WO2024045551A1

WO2024045551A1 - Phase-locked low light microscopic imaging method and apparatus

Info

Publication number: WO2024045551A1
Application number: PCT/CN2023/081378
Authority: WO
Inventors: 张家晨
Original assignee: 合肥锁相光学科技有限公司
Priority date: 2022-09-01
Filing date: 2023-03-14
Publication date: 2024-03-07
Also published as: CN115219480A; CN115219480B

Abstract

A phase-locked low light microscopic imaging method and apparatus. The method comprises: setting an excitation source parameter; collecting a sample image; acquiring an intensity image; superimposing the intensity image and the sample image; and outputting a result. An excitation signal is inputted into an electrode of a sample being measured (4), so that said sample (4) periodically emits an optical signal at a failure point after said sample (4) is electrified; the optical signal is optically amplified by a microscopic system (3) and the sample image is collected by a camera (2); a digital phase-locked algorithm, i.e., the orthogonality of a trigonometric function, is used to separate the magnitude of a periodic change of a pixel value having the same frequency as an excitation source (5) over time, so as to suppress irregular fluctuations in measurement data due to temperature drift and thermal noise of an electronic component and environmental disturbance, thereby increasing the signal-to-noise ratio of the measurement data.

Description

A phase-locked low-light microscopy imaging method and device

Technical field

The present invention relates to the technical fields of non-destructive testing and failure analysis, and in particular to a phase-locked low-light microscopy imaging method and device.

Background technique

Semiconductor microelectronic devices are miniaturized electronic system chips and devices implemented using microelectronic process technology. They have been widely used in various fields. Semiconductor microelectronic devices will inevitably have abnormal working conditions during use. Find out which semiconductor The causes of failure of microelectronic devices in abnormal working conditions and taking effective measures can prevent similar failure problems from recurring, greatly avoid economic losses, and even avoid casualties. Therefore, failure analysis of microelectronic devices is particularly important.

Currently, in microelectronic circuits used in semiconductor microelectronic devices, failures such as gate leakage current, dielectric breakdown, PN junction interface leakage, and oxide defects will lead to the recombination of electrons and holes, and the recombination of electrons and holes will generate photons. , the photons emitted from the material can be detected by the camera. In failure analysis and testing in the semiconductor field, the detection of a luminous point at a certain location on the material is often used to locate the fault point.

With the continuous optimization of semiconductor processes, the characteristic sizes of semiconductor microelectronic devices are getting smaller and smaller. In order not to cause damage to electronic devices during the detection process, the voltage and current applied to electronic devices are also getting smaller and smaller. Correspondingly, the failure points of microelectronic devices emit fewer and fewer photons, and the radiation intensity becomes weaker and weaker. In order to effectively detect these very weak optical radiations, the existing technology uses methods to reduce the temperature of the photosensitive device (detector) to reduce the dark current of the camera and improve the signal-to-noise ratio and sensitivity of the imaging results. However, such detection methods often have Questions are as follows:

(1) The above cooling method requires the detector temperature to be lowered to the liquid nitrogen temperature. The device is complex, the operation is difficult, and the energy consumption is high.

(2) Some fault points have high luminous intensity and easily form a light spot on the image, making it impossible to accurately locate the failure point of the device.

(3) The device under test must be placed in a dark room to prevent external light signals from interfering with the detector's measurement of the weak light signals emitted by the device.

Contents of the invention

In view of the above shortcomings of the prior art, the purpose of the present invention is to provide a phase-locked low-light microscopy imaging method and device to solve one or more problems in the prior art.

In order to achieve the above objects, the technical solutions of the present invention are as follows:

A phase-locked low-light microscopy imaging method includes the following steps:

Set the excitation source parameters;

Collect sample images;

Get intensity image;

Overlaying the intensity image with the sample image;

Output results.

Further, the steps of collecting sample images include the following steps:

Excite the sample under test through a periodic excitation source, causing the failure point of the sample under test to periodically emit light signals;

Receive the optical signal through a microscope system and obtain a sample image through optical amplification;

A camera captures an image of the sample.

Furthermore, the shooting frame rate of the camera is in a fixed integer multiple relationship with the frequency of the excitation source.

Further, the shooting start time of the camera is the same as or different from the signal start time of the excitation source.

Furthermore, the sample under test, the microscope system and the camera remain relatively stationary during the shooting of the sample image.

Further, the steps of obtaining the intensity image include the following steps:

Do the inner product of the sample image and the sinusoidal reference signal of the same frequency as the excitation source to obtain the accumulation result of the sinusoidal components;

Do the inner product of the sample image and the cosine reference signal of the same frequency as the excitation source to obtain the accumulation result of the cosine components.

According to the signal orthogonality, the sine component accumulation result and the cosine component accumulation result are obtained, and the results are used to calculate the amplitude of the pixel value of the pixel point at the specified position that changes periodically with the excitation signal.

Further, the calculation formula for the inner product of the sinusoidal reference signal of the same frequency as the sample image and the excitation source is as follows:

Among them, x and y are the spatial position coordinates of the pixel, and i represents the i-th image taken by the camera. f(x, y, i) represents the pixel value size of the pixel at the (x, y) position in the i-th image, k represents the number of cycles, and N represents the sample captured by the camera in each cycle of the excitation signal change. The number of images, while A ₁ (x, y) is expressed as the accumulation result of sinusoidal components, Represents a sinusoidal reference signal.

Further, the calculation formula for the inner product of the cosine reference signal of the same frequency as the sample image and the excitation source is as follows:

Among them, x and y are the spatial position coordinates of the pixel, and i represents the i-th image taken by the camera. f(x, y, i) represents the pixel value size of the pixel at the (x, y) position in the i-th image, k represents the number of cycles, and N represents the sample captured by the camera in each cycle of the excitation signal change. The number of images, and A ₂ (x, y) is expressed as the accumulation result of the cosine components, Represents the cosine reference signal.

Further, the calculation formula for the amplitude of the periodic change of the pixel value of the pixel point at the specified position with the excitation signal is as follows:

Where A (x, y) is the amplitude of the periodic change of the pixel value of the pixel at the specified position with the excitation signal, and A ₁ (x, y) is expressed as the accumulation result of the sinusoidal component, and A ₂ (x, y) is expressed as The cumulative result of the cosine components.

Correspondingly, the present invention also provides a device for imaging using the phase-locked low-light microscopy imaging method, including

An excitation source, which is used to excite the sample under test so that the failure point of the sample under test periodically emits a light signal;

A microscope system, which is used to receive the optical signal and obtain a sample image through optical amplification;

A camera, the camera is used to capture the sample image and send it to the computer;

A computer, the computer is used to acquire the sample image, acquire the intensity image through a digital phase locking algorithm, superimpose the intensity image and the sample image and output the result.

Compared with the existing technology, the beneficial technical effects of the present invention are as follows:

(1) The present invention passes the excitation signal into the electrode of the sample to be tested, so that the sample to be tested periodically emits a light signal at its failure point after being energized, and uses the microscope system to optically amplify and collect the sample image by the camera, and digitally The phase-locking algorithm uses the orthogonality of trigonometric functions to isolate the amplitude of pixel values that change periodically with time at the same frequency as the excitation source, thereby suppressing the temperature drift of electronic components, thermal noise, and environmental disturbances. irregular fluctuations in the measurement data, which can greatly improve the signal-to-noise ratio of the measurement data.

(2) Further, the present invention no longer needs to lower the detector temperature to the liquid nitrogen temperature, effectively saving energy consumption, and the device under test does not need to be in a dark room, avoiding interference of the detector with the device due to external light signals. Measurement of weak light signals emitted from the device.

Description of drawings

Figure 1 shows a schematic structural diagram of a phase-locked low-light microscopy imaging device according to an embodiment of the present invention.

Figure 2 shows a schematic flow chart of a phase-locked low-light microscopy imaging method according to an embodiment of the present invention.

Figure 3 shows a schematic diagram of the sample being tested in a phase-locked low-light microscopy imaging method according to an embodiment of the present invention.

Figure 4 shows a schematic diagram of the output results of a phase-locked low-light microscopy imaging method according to an embodiment of the present invention.

Labels in the drawings: 1. Computer; 2. Camera; 3. Microscope system; 4. Sample to be measured; 5. Excitation source.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention more clear, the phase-locked low-light microscopy imaging method and device proposed by the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. The advantages and features of the present invention will become clearer from the following description. It should be noted that the drawings are in a very simplified form and use imprecise proportions, and are only used to conveniently and clearly assist in explaining the embodiments of the present invention. In order to make the objects, features and advantages of the present invention more apparent, please refer to the accompanying drawings. It should be noted that the structures, proportions, sizes, etc. shown in the drawings attached to this specification are only used to coordinate with the content disclosed in the specification for the understanding and reading of those familiar with this technology, and are not used to limit the implementation of the present invention. conditions, it has no technical substantive significance. Any structural modifications, changes in proportions, or adjustments in size should still fall within the scope of the present invention without affecting the efficacy and purpose of the present invention. Within the scope of the disclosed technical content.

Example 1:

A phase-locked low-light microscopy imaging device includes an excitation source 5, a microscope system 3, a camera 2 and a computer 1.

Please refer to Figure 1. The sample to be tested 4 is disposed between the excitation source 5 and the microscope system 3. Specifically, in the phase-locked low-light microscopy imaging device of the first embodiment, the sample to be tested 4 for wafer samples.

Please continue to refer to Figure 1. In the phase-locked low-light microscopy imaging device of the first embodiment, the excitation source 5 generates an excitation signal for measurement. The excitation signal is an electrical signal. The excitation signal is passed into the crystal. In the electrodes of the circular sample, the failure point on the wafer periodically emits a light signal.

Specifically, after the wafer sample is energized, its electron-hole pairs recombine and emit a light signal, and the light signal enters the microscopic system 3. Preferably, the microscopic system 3 adopts known technology, and is preferably a probe station. The microscope specifically includes an eyepiece, a nosepiece, a tube lens, a probe station, and a stage. The eyepiece, the nosepiece, and the tube lens are all arranged above the stage, and there is a movable probe seat inside the probe station. There is a probe on the probe holder, which adsorbs the sample to be measured on the stage and then pushes it into the probe station. The probe holder is used to move the probe precisely, and the probe is observed through a microscope composed of an eyepiece, an objective lens turntable, and a tube lens. When in contact with the sample 4 to be measured, the optical signal is received by the microscope system 3 and optical amplification is performed to obtain amplified image information, that is, a sample image.

Further, please continue to refer to FIG. 1 . The camera 2 is used to capture the sample image from the microscope system 3 and transmit it to the computer 1 .

Further, please continue to refer to Figure 1. The computer 1 is used to obtain the sample image. In this embodiment, the acquisition of the sample image can be achieved by a USB interface on the computer 1. The computer 1 is acquiring the sample image. The sample image is then processed through a digital phase locking algorithm (the digital phase locking algorithm is described in detail in the following method) to obtain an intensity image, the intensity image is superimposed on the sample image and the result is output.

Of course, in other embodiments of the present invention, the sample image can also be obtained through other methods besides the USB interface, for example, it can be transmitted through Ethernet, CameraLink, or it can also be transmitted wirelessly. Therefore, the present invention is not further limited.

A method for microscopic imaging using the above-mentioned phase-locked low-light microscopic imaging device, including the following steps:

S1: Set the excitation source parameters, which include any one or a combination of voltage frequency, current frequency, voltage amplitude, current amplitude, voltage limiting protection, and current limiting protection.

S2: Collect sample images. The specific steps for collecting sample images are as follows:

S200: Excite the sample 4 under test through a periodic excitation source. Specifically, the excitation source is an electrical signal. In the phase-locked low-light microscopy imaging method described in Embodiment 1, the electrical signal changes with time. square wave. Of course, in other embodiments of the present invention, the electrical signal may also be other forms of periodic current signals or voltage signals, which will not be described further in the present invention.

Further, the excitation signal is passed to the electrode of the sample 4 under test, that is, the wafer sample. Specifically, the sample 4 under test is placed on the probe table of the microscope system 3, and the illumination light source is turned on. The light source passes through electric epi-illumination. The device and the 50/50 visible light semi-transparent and semi-reflective mirror irradiate light to the sample 4 to be tested, use the eyepiece in the microscope system 3 to observe the sample 4 to be tested, and operate the probe to press the designated electrode on the sample 4 to be tested , that is, the excitation signal is passed into the sample 4 under test.

Furthermore, the above-mentioned method of pressing the probe can press the probe on the front side, that is, observe the sample 4 under test through the eyepiece. In other embodiments of the present invention, the probe can also be pressed on the back side, that is, observed through the camera included in the probe station microscope.

Under the excitation source, that is, an electrical signal, the failure point (ie, a specific area) of the tested sample 4 will periodically emit optical signals after it is powered on. Specifically, the current of the above-mentioned excitation source is a weak current. If a strong current is used, the semiconductor electronic device will be damaged.

S201: Since the area where the light signal is emitted from the failure point of the tested sample 4 is small, this area needs to be amplified through the microscope system 3. The microscope system 3 receives the light signal and obtains the sample image through optical amplification.

S202: Specifically, by switching the reflective lens of the electric epi-illumination device to a combination of a 50/50 semi-reflective lens in the near-infrared band and a high-pass filter in the near-infrared band, the near-infrared light in the light source is illuminated into the sample 4 under test. , that is, the microscope system 3 acquires the sample image, and then the camera 2 collects the sample image. Please refer to Figure 3 for sample images.

Furthermore, the acquisition start time of the camera 2 is different from the signal start time of the excitation source, that is, the shooting action of the camera 2 does not need to be time-domain synchronized with the electrical signal of the excitation source, but during the shooting process of the camera 2, The shooting frame rate of the camera 2 is in a fixed integer multiple relationship with the frequency of the excitation source.

The purpose of the above-mentioned shooting frame rate of the camera 2 being in a fixed integer multiple relationship with the frequency of the excitation source is to ensure that the number of photos taken by the camera 2 is consistent during the period when the excitation source changes. That is, sampling and calculation are performed under the same conditions within several cycles of the excitation source changing, and the final calculated result can minimize the impact of noise.

A further example is: Camera 2 collects 10 sample images in the first cycle, and Camera 2 collects 10 sample images in the second, third... and nth cycles, which is the shooting frame rate of Camera 2. Maintains a fixed relationship of 10 times with the frequency of the excitation source.

The measured sample 4 and the camera 2 are photographed and the microscopy system 3 remains relatively stationary, that is, the position of the pixel point corresponding to the area that emits a light signal on the measured sample 4 is in the photographed and collected sample image. remains unchanged, but the pixel value of the pixel changes periodically with the picture sequence, and finally the sample image is transmitted to the computer 1 through the camera 2.

Specifically, at the failure position of the tested sample 4, there will be electron-hole pair recombination or interaction between carriers, phonons, defects, etc., causing energy to be emitted from the tested sample 4 in the form of photons, and then in The failure location forms a luminous point. The light emitted from the above-mentioned light-emitting point reaches the camera 2 after passing through the objective lens and tube lens of the microscope system 3 .

Furthermore, since the phase locking process requires superimposing multiple images for noise reduction and then locking the position of the light-emitting point, the position of the pixel corresponding to the area emitting the light signal on the tested sample 4 is in the captured and collected sample image. Keep it unchanged, so that the calculation result of each pixel position is accurate, and further the accurate position of the light-emitting point can be obtained.

S3: Obtain the intensity image. The steps of obtaining the intensity image include the following steps:

S300: Do the inner product of the sample image and the sinusoidal reference signal of the same frequency as the excitation source to obtain the accumulation result of the sinusoidal components.

Specifically, the calculation formula for the inner product of the sample image and the sinusoidal reference signal of the same frequency as the excitation source is as follows:

S301: Do an inner product of the sample image and the cosine reference signal of the same frequency as the excitation source to obtain the accumulation result of the cosine components.

Specifically, the calculation formula for the inner product of the sample image and the cosine reference signal of the same frequency as the excitation source is as follows:

S302: Calculate the amplitude of the periodic change of the pixel value of the pixel point at the specified position with the excitation signal based on the accumulation result of the sine component and the accumulation result of the cosine component. The calculation formula is as follows:

Through the above calculation results, the orthogonality of trigonometric functions can be used to separate the changes in pixel values with the same frequency as the excitation signal over time. At the same time, it can greatly suppress the temperature drift of electronic components, thermal noise and environmental disturbances. irregular fluctuations in the measurement data, which can greatly improve the signal-to-noise ratio of the measurement data. And as the measurement time, that is, the number of measurement cycles, is extended, the signal-to-noise ratio can be continuously improved.

S4: Superimpose the intensity image and the sample image. The superposition action is performed by the computer. Specifically, the sampling image taken by camera 2 is used as the background, and the high-intensity ones in the intensity image are retained and the low-intensity ones are set to transparent, and then displayed after superposition. Find the failure location on the sample.

S5: Computer 1 outputs the calculation result and illustrates it with an image. Please refer to Figure 4. From Figure 4, it can be seen that the position corresponding to the bright part in the image is the position of the failure point of the semiconductor electronic device.

The technical features of the above-described embodiments can be combined in any way. To simplify the description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, All should be considered to be within the scope of this manual.

The above-mentioned embodiments only express several implementation modes of the present invention. The descriptions are relatively specific and detailed, but do not This can be understood as a limitation on the scope of the invention patent. It should be noted that, for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the scope of protection of the patent of the present invention should be determined by the appended claims.

Claims

A phase-locked low-light microscopy imaging method, characterized by including the following steps:

Set the excitation source parameters;

Collect sample images;

Get intensity image;

Overlaying the intensity image with the sample image;

Output results;

The steps of obtaining the intensity image include the following steps:

Do the inner product of the sample image and the sinusoidal reference signal of the same frequency as the excitation source to obtain the accumulation result of the sinusoidal components;

Do the inner product of the sample image and the cosine reference signal of the same frequency as the excitation source to obtain the accumulation result of the cosine component;

According to the signal orthogonality, the sine component accumulation result and the cosine component accumulation result are obtained, and the results are used to calculate the amplitude of the pixel value of the pixel point at the specified position that changes periodically with the excitation signal.
A phase-locked low-light microscopy imaging method as claimed in claim 1, characterized in that: collecting sample images includes the following steps:

Excite the sample under test through a periodic excitation source, causing the failure point of the sample under test to periodically emit light signals;

Receive the optical signal through a microscope system and obtain a sample image;

A camera captures an image of the sample.
A phase-locked low-light microscopy imaging method as claimed in claim 2, characterized in that: the shooting frame rate of the camera is in a fixed integer multiple relationship with the frequency of the excitation source.
A phase-locked low-light microscopy imaging method according to claim 2, characterized in that: the shooting start time of the camera is the same as or different from the signal start time of the excitation source.
A phase-locked low-light microscopy imaging method as claimed in claim 2, characterized in that the tested sample, the microscope system and the camera remain relatively stationary during the shooting of the sample image.
A phase-locked low-light microscopy imaging method as claimed in claim 1, characterized in that: the calculation formula for the inner product of the sinusoidal reference signal of the same frequency as the sample image and the excitation source is as follows:

where x, y are the spatial position coordinates of the pixel, i represents the i-th image taken by the camera, and f(x, y, i) represents the pixel at the (x, y) position in the i-th image. Value size, k represents the number of cycles, N represents the camera’s excitation signal The number of sample images taken in each cycle of the signal change, and A 1 (x, y) is expressed as the accumulation result of the sinusoidal components, Represents a sinusoidal reference signal.
A phase-locked low-light microscopy imaging method as claimed in claim 1, characterized in that: the calculation formula for the inner product of the cosine reference signal of the same frequency as the sample image and the excitation source is as follows:

where x, y are the spatial position coordinates of the pixel, i represents the i-th image taken by the camera, and f(x, y, i) represents the pixel at the (x, y) position in the i-th image. Value size, k represents the number of cycles, N represents the number of sample images taken by the camera in each cycle of the excitation signal change, and A 2 (x, y) represents the accumulation result of the cosine component, Represents the cosine reference signal.
A phase-locked low-light microscopy imaging method according to claim 1, characterized in that: the calculation formula for the amplitude of the periodic change of the pixel value of the pixel point at the specified position with the excitation signal is as follows:

Where A (x, y) is the amplitude of the periodic change of the pixel value of the pixel at the specified position with the excitation signal, and A 1 (x, y) is expressed as the accumulation result of the sinusoidal component, and A 2 (x, y) is expressed as The cumulative result of the cosine components.
A device for imaging using a phase-locked low-light microscopy imaging method according to any one of claims 1 to 8, characterized in that it includes:

An excitation source, which is used to excite the sample under test so that the failure point of the sample under test periodically emits a light signal;

A microscope system, which is used to receive the optical signal and obtain a sample image through optical amplification;

A camera, the camera is used to take images of the sample and send them to a computer;

A computer, the computer is used to obtain the sample image, obtain an intensity image through a digital phase locking algorithm, superimpose the intensity image and the sample image and output the result.