CN105353170B - Nano stepping sample scanning metering type scanning electron microscope - Google Patents

Abstract

The invention relates to a scanning electron microscope of nanometer stepping sample scanning measurement type. The two-dimensional laser interferometer includes two interferometers, the interferometers are respectively located in the X direction and the Y direction of the measurement sample, and the light source of the interferometer is transmitted from the laser to Introduction, the vacuum window that passes through the glass window is divided into two beams in the electron microscope, which are respectively incident on two interference mirrors; when the ultrasonic motor roughly adjusts the displacement stage to perform scanning motion, an outgoing interference light enters the photodetector through the vacuum window as The X-axis displacement data signal of the displacement platform; another beam of interference light is reflected by the plane mirror and then enters the interferometer near the hatch door, and the outgoing interference light is received by another detector as the Y-axis displacement data signal of the displacement platform; the X, Y The axial displacement data is combined with the electron microscope to collect the secondary electron signal excited by the electron beam on the sample surface, and the measurement data traced to the source by the laser interferometer is obtained. Provides an electron microscope capable of direct traceability of its measurements to a meter-defining national benchmark standard.

Description

A Scanning Metrology Scanning Electron Microscope with Nano Stepped Samples

technical field

The invention relates to the technical field of scanning electron microscopes, in particular to a nano-stepping sample scanning metrology scanning electron microscope.

Background technique

As an effective microstructure analysis tool, scanning electron microscope (SEM) can observe and analyze various forms of surfaces of various materials. The characteristics of the scanning electron microscope are: it can directly observe the surface structure of the sample; the depth of field is large, the image is full of three-dimensional effect; the image has a wide range of magnification and the resolution is relatively high; The other signals are used for micro-component analysis to observe various morphology features of the sample.

Scanning electron microscopy usually uses a focused electron beam to scan point by point on the sample surface, interacting with the sample to generate secondary electrons, backscattered electrons, etc. The number of secondary electrons is related to the incident angle of the electron beam, that is to say, to the surface structure of the sample. The secondary electrons are collected by the detector, where they are converted into optical signals by the scintillator, and then converted by the photomultiplier tube and the amplifier. It controls the intensity of the electron beam on the fluorescent screen for electrical signals, and displays a scanning image synchronized with the electron beam, which reflects the surface structure of the specimen.

Since the conventional scanning electron microscope uses a coil to control the deflection of the electron beam to scan and obtain an image, the magnification and image distortion of the scanning electron microscope image are affected by the current image of the coil, and often cannot be predicted and controlled, making the measurement of the scanning electron microscope uncertain Degree assessment is difficult to carry out.

Therefore, there are defects in the prior art and need to be further improved and developed.

Contents of the invention

The object of the present invention is to provide an electron microscope capable of directly tracing its measurements to a standard defining a national benchmark in meters.

In order to achieve the above object, the present invention adopts the following technical solutions:

A nano-stepping sample scanning metrology scanning electron microscope, which includes a high-speed nano-displacement scanning

Scanning table, two-dimensional laser interferometer and ultrasonic motor coarse adjustment stage:

The ultrasonic motor coarse-adjustment translation stage fixes the high-speed nano-displacement scanning platform, and the high-speed nano-displacement scanning platform is provided with a sample stage and a pole shoe of an electron gun of an electron microscope;

The two-dimensional laser interferometer includes two interferometers, the interferometers are respectively located in the X direction and the Y direction of the measurement sample, the light source of the interferometer is introduced from the laser through an optical fiber, passes through the vacuum window of the glass window, and is placed in the electron microscope. Divided into two beams, respectively incident on two interference mirrors;

The electron gun of the electron microscope emits electron beams to the surface of the sample, and the generated secondary electrons are received by the electron microscope receiver, and the high-speed nano-table drives the sample to scan at high speed;

When the ultrasonic motor coarsely adjusts the displacement stage to perform scanning motion, one outgoing interference light is incident on the photodetector through the vacuum window as the X-axis displacement data signal of the displacement platform; Interferometer, the outgoing interference light is received by another detector as the Y-axis displacement data signal of the displacement platform;

The X-axis and Y-axis displacement data cooperate with the electron microscope to collect the secondary electron signal excited by the electron beam on the surface of the sample, and obtain the measurement data traceable by the laser interferometer.

The metrological scanning electron microscope, wherein the two-dimensional laser interferometer includes a laser beam incident fiber, a through-hole flange, a vacuum window, a cube beam splitter, an elastic hinge, a plane mirror, a receiver, an interferometer and an L-shaped 2D mirrors.

The metrological scanning electron microscope, wherein, the coilless ultrasonic motor coarse-adjustment stage is connected to the high-speed nano-displacement scanning stage through a first connecting plate, and the high-speed nano-displacement scanning stage is connected to a second connecting plate. The fine-tuning sample stage is provided with the sample to be tested and the pole piece of the electron gun of the electron microscope on the fine-tunable sample stage.

In the metrological scanning electron microscope, the natural resonance frequency of the elastic hinge can be higher than 200 Hz.

In the metrological scanning electron microscope, the material of the L-shaped two-dimensional mirror is glass ceramics.

The metrological scanning electron microscope, wherein the interferometer is a 2-fold optical path, one period of the interference signal corresponds to 158nm, and the interference signal of one period is subdivided by the circuit 1024 or 2048, and the resolution is 0.15nm or 0.075nm nm.

The invention provides a standard measurement device that can directly trace its measurement value to the national benchmark defined in meters. The measurement method is to directly connect a laser interferometer to the sample stage of the scanning electron microscope, and measure the displacement of the sample and the two The signal of secondary electrons or backscattered electrons is used to measure the length to be measured on the sample. The measured value can be directly traced to meters to define the international unit. This is an absolute measurement method. The biggest difference from the conventional scanning electron microscope is that it does not use electron beam scanning. , the electron beam spot of the electron microscope is in a static state during the imaging measurement, and the measurement image is obtained by the scanning motion of the high-speed translation stage carrying the measured sample. Use a laser interferometer to measure the displacement of the displacement stage. The measuring mirror of the laser interferometer is fixed on the displacement stage, so that the displacement of the displacement stage measured by the laser interferometer can be directly traced to the laser wavelength and the meter defines the SI unit, so that Realize the traceability of the measured value of the metrological scanning electron microscope.

Description of drawings

Fig. 1 is the structure schematic diagram of the scanning electron microscope of nano-stepping sample scanning metrology type scanning electron microscope of the present invention;

Fig. 2 is a structural schematic diagram of the measurement optical path of the interferometer of the present invention.

Detailed ways

The present invention will be described in further detail below in conjunction with preferred embodiments.

The present invention provides a nano-stepping sample scanning metrology scanning electron microscope including a high-speed nano-displacement scanning stage, a two-dimensional laser interferometer and an ultrasonic motor coarse-adjustment displacement stage, and the ultrasonic motor coarse-adjustment displacement stage does not include control electron beam deflection the coil. In order to reduce the impact of electron beam drift on the measurement, the ultrasonic motor coarse-adjustment displacement platform adopts a nano-displacement scanning platform with an elastic hinge system whose natural resonance frequency can reach more than 200 Hz when the load is 0.5 kg. The invention uses a two-dimensional laser interferometer to measure the position of the sample stage. The laser beams in two directions intersect with the electron beam of the electron microscope to reduce the Abbe error in measurement. The interferometer is located inside the electron microscope, and the laser is introduced through the optical fiber. Partitioned interior. The measuring mirror of the two-dimensional laser interferometer is fixed on the sample stage 24 and moves along with the sample scanning.

Described two-dimensional laser interferometer, as shown in Figure 1 and Figure 2, comprises laser beam incident optical fiber 10, through-hole flange 11, vacuum window plate 17, cube beam splitter 12, elastic hinge 13, plane mirror 14, receiver 16 , an interferometer 15 and an L-shaped two-dimensional mirror 25 .

The coilless ultrasonic motor coarse adjustment displacement stage 20, as shown in FIG. The sample stage 24 can be finely adjusted, and the sample to be tested 26 and the pole shoe 27 of the electron gun of the electron microscope are arranged on the finely adjustable sample stage 24, and these constitute the rough adjustment positioning structure of the sample stage.

The laser interferometry optical path of the two-dimensional laser interferometer, as shown in Figure 2, includes two interferometers 15, the interferometers 15 are respectively located at the position of the measurement sample in the XY direction, and the light source of the interferometer 15 is introduced from the laser through the optical fiber 10 , pass through the vacuum window 17 of the glass window, split into two beams in the electron microscope, and enter the two interference mirrors respectively.

The light that sends from optical fiber 10 injects electron microscope vacuum cabin through the vacuum window (11,17) on the side door of electron microscope, is divided into two beams of light through spectroscope 12, and a bunch directly injects the interferometer 15 far away from cabin door. When the ultrasonic motor roughly adjusts the displacement platform 22 to perform scanning motion, its outgoing interference light is incident on the photodetector 16 as the X-axis displacement data signal of the displacement platform through the vacuum window; the other beam of light is reflected by the plane mirror 25 and then incident close to the cabin door The interferometer 15, when the ultrasonic motor roughly adjusts the displacement platform 22 to perform scanning motion, the outgoing interference light is received by another detector as the Y-axis displacement data signal of the displacement platform. The X and Y axis displacement data are processed by the computer and combined with the electron microscope to collect the secondary electron signal excited by the electron beam on the surface of the sample, and finally obtain the measurement data traced by the laser interferometer.

Coilless ultrasonic motor coarse adjustment stage 20 is used for sample positioning, and the ultrasonic motor has no magnetic field and will not affect the electron beam. On the ultrasonic motor coarse-adjustment displacement platform 20 is a high-speed nano-displacement scanning platform 22 , which is fixed by the first connecting plate 21 . The nano-displacement scanning stage 22 carries a sample stage 24 and a two-dimensional mirror 25 . The sample stage 24 can be rotated and fine-tuned in the horizontal plane and pitched in the vertical plane through the fine-tuning screws located on the two arms, and the sample 26 to be tested can be placed on the center of the sample stage. The mirror 25 is used to reflect the laser light of the interferometer to measure the position of the sample, and the position measured by the interferometer is synchronized with the electronic signal to obtain a two-dimensional surface image of the sample.

The interferometer of the present invention is a 2-fold optical path, and the beam returns twice between the interference mirror and the measuring mirror. One cycle of the interference signal corresponds to 158nm, and at the same time, the interference signal of one cycle is subdivided by the circuit 1024 or 2048, and the final resolution 0.15nm or 0.075nm.

The electron gun of the metering scanning electron microscope of the present invention emits electron beams to the sample surface, and the generated secondary electrons are received by the electron microscope receiver, and the high-speed nano-stage drives the sample to scan at high speed, and the scanning speed of the nano-stage reaches 200 Hz. An L-shaped two-dimensional reflector is carried on the sample stage, and the material of the L-shaped two-dimensional reflector is glass ceramics to reduce expansion caused by temperature changes. The laser interferometer measures the displacement of the stage, and the measured value is directly traced to the laser wavelength and the meter defines the SI unit.

The invention provides a standard measurement device that can directly trace its measurement value to the national benchmark defined in meters. The measurement method is to directly connect a laser interferometer to the sample stage of the scanning electron microscope, and measure the displacement of the sample and the two The signal of secondary electrons or backscattered electrons is used to measure the length to be measured on the sample. The measured value can be directly traced to meters to define the international unit. This is an absolute measurement method. The biggest difference from the conventional scanning electron microscope is that it does not use electron beam scanning. , the electron beam spot of the electron microscope is in a static state during the imaging measurement, and the measurement image is obtained by the scanning motion of the high-speed translation stage carrying the measured sample. Use a laser interferometer to measure the displacement of the displacement stage. The measuring mirror of the laser interferometer is fixed on the displacement stage, so that the displacement of the displacement stage measured by the laser interferometer can be directly traced to the laser wavelength and the meter defines the SI unit, so that Realize the traceability of the measured value of the metrological scanning electron microscope.

The above content is a description of preferred embodiments of the present invention, which can help those skilled in the art to more fully understand the technical solution of the present invention. However, these Examples are merely illustrations, and it cannot be assumed that the specific embodiment of the present invention is limited to the description of these Examples.

Claims (6)

1. A nano-stepping sample scanning metrology scanning electron microscope is characterized in that it includes a high-speed nano-displacement scanning stage, a two-dimensional laser interferometer and an ultrasonic motor coarse adjustment displacement stage: The ultrasonic motor coarse-adjustment translation stage fixes the high-speed nano-displacement scanning platform, and the high-speed nano-displacement scanning platform is provided with a sample stage and a pole shoe of an electron gun of an electron microscope; The two-dimensional laser interferometer includes two interferometers, the interferometers are respectively located in the X direction and the Y direction of the measurement sample, the light source of the interferometer is introduced from the laser through an optical fiber, passes through the vacuum window of the glass window, and is placed in the electron microscope. Divided into two beams, respectively incident on two interference mirrors; The electron gun of the electron microscope emits electron beams to the surface of the sample, and the generated secondary electrons are received by the electron microscope receiver, and the high-speed nano-table drives the sample to scan at high speed; When the ultrasonic motor coarsely adjusts the displacement stage to perform scanning motion, one outgoing interference light is incident on the photodetector through the vacuum window as the X-axis displacement data signal of the displacement platform; Interferometer, the outgoing interference light is received by another detector as the Y-axis displacement data signal of the displacement platform; The X-axis and Y-axis displacement data cooperate with the electron microscope to collect the secondary electron signal excited by the electron beam on the surface of the sample, and obtain the measurement data traceable by the laser interferometer. 2. The metrological scanning electron microscope according to claim 1, wherein the two-dimensional laser interferometer comprises a laser beam incident fiber, a through-hole flange, a vacuum window, a cube beam splitter, an elastic hinge, a plane reflector, Receiver, interferometer and L-shaped two-dimensional mirror. 3. The metrological scanning electron microscope according to claim 2, characterized in that, the coilless ultrasonic motor coarse-adjustment translation stage is connected to the high-speed nano-displacement scanning platform through the first connecting plate, and the high-speed nano-displacement scanning The stage is connected to the fine-adjustable sample stage through the second connecting plate, and the sample to be tested and the pole shoe of the electron gun of the electron microscope are arranged on the fine-adjustable sample stage. 4. The metrological scanning electron microscope according to claim 3, wherein the natural resonance frequency of the elastic hinge can be higher than 200 Hz. 5. The metrological scanning electron microscope according to claim 3, wherein the material of the L-shaped two-dimensional mirror is glass ceramics. 6. The metrological scanning electron microscope according to claim 3, wherein the interferometer is a 2-fold optical path, one cycle of the interference signal corresponds to 158nm, and the interference signal of one cycle is subdivided by circuit 1024 or 2048 , the resolution is 0.15nm or 0.075nm.

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