CN116358424A - Method for measuring needle height of probe station based on monocular distance measurement - Google Patents
Method for measuring needle height of probe station based on monocular distance measurement Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
- G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
- G01B11/0608—Height gauges
Abstract
The invention relates to a probe station needle height measuring method based on monocular distance measurement, which comprises the following steps: s1, accurately positioning a wafer on a slide holder to enable crystal grains of the wafer to be positioned near an aggregation position of a fixed-focus camera; s2, lifting the slide holder, changing object distance, shooting a plurality of wafer images, and finding out the clearest wafer image through a square gradient function to be used as an aggregate image; s3, keeping the slide holder at the height for obtaining the collected image, slightly changing the image distance of the fixed focus camera, and shooting at least two defocused images with different degrees; s4, calculating the object distance u of the collected image through a point spread function of Gaussian distribution based on parameters of two defocused images; s5, obtaining the alignment height based on the object distance u of the collected image and the height difference between the free end of the probe and the focusing camera. The invention has high measurement precision, so that the probe station can accurately needle.
Description
Technical Field
The invention relates to the field of integrated circuit testing, in particular to a probe station-to-needle height measuring method based on monocular ranging.
Background
With the development of semiconductor and integrated circuit industries, the development of a probe station is more and more important in various industries. The probe station is widely applied to research and development of precise electric measurement of complex and high-speed devices, and can reduce research and development time and cost of device manufacturing process on the premise of ensuring quality and reliability. With the progress of semiconductor technology, the probe station is also developing to a high precision direction to adapt to the production requirement, and high-efficiency and high-precision positioning is becoming an important performance evaluation index of probe testing equipment.
The probe station is mainly applied to testing of semiconductors, integrated circuits and packages, and mainly ensures the quality of products and shortens the manufacturing cost. The probe station can fix a wafer or a chip and accurately position an object to be measured. The probe station directly contacts with the crystal grains on the wafer by using the probe to lead out signals so as to achieve the purpose of testing. The probe station is operationally divided into: manual probe station, semi-automatic probe station and full-automatic probe station. The alignment needle of the manual probe station is mainly used for installing a probe arm and a probe into a manipulator by a user, and placing a probe tip at a correct position on an object to be tested by using a microscope, and when all the probe tips are arranged at the correct positions, the object to be tested can be tested. The operation is automated using a mechanized table and machine vision at both the semi-automated and fully automated probe stations to complete the entire process. Currently, in semi-automatic and full-automatic probe stations, the accuracy of measuring the height of the needle is low, so that the needle cannot contact with the die or excessively embossed needle during needle alignment, and therefore, development of a needle height measuring method with high measuring accuracy is needed.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, and provides a probe-to-needle height measurement method based on monocular ranging, which has high measurement precision, so that a probe station can accurately align needles.
In order to solve the technical problems, the technical scheme of the invention is as follows: a probe station-to-needle height measurement method based on monocular ranging comprises the following steps:
s1, accurately positioning a wafer on a slide holder to enable crystal grains of the wafer to be positioned near an aggregation position of a fixed-focus camera;
s2, lifting the slide holder, changing object distance, shooting a plurality of wafer images, and finding out the clearest wafer image through a square gradient function to be used as an aggregate image;
s3, keeping the slide holder at the height for obtaining the collected image, slightly changing the image distance of the fixed focus camera, and shooting at least two defocused images with different degrees;
s4, calculating the object distance u of the collected image through a point spread function of Gaussian distribution based on parameters of two defocused images;
s5, obtaining the alignment height based on the object distance u of the collected image and the height difference between the free end of the probe and the focusing camera.
Further, the step S2 specifically includes:
the slide holder moves upwards for a preset distance each time to change the object distance, and the fixed-focus camera shoots a wafer image each time the slide holder moves once;
and carrying out quantitative evaluation on the definition of each wafer image by adopting a square gradient function, and taking the clearest wafer image as the aggregate image.
Further, the step S4 specifically includes:
the point M is regarded as a point light source, the fixed focus camera is regarded as a thin convex lens, and a focusing image M' is obtained after passing through the thin convex lens; assuming that the focal length of the thin convex lens is f, the distance between the point light source and the thin convex lens, namely the object distance is u, the distance between the focusing image and the lens, namely the image distance is v, and the point light source imaging principle is represented by the formula (2):
according to the defocusing imaging principle, defocusing images are images which cannot be focused, namely M points are focused by a fixed-focus camera to obtain a blurred light spot M' instead of a focused point, and the lens is circular, so that the obtained blurred light spot is also circular, and the defocusing images are obtained by the formula (2) and the defocusing imaging principle:
wherein D is the lens diameter of the prime camera, f is the focal length of the prime camera, s is the distance from the imaging surface to the lens, u is the object distance, and R is the radius of the diffuse spot, namely the radius of the blurred spot;
the imaging system uses a two-dimensional cauchy distribution function as a point spread function, which is:
wherein h (x, y) is a point spread function, x and y represent coordinates of pixel points, sigma is a Gaussian standard deviation, and is used for representing the size of the blurring degree, namely the size of a light spot;
r is proportional to σ, assuming σ=k 1 R is R; let σ=k 1 R brings the defocus imaging principle into:
wherein the method comprises the steps of
One of the defocused images is represented by s, f, D, and the other defocused image is represented by s+Δs, f, D, since the imaging system is a linear system, the result is:
where P (w, v) is the power spectral density of the aggregate image, F is the Fourier transform function of the aggregate image, F * Is the conjugation of F;
from equation (5), we get:
from equation (6), we get:
ΔP＝-2(ω 2 +v 2 )PσΔσ (8)
the method comprises the following steps:
this time order
To reduce errors and improve stability, the average value of a section of area is used in calculation and is expressed as:
where C represents an average value of the regions, and D represents a frequency region excluding dP (w, v) =0;
according to the formula (5) and the formula (7), the following is obtained:
from equation (9), equation (10) and equation (12), we get:
solving the equation to obtain:
after the technical scheme is adopted, the invention has the following beneficial effects:
(1) The image definition is evaluated by introducing a square gradient function in automatic focusing, the unimodal property is good, and the focusing is faster and more effective;
(2) And a point spread function is introduced through a defocusing ranging algorithm, the object distance of an aggregate image is calculated and obtained, the needle alignment height is obtained based on the object distance, and the ranging precision is improved.
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Fig. 1 is a flow chart of the method for measuring the needle height of the probe station based on monocular ranging according to the invention.
Detailed Description
In order that the invention may be more readily understood, a more particular description of the invention will be rendered by reference to specific embodiments that are illustrated in the appended drawings.
As shown in fig. 1, a probe station-to-needle height measurement method based on monocular ranging includes:
s1, accurately positioning a wafer on a slide holder to enable crystal grains of the wafer to be positioned near an aggregation position of a fixed-focus camera;
s2, lifting the slide holder, changing object distance, shooting a plurality of wafer images, and finding out the clearest wafer image through a square gradient function to be used as an aggregate image;
s3, keeping the slide holder at the height for obtaining the collected image, slightly changing the image distance of the fixed focus camera, and shooting at least two defocused images with different degrees;
s4, calculating the object distance u of the collected image through a point spread function of Gaussian distribution based on parameters of two defocused images;
s5, obtaining the alignment height based on the object distance u of the collected image and the height difference between the free end of the probe and the focusing camera.
The automatic focusing of the invention evaluates the image definition by introducing a square gradient function, has good unimodal property, and focuses more quickly and effectively; and a point spread function is introduced through a defocusing ranging algorithm, the object distance u of the collected image is calculated, the needle alignment height is obtained based on the object distance u, and the ranging precision is improved.
In this embodiment, when the free end of the probe and the focusing camera are located at the same height, the calculated object distance u, i.e. the alignment height, is calculated.
In this embodiment, in step S1, the precise positioning of the wafer on the stage further includes determining the relative positions of the wafer and the fixed focus camera in the x and y directions, that is, obtaining the x and y coordinates of the wafer and the diameter of the wafer, and then moving the center of the wafer on the stage to a position under the fixed focus camera by the control system.
The slide holder moves upwards for a preset distance each time to change the object distance, and the fixed-focus camera shoots a wafer image each time the slide holder moves once;
and carrying out quantitative evaluation on the definition of each wafer image by adopting a square gradient function, and taking the clearest wafer image as the aggregate image.
The preset distance can be 1 micron, a wafer image is shot every 1 micron after moving, and the wafer is stopped after 20 microns of movement; and a square gradient function is introduced to evaluate the definition of the image, wherein the square gradient function is used for quantitatively evaluating the definition of the image by summing the squares of the differences between adjacent gray values in each column and the squares of the differences between adjacent gray values in each row, and the larger the image is, the larger the pixel difference between adjacent pixels is, and the more square gradient is, so that the clearest image, namely the focused image, is found by the square gradient function. At the moment, the whole automatic focusing process is finished, the unimodal property of the square gradient function is better, in order to give consideration to the real-time property and the accuracy in the focusing process, the focusing area can be highlighted by using the square gradient function, the calculated amount is reduced, and the detection efficiency is improved; the concrete expression of the square gradient function is as follows:
where I (x, y) is the gray value of the image at point (x, y). The larger f (I), the sharper the image.
In this embodiment, step S4 specifically includes:
process 1: firstly, analyzing a point light source imaging principle, regarding M points as a point light source, regarding a fixed focus camera as a thin convex lens, and obtaining a focusing image M' after passing through the thin convex lens; assuming that the focal length of the thin convex lens is f, the distance between the point light source and the thin convex lens, namely the object distance is u, the distance between the focusing image and the lens, namely the image distance is v, and the point light source imaging principle is represented by the formula (2):
the object distance u can be obtained by the formula (2) and the focal length f and the image distance v are known.
Then, according to a defocusing imaging principle, defocusing images are unfocused images, namely M points are obtained through a fixed-focus camera to form a blurred spot M' instead of a focused point, and the lens is circular, so that the obtained blurred spot is also circular, and the blurred spot is obtained through a formula (2) and the defocusing imaging principle:
wherein D is the lens diameter of the prime camera, f is the focal length of the prime camera, s is the distance from the imaging surface to the lens, u is the object distance, and R is the radius of the diffuse spot, namely the radius of the blurred spot;
considering the non-ideal case of lens imaging, describing the scattered point spread distribution function using a cylindrical distribution point spread function is inaccurate, mainly because the boundary of the M point on the imaging plane is not clear but a spot with gradually blurred edges, and thus using a two-dimensional cauchy distribution function as the point spread function, the point spread function is:
wherein h (x, y) is a point spread function, x and y represent coordinates of pixel points, sigma is a Gaussian standard deviation, and is used for representing the size of the blurring degree, namely the size of a light spot;
the greater the Gaussian standard deviation, the greater the degree of blurring, the greater the R, the better the degree of focusing, and the smaller the Gaussian standard deviation, so the sigma is also called as a blurring parameter; from the above, it can be assumed that R is proportional to σ, and that: σ=k·r; bringing this into defocus imaging principle can be achieved:
wherein the method comprises the steps of
One of the defocused images is represented by s, f, D, and the other defocused image is represented by s+Δs, f, D, since the imaging system is a linear system, the result is:
where P (w, v) is the power spectral density of the aggregate image, F is the Fourier transform function of the aggregate image, F * Is the conjugation of F;
from equation (5), we get:
from equation (6), we get:
ΔP＝-2(ω 2 +υ 2 )PσΔσ (8)
the method comprises the following steps:
this time order
To reduce errors and improve stability, the average value of a section of area is used in calculation and is expressed as:
where C represents an average value of the regions, and D represents a frequency region excluding dP (w, v) =0;
according to the formula (5) and the formula (7), the following is obtained:
from equation (9), equation (10) and equation (12), we get:
solving the equation to obtain:
with the above-described preferred embodiments according to the present invention as an illustration, the above-described descriptions can be used by persons skilled in the relevant art to make various changes and modifications without departing from the scope of the technical idea of the present invention. The technical scope of the present invention is not limited to the description, but must be determined according to the scope of claims.
Claims (3)
1. A probe station-to-needle height measurement method based on monocular ranging is characterized in that,
comprising the following steps:
s1, accurately positioning a wafer on a slide holder to enable crystal grains of the wafer to be positioned near an aggregation position of a fixed-focus camera;
s2, lifting the slide holder, changing object distance, shooting a plurality of wafer images, and finding out the clearest wafer image through a square gradient function to be used as an aggregate image;
s3, keeping the slide holder at the height for obtaining the collected image, slightly changing the image distance of the fixed focus camera, and shooting at least two defocused images with different degrees;
s4, calculating the object distance u of the collected image through a point spread function of Gaussian distribution based on parameters of two defocused images;
s5, obtaining the alignment height based on the object distance u of the collected image and the height difference between the free end of the probe and the focusing camera.
2. The method for measuring the probe station-to-needle height based on monocular ranging according to claim 1, wherein,
the step S2 specifically comprises the following steps:
the slide holder moves upwards for a preset distance each time to change the object distance, and the fixed-focus camera shoots a wafer image each time the slide holder moves once;
and carrying out quantitative evaluation on the definition of each wafer image by adopting a square gradient function, and taking the clearest wafer image as the aggregate image.
3. The method for measuring the probe station-to-needle height based on monocular ranging according to claim 1, wherein,
the step S4 specifically comprises the following steps:
the point M is regarded as a point light source, the fixed focus camera is regarded as a thin convex lens, and a focusing image M' is obtained after passing through the thin convex lens; assuming that the focal length of the thin convex lens is f, the distance between the point light source and the thin convex lens, namely the object distance is u, the distance between the focusing image and the lens, namely the image distance is v, and the point light source imaging principle is represented by the formula (2):
according to the defocusing imaging principle, defocusing images are images which cannot be focused, namely M points are focused by a fixed-focus camera to obtain a blurred light spot M' instead of a focused point, and the lens is circular, so that the obtained blurred light spot is also circular, and the defocusing images are obtained by the formula (2) and the defocusing imaging principle:
wherein D is the lens diameter of the prime camera, f is the focal length of the prime camera, s is the distance from the imaging surface to the lens, u is the object distance, and R is the radius of the diffuse spot, namely the radius of the blurred spot;
the imaging system uses a two-dimensional cauchy distribution function as a point spread function, which is:
wherein h (x, y) is a point spread function, x and y represent coordinates of pixel points, sigma is a Gaussian standard deviation, and is used for representing the size of the blurring degree, namely the size of a light spot;
r is proportional to σ, assuming σ=k 1 R is R; let σ=k 1 R brings the defocus imaging principle into:
wherein the method comprises the steps of
One of the defocused images is represented by s, f, D, and the other defocused image is represented by s+Δs, f, D, since the imaging system is a linear system, the result is:
where P (w, v) is the power spectral density of the aggregate image, F is the Fourier transform function of the aggregate image, F * Is the conjugation of F;
from equation (5), we get:
from equation (6), we get:
ΔP＝-2(ω 2 +v 2 )PσΔσ (8)
the method comprises the following steps:
this time order
To reduce errors and improve stability, the average value of a section of area is used in calculation and is expressed as:
where C represents an average value of the regions, and D represents a frequency region excluding Δp (w, v) =0;
according to the formula (5) and the formula (7), the following is obtained:
from equation (9), equation (10) and equation (12), we get:
solving the equation to obtain:
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