difference and expanding and solving, the refractive index n is a=(4λ ² ₃・λ ² ₁ −λ ² ₁・λ ² ₂ −λB ² ₂・λ ² ₃ C) ² −4λ ² ₁・λ ² ₂・λ ² ₃ b=2(4λ ² ₃・λ ² ₁ −λ ² ₁・λ ² ₂ λ ² ₂・λ ² ₃ ) × (λ ² ₂・λ ² ₃・sin ² θ ₁ −4λ ² ₃・λ ² ₁・sin ² θ ₂ +λ ² ₁・λ ² ₂・sin ² θ ₃ ) +4λ ² ₁・λ ₂ ²・λ ² ₃ × (sin ² θ ₁ + sin ² θ ₃ ) C=(λ ² ₂・λ ² ₃・sin ² θ ₁ −4λ ² ₃・λ ² ₁・sin ² θ ₂ +λ ² ₁・λ ² ₂・sin ² θ ₃ ) ² −4λ ² ₁・λ ² ₂・λ ² ₃ ×sin ² θ ₁・sin ² θ _3Expressed as in the above equation It will be done.

Therefore, if the wavelengths λ ₁ , λ ₂ , λ ₃ of the incident light on the film to be measured are given, and the incident angles θ ₁ , θ ₂ , θ ₃ are divided from the extreme values of the change in the intensity of the interference light, then The refractive index n of the film to be measured can be determined. This n can be expressed as (6) or (9)
The film thickness h can be determined by substituting into the equation.

[Experiment example] As a sample, chromium (Cr) was placed on a glass substrate.
was coated to form a substrate with a reflective surface, and magnesium fluoride (MgF ₂ ) was coated on the reflective surface to form a film to be measured. When the thickness of the film to be measured was measured using a He-Ne laser, a value of d = 1.24 μm was obtained. When the same sample was measured using a stylus type surface roughness measuring device, the thickness was approx.
A value of 1.25 μm was obtained. It can be seen that the values obtained by both methods are in good agreement.

[Other methods] In the embodiments described above, the cylindrical mirror 12 is used as a reflection device, but as shown in FIG. It can also be substituted.

(c) Effects of the Invention As described above, according to the film thickness measuring device using interference of the present invention, the film thickness of a thin film can be easily measured with high accuracy and in a non-contact manner. Furthermore, the film thickness α can be measured even when there is no level difference between the substrate and the film to be measured.

Furthermore, since there is no need to rotate the photodetector 17 and the like in accordance with the rotation of the film to be measured 10, the configuration of the apparatus is simple.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the configuration of a film thickness measuring device according to an embodiment of the present invention, FIG. 2 is an enlarged explanatory diagram showing an optical path in a film to be measured, and FIG. 3 is an explanatory diagram of another embodiment of the invention. A configuration explanatory diagram showing a film thickness measuring device, FIG. 4 is an explanatory diagram showing a stylus type film thickness measuring device,
and FIG. 5 are configuration explanatory diagrams showing a conventional interferometric film thickness measuring device. 1...Film thickness measuring device, 2...Laser light source, 3...
... Lens, 4 ... Beam splitter, 5 ... Beam splitter, 6 ... Pinhole, 7 ... Lens, 8 ... Screen, 10 ... Film to be measured, 11
... Cylindrical lens, 12 ... Cylindrical mirror, 13 ... Back surface, 14 ... Substrate, 15
...Pulse rotation stage, 16...Controller, 17...Photodetector, 18...Amplifier, 20...
... Reflection device, 21 ... Data analysis device, 22 ...
Processing device, 23... printer, 24... monitor
TV, 25...plane mirror, 30...interferometer, 4
0... Light intensity measuring device, 50... Rotating device.

Claims (1)

[Scope of Claims] 1. A laser light source capable of illuminating a film body, which is an object to be measured, with a laser beam; and a laser beam source that is capable of illuminating a film body that is an object to be measured; a reflection device that returns the light transmitted through the object to be measured and reflected on the back surface through the incident point in the direction of the optical path of the incident light; and the light reflected on the surface of the object to be measured that is returned by the reflection device. an interferometer that forms interference fringes by interfering with light transmitted through the object to be measured and reflected on the back surface; a light intensity measuring device that measures the intensity of the interference fringes; and a light intensity measuring device that measures the intensity of the interference fringes; A sample rotation type interferometry film thickness measurement device, comprising: a measuring object rotation device that changes an incident angle. 2. The rotating interferometry film according to claim 1, wherein the reflection device includes a cylindrical mirror centered on the rotation axis of the object to be measured, which is disposed near the object to be measured. Thickness measuring device. 3. The rotation according to claim 1, wherein the reflecting device includes a plane mirror that rotates by the same amount of rotation as the amount of rotation of the object to be measured about a rotation axis common to the rotation axis of the object to be measured. Type interferometry film thickness measurement device.