CN1238688C - Co-optical circuit double-frequency heterodyne confocal micromeasurer - Google Patents

Abstract

The utility model relates to a dual-frequency heterodyne confocal microscopic measurement device with a common optical path, which belongs to the technical field of surface topography measurement. In order to ensure the high stability of the system while improving the resolution and range, the invention discloses a common optical path dual-frequency heterodyne confocal microscopic measurement device, which includes a transverse Zeeman dual-frequency laser, which is sequentially arranged on the axis of the laser emitting end The beam splitter, the first converging lens, the first pinhole, the first cemented lens, the first half mirror, the birefringent lens group and the microscope objective lens, and the first photodetector arranged on the reflected light path of the beam splitter ; Also include the second half-mirror that is arranged on the reflected light path of the first half-mirror, and the Glan prism, the second cemented lens, the second half-mirror that are respectively arranged on the reflected light path of the second half-mirror Two pinholes, a second photodetector, an aperture arranged on the transmitted light path, a second converging lens, and a third photodetector. The invention has the characteristics of low drift and strong anti-vibration interference ability, and has low cost.

Description

Common optical path dual-frequency heterodyne confocal microscopic measurement device

technical field

The invention belongs to the technical field of surface topography measurement, in particular to a microscopic measuring device for step height standard measurement.

Background technique

Confocal scanning imaging was proposed by Minsky as early as the 1950s, and then Davidovits, Sheppard and Wilson made further research on confocal microscopy systems. The research results show that: the confocal scanning microscope system can not only suppress the weak stray light in imaging, but also under the same imaging conditions, its axial resolution is 1.4 times that of the ordinary microscope system, and it has the function of three-dimensional tomography. Figure 1 is the optical path diagram of a common reflective confocal microscope, assuming that the measured object is a total reflector and scanned along the axis of the objective lens. When the object is in the focal plane (solid line in Figure 1), the reflected light is precisely focused on the point detector, which receives a large amount of incident light energy. If the reflector moves away from the focal plane (dotted line in Figure 1), the reflected light is focused at a position in front of or behind the point detector (depending on the scanning direction), and only A fraction of the energy, the signal on out-of-focus is weaker than that on focus. For a real thick object, a series of cross-sectional images of different longitudinal depths are firstly recorded, and then the complete image of the thick object is reconstructed by using these cross-sectional images. It is this three-dimensional imaging capability that has made confocal microscopy widely used in the fields of biology, biomedicine, industrial detection, and metrology.

However, the axial resolution of ordinary confocal microscopes is still only at the submicron level, and the noise and drift of the light source directly affect the measurement results. For this reason, Tan Jiubin from Harbin Institute of Technology proposed a differential confocal nanoscale optical Focus detection system, as shown in Figure 2. The light output from the light source 101 first passes through the half-mirror 102, is converged by the microscope objective lens 103 to the surface of the sample 104 to be tested, and after being reflected back by the sample 104, it is reflected by the half-mirror 102 out of the original optical path, and then by the light splitter. The mirror 105 is divided into two beams of light, transmission and reflection, and a pinhole and a detector are respectively placed behind the reflected light and the transmitted light. The signals of the detectors 107, 109 are subtracted and summed to give the measuring light focus signal. When the surface of the sample to be measured is on the focal plane, the positions of the two pinholes are symmetrical to the focal plane of the image, and the difference between the two detectors is zero; when the surface of the sample deviates from the focal plane by a small displacement, the image points approach to it respectively. One of the pinholes is far away from the other pinhole, so that the detected optical power increases and decreases, so that the magnitude and direction of the displacement can be reflected by the differential signal. Although this method can make the axial resolution of the measurement reach 2nm, the measurement range is limited by the linear region of the light intensity differential curve, and cannot provide a larger range of measurement. At the same time, since the relationship between the change of light intensity and the displacement of the sample surface is not completely linear, the measurement accuracy cannot be very high.

The applicant filed a patent application with the application number 02120884.0 on June 7, 2002, entitled "Dual-frequency Confocal Step Height Microscopic Measuring Device", and the publication date was December 11, 2002. The structure of the device described in this patent is shown in Figure 3. The device includes a transverse Zeeman dual-frequency laser 1, and a beam splitter 2, a Faraday cell 20, a 1/2 wave plate 21, a first converging lens 4, a first pinhole 5, a first Cemented lens 6 and polarizing beam splitter (PBS) 7, 1/4 wave plate 8 and tetrahedron 22 placed on PBS reflected light path, 1/4 wave plate 14 and microscope objective lens 9 placed on PBS transmitted light path; Measurement The light and the reference light are divided into two parts after being combined by the PBS and used for light intensity measurement and phase measurement respectively. The device also includes a second half mirror (BS) 11, which is respectively placed on the The Glan prism 16, the second cemented lens 17, the second pinhole 18 and the second photodetector 19 on the 11 reflected light path, the diaphragm 12 placed on the transmitted light path of the second half-mirror 11, the second converging lens 13 and a third photodetector 15 . Although this solution achieves large-scale and high-resolution measurement, because the measurement light and reference light do not conform to the principle of common path, the measurement device is greatly affected by vibration and temperature drift, which limits the measurement accuracy.

Contents of the invention

The purpose of the present invention is to provide a new surface topography measuring device which maintains the advantages of the prior art, conforms to the common optical path principle, and improves the measurement stability of the device.

The present invention proposes a common optical path design using a birefringent lens, and combines dual-frequency heterodyne laser interference and scanning confocal microscopy technology, thereby realizing a common optical path dual-frequency heterodyne with high stability, high resolution and a large range The confocal microscopic measurement device is characterized in that the device includes a transverse Zeeman dual-frequency laser, a beam splitter, a first converging lens, a first pinhole, a first cemented lens, and a first Half-mirror, birefringent lens group and microscope objective lens, and the first photodetector that is arranged on the reflection light path of described beam splitter; The second half-mirror, and the Glan prism, the second cemented lens, the second pinhole, the second photodetector that are respectively arranged on the reflected light path of the second half-mirror, and are arranged on the second half-mirror. The diaphragm on the transmission light path of the half mirror, the second converging lens, and the third photodetector.

The birefringent lens group of the present invention includes a convex-concave negative lens and a cemented birefringent lens.

The cemented birefringent lens of the present invention is formed by cementing a biconvex positive lens and a biconcave negative lens.

The material of the biconcave negative lens in the present invention is calcite, and the optical axis of the calcite is parallel to the surface of the biconcave negative lens.

The common optical path heterodyne interference confocal microscopic measurement device of the present invention improves the optical path design so that the optical path meets the common path principle, so that the present invention not only maintains the high measurement accuracy and large measurement accuracy of the previous patent application with application number 02120884.0 The advantage of range, and the present invention has obvious restraining effect on vibration and drift. The invention not only satisfies the needs of the recent development of microelectronic technology, but also can be further popularized and applied in other fields of surface topography measurement.

Description of drawings

Figure 1 is an optical path diagram of an existing common reflective confocal microscope.

FIG. 2 is a schematic diagram of an existing differential confocal optical focusing detection system.

Fig. 3 is a schematic block diagram of the dual-frequency confocal micro-interference system.

Fig. 4 is an optical path diagram of the common optical path heterodyne interference confocal microscopic measurement device of the present invention.

FIG. 5 is an enlarged schematic diagram of the structure of the birefringent lens group according to the present invention.

Detailed ways

The specific details of the present invention will be described below in conjunction with the accompanying drawings.

The structure of the embodiment of the present invention is shown in Figure 4, the device includes a transverse Zeeman dual-frequency laser 1, a beam splitter 2, a first converging lens 4, a first pinhole 5, The first cemented lens 6, the first half-mirror 7, the birefringent lens group 8 and the microscopic objective lens 9, and the first photodetector 3 arranged on the reflected light path of the beam splitter 2; the device also includes setting The second half-mirror 11 on the reflected light path of the first half-mirror 7, and the Glan prism 16 and the second cemented lens that are respectively arranged on the reflected light path of the second half-mirror 11 17. The second pinhole 18, the second photodetector 19, and the diaphragm 12, the second converging lens 13, and the third photodetector 15 arranged on the transmission light path of the second half mirror 11.

Described birefringent lens group 8 comprises a convex-concave negative lens 201 (material is ZF1) and a cemented birefringent lens, wherein the cemented birefringent lens is made of a biconvex positive lens 202 (material is ZF1) and a double concave negative lens The lens 203 (made of calcite) is cemented. The optical axis of the calcite is parallel to the surface of the double-concave negative lens. The convex-concave negative lens is located in front of the cemented birefringent lens, as shown in FIG. 5 . Its function is to make the light whose polarization direction is parallel to the optical axis of the calcite lens exit in parallel, and make the light whose polarization direction is perpendicular to the optical axis direction converge.

The measurement principle of the common optical path dual-frequency heterodyne confocal microscopic measurement device proposed by the present invention is similar to the applicant's previous patent application with application number 02120884.0, and the specific measurement steps are as follows:

1) The transverse Zeeman He-Ne laser 1 outputs orthogonal dual-frequency laser light (p light and s light), and the output light is divided into reflected light and transmitted light by the beam splitter 2, and the reflected light is received by the first photodetector 3 Then form a reference signal.

2) The transmitted light is converged on the first pinhole 5 through the first converging lens 4 , the stray light is filtered out through the first pinhole 5 , and the beam is expanded into a parallel beam by the first cemented lens 6 .

3) The parallel light beam first passes through the first half mirror 7, and then passes through the birefringent lens group 8. The main axis direction of the birefringent lens group 8 is the same as the polarization direction of the p light. After passing through the lens group, the p light and the s light are separated , p light is still parallel light, s light becomes converging light.

4) The separated light beam passes through the microscopic objective lens 9, and the front focal point of the microscopic objective lens 9 coincides with the focal point of the s-ray. Therefore, after passing through the microscope objective lens 9, the original parallel p converges on the surface of the sample to be measured 10, which is the measurement light of the measuring device; the s light is emitted in parallel, and shines on the surface of the sample to be measured with a larger spot, which is the reference light of the measurement system .

5) Both the measurement light and the reference light are reflected by the sample 10, pass through the microscope objective lens 9 and the birefringent lens group 8 again, and recombine the light.

6) After the light is combined, the light beam is reflected out of the optical path by the first half mirror 7, and the outgoing light is divided into reflected light and transmitted light by the second half mirror 11.

7) After the transmitted light passes through the diaphragm 12 and the second converging lens 13, it is received by the second photodetector 15 to form a phase measurement signal, which is compared with the reference signal collected by the first photodetector 3 for phase measurement, so that the common path The measurement resolution of the differential dual-frequency confocal microscopy system is improved to below 1 nanometer.

8) After the reflected light passes through the Glan prism 16 whose optical axis direction is parallel to the p light, only the p light passes through, and the p light is then converged by the second cemented lens 17 (same as the first cemented lens 6) and passes through the second pinhole 18 , incident to the second photodetector 19, the light intensity information is received by the second photodetector 19, and the measurement surface deviation from the focus can be calculated from the light intensity information, the order of the interference phase is determined, and the range of the interferometric measurement is expanded. Make the longitudinal measurement range reach more than 5 microns.

Because the measuring device of the present invention adopts a birefringent lens group, the measuring optical path satisfies the principle of common path, so that the device effectively overcomes the influence of vibration and drift on the measurement. In an ordinary laboratory environment without constant temperature and no vibration isolation, a long-term stability experiment was carried out on the measuring device, and the drift of the system in 3 hours was 8 degrees (corresponding to a measurement height change of 7nm), which is better than that of the applicant whose application number is 02120884.0 The embodiment described in the previous patent application has been improved by 3 times, which proves that the device of the present invention has outstanding stability and anti-interference ability.

The models and parameters of the main components of the embodiments of the present invention:

The frequency difference of the transverse Zeeman He-Ne dual-frequency laser 1 is tens to hundreds of kilohertz, the transmittance of the beam splitter 2 is 90%, and the reflectance is 10%. The photodetectors 3, 15, and 19 are PIN tubes, glued together The focal length of lenses 6 and 17 is 180 millimeters, the reflectivity and transmittance of half mirrors 7 and 11 are 50%, the pinholes 5 and 18 are 20 microns, and the birefringent lens group has two focal lengths, which are infinity and 45 mm, the focal length of the microscope objective lens is 18 mm.

Claims (4)

1. common-path dual-frequency heterodyne confocal micro-measurement device, it is characterized in that: this device comprises the transversal zeeman double-frequency laser device, be successively set on spectroscope (2), first convergent lens (4), first pin hole (5), first balsaming lens (6), first semi-transparent semi-reflecting lens (7), birefringent lens group (8) and microcobjective (9) on the described laser instrument transmitting terminal axis, and be arranged on first photodetector (3) on described spectroscope (2) reflected light path; This device also comprises second semi-transparent semi-reflecting lens (11) on the reflected light path that is arranged on first semi-transparent semi-reflecting lens (7), and be separately positioned on Glan prism (16), second balsaming lens (17), second pin hole (18), second photodetector (19) on described second semi-transparent semi-reflecting lens (11) reflected light path and be arranged on diaphragm (12), second convergent lens (13), the 3rd photodetector (15) on second semi-transparent semi-reflecting lens (11) transmitted light path.

2. measurement mechanism according to claim 1 is characterized in that: described birefringent lens group (8) comprises a convex-concave negative lens (201) and a gummed birefringent lens.

3. measurement mechanism according to claim 2 is characterized in that: described gummed birefringent lens is to be formed by a biconvex positive lens (202) and a double-concave negative lens (203) gummed.

4. measurement mechanism according to claim 3 is characterized in that: the material of described double-concave negative lens (203) is a kalzit, and the optical axis of described kalzit is parallel to the surface of described double-concave negative lens (203).

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