Reflection type z scanning device and method

Abstract

The invention discloses a reflective z scanning device and method, the reflective z scanning device comprises a laser, a lens, a detector, a first displacement platform and a template, incident light of an incident film is collimated and focused by the laser through the lens, and the incident light is obliquely incident; the first displacement platform is used for placing and moving a sample; the template is used for allowing incident light and reflected light of an interface between the film and the substrate to pass through, and filtering the reflected light of the interface behind the substrate; the template moves up and down through a displacement platform; the detector and the laser are arranged on the same side and used for detecting reflected light of an interface between the film and the substrate; during z scanning, the first displacement platform is moved to enable laser to be focused at a certain distance in front of the film, then the first displacement platform is moved equidistantly, a power value measured by the detector is recorded, a z scanning curve is obtained, finally, the z scanning curve is fitted, and a nonlinear absorption coefficient is obtained. The influence of substrate absorption on the measurement of the nonlinear absorptivity of the thin film can be avoided, and the measurement result is more accurate.

Description

Technical Field

[0001] The present invention relates to z-scanning measurement, and in particular to a reflective z-scanning device and method. Background Art

[0002] Z-scanning is one of the conventional methods for measuring bulk materials. It uses focused laser incident and analyzes the effect of absorption at the focus on the transmitted laser power. For thin film materials, since the film is very thin and has a thick substrate, the absorption of the substrate will have a greater impact on the measurement. Therefore, traditional transmission z-scanning is not suitable for thin film measurement. Summary of the invention

[0003] Objects of the invention: The first object of the present invention is to provide a reflective z scanning device capable of accurately measuring the nonlinear absorption rate of a thin film; the second object of the present invention is to provide a reflective z scanning method.

[0004] Technical solution: The reflective z scanning device described in the present invention includes a laser, a lens, a detector and a first displacement platform. The incident light incident on the film is collimated and focused by the laser through the lens. The first displacement platform is used to place and move the sample. The incident light is incident at an angle. The reflective z scanning device also includes a template. The template is used to allow the incident light and the reflected light at the interface between the film and the substrate to pass through, while filtering out the reflected light at the interface behind the substrate; the template also moves up and down through a displacement platform; the detector is set on the same side as the laser, and is used to detect the reflected light at the interface between the film and the substrate.

[0005] Furthermore, the template adopts a pinhole template, the pinhole allows incident light and reflected light at the interface between the film and the substrate to pass through, and the non-pinhole area on the pinhole template blocks the reflected light at the interface behind the substrate.

[0006] Further, the pinhole diameter D, the incident angle θ and the substrate thickness H satisfy: D=2H×tg(θ).

[0007] Furthermore, the template adopts a knife-edge template, the front end of the knife-edge template is a transparent area for incident light and reflected light from the interface between the film and the substrate to pass through, and the non-transparent area of ​​the knife-edge template blocks the reflected light from the rear interface of the substrate.

[0008] Furthermore, the small hole or the knife edge is processed by coating and etching processes.

[0009] Furthermore, the laser wavelength λ ranges from 0.4μm≤λ≤5.0μm, and the laser power I 0 The range is 0.1W≤I 0 ≤10.0W.

[0010] Furthermore, the first displacement platform adopts a piezoelectric ceramic displacement platform.

[0011] The reflective z scanning method described in the present invention adopts the reflective z scanning device; the reflective z scanning method includes: placing the sample on a first displacement platform, moving the first displacement platform to focus the laser at a certain distance in front of the film, then moving the first displacement platform at an equal distance and recording the power value measured by the detector to obtain a z scanning curve, and finally fitting the z scanning curve to obtain a nonlinear absorption coefficient.

[0012] Furthermore, a combination of multiple lasers and multiple wavelengths is used to detect with multiple wavelengths in turn to obtain nonlinear absorption coefficients of different wavelengths.

[0013] Furthermore, the plurality of lasers include solid-state lasers, fiber lasers, and optical parametric oscillators.

[0014] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the present invention uses a tightly focused Gaussian beam to obliquely incident to scan the film, uses a template to allow the incident light and the reflected light at the interface between the film and the substrate to pass through, and at the same time spatially filters the reflected light at the rear interface of the substrate, and the detector detects the reflected light at the interface between the film and the substrate. The present invention avoids the influence of substrate absorption on the measurement of nonlinear absorptivity of the film, and the measurement result is more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a structural schematic diagram of a reflective z scanning device provided by an embodiment of the present invention;

[0016] Figure 2 Schematic diagram of the size relationship of the small hole template in the embodiment of the present invention;

[0017] Figure 3 is a schematic structural diagram of another reflective z scanning device provided by an embodiment of the present invention;

[0018] Figure 4 It is a curve showing the relationship between the intensity and displacement measured by the detector in the embodiment of the present invention. DETAILED DESCRIPTION

[0019] The basic idea of ​​the present invention is to use incident light with an inclined angle and reflected light from the interface between the film and the substrate to perform z-scan measurement.

[0020] The present invention will be further described below in conjunction with the accompanying drawings.

[0021] Attached Figures 1 to 4 The reference numerals in the figures are as follows:

[0022] 1, template; 101, small hole; 102, transparent area; 2, first displacement platform.

[0023] like Figure 1As shown, an embodiment of the present invention provides a reflective z scanning device, including a laser, a lens, a detector, a template 1 and a first displacement platform 2 (the laser, the lens and the detector are conventional configurations of z scanning, not shown in the figure), the incident light incident on the film is collimated and focused by the laser through the lens, and the incident light is incident at an angle. The first displacement platform 2 is used to place and move the sample. The detector is used to receive the reflected light.

[0024] In one embodiment, the template 1 is a pinhole template, and the incident laser of the z scan has a wavelength λ, an initial power I 0 The laser is focused by the lens and passes through the small hole 101. The waist of the focused spot is ω 1 After being absorbed by the film and reflected at the interface between the film and the substrate, the light is detected by the detector through the small hole 101. The reflected light at the rear interface of the substrate is filtered out through the small hole 101 on the template 1.

[0025] In another embodiment, if Figure 3 As shown, the template 1 adopts a knife-edge template, and the front end of the knife-edge template is a transparent area 102 for incident light and reflected light from the interface between the film and the substrate to pass through, and the knife edge is used to filter out the reflected light from the interface behind the substrate.

[0026] Specifically, Figure 1 and Figure 3 As shown, the reflected light from the rear interface of the substrate is represented by a dotted line. Since the incident light is incident at an angle, the reflected light from the reflecting surface has a certain displacement from the reflected light from the interface between the film and the substrate. Therefore, only the solid reflected light can be transmitted through the small hole 101 or the knife edge, while the dotted reflected light can be filtered out.

[0027] The small hole 101 and the knife edge can be processed by coating and etching processes.

[0028] For a simpler knife-edge template, the position of the knife-edge template can be moved so that the dotted line reflected light is blocked and the solid line reflected light is transmitted. Here the template can be installed on a manual or electric translation displacement platform.

[0029] For small hole templates, such as Figure 2 As shown, the diameter D of the small hole 101, the incident angle θ and the substrate thickness H satisfy the following relationship:

[0030] D = 2H x tg(θ).

[0031] In this embodiment, the laser wavelength λ ranges from 0.4μm≤λ≤5.0μm. For visible light, such as 0.532μm, a frequency-doubled solid laser is used. For near-infrared light, such as 1.064μm, a solid laser or a fiber laser is used. For mid-infrared light, such as 3.4μm, an optical parametric oscillator is used. In this embodiment, the power of the laser I0 The range is 0.1W≤I 0 ≤10.0W.

[0032] The film thickness to be measured is 0.1μm≤d≤10μm, and the substrate thickness is generally greater than 100μm. Therefore, when the substrate thickness is thin, such as 100μm, the Rayleigh distance z is required. R Smaller spot size, such as z R =5.0μm; for thicker substrates, such as 500μm, the Rayleigh distance z can be used R Larger spot size, such as z R =200.0μm. Generally speaking, z R Smaller spot size is suitable for wider measurement, so z is preferred. R =5.0μm.

[0033] The sample and the template are moved up and down by the displacement platform and scanned a certain distance, which is the z direction, that is, the up and down direction.

[0034] In this embodiment, the first displacement platform 2 is a piezoelectric ceramic displacement platform with a moving range of 30 μm and an accuracy of 10 nm.

[0035] The embodiment of the present invention further provides a reflective z scanning method, which uses the reflective z scanning device described in the embodiment of the present invention, and includes the following steps:

[0036] The sample is placed on the first displacement platform 2, and the first displacement platform 2 is moved to focus the laser at a certain distance in front of the film. The first displacement platform 2 is then moved an equal distance (i.e., the z distance) and the power value measured by the detector is recorded to obtain the z scanning curve. Finally, the z scanning curve is fitted to obtain the nonlinear absorption coefficient.

[0037] In addition, multiple lasers and multiple wavelengths can be used in combination to detect with multiple wavelengths in turn to obtain nonlinear absorption coefficients of different wavelengths.

[0038] A specific example is given below.

[0039] The test sample is a thin film lithium niobate, wherein the thickness of the thin film lithium niobate is 0.3 μm, and the substrate is silicon dioxide, and the thickness is 500 μm.

[0040] A 1.064μm solid-state laser is used to output a quasi-continuous laser with a maximum average power of 1W, a pulse length of 10ns, and a repetition frequency of 1KHz. The beam spot is expanded to ω 0 =10.0mm. The focal length of the lens is 3mm, and the laser is focused to ω=1.3μm.

[0041] The incident laser is incident at an incident angle of θ = 45°, and a small hole template is used. According to the above formula, H = 0.5 mm, D = 2H × tg (θ) = 2 × 0.5 mm × tg (45°) = 1 mm is obtained. A small hole with a diameter of 1 mm is prepared by plating a metal film on the surface of quartz glass, photolithography, and etching; or a small hole with a diameter of 1 mm is prepared by plating a metal film on the surface of quartz glass and laser processing.

[0042] Place the sample on the first displacement platform 2. First, move the first displacement platform 2 to focus the laser at 15 μm in front of the film. Move the first displacement platform 2 every 10 nm and record the power value measured by the detector until the moving distance is 30 μm. Record the data as follows: Figure 4 As shown, the curve is fitted (which is the prior art) to obtain the nonlinear absorption coefficient.

[0043] It should be noted that the film surface also generates reflected light, but the reflected light on the film surface does not carry sample information, because the surface only has a reflective effect, and the film carries useful information after absorption. Therefore, it only increases a fixed light intensity and does not affect the measurement results.

Claims

1. A reflective z scanning device, comprising a laser, a lens, a detector and a first displacement platform (2), wherein the incident light incident on the film is collimated and focused by the laser through the lens, and the first displacement platform (2) is used to place and move the sample, characterized in that: The incident light is incident at an angle, and the reflective z scanning device also includes a template (1), which is used to allow the incident light and the reflected light at the interface between the film and the substrate to pass through, while filtering out the reflected light at the interface behind the substrate; the template (1) also moves up and down through a displacement platform; the detector is arranged on the same side as the laser, and is used to detect the reflected light at the interface between the film and the substrate.

2. The reflective z-scanning device according to claim 1, characterized in that: The template (1) is a pinhole template, the pinhole (101) allows incident light and reflected light at the interface between the film and the substrate to pass through, and the non-pinhole area on the pinhole template blocks the reflected light at the interface behind the substrate.

3. The reflective z-scanning device according to claim 2, characterized in that: The diameter D of the small hole (101), the incident angle θ and the substrate thickness H satisfy: D=2H×tg(θ).

4. The reflective z-scanning device according to claim 1, wherein: The template (1) adopts a knife-edge template. The front end of the knife-edge template is a transparent area (102) for incident light and reflected light from the interface between the film and the substrate to pass through, and the non-transparent area of ​​the knife-edge template blocks the reflected light from the interface behind the substrate.

5. The reflective z-scanning device according to any one of claims 2 to 4, characterized in that: The small hole (101) or the knife edge is processed by coating and etching processes.

6. The reflective z-scanning device according to claim 1, wherein: The laser wavelength λ ranges from 0.4μm≤λ≤5.0μm, and the laser power I0 ranges from 0.1W≤I0≤10.0W.

7. The reflective z-scanning device according to claim 1, wherein: The first displacement platform (2) adopts a piezoelectric ceramic displacement platform.

8. A reflective z-scanning method, characterized in that: A reflective z scanning device as described in any one of claims 1 to 7 is used; the reflective z scanning method comprises: placing the sample on a first displacement platform (2), moving the first displacement platform (2) to focus the laser at a certain distance in front of the film, then moving the first displacement platform (2) at an equal distance and recording the power value measured by the detector to obtain a z scanning curve, and finally fitting the z scanning curve to obtain a nonlinear absorption coefficient.

9. The reflective z-scanning method according to claim 8, characterized in that: By using a combination of multiple lasers and multiple wavelengths, multiple wavelengths are used in turn to detect and obtain nonlinear absorption coefficients of different wavelengths.

10. The reflective z-scanning method according to claim 9, wherein: The plurality of lasers include solid-state lasers, fiber lasers, and optical parametric oscillators.

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