TWI390174B - An architecture for measuring the thickness and refractive index of transparent substrates - Google Patents

Description

An architecture for measuring the thickness and refractive index of a transparent substrate

The invention relates to the technical field of measuring a transparent substrate, in particular to a structure with simple operation and high accuracy for measuring the thickness and refractive index of a transparent substrate, thereby improving precision, reducing system cost and effectively improving measurement quality.

According to the continuous deduction of optical technology measurement technology in recent years, the relationship between precision industry and optoelectronic industry is inseparable. It seems that the development of high-precision testing institutions has become an important trend. Optical films, glass or transparent substrates used in precision optical instruments, as well as many objective lenses for optical or biological, medically used precision optical devices, thin film coated on lenses or transparent substrates, require very accurate specifications, if Unable to provide accurate parameter specifications, the reliability of the experiment is definitely relatively reduced. Therefore, it is directly affected by the thickness and refractive index measurement of the transmissive optical film, glass or transparent substrate used in the precision optical device to directly affect the quality of the transparent substrate.

For the measurement of the thickness and refractive index of optical films, glass or transparent substrates, for example, Ellipsometry, Photometry, multi-beam interferometry, etc. used in ellipsometers, The optical fiber method, the solution method, the optical waveguide measurement method, the m-line method, etc., can simultaneously and effectively measure the thickness and refractive index of the film.

But the elliptical polarization method (Ellipsometrv) cannot directly measure the test The physical parameters of the transparent substrate, but the physical properties of the transparent substrate to be tested must be described by a model, the physical parameters of the actual sample are obtained by numerical analysis, and the method of numerical analysis is required to use the zeroing method. Or complex methods such as phase modulation photometrics. Photometry is to measure the intensity of light after passing through or reflecting from a transparent substrate to be tested. Since there are many limitations in the measurement of strongly absorbing materials, the scope of use is Not extensive; although fiber measurement can increase the measurement speed, but the price is more expensive. As for the multi-beam interferometry method and the solution measurement method, complicated calculations are required, and the structure is large, and there are many uncertain factors. Another m-line method is to record the angle when observing the m-line by the naked eye, and then the effective refractive index can be calculated, but the human eye has a large error and is not easy to be observed for some m-line methods (such as waveguide The m-line method is not very effective if the loss is large or the wavelength of the light wave is long.

In other words, if the problem of the above-described measurement method can be improved, and it can be composed of simple optical components, the measurement cost can be reduced, and if it can be further miniaturized, the existing complicated calculation process can be simplified, and the use is simple. The geometric formula can be easily solved to achieve convenient operation and fast measurement, and to improve the accuracy of measurement.

The reason is that the inventors of the present invention, in view of the problems faced by the above-mentioned conventional transparent substrate in thickness and refractive index measurement, and actively seek solutions through the research and development experience of the inventors in related industries, have been continuously researching and trialing. Finally, successfully developed a framework for measuring the thickness and refractive index of transparent substrates. To solve the problem of the existing structure is complicated, the operation is inconvenient and the accuracy is not good.

The object of the present invention is to provide a structure for measuring the thickness and refractive index of a transparent substrate, thereby simplifying the existing complicated calculation process, which can be easily solved by using a simple geometric formula, and can improve the accuracy of measurement, and the present invention. One object is to provide an architecture for measuring the thickness and refractive index of a transparent substrate, which has a simple overall structure, small volume, convenient operation, low cost of a conjugated focal head and a semiconductor laser head, and fast calculation parameters, and another method of the present invention. One objective is to provide an architecture for measuring the thickness and refractive index of a transparent substrate without using other samples as a basis for reducing errors and improving measurement accuracy.

An architecture for measuring the thickness and refractive index of a transparent substrate that achieves the above objects includes: a conjugated focal head that produces a light source, the conjugated focal head having a laser diode that emits laser light, The conjugated focal head is provided on the side of the laser diode with a beam splitter that can separate the laser light into the transmitted light and the reflected light, and a four-pointer that can change the line-polar light into a circular apolar light under the beam splitter. One of the wave plates, and a quarter-wave plate is provided with a collimating lens capable of turning the circularly polarized light into a parallel beam, and a semi-cylindrical lens is arranged above the beam splitter to focus the light into different sizes of light spots. a lens, and a photodetector for receiving the light spot is disposed above the semi-cylindrical lens; an objective lens is disposed under the conjugate focal head, the objective lens can produce a focusing effect; and a mirror is disposed on the objective lens Below, a space to be measured is formed between the mirror and the objective lens, and the mirror can reversely emit the light beam according to the law of reflection; a semiconductor laser head is disposed on the other side of the conjugated focus head, the semiconductor laser Head axis and conjugate focal length The angle [theta] is a fixed axis, and a head having a semiconductor laser can emit laser light of a laser diode, laser diode front and can be provided with a positive reversal of the rotation means, and the rotation is provided with a focusing device A four-quadrant sensor is disposed on an axis of a laser diode of a semiconductor laser that passes through a side of the region to be tested, and the four-quadrant sensor can be used to receive a defocus signal.

The measuring method is as follows: First, the conjugate focal head emits laser light, so that the laser light enters the objective lens, and the laser light starts to focus, and then enters a transparent substrate to be tested, so that the laser light is refracted and incident on the reflection On the mirror, the defocus signal is reflected back to the original optical path, and then incident on the conjugated focal head to obtain a displacement value Δx1; then, the semiconductor laser is laser-exposed, and the rotating device is used to rotate the semiconductor laser head. Focusing the lens, causing the laser light to enter the focusing lens and start focusing, then incident on the transparent substrate, causing the laser light to refract, incident on the four-quadrant sensor, and receiving the out-of-focus signal, and obtaining a displacement value Δx2; The obtained Δx1 and △x2 are substituted into the solution equation, and The refractive index and thickness of the transparent substrate to be tested.

Therefore, through the display of the foregoing technical means of the present invention, the present invention can be used as a basis for measurement without the need for a large measuring device and other samples as in the prior art, and the measuring operation step is simple, and can be accurate at the same time. The thickness and the refractive index of the transparent substrate to be tested are obtained, thereby improving the accuracy of the measurement, reducing the system cost, and effectively improving the measurement quality.

The following is a description of the preferred embodiments of the present invention, and is described in detail with reference to the drawings, and the .

Referring to FIG. 1 , the architecture for measuring the thickness and refractive index of a transparent substrate provided by the present invention mainly includes: a conjugate focal length head 10, an objective lens 20, a mirror 30, a semiconductor laser head 40, and a fourth. The quadrant sensor 50 is configured; wherein the conjugated focal head 10 has a laser diode 11 that can emit laser light, and the conjugated focal head 10 is provided on the side of the laser diode 11 The laser beam is divided into a beam splitter 12 that transmits light and reflects light. The beam splitter 12 can cause the laser beam of the laser diode 11 to be turned in a vertical staggered direction, and a light deflecting light can be changed under the beam splitter 12. It is a quarter-wave plate 13 with a circular apolar light, and a collimating lens 14 capable of turning a circularly polarized light into a parallel beam is disposed under the quarter-wave plate 13, and a semi-cylindrical lens is disposed above the beam splitter 12 15. The semi-cylindrical lens 15 can focus the light into spots of different magnitudes, and a photodetector 16 (PDIC) is disposed above the semi-cylindrical lens 15 to place the conjugated coke head 10 in a positive focus state. The photodetector 16 can be used to convert the optical signal into an electrical signal for interpretation by a computer; The 20 series is disposed under the collimating lens 14 of the conjugate focal head 10, so that the parallel beam emitted by the collimating lens 14 can produce a focusing effect; and the mirror 30 is disposed under the objective lens 20 and is disposed on the mirror 30. A space for detecting the transparent substrate 60 to be tested is formed between the objective lens 20, and the mirror 30 can reversely emit the light beam according to the law of reflection; and the semiconductor laser head 40 is disposed on the conjugated focal head 10 The other side is located obliquely above the transparent substrate 60 to be tested, and the axis of the semiconductor laser head 40 is at a fixed angle θ with the axis of the conjugated focal head 10, and the axis and conjugate of the semiconductor laser head 40 are conjugated. The angle defined by the axis of the focal head 10 is between 30 degrees and 80 degrees, and the semiconductor laser head 40 has a laser diode 41 capable of emitting laser light, and the semiconductor laser head 40 is coupled to the laser. A positive and reverse rotating device 42 is disposed in front of the diode 41, and a rotating lens 42 is disposed on the rotating device 42 in front of the laser diode 41 for positive and negative rotation of the rotating device 42 to change the focus. Position; and the aforementioned four-quadrant sensor 50 is disposed on a semiconductor laser 40 laser diode 41 laser light passes through the axis of one side of the transparent substrate 60, the four-quadrant sensor 50 can be used to receive the defocus signal, and convert the optical signal into an electrical signal for computer interpretation; Therefore, it is possible to form a structure with a simple structure and high precision to measure the thickness of the transparent substrate and the refractive index.

As for the actual measurement of the transparent substrate 60 of the present invention, as shown in FIG. 2, the laser diode L1 is emitted from the laser diode 11 of the conjugate focal head 10, and the laser beam L1 is incident on the beam splitter 12. Then, the reflected light L2-1 is generated, and then the quarter wave plate 13 is incident, and the laser light L3-1 is generated, and at the same time, the laser beam is converted into the parallel light beam L4-1 by the collimator lens 14, so that the parallel The light beam L4-1 is incident on the objective lens 20, so that the parallel light beam L4-1 starts to focus, and the focused light L5-1 is generated, which is incident on the mirror 30, and is reflected back to the original light path to generate the reflected light L5-2. The incident objective lens 20, which in turn generates the laser beam L4-2, is incident on the collimator lens 14, and generates the laser beam L3-2, and passes through the quarter-wave plate 13 to generate the laser beam L2-2 and is incident. The beam splitter 12 generates the transmitted light L6, and the spotted light is incident on the photodetector 16 by focusing on the light spot L7 of the different size directions. The light detector 16 receives the optical signal and converts it into an electrical signal for computer interpretation. And the conjugated focal head 10 is in a positive focus state; then, the laser diode 41 of the semiconductor laser head 40 emits a laser L16, and the focusing lens 43 is rotated by the rotating device 42, when the laser beam is incident on the focusing lens 43, the focusing is started, and the focused beam L17 is incident on the four-quadrant sensor 50, so that the focused beam L17 is in the four-quadrant sensor. The focus state of 50; after that, the transparent substrate 60 to be tested is placed in the area to be tested between the objective lens 20 and the mirror 30, and the transparent substrate 60 is parallel to the conjugate focal head 10 to make the conjugate focal length The laser diode 11 of the head 10 emits a laser beam L1, And after the incident beam splitter 12 is generated, the reflected light L2-1 is generated, and then the quarter wave plate 13 is incident to generate the laser light L3-1, and at the same time, the laser beam is converted into the parallel light beam L4-1 by the collimating lens 14. The parallel light beam is incident on the objective lens 20, and the laser light starts to focus, thereby generating the focused light L5-1, and then incident on the transparent substrate 60 to be tested, causing the first refraction, generating the refracted light and then exiting the transparent substrate to be tested. 60, causing the second refraction, generating the refracted light L8 through the mirror 30, generating the reflected light L9, the reflected light is incident on the transparent substrate 60, causing the first refraction, generating the refracted light and then emitting the object to be tested, resulting in the second refraction The light L10, the re-incidence objective lens 20 generates the laser light L11, and then enters the collimator lens 14 to generate the laser beam L12. The laser beam L13 is generated through the quarter-wave plate 13, and the incident beam splitter 12 generates the transmitted light L14. Then, the light spot L15, which is incident on the semi-cylindrical lens 15 and focused in different magnitude directions, is incident on the photodetector 16, and the signal is received by the photodetector 16, and the received light signal is received by the photodetector. The optical signal is converted into a voltage signal, and a displacement value Δx1; then the laser diode 41 of the semiconductor laser head 40 emits laser light L16, and the focusing lens 43 is rotated by the rotating device 42, so that the laser beam is incident on the focusing lens (43) and begins to focus, resulting in Focusing the light beam L17, entering the transparent substrate 60, causing the laser light to generate the first refracted light, and then exiting the transparent substrate 60 to generate the second refracted light L18, incident on the four-quadrant sensor 50, and receiving the defocus signal, and obtaining A displacement value Δx2; finally, the obtained Δx1 and Δx2 are respectively brought into a cubic equation of thickness and refractive index, and the refractive index and thickness of the transparent substrate 60 to be tested are obtained.

As for the actual calculation of the refractive index and thickness of the present invention, the astigmatism method and the algorithm of Snell's Law are used, wherein the astigmatism law is shown in FIG. 3, which uses light through a semi-cylindrical lens. 15 will cause different aberrations before and after the focus point, just at the focus point, the light spot will be a perfect circle (as shown in Figure 4a), in near focus (as shown in Figure 4b) and far focus (as shown in Figure 4c). The point will be an ellipse, and then the photodetector 16 will determine whether the position of the focus is correct.

As for Snell's Law, as shown in Figure 5, it describes the relationship of light travel between different media. When the light ray L1 is incident on the medium 2 from the medium 1, there is reflected light L2, there is transmitted light L3, θ 1 represents an incident angle, θ r represents a reflection angle, and θ t represents a refraction angle. And n ₁ and n ₂ are the refractive indices of medium 1 and medium 2, respectively, and Snell's Law should follow the following relationship: θ 1 =θr

N1 × sin θi = n2 × sin θt

In addition, the conjugated coke head 10 formula of the present invention is when the object to be tested is not placed in the measurement area, and the relative block of FIG. 6 shows that f is the equi-focus distance of the focus lens 43 of the present invention, and w is the parallel beam incident focus. The entrance radius of the lens 43 is the incident angle of the beam of the present invention, so that the following equation (1-1) can be obtained according to the triangle theorem:

When the equivalent measuring zone is placed into an object of thickness d, according to Snell's Law, it is known that when the light ray penetrates different media, refraction occurs, where n ₁ is the refractive index of air and n ₂ is the measured The refractive index of the transparent substrate 60 and θ ₂ are the angles of refraction of the transparent substrate 60 incident on the light beam. Using this theorem, the following equation (1-2) can be obtained: n ₁ sin θ ₁ =n ₂ sin θ ₂ (1- 2)

Since the beam is incident on different media, the equivalent focal length will be changed to f', and the plane mirror is extended back to the conjugated laser probe and received, and the error error signal to be measured is obtained, and an astigmatic displacement is obtained after conversion. The quantity △X, and f'=f+△X is known from the figure. It can be seen from the figure that the blue block is the direction of the refracting direction when the light passes through the object to be tested, and the extension line L is known to have the light displacement of z, which can be obtained as follows (1-3) shows:

The following formula is known from △ABC:

The following formula is known from △ABD:

It can be obtained by (1-4) and (1-5)

According to the formulas (1-1) and (1-3), tan θ ₁ × f = w tan θ ₁ × f + tan θ ₁ × ΔX = w + zz = tan θ ₁ × ΔX (1-7 )

Bring (1-7) into (1-6) to get

According to the Gauss's theorem, when the beam passes through the focusing lens, its aperture size is W, and NA ₀ is the numerical aperture of the system, which is obtained as shown in the following formula 1-9:

It can be sorted into 1-10 by the Snell's Law of the former 1-2, and the following formulas 1-11 and 1-12 are derived from the triangle theorem: NA ₀ = n ₁ sin θ ₁ = n ₂ sin θ ₂ (1-10)

(1-9), (1-10) bring in (1-8), and n ₁ is the refractive index of light in air, so n ₁ =1, and finally can be expressed as shown in the following 1-13: Get the following

Here, ΔX is first marked as ΔX1 to make a difference from the four-quadrant sensor 50 portion.

As for the formula of the semiconductor laser head 40, when the laser diode 41 emits a laser beam and enters the object to be tested, as shown in FIG. 7, the incident angle is called θ ₁ , and enters the transparent substrate 60 to be tested. A refraction angle θ _{2 is} generated, and a triangular relationship is derived using θ ₁ and θ ₂ : the following formula is known from ΔABC:

The following formula is known from △ABD:

Available from (2-1) and (2-2)

So taking (2-5) into equation (2-4) gives

By Snell's Law n ₁ sin θ ₁ =n ₂ sin θ ₂ (2-7)

And n ₁ =1 (air), so n ₂ sin θ ₂ = sin θ ₁

Derived from the trigonometric formula, you can get

Bring (2-9) back to (2-6)

Here, ΔX is marked as ΔX2 to make a difference from the conjugated focal head portion, and the (1-11) equation obtained by the conjugated focal head formula and the semiconductor laser head formula (2-10) are obtained. When the two are connected, the thickness and the refractive index can be obtained at the same time.

Through the foregoing architecture design and measurement method, the present invention can provide high measurement accuracy and reduce the cost of the overall architecture, and because the architecture is greatly simplified, the measurement operation is more convenient, and the measurement speed is extremely fast. At the same time, without obtaining damage to the transparent substrate 60 to be tested, the information of the transparent substrate 60 to be tested can be obtained, and the measurement quality can be effectively improved, and the transparent substrate, the optical glass, the film, etc. can be manufactured for the detection. Provides better measurement quality and accuracy in terms of thickness and refractive index.

In summary, this case is not only innovative in terms of space type, but also can enhance the above-mentioned multiple functions compared with the customary items. It should fully comply with the statutory invention patent requirements of novelty and progressiveness, and apply for it according to law. This invention patent application, in order to invent invention, to the sense of virtue.

10‧‧‧Conjugate focal head

11‧‧‧Laser diode

12‧‧‧beam splitter

13‧‧‧ Quarter Slide

14‧‧‧ Collimating lens

15‧‧‧Semi-cylindrical lens

16‧‧‧Photodetector

20‧‧‧ Objective lens

30‧‧‧Mirror

40‧‧‧Semiconductor laser head

41‧‧‧Laser diode

42‧‧‧Rotating device

43‧‧‧focus lens

50‧‧‧ four-quadrant sensor

60‧‧‧Transparent substrate

1 is a schematic diagram of a system architecture for measuring the thickness and refractive index of a transparent substrate according to the present invention; and FIG. 2 is a schematic diagram of a system optical path for measuring the thickness and refractive index of a transparent substrate; 3 is a schematic diagram of the astigmatism method applied in the present invention; FIG. 4 is a schematic diagram of imaging of the astigmatism method applied in the present invention, wherein (A) is the focus, (B) is the near focus, and (C) is the far focus; 5 is a schematic diagram of the Snell's Law applied in the present invention; FIG. 6 is a schematic diagram of the optical path of the conjugated focal head in the present invention; and FIG. 7 is a schematic diagram of the optical path of the semiconductor laser head in the present invention.

10‧‧‧Conjugate focal head

11‧‧‧Laser diode

12‧‧‧beam splitter

13‧‧‧ Quarter Slide

14‧‧‧ Collimating lens

15‧‧‧Semi-cylindrical lens

16‧‧‧Photodetector

20‧‧‧ Objective lens

30‧‧‧Mirror

40‧‧‧Semiconductor laser head

41‧‧‧Laser diode

42‧‧‧Rotating device

43‧‧‧focus lens

50‧‧‧ four-quadrant sensor

60‧‧‧Transparent substrate

Claims (10)

An architecture for measuring the thickness and refractive index of a transparent substrate comprises: a conjugated focal head capable of generating laser light, and a splitter mirror for splitting the laser light into the reflected light and the reflected light, and a beam splitter Below is a quarter-wave plate that converts the line-polarized light into a circularly polarized light, and a quarter-wave plate is provided with a collimating lens that can convert the circularly polarized light into a parallel beam, and then above the beam splitter a semi-cylindrical lens is provided for focusing light into spots of different magnitudes, and a photodetector for receiving a light spot is disposed above the semi-cylindrical lens; an objective lens is disposed under the conjugate focal head, the objective lens can be Producing a focusing effect; a mirror is disposed under the objective lens, a space to be measured is formed between the mirror and the objective lens, and the mirror can reversely emit the light beam according to the law of reflection; a semiconductor laser head is disposed at the conjugate focal length On the other side of the head, the axis of the semiconductor laser head is disposed at an angle with the axis of the conjugated focal head, and a rotating device is disposed in front of the laser diode, and a focusing lens is disposed on the rotating device; Sensor, The semiconductor laser provided on the head of the laser diode via the laser beam through the measuring region on the side of the axis, the four-quadrant sensor operable to receive defocus signal. A structure for measuring the thickness and refractive index of a transparent substrate according to claim 1 , wherein the conjugated focal head emits laser light, causes the laser light to enter the objective lens, and causes the laser light to start focusing, and then enters the incident Measuring the transparent substrate, causing the laser light to refract, incident on the mirror, generating a defocus signal reflected back to the original light path, and then incident on the conjugated focal head to obtain a displacement value Δx1; then, causing the semiconductor laser to exit Laser light, and using a rotating device, rotates the focusing lens in front of the semiconductor laser head, so that the laser light enters the focusing lens and starts focusing, and then enters the transparent substrate to refract the laser light, is incident on the four-quadrant sensor, and receives Defocusing the signal, and obtaining a displacement value Δx2; taking the obtained Δx1 and Δx2 into a simultaneous equation of thickness and refractive index, and decomposing the cubic equation, the refractive index of the transparent substrate to be tested is obtained. thickness. An architecture for measuring the thickness and refractive index of a transparent substrate according to claim 1 , wherein the photodetector converts the optical signals received to the light spots of different sizes on the semi-cylindrical lens into electrical signals. For computer interpretation. An apparatus for measuring thickness and refractive index of a transparent substrate according to claim 1 , wherein the semiconductor laser head has a high directivity and coherence. A structure for measuring the thickness and refractive index of a transparent substrate according to claim 1 , wherein the rotating device can be rotated clockwise or counterclockwise to change the focus position. The structure of measuring the thickness and refractive index of a transparent substrate according to claim 1 , wherein the four-quadrant sensor can receive the optical signal of the reflected laser light and convert it into an electrical signal for computer interpretation. A structure for measuring the thickness and refractive index of a transparent substrate according to claim 2 , wherein the transparent substrate may be a transmissive measuring object. An architecture for measuring the thickness and refractive index of a transparent substrate according to claim 1 , wherein the conjugated focal head has a laser diode that emits laser light. A structure for measuring the thickness and refractive index of a transparent substrate according to claim 1 , wherein the axis of the semiconductor laser head is at a fixed angle θ with the axis of the conjugated focal head. An architecture for measuring the thickness and refractive index of a transparent substrate according to claim 1 , wherein the semiconductor laser head has a laser diode capable of emitting laser light.